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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
This file is part of systemd.
Copyright 2010 Lennart Poettering
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
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You should have received a copy of the GNU Lesser General Public License
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-->
<refentry id="systemd.exec">
<refentryinfo>
<title>systemd.exec</title>
<productname>systemd</productname>
<authorgroup>
<author>
<contrib>Developer</contrib>
<firstname>Lennart</firstname>
<surname>Poettering</surname>
<email>lennart@poettering.net</email>
</author>
</authorgroup>
</refentryinfo>
<refmeta>
<refentrytitle>systemd.exec</refentrytitle>
<manvolnum>5</manvolnum>
</refmeta>
<refnamediv>
<refname>systemd.exec</refname>
<refpurpose>Execution environment configuration</refpurpose>
</refnamediv>
<refsynopsisdiv>
<para><filename><replaceable>service</replaceable>.service</filename>,
<filename><replaceable>socket</replaceable>.socket</filename>,
<filename><replaceable>mount</replaceable>.mount</filename>,
<filename><replaceable>swap</replaceable>.swap</filename></para>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>Unit configuration files for services, sockets, mount
points, and swap devices share a subset of configuration options
which define the execution environment of spawned
processes.</para>
<para>This man page lists the configuration options shared by
these four unit types. See
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for the common options of all unit configuration files, and
<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
and
<citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for more information on the specific unit configuration files. The
execution specific configuration options are configured in the
[Service], [Socket], [Mount], or [Swap] sections, depending on the
unit type.</para>
</refsect1>
<refsect1>
<title>Options</title>
<variablelist class='unit-directives'>
<varlistentry>
<term><varname>WorkingDirectory=</varname></term>
<listitem><para>Takes an absolute directory path. Sets the
working directory for executed processes. If not set, defaults
to the root directory when systemd is running as a system
instance and the respective user's home directory if run as
user.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>RootDirectory=</varname></term>
<listitem><para>Takes an absolute directory path. Sets the
root directory for executed processes, with the
<citerefentry project='man-pages'><refentrytitle>chroot</refentrytitle><manvolnum>2</manvolnum></citerefentry>
system call. If this is used, it must be ensured that the
process and all its auxiliary files are available in the
<function>chroot()</function> jail.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>User=</varname></term>
<term><varname>Group=</varname></term>
<listitem><para>Sets the Unix user or group that the processes
are executed as, respectively. Takes a single user or group
name or ID as argument. If no group is set, the default group
of the user is chosen.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>SupplementaryGroups=</varname></term>
<listitem><para>Sets the supplementary Unix groups the
processes are executed as. This takes a space-separated list
of group names or IDs. This option may be specified more than
once in which case all listed groups are set as supplementary
groups. When the empty string is assigned the list of
supplementary groups is reset, and all assignments prior to
this one will have no effect. In any way, this option does not
override, but extends the list of supplementary groups
configured in the system group database for the
user.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Nice=</varname></term>
<listitem><para>Sets the default nice level (scheduling
priority) for executed processes. Takes an integer between -20
(highest priority) and 19 (lowest priority). See
<citerefentry><refentrytitle>setpriority</refentrytitle><manvolnum>2</manvolnum></citerefentry>
for details.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>OOMScoreAdjust=</varname></term>
<listitem><para>Sets the adjustment level for the
Out-Of-Memory killer for executed processes. Takes an integer
between -1000 (to disable OOM killing for this process) and
1000 (to make killing of this process under memory pressure
very likely). See <ulink
url="https://www.kernel.org/doc/Documentation/filesystems/proc.txt">proc.txt</ulink>
for details.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>IOSchedulingClass=</varname></term>
<listitem><para>Sets the IO scheduling class for executed
processes. Takes an integer between 0 and 3 or one of the
strings <option>none</option>, <option>realtime</option>,
<option>best-effort</option> or <option>idle</option>. See
<citerefentry><refentrytitle>ioprio_set</refentrytitle><manvolnum>2</manvolnum></citerefentry>
for details.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>IOSchedulingPriority=</varname></term>
<listitem><para>Sets the IO scheduling priority for executed
processes. Takes an integer between 0 (highest priority) and 7
(lowest priority). The available priorities depend on the
selected IO scheduling class (see above). See
<citerefentry><refentrytitle>ioprio_set</refentrytitle><manvolnum>2</manvolnum></citerefentry>
for details.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>CPUSchedulingPolicy=</varname></term>
<listitem><para>Sets the CPU scheduling policy for executed
processes. Takes one of
<option>other</option>,
<option>batch</option>,
<option>idle</option>,
<option>fifo</option> or
<option>rr</option>. See
<citerefentry><refentrytitle>sched_setscheduler</refentrytitle><manvolnum>2</manvolnum></citerefentry>
for details.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>CPUSchedulingPriority=</varname></term>
<listitem><para>Sets the CPU scheduling priority for executed
processes. The available priority range depends on the
selected CPU scheduling policy (see above). For real-time
scheduling policies an integer between 1 (lowest priority) and
