man/systemd.socket.xml

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  25 <refentry id="systemd.socket">
  26         <refentryinfo>
  27                 <title>systemd.socket</title>
  28                 <productname>systemd</productname>
  29
  30                 <authorgroup>
  31                         <author>
  32                                 <contrib>Developer</contrib>
  33                                 <firstname>Lennart</firstname>
  34                                 <surname>Poettering</surname>
  35                                 <email>lennart@poettering.net</email>
  36                         </author>
  37                 </authorgroup>
  38         </refentryinfo>
  39
  40         <refmeta>
  41                 <refentrytitle>systemd.socket</refentrytitle>
  42                 <manvolnum>5</manvolnum>
  43         </refmeta>
  44
  45         <refnamediv>
  46                 <refname>systemd.socket</refname>
  47                 <refpurpose>systemd socket configuration files</refpurpose>
  48         </refnamediv>
  49
  50         <refsynopsisdiv>
  51                 <para><filename>systemd.socket</filename></para>
  52         </refsynopsisdiv>
  53
  54         <refsect1>
  55                 <title>Description</title>
  56
  57                 <para>A unit configuration file whose name ends in
  58                 <filename>.socket</filename> encodes information about
  59                 an IPC or network socket or a file system FIFO
  60                 controlled and supervised by systemd, for socket-based
  61                 activation.</para>
  62
  63                 <para>This man page lists the configuration options
  64                 specific to this unit type. See
  65                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  66                 for the common options of all unit configuration
  67                 files. The common configuration items are configured
  68                 in the generic [Unit] and [Install] sections. The
  69                 socket specific configuration options are configured
  70                 in the [Socket] section.</para>
  71
  72                 <para>Additional options are listed in
  73                 <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  74                 which define the execution environment the
  75                 <option>ExecStartPre=</option>,
  76                 <option>ExecStartPost=</option>,
  77                 <option>ExecStopPre=</option> and
  78                 <option>ExecStoptPost=</option> commands are executed
  79                 in.</para>
  80
  81                 <para>For each socket file a matching service file
  82                 (see
  83                 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  84                 for details) must exist, describing the service to
  85                 start on incoming traffic on the socket. Depending on
  86                 the setting of <option>Accept=</option> (see below),
  87                 this must either be named like the socket unit, but
  88                 with the suffix replaced; or it must be a template
  89                 file named the same way. Example: a socket file
  90                 <filename>foo.socket</filename> needs a matching
  91                 service <filename>foo.service</filename> if
  92                 <option>Accept=false</option> is set. If
  93                 <option>Accept=true</option> is set a service template
  94                 file <filename>foo@.service</filename> must exist from
  95                 which services are instantiated for each incoming
  96                 connection.</para>
  97
  98                 <para>Unless <varname>DefaultDependencies=</varname>
  99                 is set to <option>false</option>, socket units will
 100                 implicitly have dependencies of type
 101                 <varname>Requires=</varname> and
 102                 <varname>After=</varname> on
 103                 <filename>sysinit.target</filename> as well as
 104                 dependencies of type <varname>Conflicts=</varname> and
 105                 <varname>Before=</varname> on
 106                 <filename>shutdown.target</filename>. These ensure
 107                 that socket units pull in basic system
 108                 initialization, and are terminated cleanly prior to
 109                 system shutdown. Only sockets involved with early
 110                 boot or late system shutdown should disable this
 111                 option.</para>
 112
 113                 <para>Socket units may be used to implement on-demand
 114                 starting of services, as well as parallelized starting
 115                 of services.</para>
 116
 117                 <para>Note that the daemon software configured for
 118                 socket activation with socket units needs to be able
 119                 to accept sockets from systemd, either via systemd's
 120                 native socket passing interface (see
 121                 <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 122                 for details) or via the traditional
 123                 <citerefentry><refentrytitle>inetd</refentrytitle><manvolnum>8</manvolnum></citerefentry>-style
 124                 socket passing (i.e. sockets passed in via STDIN and
 125                 STDOUT, using <varname>StandardInput=socket</varname>
 126                 in the service file).</para>
 127         </refsect1>
 128
 129         <refsect1>
 130                 <title>Options</title>
 131
 132                 <para>Socket files must include a [Socket] section,
 133                 which carries information about the socket or FIFO it
 134                 supervises. A number of options that may be used in
 135                 this section are shared with other unit types. These
 136                 options are documented in
 137                 <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>. The
 138                 options specific to the [Socket] section of socket
 139                 units are the following:</para>
 140
 141                 <variablelist>
 142                         <varlistentry>
 143                                 <term><varname>ListenStream=</varname></term>
 144                                 <term><varname>ListenDatagram=</varname></term>
 145                                 <term><varname>ListenSequentialPacket=</varname></term>
 146                                 <listitem><para>Specifies an address
