I have recently get a bad experience on blowing up my home Ubuntu desktop by adding jimmy as the user again. Jimmy is no longer belongs to the sudoer group and I fail to add anyone back to the sudoer group. I need to use the linux single user mode / recovery mode to get back my account.

The sequence is as followed.

1. In GRUB, select recovery
2. I will be prompted with a root shell. However, the root FS is just mount as read only.

mount -o rw,remount /

3. Add back sudoer to jimmy

useradd jimmy -G sudo