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man: improve description of environment block creation
This adds a general description of "philosphy" of keeping the environemnt block small and hints about systemd-run -P env. The list of generated variables is split out to a subsection. Viewing the patch with ignoring whitespace changes is recommended. We don't ignore invalid assignments (except in import-environment to some extent), previous description was wrong. For https://bugzilla.redhat.com/show_bug.cgi?id=1912046#c17.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek
parent
a084b38789
commit
82651d5b6b
@ -1123,10 +1123,12 @@ Jan 12 10:46:45 example.com bluetoothd[8900]: gatt-time-server: Input/output err
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<listitem>
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<para>Import all, one or more environment variables set on the client into the systemd manager
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environment block. If no arguments are passed, the entire environment block is imported.
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Otherwise, a list of one or more environment variable names should be passed, whose client-side
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values are then imported into the manager's environment block. This command will silently ignore
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any assignments which do not conform to the rules listed above.</para>
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environment block. If a list of environment variable names is passed, client-side values are then
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imported into the manager's environment block. If any names are not valid environment variable
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names or have invalid values according to the rules described above, an error is raised. If no
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arguments are passed, the entire environment block inherited by the <command>systemctl</command>
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process is imported. In this mode, any inherited invalid environment variables are quietly
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ignored.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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@ -2304,10 +2304,10 @@ SystemCallErrorNumber=EPERM</programlisting>
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set by the service manager itself (such as <varname>$NOTIFY_SOCKET</varname> and such), or set by a PAM module
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(in case <varname>PAMName=</varname> is used).</para>
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<para>
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See <citerefentry
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project='man-pages'><refentrytitle>environ</refentrytitle><manvolnum>7</manvolnum></citerefentry> for details
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about environment variables.</para></listitem>
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<para>See "Environment Variables in Spawned Processes" below for a description of how those
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settings combine to form the inherited environment. See <citerefentry
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project='man-pages'><refentrytitle>environ</refentrytitle><manvolnum>7</manvolnum></citerefentry> for general
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information about environment variables.</para></listitem>
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</varlistentry>
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</variablelist>
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@ -2809,7 +2809,7 @@ StandardInputData=SWNrIHNpdHplIGRhIHVuJyBlc3NlIEtsb3BzLAp1ZmYgZWVtYWwga2xvcHAncy
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</refsect1>
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<refsect1>
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<title>Environment variables in spawned processes</title>
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<title>Environment Variables in Spawned Processes</title>
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<para>Processes started by the service manager are executed with an environment variable block assembled from
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multiple sources. Processes started by the system service manager generally do not inherit environment variables
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@ -2822,30 +2822,48 @@ StandardInputData=SWNrIHNpdHplIGRhIHVuJyBlc3NlIEtsb3BzLAp1ZmYgZWVtYWwga2xvcHAncy
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<itemizedlist>
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<listitem><para>Variables globally configured for the service manager, using the
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<varname>DefaultEnvironment=</varname> setting in
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<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>, the kernel command line option <varname>systemd.setenv=</varname> (see
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>) or via
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<command>systemctl set-environment</command> (see <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>).</para></listitem>
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<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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the kernel command line option <varname>systemd.setenv=</varname> understood by
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, or via
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<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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<command>set-environment</command> verb.</para></listitem>
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<listitem><para>Variables defined by the service manager itself (see the list below)</para></listitem>
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<listitem><para>Variables defined by the service manager itself (see the list below).</para></listitem>
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<listitem><para>Variables set in the service manager's own environment variable block (subject to <varname>PassEnvironment=</varname> for the system service manager)</para></listitem>
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<listitem><para>Variables set in the service manager's own environment variable block (subject to
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<varname>PassEnvironment=</varname> for the system service manager).</para></listitem>
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<listitem><para>Variables set via <varname>Environment=</varname> in the unit file</para></listitem>
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<listitem><para>Variables set via <varname>Environment=</varname> in the unit file.</para></listitem>
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<listitem><para>Variables read from files specified via <varname>EnvironmentFile=</varname> in the unit file</para></listitem>
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<listitem><para>Variables read from files specified via <varname>EnvironmentFile=</varname> in the unit
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file.</para></listitem>
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<listitem><para>Variables set by any PAM modules in case <varname>PAMName=</varname> is in effect,
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cf. <citerefentry
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project='man-pages'><refentrytitle>pam_env</refentrytitle><manvolnum>8</manvolnum></citerefentry></para></listitem>
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project='man-pages'><refentrytitle>pam_env</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
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</para></listitem>
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</itemizedlist>
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<para>If the same environment variables are set by multiple of these sources, the later source — according to the
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order of the list above — wins. Note that as final step all variables listed in
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<varname>UnsetEnvironment=</varname> are removed again from the compiled environment variable list, immediately
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<para>If the same environment variable is set by multiple of these sources, the later source — according
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to the order of the list above — wins. Note that as the final step all variables listed in
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<varname>UnsetEnvironment=</varname> are removed from the compiled environment variable list, immediately
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before it is passed to the executed process.</para>
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<para>The following environment variables are set or propagated by the service manager for each invoked
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process:</para>
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<para>The general philosophy is to expose a small curated list of environment variables to processes.
