Working with systemd targets on RHEL7 Linux: A Beginner’s Cheatsheet

Table of Contents#

1. Understanding systemd Targets
   • What Are Targets?
   • Targets vs. Runlevels (RHEL6 Comparison)
   • Targets vs. Services
2. Common systemd Targets in RHEL7
3. Essential systemd Target Commands
   • View Current Target
   • List All Targets
   • Set Default Target
   • Switch Targets Temporarily
   • Check Target Dependencies
   • View Target Unit Files
4. Practical Example: Switch to Multi-User (CLI) Mode
5. Troubleshooting Common Target Issues
6. Conclusion
7. References

1. Understanding systemd Targets#

What Are Targets?#

In systemd, a target is a unit file (.target) that defines a system state by grouping other units (services, sockets, mount points, etc.). Think of targets as “system profiles”—they determine which services start when the system boots or switches states.

For example:

• graphical.target starts all services needed for a graphical desktop (e.g., gdm.service, network.service).
• multi-user.target starts services for a text-only (CLI) environment (no GUI, but includes SSH, networking, etc.).

Targets vs. Runlevels (RHEL6 Comparison)#

If you’re familiar with RHEL6 or earlier, you might remember runlevels (e.g., runlevel 3 for CLI, runlevel 5 for GUI). Targets replace runlevels in systemd, but they’re more flexible:

• Runlevels were numbered (0-6) and rigidly defined.
• Targets have human-readable names (e.g., multi-user.target) and can be customized or extended.

Here’s how RHEL6 runlevels map to RHEL7 targets:

Targets vs. Services#

Targets are not services—they are groups of services. For example:

• sshd.service is a service that starts the SSH daemon.
• multi-user.target includes sshd.service (along with network.service, crond.service, etc.) to define a CLI environment.

2. Common systemd Targets in RHEL7#

Here are the most frequently used targets in RHEL7, with their purposes and runlevel equivalents:

3. Essential systemd Target Commands#

All systemd target management is done with the systemctl command. Below are key commands to view, configure, and switch targets.

View Current Target#

To check which target the system is currently running:

systemctl get-default  

Example Output:

multi-user.target  # System boots to CLI by default  

List All Targets#

To list all targets (active and inactive), use:

systemctl list-targets  

Example Output (truncated):

UNIT                   LOAD   ACTIVE SUB    DESCRIPTION  
basic.target           loaded active active Basic System  
cryptsetup.target      loaded active active Local Encrypted Volumes  
getty.target           loaded active active Login Prompts  
graphical.target       loaded active active Graphical Interface  # Active if GUI is running  
multi-user.target      loaded active active Multi-User System  
network.target         loaded active active Network  
...  

Set Default Target#

The default target determines the system’s state at boot. To set a new default (persistent across reboots):

sudo systemctl set-default <target-name>  

Examples:

• Set default to CLI (multi-user):

  sudo systemctl set-default multi-user.target  

• Set default to GUI (graphical):

  sudo systemctl set-default graphical.target  

Switch Targets Temporarily#

To switch to a target immediately (without rebooting), use isolate (temporarily activates the target and stops conflicting units):

sudo systemctl isolate <target-name>  

Examples:

• Switch to GUI mode temporarily:

  sudo systemctl isolate graphical.target  

• Switch to rescue mode (single-user):

  sudo systemctl isolate rescue.target  

Check Target Dependencies#

To see which services/targets a target depends on (e.g., what graphical.target includes):

systemctl list-dependencies <target-name>  

Example:

systemctl list-dependencies graphical.target  

Output (truncated):

graphical.target  
├─accounts-daemon.service  
├─gdm.service               # Gnome Display Manager (GUI)  
├─rtkit-daemon.service  
├─systemd-update-utmp-runlevel.service  
└─multi-user.target         # Includes all services from multi-user  
  ├─auditd.service  
  ├─crond.service  
  ├─network.service  
  └─sshd.service            # SSH daemon  

View Target Unit File#

To inspect the raw configuration of a target (e.g., multi-user.target):

systemctl cat <target-name>  

Example:

systemctl cat multi-user.target  

Output:

# /usr/lib/systemd/system/multi-user.target  
[Unit]  
Description=Multi-User System  
Documentation=man:systemd.special(7)  
Requires=basic.target  
Conflicts=rescue.service rescue.target  
After=basic.target rescue.service rescue.target  
AllowIsolate=yes  

4. Practical Example: Switch to Multi-User (CLI) Mode#

Let’s walk through a common scenario: A RHEL7 desktop is booting to GUI (graphical.target), but you want to switch to CLI (multi-user.target) as the default.

Step 1: Check Current Default Target#

systemctl get-default  

Output:

graphical.target  # Currently boots to GUI  

Step 2: Switch Temporarily to CLI#

To test CLI mode without changing the default:

sudo systemctl isolate multi-user.target  

The GUI will close, and you’ll land at a text-based login prompt.

Step 3: Set CLI as Default (Persistent)#

To make CLI the default boot target:

sudo systemctl set-default multi-user.target  

Output:

Removed symlink /etc/systemd/system/default.target.  
Created symlink from /etc/systemd/system/default.target to /usr/lib/systemd/system/multi-user.target.  

Step 4: Verify the Change#

Reboot to confirm the system now boots to CLI:

sudo reboot  

After reboot, you’ll see a text-based login prompt (no GUI).

5. Troubleshooting Common Target Issues#

Default Target Not Persisting#

If set-default doesn’t save your default target, check the default.target symlink:

ls -l /etc/systemd/system/default.target  

Expected Output:

lrwxrwxrwx. 1 root root 37 Jun 10 14:22 /etc/systemd/system/default.target -> /usr/lib/systemd/system/multi-user.target  

If the symlink is missing/corrupted, recreate it manually:

sudo ln -sf /usr/lib/systemd/system/multi-user.target /etc/systemd/system/default.target  

Target Fails to Activate#

If switching to a target (e.g., rescue.target) fails, check the system logs with journalctl:

journalctl -u <target-name>  # e.g., journalctl -u rescue.target  

Look for errors like “Failed to start Rescue Mode” to diagnose issues (e.g., missing dependencies).

Stuck in Emergency Mode#

If the system boots to emergency.target, it’s likely due to critical errors (e.g., invalid /etc/fstab entries). To fix:

1. Enter the root password when prompted.
2. Run journalctl -xe to check logs for failures.
3. Fix the issue (e.g., edit /etc/fstab with vi /etc/fstab).
4. Reboot: systemctl reboot.

6. Conclusion#

systemd targets are the backbone of system state management in RHEL7. By mastering targets, you can control your system’s boot behavior, switch between CLI/GUI modes, and troubleshoot boot issues with confidence.

Start with the basics: Use systemctl get-default to check your current target, set-default to configure boot behavior, and isolate to switch states temporarily. Refer to the common targets table for quick reference, and don’t hesitate to inspect dependencies with list-dependencies.

7. References#

• Red Hat Enterprise Linux 7 System Administrator’s Guide: Working with systemd Targets
• systemd Target Documentation
• systemctl Man Page
• RHEL7 Runlevels to systemd Targets Mapping