On a HP dc7900 i have Ubuntu 16.04 on /dev/sda2 and 18.04 on /dev/sda1, both booted via grub.

I never had any problems with 16.04, so I guess the hardware is OK.

Suddenly 18.04 does not boot anymore. At some point during booting:

uuid=5fa5fa5f-dbb5-4986-991d-49a793bb5711 not found ...

I don't know the exact message anymore. Boot-Repair intelligently removed 18.04 from grub. How can I add 18.04 back to grub?

fsck.ext4 -v /dev/sda1

e2fsck 1.42.13 (17-May-2015)
/dev/sda1 has unsupported feature(s): metadata_csum
e2fsck: Get a newer version of e2fsck!

mount -t ext4 /dev/sda1 /mnt

No problem filesystem on sda1 is read/write accessible, no errors at all! So the filesystem seems to be still OK?

Ubuntu program Disks => sda1 unknown partition type

Program GParted => ext4

mke2fs -n /dev/sda1

mke2fs 1.42.13 (17-May-2015)
Creating filesystem with 5120000 4k blocks and 1281120 inodes
Filesystem UUID: fb4ee7db-bcd6-4a78-9986-86e56ac24f0c
Superblock backups stored on blocks: 
    32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 

e2fsck -f -b 32768 /dev/sda1
e2fsck 1.42.13 (17-May-2015)
e2fsck: Bad magic number in super-block while trying to open /dev/sda1

The superblock could not be read or does not describe a valid ext2/ext3/ext4
filesystem. If the device is valid and it really contains an ext2/ext3/ext4

Are all these superblocks defect or is there some other problem?

To me it seems the information about the filesystem type may have been damaged. How can I set it to ext4? Can the 18.04 instance be rescued or reinstalled?

The 18.04 was not quite stable:

  • sometimes it hung when powered down.
  • when clicking "settings" it would definitely freeze.
    What wondered me, at reboot I never saw a fsck.
    Are superblocks updated at powerdown? can these freezes be the cause of defect superblocks?

No Windows on this system.

sdb      8:16   0 931,5G  0 disk 
├─sdb9   8:25   0     8M  0 part 
└─sdb1   8:17   0 931,5G  0 part 
sr0     11:0    1  1024M  0 rom  
loop2    7:2    0  87,7M  1 loop /snap/keepassxc/49
loop0    7:0    0    45M  1 loop /snap/core18/442
sdc      8:32   0 931,5G  0 disk 
├─sdc9   8:41   0     8M  0 part 
└─sdc1   8:33   0 931,5G  0 part 
sda      8:0    0 465,8G  0 disk 
├─sda4   8:4    0     7M  0 part 
├─sda2   8:2    0  19,5G  0 part /
├─sda3   8:3    0 426,7G  0 part /sda3
└─sda1   8:1    0  19,5G  0 part 

sda1 is the bad one

sda2 16.04

sda3 holds data

sdb and sdc are zfs mirror disks, not relevant.

gdisk -l /dev/sda
GPT fdisk (gdisk) version 1.0.1

Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.
Disk /dev/sda: 976773168 sectors, 465.8 GiB
Logical sector size: 512 bytes
Disk identifier (GUID): 590C357D-ECF5-4EC4-A2A0-D50995D7C934
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 976773134
Partitions will be aligned on 2048-sector boundaries
Total free space is 2029 sectors (1014.5 KiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048        40962047   19.5 GiB    8300  
   2        40962048        81922047   19.5 GiB    8300  ubuntu2
   3        81922048       976758783   426.7 GiB   8300  home
   4       976758784       976773119   7.0 MiB     EF02  

mount -t ext4 /dev/sda1 /mnt
cat /mnt/etc/fstab :

UUID=5fa5fa5f-dbb5-4986-991d-49a793bb5711 /               ext4    errors=remount-ro 0   1  
/swapfile                                 none            swap    sw                0   0  
UUID="9b34e80a-e998-424e-98b9-8decdfe851d6" /sda3     ext4    errors=remount-ro 0   2     


= = = = Next steps:

Started Ubuntu 18.04 LiveCD

  1. fsck -f /dev/sda1 => OK no errors
  2. tune2fs -U 5fa5fa5f-dbb5-4986-991d-49a793bb5711 /dev/sda1 => OK
  3. blkid still does not show sda1 (sda2,sda3, rest are all in the output)

I tried boot-repair: it issues an error. To me it seems the filesystem type is missing on sda1.

