Configure systems to boot into a specific target automatically

7. Deploy, Configure, and Maintain Systems

📘Red Hat Certified System Administrator (RHCSA – EX200)

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1. Understanding Boot Targets in Linux (RHEL/CentOS/AlmaLinux)

In RHEL 7 and later, Linux uses systemd to manage services and the boot process.

• A target is like a “mode” that the system boots into.
• Each target defines what services start and which do not.

Think of targets as “system states” in IT terms:

Target	Description	Common Use Case
graphical.target	Full graphical desktop environment	Workstations or systems with GUI
multi-user.target	Text-based login (no GUI)	Servers accessed via SSH
rescue.target	Single-user mode for recovery	Fixing system problems
emergency.target	Minimal system, root only	Deep troubleshooting or repairing disks

Exam tip: You need to know graphical.target vs multi-user.target, because most servers use multi-user.target.

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2. Viewing the Current Default Boot Target

To check what target your system boots into by default, use:

systemctl get-default

Example:

$ systemctl get-default
graphical.target

• This means the system currently boots into GUI mode.
• For a server, you might want multi-user.target instead.

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3. Changing the Default Boot Target

To change the system’s default target, use:

systemctl set-default <target_name>

Example: Set server to boot into multi-user (no GUI):

sudo systemctl set-default multi-user.target

Verify the change:

systemctl get-default
# Output should now be multi-user.target

• This change is permanent – it will remain across reboots.

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4. Switching Targets Without Rebooting

Sometimes you need to switch targets immediately without rebooting:

sudo systemctl isolate <target_name>

Example: Switch to rescue mode immediately:

sudo systemctl isolate rescue.target

• Note: Using isolate changes the current running target and stops services not needed by the new target.

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5. Checking Which Targets Are Available

To list all systemd targets:

systemctl list-unit-files --type=target

You’ll see something like:

graphical.target      enabled
multi-user.target     enabled
rescue.target         disabled
emergency.target      disabled

• enabled means the target can be used normally.
• disabled typically means it’s only used manually in emergencies.

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6. Example Scenarios in IT

1. Server Boot to Text Mode for SSH Management
   • Servers don’t need GUI, so you set default to multi-user.target.
   • Commands: sudo systemctl set-default multi-user.target
     sudo systemctl get-default
2. Workstation Boot to GUI
   • Workstations with desktop environments need GUI, so graphical.target is default.
   • Commands: sudo systemctl set-default graphical.target
3. Rescue Mode for Disk Repair
   • If a server fails to boot normally, you can boot into rescue.target using GRUB or: sudo systemctl isolate rescue.target

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7. Temporary Boot Target via GRUB

Sometimes you don’t want to change the default, but want to boot into a different target once:

1. Reboot the system.
2. At GRUB menu, press e to edit the boot entry.
3. Find the line starting with linux or linux16.
4. Add the target at the end:

systemd.unit=multi-user.target

5. Press Ctrl+X to boot.

• This only affects the current boot; default remains unchanged.

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8. RHCSA Exam Checklist for Boot Targets

To make sure you’re ready for the exam, practice these tasks:

1. Check the current default boot target: systemctl get-default
2. Change the default target permanently: sudo systemctl set-default multi-user.target
3. Switch targets immediately without reboot: sudo systemctl isolate rescue.target
4. List all available targets: systemctl list-unit-files –type=target
5. Temporary boot target via GRUB (one-time):
   • Edit GRUB at boot → append systemd.unit=multi-user.target

Tip: In the exam, they may ask you to change the system to boot in a specific target and verify it. Always check with systemctl get-default.

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✅ Key Takeaways for Students

• Targets control what services run at boot.
• graphical.target = GUI, multi-user.target = server mode.
• Use systemctl set-default for permanent changes.
• Use systemctl isolate to change immediately without reboot.
• Use GRUB for one-time boot targets.
• Always verify with systemctl get-default.