If you are getting kernel errors like
EXT4-fs (sda2): unable to read superblock EXT4-fs (sda2): unable to read superblock EXT4-fs (sda2): unable to read superblock FAT-fs (sda2): bogus number of reserved sectors FAT-fs (sda2): bogus number of reserved sectors qnx4: no qnx4 filesystem (no root dir).
for almost every storage like device in /dev/, you know something has to be wrong! However, we ignored those messages for months since everything seemed to be fined. Still, I was concerned.
Yesterday I decided to look into this again. Between the errors quoted above, there was a kernel warning saying
>>>WARNING<<< Wrong ufstype may corrupt your filesystem,
which didn’t sounded any better. Finally I found Debian Bug #788062 “os-prober corrupts LVs/partitions while being mounted inside a VM”. And indeed, our suspicious log entries start with
"debug: running /usr/lib/os-probes/50mounted-tests on /dev/sda2"
On kernel updates or manual grup-update usage this bug might corrupt your storage or put your file systems into read only without having any idea where to look for the problem.
And the moral of this story: apt purge os-prober on your servers and don’t expect debian-boot to react to such a bug within 6 months.
Update: I have noticed that the general behavior has been reported to Debian BTS back in Dec 2014. But it has been considered “entirely cosmetic”. It is also on Launchpad (Ub***u) since 2014. However, back then no severe impact has been reported.
