1. Understand and Use Essential Tools

📘Red Hat Certified System Administrator (RHCSA – EX200)

This is a very important objective in the RHCSA exam. You must understand:

How Linux handles multiple users
What multiuser targets are
How to log in locally and remotely
How to switch between users
How to become the root user safely
How to manage sessions correctly

The exam is performance-based, so you must know the exact commands and how to use them.

1. Understanding Multiuser in Linux

Linux is a multiuser operating system.

This means:

Multiple users can use the same system.
Different users can log in at the same time.
Each user has their own permissions and environment.

For example in an IT environment:

A system administrator manages the server.
A developer deploys applications.
A database administrator manages databases.
All of them may be logged in at the same time.

Linux controls this using systemd targets.

2. What is a Target?

Modern Red Hat Enterprise Linux uses systemd.

The main command to manage system state:

systemctl

In older Linux versions, we had “runlevels”.
Now we use targets.

A target defines:

What services start
Whether graphical interface starts
Whether multiple users can log in

Important Targets for RHCSA

1️⃣ multi-user.target

This is the most important for the RHCSA exam.

Entity reference:

multi-user.target

This target:

Enables multi-user mode
Starts networking
Starts system services
Does NOT start graphical interface
Uses text-based login (CLI)

This is similar to old runlevel 3.

2️⃣ graphical.target

Entity reference:

graphical.target

This:

Starts everything in multi-user
Plus graphical desktop (GUI)

Similar to old runlevel 5.

3. How to Check Current Target

Use:

systemctl get-default

To see current active target:

systemctl list-units --type=target

To check what the system is currently running:

systemctl get-default

4. How to Change Target

Temporarily change target (without reboot)

Switch to multi-user:

sudo systemctl isolate multi-user.target

Switch to graphical:

sudo systemctl isolate graphical.target

Permanently set default target

sudo systemctl set-default multi-user.target

sudo systemctl set-default graphical.target

Very important for exam:

Know difference between isolate and set-default.

5. Logging In to the System

There are two main types:

1️⃣ Local Login

This means:

Logging directly from the system console.
Could be text login or GUI login.

In multi-user target:

You see a text login prompt.
Enter username.
Enter password.

Example:

localhost login:

2️⃣ Remote Login (SSH)

Very important for RHCSA.

Linux uses:

Entity reference:

OpenSSH

To connect to a remote system:

ssh username@server-ip

Example:

ssh student@192.168.1.10

You will be prompted for:

Password (unless key-based authentication is configured)

To log out:

exit

logout

6. Switching Users

In Linux, you can switch users without logging out.

Two main commands:

su
sudo

You must clearly understand the difference.

7. The su Command (Switch User)

su means substitute user.

Switch to another user:

su username

Example:

su student

It asks for:

The target user’s password

Switch to root user

su -

This is very important.

The - means:

Load the target user’s full environment.
Acts like a full login.

Without -, environment variables are not fully loaded.

For RHCSA:
You should use:

su -

to become root properly.

8. The sudo Command

sudo = superuser do

This allows a normal user to execute commands as root.

Example:

sudo dnf install httpd

It:

Asks for your password (not root password)
Checks if you are allowed in sudoers file

This is more secure than logging in directly as root.

Difference Between su and sudo

Command	Password Required	Environment	Usage
su	Target user password	Not full (unless – used)	Switch user
su –	Target user password	Full login shell	Become root
sudo	Your password	Only runs one command	Run admin command

For exam:

Understand when to use each.
Know that sudo is preferred in enterprise environments.

9. Root Login

Root is the superuser.

Root can:

Modify system files
Install software
Manage users
Stop services

Best practice in IT environments:

Do NOT allow direct root SSH login.
Use sudo instead.

Root login via SSH can be controlled in:

/etc/ssh/sshd_config

Look for:

PermitRootLogin

10. Checking Logged-in Users

Important exam commands:

See who is logged in:

who

More detailed:

Current user:

whoami

User ID information:

id

11. Managing Sessions

Each login creates a session.

To see sessions:

loginctl

This is part of systemd.

It shows:

User sessions
Session ID
State

To terminate a session:

loginctl terminate-session ID

12. Console Switching (TTY)

Linux supports multiple virtual terminals.

Switch between consoles:

Ctrl + Alt + F1 to F6

Each opens a separate login prompt.

This is very important in troubleshooting situations in IT environments:

One console for admin work
Another for log monitoring
Another for service management

13. Important Exam Scenarios

For RHCSA, you may be required to:

✔ Switch from normal user to root
✔ Log in via SSH
✔ Set system to multi-user target
✔ Disable graphical interface
✔ Identify current user
✔ Check logged-in users
✔ Exit safely from root

Practice these repeatedly.

14. Common Mistakes to Avoid

❌ Forgetting - with su
❌ Editing system files without root privileges
❌ Not exiting from root after work
❌ Confusing isolate and set-default
❌ Trying to run admin commands without sudo

15. Quick Practice Commands (Must Know)

systemctl get-default
systemctl set-default multi-user.target
systemctl isolate multi-user.target
ssh user@host
su -
sudo command
who
w
whoami
id
loginctl
exit

Final Exam Tips

For RHCSA:

Practice logging in and switching users many times.
Understand difference between multi-user and graphical target.
Know how to become root properly.
Be comfortable working in text-only mode.
Practice SSH connections.

This topic is foundational.
If you master this, you will be comfortable working in real Red Hat Enterprise Linux environments.