Linux – regular user to admin user in linux

If the admin user should be able to edit many things, then admin should be a member of ville's group, not the other way around.

The way I manage users and groups is to give each user his/her own private group and set the default umask to 002 (you could do 007 if you want to make sure users cannot read each other's files by default as well). Then, when users need to be able to write to the same files, put them in a shared group, chgrp the directory to that group, and set the setgid flag on the directory (that will make sure any additional files or subdirectories created will have the same group).

You'll have to boot into recovery mode to gain root (system-wide) access in order to repair

If you have a single-boot (Ubuntu is the only operating system on your computer), to get the boot menu to show, you have to hold down the Shift key during bootup.

From the boot menu, select recovery mode

After you select recovery mode and wait for all the boot-up processes to finish, you'll be presented with a few options. In this case, you want the Drop to root shell prompt option.

/etc/group is the file that defines the groups on the system

You can then use adduser username admin to readd your user to the admin group.

Alternatively you can use the vigr command to edit the /etc/group file safely

format example;

group-name:x:group-number:user1,user2
admin:x:110:username