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6 This file is part of systemd.
8 Copyright 2010 Lennart Poettering
10 systemd is free software; you can redistribute it and/or modify it
11 under the terms of the GNU Lesser General Public License as published by
12 the Free Software Foundation; either version 2.1 of the License, or
13 (at your option) any later version.
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24 <refentry id="systemd.exec">
26 <title>systemd.exec</title>
27 <productname>systemd</productname>
31 <contrib>Developer</contrib>
32 <firstname>Lennart</firstname>
33 <surname>Poettering</surname>
34 <email>lennart@poettering.net</email>
40 <refentrytitle>systemd.exec</refentrytitle>
41 <manvolnum>5</manvolnum>
45 <refname>systemd.exec</refname>
46 <refpurpose>Execution environment configuration</refpurpose>
50 <para><filename><replaceable>service</replaceable>.service</filename>,
51 <filename><replaceable>socket</replaceable>.socket</filename>,
52 <filename><replaceable>mount</replaceable>.mount</filename>,
53 <filename><replaceable>swap</replaceable>.swap</filename></para>
57 <title>Description</title>
59 <para>Unit configuration files for services, sockets,
60 mount points, and swap devices share a subset of
61 configuration options which define the execution
62 environment of spawned processes.</para>
64 <para>This man page lists the configuration options
65 shared by these four unit types. See
66 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
67 for the common options of all unit configuration
69 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
70 <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
71 <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
73 <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>
74 for more information on the specific unit
75 configuration files. The execution specific
76 configuration options are configured in the [Service],
77 [Socket], [Mount], or [Swap] sections, depending on the unit
82 <title>Options</title>
84 <variablelist class='unit-directives'>
87 <term><varname>WorkingDirectory=</varname></term>
89 <listitem><para>Takes an absolute
90 directory path. Sets the working
91 directory for executed processes. If
92 not set, defaults to the root directory
93 when systemd is running as a system
94 instance and the respective user's
95 home directory if run as
96 user.</para></listitem>
100 <term><varname>RootDirectory=</varname></term>
102 <listitem><para>Takes an absolute
103 directory path. Sets the root
104 directory for executed processes, with
106 <citerefentry project='man-pages'><refentrytitle>chroot</refentrytitle><manvolnum>2</manvolnum></citerefentry>
107 system call. If this is used, it must
108 be ensured that the process and all
109 its auxiliary files are available in
110 the <function>chroot()</function>
111 jail.</para></listitem>
115 <term><varname>User=</varname></term>
116 <term><varname>Group=</varname></term>
118 <listitem><para>Sets the Unix user
119 or group that the processes are executed
120 as, respectively. Takes a single user or group
121 name or ID as argument. If no group is
122 set, the default group of the user is
123 chosen.</para></listitem>
127 <term><varname>SupplementaryGroups=</varname></term>
129 <listitem><para>Sets the supplementary
130 Unix groups the processes are executed
131 as. This takes a space-separated list
132 of group names or IDs. This option may
133 be specified more than once in which
134 case all listed groups are set as
135 supplementary groups. When the empty
136 string is assigned the list of
137 supplementary groups is reset, and all
138 assignments prior to this one will
139 have no effect. In any way, this
140 option does not override, but extends
141 the list of supplementary groups
142 configured in the system group
144 user.</para></listitem>
148 <term><varname>Nice=</varname></term>
150 <listitem><para>Sets the default nice
151 level (scheduling priority) for
152 executed processes. Takes an integer
153 between -20 (highest priority) and 19
154 (lowest priority). See
155 <citerefentry><refentrytitle>setpriority</refentrytitle><manvolnum>2</manvolnum></citerefentry>
156 for details.</para></listitem>
160 <term><varname>OOMScoreAdjust=</varname></term>
162 <listitem><para>Sets the adjustment
163 level for the Out-Of-Memory killer for
164 executed processes. Takes an integer
165 between -1000 (to disable OOM killing
166 for this process) and 1000 (to make
167 killing of this process under memory
168 pressure very likely). See <ulink
169 url="https://www.kernel.org/doc/Documentation/filesystems/proc.txt">proc.txt</ulink>
170 for details.</para></listitem>
174 <term><varname>IOSchedulingClass=</varname></term>
176 <listitem><para>Sets the IO scheduling
177 class for executed processes. Takes an
178 integer between 0 and 3 or one of the
179 strings <option>none</option>,
180 <option>realtime</option>,
181 <option>best-effort</option> or
182 <option>idle</option>. See
183 <citerefentry><refentrytitle>ioprio_set</refentrytitle><manvolnum>2</manvolnum></citerefentry>
184 for details.</para></listitem>
188 <term><varname>IOSchedulingPriority=</varname></term>
190 <listitem><para>Sets the IO scheduling
191 priority for executed processes. Takes
192 an integer between 0 (highest
193 priority) and 7 (lowest priority). The
194 available priorities depend on the
195 selected IO scheduling class (see
197 <citerefentry><refentrytitle>ioprio_set</refentrytitle><manvolnum>2</manvolnum></citerefentry>
198 for details.</para></listitem>
202 <term><varname>CPUSchedulingPolicy=</varname></term>
204 <listitem><para>Sets the CPU
205 scheduling policy for executed
206 processes. Takes one of
207 <option>other</option>,
208 <option>batch</option>,
209 <option>idle</option>,
210 <option>fifo</option> or
211 <option>rr</option>. See
212 <citerefentry><refentrytitle>sched_setscheduler</refentrytitle><manvolnum>2</manvolnum></citerefentry>
213 for details.</para></listitem>
217 <term><varname>CPUSchedulingPriority=</varname></term>
219 <listitem><para>Sets the CPU
220 scheduling priority for executed
221 processes. The available priority
222 range depends on the selected CPU
223 scheduling policy (see above). For
224 real-time scheduling policies an
225 integer between 1 (lowest priority)
226 and 99 (highest priority) can be used.
