User Management Basics
This will cover the basics of user and group management as well as touch on the abilities of super users.
Users and superusers
GNU/Linux is designed to keep you from doing things that would damage your system. Each person is given their own account. All of a user’s files are labeled as their own and other people usually can’t change them. It is the same way for processes. Processes are labeled as belonging to someone, and you can only start and stop processes that belong to you.
But some processes belong to no one, and sometimes processes belonging to someone else get out of control. To affect those processes you have to become a superuser. A superuser, like a superhero, has amazing powers that mere mortals do not. They can start or stop any process; restrict access to files, or free them; add and remove users; and any of a number of incredible things. A superuser can also completely trash your system, so remember “with great power comes great responsibility”.
Since being a superuser is so dangerous, most people only become one when they must. This is one of the major reasons that people use the command line. They login to a terminal as a superuser, and they logout when they have finished the task that they came to do.
On a GNU/Linux system, the superuser is called “root”. When you run top you will often find processes that are owned by root, and only root can kill those processes. To become root you must switch user using the command su. When you type su root it will prompt you for a password.
rosalyn@onizuka:~$ su root Password:
You had to set a root password when you installed the Linux kernel, so the person who installed your system should have the root password. When you have the root password, you have ABSOLUTE CONTROL over the system, so it should not be given out casually.
If the person guarding the password refuses to give you this power, and you are tired of asking them to do something for you such as install new packages in a Debian system using apt-get install, they can give you partial power by using the command sudo. It means “switch user and do”.
User Management
How to add a user
While logged in as root, type:
adduser username
Where “username” is the name of the user you want ot add. Enter the password for the user when prompted.
How to change a password
While logged in as root or the user that will be changed, type:
passwd username
Where “username” is the name of the user whose password you want to change. If “passwd” is typed, the password will be changed for the user, you are logged in as.
How to remove a user
While logged in as root, type:
userdel -r username
Where “username” is the name of the user you want to remove. This will remove the user’s home directory. You can delete the user without the “-r” option and delete the user’s home directory manually. If the group the user was in, is no longer needed, you may delete it by editing the “/etc/group” file.
Group Management
To add a new group use groupadd command
To delete a group use groupdel command
To modify a group use groupmod command
/etc/group is a group file. You can edit group file using vi text editor.
Create a group named webusers
Code:
groupadd webusers
Create a group named ftpusers with GID 300
Code:
groupadd -g 300 ftpusers
Rename a group i.e. change ftpusers to inetuser
Code:
groupmod -n inetuser ftpusers
Remove or delete a group
Code:
groupdel ftpusers
For more info and options on these commands read:
Code:
man groupadd man groupdel man groupdel man 4 group
Please see: Understanding /etc/passwd, /etc/group, /etc/sudoers, and /etc/skel/ for further information.
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