1SYSTEMD.SOCKET(5)               systemd.socket               SYSTEMD.SOCKET(5)
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3
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NAME

6       systemd.socket - Socket unit configuration
7

SYNOPSIS

9       socket.socket
10

DESCRIPTION

12       A unit configuration file whose name ends in ".socket" encodes
13       information about an IPC or network socket or a file system FIFO
14       controlled and supervised by systemd, for socket-based activation.
15
16       This man page lists the configuration options specific to this unit
17       type. See systemd.unit(5) for the common options of all unit
18       configuration files. The common configuration items are configured in
19       the generic [Unit] and [Install] sections. The socket specific
20       configuration options are configured in the [Socket] section.
21
22       Additional options are listed in systemd.exec(5), which define the
23       execution environment the ExecStartPre=, ExecStartPost=, ExecStopPre=
24       and ExecStopPost= commands are executed in, and in systemd.kill(5),
25       which define the way the processes are terminated, and in
26       systemd.resource-control(5), which configure resource control settings
27       for the processes of the socket.
28
29       For each socket unit, a matching service unit must exist, describing
30       the service to start on incoming traffic on the socket (see
31       systemd.service(5) for more information about .service units). The name
32       of the .service unit is by default the same as the name of the .socket
33       unit, but can be altered with the Service= option described below.
34       Depending on the setting of the Accept= option described below, this
35       .service unit must either be named like the .socket unit, but with the
36       suffix replaced, unless overridden with Service=; or it must be a
37       template unit named the same way. Example: a socket file foo.socket
38       needs a matching service foo.service if Accept=no is set. If Accept=yes
39       is set, a service template foo@.service must exist from which services
40       are instantiated for each incoming connection.
41
42       No implicit WantedBy= or RequiredBy= dependency from the socket to the
43       service is added. This means that the service may be started without
44       the socket, in which case it must be able to open sockets by itself. To
45       prevent this, an explicit Requires= dependency may be added.
46
47       Socket units may be used to implement on-demand starting of services,
48       as well as parallelized starting of services. See the blog stories
49       linked at the end for an introduction.
50
51       Note that the daemon software configured for socket activation with
52       socket units needs to be able to accept sockets from systemd, either
53       via systemd's native socket passing interface (see sd_listen_fds(3) for
54       details about the precise protocol used and the order in which the file
55       descriptors are passed) or via traditional inetd(8)-style socket
56       passing (i.e. sockets passed in via standard input and output, using
57       StandardInput=socket in the service file).
58
59       All network sockets allocated through .socket units are allocated in
60       the host's network namespace (see network_namespaces(7)). This does not
61       mean however that the service activated by a configured socket unit has
62       to be part of the host's network namespace as well. It is supported and
63       even good practice to run services in their own network namespace (for
64       example through PrivateNetwork=, see systemd.exec(5)), receiving only
65       the sockets configured through socket-activation from the host's
66       namespace. In such a set-up communication within the host's network
67       namespace is only permitted through the activation sockets passed in
68       while all sockets allocated from the service code itself will be
69       associated with the service's own namespace, and thus possibly subject
70       to a restrictive configuration.
71

AUTOMATIC DEPENDENCIES

73   Implicit Dependencies
74       The following dependencies are implicitly added:
75
76       •   Socket units automatically gain a Before= dependency on the service
77           units they activate.
78
79       •   Socket units referring to file system paths (such as AF_UNIX
80           sockets or FIFOs) implicitly gain Requires= and After= dependencies
81           on all mount units necessary to access those paths.
82
83       •   Socket units using the BindToDevice= setting automatically gain a
84           BindsTo= and After= dependency on the device unit encapsulating the
85           specified network interface.
86
87       Additional implicit dependencies may be added as result of execution
88       and resource control parameters as documented in systemd.exec(5) and
89       systemd.resource-control(5).
90
91   Default Dependencies
92       The following dependencies are added unless DefaultDependencies=no is
93       set:
94
95       •   Socket units automatically gain a Before= dependency on
96           sockets.target.
97
98       •   Socket units automatically gain a pair of After= and Requires=
99           dependency on sysinit.target, and a pair of Before= and Conflicts=
100           dependencies on shutdown.target. These dependencies ensure that the
101           socket unit is started before normal services at boot, and is
102           stopped on shutdown. Only sockets involved with early boot or late
103           system shutdown should disable DefaultDependencies= option.
104