227 See <citerefentry><refentrytitle>sched_setscheduler</refentrytitle><manvolnum>2</manvolnum></citerefentry>
233 <term><varname>CPUSchedulingResetOnFork=</varname></term>
235 <listitem><para>Takes a boolean
236 argument. If true, elevated CPU
237 scheduling priorities and policies
238 will be reset when the executed
239 processes fork, and can hence not leak
240 into child processes. See
241 <citerefentry><refentrytitle>sched_setscheduler</refentrytitle><manvolnum>2</manvolnum></citerefentry>
242 for details. Defaults to false.</para></listitem>
246 <term><varname>CPUAffinity=</varname></term>
248 <listitem><para>Controls the CPU
249 affinity of the executed
250 processes. Takes a space-separated
251 list of CPU indices. This option may
252 be specified more than once in which
253 case the specificed CPU affinity masks
254 are merged. If the empty string is
255 assigned, the mask is reset, all
256 assignments prior to this will have no
258 <citerefentry><refentrytitle>sched_setaffinity</refentrytitle><manvolnum>2</manvolnum></citerefentry>
259 for details.</para></listitem>
263 <term><varname>UMask=</varname></term>
265 <listitem><para>Controls the file mode
266 creation mask. Takes an access mode in
268 <citerefentry><refentrytitle>umask</refentrytitle><manvolnum>2</manvolnum></citerefentry>
269 for details. Defaults to
270 0022.</para></listitem>
274 <term><varname>Environment=</varname></term>
276 <listitem><para>Sets environment
277 variables for executed
278 processes. Takes a space-separated
279 list of variable assignments. This
280 option may be specified more than once
281 in which case all listed variables
282 will be set. If the same variable is
283 set twice, the later setting will
284 override the earlier setting. If the
285 empty string is assigned to this
286 option, the list of environment
287 variables is reset, all prior
288 assignments have no effect.
289 Variable expansion is not performed
290 inside the strings, however, specifier
291 expansion is possible. The $ character has
293 If you need to assign a value containing spaces
294 to a variable, use double quotes (")
295 for the assignment.</para>
298 <programlisting>Environment="VAR1=word1 word2" VAR2=word3 "VAR3=$word 5 6"</programlisting>
299 gives three variables <literal>VAR1</literal>,
300 <literal>VAR2</literal>, <literal>VAR3</literal>
301 with the values <literal>word1 word2</literal>,
302 <literal>word3</literal>, <literal>$word 5 6</literal>.
307 <citerefentry project='man-pages'><refentrytitle>environ</refentrytitle><manvolnum>7</manvolnum></citerefentry>
308 for details about environment variables.</para></listitem>
311 <term><varname>EnvironmentFile=</varname></term>
312 <listitem><para>Similar to
313 <varname>Environment=</varname> but
314 reads the environment variables from a
315 text file. The text file should
316 contain new-line-separated variable
317 assignments. Empty lines and lines
318 starting with ; or # will be ignored,
319 which may be used for commenting. A line
320 ending with a backslash will be concatenated
321 with the following one, allowing multiline variable
322 definitions. The parser strips leading
323 and trailing whitespace from the values
324 of assignments, unless you use
325 double quotes (").</para>
327 <para>The argument passed should be an
328 absolute filename or wildcard
329 expression, optionally prefixed with
330 <literal>-</literal>, which indicates
331 that if the file does not exist, it
332 will not be read and no error or warning
333 message is logged. This option may be
334 specified more than once in which case
335 all specified files are read. If the
336 empty string is assigned to this
337 option, the list of file to read is
338 reset, all prior assignments have no
341 <para>The files listed with this
342 directive will be read shortly before
343 the process is executed (more
344 specifically, after all
345 processes from a previous unit state
346 terminated. This means you can
347 generate these files in one unit
348 state, and read it with this option in
349 the next). Settings from these files
350 override settings made with
351 <varname>Environment=</varname>. If
352 the same variable is set twice from
353 these files, the files will be read in
354 the order they are specified and the
355 later setting will override the
356 earlier setting.</para></listitem>
360 <term><varname>StandardInput=</varname></term>
361 <listitem><para>Controls where file
362 descriptor 0 (STDIN) of the executed
363 processes is connected to. Takes one
364 of <option>null</option>,
365 <option>tty</option>,
366 <option>tty-force</option>,
367 <option>tty-fail</option> or
368 <option>socket</option>.</para>
370 <para>If <option>null</option> is
371 selected, standard input will be
373 <filename>/dev/null</filename>,
374 i.e. all read attempts by the process
375 will result in immediate EOF.</para>
377 <para>If <option>tty</option> is
378 selected, standard input is connected
379 to a TTY (as configured by
380 <varname>TTYPath=</varname>, see
381 below) and the executed process
382 becomes the controlling process of the
383 terminal. If the terminal is already
384 being controlled by another process,
385 the executed process waits until the
386 current controlling process releases
389 <para><option>tty-force</option> is similar
390 to <option>tty</option>, but the
391 executed process is forcefully and
392 immediately made the controlling
393 process of the terminal, potentially
394 removing previous controlling
398 <para><option>tty-fail</option> is
399 similar to <option>tty</option> but if
400 the terminal already has a controlling
401 process start-up of the executed
402 process fails.</para>
404 <para>The <option>socket</option>
405 option is only valid in
406 socket-activated services, and only
407 when the socket configuration file
409 <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
410 for details) specifies a single socket
411 only. If this option is set, standard
412 input will be connected to the socket
413 the service was activated from, which
414 is primarily useful for compatibility
415 with daemons designed for use with the