99 (highest priority) can be used. See
<citerefentry><refentrytitle>sched_setscheduler</refentrytitle><manvolnum>2</manvolnum></citerefentry>
for details. </para></listitem>
</varlistentry>
<varlistentry>
<term><varname>CPUSchedulingResetOnFork=</varname></term>
<listitem><para>Takes a boolean argument. If true, elevated
CPU scheduling priorities and policies will be reset when the
executed processes fork, and can hence not leak into child
processes. See
<citerefentry><refentrytitle>sched_setscheduler</refentrytitle><manvolnum>2</manvolnum></citerefentry>
for details. Defaults to false.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>CPUAffinity=</varname></term>
<listitem><para>Controls the CPU affinity of the executed
processes. Takes a space-separated list of CPU indices. This
option may be specified more than once in which case the
specified CPU affinity masks are merged. If the empty string
is assigned, the mask is reset, all assignments prior to this
will have no effect. See
<citerefentry><refentrytitle>sched_setaffinity</refentrytitle><manvolnum>2</manvolnum></citerefentry>
for details.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>UMask=</varname></term>
<listitem><para>Controls the file mode creation mask. Takes an
access mode in octal notation. See
<citerefentry><refentrytitle>umask</refentrytitle><manvolnum>2</manvolnum></citerefentry>
for details. Defaults to 0022.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Environment=</varname></term>
<listitem><para>Sets environment variables for executed
processes. Takes a space-separated list of variable
assignments. This option may be specified more than once in
which case all listed variables will be set. If the same
variable is set twice, the later setting will override the
earlier setting. If the empty string is assigned to this
option, the list of environment variables is reset, all prior
assignments have no effect. Variable expansion is not
performed inside the strings, however, specifier expansion is
possible. The $ character has no special meaning. If you need
to assign a value containing spaces to a variable, use double
quotes (") for the assignment.</para>
<para>Example:
<programlisting>Environment="VAR1=word1 word2" VAR2=word3 "VAR3=$word 5 6"</programlisting>
gives three variables <literal>VAR1</literal>,
<literal>VAR2</literal>, <literal>VAR3</literal>
with the values <literal>word1 word2</literal>,
<literal>word3</literal>, <literal>$word 5 6</literal>.
</para>
<para>
See
<citerefentry project='man-pages'><refentrytitle>environ</refentrytitle><manvolnum>7</manvolnum></citerefentry>
for details about environment variables.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>EnvironmentFile=</varname></term>
<listitem><para>Similar to <varname>Environment=</varname> but
reads the environment variables from a text file. The text
file should contain new-line-separated variable assignments.
Empty lines and lines starting with ; or # will be ignored,
which may be used for commenting. A line ending with a
backslash will be concatenated with the following one,
allowing multiline variable definitions. The parser strips
leading and trailing whitespace from the values of
assignments, unless you use double quotes (").</para>
<para>The argument passed should be an absolute filename or
wildcard expression, optionally prefixed with
<literal>-</literal>, which indicates that if the file does
not exist, it will not be read and no error or warning message
is logged. This option may be specified more than once in
which case all specified files are read. If the empty string
is assigned to this option, the list of file to read is reset,
all prior assignments have no effect.</para>
<para>The files listed with this directive will be read
shortly before the process is executed (more specifically,
after all processes from a previous unit state terminated.
This means you can generate these files in one unit state, and
read it with this option in the next). Settings from these
files override settings made with
<varname>Environment=</varname>. If the same variable is set
twice from these files, the files will be read in the order
they are specified and the later setting will override the
earlier setting.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>StandardInput=</varname></term>
<listitem><para>Controls where file descriptor 0 (STDIN) of
the executed processes is connected to. Takes one of
<option>null</option>,
<option>tty</option>,
<option>tty-force</option>,
<option>tty-fail</option> or
<option>socket</option>.</para>
<para>If <option>null</option> is selected, standard input
will be connected to <filename>/dev/null</filename>, i.e. all
read attempts by the process will result in immediate
EOF.</para>
<para>If <option>tty</option> is selected, standard input is
connected to a TTY (as configured by
<varname>TTYPath=</varname>, see below) and the executed
process becomes the controlling process of the terminal. If
the terminal is already being controlled by another process,
the executed process waits until the current controlling
process releases the terminal.</para>
<para><option>tty-force</option> is similar to
<option>tty</option>, but the executed process is forcefully
and immediately made the controlling process of the terminal,
potentially removing previous controlling processes from the
terminal.</para>
<para><option>tty-fail</option> is similar to
<option>tty</option> but if the terminal already has a
controlling process start-up of the executed process
fails.</para>
<para>The <option>socket</option> option is only valid in
socket-activated services, and only when the socket
configuration file (see
<citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for details) specifies a single socket only. If this option is
set, standard input will be connected to the socket the
service was activated from, which is primarily useful for
compatibility with daemons designed for use with the
traditional
<citerefentry><refentrytitle>inetd</refentrytitle><manvolnum>8</manvolnum></citerefentry>
daemon.</para>
<para>This setting defaults to
