From bb9c2f82137bb6d1a352341eb81ed2a0ac96d4cb Mon Sep 17 00:00:00 2001 From: Lennart Poettering Date: Wed, 11 Dec 2013 18:38:51 +0100 Subject: [PATCH] man: explain in more detail how SYSTEMD_READY= influences SYSTEMD_WANTS= in udev rules https://bugzilla.redhat.com/show_bug.cgi?id=1026860 --- man/systemd.device.xml | 45 +++++++++++++++++++++++++++++++-------------- 1 file changed, 31 insertions(+), 14 deletions(-) diff --git a/man/systemd.device.xml b/man/systemd.device.xml index 96ebe89..002b647 100644 --- a/man/systemd.device.xml +++ b/man/systemd.device.xml @@ -70,12 +70,15 @@ since no device-specific options may be configured. - 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. + 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 TAG+="systemd" in + the udev rules file, see + udev7 + for details. Device units are named after the /sys and @@ -93,7 +96,7 @@ 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: @@ -101,16 +104,26 @@ SYSTEMD_WANTS= Adds dependencies of type Wants 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 systemd string in the udev database, because otherwise the device is not exposed as systemd - unit. + unit (see above). Note that systemd + will only act on + Wants dependencies + when a device first becomes active, it + will not act on them if they are added + to devices that are already + active. Use + SYSTEMD_READY= (see + below) to influence on which udev + event to trigger the device + dependencies. @@ -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. + uninitialized state in the tree, and + for which a changed + event is generated the moment they are + fully set up. Note that + SYSTEMD_WANTS= (see + above) is not acted on as long as + SYSTEMD_READY=0 is + set for a device.