My root filesystem is btrfs. There were some system updates that were installed by Software Updater. I was also backing up another partition using grsync on an external disk that was cloned using Clonezilla (so the root partition on the external disk has the same UUID as the root partition on the system - I know it's a bad idea). When the external drive got mounted, the root mount point also changed to the external disk's root partition automatically. I wanted to avoid auto mounting of the root partition in the external disk but couldn't get it changed since it was already mounted. I may have messed up /etc/fstab.

Long story short, now I'm unable to complete the boot (which was working well before) - the external disk is not connected, and so there are no UUID conflicts. The system shows the message "Scanning for Btrfs filesystems" and waits there indefinitely (waited several tens of minutes).

Since my filesystems is indeed btrfs, I can't remove btrfs even from recovery mode.

  • I have used recovery mode to check the disks.
  • I have also run btrfs scrub / and it was successful (no errors).

If I switch to the shell using Ctrl Alt F1, it doesn't show /home as mounted (this is on the same disk/partition as /).

What can I do to troubleshoot what's happening and resolve this issue?

  • What's the output of /etc/fstab? Are all of the partitions listed in there available to mount? – Simon Quigley Jul 30 '17 at 8:58
  • /etc/fstab has entries for /boot/efi, one for swap, and another two entries for a couple of data partitions (/dev/disk/by-label entries). I don't see entries for / or /home/home ("home" is also the username here). Don't know if they're supposed to be there because I didn't remove them from this file. Plus, /home/home is a btrfs subvolume (default way of /@ and /@home being created). I'm not very clear on these distinctions. – www Jul 30 '17 at 9:11
  • There are just two comment lines in /etc/fstab saying "/ was on /dev/sda4 during installation" and "/home was on /dev/sda4 during installation". The disk /dev/sda4 is my root partition. I would really like to avoid reinstalling the OS and reinstalling/reconfiguring applications. – www Jul 30 '17 at 9:13
  • Thanks a lot, @SimonQuigley for pointing me to look at /etc/fstab closely. – www Jul 30 '17 at 10:32

Luckily, I had a backup of /etc/fstab and found that it had the mount points (btrfs type) for both / and /home (missing in /etc/fstab in the current system). So I added the two entries as-is from the backup into /etc/fstab to mount these two and the system booted successfully (not sure how those entries got removed).

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