OPTIONS

106       Socket unit files may include [Unit] and [Install] sections, which are
107       described in systemd.unit(5).
108
109       Socket unit files must include a [Socket] section, which carries
110       information about the socket or FIFO it supervises. A number of options
111       that may be used in this section are shared with other unit types.
112       These options are documented in systemd.exec(5) and systemd.kill(5).
113       The options specific to the [Socket] section of socket units are the
114       following:
115
116       ListenStream=, ListenDatagram=, ListenSequentialPacket=
117           Specifies an address to listen on for a stream (SOCK_STREAM),
118           datagram (SOCK_DGRAM), or sequential packet (SOCK_SEQPACKET)
119           socket, respectively. The address can be written in various
120           formats:
121
122           If the address starts with a slash ("/"), it is read as file system
123           socket in the AF_UNIX socket family.
124
125           If the address starts with an at symbol ("@"), it is read as
126           abstract namespace socket in the AF_UNIX family. The "@" is
127           replaced with a NUL character before binding. For details, see
128           unix(7).
129
130           If the address string is a single number, it is read as port number
131           to listen on via IPv6. Depending on the value of BindIPv6Only= (see
132           below) this might result in the service being available via both
133           IPv6 and IPv4 (default) or just via IPv6.
134
135           If the address string is a string in the format "v.w.x.y:z", it is
136           interpreted as IPv4 address v.w.x.y and port z.
137
138           If the address string is a string in the format "[x]:y", it is
139           interpreted as IPv6 address x and port y. An optional interface
140           scope (interface name or number) may be specified after a "%"
141           symbol: "[x]:y%dev". Interface scopes are only useful with
142           link-local addresses, because the kernel ignores them in other
143           cases. Note that if an address is specified as IPv6, it might still
144           make the service available via IPv4 too, depending on the
145           BindIPv6Only= setting (see below).
146
147           If the address string is a string in the format "vsock:x:y", it is
148           read as CID x on a port y address in the AF_VSOCK family. The CID
149           is a unique 32-bit integer identifier in AF_VSOCK analogous to an
150           IP address. Specifying the CID is optional, and may be set to the
151           empty string.
152
153           Note that SOCK_SEQPACKET (i.e.  ListenSequentialPacket=) is only
154           available for AF_UNIX sockets.  SOCK_STREAM (i.e.  ListenStream=)
155           when used for IP sockets refers to TCP sockets, SOCK_DGRAM (i.e.
156           ListenDatagram=) to UDP.
157
158           These options may be specified more than once, in which case
159           incoming traffic on any of the sockets will trigger service
160           activation, and all listed sockets will be passed to the service,
161           regardless of whether there is incoming traffic on them or not. If
162           the empty string is assigned to any of these options, the list of
163           addresses to listen on is reset, all prior uses of any of these
164           options will have no effect.
165
166           It is also possible to have more than one socket unit for the same
167           service when using Service=, and the service will receive all the
168           sockets configured in all the socket units. Sockets configured in
169           one unit are passed in the order of configuration, but no ordering
170           between socket units is specified.
171
172           If an IP address is used here, it is often desirable to listen on
173           it before the interface it is configured on is up and running, and
174           even regardless of whether it will be up and running at any point.
175           To deal with this, it is recommended to set the FreeBind= option
176           described below.
177
178       ListenFIFO=
179           Specifies a file system FIFO (see fifo(7) for details) to listen
180           on. This expects an absolute file system path as argument. Behavior
181           otherwise is very similar to the ListenDatagram= directive above.
182
183       ListenSpecial=
184           Specifies a special file in the file system to listen on. This
185           expects an absolute file system path as argument. Behavior
186           otherwise is very similar to the ListenFIFO= directive above. Use
187           this to open character device nodes as well as special files in
188           /proc/ and /sys/.
189
190       ListenNetlink=
191           Specifies a Netlink family to create a socket for to listen on.
192           This expects a short string referring to the AF_NETLINK family name
193           (such as audit or kobject-uevent) as argument, optionally suffixed
194           by a whitespace followed by a multicast group integer. Behavior
195           otherwise is very similar to the ListenDatagram= directive above.
196
197       ListenMessageQueue=
198           Specifies a POSIX message queue name to listen on (see
199           mq_overview(7) for details). This expects a valid message queue
