Keep an exec running?

Zeno McDohl · 08-24-2007, 01:19 PM

I'm looking to write a script (csh perhaps) that keeps an exec running. So when it dies, the script will boot it back up. I've tried a few things, with no luck.

b0uncer · 08-24-2007, 01:28 PM

What have you tried? Any examples? What didn't work in them, what was the actual problem?

People here will more likely help you if you have actual problems to show, to show that you've already tried something. If you just come here and say "hey guys, I need a complete firewalling-and-security-hardening plan for a 1000 machine corporation, and I need it in two hours!" you'll probably get zero answers.

You have several options, one being to check if the process ID exists (and corresponds to the process name), and if not, launch the program and save it's new ID etc..

Zeno McDohl · 08-24-2007, 01:30 PM

This is what I have:

Code:

#! /bin/csh -f

set port = 54230

while ( 1 )

    # Run Server.
    # Check if already running
    set matches = `netstat -an | grep ":$port " | grep -c LISTEN`
    if ( $matches >= 1 ) then
        # Already running
        echo Port $port is already in use.
        exit 0
    endif
    ./server

end

I would expect the script to always be running, but it ends right after being run.

jailbait · 08-24-2007, 01:48 PM

Quote:

Originally Posted by Zeno McDohl

This is what I have:

Code:

#! /bin/csh -f

set port = 54230

while ( 1 )

    # Run Server.
    # Check if already running
    set matches = `netstat -an | grep ":$port " | grep -c LISTEN`
    if ( $matches >= 1 ) then
        # Already running
        echo Port $port is already in use.
        exit 0
    endif
    ./server

end

I would expect the script to always be running, but it ends right after being run.

$matches will always be >= 1 so you will always take exit 0 which is what you report always happens. What condition(s) are you trying to check? Netscape running? Port 54230 in use? What is LISTEN?

--------------
Steve Stites

Zeno McDohl · 08-24-2007, 01:56 PM

The exec uses port 54230, so I check if that port is in use.

LISTEN is used to look for that in netstat.

Zeno McDohl · 08-26-2007, 10:08 AM

Anyone have any suggestions?

unSpawn · 08-26-2007, 10:54 AM

A loop wouldn't make sense IMHO because it would keep executing instances of server. And usually a "server" implies something that forks itself off into the background so you wouldn't want to keep the script alive anyway. You also don't need two 'grep' instances and you don't need to "see" anything: just use the exit status. Exit status of a script on errorless completion should AFAIK be zero and any other values to denote errors. If the "server" doesn't background itself this is what happens (run with 'csh -x' to see what I mean):

Code:

#!/bin/csh -f
[ ! -f ./server ] && echo read > server; chmod 0750 server
[ ! -x ./server ] && exit 127
set port = 54230
netstat -an | grep -q ":${port}.*LISTEN"
[ $? -eq 1 ] && exit 1 || ./server
exit 0

HTH

Zeno McDohl · 08-26-2007, 01:10 PM

Quote:

so you wouldn't want to keep the script alive anyway

You lost me. If the script isn't running, how is it suppose to boot the server back up when it dies?

unSpawn · 08-26-2007, 05:46 PM

What exactly is this "server" if you don't mind me asking?

Zeno McDohl · 08-26-2007, 06:52 PM

It's a MUD.

unSpawn · 08-27-2007, 01:45 AM

how is it suppose to boot the server back up when it dies?
And why would it die? Wouldn't it be "better" to first find out *why* it dies and work on that before trying to implement a workaround? BTW, if it writes a PID somewhere and can use an initscript it would be easier to run a "real" process checker like Monit.

Zeno McDohl · 08-27-2007, 01:40 PM

I know that. It dumps cores when it crashes. I gdb those and fix the bugs. But I can't predict the future and know when it'll crash.

So again. I'd like to figure out how to write a script to keep it running. And I don't think it writes the PID anywhere.

unSpawn · 08-27-2007, 04:03 PM

Code:

#!/bin/bash --
runServer() { ./server || runServer; }; netstat -ntl \
| grep -q ":54230[[:blank:]]" || runServer; exit 0

nan0meter · 08-27-2007, 06:53 PM

Well doing this would consume quite an ammount of memory and CPU power wouldn't it? Can't you better poll for it with a timeout?