User Management Basics: Getting Started with useradd, usermod, and userdel

2026-05-31 Reading time: About 12 min Difficulty: Intermediate+

What You'll Learn

• You will be able to create a user with useradd and get it to a state where it can log in.
• You will be able to add groups safely with usermod -aG.
• You will be able to understand what userdel removes and delete through a recoverable procedure.

Who this is for: anyone who now has to create server accounts for new team members.

Terms defined up front

Each term below is defined once, here.

• A user is the identity that logs into Linux and operates it. There are two kinds: accounts people use, and accounts services use (system users).
• A group is a collection of users. Permissions on files and commands can be granted per group, not only per user.
• UID / GID are the ID numbers assigned to users and groups. Internally Linux decides by these numbers, not by names.
• A login shell is the shell that starts right after login. /bin/bash is typical; setting /usr/sbin/nologin blocks login entirely.
• A supplementary group is any group beyond the first that a user belongs to. It is also called a secondary group. The first one is the primary group.
• A home directory is the user's own workspace, /home/<username>.

What Can You Do with useradd, usermod, and userdel?

Linux user management comes down to three commands: useradd to create users, usermod to modify their attributes, and userdel to remove them. This guide covers both Ubuntu/Debian and RHEL/CentOS with practical command examples.

Every command below needs sudo. User records are system-wide configuration, and an ordinary user cannot rewrite them.

sudo useradd -m -s /bin/bash alice    # Create user
sudo passwd alice                      # Set password
sudo usermod -aG sudo alice            # Grant sudo privileges
sudo userdel -r alice                  # Delete user and home directory

1. How to Create a User with useradd

The useradd command adds a new user to the system. Without options, it does not create a home directory — always use the -m flag in practice.

sudo useradd -m -s /bin/bash alice

Common Options:

Setting a Password

useradd alone does not set a password — the account cannot log in until you run passwd:

sudo passwd alice

Verifying the New User

id alice

uid=1001(alice) gid=1001(alice) groups=1001(alice)

grep alice /etc/passwd

alice:x:1001:1001::/home/alice:/bin/bash

The /etc/passwd fields are: username:password(x):UID:GID:comment:home:shell.

sudo adduser alice    # Interactive setup including password

2. How to Modify a User with usermod

usermod changes attributes of an existing user. The most frequent operation is adding a user to a group.

Granting sudo Privileges

sudo usermod -aG sudo alice       # Ubuntu/Debian
sudo usermod -aG wheel alice      # RHEL/CentOS/Fedora

id alice              # record memberships before
sudo usermod -aG sudo alice
id alice              # confirm the addition

Other Common Changes

Change home directory:

sudo usermod -d /new/home -m alice    # -m moves existing files

Change login shell:

sudo usermod -s /bin/zsh alice

Lock or unlock an account:

sudo usermod -L alice    # Lock password auth (key-based login still works)
sudo usermod -U alice    # Unlock

Verifying Changes

id alice
groups alice

uid=1001(alice) gid=1001(alice) groups=1001(alice),27(sudo)

3. How to Delete a User with userdel

userdel removes a user from the system. Use -r to also delete the home directory and mail spool.

sudo userdel -r alice

Behavior comparison:

sudo ls -la /home/alice        # inspect what will be deleted
sudo du -sh /home/alice        # check the size

sudo tar czf /root/alice-home.tar.gz /home/alice

sudo usermod -L alice                    # disable password authentication
sudo chage -E 0 alice                    # expire the account (key-based login is refused too)
sudo usermod -s /usr/sbin/nologin alice  # disable the login shell

Deleting a Logged-in User

A logged-in user cannot be deleted. The command refuses with something like userdel: user alice is currently used by process 1234.

who                    # Check who is logged in
sudo pkill -u alice    # Kill all processes owned by alice
sudo userdel -r alice

4. Group Management Basics

Users and groups are tightly coupled in Linux. Here are the essential group operations.

Create a Group

sudo groupadd developers

Add a User to a Group

sudo usermod -aG developers alice

Delete a Group

sudo groupdel developers

Check Group Membership

grep developers /etc/group

developers:x:1002:alice

/etc/group fields: groupname:password:GID:member-list

5. Password Policy and Account Expiry

Use chage to inspect and configure password aging policies.

sudo chage -l alice

Last password change                                    : May 31, 2026
Password expires                                        : never
Account expires                                         : never

Setting expiry:

sudo chage -M 90 alice         # Expire password after 90 days
sudo chage -E 2026-12-31 alice # Set account expiry date

6. System Accounts for Services

Service daemons (nginx, postgres, etc.) run under dedicated system accounts that cannot log in interactively. Create them with -r:

sudo useradd -r -s /usr/sbin/nologin -d /var/lib/myapp myapp

Key flags for service accounts:

Summary: Practical Command Patterns

Standard Flow for a New User

sudo useradd -m -s /bin/bash -c "Alice Smith" alice
sudo passwd alice
sudo usermod -aG sudo alice
id alice    # Verify

Quick Reference Commands

id username               # UID/GID and group list
groups username           # Group memberships
grep username /etc/passwd # passwd entry
grep username /etc/group  # Group memberships
sudo cat /etc/shadow      # Password hash info

Troubleshooting

Symptom: the new user cannot log in

Cause: passwd was never run, so the password is unset and the account is locked.

Check:

sudo passwd -S alice

alice L 05/31/2026 0 99999 7 -1

The second field is L for locked, P when a password is set.

Fix:

sudo passwd alice

Symptom: useradd succeeded but there is no home directory

Cause: it was run without -m. On Ubuntu, useradd does not create a home by default.

Check:

ls -ld /home/alice

Fix: copy the contents of /etc/skel (the skeleton directory for new users) first, then set the owner and permissions. Without the skeleton, there is no .bashrc or .profile, which leads to a different set of problems: a broken prompt, no aliases, and ~/.local/bin missing from PATH.

sudo mkdir /home/alice
sudo cp -a /etc/skel/. /home/alice/
sudo chown -R alice:alice /home/alice
sudo chmod 700 /home/alice

On Ubuntu and Debian, sudo mkhomedir_helper alice performs the same work in one step.

Symptom: a group was added but the privileges do not apply

Cause: group changes take effect at the user's next login. The current session still holds the old information.

Check:

id alice        # the current state in /etc/group
groups          # what this session is carrying

Fix: log out and back in. To apply it immediately, run newgrp sudo.

Symptom: userdel fails with currently used by process

Cause: processes owned by that user are still running.

Check:

ps -u alice

Fix: review the list, run sudo pkill -u alice, then delete.

Completion Checklist

• [ ] Created the home directory with useradd -m
• [ ] Set a password with passwd so the account can log in
• [ ] Added groups with usermod -aG (with the -a)
• [ ] Verified UID, GID, and memberships with id
• [ ] Inspected the home directory and took a backup before deleting
• [ ] When locking instead of deleting, went as far as chage -E 0 to stop key-based login too