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systemd/man/systemd.socket.xml
2011-04-20 05:02:23 +02:00

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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
3min.</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>