I have a bash script that monitors a log file using swatch. I have had problems with swatch after the log file is rotated, so I setup a cron job to restart the script after the log file rotation, however this introduces a new problem. the daemon script I use to start swatch in the background becomes unavailable to me, so I end up with many defunct process, or child process that I cannot kill. What is the best way to create a deamon script (in /etc/init.d) that will call my bash script, yet all me to keep control of it and any child processes. The prog needs to run in the background.
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It's not. What I have is a script we can call myscript.sh. It pretty much calls swatch to monitor a file. I then have another script in /etc/init.d called mydaemonscript.sh that calls myscript.sh. The mydaemonscript should handle starting / stopping and killing any processes associated with myscript.sh. Right now it either creates several swatch processes, or the swatch process does not work. Killing the processes leaves me with zombies.
Does this clarify?
Hi,
Linux has a mechanism to start processes and monitor them with inittab. So, you may add an entry to /etc/inittab file (use man inittab to see the format anf how to use it) to monitor your script that rotate and restart swatch. With the respawn action in inittab, the system will monitor your script and if it dies (it can not handle hanging processes) it restart it.
Now, in your script you can run swatch, rotate logs, etc. then sleep (keep looping / repeating the steps).
I did some research and found that the swatch proc kicks off a tail -f proc. This one was not being killed. I now catch the two pids when I start the deamon, and can kill them when necessary. Also to handle the log rotation I pass command line parameters through swatch to the tail process it calls. These params then keep it from locking when the file is rotated, as by default swatch calls tailing and it follows the file descriptor, thus it continues to monitor my rotatated log file, not the new log file. By telling swatch / tail to monitor the filename, It continues to monitor as expected.
ravenpl: the unkilled tail process where causing the zombie process, once I did a ps aux | grep for tail, I saw all of the associated tail procs kicked off by swatch. Killing them killed the zombie processes.
THe problem is resolved, but I'm not sure how to score this, as I located the answer myself. However all were good comments, but none were solutions. Any suggestions?
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by: ravenplPosted on 2007-09-18 at 12:19:36ID: 19915786
I'm not sure if I undestand.
Why those zombies are created? You said You are restarting the script. Killing it should wipe any zombies(children) as well...