Hi

I have written the app that has a GUI part (it generates images from invisible javafx controls and saves them into images). As a next step I'd like to make it an application that is always running, i.e. something like a service.

I have looked at monit to make it a service, but monit complains:

Failed in XOpenDisplay
(java:4465): Gtk-WARNING **: cannot open display:

Do you have an idea if I can use monit or any similar application to directly run my app?

Features I need:

start my app after reboot
restart my app if it goes down

Any help is appreciated.

Thank you,
Jozsef

Have you tried having the GUI user enabling local access to their X display?

You have directed me to the right direction (knew what to search for on the internet), thank you for your help.

For beginners like I am:

If you want to run a process from a shell that is not a child process of X, define an environment variable:

export DISPLAY=:0

Maybe you'll need to run the above recommended

/usr/bin/xhost +localhost

and then start your app, and it will find the primary X server (of course X server has to be running for this).

So now to run my app as a service, I run monit from an ordinary user account with the -c switch (how to do it during pc start is the next thing I'll need to look at)
(I need the -c switch so that it uses a config file that I supply rather than the config file in /etc which is set up so that it needs to be run as root because it reads/writes everything in /var)
To run monit as a daemon I do monit -c <conffile> -d 60
And in the startMyApp script I simply added

export DISPLAY=:0
/usr/bin/xhost +localhost

So I can run monit from a shell that is not a child process of X and my app will be able to use the GUI.