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diff --git a/man/systemd.socket.xml b/man/systemd.socket.xml new file mode 100644 index 0000000..69aa9f3 --- /dev/null +++ b/man/systemd.socket.xml @@ -0,0 +1,875 @@ +<?xml version='1.0'?> +<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" + "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> +<!-- SPDX-License-Identifier: LGPL-2.1-or-later --> + +<refentry id="systemd.socket" xmlns:xi="http://www.w3.org/2001/XInclude"> + <refentryinfo> + <title>systemd.socket</title> + <productname>systemd</productname> + </refentryinfo> + + <refmeta> + <refentrytitle>systemd.socket</refentrytitle> + <manvolnum>5</manvolnum> + </refmeta> + + <refnamediv> + <refname>systemd.socket</refname> + <refpurpose>Socket unit configuration</refpurpose> + </refnamediv> + + <refsynopsisdiv> + <para><filename><replaceable>socket</replaceable>.socket</filename></para> + </refsynopsisdiv> + + <refsect1> + <title>Description</title> + + <para>A unit configuration file whose name ends in + <literal>.socket</literal> 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>ExecStopPost=</option> + commands are executed in, and in + <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>, + which define the way the processes are terminated, and in + <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>, + which configure resource control settings for the processes of the + socket.</para> + + <para>For each socket unit, a matching service unit must exist, + describing the service to start on incoming traffic on the socket + (see + <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry> + for more information about .service units). The name of the + .service unit is by default the same as the name of the .socket + unit, but can be altered with the <option>Service=</option> option + described below. Depending on the setting of the + <option>Accept=</option> option described below, this .service + unit must either be named like the .socket unit, but with the + suffix replaced, unless overridden with <option>Service=</option>; + or it must be a template unit named the same way. Example: a + socket file <filename>foo.socket</filename> needs a matching + service <filename>foo.service</filename> if + <option>Accept=no</option> is set. If + <option>Accept=yes</option> is set, a service template + <filename>foo@.service</filename> must exist from which services + are instantiated for each incoming connection.</para> + + <para>No implicit <varname>WantedBy=</varname> or + <varname>RequiredBy=</varname> dependency from the socket to the + service is added. This means that the service may be started + without the socket, in which case it must be able to open sockets + by itself. To prevent this, an explicit + <varname>Requires=</varname> dependency may be added.</para> + + <para>Socket units may be used to implement on-demand starting of + services, as well as parallelized starting of services. See the + blog stories linked at the end for an introduction.</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 about the precise protocol used and the order in which the file descriptors are passed) or via + traditional <citerefentry + project='freebsd'><refentrytitle>inetd</refentrytitle><manvolnum>8</manvolnum></citerefentry>-style + socket passing (i.e. sockets passed in via standard input and output, using + <varname>StandardInput=socket</varname> in the service file).</para> + + <para>All network sockets allocated through <filename>.socket</filename> units are allocated in the host's network + namespace (see <citerefentry + project='man-pages'><refentrytitle>network_namespaces</refentrytitle><manvolnum>7</manvolnum></citerefentry>). This + does not mean however that the service activated by a configured socket unit has to be part of the host's network + namespace as well. It is supported and even good practice to run services in their own network namespace (for + example through <varname>PrivateNetwork=</varname>, see + <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>), receiving only + the sockets configured through socket-activation from the host's namespace. In such a set-up communication within + the host's network namespace is only permitted through the activation sockets passed in while all sockets allocated + from the service code itself will be associated with the service's own namespace, and thus possibly subject to a + restrictive configuration.</para> + </refsect1> + + <refsect1> + <title>Automatic Dependencies</title> + + <refsect2> + <title>Implicit Dependencies</title> + + <para>The following dependencies are implicitly added:</para> + + <itemizedlist> + <listitem><para>Socket units automatically gain a <varname>Before=</varname> + dependency on the service units they activate.</para></listitem> + + <listitem><para>Socket units referring to file system paths (such as <constant>AF_UNIX</constant> + sockets or FIFOs) implicitly gain <varname>Requires=</varname> and <varname>After=</varname> + dependencies on all mount units necessary to access those paths.