Bug#378144: broken(?) snapshot produces hopeless error message
Ian Jackson
Version: 2.01.04-5
I am submitting two bug reports about this one experience; please do
not confuse them. This report is about the hopeless error message:
root@(none):~# lvchange -a y /dev/vg-main/lv-usr
Can't expand LV: Snapshot support missing from kernel?
root@(none):~#
This is nearly the worst kind of error message possible. (Worse would
have been no message at all.)
It:
* Fails to give the details of what lvchange tried and why it
didn't work, which is the whole point of an error message.
* Lies (I wasn't trying to expand any LV)
* Speculates wrongly about the cause
Even an incomprehensible message giving obscure details of the innards
would be better. Eg,
lvchange: neutron flow polarisation violates Fermi principle
or
lvchange: IONFPLR: No such device or address
If no useful details are available then it should say
LVM system: the operation failed and we are too lame to say what went wrong
which is at least truthful.
As an interim measure I suggest that all messages in the LVM tree
which appear to be speculations rather than reports about the causes
should be changed to say something like:
LVM operation failed. "Can't expand LV: Snapshot support missing
from kernel?" may help or may be a lie
Ian.
Transcript:
-----------
I had to reboot my machine. During shutdown, this happened:
The system is going down for reboot NOW!
INIT: Sending processes the TERM signal
...
Unmounting remote and non-toplevel virtual filesystems...done.
Deconfiguring network interfaces...done.
Deactivating swap...done.
Unmounting local filesystems...umount: /var: device is busy
umount: /dev/mapper/vg--main-lv--usr busy - remounted read-only
umount: /: device is busy
done.
mount: / is busy
Shutting down LVM Volume Groups...
Can't deactivate volume group "vg-main" with 2 open logical volume(s)
Rebooting... Restarting system.
I don't know why /var and /usr were busy.
Before the reboot, lv-usr had an snapshot which may or may not have
become full. The snapshot was created, I think, some time ago, and I
can't find any record of it having been dropped or removed.
After the first reboot, e2fsck demanded a reboot after fiddling with
my non-LVM'd /.
After the second reboot, this happened:
Setting up LVM Volume Groups...
Reading all physical volumes. This may take a while...
Found volume group "vg-main" using metadata type lvm2
Can't expand LV: Snapshot support missing from kernel?
8 logical volume(s) in volume group "vg-main" now active
Checking all file systems...
fsck 1.37 (21-Mar-2005)
Failed to open the device '/dev/mapper/vg--main-lv--usr': No such file or directory
[ various messages about fscks of other volumes elided ]
fsck failed. Please repair manually.
CONTROL-D will exit from this shell and continue system startup.
Give root password for maintenance
(or type Control-D to continue):
root@(none):~# mount
/dev/sdb1 on / type ext2 (rw)
proc on /proc type proc (rw,paranoid)
sysfs on /sys type sysfs (rw)
devpts on /dev/pts type devpts (rw,gid=5,mode=620)
tmpfs on /dev/shm type tmpfs (rw)
root@(none):~# ls /dev/mapper/vg--main-lv*
/dev/mapper/vg--main-lv--log /dev/mapper/vg--main-lv--u2
/dev/mapper/vg--main-lv--news /dev/mapper/vg--main-lv--u3
/dev/mapper/vg--main-lv--swap /dev/mapper/vg--main-lv--var
/dev/mapper/vg--main-lv--u /dev/mapper/vg--main-lv--volt
root@(none):~# vgchange -a y
Can't expand LV: Snapshot support missing from kernel?
8 logical volume(s) in volume group "vg-main" now active
root@(none):~# vgchange -a y /dev/mapper/vg--main-lv--usr
Invalid volume group name: mapper/vg--main-lv--usr
root@(none):~# lvchange -a y /dev/mapper/vg--main-lv--usr
Volume group "mapper" not found
root@(none):~# lvchange -a y /dev/vg-main/lv-usr
Can't expand LV: Snapshot support missing from kernel?
