Users and Groups

Users and groups are fundamental to Linux security and access control.

User Types

Root User:

UID 0
Has unrestricted access
Use sudo for administrative tasks

System Users:

UID < 1000 (typically)
Created for services (www-data, mysql, etc.)
Usually no login shell

Regular Users:

UID >= 1000
Standard user accounts
Have limited privileges

User Management

Creating Users

# Create a new user
useradd username

# Create with specific options
useradd -m -d /home/username -s /bin/bash -c "Full Name" username
# -m: create home directory
# -d: specify home directory
# -s: set login shell
# -c: set comment/full name

# Create with sudo privileges
useradd -G sudo username

# Create system user
useradd -r -s /bin/false serviceuser

Modifying Users

# Change password
passwd username

# Modify user properties
usermod -d /new/home/path username # change home directory
usermod -s /bin/zsh username # change shell
usermod -aG groupname username # add to group
usermod -l newname oldname # rename user

# Lock/unlock user account
usermod -L username # lock
usermod -U username # unlock

Deleting Users

# Delete user (keep home directory)
userdel username

# Delete user and home directory
userdel -r username

Group Management

Creating Groups

# Create a new group
groupadd groupname

# Create system group
groupadd -r servicegroupname

Managing Group Membership

# Add user to group
usermod -aG groupname username

# Add multiple users to group
for user in user1 user2 user3; do usermod -aG groupname $user; done

# Remove user from group
gpasswd -d username groupname

# Remove from all groups except primary
changing groups is tricky - use usermod

Modifying Groups

# Change group name
groupmod -n newname oldname

# Change group ID
groupmod -g 1001 groupname

Deleting Groups

# Delete group
groupdel groupname

Viewing User and Group Information

# List all users
cat /etc/passwd

# List all groups
cat /etc/group

# View current user
whoami

# View user ID and group membership
id username

# List all groups for a user
groups username

# View user details
finger username

Sudo Access

# Grant sudo access
usermod -aG sudo username

# Check sudo privileges
sudo -l

# Edit sudoers file safely
sudo visudo

Best Practices

Don't use root for daily tasks - use sudo
Create separate users for different services
Use strong passwords
Regularly audit user accounts and permissions
Remove inactive user accounts
Use groups to manage permissions efficiently
Limit sudo access to necessary users only

Users and Groups

On this page