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| Copyright 2010 Lennart Poettering |
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| |
| <refentry id="systemd.socket"> |
| <refentryinfo> |
| <title>systemd.socket</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.socket</refentrytitle> |
| <manvolnum>5</manvolnum> |
| </refmeta> |
| |
| <refnamediv> |
| <refname>systemd.socket</refname> |
| <refpurpose>systemd socket configuration files</refpurpose> |
| </refnamediv> |
| |
| <refsynopsisdiv> |
| <para><filename>systemd.socket</filename></para> |
| </refsynopsisdiv> |
| |
| <refsect1> |
| <title>Description</title> |
| |
| <para>A unit configuration file whose name ends in |
| <filename>.socket</filename> encodes information about |
| an IPC or network socket or a file system FIFO |
| controlled and supervised by systemd, for socket-based |
| activation.</para> |
| |
| <para>This man page lists the configuration options |
| specific to this unit type. See |
| <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry> |
| for the common options of all unit configuration |
| files. The common configuration items are configured |
| in the generic [Unit] and [Install] sections. The |
| socket specific configuration options are configured |
| in the [Socket] section.</para> |
| |
| <para>Additional options are listed in |
| <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>, |
| which define the execution environment the |
| <option>ExecStartPre=</option>, |
| <option>ExecStartPost=</option>, |
| <option>ExecStopPre=</option> and |
| <option>ExecStoptPost=</option> commands are executed |
| in.</para> |
| |
| <para>For each socket file a matching service file |
| (see |
| <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry> |
| for details) must exist, describing the service to |
| start on incoming traffic on the socket. Depending on |
| the setting of <option>Accept=</option> (see below), |
| this must either be named like the socket unit, but |
| with the suffix replaced; or it must be a template |
| file named the same way. Example: a socket file |
| <filename>foo.socket</filename> needs a matching |
| service <filename>foo.service</filename> if |
| <option>Accept=false</option> is set. If |
| <option>Accept=true</option> is set a service template |
| file <filename>foo@.service</filename> must exist from |
| which services are instantiated for each incoming |
| connection.</para> |
| |
| <para>Unless <varname>DefaultDependencies=</varname> |
| is set to <option>false</option>, socket units will |
| implicitly have dependencies of type |
| <varname>Requires=</varname> and |
| <varname>After=</varname> on |
| <filename>sysinit.target</filename> as well as |
| dependencies of type <varname>Conflicts=</varname> and |
| <varname>Before=</varname> on |
| <filename>shutdown.target</filename>. These ensure |
| that socket units pull in basic system |
| initialization, and are terminated cleanly prior to |
| system shutdown. Only sockets involved with early |
| boot or late system shutdown should disable this |
| option.</para> |
| |
| <para>Socket units may be used to implement on-demand |
| starting of services, as well as parallelized starting |
| of services.</para> |
| |
| <para>Note that the daemon software configured for |
| socket activation with socket units needs to be able |
| to accept sockets from systemd, either via systemd's |
| native socket passing interface (see |
| <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry> |
| for details) or via the traditional |
| <citerefentry><refentrytitle>inetd</refentrytitle><manvolnum>8</manvolnum></citerefentry>-style |
| socket passing (i.e. sockets passed in via STDIN and |
| STDOUT, using <varname>StandardInput=socket</varname> |
| in the service file).</para> |
| </refsect1> |
| |
| <refsect1> |
| <title>Options</title> |
| |
| <para>Socket files must include a [Socket] section, |
| which carries information about the socket or FIFO it |
| supervises. A number of options that may be used in |
| this section are shared with other unit types. These |
| options are documented in |
| <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>. The |
| options specific to the [Socket] section of socket |
| units are the following:</para> |
| |
| <variablelist> |
| <varlistentry> |
| <term><varname>ListenStream=</varname></term> |
| <term><varname>ListenDatagram=</varname></term> |
| <term><varname>ListenSequentialPacket=</varname></term> |
| <listitem><para>Specifies an address |
| to listen on for a stream |
| (SOCK_STREAM), datagram (SOCK_DGRAM) |
| resp. sequential packet |
| (SOCK_SEQPACKET) socket. The address |
| can be written in various formats:</para> |
| |
| <para>If the address starts with a |
| slash (/), it is read as file system |
| socket in the AF_UNIX socket |
| family.</para> |
| |
| <para>If the address starts with an |
