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man: explain in more detail how SYSTEMD_READY= influences SYSTEMD_WANTS= in udev rules 

https://bugzilla.redhat.com/show_bug.cgi?id=1026860
This commit is contained in:
Lennart Poettering 2013-12-11 18:38:51 +01:00
parent cde93897cd
commit 419173e60a
1 changed files with 31 additions and 14 deletions
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45
man/systemd.device.xml
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@ -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>