</para></listitem> + + <listitem><para>Socket units using the <varname>BindToDevice=</varname> + setting automatically gain a <varname>BindsTo=</varname> and + <varname>After=</varname> dependency on the device unit + encapsulating the specified network interface.</para></listitem> + </itemizedlist> + + <para>Additional implicit dependencies may be added as result of + execution and resource control parameters as documented in + <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> + and + <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para> + </refsect2> + + <refsect2> + <title>Default Dependencies</title> + + <para>The following dependencies are added unless + <varname>DefaultDependencies=no</varname> is set:</para> + + <itemizedlist> + <listitem><para>Socket units automatically gain a + <varname>Before=</varname> dependency on + <filename>sockets.target</filename>.</para></listitem> + + <listitem><para>Socket units automatically gain a pair of + <varname>After=</varname> and <varname>Requires=</varname> + dependency on <filename>sysinit.target</filename>, and a pair of + <varname>Before=</varname> and <varname>Conflicts=</varname> + dependencies on <filename>shutdown.target</filename>. These + dependencies ensure that the socket unit is started before normal + services at boot, and is stopped on shutdown. Only sockets + involved with early boot or late system shutdown should disable + <varname>DefaultDependencies=</varname> option.</para></listitem> + </itemizedlist> + </refsect2> + </refsect1> + + <refsect1> + <title>Options</title> + + <para>Socket unit files may include [Unit] and [Install] sections, which are described in + <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>. + </para> + + <para>Socket unit 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> + and + <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>. + The options specific to the [Socket] section of socket units are + the following:</para> + + <variablelist class='unit-directives'> + <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 + (<constant>SOCK_STREAM</constant>), datagram + (<constant>SOCK_DGRAM</constant>), or sequential packet + (<constant>SOCK_SEQPACKET</constant>) socket, respectively. + The address can be written in various formats:</para> + + <para>If the address starts with a slash + (<literal>/</literal>), it is read as file system socket in + the <constant>AF_UNIX</constant> socket family.</para> + + <para>If the address starts with an at symbol + (<literal>@</literal>), it is read as abstract namespace + socket in the <constant>AF_UNIX</constant> family. The + <literal>@</literal> is replaced with a + <constant>NUL</constant> character before binding. For + details, see + <citerefentry project='man-pages'><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 via IPv6. Depending on the value of + <varname>BindIPv6Only=</varname> (see below) this might result + in the service being available via both IPv6 and IPv4 + (default) or just via IPv6. + </para> + + <para>If the address string is a string in the format + <literal><replaceable>v.w.x.y</replaceable>:<replaceable>z</replaceable></literal>, it is interpreted + as IPv4 address <replaceable>v.w.x.y</replaceable> and port <replaceable>z</replaceable>.</para> + + <para>If the address string is a string in the format + <literal>[<replaceable>x</replaceable>]:<replaceable>y</replaceable></literal>, it is interpreted as + IPv6 address <replaceable>x</replaceable> and port <replaceable>y</replaceable>. An optional + interface scope (interface name or number) may be specified after a <literal>%</literal> symbol: + <literal>[<replaceable>x</replaceable>]:<replaceable>y</replaceable>%<replaceable>dev</replaceable></literal>. + Interface scopes are only useful with link-local addresses, because the kernel ignores them in other + cases. Note that if an address is specified as IPv6, it might still make the service available via + IPv4 too, depending on the <varname>BindIPv6Only=</varname> setting (see below).</para> + + <para>If the address string is a string in the format + <literal>vsock:<replaceable>x</replaceable>:<replaceable>y</replaceable></literal>, it is read as CID + <replaceable>x</replaceable> on a port <replaceable>y</replaceable> address in the + <constant>AF_VSOCK</constant> family. The CID is a unique 32-bit integer identifier in + <constant>AF_VSOCK</constant> analogous to an IP address. Specifying the CID is optional, and may be + set to the empty string.</para> + + <para>Note that <constant>SOCK_SEQPACKET</constant> (i.e. + <varname>ListenSequentialPacket=</varname>) is only available + for <constant>AF_UNIX</constant> sockets. + <constant>SOCK_STREAM</constant> (i.e. + <varname>ListenStream=</varname>) when used for IP sockets + refers to TCP sockets, <constant>SOCK_DGRAM</constant> (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 of whether there is incoming traffic + on them or not. If the empty string is assigned to any of + these options, the list of addresses to listen on is reset, + all prior uses of any of these options will have no + effect.