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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><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 indexes. This option may
                                be specified more than once in which
                                case the specificed 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><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. 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>. 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. 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.
                                <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. <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.  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. 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>syslog</option>,
                                <option>kmsg</option>,
                                <option>journal</option>,
                                <option>syslog+console</option>,
                                <option>kmsg+console</option>,
                                <option>journal+console</option> or
                                <option>socket</option>. If set to
                                <option>inherit</option>, the file
                                descriptor of standard input is
                                duplicated for standard output. If set
                                to <option>null</option>, standard
                                output will be connected to
                                <filename>/dev/null</filename>,
                                i.e. everything written to it will be
                                lost. If set to <option>tty</option>,
                                standard output will be connected 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. <option>syslog</option>
                                connects standard output to the
                                <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                                system syslog
                                service. <option>kmsg</option>
                                connects it with the kernel log buffer
                                which is accessible via
                                <citerefentry><refentrytitle>dmesg</refentrytitle><manvolnum>1</manvolnum></citerefentry>. <option>journal</option>
                                connects it 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 is implicitly stored
                                in the journal as well, those options
                                are hence supersets of this
                                one). <option>syslog+console</option>,
                                <option>journal+console</option> and
                                <option>kmsg+console</option> work
                                similarly but copy the output to the
                                system console as
                                well. <option>socket</option> connects
                                standard output to a socket from
                                socket activation, semantics are
                                similar to the respective option of
                                <varname>StandardInput=</varname>.
                                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 STDIN, STDOUT,
                                or STDERR 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 syslog 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> or
                                <option>kmsg</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><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><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 control
                                various resource limits 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>
                        </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><refentrytitle>pam</refentrytitle><manvolnum>8</manvolnum></citerefentry>
                                for details.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>TCPWrapName=</varname></term>
                                <listitem><para>If this is a
                                socket-activated service, this sets the
                                tcpwrap service name to check the
                                permission for the current connection
                                with. This is only useful in
                                conjunction with socket-activated
                                services, and stream sockets (TCP) in
                                particular. It has no effect on other
                                socket types (e.g. datagram/UDP) and
                                on processes unrelated to socket-based
                                activation. If the tcpwrap
                                verification fails, daemon start-up
                                will fail and the connection is
                                terminated. See
                                <citerefentry><refentrytitle>tcpd</refentrytitle><manvolnum>8</manvolnum></citerefentry>
                                for details. Note that this option may
                                be used to do access control checks
                                only. Shell commands and commands
                                described in
                                <citerefentry><refentrytitle>hosts_options</refentrytitle><manvolnum>5</manvolnum></citerefentry>
                                are not supported.</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><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. See
                                <citerefentry><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
                                for details. Takes a list of strings:
                                <option>keep-caps</option>,
                                <option>keep-caps-locked</option>,
                                <option>no-setuid-fixup</option>,
                                <option>no-setuid-fixup-locked</option>,
                                <option>noroot</option> and/or
                                <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.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>Capabilities=</varname></term>
                                <listitem><para>Controls the
                                <citerefentry><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 by the capabilities
                                attached to the executed file. Due to
                                that
                                <varname>CapabilityBoundingSet=</varname>
                                is probably the 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. You must list
                                submounts separately in these settings
                                to ensure the same limited
                                access. 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.</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. All temporary data created
                                by service will be removed after
                                the service is stopped. Defaults to
                                false. Note that 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.</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. Note that
                                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.</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> 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.</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 the file system
                                namespace set up for this unit's
                                processes will receive or propagate
                                new mounts. See
                                <citerefentry><refentrytitle>mount</refentrytitle><manvolnum>2</manvolnum></citerefentry>
                                for details. Default to
                                <option>shared</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 autorize 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>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 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 (e.g. 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>

                                <para>Note that setting
                                <varname>SystemCallFilter=</varname>
                                implies a
                                <varname>SystemCallArchitectures=</varname>
                                setting of <literal>native</literal>
                                (see below), unless that option is
                                configured otherwise.</para>
                        </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
                                <literal>EPERM</literal>,
                                <literal>EACCES</literal> or
                                <literal>EUCLEAN</literal>. 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
                                <literal>x86</literal>,
                                <literal>x86-64</literal>,
                                <literal>x32</literal>,
                                <literal>arm</literal> as well as the
                                special identifier
                                <literal>native</literal>. 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 32bit
                                x86 binaries on 64bit x86-64
                                systems. The special
                                <literal>native</literal> identifier
                                implicitly maps to the native
                                architecture of the system (or more
                                strictly: to the architecture the
                                system manager is compiled for). Note
                                that setting this option to a
                                non-empty list implies that
                                <literal>native</literal> is included
                                too. By default this option is set to
                                the empty list, i.e. no architecture
                                system call filtering is applied. Note
                                that configuring a system call filter
                                with
                                <varname>SystemCallFilter=</varname>
                                (above) implies a
                                <literal>native</literal> architecture
                                list, unless configured
                                otherwise.</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 directiories 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>$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><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,
                c.f. <citerefentry><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>8</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>exec</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                  </para>
        </refsect1>

</refentry>