<option>null</option>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>StandardOutput=</varname></term>
<listitem><para>Controls where file descriptor 1 (STDOUT) of
the executed processes is connected to. Takes one of
<option>inherit</option>,
<option>null</option>,
<option>tty</option>,
<option>journal</option>,
<option>syslog</option>,
<option>kmsg</option>,
<option>journal+console</option>,
<option>syslog+console</option>,
<option>kmsg+console</option> or
<option>socket</option>.</para>
<para><option>inherit</option> duplicates the file descriptor
of standard input for standard output.</para>
<para><option>null</option> connects standard output to
<filename>/dev/null</filename>, i.e. everything written to it
will be lost.</para>
<para><option>tty</option> connects standard output to a tty
(as configured via <varname>TTYPath=</varname>, see below). If
the TTY is used for output only, the executed process will not
become the controlling process of the terminal, and will not
fail or wait for other processes to release the
terminal.</para>
<para><option>journal</option> connects standard output with
the journal which is accessible via
<citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
Note that everything that is written to syslog or kmsg (see
below) is implicitly stored in the journal as well, the
specific two options listed below are hence supersets of this
one.</para>
<para><option>syslog</option> connects standard output to the
<citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
system syslog service, in addition to the journal. Note that
the journal daemon is usually configured to forward everything
it receives to syslog anyway, in which case this option is no
different from <option>journal</option>.</para>
<para><option>kmsg</option> connects standard output with the
kernel log buffer which is accessible via
<citerefentry project='man-pages'><refentrytitle>dmesg</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
in addition to the journal. The journal daemon might be
configured to send all logs to kmsg anyway, in which case this
option is no different from <option>journal</option>.</para>
<para><option>journal+console</option>,
<option>syslog+console</option> and
<option>kmsg+console</option> work in a similar way as the
three options above but copy the output to the system console
as well.</para>
<para><option>socket</option> connects standard output to a
socket acquired via socket activation. The semantics are
similar to the same option of
<varname>StandardInput=</varname>.</para>
<para>This setting defaults to the value set with
<option>DefaultStandardOutput=</option> in
<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
which defaults to <option>journal</option>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>StandardError=</varname></term>
<listitem><para>Controls where file descriptor 2 (STDERR) of
the executed processes is connected to. The available options
are identical to those of <varname>StandardOutput=</varname>,
with one exception: if set to <option>inherit</option> the
file descriptor used for standard output is duplicated for
standard error. This setting defaults to the value set with
<option>DefaultStandardError=</option> in
<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
which defaults to <option>inherit</option>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>TTYPath=</varname></term>
<listitem><para>Sets the terminal device node to use if
standard input, output, or error are connected to a TTY (see
above). Defaults to
<filename>/dev/console</filename>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>TTYReset=</varname></term>
<listitem><para>Reset the terminal device specified with
<varname>TTYPath=</varname> before and after execution.
Defaults to <literal>no</literal>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>TTYVHangup=</varname></term>
<listitem><para>Disconnect all clients which have opened the
terminal device specified with <varname>TTYPath=</varname>
before and after execution. Defaults to
<literal>no</literal>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>TTYVTDisallocate=</varname></term>
<listitem><para>If the terminal device specified with
<varname>TTYPath=</varname> is a virtual console terminal, try
to deallocate the TTY before and after execution. This ensures
that the screen and scrollback buffer is cleared. Defaults to
<literal>no</literal>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>SyslogIdentifier=</varname></term>
<listitem><para>Sets the process name to prefix log lines sent
to the logging system or the kernel log buffer with. If not
set, defaults to the process name of the executed process.
This option is only useful when
<varname>StandardOutput=</varname> or
<varname>StandardError=</varname> are set to
<option>syslog</option>, <option>journal</option> or
<option>kmsg</option> (or to the same settings in combination
with <option>+console</option>).</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>SyslogFacility=</varname></term>
<listitem><para>Sets the syslog facility to use when logging
to syslog. One of <option>kern</option>,
<option>user</option>, <option>mail</option>,
<option>daemon</option>, <option>auth</option>,
<option>syslog</option>, <option>lpr</option>,
<option>news</option>, <option>uucp</option>,
<option>cron</option>, <option>authpriv</option>,
<option>ftp</option>, <option>local0</option>,
<option>local1</option>, <option>local2</option>,
<option>local3</option>, <option>local4</option>,
<option>local5</option>, <option>local6</option> or
<option>local7</option>. See
<citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
for details. This option is only useful when
<varname>StandardOutput=</varname> or
<varname>StandardError=</varname> are set to
<option>syslog</option>. Defaults to
<option>daemon</option>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>SyslogLevel=</varname></term>
<listitem><para>Default syslog level to use when logging to
syslog or the kernel log buffer. One of
<option>emerg</option>,
<option>alert</option>,
<option>crit</option>,
<option>err</option>,
<option>warning</option>,
<option>notice</option>,
<option>info</option>,
<option>debug</option>. See
<citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
for details. This option is only useful when
<varname>StandardOutput=</varname> or
<varname>StandardError=</varname> are set to
<option>syslog</option> or <option>kmsg</option>. Note that
individual lines output by the daemon might be prefixed with a
different log level which can be used to override the default
log level specified here. The interpretation of these prefixes
may be disabled with <varname>SyslogLevelPrefix=</varname>,
see below. For details see
<citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
Defaults to
<option>info</option>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>SyslogLevelPrefix=</varname></term>
<listitem><para>Takes a boolean argument. If true and
<varname>StandardOutput=</varname> or
<varname>StandardError=</varname> are set to
<option>syslog</option>, <option>kmsg</option> or
<option>journal</option>, log lines written by the executed
process that are prefixed with a log level will be passed on
to syslog with this log level set but the prefix removed. If
set to false, the interpretation of these prefixes is disabled
and the logged lines are passed on as-is. For details about
this prefixing see
<citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
Defaults to true.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>TimerSlackNSec=</varname></term>
<listitem><para>Sets the timer slack in nanoseconds for the
executed processes. The timer slack controls the accuracy of
wake-ups triggered by timers. See
<citerefentry><refentrytitle>prctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
for more information. Note that in contrast to most other time
span definitions this parameter takes an integer value in
nano-seconds if no unit is specified. The usual time units are
understood too.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>LimitCPU=</varname></term>
<term><varname>LimitFSIZE=</varname></term>
<term><varname>LimitDATA=</varname></term>
<term><varname>LimitSTACK=</varname></term>
<term><varname>LimitCORE=</varname></term>
<term><varname>LimitRSS=</varname></term>
<term><varname>LimitNOFILE=</varname></term>
<term><varname>LimitAS=</varname></term>
<term><varname>LimitNPROC=</varname></term>
<term><varname>LimitMEMLOCK=</varname></term>
<term><varname>LimitLOCKS=</varname></term>
<term><varname>LimitSIGPENDING=</varname></term>
<term><varname>LimitMSGQUEUE=</varname></term>
<term><varname>LimitNICE=</varname></term>
<term><varname>LimitRTPRIO=</varname></term>
<term><varname>LimitRTTIME=</varname></term>
<listitem><para>These settings set both soft and hard limits
of various resources for executed processes. See
<citerefentry><refentrytitle>setrlimit</refentrytitle><manvolnum>2</manvolnum></citerefentry>
for details. Use the string <varname>infinity</varname> to
configure no limit on a specific resource.</para></listitem>
<table>
<title>Limit directives and their equivalent with ulimit</title>
<tgroup cols='2'>
<colspec colname='directive' />
<colspec colname='equivalent' />
<thead>
<row>
<entry>Directive</entry>
<entry>ulimit equivalent</entry>
</row>
</thead>
<tbody>
<row>
<entry>LimitCPU</entry>
<entry>ulimit -t</entry>
</row>
<row>
<entry>LimitFSIZE</entry>
<entry>ulimit -f</entry>
</row>
<row>
<entry>LimitDATA</entry>
<entry>ulimit -d</entry>
</row>
<row>
<entry>LimitSTACK</entry>
<entry>ulimit -s</entry>
</row>
<row>
<entry>LimitCORE</entry>
<entry>ulimit -c</entry>
</row>
<row>
<entry>LimitRSS</entry>
<entry>ulimit -m</entry>
</row>
<row>
<entry>LimitNOFILE</entry>
<entry>ulimit -n</entry>
</row>
<row>
<entry>LimitAS</entry>
<entry>ulimit -v</entry>
</row>
<row>
<entry>LimitNPROC</entry>
<entry>ulimit -u</entry>
</row>
<row>
<entry>LimitMEMLOCK</entry>
<entry>ulimit -l</entry>
</row>
<row>
<entry>LimitLOCKS</entry>
<entry>ulimit -x</entry>
</row>
<row>
<entry>LimitSIGPENDING</entry>
<entry>ulimit -i</entry>
</row>
<row>
<entry>LimitMSGQUEUE</entry>
<entry>ulimit -q</entry>
</row>
<row>
<entry>LimitNICE</entry>
<entry>ulimit -e</entry>
</row>
<row>
<entry>LimitRTPRIO</entry>
<entry>ulimit -r</entry>
</row>
<row>
<entry>LimitRTTIME</entry>
<entry>No equivalent</entry>
</row>
</tbody>
</tgroup>
</table>
</varlistentry>
<varlistentry>
<term><varname>PAMName=</varname></term>
<listitem><para>Sets the PAM service name to set up a session
as. If set, the executed process will be registered as a PAM
session under the specified service name. This is only useful
in conjunction with the <varname>User=</varname> setting. If
not set, no PAM session will be opened for the executed
processes. See
<citerefentry project='man-pages'><refentrytitle>pam</refentrytitle><manvolnum>8</manvolnum></citerefentry>
for details.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>CapabilityBoundingSet=</varname></term>
<listitem><para>Controls which capabilities to include in the
capability bounding set for the executed process. See
<citerefentry project='man-pages'><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
for details. Takes a whitespace-separated list of capability
names as read by
<citerefentry><refentrytitle>cap_from_name</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
e.g. <constant>CAP_SYS_ADMIN</constant>,
<constant>CAP_DAC_OVERRIDE</constant>,
<constant>CAP_SYS_PTRACE</constant>. Capabilities listed will
be included in the bounding set, all others are removed. If
the list of capabilities is prefixed with
<literal>~</literal>, all but the listed capabilities will be
included, the effect of the assignment inverted. Note that
this option also affects the respective capabilities in the
effective, permitted and inheritable capability sets, on top
of what <varname>Capabilities=</varname> does. If this option
is not used, the capability bounding set is not modified on
process execution, hence no limits on the capabilities of the
process are enforced. This option may appear more than once in
which case the bounding sets are merged. If the empty string
is assigned to this option, the bounding set is reset to the
empty capability set, and all prior settings have no effect.
