Booting
Bootstraping process
- computer is turned on
- executes boot code, that stored in ROM
- code attempts to run the kernel
- kernel probs system hardware and then start init process, that is always 1
- filesystem must be checked by init, system daemons to be started (init scripts by init)
booting to a single-user mode/recovery/maintainence mode
- while booting
- or if the system is already ip - shutdown or telinit
runlevel
state of the operational system
- 0 - the system can be safely powered off
- 1 - single user mode
- 2 - multiple user mode (without NFS - network file system)
- 3 - multiple user mode, no GUI
- 4 - user definable
- 5 - multiple user mode + GUI
- 6 - reboot
can be checked by
thor@jump_host ~$ runlevel
N 3
or
thor@jump_host ~$ who -r
run-level 3 2023-09-26 15:35
to change runlevel
sudo init 3
Kernel in /boot
Example task
change the default runlevel so that they can boot in GUI (graphical user interface) by default.
systemctl get-default
multi-user.target
sudo systemctl set-default graphical.target
tony@stapp01 ~]$ sudo systemctl start graphical.target
[tony@stapp01 ~]$ systemctl status graphical.target
● graphical.target - Graphical Interface
Loaded: loaded (/usr/lib/systemd/system/graphical.target; indirect; v
endor preset: disabled)
Active: active since Tue 2023-09-26 13:34:36 UTC; 15s ago
Docs: man:systemd.special(7)
Sep 26 13:34:36 stapp01.stratos.xfusioncorp.com systemd[1]:
graphical.target: Job graphical.target/start finished, resul
t=done
Sep 26 13:34:36 stapp01.stratos.xfusioncorp.com systemd[1]: Reached targ
et Graphical Interface.
[tony@stapp01 ~]$ systemctl get-default
graphical.target