.TH "LVMAUTOACTIVATION" "7" "LVM TOOLS 2.03.14(2)-RHEL8 (2021-10-20)" "Red Hat, Inc" "\""
.
.SH NAME
.
lvmautoactivation \(em LVM autoactivation
.
.SH DESCRIPTION
.
Autoactivation is the activation of LVs performed automatically by the
system in response to LVM devices being attached to the machine.  When all
PVs in a VG have been attached, the VG is complete, and LVs in the VG are
activated.
.P
Autoactivation of VGs, or specific LVs, can be prevented using vgchange or
lvchange \-\-setautoactivation n.  The lvm.conf auto_activation_volume_list
is another way to limit autoactivation.
.
.SS event autoactivation
.P
The most common form of autoactivation is "event based", in which complete
VGs are activated in response to uevents which occur during system startup
or at any time after the system has started.  Another form of
autoactivation is "static" in which complete VGs are activated at a fixed
point during system startup by a systemd service, and not in response to
events.  This can be controlled with the lvm.conf setting
event_activation.
.P
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
kernel to notify userspace of the new device.  systemd-udev runs udev
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, which triggers autoactivation.
.P
There are two variations of event baed autoactivation that may be used on
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
which lead to autoactivation:
.P
.B 69\-dm\-lvm\-metad.rules
.
.IP \[bu] 2
device /dev/name with major:minor X:Y is attached to the machine
.
.IP \[bu] 2
systemd/udev runs blkid to identify /dev/name as an LVM PV
.
.IP \[bu] 2
udev rule 69\-dm\-lvm\-metad.rules is run for /dev/name
.
.IP \[bu] 2
the lvm udev rule runs the systemd service lvm2\-pvscan@X:Yservice
.
.IP \[bu] 2
the lvm2\-pvscan service runs:
.br
pvscan \-\-cache \-aay \-\-major X \-\-minor Y
.
.IP \[bu] 2
pvscan reads the device, records that the PV is online
(see pvs_online), and checks if the VG is complete.
.
.IP \[bu] 2
if the VG is complete, pvscan creates the vgs_online temp file,
and activates the VG.
.
.IP \[bu] 2
the activation command output can be seen from
systemctl status lvm2\-pvscan*
.P
.B 69\-dm\-lvm.rules
.
.IP \[bu] 2
device /dev/name with major:minor X:Y is attached to the machine
.
.IP \[bu] 2
systemd/udev runs blkid to identify /dev/name as an LVM PV
.
.IP \[bu] 2
udev rule 69\-dm\-lvm.rules is run for /dev/name
.
.IP \[bu] 2
the lvm udev rule runs:
.br
pvscan \-\-cache \-\-listvg \-\-checkcomplete \-\-vgonline
.br
\-\-autoactivation event \-\-udevoutput \-\-journal=output /dev/name
.
.IP \[bu] 2
pvscan reads the device, records that the PV is online
(see pvs_online), and checks if the VG is complete.
.
.IP \[bu] 2
if the VG is complete, pvscan creates the vgs_online temp file,
and prints the name of the VG for the udev rule to import:
LVM_VG_NAME_COMPLETE='vgname'
.
.IP \[bu] 2
if the lvm udev rule sees LVM_VG_NAME_COMPLETE from pvscan,
it activates the VG using a transient systemd service named
lvm-activate\-<vgname>.
.
.IP \[bu] 2
the lvm-activate\-<vgname> service runs
.br
vgchange \-aay \-\-autoactivation event <vgname>
.
.IP \[bu] 2
the activation command output can be seen from
journalctl \-u lvm-activate\-<vgname>
.P
.
.SS pvscan options
.P
.B \-\-cache
.br
Read the <device> arg (and only that device), and record that
the PV is online by creating the /run/lvm/pvs_online/<pvid>
file containing the name of the VG and the device for the PV.
.P
.B \-aay
.br
Activate the VG from the pvscan command
(includes implicit \-\-checkcomplete and \-\-vgonline.)
.P
.B \-\-checkcomplete
.br
Check if the VG is complete, i.e. all PVs are present on
the system, by checking /run/lvm/pvs_online/<pvid> files.
.P
.B \-\-vgonline
.br
Create /run/lvm/vgs_online/<vgname> if the VG is complete
(used to ensure only one command performs activation.)
.P
.B \-\-autoactivation event
.br
Inform the command it is used for event based autoactivation.
.P
.B \-\-listvg
.br
Print the name of the VG using the device.
.P
.B \-\-udevoutput
.br
Only print output that can be imported to the udev rule,
using the udev environment key format, i.e. NAME='value'.
.P
.B \-\-journal=output
.br
Send standard command output to the journal (when stdout
is reserved for udev output.)
.P
.SS run files
.P
Autoactivation commands use a number of temp files in /run/lvm (with the
expectation that /run is cleared between boots.)
.P
.B pvs_online
.br
pvscan \-\-cache creates a file here for each PV that is attached.  The file
is named with the PVID and contains the VG name and device information.
The existence of the file is used to determine when all PVs for a given VG
are present.  The device information in these files is also used to
optimize locating devices for a VG when the VG is activated.
.P
.B pvs_lookup
.br
pvscan \-\-cache creates a file here named for a VG (if one doesn't already
exist.)  The file contains a list of PVIDs in the VG.  This is needed when
a PV is processed which has no VG metadata, in which case the list of
PVIDs from the lookup file is used to check if the VG is complete.
.P
.B vgs_online
.br
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
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
.P
VG "vg" contains two PVs:
.nf
$ pvs \-o name,vgname,uuid /dev/sdb /dev/sdc
  PV         VG PV UUID                               
  /dev/sdb   vg 1uKpaT\-lFOZ\-NLHX\-j4jI\-OBi1\-QpdE\-HZ5hZY
  /dev/sdc   vg 5J3tM8\-aIPe\-2vbd\-DBe7\-bvRq\-TGj0\-DaKV2G
.fi
.P
use of \-\-cache:
.nf
$ pvscan \-\-cache /dev/sdb
  pvscan[12922] PV /dev/sdb online.
$ pvscan \-\-cache /dev/sdc
  pvscan[12923] PV /dev/sdc online.

