Regain Sudo rights after removing from admin group [duplicate]

Question

I accidentally removed myself from the admin group when editing the user. Now I can no longer use sudo. The error says: ber is not in the sudoers file. This incident will be reported.

I booted up in rescue mode, but, when going into root prompt, it asks me for the root password. I don't have one, and providing with my own (first and only ubuntu-user) password, it won't allow entrance.

My harddisk is encrypted, but only the /home/user part, not the entire disk, afaik.

What can I do?

Answer 1

Hmm well you've covered what I would have suggested first. Seems annoying that Rescue mode would hassle you for a password if the entire disk weren't encrypted (I don't know, that might be standard protocol).

I'd personally jump into a live environment (via Live CD or Live USB), mount the filesystem (assuming it isn't encrypted) and edit its etc/group file and add yourself back in. The resulting line should look something like this (though the GID may be different):

admin:x:115:oli

Or on Ubuntu 12.04, find the line for the sudo group instead of the admin group.

---

Alternatively, you can probably chroot from the LiveCD to run commands. (sudo password for the LiveCD is a blank password, just press return when prompted)

sudo mount /dev/sdYY /mnt  # change sdYY to your root partition
sudo mount --bind /dev  /mnt/dev
sudo mount --bind /dev/pts  /mnt/dev/pts
sudo mount --bind /proc /mnt/proc
sudo mount --bind /sys  /mnt/sys
sudo chroot /mnt

sudo adduser your-username admin

For Ubuntu 12.04 and later, add the user to the sudo group instead of the admin group:

sudo adduser your-username sudo

chroot drops you off at a root shell inside your filesystem so should let you do fancy things like adding users to groups. It's most useful for fixing boot issues but it can do a lot of gubbins.

Answer 2

At the grub boot-up menu, press e to edit the kernel launch command-line and append the word single at its end. This should boot the system on single-user mode (as root) and allow you to perform any modifications.