417 <citerefentry><refentrytitle>inetd</refentrytitle><manvolnum>8</manvolnum></citerefentry>
420 <para>This setting defaults to
421 <option>null</option>.</para></listitem>
424 <term><varname>StandardOutput=</varname></term>
425 <listitem><para>Controls where file
426 descriptor 1 (STDOUT) of the executed
427 processes is connected to. Takes one
428 of <option>inherit</option>,
429 <option>null</option>,
430 <option>tty</option>,
431 <option>journal</option>,
432 <option>syslog</option>,
433 <option>kmsg</option>,
434 <option>journal+console</option>,
435 <option>syslog+console</option>,
436 <option>kmsg+console</option> or
437 <option>socket</option>.</para>
439 <para><option>inherit</option>
440 duplicates the file descriptor of
441 standard input for standard
444 <para><option>null</option> connects
446 <filename>/dev/null</filename>,
447 i.e. everything written to it will be
450 <para><option>tty</option> connects
451 standard output to a tty (as
453 <varname>TTYPath=</varname>, see
454 below). If the TTY is used for output
455 only, the executed process will not
456 become the controlling process of the
457 terminal, and will not fail or wait
458 for other processes to release the
461 <para><option>journal</option>
462 connects standard output with the
463 journal which is accessible via
464 <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
465 Note that everything that is written
466 to syslog or kmsg (see below) is
467 implicitly stored in the journal as
468 well, the specific two options listed
469 below are hence supersets of this
472 <para><option>syslog</option> connects
473 standard output to the <citerefentry
474 project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
475 system syslog service, in addition to
476 the journal. Note that the journal
477 daemon is usually configured to
478 forward everything it receives to
479 syslog anyway, in which case this
480 option is no different from
481 <option>journal</option>.</para>
483 <para><option>kmsg</option> connects
484 standard output with the kernel log
485 buffer which is accessible via
487 project='man-pages'><refentrytitle>dmesg</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
488 in addition to the journal. The
489 journal daemon might be configured to
490 send all logs to kmsg anyway, in which
491 case this option is no different from
492 <option>journal</option>.</para>
494 <para><option>journal+console</option>,
495 <option>syslog+console</option> and
496 <option>kmsg+console</option> work in
497 a similar way as the three options
498 above but copy the output to the
499 system console as well.</para>
501 <para><option>socket</option> connects
502 standard output to a socket acquired
503 via socket activation. The semantics
504 are similar to the same option of
505 <varname>StandardInput=</varname>.</para>
507 <para>This setting defaults to the
509 <option>DefaultStandardOutput=</option>
511 <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
513 <option>journal</option>.</para></listitem>
516 <term><varname>StandardError=</varname></term>
517 <listitem><para>Controls where file
518 descriptor 2 (STDERR) of the
519 executed processes is connected to.
520 The available options are identical to
522 <varname>StandardOutput=</varname>,
523 with one exception: if set to
524 <option>inherit</option> the file
525 descriptor used for standard output is
526 duplicated for standard error. This
527 setting defaults to the value set with
528 <option>DefaultStandardError=</option>
530 <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
532 <option>inherit</option>.</para></listitem>
535 <term><varname>TTYPath=</varname></term>
536 <listitem><para>Sets the terminal
537 device node to use if standard input, output,
538 or error are connected to a
539 TTY (see above). Defaults to
540 <filename>/dev/console</filename>.</para></listitem>
543 <term><varname>TTYReset=</varname></term>
544 <listitem><para>Reset the terminal
545 device specified with
546 <varname>TTYPath=</varname> before and
547 after execution. Defaults to
548 <literal>no</literal>.</para></listitem>
551 <term><varname>TTYVHangup=</varname></term>
552 <listitem><para>Disconnect all clients
553 which have opened the terminal device
555 <varname>TTYPath=</varname>
556 before and after execution. Defaults
558 <literal>no</literal>.</para></listitem>
561 <term><varname>TTYVTDisallocate=</varname></term>
562 <listitem><para>If the terminal
563 device specified with
564 <varname>TTYPath=</varname> is a
565 virtual console terminal, try to
566 deallocate the TTY before and after
567 execution. This ensures that the
568 screen and scrollback buffer is
570 <literal>no</literal>.</para></listitem>
573 <term><varname>SyslogIdentifier=</varname></term>
574 <listitem><para>Sets the process name
575 to prefix log lines sent to the
576 logging system or the kernel log
577 buffer with. If not set, defaults to
578 the process name of the executed
579 process. This option is only useful
581 <varname>StandardOutput=</varname> or
582 <varname>StandardError=</varname> are
583 set to <option>syslog</option>,
584 <option>journal</option> or
585 <option>kmsg</option> (or to the same
586 settings in combination with
587 <option>+console</option>).</para></listitem>
590 <term><varname>SyslogFacility=</varname></term>
591 <listitem><para>Sets the syslog
592 facility to use when logging to
593 syslog. One of <option>kern</option>,
594 <option>user</option>,
595 <option>mail</option>,
596 <option>daemon</option>,
597 <option>auth</option>,
598 <option>syslog</option>,
599 <option>lpr</option>,
600 <option>news</option>,
601 <option>uucp</option>,
602 <option>cron</option>,
603 <option>authpriv</option>,
604 <option>ftp</option>,
605 <option>local0</option>,
606 <option>local1</option>,
607 <option>local2</option>,
608 <option>local3</option>,
609 <option>local4</option>,
610 <option>local5</option>,
611 <option>local6</option> or
612 <option>local7</option>. See
613 <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
614 for details. This option is only
616 <varname>StandardOutput=</varname> or
617 <varname>StandardError=</varname> are
618 set to <option>syslog</option>.
