Unix or Linux commands for changing user rights

Recently I received the question via email -- "...How do I change user rights under UNIX? I am using Red Hat Enterprise Linux and my background includes Windows network..."

This is one of the fundamental questions asked by new Linux system administrators. As many of you may already know, both Linux and Windows are multi-user and control access to resources is based upon user id or usernames. Further users grouped into groups for ease of management and security.

However, Linux (and UNIX) stores and process user database in different format.

The root user

• The root user is the super user.
• The root user can control entire Linux system including files, process, applications etc. The root user has full access to system.
• You should not use root for day-to-day tasks as root has full system access.
• Never ever, give root password to anyone.

For more information see What defines a user account?

User database

• User database is stored in /etc/passwd file
• User passwords and password expiry information stored in /etc/shadow file

Group database

• User group information is stored in /etc/group file

UNIX/Linux User rights

There are two types of user rights (traditional):

• File level user rights or permissions granted using chmod and chown command
• Administrative (root) level rights granted using sudo.

If you type the following command:

$ ls -l

You’ll see something like the following:

-rw-r--r-- 1 vivek webusers 14814 2006-07-26 13:25 working-nixcraft.txt

Look at 3rd, 4th and last columns.

• vivek is username or the owner of the file (userid)
• webusers is group name, so all users in webusers can access file working-nixcraft.txt
• working-nixcraft.txt is the file name.

As the root user you can change or setup user file related rights/permission using chmod and chown command.

Task: change file owner and group

Consider following example:

$ ls -l foo.txt

Output:

-rw-r--r-- 1 vivek webgroups 8 2006-08-08 17:57 foo.txt

Change files ownership to tony user:

# chown tony foo.txt
# ls -l foo.txt

Output:

-rw-r--r-- 1 tony webgroups 8 2006-08-08 17:57 foo.txt

Change foo.txt group to ftpusers:

# chown tony:ftpusers foo.txt
# ls -l foo.txt

Output:

-rw-r--r-- 1 tony ftpuseers 8 2006-08-08 17:57 foo.txt

You can also operate on files and directories recursively using -R option. For example setup /var/www/html ownership to user lighttpd including subdirectories:

# chown -R lighttpd /var/www/html

Task: change files access rights/permissions

You need to use chmod command. Please refer the old article - how Linux file permissions work.

Task: Grant administrative rights to a normal user

You need to use sudo tool. It allows a permitted user to execute a command as the superuser or another user, as specified in the /etc/sudoers configuration file. Please refer previous article for more information.

A note for Ubuntu Linux users

You can use chmod and chown command to setup user rights. Make sure you prefix all commands with word (command) sudo:

$ sudo chown tony:ftpusers foo.txt

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