Signal and Sigaction (The GNU C Library)

#### 25.3.3 Interaction of `signal` and `sigaction` ¶

It’s possible to use both the `signal` and `sigaction` functions within a single program, but you have to be careful because they can interact in slightly strange ways.

The `sigaction` function specifies more information than the `signal` function, so the return value from `signal` cannot express the full range of `sigaction` possibilities. Therefore, if you use `signal` to save and later reestablish an action, it may not be able to reestablish properly a handler that was established with `sigaction`.

To avoid having problems as a result, always use `sigaction` to save and restore a handler if your program uses `sigaction` at all. Since `sigaction` is more general, it can properly save and reestablish any action, regardless of whether it was established originally with `signal` or `sigaction`.

On some systems if you establish an action with `signal` and then examine it with `sigaction`, the handler address that you get may not be the same as what you specified with `signal`. It may not even be suitable for use as an action argument with `signal`. But you can rely on using it as an argument to `sigaction`. This problem never happens on GNU systems.

So, you’re better off using one or the other of the mechanisms consistently within a single program.

Portability Note: The basic `signal` function is a feature of ISO C, while `sigaction` is part of the POSIX.1 standard. If you are concerned about portability to non-POSIX systems, then you should use the `signal` function instead.