620 <option>daemon</option>.</para></listitem>
623 <term><varname>SyslogLevel=</varname></term>
624 <listitem><para>Default syslog level
625 to use when logging to syslog or the
626 kernel log buffer. One of
627 <option>emerg</option>,
628 <option>alert</option>,
629 <option>crit</option>,
630 <option>err</option>,
631 <option>warning</option>,
632 <option>notice</option>,
633 <option>info</option>,
634 <option>debug</option>. See
635 <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
636 for details. This option is only
638 <varname>StandardOutput=</varname> or
639 <varname>StandardError=</varname> are
640 set to <option>syslog</option> or
641 <option>kmsg</option>. Note that
642 individual lines output by the daemon
643 might be prefixed with a different log
644 level which can be used to override
645 the default log level specified
646 here. The interpretation of these
647 prefixes may be disabled with
648 <varname>SyslogLevelPrefix=</varname>,
649 see below. For details see
650 <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
653 <option>info</option>.</para></listitem>
657 <term><varname>SyslogLevelPrefix=</varname></term>
658 <listitem><para>Takes a boolean
659 argument. If true and
660 <varname>StandardOutput=</varname> or
661 <varname>StandardError=</varname> are
662 set to <option>syslog</option>,
663 <option>kmsg</option> or
664 <option>journal</option>, log lines
665 written by the executed process that
666 are prefixed with a log level will be
667 passed on to syslog with this log
668 level set but the prefix removed. If
669 set to false, the interpretation of
670 these prefixes is disabled and the
671 logged lines are passed on as-is. For
672 details about this prefixing see
673 <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
674 Defaults to true.</para></listitem>
678 <term><varname>TimerSlackNSec=</varname></term>
679 <listitem><para>Sets the timer slack
680 in nanoseconds for the executed
681 processes. The timer slack controls
682 the accuracy of wake-ups triggered by
684 <citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
685 for more information. Note that in
686 contrast to most other time span
687 definitions this parameter takes an
688 integer value in nano-seconds if no
689 unit is specified. The usual time
691 too.</para></listitem>
695 <term><varname>LimitCPU=</varname></term>
696 <term><varname>LimitFSIZE=</varname></term>
697 <term><varname>LimitDATA=</varname></term>
698 <term><varname>LimitSTACK=</varname></term>
699 <term><varname>LimitCORE=</varname></term>
700 <term><varname>LimitRSS=</varname></term>
701 <term><varname>LimitNOFILE=</varname></term>
702 <term><varname>LimitAS=</varname></term>
703 <term><varname>LimitNPROC=</varname></term>
704 <term><varname>LimitMEMLOCK=</varname></term>
705 <term><varname>LimitLOCKS=</varname></term>
706 <term><varname>LimitSIGPENDING=</varname></term>
707 <term><varname>LimitMSGQUEUE=</varname></term>
708 <term><varname>LimitNICE=</varname></term>
709 <term><varname>LimitRTPRIO=</varname></term>
710 <term><varname>LimitRTTIME=</varname></term>
711 <listitem><para>These settings control
712 various resource limits for executed
714 <citerefentry><refentrytitle>setrlimit</refentrytitle><manvolnum>2</manvolnum></citerefentry>
715 for details. Use the string
716 <varname>infinity</varname> to
717 configure no limit on a specific
718 resource.</para></listitem>
722 <term><varname>PAMName=</varname></term>
723 <listitem><para>Sets the PAM service
724 name to set up a session as. If set,
725 the executed process will be
726 registered as a PAM session under the
727 specified service name. This is only
728 useful in conjunction with the
729 <varname>User=</varname> setting. If
730 not set, no PAM session will be opened
731 for the executed processes. See
732 <citerefentry project='man-pages'><refentrytitle>pam</refentrytitle><manvolnum>8</manvolnum></citerefentry>
733 for details.</para></listitem>
737 <term><varname>CapabilityBoundingSet=</varname></term>
739 <listitem><para>Controls which
740 capabilities to include in the
741 capability bounding set for the
742 executed process. See
743 <citerefentry project='man-pages'><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
744 for details. Takes a whitespace-separated
745 list of capability names as read by
746 <citerefentry><refentrytitle>cap_from_name</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
747 e.g. <constant>CAP_SYS_ADMIN</constant>,
748 <constant>CAP_DAC_OVERRIDE</constant>,
749 <constant>CAP_SYS_PTRACE</constant>.
750 Capabilities listed will be included
751 in the bounding set, all others are
752 removed. If the list of capabilities
753 is prefixed with <literal>~</literal>,
754 all but the listed capabilities will
755 be included, the effect of the
756 assignment inverted. Note that this
757 option also affects the respective
758 capabilities in the effective,
759 permitted and inheritable capability
761 <varname>Capabilities=</varname>
762 does. If this option is not used, the
763 capability bounding set is not
764 modified on process execution, hence
765 no limits on the capabilities of the
766 process are enforced. This option may
767 appear more than once in which case
768 the bounding sets are merged. If the
769 empty string is assigned to this
770 option, the bounding set is reset to
771 the empty capability set, and all
772 prior settings have no effect. If set
773 to <literal>~</literal> (without any
774 further argument), the bounding set is
775 reset to the full set of available
776 capabilities, also undoing any
777 previous settings.</para></listitem>
781 <term><varname>SecureBits=</varname></term>
782 <listitem><para>Controls the secure
783 bits set for the executed process.
784 Takes a space-separated combination of
785 options from the following list:
786 <option>keep-caps</option>,
787 <option>keep-caps-locked</option>,
788 <option>no-setuid-fixup</option>,
789 <option>no-setuid-fixup-locked</option>,
790 <option>noroot</option>, and
791 <option>noroot-locked</option>. This
792 option may appear more than once in
793 which case the secure bits are ORed.
