Day 4 of Learning Linux: Demystifying User Management in Linux 🐧

Published on: 16 May 2025

User management is one of the core pillars of Linux system administration. Whether you're managing a multi-user server or securing your personal development environment, understanding how users, groups, and permissions work is essential.

Today, I dove deep into the world of user management in Linux—and I'm here to break it down for you, step by step.

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What Is a User in Linux?

In Linux, everything is a file, and every action is performed by a user. Each user on the system has:

• A username

• A user ID (UID)

• A default group

• A home directory

• A shell (like bash or zsh)

Users can be human users or system users (used by services like mysql, nginx, etc.).

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Key Files That Store User Data

Understanding where user info is stored is critical.

You can view them with commands like cat /etc/passwd or less /etc/shadow (needs root).

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Managing Users: Key Commands

➕ Create a New User

bashCopyEditsudo adduser john

This creates the user, home directory, and sets default shell. You'll be prompted to set a password and fill in user info.

Alternate:

bashCopyEditsudo useradd -m john

Flags:

• -m: create home directory

• -s /bin/bash: specify shell

Set or Change a User Password

bashCopyEditsudo passwd john

To expire a password (force change at next login):

bashCopyEditsudo passwd -e john

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Delete a User

bashCopyEditsudo deluser john

To remove the user's home directory too:

bashCopyEditsudo deluser --remove-home john

Alternative:

bashCopyEditsudo userdel -r john

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Groups in Linux

Groups help manage permissions for multiple users. Each user belongs to:

• A primary group (usually same as their username)

• Supplementary groups (optional extra groups)

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Group Management Commands

➕ Create a Group

bashCopyEditsudo addgroup developers

➕ Add a User to a Group

bashCopyEditsudo usermod -aG developers john

• -aG: append to group without removing from others

View Groups for a User

bashCopyEditgroups john

Or:

bashCopyEditid john

Remove a User from a Group

bashCopyEditsudo gpasswd -d john developers

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Switching Between Users

To switch to another user:

bashCopyEditsu - john

To return to your session: press Ctrl+D or type exit.

Or, use sudo (if you're in the sudo group):

bashCopyEditsudo -u john command_here

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Sudo: Giving Users Admin Power (With Caution )

Users in the sudo group can run commands as root:

bashCopyEditsudo apt update

To add a user to the sudo group:

bashCopyEditsudo usermod -aG sudo john

Check if you're in the sudo group:

bashCopyEditgroups

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Lock and Unlock User Accounts

Lock a user:

bashCopyEditsudo usermod -L john

Unlock:

bashCopyEditsudo usermod -U john

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Account Expiration & Info

Set an expiration date for a user:

bashCopyEditsudo chage -E 2025-12-31 john

View user aging info:

bashCopyEditsudo chage -l john

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Summary Cheat Sheet

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Pro Tips

• Avoid using root directly—use sudo where possible.

• Always back up before deleting users or modifying access.

• Combine user management with file permissions (chmod, chown) for robust security.

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What I Learned

Today gave me a much clearer picture of how Linux handles users and groups. The commands might seem intimidating at first, but with hands-on practice, they become second nature.

Managing users is about more than just creating accounts—it's about controlling access, securing your system, and understanding how Linux keeps things organized behind the scenes.

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Coming Next…

Tomorrow, I’ll dive into file permissions and ownership—how to use chmod, chown, and umask to control who can read, write, and execute your files.

Stay tuned and follow along for more daily Linux learnings! 🚀