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<refentry id="systemd.exec">
<refentryinfo>
<title>systemd.exec</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>systemd.exec</refentrytitle>
<manvolnum>5</manvolnum>
</refmeta>
<refnamediv>
<refname>systemd.exec</refname>
<refpurpose>Execution environment configuration</refpurpose>
</refnamediv>
<refsynopsisdiv>
<para><filename><replaceable>service</replaceable>.service</filename>,
<filename><replaceable>socket</replaceable>.socket</filename>,
<filename><replaceable>mount</replaceable>.mount</filename>,
<filename><replaceable>swap</replaceable>.swap</filename></para>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>Unit configuration files for services, sockets, mount points, and swap devices share a subset of
configuration options which define the execution environment of spawned processes.</para>
<para>This man page lists the configuration options shared by these four unit types. See
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry> for the common
options of all unit configuration files, and
<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>, and
<citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry> for more
information on the specific unit configuration files. The execution specific configuration options are configured
in the [Service], [Socket], [Mount], or [Swap] sections, depending on the unit type.</para>
<para>In addition, options which control resources through Linux Control Groups (cgroups) are listed in
<citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
Those options complement options listed here.</para>
</refsect1>
<refsect1>
<title>Implicit Dependencies</title>
<para>A few execution parameters result in additional, automatic dependencies to be added:</para>
<itemizedlist>
<listitem><para>Units with <varname>WorkingDirectory=</varname>, <varname>RootDirectory=</varname>,
<varname>RootImage=</varname>, <varname>RuntimeDirectory=</varname>, <varname>StateDirectory=</varname>,
<varname>CacheDirectory=</varname>, <varname>LogsDirectory=</varname> or
<varname>ConfigurationDirectory=</varname> set automatically gain dependencies of type
<varname>Requires=</varname> and <varname>After=</varname> on all mount units required to access the specified
paths. This is equivalent to having them listed explicitly in
<varname>RequiresMountsFor=</varname>.</para></listitem>
<listitem><para>Similar, units with <varname>PrivateTmp=</varname> enabled automatically get mount unit
dependencies for all mounts required to access <filename>/tmp</filename> and <filename>/var/tmp</filename>. They
will also gain an automatic <varname>After=</varname> dependency on
<citerefentry><refentrytitle>systemd-tmpfiles-setup.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para></listitem>
<listitem><para>Units whose standard output or error output is connected to <option>journal</option>,
<option>syslog</option> or <option>kmsg</option> (or their combinations with console output, see below)
automatically acquire dependencies of type <varname>After=</varname> on
<filename>systemd-journald.socket</filename>.</para></listitem>
</itemizedlist>
</refsect1>
<!-- We don't have any default dependency here. -->
<refsect1>
<title>Paths</title>
<variablelist class='unit-directives'>
<varlistentry>
<term><varname>WorkingDirectory=</varname></term>
<listitem><para>Takes a directory path relative to the service's root directory specified by
<varname>RootDirectory=</varname>, or the special value <literal>~</literal>. Sets the working directory for
executed processes. If set to <literal>~</literal>, the home directory of the user specified in
<varname>User=</varname> is used. If not set, defaults to the root directory when systemd is running as a
system instance and the respective user's home directory if run as user. If the setting is prefixed with the
<literal>-</literal> character, a missing working directory is not considered fatal. If
<varname>RootDirectory=</varname>/<varname>RootImage=</varname> is not set, then
<varname>WorkingDirectory=</varname> is relative to the root of the system running the service manager. Note
that setting this parameter might result in additional dependencies to be added to the unit (see
above).</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>RootDirectory=</varname></term>
<listitem><para>Takes a directory path relative to the host's root directory (i.e. the root of the system
running the service manager). Sets the root directory for executed processes, with the <citerefentry
project='man-pages'><refentrytitle>chroot</refentrytitle><manvolnum>2</manvolnum></citerefentry> system
call. If this is used, it must be ensured that the process binary and all its auxiliary files are available in
the <function>chroot()</function> jail. Note that setting this parameter might result in additional
dependencies to be added to the unit (see above).</para>
<para>The <varname>MountAPIVFS=</varname> and <varname>PrivateUsers=</varname> settings are particularly useful
in conjunction with <varname>RootDirectory=</varname>. For details, see below.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>RootImage=</varname></term>
<listitem><para>Takes a path to a block device node or regular file as argument. This call is similar to
<varname>RootDirectory=</varname> however mounts a file system hierarchy from a block device node or loopback
file instead of a directory. The device node or file system image file needs to contain a file system without a
partition table, or a file system within an MBR/MS-DOS or GPT partition table with only a single
Linux-compatible partition, or a set of file systems within a GPT partition table that follows the <ulink
url="https://www.freedesktop.org/wiki/Specifications/DiscoverablePartitionsSpec/">Discoverable Partitions
Specification</ulink>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>MountAPIVFS=</varname></term>
<listitem><para>Takes a boolean argument. If on, a private mount namespace for the unit's processes is created
and the API file systems <filename>/proc</filename>, <filename>/sys</filename>, and <filename>/dev</filename>
are mounted inside of it, unless they are already mounted. Note that this option has no effect unless used in
conjunction with <varname>RootDirectory=</varname>/<varname>RootImage=</varname> as these three mounts are
generally mounted in the host anyway, and unless the root directory is changed, the private mount namespace
will be a 1:1 copy of the host's, and include these three mounts. Note that the <filename>/dev</filename> file
system of the host is bind mounted if this option is used without <varname>PrivateDevices=</varname>. To run
the service with a private, minimal version of <filename>/dev/</filename>, combine this option with
<varname>PrivateDevices=</varname>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>BindPaths=</varname></term>
<term><varname>BindReadOnlyPaths=</varname></term>
<listitem><para>Configures unit-specific bind mounts. A bind mount makes a particular file or directory
available at an additional place in the unit's view of the file system. Any bind mounts created with this
option are specific to the unit, and are not visible in the host's mount table. This option expects a
whitespace separated list of bind mount definitions. Each definition consists of a colon-separated triple of
source path, destination path and option string, where the latter two are optional. If only a source path is
specified the source and destination is taken to be the same. The option string may be either
<literal>rbind</literal> or <literal>norbind</literal> for configuring a recursive or non-recursive bind
mount. If the destination path is omitted, the option string must be omitted too.
Each bind mount definition may be prefixed with <literal>-</literal>, in which case it will be ignored
when its source path does not exist.</para>
<para><varname>BindPaths=</varname> creates regular writable bind mounts (unless the source file system mount
is already marked read-only), while <varname>BindReadOnlyPaths=</varname> creates read-only bind mounts. These
settings may be used more than once, each usage appends to the unit's list of bind mounts. If the empty string
is assigned to either of these two options the entire list of bind mounts defined prior to this is reset. Note
that in this case both read-only and regular bind mounts are reset, regardless which of the two settings is
used.</para>
<para>This option is particularly useful when <varname>RootDirectory=</varname>/<varname>RootImage=</varname>
is used. In this case the source path refers to a path on the host file system, while the destination path
refers to a path below the root directory of the unit.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Credentials</title>
<variablelist class='unit-directives'>
<varlistentry>
<term><varname>User=</varname></term>
<term><varname>Group=</varname></term>
<listitem><para>Set the UNIX user or group that the processes are executed as, respectively. Takes a single
user or group name, or a numeric ID as argument. For system services (services run by the system service
manager, i.e. managed by PID 1) and for user services of the root user (services managed by root's instance of
<command>systemd --user</command>), the default is <literal>root</literal>, but <varname>User=</varname> may be
used to specify a different user. For user services of any other user, switching user identity is not
permitted, hence the only valid setting is the same user the user's service manager is running as. If no group
is set, the default group of the user is used. This setting does not affect commands whose command line is
prefixed with <literal>+</literal>.</para>
<para>Note that restrictions on the user/group name syntax are enforced: the specified name must consist only
of the characters a-z, A-Z, 0-9, <literal>_</literal> and <literal>-</literal>, except for the first character
which must be one of a-z, A-Z or <literal>_</literal> (i.e. numbers and <literal>-</literal> are not permitted
as first character). The user/group name must have at least one character, and at most 31. These restrictions
are enforced in order to avoid ambiguities and to ensure user/group names and unit files remain portable among
Linux systems.</para>
<para>When used in conjunction with <varname>DynamicUser=</varname> the user/group name specified is
dynamically allocated at the time the service is started, and released at the time the service is stopped —
unless it is already allocated statically (see below). If <varname>DynamicUser=</varname> is not used the
specified user and group must have been created statically in the user database no later than the moment the
service is started, for example using the
<citerefentry><refentrytitle>sysusers.d</refentrytitle><manvolnum>5</manvolnum></citerefentry> facility, which
is applied at boot or package install time.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>DynamicUser=</varname></term>
<listitem><para>Takes a boolean parameter. If set, a UNIX user and group pair is allocated dynamically when the
unit is started, and released as soon as it is stopped. The user and group will not be added to
<filename>/etc/passwd</filename> or <filename>/etc/group</filename>, but are managed transiently during
runtime. The <citerefentry><refentrytitle>nss-systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>
glibc NSS module provides integration of these dynamic users/groups into the system's user and group
databases. The user and group name to use may be configured via <varname>User=</varname> and
<varname>Group=</varname> (see above). If these options are not used and dynamic user/group allocation is
enabled for a unit, the name of the dynamic user/group is implicitly derived from the unit name. If the unit
name without the type suffix qualifies as valid user name it is used directly, otherwise a name incorporating a
hash of it is used. If a statically allocated user or group of the configured name already exists, it is used
and no dynamic user/group is allocated. Note that if <varname>User=</varname> is specified and the static group
with the name exists, then it is required that the static user with the name already exists. Similarly, if
<varname>Group=</varname> is specified and the static user with the name exists, then it is required that the
static group with the name already exists. Dynamic users/groups are allocated from the UID/GID range
61184…65519. It is recommended to avoid this range for regular system or login users. At any point in time
each UID/GID from this range is only assigned to zero or one dynamically allocated users/groups in
use. However, UID/GIDs are recycled after a unit is terminated. Care should be taken that any processes running
as part of a unit for which dynamic users/groups are enabled do not leave files or directories owned by these
users/groups around, as a different unit might get the same UID/GID assigned later on, and thus gain access to
these files or directories. If <varname>DynamicUser=</varname> is enabled, <varname>RemoveIPC=</varname>,
<varname>PrivateTmp=</varname> are implied. This ensures that the lifetime of IPC objects and temporary files
created by the executed processes is bound to the runtime of the service, and hence the lifetime of the dynamic
user/group. Since <filename>/tmp</filename> and <filename>/var/tmp</filename> are usually the only
world-writable directories on a system this ensures that a unit making use of dynamic user/group allocation
cannot leave files around after unit termination. Moreover <varname>ProtectSystem=strict</varname> and
<varname>ProtectHome=read-only</varname> are implied, thus prohibiting the service to write to arbitrary file
system locations. In order to allow the service to write to certain directories, they have to be whitelisted
using <varname>ReadWritePaths=</varname>, but care must be taken so that UID/GID recycling doesn't create
security issues involving files created by the service. Use <varname>RuntimeDirectory=</varname> (see below) in
order to assign a writable runtime directory to a service, owned by the dynamic user/group and removed
automatically when the unit is terminated. Use <varname>StateDirectory=</varname>,
<varname>CacheDirectory=</varname> and <varname>LogsDirectory=</varname> in order to assign a set of writable
directories for specific purposes to the service in a way that they are protected from vulnerabilities due to
UID reuse (see below). Defaults to off.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>SupplementaryGroups=</varname></term>
<listitem><para>Sets the supplementary Unix groups the processes are executed as. This takes a space-separated
list of group names or IDs. This option may be specified more than once, in which case all listed groups are
set as supplementary groups. When the empty string is assigned, the list of supplementary groups is reset, and
all assignments prior to this one will have no effect. In any way, this option does not override, but extends
the list of supplementary groups configured in the system group database for the user. This does not affect
commands prefixed with <literal>+</literal>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>PAMName=</varname></term>
<listitem><para>Sets the PAM service name to set up a session as. If set, the executed process will be
registered as a PAM session under the specified service name. This is only useful in conjunction with the
<varname>User=</varname> setting, and is otherwise ignored. If not set, no PAM session will be opened for the
executed processes. See <citerefentry
project='man-pages'><refentrytitle>pam</refentrytitle><manvolnum>8</manvolnum></citerefentry> for
details.</para>
<para>Note that for each unit making use of this option a PAM session handler process will be maintained as
part of the unit and stays around as long as the unit is active, to ensure that appropriate actions can be
taken when the unit and hence the PAM session terminates. This process is named <literal>(sd-pam)</literal> and
is an immediate child process of the unit's main process.</para>
<para>Note that when this option is used for a unit it is very likely (depending on PAM configuration) that the
main unit process will be migrated to its own session scope unit when it is activated. This process will hence
be associated with two units: the unit it was originally started from (and for which
<varname>PAMName=</varname> was configured), and the session scope unit. Any child processes of that process
will however be associated with the session scope unit only. This has implications when used in combination
with <varname>NotifyAccess=</varname><option>all</option>, as these child processes will not be able to affect
changes in the original unit through notification messages. These messages will be considered belonging to the
session scope unit and not the original unit. It is hence not recommended to use <varname>PAMName=</varname> in
combination with <varname>NotifyAccess=</varname><option>all</option>.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Capabilities</title>
<variablelist class='unit-directives'>
<varlistentry>
<term><varname>CapabilityBoundingSet=</varname></term>
<listitem><para>Controls which capabilities to include in the capability bounding set for the executed
process. See <citerefentry
project='man-pages'><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
details. Takes a whitespace-separated list of capability names, e.g. <constant>CAP_SYS_ADMIN</constant>,
<constant>CAP_DAC_OVERRIDE</constant>, <constant>CAP_SYS_PTRACE</constant>. Capabilities listed will be
included in the bounding set, all others are removed. If the list of capabilities is prefixed with
<literal>~</literal>, all but the listed capabilities will be included, the effect of the assignment
inverted. Note that this option also affects the respective capabilities in the effective, permitted and
inheritable capability sets. If this option is not used, the capability bounding set is not modified on process
execution, hence no limits on the capabilities of the process are enforced. This option may appear more than
once, in which case the bounding sets are merged by <constant>OR</constant>, or by <constant>AND</constant> if
the lines are prefixed with <literal>~</literal> (see below). If the empty string is assigned to this option,
the bounding set is reset to the empty capability set, and all prior settings have no effect. If set to
<literal>~</literal> (without any further argument), the bounding set is reset to the full set of available
capabilities, also undoing any previous settings. This does not affect commands prefixed with
<literal>+</literal>.</para>
<para>Example: if a unit has the following,
<programlisting>CapabilityBoundingSet=CAP_A CAP_B
CapabilityBoundingSet=CAP_B CAP_C</programlisting>
then <constant>CAP_A</constant>, <constant>CAP_B</constant>, and <constant>CAP_C</constant> are set.