200           name (i.e. beginning with "/"). Behavior otherwise is very similar
201           to the ListenFIFO= directive above. On Linux message queue
202           descriptors are actually file descriptors and can be inherited
203           between processes.
204
205       ListenUSBFunction=
206           Specifies a USB FunctionFS[1] endpoints location to listen on, for
207           implementation of USB gadget functions. This expects an absolute
208           file system path of a FunctionFS mount point as the argument.
209           Behavior otherwise is very similar to the ListenFIFO= directive
210           above. Use this to open the FunctionFS endpoint ep0. When using
211           this option, the activated service has to have the
212           USBFunctionDescriptors= and USBFunctionStrings= options set.
213
214       SocketProtocol=
215           Takes one of udplite or sctp. The socket will use the UDP-Lite
216           (IPPROTO_UDPLITE) or SCTP (IPPROTO_SCTP) protocol, respectively.
217
218       BindIPv6Only=
219           Takes one of default, both or ipv6-only. Controls the IPV6_V6ONLY
220           socket option (see ipv6(7) for details). If both, IPv6 sockets
221           bound will be accessible via both IPv4 and IPv6. If ipv6-only, they
222           will be accessible via IPv6 only. If default (which is the default,
223           surprise!), the system wide default setting is used, as controlled
224           by /proc/sys/net/ipv6/bindv6only, which in turn defaults to the
225           equivalent of both.
226
227       Backlog=
228           Takes an unsigned integer argument. Specifies the number of
229           connections to queue that have not been accepted yet. This setting
230           matters only for stream and sequential packet sockets. See
231           listen(2) for details. Defaults to SOMAXCONN (128).
232
233       BindToDevice=
234           Specifies a network interface name to bind this socket to. If set,
235           traffic will only be accepted from the specified network
236           interfaces. This controls the SO_BINDTODEVICE socket option (see
237           socket(7) for details). If this option is used, an implicit
238           dependency from this socket unit on the network interface device
239           unit is created (see systemd.device(5)). Note that setting this
240           parameter might result in additional dependencies to be added to
241           the unit (see above).
242
243       SocketUser=, SocketGroup=
244           Takes a UNIX user/group name. When specified, all AF_UNIX sockets
245           and FIFO nodes in the file system are owned by the specified user
246           and group. If unset (the default), the nodes are owned by the root
247           user/group (if run in system context) or the invoking user/group
248           (if run in user context). If only a user is specified but no group,
249           then the group is derived from the user's default group.
250
251       SocketMode=
252           If listening on a file system socket or FIFO, this option specifies
253           the file system access mode used when creating the file node. Takes
254           an access mode in octal notation. Defaults to 0666.
255
256       DirectoryMode=
257           If listening on a file system socket or FIFO, the parent
258           directories are automatically created if needed. This option
259           specifies the file system access mode used when creating these
260           directories. Takes an access mode in octal notation. Defaults to
261           0755.
262
263       Accept=
264           Takes a boolean argument. If yes, a service instance is spawned for
265           each incoming connection and only the connection socket is passed
266           to it. If no, all listening sockets themselves are passed to the
267           started service unit, and only one service unit is spawned for all
268           connections (also see above). This value is ignored for datagram
269           sockets and FIFOs where a single service unit unconditionally
270           handles all incoming traffic. Defaults to no. For performance
271           reasons, it is recommended to write new daemons only in a way that
272           is suitable for Accept=no. A daemon listening on an AF_UNIX socket
273           may, but does not need to, call close(2) on the received socket
274           before exiting. However, it must not unlink the socket from a file
275           system. It should not invoke shutdown(2) on sockets it got with
276           Accept=no, but it may do so for sockets it got with Accept=yes set.
277           Setting Accept=yes is mostly useful to allow daemons designed for
278           usage with inetd(8) to work unmodified with systemd socket
279           activation.
280
281           For IPv4 and IPv6 connections, the REMOTE_ADDR environment variable
282           will contain the remote IP address, and REMOTE_PORT will contain
283           the remote port. This is the same as the format used by CGI. For
284           SOCK_RAW, the port is the IP protocol.
285
286           It is recommended to set CollectMode=inactive-or-failed for service
287           instances activated via Accept=yes, to ensure that failed
288           connection services are cleaned up and released from memory, and do
289           not accumulate.
290
291       Writable=
