signal

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.1‐2008 defers
       to the ISO C standard.

       Use of this function is unspecified in a multi-threaded process.

       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, pause(), raise(), sigaction(),
       sigsuspend(), waitid()

       The Base Definitions volume of POSIX.1‐2008, <signal.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical
       and Electronics Engineers, Inc and The Open Group.  (This is POSIX.1-2008
       with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/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                   2013                            SIGNAL(3P)