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Diffstat (limited to 'man/systemd.unit.xml')
| -rw-r--r-- | man/systemd.unit.xml | 113 |
1 files changed, 61 insertions, 52 deletions
diff --git a/man/systemd.unit.xml b/man/systemd.unit.xml index 85a7b12d76..40c4cfd854 100644 --- a/man/systemd.unit.xml +++ b/man/systemd.unit.xml @@ -144,61 +144,69 @@ <option>false</option> and <option>off</option> are equivalent.</para> - <para>Time span values encoded in unit files can be written in - various formats. A stand-alone number specifies a time in seconds. - If suffixed with a time unit, the unit is honored. A concatenation - of multiple values with units is supported, in which case the - values are added up. Example: "50" refers to 50 seconds; "2min - 200ms" refers to 2 minutes plus 200 milliseconds, i.e. 120200ms. - The following time units are understood: s, min, h, d, w, ms, us. - For details see + <para>Time span values encoded in unit files can be written in various formats. A stand-alone + number specifies a time in seconds. If suffixed with a time unit, the unit is honored. A + concatenation of multiple values with units is supported, in which case the values are added + up. Example: <literal>50</literal> refers to 50 seconds; <literal>2min 200ms</literal> refers to + 2 minutes and 200 milliseconds, i.e. 120200 ms. The following time units are understood: + <literal>s</literal>, <literal>min</literal>, <literal>h</literal>, <literal>d</literal>, + <literal>w</literal>, <literal>ms</literal>, <literal>us</literal>. For details see <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para> - <para>Empty lines and lines starting with # or ; are - ignored. This may be used for commenting. Lines ending - in a backslash are concatenated with the following - line while reading and the backslash is replaced by a - space character. This may be used to wrap long lines.</para> - - <para>Along with a unit file <filename>foo.service</filename>, the - directory <filename>foo.service.wants/</filename> may exist. All - unit files symlinked from such a directory are implicitly added as - dependencies of type <varname>Wants=</varname> to the unit. This - is useful to hook units into the start-up of other units, without - having to modify their unit files. For details about the semantics - of <varname>Wants=</varname>, see below. The preferred way to - create symlinks in the <filename>.wants/</filename> directory of a - unit file is with the <command>enable</command> command of the + <para>Empty lines and lines starting with <literal>#</literal> or <literal>;</literal> are + ignored. This may be used for commenting. Lines ending in a backslash are concatenated with the + following line while reading and the backslash is replaced by a space character. This may be + used to wrap long lines.</para> + + <para>Units can be aliased (have an alternative name), by creating a symlink from the new name + to the existing name in one of the unit search paths. For example, + <filename>systemd-networkd.service</filename> has the alias + <filename>dbus-org.freedesktop.network1.service</filename>, created during installation as the + symlink <filename>/usr/lib/systemd/system/dbus-org.freedesktop.network1.service</filename>. In + addition, unit files may specify aliases through the <varname>Alias=</varname> directive in the + [Install] section; those aliases are only effective when the unit is enabled. When the unit is + enabled, symlinks will be created for those names, and removed when the unit is disabled. For + example, <filename>reboot.target</filename> specifies + <varname>Alias=ctrl-alt-del.target</varname>, so when enabled it will be invoked whenever + CTRL+ALT+DEL is pressed. Alias names may be used in commands like <command>enable</command>, + <command>disable</command>, <command>start</command>, <command>stop</command>, + <command>status</command>, …, and in unit dependency directives <varname>Wants=</varname>, + <varname>Requires=</varname>, <varname>Before=</varname>, <varname>After=</varname>, …, with the + limitation that aliases specified through <varname>Alias=</varname> are only effective when the + unit is enabled. Aliases cannot be used with the <command>preset</command> command.</para> + + <para>Along with a unit file <filename>foo.service</filename>, the directory + <filename>foo.service.wants/</filename> may exist. All unit files symlinked from such a + directory are implicitly added as dependencies of type <varname>Wants=</varname> to the unit. + This is useful to hook units into the start-up of other units, without having to modify their + unit files. For details about the semantics of <varname>Wants=</varname>, see below. The + preferred way to create symlinks in the <filename>.wants/</filename> directory of a unit file is + with the <command>enable</command> command of the <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> - tool which reads information from the [Install] section of unit - files (see below). A similar functionality exists for - <varname>Requires=</varname> type dependencies as well, the - directory suffix is <filename>.requires/</filename> in this - case.