sgetmask(2)



SIGNAL(2)                  Linux Programmer's Manual                 SIGNAL(2)

NAME
       signal - ANSI C signal handling

SYNOPSIS
       #include <signal.h>

       typedef void (*sighandler_t)(int);

       sighandler_t signal(int signum, sighandler_t handler);

DESCRIPTION
       The  signal()  system call installs a new signal handler for the signal
       with number signum.  The signal handler is set to sighandler which  may
       be a user specified function, or either SIG_IGN or SIG_DFL.

       Upon  arrival of a signal with number signum the following happens.  If
       the corresponding handler  is  set  to  SIG_IGN,  then  the  signal  is
       ignored.   If  the  handler  is set to SIG_DFL, then the default action
       associated with the signal (see signal(7))  occurs.   Finally,  if  the
       handler  is  set to a function sighandler then first either the handler
       is reset to SIG_DFL or an implementation-dependent blocking of the sig-
       nal is performed and next sighandler is called with argument signum.

       Using  a  signal  handler function for a signal is called "catching the
       signal".  The signals SIGKILL and SIGSTOP cannot be caught or  ignored.

RETURN VALUE
       The signal() function returns the previous value of the signal handler,
       or SIG_ERR on error.

PORTABILITY
       The original Unix signal() would reset the handler to SIG_DFL, and Sys-
       tem  V  (and the Linux kernel and libc4,5) does the same.  On the other
       hand, BSD does not reset the handler, but blocks new instances of  this
       signal from occurring during a call of the handler.  The glibc2 library
       follows the BSD behaviour.

       If one on a libc5 system includes <bsd/signal.h> instead of  <signal.h>
       then  signal()  is  redefined  as  __bsd_signal  and signal has the BSD
       semantics.  This is not recommended.

       If one on a  glibc2  system  defines  a  feature  test  macro  such  as
       _XOPEN_SOURCE  or  uses  a  separate  sysv_signal function, one obtains
       classical behaviour.  This is not recommended.

       Trying to change the semantics of this call using defines and  includes
       is not a good idea.  It is better to avoid signal() altogether, and use
       sigaction(2) instead.

NOTES
       The effects of this call in a multi-threaded process are unspecified.

       The routine handler must be very careful,  since  processing  elsewhere
       was interrupted at some arbitrary point. POSIX has the concept of "safe
       function".  If a signal interrupts  an  unsafe  function,  and  handler
       calls  an  unsafe  function, then the behavior is undefined. Safe func-
       tions are listed explicitly in the various standards.  The POSIX.1-2003
       list is

       _Exit()  _exit()  abort()  accept()  access()  aio_error() aio_return()
       aio_suspend() alarm() bind() cfgetispeed() cfgetospeed()  cfsetispeed()
       cfsetospeed() chdir() chmod() chown() clock_gettime() close() connect()
       creat() dup() dup2() execle() execve() fchmod() fchown() fcntl() fdata-
       sync()   fork()   fpathconf()  fstat()  fsync()  ftruncate()  getegid()
       geteuid() getgid() getgroups() getpeername() getpgrp()  getpid()  getp-
       pid()   getsockname()  getsockopt()  getuid()  kill()  link()  listen()
       lseek() lstat()  mkdir()  mkfifo()  open()  pathconf()  pause()  pipe()
       poll()  posix_trace_event()  pselect() raise() read() readlink() recv()
       recvfrom()  recvmsg()  rename()  rmdir()  select()  sem_post()   send()
       sendmsg()  sendto()  setgid()  setpgid() setsid() setsockopt() setuid()
       shutdown()  sigaction()  sigaddset()  sigdelset()  sigemptyset()   sig-
       fillset()  sigismember() signal() sigpause() sigpending() sigprocmask()
       sigqueue() sigset() sigsuspend() sleep() socket()  socketpair()  stat()
       symlink()  sysconf()  tcdrain()  tcflow() tcflush() tcgetattr() tcgetp-
       grp() tcsendbreak() tcsetattr() tcsetpgrp()  time()  timer_getoverrun()
       timer_gettime()   timer_settime()   times()  umask()  uname()  unlink()
       utime() wait() waitpid() write().

       According to POSIX, the behaviour of a process is  undefined  after  it
       ignores  a  SIGFPE, SIGILL, or SIGSEGV signal that was not generated by
       the kill(2) or the raise(3) functions.  Integer division  by  zero  has
       undefined result.  On some architectures it will generate a SIGFPE sig-
       nal.  (Also dividing the most  negative  integer  by  -1  may  generate
       SIGFPE.)  Ignoring this signal might lead to an endless loop.

       See  sigaction(2)  for  details  on what happens when SIGCHLD is set to
       SIG_IGN.

       The use of sighandler_t is a GNU extension.  Various versions  of  libc
       predefine  this  type;  libc4  and  libc5  define  SignalHandler, glibc
       defines sig_t and, when _GNU_SOURCE is defined, also sighandler_t.

CONFORMING TO
       C89, POSIX.1-2001.

SEE ALSO
       kill(1), alarm(2), kill(2), pause(2), sigaction(2), sigpending(2), sig-
       procmask(2),  sigqueue(2),  sigsuspend(2),  killpg(3), raise(3), sigse-
       tops(3), sigvec(3), feature_test_macros(7), signal(7)

Linux 2.2                         2000-04-28                         SIGNAL(2)

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