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<refentry id="systemd.exec">
<refentryinfo>
<title>systemd.exec</title>
<productname>systemd</productname>
<authorgroup>
<author>
<contrib>Developer</contrib>
<firstname>Lennart</firstname>
<surname>Poettering</surname>
<email>lennart@poettering.net</email>
</author>
</authorgroup>
</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>
</refsect1>
<refsect1>
<title>Options</title>
<variablelist class='unit-directives'>
<varlistentry>
<term><varname>WorkingDirectory=</varname></term>
<listitem><para>Takes an absolute
directory path. Sets the working
directory for executed processes. 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.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>RootDirectory=</varname></term>
<listitem><para>Takes an absolute
directory path. Sets the root
directory for executed processes, with
the
<citerefentry><refentrytitle>chroot</refentrytitle><manvolnum>2</manvolnum></citerefentry>
system call. If this is used, it must
be ensured that the process and all
its auxiliary files are available in
the <function>chroot()</function>
jail.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>User=</varname></term>
<term><varname>Group=</varname></term>
<listitem><para>Sets the Unix user
or group that the processes are executed
as, respectively. Takes a single user or group
name or ID as argument. If no group is
set, the default group of the user is
chosen.</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.</para></listitem>
</varlistentry>
<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>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>IOSchedulingClass=</varname></term>
<listitem><para>Sets the IO 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>. 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 IO scheduling
priority for executed processes. Takes
an integer between 0 (highest
priority) and 7 (lowest priority). The
available priorities depend on the
selected IO scheduling class (see
above). See
<citerefentry><refentrytitle>ioprio_set</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 space-separated
list of CPU indices. This option may
be specified more than once in which
case the specificed 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>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>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
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><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 and 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). 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>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> or
<option>socket</option>. 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. 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.
<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. <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. The
<option>socket</option> option is only
valid in socket-activated services,
and only when the socket configuration
file (see
<citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for details) specifies 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><refentrytitle>inetd</refentrytitle><manvolnum>8</manvolnum></citerefentry>
daemon. 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>syslog</option>,
<option>kmsg</option>,
<option>journal</option>,
<option>syslog+console</option>,
<option>kmsg+console</option>,
<option>journal+console</option> or
<option>socket</option>. If set to
<option>inherit</option>, the file
descriptor of standard input is
duplicated for standard output. If set
to <option>null</option>, standard
output will be connected to
<filename>/dev/null</filename>,
i.e. everything written to it will be
lost. If set to <option>tty</option>,
standard output will be connected 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. <option>syslog</option>
connects standard output to the
<citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
system syslog
service. <option>kmsg</option>
connects it with the kernel log buffer
which is accessible via
<citerefentry><refentrytitle>dmesg</refentrytitle><manvolnum>1</manvolnum></citerefentry>. <option>journal</option>
connects it 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 is implicitly stored
in the journal as well, those options
are hence supersets of this
one). <option>syslog+console</option>,
<option>journal+console</option> and
<option>kmsg+console</option> work
similarly but copy the output to the
system console as
well. <option>socket</option> connects
standard output to a socket from
socket activation, semantics are
similar to the respective option of
<varname>StandardInput=</varname>.
This setting defaults to the value set
with
<option>DefaultStandardOutput=</option>
in
<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
which defaults to
<option>journal</option>.</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 one exception: if set to
<option>inherit</option> the file
descriptor used for standard output is
duplicated for standard error. This
setting defaults to the value set with
<option>DefaultStandardError=</option>
in
<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
which defaults to
<option>inherit</option>.</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>
<varlistentry>
<term><varname>SyslogIdentifier=</varname></term>
<listitem><para>Sets the process name
to prefix log lines sent to syslog 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>syslog</option> or
<option>kmsg</option>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>SyslogFacility=</varname></term>
<listitem><para>Sets the syslog
facility to use when logging to
syslog. 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><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>syslog</option>.
