Reasons why console app crashes during daemonize code?

Hello all.

I’m not terribly good with Linux and after searching for a cause, the only answer I can find for a console app crashing/not daemonizing is that it is not set up with a script during boot. However, I thought (from windoz world) that even a daemon or service app can be run from command line and run as a service (in windows world) or daemon in Linux land.

Can anyone shed some light on this to help me?

This is the code used:

#if TargetLinux then
  If (args(1) = "start" or args(1) = "-d") then
    If Not App.Daemonize then
      System.Log( System.LogLevelCritical, "Could not daemonize the application")
      Return -1

In this case, it is compiled as Linux ARM console app.

Thank you in advance!

So which is it? Is it crashing or is it just not daemonizing?

Crashing would indicate that you didn’t get to the logging line.

You might also want to try replacing that with

stderr.writeline "could not daemonize"

And then the error would just go to the console when launching from terminal.

Also, look in the system log and see if there are any errors about your app.

In Linux you can execute a command and put it into the background simply by putting “&” after the command.

For instance: /my/App &

Depending on the shell you may find it still disconnects when you log out, in which case you can use the nohup command like this:

nohup /my/App &

For a more robust solution, launch your daemons using your OS’s init system. Usually upstart or systemd nowadays, but there are others. It is no more complicated then putting a config file in a directory and issuing a command or two. This provides a lot of benefits such as automatic startup, shutdown, restarting on crash, control over logs, control over environment and control over user:group the app executes under, etc…

Does it crash or does it just fail to demonize and log that message to console?

Hello all!

I did use the wrong terms to describe the action - it is not daemonizing. The system log shows the failure to daemonize.

I was launching from a terminal, is that not the best way to do it for non-production (for testing) use? Also, in my console command, I am not including an amperstand ‘&’. Should I?

John Royce brings up another question - will it only continue to run while logged into the console? If not then how to make that happen but start manually?

Also, to stop is it better to add a console command to the app that would allow it to shut down gracefully rather than using the system to kill it?


You certainly can launch a console app from the terminal, for testing or otherwise. You can also use the init system for this using a ‘restart’ command (depends on your system). If you update your app files with new ones, then issue a restart, you have the new app. Either way is fine, it depends on you and your needs really.

I believe that the app.daemonize command is supposed to put the app in the background (return you to a prompt). But, you can also add a & at the end of the command and it will also launch it in the background.

If you are starting the app from the command line via a terminal then it may indeed quit the app when you log out. To prevent this you can launch it into the background as a daemon using any of the methods we are discussing here. Sometimes & is not enough to prevent termination on logout in which case you need nohup - OR - use the init system.

How graceful it needs to be is really a function of how your app is written and what it is doing. If there are open files or half written database queries I suppose it could cause problems if you kill it at the wrong moment. I guess you need to weigh those risks. I kill or restart my apps whenever I am updating them and I have never had any issue. However, I use transactions in the database and other protections against data corruption.