</para> + tool which reads information from the [Install] section of unit files (see below). A similar + functionality exists for <varname>Requires=</varname> type dependencies as well, the directory + suffix is <filename>.requires/</filename> in this case.</para> <para>Along with a unit file <filename>foo.service</filename>, a "drop-in" directory - <filename>foo.service.d/</filename> may exist. All files with the suffix <literal>.conf</literal> from this - directory will be parsed after the file itself is parsed. This is useful to alter or add configuration settings for - a unit, without having to modify unit files. Each drop-in file must have appropriate section headers. Note that for - instantiated units, this logic will first look for the instance <literal>.d/</literal> subdirectory and read its - <literal>.conf</literal> files, followed by the template <literal>.d/</literal> subdirectory and the - <literal>.conf</literal> files there. Also note that settings from the <literal>[Install]</literal> section are not - honoured in drop-in unit files, and have no effect.</para> - - <para>In addition to <filename>/etc/systemd/system</filename>, - the drop-in <literal>.conf</literal> files for system services - can be placed in <filename>/usr/lib/systemd/system</filename> or - <filename>/run/systemd/system</filename> directories. Drop-in - files in <filename>/etc</filename> take precedence over those in - <filename>/run</filename> which in turn take precedence over - those in <filename>/usr/lib</filename>. Drop-in files under any of - these directories take precedence over unit files wherever located. - (Of course, since <filename>/run</filename> is temporary and - <filename>/usr/lib</filename> is for vendors, it is unlikely - drop-ins should be used in either of those places.)</para> - <!-- Note that we do not document .include here, as we - consider it mostly obsolete, and want people to - use .d/ drop-ins instead. --> + <filename>foo.service.d/</filename> may exist. All files with the suffix + <literal>.conf</literal> from this directory will be parsed after the file itself is + parsed. This is useful to alter or add configuration settings for a unit, without having to + modify unit files. Each drop-in file must have appropriate section headers. Note that for + instantiated units, this logic will first look for the instance <literal>.d/</literal> + subdirectory and read its <literal>.conf</literal> files, followed by the template + <literal>.d/</literal> subdirectory and the <literal>.conf</literal> files there. Also note that + settings from the <literal>[Install]</literal> section are not honored in drop-in unit files, + and have no effect.</para> + + <para>In addition to <filename>/etc/systemd/system</filename>, the drop-in <literal>.d</literal> + directories for system services can be placed in <filename>/usr/lib/systemd/system</filename> or + <filename>/run/systemd/system</filename> directories. Drop-in files in <filename>/etc</filename> + take precedence over those in <filename>/run</filename> which in turn take precedence over those + in <filename>/usr/lib</filename>. Drop-in files under any of these directories take precedence + over unit files wherever located.</para> + + <!-- Note that we do not document .include here, as we consider it mostly obsolete, and want + people to use .d/ drop-ins instead. --> <para>Some unit names reflect paths existing in the file system namespace. Example: a device unit @@ -900,7 +908,8 @@ <varname>systemd-nspawn</varname>, <varname>docker</varname>, <varname>rkt</varname> to test - against a specific implementation. See + against a specific implementation, or + <varname>private-users</varname> to check whether we are running in a user namespace. See <citerefentry><refentrytitle>systemd-detect-virt</refentrytitle><manvolnum>1</manvolnum></citerefentry> for a full list of known virtualization technologies and their identifiers. If multiple virtualization technologies are @@ -1244,7 +1253,7 @@ <row> <entry><literal>%r</literal></entry> <entry>Control group path of the slice the unit is placed in</entry> - <entry>This usually maps to the parent cgroup path of <literal>%c</literal>.</entry> + <entry>This usually maps to the parent control group path of <literal>%c</literal>.</entry> </row> <row> <entry><literal>%R</literal></entry> |