Defaults to
<option>daemon</option>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>SyslogLevel=</varname></term>
<listitem><para>Default syslog level
to use when logging to syslog 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><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>syslog</option> or
<option>kmsg</option>. Note that
individual lines output by the daemon
might 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>syslog</option>,
<option>kmsg</option> or
<option>journal</option>, log lines
written by the executed process that
are prefixed with a log level will be
passed on to syslog 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. For
details about this prefixing see
<citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
Defaults to true.</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>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>These settings control
various resource limits for executed
processes. See
<citerefentry><refentrytitle>setrlimit</refentrytitle><manvolnum>2</manvolnum></citerefentry>
for details. Use the string
<varname>infinity</varname> to
configure no limit on a specific
resource.</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. If
not set, no PAM session will be opened
for the executed processes. See
<citerefentry><refentrytitle>pam</refentrytitle><manvolnum>8</manvolnum></citerefentry>
for details.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>CapabilityBoundingSet=</varname></term>
<listitem><para>Controls which
capabilities to include in the
capability bounding set for the
executed process. See
<citerefentry><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
for details. Takes a whitespace-separated
list of capability names as read by
<citerefentry><refentrytitle>cap_from_name</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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, on top of what
<varname>Capabilities=</varname>
does. 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. 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.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>SecureBits=</varname></term>
<listitem><para>Controls the secure
bits set for the executed process. See
<citerefentry><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
for details. Takes a list of strings:
<option>keep-caps</option>,
<option>keep-caps-locked</option>,
<option>no-setuid-fixup</option>,
<option>no-setuid-fixup-locked</option>,
<option>noroot</option> and/or
<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.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Capabilities=</varname></term>
<listitem><para>Controls the
<citerefentry><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
set for the executed process. Take a
capability string describing the
effective, permitted and inherited
capability sets as documented in
<citerefentry><refentrytitle>cap_from_text</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
Note that these capability sets are
usually influenced (and filtered) by the capabilities
attached to the executed file. Due to
that
<varname>CapabilityBoundingSet=</varname>
is probably the much more useful
setting.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>ReadWriteDirectories=</varname></term>
<term><varname>ReadOnlyDirectories=</varname></term>
<term><varname>InaccessibleDirectories=</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 main file system
hierarchy. Each setting takes a
space-separated list of absolute
directory paths. Directories listed in
<varname>ReadWriteDirectories=</varname>
are accessible from within the
namespace with the same access rights
as from outside. Directories listed in
<varname>ReadOnlyDirectories=</varname>
are accessible for reading only,
writing will be refused even if the
usual file access controls would
permit this. Directories listed in
<varname>InaccessibleDirectories=</varname>
will be made inaccessible for
processes inside the namespace. Note
that restricting access with these
options does not extend to submounts
of a directory that are created later
on. These options may be specified
more than once in which case all
directories 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>ReadOnlyDirectories=</varname>
and
<varname>InaccessibleDirectories=</varname>
may be prefixed with
<literal>-</literal>, in which case
they will be ignored when they do not
exist. 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.</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. 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.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>PrivateDevices=</varname></term>
<listitem><para>Takes a boolean
argument. If true, sets up a new /dev
namespace 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>. This is
useful to securely turn off physical
device access by the executed
process. Defaults to false. Enabling
this option will also remove
<constant>CAP_MKNOD</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.</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 securely 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></listitem>
</varlistentry>
<varlistentry>
<term><varname>ProtectSystem=</varname></term>
<listitem><para>Takes a boolean
argument or
<literal>full</literal>. If true,
mounts the <filename>/usr</filename>
directory read-only for processes
invoked by this unit. If set to
<literal>full</literal> the
<filename>/etc</filename> is mounted
read-only, too. This setting ensures
that any modification of the vendor
