How to reproduce:
1. delete an NTFS partition on secondary disk (rewrite with zeroes).
2. put there EXT4 partition instead.
3. reboot computer
=> ubuntu doesn't boot, allows only single-user mode.
By checking system log, I found out system was trying to mount the old NTFS partition and hanged on it, even though that is not at all a necessary partition. Then I checked /etc/fstab and found out the GUI tool did NOT remove the original record, when it deleted the partition on the drive.
By commenting it out I was able to get into the GUI again.
Ubuntu 15.10
pkg: gnome-disk-utility 3.16.2-0ubuntu2 0
The original line, that was left behind:
UUID=52D09468D09453D7 /backup ntfs defaults,umask=007,gid=46 0 0
The new line that the tool created:
/dev/disk/by-uuid/414e95a1-fb40-45a6-9b90-487a45337fdd /extdata auto nosuid,nodev,nofail,x-gvfs-show 0 0
ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: gnome-disk-utility 3.16.2-0ubuntu2
ProcVersionSignature: Ubuntu 4.2.0-30.35-generic 4.2.8-ckt3
Uname: Linux 4.2.0-30-generic x86_64
ApportVersion: 2.19.1-0ubuntu5
Architecture: amd64
CurrentDesktop: Unity
Date: Thu Feb 25 08:34:50 2016
EcryptfsInUse: Yes
InstallationDate: Installed on 2016-02-24 (0 days ago)
InstallationMedia: Ubuntu 15.10 "Wily Werewolf" - Release amd64 (20151021)
SourcePackage: gnome-disk-utility
UpgradeStatus: No upgrade log present (probably fresh install)
Thank you for taking the time to report this bug and helping to make Ubuntu better. The issue you are reporting is an upstream one and it would be nice if somebody having it could send the bug to the developers of the software by following the instructions at https:/