signal man page on DigitalUNIX

Man page or keyword search:  
man Server   12896 pages
apropos Keyword Search (all sections)
Output format
DigitalUNIX logo
[printable version]

signal(4)							     signal(4)

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

       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).
       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 termi‐
			    nal.  (3)
       SIGTTOU	   22	    Background	write attempted from control ter‐
			    minal.  (3)
       SIGIO	   23	    Input/Output possible or completed. (2)
       SIGXCPU	   24	    CPU time limit exceeded (see the  setrlimit()
       SIGXFSZ	   25	    File size limit exceeded (see the setrlimit()
       SIGVTALRM   26	    Virtual time alarm (see the setitimer() func‐
       SIGPROF	   27	    Profiling  time  alarm  (see  the setitimer()
       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 receiv‐
       ing 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 properties: The access permission code 0600, modi‐
	      fied 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 continue 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 tempo‐
	      rarily. When a process stops, a SIGCHLD signal is	 sent  to  its
	      parent  process, unless the parent process has set the SA_NOCLD‐
	      STOP 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 pend‐
	      ing, 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 pend‐
	      ing, 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() system
       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  sig‐
       nal-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 execu‐
       tion at the point it was interrupted.

       The signal-catching function can cause the process to resume in a  dif‐
       ferent  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

       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 stan‐
       dard 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  sig‐
       nal-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 func‐
       tions since their behavior is undefined.

       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)


List of man pages available for DigitalUNIX

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
Vote for polarhome
Free Shell Accounts :: the biggest list on the net