794 If the empty string is assigned to
795 this option, the bits are reset to 0.
797 project='man-pages'><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
798 for details.</para></listitem>
802 <term><varname>Capabilities=</varname></term>
803 <listitem><para>Controls the
804 <citerefentry project='man-pages'><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
805 set for the executed process. Take a
806 capability string describing the
807 effective, permitted and inherited
808 capability sets as documented in
809 <citerefentry><refentrytitle>cap_from_text</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
810 Note that these capability sets are
811 usually influenced (and filtered) by the capabilities
812 attached to the executed file. Due to
814 <varname>CapabilityBoundingSet=</varname>
815 is probably a much more useful
816 setting.</para></listitem>
820 <term><varname>ReadWriteDirectories=</varname></term>
821 <term><varname>ReadOnlyDirectories=</varname></term>
822 <term><varname>InaccessibleDirectories=</varname></term>
824 <listitem><para>Sets up a new file
825 system namespace for executed
826 processes. These options may be used
827 to limit access a process might have
828 to the main file system
829 hierarchy. Each setting takes a
830 space-separated list of absolute
831 directory paths. Directories listed in
832 <varname>ReadWriteDirectories=</varname>
833 are accessible from within the
834 namespace with the same access rights
835 as from outside. Directories listed in
836 <varname>ReadOnlyDirectories=</varname>
837 are accessible for reading only,
838 writing will be refused even if the
839 usual file access controls would
840 permit this. Directories listed in
841 <varname>InaccessibleDirectories=</varname>
842 will be made inaccessible for
843 processes inside the namespace. Note
844 that restricting access with these
845 options does not extend to submounts
846 of a directory that are created later
847 on. These options may be specified
848 more than once in which case all
849 directories listed will have limited
850 access from within the namespace. If
851 the empty string is assigned to this
852 option, the specific list is reset,
853 and all prior assignments have no
856 <varname>ReadOnlyDirectories=</varname>
858 <varname>InaccessibleDirectories=</varname>
860 <literal>-</literal>, in which case
861 they will be ignored when they do not
862 exist. Note that using this
863 setting will disconnect propagation of
864 mounts from the service to the host
865 (propagation in the opposite direction
866 continues to work). This means that
867 this setting may not be used for
868 services which shall be able to
869 install mount points in the main mount
870 namespace.</para></listitem>
874 <term><varname>PrivateTmp=</varname></term>
876 <listitem><para>Takes a boolean
877 argument. If true, sets up a new file
878 system namespace for the executed
879 processes and mounts private
880 <filename>/tmp</filename> and
881 <filename>/var/tmp</filename>
882 directories inside it that is not
883 shared by processes outside of the
884 namespace. This is useful to secure
885 access to temporary files of the
886 process, but makes sharing between
888 <filename>/tmp</filename> or
889 <filename>/var/tmp</filename>
890 impossible. If this is enabled, all
891 temporary files created by a service
892 in these directories will be removed
893 after the service is stopped. Defaults
894 to false. It is possible to run two or
895 more units within the same private
896 <filename>/tmp</filename> and
897 <filename>/var/tmp</filename>
898 namespace by using the
899 <varname>JoinsNamespaceOf=</varname>
901 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
902 for details. Note that using this
903 setting will disconnect propagation of
904 mounts from the service to the host
905 (propagation in the opposite direction
906 continues to work). This means that
907 this setting may not be used for
908 services which shall be able to install
909 mount points in the main mount
910 namespace.</para></listitem>
914 <term><varname>PrivateDevices=</varname></term>
916 <listitem><para>Takes a boolean
917 argument. If true, sets up a new /dev
918 namespace for the executed processes
919 and only adds API pseudo devices such
920 as <filename>/dev/null</filename>,
921 <filename>/dev/zero</filename> or
922 <filename>/dev/random</filename> (as
923 well as the pseudo TTY subsystem) to
924 it, but no physical devices such as
925 <filename>/dev/sda</filename>. This is
926 useful to securely turn off physical
927 device access by the executed
928 process. Defaults to false. Enabling
929 this option will also remove
930 <constant>CAP_MKNOD</constant> from
931 the capability bounding set for the
932 unit (see above), and set
933 <varname>DevicePolicy=closed</varname>
935 <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>
936 for details). Note that using this
937 setting will disconnect propagation of
938 mounts from the service to the host
939 (propagation in the opposite direction
940 continues to work). This means that
941 this setting may not be used for
942 services which shall be able to
943 install mount points in the main mount
944 namespace.</para></listitem>
948 <term><varname>PrivateNetwork=</varname></term>
950 <listitem><para>Takes a boolean
951 argument. If true, sets up a new
952 network namespace for the executed
953 processes and configures only the
954 loopback network device
955 <literal>lo</literal> inside it. No
956 other network devices will be
957 available to the executed process.
