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man: add section about static autoactivation

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David Teigland 2021-12-06 13:20:32 -06:00
parent ae54e75176
commit d803d9202c
1 changed files with 41 additions and 7 deletions
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48
man/lvmautoactivation.7_main
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@ -14,14 +14,16 @@ activated.
Autoactivation of VGs, or specific LVs, can be prevented using vgchange or Autoactivation of VGs, or specific LVs, can be prevented using vgchange or
lvchange --setautoactivation n. The lvm.conf auto_activation_volume_list lvchange --setautoactivation n. The lvm.conf auto_activation_volume_list
is another way to limit autoactivation. is another way to limit autoactivation.
.
.SS event autoactivation
.P .P
The most common form of autoactivation is "event based", in which complete The most common form of autoactivation is "event based", in which complete
VGs are activated in response to uevents which occur during system startup VGs are activated in response to uevents which occur during system startup
or at any time after the system has started. Another form of or at any time after the system has started. Another form of
autoactivation is "service based" in which complete VGs are activated at a autoactivation is "static" in which complete VGs are activated at a fixed
fixed point during system startup by a systemd service, and are not point during system startup by a systemd service, and not in response to
activated in response to uevents. This can be controlled with the events. This can be controlled with the lvm.conf setting
lvm.conf setting event_activation. event_activation.
.P .P
Event based autoactivation is driven by udev, udev rules, and systemd. Event based autoactivation is driven by udev, udev rules, and systemd.
When a device is attached to a machine, a uevent is generated by the When a device is attached to a machine, a uevent is generated by the
@ -30,8 +32,8 @@ rules to process the new device. Udev rules use blkid to identify the
device as an LVM PV and then execute the lvm-specific udev rule for the device as an LVM PV and then execute the lvm-specific udev rule for the
device, which triggers autoactivation. device, which triggers autoactivation.
.P .P
There are two variations of event based autoactivation that may be used a There are two variations of event baed autoactivation that may be used on
system, depending on the LVM udev rule that is installed (found in a system, depending on the LVM udev rule that is installed (found in
/lib/udev/rules.d/.) The following summarizes the steps in each rule /lib/udev/rules.d/.) The following summarizes the steps in each rule
which lead to autoactivation: which lead to autoactivation:
.P .P
@ -149,7 +151,7 @@ using the udev environment key format, i.e. NAME='value'.
Send standard command output to the journal (when stdout Send standard command output to the journal (when stdout
is reserved for udev output.) is reserved for udev output.)
.P .P
.SS Temp files .SS run files
.P .P
Autoactivation commands use a number of temp files in /run/lvm (with the Autoactivation commands use a number of temp files in /run/lvm (with the
expectation that /run is cleared between boots.) expectation that /run is cleared between boots.)
@ -175,6 +177,38 @@ The first activation command (pvscan or vgchange) to create a file here,
named for the VG, will activate the VG. This resolves a race when named for the VG, will activate the VG. This resolves a race when
concurrent commands attempt to activate a VG at once. concurrent commands attempt to activate a VG at once.
. .
.SS static autoactivation
.P
When event autoactivation is disabled by setting lvm.conf
event_activation=0, autoactivation is performed at one or more static
points during system startup. At these points, a vgchange -aay command is
run to activate complete VGs from devices that are present on the system
at that time. pvscan commands (and lvm2-pvscan services) do not perform
autoactivation in this mode. pvscan commands may still be run from
uevents but will do nothing when they read the event_activation=0 setting.
.P
The static vgchange -aay commands are run by three systemd services at
three points during startup: lvm2-activation-early, lvm2-activation, and
lvm2-activation-net. These static activation services are "generated
services", so the service files are created at run time by the
lvm2-activation-generator command (run by systemd).
lvm2-activation-generator creates the services if lvm.conf
event_activation=0.
.P
The limitation of this method is that devices may not be attached to the
system (or set up) at a reliable point in time during startup, and they
may not be present when the services run vgchange. In this case, the VGs
will not be autoactivated. So, the timing of device attachment/setup
determines whether static autoactivation will produce the same results as
event autoactivation. For this reason, static autoactivation is not
recommended.
.P
Sometimes, static autoactivation is mistakenly expected to disable all
autoactivation of particular VGs. This may appear to be effective if those
VGs are slow to be attached or set up. But, the only correct and reliable
way to disable autoactivation is using vgchange/lvchange
--setautoactivation n, or lvm.conf auto_activation_volume_list.
.
.SH EXAMPLES .SH EXAMPLES
.P .P
VG "vg" contains two PVs: VG "vg" contains two PVs: