</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>
+ <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
which define the way the processes are
- terminated.</para>
+ terminated, and in
+ <citerefentry><refentrytitle>systemd.cgroup</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+ which configure control group settings for the
+ processes of the service.</para>
<para>For each socket file a matching service file
(see
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
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 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>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
+ running ever at all. 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
<varlistentry>
<term><varname>DirectoryMode=</varname></term>
<listitem><para>If listening on a file
- system socket of FIFO, the parent
+ system socket or FIFO, the parent
directories are automatically created
if needed. This option specifies the
file system access mode used when
<varlistentry>
<term><varname>SocketMode=</varname></term>
<listitem><para>If listening on a file
- system socket of FIFO, this option
+ system socket or FIFO, this option
specifies the file system access mode
used when creating the file
node. Takes an access mode in octal
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
- <option>Accept=no</option> or datagram
+ effect on sockets configured with
+ <option>Accept=false</option> or datagram
sockets. Defaults to
64.</para></listitem>
</varlistentry>
for details.</para></listitem>
</varlistentry>
+ <varlistentry>
+ <term><varname>ReusePort=</varname></term>
+ <listitem><para>Takes a boolean
+ value. If true, allows multiple bind()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>
<listitem><para>Takes an integer
value. 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>
</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
<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.cgroup</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