Dealing with “Enter root passwd for maintenance mode”

If there is an error at boot because of editing improperly /dev/sdb1, could request root password.
Troubleshooting mode > Emergency mode.
Check the logs:
# journalctl -xb (booting messages).
q – quit journalctl.
Check if you can write in file system:
# touch fileName
Identify error into /etc/fstab and correct it.
# systemctl reboot