If the second line is prefixed with <literal>~</literal>, e.g.,
<programlisting>CapabilityBoundingSet=CAP_A CAP_B
CapabilityBoundingSet=~CAP_B CAP_C</programlisting>
then, only <constant>CAP_A</constant> is set.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>AmbientCapabilities=</varname></term>
<listitem><para>Controls which capabilities to include in the ambient capability set for the executed
process. Takes a whitespace-separated list of capability names, e.g. <constant>CAP_SYS_ADMIN</constant>,
<constant>CAP_DAC_OVERRIDE</constant>, <constant>CAP_SYS_PTRACE</constant>. This option may appear more than
once in which case the ambient capability sets are merged (see the above examples in
<varname>CapabilityBoundingSet=</varname>). If the list of capabilities is prefixed with <literal>~</literal>,
all but the listed capabilities will be included, the effect of the assignment inverted. If the empty string is
assigned to this option, the ambient capability set is reset to the empty capability set, and all prior
settings have no effect. If set to <literal>~</literal> (without any further argument), the ambient capability
set is reset to the full set of available capabilities, also undoing any previous settings. Note that adding
capabilities to ambient capability set adds them to the process's inherited capability set. </para><para>
Ambient capability sets are useful if you want to execute a process as a non-privileged user but still want to
give it some capabilities. Note that in this case option <constant>keep-caps</constant> is automatically added
to <varname>SecureBits=</varname> to retain the capabilities over the user
change. <varname>AmbientCapabilities=</varname> does not affect commands prefixed with
<literal>+</literal>.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Security</title>
<variablelist class='unit-directives'>
<varlistentry>
<term><varname>NoNewPrivileges=</varname></term>
<listitem><para>Takes a boolean argument. If true, ensures that the service process and all its children can
never gain new privileges through <function>execve()</function> (e.g. via setuid or setgid bits, or filesystem
capabilities). This is the simplest and most effective way to ensure that a process and its children can never
elevate privileges again. Defaults to false, but certain settings override this and ignore the value of this
setting. This is the case when <varname>SystemCallFilter=</varname>,
<varname>SystemCallArchitectures=</varname>, <varname>RestrictAddressFamilies=</varname>,
<varname>RestrictNamespaces=</varname>, <varname>PrivateDevices=</varname>,
<varname>ProtectKernelTunables=</varname>, <varname>ProtectKernelModules=</varname>,
<varname>MemoryDenyWriteExecute=</varname>, <varname>RestrictRealtime=</varname>, or
<varname>LockPersonality=</varname> are specified. Note that even if this setting is overridden by them,
<command>systemctl show</command> shows the original value of this setting. Also see
<ulink url="https://www.kernel.org/doc/html/latest/userspace-api/no_new_privs.html">No New Privileges
Flag</ulink>. </para></listitem>
</varlistentry>
<varlistentry>
<term><varname>SecureBits=</varname></term>
<listitem><para>Controls the secure bits set for the executed process. Takes a space-separated combination of
options from the following list: <option>keep-caps</option>, <option>keep-caps-locked</option>,
<option>no-setuid-fixup</option>, <option>no-setuid-fixup-locked</option>, <option>noroot</option>, and
<option>noroot-locked</option>. This option may appear more than once, in which case the secure bits are
ORed. If the empty string is assigned to this option, the bits are reset to 0. This does not affect commands
prefixed with <literal>+</literal>. See <citerefentry
project='man-pages'><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
details.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Mandatory Access Control</title>
<variablelist>
<varlistentry>
<term><varname>SELinuxContext=</varname></term>
<listitem><para>Set the SELinux security context of the executed process. If set, this will override the
automated domain transition. However, the policy still needs to authorize the transition. This directive is
ignored if SELinux is disabled. If prefixed by <literal>-</literal>, all errors will be ignored. This does not
affect commands prefixed with <literal>+</literal>. See <citerefentry
project='die-net'><refentrytitle>setexeccon</refentrytitle><manvolnum>3</manvolnum></citerefentry> for
details.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>AppArmorProfile=</varname></term>
<listitem><para>Takes a profile name as argument. The process executed by the unit will switch to this profile
when started. Profiles must already be loaded in the kernel, or the unit will fail. This result in a non
operation if AppArmor is not enabled. If prefixed by <literal>-</literal>, all errors will be ignored. This
does not affect commands prefixed with <literal>+</literal>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>SmackProcessLabel=</varname></term>
<listitem><para>Takes a <option>SMACK64</option> security label as argument. The process executed by the unit
will be started under this label and SMACK will decide whether the process is allowed to run or not, based on
it. The process will continue to run under the label specified here unless the executable has its own
<option>SMACK64EXEC</option> label, in which case the process will transition to run under that label. When not
specified, the label that systemd is running under is used. This directive is ignored if SMACK is
disabled.</para>
<para>The value may be prefixed by <literal>-</literal>, in which case all errors will be ignored. An empty
value may be specified to unset previous assignments. This does not affect commands prefixed with
<literal>+</literal>.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Process Properties</title>
<variablelist>
<varlistentry>
<term><varname>LimitCPU=</varname></term>
<term><varname>LimitFSIZE=</varname></term>
<term><varname>LimitDATA=</varname></term>
<term><varname>LimitSTACK=</varname></term>
<term><varname>LimitCORE=</varname></term>
<term><varname>LimitRSS=</varname></term>
<term><varname>LimitNOFILE=</varname></term>
<term><varname>LimitAS=</varname></term>
<term><varname>LimitNPROC=</varname></term>
<term><varname>LimitMEMLOCK=</varname></term>
<term><varname>LimitLOCKS=</varname></term>
<term><varname>LimitSIGPENDING=</varname></term>
<term><varname>LimitMSGQUEUE=</varname></term>
<term><varname>LimitNICE=</varname></term>
<term><varname>LimitRTPRIO=</varname></term>
<term><varname>LimitRTTIME=</varname></term>
<listitem><para>Set soft and hard limits on various resources for executed processes. See
<citerefentry><refentrytitle>setrlimit</refentrytitle><manvolnum>2</manvolnum></citerefentry> for details on
the resource limit concept. Resource limits may be specified in two formats: either as single value to set a
specific soft and hard limit to the same value, or as colon-separated pair <option>soft:hard</option> to set
both limits individually (e.g. <literal>LimitAS=4G:16G</literal>). Use the string <option>infinity</option> to
configure no limit on a specific resource. The multiplicative suffixes K, M, G, T, P and E (to the base 1024)
may be used for resource limits measured in bytes (e.g. LimitAS=16G). For the limits referring to time values,
the usual time units ms, s, min, h and so on may be used (see
<citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
details). Note that if no time unit is specified for <varname>LimitCPU=</varname> the default unit of seconds
is implied, while for <varname>LimitRTTIME=</varname> the default unit of microseconds is implied. Also, note
that the effective granularity of the limits might influence their enforcement. For example, time limits
specified for <varname>LimitCPU=</varname> will be rounded up implicitly to multiples of 1s. For
<varname>LimitNICE=</varname> the value may be specified in two syntaxes: if prefixed with <literal>+</literal>
or <literal>-</literal>, the value is understood as regular Linux nice value in the range -20..19. If not
prefixed like this the value is understood as raw resource limit parameter in the range 0..40 (with 0 being
equivalent to 1).</para>
<para>Note that most process resource limits configured with these options are per-process, and processes may
fork in order to acquire a new set of resources that are accounted independently of the original process, and
may thus escape limits set. Also note that <varname>LimitRSS=</varname> is not implemented on Linux, and
setting it has no effect. Often it is advisable to prefer the resource controls listed in
<citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>
over these per-process limits, as they apply to services as a whole, may be altered dynamically at runtime, and
are generally more expressive. For example, <varname>MemoryLimit=</varname> is a more powerful (and working)
replacement for <varname>LimitRSS=</varname>.</para>
<para>For system units these resource limits may be chosen freely. For user units however (i.e. units run by a
per-user instance of
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>), these limits are
bound by (possibly more restrictive) per-user limits enforced by the OS.</para>
<para>Resource limits not configured explicitly for a unit default to the value configured in the various
<varname>DefaultLimitCPU=</varname>, <varname>DefaultLimitFSIZE=</varname>, … options available in
<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>, and –
if not configured there – the kernel or per-user defaults, as defined by the OS (the latter only for user
services, see above).</para>
<table>
<title>Resource limit directives, their equivalent <command>ulimit</command> shell commands and the unit used</title>
<tgroup cols='3'>
<colspec colname='directive' />
<colspec colname='equivalent' />
<colspec colname='unit' />
<thead>
<row>
<entry>Directive</entry>
<entry><command>ulimit</command> equivalent</entry>
<entry>Unit</entry>
</row>
</thead>
<tbody>
<row>
<entry>LimitCPU=</entry>
<entry>ulimit -t</entry>
<entry>Seconds</entry>
</row>
<row>
<entry>LimitFSIZE=</entry>
<entry>ulimit -f</entry>
<entry>Bytes</entry>
</row>
<row>
<entry>LimitDATA=</entry>
<entry>ulimit -d</entry>
<entry>Bytes</entry>
</row>
<row>
<entry>LimitSTACK=</entry>
<entry>ulimit -s</entry>
<entry>Bytes</entry>
</row>
<row>
<entry>LimitCORE=</entry>
<entry>ulimit -c</entry>
<entry>Bytes</entry>
</row>
<row>
<entry>LimitRSS=</entry>
<entry>ulimit -m</entry>
<entry>Bytes</entry>
</row>
<row>
<entry>LimitNOFILE=</entry>
<entry>ulimit -n</entry>
<entry>Number of File Descriptors</entry>
</row>
<row>
<entry>LimitAS=</entry>
<entry>ulimit -v</entry>
<entry>Bytes</entry>
</row>
<row>
<entry>LimitNPROC=</entry>
<entry>ulimit -u</entry>
<entry>Number of Processes</entry>
</row>
<row>
<entry>LimitMEMLOCK=</entry>
<entry>ulimit -l</entry>
<entry>Bytes</entry>
</row>
<row>
<entry>LimitLOCKS=</entry>
<entry>ulimit -x</entry>
<entry>Number of Locks</entry>
</row>
<row>
<entry>LimitSIGPENDING=</entry>
<entry>ulimit -i</entry>
<entry>Number of Queued Signals</entry>
</row>
<row>
<entry>LimitMSGQUEUE=</entry>
<entry>ulimit -q</entry>
<entry>Bytes</entry>
</row>
<row>
<entry>LimitNICE=</entry>
<entry>ulimit -e</entry>
<entry>Nice Level</entry>
</row>
<row>
<entry>LimitRTPRIO=</entry>
<entry>ulimit -r</entry>
<entry>Realtime Priority</entry>
</row>
<row>
<entry>LimitRTTIME=</entry>
<entry>No equivalent</entry>
<entry>Microseconds</entry>
</row>
</tbody>
</tgroup>
</table></listitem>
</varlistentry>
<varlistentry>
<term><varname>UMask=</varname></term>
<listitem><para>Controls the file mode creation mask. Takes an access mode in octal notation. See
<citerefentry><refentrytitle>umask</refentrytitle><manvolnum>2</manvolnum></citerefentry> for details. Defaults
to 0022.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>KeyringMode=</varname></term>
<listitem><para>Controls how the kernel session keyring is set up for the service (see <citerefentry
project='man-pages'><refentrytitle>session-keyring</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
details on the session keyring). Takes one of <option>inherit</option>, <option>private</option>,
<option>shared</option>. If set to <option>inherit</option> no special keyring setup is done, and the kernel's
default behaviour is applied. If <option>private</option> is used a new session keyring is allocated when a
service process is invoked, and it is not linked up with any user keyring. This is the recommended setting for
system services, as this ensures that multiple services running under the same system user ID (in particular
the root user) do not share their key material among each other. If <option>shared</option> is used a new
session keyring is allocated as for <option>private</option>, but the user keyring of the user configured with
<varname>User=</varname> is linked into it, so that keys assigned to the user may be requested by the unit's
processes. In this modes multiple units running processes under the same user ID may share key material. Unless
<option>inherit</option> is selected the unique invocation ID for the unit (see below) is added as a protected
key by the name <literal>invocation_id</literal> to the newly created session keyring. Defaults to
<option>private</option> for services of the system service manager and to <option>inherit</option> for
non-service units and for services of the user service manager.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>OOMScoreAdjust=</varname></term>
<listitem><para>Sets the adjustment level for the Out-Of-Memory killer for executed processes. Takes an integer
between -1000 (to disable OOM killing for this process) and 1000 (to make killing of this process under memory
pressure very likely). See <ulink
url="https://www.kernel.org/doc/Documentation/filesystems/proc.txt">proc.txt</ulink> for
details.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>TimerSlackNSec=</varname></term>
<listitem><para>Sets the timer slack in nanoseconds for the executed processes. The timer slack controls the
accuracy of wake-ups triggered by timers. See
<citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry> for more
information. Note that in contrast to most other time span definitions this parameter takes an integer value in
nano-seconds if no unit is specified. The usual time units are understood too.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Personality=</varname></term>
<listitem><para>Controls which kernel architecture <citerefentry
project='man-pages'><refentrytitle>uname</refentrytitle><manvolnum>2</manvolnum></citerefentry> shall report,
when invoked by unit processes. Takes one of the architecture identifiers <constant>x86</constant>,
<constant>x86-64</constant>, <constant>ppc</constant>, <constant>ppc-le</constant>, <constant>ppc64</constant>,
<constant>ppc64-le</constant>, <constant>s390</constant> or <constant>s390x</constant>. Which personality
architectures are supported depends on the system architecture. Usually the 64bit versions of the various
system architectures support their immediate 32bit personality architecture counterpart, but no others. For
example, <constant>x86-64</constant> systems support the <constant>x86-64</constant> and
<constant>x86</constant> personalities but no others. The personality feature is useful when running 32-bit
services on a 64-bit host system. If not specified, the personality is left unmodified and thus reflects the
personality of the host system's kernel.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>IgnoreSIGPIPE=</varname></term>
<listitem><para>Takes a boolean argument. If true, causes <constant>SIGPIPE</constant> to be ignored in the
executed process. Defaults to true because <constant>SIGPIPE</constant> generally is useful only in shell
pipelines.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Scheduling</title>
<variablelist>
<varlistentry>
<term><varname>Nice=</varname></term>
<listitem><para>Sets the default nice level (scheduling priority) for executed processes. Takes an integer
between -20 (highest priority) and 19 (lowest priority). See
<citerefentry><refentrytitle>setpriority</refentrytitle><manvolnum>2</manvolnum></citerefentry> for
details.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>CPUSchedulingPolicy=</varname></term>
<listitem><para>Sets the CPU scheduling policy for executed processes. Takes one of <option>other</option>,
<option>batch</option>, <option>idle</option>, <option>fifo</option> or <option>rr</option>. See
<citerefentry><refentrytitle>sched_setscheduler</refentrytitle><manvolnum>2</manvolnum></citerefentry> for
details.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>CPUSchedulingPriority=</varname></term>
<listitem><para>Sets the CPU scheduling priority for executed processes. The available priority range depends
on the selected CPU scheduling policy (see above). For real-time scheduling policies an integer between 1
(lowest priority) and 99 (highest priority) can be used. See
<citerefentry><refentrytitle>sched_setscheduler</refentrytitle><manvolnum>2</manvolnum></citerefentry> for
details. </para></listitem>
</varlistentry>
<varlistentry>
<term><varname>CPUSchedulingResetOnFork=</varname></term>
<listitem><para>Takes a boolean argument. If true, elevated CPU scheduling priorities and policies will be
reset when the executed processes fork, and can hence not leak into child processes. See
<citerefentry><refentrytitle>sched_setscheduler</refentrytitle><manvolnum>2</manvolnum></citerefentry> for
details. Defaults to false.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>CPUAffinity=</varname></term>
<listitem><para>Controls the CPU affinity of the executed processes. Takes a list of CPU indices or ranges
separated by either whitespace or commas. CPU ranges are specified by the lower and upper CPU indices separated
by a dash. This option may be specified more than once, in which case the specified CPU affinity masks are
merged. If the empty string is assigned, the mask is reset, all assignments prior to this will have no
effect. See
<citerefentry><refentrytitle>sched_setaffinity</refentrytitle><manvolnum>2</manvolnum></citerefentry> for
details.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>NUMAPolicy=</varname></term>
<listitem><para>Controls the NUMA memory policy of the executed processes. Takes a policy type, one of:
<option>default</option>, <option>preferred</option>, <option>bind</option>, <option>interleave</option> and
<option>local</option>. A list of NUMA nodes that should be associated with the policy must be specified
in <varname>NUMAMask=</varname>. For more details on each policy please see,
<citerefentry><refentrytitle>set_mempolicy</refentrytitle><manvolnum>2</manvolnum></citerefentry>. For overall
overview of NUMA support in Linux see,
<citerefentry><refentrytitle>numa</refentrytitle><manvolnum>7</manvolnum></citerefentry>
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>NUMAMask=</varname></term>
<listitem><para>Controls the NUMA node list which will be applied alongside with selected NUMA policy.
Takes a list of NUMA nodes and has the same syntax as a list of CPUs for <varname>CPUAffinity=</varname>
option. Note that the list of NUMA nodes is not required for <option>default</option> and <option>local</option>
policies and for <option>preferred</option> policy we expect a single NUMA node.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>IOSchedulingClass=</varname></term>
<listitem><para>Sets the I/O scheduling class for executed processes. Takes an integer between 0 and 3 or one
of the strings <option>none</option>, <option>realtime</option>, <option>best-effort</option> or
<option>idle</option>. If the empty string is assigned to this option, all prior assignments to both
<varname>IOSchedulingClass=</varname> and <varname>IOSchedulingPriority=</varname> have no effect. See
<citerefentry><refentrytitle>ioprio_set</refentrytitle><manvolnum>2</manvolnum></citerefentry> for
details.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>IOSchedulingPriority=</varname></term>
<listitem><para>Sets the I/O scheduling priority for executed processes. Takes an integer between 0 (highest
priority) and 7 (lowest priority). The available priorities depend on the selected I/O scheduling class (see
above). If the empty string is assigned to this option, all prior assignments to both
<varname>IOSchedulingClass=</varname> and <varname>IOSchedulingPriority=</varname> have no effect.
