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alexkOffline
Post subject: Partition error upon kernel removal  PostPosted: 13.02.2016, 20:54



Joined: 2010-10-01
Posts: 288

Status: Offline
Every time I remove a kernel for many months now, I get an error related to my extended partition (sda4):
      Code:
[14124.540489] EXT4-fs (sda4): unable to read superblock
[14124.544555] EXT2-fs (sda4): error: unable to read superblock
[14124.550939] FAT-fs (sda4): bogus number of reserved sectors
[14124.558322] ufs: You didn't specify the type of your ufs filesystem
[14124.558322]
[14124.558322] mount -t ufs -o ufstype=sun|sunx86|44bsd|ufs2|5xbsd|old|hp|nextstep|nextstep-cd|openstep ...
[14124.558322]
[14124.558322] >>>WARNING<<< Wrong ufstype may corrupt your filesystem, default is ufstype=old

Something wrong with my extended partition?
      Code:
$ sfdisk -Vl /dev/sda4
Failed to read extended partition table (offset=33688305): Invalid argument
Disk /dev/sda4: 1 KiB, 1024 bytes, 2 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x00000000

Device      Boot    Start      End  Sectors  Size Id Type
/dev/sda4p1            63 33688304 33688242 16.1G 82 Linux swap / Solaris
/dev/sda4p2      33688305 96630974 62942670   30G  5 Extended
Total allocated sectors 33688305 greater than the maximum 2.

$ sfdisk -Vl
Disk /dev/sda: 298.1 GiB, 320072933376 bytes, 625142448 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xffffffff

Device     Boot     Start       End   Sectors  Size Id Type
/dev/sda1              63 167766794 167766732   80G  b W95 FAT32
/dev/sda2       167766795 213905474  46138680   22G 83 Linux
/dev/sda3       213905475 465563699 251658225  120G 83 Linux
/dev/sda4       465563700 625137344 159573645 76.1G  5 Extended
/dev/sda5       465563763 499252004  33688242 16.1G 82 Linux swap / Solaris
/dev/sda6       499252068 562194674  62942607   30G 83 Linux
/dev/sda7       562194738 616751414  54556677   26G 83 Linux
/dev/sda8       616755200 625135615   8380416    4G  b W95 FAT32
Remaining 10802 unallocated 512-byte sectors.
 
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slhOffline
Post subject: RE: Partition error upon kernel removal  PostPosted: 13.02.2016, 22:12



Joined: 2010-08-25
Posts: 949

Status: Offline
Yes, and no.

The error message in question comes from "os-prober", which is called as a hook whenever kernel are installed/ removed or grub2 is updating. os-prober is designed to scan your system for other installed operating systems (Windows, but also other Linux systems, *BSD, Solaris, etc.) in order to add them to your grub.cfg and make them selectable from grub2's boot menu. Given that there are a lot of weird ways some operating systems need to set up their boot environment (some of which aren't even mountable from Linux - and os-prober doesn't required those to be permanently mounted either), os-prober employs quite a few heuristics for trying to match up the situation found on your system to its internal detection mechanisms. This also involves trying to access (even mount) partitions that look weird or empty, whenever os-prober fails (e.g. because a partition really is empty, or something the kernel can't make any sense of), it can leave some noisy error messages (this is more of a cosmetic, but often scary issue). In some very rare circumstances, os-prober's detection attempts might even be problematic to disk integrity (mounting usually involves replaying the fs journal, which would be bad if there are concurrent accesses to the same filesystem from independent OS instances, think virtual machines with seemingly exclusive access to a block device, like a sub-partitioned lvm2 logical volume).

So scary error messages caused by os-prober usually aren't really that scary once you know what happens/ why the kernel complains. If you don't need os-prober (no parallel booting required), it's safe to purge the package (and also saves some time during kernel installs/ removals).

What is a bit worrying, is what "sfdisk -Vl /dev/sda4" seems to tell you, which appears like you might have sub-partitioned /dev/sda4 even further (not by using logical partitions, but more like in the sense of BSD disk slices or the virtual machine case with its own sub-partitions on its own block device), unless you have a reason for this being the case, it might be a hint for partitioning problems on your system.
 
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