From: Robert Klemme <shortcutter@...>
Date: 2009-05-07T06:40:05+09:00
Subject: Re: system call not working under cron

On 06.05.2009 23:10, Michael Satterwhite wrote:
> I have a short ruby script to periodically change the screen background
> under gnome (Ubuntu Linux). Trace statements in the script show that the
> script itself is running. The problem is that the system() call is not
> working. Note that I'm running it as myself, not as root. The same
> script works perfectly when run in a console.
> 
> Here's the command that isn't working.
> 
> ret = system("gconftool -t str --set
> /desktop/gnome/background/picture_filename '#{new_picture}'")
> 
> Please accept that the "new_picture" variable has a good value pointing
> to a new background. There are traces in the program that write values
> to a trace file that I can examine after the fact. The fact that the
> trace file is updated also shows the script is running.
> 
> Does anyone know why this command would work from a console, but not
> from a cron job?

This is likely due to X11's handling of permissions.  Your cron job 
simply does not have access rights to the X session.  I do not know the 
details but the man page of "xhost" may be a good starting point.  Error 
message that you get might also be a good indication.

Kind regards

	robert