$ blkid
/dev/sda2: UUID="28bb4996-360d-4639-9e50-86aae98011fe" TYPE="ext4" PARTLABEL="ubuntu2" PARTUUID="2e36442b-f19f-4226-8912-aa2f7238d7c1"
/dev/sda3: UUID="9b34e80a-e998-424e-98b9-8decdfe851d6" TYPE="ext4" PARTLABEL="home" PARTUUID="62ee15b5-cbc6-4a84-98a9-cdfe9989549f"
/dev/sdc1: LABEL="zfs-samba" UUID="4660143235353326727" UUID_SUB="4506863601154525374" TYPE="zfs_member" PARTLABEL="zfs-42c380b70bbdd342" PARTUUID="000598e0-1e8f-0240-af28-8d231f696a01"
/dev/loop0: TYPE="squashfs"
/dev/loop1: TYPE="squashfs"
/dev/loop2: TYPE="squashfs"
/dev/loop3: TYPE="squashfs"
/dev/loop4: TYPE="squashfs"
/dev/loop5: TYPE="squashfs"
/dev/loop6: TYPE="squashfs"
/dev/loop7: TYPE="squashfs"
/dev/sdb1: LABEL="zfs-samba" UUID="4660143235353326727" UUID_SUB="15368172379392166768" TYPE="zfs_member" PARTLABEL="zfs-00675688e5b3099d" PARTUUID="79a673f3-670f-7744-8a4c-27a45ad7597b"
/dev/sdd1: UUID="2018-07-25-03-21-56-00" LABEL="Ubuntu 18.04.1 LTS amd64" TYPE="iso9660" PTUUID="663eb4c4" PTTYPE="dos" PARTUUID="663eb4c4-01"
/dev/sdd2: SEC_TYPE="msdos" UUID="0D5F-1DB6" TYPE="vfat" PARTUUID="663eb4c4-02"
/dev/sda4: PARTUUID="68954dcd-3db6-484b-af0c-986360d2d0d7"
/dev/sdb9: PARTUUID="5c43b7a9-635c-ea4b-bc14-fd863ff0aea5"
/dev/sdc9: PARTUUID="682730d5-bc4a-4c4c-b4b4-262ffed34722"

No sda1 reported!

But again I can still mount by explicitly stating the filesystem type:

mount -t ext4 /dev/sda1 /mnt

Without -t ext4 it fails.

  • Do you dual/triple boot with Windows? Is your disk MBR or GPT formatted? Do you have access to a 18.xx Ubuntu Live DVD/USB? If so, the fsck needs to run from there, as it's newer than the fsck that you probably ran from 16.04. Can you edit your question with 1) a gparted screenshot, 2) sudo blkid, 3) cat /etc/fstab from sda1? Report back to @heynnema – heynnema Jan 7 at 16:03
  • @heynnema, see the extra info in the original question. – RobF Jan 7 at 18:06
  • Best is to run boot-repair to create boot-info-summary and provide link, this will give us better overview. – mook765 Jan 7 at 18:17
  • @RobF thanks for the info. You forgot sudo blkid. I'm a little confused with the info that you did provide. What is sda1 used for? 18.04? Did it ever boot to 18.04? Have you been playing with partitions, or editing /etc/fstab? Do you know how you got to this point? Do you have a Ubuntu Live DVD/USB 18.xx? – heynnema Jan 7 at 20:17
  • @heynnema sda1=ubuntu18.04 , sda2=ubuntu16.04. Both worked for a long time, but suddenly sda1 will not boot anymore. blkid /dev/sda1 => no info. blkid /dev/sda2 => expected info (type,uuid, label) – RobF Jan 7 at 20:44

You MUST have good backups before proceeding!

  • boot to a Ubuntu Live DVD/USB 18.xx
  • /dev/sda1 should not be mounted
  • open a terminal and type:

    sudo fsck -f /dev/sda1

If you have any problems at this point, then STOP, ping @heynnema with info.

  • in terminal type:

    sudo tune2fs -U 5fa5fa5f-dbb5-4986-991d-49a793bb5711 /dev/sda1

  • run Boot-Repair

  • boot to the GRUB menu and see if 18.04 appears and if you can now boot to it

  • I'm certainly not going to do anything when you put up a banner like that. – karel Jan 8 at 14:14
  • @karel that's good. I don't want the OP to use it, yet, either... until they complete my request for additional info (sudo blkid) that would support my answer completely :-) – heynnema Jan 8 at 14:24
  • @karel oh well, the OP didn't give me sudo blkid, AND went and did my answer anyway... – heynnema Jan 8 at 14:39

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