How do I daemonize an arbitrary script in unix?

Question

I\'d like a daemonizer that can turn an arbitrary, generic script or command into a daemon.

There are two common cases I\'d like to deal with:

1. I hav

Answer 1

If you're using OS X specifically, I suggest you take a look at how launchd works. It will automatically check to ensure your script is running and relaunch it if necessary. It also includes all sorts of scheduling features, etc. It should satisfy both requirement 1 and 2.

As for ensuring only one copy of your script can run, you need to use a PID file. Generally I write a file to /var/run/.pid that contains a PID of the current running instance. if the file exists when the program runs, it checks if the PID in the file is actually running (the program may have crashed or otherwise forgotten to delete the PID file). If it is, abort. If not, start running and overwrite the PID file.