diff options
| -rw-r--r-- | man/systemd.device.xml | 45 |
1 files changed, 31 insertions, 14 deletions
diff --git a/man/systemd.device.xml b/man/systemd.device.xml index 96ebe89095..002b647ff9 100644 --- a/man/systemd.device.xml +++ b/man/systemd.device.xml @@ -70,12 +70,15 @@ since no device-specific options may be configured.</para> - <para>systemd will automatically create dynamic device - units for all kernel devices that are marked with the - "systemd" udev tag (by default all block and network - devices, and a few others). This may be used to define - dependencies between devices and other - units.</para> + <para>systemd will dynamically create device units for + all kernel devices that are marked with the "systemd" + udev tag (by default all block and network devices, + and a few others). This may be used to define + dependencies between devices and other units. To tag a + udev device use <literal>TAG+="systemd"</literal> in + the udev rules file, see + <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry> + for details.</para> <para>Device units are named after the <filename>/sys</filename> and @@ -93,7 +96,7 @@ <para>The settings of device units may either be configured via unit files, or directly from the udev - database (which is recommended). The following udev + database (which is recommended). The following udev device properties are understood by systemd:</para> <variablelist class='udev-directives'> @@ -101,16 +104,26 @@ <term><varname>SYSTEMD_WANTS=</varname></term> <listitem><para>Adds dependencies of type <varname>Wants</varname> from - this unit to all listed units. This + the device unit to all listed units. This may be used to activate arbitrary - units, when a specific device becomes + units when a specific device becomes available. Note that this and the other tags are not taken into account unless the device is tagged with the <literal>systemd</literal> string in the udev database, because otherwise the device is not exposed as systemd - unit.</para></listitem> + unit (see above). Note that systemd + will only act on + <varname>Wants</varname> dependencies + when a device first becomes active, it + will not act on them if they are added + to devices that are already + active. Use + <varname>SYSTEMD_READY=</varname> (see + below) to influence on which udev + event to trigger the device + dependencies.</para></listitem> </varlistentry> <varlistentry> @@ -135,10 +148,14 @@ device disappears from the udev tree. This option is useful to support devices that initially show up in an - uninitialized state in the tree, and for - which a changed event is generated the - moment they are fully set - up.</para></listitem> + uninitialized state in the tree, and + for which a <literal>changed</literal> + event is generated the moment they are + fully set up. Note that + <varname>SYSTEMD_WANTS=</varname> (see + above) is not acted on as long as + <varname>SYSTEMD_READY=0</varname> is + set for a device.</para></listitem> </varlistentry> <varlistentry> |