See <citerefentry><refentrytitle>ioprio_set</refentrytitle><manvolnum>2</manvolnum></citerefentry> for
details.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Sandboxing</title>
<variablelist>
<varlistentry>
<term><varname>ProtectSystem=</varname></term>
<listitem><para>Takes a boolean argument or the special values <literal>full</literal> or
<literal>strict</literal>. If true, mounts the <filename>/usr</filename> and <filename>/boot</filename>
directories read-only for processes invoked by this unit. If set to <literal>full</literal>, the
<filename>/etc</filename> directory is mounted read-only, too. If set to <literal>strict</literal> the entire
file system hierarchy is mounted read-only, except for the API file system subtrees <filename>/dev</filename>,
<filename>/proc</filename> and <filename>/sys</filename> (protect these directories using
<varname>PrivateDevices=</varname>, <varname>ProtectKernelTunables=</varname>,
<varname>ProtectControlGroups=</varname>). This setting ensures that any modification of the vendor-supplied
operating system (and optionally its configuration, and local mounts) is prohibited for the service. It is
recommended to enable this setting for all long-running services, unless they are involved with system updates
or need to modify the operating system in other ways. If this option is used,
<varname>ReadWritePaths=</varname> may be used to exclude specific directories from being made read-only. This
setting is implied if <varname>DynamicUser=</varname> is set. For this setting the same restrictions regarding
mount propagation and privileges apply as for <varname>ReadOnlyPaths=</varname> and related calls, see
below. Defaults to off.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>ProtectHome=</varname></term>
<listitem><para>Takes a boolean argument or the special values <literal>read-only</literal> or
<literal>tmpfs</literal>. If true, the directories <filename>/home</filename>, <filename>/root</filename> and
<filename>/run/user</filename> are made inaccessible and empty for processes invoked by this unit. If set to
<literal>read-only</literal>, the three directories are made read-only instead. If set to <literal>tmpfs</literal>,
temporary file systems are mounted on the three directories in read-only mode. The value <literal>tmpfs</literal>
is useful to hide home directories not relevant to the processes invoked by the unit, while necessary directories
are still visible by combining with <varname>BindPaths=</varname> or <varname>BindReadOnlyPaths=</varname>.</para>
<para>Setting this to <literal>yes</literal> is mostly equivalent to set the three directories in
<varname>InaccessiblePaths=</varname>. Similarly, <literal>read-only</literal> is mostly equivalent to
<varname>ReadOnlyPaths=</varname>, and <literal>tmpfs</literal> is mostly equivalent to
<varname>TemporaryFileSystem=</varname>.</para>
<para> It is recommended to enable this setting for all long-running services (in particular network-facing ones),
to ensure they cannot get access to private user data, unless the services actually require access to the user's
private data. This setting is implied if <varname>DynamicUser=</varname> is set. For this setting the same
restrictions regarding mount propagation and privileges apply as for <varname>ReadOnlyPaths=</varname> and related
calls, see below.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>RuntimeDirectory=</varname></term>
<term><varname>StateDirectory=</varname></term>
<term><varname>CacheDirectory=</varname></term>
<term><varname>LogsDirectory=</varname></term>
<term><varname>ConfigurationDirectory=</varname></term>
<listitem><para>These options take a whitespace-separated list of directory names. The specified directory
names must be relative, and may not include <literal>..</literal>. If set, one or more
directories by the specified names will be created (including their parents) below the locations
defined in the following table, when the unit is started.</para>
<table>
<title>Automatic directory creation</title>
<tgroup cols='3'>
<thead>
<row>
<entry>Locations</entry>
<entry>for system</entry>
<entry>for users</entry>
</row>
</thead>
<tbody>
<row>
<entry><varname>RuntimeDirectory=</varname></entry>
<entry><filename>/run</filename></entry>
<entry><varname>$XDG_RUNTIME_DIR</varname></entry>
</row>
<row>
<entry><varname>StateDirectory=</varname></entry>
<entry><filename>/var/lib</filename></entry>
<entry><varname>$XDG_CONFIG_HOME</varname></entry>
</row>
<row>
<entry><varname>CacheDirectory=</varname></entry>
<entry><filename>/var/cache</filename></entry>
<entry><varname>$XDG_CACHE_HOME</varname></entry>
</row>
<row>
<entry><varname>LogsDirectory=</varname></entry>
<entry><filename>/var/log</filename></entry>
<entry><varname>$XDG_CONFIG_HOME</varname><filename>/log</filename></entry>
</row>
<row>
<entry><varname>ConfigurationDirectory=</varname></entry>
<entry><filename>/etc</filename></entry>
<entry><varname>$XDG_CONFIG_HOME</varname></entry>
</row>
</tbody>
</tgroup>
</table>
<para>In case of <varname>RuntimeDirectory=</varname> the lowest subdirectories are removed when the unit is
stopped. It is possible to preserve the specified directories in this case if
<varname>RuntimeDirectoryPreserve=</varname> is configured to <option>restart</option> or <option>yes</option>
(see below). The directories specified with <varname>StateDirectory=</varname>,
<varname>CacheDirectory=</varname>, <varname>LogsDirectory=</varname>,
<varname>ConfigurationDirectory=</varname> are not removed when the unit is stopped.</para>
<para>Except in case of <varname>ConfigurationDirectory=</varname>, the innermost specified directories will be
owned by the user and group specified in <varname>User=</varname> and <varname>Group=</varname>. If the
specified directories already exist and their owning user or group do not match the configured ones, all files
and directories below the specified directories as well as the directories themselves will have their file
ownership recursively changed to match what is configured. As an optimization, if the specified directories are
already owned by the right user and group, files and directories below of them are left as-is, even if they do
not match what is requested. The innermost specified directories will have their access mode adjusted to the
what is specified in <varname>RuntimeDirectoryMode=</varname>, <varname>StateDirectoryMode=</varname>,
<varname>CacheDirectoryMode=</varname>, <varname>LogsDirectoryMode=</varname> and
<varname>ConfigurationDirectoryMode=</varname>.</para>
<para>These options imply <varname>BindPaths=</varname> for the specified paths. When combined with
<varname>RootDirectory=</varname> or <varname>RootImage=</varname> these paths always reside on the host and
are mounted from there into the unit's file system namespace.</para>
<para>If <varname>DynamicUser=</varname> is used in conjunction with <varname>StateDirectory=</varname>,
<varname>CacheDirectory=</varname> and <varname>LogsDirectory=</varname> is slightly altered: the directories
are created below <filename>/var/lib/private</filename>, <filename>/var/cache/private</filename> and
<filename>/var/log/private</filename>, respectively, which are host directories made inaccessible to
unprivileged users, which ensures that access to these directories cannot be gained through dynamic user ID
recycling. Symbolic links are created to hide this difference in behaviour. Both from perspective of the host
and from inside the unit, the relevant directories hence always appear directly below
<filename>/var/lib</filename>, <filename>/var/cache</filename> and <filename>/var/log</filename>.</para>
<para>Use <varname>RuntimeDirectory=</varname> to manage one or more runtime directories for the unit and bind
their lifetime to the daemon runtime. This is particularly useful for unprivileged daemons that cannot create
runtime directories in <filename>/run</filename> due to lack of privileges, and to make sure the runtime
directory is cleaned up automatically after use. For runtime directories that require more complex or different
configuration or lifetime guarantees, please consider using
<citerefentry><refentrytitle>tmpfiles.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
<para>Example: if a system service unit has the following,
<programlisting>RuntimeDirectory=foo/bar baz</programlisting>
the service manager creates <filename>/run/foo</filename> (if it does not exist),
<filename>/run/foo/bar</filename>, and <filename>/run/baz</filename>. The directories
<filename>/run/foo/bar</filename> and <filename>/run/baz</filename> except <filename>/run/foo</filename> are
owned by the user and group specified in <varname>User=</varname> and <varname>Group=</varname>, and removed
when the service is stopped.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>RuntimeDirectoryMode=</varname></term>
<term><varname>StateDirectoryMode=</varname></term>
<term><varname>CacheDirectoryMode=</varname></term>
<term><varname>LogsDirectoryMode=</varname></term>
<term><varname>ConfigurationDirectoryMode=</varname></term>
<listitem><para>Specifies the access mode of the directories specified in <varname>RuntimeDirectory=</varname>,
<varname>StateDirectory=</varname>, <varname>CacheDirectory=</varname>, <varname>LogsDirectory=</varname>, or
<varname>ConfigurationDirectory=</varname>, respectively, as an octal number. Defaults to
<constant>0755</constant>. See "Permissions" in <citerefentry
project='man-pages'><refentrytitle>path_resolution</refentrytitle><manvolnum>7</manvolnum></citerefentry> for a
discussion of the meaning of permission bits.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>RuntimeDirectoryPreserve=</varname></term>
<listitem><para>Takes a boolean argument or <option>restart</option>. If set to <option>no</option> (the
default), the directories specified in <varname>RuntimeDirectory=</varname> are always removed when the service
stops. If set to <option>restart</option> the directories are preserved when the service is both automatically
and manually restarted. Here, the automatic restart means the operation specified in
<varname>Restart=</varname>, and manual restart means the one triggered by <command>systemctl restart
foo.service</command>. If set to <option>yes</option>, then the directories are not removed when the service is
stopped. Note that since the runtime directory <filename>/run</filename> is a mount point of
<literal>tmpfs</literal>, then for system services the directories specified in
<varname>RuntimeDirectory=</varname> are removed when the system is rebooted.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>ReadWritePaths=</varname></term>
<term><varname>ReadOnlyPaths=</varname></term>
<term><varname>InaccessiblePaths=</varname></term>
<listitem><para>Sets up a new file system namespace for executed processes. These options may be used to limit
access a process might have to the file system hierarchy. Each setting takes a space-separated list of paths
relative to the host's root directory (i.e. the system running the service manager). Note that if paths
contain symlinks, they are resolved relative to the root directory set with
<varname>RootDirectory=</varname>/<varname>RootImage=</varname>.</para>
<para>Paths listed in <varname>ReadWritePaths=</varname> are accessible from within the namespace with the same
access modes as from outside of it. Paths listed in <varname>ReadOnlyPaths=</varname> are accessible for
reading only, writing will be refused even if the usual file access controls would permit this. Nest
<varname>ReadWritePaths=</varname> inside of <varname>ReadOnlyPaths=</varname> in order to provide writable
subdirectories within read-only directories. Use <varname>ReadWritePaths=</varname> in order to whitelist
specific paths for write access if <varname>ProtectSystem=strict</varname> is used.</para>
<para>Paths listed in <varname>InaccessiblePaths=</varname> will be made inaccessible for processes inside
the namespace along with everything below them in the file system hierarchy. This may be more restrictive than
desired, because it is not possible to nest <varname>ReadWritePaths=</varname>, <varname>ReadOnlyPaths=</varname>,
<varname>BindPaths=</varname>, or <varname>BindReadOnlyPaths=</varname> inside it. For a more flexible option,
see <varname>TemporaryFileSystem=</varname>.</para>
<para>Note that restricting access with these options does not extend to submounts of a directory that are
created later on. Non-directory paths may be specified as well. These options may be specified more than once,
in which case all paths listed will have limited access from within the namespace. If the empty string is
assigned to this option, the specific list is reset, and all prior assignments have no effect.</para>
<para>Paths in <varname>ReadWritePaths=</varname>, <varname>ReadOnlyPaths=</varname> and
<varname>InaccessiblePaths=</varname> may be prefixed with <literal>-</literal>, in which case they will be
ignored when they do not exist. If prefixed with <literal>+</literal> the paths are taken relative to the root
directory of the unit, as configured with <varname>RootDirectory=</varname>/<varname>RootImage=</varname>,
instead of relative to the root directory of the host (see above). When combining <literal>-</literal> and
<literal>+</literal> on the same path make sure to specify <literal>-</literal> first, and <literal>+</literal>
second.</para>
<para>Note that using this setting will disconnect propagation of mounts from the service to the host
(propagation in the opposite direction continues to work). This means that this setting may not be used for
services which shall be able to install mount points in the main mount namespace. Note that the effect of these
settings may be undone by privileged processes. In order to set up an effective sandboxed environment for a
unit it is thus recommended to combine these settings with either
<varname>CapabilityBoundingSet=~CAP_SYS_ADMIN</varname> or
<varname>SystemCallFilter=~@mount</varname>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>TemporaryFileSystem=</varname></term>
<listitem><para>Takes a space-separated list of mount points for temporary file systems (tmpfs). If set, a new file
system namespace is set up for executed processes, and a temporary file system is mounted on each mount point.
This option may be specified more than once, in which case temporary file systems are mounted on all listed mount
points. If the empty string is assigned to this option, the list is reset, and all prior assignments have no effect.
Each mount point may optionally be suffixed with a colon (<literal>:</literal>) and mount options such as
<literal>size=10%</literal> or <literal>ro</literal>. By default, each temporary file system is mounted
with <literal>nodev,strictatime,mode=0755</literal>. These can be disabled by explicitly specifying the corresponding
mount options, e.g., <literal>dev</literal> or <literal>nostrictatime</literal>.</para>
<para>This is useful to hide files or directories not relevant to the processes invoked by the unit, while necessary
files or directories can be still accessed by combining with <varname>BindPaths=</varname> or
<varname>BindReadOnlyPaths=</varname>. See the example below.</para>
<para>Example: if a unit has the following,
<programlisting>TemporaryFileSystem=/var:ro
BindReadOnlyPaths=/var/lib/systemd</programlisting>
then the invoked processes by the unit cannot see any files or directories under <filename>/var</filename> except for
<filename>/var/lib/systemd</filename> or its contents.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>PrivateTmp=</varname></term>
<listitem><para>Takes a boolean argument. If true, sets up a new file system namespace for the executed
processes and mounts private <filename>/tmp</filename> and <filename>/var/tmp</filename> directories inside it
that is not shared by processes outside of the namespace. This is useful to secure access to temporary files of
the process, but makes sharing between processes via <filename>/tmp</filename> or <filename>/var/tmp</filename>
impossible. If this is enabled, all temporary files created by a service in these directories will be removed
after the service is stopped. Defaults to false. It is possible to run two or more units within the same
private <filename>/tmp</filename> and <filename>/var/tmp</filename> namespace by using the
<varname>JoinsNamespaceOf=</varname> directive, see
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
details. This setting is implied if <varname>DynamicUser=</varname> is set. For this setting the same
restrictions regarding mount propagation and privileges apply as for <varname>ReadOnlyPaths=</varname> and
related calls, see above. Enabling this setting has the side effect of adding <varname>Requires=</varname> and
<varname>After=</varname> dependencies on all mount units necessary to access <filename>/tmp</filename> and
<filename>/var/tmp</filename>. Moreover an implicitly <varname>After=</varname> ordering on
<citerefentry><refentrytitle>systemd-tmpfiles-setup.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
is added.</para>
<para>Note that the implementation of this setting might be impossible (for example if mount namespaces are not
available), and the unit should be written in a way that does not solely rely on this setting for
security.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>PrivateDevices=</varname></term>
<listitem><para>Takes a boolean argument. If true, sets up a new <filename>/dev</filename> mount for the
executed processes and only adds API pseudo devices such as <filename>/dev/null</filename>,
<filename>/dev/zero</filename> or <filename>/dev/random</filename> (as well as the pseudo TTY subsystem) to it,
but no physical devices such as <filename>/dev/sda</filename>, system memory <filename>/dev/mem</filename>,
system ports <filename>/dev/port</filename> and others. This is useful to securely turn off physical device
access by the executed process. Defaults to false. Enabling this option will install a system call filter to
block low-level I/O system calls that are grouped in the <varname>@raw-io</varname> set, will also remove
<constant>CAP_MKNOD</constant> and <constant>CAP_SYS_RAWIO</constant> from the capability bounding set for the
unit (see above), and set <varname>DevicePolicy=closed</varname> (see
<citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for details). Note that using this setting will disconnect propagation of mounts from the service to the host
(propagation in the opposite direction continues to work). This means that this setting may not be used for
services which shall be able to install mount points in the main mount namespace. The new
<filename>/dev</filename> will be mounted read-only and 'noexec'. The latter may break old programs which try
to set up executable memory by using
<citerefentry><refentrytitle>mmap</refentrytitle><manvolnum>2</manvolnum></citerefentry> of
<filename>/dev/zero</filename> instead of using <constant>MAP_ANON</constant>. For this setting the same
restrictions regarding mount propagation and privileges apply as for <varname>ReadOnlyPaths=</varname> and
related calls, see above. If turned on and if running in user mode, or in system mode, but without the
<constant>CAP_SYS_ADMIN</constant> capability (e.g. setting <varname>User=</varname>),
<varname>NoNewPrivileges=yes</varname> is implied.</para>
<para>Note that the implementation of this setting might be impossible (for example if mount namespaces are not
available), and the unit should be written in a way that does not solely rely on this setting for
security.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>PrivateNetwork=</varname></term>
<listitem><para>Takes a boolean argument. If true, sets up a new network namespace for the executed processes
and configures only the loopback network device <literal>lo</literal> inside it. No other network devices will
be available to the executed process. This is useful to turn off network access by the executed process.
