I use Ubuntu 9.10
I changed my password. After I restarted my machine and tried to do sudo whatever...
I got
"username" is not in the sudoer list.
What should I do to get back in there?
On Ubuntu, you need to be in the admin
group. If you have left the admin group, then try booting to the recovery console:
# usermod -a -G admin your username
You have to check the /etc/sudoers
file.
It is worth it to note that you will have to be root in order to read / edit the file. See visudo.