292           Takes a boolean argument. May only be used in conjunction with
293           ListenSpecial=. If true, the specified special file is opened in
294           read-write mode, if false, in read-only mode. Defaults to false.
295
296       FlushPending=
297           Takes a boolean argument. May only be used when Accept=no. If yes,
298           the socket's buffers are cleared after the triggered service
299           exited. This causes any pending data to be flushed and any pending
300           incoming connections to be rejected. If no, the socket's buffers
301           won't be cleared, permitting the service to handle any pending
302           connections after restart, which is the usually expected behaviour.
303           Defaults to no.
304
305       MaxConnections=
306           The maximum number of connections to simultaneously run services
307           instances for, when Accept=yes is set. If more concurrent
308           connections are coming in, they will be refused until at least one
309           existing connection is terminated. This setting has no effect on
310           sockets configured with Accept=no or datagram sockets. Defaults to
311           64.
312
313       MaxConnectionsPerSource=
314           The maximum number of connections for a service per source IP
315           address. This is very similar to the MaxConnections= directive
316           above. Disabled by default.
317
318       KeepAlive=
319           Takes a boolean argument. If true, the TCP/IP stack will send a
320           keep alive message after 2h (depending on the configuration of
321           /proc/sys/net/ipv4/tcp_keepalive_time) for all TCP streams accepted
322           on this socket. This controls the SO_KEEPALIVE socket option (see
323           socket(7) and the TCP Keepalive HOWTO[2] for details.) Defaults to
324           false.
325
326       KeepAliveTimeSec=
327           Takes time (in seconds) as argument. The connection needs to remain
328           idle before TCP starts sending keepalive probes. This controls the
329           TCP_KEEPIDLE socket option (see socket(7) and the TCP Keepalive
330           HOWTO[2] for details.) Defaults value is 7200 seconds (2 hours).
331
332       KeepAliveIntervalSec=
333           Takes time (in seconds) as argument between individual keepalive
334           probes, if the socket option SO_KEEPALIVE has been set on this
335           socket. This controls the TCP_KEEPINTVL socket option (see
336           socket(7) and the TCP Keepalive HOWTO[2] for details.) Defaults
337           value is 75 seconds.
338
339       KeepAliveProbes=
340           Takes an integer as argument. It is the number of unacknowledged
341           probes to send before considering the connection dead and notifying
342           the application layer. This controls the TCP_KEEPCNT socket option
343           (see socket(7) and the TCP Keepalive HOWTO[2] for details.)
344           Defaults value is 9.
345
346       NoDelay=
347           Takes a boolean argument. TCP Nagle's algorithm works by combining
348           a number of small outgoing messages, and sending them all at once.
349           This controls the TCP_NODELAY socket option (see tcp(7)). Defaults
350           to false.
351
352       Priority=
353           Takes an integer argument controlling the priority for all traffic
354           sent from this socket. This controls the SO_PRIORITY socket option
355           (see socket(7) for details.).
356
357       DeferAcceptSec=
358           Takes time (in seconds) as argument. If set, the listening process
359           will be awakened only when data arrives on the socket, and not
360           immediately when connection is established. When this option is
361           set, the TCP_DEFER_ACCEPT socket option will be used (see tcp(7)),
362           and the kernel will ignore initial ACK packets without any data.
363           The argument specifies the approximate amount of time the kernel
364           should wait for incoming data before falling back to the normal
365           behavior of honoring empty ACK packets. This option is beneficial
366           for protocols where the client sends the data first (e.g. HTTP, in
367           contrast to SMTP), because the server process will not be woken up
368           unnecessarily before it can take any action.
369
370           If the client also uses the TCP_DEFER_ACCEPT option, the latency of
371           the initial connection may be reduced, because the kernel will send
372           data in the final packet establishing the connection (the third
373           packet in the "three-way handshake").
374
375           Disabled by default.
376
377       ReceiveBuffer=, SendBuffer=
378           Takes an integer argument controlling the receive or send buffer
379           sizes of this socket, respectively. This controls the SO_RCVBUF and
380           SO_SNDBUF socket options (see socket(7) for details.). The usual
381           suffixes K, M, G are supported and are understood to the base of
382           1024.
383
384       IPTOS=
385           Takes an integer argument controlling the IP Type-Of-Service field
386           for packets generated from this socket. This controls the IP_TOS
387           socket option (see ip(7) for details.). Either a numeric string or
388           one of low-delay, throughput, reliability or low-cost may be
