The Problem
I recently migrated my hard drives to a ZFS pool and found myself stuck in Ubuntu's emergency mode after the first reboot I performed after creating the ZFS pool.
My server was stuck in the boot process and showed the following error on the screen:
You are in emergency mode.
After logging in, type "journalctl -xb" to view system logs,
"systemctl reboot" to reboot, "systemctl default"
or ^D to try again to boot into default mode".
After rebooting the server and watching the logs scroll on a monitor, I noticed the root cause was related to a very long search for certain drives. I kept seeing errors like this:
[ TIME ] Timed out waiting of device dev-disk-by/[disk-uuid]
I realized that I had not removed the /etc/fstab references that asked Ubuntu
to mount two disks on boot, but I had recently changed those disks to be part of
my ZFS pool instead. Therefore, Ubuntu was trying to identify and mount a disk
that was not available.
Now that we have an idea of the issue, let's move to solution.
The Solution
In order to fix the issue, I waited until I was allowed to type the root user's password, and then I executed the following command:
Within the fstab file, I needed to comment/remove the following lines at the
bottom of the file. You can comment-out a line by prepending a # symbol at the
beginning of the line. You can also delete the line entirely.
UUID=B64E53824E5339F7 /mnt/white-01 ntfs-3g uid=1000,gid=1000 0 0
UUID=E69867E59867B32B /mnt/white-02 ntfs-3g uid=1000,gid=1000 0 0
Once removing the lines above from the /etc/fstab file, save and exit the file
by hitting the Ctrl + x key combo.
You can now hit Ctrl + D to continue, or reboot:
Once rebooted, I was able to watch the machine boot properly and launch to the TTY login screen without errors!