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Services started by the system manager (PID 1) will be started, without additional service-specific
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configuration, with just a few environment variables. The user manager inherits environment variables as
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any other system service, but in addition may receive additional environment variables from PAM, and,
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typically, additional imported variables when the user starts a graphical session. It is recommended to
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keep the environment blocks in both the system and user managers managers lean.</para>
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<para>Hint: <command>systemd-run -P env</command> and <command>systemd-run --user -P env</command> print
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the effective system and user service environment blocks.</para>
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<refsect2>
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<title>Environment Variables Set or Propagated by the Service Manager</title>
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<para>The following environment variables are propagated by the service manager or generated internally
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for each invoked process:</para>
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<variablelist class='environment-variables'>
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<varlistentry>
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@ -2854,22 +2872,21 @@ StandardInputData=SWNrIHNpdHplIGRhIHVuJyBlc3NlIEtsb3BzLAp1ZmYgZWVtYWwga2xvcHAncy
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<listitem><para>Colon-separated list of directories to use when launching
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executables. <command>systemd</command> uses a fixed value of
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<literal><filename>/usr/local/sbin</filename>:<filename>/usr/local/bin</filename>:<filename>/usr/sbin</filename>:<filename>/usr/bin</filename></literal>
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in the system manager. When compiled for systems with "unmerged /usr" (<filename>/bin</filename> is
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not a symlink to <filename>/usr/bin</filename>),
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<literal>:<filename>/sbin</filename>:<filename>/bin</filename></literal> is appended. In case of the
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the user manager, a different path may be configured by the distribution. It is recommended to not
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rely on the order of entries, and have only one program with a given name in
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in the system manager. When compiled for systems with "unmerged <filename>/usr/</filename>"
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(<filename>/bin</filename> is not a symlink to <filename>/usr/bin</filename>),
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<literal>:<filename>/sbin</filename>:<filename>/bin</filename></literal> is appended. In case of
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the the user manager, a different path may be configured by the distribution. It is recommended to
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not rely on the order of entries, and have only one program with a given name in
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<varname>$PATH</varname>.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>$LANG</varname></term>
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<listitem><para>Locale. Can be set in
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<citerefentry project='man-pages'><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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<listitem><para>Locale. Can be set in <citerefentry
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project='man-pages'><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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or on the kernel command line (see
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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and
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> and
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<citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>).
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</para></listitem>
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</varlistentry>
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@ -3200,16 +3217,14 @@ StandardInputData=SWNrIHNpdHplIGRhIHVuJyBlc3NlIEtsb3BzLAp1ZmYgZWVtYWwga2xvcHAncy
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</row>
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</tbody>
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</tgroup>
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</table>
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</listitem>
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</table></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>$PIDFILE</varname></term>
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<listitem><para>The path to the configured PID file, in case the process is forked off on behalf of a
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service that uses the <varname>PIDFile=</varname> setting, see
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<listitem><para>The path to the configured PID file, in case the process is forked off on behalf of
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a service that uses the <varname>PIDFile=</varname> setting, see
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<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for details. Service code may use this environment variable to automatically generate a PID file at
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the location configured in the unit file. This field is set to an absolute path in the file
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@ -3222,10 +3237,12 @@ StandardInputData=SWNrIHNpdHplIGRhIHVuJyBlc3NlIEtsb3BzLAp1ZmYgZWVtYWwga2xvcHAncy
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of the selected PAM stack, additional environment variables defined by systemd may be set for
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services. Specifically, these are <varname>$XDG_SEAT</varname>, <varname>$XDG_VTNR</varname>, see
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<citerefentry><refentrytitle>pam_systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry> for details.</para>
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</refsect2>
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</refsect1>
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<refsect1>
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<title>Process exit codes</title>
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<title>Process Exit Codes</title>
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<para>When invoking a unit process the service manager possibly fails to apply the execution parameters configured
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with the settings above. In that case the already created service process will exit with a non-zero exit code
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