Basic linux commands For user management

Managing users in Linux is an essential aspect of system administration.

Linux provides a number of commands for creating, deleting, and modifying user accounts.

Below is a guide to some basic Linux user management commands that are commonly used:

Table of Contents

Key Commands for Linux user management

1. Viewing Current Users and Information

List all users: To list all users in the system, you can view the contents of the /etc/passwd file:
```
cat /etc/passwd
```
Each line in this file represents a user.
View information about a specific user: You can use the id command to view user information such as UID, GID, and group memberships:
```
id username
```
Show user login history: You can use the last command to show the login history of users:
```
last
```

2. Adding Users

Add a new user: To add a new user, you can use the useradd command. This will create a new user account:
```
sudo useradd username
```
Add a new user with a home directory and other options: You can specify options like the home directory, shell, and group with the -m, -s, and -G flags:
```
sudo useradd -m -s /bin/bash -G groupname username
```
- -m creates the home directory for the user.
- -s /bin/bash sets the shell for the user.
- -G groupname adds the user to a group.
Set a password for the user: After creating the user, you need to set a password:
```
sudo passwd username
```

3. Modifying User Accounts

Change a user’s password: To change the password of a user, use the passwd command:
```
sudo passwd username
```
Modify user details (like shell, home directory): To modify a user’s details, use the usermod command. Here are a few examples:
- Change the user’s home directory:
```
sudo usermod -d /new/home/directory username
```
- Change the user’s default shell:
```
sudo usermod -s /bin/zsh username
```
Add the user to a new group: To add a user to an additional group:
```
sudo usermod -aG groupname username
```
- -a appends the group to the user’s list of groups.
- -G is followed by the name of the group.

4. Deleting Users

Delete a user: To delete a user, you can use the userdel command:
```
sudo userdel username
```
This will remove the user but keep their home directory and files.
Delete a user and their home directory: If you want to delete the user and their home directory, use the -r option:
```
sudo userdel -r username
```

5. Managing Groups

Create a new group: Use the groupadd command to create a new group:
```
sudo groupadd groupname
```
Add a user to an existing group: To add a user to an existing group, use the usermod command:
```
sudo usermod -aG groupname username
```
Delete a group: To delete a group, use the groupdel command:
```
sudo groupdel groupname
```
Change a user’s primary group: Use the usermod command to change a user’s primary group:
```
sudo usermod -g groupname username
```

6. Locking and Unlocking User Accounts

Lock a user account: To prevent a user from logging in, use the passwd command with the -l option:
```
sudo passwd -l username
```
Unlock a user account: To unlock a user account, use the passwd command with the -u option:
```
sudo passwd -u username
```

7. Viewing and Managing User Processes

View processes running by a user: To see which processes a particular user is running:
```
ps -u username
```
Kill processes owned by a user: If you need to kill all processes belonging to a specific user:
```
sudo pkill -u username
```

8. Viewing User’s Last Login Time

Check when the user last logged in: Use the lastlog command to see the last login of each user:
```
sudo lastlog
```

9. Other User Management Commands

List groups for a user: To list the groups to which a user belongs:
```
groups username
```
Show a user’s account expiration date: Use the chage command to display user account expiration details:
```
sudo chage -l username
```
Set a user account expiration date: You can set an account expiration date using the chage command:
```
sudo chage -E YYYY-MM-DD username
```

10. Sudo (Superuser) Permissions

Add a user to the sudo group: To give a user the ability to execute commands with sudo, you can add them to the sudo group:
```
sudo usermod -aG sudo username
```
Check if a user has sudo privileges: You can check if a user has sudo privileges by using:
```
sudo -l -U username
```

Summary of Key Commands

Command	Description
`useradd username`	Add a new user
`passwd username`	Set or change a user’s password
`usermod -d /new/home username`	Change a user’s home directory
`usermod -s /bin/bash username`	Change a user’s shell
`usermod -aG groupname username`	Add user to an additional group
`userdel username`	Delete a user account
`userdel -r username`	Delete a user and their home directory
`groupadd groupname`	Create a new group
`groupdel groupname`	Delete a group
`passwd -l username`	Lock a user account
`passwd -u username`	Unlock a user account
`ps -u username`	List processes for a specific user
`sudo usermod -aG sudo username`	Grant sudo privileges to a user

These commands are essential for managing users and groups in a Linux system, which is an important aspect of system administration. Be sure to use these commands carefully, especially when modifying or deleting user accounts, to avoid losing important data or access.

Basic linux commands For user management