How to Set Cron to Display Gui Application

how to set cron to display gui application

You can do this by setting the DISPLAY variable to :0. For instance:

* * * * * export DISPLAY=:0; gedit

This crontab line will open the gui software gedit every minute.

Launching an external GUI application from Python via crontab

Cron run in a specific environment, without display manager. If you try to do a echo $DISPLAY return null.
You need to set DISPLAY in your command, like that:

* * * * * DISPLAY=:0 <YOUR-COMMAND>

if your display is not 0, you can find, in X server with ps aux | grep Xorg

Running a tkinter GUI using crontab

The sudo will run without a tty and display that is why you command won't work.

Try having xvfb installed and use

0 18 * * * cd /home/pi/gui && xvfb-run python3 gui.py

Update-1: 22-Jun-18

If you want to use your actual display then you need to make sure that you use below command

XAUTHORITY=/home/<user>/.Xauthority DISPLAY=:0 python3 gui.py

And also make sure the cron is for your user. The default DISPLAY is :0.

When you have a XServer (GUI display), you cannot just connect to it without an authorization. When system start it creates a file and that location is stored in environment variable XAUTHORITY.

When you run a cron, you have limited environment variables. There is no existing XAUTHORITY or DISPLAY defined
to be able to connect to display you need. So you need to define every environment variable that would be required by your program

So you define DISPLAY=:0 to select the default display and you need to set XAUTHORITY=/home/<user>/.Xauthority to prove that you are authorized to connect to the display

How to show a Kivy GUI using cron planner?

The solution was to change the command behaviour to X application (rather than Default behaviour). After that change, the console shows up and the GUI is displayed.

Cron job: how to run a script that requires to open display?

You will need a valid DISPLAY and XAUTHORITY to use X-Programms in Cron!

To set DISPLAY is very easy, type in the Bash:

export DISPLAY=":0.0"

In order to get a valid XAUTHORITY you have to look for it.
Under Debian/Gnome/gdm3 they are saved in var/run/gdm3/*/database
I used the following script:

export DISPLAY=":0.0"
[ -z $USER ] && USER=$( who | awk '{ print $1 }' | sort | uniq >/tmp/test )
for I in /var/run/gdm3/*; do
    AUTHUSER="`echo $I | awk -F '-' '{ print $3 }'`"
    for J in $USER; do
        [ "${AUTHUSER}" = "${J}" ] || continue
        USER="$J"
        export XAUTHORITY="${I}/database" && break
    done
done
sudo -u ${USER} /Path/to/xProgramm

The Var $USER can be empty, than the script looks for a valid user, otherwise you can tell the script the var!

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