 147                                 to listen on for a stream
 148                                 (SOCK_STREAM), datagram (SOCK_DGRAM)
 149                                 resp. sequential packet
 150                                 (SOCK_SEQPACKET) socket. The address
 151                                 can be written in various formats:</para>
 152
 153                                 <para>If the address starts with a
 154                                 slash (/), it is read as file system
 155                                 socket in the AF_UNIX socket
 156                                 family.</para>
 157
 158                                 <para>If the address starts with an
 159                                 ampersand (@) it is read as abstract
 160                                 namespace socket in the AF_UNIX
 161                                 family. The @ is replaced with a NUL
 162                                 character before binding. For details
 163                                 see
 164                                 <citerefentry><refentrytitle>unix</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 165
 166                                 <para>If the address string is a
 167                                 single number it is read as port
 168                                 number to listen on for both IPv4 and
 169                                 IPv6.</para>
 170
 171                                 <para>If the address string is a
 172                                 string in the format v.w.x.y:z it is
 173                                 read as IPv4 specifier for listening
 174                                 on an address v.w.x.y on a port
 175                                 z.</para>
 176
 177                                 <para>If the address string is a
 178                                 string in the format [x]:y it is read
 179                                 as IPv6 address x on a port y.</para>
 180
 181                                 <para>Note that SOCK_SEQPACKET
 182                                 (i.e. <varname>ListenSequentialPacket=</varname>)
 183                                 is only available for AF_UNIX
 184                                 sockets. SOCK_STREAM
 185                                 (i.e. <varname>ListenStream=</varname>)
 186                                 when used for IP sockets refers to TCP
 187                                 sockets, SOCK_DGRAM
 188                                 (i.e. <varname>ListenDatagram=</varname>)
 189                                 to UDP.</para>
 190
 191                                 <para>These options may be specified
 192                                 more than once in which case incoming
 193                                 traffic on any of the sockets will trigger
 194                                 service activation, and all listed
 195                                 sockets will be passed to the service,
 196                                 regardless whether there is incoming
 197                                 traffic on them or not.</para>
 198
 199                                 <para>If an IP address is used here, it
 200                                 is often desirable to listen on it
 201                                 before the interface it is configured
 202                                 on is up and running, and even
 203                                 regardless whether it will be up and
 204                                 running ever at all. To deal with this it is
 205                                 recommended to set the
 206                                 <varname>FreeBind=</varname> option
 207                                 described below.</para></listitem>
 208                         </varlistentry>
 209
 210                         <varlistentry>
 211                                 <term><varname>ListenFIFO=</varname></term>
 212                                 <listitem><para>Specifies a file
 213                                 system FIFO to listen on. This expects
 214                                 an absolute file system path as
 215                                 argument. Behaviour otherwise is very
 216                                 similar to the
 217                                 <varname>ListenDatagram=</varname>
 218                                 directive above.</para></listitem>
 219                         </varlistentry>
 220
 221                         <varlistentry>
 222                                 <term><varname>BindIPv6Only=</varname></term>
 223                                 <listitem><para>Takes a one of
 224                                 <option>default</option>,
 225                                 <option>both</option> or
 226                                 <option>ipv6-only</option>. Controls
 227                                 the IPV6_V6ONLY socket option (see
 228                                 <citerefentry><refentrytitle>ipv6</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 229                                 for details). If
 230                                 <option>both</option>, IPv6 sockets
 231                                 bound will be accessible via both IPv4
 232                                 and IPv6. If
 233                                 <option>ipv6-only</option>, they will
 234                                 be accessible via IPv6 only. If
 235                                 <option>default</option> (which is the
 236                                 default, surprise!) the system wide
 237                                 default setting is used, as controlled
 238                                 by
 239                                 <filename>/proc/sys/net/ipv6/bindv6only</filename>.</para>
 240                                 </listitem>
 241                         </varlistentry>
 242
 243                         <varlistentry>
 244                                 <term><varname>Backlog=</varname></term>
 245                                 <listitem><para>Takes an unsigned
 246                                 integer argument. Specifies the number
 247                                 of connections to queue that have not
 248                                 been accepted yet. This setting
 249                                 matters only for stream and sequential
 250                                 packet sockets. See
 251                                 <citerefentry><refentrytitle>listen</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 252                                 for details. Defaults to SOMAXCONN
