/etc/crontab :

# /etc/crontab: system-wide crontab
# Unlike any other crontab you don't have to run the `crontab'
# command to install the new version when you edit this file
# and files in /etc/cron.d. These files also have username fields,
# that none of the other crontabs do.

SHELL=/bin/sh
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin

# m h dom mon dow user command
17 * * * * root cd / && run-parts --report /etc/cron.hourly
25 6 * * * root test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.daily )
47 6 * * 7 root test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.weekly )
52 6 1 * * root test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.monthly )
#0,5,10,15,20,25,26,30,35,40,45,50,55 * * * * mserkan python /home/mserkan/.myscripts/randomwallpaper.py
* * * * * mserkan python /home/mserkan/.myscripts/randomwallpaper.py >/home/mserkan/.myscripts/myscript.log 2>&1
#


/home/mserkan/.myscripts/randomwallpapers.py :

#!/usr/bin/env python

from os import listdir, system
from random import sample

#get list of files in /mnt/Work/resources/visuals/wallpapers/
fileList = listdir("/mnt/Work/resources/visuals/wallpapers/")
#randomly choose one
theChosenOne = sample(fileList, 1)
#set wallpaper
system('gconftool-2 --type string --set /desktop/gnome/background/picture_filename "/mnt/Work/resources/visuals/wallpapers/' + str(theChosenOne[0]) + '"')
#scale wallpaper
system('gconftool-2 --type string --set /desktop/gnome/background/picture_options "zoom"')

here's my ls -l output :

mserkan@UbuntuPC:~/.myscripts$ ls -l
total 8
-rw-r--r-- 1 mserkan mserkan 0 2009-04-29 18:21 myscript.log
-rwxr-xr-x 1 mserkan mserkan 539 2009-04-29 17:50 randomwallpaper.py
-rw-r--r-- 1 mserkan mserkan 593 2009-04-29 17:49 randomwallpaper.py~
mserkan@UbuntuPC:~/.myscripts$



In a terminal when I run :
mserkan@UbuntuPC:~/.myscripts$ python randomwallpaper.py
it works, the wallpaper changes immediately.
when I delete the myscript.log file, it is created every minute again, hence I guess the python script is being run every minute. the created log file is empty.

this script worked in Ubuntu 8.04 through a crontab entry
but I couldn't get it work through a crontab entry in Ubuntu 9.04.

can anybody help me ?

Personal cronjobs should not be run from system-wide /etc/crontab but from what you get when you run 'crontab -e' as unprivileged user "mserkan". Your logfile may be empty because there's no stdout or stderr to log and because you don't append but clobber the log. And with respect to reinventing the wheel, doesn't your Desktop Environment come with wallpaper changing functionality?

Try executing the exact command line from the prompt:

What is outputting to the log or screen when you manually execute it that way? Secondarily you should have it in your personal crontab (crontab -e) not system wide... my guess is change of python version or loss of a system variable that was set before (/security changes related to x?)

Consider me as a totally newbie. the blog where I found this script says to use the crontab in /etc.

'crontab -e' -> GNU nano 2.0.9 File : /tmp/crontab.UznAaV/crontab

it produces a tmp file, so I guess you say that a crontab file should be created. but where ? directly in my home folder "/home/mserkan" ?

When an error occurs, it is output in the log file (I made intentionally an error in the script to see if it works).
Ubuntu 9.04 comes with Gnome 2.26.1, but afaik there's no such tool like in KDE.

absolutely nothing, neither in log nor on screen. but the wallpaper changes.

crontab -e : it produces a tmp file. where do I have to create one ?

I've installed Ubuntu 9.04 yesterday. so I guess it comes with one of the latest versions.

Edit your crontab by using "crontab -e". Crontab should install the result in the correct place, and you shouldn't need to worry about it.

I've removed the lines from /etc/crontab and did as you say.
after (ctrl + x) exiting nano editor it said :

mserkan@UbuntuPC:~$ crontab -e
no crontab for mserkan - using an empty one
crontab: installing new crontab
mserkan@UbuntuPC:~$

I deleted the log file and waited one minute. the log file got created with this error message in it :

/bin/sh: mserkan: not found

when I type crontab -e again nano editor now opens :

# m h dom mon dow command
#0,5,10,15,20,25,26,30,35,40,45,50,55 * * * * mserkan python /home/mserkan/.myscripts/randomwallpaper.py
* * * * * mserkan python /home/mserkan/.myscripts/randomwallpaper.py >/home/mserkan/.myscripts/myscript.log 2>&1

I removed mserkan in nano editor, becaus it says there at the top :

# m h dom mon dow command

so no user.

now every minute the log file is created but empty. and the wallpaper doesn't change at all.

I removed the lines in /etc/crontab before. now the crontab of mserkan works.

in terminal, this works and the wallpaper changes.
mserkan@UbuntuPC:~/.myscripts$ python randomwallpaper.py
mserkan@UbuntuPC:~/.myscripts$

but crontab runs the script, gives no errors but doesn'T change the wallpaper.

can you help ?

You don't need 'python' and the path to python in the 1st line of the script. That's redundant.
cron prob can't find the first python because you haven't specified the full path (a typical issue with cron; always specify complete absolute paths to cmds/files).
Anyway, drop the 'python' in the cron cmd and just ensure you have the path in the script (as you have) and also that the script has executable perms on.

I made it so and the result is the same. then I added print "1" to "4" as debug code between every line in the script. the output in the log file was

h1
h2
h3
h4

but when I open gconf-editor the background value isn't changed. when I change it manually, the wallpaper also changes immediately.

in terminal :
mserkan@UbuntuPC:~/.myscripts$ ls -l
total 12
-rw-r--r-- 1 mserkan mserkan 18 2009-04-30 02:29 myscript.log
-rwxr-xr-x 1 mserkan mserkan 712 2009-04-30 02:26 randomwallpaper.py
-rw-r--r-- 1 mserkan mserkan 712 2009-04-30 02:25 randomwallpaper.py~
mserkan@UbuntuPC:~/.myscripts$



now sorry for asking this (prob.) very simple question, but what is the command for changing it to executable ?

I tried chmod 777. as I said I'm really new to Linux.

could it be that python doesn't have the rights to change something in gconf ?

cron runs detached, ie not attached to any terminal, unlike eg '&' which puts it in the background, but is still attached to the terminal. Its more like 'nohup'.
You should prob just set up the python script as a daemon (ie an infinite lop) and run it in the background.
There may(!) be a way to get cron to talk to an interactive session, but I don't know how.

@Chris

this worked in Ubuntu 8.04 flawlessly. I used the /etc/crontab file there (I wasn't even aware of user specific crontab files until this thread).

do you (or anybody else) have any clue why it wouldn't work in 9.04 ?

btw, I got this script from : http://trishankkarthik.blogspot.com/...pers-with.html

... and the wallpaper is being changed every time I logout/login/restart.

that would mean that some process is invoking the script, right ?

There is a solution for this problem :

http://ubuntuforums.org/showpost.php...8&postcount=12

it worked for me.

I'm copy-pasting the solution, in case the post at 'ubuntuforums.org' got deleted :