[Web-SIG] Daemon server management

mso@oz.net mso at oz.net
Thu Jun 9 23:12:25 CEST 2005

Shannon -jj Behrens said:
> I usually just write a wrapper that matches whatever OS I'm on.  I.e.
> I sacrifice the cross-platform requirement.  Creating a FreeBSD
> rc.sh-type script is quite simple.  Perhaps I'm being naive.

I've got a similar situation now.  I've been using start-stop-daemon on
Linux to daemonize a naive Quixote application, but there's no equivalent
wrapper for Mac OSX 10.3.  We're looking at teaching the Python program
itself to daemonize, although I think that's less ideal than using a
platform-standard wrapper.  There's a couple examples in the Python
Cookbook (search for "daemon"); this is the one we're going to try:

Essentially, your application calls a function and then continues,
blissfully unaware it's been forked.  However, it doesn't make a PID file
or change uid.  These are essential for production services.  We're
looking at extending the function to do these.

The top-level executable needs --pidfile, --user and --group flags or the
equivalent.  (start-stop-daemon uses --chuid USER:GROUP).

> As for the pid file, if the user tries to start the server and I see
> that it exists, I exit with an error.  If the user tries to stop a
> server, and there is no pid file, I exit with an error.

Yes, that's what most applications do.  If the process doesn't exist it's
OK to overwrite the file, but there's also an argument for forcing the
user to do it manually.  If the process does exist, we can't tell whether
it's a conflicting Paste or an unrelated process, so we have to abort.

-- Mike Orr <mso at oz.net>

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