Linux Shutdown and reboot/restart procedure

1. Command Line Methods:

a) Shutdown:

To shut down immediately: sudo shutdown -h now
To shut down after a delay: sudo shutdown -h +m (replace m with minutes)
To shut down at a specific time: sudo shutdown -h HH:MM (24-hour format)

b) Restart:

To restart immediately: sudo shutdown -r now or sudo reboot
To restart after a delay: sudo shutdown -r +m (replace m with minutes)
To restart at a specific time: sudo shutdown -r HH:MM (24-hour format)

c) Cancel a scheduled shutdown or restart:

sudo shutdown -c

2. Using systemctl (for systemd-based distributions):

Shutdown: sudo systemctl poweroff
Restart: sudo systemctl reboot

3. Legacy commands (still work on most systems):

Shutdown: sudo halt or sudo poweroff
Restart: sudo reboot

4. GUI Methods:

Most desktop environments (GNOME, KDE, Xfce, etc.) have a menu option for shutting down or restarting. Usually found in the main menu or by clicking on the user name/icon.

5. Emergency Immediate Shutdown:

In case of an unresponsive system, you can use the magic SysRq key combinations:

Hold Alt + SysRq (usually Print Screen), then press these keys in sequence: R E I S U B #This will reboot your system
Hold Alt + SysRq (usually Print Screen), then press these keys in sequence: R E I S U O #This will power-off your system

6. Sending Signals:

You can use the kill command to send signals to the init process:

Shutdown: sudo kill -s SIGINT 1 #kill the init PID - resulting in machine power-off
Restart: sudo kill -s SIGTERM 1 #kill the init PID - resulting in machine power-off

7. Additional Options and Considerations:

a) Force shutdown (use cautiously): sudo shutdown -h -f now b) Schedule a shutdown message: sudo shutdown -h +m "System will shutdown in m minutes" c) Shut down without sudo (if configured): shutdown -h now

8. Shutting down remote systems:

SSH into the system and use any of the above commands
Use ssh user@host "sudo shutdown -h now" from another machine - you will NOT be able to reconnect without physical access to the machine!

9. Checking shutdown/restart history:

View last shutdown: last -x shutdown
View last reboot: last reboot
Check system logs: journalctl --since "1 hour ago" | grep -i "shut down\|reboot"

10. Best Practices:

Always ensure all important data is saved before shutting down or restarting
Close all running applications to prevent data loss
For servers, notify users before scheduling a shutdown or restart
Use delayed shutdowns to give time for important processes to complete
Regularly check system logs for any shutdown/restart issues

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