signal(2)                                                         signal(2)


   NAME
         signal, sigset, sighold, sigrelse, sigignore, sigpause - simplified
         signal management

   SYNOPSIS
         #include <signal.h>
         void (*signal(int sig, void (*disp)(int)))(int);
         void (*sigset(int sig, void (*disp)(int)))(int);
         int sighold(int sig);
         int sigrelse(int sig);
         int sigignore(int sig);
         int sigpause(int sig);

   DESCRIPTION
         These functions provide simplified signal management for application
         processes.  See signal(5) for an explanation of general signal
         concepts.

         signal and sigset are used to modify signal dispositions.  sig
         specifies the signal, which may be any signal except SIGKILL and
         SIGSTOP.  disp specifies the signal's disposition, which may be
         SIGDFL, SIGIGN, or the address of a signal handler.  If signal is
         used, disp is the address of a signal handler, and sig is not SIGILL,
         SIGTRAP, or SIGPWR, the system first sets the signal's disposition to
         SIGDFL before executing the signal handler.  If sigset is used and
         disp is the address of a signal handler, the system adds sig to the
         calling process's signal mask before executing the signal handler;
         when the signal handler returns, the system restores the calling
         process's signal mask to its state prior to the delivery of the
         signal.  In addition, if sigset is used and disp is equal to
         SIGHOLD, sig is added to the calling process's signal mask and the
         signal's disposition remains unchanged.

         sighold adds sig to the calling process's signal mask.

         sigrelse removes sig from the calling process's signal mask.

         sigignore sets the disposition of sig to SIGIGN.

         sigpause removes sig from the calling process's signal mask and
         suspends the calling process until a signal is received.

         These functions fail if any of the following are true.

         EINVAL         The value of the sig argument is not a valid signal or
                        is equal to SIGKILL or SIGSTOP.

         EINTR          A signal was caught during the system call sigpause.





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   signal(2)                                                         signal(2)


   NOTES
         sighold in conjunction with sigrelse or sigpause may be used to
         establish critical regions of code that require the delivery of a
         signal to be temporarily deferred.

         If signal or sigset is used to set SIGCHLD's disposition to a signal
         handler, SIGCHLD will not be sent when the calling process's children
         are stopped or continued.

         If any of the above functions are used to set SIGCHLD's disposition
         to SIGIGN, the calling process's child processes will not create
         zombie processes when they terminate [see exit(2)].  If the calling
         process subsequently waits for its children, it blocks until all of
         its children terminate; it then returns a value of -1 with errno set
         to ECHILD [see wait(2), waitid(2)].

   DIAGNOSTICS
         On success, signal returns the signal's previous disposition.  On
         failure, it returns SIGERR and sets errno to indicate the error.

         On success, sigset returns SIGHOLD if the signal had been blocked or
         the signal's previous disposition if it had not been blocked.  On
         failure, it returns SIGERR and sets errno to indicate the error.

         All other functions return zero on success.  On failure, they return
         -1 and set errno to indicate the error.

   SEE ALSO
         kill(2), pause(2), sigaction(2), sigsend(2), wait(2), waitid(2),
         signal(5).























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