supplied operating system (and
optionally its configuration) 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. Note however, that
processes retaining the CAP_SYS_ADMIN
capability can undo the effect of this
setting. This setting is hence
particularly useful for daemons which
have this capability removed, for
example with
<varname>CapabilityBoundingSet=</varname>. Defaults
to off.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>ProtectHome=</varname></term>
<listitem><para>Takes a boolean
argument or
<literal>read-only</literal>. If true,
the directories
<filename>/home</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
two directores are made read-only
instead. 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. Note however,
that processes retaining the
CAP_SYS_ADMIN capability can undo the
effect of this setting. This setting
is hence particularly useful for
daemons which have this capability
removed, for example with
<varname>CapabilityBoundingSet=</varname>. Defaults
to off.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>MountFlags=</varname></term>
<listitem><para>Takes a mount
propagation flag:
<option>shared</option>,
<option>slave</option> or
<option>private</option>, which
control whether mounts in the file
system namespace set up for this
unit's processes will receive or
propagate mounts or unmounts. See
<citerefentry><refentrytitle>mount</refentrytitle><manvolnum>2</manvolnum></citerefentry>
for details. Defaults to
<option>shared</option>. Use
<option>shared</option> to ensure that
mounts and unmounts are propagated
from the host to the container and
vice versa. Use <option>slave</option>
to run processes so that none of their
mounts and unmounts will propagate to
the host. Use <option>private</option>
to also ensure that no mounts and
unmounts from the host will propagate
into the unit processes'
namespace. Note that
<option>slave</option> means that file
systems mounted on the host might stay
mounted continously in the unit's
namespace, and thus keep the device
busy. Note that the file system
namespace related options
(<varname>PrivateTmp=</varname>,
<varname>PrivateDevices=</varname>,
<varname>ReadOnlySystem=</varname>,
<varname>ProtectedHome=</varname>,
<varname>ReadOnlyDirectories=</varname>,
<varname>InaccessibleDirectories=</varname>
and
<varname>ReadWriteDirectories=</varname>)
require that mount and unmount
propagation from the unit's file
system namespace is disabled, and
hence downgrade
<option>shared</option> to
<option>slave</option>.
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>UtmpIdentifier=</varname></term>
<listitem><para>Takes a four
character identifier string for an
utmp/wtmp entry for this service. This
should only be set for services such
as <command>getty</command>
implementations where utmp/wtmp
entries must be created and cleared
before and after execution. 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>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 autorize the transition. This
directive is ignored if SELinux is
disabled. If prefixed by
<literal>-</literal>, all errors will
be ignored. See
<citerefentry><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.
</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>
<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. This
option is more powerful than the respective
secure bits flags (see above), as it
also prohibits UID changes of any
kind. This is the simplest, most
effective way to ensure that a process
and its children can never elevate
privileges again.</para></listitem>
</varlistentry>
<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). If running in user
mode and this option is used,
<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>rt_sigreturn</function>,
<function>sigreturn</function>,
<function>exit_group</function>,
<function>exit</function> system calls
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.</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></listitem>
</varlistentry>
<varlistentry>
<term><varname>SystemCallErrorNumber=</varname></term>
<listitem><para>Takes an
<literal>errno</literal> error number
name to return when the system call
filter configured with
<varname>SystemCallFilter=</varname>
is triggered, instead of terminating
the process immediately. Takes an
error name such as
<constant>EPERM</constant>,
<constant>EACCES</constant> or
<constant>EUCLEAN</constant>. 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
<constant>x86</constant>,
<constant>x86-64</constant>,
<constant>x32</constant>,
<constant>arm</constant> as well as
the special identifier
<constant>native</constant>. Only
system calls of the specified
architectures will be permitted to
processes of this unit. This is an
effective way to disable compatibility
with non-native architectures for
processes, for example to prohibit
execution of 32-bit x86 binaries on
64-bit x86-64 systems. The special
<constant>native</constant> identifier
implicitly maps to the native
architecture of the system (or more
strictly: to the architecture the
system manager is compiled for). If
running in user mode and this option
is used,
<varname>NoNewPrivileges=yes</varname>
is implied. Note that setting this
option to a non-empty list implies
that <constant>native</constant> is
included too. By default, this option
is set to the empty list, i.e. no
architecture system call filtering is
applied.</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><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 and is ignored (but works
