I inadvertently failed to append myself to a group by using usermod -G group_name user_name instead of usermod -aG group_name user_name and now belong only to the group_name group.

The problem is: I can not bring up the grub2 menu with Left-Shift on boot, therefore I can not drop to root login and reinstate my sudo membership.

Is there another way?

To be clear, I have not lost my password, I have inadvertently removed myself from the admin group.


Following the advice given here I did the following:

  1. Boot from the installation stick (or disk)
  2. In Unity bring up a terminal with ctrl+T. If the boot sequence stalls for any reason (graphics in my case) switch to another tty. I switched to tty2 with ctrl+alt+F2.
  3. Mount your system root drive. On my system this requires sudo mount /dev/sda2 /mnt
  4. Gain access to the installed system by chrooting into it. In my example I typed sudo chroot /mnt, because my system's root directory / is mounted there from the previous command. You now have a bash session in your original installation with full privileges.
  5. Enter usermod -aG sudo user_name
  6. Reboot normally.
  7. Rejoin all the default groups with

    sudo usermod -aG lpadmin,sambashare,adm,cdrom,dip,plugdev user_name
  • Just stop using usermod for adding groups. This whole mess could have been avoided if you'd run adduser user_name group_name in the first place. – muru Mar 5 '16 at 8:25
  • So, @muru, the solution is to know everything about linux beforehand? I'll try to be omniscient in future. – Tony Martin Mar 5 '16 at 15:21
  • don't be stupid. Your problem was originally caused by you missing a crucial usermod option - -a. The solution is to be careful when you're messing with accounts. My comment was prompted by your continued usage of usermod when safer alternatives exist. – muru Mar 5 '16 at 15:24
  • I simply followed a tutorial on how to set up kismet, made a slip of the keyboard and found myself in the situation described. The tutorial did not offer alternatives. Nor did it offer a tutorial in all aspects of using and administering a Linux system. But thank you for the intelligence assessment. – Tony Martin Mar 6 '16 at 1:58
  • You're most welcome. – muru Mar 6 '16 at 1:59

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