958 This is useful to securely turn off
959 network access by the executed
960 process. Defaults to false. It is
961 possible to run two or more units
962 within the same private network
963 namespace by using the
964 <varname>JoinsNamespaceOf=</varname>
966 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
967 for details. Note that this option
968 will disconnect all socket families
969 from the host, this includes
970 AF_NETLINK and AF_UNIX. The latter has
971 the effect that AF_UNIX sockets in the
972 abstract socket namespace will become
973 unavailable to the processes (however,
974 those located in the file system will
976 accessible).</para></listitem>
980 <term><varname>ProtectSystem=</varname></term>
982 <listitem><para>Takes a boolean
984 <literal>full</literal>. If true,
985 mounts the <filename>/usr</filename>
986 directory read-only for processes
987 invoked by this unit. If set to
988 <literal>full</literal>, the
989 <filename>/etc</filename> directory is mounted
990 read-only, too. This setting ensures
991 that any modification of the vendor
992 supplied operating system (and
993 optionally its configuration) is
994 prohibited for the service. It is
995 recommended to enable this setting for
996 all long-running services, unless they
997 are involved with system updates or
998 need to modify the operating system in
999 other ways. Note however that
1000 processes retaining the CAP_SYS_ADMIN
1001 capability can undo the effect of this
1002 setting. This setting is hence
1003 particularly useful for daemons which
1004 have this capability removed, for
1006 <varname>CapabilityBoundingSet=</varname>. Defaults
1007 to off.</para></listitem>
1011 <term><varname>ProtectHome=</varname></term>
1013 <listitem><para>Takes a boolean
1015 <literal>read-only</literal>. If true,
1017 <filename>/home</filename> and
1018 <filename>/run/user</filename> are
1019 made inaccessible and empty for
1020 processes invoked by this unit. If set
1021 to <literal>read-only</literal>, the
1022 two directories are made read-only
1023 instead. It is recommended to enable
1024 this setting for all long-running
1025 services (in particular network-facing
1026 ones), to ensure they cannot get access
1027 to private user data, unless the
1028 services actually require access to
1029 the user's private data. Note however
1030 that processes retaining the
1031 CAP_SYS_ADMIN capability can undo the
1032 effect of this setting. This setting
1033 is hence particularly useful for
1034 daemons which have this capability
1035 removed, for example with
1036 <varname>CapabilityBoundingSet=</varname>. Defaults
1037 to off.</para></listitem>
1041 <term><varname>MountFlags=</varname></term>
1043 <listitem><para>Takes a mount
1045 <option>shared</option>,
1046 <option>slave</option> or
1047 <option>private</option>, which
1048 control whether mounts in the file
1049 system namespace set up for this
1050 unit's processes will receive or
1051 propagate mounts or unmounts. See
1052 <citerefentry><refentrytitle>mount</refentrytitle><manvolnum>2</manvolnum></citerefentry>
1053 for details. Defaults to
1054 <option>shared</option>. Use
1055 <option>shared</option> to ensure that
1056 mounts and unmounts are propagated
1057 from the host to the container and
1058 vice versa. Use <option>slave</option>
1059 to run processes so that none of their
1060 mounts and unmounts will propagate to
1061 the host. Use <option>private</option>
1062 to also ensure that no mounts and
1063 unmounts from the host will propagate
1064 into the unit processes'
1065 namespace. Note that
1066 <option>slave</option> means that file
1067 systems mounted on the host might stay
1068 mounted continuously in the unit's
1069 namespace, and thus keep the device
1070 busy. Note that the file system
1071 namespace related options
1072 (<varname>PrivateTmp=</varname>,
1073 <varname>PrivateDevices=</varname>,
1074 <varname>ProtectSystem=</varname>,
1075 <varname>ProtectHome=</varname>,
1076 <varname>ReadOnlyDirectories=</varname>,
1077 <varname>InaccessibleDirectories=</varname>
1079 <varname>ReadWriteDirectories=</varname>)
1080 require that mount and unmount
1081 propagation from the unit's file
1082 system namespace is disabled, and
1084 <option>shared</option> to
1085 <option>slave</option>.
1090 <term><varname>UtmpIdentifier=</varname></term>
1092 <listitem><para>Takes a four
1093 character identifier string for an
1094 utmp/wtmp entry for this service. This
1095 should only be set for services such
1096 as <command>getty</command>
1097 implementations where utmp/wtmp
1098 entries must be created and cleared
1099 before and after execution. If the
1100 configured string is longer than four
1101 characters, it is truncated and the
1102 terminal four characters are
1103 used. This setting interprets %I style
1104 string replacements. This setting is
1105 unset by default, i.e. no utmp/wtmp
1106 entries are created or cleaned up for
1107 this service.</para></listitem>
1111 <term><varname>SELinuxContext=</varname></term>
1113 <listitem><para>Set the SELinux
1114 security context of the executed
1115 process. If set, this will override
1116 the automated domain
1117 transition. However, the policy still
1118 needs to autorize the transition. This
1119 directive is ignored if SELinux is
1120 disabled. If prefixed by
1121 <literal>-</literal>, all errors will
1123 <citerefentry><refentrytitle>setexeccon</refentrytitle><manvolnum>3</manvolnum></citerefentry>
1124 for details.</para></listitem>
1128 <term><varname>AppArmorProfile=</varname></term>
1130 <listitem><para>Takes a profile name as argument.
1131 The process executed by the unit will switch to
1132 this profile when started. Profiles must already
1133 be loaded in the kernel, or the unit will fail.
