2.2. Booting into a target system state

Procedure

1. Determine the current default target unit systemd uses to start the system:

   # systemctl get-default
   graphical.target

2. List the currently loaded targets:

   # systemctl list-units --type target

3. Configure the system to use a different target unit by default:

   # systemctl set-default <name>.target

   Replace <name> with the name of the target unit you want to use by default.

   Example:
   # systemctl set-default multi-user.target
   Removed /etc/systemd/system/default.target
   Created symlink /etc/systemd/system/default.target -> /usr/lib/systemd/system/multi-user.target

4. Verify the default target unit:

   # systemctl get-default
   multi-user.target

5. Optional: Switch to the new default target:

   # systemctl isolate default.target

   Alternatively, reboot the system.

Procedure

1. Optional: Display the list of targets you can select:

   $ systemctl list-units --type target

   注意

   You can only isolate targets that have the AllowIsolate=yes option set in the unit files.

2. Change to a different target unit in the current boot:

   # systemctl isolate <name>.target

   Replace <name> with the name of the target unit you want to use in the current boot.

   Example:
   # systemctl isolate multi-user.target

   This command starts the target unit named multi-user and all dependent units, and immediately stops all other unit.

   For more information, see the systemctl(1) man page on your system.

Procedure

1. Reboot the system, and interrupt the boot loader menu countdown by pressing any key except the Enter key, which would initiate a normal boot.
2. Move the cursor to the kernel entry that you want to start.
3. Press the E key to edit the current entry.

4. Move to the end of the line that starts with linux and press Ctrl+E to jump to the end of the line:

   linux ($root)/vmlinuz-5.14.0-70.22.1.e19_0.x86_64 root=/dev/mapper/rhel-root ro crash\
   kernel=auto resume=/dev/mapper/rhel-swap rd.lvm.lv/swap rhgb quiet

5. To choose an alternate boot target, append the systemd.unit= parameter to the end of the line that starts with linux:

   linux ($root)/vmlinuz-5.14.0-70.22.1.e19_0.x86_64 root=/dev/mapper/rhel-root ro crash\
   kernel=auto resume=/dev/mapper/rhel-swap rd.lvm.lv/swap rhgb quiet systemd.unit=<name>.target

   Replace <name> with the name of the target unit you want to use. For example, systemd.unit=emergency.target

6. Press Ctrl+X to boot with these settings.