root@(none):~# vgdisplay
--- Volume group ---
VG Name vg-main
System ID chiark1090621977
Format lvm2
Metadata Areas 5
Metadata Sequence No 191
VG Access read/write
VG Status resizable
MAX LV 256
Cur LV 10
Open LV 0
Max PV 256
Cur PV 5
Act PV 5
VG Size 187.65 GB
PE Size 4.00 MB
Total PE 48039
Alloc PE / Size 17025 / 66.50 GB
Free PE / Size 31014 / 121.15 GB
VG UUID GgVUxo-Oj7N-PwQi-cNJq-OsHQ-kRNa-TI2HYf
root@(none):~# vgdisplay -v
Finding all volume groups
Finding volume group "vg-main"
--- Volume group ---
VG Name vg-main
System ID chiark1090621977
Format lvm2
Metadata Areas 5
Metadata Sequence No 191
VG Access read/write
VG Status resizable
MAX LV 256
Cur LV 10
Open LV 0
Max PV 256
Cur PV 5
Act PV 5
VG Size 187.65 GB
PE Size 4.00 MB
Total PE 48039
Alloc PE / Size 17025 / 66.50 GB
Free PE / Size 31014 / 121.15 GB
VG UUID GgVUxo-Oj7N-PwQi-cNJq-OsHQ-kRNa-TI2HYf
--- Logical volume ---
LV Name /dev/vg-main/lv-var
VG Name vg-main
LV UUID 000000-0000-0000-0000-0000-0000-000000
LV Write Access read/write
LV Status available
# open 0
LV Size 3.00 GB
Current LE 768
Segments 2
Allocation normal
Read ahead sectors 1024
Block device 254:0
--- Logical volume ---
LV Name /dev/vg-main/lv-u2
VG Name vg-main
LV UUID 000000-0000-0000-0000-0000-0000-000001
LV Write Access read/write
LV Status available
# open 0
LV Size 7.95 GB
Current LE 2036
Segments 4
Allocation normal
Read ahead sectors 1024
Block device 254:1
--- Logical volume ---
LV Name /dev/vg-main/lv-swap
VG Name vg-main
LV UUID 000000-0000-0000-0000-0000-0000-000002
LV Write Access read/write
LV Status available
# open 0
LV Size 1.00 GB
Current LE 256
Segments 1
Allocation contiguous
Read ahead sectors 16
Block device 254:2
--- Logical volume ---
LV Name /dev/vg-main/lv-u
VG Name vg-main
LV UUID 000000-0000-0000-0000-0000-0000-000003
LV Write Access read/write
LV Status available
# open 0
LV Size 5.88 GB
Current LE 1506
Segments 1
Allocation normal
Read ahead sectors 1024
Block device 254:3
--- Logical volume ---
LV Name /dev/vg-main/lv-usr
VG Name vg-main
LV UUID 000000-0000-0000-0000-0000-0000-000004
LV Write Access read/write
LV snapshot status source of
device-mapper ioctl cmd 12 failed: No such device or address
device-mapper ioctl cmd 12 failed: No such device or address
/dev/vg-main/chiark-backup [INACTIVE]
LV Status NOT available
LV Size 2.27 GB
Current LE 581
Segments 1
Allocation normal
Read ahead sectors 1024
--- Logical volume ---
LV Name /dev/vg-main/lv-volt
VG Name vg-main
LV UUID 000000-0000-0000-0000-0000-0000-000005
LV Write Access read/write
LV Status available
# open 0
LV Size 29.49 GB
Current LE 7549
Segments 6
Allocation normal
Read ahead sectors 1024
Block device 254:4
--- Logical volume ---
LV Name /dev/vg-main/lv-log
VG Name vg-main
LV UUID 000000-0000-0000-0000-0000-0000-000006
LV Write Access read/write
LV Status available
# open 0
LV Size 4.92 GB
Current LE 1259
Segments 1
Allocation normal
Read ahead sectors 1024
Block device 254:5
--- Logical volume ---
LV Name /dev/vg-main/lv-u3
VG Name vg-main
LV UUID 000000-0000-0000-0000-0000-0000-000007
LV Write Access read/write
LV Status available
# open 0
LV Size 3.91 GB
Current LE 1000
Segments 1
Allocation normal
Read ahead sectors 1024
Block device 254:6
--- Logical volume ---
LV Name /dev/vg-main/lv-news
VG Name vg-main
LV UUID 000000-0000-0000-0000-0000-0000-000008
LV Write Access read/write
LV Status available
# open 0
LV Size 5.59 GB
Current LE 1431
Segments 2
Allocation normal
Read ahead sectors 1024
Block device 254:7
--- Logical volume ---
LV Name /dev/vg-main/chiark-backup
VG Name vg-main
LV UUID 1rwSbR-73Wz-Cul1-Exjf-raA0-vy4m-QGm8o9
LV Write Access read/write
device-mapper ioctl cmd 12 failed: No such device or address
device-mapper ioctl cmd 12 failed: No such device or address
LV snapshot status INACTIVE destination for /dev/vg-main/lv-usr
LV Status NOT available
LV Size 2.27 GB
Current LE 581
Segments 3
Snapshot chunk size 8.00 KB
Allocated to snapshot 100.00%
Allocation inherit
Read ahead sectors 0
--- Physical volumes ---
PV Name /dev/sda2
PV UUID 3zbY3o-brwM-ctB4-QNV3-RQ3K-YC3V-cjkapA
PV Status allocatable
Total PE / Free PE 4326 / 0
PV Name /dev/sdc1
PV UUID 4JEgFW-nB6H-B59f-Wecn-Vnq7-SJpE-Seu2qv
PV Status allocatable
Total PE / Free PE 1429 / 0
PV Name /dev/sdc2
PV UUID wXEBZz-JEh7-rSUL-zDUR-Pktw-mPJO-G716I4
PV Status allocatable
Total PE / Free PE 833 / 0
PV Name /dev/sdc3
PV UUID YuuRB9-doSq-7X67-CGXl-2z05-Br8G-x0jjOb
PV Status allocatable
Total PE / Free PE 6484 / 0
PV Name /dev/sdb2
PV UUID 4quhV2-NTz5-1PVJ-GurZ-13Rg-WxbK-C1pq9y
PV Status allocatable
Total PE / Free PE 34967 / 31014
root@(none):~# lvremove /dev/vg-main/chiark-backup
Logical volume "chiark-backup" successfully removed
root@(none):~# lvchange -a y /dev/vg-main/lv-usr
root@(none):~# df
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sdb1 139986 81616 51143 62% /
tmpfs 518008 0 518008 0% /dev/shm
root@(none):~# mount -o remount,ro /
root@(none):~# reboot
And then all was well.
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