</para> + + <para>It is also possible to have more than one socket unit + for the same service when using <varname>Service=</varname>, + and the service will receive all the sockets configured in all + the socket units. Sockets configured in one unit are passed in + the order of configuration, but no ordering between socket + units is specified.</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 of whether it will be up and + running at any point. 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 (see <citerefentry + project='man-pages'><refentrytitle>fifo</refentrytitle><manvolnum>7</manvolnum></citerefentry> for + details) to listen on. This expects an absolute file system path as argument. Behavior 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. Behavior 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 + <constant>AF_NETLINK</constant> 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. Behavior otherwise is very similar to + the <varname>ListenDatagram=</varname> directive + above.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>ListenMessageQueue=</varname></term> + <listitem><para>Specifies a POSIX message queue name to listen on (see <citerefentry + project='man-pages'><refentrytitle>mq_overview</refentrytitle><manvolnum>7</manvolnum></citerefentry> + for details). This expects a valid message queue name (i.e. beginning with + <literal>/</literal>). Behavior otherwise is very similar to the <varname>ListenFIFO=</varname> + directive above. On Linux message queue descriptors are actually file descriptors and can be + inherited between processes.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>ListenUSBFunction=</varname></term> + <listitem><para>Specifies a <ulink + url="https://docs.kernel.org/usb/functionfs.html">USB + FunctionFS</ulink> endpoints location to listen on, for + implementation of USB gadget functions. This expects an + absolute file system path of a FunctionFS mount point as the argument. + Behavior otherwise is very similar to the <varname>ListenFIFO=</varname> + directive above. Use this to open the FunctionFS endpoint + <filename>ep0</filename>. When using this option, the + activated service has to have the + <varname>USBFunctionDescriptors=</varname> and + <varname>USBFunctionStrings=</varname> options set. + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>SocketProtocol=</varname></term> + <listitem><para>Takes one of <option>udplite</option> + or <option>sctp</option>. The socket will use the UDP-Lite + (<constant>IPPROTO_UDPLITE</constant>) or SCTP + (<constant>IPPROTO_SCTP</constant>) protocol, respectively.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>BindIPv6Only=</varname></term> + <listitem><para>Takes one of <option>default</option>, + <option>both</option> or <option>ipv6-only</option>. Controls + the IPV6_V6ONLY socket option (see + <citerefentry project='die-net'><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>, which in + turn defaults to the equivalent of + <option>both</option>.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>Backlog=</varname></term> + <listitem><para>Takes an unsigned 32bit 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. Note that this value is silently capped by the <literal>net.core.somaxconn</literal> sysctl, + which typically defaults to 4096. By default this is set to 4294967295, so that the sysctl takes full + effect.</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 + <constant>SO_BINDTODEVICE</constant> socket option (see <citerefentry + project='man-pages'><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry> for + details). If this option is used, an implicit dependency from this socket unit on the network + interface device unit is created + (see <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>). + Note that setting this parameter might result in additional dependencies to be added to the unit (see + above).</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>SocketUser=</varname></term> + <term><varname>SocketGroup=</varname></term> + + <listitem><para>Takes a UNIX user/group name. When specified, all <constant>AF_UNIX</constant> + sockets and FIFO nodes in the file system are owned by the specified user and group. If unset (the + default), the nodes are owned by the root user/group (if run in system context) or the invoking + user/group (if run in user context). If only a user is specified but no group, then the group is + derived from the user's default group.