While adding myself to the www-data group ( long story ) on my Ubuntu 12.04 server, I inadvertently forgot the -a
usermod -G www-data mark
Before long, I was told my username was not in the sudoers file and the incident was going to be reported, apparently back to me. Short story, here’s how I fixed it:
Reboot into recovery mode ( you know, the second option – Ubuntu, with Linux 3.5.0-45-generic (recovery mode) )
Select root – Drop to root shell prompt
Execute the following:
mount -o remount,rw / usermod -a -G sudo mark reboot
That first line got me out of read-only mode, the second added me back to the sudo/admin group and the last rebooted. Problem solved.
note: prior to 12.04, I believe you would need to use admin instead of sudo
