chiark / gitweb /
socket: enforce limit on number of concurrent connections
[elogind.git] / man / systemd.special.xml.in
1 <?xml version='1.0'?> <!--*-nxml-*-->
2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
3         "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
4
5 <!--
6   This file is part of systemd.
7
8   Copyright 2010 Lennart Poettering
9
10   systemd is free software; you can redistribute it and/or modify it
11   under the terms of the GNU General Public License as published by
12   the Free Software Foundation; either version 2 of the License, or
13   (at your option) any later version.
14
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16   WITHOUT ANY WARRANTY; without even the implied warranty of
17   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
18   General Public License for more details.
19
20   You should have received a copy of the GNU General Public License
21   along with systemd; If not, see <http://www.gnu.org/licenses/>.
22 -->
23
24 <refentry id="systemd.special">
25
26         <refentryinfo>
27                 <title>systemd.special</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.special</refentrytitle>
42                 <manvolnum>7</manvolnum>
43         </refmeta>
44
45         <refnamediv>
46                 <refname>systemd.special</refname>
47                 <refpurpose>special systemd units</refpurpose>
48         </refnamediv>
49
50         <refsynopsisdiv>
51                 <para><filename>basic.target</filename>,
52                 <filename>ctrl-alt-del.target</filename>,
53                 <filename>@SPECIAL_DBUS_SERVICE@</filename>,
54                 <filename>default.target</filename>,
55                 <filename>display-manager.service</filename>,
56                 <filename>emergency.service</filename>,
57                 <filename>exit.service</filename>,
58                 <filename>graphical.target</filename>,
59                 <filename>halt.target</filename>,
60                 <filename>kbrequest.target</filename>,
61                 <filename>local-fs.target</filename>,
62                 <filename>mail-transfer-agent.target</filename>,
63                 <filename>multi-user.target</filename>,
64                 <filename>network.target</filename>,
65                 <filename>nss-lookup.target</filename>,
66                 <filename>poweroff.target</filename>,
67                 <filename>reboot.target</filename>,
68                 <filename>remote-fs.target</filename>,
69                 <filename>rescue.target</filename>,
70                 <filename>rpcbind.target</filename>,
71                 <filename>rtc-set.target</filename>,
72                 <filename>runlevel2.target</filename>,
73                 <filename>runlevel3.target</filename>,
74                 <filename>runlevel4.target</filename>,
75                 <filename>runlevel5.target</filename>,
76                 <filename>shutdown.target</filename>,
77                 <filename>sigpwr.target</filename>,
78                 <filename>sockets.target</filename>,
79                 <filename>swap.target</filename>,
80                 <filename>sysinit.target</filename>,
81                 <filename>syslog.target</filename>,
82                 <filename>@SPECIAL_SYSLOG_SERVICE@</filename>,
83                 <filename>systemd-initctl.service</filename>,
84                 <filename>systemd-initctl.socket</filename>,
85                 <filename>systemd-logger.service</filename>,
86                 <filename>systemd-logger.socket</filename></para>
87         </refsynopsisdiv>
88
89         <refsect1>
90                 <title>Description</title>
91
92                 <para>A few units are treated specially by
93                 systemd. They have special internal semantics and
94                 cannot be renamed.</para>
95         </refsect1>
96
97         <refsect1>
98                 <title>Special System Units</title>
99
100                 <variablelist>
101                         <varlistentry>
102                                 <term><filename>basic.target</filename></term>
103                                 <listitem>
104                                         <para>A special target unit
105                                         covering early boot-up.</para>
106                                         <para>systemd automatically
107                                         adds dependencies of the types
108                                         Requires and After for this
109                                         target unit to all SysV
110                                         service units configured for
111                                         runlevel 1 to 5.</para>
112                                         <para>Usually this should pull
113                                         in all sockets, mount points,
114                                         swap devices and other basic
115                                         initialization necessary for
116                                         the general purpose
117                                         daemons. Most normal daemon
118                                         should have dependencies of
119                                         type After and Requires on
120                                         this unit.</para>
121                                 </listitem>
122                         </varlistentry>
123                         <varlistentry>
124                                 <term><filename>ctrl-alt-del.target</filename></term>
125                                 <listitem>
126                                         <para>systemd starts this
127                                         target whenever
128                                         Control+Alt+Del is pressed on
129                                         the console. Usually this
130                                         should be aliased (symlinked)
131                                         to
132                                         <filename>reboot.target</filename>.</para>
133                                 </listitem>
134                         </varlistentry>
135                         <varlistentry>
136                                 <term><filename>@SPECIAL_DBUS_SERVICE@</filename></term>
137                                 <listitem>
138                                         <para>A special unit for the
139                                         D-Bus system bus. As soon as
140                                         this service is fully started
141                                         up systemd will connect to it
142                                         and register its
143                                         service.</para>
144                                 </listitem>
145                         </varlistentry>
146                         <varlistentry>
147                                 <term><filename>default.target</filename></term>
148                                 <listitem>
149                                         <para>The default unit systemd
150                                         starts at bootup. Usually this
151                                         should be aliased (symlinked)
152                                         to
153                                         <filename>multi-user.target</filename>
154                                         or
155                                         <filename>graphical.target</filename>.</para>
156                                         <para>The default unit systemd
157                                         starts at bootup can be
158                                         overriden with the
159                                         <varname>systemd.default=</varname>
160                                         kernel command line option.</para>
161                                 </listitem>
162                         </varlistentry>
163                         <varlistentry>
164                                 <term><filename>display-manager.service</filename></term>
165                                 <listitem>
