Cannot lock '/etc/group' in recovery mode
I have a laptop with Ubuntu 11.10 that is shared between myself and two other family members. My user id was setup as the only "Administrator" on the laptop. The other users were setup as "Standard" users. In my attempt to try to add myself to the user groups for the other users, I somehow deleted myself from the admin groups. I used the "usermod" command from the terminal. I must have neglected to include the proper switches or syntax for the update.
It looks like I successfully added my userid to the group associated with my wife's account. When I use the "groups" command, I can see only my id and my wife's id in the list. I no longer see the "admin" or "adm" groups, and others that used to be listed. When I go into System Settings > User Accounts it looks like my ID is now listed as a "Standard" user. I would like to change my account back to "Administrator", but now I can't.
I did some searches for solutions and found that I would need to boot into Recovery Mode and execute the usermod command from the root session. I was able to successfully boot into Recovery Mode and get to the root session. I was trying to execute the command "usermod -a -G admin user1" to add my id (user1) back to the admin group.
When I execute the command from the root session, I get the error message "usermod: cannot lock /etc/passwd; try again later". I tried preceding the usermod command with "sudo", but it didn't make a difference, same error. I then tried adding a new user using adduser, thinking I would try to create a new userid and make the new userid part of the admin group. I get the same error using the adduser command.
I saw some posts that recommend looking for and deleting files that end in ".lock" in the etc directory. The only file I found was .pwd.lock which I haven't touched.
I am at a loss as to what to try next. I am relatively inexperienced with Ubuntu and Linux, so alot of this is new to me. Any help you can provide would be much appreciated.