 253                                 (128).</para></listitem>
 254                         </varlistentry>
 255
 256                         <varlistentry>
 257                                 <term><varname>BindToDevice=</varname></term>
 258                                 <listitem><para>Specifies a network
 259                                 interface name to bind this socket
 260                                 to. If set traffic will only be
 261                                 accepted from the specified network
 262                                 interfaces. This controls the
 263                                 SO_BINDTODEVICE socket option (see
 264                                 <citerefentry><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 265                                 for details). If this option is used,
 266                                 an automatic dependency from this
 267                                 socket unit on the network interface
 268                                 device unit
 269                                 (<citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 270                                 is created.</para></listitem>
 271                         </varlistentry>
 272
 273                         <varlistentry>
 274                                 <term><varname>DirectoryMode=</varname></term>
 275                                 <listitem><para>If listening on a file
 276                                 system socket of FIFO, the parent
 277                                 directories are automatically created
 278                                 if needed. This option specifies the
 279                                 file system access mode used when
 280                                 creating these directories. Takes an
 281                                 access mode in octal
 282                                 notation. Defaults to
 283                                 0755.</para></listitem>
 284                         </varlistentry>
 285
 286                         <varlistentry>
 287                                 <term><varname>SocketMode=</varname></term>
 288                                 <listitem><para>If listening on a file
 289                                 system socket of FIFO, this option
 290                                 specifies the file system access mode
 291                                 used when creating the file
 292                                 node. Takes an access mode in octal
 293                                 notation. Defaults to
 294                                 0666.</para></listitem>
 295                         </varlistentry>
 296
 297                         <varlistentry>
 298                                 <term><varname>Accept=</varname></term>
 299                                 <listitem><para>Takes a boolean
 300                                 argument. If true, a service instance
 301                                 is spawned for each incoming
 302                                 connection and only the connection
 303                                 socket is passed to it. If false, all
 304                                 listening sockets themselves are
 305                                 passed to the started service unit,
 306                                 and only one service unit is spawned
 307                                 for all connections (also see
 308                                 above). This value is ignored for
 309                                 datagram sockets and FIFOs where
 310                                 a single service unit unconditionally
 311                                 handles all incoming traffic. Defaults
 312                                 to <option>false</option>. For
 313                                 performance reasons, it is recommended
 314                                 to write new daemons only in a way
 315                                 that is suitable for
 316                                 <option>Accept=false</option>. This
 317                                 option is mostly useful to allow
 318                                 daemons designed for usage with
 319                                 <citerefentry><refentrytitle>inetd</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 320                                 to work unmodified with systemd socket
 321                                 activation.</para></listitem>
 322                         </varlistentry>
 323
 324                         <varlistentry>
 325                                 <term><varname>MaxConnections=</varname></term>
 326                                 <listitem><para>The maximum number of
 327                                 connections to simultaneously run
 328                                 services instances for, when
 329                                 <option>Accept=true</option> is
 330                                 set. If more concurrent connections
 331                                 are coming in, they will be refused
 332                                 until at least one existing connection
 333                                 is terminated. This setting has no
 334                                 effect for sockets configured with
 335                                 <option>Accept=no</option> or datagram
 336                                 sockets. Defaults to
 337                                 64.</para></listitem>
 338                         </varlistentry>
 339
 340                         <varlistentry>
 341                                 <term><varname>KeepAlive=</varname></term>
 342                                 <listitem><para>Takes a boolean
 343                                 argument. If true, the TCP/IP stack
 344                                 will send a keep alive message after
 345                                 2h (depending on the configuration of
 346                                 <filename>/proc/sys/net/ipv4/tcp_keepalive_time</filename>)
 347                                 for all TCP streams accepted on this
 348                                 socket. This controls the SO_KEEPALIVE
 349                                 socket option (see
 350                                 <citerefentry><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 351                                 and the <ulink
 352                                 url="http://www.tldp.org/HOWTO/html_single/TCP-Keepalive-HOWTO/">TCP
