signal(2)

NAME

       signal - ANSI C signal handling

SYNOPSIS

       #include <signal.h>


       typedef void (*sighandler_t)(int);


       sighandler_t signal(int signum, sighandler_t action);

DESCRIPTION

       The  signal  system call installs a new signal handler for
       the signal with number signum.  The signal handler is  set
       to  handler which may be a user specified function, or one
       of the following:

              SIG_IGN
                     Ignore the signal.

              SIG_DFL
                     Reset the signal to its default behavior.

       The integer argument that is handed  over  to  the  signal
       handler routine is the signal number. This makes it possi­
       ble to use one signal handler for several signals.

       Signal handlers are called whenever the  process  receives
       the  corresponding  signal.   The  default  signal handler
       behaviour  varies  among  the  different  signals,   these
       behaviours are documented in signal(7).

RETURN VALUE

       signal  returns  the previous value of the signal handler,
       or SIG_ERR on error.

NOTES

       Signal handlers cannot be set for SIGKILL or SIGSTOP.

       Since libc6, signal uses BSD  semantics  and  the  default
       behaviour  is not reset when the signal is raised. You may
       use sysv_signal to get SysV semantics.

       Both signal and sysv_signal are library routines built  on
       top of sigaction(2).

       According  to  POSIX,  the behaviour of a process is unde­
       fined after it ignores a SIGFPE, SIGILL, or SIGSEGV signal
       that  was  not  generated  by  the kill(2) or the raise(2)
       functions.  Integer division by zero has undefined result.
       On  some  architectures  it  will generate a SIGFPE signal



       (dividing the most negative integer by -1 may also  gener­
       ate  SIGFPE).   Ignoring this signal might lead to an end­
       less loop.

       According to POSIX (B.3.3.1.3) you must not set the action
       for  SIGCHLD  to SIG_IGN. Here the BSD and SYSV behaviours
       differ, causing BSD software  that  sets  the  action  for
       SIGCHLD to SIG_IGN to fail on Linux.

       The  use  of  the sighandler_t is a GNU extension, and the
       type is only present when _GNU_SOURCE is defined.

CONFORMING TO

       ANSI C

SEE ALSO

       kill(1), kill(2), killpg(2),  pause(2),  raise(3),  sigac­
       tion(2), signal(7), sigsetops(3), sigvec(2), alarm(2)