man/systemd.socket.xml

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   7   This file is part of systemd.
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   9   Copyright 2010 Lennart Poettering
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  24
  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>ListenNetlink=</varname></term>
 223                                 <listitem><para>Specifies a Netlink
 224                                 family to create a socket for to
 225                                 listen on. This expects a short string
 226                                 referring to the AF_NETLINK family
 227                                 name (such as <varname>audit</varname>
 228                                 or <varname>kobject-uevent</varname>)
 229                                 as argument, optionally suffixed by a
 230                                 whitespace followed by a multicast
 231                                 group integer. Behaviour otherwise is
 232                                 very similar to the
 233                                 <varname>ListenDatagram=</varname>
 234                                 directive above.</para></listitem>
 235                         </varlistentry>
 236
 237                         <varlistentry>
 238                                 <term><varname>BindIPv6Only=</varname></term>
 239                                 <listitem><para>Takes a one of
 240                                 <option>default</option>,
 241                                 <option>both</option> or
 242                                 <option>ipv6-only</option>. Controls
 243                                 the IPV6_V6ONLY socket option (see
 244                                 <citerefentry><refentrytitle>ipv6</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 245                                 for details). If
 246                                 <option>both</option>, IPv6 sockets
 247                                 bound will be accessible via both IPv4
 248                                 and IPv6. If
 249                                 <option>ipv6-only</option>, they will
 250                                 be accessible via IPv6 only. If
 251                                 <option>default</option> (which is the
 252                                 default, surprise!) the system wide
 253                                 default setting is used, as controlled
 254                                 by
 255                                 <filename>/proc/sys/net/ipv6/bindv6only</filename>.</para>
 256                                 </listitem>
 257                         </varlistentry>
 258
 259                         <varlistentry>
 260                                 <term><varname>Backlog=</varname></term>
 261                                 <listitem><para>Takes an unsigned
 262                                 integer argument. Specifies the number
 263                                 of connections to queue that have not
 264                                 been accepted yet. This setting
 265                                 matters only for stream and sequential
 266                                 packet sockets. See
 267                                 <citerefentry><refentrytitle>listen</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 268                                 for details. Defaults to SOMAXCONN
 269                                 (128).</para></listitem>
 270                         </varlistentry>
 271
 272                         <varlistentry>
 273                                 <term><varname>BindToDevice=</varname></term>
 274                                 <listitem><para>Specifies a network
 275                                 interface name to bind this socket
 276                                 to. If set traffic will only be
 277                                 accepted from the specified network
 278                                 interfaces. This controls the
 279                                 SO_BINDTODEVICE socket option (see
 280                                 <citerefentry><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 281                                 for details). If this option is used,
 282                                 an automatic dependency from this
 283                                 socket unit on the network interface
 284                                 device unit
 285                                 (<citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 286                                 is created.</para></listitem>
 287                         </varlistentry>
 288
 289                         <varlistentry>
 290                                 <term><varname>DirectoryMode=</varname></term>
 291                                 <listitem><para>If listening on a file
 292                                 system socket of FIFO, the parent
 293                                 directories are automatically created
 294                                 if needed. This option specifies the
 295                                 file system access mode used when
 296                                 creating these directories. Takes an
 297                                 access mode in octal
 298                                 notation. Defaults to
 299                                 0755.</para></listitem>
 300                         </varlistentry>
 301
 302                         <varlistentry>
 303                                 <term><varname>SocketMode=</varname></term>
 304                                 <listitem><para>If listening on a file
 305                                 system socket of FIFO, this option
 306                                 specifies the file system access mode
 307                                 used when creating the file
 308                                 node. Takes an access mode in octal
 309                                 notation. Defaults to
 310                                 0666.</para></listitem>
 311                         </varlistentry>
 312
 313                         <varlistentry>
 314                                 <term><varname>Accept=</varname></term>
 315                                 <listitem><para>Takes a boolean
 316                                 argument. If true, a service instance
 317                                 is spawned for each incoming
 318                                 connection and only the connection
 319                                 socket is passed to it. If false, all
 320                                 listening sockets themselves are
 321                                 passed to the started service unit,
 322                                 and only one service unit is spawned
 323                                 for all connections (also see
 324                                 above). This value is ignored for
 325                                 datagram sockets and FIFOs where
 326                                 a single service unit unconditionally
 327                                 handles all incoming traffic. Defaults
 328                                 to <option>false</option>. For
 329                                 performance reasons, it is recommended
 330                                 to write new daemons only in a way
 331                                 that is suitable for
 332                                 <option>Accept=false</option>. This
 333                                 option is mostly useful to allow
 334                                 daemons designed for usage with
 335                                 <citerefentry><refentrytitle>inetd</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 336                                 to work unmodified with systemd socket
 337                                 activation.</para></listitem>
 338                         </varlistentry>
 339
 340                         <varlistentry>
 341                                 <term><varname>MaxConnections=</varname></term>
 342                                 <listitem><para>The maximum number of
 343                                 connections to simultaneously run
 344                                 services instances for, when
 345                                 <option>Accept=true</option> is
 346                                 set. If more concurrent connections
 347                                 are coming in, they will be refused
 348                                 until at least one existing connection
 349                                 is terminated. This setting has no
 350                                 effect for sockets configured with
 351                                 <option>Accept=no</option> or datagram
 352                                 sockets. Defaults to
 353                                 64.</para></listitem>
 354                         </varlistentry>
 355
 356                         <varlistentry>
 357                                 <term><varname>KeepAlive=</varname></term>
 358                                 <listitem><para>Takes a boolean
 359                                 argument. If true, the TCP/IP stack
 360                                 will send a keep alive message after
 361                                 2h (depending on the configuration of
 362                                 <filename>/proc/sys/net/ipv4/tcp_keepalive_time</filename>)
 363                                 for all TCP streams accepted on this
 364                                 socket. This controls the SO_KEEPALIVE
 365                                 socket option (see
 366                                 <citerefentry><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 367                                 and the <ulink
 368                                 url="http://www.tldp.org/HOWTO/html_single/TCP-Keepalive-HOWTO/">TCP