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>SocketMode=</varname></term> + <listitem><para>If listening on a file system socket or 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>DirectoryMode=</varname></term> + <listitem><para>If listening on a file system socket or 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>Accept=</varname></term> + <listitem><para>Takes a boolean argument. If yes, a service instance is spawned for each incoming + connection and only the connection socket is passed to it. If no, 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>no</option>. For performance + reasons, it is recommended to write new daemons only in a way that is suitable for + <option>Accept=no</option>. A daemon listening on an <constant>AF_UNIX</constant> socket may, but + does not need to, call + <citerefentry><refentrytitle>close</refentrytitle><manvolnum>2</manvolnum></citerefentry> on the + received socket before exiting. However, it must not unlink the socket from a file system. It should + not invoke + <citerefentry><refentrytitle>shutdown</refentrytitle><manvolnum>2</manvolnum></citerefentry> on + sockets it got with <varname>Accept=no</varname>, but it may do so for sockets it got with + <varname>Accept=yes</varname> set. Setting <varname>Accept=yes</varname> is mostly useful to allow + daemons designed for usage with <citerefentry + project='freebsd'><refentrytitle>inetd</refentrytitle><manvolnum>8</manvolnum></citerefentry> to work + unmodified with systemd socket activation.</para> + + <para>Note that depending on this setting the services activated by units of this type are either + regular services (in case of <varname>Accept=</varname><option>no</option>) or instances of templated + services (in case of <varname>Accept=</varname><option>yes</option>). See the Description section + above for a more detailed discussion of the naming rules of triggered services.</para> + + <para>For IPv4 and IPv6 connections, the <varname>REMOTE_ADDR</varname> environment variable will + contain the remote IP address, and <varname>REMOTE_PORT</varname> will contain the remote port. This + is the same as the format used by CGI. For <constant>SOCK_RAW</constant>, the port is the IP + protocol.</para> + + <para>It is recommended to set <varname>CollectMode=inactive-or-failed</varname> for service + instances activated via <varname>Accept=yes</varname>, to ensure that failed connection services are + cleaned up and released from memory, and do not accumulate.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>Writable=</varname></term> + <listitem><para>Takes a boolean argument. May only be used in + conjunction with <varname>ListenSpecial=</varname>. If true, + the specified special file is opened in read-write mode, if + false, in read-only mode. Defaults to false.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>FlushPending=</varname></term> + <listitem><para>Takes a boolean argument. May only be used when + <option>Accept=no</option>. If yes, the socket's buffers are cleared after the + triggered service exited. This causes any pending data to be + flushed and any pending incoming connections to be rejected. If no, the + socket's buffers won't be cleared, permitting the service to handle any + pending connections after restart, which is the usually expected behaviour. + Defaults to <option>no</option>. + </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=yes</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 on sockets configured with + <option>Accept=no</option> or datagram sockets. Defaults to + 64.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>MaxConnectionsPerSource=</varname></term> + <listitem><para>The maximum number of connections for a service per source IP address. + This is very similar to the <varname>MaxConnections=</varname> directive + above. Disabled by default.</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 <constant>SO_KEEPALIVE</constant> socket option (see <citerefentry + project='man-pages'><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>KeepAliveTimeSec=</varname></term> + <listitem><para>Takes time (in seconds) as argument. The connection needs to remain + idle before TCP starts sending keepalive probes. This controls the TCP_KEEPIDLE + socket option (see + <citerefentry project='man-pages'><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 value is 7200 seconds (2 hours).</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>KeepAliveIntervalSec=</varname></term> + <listitem><para>Takes time (in seconds) as argument between individual keepalive probes, if the + socket option <constant>SO_KEEPALIVE</constant> has been set on this socket. This controls the + <constant>TCP_KEEPINTVL</constant> socket option (see <citerefentry + project='man-pages'><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 value is 75 seconds.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>KeepAliveProbes=</varname></term> + <listitem><para>Takes an integer as argument. It is the number of + unacknowledged probes to send before considering the + connection dead and notifying the application layer. This + controls the TCP_KEEPCNT socket option (see + <citerefentry project='man-pages'><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 value is + 9.