166                                         <para>The display manager
167                                         service. Usually this should
168                                         be aliased (symlinked) to
169                                         <filename>gdm.service</filename>
170                                         or a similar display manager
171                                         service.</para>
172                                         <para>systemd automatically
173                                         adds dependencies of type
174                                         After for this target unit to
175                                         all SysV init script service
176                                         units with an LSB header
177                                         referring to the
178                                         <literal>$x-display-manager</literal>
179                                         facility, for compatibility
180                                         with Debian.</para>
181                                 </listitem>
182                         </varlistentry>
183                         <varlistentry>
184                                 <term><filename>emergency.service</filename></term>
185                                 <listitem>
186                                         <para>A special service unit
187                                         that starts an emergency
188                                         shell on the main
189                                         console. This unit is supposed
190                                         to be used with the kernel
191                                         command line option
192                                         <varname>systemd.default=</varname>
193                                         and has otherwise little use.
194                                         </para>
195                                 </listitem>
196                         </varlistentry>
197                         <varlistentry>
198                                 <term><filename>graphical.target</filename></term>
199                                 <listitem>
200                                         <para>A special target unit
201                                         for setting up a graphical
202                                         login screen. This pulls in
203                                         <filename>multi-user.target</filename>.</para>
204
205                                         <para>Units that are needed
206                                         for graphical login shall add
207                                         Wants dependencies for their
208                                         unit to this unit (or
209                                         <filename>multi-user.target</filename>)
210                                         during installation.</para>
211                                 </listitem>
212                         </varlistentry>
213                         <varlistentry>
214                                 <term><filename>halt.target</filename></term>
215                                 <listitem>
216                                         <para>A special target unit
217                                         for shutting down and halting the system.</para>
218
219                                         <para>Applications wanting to
220                                         halt the system should start
221                                         this unit.</para>
222                                 </listitem>
223                         </varlistentry>
224                         <varlistentry>
225                                 <term><filename>kbrequest.target</filename></term>
226                                 <listitem>
227                                         <para>systemd starts this
228                                         target whenever Alt+ArrowUp is
229                                         pressed on the console. This
230                                         is a good candidate to be
231                                         aliased (symlinked) to
232                                         <filename>rescue.target</filename>.</para>
233                                 </listitem>
234                         </varlistentry>
235                         <varlistentry>
236                                 <term><filename>local-fs.target</filename></term>
237                                 <listitem>
238                                         <para>systemd automatically
239                                         adds dependencies of type
240                                         After to all mount units that
241                                         refer to local mount points
242                                         for this target unit. In
243                                         addition, systemd adds
244                                         dependencies of type Wants to
245                                         this target unit for those
246                                         mounts listed in
247                                         <filename>/etc/fstab</filename>
248                                         that have the
249                                         <literal>auto</literal> and
250                                         <literal>comment=systemd.mount</literal>
251                                         mount options set.</para>
252
253                                         <para>systemd automatically
254                                         adds dependencies of type
255                                         After for this target unit to
256                                         all SysV init script service
257                                         units with an LSB header
258                                         referring to the
259                                         <literal>$local_fs</literal>
260                                         facility.</para>
261                                 </listitem>
262                         </varlistentry>
263                         <varlistentry>
264                                 <term><filename>mail-transfer-agent.target</filename></term>
265                                 <listitem>
266                                         <para>The mail transfer agent
267                                         (MTA) service. Usually this
268                                         should pull in all units
269                                         necessary for
270                                         sending/receiving mails on the
271                                         local host.</para>
272
273                                         <para>systemd automatically
274                                         adds dependencies of type
275                                         After for this target unit to
276                                         all SysV init script service
277                                         units with an LSB header
278                                         referring to the
279                                         <literal>$mail-transfer-argent</literal>
280                                         or
281                                         <literal>$mail-transport-agent</literal>
282                                         facilities, for compatibility
283                                         with Debian.</para>
284                                 </listitem>
285                         </varlistentry>
286                         <varlistentry>
287                                 <term><filename>multi-user.target</filename></term>
288                                 <listitem>
289                                         <para>A special target unit
290                                         for setting up a multi-user
291                                         system (non-graphical). This
292                                         is pulled in by
293                                         <filename>graphical.target</filename>.</para>
294
