Essential Linux Commands for Managing Users and Groups

User Management

1. useradd → Creates new user account in system.

   useradd john

2. passwd → Sets/update a user’s password

   passwd john

3. usermod → modifies a user’s account properties such as username, home directory or shell

   usermod -l newname john

4. userdel → Deletes a user account from the system

   userdel john

5. chage → Manages password expiration settings for a user

   chage -l john (to list password expiration details)

6. su → switches the current user session to another user account(like root)

   su - john

7. whoami → Displays the username of current user

   whoami

8. id → Shows the user ID(UID) and group ID(GID) of a user

   id john

9. finger → Displays detailed information about a user, such as login time and home directory

   finger john

Group Management

1. groupadd → Creates a new group in the system.

   groupadd devops

2. groupdel → Deletes an existing group from the system.

   groupdel devops

3. groupmod → Modifies name or GID of a group

   groupmod -n newgroup devops

4. gpasswd → Administers a group by adding or removing members

   gpasswd -a john devops (adds user to group)

User and Group Administration

1. usermod -aG → adds a user to a supplementary group

   usermod -aG sudo john

2. groups → Displays the groups that a user belongs to.

   groups john

3. newgrp → login to a new group , changing the user’s group ID during session.

   newgrp devops

4. chown → Changes the ownership of the file or directory to a users or group

   chown john:devops file.txt

5. chmod → Modifies the permissions of a file or directory for users, groups and others

   chmod 755 file.txt

6. getent →Retrieves entries from the system’s user, group or other administrative database

   getent passwd john(fetches user info)

7. last → Displays a list of the last logged on users

   last

8. w → Shows who is logged in and what they are doing.

   w

9. who → Displays the list of currently logged-in users

   who

These commands are foundational for managing users and groups in Linux systems, helping with tasks from creating accounts to handling permissions.