correctly on x86-64). If running in user
mode and this option is used,
<varname>NoNewPrivileges=yes</varname>
is implied. By default, no
restriction applies, all address
families are accessible to
processes. If assigned the empty
string, any previous list changes are
undone.</para>
<para>Use this option to limit
exposure of processes to remote
systems, in particular via exotic
network protocols. 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>Personality=</varname></term>
<listitem><para>Controls which
kernel architecture
<citerefentry><refentrytitle>uname</refentrytitle><manvolnum>2</manvolnum></citerefentry>
shall report, when invoked by unit
processes. Takes one of
<constant>x86</constant> and
<constant>x86-64</constant>. This 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>RuntimeDirectory=</varname></term>
<term><varname>RuntimeDirectoryMode=</varname></term>
<listitem><para>Takes a list of
directory names. If set, one or more
directories by the specified names
will be created below
<filename>/run</filename> (for system
services) or below
<varname>$XDG_RUNTIME_DIR</varname>
(for user services) when the unit is
started, and removed when the unit is
stopped. The directories will have the
access mode specified in
<varname>RuntimeDirectoryMode=</varname>,
and will be owned by the user and
group specified in
<varname>User=</varname> and
<varname>Group=</varname>. Use this to
manage one or more runtime directories
of the unit and bind their lifetime to
the daemon runtime. The specified
directory names must be relative, and
may not include a
<literal>/</literal>, i.e. must refer
to simple directories to create or
remove. This is particularly useful
for unprivileged daemons that cannot
create runtime directories in
<filename>/run</filename> due to lack
of privileges, and to make sure the
runtime directory is cleaned up
automatically after use. For runtime
directories that require more complex
or different configuration or lifetime
guarantees, please consider using
<citerefentry><refentrytitle>tmpfiles.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Environment variables in spawned processes</title>
<para>Processes started by the system are executed in
a clean environment in which select variables
listed below are set. System processes started by systemd
do not inherit variables from PID 1, but processes
started by user systemd instances inherit all
environment variables from the user systemd instance.
</para>
<variablelist class='environment-variables'>
<varlistentry>
<term><varname>$PATH</varname></term>
<listitem><para>Colon-separated list
of directiories 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>$LANG</varname></term>
<listitem><para>Locale. Can be set in
<citerefentry><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
or on the kernel command line (see
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
and
<citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>).
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>$USER</varname></term>
<term><varname>$LOGNAME</varname></term>
<term><varname>$HOME</varname></term>
<term><varname>$SHELL</varname></term>
<listitem><para>User name (twice), home
directory, and the login shell.
The variables are set for the units that
have <varname>User=</varname> set,
which includes user
<command>systemd</command> instances.
See
<citerefentry><refentrytitle>passwd</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>$XDG_RUNTIME_DIR</varname></term>
<listitem><para>The directory for volatile
state. Set for the user <command>systemd</command>
instance, and also in user sessions.
See
<citerefentry><refentrytitle>pam_systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>$XDG_SESSION_ID</varname></term>
<term><varname>$XDG_SEAT</varname></term>
<term><varname>$XDG_VTNR</varname></term>
<listitem><para>The identifier of the
session, the seat name, and
virtual terminal of the session. Set
by
<citerefentry><refentrytitle>pam_systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>
for login sessions.
<varname>$XDG_SEAT</varname> and
<varname>$XDG_VTNR</varname> will
only be set when attached to a seat and a
tty.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>$MAINPID</varname></term>
<listitem><para>The PID of the units
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>$LISTEN_PID</varname></term>
<listitem><para>Information about file
descriptors passed to a service for
socket activation. See
<citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>$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><refentrytitle>termcap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
</para></listitem>
</varlistentry>
</variablelist>
<para>Additional variables may be configured by the
following means: for processes spawned in specific
units, use the <varname>Environment=</varname> and
<varname>EnvironmentFile=</varname> options above; to
specify variables globally, use
<varname>DefaultEnvironment=</varname> (see
<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>)
or the kernel option
<varname>systemd.setenv=</varname> (see
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>). Additional
variables may also be set through PAM,
cf. <citerefentry><refentrytitle>pam_env</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>8</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.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
<citerefentry><refentrytitle>tmpfiles.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>exec</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>