Ubuntu – Background not changing using gsettings from cron

cronenvironment-variablesgnomegsettings

I'm trying to change my wallpaper to a random image using Indrajith Indraprastham's suggested script here:
How to change desktop background from command line in Unity?

When I run the script from a terminal window, the bg changes just fine, but when it's run from cron, I'm mailed this error:

(process:21901): dconf-WARNING **: failed to commit changes to dconf: Error spawning command line 'dbus-launch –autolaunch=00216c114dcf433c9bb9009985d607d6 –binary-syntax –close-stderr': Child process exited with code 1

I would appreciate any suggestions.

Best Answer

Editing gsettings from cron; missing environment variable

If you run the script from your own environment (e.g. from a terminal window or from Startup Applications), a number of environment variables will be set. cron however runs your script with a limited set of environment variables.

To edit gsettings successfully from cron, you need to set the DBUS_SESSION_BUS_ADDRESS environment variable. You can do that by adding two lines to your script, as described here (and below).

Your script, including setting the needed variable

The script from here, edited to include the DBUS_SESSION_BUS_ADDRESS environment variable, then becomes:

#!/bin/bash

PID=$(pgrep gnome-session)
export DBUS_SESSION_BUS_ADDRESS=$(grep -z DBUS_SESSION_BUS_ADDRESS /proc/$PID/environ|cut -d= -f2-)

DIR="/home/indra/Pictures/wallpapers"
PIC=$(ls $DIR/* | shuf -n1)
gsettings set org.gnome.desktop.background picture-uri "file://$PIC"

Related: Running .sh every 5 minutes

Related Solutions

Ubuntu – Cron not able to succesfully change background

Apparently gsettings needs some variables to be set. Because CRON uses only a very restricted set of environment variables you must set them before your script. Use the following code in your CRON line.

30 */2 * * * DISPLAY=:0 GSETTINGS_BACKEND=dconf /your/path/your-script.sh

In the example the job is set to run every 2 hours on the 30th minute. I've tried to insert the variables into the script, for a cleaner line, with no result, if someone find a way to do that, let us know.

Stumbled with these settings in ArchLinux forums.

The above solution no longer works with Vivid.

The best way to get this to work is indeed to find DBUS_SESSION_BUS_ADDRESS variable, in the following script I'm using a for loop to do the job because using pidof of a specific application like gnome-session doesn't always work for me and the newers applications have a different DBUS ADDRESS probably because, in my particular case, I'm starting some daemons on boot with my user name. To effectively change the wallpaper I'm using dconf but you can also use gsettings. So tweak the script to your use case.

#!/bin/bash -e
user=$(whoami)

fl=$(find /proc -maxdepth 2 -user $user -name environ -print -quit)
while [ -z $(grep -z DBUS_SESSION_BUS_ADDRESS "$fl" | cut -d= -f2- | tr -d '\000' ) ]
do
  fl=$(find /proc -maxdepth 2 -user $user -name environ -newer "$fl" -print -quit)
done

export DBUS_SESSION_BUS_ADDRESS=$(grep -z DBUS_SESSION_BUS_ADDRESS "$fl" | cut -d= -f2-)

if [ $# -gt 0 ]
then
  PICS_PATH=$1
else
  PICS_PATH="/home/public/Pictures/Wallpaper/"
fi

IMG=$(find -L $PICS_PATH -name "*.jpg" -o -name "*.png" | shuf -n1)
#gsettings set org.gnome.desktop.background picture-uri "file://${IMG}"
dconf write "/org/gnome/desktop/background/picture-uri" "'file://${IMG}'"

echo -e "$(date): ${IMG}" >> /tmp/wallch.log

in crontab add the following line to change wallpaper every even hour

0 */2 * * * /path/to-above-script.sh /path/to-wallpapers/

Ubuntu – php /var/www/html/.php is not working in terminal which is open from Menu php .php is working in terminal which is open inside php holding folder

Your script is almost certainly running and creating your file. It's just not creating it where you expect it to be. You are not using any path in your script, you just use a file name. This means that the file will be created in the directory the script is running in.

That's why, when you move into a specific directory and run the script there, you think it works. Because the file is created in the directory you ran it in and so you can see it. By default, cron runs in the home directory of the user running it. Since this is root's crontab (which, by the way, is a bad idea), the file will be created in /root. So, go check:

sudo ls /root/test.txt

So, next time, give your script a full path instead of just a file name:

<?php file_put_contents  ('/path/to/test.txt',"test content\n",FILE_APPEND); ?>

Now, the file will be created in /path/to.