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

PROLOG         top

       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         top

       signal — signal management

SYNOPSIS         top

       #include <signal.h>

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

DESCRIPTION         top

       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:


       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

        *  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

RETURN VALUE         top

       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         top

       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         top



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

RATIONALE         top




SEE ALSO         top

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

       The Base Definitions volume of POSIX.1‐2008, signal.h(0p)

COPYRIGHT         top

       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 .

       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 .

IEEE/The Open Group                 2013                          SIGNAL(3P)