signal(2)                        UNIX System V                        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 SIG_DFL, SIG_IGN, 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 SIG_DFL 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 SIG_HOLD, 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 SIG_IGN.

      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.

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.



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signal(2)                        UNIX System V                        signal(2)


      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
      SIG_IGN, 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 SIG_ERR and sets errno to indicate the error.

      On success, sigset returns SIG_HOLD if the signal had been blocked or the
      signal's previous disposition if it had not been blocked.  On failure, it
      returns SIG_ERR 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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