Defaults to false. It is possible to run two or more units within the same private network namespace by using
the <varname>JoinsNamespaceOf=</varname> directive, see
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
details. Note that this option will disconnect all socket families from the host, this includes AF_NETLINK and
AF_UNIX. The latter has the effect that AF_UNIX sockets in the abstract socket namespace will become
unavailable to the processes (however, those located in the file system will continue to be accessible).</para>
<para>Note that the implementation of this setting might be impossible (for example if network namespaces are
not available), and the unit should be written in a way that does not solely rely on this setting for
security.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>PrivateUsers=</varname></term>
<listitem><para>Takes a boolean argument. If true, sets up a new user namespace for the executed processes and
configures a minimal user and group mapping, that maps the <literal>root</literal> user and group as well as
the unit's own user and group to themselves and everything else to the <literal>nobody</literal> user and
group. This is useful to securely detach the user and group databases used by the unit from the rest of the
system, and thus to create an effective sandbox environment. All files, directories, processes, IPC objects and
other resources owned by users/groups not equaling <literal>root</literal> or the unit's own will stay visible
from within the unit but appear owned by the <literal>nobody</literal> user and group. If this mode is enabled,
all unit processes are run without privileges in the host user namespace (regardless if the unit's own
user/group is <literal>root</literal> or not). Specifically this means that the process will have zero process
capabilities on the host's user namespace, but full capabilities within the service's user namespace. Settings
such as <varname>CapabilityBoundingSet=</varname> will affect only the latter, and there's no way to acquire
additional capabilities in the host's user namespace. Defaults to off.</para>
<para>This setting is particularly useful in conjunction with
<varname>RootDirectory=</varname>/<varname>RootImage=</varname>, as the need to synchronize the user and group
databases in the root directory and on the host is reduced, as the only users and groups who need to be matched
are <literal>root</literal>, <literal>nobody</literal> and the unit's own user and group.</para>
<para>Note that the implementation of this setting might be impossible (for example if user namespaces are not
available), and the unit should be written in a way that does not solely rely on this setting for
security.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>ProtectKernelTunables=</varname></term>
<listitem><para>Takes a boolean argument. If true, kernel variables accessible through
<filename>/proc/sys</filename>, <filename>/sys</filename>, <filename>/proc/sysrq-trigger</filename>,
<filename>/proc/latency_stats</filename>, <filename>/proc/acpi</filename>,
<filename>/proc/timer_stats</filename>, <filename>/proc/fs</filename> and <filename>/proc/irq</filename> will
be made read-only to all processes of the unit. Usually, tunable kernel variables should be initialized only at
boot-time, for example with the
<citerefentry><refentrytitle>sysctl.d</refentrytitle><manvolnum>5</manvolnum></citerefentry> mechanism. Few
services need to write to these at runtime; it is hence recommended to turn this on for most services. For this
setting the same restrictions regarding mount propagation and privileges apply as for
<varname>ReadOnlyPaths=</varname> and related calls, see above. Defaults to off. If turned on and if running
in user mode, or in system mode, but without the <constant>CAP_SYS_ADMIN</constant> capability (e.g. services
for which <varname>User=</varname> is set), <varname>NoNewPrivileges=yes</varname> is implied. Note that this
option does not prevent indirect changes to kernel tunables effected by IPC calls to other processes. However,
<varname>InaccessiblePaths=</varname> may be used to make relevant IPC file system objects inaccessible. If
<varname>ProtectKernelTunables=</varname> is set, <varname>MountAPIVFS=yes</varname> is
implied.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>ProtectKernelModules=</varname></term>
<listitem><para>Takes a boolean argument. If true, explicit module loading will be denied. This allows
module load and unload operations to be turned off on modular kernels. It is recommended to turn this on for most services
that do not need special file systems or extra kernel modules to work. Defaults to off. Enabling this option
removes <constant>CAP_SYS_MODULE</constant> from the capability bounding set for the unit, and installs a
system call filter to block module system calls, also <filename>/usr/lib/modules</filename> is made
inaccessible. For this setting the same restrictions regarding mount propagation and privileges apply as for
<varname>ReadOnlyPaths=</varname> and related calls, see above. Note that limited automatic module loading due
to user configuration or kernel mapping tables might still happen as side effect of requested user operations,
both privileged and unprivileged. To disable module auto-load feature please see
<citerefentry><refentrytitle>sysctl.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>
<constant>kernel.modules_disabled</constant> mechanism and
<filename>/proc/sys/kernel/modules_disabled</filename> documentation. If turned on and if running in user
mode, or in system mode, but without the <constant>CAP_SYS_ADMIN</constant> capability (e.g. setting
<varname>User=</varname>), <varname>NoNewPrivileges=yes</varname> is implied.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>ProtectControlGroups=</varname></term>
<listitem><para>Takes a boolean argument. If true, the Linux Control Groups (<citerefentry
project='man-pages'><refentrytitle>cgroups</refentrytitle><manvolnum>7</manvolnum></citerefentry>) hierarchies
accessible through <filename>/sys/fs/cgroup</filename> will be made read-only to all processes of the
unit. Except for container managers no services should require write access to the control groups hierarchies;
it is hence recommended to turn this on for most services. For this setting the same restrictions regarding
mount propagation and privileges apply as for <varname>ReadOnlyPaths=</varname> and related calls, see
above. Defaults to off. If <varname>ProtectControlGroups=</varname> is set, <varname>MountAPIVFS=yes</varname>
is implied.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>RestrictAddressFamilies=</varname></term>
<listitem><para>Restricts the set of socket address families accessible to the processes of this unit. Takes a
space-separated list of address family names to whitelist, such as <constant>AF_UNIX</constant>,
<constant>AF_INET</constant> or <constant>AF_INET6</constant>. When prefixed with <constant>~</constant> the
listed address families will be applied as blacklist, otherwise as whitelist. Note that this restricts access
to the <citerefentry
project='man-pages'><refentrytitle>socket</refentrytitle><manvolnum>2</manvolnum></citerefentry> system call
only. Sockets passed into the process by other means (for example, by using socket activation with socket
units, see <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>)
are unaffected. Also, sockets created with <function>socketpair()</function> (which creates connected AF_UNIX
sockets only) are unaffected. Note that this option has no effect on 32-bit x86, s390, s390x, mips, mips-le,
ppc, ppc-le, pcc64, ppc64-le and is ignored (but works correctly on other ABIs, including x86-64). Note that on
systems supporting multiple ABIs (such as x86/x86-64) it is recommended to turn off alternative ABIs for
services, so that they cannot be used to circumvent the restrictions of this option. Specifically, it is
recommended to combine this option with <varname>SystemCallArchitectures=native</varname> or similar. If
running in user mode, or in system mode, but without the <constant>CAP_SYS_ADMIN</constant> capability
(e.g. setting <varname>User=nobody</varname>), <varname>NoNewPrivileges=yes</varname> is implied. By default,
no restrictions apply, all address families are accessible to processes. If assigned the empty string, any
previous address familiy restriction changes are undone. This setting does not affect commands prefixed with
<literal>+</literal>.</para>
<para>Use this option to limit exposure of processes to remote access, in particular via exotic and sensitive
network protocols, such as <constant>AF_PACKET</constant>. Note that in most cases, the local
<constant>AF_UNIX</constant> address family should be included in the configured whitelist as it is frequently
used for local communication, including for
<citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>2</manvolnum></citerefentry>
logging.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>RestrictNamespaces=</varname></term>
<listitem><para>Restricts access to Linux namespace functionality for the processes of this unit. For details
about Linux namespaces, see <citerefentry
project='man-pages'><refentrytitle>namespaces</refentrytitle><manvolnum>7</manvolnum></citerefentry>. Either
takes a boolean argument, or a space-separated list of namespace type identifiers. If false (the default), no
restrictions on namespace creation and switching are made. If true, access to any kind of namespacing is
prohibited. Otherwise, a space-separated list of namespace type identifiers must be specified, consisting of
any combination of: <constant>cgroup</constant>, <constant>ipc</constant>, <constant>net</constant>,
<constant>mnt</constant>, <constant>pid</constant>, <constant>user</constant> and <constant>uts</constant>. Any
namespace type listed is made accessible to the unit's processes, access to namespace types not listed is
prohibited (whitelisting). By prepending the list with a single tilde character (<literal>~</literal>) the
effect may be inverted: only the listed namespace types will be made inaccessible, all unlisted ones are
permitted (blacklisting). If the empty string is assigned, the default namespace restrictions are applied,
which is equivalent to false. This option may appear more than once, in which case the namespace types are
merged by <constant>OR</constant>, or by <constant>AND</constant> if the lines are prefixed with
<literal>~</literal> (see examples below). Internally, this setting limits access to the
<citerefentry><refentrytitle>unshare</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
<citerefentry><refentrytitle>clone</refentrytitle><manvolnum>2</manvolnum></citerefentry> and
<citerefentry><refentrytitle>setns</refentrytitle><manvolnum>2</manvolnum></citerefentry> system calls, taking
the specified flags parameters into account. Note that — if this option is used — in addition to restricting
creation and switching of the specified types of namespaces (or all of them, if true) access to the
<function>setns()</function> system call with a zero flags parameter is prohibited. This setting is only
supported on x86, x86-64, mips, mips-le, mips64, mips64-le, mips64-n32, mips64-le-n32, ppc64, ppc64-le, s390
and s390x, and enforces no restrictions on other architectures. If running in user mode, or in system mode, but
without the <constant>CAP_SYS_ADMIN</constant> capability (e.g. setting <varname>User=</varname>),
<varname>NoNewPrivileges=yes</varname> is implied.</para>
<para>Example: if a unit has the following,
<programlisting>RestrictNamespaces=cgroup ipc
RestrictNamespaces=cgroup net</programlisting>
then <constant>cgroup</constant>, <constant>ipc</constant>, and <constant>net</constant> are set.
If the second line is prefixed with <literal>~</literal>, e.g.,
<programlisting>RestrictNamespaces=cgroup ipc
RestrictNamespaces=~cgroup net</programlisting>
then, only <constant>ipc</constant> is set.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>LockPersonality=</varname></term>
<listitem><para>Takes a boolean argument. If set, locks down the <citerefentry
project='man-pages'><refentrytitle>personality</refentrytitle><manvolnum>2</manvolnum></citerefentry> system
call so that the kernel execution domain may not be changed from the default or the personality selected with
<varname>Personality=</varname> directive. This may be useful to improve security, because odd personality
emulations may be poorly tested and source of vulnerabilities. If running in user mode, or in system mode, but
without the <constant>CAP_SYS_ADMIN</constant> capability (e.g. setting <varname>User=</varname>),
<varname>NoNewPrivileges=yes</varname> is implied.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>MemoryDenyWriteExecute=</varname></term>
<listitem><para>Takes a boolean argument. If set, attempts to create memory mappings that are writable and
executable at the same time, or to change existing memory mappings to become executable, or mapping shared
memory segments as executable are prohibited. Specifically, a system call filter is added that rejects
<citerefentry><refentrytitle>mmap</refentrytitle><manvolnum>2</manvolnum></citerefentry> system calls with both
<constant>PROT_EXEC</constant> and <constant>PROT_WRITE</constant> set,
<citerefentry><refentrytitle>mprotect</refentrytitle><manvolnum>2</manvolnum></citerefentry> or
<citerefentry><refentrytitle>pkey_mprotect</refentrytitle><manvolnum>2</manvolnum></citerefentry> system calls
with <constant>PROT_EXEC</constant> set and
<citerefentry><refentrytitle>shmat</refentrytitle><manvolnum>2</manvolnum></citerefentry> system calls with
<constant>SHM_EXEC</constant> set. Note that this option is incompatible with programs and libraries that
generate program code dynamically at runtime, including JIT execution engines, executable stacks, and code
"trampoline" feature of various C compilers. This option improves service security, as it makes harder for
software exploits to change running code dynamically. Note that this feature is fully available on x86-64, and
partially on x86. Specifically, the <function>shmat()</function> protection is not available on x86. Note that
on systems supporting multiple ABIs (such as x86/x86-64) it is recommended to turn off alternative ABIs for
services, so that they cannot be used to circumvent the restrictions of this option. Specifically, it is
recommended to combine this option with <varname>SystemCallArchitectures=native</varname> or similar. If
running in user mode, or in system mode, but without the <constant>CAP_SYS_ADMIN</constant> capability
(e.g. setting <varname>User=</varname>), <varname>NoNewPrivileges=yes</varname> is implied.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>RestrictRealtime=</varname></term>
<listitem><para>Takes a boolean argument. If set, any attempts to enable realtime scheduling in a process of
the unit are refused. This restricts access to realtime task scheduling policies such as
<constant>SCHED_FIFO</constant>, <constant>SCHED_RR</constant> or <constant>SCHED_DEADLINE</constant>. See
<citerefentry project='man-pages'><refentrytitle>sched</refentrytitle><manvolnum>7</manvolnum></citerefentry>
for details about these scheduling policies. If running in user mode, or in system mode, but without the
<constant>CAP_SYS_ADMIN</constant> capability (e.g. setting <varname>User=</varname>),
<varname>NoNewPrivileges=yes</varname> is implied. Realtime scheduling policies may be used to monopolize CPU
time for longer periods of time, and may hence be used to lock up or otherwise trigger Denial-of-Service
situations on the system. It is hence recommended to restrict access to realtime scheduling to the few programs
that actually require them. Defaults to off.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>RemoveIPC=</varname></term>
<listitem><para>Takes a boolean parameter. If set, all System V and POSIX IPC objects owned by the user and
group the processes of this unit are run as are removed when the unit is stopped. This setting only has an
effect if at least one of <varname>User=</varname>, <varname>Group=</varname> and
<varname>DynamicUser=</varname> are used. It has no effect on IPC objects owned by the root user. Specifically,
this removes System V semaphores, as well as System V and POSIX shared memory segments and message queues. If
multiple units use the same user or group the IPC objects are removed when the last of these units is
stopped. This setting is implied if <varname>DynamicUser=</varname> is set.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>PrivateMounts=</varname></term>
<listitem><para>Takes a boolean parameter. If set, the processes of this unit will be run in their own private
file system (mount) namespace with all mount propagation from the processes towards the host's main file system
namespace turned off. This means any file system mount points established or removed by the unit's processes
will be private to them and not be visible to the host. However, file system mount points established or
removed on the host will be propagated to the unit's processes. See <citerefentry
project='man-pages'><refentrytitle>mount_namespaces</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
details on file system namespaces. Defaults to off.</para>
<para>When turned on, this executes three operations for each invoked process: a new
<constant>CLONE_NEWNS</constant> namespace is created, after which all existing mounts are remounted to
<constant>MS_SLAVE</constant> to disable propagation from the unit's processes to the host (but leaving
propagation in the opposite direction in effect). Finally, the mounts are remounted again to the propagation
mode configured with <varname>MountFlags=</varname>, see below.</para>
<para>File system namespaces are set up individually for each process forked off by the service manager. Mounts
established in the namespace of the process created by <varname>ExecStartPre=</varname> will hence be cleaned
up automatically as soon as that process exits and will not be available to subsequent processes forked off for
<varname>ExecStart=</varname> (and similar applies to the various other commands configured for
units). Similarly, <varname>JoinsNamespaceOf=</varname> does not permit sharing kernel mount namespaces between
units, it only enables sharing of the <filename>/tmp/</filename> and <filename>/var/tmp/</filename>
directories.</para>
<para>Other file system namespace unit settings — <varname>PrivateMounts=</varname>,
<varname>PrivateTmp=</varname>, <varname>PrivateDevices=</varname>, <varname>ProtectSystem=</varname>,
<varname>ProtectHome=</varname>, <varname>ReadOnlyPaths=</varname>, <varname>InaccessiblePaths=</varname>,
<varname>ReadWritePaths=</varname>, … — also enable file system namespacing in a fashion equivalent to this
option. Hence it is primarily useful to explicitly request this behaviour if none of the other settings are
used.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>MountFlags=</varname></term>
<listitem><para>Takes a mount propagation setting: <option>shared</option>, <option>slave</option> or
<option>private</option>, which controls whether file system mount points in the file system namespaces set up
for this unit's processes will receive or propagate mounts and unmounts from other file system namespaces. See
<citerefentry project='man-pages'><refentrytitle>mount</refentrytitle><manvolnum>2</manvolnum></citerefentry>
for details on mount propagation, and the three propagation flags in particular.</para>
<para>This setting only controls the <emphasis>final</emphasis> propagation setting in effect on all mount
points of the file system namespace created for each process of this unit. Other file system namespacing unit
settings (see the discussion in <varname>PrivateMounts=</varname> above) will implicitly disable mount and
unmount propagation from the unit's processes towards the host by changing the propagation setting of all mount
points in the unit's file system namepace to <option>slave</option> first. Setting this option to
<option>shared</option> does not reestablish propagation in that case. Conversely, if this option is set, but
no other file system namespace setting is used, then new file system namespaces will be created for the unit's
processes and this propagation flag will be applied right away to all mounts within it, without the
intermediary application of <option>slave</option>.</para>
<para>If not set – but file system namespaces are enabled through another file system namespace unit setting –
<option>shared</option> mount propagation is used, but — as mentioned — as <option>slave</option> is applied
first, propagation from the unit's processes to the host is still turned off.</para>
<para>It is not recommended to to use <option>private</option> mount propagation for units, as this means
temporary mounts (such as removable media) of the host will stay mounted and thus indefinitely busy in forked
off processes, as unmount propagation events won't be received by the file system namespace of the unit.</para>
<para>Usually, it is best to leave this setting unmodified, and use higher level file system namespacing
options instead, in particular <varname>PrivateMounts=</varname>, see above.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>System Call Filtering</title>
<variablelist>
<varlistentry>
<term><varname>SystemCallFilter=</varname></term>
<listitem><para>Takes a space-separated list of system call names. If this setting is used, all system calls
executed by the unit processes except for the listed ones will result in immediate process termination with the
<constant>SIGSYS</constant> signal (whitelisting). If the first character of the list is <literal>~</literal>,
the effect is inverted: only the listed system calls will result in immediate process termination
(blacklisting). Blacklisted system calls and system call groups may optionally be suffixed with a colon
(<literal>:</literal>) and <literal>errno</literal> error number (between 0 and 4095) or errno name such as
<constant>EPERM</constant>, <constant>EACCES</constant> or <constant>EUCLEAN</constant>. This value will be
returned when a blacklisted system call is triggered, instead of terminating the processes immediately. This
value takes precedence over the one given in <varname>SystemCallErrorNumber=</varname>. If running in user
mode, or in system mode, but without the <constant>CAP_SYS_ADMIN</constant> capability (e.g. setting
<varname>User=nobody</varname>), <varname>NoNewPrivileges=yes</varname> is implied. This feature makes use of
the Secure Computing Mode 2 interfaces of the kernel ('seccomp filtering') and is useful for enforcing a
minimal sandboxing environment. Note that the <function>execve</function>, <function>exit</function>,
<function>exit_group</function>, <function>getrlimit</function>, <function>rt_sigreturn</function>,
<function>sigreturn</function> system calls and the system calls for querying time and sleeping are implicitly
whitelisted and do not need to be listed explicitly. This option may be specified more than once, in which case
the filter masks are merged. If the empty string is assigned, the filter is reset, all prior assignments will
have no effect. This does not affect commands prefixed with <literal>+</literal>.</para>
<para>Note that on systems supporting multiple ABIs (such as x86/x86-64) it is recommended to turn off
alternative ABIs for services, so that they cannot be used to circumvent the restrictions of this
option. Specifically, it is recommended to combine this option with
<varname>SystemCallArchitectures=native</varname> or similar.</para>
<para>Note that strict system call filters may impact execution and error handling code paths of the service
invocation. Specifically, access to the <function>execve</function> system call is required for the execution
of the service binary — if it is blocked service invocation will necessarily fail. Also, if execution of the
service binary fails for some reason (for example: missing service executable), the error handling logic might
require access to an additional set of system calls in order to process and log this failure correctly. It
might be necessary to temporarily disable system call filters in order to simplify debugging of such
failures.</para>
<para>If you specify both types of this option (i.e. whitelisting and blacklisting), the first encountered
will take precedence and will dictate the default action (termination or approval of a system call). Then the
next occurrences of this option will add or delete the listed system calls from the set of the filtered system
calls, depending of its type and the default action. (For example, if you have started with a whitelisting of
<function>read</function> and <function>write</function>, and right after it add a blacklisting of
<function>write</function>, then <function>write</function> will be removed from the set.)</para>
<para>As the number of possible system calls is large, predefined sets of system calls are provided. A set
starts with <literal>@</literal> character, followed by name of the set.
