Linux allows users to:
- Switch to another user
- Run commands as another user
- Get administrative access securely
Main commands:
- su
- sudo
1. su Command
Meaning
su = substitute user
Used to switch from one user to another.
Basic Syntax
su username
Example
su devuser
System asks:
Password:
Requires target user's password.
Switch to Root User
su -
or
su root
Difference Between su and su -
| Command | Behavior |
|---|---|
| su | Switch user only |
| su - | Full login shell |
Example
su - devuser
Loads:
- User environment
- PATH variables
- Home directory
Exit Switched User
exit
Real-World Usage
Switch to Application User
su - nginx
2. sudo Command
Meaning
sudo = Super User DO
Runs a command with elevated privileges.
Basic Syntax
sudo command
Example
sudo apt update
Important Difference
| su | sudo |
|---|---|
| Switches entire user | Runs single command |
| Needs target password | Needs current user password |
| Full shell access | Controlled access |
Why sudo is Preferred
- Better security
- Logging and auditing
- Limited root access
- Safer administration
Run Root Shell with sudo
sudo -i
or
sudo su
Run Command as Another User
sudo -u nginx whoami
Example Output
nginx
Sudo Permissions
Controlled by:
/etc/sudoers
Safe Editing
Use:
sudo visudo
Add User to sudo Group
Ubuntu/Debian:
sudo usermod -aG sudo devuser
RHEL/CentOS:
sudo usermod -aG wheel devuser
Real-World DevOps Usage
Restart Service
sudo systemctl restart nginx
Install Packages
sudo apt install docker.io
Kubernetes Admin Commands
sudo kubectl get nodes
Common sudo Options
| Command | Purpose |
|---|---|
| sudo -i | Root shell |
| sudo -u user | Run as another user |
| sudo -k | Forget cached password |
| sudo -l | Show allowed commands |
Principle of Least Privilege
Give users:
- Only required permissions
- Not full root access
Real-World Example
DevOps User Setup
sudo useradd -m devops
sudo usermod -aG sudo,docker devops
Now user can:
sudo docker ps
Common Mistakes
Using Root Directly
Bad practice:
su -
for daily tasks.
Better:
sudo command
Security Risks
Improper sudo access can allow:
- Privilege escalation
- Full server compromise
- Accidental system damage
Best Practices
- Prefer sudo over direct root login
- Avoid sharing root password
- Audit sudo access regularly
- Use visudo for editing sudoers
- Grant minimum required permissions