Ubuntu Manpage: Config::Model::models::Systemd::Section::Socket

Provided by: libconfig-model-systemd-perl_0.236.1-1_all

NAME

       Config::Model::models::Systemd::Section::Socket - Configuration class
       Systemd::Section::Socket

DESCRIPTION

Configuration classes used by Config::Model

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, and in systemd.kill(5), which define the way the processes are terminated,
and in systemd.resource-control(5), which configure resource control settings for the
processes of the socket.

For each socket file, a matching service file must exist, describing the service to start
on incoming traffic on the socket (see systemd.service(5) 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 "Service" option described below. Depending on
the setting of the "Accept" option described below, this .service unit must either be
named like the .socket unit, but with the suffix replaced, unless overridden with
"Service"; or it must be a template unit 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.

No implicit "WantedBy" or "RequiredBy" 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 "Requires" dependency may be
added.

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.

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 standard input and output, using
"StandardInput=socket" in the service file). This configuration class was generated from
systemd documentation. by parse-man.pl <https://github.com/dod38fr/config-model-
systemd/contrib/parse-man.pl>

Elements

ListenStream
Specifies an address to listen on for a stream ("SOCK_STREAM"), datagram ("SOCK_DGRAM"),
or sequential packet ("SOCK_SEQPACKET") socket, respectively. 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 via IPv6.
Depending on the value of "BindIPv6Only" (see below) this might result in the service
being available via both IPv6 and IPv4 (default) or just via 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 this might make the service available via IPv4, too, depending on the
"BindIPv6Only" setting (see below).

If the address string is a string in the format "vsock:x:y", it is read as CID "x" on a
port "y" address in the "AF_VSOCK" family. The CID is a unique 32-bit integer identifier
in "AF_VSOCK" analogous to an IP address. Specifying the CID is optional, and may be set
to the empty string.

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 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.

It is also possible to have more than one socket unit for the same service when using
"Service", 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.

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 "FreeBind" option
described below. Optional. Type list of uniline.

ListenDatagram
Specifies an address to listen on for a stream ("SOCK_STREAM"), datagram ("SOCK_DGRAM"),
or sequential packet ("SOCK_SEQPACKET") socket, respectively. 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 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.

ListenSequentialPacket
Specifies an address to listen on for a stream ("SOCK_STREAM"), datagram ("SOCK_DGRAM"),
or sequential packet ("SOCK_SEQPACKET") socket, respectively. 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 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.

ListenFIFO
Specifies a file system FIFO to listen on. This expects an absolute file system path as
argument. Behavior otherwise is very similar to the "ListenDatagram" directive above.
Optional. Type list of uniline.

ListenSpecial
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 "ListenFIFO" directive
above. Use this to open character device nodes as well as special files in /proc and /sys.
Optional. Type list of uniline.

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.
Behavior otherwise is very similar to the "ListenDatagram" directive above. Optional.
Type list of uniline.

ListenMessageQueue
Specifies a POSIX message queue name to listen on. This expects a valid message queue name
(i.e. beginning with /). Behavior otherwise is very similar to the "ListenFIFO" directive
above. On Linux message queue descriptors are actually file descriptors and can be
inherited between processes. Optional. Type list of uniline.

ListenUSBFunction
Specifies a USB FunctionFS endpoints location to listen on, for implementation of USB
gadget functions. This expects an absolute file system path of functionfs mount point as
the argument. Behavior otherwise is very similar to the "ListenFIFO" directive above. Use
this to open the FunctionFS endpoint ep0. When using this option, the activated service
has to have the "USBFunctionDescriptors" and "USBFunctionStrings" options set. Optional.
Type list of uniline.

SocketProtocol
Takes a one of "udplite" or "sctp". Specifies a socket protocol ("IPPROTO_UDPLITE") UDP-
Lite ("IPPROTO_SCTP") SCTP socket respectively. Optional. Type uniline.

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, which in turn defaults to the equivalent of "both".
Optional. Type uniline.

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). Optional. Type uniline.

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 implicit dependency from
this socket unit on the network interface device unit (systemd.device(5) is created. Note
that setting this parameter might result in additional dependencies to be added to the
unit (see above). Optional. Type uniline.

SocketUser
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. Optional. Type uniline.

SocketGroup
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. Optional. Type uniline.

SocketMode
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. Optional. Type uniline.

DirectoryMode
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. Optional.
Type uniline.

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". A daemon listening on an "AF_UNIX" socket may, but
does not need to, call close(2) on the received socket before exiting. However, it must
not unlink the socket from a file system. It should not invoke shutdown(2) on sockets it
got with "Accept=false", but it may do so for sockets it got with "Accept=true" set.
Setting "Accept=true" is mostly useful to allow daemons designed for usage with inetd(8)
to work unmodified with systemd socket activation.

For IPv4 and IPv6 connections, the "REMOTE_ADDR" environment variable will contain the
remote IP address, and "REMOTE_PORT" will contain the remote port. This is the same as the
format used by CGI. For SOCK_RAW, the port is the IP protocol. Optional. Type boolean.

Writable
Takes a boolean argument. May only be used in conjunction with "ListenSpecial". If true,
the specified special file is opened in read-write mode, if false, in read-only mode.
Defaults to false. Optional. Type boolean.

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 on
sockets configured with "Accept=false" or datagram sockets. Defaults to 64. Optional.
Type uniline.

MaxConnectionsPerSource
The maximum number of connections for a service per source IP address. This is very
similar to the "MaxConnections" directive above. Disabled by default. Optional. Type
uniline.

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 for details.) Defaults to "false". Optional. Type
boolean.

KeepAliveTimeSec
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 socket(7) and
the TCP Keepalive HOWTO for details.) Defaults value is 7200 seconds (2 hours).
Optional. Type integer.

