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>Socket units may be used to implement on-demand
  99                 starting of services, as well as parallelized starting
 100                 of services.</para>
 101         </refsect1>
 102
 103         <refsect1>
 104                 <title>Options</title>
 105
 106                 <para>Socket files must include a [Socket] section,
 107                 which carries information about the socket or FIFO it
 108                 supervises. A number of options that may be used in
 109                 this section are shared with other unit types. These
 110                 options are documented in
 111                 <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>. The
 112                 options specific to the [Socket] section of socket
 113                 units are the following:</para>
 114
 115                 <variablelist>
 116                         <varlistentry>
 117                                 <term><varname>ListenStream=</varname></term>
 118                                 <term><varname>ListenDatagram=</varname></term>
 119                                 <term><varname>ListenSequentialPacket=</varname></term>
 120                                 <listitem><para>Specifies an address
 121                                 to listen on for a stream
 122                                 (SOCK_STREAM), datagram (SOCK_DGRAM)
 123                                 resp. sequential packet
 124                                 (SOCK_SEQPACKET) socket. The address
 125                                 can be written in various formats:</para>
 126
 127                                 <para>If the address starts with a
 128                                 slash (/), it is read as file system
 129                                 socket in the AF_UNIX socket
 130                                 family.</para>
 131
 132                                 <para>If the address starts with an
 133                                 ampersand (@) it is read as abstract
 134                                 namespace socket in the AF_UNIX
 135                                 family. The @ is replaced with a NUL
 136                                 character before binding. For details
 137                                 see
 138                                 <citerefentry><refentrytitle>unix</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 139
 140                                 <para>If the address string is a
 141                                 single number it is read as port
 142                                 number to listen on for both IPv4 and
 143                                 IPv6.</para>
 144
 145                                 <para>If the address string is a
 146                                 string in the format v.w.x.y:z it is
 147                                 read as IPv4 specifier for listening
 148                                 on an address v.w.x.y on a port
 149                                 z.</para>
 150
 151                                 <para>If the address string is a
 152                                 string in the format [x]:y it is read
 153                                 as IPv6 address x on a port y.</para>
 154
 155                                 <para>Note that SOCK_SEQPACKET
 156                                 (i.e. <varname>ListenSequentialPacket=</varname>)
 157                                 is only available for AF_UNIX
 158                                 sockets. SOCK_STREAM
 159                                 (i.e. <varname>ListenStream=</varname>)
 160                                 when used for IP sockets refers to TCP
 161                                 sockets, SOCK_DGRAM
 162                                 (i.e. <varname>ListenDatagram=</varname>)
 163                                 to UDP.</para>
 164
 165                                 <para>These options may be specified
 166                                 more than once in which case incoming
 167                                 traffic on any of the sockets will trigger
 168                                 service activation, and all listed
 169                                 sockets will be passed to the service,
 170                                 regardless whether there is incoming
 171                                 traffic on them or not.</para>
 172
 173                                 <para>If an IP address is used here, it
 174                                 is often desirable to listen on it
 175                                 before the interface it is configured
 176                                 on is up and running, and even
 177                                 regardless whether it will be up and
 178                                 running ever at all. To deal with this it is
 179                                 recommended to set the
 180                                 <varname>FreeBind=</varname> option
 181                                 described below.</para></listitem>
 182                         </varlistentry>
 183
 184                         <varlistentry>
 185                                 <term><varname>ListenFIFO=</varname></term>
 186                                 <listitem><para>Specifies a file
 187                                 system FIFO to listen on. This expects
 188                                 an absolute file system path as
 189                                 argument. Behaviour otherwise is very
 190                                 similar to the
 191                                 <varname>ListenDatagram=</varname>
 192                                 directive above.</para></listitem>
 193                         </varlistentry>
 194
 195                         <varlistentry>
 196                                 <term><varname>BindIPv6Only=</varname></term>
 197                                 <listitem><para>Takes a one of
 198                                 <option>default</option>,
 199                                 <option>both</option> or
 200                                 <option>ipv6-only</option>. Controls
 201                                 the IPV6_V6ONLY socket option (see
 202                                 <citerefentry><refentrytitle>ipv6</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 203                                 for details). If
 204                                 <option>both</option>, IPv6 sockets
 205                                 bound will be accessible via both IPv4
 206                                 and IPv6. If
 207                                 <option>ipv6-only</option>, they will
 208                                 be accessible via IPv6 only. If
 209                                 <option>default</option> (which is the
 210                                 default, surprise!) the system wide
 211                                 default setting is used, as controlled
 212                                 by
 213                                 <filename>/proc/sys/net/ipv6/bindv6only</filename>.</para>
 214                                 </listitem>
