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>ListenSpecial=</varname></term>
 223                                 <listitem><para>Specifies a special
 224                                 file in the file system to listen
 225                                 on. This expects an absolute file
 226                                 system path as argument. Behaviour
 227                                 otherwise is very similar to the
 228                                 <varname>ListenFIFO=</varname>
 229                                 directive above. Use this to open
 230                                 character device nodes as well as
 231                                 special files in
 232                                 <filename>/proc</filename> and
 233                                 <filename>/sys</filename>.</para></listitem>
 234                         </varlistentry>
 235
 236                         <varlistentry>
 237                                 <term><varname>ListenNetlink=</varname></term>
 238                                 <listitem><para>Specifies a Netlink
 239                                 family to create a socket for to
 240                                 listen on. This expects a short string
 241                                 referring to the AF_NETLINK family
 242                                 name (such as <varname>audit</varname>
 243                                 or <varname>kobject-uevent</varname>)
 244                                 as argument, optionally suffixed by a
 245                                 whitespace followed by a multicast
 246                                 group integer. Behaviour otherwise is
 247                                 very similar to the
 248                                 <varname>ListenDatagram=</varname>
 249                                 directive above.</para></listitem>
 250                         </varlistentry>
 251
 252                         <varlistentry>
 253                                 <term><varname>BindIPv6Only=</varname></term>
 254                                 <listitem><para>Takes a one of
 255                                 <option>default</option>,
 256                                 <option>both</option> or
 257                                 <option>ipv6-only</option>. Controls
 258                                 the IPV6_V6ONLY socket option (see
 259                                 <citerefentry><refentrytitle>ipv6</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 260                                 for details). If
 261                                 <option>both</option>, IPv6 sockets
 262                                 bound will be accessible via both IPv4
 263                                 and IPv6. If
 264                                 <option>ipv6-only</option>, they will
 265                                 be accessible via IPv6 only. If
 266                                 <option>default</option> (which is the
 267                                 default, surprise!) the system wide
 268                                 default setting is used, as controlled
 269                                 by
 270                                 <filename>/proc/sys/net/ipv6/bindv6only</filename>.</para>
 271                                 </listitem>
 272                         </varlistentry>
 273
 274                         <varlistentry>
 275                                 <term><varname>Backlog=</varname></term>
 276                                 <listitem><para>Takes an unsigned
 277                                 integer argument. Specifies the number
 278                                 of connections to queue that have not
 279                                 been accepted yet. This setting
 280                                 matters only for stream and sequential
 281                                 packet sockets. See
 282                                 <citerefentry><refentrytitle>listen</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 283                                 for details. Defaults to SOMAXCONN
 284                                 (128).</para></listitem>
 285                         </varlistentry>
 286
 287                         <varlistentry>
 288                                 <term><varname>BindToDevice=</varname></term>
 289                                 <listitem><para>Specifies a network
 290                                 interface name to bind this socket
 291                                 to. If set traffic will only be
 292                                 accepted from the specified network
 293                                 interfaces. This controls the
 294                                 SO_BINDTODEVICE socket option (see
 295                                 <citerefentry><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 296                                 for details). If this option is used,
 297                                 an automatic dependency from this
 298                                 socket unit on the network interface
 299                                 device unit
 300                                 (<citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 301                                 is created.</para></listitem>
 302                         </varlistentry>
 303
 304                         <varlistentry>
 305                                 <term><varname>DirectoryMode=</varname></term>
 306                                 <listitem><para>If listening on a file
 307                                 system socket of FIFO, the parent
 308                                 directories are automatically created
 309                                 if needed. This option specifies the
 310                                 file system access mode used when
 311                                 creating these directories. Takes an
 312                                 access mode in octal
 313                                 notation. Defaults to
 314                                 0755.</para></listitem>
 315                         </varlistentry>
 316
 317                         <varlistentry>
 318                                 <term><varname>SocketMode=</varname></term>
 319                                 <listitem><para>If listening on a file
 320                                 system socket of FIFO, this option
 321                                 specifies the file system access mode
 322                                 used when creating the file
 323                                 node. Takes an access mode in octal
 324                                 notation. Defaults to
 325                                 0666.</para></listitem>
 326                         </varlistentry>
 327
 328                         <varlistentry>
 329                                 <term><varname>Accept=</varname></term>
 330                                 <listitem><para>Takes a boolean
 331                                 argument. If true, a service instance
 332                                 is spawned for each incoming
 333                                 connection and only the connection
 334                                 socket is passed to it. If false, all
 335                                 listening sockets themselves are
 336                                 passed to the started service unit,
 337                                 and only one service unit is spawned
 338                                 for all connections (also see
 339                                 above). This value is ignored for
 340                                 datagram sockets and FIFOs where
 341                                 a single service unit unconditionally
 342                                 handles all incoming traffic. Defaults
 343                                 to <option>false</option>. For
 344                                 performance reasons, it is recommended
 345                                 to write new daemons only in a way
 346                                 that is suitable for
 347                                 <option>Accept=false</option>. This
