Ubuntu 12.04 LTS and later
Administrators are added to the sudo
group, but the admin
group is supported for backward compatibility. From the release notes:
Up until Ubuntu 11.10, administrator access using the sudo tool was granted via the admin
Unix group. In Ubuntu 12.04, administrator access will be granted via the sudo
group. This makes Ubuntu more consistent with the upstream implementation and Debian. For compatibility purposes, the admin
group will continue to provide sudo/administrator access in 12.04.
It is not created when you do a fresh install, though it is still present if you upgraded from previous distributions. Either way, the admin
group appears in the /etc/sudoers
file.
See implementation details and the official documentation.
Yes the root user is an official one.
That user comes from a long line of historical influences. It's the conventional name of the user who has all rights or permissions. Most Unix-linke operating systems have a root user. It's not always called "root". You may know the Administrator of Windows operating systems.
Some Linux derivates like Ubuntu allow administrator accounts which provide greater access (not a root account). In some cases, specially Ubuntu, the root user is disabled defaultly, because you can destroy the system with the root user if you do not know what you do.
The root user can do things that a normal user cannot for example:
- He can change the owner of files/directories
- He can bind network ports below 1024
- He has always the uid 0 and can be indentified by this id.
- Ergo: There is only one root
In Ubuntu (and other Linux derivates) there is a mechanism to gain root priviledges for a short amount of time. One of those mechanisms is sudo
. sudo
can be used to run a program with root priviledges, but with the users environment.
Edit: Short digression about sudo
:
The clue is the so called suid-bit that is on some programs such as sudo
. It allows to run the program with root priviledges, even if the root account is disabled (as in ubuntu). sudo
itself controls whether the user has the right to execute whatever he wants. So, you execute sudo
as root and sudo
decides if it executes the given command as root.
The system would not be operable without the root user. There must be a user with the id 0 and the name root (but it can be disabled due to suid/sudo). Or such mechanisms as the suid bit will not work. Hence your will not be able to gain root priviledges.
Source: Wikipedia
Best Answer
root: is a special account which is usually locked in Ubuntu. This account is in effect the ultimate super user and can change anything on the system. If you want to enable this account you can but its not recommended see How to enable root login? For how this can be done and a discussion on why its not recommended.
user: These are the users of your systems there are three types administrators, normal users and guest. Administrators can make major changes to the system while normal users can not. There is a useful summary in the RootSudo Comunity Documentation. The guest account is used to provide casual access to someone (to play a game, surf the web, etc.) without giving them access to other users files. Any files they create are automatically removed when they log out.
groups A user can be a member of one or more groups groups are used to control privileges within the system for example all administrators are in the
sudo
group but you can also create you own groups. You may for example have a sales team who need to share some files but you want to prevent other people from accessing these files. By creating a special group for these people you can do that. See:How can I share a directory with an another user? for how you can set this up.