1LVMAUTOACTIVATION(7) LVMAUTOACTIVATION(7)
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6 lvmautoactivation — LVM autoactivation
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9 Autoactivation is the activation of LVs performed automatically by the
10 system in response to LVM devices being attached to the machine. When
11 all PVs in a VG have been attached, the VG is complete, and LVs in the
12 VG are activated.
13 Autoactivation of VGs, or specific LVs, can be prevented using vgchange
15 or lvchange --setautoactivation n. The lvm.conf auto_activation_vol‐
16 ume_list is another way to limit autoactivation.
17 event autoactivation
19 LVM autoactivation is "event based", in which complete VGs are acti‐
20 vated in response to uevents which occur during system startup or at
21 any time after the system has started. An old form of autoactivation
22 was "static" in which complete VGs are activated at a fixed point dur‐
23 ing system startup by a systemd service, and not in response to events.
24 Event based autoactivation is driven by udev, udev rules, and systemd.
26 When a device is attached to a machine, a uevent is generated by the
27 kernel to notify userspace of the new device. systemd-udev runs udev
28 rules to process the new device. Udev rules use blkid to identify the
29 device as an LVM PV and then execute the lvm-specific udev rule for the
30 device, which triggers autoactivation.
31 There are two variations of event based autoactivation that may be used
33 on a system, depending on the LVM udev rule that is installed (found in
34 /lib/udev/rules.d/.) The following summarizes the steps in each rule
35 which lead to autoactivation:
36 69-dm-lvm-metad.rules
38 • device /dev/name with major:minor X:Y is attached to the machine
40 • systemd/udev runs blkid to identify /dev/name as an LVM PV
42 • udev rule 69-dm-lvm-metad.rules is run for /dev/name
44 • the lvm udev rule runs the systemd service lvm2-pvscan@X:Yservice
46 • the lvm2-pvscan service runs:
48 pvscan --cache -aay --major X --minor Y
49 • pvscan reads the device, records that the PV is online (see pvs_on‐
51 line), and checks if the VG is complete.
52 • if the VG is complete, pvscan creates the vgs_online temp file, and
54 activates the VG.
55 • the activation command output can be seen from systemctl status
57 lvm2-pvscan*
58 69-dm-lvm.rules
60 • device /dev/name with major:minor X:Y is attached to the machine
62 • systemd/udev runs blkid to identify /dev/name as an LVM PV
64 • udev rule 69-dm-lvm.rules is run for /dev/name
66 • the lvm udev rule runs:
68 pvscan --cache --listvg --checkcomplete --vgonline
69 --autoactivation event --udevoutput --journal=output /dev/name
70 • pvscan reads the device, records that the PV is online (see pvs_on‐
72 line), and checks if the VG is complete.
73 • if the VG is complete, pvscan creates the vgs_online temp file, and
75 prints the name of the VG for the udev rule to import:
76 LVM_VG_NAME_COMPLETE='vgname'
77 • if the lvm udev rule sees LVM_VG_NAME_COMPLETE from pvscan, it acti‐
79 vates the VG using a transient systemd service named lvm-acti‐
80 vate-<vgname>.
81 • the lvm-activate-<vgname> service runs
83 vgchange -aay --autoactivation event <vgname>
84 • the activation command output can be seen from journalctl -u lvm-ac‐
86 tivate-<vgname>
87 pvscan options
89 --cache
90 Read the <device> arg (and only that device), and record that the PV is
91 online by creating the /run/lvm/pvs_online/<pvid> file containing the
92 name of the VG and the device for the PV.
93 -aay
95 Activate the VG from the pvscan command (includes implicit --checkcom‐
96 plete and --vgonline.)
97 --checkcomplete
99 Check if the VG is complete, i.e. all PVs are present on the system, by
100 checking /run/lvm/pvs_online/<pvid> files.
101 --vgonline
103 Create /run/lvm/vgs_online/<vgname> if the VG is complete (used to en‐
104 sure only one command performs activation.)
105 --autoactivation event
107 Inform the command it is used for event based autoactivation.
108 --listvg
110 Print the name of the VG using the device.
111 --udevoutput
113 Only print output that can be imported to the udev rule, using the udev
114 environment key format, i.e. NAME='value'.
115 --journal=output
117 Send standard command output to the journal (when stdout is reserved
118 for udev output.)
119 run files
121 Autoactivation commands use a number of temp files in /run/lvm (with
122 the expectation that /run is cleared between boots.)
123 pvs_online
125 pvscan --cache creates a file here for each PV that is attached. The
126 file is named with the PVID and contains the VG name and device infor‐
127 mation. The existence of the file is used to determine when all PVs
128 for a given VG are present. The device information in these files is
129 also used to optimize locating devices for a VG when the VG is acti‐
130 vated.
131 pvs_lookup
133 pvscan --cache creates a file here named for a VG (if one doesn't al‐
134 ready exist.) The file contains a list of PVIDs in the VG. This is
135 needed when a PV is processed which has no VG metadata, in which case
136 the list of PVIDs from the lookup file is used to check if the VG is
137 complete.
138 vgs_online
140 The first activation command (pvscan or vgchange) to create a file
141 here, named for the VG, will activate the VG. This resolves a race
142 when concurrent commands attempt to activate a VG at once.
