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

       signal -	list of	available signals

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

   Standard Signals
       Linux supports the standard signals listed below. Several  signal  num-
       bers  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	archi-

       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,	 SIGX-
       CPU,  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 terminate 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	termi-
       nate 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 con-
	   trast, if multiple instances	of a  standard	signal	are  delivered
	   while  that	signal is currently blocked, then only one instance is

       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	signals	are sent to a process,
	   they	 are  delivered	 starting  with	 the  lowest-numbered  signal.
	   (I.e., low-numbered signals have highest priority.)

       If both standard	and real-time signals are pending for a	process, POSIX
       leaves it unspecified 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 sys-
       tem-wide	limit on the number of queued real-time	signals	for  all  pro-
       cesses.	 This limit can	be viewed (and with privilege) changed via the
       /proc/sys/kernel/rtsig-max  file.   A  related	file,	/proc/sys/ker-
       nel/rtsig-max,  can  be used to find out	how many real-time signals are
       currently queued.


       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.

       kill(1),	 kill(2),  setitimer(2),  sigaction(2),	 signal(2),   sigproc-
       mask(2),	sigqueue(2)

Linux 2.4.18			  2002-06-13			     SIGNAL(7)


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