| ampersand (@) it is read as abstract |
| namespace socket in the AF_UNIX |
| family. The @ is replaced with a NUL |
| character before binding. For details |
| see |
| <citerefentry><refentrytitle>unix</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para> |
| |
| <para>If the address string is a |
| single number it is read as port |
| number to listen on for both IPv4 and |
| IPv6.</para> |
| |
| <para>If the address string is a |
| string in the format v.w.x.y:z it is |
| read as IPv4 specifier for listening |
| on an address v.w.x.y on a port |
| z.</para> |
| |
| <para>If the address string is a |
| string in the format [x]:y it is read |
| as IPv6 address x on a port y.</para> |
| |
| <para>Note that SOCK_SEQPACKET |
| (i.e. <varname>ListenSequentialPacket=</varname>) |
| is only available for AF_UNIX |
| sockets. SOCK_STREAM |
| (i.e. <varname>ListenStream=</varname>) |
| when used for IP sockets refers to TCP |
| sockets, SOCK_DGRAM |
| (i.e. <varname>ListenDatagram=</varname>) |
| to UDP.</para> |
| |
| <para>These options may be specified |
| more than once in which case incoming |
| traffic on any of the sockets will trigger |
| service activation, and all listed |
| sockets will be passed to the service, |
| regardless whether there is incoming |
| traffic on them or not.</para> |
| |
| <para>If an IP address is used here, it |
| is often desirable to listen on it |
| before the interface it is configured |
| on is up and running, and even |
| regardless whether it will be up and |
| running ever at all. To deal with this it is |
| recommended to set the |
| <varname>FreeBind=</varname> option |
| described below.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>ListenFIFO=</varname></term> |
| <listitem><para>Specifies a file |
| system FIFO to listen on. This expects |
| an absolute file system path as |
| argument. Behaviour otherwise is very |
| similar to the |
| <varname>ListenDatagram=</varname> |
| directive above.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>ListenSpecial=</varname></term> |
| <listitem><para>Specifies a special |
| file in the file system to listen |
| on. This expects an absolute file |
| system path as argument. Behaviour |
| otherwise is very similar to the |
| <varname>ListenFIFO=</varname> |
| directive above. Use this to open |
| character device nodes as well as |
| special files in |
| <filename>/proc</filename> and |
| <filename>/sys</filename>.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>ListenNetlink=</varname></term> |
| <listitem><para>Specifies a Netlink |
| family to create a socket for to |
| listen on. This expects a short string |
| referring to the AF_NETLINK family |
| name (such as <varname>audit</varname> |
| or <varname>kobject-uevent</varname>) |
| as argument, optionally suffixed by a |
| whitespace followed by a multicast |
| group integer. Behaviour otherwise is |
| very similar to the |
| <varname>ListenDatagram=</varname> |
| directive above.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>BindIPv6Only=</varname></term> |
| <listitem><para>Takes a one of |
| <option>default</option>, |
| <option>both</option> or |
| <option>ipv6-only</option>. Controls |
| the IPV6_V6ONLY socket option (see |
| <citerefentry><refentrytitle>ipv6</refentrytitle><manvolnum>7</manvolnum></citerefentry> |
| for details). If |
| <option>both</option>, IPv6 sockets |
| bound will be accessible via both IPv4 |
| and IPv6. If |
| <option>ipv6-only</option>, they will |
| be accessible via IPv6 only. If |
| <option>default</option> (which is the |
| default, surprise!) the system wide |
| default setting is used, as controlled |
| by |
| <filename>/proc/sys/net/ipv6/bindv6only</filename>.</para> |
| </listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>Backlog=</varname></term> |
| <listitem><para>Takes an unsigned |
| integer argument. Specifies the number |
| of connections to queue that have not |
| been accepted yet. This setting |
| matters only for stream and sequential |
| packet sockets. See |
| <citerefentry><refentrytitle>listen</refentrytitle><manvolnum>2</manvolnum></citerefentry> |
| for details. Defaults to SOMAXCONN |
| (128).</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>BindToDevice=</varname></term> |
| <listitem><para>Specifies a network |
| interface name to bind this socket |
| to. If set traffic will only be |
| accepted from the specified network |
| interfaces. This controls the |
| SO_BINDTODEVICE socket option (see |
| <citerefentry><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry> |
| for details). If this option is used, |
| an automatic dependency from this |
| socket unit on the network interface |
| device unit |
| (<citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry> |
| is created.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>DirectoryMode=</varname></term> |