 353                                 Keepalive HOWTO</ulink> for details.)
 354                                 Defaults to
 355                                 <option>false</option>.</para></listitem>
 356                         </varlistentry>
 357
 358                         <varlistentry>
 359                                 <term><varname>Priority=</varname></term>
 360                                 <listitem><para>Takes an integer
 361                                 argument controlling the priority for
 362                                 all traffic sent from this
 363                                 socket. This controls the SO_PRIORITY
 364                                 socket option (see
 365                                 <citerefentry><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 366                                 for details.).</para></listitem>
 367                         </varlistentry>
 368
 369                         <varlistentry>
 370                                 <term><varname>ReceiveBuffer=</varname></term>
 371                                 <term><varname>SendBuffer=</varname></term>
 372                                 <listitem><para>Takes an integer
 373                                 argument controlling the receive
 374                                 resp. send buffer sizes of this
 375                                 socket. This controls the SO_RCVBUF
 376                                 resp. SO_SNDBUF socket options (see
 377                                 <citerefentry><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 378                                 for details.).</para></listitem>
 379                         </varlistentry>
 380
 381                         <varlistentry>
 382                                 <term><varname>IPTOS=</varname></term>
 383                                 <listitem><para>Takes an integer
 384                                 argument controlling the IP
 385                                 Type-Of-Service field for packets
 386                                 generated from this socket. This
 387                                 controls the IP_TOS socket option (see
 388                                 <citerefentry><refentrytitle>ip</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 389                                 for details.). Either a numeric string
 390                                 or one of <option>low-delay</option>,
 391                                 <option>throughput</option>,
 392                                 <option>reliability</option> or
 393                                 <option>low-cost</option> may be
 394                                 specified.</para></listitem>
 395                         </varlistentry>
 396
 397                         <varlistentry>
 398                                 <term><varname>IPTTL=</varname></term>
 399                                 <listitem><para>Takes an integer
 400                                 argument controlling the IPv4
 401                                 Time-To-Live/IPv6 Hop-Count field for
 402                                 packets generated from this
 403                                 socket. This sets the
 404                                 IP_TTL/IPV6_UNICAST_HOPS socket
 405                                 options (see
 406                                 <citerefentry><refentrytitle>ip</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 407                                 and
 408                                 <citerefentry><refentrytitle>ipv6</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 409                                 for details.)</para></listitem>
 410                         </varlistentry>
 411
 412                         <varlistentry>
 413                                 <term><varname>Mark=</varname></term>
 414                                 <listitem><para>Takes an integer
 415                                 value. Controls the firewall mark of
 416                                 packets generated by this socket. This
 417                                 can be used in the firewall logic to
 418                                 filter packets from this socket. This
 419                                 sets the SO_MARK socket option. See
 420                                 <citerefentry><refentrytitle>iptables</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 421                                 for details.</para></listitem>
 422                         </varlistentry>
 423
 424                         <varlistentry>
 425                                 <term><varname>PipeSize=</varname></term>
 426                                 <listitem><para>Takes an integer
 427                                 value. Controls the pipe buffer size
 428                                 of FIFOs configured in this socket
 429                                 unit.  See
 430                                 <citerefentry><refentrytitle>fcntl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 431                                 for details.</para></listitem>
 432                         </varlistentry>
 433
 434                         <varlistentry>
 435                                 <term><varname>FreeBind=</varname></term>
 436                                 <listitem><para>Takes a boolean
 437                                 value. Controls whether the socket can
 438                                 be bound to non-local IP
 439                                 addresses. This is useful to configure
 440                                 sockets listening on specific IP
 441                                 addresses before those IP addresses
 442                                 are successfully configured on a
 443                                 network interface. This sets the
 444                                 IP_FREEBIND socket option. For
 445                                 robustness reasons it is recommended
 446                                 to use this option whenever you bind a
 447                                 socket to a specific IP
 448                                 address. Defaults to <option>false</option>.</para></listitem>
 449                         </varlistentry>
 450
 451                         <varlistentry>
 452                                 <term><varname>TCPCongestion=</varname></term>
 453                                 <listitem><para>Takes a string
 454                                 value. Controls the TCP congestion
 455                                 algorithm used by this socket. Should
 456                                 be one of "westwood", "veno", "cubic",
 457                                 "lp" or any other available algorithm
 458                                 supported by the IP stack. This
 459                                 setting applies only to stream
 460                                 sockets.</para></listitem>
