signal man page on DigitalUNIX

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signal(2)							     signal(2)

       signal - Modifies signal functions

       #include <signal.h>

       void (*signal(
	       int sig,
	       void (*function)(int)) (int) );

       Interfaces  documented on this reference page conform to industry stan‐
       dards as follows:

       signal():  XPG4, XPG4-UNIX

       Refer to the standards(5) reference page	 for  more  information	 about
       industry standards and associated tags.

       Defines	the  signal.   All  signals  are  valid	 with the exception of
       SIGKILL and SIGSTOP.  Specifies the address of a signal handler.

       The signal function provides compatibility for older  versions  of  the
       operating  system whose function is a subset of the sigaction function.
       The signal function sets the action associated with a signal. The func‐
       tion  parameter uses the values SIG_DFL, SIG_IGN, or it can point to an
       address of a signal handler.

       A SIG_DFL value specifies the default action that is to be  taken  when
       the  signal is delivered.  A value of SIG_IGN specifies that the signal
       has no effect on	 the  receiving	 process.  A  pointer  to  a  function
       requests	 that  the  signal be caught; that is, the signal should cause
       the function to be called. These actions are more  fully	 described  in
       the <signal.h> file.

       The  sigaction()	 function  provides  a more comprehensive and reliable
       mechanism for controlling signals and is recommended  instead  of  sig‐
       nal() for new applications.

       [Tru64  UNIX]  The  effect of calling the signal function behavior dif‐
       fers depending on whether the calling program is linked with either  of
       the  special libraries, libbsd or libsys5, which supply BSD or System V
       signaling characteristics respectively. If neither library is used, the
       behavior	 is  the  same	as that of the sigaction function with all the
       flags set to 0 (zero).  If the libsys5 library is used (through	compi‐
       lation  with  the  -lsys5  switch),  then  the  specified signal is not
       blocked from delivery when the handler is entered, and the  disposition
       of  the signal reverts to SIG_DFL when the signal is delivered.	If the
       libbsd library or the bsd_signal() function is used,  the  behavior  is
       the  same  as that of the sigaction() function with the SA_RESTART flag

       [Tru64 UNIX]  When compiled in the X/Open UNIX  environment,  calls  to
       the  signal()  function	are internally renamed by prepending _E to the
       function name.  When you are debugging a module that includes the  libc
       version	of  the signal() function and for which _XOPEN_SOURCE_EXTENDED
       has been defined, use _Esignal to refer	to  the	 signal()  call.   See
       standards(5)  for  information on when the _XOPEN_SOURCE_EXTENDED macro
       is defined.

       Upon successful completion of the signal function,  the	value  of  the
       previous	 signal action is returned. Otherwise, SIG_ERR is returned and
       errno is set to indicate the error.

       The signal() function sets errno to the specified values for  the  fol‐
       lowing conditions: The sig parameter is not a valid signal number or an
       attempt was made to catch a signal that cannot be caught or to ignore a
       signal that cannot be ignored.

       Commands:  kill(1)

       Functions:  acct(2),   bsd_signal(2),   exit(2),	  kill(2),   pause(3),
       ptrace(2), setjmp(3), sigaction(2), sigblock(2), sigpause(3),  sigproc‐
       mask(2), sigstack(2), sigsuspend(2), sigvec(2), umask(2), wait(2)

       Files:  signal(4)

       Standards:  standards(5)


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