Repeatedly running commands over SSH

[dane]

Hello everybody,

I want to repeatedly run one (or several commands) over SSH to check the load on the server (and maybe other things).

This is what I got so far:

http://play.golang.org/p/3z513UKrOY

First question: Is there a better way to do this?

Second question: Can I somehow get rid of the user@host:~$  thing in the ssh stdout,

so that the output is actually only the output of the command I enter.

Third question: Is it guaranteed, that I get all the output of the command with one read on the

stdout of the ssh session?

Thanks for your help!

Best Regards

David

[James Bardin]

On Thursday, September 19, 2013 2:33:10 PM UTC-4, dane wrote:

Hello everybody,

I want to repeatedly run one (or several commands) over SSH to check the load on the server (and maybe other things).

This is what I got so far:

http://play.golang.org/p/3z513UKrOY

First question: Is there a better way to do this?

I would highly suggest *not* using a shell. I believe what you want is the Output or CombinedOutput (or even Run) methods (I haven't yet used go's ssh library, but I am very familiar some others).

This isolates your commands, and lets you wait for the process to complete, and get an exit status of some sort.

Second question: Can I somehow get rid of the user@host:~$  thing in the ssh stdout,

so that the output is actually only the output of the command I enter.

This is output by the shell, see my previous comment. When you have a shell, you have to parsing all the output, including command prompts, to determine when your process is actually complete. You end up needing something like the `expect` command.

 

Third question: Is it guaranteed, that I get all the output of the command with one read on the

stdout of the ssh session?

Not if you're using a shell, you have to poll for a command prompt, or some other indicator that your command ran to completion. 

 

[dane]

I realize that I could use separate sessions and the Run method, but then every session has to establish a new ssh connection, right?

So it could be possible that the goroutine cannot keep up at higher polling frequencies.

[Keith Rarick]

You can call NewSession repeatedly on a single ssh client connection. Use the Output method on each session as James suggested.

You might also consider github.com/kr/sshpool if you'll be juggling  connections to many hosts. 

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[James Bardin]

On Thursday, September 19, 2013 3:32:20 PM UTC-4, dane wrote:

I realize that I could use separate sessions and the Run method, but then every session has to establish a new ssh connection, right?

No, NewSession is a method of a connection. You con't need to create a new connection each time. A Session seems to be what this library calls a channel for the client, and many channels are multiplexed in a single connection.

 

So it could be possible that the goroutine cannot keep up at higher polling frequencies.

I doubt there's any polling going on here, unless it's in your code.

 

[dane]

Ok, that makes more sense, I was somehow a bit confused by the documentation.