Start background process/daemon from CGI script

Question

I\'m trying to launch a background process from a CGI scripts. Basically, when a form is submitted the CGI script will indicate to the user that his or her request is being

Answer 1

Don't fork - run batch separately

This double-forking approach is some kind of hack, which to me is indication it shouldn't be done :). For CGI anyway. Under the general principle that if something is too hard to accomplish, you are probably approaching it the wrong way.

Luckily you give the background info on what you need - a CGI call to initiate some processing that happens independently and to return back to the caller. Well sure - there are unix commands that do just that - schedule command to run at specific time (at) or whenever CPU is free (batch). So do this instead:

import os

os.system("batch <<< '/home/some_user/do_the_due.py'")
# or if you don't want to wait for system idle, 
#   os.system("at now <<< '/home/some_user/do_the_due.py'")

print 'Content-type: text/html\n'
print 'Done!'

And there you have it. Keep in mind that if there is some output to stdout/stderr, that will be mailed to the user (which is good for debugging but otherwise script probably should keep quiet).

PS. i just remembered that Windows also has version of at, so with minor modification of the invocation you can have that work under apache on windows too (vs fork trick that won't work on windows).

PPS. make sure the process running CGI is not excluded in /etc/at.deny from scheduling batch jobs