Automatically disown application when running it from a terminal

The fact that a process is "disowned" has only a meaning for the interactive shell that created this process. It means that the shell doesn't include (anymore) the process in its jobs table, and that SIGHUP will not be sent to this process when the shell exits. It is not really related with your questions.

About what happens to the outputs that are sent to a deleted virtual terminal: I made some tests myself, and I noticed that /dev/pts/x devices are not accessible, and won't be allocated again until all filedescriptors that point to them have been closed. So, I can't see a reason why writes to a deleted terminal would be stored. I guess this is not even defined by POSIX.

About grabbing the output of some process that writes to a terminal, I don't think it is possible, even when the terminal is still alive¹. All you can do is grabbing the direct input to the terminal (i.e. keystrokes, or simulated keystrokes by the master part of a pty). If processes would read on stdin what is written to their terminals, that would lead to a self io loop for most process.

About the last remark on process termination, I don't really know what is happening, but I would suspect rather strange behaviors with signals (SIGTTOU, SIGTTIN, SIGHUP, or others) related to foreground/background state of process groups, when the session leader exits (e.g. su, in the case you mentioned).

Answer to the Edit: No, with respect to output, nothing changes when a process is disowned: it is still attached to its controlling terminal (unless it detached itself already like daemons do). You can see that using ps. However, you will not be able to use fg/bg/jobs commands provided by the shell anymore for this process. That means it might be difficult to feed it with input from the terminal (requires to be in the foreground process group).

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^{1. unless the process is willing to, or hijacked with some debugging tools (see comments above).}

In general this should be fine to do it this way.

When you click the "X" to close the terminal window, that is sending a "signal" from your desktop (GNOME, KDE, etc.) to the terminal application, telling it to shut itself down. Since you're running MATLAB in this shell it's considered a child process to the terminal application.

So part of the responsibilities of being a parent process, is that you in turn send this same close "signal" to your children.

Now if you understand conceptually what I just explained then let's substitute in a bit more of the real terminology.

signals

First with the "signal", there are actually a whole family of different signals that you can send to Unix processes. To keep it simple there are 4 that you'll often see, SIGHUP, SIGTERM, SIGINT, and SIGKILL.

• SIGHUP

  The SIGHUP signal is sent to a process when its controlling terminal is closed. It was originally designed to notify the process of a serial line drop. In modern systems, this signal usually means that controlling pseudo or virtual terminal has been closed.

• SIGTERM

  The SIGTERM signal is a generic signal used to cause program termination. Unlike SIGKILL, this signal can be blocked, handled, and ignored. It is the normal way to politely ask a program to terminate.

• SIGINT

  The SIGINT (“program interrupt”) signal is sent when the user types the INTR character (normally C-c).

• SIGKILL

  The SIGKILL signal is used to cause immediate program termination. It cannot be handled or ignored, and is therefore always fatal. It is also not possible to block this signal.

NOTE: SIGINT is what gets sent when you use Ctrl+C to "break" a program from the command line while it's in the middle of running.

which one is getting used?

Most likely the SIGTERM is being called by your windowing environment and being passed down to your terminal. Your terminal is then most likely then sending SIGHUP down to MATLAB. This signal gives all the processes the opportunity to do any local clean-up (closing files, ending processes, etc.) themselves.

kill command

You can send signals yourself using the poorly named command, kill. So to send the SIGTERM signal to your terminal or the SIGHUP to MATLAB, you could determine their PID usingps` and then run this command to send them the signal:

$ kill -SIGTERM <PID>

or this:

$ kill -SIGHUP <PID>

You can get a complete list of the signals using this command:

$ kill -l
 1) SIGHUP   2) SIGINT   3) SIGQUIT  4) SIGILL   5) SIGTRAP
 6) SIGABRT  7) SIGBUS   8) SIGFPE   9) SIGKILL 10) SIGUSR1
11) SIGSEGV 12) SIGUSR2 13) SIGPIPE 14) SIGALRM 15) SIGTERM
...
...

Notice that the signals have numbers? You'll often times see them used like that instead of by their names:

$ kill -15 <PID>

Or the infamous -9, which can kill pretty much any process.