signal(4)						     Kernel Interfaces Manual							 signal(4)

NAME

       signal, signal.h - Contains definitions and variables used by signal functions

DESCRIPTION

       The /usr/include/signal.h file defines the signals described in the following table.

       ------------------------------------------------------------------------------
       Signal	   Number   Meaning
       ------------------------------------------------------------------------------

       SIGHUP	     1	    Hangup.
       SIGINT	     2	    Interrupt.
       SIGQUIT	     3	    Quit.  (1)
       SIGILL	     4	    Invalid instruction (not reset when caught).  (1)
       SIGTRAP	     5	    Trace trap (not reset when caught).  (1)
       SIGABRT	     6	    End process (see the abort() function).  (1)
       SIGEMT	     7	    EMT instruction.
       SIGFPE	     8	    Arithmetic exception, integer divide by 0 (zero),
			    or floating-point exception.  (1)
       SIGKILL	     9	    Kill (cannot be caught or ignored).
       SIGBUS	     10     Specification exception.  (1)
       SIGSEGV	     11     Segmentation violation.  (1)
       SIGSYS	     12     Invalid parameter to system call.  (1)
       SIGPIPE	     13     Write on a pipe when there is no process to read it.
       SIGALRM	     14     Alarm clock.
       SIGTERM	     15     Software termination signal.
       SIGURG	     16     Urgent condition on I/O channel.  (2)
       SIGSTOP	     17     Stop (cannot be caught or ignored).  (3)
       SIGTSTP	     18     Interactive stop.  (3)
       SIGCONT	     19     Continue if stopped.  (4)
       SIGCHLD	     20     To parent on child stop or exit.  (2)
       SIGTTIN	     21     Background read attempted from control terminal.  (3)
       SIGTTOU	     22     Background write attempted from control terminal.  (3)
       SIGIO	     23     Input/Output possible or completed.  (2)
       SIGXCPU	     24     CPU time limit exceeded (see the setrlimit() function).
       SIGXFSZ	     25     File size limit exceeded (see the setrlimit() function).
       SIGVTALRM     26     Virtual time alarm (see the setitimer() function).
       SIGPROF	     27     Profiling time alarm (see the setitimer() function).
       SIGWINCH      28     Window size change.  (2)
       SIGINFO	     29     Information request.  (2)
       SIGUSR1	     30     User-defined signal 1.
       SIGUSR2	     31     User-defined signal 2.

       Notes to table:

       Default	action	includes  creating  a  core  dump file.  Default action is to ignore these signals.  Default action is to stop the process
       receiving these signals.  Default action is to restart or continue the process receiving these signals.

       The three types of actions that can be associated with a signal: SIG_DFL, SIG_IGN, or a pointer to a function  are  described  as  follows:
       Default action: signal-specific default action.

	      Except for those signal numbers marked with a (2), (3), or (4), the default action for a signal is to end the receiving process with
	      all of the consequences described in the _exit() system call. In addition, a memory image file is created in the	current  directory
	      of  the  receiving  process if the signal parameter is one for which a superscript 1 appears in the preceding list and the following
	      conditions are met: The effective user ID and the real user ID of the receiving process are equal.   An  ordinary  file  named  core
	      exists in the current directory and is writable, or it can be created. If the file must be created, it will have the following prop-
	      erties: The access permission code 0600, modified by the file creation mask (see the umask() function).  A file owner ID that is the
	      same  as	the  effective	user ID of the receiving process.  A file group ID that is inherited from the containing directory (if the
	      file system is mounted grpid) or from the owning process (if the file system is mounted nogrpid).

	      For signal numbers marked with a superscript 4, the default action is to restart the receiving process if it is stopped, or to  con-
	      tinue execution of the receiving process.