295                                         <para>Units that are needed
296                                         for a multi-user system shall
297                                         add Wants dependencies to
298                                         this unit for their unit during
299                                         installation.</para>
300                                 </listitem>
301                         </varlistentry>
302                         <varlistentry>
303                                 <term><filename>network.target</filename></term>
304                                 <listitem>
305                                         <para>systemd automatically
306                                         adds dependencies of type
307                                         After for this target unit to
308                                         all SysV init script service
309                                         units with an LSB header
310                                         referring to the
311                                         <literal>$network</literal>
312                                         facility.</para>
313                                 </listitem>
314                         </varlistentry>
315                         <varlistentry>
316                                 <term><filename>nss-lookup.target</filename></term>
317                                 <listitem>
318                                         <para>systemd automatically
319                                         adds dependencies of type
320                                         After for this target unit to
321                                         all SysV init script service
322                                         units with an LSB header
323                                         referring to the
324                                         <literal>$named</literal>
325                                         facility.</para>
326                                 </listitem>
327                         </varlistentry>
328                         <varlistentry>
329                                 <term><filename>poweroff.target</filename></term>
330                                 <listitem>
331                                         <para>A special target unit
332                                         for shutting down and powering off the system.</para>
333
334                                         <para>Applications wanting to
335                                         power off the system should start
336                                         this unit.</para>
337
338                                         <para><filename>runlevel0.target</filename>
339                                         is an alias for this target
340                                         unit, for compatibility with SysV.</para>
341                                 </listitem>
342                         </varlistentry>
343                         <varlistentry>
344                                 <term><filename>reboot.target</filename></term>
345                                 <listitem>
346                                         <para>A special target unit
347                                         for shutting down and rebooting the system.</para>
348
349                                         <para>Applications wanting to
350                                         reboot the system should start
351                                         this unit.</para>
352
353                                         <para><filename>runlevel6.target</filename>
354                                         is an alias for this target
355                                         unit, for compatibility with SysV.</para>
356                                 </listitem>
357                         </varlistentry>
358                         <varlistentry>
359                                 <term><filename>remote-fs.target</filename></term>
360                                 <listitem>
361                                         <para>Similar to
362                                         <filename>local-fs.target</filename>,
363                                         but for remote mount
364                                         points.</para>
365
366                                         <para>systemd automatically
367                                         adds dependencies of type
368                                         After for this target unit to
369                                         all SysV init script service
370                                         units with an LSB header
371                                         referring to the
372                                         <literal>$remote_fs</literal>
373                                         facility.</para>
374                                 </listitem>
375                         </varlistentry>
376                         <varlistentry>
377                                 <term><filename>rescue.target</filename></term>
378                                 <listitem>
379                                         <para>A special target unit
380                                         for setting up the base system
381                                         and a rescue shell.</para>
382
383                                         <para><filename>runlevel1.target</filename>
384                                         is an alias for this target
385                                         unit, for compatibility with SysV.</para>
386                                 </listitem>
387                         </varlistentry>
388                         <varlistentry>
389                                 <term><filename>rpcbind.target</filename></term>
390                                 <listitem>
391                                         <para>systemd automatically
392                                         adds dependencies of type
393                                         After for this target unit to
394                                         all SysV init script service
395                                         units with an LSB header
396                                         referring to the
397                                         <literal>$rpcbind</literal>
398                                         facility.</para>
399                                 </listitem>
400                         </varlistentry>
401                         <varlistentry>
402                                 <term><filename>rtc-set.target</filename></term>
403                                 <listitem>
404                                         <para>systemd automatically
405                                         adds dependencies of type
406                                         After for this target unit to
407                                         all SysV init script service
408                                         units with an LSB header
409                                         referring to the
410                                         <literal>$time</literal>
411                                         facility.</para>
412                                 </listitem>
413                         </varlistentry>
414                         <varlistentry>
415                                 <term><filename>runlevel2.target</filename></term>
416                                 <listitem>
417                                         <para>This is a target that is
418                                         called whever the SysV
419                                         compatibility code asks for
420                                         runlevel 2. It is a good idea
421                                         to make this an alias for
422                                         (i.e. symlink to)
423                                         <filename>multi-user.target</filename>.</para>
424                                 </listitem>
425                         </varlistentry>
426                         <varlistentry>
427                                 <term><filename>runlevel3.target</filename></term>
