From: Rob Biedenharn <Rob@...>
Date: 2008-12-18T23:54:30+09:00
Subject: Re: Net::SSH - kick off background job

On Dec 18, 2008, at 9:26 AM, Douglas Seifert wrote:
> On Thu, Dec 18, 2008 at 2:27 AM, Brian Candler <b.candler@pobox.com>  
> wrote:
>> Sebastian W. wrote:
>>> Does anyone know of a way to tell Net::SSH to start running a  
>>> script but
>>> then effectively "disown" that process?
>>>
>>> I have a long-running job I'd like to kick off using Net::SSH but I
>>> don't want the connection to persist for the entire length of the  
>>> job. I
>>> just want to kick off the job, let it start running and then  
>>> basically
>>> not care what happens. Of course I care, but I have a different  
>>> process
>>> that will actually pick up whether or not the long-running task was
>>> successful or not.
>>
>> nohup somecommand someargs &
>>
> You probably need something like this:
> nohup somecommand someargs > /tmp/out.log < /dev/null &
>
> the "< /dev/null" lets you detach the job from the terminal.
>
> Cheers,
> Doug Seifert


If your platform has setsid (set session id), that is a better option  
for something like this.

setsid somecommand someargs > /tmp/out.log 2>&1

Note the use of 2>&1 to redirect stderr(2) to(>) the same(&) place as  
stdout(1).  The order is important, redirect stdout first.

Also note that you do not put this command in the background with &  
like in the nohup case.  A new process is forked by setsid  so that  
the session id can be set and the controlling terminal disassociated  
from the process.

-Rob

P.S. Of course, this isn't Net::SSH specific, but applies to any Linux  
system.

Rob Biedenharn		http://agileconsultingllc.com
Rob@AgileConsultingLLC.com