How do I reboot over a ssh connection without a return code of -1?

Question

The system I am working with uses ssh to remotely connect to a Linux machine. It then executes a single shell command and analyses the output from the shell command.

If I run reboot, I get exit code -1, since rebooting of course kills the ssh connection. Any exit code other than 0 makes the system register a failure, thus I have been trying to write a single line command that will reboot and exit the ssh session gracefully.

The machines in question are very bare bones and the reboot utility does not allow any options so I can't just schedule a reboot for later.

After some thought I tried running

$ sleep 3 && reboot & exit

Which works when I call it manually: the connection closes with error code 0 and 3 seconds later the machine reboots. Great.

But the same command run through our system doesn't actually reboot. It just returns exit code 0 and the reboot never happens.

Why would this be?

Solution 1

Use the shutdown command.

shutdown --reboot +1 "System is going down for reboot in 1 minute"

I suspect the reason reboot doesn't work is because it requires a tty. You could try running it with a background tty, but the shutdown command has everything you need, including cancelling -- as it says in response:

Shutdown scheduled for Thu 2018-02-22 15:19:33 MST, use 'shutdown -c' to cancel.

Solution 2

Usually you can return true and that will return an exit code of 0 so:

shutdown -r now || true

Comments

[Admin]

I'm not certain why it's not working, but you could try ssh user@host "nohup init 6 < /dev/null > /dev/null 2>/dev/null". Alternatively, ssh user@host "nohup shutdown -r +1 > /dev/null 2>/dev/null" which will reboot the system one minute after the command is sent.

[YetAnotherRCG]

That explains it, one minute is a little long to wait but it does work thanks.

[Rich]

Say now instead of +1 and change the message to suit. There isn't a way to specify a shorter interval (e.g. +15s would mean "in fifteen seconds"), but you can specify the next minute, so if it's 10:57 now, you could say 10:58 as your time specification.

[Admin]

Unfortunately, this didn't work for me.