If set to <literal>~</literal> (without any further argument),
the bounding set is reset to the full set of available
capabilities, also undoing any previous
settings.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>SecureBits=</varname></term>
<listitem><para>Controls the secure bits set for the executed
process. Takes a space-separated combination of options from
the following list:
<option>keep-caps</option>,
<option>keep-caps-locked</option>,
<option>no-setuid-fixup</option>,
<option>no-setuid-fixup-locked</option>,
<option>noroot</option>, and
<option>noroot-locked</option>.
This option may appear more than once in which case the secure
bits are ORed. If the empty string is assigned to this option,
the bits are reset to 0. See
<citerefentry project='man-pages'><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
for details.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Capabilities=</varname></term>
<listitem><para>Controls the
<citerefentry project='man-pages'><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
set for the executed process. Take a capability string
describing the effective, permitted and inherited capability
sets as documented in
<citerefentry><refentrytitle>cap_from_text</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
Note that these capability sets are usually influenced (and
filtered) by the capabilities attached to the executed file.
Due to that <varname>CapabilityBoundingSet=</varname> is
probably a much more useful setting.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>ReadWriteDirectories=</varname></term>
<term><varname>ReadOnlyDirectories=</varname></term>
<term><varname>InaccessibleDirectories=</varname></term>
<listitem><para>Sets up a new file system namespace for
executed processes. These options may be used to limit access
a process might have to the main file system hierarchy. Each
setting takes a space-separated list of absolute directory
paths. Directories listed in
<varname>ReadWriteDirectories=</varname> are accessible from
within the namespace with the same access rights as from
outside. Directories listed in
<varname>ReadOnlyDirectories=</varname> are accessible for
reading only, writing will be refused even if the usual file
access controls would permit this. Directories listed in
<varname>InaccessibleDirectories=</varname> will be made
inaccessible for processes inside the namespace. Note that
restricting access with these options does not extend to
submounts of a directory that are created later on. These
options may be specified more than once in which case all
directories listed will have limited access from within the
namespace. If the empty string is assigned to this option, the
specific list is reset, and all prior assignments have no
effect.</para>
<para>Paths in
<varname>ReadOnlyDirectories=</varname>
and
<varname>InaccessibleDirectories=</varname>
may be prefixed with
<literal>-</literal>, in which case
they will be ignored when they do not
exist. Note that using this
setting will disconnect propagation of
mounts from the service to the host
(propagation in the opposite direction
continues to work). This means that
this setting may not be used for
services which shall be able to
install mount points in the main mount
namespace.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>PrivateTmp=</varname></term>
<listitem><para>Takes a boolean argument. If true, sets up a
new file system namespace for the executed processes and
mounts private <filename>/tmp</filename> and
<filename>/var/tmp</filename> directories inside it that is
not shared by processes outside of the namespace. This is
useful to secure access to temporary files of the process, but
makes sharing between processes via <filename>/tmp</filename>
or <filename>/var/tmp</filename> impossible. If this is
enabled, all temporary files created by a service in these
directories will be removed after the service is stopped.
Defaults to false. It is possible to run two or more units
within the same private <filename>/tmp</filename> and
<filename>/var/tmp</filename> namespace by using the
<varname>JoinsNamespaceOf=</varname> directive, see
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for details. Note that using this setting will disconnect
propagation of mounts from the service to the host
(propagation in the opposite direction continues to work).
This means that this setting may not be used for services
which shall be able to install mount points in the main mount
namespace.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>PrivateDevices=</varname></term>
<listitem><para>Takes a boolean argument. If true, sets up a
new /dev namespace for the executed processes and only adds
API pseudo devices such as <filename>/dev/null</filename>,
<filename>/dev/zero</filename> or
<filename>/dev/random</filename> (as well as the pseudo TTY
subsystem) to it, but no physical devices such as
<filename>/dev/sda</filename>. This is useful to securely turn
off physical device access by the executed process. Defaults
to false. Enabling this option will also remove
<constant>CAP_MKNOD</constant> from the capability bounding
set for the unit (see above), and set
<varname>DevicePolicy=closed</varname> (see
<citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for details). Note that using this setting will disconnect
propagation of mounts from the service to the host
(propagation in the opposite direction continues to work).
This means that this setting may not be used for services
which shall be able to install mount points in the main mount
namespace.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>PrivateNetwork=</varname></term>
<listitem><para>Takes a boolean argument. If true, sets up a
new network namespace for the executed processes and
configures only the loopback network device
<literal>lo</literal> inside it. No other network devices will
be available to the executed process. This is useful to
securely turn off network access by the executed process.