1134 This result in a non operation if AppArmor is not
1135 enabled. If prefixed by <literal>-</literal>, all errors
1141 <term><varname>IgnoreSIGPIPE=</varname></term>
1143 <listitem><para>Takes a boolean
1144 argument. If true, causes <constant>SIGPIPE</constant> to be
1145 ignored in the executed
1146 process. Defaults to true because
1147 <constant>SIGPIPE</constant> generally is useful only in
1148 shell pipelines.</para></listitem>
1152 <term><varname>NoNewPrivileges=</varname></term>
1154 <listitem><para>Takes a boolean
1155 argument. If true, ensures that the
1156 service process and all its children
1157 can never gain new privileges. This
1158 option is more powerful than the respective
1159 secure bits flags (see above), as it
1160 also prohibits UID changes of any
1161 kind. This is the simplest, most
1162 effective way to ensure that a process
1163 and its children can never elevate
1164 privileges again.</para></listitem>
1168 <term><varname>SystemCallFilter=</varname></term>
1170 <listitem><para>Takes a
1171 space-separated list of system call
1172 names. If this setting is used, all
1173 system calls executed by the unit
1174 processes except for the listed ones
1175 will result in immediate process
1176 termination with the
1177 <constant>SIGSYS</constant> signal
1178 (whitelisting). If the first character
1179 of the list is <literal>~</literal>,
1180 the effect is inverted: only the
1181 listed system calls will result in
1182 immediate process termination
1183 (blacklisting). If running in user
1184 mode and this option is used,
1185 <varname>NoNewPrivileges=yes</varname>
1186 is implied. This feature makes use of the
1187 Secure Computing Mode 2 interfaces of
1188 the kernel ('seccomp filtering') and
1189 is useful for enforcing a minimal
1190 sandboxing environment. Note that the
1191 <function>execve</function>,
1192 <function>rt_sigreturn</function>,
1193 <function>sigreturn</function>,
1194 <function>exit_group</function>,
1195 <function>exit</function> system calls
1196 are implicitly whitelisted and do not
1197 need to be listed explicitly. This
1198 option may be specified more than once
1199 in which case the filter masks are
1200 merged. If the empty string is
1201 assigned, the filter is reset, all
1202 prior assignments will have no
1205 <para>If you specify both types of
1206 this option (i.e. whitelisting and
1207 blacklisting), the first encountered
1208 will take precedence and will dictate
1209 the default action (termination or
1210 approval of a system call). Then the
1211 next occurrences of this option will
1212 add or delete the listed system calls
1213 from the set of the filtered system
1214 calls, depending of its type and the
1215 default action. (For example, if you have started
1216 with a whitelisting of
1217 <function>read</function> and
1218 <function>write</function>, and right
1219 after it add a blacklisting of
1220 <function>write</function>, then
1221 <function>write</function> will be
1222 removed from the set.)
1227 <term><varname>SystemCallErrorNumber=</varname></term>
1229 <listitem><para>Takes an
1230 <literal>errno</literal> error number
1231 name to return when the system call
1232 filter configured with
1233 <varname>SystemCallFilter=</varname>
1234 is triggered, instead of terminating
1235 the process immediately. Takes an
1237 <constant>EPERM</constant>,
1238 <constant>EACCES</constant> or
1239 <constant>EUCLEAN</constant>. When this
1240 setting is not used, or when the empty
1241 string is assigned, the process will be
1242 terminated immediately when the filter
1243 is triggered.</para></listitem>
1247 <term><varname>SystemCallArchitectures=</varname></term>
1249 <listitem><para>Takes a space
1250 separated list of architecture
1251 identifiers to include in the system
1252 call filter. The known architecture
1254 <constant>x86</constant>,
1255 <constant>x86-64</constant>,
1256 <constant>x32</constant>,
1257 <constant>arm</constant> as well as
1258 the special identifier
1259 <constant>native</constant>. Only
1260 system calls of the specified
1261 architectures will be permitted to
1262 processes of this unit. This is an
1263 effective way to disable compatibility
1264 with non-native architectures for
1265 processes, for example to prohibit
1266 execution of 32-bit x86 binaries on
1267 64-bit x86-64 systems. The special
1268 <constant>native</constant> identifier
1269 implicitly maps to the native
1270 architecture of the system (or more
1271 strictly: to the architecture the
1272 system manager is compiled for). If
1273 running in user mode and this option
1275 <varname>NoNewPrivileges=yes</varname>
1276 is implied. Note that setting this
1277 option to a non-empty list implies
1278 that <constant>native</constant> is
1279 included too. By default, this option
1280 is set to the empty list, i.e. no
1281 architecture system call filtering is
1282 applied.</para></listitem>
1286 <term><varname>RestrictAddressFamilies=</varname></term>
1288 <listitem><para>Restricts the set of
1289 socket address families accessible to
1290 the processes of this unit. Takes a
1291 space-separated list of address family
1292 names to whitelist, such as
1293 <constant>AF_UNIX</constant>,
1294 <constant>AF_INET</constant> or
1295 <constant>AF_INET6</constant>. When
1296 prefixed with <constant>~</constant>
1297 the listed address families will be
1298 applied as blacklist, otherwise as
1299 whitelist. Note that this restricts
1301 <citerefentry><refentrytitle>socket</refentrytitle><manvolnum>2</manvolnum></citerefentry>
1302 system call only. Sockets passed into
1303 the process by other means (for
1304 example, by using socket activation
1305 with socket units, see
1306 <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>)
1307 are unaffected. Also, sockets created
1308 with <function>socketpair()</function>
1309 (which creates connected AF_UNIX
1310 sockets only) are unaffected. Note
1311 that this option has no effect on
1312 32-bit x86 and is ignored (but works
1313 correctly on x86-64). If running in user
1314 mode and this option is used,
1315 <varname>NoNewPrivileges=yes</varname>
1316 is implied. By default, no
1317 restriction applies, all address
1318 families are accessible to
1319 processes. If assigned the empty
1320 string, any previous list changes are
1323 <para>Use this option to limit
1324 exposure of processes to remote
1325 systems, in particular via exotic
1326 network protocols. Note that in most
1328 <constant>AF_UNIX</constant> address
1329 family should be included in the
1330 configured whitelist as it is
1331 frequently used for local
1332 communication, including for
1333 <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>2</manvolnum></citerefentry>
1334 logging.</para></listitem>
1338 <term><varname>Personality=</varname></term>
1340 <listitem><para>Controls which