<table>
<title>Currently predefined system call sets</title>
<tgroup cols='2'>
<colspec colname='set' />
<colspec colname='description' />
<thead>
<row>
<entry>Set</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry>@aio</entry>
<entry>Asynchronous I/O (<citerefentry project='man-pages'><refentrytitle>io_setup</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>io_submit</refentrytitle><manvolnum>2</manvolnum></citerefentry>, and related calls)</entry>
</row>
<row>
<entry>@basic-io</entry>
<entry>System calls for basic I/O: reading, writing, seeking, file descriptor duplication and closing (<citerefentry project='man-pages'><refentrytitle>read</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>write</refentrytitle><manvolnum>2</manvolnum></citerefentry>, and related calls)</entry>
</row>
<row>
<entry>@chown</entry>
<entry>Changing file ownership (<citerefentry project='man-pages'><refentrytitle>chown</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>fchownat</refentrytitle><manvolnum>2</manvolnum></citerefentry>, and related calls)</entry>
</row>
<row>
<entry>@clock</entry>
<entry>System calls for changing the system clock (<citerefentry project='man-pages'><refentrytitle>adjtimex</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>settimeofday</refentrytitle><manvolnum>2</manvolnum></citerefentry>, and related calls)</entry>
</row>
<row>
<entry>@cpu-emulation</entry>
<entry>System calls for CPU emulation functionality (<citerefentry project='man-pages'><refentrytitle>vm86</refentrytitle><manvolnum>2</manvolnum></citerefentry> and related calls)</entry>
</row>
<row>
<entry>@debug</entry>
<entry>Debugging, performance monitoring and tracing functionality (<citerefentry project='man-pages'><refentrytitle>ptrace</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>perf_event_open</refentrytitle><manvolnum>2</manvolnum></citerefentry> and related calls)</entry>
</row>
<row>
<entry>@file-system</entry>
<entry>File system operations: opening, creating files and directories for read and write, renaming and removing them, reading file properties, or creating hard and symbolic links.</entry>
</row>
<row>
<entry>@io-event</entry>
<entry>Event loop system calls (<citerefentry project='man-pages'><refentrytitle>poll</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>select</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>eventfd</refentrytitle><manvolnum>2</manvolnum></citerefentry> and related calls)</entry>
</row>
<row>
<entry>@ipc</entry>
<entry>Pipes, SysV IPC, POSIX Message Queues and other IPC (<citerefentry project='man-pages'><refentrytitle>mq_overview</refentrytitle><manvolnum>7</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>svipc</refentrytitle><manvolnum>7</manvolnum></citerefentry>)</entry>
</row>
<row>
<entry>@keyring</entry>
<entry>Kernel keyring access (<citerefentry project='man-pages'><refentrytitle>keyctl</refentrytitle><manvolnum>2</manvolnum></citerefentry> and related calls)</entry>
</row>
<row>
<entry>@memlock</entry>
<entry>Locking of memory into RAM (<citerefentry project='man-pages'><refentrytitle>mlock</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>mlockall</refentrytitle><manvolnum>2</manvolnum></citerefentry> and related calls)</entry>
</row>
<row>
<entry>@module</entry>
<entry>Loading and unloading of kernel modules (<citerefentry project='man-pages'><refentrytitle>init_module</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>delete_module</refentrytitle><manvolnum>2</manvolnum></citerefentry> and related calls)</entry>
</row>
<row>
<entry>@mount</entry>
<entry>Mounting and unmounting of file systems (<citerefentry project='man-pages'><refentrytitle>mount</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>chroot</refentrytitle><manvolnum>2</manvolnum></citerefentry>, and related calls)</entry>
</row>
<row>
<entry>@network-io</entry>
<entry>Socket I/O (including local AF_UNIX): <citerefentry project='man-pages'><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>unix</refentrytitle><manvolnum>7</manvolnum></citerefentry></entry>
</row>
<row>
<entry>@obsolete</entry>
<entry>Unusual, obsolete or unimplemented (<citerefentry project='man-pages'><refentrytitle>create_module</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>gtty</refentrytitle><manvolnum>2</manvolnum></citerefentry>, …)</entry>
</row>
<row>
<entry>@privileged</entry>
<entry>All system calls which need super-user capabilities (<citerefentry project='man-pages'><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>)</entry>
</row>
<row>
<entry>@process</entry>
<entry>Process control, execution, namespaceing operations (<citerefentry project='man-pages'><refentrytitle>clone</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>kill</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>namespaces</refentrytitle><manvolnum>7</manvolnum></citerefentry>, …</entry>
</row>
<row>
<entry>@raw-io</entry>
<entry>Raw I/O port access (<citerefentry project='man-pages'><refentrytitle>ioperm</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>iopl</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <function>pciconfig_read()</function>, …)</entry>
</row>
<row>
<entry>@reboot</entry>
<entry>System calls for rebooting and reboot preparation (<citerefentry project='man-pages'><refentrytitle>reboot</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <function>kexec()</function>, …)</entry>
</row>
<row>
<entry>@resources</entry>
<entry>System calls for changing resource limits, memory and scheduling parameters (<citerefentry project='man-pages'><refentrytitle>setrlimit</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>setpriority</refentrytitle><manvolnum>2</manvolnum></citerefentry>, …)</entry>
</row>
<row>
<entry>@setuid</entry>
<entry>System calls for changing user ID and group ID credentials, (<citerefentry project='man-pages'><refentrytitle>setuid</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>setgid</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>setresuid</refentrytitle><manvolnum>2</manvolnum></citerefentry>, …)</entry>
</row>
<row>
<entry>@signal</entry>
<entry>System calls for manipulating and handling process signals (<citerefentry project='man-pages'><refentrytitle>signal</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>sigprocmask</refentrytitle><manvolnum>2</manvolnum></citerefentry>, …)</entry>
</row>
<row>
<entry>@swap</entry>
<entry>System calls for enabling/disabling swap devices (<citerefentry project='man-pages'><refentrytitle>swapon</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>swapoff</refentrytitle><manvolnum>2</manvolnum></citerefentry>)</entry>
</row>
<row>
<entry>@sync</entry>
<entry>Synchronizing files and memory to disk: (<citerefentry project='man-pages'><refentrytitle>fsync</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>msync</refentrytitle><manvolnum>2</manvolnum></citerefentry>, and related calls)</entry>
</row>
<row>
<entry>@system-service</entry>
<entry>A reasonable set of system calls used by common system services, excluding any special purpose calls. This is the recommended starting point for whitelisting system calls for system services, as it contains what is typically needed by system services, but excludes overly specific interfaces. For example, the following APIs are excluded: <literal>@clock</literal>, <literal>@mount</literal>, <literal>@swap</literal>, <literal>@reboot</literal>.</entry>
</row>
<row>
<entry>@timer</entry>
<entry>System calls for scheduling operations by time (<citerefentry project='man-pages'><refentrytitle>alarm</refentrytitle><manvolnum>2</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>timer_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>, …)</entry>
</row>
</tbody>
</tgroup>
</table>
Note, that as new system calls are added to the kernel, additional system calls might be added to the groups
above. Contents of the sets may also change between systemd versions. In addition, the list of system calls
depends on the kernel version and architecture for which systemd was compiled. Use
<command>systemd-analyze syscall-filter</command> to list the actual list of system calls in each
filter.</para>
<para>Generally, whitelisting system calls (rather than blacklisting) is the safer mode of operation. It is
recommended to enforce system call whitelists for all long-running system services. Specifically, the
following lines are a relatively safe basic choice for the majority of system services:</para>
<programlisting>[Service]
SystemCallFilter=@system-service
SystemCallErrorNumber=EPERM</programlisting>
<para>It is recommended to combine the file system namespacing related options with
<varname>SystemCallFilter=~@mount</varname>, in order to prohibit the unit's processes to undo the
mappings. Specifically these are the options <varname>PrivateTmp=</varname>,
<varname>PrivateDevices=</varname>, <varname>ProtectSystem=</varname>, <varname>ProtectHome=</varname>,
<varname>ProtectKernelTunables=</varname>, <varname>ProtectControlGroups=</varname>,
<varname>ReadOnlyPaths=</varname>, <varname>InaccessiblePaths=</varname> and
<varname>ReadWritePaths=</varname>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>SystemCallErrorNumber=</varname></term>
<listitem><para>Takes an <literal>errno</literal> error number (between 1 and 4095) or errno name such as
<constant>EPERM</constant>, <constant>EACCES</constant> or <constant>EUCLEAN</constant>, to return when the
system call filter configured with <varname>SystemCallFilter=</varname> is triggered, instead of terminating
the process immediately. When this setting is not used, or when the empty string is assigned, the process will
be terminated immediately when the filter is triggered.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>SystemCallArchitectures=</varname></term>
<listitem><para>Takes a space-separated list of architecture identifiers to include in the system call
filter. The known architecture identifiers are the same as for <varname>ConditionArchitecture=</varname>
described in <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
as well as <constant>x32</constant>, <constant>mips64-n32</constant>, <constant>mips64-le-n32</constant>, and
the special identifier <constant>native</constant>. The special identifier <constant>native</constant>
implicitly maps to the native architecture of the system (or more precisely: to the architecture the system
manager is compiled for). If running in user mode, or in system mode, but without the
<constant>CAP_SYS_ADMIN</constant> capability (e.g. setting <varname>User=nobody</varname>),
<varname>NoNewPrivileges=yes</varname> is implied. By default, this option is set to the empty list, i.e. no
system call architecture filtering is applied.</para>
<para>If this setting is used, processes of this unit will only be permitted to call native system calls, and
system calls of the specified architectures. For the purposes of this option, the x32 architecture is treated
as including x86-64 system calls. However, this setting still fulfills its purpose, as explained below, on
x32.</para>
<para>System call filtering is not equally effective on all architectures. For example, on x86
filtering of network socket-related calls is not possible, due to ABI limitations — a limitation that x86-64
does not have, however. On systems supporting multiple ABIs at the same time — such as x86/x86-64 — it is hence
recommended to limit the set of permitted system call architectures so that secondary ABIs may not be used to
circumvent the restrictions applied to the native ABI of the system. In particular, setting
<varname>SystemCallArchitectures=native</varname> is a good choice for disabling non-native ABIs.</para>
<para>System call architectures may also be restricted system-wide via the
<varname>SystemCallArchitectures=</varname> option in the global configuration. See
<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
details.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Environment</title>
<variablelist>
<varlistentry>
<term><varname>Environment=</varname></term>
<listitem><para>Sets environment variables for executed processes. Takes a space-separated list of variable
assignments. This option may be specified more than once, in which case all listed variables will be set. If
the same variable is set twice, the later setting will override the earlier setting. If the empty string is
assigned to this option, the list of environment variables is reset, all prior assignments have no
effect. Variable expansion is not performed inside the strings, however, specifier expansion is possible. The $
character has no special meaning. If you need to assign a value containing spaces or the equals sign to a
variable, use double quotes (") for the assignment.</para>
<para>Example:
<programlisting>Environment="VAR1=word1 word2" VAR2=word3 "VAR3=$word 5 6"</programlisting>
gives three variables <literal>VAR1</literal>,
<literal>VAR2</literal>, <literal>VAR3</literal>
with the values <literal>word1 word2</literal>,
<literal>word3</literal>, <literal>$word 5 6</literal>.
