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Old 01-04-2005, 05:20 PM   #1
Registered: Feb 2004
Posts: 47

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Bash - background process and exit ??


I have a bash script that acks like a wrapper, I start it with a "&" and it runs continuely untill it incounters an error or it shutdown.

It is used to monitor other processes.

I have noticed that after I start the script:

./scriptname start &

and logout ... it appears to exit after some random time, because a command returns an error. I have traps setup to exit if an error occurs:

trap cmd_error ERR

function cmd_error
echo "Command failed ${1}"
setterm -bold off
exit 1

I have standout being redirected to a file using:

##### Start of logging to file
exec 1>&2
exec 6>&1

exec > ${masterhome}/${masterlogs}/log-$$

echo ""
echo "Opening and starting logfile log-$$"
echo "Log file open ... $( date )"

I believe that after I logout ... the script tries to write to STDOUT, which is being redirected to a file ... but since I have exited ... my STDOUT is not longer being redirected to a file, so a error occurs causing the trap to exit the script.

I hops this makes sense ... please let me know if this is possible or if I am way off track.


Old 01-04-2005, 05:50 PM   #2
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Registered: Aug 2002
Location: Groningen, The Netherlands
Distribution: ubuntu
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Maybe stderr is not redirected?

If want to have a program or script running in the background, and continue to run when the shell closes it was started from, use "nohup" ("No Hang Up"). Nohup will redirect its output to a file called "nohup.out". If you don't like that, redirect stdin and stder both to /dev/null (or a file of your choice). Then no file will be created.
bash$ nohup ./ >/dev/null 2>&1 &
Read "info coreutils nohup" or "man nohup" for more info.

Last edited by Hko; 01-04-2005 at 05:51 PM.
Old 01-04-2005, 06:02 PM   #3
Registered: Feb 2004
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I ran some test ... what I was discribing does not seem to be causing the exit. I will continue trouble shooting.

Old 01-04-2005, 07:31 PM   #4
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Registered: Jan 2005
Location: UK
Distribution: Debian
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there's a program called 'screen' that can be used a little like nohup. I think it comes as standard with most distributions of linux.

You type 'screen' and it launches some kind of virtual console thing . You can launch a program in that, then use some keybinding (I can't remember which, look at the man page) to 'detatch' the screen, whereupon it closes the virtual console like thing, but keeps the process running in the background. When you next login you can run screen again and 'reattatch' the previous session and it will act as if you've been sitting there logged on the whole time.

Dosn't really answer your question, I'm afraid, but it might work as a temporary solution.

Old 01-05-2005, 11:03 AM   #5
Registered: Feb 2004
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Oh ... I like the screen option, because right now the program has a debug mode. Send the process a signal 10 and debug mode starts. Send it signal 10 again and debug mode stops. Debug mode works by printing everything to standard out.

So one I log out and log back in ... there is no more STDOUT for the process.

Thanks for the info.



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