how the terminal control the applications started by themself

Question

Normally, we started applications from the terminals(or console), and the terminal which starts the applications will be the standard io of the applications.

1. If we close the terminals, the applications started by the terminal will normally be closed as well. But for those daemon processes are not closed. My questions is how terminal decides which applications to close, which not? And if I wanna write a daemon application, what shall I do to prevent being closed?

2. For those applications not closed, what happens if they print out something to the standout. Since the terminal is closed, where will the output go?

Thanks.

Answer 1

For your first question, I am assuming unix-like. If you want a daemon in a unix-like systems, you use something like: java& . Note the ampersand at the end of the command - that tells the shell to run it as a daemon.

For your second question, if I remember correctly, unless you pipe standard out somewhere else (like a file) it is simply swallowed when the process is a daemon process.

Hope that helps.

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edit: struck out the ampersand background portion as per Dirk's comment.

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Additional edit: Take a look at the Wikipedia article on Job Control. It has interesting information, especially about using disown along with a background process to turn it into a daemon.

Answer 2

Try the Apache JSVC package. It provides a proper executable, which knows how to arrange things in order for a java process to run as daemon under unix. It will also take care of the stdout/err channels, redirecting them into files or whatever you need. For windows, the procrun tool provides the capabilities to run a java VM as standard windows service.