From kragen@dnaco.net Tue Sep 29 17:21:47 1998
Date: Tue, 29 Sep 1998 17:21:45 -0400 (EDT)
From: Kragen <kragen@dnaco.net>
To: systalk@ml.org
Subject: Re: [ST] Starting jobs in the background in UNIX
In-Reply-To: <01bdebd6$eceb1540$0b4515c4@fireclaw.icon.co.za>
Message-ID: <Pine.SUN.3.96.980929170917.21177Y-100000@picard.dnaco.net>
MIME-Version: 1.0
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Status: O
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On Tue, 29 Sep 1998, Sean Preston wrote:
> I am trying to start a set of commands in the background.  I know the one
> way is to use the at command and give it a file with the commands in it.  I
> do not have access to this.  I was told there is a way of doing it using
> nohup but I am unsure as to how to give this command the file with all of my
> commands in it.  I am doing this through a telnet session as I am not going
> to have access to the console of the system.  I have permission to start
> jobs in the background.
> 
> The main reason I need to start the commands in the background is because I
> am dialling in from home, starting the commands and then logging off.  I
> need it to continue while I am not there.  There is no screen command on the
> system.

Well, if it's just a compute job -- something that won't require user
interaction -- you can do it as follows:

egrep kragen www/logs/access_log > acclog &

In this case, I'm starting the 'egrep' command with some arguments and
redirecting its output to 'acclog'.  It might be a good idea to
redirect its standard error to somewhere, too.

If you want to do something more complicated, you can write a shell
script, like this one:

#!/bin/sh
ls -l
sleep 10
ls -l
finger kragen
sleep 30
finger kragen

(just a bunch of useless commands, in this case, but you can replace
them with your own useful ones.)

Then you can put the shell script in a file -- say 'myscript' -- and
then you can do something like this:

bash$ chmod u+x myscript
(that makes it executable, indicating it's a shell script, not just a
text file)
bash$ ./myscript > myscript.out &

'nohup' does something about shielding from the hangup signal, but if
your login shell is csh or bash (or something derived from one of them)
you don't need to do that.  You only need to do that, in fact, if your
shell is 'sh'.  nohup also automatically redirects the output of your
commands, so you don't have to do that by hand.  You can run it like
this:

bash$ nohup ./myscript &

You can give any command this way -- egrep if you want:

bash$ nohup egrep kragen www/logs/access_log > myaccesses &

Later on, you can use 'ps' to see if your job is still running:

bash$ ps -elf | egrep myscript

ps -elf shows all the processes on your (Solaris or other System V)
system, including all their arguments; the 'egrep' will filter out most
of them, except those that have the string 'myscript' in them
somewhere.

If you're using a Linux or BSD-derived system (like SunOS 4) you should
use 'ps auxwwwwww' instead of 'ps -elf'.

Hope this helps!

Kragen

-- 
<kragen@pobox.com>       Kragen Sitaker     <http://www.pobox.com/~kragen/>
A well designed system must take people into account.  . . .  It's hard to
build a system that provides strong authentication on top of systems that
can be penetrated by knowing someone's mother's maiden name.  -- Schneier