Basic Linux commands

Overview

This guide covers essential Linux commands for user and group management, which are fundamental for system administration and security. Whether you’re managing a single server or multiple systems, these commands will help you maintain user accounts efficiently.

Note

Most of these commands require sudo (superuser) privileges. If you’re not in the sudoers group, ask your system administrator to grant access before proceeding.

User Management

List All Users

Display all user accounts on the system:

cat /etc/passwd

Each line shows: username, password hash, UID, GID, full name, home directory, and login shell.

Add a New User

Create a new user account with a home directory:

sudo adduser username

This command will prompt you to:

Set a password
Confirm the password
Enter user information (name, room number, phone, etc.) — leave blank if not needed

Add User to Sudo Group

Grant administrative privileges to an existing user:

sudo usermod -aG sudo username

The -aG flag means: -a (append) and -G (groups). The user is added to the sudo group without removing from other groups.

Warning (Sudo Access)

Only add trusted users to the sudo group, as they gain root-level access. Always verify before granting sudo privileges.

Delete a User

Remove a user account while keeping their home directory:

sudo deluser username

Delete User and Home Directory

Completely remove a user and all their files:

sudo deluser --remove-home username

Danger (Permanent Deletion)

This command permanently deletes the user’s home directory and all files. There is no undo — ensure you have backups before proceeding.

Group Management

List All Groups

Display all groups on the system:

cat /etc/group

Each line shows: group name, password field, GID, and member list.

Create a New Group

sudo addgroup groupname

Add User to Group

sudo usermod -aG groupname username

Remove User from Group

sudo deluser username groupname

File Permissions and Ownership

Change Group Ownership

Assign a group to a directory and all its contents recursively:

sudo chgrp -R groupname directoryname

The -R flag applies the change recursively to all files and subdirectories.

Tip

For example, to give the www-data group ownership of a web directory:

sudo chgrp -R www-data /var/www/mysite

Change File Ownership

Change both user and group ownership:

sudo chown -R username:groupname directoryname

Example:

sudo chown -R ubuntu:ubuntu /home/ubuntu/myproject

View File Permissions

ls -l filename

Output shows permissions, owner, group, size, date, and filename.

Summary

These fundamental commands are essential for managing users, groups, and permissions in Linux systems. Regular practice will make these operations second nature for system administration tasks.

To make directory read write access to group

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sudo chmod g+rwx -R directoryname