man: say that .device units need udev

This was implied by the need to tag them with "systemd", but let's make this
obvious, since it's rather easy to trip over this as a user.

Inspired by https://bugzilla.redhat.com/show_bug.cgi?id=1941458.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek 2021-03-22 21:45:04 +01:00
parent d229704743
commit ccd593a61c

View file

@ -26,11 +26,10 @@
<refsect1>
<title>Description</title>
<para>A unit configuration file whose name ends in
<literal>.device</literal> encodes information about a device unit
as exposed in the
sysfs/<citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>
device tree.</para>
<para>A unit configuration file whose name ends in <literal>.device</literal> encodes information about a
device unit as exposed in the
sysfs/<citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry> device
tree. This may be used to define dependencies between devices and other units.</para>
<para>This unit type has no specific options. See
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
@ -40,14 +39,10 @@
sections. A separate [Device] section does not
exist, since no device-specific options may be configured.</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>systemd will dynamically create device units for all kernel devices that are marked with the
<literal>systemd</literal> udev tag (by default all block and network devices, and a few others). Note
that <emphasis>if <filename>systemd-udev.service</filename> is not running, no device units will be
available (for example in a typical container)</emphasis>.</para>
<para>Device units are named after the <filename>/sys/</filename>
and <filename>/dev/</filename> paths they control. Example: the
@ -57,6 +52,10 @@
name see
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
<para>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 will be reloaded by systemd whenever the
corresponding device generates a <literal>changed</literal> event.
Other units can use <varname>ReloadPropagatedFrom=</varname> to react