signal(3p) — Linux manual page

SIGNAL(3P)              POSIX Programmer's Manual             SIGNAL(3P)

PROLOG

       This manual page is part of the POSIX Programmer's Manual.  The
       Linux implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior),
       or the interface may not be implemented on Linux.

NAME

       signal — signal management

SYNOPSIS

       #include <signal.h>

       void (*signal(int sig, void (*func)(int)))(int);

DESCRIPTION

       The functionality described on this reference page is aligned
       with the ISO C standard. Any conflict between the requirements
       described here and the ISO C standard is unintentional. This
       volume of POSIX.1‐2017 defers to the ISO C standard.

       The signal() function chooses one of three ways in which receipt
       of the signal number sig is to be subsequently handled. If the
       value of func is SIG_DFL, default handling for that signal shall
       occur.  If the value of func is SIG_IGN, the signal shall be
       ignored.  Otherwise, the application shall ensure that func
       points to a function to be called when that signal occurs. An
       invocation of such a function because of a signal, or
       (recursively) of any further functions called by that invocation
       (other than functions in the standard library), is called a
       ``signal handler''.

       When a signal occurs, and func points to a function, it is
       implementation-defined whether the equivalent of a:

           signal(sig, SIG_DFL);

       is executed or the implementation prevents some implementation-
       defined set of signals (at least including sig) from occurring
       until the current signal handling has completed. (If the value of
       sig is SIGILL, the implementation may alternatively define that
       no action is taken.) Next the equivalent of:

           (*func)(sig);

       is executed. If and when the function returns, if the value of
       sig was SIGFPE, SIGILL, or SIGSEGV or any other implementation-
       defined value corresponding to a computational exception, the
       behavior is undefined. Otherwise, the program shall resume
       execution at the point it was interrupted. The ISO C standard
       places a restriction on applications relating to the use of
       raise() from signal handlers.  This restriction does not apply to
       POSIX applications, as POSIX.1‐2008 requires raise() to be async-
       signal-safe (see Section 2.4.3, Signal Actions).

       If the process is multi-threaded, or if the process is single-
       threaded and a signal handler is executed other than as the
       result of:

        *  The process calling abort(), raise(), kill(), pthread_kill(),
           or sigqueue() to generate a signal that is not blocked

        *  A pending signal being unblocked and being delivered before
           the call that unblocked it returns

       the behavior is undefined if the signal handler refers to any
       object other than errno with static storage duration other than
       by assigning a value to an object declared as volatile
       sig_atomic_t, or if the signal handler calls any function defined
       in this standard other than one of the functions listed in
       Section 2.4, Signal Concepts.

       At program start-up, the equivalent of:

           signal(sig, SIG_IGN);

       is executed for some signals, and the equivalent of:

           signal(sig, SIG_DFL);

       is executed for all other signals (see exec).

       The signal() function shall not change the setting of errno if
       successful.

RETURN VALUE

       If the request can be honored, signal() shall return the value of
       func for the most recent call to signal() for the specified
       signal sig.  Otherwise, SIG_ERR shall be returned and a positive
       value shall be stored in errno.

ERRORS

       The signal() function shall fail if:

       EINVAL The sig argument is not a valid signal number or an
              attempt is made to catch a signal that cannot be caught or
              ignore a signal that cannot be ignored.

       The signal() function may fail if:

       EINVAL An attempt was made to set the action to SIG_DFL for a
              signal that cannot be caught or ignored (or both).

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       The sigaction() function provides a more comprehensive and
       reliable mechanism for controlling signals; new applications
       should use sigaction() rather than signal().

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       Section 2.4, Signal Concepts, exec(1p), pause(3p), raise(3p),
       sigaction(3p), sigsuspend(3p), waitid(3p)

       The Base Definitions volume of POSIX.1‐2017, signal.h(0p)

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  In the event of any
       discrepancy between this version and the original IEEE and The
       Open Group Standard, the original IEEE and The Open Group
       Standard is the referee document. The original Standard can be
       obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page
       are most likely to have been introduced during the conversion of
       the source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group               2017                        SIGNAL(3P)

Pages that refer to this page: signal.h(0p), stropts.h(0p), nohup(1p), sh(1p), abort(3p), fork(3p), sigaction(3p), sighold(3p), sigsetjmp(3p)

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