chiark / gitweb /
man: improve documentation for StandardOutput= and StandardInput=
[elogind.git] / man / systemd.exec.xml
index 5d39bd1..cfcf996 100644 (file)
                                 directory path. Sets the root
                                 directory for executed processes, with
                                 the
-                                <citerefentry><refentrytitle>chroot</refentrytitle><manvolnum>2</manvolnum></citerefentry>
+                                <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
 
                                 <para>
                                 See
-                                <citerefentry><refentrytitle>environ</refentrytitle><manvolnum>7</manvolnum></citerefentry>
+                                <citerefentry project='man-pages'><refentrytitle>environ</refentrytitle><manvolnum>7</manvolnum></citerefentry>
                                 for details about environment variables.</para></listitem>
                         </varlistentry>
                         <varlistentry>
                                 <para>The files listed with this
                                 directive will be read shortly before
                                 the process is executed (more
-                                specifically, this means after all
+                                specifically, after all
                                 processes from a previous unit state
                                 terminated. This means you can
                                 generate these files in one unit
                                 <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
+                                <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. If
-                                <option>tty</option> is selected,
-                                standard input is connected to a TTY
-                                (as configured by
+                                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.
-                                <option>tty-force</option>
-                                is similar to <option>tty</option>,
-                                but the executed process is forcefully
-                                and immediately made the controlling
+                                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. <option>tty-fail</option> is
+                                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.  The
-                                <option>socket</option> option is only
-                                valid in socket-activated services,
-                                and only when the socket configuration
-                                file (see
+                                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
                                 with daemons designed for use with the
                                 traditional
                                 <citerefentry><refentrytitle>inetd</refentrytitle><manvolnum>8</manvolnum></citerefentry>
-                                daemon. This setting defaults to
+                                daemon.</para>
+
+                                <para>This setting defaults to
                                 <option>null</option>.</para></listitem>
                         </varlistentry>
                         <varlistentry>
                                 of <option>inherit</option>,
                                 <option>null</option>,
                                 <option>tty</option>,
+                                <option>journal</option>,
                                 <option>syslog</option>,
                                 <option>kmsg</option>,
-                                <option>journal</option>,
+                                <option>journal+console</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
+                                <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. If set to <option>tty</option>,
-                                standard output will be connected to a
-                                tty (as configured via
+                                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. <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
+                                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>,
                                 <option>local5</option>,
                                 <option>local6</option> or
                                 <option>local7</option>. See
-                                <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+                                <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                                 for details. This option is only
                                 useful when
                                 <varname>StandardOutput=</varname> or
                                 <option>notice</option>,
                                 <option>info</option>,
                                 <option>debug</option>. See
-                                <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+                                <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                                 for details. This option is only
                                 useful when
                                 <varname>StandardOutput=</varname> or
                                 <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>
+                                <citerefentry project='man-pages'><refentrytitle>pam</refentrytitle><manvolnum>8</manvolnum></citerefentry>
                                 for details.</para></listitem>
                         </varlistentry>
 
                                 capabilities to include in the
                                 capability bounding set for the
                                 executed process. See
-                                <citerefentry><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
+                                <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>,
                                 <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>
+                                <citerefentry project='man-pages'><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
                                 for details. Takes a list of strings:
                                 <option>keep-caps</option>,
                                 <option>keep-caps-locked</option>,
                         <varlistentry>
                                 <term><varname>Capabilities=</varname></term>
                                 <listitem><para>Controls the
-                                <citerefentry><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
+                                <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 by the capabilities
+                                usually influenced (and filtered) by the capabilities
                                 attached to the executed file. Due to
                                 that
                                 <varname>CapabilityBoundingSet=</varname>
                                 <term><varname>ReadOnlyDirectories=</varname></term>
                                 <term><varname>InaccessibleDirectories=</varname></term>
 
-                                <listitem><para>Sets up a new
-                                file system namespace for executed
+                                <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
                                 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
+                                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
+                                option, the specific list is reset,
+                                and all prior assignments have no
                                 effect.</para>
                                 <para>Paths in
                                 <varname>ReadOnlyDirectories=</varname>
                                 processes via
                                 <filename>/tmp</filename> or
                                 <filename>/var/tmp</filename>
-                                impossible. If this is enabled all
+                                impossible. If this is enabled, all
                                 temporary files created by a service
                                 in these directories will be removed
                                 after the service is stopped. Defaults
                         </varlistentry>
 
                         <varlistentry>
+                                <term><varname>ProtectSystem=</varname></term>
+
+                                <listitem><para>Takes a boolean
+                                argument or
+                                <literal>full</literal>. If true,
+                                mounts the <filename>/usr</filename>
+                                directory 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 directores 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
                                 namespace related options
                                 (<varname>PrivateTmp=</varname>,
                                 <varname>PrivateDevices=</varname>,
+                                <varname>ProtectSystem=</varname>,
+                                <varname>ProtectHome=</varname>,
                                 <varname>ReadOnlyDirectories=</varname>,
                                 <varname>InaccessibleDirectories=</varname>
                                 and
                         <varlistentry>
                                 <term><varname>AppArmorProfile=</varname></term>
 
-                                <listitem><para>Take a profile name as argument.
+                                <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.
                                 (which creates connected AF_UNIX
                                 sockets only) are unaffected. Note
                                 that this option has no effect on
-                                32bit x86 and is ignored (but works
+                                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
+                                is implied. By default, no
                                 restriction applies, all address
                                 families are accessible to
                                 processes. If assigned the empty
-                                string any previous list changes are
+                                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
+                                cases, the local
                                 <constant>AF_UNIX</constant> address
                                 family should be included in the
                                 configured whitelist as it is
                                 processes. Takes one of
                                 <constant>x86</constant> and
                                 <constant>x86-64</constant>. This is
-                                useful when running 32bit services on
-                                a 64bit host system. If not specified
+                                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
                                 <term><varname>RuntimeDirectoryMode=</varname></term>
 
                                 <listitem><para>Takes a list of
-                                directory names. If set one or more
+                                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
+                                started, and removed when the unit is
                                 stopped. The directories will have the
                                 access mode specified in
                                 <varname>RuntimeDirectoryMode=</varname>,
                                 <literal>/</literal>, i.e. must refer
                                 to simple directories to create or
                                 remove. This is particularly useful
-                                for unpriviliges daemons that cannot
+                                for unprivileged daemons that cannot
                                 create runtime directories in
                                 <filename>/run</filename> due to lack
                                 of privileges, and to make sure the
                                 or
                                 <varname>StandardError=tty</varname>).
                                 See
-                                <citerefentry><refentrytitle>termcap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
+                                <citerefentry project='man-pages'><refentrytitle>termcap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
                                 </para></listitem>
                         </varlistentry>
                 </variablelist>
                 <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>
+                cf. <citerefentry project='man-pages'><refentrytitle>pam_env</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
         </refsect1>
 
         <refsect1>
                           <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><refentrytitle>exec</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+                          <citerefentry project='man-pages'><refentrytitle>exec</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                   </para>
         </refsect1>