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>NoDelay=</varname></term> + <listitem><para>Takes a boolean argument. TCP Nagle's + algorithm works by combining a number of small outgoing + messages, and sending them all at once. This controls the + TCP_NODELAY socket option (see + <citerefentry project='die-net'><refentrytitle>tcp</refentrytitle><manvolnum>7</manvolnum></citerefentry>). + 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 <constant>SO_PRIORITY</constant> socket option (see <citerefentry + project='man-pages'><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry> for + details.).</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>DeferAcceptSec=</varname></term> + + <listitem><para>Takes time (in seconds) as argument. If set, + the listening process will be awakened only when data arrives + on the socket, and not immediately when connection is + established. When this option is set, the + <constant>TCP_DEFER_ACCEPT</constant> socket option will be + used (see + <citerefentry project='die-net'><refentrytitle>tcp</refentrytitle><manvolnum>7</manvolnum></citerefentry>), + and the kernel will ignore initial ACK packets without any + data. The argument specifies the approximate amount of time + the kernel should wait for incoming data before falling back + to the normal behavior of honoring empty ACK packets. This + option is beneficial for protocols where the client sends the + data first (e.g. HTTP, in contrast to SMTP), because the + server process will not be woken up unnecessarily before it + can take any action. + </para> + + <para>If the client also uses the + <constant>TCP_DEFER_ACCEPT</constant> option, the latency of + the initial connection may be reduced, because the kernel will + send data in the final packet establishing the connection (the + third packet in the "three-way handshake").</para> + + <para>Disabled by default.</para> + </listitem> + </varlistentry> + + <varlistentry> + <term><varname>ReceiveBuffer=</varname></term> + <term><varname>SendBuffer=</varname></term> + <listitem><para>Takes an integer argument controlling the receive or send buffer sizes of this + socket, respectively. This controls the <constant>SO_RCVBUF</constant> and + <constant>SO_SNDBUF</constant> socket options (see <citerefentry + project='man-pages'><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry> for + details.). The usual suffixes K, M, G are supported and are understood to the base of + 1024.</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 <constant>IP_TOS</constant> socket option (see + <citerefentry + project='die-net'><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 + <constant>IP_TTL</constant>/<constant>IPV6_UNICAST_HOPS</constant> socket options (see <citerefentry + project='die-net'><refentrytitle>ip</refentrytitle><manvolnum>7</manvolnum></citerefentry> and + <citerefentry + project='die-net'><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 + <constant>SO_MARK</constant> socket option. See <citerefentry + project='die-net'><refentrytitle>iptables</refentrytitle><manvolnum>8</manvolnum></citerefentry> for + details.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>ReusePort=</varname></term> + <listitem><para>Takes a boolean value. If true, allows multiple + <citerefentry><refentrytitle>bind</refentrytitle><manvolnum>2</manvolnum></citerefentry>s to this TCP + or UDP port. This controls the <constant>SO_REUSEPORT</constant> socket option. See <citerefentry + project='man-pages'><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry> for + details.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>SmackLabel=</varname></term> + <term><varname>SmackLabelIPIn=</varname></term> + <term><varname>SmackLabelIPOut=</varname></term> + <listitem><para>Takes a string value. Controls the extended + attributes <literal>security.SMACK64</literal>, + <literal>security.SMACK64IPIN</literal> and + <literal>security.SMACK64IPOUT</literal>, respectively, i.e. + the security label of the FIFO, or the security label for the + incoming or outgoing connections of the socket, respectively. + See <ulink + url="https://docs.kernel.org/admin-guide/LSM/Smack.html">Smack</ulink> + for details.