User & Group management : Complete Beginner’s Guide

One of the major work of a System Administrator is User & Group Management. We have to create new users & groups, delete old ones, providing users access to a group or folder etc etc. So, in this tutorial, we will learn how we can manage users & groups.

Linux systems have two types of users, general/normal user and root/super user . While general users have limited access to the Linux system, root users have access to anything & everything on the Linux system.

When a user is created a group with the same user name is also created. Every user has its own home directory, for user root its /root & for general users its located in /home/. Records with all the user information for all the users is maintained in /etc/passwd file & records for all the groups are kept /etc/group.

Let’s discuss these files in brief before we discuss the commands for user & group management.

/etc/passwd

This file contains list of all users with every line of the file containing information regarding single user. Format for each line is

Username:x:UID:GID:Comment:Home Directory: Default shell

Here, x is password for the user in encrypted form (stored in /etc/shadow file)

UID, is the user id

& GID is the group id for the user.

/etc/group

Just like /etc/passwd, it contains information for groups with each line having information for single group. Format for entries in this file is

Group name:x:GID:members

Where, x again means password in encrypted format.

Now let’s discuss commands for user & group management.

USER Management

Below mentioned are the commands that are used for user management,

Purpose                                                              Command

• Adding a user                                               useradd dan
• Assigning password to user                       passwd dan
• Changing home directory for user             useradd dan –d /home/new
• Setting expiry for user                                 useradd dan –e 2017-11-25
• Addding inactive period before expiry      useradd dan –f 2
• Changing default shell                                useradd dan –s /bin/sh
• Removing user                                             userdel dan
• Removing user with home directory         userdel –r dan

We can also modify default settings of a user after it has bee added with usermod command

• Setting expiry for user                      usermod –e 2017-11-25 dan
• Changing home directory                 usermod –d /home/new dan
• Changing default shell                      usermod –s /bin/sh dan
• Locking an account                           usermod –L dan
• Unlocking a locked account             usermod –u dan

Group Management

Following are the commands for managing groups

• Adding a group                                  groupadd  linuxgroup
• Adding user to group                        usermod –aG linuxgroup dan
• Changing owner & group of a file    chown dan:linuxgroup newfile.txt
• Changing only owner of a file          chown dan: newfile.txt
• Changing only group of a file          chown :linuxgroup newfile.txt
• Deleting a group                               groupdel linuxgroup

This completes our tutorial on user & group management.