Services, Targets and Boot

You will be able to

• Start, stop, enable, disable and mask services, and check why one failed.
• Read and set the default target, switch targets on a running system, and boot into a chosen target once.
• Change kernel parameters temporarily at boot and permanently with grubby.
• Reset a forgotten root password by interrupting the boot process, and restore SELinux labels afterwards.

Lessons

1. 01Controlling services with systemctlStart, stop, restart and reload services, decide what starts at boot, and find out why a service failed.systemctlsystemctl statussystemctl enable --nowsystemctl masksystemctl --failedsystemctl edit0/5 exercises
2. 02Targets, the default target and power controlUnderstand what a target is, set the default one, switch on a running system, and shut down or reboot safely.systemctl get-defaultsystemctl set-defaultsystemctl isolatesystemctl list-dependenciesrebootpoweroff0/5 exercises
3. 03The boot process and the GRUB boot loaderFollow a boot from firmware to target, boot once into a chosen target from the GRUB menu, and change boot loader settings permanently.grubbygrub2-mkconfig/etc/default/grub/proc/cmdlinegrub2-setpasswordsystemd.unit=0/5 exercises
4. 04Recovering root access: rd.break and SELinux relabelInterrupt the boot before the real system starts, set a new root password, and make sure SELinux still lets you log in.rd.breakmount -o remount,rw /sysrootchroot /sysrootpasswdtouch /.autorelabelrestorecon0/4 exercises