 348                                 option is mostly useful to allow
 349                                 daemons designed for usage with
 350                                 <citerefentry><refentrytitle>inetd</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 351                                 to work unmodified with systemd socket
 352                                 activation.</para></listitem>
 353                         </varlistentry>
 354
 355                         <varlistentry>
 356                                 <term><varname>MaxConnections=</varname></term>
 357                                 <listitem><para>The maximum number of
 358                                 connections to simultaneously run
 359                                 services instances for, when
 360                                 <option>Accept=true</option> is
 361                                 set. If more concurrent connections
 362                                 are coming in, they will be refused
 363                                 until at least one existing connection
 364                                 is terminated. This setting has no
 365                                 effect for sockets configured with
 366                                 <option>Accept=no</option> or datagram
 367                                 sockets. Defaults to
 368                                 64.</para></listitem>
 369                         </varlistentry>
 370
 371                         <varlistentry>
 372                                 <term><varname>KeepAlive=</varname></term>
 373                                 <listitem><para>Takes a boolean
 374                                 argument. If true, the TCP/IP stack
 375                                 will send a keep alive message after
 376                                 2h (depending on the configuration of
 377                                 <filename>/proc/sys/net/ipv4/tcp_keepalive_time</filename>)
 378                                 for all TCP streams accepted on this
 379                                 socket. This controls the SO_KEEPALIVE
 380                                 socket option (see
 381                                 <citerefentry><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 382                                 and the <ulink
 383                                 url="http://www.tldp.org/HOWTO/html_single/TCP-Keepalive-HOWTO/">TCP
 384                                 Keepalive HOWTO</ulink> for details.)
 385                                 Defaults to
 386                                 <option>false</option>.</para></listitem>
 387                         </varlistentry>
 388
 389                         <varlistentry>
 390                                 <term><varname>Priority=</varname></term>
 391                                 <listitem><para>Takes an integer
 392                                 argument controlling the priority for
 393                                 all traffic sent from this
 394                                 socket. This controls the SO_PRIORITY
 395                                 socket option (see
 396                                 <citerefentry><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 397                                 for details.).</para></listitem>
 398                         </varlistentry>
 399
 400                         <varlistentry>
 401                                 <term><varname>ReceiveBuffer=</varname></term>
 402                                 <term><varname>SendBuffer=</varname></term>
 403                                 <listitem><para>Takes an integer
 404                                 argument controlling the receive
 405                                 resp. send buffer sizes of this
 406                                 socket. This controls the SO_RCVBUF
 407                                 resp. SO_SNDBUF socket options (see
 408                                 <citerefentry><refentrytitle>socket</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 409                                 for details.).</para></listitem>
 410                         </varlistentry>
 411
 412                         <varlistentry>
 413                                 <term><varname>IPTOS=</varname></term>
 414                                 <listitem><para>Takes an integer
 415                                 argument controlling the IP
 416                                 Type-Of-Service field for packets
 417                                 generated from this socket. This
 418                                 controls the IP_TOS socket option (see
 419                                 <citerefentry><refentrytitle>ip</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 420                                 for details.). Either a numeric string
 421                                 or one of <option>low-delay</option>,
 422                                 <option>throughput</option>,
 423                                 <option>reliability</option> or
 424                                 <option>low-cost</option> may be
 425                                 specified.</para></listitem>
 426                         </varlistentry>
 427
 428                         <varlistentry>
 429                                 <term><varname>IPTTL=</varname></term>
 430                                 <listitem><para>Takes an integer
 431                                 argument controlling the IPv4
 432                                 Time-To-Live/IPv6 Hop-Count field for
 433                                 packets generated from this
 434                                 socket. This sets the
 435                                 IP_TTL/IPV6_UNICAST_HOPS socket
 436                                 options (see
 437                                 <citerefentry><refentrytitle>ip</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 438                                 and
 439                                 <citerefentry><refentrytitle>ipv6</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 440                                 for details.)</para></listitem>
 441                         </varlistentry>
 442
 443                         <varlistentry>
 444                                 <term><varname>Mark=</varname></term>
 445                                 <listitem><para>Takes an integer
 446                                 value. Controls the firewall mark of
 447                                 packets generated by this socket. This
 448                                 can be used in the firewall logic to
 449                                 filter packets from this socket. This
 450                                 sets the SO_MARK socket option. See
 451                                 <citerefentry><refentrytitle>iptables</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 452                                 for details.</para></listitem>
 453                         </varlistentry>
 454
 455                         <varlistentry>
 456                                 <term><varname>PipeSize=</varname></term>
 457                                 <listitem><para>Takes an integer
 458                                 value. Controls the pipe buffer size
 459                                 of FIFOs configured in this socket
 460                                 unit.  See
 461                                 <citerefentry><refentrytitle>fcntl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 462                                 for details.</para></listitem>
 463                         </varlistentry>
 464
 465                         <varlistentry>
 466                                 <term><varname>FreeBind=</varname></term>
 467                                 <listitem><para>Takes a boolean
 468                                 value. Controls whether the socket can
 469                                 be bound to non-local IP
 470                                 addresses. This is useful to configure
 471                                 sockets listening on specific IP
 472                                 addresses before those IP addresses
