Description: Candidates should be able to manage the SysVinit runlevel or systemd boot target of the system. This objective includes changing to single user mode, shutdown or rebooting the system. Candidates should be able to alert users before switching runlevels / boot targets and properly terminate processes. This objective also includes setting the default SysVinit runlevel or systemd boot target. It also includes awareness of Upstart as an alternative to SysVinit or systemd.
Key Knowledge Areas:
- Set the default runlevel or boot target
- Change between runlevels / boot targets including single user mode
- Shutdown and reboot from the command line
- Alert users before switching runlevels / boot targets or other major system events
- Properly terminate processes
Terms and Utilities:
Determining the Default Runlevel
jalo@u1604:~$ runlevel N 5 jalo@u1604:~$ systemctl get-default graphical.target
On systemd system use
systemctl get-default to determine
what the default target is.
Change system default runlevel in /etc/inittab: id:3:initdefault:
Change current runlevel by using command
Change system default runlevel by specifying a given target
via a symlink:
ln -sf /usr/lib/systemd/system/graphical.target /etc/systemd/system/default.target
Change current runlevel by using command:
systemctl isolate runlevel5.target
isolate: Start the unit specified on the command line and its dependencies and stop all others. This is similar to changing the runlevel in a traditional init system. The isolate command will immediately stop processes that are not enabled in the new unit, possibly including the graphical environment or terminal you are currently using.
Shut Down and Reboot from the Command Line
shutdown brings the system down in a secure way. All logged-in users are notified that the system is going down, and login(1) is blocked.
shutdown -H now Will halt the machine(you need press the power button manually after this)
shutdown -h 20:00 Equivalent to poweroff, unless --halt is specified.
shutdown -P +30 "System going down in 30 minutes" Power-off the machine (the default).
shutdown -c Cancel scheduled shutdown operation
kill and killall
kill -9 PID This forcibly removes the processes from memory without even allowing them time
to clean up memory and disk processes.
kill -HUP 2112 or
kill -1 2112 send SIGHUP signal to process make it reload its configuration file