Defaults to false. It is possible to run two or more units
within the same private network namespace by using the
<varname>JoinsNamespaceOf=</varname> directive, see
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for details. Note that this option will disconnect all socket
families from the host, this includes AF_NETLINK and AF_UNIX.
The latter has the effect that AF_UNIX sockets in the abstract
socket namespace will become unavailable to the processes
(however, those located in the file system will continue to be
accessible).</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>ProtectSystem=</varname></term>
<listitem><para>Takes a boolean argument or
<literal>full</literal>. If true, mounts the
<filename>/usr</filename> and <filename>/boot</filename>
directories read-only for processes invoked by this unit. If
set to <literal>full</literal>, the <filename>/etc</filename>
directory is mounted read-only, too. This setting ensures that
any modification of the vendor supplied operating system (and
optionally its configuration) is prohibited for the service.
It is recommended to enable this setting for all long-running
services, unless they are involved with system updates or need
to modify the operating system in other ways. Note however
that processes retaining the CAP_SYS_ADMIN capability can undo
the effect of this setting. This setting is hence particularly
useful for daemons which have this capability removed, for
example with <varname>CapabilityBoundingSet=</varname>.
Defaults to off.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>ProtectHome=</varname></term>
<listitem><para>Takes a boolean argument or
<literal>read-only</literal>. If true, the directories
<filename>/home</filename> and <filename>/run/user</filename>
are made inaccessible and empty for processes invoked by this
unit. If set to <literal>read-only</literal>, the two
directories are made read-only instead. It is recommended to
enable this setting for all long-running services (in
particular network-facing ones), to ensure they cannot get
access to private user data, unless the services actually
require access to the user's private data. Note however that
processes retaining the CAP_SYS_ADMIN capability can undo the
effect of this setting. This setting is hence particularly
useful for daemons which have this capability removed, for
example with <varname>CapabilityBoundingSet=</varname>.
Defaults to off.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>MountFlags=</varname></term>
<listitem><para>Takes a mount propagation flag:
<option>shared</option>, <option>slave</option> or
<option>private</option>, which control whether mounts in the
file system namespace set up for this unit's processes will
receive or propagate mounts or unmounts. See
<citerefentry><refentrytitle>mount</refentrytitle><manvolnum>2</manvolnum></citerefentry>
for details. Defaults to <option>shared</option>. Use
<option>shared</option> to ensure that mounts and unmounts are
propagated from the host to the container and vice versa. Use
<option>slave</option> to run processes so that none of their
mounts and unmounts will propagate to the host. Use
<option>private</option> to also ensure that no mounts and
unmounts from the host will propagate into the unit processes'
namespace. Note that <option>slave</option> means that file
systems mounted on the host might stay mounted continuously in
the unit's namespace, and thus keep the device busy. Note that
the file system namespace related options
(<varname>PrivateTmp=</varname>,
<varname>PrivateDevices=</varname>,
<varname>ProtectSystem=</varname>,
<varname>ProtectHome=</varname>,
<varname>ReadOnlyDirectories=</varname>,
<varname>InaccessibleDirectories=</varname> and
<varname>ReadWriteDirectories=</varname>) require that mount
and unmount propagation from the unit's file system namespace
is disabled, and hence downgrade <option>shared</option> to
<option>slave</option>. </para></listitem>
</varlistentry>
<varlistentry>
<term><varname>UtmpIdentifier=</varname></term>
<listitem><para>Takes a four character identifier string for
an utmp/wtmp entry for this service. This should only be set
for services such as <command>getty</command> implementations
where utmp/wtmp entries must be created and cleared before and
after execution. If the configured string is longer than four
characters, it is truncated and the terminal four characters
are used. This setting interprets %I style string
replacements. This setting is unset by default, i.e. no
utmp/wtmp entries are created or cleaned up for this
service.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>SELinuxContext=</varname></term>
<listitem><para>Set the SELinux security context of the
executed process. If set, this will override the automated
domain transition. However, the policy still needs to
authorize the transition. This directive is ignored if SELinux
is disabled. If prefixed by <literal>-</literal>, all errors
will be ignored. See
<citerefentry><refentrytitle>setexeccon</refentrytitle><manvolnum>3</manvolnum></citerefentry>
for details.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>AppArmorProfile=</varname></term>
<listitem><para>Takes a profile name as argument. The process
executed by the unit will switch to this profile when started.