1342 <citerefentry><refentrytitle>uname</refentrytitle><manvolnum>2</manvolnum></citerefentry>
1343 shall report, when invoked by unit
1344 processes. Takes one of
1345 <constant>x86</constant> and
1346 <constant>x86-64</constant>. This is
1347 useful when running 32-bit services on
1348 a 64-bit host system. If not specified,
1349 the personality is left unmodified and
1350 thus reflects the personality of the
1352 kernel.</para></listitem>
1356 <term><varname>RuntimeDirectory=</varname></term>
1357 <term><varname>RuntimeDirectoryMode=</varname></term>
1359 <listitem><para>Takes a list of
1360 directory names. If set, one or more
1361 directories by the specified names
1362 will be created below
1363 <filename>/run</filename> (for system
1365 <varname>$XDG_RUNTIME_DIR</varname>
1366 (for user services) when the unit is
1367 started, and removed when the unit is
1368 stopped. The directories will have the
1369 access mode specified in
1370 <varname>RuntimeDirectoryMode=</varname>,
1371 and will be owned by the user and
1373 <varname>User=</varname> and
1374 <varname>Group=</varname>. Use this to
1375 manage one or more runtime directories
1376 of the unit and bind their lifetime to
1377 the daemon runtime. The specified
1378 directory names must be relative, and
1380 <literal>/</literal>, i.e. must refer
1381 to simple directories to create or
1382 remove. This is particularly useful
1383 for unprivileged daemons that cannot
1384 create runtime directories in
1385 <filename>/run</filename> due to lack
1386 of privileges, and to make sure the
1387 runtime directory is cleaned up
1388 automatically after use. For runtime
1389 directories that require more complex
1390 or different configuration or lifetime
1391 guarantees, please consider using
1392 <citerefentry><refentrytitle>tmpfiles.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
1399 <title>Environment variables in spawned processes</title>
1401 <para>Processes started by the system are executed in
1402 a clean environment in which select variables
1403 listed below are set. System processes started by systemd
1404 do not inherit variables from PID 1, but processes
1405 started by user systemd instances inherit all
1406 environment variables from the user systemd instance.
1409 <variablelist class='environment-variables'>
1411 <term><varname>$PATH</varname></term>
1413 <listitem><para>Colon-separated list
1414 of directiories to use when launching
1415 executables. Systemd uses a fixed
1417 <filename>/usr/local/sbin</filename>:<filename>/usr/local/bin</filename>:<filename>/usr/sbin</filename>:<filename>/usr/bin</filename>:<filename>/sbin</filename>:<filename>/bin</filename>.
1422 <term><varname>$LANG</varname></term>
1424 <listitem><para>Locale. Can be set in
1425 <citerefentry><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1426 or on the kernel command line (see
1427 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
1429 <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>).
1434 <term><varname>$USER</varname></term>
1435 <term><varname>$LOGNAME</varname></term>
1436 <term><varname>$HOME</varname></term>
1437 <term><varname>$SHELL</varname></term>
1439 <listitem><para>User name (twice), home
1440 directory, and the login shell.
1441 The variables are set for the units that
1442 have <varname>User=</varname> set,
1444 <command>systemd</command> instances.
1446 <citerefentry><refentrytitle>passwd</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
1451 <term><varname>$XDG_RUNTIME_DIR</varname></term>
1453 <listitem><para>The directory for volatile
1454 state. Set for the user <command>systemd</command>
1455 instance, and also in user sessions.
1457 <citerefentry><refentrytitle>pam_systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
1462 <term><varname>$XDG_SESSION_ID</varname></term>
1463 <term><varname>$XDG_SEAT</varname></term>
1464 <term><varname>$XDG_VTNR</varname></term>
1466 <listitem><para>The identifier of the
1467 session, the seat name, and
1468 virtual terminal of the session. Set
1470 <citerefentry><refentrytitle>pam_systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1472 <varname>$XDG_SEAT</varname> and
1473 <varname>$XDG_VTNR</varname> will
1474 only be set when attached to a seat and a
1475 tty.</para></listitem>
1479 <term><varname>$MAINPID</varname></term>
1481 <listitem><para>The PID of the units
1482 main process if it is known. This is
1483 only set for control processes as
1485 <varname>ExecReload=</varname> and
1486 similar. </para></listitem>
1490 <term><varname>$MANAGERPID</varname></term>
1492 <listitem><para>The PID of the user
1493 <command>systemd</command> instance,
1494 set for processes spawned by it.
1499 <term><varname>$LISTEN_FDS</varname></term>
1500 <term><varname>$LISTEN_PID</varname></term>
1502 <listitem><para>Information about file
1503 descriptors passed to a service for
1504 socket activation. See
1505 <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
1510 <term><varname>$TERM</varname></term>
1512 <listitem><para>Terminal type, set
1513 only for units connected to a terminal
1514 (<varname>StandardInput=tty</varname>,
1515 <varname>StandardOutput=tty</varname>,
1517 <varname>StandardError=tty</varname>).
1519 <citerefentry project='man-pages'><refentrytitle>termcap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
1524 <para>Additional variables may be configured by the
1525 following means: for processes spawned in specific
1526 units, use the <varname>Environment=</varname> and
1527 <varname>EnvironmentFile=</varname> options above; to
1528 specify variables globally, use
1529 <varname>DefaultEnvironment=</varname> (see
1530 <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>)
1531 or the kernel option
1532 <varname>systemd.setenv=</varname> (see
1533 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>). Additional
1534 variables may also be set through PAM,
1535 cf. <citerefentry project='man-pages'><refentrytitle>pam_env</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
1539 <title>See Also</title>
1541 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1542 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1543 <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
1544 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1545 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1546 <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1547 <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1548 <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1549 <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1550 <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1551 <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1552 <citerefentry><refentrytitle>tmpfiles.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1553 <citerefentry project='man-pages'><refentrytitle>exec</refentrytitle><manvolnum>3</manvolnum></citerefentry>