| <listitem><para>If listening on a file |
| system socket of FIFO, the parent |
| directories are automatically created |
| if needed. This option specifies the |
| file system access mode used when |
| creating these directories. Takes an |
| access mode in octal |
| notation. Defaults to |
| 0755.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>SocketMode=</varname></term> |
| <listitem><para>If listening on a file |
| system socket of FIFO, this option |
| specifies the file system access mode |
| used when creating the file |
| node. Takes an access mode in octal |
| notation. Defaults to |
| 0666.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>Accept=</varname></term> |
| <listitem><para>Takes a boolean |
| argument. If true, a service instance |
| is spawned for each incoming |
| connection and only the connection |
| socket is passed to it. If false, all |
| listening sockets themselves are |
| passed to the started service unit, |
| and only one service unit is spawned |
| for all connections (also see |
| above). This value is ignored for |
| datagram sockets and FIFOs where |
| a single service unit unconditionally |
| handles all incoming traffic. Defaults |
| to <option>false</option>. For |
| performance reasons, it is recommended |
| to write new daemons only in a way |
| that is suitable for |
| <option>Accept=false</option>. This |
| option is mostly useful to allow |
| daemons designed for usage with |
| <citerefentry><refentrytitle>inetd</refentrytitle><manvolnum>8</manvolnum></citerefentry>, |
| to work unmodified with systemd socket |
| activation.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>MaxConnections=</varname></term> |
| <listitem><para>The maximum number of |
| connections to simultaneously run |
| services instances for, when |
| <option>Accept=true</option> is |
| set. If more concurrent connections |
| are coming in, they will be refused |
| until at least one existing connection |
| is terminated. This setting has no |
| effect for sockets configured with |
| <option>Accept=no</option> or datagram |
| sockets. Defaults to |
| 64.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>KeepAlive=</varname></term> |
| <listitem><para>Takes a boolean |
| argument. If true, the TCP/IP stack |
| will send a keep alive message after |
| 2h (depending on the configuration of |
| <filename>/proc/sys/net/ipv4/tcp_keepalive_time</filename>) |
| for all TCP streams accepted on this |
| socket. This controls the SO_KEEPALIVE |
| socket option (see |
| <citerefentry><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry> |
| and the <ulink |
| url="http://www.tldp.org/HOWTO/html_single/TCP-Keepalive-HOWTO/">TCP |
| Keepalive HOWTO</ulink> for details.) |
| Defaults to |
| <option>false</option>.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>Priority=</varname></term> |
| <listitem><para>Takes an integer |
| argument controlling the priority for |
| all traffic sent from this |
| socket. This controls the SO_PRIORITY |
| socket option (see |
| <citerefentry><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry> |
| for details.).</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>ReceiveBuffer=</varname></term> |
| <term><varname>SendBuffer=</varname></term> |
| <listitem><para>Takes an integer |
| argument controlling the receive |
| resp. send buffer sizes of this |
| socket. This controls the SO_RCVBUF |
| resp. SO_SNDBUF socket options (see |
| <citerefentry><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry> |
| for details.).</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>IPTOS=</varname></term> |
| <listitem><para>Takes an integer |
| argument controlling the IP |
| Type-Of-Service field for packets |
| generated from this socket. This |
| controls the IP_TOS socket option (see |
| <citerefentry><refentrytitle>ip</refentrytitle><manvolnum>7</manvolnum></citerefentry> |
| for details.). Either a numeric string |
| or one of <option>low-delay</option>, |
| <option>throughput</option>, |
| <option>reliability</option> or |
| <option>low-cost</option> may be |
| specified.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>IPTTL=</varname></term> |
| <listitem><para>Takes an integer |
| argument controlling the IPv4 |
| Time-To-Live/IPv6 Hop-Count field for |
| packets generated from this |
| socket. This sets the |
| IP_TTL/IPV6_UNICAST_HOPS socket |
| options (see |
| <citerefentry><refentrytitle>ip</refentrytitle><manvolnum>7</manvolnum></citerefentry> |
| and |
| <citerefentry><refentrytitle>ipv6</refentrytitle><manvolnum>7</manvolnum></citerefentry> |
| for details.)</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>Mark=</varname></term> |
| <listitem><para>Takes an integer |
| value. Controls the firewall mark of |
| packets generated by this socket. This |
| can be used in the firewall logic to |
| filter packets from this socket. This |