Profiles must already be loaded in the kernel, or the unit
will fail. This result in a non operation if AppArmor is not
enabled. If prefixed by <literal>-</literal>, all errors will
be ignored. </para></listitem>
</varlistentry>
<varlistentry>
<term><varname>SmackProcessLabel=</varname></term>
<listitem><para>Takes a <option>SMACK64</option> security
label as argument. The process executed by the unit will be
started under this label and SMACK will decide whether the
processes is allowed to run or not based on it. The process
will continue to run under the label specified here unless the
executable has its own <option>SMACK64EXEC</option> label, in
which case the process will transition to run under that
label. When not specified, the label that systemd is running
under is used. This directive is ignored if SMACK is
disabled.</para>
<para>The value may be prefixed by <literal>-</literal>, in
which case all errors will be ignored. An empty value may be
specified to unset previous assignments.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>IgnoreSIGPIPE=</varname></term>
<listitem><para>Takes a boolean argument. If true, causes
<constant>SIGPIPE</constant> to be ignored in the executed
process. Defaults to true because <constant>SIGPIPE</constant>
generally is useful only in shell pipelines.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>NoNewPrivileges=</varname></term>
<listitem><para>Takes a boolean argument. If true, ensures
that the service process and all its children can never gain
new privileges. This option is more powerful than the
respective secure bits flags (see above), as it also prohibits
UID changes of any kind. This is the simplest, most effective
way to ensure that a process and its children can never
elevate privileges again.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>SystemCallFilter=</varname></term>
<listitem><para>Takes a space-separated list of system call
names. If this setting is used, all system calls executed by
the unit processes except for the listed ones will result in
immediate process termination with the
<constant>SIGSYS</constant> signal (whitelisting). If the
first character of the list is <literal>~</literal>, the
effect is inverted: only the listed system calls will result
in immediate process termination (blacklisting). If running in
user mode and this option is used,
<varname>NoNewPrivileges=yes</varname> is implied. This
feature makes use of the Secure Computing Mode 2 interfaces of
the kernel ('seccomp filtering') and is useful for enforcing a
minimal sandboxing environment. Note that the
<function>execve</function>,
<function>rt_sigreturn</function>,
<function>sigreturn</function>,
<function>exit_group</function>, <function>exit</function>
system calls are implicitly whitelisted and do not need to be
listed explicitly. This option may be specified more than once
in which case the filter masks are merged. If the empty string
is assigned, the filter is reset, all prior assignments will
have no effect.</para>
<para>If you specify both types of this option (i.e.
whitelisting and blacklisting), the first encountered will
take precedence and will dictate the default action
(termination or approval of a system call). Then the next
occurrences of this option will add or delete the listed
system calls from the set of the filtered system calls,
depending of its type and the default action. (For example, if
you have started with a whitelisting of
<function>read</function> and <function>write</function>, and
right after it add a blacklisting of
<function>write</function>, then <function>write</function>
will be removed from the set.) </para></listitem>
</varlistentry>
<varlistentry>
<term><varname>SystemCallErrorNumber=</varname></term>
<listitem><para>Takes an <literal>errno</literal> error number
name to return when the system call filter configured with
<varname>SystemCallFilter=</varname> is triggered, instead of
terminating the process immediately. Takes an error name such
as <constant>EPERM</constant>, <constant>EACCES</constant> or
<constant>EUCLEAN</constant>. When this setting is not used,
or when the empty string is assigned, the process will be
terminated immediately when the filter is
triggered.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>SystemCallArchitectures=</varname></term>
<listitem><para>Takes a space separated list of architecture
identifiers to include in the system call filter. The known
architecture identifiers are <constant>x86</constant>,
<constant>x86-64</constant>, <constant>x32</constant>,
<constant>arm</constant> as well as the special identifier
<constant>native</constant>. Only system calls of the
specified architectures will be permitted to processes of this
unit. This is an effective way to disable compatibility with
non-native architectures for processes, for example to
prohibit execution of 32-bit x86 binaries on 64-bit x86-64
systems. The special <constant>native</constant> identifier
implicitly maps to the native architecture of the system (or
more strictly: to the architecture the system manager is
compiled for). If running in user mode and this option is
used, <varname>NoNewPrivileges=yes</varname> is implied. Note
that setting this option to a non-empty list implies that
<constant>native</constant> is included too. By default, this
option is set to the empty list, i.e. no architecture system
call filtering is applied.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>RestrictAddressFamilies=</varname></term>
<listitem><para>Restricts the set of socket address families
accessible to the processes of this unit. Takes a
space-separated list of address family names to whitelist,
such as
<constant>AF_UNIX</constant>,
<constant>AF_INET</constant> or
<constant>AF_INET6</constant>. When
prefixed with <constant>~</constant> the listed address
families will be applied as blacklist, otherwise as whitelist.
