If you are managing your Linux machines you are aware of some useful shutdown/ powercycle commands. You might have used one of the commands to reboot/ powercycle or shutdown a box: reboot, halt, shutdown, poweroff, telinit

bitarray>ls -rplt /sbin/|egrep "halt|shutdown|reboot"
lrwxrwxrwx 1 root root 14 Mar 8 17:51 shutdown -> /bin/systemctl
lrwxrwxrwx 1 root root 14 Mar 8 17:51 reboot -> /bin/systemctl
lrwxrwxrwx 1 root root 14 Mar 8 17:51 halt -> /bin/systemctl
lrwxrwxrwx 1 root root 14 Mar 8 17:51 telinit -> /bin/systemctl
bitarray>

so they all point to systemctl (since 2014). You need to be root to shutdown the system.

How to schedule a shutdown?

• shutdown  now # will shutdown now graceful shutdown for all processes
• shutdown 10 # shutdown after 10 mins
• shutdown 23:59 # shutdown at time 23:59
• shutdown -c # cancel shutdown
• shutdown -r # reboot the machine
• shutdown -P # poweroff the machine (it won’t get started)

remember when shutdown time is < 5mins then no users will be allowed to login.

In systemd reboot, halt, poweroff, telinit, and shutdown are same systemctl command.

example# setting shutdown after 100 mins

bitarray>date
Fri Aug 24 19:35:33 EDT 2018
bitarray>shutdown 100
Shutdown scheduled for Fri 2018-08-24 21:15:38 EDT, use 'shutdown -c' to cancel.

Canceling shutdown

shutdown -c

bitarray>shutdown -c
Broadcast message from root@hostmaster (Fri 2018-08-24 19:37:23 EDT):
The system shutdown has been cancelled at Fri 2018-08-24 19:38:23 EDT!
bitarray>

How do we know if there is a scheduled shutdown?

just do a ps -ef and you will see the shutdown process

bitarray>ps -ef|grep shut
root      8446     1  0 19:35 ?        00:00:00 /usr/lib/systemd/systemd-shutdownd

During the shutdown, all processes are sent TERM signal (for a graceful exit).

How to check previous shutdowns:

#last -x|grep shutdown
shutdown system down  3.10.0-693.11.6. Sun Aug 19 19:15 - 19:15  (00:00)    
shutdown system down  3.10.0-693.11.6. Thu Aug 16 19:35 - 19:36  (00:01)    
shutdown system down  3.10.0-693.11.6. Wed Aug 15 20:25 - 20:34  (00:08)    
shutdown system down  3.10.0-693.11.6. Thu Jul 12 19:06 - 19:06  (00:00)    
shutdown system down  3.10.0-693.11.6. Thu Jan 25 15:06 - 20:08  (05:02)    
shutdown system down  3.10.0-514.21.2. Thu Jan 25 13:27 - 13:28  (00:00)