KeepAliveIntervalSec
Takes time (in seconds) as argument between individual keepalive probes, if the socket
option SO_KEEPALIVE has been set on this socket. This controls the TCP_KEEPINTVL socket
option (see socket(7) and the TCP Keepalive HOWTO for details.) Defaults value is 75
seconds. Optional. Type integer.

KeepAliveProbes
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 socket(7) and the TCP Keepalive HOWTO for details.)
Defaults value is 9. Optional. Type integer.

NoDelay
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 tcp(7) Defaults to "false". Optional. Type boolean.

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.). Optional. Type
integer.

DeferAcceptSec
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 "TCP_DEFER_ACCEPT" socket option will be used (see tcp(7)), 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.

If the client also uses the "TCP_DEFER_ACCEPT" 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").

Disabled by default. Optional. Type integer.

ReceiveBuffer
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 socket(7) for
details.). The usual suffixes K, M, G are supported and are understood to the base of
1024. Optional. Type uniline.

SendBuffer
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 socket(7) for
details.). The usual suffixes K, M, G are supported and are understood to the base of
1024. Optional. Type uniline.

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. Optional. Type integer.

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.) Optional. Type integer.

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. Optional. Type integer.

ReusePort
Takes a boolean value. If true, allows multiple bind(2)s to this TCP or UDP port. This
controls the SO_REUSEPORT socket option. See socket(7) for details. Optional. Type
boolean.

SmackLabel
Takes a string value. Controls the extended attributes "security.SMACK64",
"security.SMACK64IPIN" and "security.SMACK64IPOUT", respectively, i.e. the security label
of the FIFO, or the security label for the incoming or outgoing connections of the socket,
respectively. See Smack.txt for details. Optional. Type uniline.

SmackLabelIPIn
Takes a string value. Controls the extended attributes "security.SMACK64",
"security.SMACK64IPIN" and "security.SMACK64IPOUT", respectively, i.e. the security label
of the FIFO, or the security label for the incoming or outgoing connections of the socket,
respectively. See Smack.txt for details. Optional. Type uniline.

SmackLabelIPOut
Takes a string value. Controls the extended attributes "security.SMACK64",
"security.SMACK64IPIN" and "security.SMACK64IPOUT", respectively, i.e. the security label
of the FIFO, or the security label for the incoming or outgoing connections of the socket,
respectively. See Smack.txt for details. Optional. Type uniline.

SELinuxContextFromNet
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 "SELinuxContext"
option. This configuration option only affects sockets with "Accept" mode set to "true".
Also note that this option is useful only when MLS/MCS SELinux policy is deployed.
Defaults to "false". Optional. Type boolean.

PipeSize
Takes a size in bytes. Controls the pipe buffer size of FIFOs configured in this socket
unit. See fcntl(2) for details. The usual suffixes K, M, G are supported and are
understood to the base of 1024. Optional. Type uniline.

MessageQueueMaxMessages
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 mq_setattr(3) for details. Optional. Type uniline.

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". Optional. Type boolean.

Transparent
Takes a boolean value. Controls the IP_TRANSPARENT socket option. Defaults to "false".
Optional. Type boolean.

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". Optional. Type
boolean.

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". Optional. Type boolean.

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". Optional. Type boolean.

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. Optional. Type uniline.

ExecStartPre
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 "ExecStartPre" of service
unit files. Optional. Type list of uniline.

ExecStartPost
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 "ExecStartPre" of service
unit files. Optional. Type list of uniline.

ExecStopPre
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 "ExecStartPre" of service unit files. Optional. Type list of
uniline.

ExecStopPost
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 "ExecStartPre" of service unit files. Optional. Type list of
uniline.

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" in systemd.kill(5).) 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 "DefaultTimeoutStartSec" from the manager configuration file (see
systemd-system.conf(5)). Optional. Type uniline.

Service
Specifies the service unit name to activate on incoming traffic. This setting is only
allowed for sockets with "Accept=no". 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). Optional. Type uniline.

RemoveOnStop
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, FIFOs, as well as any symlinks to them configured with "Symlinks".
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.
Optional. Type boolean.

Symlinks
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. 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. Optional. Type uniline.

FileDescriptorName
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 sd_listen_fds_with_names(3) call to acquire the names configured for
the received file descriptors. Names may contain any ASCII character, but must exclude
control characters and ":", 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 .socket suffix. Optional. Type uniline.

TriggerLimitIntervalSec
Configures a limit on how often this socket unit my be activated within a specific time
interval. The "TriggerLimitIntervalSec" may be used to configure the length of the time
interval in the usual time units "us", "ms", "s", "min", "h", X and defaults to 2s (See
systemd.time(7) for details on the various time units understood). The "TriggerLimitBurst"
setting takes a positive integer value and specifies the number of permitted activations
per time interval, and defaults to 200 for "Accept=yes" 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. Optional. Type uniline.

TriggerLimitBurst
Configures a limit on how often this socket unit my be activated within a specific time
interval. The "TriggerLimitIntervalSec" may be used to configure the length of the time
interval in the usual time units "us", "ms", "s", "min", "h", X and defaults to 2s (See
systemd.time(7) for details on the various time units understood). The "TriggerLimitBurst"
setting takes a positive integer value and specifies the number of permitted activations
per time interval, and defaults to 200 for "Accept=yes" 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. Optional. Type uniline.

COPYRIGHT

       2010-2016 Lennart Poettering and others
       2016 Dominique Dumont

LICENSE

       LGPLv2.1+

perl v5.26.1                                2Config::Model::models::Systemd::Section::Socket(3pm)

NAME

DESCRIPTION

Elements

SEE ALSO

COPYRIGHT

LICENSE