 215                         </varlistentry>
 216
 217                         <varlistentry>
 218                                 <term><varname>Backlog=</varname></term>
 219                                 <listitem><para>Takes an unsigned
 220                                 integer argument. Specifies the number
 221                                 of connections to queue that have not
 222                                 been accepted yet. This setting
 223                                 matters only for stream and sequential
 224                                 packet sockets. See
 225                                 <citerefentry><refentrytitle>listen</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 226                                 for details. Defaults to SOMAXCONN
 227                                 (128).</para></listitem>
 228                         </varlistentry>
 229
 230                         <varlistentry>
 231                                 <term><varname>BindToDevice=</varname></term>
 232                                 <listitem><para>Specifies a network
 233                                 interface name to bind this socket
 234                                 to. If set traffic will only be
 235                                 accepted from the specified network
 236                                 interfaces. This controls the
 237                                 SO_BINDTODEVICE socket option (see
 238                                 <citerefentry><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 239                                 for details). If this option is used,
 240                                 an automatic dependency from this
 241                                 socket unit on the network interface
 242                                 device unit
 243                                 (<citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 244                                 is created.</para></listitem>
 245                         </varlistentry>
 246
 247                         <varlistentry>
 248                                 <term><varname>DirectoryMode=</varname></term>
 249                                 <listitem><para>If listening on a file
 250                                 system socket of FIFO, the parent
 251                                 directories are automatically created
 252                                 if needed. This option specifies the
 253                                 file system access mode used when
 254                                 creating these directories. Defaults
 255                                 to 0755.</para></listitem>
 256                         </varlistentry>
 257
 258                         <varlistentry>
 259                                 <term><varname>SocketMode=</varname></term>
 260                                 <listitem><para>If listening on a file
 261                                 system socket of FIFO, this option
 262                                 specifies the file system access mode
 263                                 used when creating the file
 264                                 node. Defaults to
 265                                 0666.</para></listitem>
 266                         </varlistentry>
 267
 268                         <varlistentry>
 269                                 <term><varname>Accept=</varname></term>
 270                                 <listitem><para>Takes a boolean
 271                                 argument. If true, a service instance
 272                                 is spawned for each incoming
 273                                 connection and only the connection
 274                                 socket is passed to it. If false, all
 275                                 listening sockets themselves are
 276                                 passed to the started service unit,
 277                                 and only one service unit is spawned
 278                                 for all connections (also see
 279                                 above). This value is ignored for
 280                                 datagram sockets and FIFOs where
 281                                 a single service unit unconditionally
 282                                 handles all incoming traffic. Defaults
 283                                 to <option>false</option>. For
 284                                 performance reasons, it is recommended
 285                                 to write new daemons only in a way
 286                                 that is suitable for
 287                                 <option>Accept=false</option>. This
 288                                 option is mostly useful to allow
 289                                 daemons designed for usage with
 290                                 <citerefentry><refentrytitle>inetd</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 291                                 to work unmodified with systemd socket
 292                                 activation.</para></listitem>
 293                         </varlistentry>
 294
 295                         <varlistentry>
 296                                 <term><varname>MaxConnections=</varname></term>
 297                                 <listitem><para>The maximum number of
 298                                 connections to simultaneously run
 299                                 services instances for, when
 300                                 <option>Accept=true</option> is
 301                                 set. If more concurrent connections
 302                                 are coming in, they will be refused
 303                                 until at least one existing connection
 304                                 is terminated. This setting has no
 305                                 effect for sockets configured with
 306                                 <option>Accept=no</option> or datagram
 307                                 sockets. Defaults to
 308                                 64.</para></listitem>
 309                         </varlistentry>
 310
 311                         <varlistentry>
 312                                 <term><varname>KeepAlive=</varname></term>
 313                                 <listitem><para>Takes a boolean
 314                                 argument. If true, the TCP/IP stack
 315                                 will send a keep alive message after
 316                                 2h (depending on the configuration of
 317                                 <filename>/proc/sys/net/ipv4/tcp_keepalive_time</filename>)
 318                                 for all TCP streams accepted on this
 319                                 socket. This controls the SO_KEEPALIVE
 320                                 socket option (see
 321                                 <citerefentry><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 322                                 and the <ulink
 323                                 url="http://www.tldp.org/HOWTO/html_single/TCP-Keepalive-HOWTO/">TCP
