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RedHat 9 (Linux i386) - man page for signal (redhat section 7)

SIGNAL(7)			    Linux Programmer's Manual				SIGNAL(7)

NAME
       signal - list of available signals

DESCRIPTION
       Linux  supports	both  POSIX  reliable  signals (hereinafter "standard signals") and POSIX
       real-time signals.

   Standard Signals
       Linux supports the standard signals listed below. Several signal numbers are  architecture
       dependent,  as  indicated in the "Value" column.  (Where three values are given, the first
       one is usually valid for alpha and sparc, the middle one for i386, ppc  and  sh,  and  the
       last  one  for  mips.   A - denotes that a signal is absent on the corresponding architec-
       ture.)

       The entries in the "Action" column of the table specify the default action for the signal,
       as follows:

       Term   Default action is to terminate the process.

       Ign    Default action is to ignore the signal.

       Core   Default action is to terminate the process and dump core.

       Stop   Default action is to stop the process.

       First the signals described in the original POSIX.1 standard.

       Signal	  Value     Action   Comment
       -------------------------------------------------------------------------
       SIGHUP	     1	     Term    Hangup detected on controlling terminal
				     or death of controlling process
       SIGINT	     2	     Term    Interrupt from keyboard
       SIGQUIT	     3	     Core    Quit from keyboard
       SIGILL	     4	     Core    Illegal Instruction
       SIGABRT	     6	     Core    Abort signal from abort(3)
       SIGFPE	     8	     Core    Floating point exception
       SIGKILL	     9	     Term    Kill signal
       SIGSEGV	    11	     Core    Invalid memory reference
       SIGPIPE	    13	     Term    Broken pipe: write to pipe with no readers
       SIGALRM	    14	     Term    Timer signal from alarm(2)
       SIGTERM	    15	     Term    Termination signal
       SIGUSR1	 30,10,16    Term    User-defined signal 1
       SIGUSR2	 31,12,17    Term    User-defined signal 2
       SIGCHLD	 20,17,18    Ign     Child stopped or terminated
       SIGCONT	 19,18,25	     Continue if stopped
       SIGSTOP	 17,19,23    Stop    Stop process
       SIGTSTP	 18,20,24    Stop    Stop typed at tty
       SIGTTIN	 21,21,26    Stop    tty input for background process
       SIGTTOU	 22,22,27    Stop    tty output for background process

       The signals SIGKILL and SIGSTOP cannot be caught, blocked, or ignored.

       Next  the  signals  not	in  the POSIX.1 standard but described in SUSv2 and SUSv3 / POSIX
       1003.1-2001.

       Signal	    Value     Action   Comment
       -------------------------------------------------------------------------
       SIGBUS	   10,7,10     Core    Bus error (bad memory access)
       SIGPOLL		       Term    Pollable event (Sys V). Synonym of SIGIO

       SIGPROF	   27,27,29    Term    Profiling timer expired
       SIGSYS	   12,-,12     Core    Bad argument to routine (SVID)
       SIGTRAP	      5        Core    Trace/breakpoint trap
       SIGURG	   16,23,21    Ign     Urgent condition on socket (4.2 BSD)
       SIGVTALRM   26,26,28    Term    Virtual alarm clock (4.2 BSD)
       SIGXCPU	   24,24,30    Core    CPU time limit exceeded (4.2 BSD)
       SIGXFSZ	   25,25,31    Core    File size limit exceeded (4.2 BSD)

       Up to and including Linux 2.2, the default behaviour for SIGSYS, SIGXCPU, SIGXFSZ, and (on
       architectures  other  than  SPARC and MIPS) SIGBUS was to terminate the process (without a
       core dump).  (On some other Unices the default action for SIGXCPU and SIGXFSZ is to termi-
       nate  the  process  without  a  core  dump.)   Linux 2.4 conforms to the POSIX 1003.1-2001
       requirements for these signals, terminating the process with a core dump.

       Next various other signals.

