Chielo Chiamaka

Posted on Apr 12 • Edited on Apr 15

User Management in Linux

#cloudwhistler #linux #opensource #redhat

What is a User in Linux?

A user is anyone with a login account on the Linux system. Users can access the system based on their permissions and roles.

Example: On a shared development server, each DevOps engineer has their own user account to isolate their files and settings.

Types of Users in Linux

a. System Users

Created automatically during installation or when system services/apps are installed.

These accounts usually don’t have login privileges.

Examples: root, apache, mysql

b. Normal Users
Created by system administrators or via scripts.

Used for actual human users who log in and interact with the system.

Unique User Identification "UID"

Every user is assigned a UID.

UID Ranges:

0: Reserved for the root user (superuser).
1–999: Typically reserved for system users.
1000+: Normal human users created manually or during OS setup.

Scenario: When setting file permissions or troubleshooting ownership, Linux refers to UIDs, not usernames.

Where Linux Stores User Account Info

/etc/passwd: Contains essential user account data.
/etc/shadow: Stores encrypted passwords and password expiry info.

Creating a User Account

Adds a new user to the system.

Setting or Changing a User Password

passwd sophia will prompt you to enter a new password.

Viewing User Account Properties

Sample output:

sophia❌1001:1001::/home/sophia:/bin/bash

Fields explained:

chielo: Username
x: Password placeholder (real password stored in /etc/shadow)
1001: UID
1001: GID (Group ID)
(empty): User full name or comment field
/home/chielo: Home directory
/bin/bash: Default shell

Viewing User Password Properties

Sample output:

chielo:$6$bD...:20190:0:99999:7:::

Fields explained:

chielo: Username
$6$bD...: Encrypted password
20190: Days since Jan 1, 1970 when password was last changed
0: Minimum password age in days
99999: Maximum password age in days
7: Warning period before password expires
Empty fields: Password inactivity and expiry info

Switching Users

su
Temporarily switch to another user account.

Deleting a User Account

Remove the account but keep home directory:

userdel

Remove the account and delete home directory:
userdel -r

Example: After an employee leaves a company, an admin can delete their Linux user account with userdel -r to clean up space and revoke access.

Conclusion

User management in Linux is foundational for system security and multi-user environments. From creating users to understanding UID ranges and system files like /etc/passwd and /etc/shadow, getting comfortable with these operations is essential for anyone working on Linux systems.

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