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 architecture.)

       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  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 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 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.  How-
       ever, rather than placing a per-process limit, Linux imposes a system-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.

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)