</refnamediv>
<refsynopsisdiv>
- <para><filename>systemd.socket</filename></para>
+ <para><filename><replaceable>socket</replaceable>.socket</filename></para>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>A unit configuration file whose name ends in
- <filename>.socket</filename> encodes information about
+ <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>
<option>ExecStartPre=</option>,
<option>ExecStartPost=</option>,
<option>ExecStopPre=</option> and
- <option>ExecStoptPost=</option> commands are executed
+ <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.</para>
-
- <para>For each socket file a matching service file
- (see
+ <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 file, a matching service file
+ must exist, describing the service to start on
+ incoming traffic on the socket (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
+ for more information about .service files). 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=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>
+ <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
boot or late system shutdown should disable this
option.</para>
+ <para>Socket units will have a
+ <varname>Before=</varname> dependency on the service
+ which they trigger added implicitly. 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.</para>
+ 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
<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>
+ socket passing (i.e. sockets passed in via standard input and
+ output, using <varname>StandardInput=socket</varname>
in the service file).</para>
</refsect1>
options specific to the [Socket] section of socket
units are the following:</para>
- <variablelist>
+ <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
- (SOCK_STREAM), datagram (SOCK_DGRAM),
+ (<constant>SOCK_STREAM</constant>), datagram (<constant>SOCK_DGRAM</constant>),
or sequential packet
- (SOCK_SEQPACKET) socket, respectively. The address
+ (<constant>SOCK_SEQPACKET</constant>) socket, respectively. 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
+ 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 (@) it is read as abstract
- namespace socket in the AF_UNIX
- family. The @ is replaced with a NUL
- character before binding. For details
- see
+ <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><refentrytitle>unix</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
<para>If the address string is a
- single number it is read as port
+ single number, it is read as port
number to listen on via
IPv6. Depending on the value of
<varname>BindIPv6Only=</varname> (see below) this
</para>
<para>If the address string is a
- string in the format v.w.x.y:z it is
+ 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
+ string in the format [x]:y, it is read
as IPv6 address x on a port y. Note
that this might make the service
available via IPv4, too, depending on
setting (see below).
</para>
- <para>Note that SOCK_SEQPACKET
+ <para>Note that <constant>SOCK_SEQPACKET</constant>
(i.e. <varname>ListenSequentialPacket=</varname>)
- is only available for AF_UNIX
- sockets. SOCK_STREAM
+ 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, SOCK_DGRAM
+ 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 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
+ 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 whether it will be up and
- running ever at all. To deal with this it is
- recommended to set the
+ 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>
<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
+ 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
<option>ipv6-only</option>, they will
be accessible via IPv6 only. If
<option>default</option> (which is the
- default, surprise!) the system wide
+ default, surprise!), the system wide
default setting is used, as controlled
by
<filename>/proc/sys/net/ipv6/bindv6only</filename>,
<term><varname>BindToDevice=</varname></term>
<listitem><para>Specifies a network
interface name to bind this socket
- to. If set traffic will only be
+ to. If set, traffic will only be
accepted from the specified network
interfaces. This controls the
SO_BINDTODEVICE socket option (see
</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>
+ <term><varname>SocketUser=</varname></term>
+ <term><varname>SocketGroup=</varname></term>
+
+ <listitem><para>Takes a UNIX
+ user/group name. When specified
+ all AF_UNIX 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>
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
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
+ 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>,
+ <option>Accept=false</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=false</varname>, but
+ it may do so for sockets it got with
+ <varname>Accept=true</varname> set.
+ Setting <varname>Accept=true</varname>
+ 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>
are coming in, they will be refused
until at least one existing connection
is terminated. This setting has no
- effect for sockets configured with
+ effect on sockets configured with
<option>Accept=false</option> or datagram
sockets. Defaults to
64.</para></listitem>
<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 SO_RCVBUF
- and SO_SNDBUF socket options (see
+ argument controlling the receive or
+ send buffer sizes of this socket,
+ respectively. This controls the
+ SO_RCVBUF and SO_SNDBUF socket options
+ (see
<citerefentry><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
- for details.).</para></listitem>
+ for details.). The usual suffixes K,
+ M, G are supported and are understood
+ to the base of 1024.</para></listitem>
</varlistentry>
<varlistentry>
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 SO_REUSEPORT socket
+ option. See
+ <citerefentry><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
+ for details.</para></listitem>
+ </varlistentry>
+
<varlistentry>
<term><varname>SmackLabel=</varname></term>
<term><varname>SmackLabelIPIn=</varname></term>
respectively, i.e. the security label
of the FIFO, or the security label for
the incoming or outgoing connections
- of the socket, respectively. See
+ of the socket, respectively. See
<ulink
url="https://www.kernel.org/doc/Documentation/security/Smack.txt">Smack.txt</ulink>
for details.</para></listitem>
<varlistentry>
<term><varname>PipeSize=</varname></term>
- <listitem><para>Takes an integer
- value. Controls the pipe buffer size
+ <listitem><para>Takes a size in
+ bytes. Controls the pipe buffer size
of FIFOs configured in this socket
- unit. See
+ unit. See
<citerefentry><refentrytitle>fcntl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
- for details.</para></listitem>
+ for details. The usual suffixes K, M,
+ G are supported and are understood to
+ the base of 1024.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>PassCredentials=</varname></term>
<listitem><para>Takes a boolean
value. This controls the SO_PASSCRED
- socket option, which allows AF_UNIX sockets to
+ socket option, which allows <constant>AF_UNIX</constant> sockets to
receive the credentials of the sending
process in an ancillary message.
Defaults to
<term><varname>PassSecurity=</varname></term>
<listitem><para>Takes a boolean
value. This controls the SO_PASSSEC
- socket option, which allows AF_UNIX
+ socket option, which allows <constant>AF_UNIX</constant>
sockets to receive the security
context of the sending process in an
- ancillary message. Defaults to
+ ancillary message. Defaults to
<option>false</option>.</para></listitem>
</varlistentry>
before or after the listening
sockets/FIFOs are created and
bound, respectively. The first token of the command
- line must be an absolute file name,
+ line must be an absolute filename,
then followed by arguments for the
process. Multiple command lines may be
specified following the same scheme as
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
+ <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 0 to disable the timeout
- logic. Defaults to
- 90s.</para></listitem>
+ logic. Defaults to <varname>TimeoutStartSec=</varname> from the
+ manager configuration file.</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>
+ 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.</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 AF_UNIX sockets in the file
+ system, POSIX message queues as well
+ as 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 AF_UNIX
+ socket path or FIFO path of this
+ socket unit. If this setting is used
+ only one AF_UNIX 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. Defaults to the
+ empty list.</para></listitem>
</varlistentry>
</variablelist>
<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.service</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>
+ </para>
+
+ <para>
+ For more extensive descriptions see the "systemd for Developers" series:
+ <ulink url="http://0pointer.de/blog/projects/socket-activation.html">Socket Activation</ulink>,
+ <ulink url="http://0pointer.de/blog/projects/socket-activation2.html">Socket Activation, part II</ulink>,
+ <ulink url="http://0pointer.de/blog/projects/inetd.html">Converting inetd Services</ulink>,
+ <ulink url="http://0pointer.de/blog/projects/socket-activated-containers.html">Socket Activated Internet Services and OS Containers</ulink>.
</para>
</refsect1>
~ianmdlvl / elogind.git / blobdiff