Managing the Boot Procedure

Nov 14, 2025
rhcsa

Boot Procedure

Modifying GRUB2 Runtime Parameters

  • From boot menu, press e to edit boot options and modify the end of the line that starts with linux
    • systemd.unit=emergency.target
    • systemd.unit=rescue.target
    • systemd.unit=multi-user.target
    • init=/bin/bash
  • Press c to enter command mode
    • Advanced, not needed for RHCSA

Changing GRUB2 Persistent Parameters

  • Edit /etc/default/grub
    • Since RHEL 9.2, the GRUB2 configuration file contains the line GRUB2_ENABLE_BLSCFG=true by default, which basically means any changes to the configuration file are ignored
  • Another option is to edit the settings for a specific kernel in /boot/loader
  • Use grub2-mkconfig -o /boot/grub2/grub.cfg to generate a configuration file

Systemd Targets

Some interesting things to have a look at

systemctl list-unit-files -t target
systemctl cat multi-user.target
ls /etc/systemd/system/multi-user.target.wants
systemctl list-dependencies multi-user.target

Setting the Default Systemd Target

systemctl get-default
systemctl set-default

Booting into a Specific Target

  • Modify grub boot command adding systemctl.unit=target-name.target
  • To change targets on a running system use systemctl isolate target-name.target or systemctl start target-name.target depending on if you are moving from an earlier target to a later target
    • Basically isolate will remove everything you don’t need, start will add everything you do need

Lab Exercise

  • Configure your system to boot into a multi-user target by default
  • Persistently remove the options that hide startup messages while booting isSubcollection: true paginate: true

- caj