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>SELinuxContextFromNet=</varname></term> + <listitem><para>Takes a boolean argument. When true, systemd + will attempt to figure out the SELinux label used for the + instantiated service from the information handed by the peer + over the network. Note that only the security level is used + from the information provided by the peer. Other parts of the + resulting SELinux context originate from either the target + binary that is effectively triggered by socket unit or from + the value of the <varname>SELinuxContext=</varname> option. + This configuration option applies only when activated service + is passed in single socket file descriptor, i.e. service + instances that have standard input connected to a socket or + services triggered by exactly one socket unit. Also note + that this option is useful only when MLS/MCS SELinux policy + is deployed. Defaults to + <literal>false</literal>. </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>PipeSize=</varname></term> + <listitem><para>Takes a size in bytes. Controls the pipe + buffer size of FIFOs configured in this socket unit. See + <citerefentry><refentrytitle>fcntl</refentrytitle><manvolnum>2</manvolnum></citerefentry> + for details. The usual suffixes K, M, G are supported and are + understood to the base of 1024.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>MessageQueueMaxMessages=</varname>, + <varname>MessageQueueMessageSize=</varname></term> + <listitem><para>These two settings take integer values and + control the mq_maxmsg field or the mq_msgsize field, + respectively, when creating the message queue. Note that + either none or both of these variables need to be set. See + <citerefentry project='die-net'><refentrytitle>mq_setattr</refentrytitle><manvolnum>3</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 + <constant>IP_FREEBIND</constant>/<constant>IPV6_FREEBIND</constant> 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>Transparent=</varname></term> + <listitem><para>Takes a boolean value. Controls the + <constant>IP_TRANSPARENT</constant>/<constant>IPV6_TRANSPARENT</constant> socket option. Defaults to + <option>false</option>.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>Broadcast=</varname></term> + <listitem><para>Takes a boolean value. This controls the <constant>SO_BROADCAST</constant> socket + option, which allows broadcast datagrams to be sent from this socket. Defaults to + <option>false</option>.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>PassCredentials=</varname></term> + <listitem><para>Takes a boolean value. This controls the <constant>SO_PASSCRED</constant> socket + option, which allows <constant>AF_UNIX</constant> sockets to receive the credentials of the sending + process in an ancillary message. Defaults to <option>false</option>.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>PassSecurity=</varname></term> + <listitem><para>Takes a boolean value. This controls the <constant>SO_PASSSEC</constant> socket + option, which allows <constant>AF_UNIX</constant> sockets to receive the security context of the + sending process in an ancillary message. Defaults to <option>false</option>.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>PassPacketInfo=</varname></term> + <listitem><para>Takes a boolean value. This controls the <constant>IP_PKTINFO</constant>, + <constant>IPV6_RECVPKTINFO</constant>, <constant>NETLINK_PKTINFO</constant> or + <constant>PACKET_AUXDATA</constant> socket options, which enable reception of additional per-packet + metadata as ancillary message, on <constant>AF_INET</constant>, <constant>AF_INET6</constant>, + <constant>AF_UNIX</constant> and <constant>AF_PACKET</constant> sockets. Defaults to + <option>false</option>.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>Timestamping=</varname></term> + <listitem><para>Takes one of <literal>off</literal>, <literal>us</literal> (alias: + <literal>usec</literal>, <literal>µs</literal>) or <literal>ns</literal> (alias: + <literal>nsec</literal>). This controls the <constant>SO_TIMESTAMP</constant> or + <constant>SO_TIMESTAMPNS</constant> socket options, and enables whether ingress network traffic shall + carry timestamping metadata. Defaults to <option>off</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 <literal>westwood</literal>, <literal>veno</literal>, + <literal>cubic</literal>, <literal>lp</literal> 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 or after the listening sockets/FIFOs are + created and bound, respectively. The first token of the + command line must be an absolute filename, 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 + or after the listening sockets/FIFOs are closed and removed, + respectively. 