389           specified.
390
391       IPTTL=
392           Takes an integer argument controlling the IPv4 Time-To-Live/IPv6
393           Hop-Count field for packets generated from this socket. This sets
394           the IP_TTL/IPV6_UNICAST_HOPS socket options (see ip(7) and ipv6(7)
395           for details.)
396
397       Mark=
398           Takes an integer value. Controls the firewall mark of packets
399           generated by this socket. This can be used in the firewall logic to
400           filter packets from this socket. This sets the SO_MARK socket
401           option. See iptables(8) for details.
402
403       ReusePort=
404           Takes a boolean value. If true, allows multiple bind(2)s to this
405           TCP or UDP port. This controls the SO_REUSEPORT socket option. See
406           socket(7) for details.
407
408       SmackLabel=, SmackLabelIPIn=, SmackLabelIPOut=
409           Takes a string value. Controls the extended attributes
410           "security.SMACK64", "security.SMACK64IPIN" and
411           "security.SMACK64IPOUT", respectively, i.e. the security label of
412           the FIFO, or the security label for the incoming or outgoing
413           connections of the socket, respectively. See Smack.txt[3] for
414           details.
415
416       SELinuxContextFromNet=
417           Takes a boolean argument. When true, systemd will attempt to figure
418           out the SELinux label used for the instantiated service from the
419           information handed by the peer over the network. Note that only the
420           security level is used from the information provided by the peer.
421           Other parts of the resulting SELinux context originate from either
422           the target binary that is effectively triggered by socket unit or
423           from the value of the SELinuxContext= option. This configuration
424           option applies only when activated service is passed in single
425           socket file descriptor, i.e. service instances that have standard
426           input connected to a socket or services triggered by exactly one
427           socket unit. Also note that this option is useful only when MLS/MCS
428           SELinux policy is deployed. Defaults to "false".
429
430       PipeSize=
431           Takes a size in bytes. Controls the pipe buffer size of FIFOs
432           configured in this socket unit. See fcntl(2) for details. The usual
433           suffixes K, M, G are supported and are understood to the base of
434           1024.
435
436       MessageQueueMaxMessages=, MessageQueueMessageSize=
437           These two settings take integer values and control the mq_maxmsg
438           field or the mq_msgsize field, respectively, when creating the
439           message queue. Note that either none or both of these variables
440           need to be set. See mq_setattr(3) for details.
441
442       FreeBind=
443           Takes a boolean value. Controls whether the socket can be bound to
444           non-local IP addresses. This is useful to configure sockets
445           listening on specific IP addresses before those IP addresses are
446           successfully configured on a network interface. This sets the
447           IP_FREEBIND/IPV6_FREEBIND socket option. For robustness reasons it
448           is recommended to use this option whenever you bind a socket to a
449           specific IP address. Defaults to false.
450
451       Transparent=
452           Takes a boolean value. Controls the IP_TRANSPARENT/IPV6_TRANSPARENT
453           socket option. Defaults to false.
454
455       Broadcast=
456           Takes a boolean value. This controls the SO_BROADCAST socket
457           option, which allows broadcast datagrams to be sent from this
458           socket. Defaults to false.
459
460       PassCredentials=
461           Takes a boolean value. This controls the SO_PASSCRED socket option,
462           which allows AF_UNIX sockets to receive the credentials of the
463           sending process in an ancillary message. Defaults to false.
464
465       PassSecurity=
466           Takes a boolean value. This controls the SO_PASSSEC socket option,
467           which allows AF_UNIX sockets to receive the security context of the
468           sending process in an ancillary message. Defaults to false.
469
470       PassPacketInfo=
471           Takes a boolean value. This controls the IP_PKTINFO,
472           IPV6_RECVPKTINFO, NETLINK_PKTINFO or PACKET_AUXDATA socket options,
473           which enable reception of additional per-packet metadata as
474           ancillary message, on AF_INET, AF_INET6, AF_UNIX and AF_PACKET
475           sockets. Defaults to false.
476
477       Timestamping=
478           Takes one of "off", "us" (alias: "usec", "µs") or "ns" (alias:
479           "nsec"). This controls the SO_TIMESTAMP or SO_TIMESTAMPNS socket
480           options, and enables whether ingress network traffic shall carry
481           timestamping metadata. Defaults to off.
482
483       TCPCongestion=
484           Takes a string value. Controls the TCP congestion algorithm used by
485           this socket. Should be one of "westwood", "veno", "cubic", "lp" or
486           any other available algorithm supported by the IP stack. This
487           setting applies only to stream sockets.
488