</para>
<para>
See <citerefentry
project='man-pages'><refentrytitle>environ</refentrytitle><manvolnum>7</manvolnum></citerefentry> for details
about environment variables.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>EnvironmentFile=</varname></term>
<listitem><para>Similar to <varname>Environment=</varname> but reads the environment variables from a text
file. The text file should contain new-line-separated variable assignments. Empty lines, lines without an
<literal>=</literal> separator, or lines starting with ; or # will be ignored, which may be used for
commenting. A line ending with a backslash will be concatenated with the following one, allowing multiline
variable definitions. The parser strips leading and trailing whitespace from the values of assignments, unless
you use double quotes (").</para>
<para>The argument passed should be an absolute filename or wildcard expression, optionally prefixed with
<literal>-</literal>, which indicates that if the file does not exist, it will not be read and no error or
warning message is logged. This option may be specified more than once in which case all specified files are
read. If the empty string is assigned to this option, the list of file to read is reset, all prior assignments
have no effect.</para>
<para>The files listed with this directive will be read shortly before the process is executed (more
specifically, after all processes from a previous unit state terminated. This means you can generate these
files in one unit state, and read it with this option in the next).</para>
<para>Settings from these files override settings made with <varname>Environment=</varname>. If the same
variable is set twice from these files, the files will be read in the order they are specified and the later
setting will override the earlier setting.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>PassEnvironment=</varname></term>
<listitem><para>Pass environment variables set for the system service manager to executed processes. Takes a
space-separated list of variable names. This option may be specified more than once, in which case all listed
variables will be passed. If the empty string is assigned to this option, the list of environment variables to
pass is reset, all prior assignments have no effect. Variables specified that are not set for the system
manager will not be passed and will be silently ignored. Note that this option is only relevant for the system
service manager, as system services by default do not automatically inherit any environment variables set for
the service manager itself. However, in case of the user service manager all environment variables are passed
to the executed processes anyway, hence this option is without effect for the user service manager.</para>
<para>Variables set for invoked processes due to this setting are subject to being overridden by those
configured with <varname>Environment=</varname> or <varname>EnvironmentFile=</varname>.</para>
<para>Example:
<programlisting>PassEnvironment=VAR1 VAR2 VAR3</programlisting>
passes three variables <literal>VAR1</literal>,
<literal>VAR2</literal>, <literal>VAR3</literal>
with the values set for those variables in PID1.</para>
<para>
See <citerefentry
project='man-pages'><refentrytitle>environ</refentrytitle><manvolnum>7</manvolnum></citerefentry> for details
about environment variables.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>UnsetEnvironment=</varname></term>
<listitem><para>Explicitly unset environment variable assignments that would normally be passed from the
service manager to invoked processes of this unit. Takes a space-separated list of variable names or variable
assignments. This option may be specified more than once, in which case all listed variables/assignments will
be unset. If the empty string is assigned to this option, the list of environment variables/assignments to
unset is reset. If a variable assignment is specified (that is: a variable name, followed by
<literal>=</literal>, followed by its value), then any environment variable matching this precise assignment is
removed. If a variable name is specified (that is a variable name without any following <literal>=</literal> or
value), then any assignment matching the variable name, regardless of its value is removed. Note that the
effect of <varname>UnsetEnvironment=</varname> is applied as final step when the environment list passed to
executed processes is compiled. That means it may undo assignments from any configuration source, including
assignments made through <varname>Environment=</varname> or <varname>EnvironmentFile=</varname>, inherited from
the system manager's global set of environment variables, inherited via <varname>PassEnvironment=</varname>,
set by the service manager itself (such as <varname>$NOTIFY_SOCKET</varname> and such), or set by a PAM module
(in case <varname>PAMName=</varname> is used).</para>
<para>
See <citerefentry
project='man-pages'><refentrytitle>environ</refentrytitle><manvolnum>7</manvolnum></citerefentry> for details
about environment variables.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Logging and Standard Input/Output</title>
<variablelist>
<varlistentry>
<term><varname>StandardInput=</varname></term>
<listitem><para>Controls where file descriptor 0 (STDIN) of the executed processes is connected to. Takes one
of <option>null</option>, <option>tty</option>, <option>tty-force</option>, <option>tty-fail</option>,
<option>data</option>, <option>file:<replaceable>path</replaceable></option>, <option>socket</option> or
<option>fd:<replaceable>name</replaceable></option>.</para>
<para>If <option>null</option> is selected, standard input will be connected to <filename>/dev/null</filename>,
i.e. all read attempts by the process will result in immediate EOF.</para>
<para>If <option>tty</option> is selected, standard input is connected to a TTY (as configured by
<varname>TTYPath=</varname>, see below) and the executed process becomes the controlling process of the
terminal. If the terminal is already being controlled by another process, the executed process waits until the
current controlling process releases the terminal.</para>
<para><option>tty-force</option> is similar to <option>tty</option>, but the executed process is forcefully and
immediately made the controlling process of the terminal, potentially removing previous controlling processes
from the terminal.</para>
<para><option>tty-fail</option> is similar to <option>tty</option>, but if the terminal already has a
controlling process start-up of the executed process fails.</para>
<para>The <option>data</option> option may be used to configure arbitrary textual or binary data to pass via
standard input to the executed process. The data to pass is configured via
<varname>StandardInputText=</varname>/<varname>StandardInputData=</varname> (see below). Note that the actual
file descriptor type passed (memory file, regular file, UNIX pipe, …) might depend on the kernel and available
privileges. In any case, the file descriptor is read-only, and when read returns the specified data followed by
EOF.</para>
<para>The <option>file:<replaceable>path</replaceable></option> option may be used to connect a specific file
system object to standard input. An absolute path following the <literal>:</literal> character is expected,
which may refer to a regular file, a FIFO or special file. If an <constant>AF_UNIX</constant> socket in the
file system is specified, a stream socket is connected to it. The latter is useful for connecting standard
input of processes to arbitrary system services.</para>
<para>The <option>socket</option> option is valid in socket-activated services only, and requires the relevant
socket unit file (see
<citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry> for details)
to have <varname>Accept=yes</varname> set, or to specify a single socket only. If this option is set, standard
input will be connected to the socket the service was activated from, which is primarily useful for
compatibility with daemons designed for use with the traditional <citerefentry
project='freebsd'><refentrytitle>inetd</refentrytitle><manvolnum>8</manvolnum></citerefentry> socket activation
daemon.</para>
<para>The <option>fd:<replaceable>name</replaceable></option> option connects standard input to a specific,
named file descriptor provided by a socket unit. The name may be specified as part of this option, following a
<literal>:</literal> character (e.g. <literal>fd:foobar</literal>). If no name is specified, the name
<literal>stdin</literal> is implied (i.e. <literal>fd</literal> is equivalent to <literal>fd:stdin</literal>).
At least one socket unit defining the specified name must be provided via the <varname>Sockets=</varname>
option, and the file descriptor name may differ from the name of its containing socket unit. If multiple
matches are found, the first one will be used. See <varname>FileDescriptorName=</varname> in
<citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry> for more
details about named file descriptors and their ordering.</para>
<para>This setting defaults to <option>null</option>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>StandardOutput=</varname></term>
<listitem><para>Controls where file descriptor 1 (STDOUT) of the executed processes is connected to. Takes one
of <option>inherit</option>, <option>null</option>, <option>tty</option>, <option>journal</option>,
<option>syslog</option>, <option>kmsg</option>, <option>journal+console</option>,
<option>syslog+console</option>, <option>kmsg+console</option>,
<option>file:<replaceable>path</replaceable></option>, <option>socket</option> or
<option>fd:<replaceable>name</replaceable></option>.</para>
<para><option>inherit</option> duplicates the file descriptor of standard input for standard output.</para>
<para><option>null</option> connects standard output to <filename>/dev/null</filename>, i.e. everything written
to it will be lost.</para>
<para><option>tty</option> connects standard output to a tty (as configured via <varname>TTYPath=</varname>,
see below). If the TTY is used for output only, the executed process will not become the controlling process of
the terminal, and will not fail or wait for other processes to release the terminal.</para>
<para><option>journal</option> connects standard output with the journal which is accessible via
<citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>. Note that
everything that is written to syslog or kmsg (see below) is implicitly stored in the journal as well, the
specific two options listed below are hence supersets of this one.</para>
<para><option>syslog</option> connects standard output to the <citerefentry
project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry> system syslog
service, in addition to the journal. Note that the journal daemon is usually configured to forward everything
it receives to syslog anyway, in which case this option is no different from <option>journal</option>.</para>
<para><option>kmsg</option> connects standard output with the kernel log buffer which is accessible via
<citerefentry project='man-pages'><refentrytitle>dmesg</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
in addition to the journal. The journal daemon might be configured to send all logs to kmsg anyway, in which
case this option is no different from <option>journal</option>.</para>
<para><option>journal+console</option>, <option>syslog+console</option> and <option>kmsg+console</option> work
in a similar way as the three options above but copy the output to the system console as well.</para>
<para>The <option>file:<replaceable>path</replaceable></option> option may be used to connect a specific file
system object to standard output. The semantics are similar to the same option of
<varname>StandardInput=</varname>, see above. If standard input and output are directed to the same file path,
it is opened only once, for reading as well as writing and duplicated. This is particular useful when the
specified path refers to an <constant>AF_UNIX</constant> socket in the file system, as in that case only a
single stream connection is created for both input and output.</para>
<para><option>socket</option> connects standard output to a socket acquired via socket activation. The
semantics are similar to the same option of <varname>StandardInput=</varname>, see above.</para>
<para>The <option>fd:<replaceable>name</replaceable></option> option connects standard output to a specific,
named file descriptor provided by a socket unit. A name may be specified as part of this option, following a
<literal>:</literal> character (e.g. <literal>fd:foobar</literal>). If no name is specified, the name
<literal>stdout</literal> is implied (i.e. <literal>fd</literal> is equivalent to
<literal>fd:stdout</literal>). At least one socket unit defining the specified name must be provided via the
<varname>Sockets=</varname> option, and the file descriptor name may differ from the name of its containing
socket unit. If multiple matches are found, the first one will be used. See
<varname>FileDescriptorName=</varname> in
<citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry> for more
details about named descriptors and their ordering.</para>
<para>If the standard output (or error output, see below) of a unit is connected to the journal, syslog or the
kernel log buffer, the unit will implicitly gain a dependency of type <varname>After=</varname> on
<filename>systemd-journald.socket</filename> (also see the "Implicit Dependencies" section above). Also note
that in this case stdout (or stderr, see below) will be an <constant>AF_UNIX</constant> stream socket, and not
a pipe or FIFO that can be re-opened. This means when executing shell scripts the construct <command>echo
"hello" &gt; /dev/stderr</command> for writing text to stderr will not work. To mitigate this use the construct
<command>echo "hello" >&amp;2</command> instead, which is mostly equivalent and avoids this pitfall.</para>
<para>This setting defaults to the value set with <varname>DefaultStandardOutput=</varname> in
<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>, which
defaults to <option>journal</option>. Note that setting this parameter might result in additional dependencies
to be added to the unit (see above).</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>StandardError=</varname></term>
<listitem><para>Controls where file descriptor 2 (STDERR) of the executed processes is connected to. The
available options are identical to those of <varname>StandardOutput=</varname>, with some exceptions: if set to
<option>inherit</option> the file descriptor used for standard output is duplicated for standard error, while
<option>fd:<replaceable>name</replaceable></option> will use a default file descriptor name of
<literal>stderr</literal>.</para>
<para>This setting defaults to the value set with <varname>DefaultStandardError=</varname> in
<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>, which
defaults to <option>inherit</option>. Note that setting this parameter might result in additional dependencies
to be added to the unit (see above).</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>StandardInputText=</varname></term>
<term><varname>StandardInputData=</varname></term>
<listitem><para>Configures arbitrary textual or binary data to pass via file descriptor 0 (STDIN) to the
executed processes. These settings have no effect unless <varname>StandardInput=</varname> is set to
<option>data</option>. Use this option to embed process input data directly in the unit file.</para>
<para><varname>StandardInputText=</varname> accepts arbitrary textual data. C-style escapes for special
characters as well as the usual <literal>%</literal>-specifiers are resolved. Each time this setting is used
the specified text is appended to the per-unit data buffer, followed by a newline character (thus every use
appends a new line to the end of the buffer). Note that leading and trailing whitespace of lines configured
with this option is removed. If an empty line is specified the buffer is cleared (hence, in order to insert an
empty line, add an additional <literal>\n</literal> to the end or beginning of a line).</para>
<para><varname>StandardInputData=</varname> accepts arbitrary binary data, encoded in <ulink
url="https://tools.ietf.org/html/rfc2045#section-6.8">Base64</ulink>. No escape sequences or specifiers are
resolved. Any whitespace in the encoded version is ignored during decoding.</para>
<para>Note that <varname>StandardInputText=</varname> and <varname>StandardInputData=</varname> operate on the
same data buffer, and may be mixed in order to configure both binary and textual data for the same input
stream. The textual or binary data is joined strictly in the order the settings appear in the unit
file. Assigning an empty string to either will reset the data buffer.</para>
<para>Please keep in mind that in order to maintain readability long unit file settings may be split into
multiple lines, by suffixing each line (except for the last) with a <literal>\</literal> character (see
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
details). This is particularly useful for large data configured with these two options. Example:</para>
<programlisting>…
StandardInput=data
StandardInputData=SWNrIHNpdHplIGRhIHVuJyBlc3NlIEtsb3BzLAp1ZmYgZWVtYWwga2xvcHAncy4KSWNrIGtpZWtl \
LCBzdGF1bmUsIHd1bmRyZSBtaXIsCnVmZiBlZW1hbCBqZWh0IHNlIHVmZiBkaWUgVMO8ci4KTmFu \
dSwgZGVuayBpY2ssIGljayBkZW5rIG5hbnUhCkpldHogaXNzZSB1ZmYsIGVyc2NodCB3YXIgc2Ug \
enUhCkljayBqZWhlIHJhdXMgdW5kIGJsaWNrZSDigJQKdW5kIHdlciBzdGVodCBkcmF1w59lbj8g \
SWNrZSEK
…</programlisting></listitem>
</varlistentry>
<varlistentry>
<term><varname>LogLevelMax=</varname></term>
<listitem><para>Configures filtering by log level of log messages generated by this unit. Takes a
<command>syslog</command> log level, one of <option>emerg</option> (lowest log level, only highest priority
messages), <option>alert</option>, <option>crit</option>, <option>err</option>, <option>warning</option>,
<option>notice</option>, <option>info</option>, <option>debug</option> (highest log level, also lowest priority
messages). See <citerefentry
project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry> for
details. By default no filtering is applied (i.e. the default maximum log level is <option>debug</option>). Use
this option to configure the logging system to drop log messages of a specific service above the specified
level. For example, set <varname>LogLevelMax=</varname><option>info</option> in order to turn off debug logging
of a particularly chatty unit. Note that the configured level is applied to any log messages written by any
of the processes belonging to this unit, sent via any supported logging protocol. The filtering is applied
early in the logging pipeline, before any kind of further processing is done. Moreover, messages which pass
through this filter successfully might still be dropped by filters applied at a later stage in the logging
subsystem. For example, <varname>MaxLevelStore=</varname> configured in
<citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> might
prohibit messages of higher log levels to be stored on disk, even though the per-unit
<varname>LogLevelMax=</varname> permitted it to be processed.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>LogExtraFields=</varname></term>
<listitem><para>Configures additional log metadata fields to include in all log records generated by processes
associated with this unit. This setting takes one or more journal field assignments in the format
<literal>FIELD=VALUE</literal> separated by whitespace. See
<citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry> for
details on the journal field concept. Even though the underlying journal implementation permits binary field
values, this setting accepts only valid UTF-8 values. To include space characters in a journal field value,
enclose the assignment in double quotes ("). The usual specifiers are expanded in all assignments (see
below). Note that this setting is not only useful for attaching additional metadata to log records of a unit,
but given that all fields and values are indexed may also be used to implement cross-unit log record
matching. Assign an empty string to reset the list.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>LogRateLimitIntervalSec=</varname></term>
<term><varname>LogRateLimitBurst=</varname></term>
<listitem><para>Configures the rate limiting that is applied to messages generated by this unit. If, in the
time interval defined by <varname>LogRateLimitIntervalSec=</varname>, more messages than specified in
<varname>LogRateLimitBurst=</varname> are logged by a service, all further messages within the interval are
dropped until the interval is over. A message about the number of dropped messages is generated. The time
specification for <varname>LogRateLimitIntervalSec=</varname> may be specified in the following units: "s",
"min", "h", "ms", "us" (see
<citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry> for details).
