The system did not boot: emergency mode

Not running Starting usually ~20 s

Step 7 of 7 · summary · 2 min

Summary

An fstab line without nofail that does not mount stops the boot in emergency mode: the console holds a root shell, and systemctl is-system-running prints maintenance.
journalctl -b -p err and systemctl --failed show the cause: the failed mount unit and Dependency failed for local-fs.target.
The repair: the root writable, the fstab fix, daemon-reload, mount -a, and systemctl default or systemctl reboot.
You choose rescue yourself when the filesystems are fine and you need to stop before the services.
At the start of the lesson findmnt --verify did not notice the szie= typo in the options, the mount failed on it, and local-fs.target took the boot into emergency mode.

Ubuntu 24.04