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 + <constant>SIGTERM</constant>, and after another delay of this + time with <constant>SIGKILL</constant>. (See + <option>KillMode=</option> in + <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>.) + Takes a unit-less value in seconds, or a time span value such + as "5min 20s". Pass <literal>0</literal> to disable the + timeout logic. Defaults to + <varname>DefaultTimeoutStartSec=</varname> from the manager + configuration file (see + <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>). + </para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>Service=</varname></term> + <listitem><para>Specifies the service unit name to activate on + incoming traffic. This setting is only allowed for sockets + with <varname>Accept=no</varname>. It defaults to the service + that bears the same name as the socket (with the suffix + replaced). In most cases, it should not be necessary to use + this 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>RemoveOnStop=</varname></term> + <listitem><para>Takes a boolean argument. If enabled, any file nodes created by this socket unit are + removed when it is stopped. This applies to <constant>AF_UNIX</constant> sockets in the file system, + POSIX message queues, FIFOs, as well as any symlinks to them configured with + <varname>Symlinks=</varname>. Normally, it should not be necessary to use this option, and is not + recommended as services might continue to run after the socket unit has been terminated and it should + still be possible to communicate with them via their file system node. Defaults to + off.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>Symlinks=</varname></term> + <listitem><para>Takes a list of file system paths. The specified paths will be created as symlinks to the + <constant>AF_UNIX</constant> socket path or FIFO path of this socket unit. If this setting is used, only one + <constant>AF_UNIX</constant> socket in the file system or one FIFO may be configured for the socket unit. Use + this option to manage one or more symlinked alias names for a socket, binding their lifecycle together. Note + that if creation of a symlink fails this is not considered fatal for the socket unit, and the socket unit may + still start. If an empty string is assigned, the list of paths is reset. Defaults to an empty + list.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>FileDescriptorName=</varname></term> + <listitem><para>Assigns a name to all file descriptors this + socket unit encapsulates. This is useful to help activated + services identify specific file descriptors, if multiple fds + are passed. Services may use the + <citerefentry><refentrytitle>sd_listen_fds_with_names</refentrytitle><manvolnum>3</manvolnum></citerefentry> + call to acquire the names configured for the received file + descriptors. Names may contain any ASCII character, but must + exclude control characters and <literal>:</literal>, and must + be at most 255 characters in length. If this setting is not + used, the file descriptor name defaults to the name of the + socket unit, including its <filename>.socket</filename> + suffix.</para></listitem> + </varlistentry> + + <varlistentry> + <term><varname>TriggerLimitIntervalSec=</varname></term> + <term><varname>TriggerLimitBurst=</varname></term> + + <listitem><para>Configures a limit on how often this socket unit may be activated within a specific time + interval. The <varname>TriggerLimitIntervalSec=</varname> may be used to configure the length of the time + interval in the usual time units <literal>us</literal>, <literal>ms</literal>, <literal>s</literal>, + <literal>min</literal>, <literal>h</literal>, … and defaults to 2s (See + <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry> for details on + the various time units understood). The <varname>TriggerLimitBurst=</varname> setting takes a positive integer + value and specifies the number of permitted activations per time interval, and defaults to 200 for + <varname>Accept=yes</varname> sockets (thus by default permitting 200 activations per 2s), and 20 otherwise (20 + activations per 2s). Set either to 0 to disable any form of trigger rate limiting. If the limit is hit, the + socket unit is placed into a failure mode, and will not be connectible anymore until restarted. Note that this + limit is enforced before the service activation is enqueued.</para></listitem> + </varlistentry> + + </variablelist> + + <xi:include href="systemd.service.xml" xpointer="shared-unit-options" /> + </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-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>, + <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>, + <citerefentry><refentrytitle>systemd.exec</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.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>, + <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>, + <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>, + <citerefentry><refentrytitle>sd_listen_fds_with_names</refentrytitle><manvolnum>3</manvolnum></citerefentry> + </para> + <para> + For more extensive descriptions see the "systemd for Developers" series: + <ulink url="https://0pointer.de/blog/projects/socket-activation.html">Socket Activation</ulink>, + <ulink url="https://0pointer.de/blog/projects/socket-activation2.html">Socket Activation, part II</ulink>, + <ulink url="https://0pointer.de/blog/projects/inetd.html">Converting inetd Services</ulink>, + <ulink url="https://0pointer.de/blog/projects/socket-activated-containers.html">Socket Activated Internet Services and OS Containers</ulink>. + </para> + </refsect1> + +</refentry> |