‘user’ is not in the sudoers file
This happens to me while i try to use sudo on any command, in case it happens to you, here is the solution.
2: Password: <ur_root_password>
3: chmod +w /etc/sudoers
4: echo 'raymond (ALL)=ALL ALL' >> /etc/sudoers
5: chmod -w /etc/sudoers
What it does is to add ur account to the sudoers file by making it writable through ur root account (su = superuser).