The default settings are set by <varname>RateLimitIntervalSec=</varname> and <varname>RateLimitBurst=</varname>
configured in <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>SyslogIdentifier=</varname></term>
<listitem><para>Sets the process name ("<command>syslog</command> tag") to prefix log lines sent to the logging
system or the kernel log buffer with. If not set, defaults to the process name of the executed process. This
option is only useful when <varname>StandardOutput=</varname> or <varname>StandardError=</varname> are set to
<option>journal</option>, <option>syslog</option> or <option>kmsg</option> (or to the same settings in
combination with <option>+console</option>) and only applies to log messages written to stdout or
stderr.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>SyslogFacility=</varname></term>
<listitem><para>Sets the <command>syslog</command> facility identifier to use when logging. One of
<option>kern</option>, <option>user</option>, <option>mail</option>, <option>daemon</option>,
<option>auth</option>, <option>syslog</option>, <option>lpr</option>, <option>news</option>,
<option>uucp</option>, <option>cron</option>, <option>authpriv</option>, <option>ftp</option>,
<option>local0</option>, <option>local1</option>, <option>local2</option>, <option>local3</option>,
<option>local4</option>, <option>local5</option>, <option>local6</option> or <option>local7</option>. See
<citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
for details. This option is only useful when <varname>StandardOutput=</varname> or
<varname>StandardError=</varname> are set to <option>journal</option>, <option>syslog</option> or
<option>kmsg</option> (or to the same settings in combination with <option>+console</option>), and only applies
to log messages written to stdout or stderr. Defaults to <option>daemon</option>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>SyslogLevel=</varname></term>
<listitem><para>The default <command>syslog</command> log level to use when logging to the logging system or
the kernel log buffer. One of <option>emerg</option>, <option>alert</option>, <option>crit</option>,
<option>err</option>, <option>warning</option>, <option>notice</option>, <option>info</option>,
<option>debug</option>. See <citerefentry
project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry> for
details. This option is only useful when <varname>StandardOutput=</varname> or
<varname>StandardError=</varname> are set to <option>journal</option>, <option>syslog</option> or
<option>kmsg</option> (or to the same settings in combination with <option>+console</option>), and only applies
to log messages written to stdout or stderr. Note that individual lines output by executed processes may be
prefixed with a different log level which can be used to override the default log level specified here. The
interpretation of these prefixes may be disabled with <varname>SyslogLevelPrefix=</varname>, see below. For
details, see <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
Defaults to <option>info</option>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>SyslogLevelPrefix=</varname></term>
<listitem><para>Takes a boolean argument. If true and <varname>StandardOutput=</varname> or
<varname>StandardError=</varname> are set to <option>journal</option>, <option>syslog</option> or
<option>kmsg</option> (or to the same settings in combination with <option>+console</option>), log lines
written by the executed process that are prefixed with a log level will be processed with this log level set
but the prefix removed. If set to false, the interpretation of these prefixes is disabled and the logged lines
are passed on as-is. This only applies to log messages written to stdout or stderr. For details about this
prefixing see <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
Defaults to true.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>TTYPath=</varname></term>
<listitem><para>Sets the terminal device node to use if standard input, output, or error are connected to a TTY
(see above). Defaults to <filename>/dev/console</filename>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>TTYReset=</varname></term>
<listitem><para>Reset the terminal device specified with <varname>TTYPath=</varname> before and after
execution. Defaults to <literal>no</literal>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>TTYVHangup=</varname></term>
<listitem><para>Disconnect all clients which have opened the terminal device specified with
<varname>TTYPath=</varname> before and after execution. Defaults to <literal>no</literal>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>TTYVTDisallocate=</varname></term>
<listitem><para>If the terminal device specified with <varname>TTYPath=</varname> is a virtual console
terminal, try to deallocate the TTY before and after execution. This ensures that the screen and scrollback
buffer is cleared. Defaults to <literal>no</literal>.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>System V Compatibility</title>
<variablelist>
<varlistentry>
<term><varname>UtmpIdentifier=</varname></term>
<listitem><para>Takes a four character identifier string for an <citerefentry
project='man-pages'><refentrytitle>utmp</refentrytitle><manvolnum>5</manvolnum></citerefentry> and wtmp entry
for this service. This should only be set for services such as <command>getty</command> implementations (such
as <citerefentry
project='die-net'><refentrytitle>agetty</refentrytitle><manvolnum>8</manvolnum></citerefentry>) where utmp/wtmp
entries must be created and cleared before and after execution, or for services that shall be executed as if
they were run by a <command>getty</command> process (see below). If the configured string is longer than four
characters, it is truncated and the terminal four characters are used. This setting interprets %I style string
replacements. This setting is unset by default, i.e. no utmp/wtmp entries are created or cleaned up for this
service.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>UtmpMode=</varname></term>
<listitem><para>Takes one of <literal>init</literal>, <literal>login</literal> or <literal>user</literal>. If
<varname>UtmpIdentifier=</varname> is set, controls which type of <citerefentry
project='man-pages'><refentrytitle>utmp</refentrytitle><manvolnum>5</manvolnum></citerefentry>/wtmp entries
for this service are generated. This setting has no effect unless <varname>UtmpIdentifier=</varname> is set
too. If <literal>init</literal> is set, only an <constant>INIT_PROCESS</constant> entry is generated and the
invoked process must implement a <command>getty</command>-compatible utmp/wtmp logic. If
<literal>login</literal> is set, first an <constant>INIT_PROCESS</constant> entry, followed by a
<constant>LOGIN_PROCESS</constant> entry is generated. In this case, the invoked process must implement a
<citerefentry
project='die-net'><refentrytitle>login</refentrytitle><manvolnum>1</manvolnum></citerefentry>-compatible
utmp/wtmp logic. If <literal>user</literal> is set, first an <constant>INIT_PROCESS</constant> entry, then a
<constant>LOGIN_PROCESS</constant> entry and finally a <constant>USER_PROCESS</constant> entry is
generated. In this case, the invoked process may be any process that is suitable to be run as session
leader. Defaults to <literal>init</literal>.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Environment variables in spawned processes</title>
<para>Processes started by the service manager are executed with an environment variable block assembled from
multiple sources. Processes started by the system service manager generally do not inherit environment variables
set for the service manager itself (but this may be altered via <varname>PassEnvironment=</varname>), but processes
started by the user service manager instances generally do inherit all environment variables set for the service
manager itself.</para>
<para>For each invoked process the list of environment variables set is compiled from the following sources:</para>
<itemizedlist>
<listitem><para>Variables globally configured for the service manager, using the
<varname>DefaultEnvironment=</varname> setting in
<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>, the kernel command line option <varname>systemd.setenv=</varname> (see
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>) or via
<command>systemctl set-environment</command> (see <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>).</para></listitem>
<listitem><para>Variables defined by the service manager itself (see the list below)</para></listitem>
<listitem><para>Variables set in the service manager's own environment variable block (subject to <varname>PassEnvironment=</varname> for the system service manager)</para></listitem>
<listitem><para>Variables set via <varname>Environment=</varname> in the unit file</para></listitem>
<listitem><para>Variables read from files specified via <varname>EnvironmentFile=</varname> in the unit file</para></listitem>
<listitem><para>Variables set by any PAM modules in case <varname>PAMName=</varname> is in effect,
cf. <citerefentry
project='man-pages'><refentrytitle>pam_env</refentrytitle><manvolnum>8</manvolnum></citerefentry></para></listitem>
</itemizedlist>
<para>If the same environment variables are set by multiple of these sources, the later source — according to the
order of the list above — wins. Note that as final step all variables listed in
<varname>UnsetEnvironment=</varname> are removed again from the compiled environment variable list, immediately
before it is passed to the executed process.</para>
<para>The following select environment variables are set or propagated by the service manager for each invoked
process:</para>
<variablelist class='environment-variables'>
<varlistentry>
<term><varname>$PATH</varname></term>
<listitem><para>Colon-separated list of directories to use
when launching executables. systemd uses a fixed value of
<filename>/usr/local/sbin</filename>:<filename>/usr/local/bin</filename>:<filename>/usr/sbin</filename>:<filename>/usr/bin</filename>:<filename>/sbin</filename>:<filename>/bin</filename>.
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>$LANG</varname></term>
<listitem><para>Locale. Can be set in
<citerefentry project='man-pages'><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
or on the kernel command line (see
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
and
<citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>).
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>$USER</varname></term>
<term><varname>$LOGNAME</varname></term>
<term><varname>$HOME</varname></term>
<term><varname>$SHELL</varname></term>
<listitem><para>User name (twice), home directory, and the
login shell. The variables are set for the units that have
<varname>User=</varname> set, which includes user
<command>systemd</command> instances. See
<citerefentry project='die-net'><refentrytitle>passwd</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>$INVOCATION_ID</varname></term>
<listitem><para>Contains a randomized, unique 128bit ID identifying each runtime cycle of the unit, formatted
as 32 character hexadecimal string. A new ID is assigned each time the unit changes from an inactive state into
an activating or active state, and may be used to identify this specific runtime cycle, in particular in data
stored offline, such as the journal. The same ID is passed to all processes run as part of the
unit.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>$XDG_RUNTIME_DIR</varname></term>
<listitem><para>The directory to use for runtime objects (such as IPC objects) and volatile state. Set for all
services run by the user <command>systemd</command> instance, as well as any system services that use
<varname>PAMName=</varname> with a PAM stack that includes <command>pam_systemd</command>. See below and
<citerefentry><refentrytitle>pam_systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry> for more
information.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>$MAINPID</varname></term>
<listitem><para>The PID of the unit's main process if it is
known. This is only set for control processes as invoked by
<varname>ExecReload=</varname> and similar. </para></listitem>
</varlistentry>
<varlistentry>
<term><varname>$MANAGERPID</varname></term>
<listitem><para>The PID of the user <command>systemd</command>
instance, set for processes spawned by it. </para></listitem>
</varlistentry>
<varlistentry>
<term><varname>$LISTEN_FDS</varname></term>
<term><varname>$LISTEN_PID</varname></term>
<term><varname>$LISTEN_FDNAMES</varname></term>
<listitem><para>Information about file descriptors passed to a
service for socket activation. See
<citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>$NOTIFY_SOCKET</varname></term>
<listitem><para>The socket
<function>sd_notify()</function> talks to. See
<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>$WATCHDOG_PID</varname></term>
<term><varname>$WATCHDOG_USEC</varname></term>
<listitem><para>Information about watchdog keep-alive notifications. See
<citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>$TERM</varname></term>
<listitem><para>Terminal type, set only for units connected to
a terminal (<varname>StandardInput=tty</varname>,
<varname>StandardOutput=tty</varname>, or
<varname>StandardError=tty</varname>). See
<citerefentry project='man-pages'><refentrytitle>termcap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>$JOURNAL_STREAM</varname></term>
<listitem><para>If the standard output or standard error output of the executed processes are connected to the
journal (for example, by setting <varname>StandardError=journal</varname>) <varname>$JOURNAL_STREAM</varname>
contains the device and inode numbers of the connection file descriptor, formatted in decimal, separated by a
colon (<literal>:</literal>). This permits invoked processes to safely detect whether their standard output or
standard error output are connected to the journal. The device and inode numbers of the file descriptors should
be compared with the values set in the environment variable to determine whether the process output is still
connected to the journal. Note that it is generally not sufficient to only check whether
<varname>$JOURNAL_STREAM</varname> is set at all as services might invoke external processes replacing their
standard output or standard error output, without unsetting the environment variable.</para>
<para>If both standard output and standard error of the executed processes are connected to the journal via a
stream socket, this environment variable will contain information about the standard error stream, as that's
usually the preferred destination for log data. (Note that typically the same stream is used for both standard
output and standard error, hence very likely the environment variable contains device and inode information
matching both stream file descriptors.)</para>
<para>This environment variable is primarily useful to allow services to optionally upgrade their used log
protocol to the native journal protocol (using
<citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>3</manvolnum></citerefentry> and other
functions) if their standard output or standard error output is connected to the journal anyway, thus enabling
delivery of structured metadata along with logged messages.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>$SERVICE_RESULT</varname></term>
<listitem><para>Only defined for the service unit type, this environment variable is passed to all
<varname>ExecStop=</varname> and <varname>ExecStopPost=</varname> processes, and encodes the service
"result". Currently, the following values are defined:</para>
<table>
<title>Defined <varname>$SERVICE_RESULT</varname> values</title>
<tgroup cols='2'>
<colspec colname='result'/>
<colspec colname='meaning'/>
<thead>
<row>
<entry>Value</entry>
<entry>Meaning</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>success</literal></entry>
<entry>The service ran successfully and exited cleanly.</entry>
</row>
<row>
<entry><literal>protocol</literal></entry>
<entry>A protocol violation occurred: the service did not take the steps required by its unit configuration (specifically what is configured in its <varname>Type=</varname> setting).</entry>
</row>
<row>
<entry><literal>timeout</literal></entry>
<entry>One of the steps timed out.</entry>
</row>
<row>
<entry><literal>exit-code</literal></entry>
<entry>Service process exited with a non-zero exit code; see <varname>$EXIT_CODE</varname> below for the actual exit code returned.</entry>
</row>
<row>
<entry><literal>signal</literal></entry>
<entry>A service process was terminated abnormally by a signal, without dumping core. See <varname>$EXIT_CODE</varname> below for the actual signal causing the termination.</entry>
</row>
<row>
<entry><literal>core-dump</literal></entry>
<entry>A service process terminated abnormally with a signal and dumped core. See <varname>$EXIT_CODE</varname> below for the signal causing the termination.</entry>
</row>
<row>
<entry><literal>watchdog</literal></entry>
<entry>Watchdog keep-alive ping was enabled for the service, but the deadline was missed.</entry>
</row>
<row>
<entry><literal>start-limit-hit</literal></entry>
<entry>A start limit was defined for the unit and it was hit, causing the unit to fail to start. See <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>'s <varname>StartLimitIntervalSec=</varname> and <varname>StartLimitBurst=</varname> for details.</entry>
</row>
<row>
<entry><literal>resources</literal></entry>
<entry>A catch-all condition in case a system operation failed.</entry>
</row>
</tbody>
</tgroup>
</table>
<para>This environment variable is useful to monitor failure or successful termination of a service. Even
though this variable is available in both <varname>ExecStop=</varname> and <varname>ExecStopPost=</varname>, it
is usually a better choice to place monitoring tools in the latter, as the former is only invoked for services
that managed to start up correctly, and the latter covers both services that failed during their start-up and
those which failed during their runtime.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>$EXIT_CODE</varname></term>
<term><varname>$EXIT_STATUS</varname></term>
<listitem><para>Only defined for the service unit type, these environment variables are passed to all
<varname>ExecStop=</varname>, <varname>ExecStopPost=</varname> processes and contain exit status/code
information of the main process of the service. For the precise definition of the exit code and status, see
<citerefentry><refentrytitle>wait</refentrytitle><manvolnum>2</manvolnum></citerefentry>. <varname>$EXIT_CODE</varname>
is one of <literal>exited</literal>, <literal>killed</literal>,
<literal>dumped</literal>. <varname>$EXIT_STATUS</varname> contains the numeric exit code formatted as string
if <varname>$EXIT_CODE</varname> is <literal>exited</literal>, and the signal name in all other cases. Note
that these environment variables are only set if the service manager succeeded to start and identify the main
process of the service.</para>
<table>
<title>Summary of possible service result variable values</title>
<tgroup cols='3'>
<colspec colname='result' />
<colspec colname='code' />
<colspec colname='status' />
<thead>
<row>
<entry><varname>$SERVICE_RESULT</varname></entry>
<entry><varname>$EXIT_CODE</varname></entry>
<entry><varname>$EXIT_STATUS</varname></entry>
</row>
</thead>
<tbody>
<row>
<entry valign="top"><literal>success</literal></entry>
<entry valign="top"><literal>exited</literal></entry>
<entry><literal>0</literal></entry>
</row>
<row>
<entry morerows="1" valign="top"><literal>protocol</literal></entry>
<entry valign="top">not set</entry>
<entry>not set</entry>
</row>
<row>
<entry><literal>exited</literal></entry>
<entry><literal>0</literal></entry>
</row>
<row>
<entry morerows="1" valign="top"><literal>timeout</literal></entry>
<entry valign="top"><literal>killed</literal></entry>
<entry><literal>TERM</literal>, <literal>KILL</literal></entry>
</row>
<row>
<entry valign="top"><literal>exited</literal></entry>
<entry><literal>0</literal>, <literal>1</literal>, <literal>2</literal>, <literal
>3</literal>, …, <literal>255</literal></entry>
</row>
<row>
<entry valign="top"><literal>exit-code</literal></entry>
<entry valign="top"><literal>exited</literal></entry>
<entry><literal>1</literal>, <literal>2</literal>, <literal
>3</literal>, …, <literal>255</literal></entry>
</row>
<row>
<entry valign="top"><literal>signal</literal></entry>
<entry valign="top"><literal>killed</literal></entry>
<entry><literal>HUP</literal>, <literal>INT</literal>, <literal>KILL</literal>, …</entry>
</row>
<row>
<entry valign="top"><literal>core-dump</literal></entry>
<entry valign="top"><literal>dumped</literal></entry>
<entry><literal>ABRT</literal>, <literal>SEGV</literal>, <literal>QUIT</literal>, …</entry>
</row>
<row>
<entry morerows="2" valign="top"><literal>watchdog</literal></entry>
<entry><literal>dumped</literal></entry>
<entry><literal>ABRT</literal></entry>
</row>
<row>
<entry><literal>killed</literal></entry>
<entry><literal>TERM</literal>, <literal>KILL</literal></entry>
</row>
<row>
<entry><literal>exited</literal></entry>
<entry><literal>0</literal>, <literal>1</literal>, <literal>2</literal>, <literal
>3</literal>, …, <literal>255</literal></entry>
</row>
<row>
<entry><literal>start-limit-hit</literal></entry>
<entry>not set</entry>
<entry>not set</entry>
</row>
<row>
<entry><literal>resources</literal></entry>
<entry>any of the above</entry>
<entry>any of the above</entry>
</row>
<row>
<entry namest="results" nameend="status">Note: the process may be also terminated by a signal not sent by systemd. In particular the process may send an arbitrary signal to itself in a handler for any of the non-maskable signals. Nevertheless, in the <literal>timeout</literal> and <literal>watchdog</literal> rows above only the signals that systemd sends have been included. Moreover, using <varname>SuccessExitStatus=</varname> additional exit statuses may be declared to indicate clean termination, which is not reflected by this table.</entry>
</row>
</tbody>
</tgroup>
</table>
</listitem>
</varlistentry>
</variablelist>
<para>For system services, when <varname>PAMName=</varname> is enabled and <command>pam_systemd</command> is part
of the selected PAM stack, additional environment variables defined by systemd may be set for
services. Specifically, these are <varname>$XDG_SEAT</varname>, <varname>$XDG_VTNR</varname>, see
<citerefentry><refentrytitle>pam_systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry> for details.</para>
</refsect1>
<refsect1>
<title>Process exit codes</title>
<para>When invoking a unit process the service manager possibly fails to apply the execution parameters configured
with the settings above. In that case the already created service process will exit with a non-zero exit code
before the configured command line is executed. (Or in other words, the child process possibly exits with these
error codes, after having been created by the <citerefentry
project='man-pages'><refentrytitle>fork</refentrytitle><manvolnum>2</manvolnum></citerefentry> system call, but
before the matching <citerefentry
project='man-pages'><refentrytitle>execve</refentrytitle><manvolnum>2</manvolnum></citerefentry> system call is
called.) Specifically, exit codes defined by the C library, by the LSB specification and by the systemd service
manager itself are used.</para>
<para>The following basic service exit codes are defined by the C library.</para>
<table>
<title>Basic C library exit codes</title>
<tgroup cols='3'>
<thead>
<row>
<entry>Exit Code</entry>
<entry>Symbolic Name</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry>0</entry>
<entry><constant>EXIT_SUCCESS</constant></entry>
<entry>Generic success code.</entry>
</row>
<row>
<entry>1</entry>
<entry><constant>EXIT_FAILURE</constant></entry>
<entry>Generic failure or unspecified error.</entry>
</row>
</tbody>
</tgroup>
</table>
<para>The following service exit codes are defined by the <ulink
url="https://refspecs.linuxbase.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/iniscrptact.html">LSB specification
</ulink>.
