scripts command-line – How to Run a Shell Script in Background

Open the file explorer Files. Press Alt+F10 and select Preferences. You should see something like this.

In the Behavior tab, select Ask each time and close it. Now double on a shell script will ask you what to do each time. If you want to straight away execute the script, select the first option Run executable text files when they are opened.

This is happen because cron uses only a very restricted set of environment variables. The only one environment variable that is responsible for running in the right way the script from the question when this is set as a cron job is DBUS_SESSION_BUS_ADDRESS.

So, you must to export DBUS_SESSION_BUS_ADDRESS environment variable in your script. See more explanations in my answer here.

In the end, your script should look like:

#!/bin/bash

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

countervar=1;
finish=0;
cd /home/guinness/.rwallpaper/
if [ -f counter ]
then
    countervar=`cat counter`
fi

for (( i=$countervar; c<=2000000; i++ ))
do
   echo $i > "counter"
   if [ ! -f wallpaper-$i.jpg ]
   then
    wget "http://wallpapers.wallbase.cc/rozne/wallpaper-$i.jpg"

    if [ -f wallpaper-$i.jpg ]
    then
        gsettings set org.gnome.desktop.background picture-uri "file:///home/guinness/.rwallpaper/wallpaper-$i.jpg"
        exit
    fi
   fi
done