Hello guys!

I've written an application (C++/Qt) and now my boss wants to run it as a daemon; when it's killed it respawns, there can only be one instance of the application running, starts at boot etc...

What I've accomplished so far:

-The daemon starts but then its process id is not found when I try to stop it:

I've started with a fairly simple application: hello world, I've noticed that when I start the daemon (/etc/init.d/example start) it starts, prints hello world and then exits, and the daemon is nowhere to be found among the process ids, so I've added an infinite loop and this time around the daemon's id was still there.

But I'm thinking that there's a better way for this, I've read about child processes and fork(), I don't know if it can be done this way:

-father process (the actual daemon) starts a child process which carries the application's code.

I'm a bit stuck here so any help would be welcome

Thank you very much

You can almost never make a Qt application that launches as a boot-time daemon. A daemon process is one which has no controlling tty. A Qt application will require an X server, in order to run. Unless the X server is hosted somewhere on another host, there will be no X server when your daemon is launched. Whether a process is respawned or not does not determine whether it is or isn't a daemon, although the notion of respawning is a related concept.

You haven't said anything about what your daemon process is supposed to do. I wonder whether your purpose couldn't be adequately served by something that simply runs periodically, such as a cron job. Your wording of the question seems a bit vague on that.

--- rod.

1 members found this post helpful.

Hello again and thanks for taking the time to help me!

I apologize for being vague, I'll try to explain a little bit more:

my Qt application doesn't rely on X but rather operates directly through the framebuffer.

My application will run in a kiosk manner; graphical interface that allows user input, if it crashes, it respawns back. cron is good but we want to exploit the openrc functionalities (I'm on Gentoo Linux), thus, a daemon would fit our needs.

I've found a possible way, but I'd be grateful if you could tell me if I'm correct:

http://www.netzmafia.de/skripten/uni...mon-howto.html

It's under the (writing the daemon code) section.

A few things that might help you out:

http://0pointer.de/lennart/projects/libdaemon/

http://software.clapper.org/daemonize/

Lyle.

1 members found this post helpful.

Hello people! sorry for my late response, I was able to run the application as a daemon on gentoo using libdaemon

thank you for your help