Note that this restricts access to the
<citerefentry><refentrytitle>socket</refentrytitle><manvolnum>2</manvolnum></citerefentry>
system call only. Sockets passed into the process by other
means (for example, by using socket activation with socket
units, see
<citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>)
are unaffected. Also, sockets created with
<function>socketpair()</function> (which creates connected
AF_UNIX sockets only) are unaffected. Note that this option
has no effect on 32-bit x86 and is ignored (but works
correctly on x86-64). If running in user mode and this option
is used, <varname>NoNewPrivileges=yes</varname> is implied. By
default, no restriction applies, all address families are
accessible to processes. If assigned the empty string, any
previous list changes are undone.</para>
<para>Use this option to limit exposure of processes to remote
systems, in particular via exotic network protocols. Note that
in most cases, the local <constant>AF_UNIX</constant> address
family should be included in the configured whitelist as it is
frequently used for local communication, including for
<citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>2</manvolnum></citerefentry>
logging.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>Personality=</varname></term>
<listitem><para>Controls which kernel architecture
<citerefentry><refentrytitle>uname</refentrytitle><manvolnum>2</manvolnum></citerefentry>
shall report, when invoked by unit processes. Takes one of
<constant>x86</constant> and <constant>x86-64</constant>. This
is useful when running 32-bit services on a 64-bit host
system. If not specified, the personality is left unmodified
and thus reflects the personality of the host system's
kernel.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>RuntimeDirectory=</varname></term>
<term><varname>RuntimeDirectoryMode=</varname></term>
<listitem><para>Takes a list of directory names. If set, one
or more directories by the specified names will be created
below <filename>/run</filename> (for system services) or below
<varname>$XDG_RUNTIME_DIR</varname> (for user services) when
the unit is started, and removed when the unit is stopped. The
directories will have the access mode specified in
<varname>RuntimeDirectoryMode=</varname>, and will be owned by
the user and group specified in <varname>User=</varname> and
<varname>Group=</varname>. Use this to manage one or more
runtime directories of the unit and bind their lifetime to the
daemon runtime. The specified directory names must be
relative, and may not include a <literal>/</literal>, i.e.
must refer to simple directories to create or remove. This is
particularly useful for unprivileged daemons that cannot
create runtime directories in <filename>/run</filename> due to
lack of privileges, and to make sure the runtime directory is
cleaned up automatically after use. For runtime directories
that require more complex or different configuration or
lifetime guarantees, please consider using
<citerefentry><refentrytitle>tmpfiles.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Environment variables in spawned processes</title>
<para>Processes started by the system are executed in a clean
environment in which select variables listed below are set. System
processes started by systemd do not inherit variables from PID 1,
but processes started by user systemd instances inherit all
environment variables from the user systemd instance.
</para>
<variablelist class='environment-variables'>
<varlistentry>
<term><varname>$PATH</varname></term>
<listitem><para>Colon-separated list of directories to use
when launching executables. Systemd uses a fixed value of
<filename>/usr/local/sbin</filename>:<filename>/usr/local/bin</filename>:<filename>/usr/sbin</filename>:<filename>/usr/bin</filename>:<filename>/sbin</filename>:<filename>/bin</filename>.
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>$LANG</varname></term>
<listitem><para>Locale. Can be set in
<citerefentry><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
or on the kernel command line (see
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
and
<citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>).
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>$USER</varname></term>
<term><varname>$LOGNAME</varname></term>
<term><varname>$HOME</varname></term>
<term><varname>$SHELL</varname></term>
<listitem><para>User name (twice), home directory, and the
login shell. The variables are set for the units that have
<varname>User=</varname> set, which includes user
<command>systemd</command> instances. See
<citerefentry><refentrytitle>passwd</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>$XDG_RUNTIME_DIR</varname></term>
<listitem><para>The directory for volatile state. Set for the
user <command>systemd</command> instance, and also in user
sessions. See
<citerefentry><refentrytitle>pam_systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>$XDG_SESSION_ID</varname></term>
<term><varname>$XDG_SEAT</varname></term>
<term><varname>$XDG_VTNR</varname></term>
<listitem><para>The identifier of the session, the seat name,
and virtual terminal of the session. Set by
<citerefentry><refentrytitle>pam_systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>
for login sessions. <varname>$XDG_SEAT</varname> and
<varname>$XDG_VTNR</varname> will only be set when attached to
a seat and a tty.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>$MAINPID</varname></term>
<listitem><para>The PID of the units main process if it is
known. This is only set for control processes as invoked by
<varname>ExecReload=</varname> and similar. </para></listitem>
</varlistentry>
<varlistentry>
<term><varname>$MANAGERPID</varname></term>
<listitem><para>The PID of the user <command>systemd</command>
instance, set for processes spawned by it. </para></listitem>
</varlistentry>
<varlistentry>
<term><varname>$LISTEN_FDS</varname></term>
<term><varname>$LISTEN_PID</varname></term>
<listitem><para>Information about file descriptors passed to a
service for socket activation. See
<citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>$TERM</varname></term>
<listitem><para>Terminal type, set only for units connected to
a terminal (<varname>StandardInput=tty</varname>,
<varname>StandardOutput=tty</varname>, or
<varname>StandardError=tty</varname>). See
<citerefentry project='man-pages'><refentrytitle>termcap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
</para></listitem>
</varlistentry>
</variablelist>
<para>Additional variables may be configured by the following
means: for processes spawned in specific units, use the
<varname>Environment=</varname> and
<varname>EnvironmentFile=</varname> options above; to specify
variables globally, use <varname>DefaultEnvironment=</varname>
(see
<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>)
or the kernel option <varname>systemd.setenv=</varname> (see
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>).
Additional variables may also be set through PAM,
cf. <citerefentry project='man-pages'><refentrytitle>pam_env</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
<citerefentry><refentrytitle>tmpfiles.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry project='man-pages'><refentrytitle>exec</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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