489       ExecStartPre=, ExecStartPost=
490           Takes one or more command lines, which are executed before or after
491           the listening sockets/FIFOs are created and bound, respectively.
492           The first token of the command line must be an absolute filename,
493           then followed by arguments for the process. Multiple command lines
494           may be specified following the same scheme as used for
495           ExecStartPre= of service unit files.
496
497       ExecStopPre=, ExecStopPost=
498           Additional commands that are executed before or after the listening
499           sockets/FIFOs are closed and removed, respectively. Multiple
500           command lines may be specified following the same scheme as used
501           for ExecStartPre= of service unit files.
502
503       TimeoutSec=
504           Configures the time to wait for the commands specified in
505           ExecStartPre=, ExecStartPost=, ExecStopPre= and ExecStopPost= to
506           finish. If a command does not exit within the configured time, the
507           socket will be considered failed and be shut down again. All
508           commands still running will be terminated forcibly via SIGTERM, and
509           after another delay of this time with SIGKILL. (See KillMode= in
510           systemd.kill(5).) Takes a unit-less value in seconds, or a time
511           span value such as "5min 20s". Pass "0" to disable the timeout
512           logic. Defaults to DefaultTimeoutStartSec= from the manager
513           configuration file (see systemd-system.conf(5)).
514
515       Service=
516           Specifies the service unit name to activate on incoming traffic.
517           This setting is only allowed for sockets with Accept=no. It
518           defaults to the service that bears the same name as the socket
519           (with the suffix replaced). In most cases, it should not be
520           necessary to use this option. Note that setting this parameter
521           might result in additional dependencies to be added to the unit
522           (see above).
523
524       RemoveOnStop=
525           Takes a boolean argument. If enabled, any file nodes created by
526           this socket unit are removed when it is stopped. This applies to
527           AF_UNIX sockets in the file system, POSIX message queues, FIFOs, as
528           well as any symlinks to them configured with Symlinks=. Normally,
529           it should not be necessary to use this option, and is not
530           recommended as services might continue to run after the socket unit
531           has been terminated and it should still be possible to communicate
532           with them via their file system node. Defaults to off.
533
534       Symlinks=
535           Takes a list of file system paths. The specified paths will be
536           created as symlinks to the AF_UNIX socket path or FIFO path of this
537           socket unit. If this setting is used, only one AF_UNIX socket in
538           the file system or one FIFO may be configured for the socket unit.
539           Use this option to manage one or more symlinked alias names for a
540           socket, binding their lifecycle together. Note that if creation of
541           a symlink fails this is not considered fatal for the socket unit,
542           and the socket unit may still start. If an empty string is
543           assigned, the list of paths is reset. Defaults to an empty list.
544
545       FileDescriptorName=
546           Assigns a name to all file descriptors this socket unit
547           encapsulates. This is useful to help activated services identify
548           specific file descriptors, if multiple fds are passed. Services may
549           use the sd_listen_fds_with_names(3) call to acquire the names
550           configured for the received file descriptors. Names may contain any
551           ASCII character, but must exclude control characters and ":", and
552           must be at most 255 characters in length. If this setting is not
553           used, the file descriptor name defaults to the name of the socket
554           unit, including its .socket suffix.
555
556       TriggerLimitIntervalSec=, TriggerLimitBurst=
557           Configures a limit on how often this socket unit may be activated
558           within a specific time interval. The TriggerLimitIntervalSec= may
559           be used to configure the length of the time interval in the usual
560           time units "us", "ms", "s", "min", "h", ... and defaults to 2s (See
561           systemd.time(7) for details on the various time units understood).
562           The TriggerLimitBurst= setting takes a positive integer value and
563           specifies the number of permitted activations per time interval,
564           and defaults to 200 for Accept=yes sockets (thus by default
565           permitting 200 activations per 2s), and 20 otherwise (20
566           activations per 2s). Set either to 0 to disable any form of trigger
567           rate limiting. If the limit is hit, the socket unit is placed into
568           a failure mode, and will not be connectible anymore until
569           restarted. Note that this limit is enforced before the service
570           activation is enqueued.
571
572       Check systemd.unit(5), systemd.exec(5), and systemd.kill(5) for more
573       settings.
574

