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SYSTEMD.SOCKET(5) | systemd.socket | SYSTEMD.SOCKET(5) |
NAME¶
systemd.socket - systemd socket configuration filesSYNOPSIS¶
systemd.socketDESCRIPTION¶
A unit configuration file whose name ends in .socket encodes information about an IPC or network socket or a file system FIFO controlled and supervised by systemd, for socket-based activation. This man page lists the configuration options specific to this unit type. See systemd.unit(5) 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. Additional options are listed in systemd.exec(5), which define the execution environment the ExecStartPre=, ExecStartPost=, ExecStopPre= and ExecStopPost= commands are executed in. For each socket file a matching service file (see systemd.service(5) for details) must exist, describing the service to start on incoming traffic on the socket. Depending on the setting of Accept= (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 foo.socket needs a matching service foo.service if Accept=false is set. If Accept=true is set a service template file foo@.service must exist from which services are instantiated for each incoming connection. Unless DefaultDependencies= is set to false, socket units will implicitly have dependencies of type Requires= and After= on sysinit.target as well as dependencies of type Conflicts= and Before= on shutdown.target. 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. Socket units may be used to implement on-demand starting of services, as well as parallelized starting of services. 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 sd_listen_fds(3) for details) or via the traditional inetd(8)-style socket passing (i.e. sockets passed in via STDIN and STDOUT, using StandardInput=socket in the service file).OPTIONS¶
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 systemd.exec(5). The options specific to the [Socket] section of socket units are the following: ListenStream=, ListenDatagram=, ListenSequentialPacket=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:
If the address starts with a slash (/), it is read as file system socket in the
AF_UNIX socket family.
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 unix(7).
If the address string is a single number it is read as port number to listen on
for both IPv4 and IPv6.
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.
If the address string is a string in the format [x]:y it is read as IPv6 address
x on a port y.
Note that SOCK_SEQPACKET (i.e. ListenSequentialPacket=) is only available
for AF_UNIX sockets. SOCK_STREAM (i.e. ListenStream=) when used for IP
sockets refers to TCP sockets, SOCK_DGRAM (i.e. ListenDatagram=) to
UDP.
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.
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 FreeBind= option described below.
ListenFIFO=
Specifies a file system FIFO to listen on.
This expects an absolute file system path as argument. Behaviour otherwise is
very similar to the ListenDatagram= directive above.
ListenSpecial=
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 ListenFIFO= directive above. Use this
to open character device nodes as well as special files in /proc and
/sys.
ListenNetlink=
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 audit or kobject-uevent) as argument,
optionally suffixed by a whitespace followed by a multicast group integer.
Behaviour otherwise is very similar to the ListenDatagram= directive
above.
ListenMessageQueue=
Specifies a POSIX message queue name to listen
on. This expects a valid message queue name (i.e. beginning with /). Behaviour
otherwise is very similar to the ListenFIFO= directive above. On Linux
message queue descriptors are actually file descriptors and can be inherited
between processes.
BindIPv6Only=
Takes a one of default, both or
ipv6-only. Controls the IPV6_V6ONLY socket option (see ipv6(7)
for details). If both, IPv6 sockets bound will be accessible via both
IPv4 and IPv6. If ipv6-only, they will be accessible via IPv6 only. If
default (which is the default, surprise!) the system wide default
setting is used, as controlled by /proc/sys/net/ipv6/bindv6only.
Backlog=
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
listen(2) for details. Defaults to SOMAXCONN (128).
BindToDevice=
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
socket(7) for details). If this option is used, an automatic dependency
from this socket unit on the network interface device unit (
systemd.device(5) is created.
DirectoryMode=
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.
SocketMode=
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.
Accept=
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 false. For performance reasons, it is recommended
to write new daemons only in a way that is suitable for Accept=false.
This option is mostly useful to allow daemons designed for usage with
inetd(8), to work unmodified with systemd socket activation.
MaxConnections=
The maximum number of connections to
simultaneously run services instances for, when Accept=true 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 Accept=no or datagram sockets. Defaults to 64.
KeepAlive=
Takes a boolean argument. If true, the TCP/IP
stack will send a keep alive message after 2h (depending on the configuration
of /proc/sys/net/ipv4/tcp_keepalive_time) for all TCP streams accepted on this
socket. This controls the SO_KEEPALIVE socket option (see socket(7) and
the TCP Keepalive HOWTO[1] for details.) Defaults to
false.
Priority=
Takes an integer argument controlling the
priority for all traffic sent from this socket. This controls the SO_PRIORITY
socket option (see socket(7) for details.).
ReceiveBuffer=, SendBuffer=
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 socket(7) for details.).
IPTOS=
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 ip(7) for details.). Either a numeric
string or one of low-delay, throughput, reliability or
low-cost may be specified.
IPTTL=
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 ip(7) and
ipv6(7) for details.)
Mark=
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 iptables(8) for details.
PipeSize=
Takes an integer value. Controls the pipe
buffer size of FIFOs configured in this socket unit. See fcntl(2) for
details.
MessageQueueMaxMessages=, MessageQueueMessageSize=
These two settings take integer values and
control the mq_maxmsg resp. mq_msgsize field when creating the message queue.
Note that either none or both of these variables need to be set. See
mq_setattr(3) for details.
FreeBind=
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
false.
Transparent=
Takes a boolean value. Controls the
IP_TRANSPARENT socket option. Defaults to false.
Broadcast=
Takes a boolean value. This controls the
SO_BROADCAST socket option, which allows broadcast datagrams to be sent from
this socket. Defaults to false.
PassCredentials=
Takes a boolean value. This controls the
SO_PASSCRED socket option, which allows AF_UNIX sockets to receive the
credentials of the sending process in an ancillary message. Defaults to
false.
PassSecurity=
Takes a boolean value. This controls the
SO_PASSSEC socket option, which allows AF_UNIX sockets to receive the security
context of the sending process in an ancillary message. Defaults to
false.
TCPCongestion=
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.
ExecStartPre=, ExecStartPost=
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 ExecStartPre= of service unit
files.
ExecStopPre=, ExecStopPost=
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
ExecStartPre= of service unit files.
TimeoutSec=
Configures the time to wait for the commands
specified in ExecStartPre=, ExecStartPost=, ExecStopPre=
and ExecStopPost= 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 KillMode= below.) Takes a
unit-less value in seconds, or a time span value such as "5min 20s".
Pass 0 to disable the timeout logic. Defaults to 90s.
KillMode=
Specifies how processes of this socket unit
shall be killed. One of control-group, process, none.
This option is mostly equivalent to the KillMode= option of service
files. See systemd.service(5) for details.
KillSignal=
Specifies which signal to use when killing a
process of this socket. Defaults to SIGTERM.
SendSIGKILL=
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".
Service=
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.
SEE ALSO¶
AUTHOR¶
Lennart Poettering <lennart@poettering.net>Developer
NOTES¶
- 1.
- TCP Keepalive HOWTO
10/07/2013 | systemd |