how to run a command remotely through a script

iFunction · 12-05-2015, 09:09 AM

Hi there,

I am writing a script that will shut down a cluster of raspberry pi's.

So far I have 2 Raspberry Pi's,:
pi_one - with keyboard, mouse and screen
pi_two - headless

A key-gen has been generated so pi_one can log into pi_two automatically.

The script connects and logs in successfully from pi_one to pi_two via ssh, but I can't work how to get it to run the command.

I am trying to get pi_one to shutdown pi_two:

Code:

#/bin/bash
clear

ssh pi@192.168.0.1 # Thanks to keygen it logs in automatically

sudo reboot

initially it logs in but just opens up an ssh session with pi_two. When I exit the ssh session, the next line executes closing down the pi_one from which I am using. What do I need to get the next line to execute the reboot command in the pi that I am connecting to?

Regards
iFunc

berndbausch · 12-05-2015, 09:56 AM

Put the sudo reboot on the same line as the ssh.

Since a new line marks the end of a command, your current script has sudo reboot executed by the local shell running on pi_one, not by ssh.

iFunction · 12-05-2015, 10:42 AM

Thank you, such a simple thing, and actually I did read it in the bash how to manual, but didn't put two and two together.

TB0ne · 12-05-2015, 10:51 AM

Quote:

Originally Posted by iFunction

Thank you, such a simple thing, and actually I did read it in the bash how to manual, but didn't put two and two together.

The man page for SSH has further details, but something like:

Code:

ssh pi@192.168.0.1 "sudo shutdown"
ssh pi2@192.168.0.2 "sudo shutdown"
<repeat until you shut them ALL down>

would be what berndbausch is talking about.

iFunction · 12-05-2015, 11:30 AM

Yes, that was what I had in mind.

I am curious about the use of Quotation marks. Both:

Code:

ssh pi@192.168.0.1 sudo shutdown

and

Code:

ssh pi@192.168.0.1 'sudo shutdown'

works and I am assuming:

Code:

ssh pi@ 192.168.0.1 "sudo shutdown"

will also work.

What is the difference please?

Regards
iFunc

pan64 · 12-06-2015, 05:16 AM

as you can see in this case there is no difference.
But in general see man bash, look for quoting

berndbausch · 12-06-2015, 05:55 AM

Quote:

Originally Posted by iFunction

Yes, that was what I had in mind.

I am curious about the use of Quotation marks. Both:

Code:

ssh pi@192.168.0.1 sudo shutdown

and

Code:

ssh pi@192.168.0.1 'sudo shutdown'

works and I am assuming:

Code:

ssh pi@ 192.168.0.1 "sudo shutdown"

will also work.

What is the difference please?

Single quotes are "stronger" than double quotes. In particular, the dollar sign inside double quotes retains its special meaning, not so in single quotes.
The remote shell will receive the string that comes after the IP address in your command. With or without quotes, it will parse it correctly. In your example, no difference.

Here is an example where you need quotes:

Code:

ssh pi@192.168.0.1 sh -c "echo hi there"

Whatever comes after the -c must be a single parameter, thus the space must be quoted. It also works this way, but is harder to read:

Code:

ssh pi@192.168.0.1 sh -c echo\ hi\ there

See the two bash links in my signature.

TB0ne · 12-06-2015, 08:03 AM

Well said, berndbausch.

iFunction · 12-06-2015, 10:31 AM

Thanks berndbausch, gives me a good starting point.