SEE ALSO

576       systemd(1), systemctl(1), systemd-system.conf(5), systemd.unit(5),
577       systemd.exec(5), systemd.kill(5), systemd.resource-control(5),
578       systemd.service(5), systemd.directives(7), sd_listen_fds(3),
579       sd_listen_fds_with_names(3)
580
581       For more extensive descriptions see the "systemd for Developers"
582       series: Socket Activation[4], Socket Activation, part II[5], Converting
583       inetd Services[6], Socket Activated Internet Services and OS
584       Containers[7].
585

NOTES

587        1. USB FunctionFS
588           https://www.kernel.org/doc/Documentation/usb/functionfs.txt
589
590        2. TCP Keepalive HOWTO
591           http://www.tldp.org/HOWTO/html_single/TCP-Keepalive-HOWTO/
592
593        3. Smack.txt
594           https://www.kernel.org/doc/Documentation/security/Smack.txt
595
596        4. Socket Activation
597           http://0pointer.de/blog/projects/socket-activation.html
598
599        5. Socket Activation, part II
600           http://0pointer.de/blog/projects/socket-activation2.html
601
602        6. Converting inetd Services
603           http://0pointer.de/blog/projects/inetd.html
604
605        7. Socket Activated Internet Services and OS Containers
606           http://0pointer.de/blog/projects/socket-activated-containers.html
607
608
609
610systemd 250                                                  SYSTEMD.SOCKET(5)
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