Initial Signal Actions - The GNU C Library

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#### 24.3.6 Initial Signal Actions

When a new process is created (see Creating a Process), it inherits handling of signals from its parent process. However, when you load a new process image using the `exec` function (see Executing a File), any signals that you've defined your own handlers for revert to their `SIG_DFL` handling. (If you think about it a little, this makes sense; the handler functions from the old program are specific to that program, and aren't even present in the address space of the new program image.) Of course, the new program can establish its own handlers.

When a program is run by a shell, the shell normally sets the initial actions for the child process to `SIG_DFL` or `SIG_IGN`, as appropriate. It's a good idea to check to make sure that the shell has not set up an initial action of `SIG_IGN` before you establish your own signal handlers.

Here is an example of how to establish a handler for `SIGHUP`, but not if `SIGHUP` is currently ignored:

         ...
         struct sigaction temp;

         sigaction (SIGHUP, NULL, &temp);

         if (temp.sa_handler != SIG_IGN)
           {
             temp.sa_handler = handle_sighup;
             sigemptyset (&temp.sa_mask);
             sigaction (SIGHUP, &temp, NULL);
           }