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User Management

In Linux, users are like different characters in a multiplayer game, each with their own roles, permissions, and access levels. Some are administrators (root), while others are regular users, who looks like they can do everything in their own /home, but when administrators says u can't, u can't. like many of us in this world.

regular users have limitations imposed by the administrators. Administrators can perform any action on the system, including installing software, changing system settings, and managing other users. Regular users, on the other hand, can only perform actions within their own permissions, such as creating files in their home directory and running applications. Even tho the administrators can delete and limit your "life" if they want. Just like many of us in this world.

Here is how administrators (root) can manipulate users in Linux.

Check User​

  1. List all user in the system
cat /etc/passwd
  1. List curently logged-in user
who # show simple output
w   # include uptime, load, and what users are doing
  1. Check user group
groups [USERNAME]
  1. Show group membership of current user
id
  1. Find Logged-In Users History
last [USERNAME]
  1. Check if user exist
genent passwd [USERNAME]

Manipulating User​

Add User​

sudo useradd [USER]
sudo useradd -g [GROUP] [USER] # Add User and Assign Primary Ggoup
sudo useradd -G [GROUP,GROUP] [USER] # Add User and Assign Secondary groups

Modify User​

sudo usermod -g [GROUP] [USER] # Change primary group 
sudo usermod -aG [GROUP,GROUP] [USER] # Append secondary groups 
sudo usermod -d [NEW_HOME] [USER] # Change home directory 
sudo usermod -l [NEW_NAME] [USER] # Change login name 
sudo usermod -L [USER] # Lock the user account 
sudo usermod -U [USER] # Unlock the user account

Delete User​

sudo userdel [USER] # Delete user account
sudo userdel -r [USER] # Delete user and their home directory

Manipulating Groups​

Linux groups allow multiple users to share the same permissions. Here’s how to manage groups:

sudo groupadd [GROUP]                    # Add Group
sudo groupmod -n [NEW_GROUP] [OLD_GROUP] # Rename a group
sudo groupmod -g [NEW_GID] [GROUP]       # Change GID
sudo groupdel [GROUP]                    # Delete group
sudo gpasswd -d [USER] [GROUP]           # Remove user from group
cat /etc/group                           # Show all groups
groups [USER]                            # Show User's Group Membership

Sudoers Management​

The sudoers file controls which users have permission to run commands as root or other privileged users. The file is located at /etc/sudoers. To edit the sudoers file safely, use:

sudo visudo

Configuring Passwordless Sudo​

Add this line to the sudoers file to make user run commands with sudo without password

# Allow a specific user to run sudo commands without entering a password
[USER] ALL=(ALL) NOPASSWD: ALL
# Allow a specific user to run specific commands with sudo commands without entering a password
[USER] ALL=(ALL) NOPASSWD: /usr/bin/dnf # example command
# Allow a specific group to run specific commands with sudo without a password:
%devs ALL=(ALL) NOPASSWD: /usr/bin/dnf  # example comand

Checking Sudo Privileges​

To check if a user has sudo privileges:

sudo -l -U [USER]