Exercise: Change how the server boots

Change how the server boots

• Set the default target and check it after a reboot.
• Add and remove a kernel argument with grubby.
• Read boot timing with systemd-analyze.

Start the exercise

On workstation, start the exercise. It makes sure servera starts from the default target graphical.target without the extra kernel argument.

[student@workstation ~]$ lab start sa-boot

Later tasks assume that you are logged in to the server they name: ssh student@servera from workstation, then sudo -i for a root shell.

Record the starting point

On servera as root (sudo -i), show the default target, the kernel command line and the boot time.

[student@workstation ~]$ ssh student@servera
[student@servera ~]$ sudo -i
[root@servera ~]# systemctl get-default
graphical.target
[root@servera ~]# cat /proc/cmdline
BOOT_IMAGE=(hd0,gpt2)/boot/vmlinuz-5.14.0-687.53.1.el9_8.x86_64 console=tty1 console=ttyS0 root=UUID=4bbdcf8d-863d-4050-957c-c815ca3838b8 ro
[root@servera ~]# systemd-analyze
Startup finished in 1.835s (kernel) + 1.517s (initrd) + 5.773s (userspace) = 9.126s
graphical.target reached after 4.932s in userspace.

Your numbers will differ.

Change the default target and the kernel arguments

Set multi-user.target as the default, and add loglevel=5 to all kernels. Confirm what grubby now records.

[root@servera ~]# systemctl set-default multi-user.target
Created symlink /etc/systemd/system/default.target → /usr/lib/systemd/system/multi-user.target.
[root@servera ~]# grubby --update-kernel=ALL --args="loglevel=5"
[root@servera ~]# grubby --info=DEFAULT | grep args
args="console=tty1 console=ttyS0 ro loglevel=5"

Nothing has changed in the running system yet: /proc/cmdline still shows the old arguments.

Reboot and check

Reboot, wait about 30 seconds, log in again, and check the target, the command line and uptime -p.

[root@servera ~]# systemctl reboot
Connection to servera closed by remote host.
[student@workstation ~]$ ssh student@servera
[student@servera ~]$ systemctl get-default
multi-user.target
[student@servera ~]$ cat /proc/cmdline
BOOT_IMAGE=(hd0,gpt2)/boot/vmlinuz-5.14.0-687.53.1.el9_8.x86_64 console=tty1 console=ttyS0 root=UUID=4bbdcf8d-863d-4050-957c-c815ca3838b8 ro loglevel=5
[student@servera ~]$ uptime -p
up 0 minutes

The machine really booted with the new argument, and into the new default target.

Look at the boot

Show the boot timing again and the critical chain, then list the boots the journal knows about. Why only one?

[student@servera ~]$ systemd-analyze | head -2
Startup finished in 1.7s (kernel) + 1.5s (initrd) + 5.1s (userspace) = 8.3s
multi-user.target reached after 4.3s in userspace.
[student@servera ~]$ journalctl --list-boots
IDX BOOT ID                          FIRST ENTRY                 LAST ENTRY
  0 40c5978bc61848209a017d48d2184fe4 Sat 2026-10-03 16:37:42 UTC Sat 2026-10-03 16:38:24 UTC

The journal lives in memory only, so the log of the boot before the reboot is gone. That is why the logging chapter makes it persistent.

Put everything back

Return to graphical.target, remove the extra argument, and confirm with grubby.

[student@servera ~]$ sudo systemctl set-default graphical.target
Created symlink /etc/systemd/system/default.target → /usr/lib/systemd/system/graphical.target.
[student@servera ~]$ sudo grubby --update-kernel=ALL --remove-args="loglevel=5"
[student@servera ~]$ sudo grubby --info=DEFAULT | grep args
args="console=tty1 console=ttyS0 ro"
[student@servera ~]$ exit

Grade and finish

Check your work with lab grade sa-boot, then put the exercise away with lab finish sa-boot.