Ubuntu
grub2 package

grub-probe: error: unknown filesystem for lvm snapshot

Asked by kodiak on 2015-02-19

I am running Ubuntu 14.04 AMD64 on a headless KVM VPS, and I am experiencing issues with grub2 and lvm snapshots.

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$ /sbin/lvcreate -L 10G --snapshot --name lvroot-snap /dev/vgserver/lvroot
Logical volume "lvroot-snap" created

$ update-grub

Generating grub configuration file ...
Found linux image: /boot/vmlinuz-3.13.0-45-generic
Found initrd image: /boot/initrd.img-3.13.0-45-generic
Found linux image: /boot/vmlinuz-3.13.0-44-generic
Found initrd image: /boot/initrd.img-3.13.0-44-generic
Found linux image: /boot/vmlinuz-3.13.0-43-generic
Found initrd image: /boot/initrd.img-3.13.0-43-generic
grub-probe: error: unknown filesystem.
/usr/sbin/grub-probe: error: unknown filesystem.
Found Ubuntu 14.04.1 LTS (14.04) on /dev/mapper/vgserver-lvroot--snap
done
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This example above finished rather harmless. Yesterdays "$ aptitude safe-upgrade" forced me to kill the process from a second shell. Removing the snapshot did not work with dmsetup and lvremove. Luckily I could reboot the sever, followed by the removal of the snapshot and reinitialisation of the upgrade.

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$ uname -a
Linux server 3.13.0-45-generic #74-Ubuntu SMP Tue Jan 13 19:36:28 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

$ dpkg -l grub-common
ii grub-common 2.02~beta2-9ubuntu1 amd64 GRand Unified Bootloader (common files)

$ vgdisplay
  --- Volume group ---
  VG Name vgserver
  System ID
  Format lvm2
  Metadata Areas 1
  Metadata Sequence No 455
  VG Access read/write
  VG Status resizable
  MAX LV 0
  Cur LV 5
  Open LV 5
  Max PV 0
  Cur PV 1
  Act PV 1
  VG Size 498.00 GiB
  PE Size 4.00 MiB
  Total PE 127487
  Alloc PE / Size 125183 / 489.00 GiB
  Free PE / Size 2304 / 9.00 GiB
  VG UUID E5YSwZ-H2oR-Pi3h-1cog-3IBx-X21L-9t8kQL

$ lvdisplay
  --- Logical volume ---
  LV Path /dev/vgserver/lvroot
  LV Name lvroot
  VG Name vgserver
  LV UUID 5rauq2-G08r-f2j3-4Eof-cD20-gs50-ABr55m
  LV Write Access read/write
  LV Creation host, time sysresccd, 2014-12-20 16:20:28 +0100
  LV snapshot status source of
                         lvroot-snap [active]
  LV Status available
  # open 1
  LV Size 20.00 GiB
  Current LE 5120
  Segments 1
  Allocation inherit
  Read ahead sectors auto
  - currently set to 256
  Block device 252:0

  --- Logical volume ---
  LV Path /dev/vgserver/lvhome
  LV Name lvhome
  VG Name vgserver
  LV UUID rnuA4w-nw7u-B365-YTD1-taDu-Hw8F-Zb4Yb2
  LV Write Access read/write
  LV Creation host, time sysresccd, 2014-12-20 16:20:48 +0100
  LV Status available
  # open 1
  LV Size 20.00 GiB
  Current LE 5120
  Segments 1
  Allocation inherit
  Read ahead sectors auto
  - currently set to 256
  Block device 252:1

  --- Logical volume ---
  LV Path /dev/vgserver/lvvar
  LV Name lvvar
  VG Name vgserver
  LV UUID jS15g7-vlKx-PQED-V0mD-Gzzp-T8Jl-lVRkvF
  LV Write Access read/write
  LV Creation host, time sysresccd, 2014-12-20 16:25:10 +0100
  LV Status available
  # open 1
  LV Size 438.00 GiB
  Current LE 112127
  Segments 1
  Allocation inherit
  Read ahead sectors auto
  - currently set to 256
  Block device 252:2

  --- Logical volume ---
  LV Path /dev/vgserver/lvswap
  LV Name lvswap
  VG Name vgserver
  LV UUID RWGGlD-CL0s-nfej-W8HG-J1sX-iHop-GFGbZE
  LV Write Access read/write
  LV Creation host, time server, 2015-01-03 20:39:40 +0100
  LV Status available
  # open 2
  LV Size 1.00 GiB
  Current LE 256
  Segments 1
  Allocation inherit
  Read ahead sectors auto
  - currently set to 256
  Block device 252:3

  --- Logical volume ---
  LV Path /dev/vgserver/lvroot-snap
  LV Name lvroot-snap
  VG Name vgserver
  LV UUID GuOtc7-idei-jvWU-y2D0-pnlX-m3A2-hqvXUC
  LV Write Access read/write
  LV Creation host, time server, 2015-02-19 12:08:43 +0100
  LV snapshot status active destination for lvroot
  LV Status available
  # open 1
  LV Size 20.00 GiB
  Current LE 5120
  COW-table size 10.00 GiB
  COW-table LE 2560
  Allocated to snapshot 0.58%
  Snapshot chunk size 4.00 KiB
  Segments 1
  Allocation inherit
  Read ahead sectors auto
  - currently set to 256
  Block device 252:4

$ cfdisk -P s /dev/vda
Partition Table for /dev/vda

First Last
# Type Sector Sector Offset Length Filesystem Type (ID) Flag
-- ------- ----------- ----------- ------ ----------- -------------------- ----
Pri/Log 0 2047* 0# 2048*Free Space None
1 Primary 2048* 4196351* 0 4194304*Linux (83) Boot
2 Primary 4196352* 1048575999* 0 1044379648*Linux LVM (8E) None

$ mount
/dev/mapper/vgserver-lvroot on / type ext4 (rw)
proc on /proc type proc (rw)
sysfs on /sys type sysfs (rw,noexec,nosuid,nodev)
none on /sys/fs/cgroup type tmpfs (rw)
none on /sys/fs/fuse/connections type fusectl (rw)
none on /sys/kernel/debug type debugfs (rw)
none on /sys/kernel/security type securityfs (rw)
udev on /dev type devtmpfs (rw,mode=0755)
devpts on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=0620)
tmpfs on /tmp type tmpfs (rw,nosuid,size=4G)
tmpfs on /run type tmpfs (rw,noexec,nosuid,size=10%,mode=0755)
none on /run/lock type tmpfs (rw,noexec,nosuid,nodev,size=5242880)
none on /run/shm type tmpfs (rw,nosuid,nodev)
none on /run/user type tmpfs (rw,noexec,nosuid,nodev,size=104857600,mode=0755)
none on /sys/fs/pstore type pstore (rw)
/dev/vda1 on /boot type ext2 (rw)
/dev/mapper/vgserver-lvhome on /home type ext4 (rw)
/dev/mapper/vgserver-lvvar on /var type ext4 (rw)
systemd on /sys/fs/cgroup/systemd type cgroup (rw,noexec,nosuid,nodev,none,name=systemd)
grub-mount on /var/lib/os-prober/mount type fuse.grub-mount (rw,nosuid,nodev)
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