 369                                 Keepalive HOWTO</ulink> for details.)
 370                                 Defaults to
 371                                 <option>false</option>.</para></listitem>
 372                         </varlistentry>
 373
 374                         <varlistentry>
 375                                 <term><varname>Priority=</varname></term>
 376                                 <listitem><para>Takes an integer
 377                                 argument controlling the priority for
 378                                 all traffic sent from this
 379                                 socket. This controls the SO_PRIORITY
 380                                 socket option (see
 381                                 <citerefentry><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 382                                 for details.).</para></listitem>
 383                         </varlistentry>
 384
 385                         <varlistentry>
 386                                 <term><varname>ReceiveBuffer=</varname></term>
 387                                 <term><varname>SendBuffer=</varname></term>
 388                                 <listitem><para>Takes an integer
 389                                 argument controlling the receive
 390                                 resp. send buffer sizes of this
 391                                 socket. This controls the SO_RCVBUF
 392                                 resp. SO_SNDBUF socket options (see
 393                                 <citerefentry><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 394                                 for details.).</para></listitem>
 395                         </varlistentry>
 396
 397                         <varlistentry>
 398                                 <term><varname>IPTOS=</varname></term>
 399                                 <listitem><para>Takes an integer
 400                                 argument controlling the IP
 401                                 Type-Of-Service field for packets
 402                                 generated from this socket. This
 403                                 controls the IP_TOS socket option (see
 404                                 <citerefentry><refentrytitle>ip</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 405                                 for details.). Either a numeric string
 406                                 or one of <option>low-delay</option>,
 407                                 <option>throughput</option>,
 408                                 <option>reliability</option> or
 409                                 <option>low-cost</option> may be
 410                                 specified.</para></listitem>
 411                         </varlistentry>
 412
 413                         <varlistentry>
 414                                 <term><varname>IPTTL=</varname></term>
 415                                 <listitem><para>Takes an integer
 416                                 argument controlling the IPv4
 417                                 Time-To-Live/IPv6 Hop-Count field for
 418                                 packets generated from this
 419                                 socket. This sets the
 420                                 IP_TTL/IPV6_UNICAST_HOPS socket
 421                                 options (see
 422                                 <citerefentry><refentrytitle>ip</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 423                                 and
 424                                 <citerefentry><refentrytitle>ipv6</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 425                                 for details.)</para></listitem>
 426                         </varlistentry>
 427
 428                         <varlistentry>
 429                                 <term><varname>Mark=</varname></term>
 430                                 <listitem><para>Takes an integer
 431                                 value. Controls the firewall mark of
 432                                 packets generated by this socket. This
 433                                 can be used in the firewall logic to
 434                                 filter packets from this socket. This
 435                                 sets the SO_MARK socket option. See
 436                                 <citerefentry><refentrytitle>iptables</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 437                                 for details.</para></listitem>
 438                         </varlistentry>
 439
 440                         <varlistentry>
 441                                 <term><varname>PipeSize=</varname></term>
 442                                 <listitem><para>Takes an integer
 443                                 value. Controls the pipe buffer size
 444                                 of FIFOs configured in this socket
 445                                 unit.  See
 446                                 <citerefentry><refentrytitle>fcntl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 447                                 for details.</para></listitem>
 448                         </varlistentry>
 449
 450                         <varlistentry>
 451                                 <term><varname>FreeBind=</varname></term>
 452                                 <listitem><para>Takes a boolean
 453                                 value. Controls whether the socket can
 454                                 be bound to non-local IP
 455                                 addresses. This is useful to configure
 456                                 sockets listening on specific IP
 457                                 addresses before those IP addresses
 458                                 are successfully configured on a
 459                                 network interface. This sets the
 460                                 IP_FREEBIND socket option. For
 461                                 robustness reasons it is recommended
 462                                 to use this option whenever you bind a
 463                                 socket to a specific IP
 464                                 address. Defaults to <option>false</option>.</para></listitem>
 465                         </varlistentry>
 466
 467                         <varlistentry>
 468                                 <term><varname>TCPCongestion=</varname></term>
 469                                 <listitem><para>Takes a string
 470                                 value. Controls the TCP congestion
 471                                 algorithm used by this socket. Should
 472                                 be one of "westwood", "veno", "cubic",
 473                                 "lp" or any other available algorithm
 474                                 supported by the IP stack. This
 475                                 setting applies only to stream