143 static autoactivation
145 A static autoactivation method is no longer provided by lvm. Setting
146 event_activation=0 still disables event based autoactivation. WARNING:
147 disabling event activation without an alternative may prevent a system
148 from booting. A custom systemd service could be written to run autoac‐
149 tivation during system startup, in which case disabling event autoacti‐
150 vation may be useful.
151 lvm.conf filter
153 Device symlinks from /dev/disk/ can be used in the lvm.conf filter to
154 guard against changes in kernel device names. The /dev/disk/by-path/ or
155 /dev/disk/by-id/ prefixes should be included in the filter names; these
156 prefixes help lvm detect that symlink names are used. Filters contain‐
157 ing symlinks require special matching by commands run in the lvm udev
158 rule.
159 Common symlinks, e.g. beginning with wwn-, scsi-, pci-, or lvm-
161 pv-uuid-, are recommended. Uncommon or custom symlinks created by cus‐
162 tom udev rules may be less reliable. If a custom udev rule creates sym‐
163 links used in the lvm filter, then the udev rule should be started
164 prior to the lvm rule.
165
167 VG "vg" contains two PVs:
168 $ pvs -o name,vgname,uuid /dev/sdb /dev/sdc
169 PV VG PV UUID
170 /dev/sdb vg 1uKpaT-lFOZ-NLHX-j4jI-OBi1-QpdE-HZ5hZY
171 /dev/sdc vg 5J3tM8-aIPe-2vbd-DBe7-bvRq-TGj0-DaKV2G
172 use of --cache:
174 $ pvscan --cache /dev/sdb
175 pvscan[12922] PV /dev/sdb online.
176 $ pvscan --cache /dev/sdc
177 pvscan[12923] PV /dev/sdc online.
178 $ cat /run/lvm/pvs_online/1uKpaTlFOZNLHXj4jIOBi1QpdEHZ5hZY
180 8:16
181 vg:vg
182 dev:/dev/sdb
183 $ cat /run/lvm/pvs_online/5J3tM8aIPe2vbdDBe7bvRqTGj0DaKV2G
184 8:32
185 vg:vg
186 dev:/dev/sdc
187 use of -aay:
189 $ pvscan --cache -aay /dev/sdb
190 pvscan[12935] PV /dev/sdb online, VG vg incomplete (need 1).
191 $ pvscan --cache -aay /dev/sdc
192 pvscan[12936] PV /dev/sdc online, VG vg is complete.
193 pvscan[12936] VG vg run autoactivation.
194 1 logical volume(s) in volume group "vg" now active
195 $ cat /run/lvm/pvs_online/1uKpaTlFOZNLHXj4jIOBi1QpdEHZ5hZY
197 8:16
198 vg:vg
199 dev:/dev/sdb
200 $ cat /run/lvm/pvs_online/5J3tM8aIPe2vbdDBe7bvRqTGj0DaKV2G
201 8:32
202 vg:vg
203 dev:/dev/sdc
204 $ ls /run/lvm/vgs_online/vg
205 /run/lvm/vgs_online/vg
206 use of --listvg:
208 $ pvscan --cache --listvg /dev/sdb
209 VG vg
210 $ pvscan --cache --listvg /dev/sdc
211 VG vg
212 $ cat /run/lvm/pvs_online/1uKpaTlFOZNLHXj4jIOBi1QpdEHZ5hZY
214 8:16
215 vg:vg
216 dev:/dev/sdb
217 $ cat /run/lvm/pvs_online/5J3tM8aIPe2vbdDBe7bvRqTGj0DaKV2G
218 8:32
219 vg:vg
220 dev:/dev/sdc
221 use of --checkcomplete:
223 $ pvscan --cache --listvg --checkcomplete --vgonline /dev/sdb
224 pvscan[12996] PV /dev/sdb online, VG vg incomplete (need 1).
225 VG vg incomplete
226 $ pvscan --cache --listvg --checkcomplete --vgonline /dev/sdc
227 pvscan[12997] PV /dev/sdc online, VG vg is complete.
228 VG vg complete
229 use of --udevoutput:
231 $ pvscan --cache --listvg --checkcomplete --vgonline --udevoutput /dev/sdb
232 LVM_VG_NAME_INCOMPLETE='vg'
233 $ pvscan --cache --listvg --checkcomplete --vgonline --udevoutput /dev/sdc
234 LVM_VG_NAME_COMPLETE='vg'
235 use of --listlvs:
237 $ lvs -o name,devices vg
238 LV Devices
239 lvol0 /dev/sdb(0)
240 lvol1 /dev/sdc(0)
241 lvol2 /dev/sdb(1),/dev/sdc(1)
242 $ pvscan --cache --listlvs --checkcomplete /dev/sdb
244 pvscan[13288] PV /dev/sdb online, VG vg incomplete (need 1).
245 VG vg incomplete
246 LV vg/lvol0 complete
247 LV vg/lvol2 incomplete
248 $ pvscan --cache --listlvs --checkcomplete /dev/sdc
249 pvscan[13289] PV /dev/sdc online, VG vg is complete.
250 VG vg complete
251 LV vg/lvol1 complete
252 LV vg/lvol2 complete
253Red Hat, Inc LVM TOOLS 2.03.22(2) (2023-08-02) LVMAUTOACTIVATION(7)