signal(3p) — Linux manual page

PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

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.1‐2017 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         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

       None.

APPLICATION USAGE         top

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

RATIONALE         top

       None.

FUTURE DIRECTIONS         top

       None.

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.1‐2017, signal.h(0p)

COPYRIGHT         top

       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)