 476                                 sockets.</para></listitem>
 477                         </varlistentry>
 478
 479                         <varlistentry>
 480                                 <term><varname>ExecStartPre=</varname></term>
 481                                 <term><varname>ExecStartPost=</varname></term>
 482                                 <listitem><para>Takes one or more
 483                                 command lines, which are executed
 484                                 before (resp. after) the listening
 485                                 sockets/FIFOs are created and
 486                                 bound. The first token of the command
 487                                 line must be an absolute file name,
 488                                 then followed by arguments for the
 489                                 process. Multiple command lines may be
 490                                 specified following the same scheme as
 491                                 used for
 492                                 <varname>ExecStartPre=</varname> of
 493                                 service unit files.</para></listitem>
 494                         </varlistentry>
 495
 496                         <varlistentry>
 497                                 <term><varname>ExecStopPre=</varname></term>
 498                                 <term><varname>ExecStopPost=</varname></term>
 499                                 <listitem><para>Additional commands
 500                                 that are executed before (resp. after)
 501                                 the listening sockets/FIFOs are closed
 502                                 and removed. Multiple command lines
 503                                 may be specified following the same
 504                                 scheme as used for
 505                                 <varname>ExecStartPre=</varname> of
 506                                 service unit files.</para></listitem>
 507                         </varlistentry>
 508
 509                         <varlistentry>
 510                                 <term><varname>TimeoutSec=</varname></term>
 511                                 <listitem><para>Configures the time to
 512                                 wait for the commands specified in
 513                                 <varname>ExecStartPre=</varname>,
 514                                 <varname>ExecStartPost=</varname>,
 515                                 <varname>ExecStopPre=</varname> and
 516                                 <varname>ExecStopPost=</varname> to
 517                                 finish. If a command does not exit
 518                                 within the configured time, the socket
 519                                 will be considered failed and be shut
 520                                 down again. All commands still running,
 521                                 will be terminated forcibly via
 522                                 SIGTERM, and after another delay of
 523                                 this time with SIGKILL. (See
 524                                 <option>KillMode=</option> below.)
 525                                 Takes a unit-less value in seconds, or
 526                                 a time span value such as "5min
 527                                 20s". Pass 0 to disable the timeout
 528                                 logic. Defaults to
 529                                 3min.</para></listitem>
 530                         </varlistentry>
 531
 532                         <varlistentry>
 533                                 <term><varname>KillMode=</varname></term>
 534                                 <listitem><para>Specifies how
 535                                 processes of this socket unit shall be
 536                                 killed. One of
 537                                 <option>control-group</option>,
 538                                 <option>process</option>,
 539                                 <option>none</option>.</para>
 540
 541                                 <para>This option is mostly equivalent
 542                                 to the <option>KillMode=</option>
 543                                 option of service files. See
 544                                 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 545                                 for details.</para></listitem>
 546                         </varlistentry>
 547
 548                         <varlistentry>
 549                                 <term><varname>KillSignal=</varname></term>
 550                                 <listitem><para>Specifies which signal
 551                                 to use when killing a process of this
 552                                 socket. Defaults to SIGTERM.
 553                                 </para></listitem>
 554                         </varlistentry>
 555
 556                         <varlistentry>
 557                                 <term><varname>SendSIGKILL=</varname></term>
 558                                 <listitem><para>Specifies whether to
 559                                 send SIGKILL to remaining processes
 560                                 after a timeout, if the normal
 561                                 shutdown procedure left processes of
 562                                 the socket around. Takes a boolean
 563                                 value. Defaults to "yes".
 564                                 </para></listitem>
 565                         </varlistentry>
 566
 567                         <varlistentry>
 568                                 <term><varname>Service=</varname></term>
 569                                 <listitem><para>Specifies the service
 570                                 unit name to activate on incoming
 571                                 traffic. This defaults to the service
 572                                 that bears the same name as the socket
 573                                 (ignoring the different suffixes). In
 574                                 most cases it should not be necessary
 575                                 to use this option.</para></listitem>
 576                         </varlistentry>
 577
 578                 </variablelist>
 579         </refsect1>
 580
 581         <refsect1>
 582                   <title>See Also</title>
 583                   <para>
 584                           <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 585                           <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 586                           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 587                           <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 588                           <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 589                   </para>
 590         </refsect1>
 591
 592 </refentry>