Reboot and shutdown in Linux

Reboot:

telinit 6 #old systems
systemctl isolate reboot.target
reboot
shutdown -r 15:30 "rebooting!!!"
shutdown -r +10 "rebooting soon!"
shutdown -r now
systemctl reboot

Shutdown:

telinit 0 #old systems
systemctl isolate poweroff.target
poweroff
shutdown -h now
shutdown 02:00
shutdown 02:00 "Shutdown with comment at 2AM"
shutdown +15
shutdown +15 "Shutting down in 15 minutes"
systemctl poweroff

Force reboot and shutdown:

systemctl reboot --force
systemctl poweroff --force

you can try with double --force too:

systemctl reboot --force --force
systemctl poweroff --force --force

Cancel the scheduled shutdown or reboot:

shutdown -c