Creating and Managing Local Users in
CentOS 7
A Comprehensive Tutorial with Labs and Examples
Table of Contents
1. Introduction to User Accounts
2. The id Command
3. Creating User Accounts
4. Managing User Passwords
5. Password Aging and Shadow Data
6. User Account Defaults
7. Modifying and Deleting User Accounts
8. Summary and Key Takeaways
9. Hands-On Labs
1. Introduction to User Accounts
In Linux, every user must have:
A User ID (UID) – A unique numerical identifier.
A Group ID (GID) – The primary group for the user.
Additional secondary groups (optional).
User accounts are stored in:
/etc/passwd (User details)
/etc/shadow (Encrypted passwords & aging info)
/etc/group (Group memberships)
2. The id Command
Displays user and group information.
Basic Usage
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id # Shows current user info
id root # Shows info for root
Useful Options
Option Description Example
-u Display UID id -u
-g Display GID id -g
-G All group IDs id -G
-Gn Group names id -Gn
Example:
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$ id -Gn tux
tux wheel
3. Creating User Accounts
Basic User Creation
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sudo useradd user1 # Creates user1 with default settings
sudo passwd user1 # Sets password for user1
Customizing User Creation
Option Description Example
-m Create home dir useradd -m user2
-N No private group useradd -N user3
-g Primary group useradd -g users user4
-G Secondary groups useradd -G adm,ftp user5
-s Default shell useradd -s /bin/sh user6
Example:
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sudo useradd -m -G adm -s /bin/bash user2
Verifying User Creation
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tail -n 1 /etc/passwd # Shows last created user
ls /home # Checks home directory creation
4. Managing User Passwords
Setting Passwords
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sudo passwd user1 # Interactive password setting
Non-Interactive Password Setting
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echo "user2:Password123" | sudo chpasswd
Locking & Unlocking Accounts
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sudo passwd -l user1 # Locks user1
sudo passwd -u user1 # Unlocks user1
Checking Password Status:
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sudo grep user1 /etc/shadow
!! = Locked account
Encrypted hash = Active password
5. Password Aging and Shadow Data
Viewing Password Aging
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sudo chage -l user1
Modifying Password Aging
Option Description Example
-M Max password age (days) sudo chage -M 90 user1
-m Min password age sudo chage -m 7 user1
-W Warning period sudo chage -W 7 user1
Example:
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sudo chage -M 60 -m 7 -W 7 user1
Shadow File Structure
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sudo grep user1 /etc/shadow
Format: username:password:last_change:min:max:warn:inactive:expire
6. User Account Defaults
Viewing Defaults
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sudo useradd -D
Modifying Defaults
Option Description Example
-b Default home dir sudo useradd -D -b /home/users
-s Default shell sudo useradd -D -s /bin/sh
-g Default group sudo useradd -D -g users
Example:
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sudo useradd -D -s /bin/bash
Configuration Files
/etc/login.defs → Password & UID/GID defaults
/etc/default/useradd → Home dir, shell, group
7. Modifying and Deleting User Accounts
Modifying Users (usermod)
Option Description Example
-c
Comment (Full sudo usermod -c "John Doe" user1
Name)
-s Change shell sudo usermod -s /bin/zsh user1
-G Add secondary groups sudo usermod -aG adm user1
Example:
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sudo usermod -aG wheel user1 # Grants sudo access
Deleting Users (userdel)
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sudo userdel user1 # Keeps home directory
sudo userdel -r user1 # Deletes home dir & mail spool
Cleaning Up Files:
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sudo find / -uid 1001 -delete # Removes files owned by UID 1001
8. Summary and Key Takeaways
Task Command
Check user info id, id username
Create user sudo useradd -m username
Set password sudo passwd username
Lock account sudo passwd -l username
Modify aging sudo chage -M 90 username
Modify user sudo usermod -s /bin/bash username
Delete user sudo userdel -r username
9. Hands-On Labs
Lab 1: Create and Configure a User
1. Create a user labuser with a home directory.
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sudo useradd -m labuser
2. Set a password for labuser.
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sudo passwd labuser
3. Add labuser to the wheel group (for sudo access).
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sudo usermod -aG wheel labuser
4. Verify the changes.
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id labuser
grep labuser /etc/group
Lab 2: Password Aging Policies
1. Set labuser to change password every 30 days.
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sudo chage -M 30 labuser
2. Verify the settings.
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sudo chage -l labuser
Lab 3: Delete a User
1. Delete labuser and remove their home directory.
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sudo userdel -r labuser
2. Verify deletion.
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ls /home
grep labuser /etc/passwd
Final Notes
Always use sudo for administrative tasks.
Prefer chpasswd for scripting user creation.
Use -r with userdel to clean up user files.