</para>
<table>
<title>LSB service exit codes</title>
<tgroup cols='3'>
<thead>
<row>
<entry>Exit Code</entry>
<entry>Symbolic Name</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry>2</entry>
<entry><constant>EXIT_INVALIDARGUMENT</constant></entry>
<entry>Invalid or excess arguments.</entry>
</row>
<row>
<entry>3</entry>
<entry><constant>EXIT_NOTIMPLEMENTED</constant></entry>
<entry>Unimplemented feature.</entry>
</row>
<row>
<entry>4</entry>
<entry><constant>EXIT_NOPERMISSION</constant></entry>
<entry>The user has insufficient privileges.</entry>
</row>
<row>
<entry>5</entry>
<entry><constant>EXIT_NOTINSTALLED</constant></entry>
<entry>The program is not installed.</entry>
</row>
<row>
<entry>6</entry>
<entry><constant>EXIT_NOTCONFIGURED</constant></entry>
<entry>The program is not configured.</entry>
</row>
<row>
<entry>7</entry>
<entry><constant>EXIT_NOTRUNNING</constant></entry>
<entry>The program is not running.</entry>
</row>
</tbody>
</tgroup>
</table>
<para>
The LSB specification suggests that error codes 200 and above are reserved for implementations. Some of them are
used by the service manager to indicate problems during process invocation:
</para>
<table>
<title>systemd-specific exit codes</title>
<tgroup cols='3'>
<thead>
<row>
<entry>Exit Code</entry>
<entry>Symbolic Name</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry>200</entry>
<entry><constant>EXIT_CHDIR</constant></entry>
<entry>Changing to the requested working directory failed. See <varname>WorkingDirectory=</varname> above.</entry>
</row>
<row>
<entry>201</entry>
<entry><constant>EXIT_NICE</constant></entry>
<entry>Failed to set up process scheduling priority (nice level). See <varname>Nice=</varname> above.</entry>
</row>
<row>
<entry>202</entry>
<entry><constant>EXIT_FDS</constant></entry>
<entry>Failed to close unwanted file descriptors, or to adjust passed file descriptors.</entry>
</row>
<row>
<entry>203</entry>
<entry><constant>EXIT_EXEC</constant></entry>
<entry>The actual process execution failed (specifically, the <citerefentry project='man-pages'><refentrytitle>execve</refentrytitle><manvolnum>2</manvolnum></citerefentry> system call). Most likely this is caused by a missing or non-accessible executable file.</entry>
</row>
<row>
<entry>204</entry>
<entry><constant>EXIT_MEMORY</constant></entry>
<entry>Failed to perform an action due to memory shortage.</entry>
</row>
<row>
<entry>205</entry>
<entry><constant>EXIT_LIMITS</constant></entry>
<entry>Failed to adjust resource limits. See <varname>LimitCPU=</varname> and related settings above.</entry>
</row>
<row>
<entry>206</entry>
<entry><constant>EXIT_OOM_ADJUST</constant></entry>
<entry>Failed to adjust the OOM setting. See <varname>OOMScoreAdjust=</varname> above.</entry>
</row>
<row>
<entry>207</entry>
<entry><constant>EXIT_SIGNAL_MASK</constant></entry>
<entry>Failed to set process signal mask.</entry>
</row>
<row>
<entry>208</entry>
<entry><constant>EXIT_STDIN</constant></entry>
<entry>Failed to set up standard input. See <varname>StandardInput=</varname> above.</entry>
</row>
<row>
<entry>209</entry>
<entry><constant>EXIT_STDOUT</constant></entry>
<entry>Failed to set up standard output. See <varname>StandardOutput=</varname> above.</entry>
</row>
<row>
<entry>210</entry>
<entry><constant>EXIT_CHROOT</constant></entry>
<entry>Failed to change root directory (<citerefentry project='man-pages'><refentrytitle>chroot</refentrytitle><manvolnum>2</manvolnum></citerefentry>). See <varname>RootDirectory=</varname>/<varname>RootImage=</varname> above.</entry>
</row>
<row>
<entry>211</entry>
<entry><constant>EXIT_IOPRIO</constant></entry>
<entry>Failed to set up IO scheduling priority. See <varname>IOSchedulingClass=</varname>/<varname>IOSchedulingPriority=</varname> above.</entry>
</row>
<row>
<entry>212</entry>
<entry><constant>EXIT_TIMERSLACK</constant></entry>
<entry>Failed to set up timer slack. See <varname>TimerSlackNSec=</varname> above.</entry>
</row>
<row>
<entry>213</entry>
<entry><constant>EXIT_SECUREBITS</constant></entry>
<entry>Failed to set process secure bits. See <varname>SecureBits=</varname> above.</entry>
</row>
<row>
<entry>214</entry>
<entry><constant>EXIT_SETSCHEDULER</constant></entry>
<entry>Failed to set up CPU scheduling. See <varname>CPUSchedulingPolicy=</varname>/<varname>CPUSchedulingPriority=</varname> above.</entry>
</row>
<row>
<entry>215</entry>
<entry><constant>EXIT_CPUAFFINITY</constant></entry>
<entry>Failed to set up CPU affinity. See <varname>CPUAffinity=</varname> above.</entry>
</row>
<row>
<entry>216</entry>
<entry><constant>EXIT_GROUP</constant></entry>
<entry>Failed to determine or change group credentials. See <varname>Group=</varname>/<varname>SupplementaryGroups=</varname> above.</entry>
</row>
<row>
<entry>217</entry>
<entry><constant>EXIT_USER</constant></entry>
<entry>Failed to determine or change user credentials, or to set up user namespacing. See <varname>User=</varname>/<varname>PrivateUsers=</varname> above.</entry>
</row>
<row>
<entry>218</entry>
<entry><constant>EXIT_CAPABILITIES</constant></entry>
<entry>Failed to drop capabilities, or apply ambient capabilities. See <varname>CapabilityBoundingSet=</varname>/<varname>AmbientCapabilities=</varname> above.</entry>
</row>
<row>
<entry>219</entry>
<entry><constant>EXIT_CGROUP</constant></entry>
<entry>Setting up the service control group failed.</entry>
</row>
<row>
<entry>220</entry>
<entry><constant>EXIT_SETSID</constant></entry>
<entry>Failed to create new process session.</entry>
</row>
<row>
<entry>221</entry>
<entry><constant>EXIT_CONFIRM</constant></entry>
<entry>Execution has been cancelled by the user. See the <varname>systemd.confirm_spawn=</varname> kernel command line setting on <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry> for details.</entry>
</row>
<row>
<entry>222</entry>
<entry><constant>EXIT_STDERR</constant></entry>
<entry>Failed to set up standard error output. See <varname>StandardError=</varname> above.</entry>
</row>
<row>
<entry>224</entry>
<entry><constant>EXIT_PAM</constant></entry>
<entry>Failed to set up PAM session. See <varname>PAMName=</varname> above.</entry>
</row>
<row>
<entry>225</entry>
<entry><constant>EXIT_NETWORK</constant></entry>
<entry>Failed to set up network namespacing. See <varname>PrivateNetwork=</varname> above.</entry>
</row>
<row>
<entry>226</entry>
<entry><constant>EXIT_NAMESPACE</constant></entry>
<entry>Failed to set up mount namespacing. See <varname>ReadOnlyPaths=</varname> and related settings above.</entry>
</row>
<row>
<entry>227</entry>
<entry><constant>EXIT_NO_NEW_PRIVILEGES</constant></entry>
<entry>Failed to disable new privileges. See <varname>NoNewPrivileges=yes</varname> above.</entry>
</row>
<row>
<entry>228</entry>
<entry><constant>EXIT_SECCOMP</constant></entry>
<entry>Failed to apply system call filters. See <varname>SystemCallFilter=</varname> and related settings above.</entry>
</row>
<row>
<entry>229</entry>
<entry><constant>EXIT_SELINUX_CONTEXT</constant></entry>
<entry>Determining or changing SELinux context failed. See <varname>SELinuxContext=</varname> above.</entry>
</row>
<row>
<entry>230</entry>
<entry><constant>EXIT_PERSONALITY</constant></entry>
<entry>Failed to set up an execution domain (personality). See <varname>Personality=</varname> above.</entry>
</row>
<row>
<entry>231</entry>
<entry><constant>EXIT_APPARMOR_PROFILE</constant></entry>
<entry>Failed to prepare changing AppArmor profile. See <varname>AppArmorProfile=</varname> above.</entry>
</row>
<row>
<entry>232</entry>
<entry><constant>EXIT_ADDRESS_FAMILIES</constant></entry>
<entry>Failed to restrict address families. See <varname>RestrictAddressFamilies=</varname> above.</entry>
</row>
<row>
<entry>233</entry>
<entry><constant>EXIT_RUNTIME_DIRECTORY</constant></entry>
<entry>Setting up runtime directory failed. See <varname>RuntimeDirectory=</varname> and related settings above.</entry>
</row>
<row>
<entry>235</entry>
<entry><constant>EXIT_CHOWN</constant></entry>
<entry>Failed to adjust socket ownership. Used for socket units only.</entry>
</row>
<row>
<entry>236</entry>
<entry><constant>EXIT_SMACK_PROCESS_LABEL</constant></entry>
<entry>Failed to set SMACK label. See <varname>SmackProcessLabel=</varname> above.</entry>
</row>
<row>
<entry>237</entry>
<entry><constant>EXIT_KEYRING</constant></entry>
<entry>Failed to set up kernel keyring.</entry>
</row>
<row>
<entry>238</entry>
<entry><constant>EXIT_STATE_DIRECTORY</constant></entry>
<entry>Failed to set up unit's state directory. See <varname>StateDirectory=</varname> above.</entry>
</row>
<row>
<entry>239</entry>
<entry><constant>EXIT_CACHE_DIRECTORY</constant></entry>
<entry>Failed to set up unit's cache directory. See <varname>CacheDirectory=</varname> above.</entry>
</row>
<row>
<entry>240</entry>
<entry><constant>EXIT_LOGS_DIRECTORY</constant></entry>
<entry>Failed to set up unit's logging directory. See <varname>LogsDirectory=</varname> above.</entry>
</row>
<row>
<entry>241</entry>
<entry><constant>EXIT_CONFIGURATION_DIRECTORY</constant></entry>
<entry>Failed to set up unit's configuration directory. See <varname>ConfigurationDirectory=</varname> above.</entry>
</row>
<row>
<entry>242</entry>
<entry><constant>EXIT_NUMA_POLICY</constant></entry>
<entry>Failed to set up unit's NUMA memory policy. See <varname>NUMAPolicy=</varname> and <varname>NUMAMask=</varname>above.</entry>
</row>
</tbody>
</tgroup>
</table>
<para>Finally, the BSD operating systems define a set of exit codes, typically defined on Linux systems too:</para>
<table>
<title>BSD exit codes</title>
<tgroup cols='3'>
<thead>
<row>
<entry>Exit Code</entry>
<entry>Symbolic Name</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry>64</entry>
<entry><constant>EX_USAGE</constant></entry>
<entry>Command line usage error</entry>
</row>
<row>
<entry>65</entry>
<entry><constant>EX_DATAERR</constant></entry>
<entry>Data format error</entry>
</row>
<row>
<entry>66</entry>
<entry><constant>EX_NOINPUT</constant></entry>
<entry>Cannot open input</entry>
</row>
<row>
<entry>67</entry>
<entry><constant>EX_NOUSER</constant></entry>
<entry>Addressee unknown</entry>
</row>
<row>
<entry>68</entry>
<entry><constant>EX_NOHOST</constant></entry>
<entry>Host name unknown</entry>
</row>
<row>
<entry>69</entry>
<entry><constant>EX_UNAVAILABLE</constant></entry>
<entry>Service unavailable</entry>
</row>
<row>
<entry>70</entry>
<entry><constant>EX_SOFTWARE</constant></entry>
<entry>internal software error</entry>
</row>
<row>
<entry>71</entry>
<entry><constant>EX_OSERR</constant></entry>
<entry>System error (e.g., can't fork)</entry>
</row>
<row>
<entry>72</entry>
<entry><constant>EX_OSFILE</constant></entry>
<entry>Critical OS file missing</entry>
</row>
<row>
<entry>73</entry>
<entry><constant>EX_CANTCREAT</constant></entry>
<entry>Can't create (user) output file</entry>
</row>
<row>
<entry>74</entry>
<entry><constant>EX_IOERR</constant></entry>
<entry>Input/output error</entry>
</row>
<row>
<entry>75</entry>
<entry><constant>EX_TEMPFAIL</constant></entry>
<entry>Temporary failure; user is invited to retry</entry>
</row>
<row>
<entry>76</entry>
<entry><constant>EX_PROTOCOL</constant></entry>
<entry>Remote error in protocol</entry>
</row>
<row>
<entry>77</entry>
<entry><constant>EX_NOPERM</constant></entry>
<entry>Permission denied</entry>
</row>
<row>
<entry>78</entry>
<entry><constant>EX_CONFIG</constant></entry>
<entry>Configuration error</entry>
</row>
</tbody>
</tgroup>
</table>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-analyze</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
<citerefentry><refentrytitle>tmpfiles.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry project='man-pages'><refentrytitle>exec</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>