 324                                 Keepalive HOWTO</ulink> for details.)
 325                                 Defaults to
 326                                 <option>false</option>.</para></listitem>
 327                         </varlistentry>
 328
 329                         <varlistentry>
 330                                 <term><varname>Priority=</varname></term>
 331                                 <listitem><para>Takes an integer
 332                                 argument controlling the priority for
 333                                 all traffic sent from this
 334                                 socket. This controls the SO_PRIORITY
 335                                 socket option (see
 336                                 <citerefentry><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 337                                 for details.).</para></listitem>
 338                         </varlistentry>
 339
 340                         <varlistentry>
 341                                 <term><varname>ReceiveBuffer=</varname></term>
 342                                 <term><varname>SendBuffer=</varname></term>
 343                                 <listitem><para>Takes an integer
 344                                 argument controlling the receive
 345                                 resp. send buffer sizes of this
 346                                 socket. This controls the SO_RCVBUF
 347                                 resp. SO_SNDBUF socket options (see
 348                                 <citerefentry><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 349                                 for details.).</para></listitem>
 350                         </varlistentry>
 351
 352                         <varlistentry>
 353                                 <term><varname>IPTOS=</varname></term>
 354                                 <listitem><para>Takes an integer
 355                                 argument controlling the IP
 356                                 Type-Of-Service field for packets
 357                                 generated from this socket. This
 358                                 controls the IP_TOS socket option (see
 359                                 <citerefentry><refentrytitle>ip</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 360                                 for details.). Either a numeric string
 361                                 or one of <option>low-delay</option>,
 362                                 <option>throughput</option>,
 363                                 <option>reliability</option> or
 364                                 <option>low-cost</option> may be
 365                                 specified.</para></listitem>
 366                         </varlistentry>
 367
 368                         <varlistentry>
 369                                 <term><varname>IPTTL=</varname></term>
 370                                 <listitem><para>Takes an integer
 371                                 argument controlling the IPv4
 372                                 Time-To-Live/IPv6 Hop-Count field for
 373                                 packets generated from this
 374                                 socket. This sets the
 375                                 IP_TTL/IPV6_UNICAST_HOPS socket
 376                                 options (see
 377                                 <citerefentry><refentrytitle>ip</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 378                                 and
 379                                 <citerefentry><refentrytitle>ipv6</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 380                                 for details.)</para></listitem>
 381                         </varlistentry>
 382
 383                         <varlistentry>
 384                                 <term><varname>Mark=</varname></term>
 385                                 <listitem><para>Takes an integer
 386                                 value. Controls the firewall mark of
 387                                 packets generated by this socket. This
 388                                 can be used in the firewall logic to
 389                                 filter packets from this socket. This
 390                                 sets the SO_MARK socket option. See
 391                                 <citerefentry><refentrytitle>iptables</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 392                                 for details.</para></listitem>
 393                         </varlistentry>
 394
 395                         <varlistentry>
 396                                 <term><varname>PipeSize=</varname></term>
 397                                 <listitem><para>Takes an integer
 398                                 value. Controls the pipe buffer size
 399                                 of FIFOs configured in this socket
 400                                 unit.  See
 401                                 <citerefentry><refentrytitle>fcntl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 402                                 for details.</para></listitem>
 403                         </varlistentry>
 404
 405                         <varlistentry>
 406                                 <term><varname>FreeBind=</varname></term>
 407                                 <listitem><para>Takes a boolean
 408                                 value. Controls whether the socket can
 409                                 be bound to non-local IP
 410                                 addresses. This is useful to configure
 411                                 sockets listening on specific IP
 412                                 addresses before those IP addresses
 413                                 are successfully configured on a
 414                                 network interface. This sets the
 415                                 IP_FREEBIND socket option. For
 416                                 robustness reasons it is recommended
 417                                 to use this option whenever you bind a
 418                                 socket to a specific IP
 419                                 address. Defaults to <option>false</option>.</para></listitem>
 420                         </varlistentry>
 421
 422                         <varlistentry>
 423                                 <term><varname>ExecStartPre=</varname></term>
 424                                 <term><varname>ExecStartPost=</varname></term>
 425                                 <listitem><para>Takes a command line,
 426                                 which is executed before (resp. after)
 427                                 the listening sockets/FIFOs are created and
 428                                 bound. The first token of the command
 429                                 line must be an absolute file name,
 430                                 then followed by arguments for the
 431                                 process. If specified more than once,
 432                                 all commands are executed one after
 433                                 the other, fully serialized. The use of
 434                                 these settings is optional.</para></listitem>
 435                         </varlistentry>
 436
 437                         <varlistentry>
 438                                 <term><varname>ExecStopPre=</varname></term>
 439                                 <term><varname>ExecStopPost=</varname></term>
 440                                 <listitem><para>Additional commands
 441                                 that are executed before (resp. after)
 442                                 the listening sockets/FIFOs are closed
 443                                 and removed. If specified more than
 444                                 once, all commands are executed one
 445                                 after the other, fully serialized. The use of
 446                                 these settings is optional.</para></listitem>
 447                         </varlistentry>
 448
 449                         <varlistentry>
 450                                 <term><varname>TimeoutSec=</varname></term>
 451                                 <listitem><para>Configures the time to
 452                                 wait for the commands specified in
 453                                 <varname>ExecStartPre=</varname>,
 454                                 <varname>ExecStartPost=</varname>,
 455                                 <varname>ExecStopPre=</varname> and
 456                                 <varname>ExecStopPost=</varname> to
 457                                 finish. If a command does not exit
 458                                 within the configured time, the socket
 459                                 will be considered failed and be shut
 460                                 down again. All commands still running,
 461                                 will be terminated forcibly via
 462                                 SIGTERM, and after another delay of
 463                                 this time with SIGKILL. (See
 464                                 <option>KillMode=</option> below.)
 465                                 Takes a unit-less value in seconds, or
 466                                 a time span value such as "5min
 467                                 20s". Pass 0 to disable the timeout
 468                                 logic. Defaults to
 469                                 60s.</para></listitem>
 470                         </varlistentry>
 471
 472                         <varlistentry>
 473                                 <term><varname>KillMode=</varname></term>
 474                                 <listitem><para>Specifies how
 475                                 processes of this socket unit shall be
 476                                 killed. One of
 477                                 <option>control-group</option>,
 478                                 <option>process-group</option>,
 479                                 <option>process</option>,
 480                                 <option>none</option>.</para>
 481
 482                                 <para>This option is mostly equivalent
 483                                 to the <option>KillMode=</option>
 484                                 option of service files. See
 485                                 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 486                                 for details.</para></listitem>
 487                         </varlistentry>
 488                 </variablelist>
 489         </refsect1>
 490
 491         <refsect1>
 492                   <title>See Also</title>
 493                   <para>
 494                           <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 495                           <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 496                           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 497                           <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 498                           <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 499                   </para>
 500         </refsect1>
 501
 502 </refentry>