428                                 <listitem>
429                                         <para>This is a target that is
430                                         called whever the SysV
431                                         compatibility code asks for
432                                         runlevel 3. It is a good idea
433                                         to make this an alias for
434                                         (i.e. symlink to)
435                                         <filename>multi-user.target</filename>
436                                         or
437                                         <filename>graphical.target</filename>.</para>
438                                 </listitem>
439                         </varlistentry>
440                         <varlistentry>
441                                 <term><filename>runlevel4.target</filename></term>
442                                 <listitem>
443                                         <para>This is a target that is
444                                         called whever the SysV
445                                         compatibility code asks for
446                                         runlevel 4. It is a good idea
447                                         to make this an alias for
448                                         (i.e. symlink to)
449                                         <filename>multi-user.target</filename>
450                                         or
451                                         <filename>graphical.target</filename>.</para>
452                                 </listitem>
453                         </varlistentry>
454                         <varlistentry>
455                                 <term><filename>runlevel5.target</filename></term>
456                                 <listitem>
457                                         <para>This is a target that is
458                                         called whever the SysV
459                                         compatibility code asks for
460                                         runlevel 5. It is a good idea
461                                         to make this an alias for
462                                         (i.e. symlink to)
463                                         <filename>multi-user.target</filename>
464                                         or
465                                         <filename>graphical.target</filename>.</para>
466                                 </listitem>
467                         </varlistentry>
468                         <varlistentry>
469                                 <term><filename>shutdown.target</filename></term>
470                                 <listitem>
471                                         <para>A special target unit
472                                         that terminates the services
473                                         on system shutdown.</para>
474
475                                         <para>Services that shall be
476                                         terminated on system shutdown
477                                         shall add Conflicts
478                                         dependencies to this unit for
479                                         their service unit during
480                                         installation.</para>
481
482                                         <para>systemd automatically
483                                         adds dependencies of type
484                                         Conflicts to this target unit
485                                         for all SysV init script
486                                         service units that shall be
487                                         terminated in SysV runlevels 0
488                                         or 6.</para>
489                                 </listitem>
490                         </varlistentry>
491                         <varlistentry>
492                                 <term><filename>sigpwr.target</filename></term>
493                                 <listitem>
494                                         <para>A special target that is
495                                         started when systemd receives
496                                         the SIGPWR process signal,
497                                         which is normally sent by the
498                                         kernel or UPS daemons when
499                                         power fails.</para>
500                                 </listitem>
501                         </varlistentry>
502                         <varlistentry>
503                                 <term><filename>sockets.target</filename></term>
504                                 <listitem>
505                                         <para>A special target unit
506                                         that sets up all service
507                                         sockets.</para>
508
509                                         <para>Services that can be
510                                         socket-activated shall add
511                                         Wants dependencies to this
512                                         unit for their socket unit
513                                         during installation.</para>
514                                 </listitem>
515                         </varlistentry>
516                         <varlistentry>
517                                 <term><filename>swap.target</filename></term>
518                                 <listitem>
519                                         <para>Similar to
520                                         <filename>local-fs.target</filename>, but for swap
521                                         partitions and swap
522                                         files.</para>
523                                 </listitem>
524                         </varlistentry>
525                         <varlistentry>
526                                 <term><filename>syslog.target</filename></term>
527                                 <listitem>
528                                         <para>systemd automatically
529                                         adds dependencies of type
530                                         After for this target unit to
531                                         all SysV init script service
532                                         units with an LSB header
533                                         referring to the
534                                         <literal>$syslog</literal>
535                                         facility.</para>
536
537                                         <para>Administrators should
538                                         ensure that this target pulls
539                                         in a service unit with the
540                                         name or alias of
541                                         <filename>@SPECIAL_SYSLOG_SERVICE@</filename>
542                                         (or a socket unit that
543                                         activates this
544                                         service).</para>
545                                 </listitem>
546                         </varlistentry>
547                         <varlistentry>
548                                 <term><filename>sysinit.target</filename></term>
549                                 <listitem>
550                                         <para>A special target unit
551                                         covering early boot-up scripts.</para>
552                                         <para>systemd automatically
553                                         adds dependencies of the types
554                                         Wants and After for all
555                                         SysV service units configured
556                                         for runlevels that are not 0
557                                         to 6 to this target unit.