| sets the SO_MARK socket option. See |
| <citerefentry><refentrytitle>iptables</refentrytitle><manvolnum>8</manvolnum></citerefentry> |
| for details.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>PipeSize=</varname></term> |
| <listitem><para>Takes an integer |
| value. Controls the pipe buffer size |
| of FIFOs configured in this socket |
| unit. See |
| <citerefentry><refentrytitle>fcntl</refentrytitle><manvolnum>2</manvolnum></citerefentry> |
| for details.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>FreeBind=</varname></term> |
| <listitem><para>Takes a boolean |
| value. Controls whether the socket can |
| be bound to non-local IP |
| addresses. This is useful to configure |
| sockets listening on specific IP |
| addresses before those IP addresses |
| are successfully configured on a |
| network interface. This sets the |
| IP_FREEBIND socket option. For |
| robustness reasons it is recommended |
| to use this option whenever you bind a |
| socket to a specific IP |
| address. Defaults to <option>false</option>.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>TCPCongestion=</varname></term> |
| <listitem><para>Takes a string |
| value. Controls the TCP congestion |
| algorithm used by this socket. Should |
| be one of "westwood", "veno", "cubic", |
| "lp" or any other available algorithm |
| supported by the IP stack. This |
| setting applies only to stream |
| sockets.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>ExecStartPre=</varname></term> |
| <term><varname>ExecStartPost=</varname></term> |
| <listitem><para>Takes one or more |
| command lines, which are executed |
| before (resp. after) the listening |
| sockets/FIFOs are created and |
| bound. The first token of the command |
| line must be an absolute file name, |
| then followed by arguments for the |
| process. Multiple command lines may be |
| specified following the same scheme as |
| used for |
| <varname>ExecStartPre=</varname> of |
| service unit files.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>ExecStopPre=</varname></term> |
| <term><varname>ExecStopPost=</varname></term> |
| <listitem><para>Additional commands |
| that are executed before (resp. after) |
| the listening sockets/FIFOs are closed |
| and removed. Multiple command lines |
| may be specified following the same |
| scheme as used for |
| <varname>ExecStartPre=</varname> of |
| service unit files.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>TimeoutSec=</varname></term> |
| <listitem><para>Configures the time to |
| wait for the commands specified in |
| <varname>ExecStartPre=</varname>, |
| <varname>ExecStartPost=</varname>, |
| <varname>ExecStopPre=</varname> and |
| <varname>ExecStopPost=</varname> to |
| finish. If a command does not exit |
| within the configured time, the socket |
| will be considered failed and be shut |
| down again. All commands still running, |
| will be terminated forcibly via |
| SIGTERM, and after another delay of |
| this time with SIGKILL. (See |
| <option>KillMode=</option> below.) |
| Takes a unit-less value in seconds, or |
| a time span value such as "5min |
| 20s". Pass 0 to disable the timeout |
| logic. Defaults to |
| 90s.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>KillMode=</varname></term> |
| <listitem><para>Specifies how |
| processes of this socket unit shall be |
| killed. One of |
| <option>control-group</option>, |
| <option>process</option>, |
| <option>none</option>.</para> |
| |
| <para>This option is mostly equivalent |
| to the <option>KillMode=</option> |
| option of service files. See |
| <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry> |
| for details.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>KillSignal=</varname></term> |
| <listitem><para>Specifies which signal |
| to use when killing a process of this |
| socket. Defaults to SIGTERM. |
| </para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>SendSIGKILL=</varname></term> |
| <listitem><para>Specifies whether to |
| send SIGKILL to remaining processes |
| after a timeout, if the normal |
| shutdown procedure left processes of |
| the socket around. Takes a boolean |
| value. Defaults to "yes". |
| </para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>Service=</varname></term> |
| <listitem><para>Specifies the service |
| unit name to activate on incoming |
| traffic. This defaults to the service |
| that bears the same name as the socket |
| (ignoring the different suffixes). In |
| most cases it should not be necessary |
| to use this option.</para></listitem> |
| </varlistentry> |
| |
| </variablelist> |
| </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>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>, |
| <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>, |
| <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry> |
| </para> |
| </refsect1> |
| |
| </refentry> |