How do I add myself into the sudoers group? [duplicate]

Possible Duplicate:
How do I add a user to the “sudo” group?

I've added myself back into the admin's group I think, by following this.

But I still can't do commands like:

sudo aptitude update

I get the message

oshirowanen is not in the sudoers file.  This incident will be reported.

How do I add myself into the sudoers group now that I am in the admin group?

Login as root or su to get root prompt

type visudo

an editor will open find a line says

root ALL=(ALL) ALL

add one with your username below that

user ALL=(ALL) ALL

Type ctrl+x Type Y to the prompt

If you're in the admin group (or the sudo group starting with Ubuntu 12.04) but that group isn't configured in /etc/sudoers to be able to run commands as root with sudo, you can fix that problem the same way you'd fix a broken sudoers file:

pkexec visudo

Then just edit the sudoers file to add whatever entries you need. In particular:

• Ubuntu systems before 12.04, or those that were upgraded from a version before 12.04, should have this:

  # Members of the admin group may gain root privileges
  %admin ALL=(ALL) ALL
  

• Ubuntu 12.04 and later should have this (even if they also have the above lines because they were upgraded from an earlier release):

  # Allow members of group sudo to execute any command
  %sudo   ALL=(ALL:ALL) ALL
  

This pkexec method works (on desktop systems) because Ubuntu systems with a GUI installed have two separate mechanisms for administrators to perform actions as root: sudo, and PolicyKit.

See this question about a different but similar problem, if you're curious and want more information:

• How to modify an invalid /etc/sudoers file? It throws an error and it's not allowing me to edit again to fix it