       Signal	    Value     Action   Comment
       --------------------------------------------------------------------
       SIGIOT	      6        Core    IOT trap. A synonym for SIGABRT
       SIGEMT	    7,-,7      Term
       SIGSTKFLT    -,16,-     Term    Stack fault on coprocessor (unused)
       SIGIO	   23,29,22    Term    I/O now possible (4.2 BSD)
       SIGCLD	    -,-,18     Ign     A synonym for SIGCHLD
       SIGPWR	   29,30,19    Term    Power failure (System V)
       SIGINFO	    29,-,-	       A synonym for SIGPWR
       SIGLOST	    -,-,-      Term    File lock lost
       SIGWINCH    28,28,20    Ign     Window resize signal (4.3 BSD, Sun)
       SIGUNUSED    -,31,-     Term    Unused signal (will be SIGSYS)

       (Signal 29 is SIGINFO / SIGPWR on an alpha but SIGLOST on a sparc.)

       SIGEMT is not specified in POSIX  1003.1-2001,  but  neverthless  appears  on  most  other
       Unices, where its default action is typically to terminate the process with a core dump.

       SIGPWR  (which  is  not specified in POSIX 1003.1-2001) is typically ignored by default on
       those other Unices where it appears.

       SIGIO (which is not specified in POSIX 1003.1-2001) is ignored by default on several other
       Unices.

   Real-time Signals
       Linux supports real-time signals as originally defined in the POSIX.4 real-time extensions
       (and now included in POSIX 1003.1-2001).  Linux supports 32  real-time  signals,  numbered
       from  32  (SIGRTMIN) to 63 (SIGRTMAX).  (Programs should always refer to real-time signals
       using notation SIGRTMIN+n, since the range  of  real-time  signal  numbers  varies  across
       Unices.)

       Unlike  standard signals, real-time signals have no predefined meanings: the entire set of
       real-time signals can be used for application-defined purposes.	(Note, however, that  the
       LinuxThreads implementation uses the first three real-time signals.)

       The  default  action  for  an  unhandled  real-time  signal  is to terminate the receiving
       process.

       Real-time signals are distinguished by the following:

       1.  Multiple instances of real-time signals can	be  queued.   By  contrast,  if  multiple
	   instances  of  a standard signal are delivered while that signal is currently blocked,
	   then only one instance is queued.

       2.  If the signal is sent using sigqueue(2), an accompanying value (either an integer or a
	   pointer)  can be sent with the signal.  If the receiving process establishes a handler
	   for this signal using the SA_SIGACTION flag to sigaction(2) then it	can  obtain  this
	   data  via  the si_value field of the siginfo_t structure passed as the second argument
	   to the handler.  Furthermore, the si_pid and si_uid fields of this  structure  can  be
	   used to obtain the PID and real user ID of the process sending the signal.

       3.  Real-time  signals are delivered in a guaranteed order.  Multiple real-time signals of
	   the same type are delivered in the order they were sent.  If different real-time  sig-
	   nals  are sent to a process, they are delivered starting with the lowest-numbered sig-
	   nal.  (I.e., low-numbered signals have highest priority.)

       If both standard and real-time signals are pending for a process, POSIX leaves it unspeci-
       fied  which is delivered first.	Linux, like many other implementations, gives priority to
       standard signals in this case.

       According to POSIX, an implementation should  permit  at  least	_POSIX_SIGQUEUE_MAX  (32)
       real-time  signals  to be queued to a process.  However, rather than placing a per-process
       limit, Linux imposes a system-wide limit on the number of queued real-time signals for all
       processes.   This  limit can be viewed (and with privilege) changed via the /proc/sys/ker-
       nel/rtsig-max file.  A related file, /proc/sys/kernel/rtsig-max, can be used to	find  out
       how many real-time signals are currently queued.

CONFORMING TO
       POSIX.1

BUGS
       SIGIO  and SIGLOST have the same value.	The latter is commented out in the kernel source,
       but the build process of some software still thinks that signal 29 is SIGLOST.

SEE ALSO
       kill(1), kill(2), setitimer(2), sigaction(2), signal(2), sigprocmask(2), sigqueue(2)

Linux 2.4.18				    2002-06-13					SIGNAL(7)


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