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, 4096000
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.

lsblk:
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.

8

1 Answer

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

3

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