	      For  signal  numbers  marked with a superscript 3, the default action is to stop the execution of the receiving process temporarily.
	      When a process stops, a SIGCHLD signal is sent to its parent process, unless the parent process has set the SA_NOCLDSTOP bit.  While
	      a  process  is  stopped,	any  additional  signals that are sent to the process are not delivered until the process is continued. An
	      exception to this is SIGKILL, which always terminates the receiving process.  Another exception is SIGCONT, which always causes  the
	      receiving  process  to  restart or continue running. A process whose parent has ended shall be sent a SIGKILL signal if the SIGTSTP,
	      SIGTTIN, or SIGTTOU signals are generated for that process.

	      For signal numbers marked with a superscript 2, the default action is to ignore the signal. In this case, delivery of the signal has
	      no effect on the receiving process.

	      If a signal action is set to SIG_DFL while the signal is pending, the signal remains pending.  Ignore signal.

	      Delivery	of  the  signal has no effect on the receiving process.  If a signal action is set to SIG_IGN while the signal is pending,
	      the pending signal is discarded.

	      Note that the SIGKILL and SIGSTOP signals cannot be ignored.  Catch signal.

	      Upon delivery of the signal, the receiving process is to run the signal-catching function specified by the pointer to function.  The
	      signal-handler subroutine can be declared as follows:

	      void handler(signal) int signal;

	      The signal parameter is the signal number.

       A new signal mask is calculated and installed for the duration of the signal-catching function (or until sigprocmask() or sigsuspend() sys-
       tem calls are made). This mask is formed by taking the union of the process signal mask, the mask associated with the action for the signal
       being  delivered,  and  a  mask	corresponding  to the signal being delivered. The mask associated with the signal-catching function is not
       allowed to block those signals that cannot be ignored.  This is enforced by the kernel without causing an error to be  indicated.   If  and
       when  the  signal-catching function returns, the original signal mask is restored (modified by any sigprocmask() calls that were made since
       the signal-catching function was called) and the receiving process resumes execution at the point it was interrupted.

       The signal-catching function can cause the process to resume in a different context by calling the longjmp() subroutine. When the longjmp()
       subroutine is called, the process leaves the signal stack, if it is currently on it, and restores the process signal mask to the state when
       the corresponding setjmp() call was made.

       Once an action is installed for a specific signal, it remains installed until another action is explicitly requested (by  another  call	to
       the sigaction() system call), or until one of the exec system calls is called.

       If a signal action is set to a pointer to a function while the signal is pending, the signal remains pending.

       When  signal-catching  functions  are  invoked asynchronously with process execution, the behavior of some of the functions defined by this
       standard is unspecified if they are called from a signal-catching function.  The following set of functions are reentrant with  respect	to
       signals (that is, applications can invoke them, without restriction, from signal-catching functions):

       _exit()	      access()	      alarm()	      chdir()
       chmod()	      chown()	      close()	      creat()
       dup2()	      dup()	      exec()	      fcntl()
       fork()	      fstat()	      getegid()       geteuid()
       getgid()       getgroups()     getpgrp()       getpid()
       getppid()      getuid()	      kill()	      link()
       lseek()	      mkdir()	      mkfifo()	      open()
       pause()	      pipe()	      read()	      rename()
       rmdir()	      sem_post()      setgid()	      setpgrp()
       setuid()       sigaction()     sigaddset()     sigdelset()
       sigfillset()   siginitset()    sigismember()   signal()
       sigpending()   sigprocmask()   sigsuspend()    sleep()
       statx()	      tcdrain()       tcflow()	      tcflush()
       tcgetattr()    tcgetprgp()     tcsendbreak()   tcsetattr()
       tcsetpgrp()    time()	      times()	      umask()
       uname()	      unlink()	      ustat()	      utime()
       wait2()	      wait()	      write()

       All other system calls should not be called from signal-catching functions since their behavior is undefined.

RELATED INFORMATION

       Functions:  sigaction(2),  sigblock(2),	sigemptyset(3), siginterrupt(3), siglongjmp(3), sigpause(3), sigpending(2), sigprocmask(2), sigre-
       turn(2), sigset(3), sigsetjmp(3), sigstack(2), sigsuspend(2), sigvec(2), sigwait(3)

       delim off

																	 signal(4)