558                                         This covers the special
559                                         boot-up runlevels some
560                                         distributions have, such as S
561                                         or b.</para>
562                                 </listitem>
563                         </varlistentry>
564                         <varlistentry>
565                                 <term><filename>@SPECIAL_SYSLOG_SERVICE@</filename></term>
566                                 <listitem>
567                                         <para>A special unit for the
568                                         syslog daemon. As soon as
569                                         this service is fully started
570                                         up systemd will connect to it
571                                         and use it for logging if it
572                                         has been configured for
573                                         that.</para>
574                                         <para>Applications should
575                                         generally not depend on this
576                                         service, and depend on
577                                         <filename>syslog.target</filename>
578                                         instead.</para>
579                                 </listitem>
580                         </varlistentry>
581                         <varlistentry>
582                                 <term><filename>systemd-initctl.service</filename></term>
583                                 <listitem>
584                                         <para>This provides
585                                         compatibility with the SysV
586                                         /dev/initctl file system FIFO
587                                         for communication with the
588                                         init system.</para>
589                                         <para>This is a
590                                         socket-activated service, see
591                                         <filename>system-initctl.socket</filename>.</para>
592                                 </listitem>
593                         </varlistentry>
594                         <varlistentry>
595                                 <term><filename>systemd-initctl.socket</filename></term>
596                                 <listitem>
597                                         <para>Socket activation unit
598                                         for
599                                         <filename>system-initctl.service</filename>.</para>
600                                 </listitem>
601                         </varlistentry>
602                         <varlistentry>
603                                 <term><filename>systemd-logger.service</filename></term>
604                                 <listitem>
605                                         <para>This is internally used
606                                         by systemd to provide syslog
607                                         logging to the processes it
608                                         maintains.</para>
609                                         <para>This is a
610                                         socket-activated service, see
611                                         <filename>system-logger.socket</filename>.</para>
612                                 </listitem>
613                         </varlistentry>
614                         <varlistentry>
615                                 <term><filename>systemd-logger.socket</filename></term>
616                                 <listitem>
617                                         <para>Socket activation unit
618                                         for
619                                         <filename>system-logger.service</filename>. systemd
620                                         will automatically add
621                                         dependencies of types Requires
622                                         and After to all units that
623                                         have been configured for
624                                         stdout or stderr to be
625                                         connected to syslog or the
626                                         kernel log buffer.</para>
627                                 </listitem>
628                         </varlistentry>
629                 </variablelist>
630         </refsect1>
631
632         <refsect1>
633                 <title>Special Session Units</title>
634
635                 <para>When systemd runs as a service instance, the
636                 following special units are available, which have
637                 similar definitions as their system counterparts:
638                 <filename>default.target</filename>,
639                 <filename>local-fs.target</filename>,
640                 <filename>remote-fs.target</filename>,
641                 <filename>shutdown.target</filename>,
642                 <filename>sockets.target</filename>,
643                 <filename>swap.target</filename>.</para>
644
645                 <para>In addition the following special unit is
646                 understood only when systemd runs as service instance:</para>
647
648                 <variablelist>
649                         <varlistentry>
650                                 <term><filename>exit.service</filename></term>
651                                 <listitem>
652                                         <para>A special service unit
653                                         for shutting down the
654                                         session.</para>
655
656                                         <para>Applications wanting to
657                                         terminate the session should
658                                         start this unit. If systemd
659                                         receives SIGTERM or SIGINT
660                                         when running as session daemon
661                                         it will start this
662                                         unit.</para>
663
664                                         <para>Normally, this pulls in
665                                         <filename>shutdown.target</filename>
666                                         which in turn should be
667                                         conflicted by all units that
668                                         want to be shut down on
669                                         session exit.</para>
670                                 </listitem>
671                         </varlistentry>
672                 </variablelist>
673         </refsect1>
674
675         <refsect1>
676                   <title>See Also</title>
677                   <para>
678                           <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
679                           <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
680                           <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
681                           <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>
682                   </para>
683         </refsect1>
684
685 </refentry>