 461                         </varlistentry>
 462
 463                         <varlistentry>
 464                                 <term><varname>ExecStartPre=</varname></term>
 465                                 <term><varname>ExecStartPost=</varname></term>
 466                                 <listitem><para>Takes one or more
 467                                 command lines, which are executed
 468                                 before (resp. after) the listening
 469                                 sockets/FIFOs are created and
 470                                 bound. The first token of the command
 471                                 line must be an absolute file name,
 472                                 then followed by arguments for the
 473                                 process. Multiple command lines may be
 474                                 specified following the same scheme as
 475                                 used for
 476                                 <varname>ExecStartPre=</varname> of
 477                                 service unit files.</para></listitem>
 478                         </varlistentry>
 479
 480                         <varlistentry>
 481                                 <term><varname>ExecStopPre=</varname></term>
 482                                 <term><varname>ExecStopPost=</varname></term>
 483                                 <listitem><para>Additional commands
 484                                 that are executed before (resp. after)
 485                                 the listening sockets/FIFOs are closed
 486                                 and removed. Multiple command lines
 487                                 may be specified following the same
 488                                 scheme as used for
 489                                 <varname>ExecStartPre=</varname> of
 490                                 service unit files.</para></listitem>
 491                         </varlistentry>
 492
 493                         <varlistentry>
 494                                 <term><varname>TimeoutSec=</varname></term>
 495                                 <listitem><para>Configures the time to
 496                                 wait for the commands specified in
 497                                 <varname>ExecStartPre=</varname>,
 498                                 <varname>ExecStartPost=</varname>,
 499                                 <varname>ExecStopPre=</varname> and
 500                                 <varname>ExecStopPost=</varname> to
 501                                 finish. If a command does not exit
 502                                 within the configured time, the socket
 503                                 will be considered failed and be shut
 504                                 down again. All commands still running,
 505                                 will be terminated forcibly via
 506                                 SIGTERM, and after another delay of
 507                                 this time with SIGKILL. (See
 508                                 <option>KillMode=</option> below.)
 509                                 Takes a unit-less value in seconds, or
 510                                 a time span value such as "5min
 511                                 20s". Pass 0 to disable the timeout
 512                                 logic. Defaults to
 513                                 60s.</para></listitem>
 514                         </varlistentry>
 515
 516                         <varlistentry>
 517                                 <term><varname>KillMode=</varname></term>
 518                                 <listitem><para>Specifies how
 519                                 processes of this socket unit shall be
 520                                 killed. One of
 521                                 <option>control-group</option>,
 522                                 <option>process-group</option>,
 523                                 <option>process</option>,
 524                                 <option>none</option>.</para>
 525
 526                                 <para>This option is mostly equivalent
 527                                 to the <option>KillMode=</option>
 528                                 option of service files. See
 529                                 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 530                                 for details.</para></listitem>
 531                         </varlistentry>
 532
 533                         <varlistentry>
 534                                 <term><varname>KillSignal=</varname></term>
 535                                 <listitem><para>Specifies which signal
 536                                 to use when killing a process of this
 537                                 socket. Defaults to SIGTERM.
 538                                 </para></listitem>
 539                         </varlistentry>
 540
 541                         <varlistentry>
 542                                 <term><varname>SendSIGKILL=</varname></term>
 543                                 <listitem><para>Specifies whether to
 544                                 send SIGKILL to remaining processes
 545                                 after a timeout, if the normal
 546                                 shutdown procedure left processes of
 547                                 the socket around. Takes a boolean
 548                                 value. Defaults to "yes".
 549                                 </para></listitem>
 550                         </varlistentry>
 551
 552                         <varlistentry>
 553                                 <term><varname>Service=</varname></term>
 554                                 <listitem><para>Specifies the service
 555                                 unit name to activate on incoming
 556                                 traffic. This defaults to the service
 557                                 that bears the same name as the socket
 558                                 (ignoring the different suffixes). In
 559                                 most cases it should not be necessary
 560                                 to use this option.</para></listitem>
 561                         </varlistentry>
 562
 563                 </variablelist>
 564         </refsect1>
 565
 566         <refsect1>
 567                   <title>See Also</title>
 568                   <para>
 569                           <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 570                           <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 571                           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 572                           <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 573                           <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 574                   </para>
 575         </refsect1>
 576
 577 </refentry>