$ cat /run/lvm/pvs_online/1uKpaTlFOZNLHXj4jIOBi1QpdEHZ5hZY 
8:16
vg:vg
dev:/dev/sdb
$ cat /run/lvm/pvs_online/5J3tM8aIPe2vbdDBe7bvRqTGj0DaKV2G 
8:32
vg:vg
dev:/dev/sdc
.fi
.P
use of \-aay:
.nf
$ pvscan \-\-cache \-aay /dev/sdb
  pvscan[12935] PV /dev/sdb online, VG vg incomplete (need 1).
$ pvscan \-\-cache \-aay /dev/sdc
  pvscan[12936] PV /dev/sdc online, VG vg is complete.
  pvscan[12936] VG vg run autoactivation.
  1 logical volume(s) in volume group "vg" now active

$ cat /run/lvm/pvs_online/1uKpaTlFOZNLHXj4jIOBi1QpdEHZ5hZY 
8:16
vg:vg
dev:/dev/sdb
$ cat /run/lvm/pvs_online/5J3tM8aIPe2vbdDBe7bvRqTGj0DaKV2G 
8:32
vg:vg
dev:/dev/sdc
$ ls /run/lvm/vgs_online/vg 
/run/lvm/vgs_online/vg
.fi
.P
use of \-\-listvg:
.nf
$ pvscan \-\-cache \-\-listvg /dev/sdb
  VG vg
$ pvscan \-\-cache \-\-listvg /dev/sdc
  VG vg

$ cat /run/lvm/pvs_online/1uKpaTlFOZNLHXj4jIOBi1QpdEHZ5hZY 
8:16
vg:vg
dev:/dev/sdb
$ cat /run/lvm/pvs_online/5J3tM8aIPe2vbdDBe7bvRqTGj0DaKV2G 
8:32
vg:vg
dev:/dev/sdc
.fi
.P
use of \-\-checkcomplete:
.nf
$ pvscan \-\-cache \-\-listvg \-\-checkcomplete \-\-vgonline /dev/sdb
  pvscan[12996] PV /dev/sdb online, VG vg incomplete (need 1).
  VG vg incomplete
$ pvscan \-\-cache \-\-listvg \-\-checkcomplete \-\-vgonline /dev/sdc
  pvscan[12997] PV /dev/sdc online, VG vg is complete.
  VG vg complete
.fi
.P
use of \-\-udevoutput:
.nf
$ pvscan \-\-cache \-\-listvg \-\-checkcomplete \-\-vgonline \-\-udevoutput /dev/sdb
LVM_VG_NAME_INCOMPLETE='vg'
$ pvscan \-\-cache \-\-listvg \-\-checkcomplete \-\-vgonline \-\-udevoutput /dev/sdc
LVM_VG_NAME_COMPLETE='vg'
.fi
.P
use of \-\-listlvs:
.nf
$ lvs \-o name,devices vg
  LV    Devices                
  lvol0 /dev/sdb(0)            
  lvol1 /dev/sdc(0)            
  lvol2 /dev/sdb(1),/dev/sdc(1)

$ pvscan \-\-cache \-\-listlvs \-\-checkcomplete /dev/sdb
  pvscan[13288] PV /dev/sdb online, VG vg incomplete (need 1).
  VG vg incomplete
  LV vg/lvol0 complete
  LV vg/lvol2 incomplete
$ pvscan \-\-cache \-\-listlvs \-\-checkcomplete /dev/sdc
  pvscan[13289] PV /dev/sdc online, VG vg is complete.
  VG vg complete
  LV vg/lvol1 complete
  LV vg/lvol2 complete
.fi