 473                                 are successfully configured on a
 474                                 network interface. This sets the
 475                                 IP_FREEBIND socket option. For
 476                                 robustness reasons it is recommended
 477                                 to use this option whenever you bind a
 478                                 socket to a specific IP
 479                                 address. Defaults to <option>false</option>.</para></listitem>
 480                         </varlistentry>
 481
 482                         <varlistentry>
 483                                 <term><varname>TCPCongestion=</varname></term>
 484                                 <listitem><para>Takes a string
 485                                 value. Controls the TCP congestion
 486                                 algorithm used by this socket. Should
 487                                 be one of "westwood", "veno", "cubic",
 488                                 "lp" or any other available algorithm
 489                                 supported by the IP stack. This
 490                                 setting applies only to stream
 491                                 sockets.</para></listitem>
 492                         </varlistentry>
 493
 494                         <varlistentry>
 495                                 <term><varname>ExecStartPre=</varname></term>
 496                                 <term><varname>ExecStartPost=</varname></term>
 497                                 <listitem><para>Takes one or more
 498                                 command lines, which are executed
 499                                 before (resp. after) the listening
 500                                 sockets/FIFOs are created and
 501                                 bound. The first token of the command
 502                                 line must be an absolute file name,
 503                                 then followed by arguments for the
 504                                 process. Multiple command lines may be
 505                                 specified following the same scheme as
 506                                 used for
 507                                 <varname>ExecStartPre=</varname> of
 508                                 service unit files.</para></listitem>
 509                         </varlistentry>
 510
 511                         <varlistentry>
 512                                 <term><varname>ExecStopPre=</varname></term>
 513                                 <term><varname>ExecStopPost=</varname></term>
 514                                 <listitem><para>Additional commands
 515                                 that are executed before (resp. after)
 516                                 the listening sockets/FIFOs are closed
 517                                 and removed. Multiple command lines
 518                                 may be specified following the same
 519                                 scheme as used for
 520                                 <varname>ExecStartPre=</varname> of
 521                                 service unit files.</para></listitem>
 522                         </varlistentry>
 523
 524                         <varlistentry>
 525                                 <term><varname>TimeoutSec=</varname></term>
 526                                 <listitem><para>Configures the time to
 527                                 wait for the commands specified in
 528                                 <varname>ExecStartPre=</varname>,
 529                                 <varname>ExecStartPost=</varname>,
 530                                 <varname>ExecStopPre=</varname> and
 531                                 <varname>ExecStopPost=</varname> to
 532                                 finish. If a command does not exit
 533                                 within the configured time, the socket
 534                                 will be considered failed and be shut
 535                                 down again. All commands still running,
 536                                 will be terminated forcibly via
 537                                 SIGTERM, and after another delay of
 538                                 this time with SIGKILL. (See
 539                                 <option>KillMode=</option> below.)
 540                                 Takes a unit-less value in seconds, or
 541                                 a time span value such as "5min
 542                                 20s". Pass 0 to disable the timeout
 543                                 logic. Defaults to
 544                                 3min.</para></listitem>
 545                         </varlistentry>
 546
 547                         <varlistentry>
 548                                 <term><varname>KillMode=</varname></term>
 549                                 <listitem><para>Specifies how
 550                                 processes of this socket unit shall be
 551                                 killed. One of
 552                                 <option>control-group</option>,
 553                                 <option>process</option>,
 554                                 <option>none</option>.</para>
 555
 556                                 <para>This option is mostly equivalent
 557                                 to the <option>KillMode=</option>
 558                                 option of service files. See
 559                                 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 560                                 for details.</para></listitem>
 561                         </varlistentry>
 562
 563                         <varlistentry>
 564                                 <term><varname>KillSignal=</varname></term>
 565                                 <listitem><para>Specifies which signal
 566                                 to use when killing a process of this
 567                                 socket. Defaults to SIGTERM.
 568                                 </para></listitem>
 569                         </varlistentry>
 570
 571                         <varlistentry>
 572                                 <term><varname>SendSIGKILL=</varname></term>
 573                                 <listitem><para>Specifies whether to
 574                                 send SIGKILL to remaining processes
 575                                 after a timeout, if the normal
 576                                 shutdown procedure left processes of
 577                                 the socket around. Takes a boolean
 578                                 value. Defaults to "yes".
 579                                 </para></listitem>
 580                         </varlistentry>
 581
 582                         <varlistentry>
 583                                 <term><varname>Service=</varname></term>
 584                                 <listitem><para>Specifies the service
 585                                 unit name to activate on incoming
 586                                 traffic. This defaults to the service
 587                                 that bears the same name as the socket
 588                                 (ignoring the different suffixes). In
 589                                 most cases it should not be necessary
 590                                 to use this option.</para></listitem>
 591                         </varlistentry>
 592
 593                 </variablelist>
 594         </refsect1>
 595
 596         <refsect1>
 597                   <title>See Also</title>
 598                   <para>
 599                           <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 600                           <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 601                           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 602                           <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 603                           <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 604                   </para>
 605         </refsect1>
 606
 607 </refentry>