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       signal.h - signals


       #include <signal.h>


       Some  of  the  functionality  described on this reference page extends the ISO C standard.
       Applications shall define the appropriate feature test macro (see  the  System  Interfaces
       volume  of  IEEE Std 1003.1-2001,  Section 2.2, The Compilation Environment) to enable the
       visibility of these symbols in this header.

       The <signal.h> header shall define the following symbolic constants, each of which expands
       to a distinct constant expression of the type:

              void (*)(int)

       whose value matches no declarable function.

              Request for default signal handling.

              Return value from signal() in case of error.

              Request that signal be held.

              Request that signal be ignored.

       The following data types shall be defined through typedef:

              Possibly  volatile-qualified  integer  type of an object that can be accessed as an
              atomic entity, even in the presence of asynchronous interrupts.

              Integer or structure type of an object used to represent sets of signals.

       pid_t  As described in <sys/types.h> .

       The <signal.h> header shall  define  the  sigevent  structure,  which  has  at  least  the
       following members:

              int                    sigev_notify            Notification type.
              int                    sigev_signo             Signal number.
              union sigval           sigev_value             Signal value.
              void(*)(union sigval)  sigev_notify_function   Notification function.
              (pthread_attr_t *)     sigev_notify_attributes Notification attributes.

       The following values of sigev_notify shall be defined:

              No asynchronous notification is delivered when the event of interest occurs.

              A  queued signal, with an application-defined value, is generated when the event of
              interest occurs.

              A notification function is called to perform notification.

       The sigval union shall be defined as:

              int    sival_int    Integer signal value.
              void  *sival_ptr    Pointer signal value.

       This header shall also declare the macros SIGRTMIN and SIGRTMAX, which evaluate to integer
       expressions,  and  specify a range of signal numbers that are reserved for application use
       and  for  which   the   realtime   signal   behavior   specified   in   this   volume   of
       IEEE Std 1003.1-2001  is supported. The signal numbers in this range do not overlap any of
       the signals specified in the following table.

       The range SIGRTMIN through SIGRTMAX inclusive shall include at  least  {RTSIG_MAX}  signal

       It  is  implementation-defined  whether  realtime  signal  behavior is supported for other

       This header also declares the constants that are used to refer to the signals  that  occur
       in  the  system. Signals defined here begin with the letters SIG. Each of the signals have
       distinct positive integer values. The value 0 is reserved for use as the null signal  (see
       kill()). Additional implementation-defined signals may occur in the system.

       The  ISO C  standard  only  requires  the  signal  names  SIGABRT, SIGFPE, SIGILL, SIGINT,
       SIGSEGV, and SIGTERM to be defined.

       The following signals shall be supported  on  all  implementations  (default  actions  are
       explained below the table):

                   Signal    Default Action Description
                   SIGABRT   A              Process abort signal.
                   SIGALRM   T              Alarm clock.
                   SIGBUS    A              Access to an undefined portion of a
                                            memory object.
                   SIGCHLD   I              Child process terminated, stopped,
                                            or continued.
                   SIGCONT   C              Continue executing, if stopped.
                   SIGFPE    A              Erroneous arithmetic operation.
                   SIGHUP    T              Hangup.
                   SIGILL    A              Illegal instruction.
                   SIGINT    T              Terminal interrupt signal.
                   SIGKILL   T              Kill (cannot be caught or ignored).
                   SIGPIPE   T              Write on a pipe with no one to read it.
                   SIGQUIT   A              Terminal quit signal.
                   SIGSEGV   A              Invalid memory reference.
                   SIGSTOP   S              Stop executing (cannot be caught or
                   SIGTERM   T              Termination signal.
                   SIGTSTP   S              Terminal stop signal.
                   SIGTTIN   S              Background process attempting read.
                   SIGTTOU   S              Background process attempting write.
                   SIGUSR1   T              User-defined signal 1.
                   SIGUSR2   T              User-defined signal 2.
                   SIGPOLL   T              Pollable event.
                   SIGPROF   T              Profiling timer expired.
                   SIGSYS    A              Bad system call.
                   SIGTRAP   A              Trace/breakpoint trap.
                   SIGURG    I              High bandwidth data is available at a
                   SIGVTALRM T              Virtual timer expired.
                   SIGXCPU   A              CPU time limit exceeded.

                   SIGXFSZ   A              File size limit exceeded.

       The default actions are as follows:

       T      Abnormal termination of the  process.  The  process  is  terminated  with  all  the
              consequences  of  _exit()  except  that  the  status  made  available to wait() and
              waitpid() indicates abnormal termination by the specified signal.

       A      Abnormal termination of the process.
              Additionally, implementation-defined abnormal termination actions, such as creation
              of a core file, may occur.

       I      Ignore the signal.

       S      Stop the process.

       C      Continue the process, if it is stopped; otherwise, ignore the signal.

       The  header  shall  provide  a  declaration  of  struct  sigaction, including at least the
       following members:

              void (*sa_handler)(int)  Pointer to a signal-catching function or one of the macros
                                       SIG_IGN or SIG_DFL.
              sigset_t sa_mask         Set of signals to be blocked during execution of the signal
                                       handling function.
              int      sa_flags        Special flags.
              void (*sa_sigaction)(int, siginfo_t *, void *)
                                       Pointer to a signal-catching function.

       The storage occupied  by  sa_handler  and  sa_sigaction  may  overlap,  and  a  conforming
       application shall not use both simultaneously.

       The following shall be declared as constants:

              Do not generate SIGCHLD when children stop
              or stopped children continue.

              The  resulting set is the union of the current set and the signal set pointed to by
              the argument set.

              The resulting set is the intersection of the current set and the complement of  the
              signal set pointed to by the argument set.

              The resulting set is the signal set pointed to by the argument set.

              Causes signal delivery to occur on an alternate stack.

              Causes signal dispositions to be set to SIG_DFL on entry to signal handlers.

              Causes certain functions to become restartable.

              Causes  extra information to be passed to signal handlers at the time of receipt of
              a signal.

              Causes implementations not to create zombie processes on child death.

              Causes signal not to be automatically blocked on entry to signal handler.

              Process is executing on an alternate signal stack.

              Alternate signal stack is disabled.

              Minimum stack size for a signal handler.

              Default size in bytes for the alternate signal stack.

       The ucontext_t structure shall be defined through typedef as described in <ucontext.h>.

       The mcontext_t type shall be defined through typedef as described in <ucontext.h>.

       The <signal.h> header shall define the stack_t type as a structure that includes at  least
       the following members:

              void     *ss_sp       Stack base or pointer.
              size_t    ss_size     Stack size.
              int       ss_flags    Flags.

       The  <signal.h>  header  shall  define  the  sigstack structure that includes at least the
       following members:

              int       ss_onstack  Non-zero when signal stack is in use.
              void     *ss_sp       Signal stack pointer.

       The <signal.h> header shall define the siginfo_t type as  a  structure  that  includes  at
       least the following members:

              int           si_signo  Signal number.

              int           si_errno  If non-zero, an errno value associated with
                                      this signal, as defined in <errno.h>.

              int           si_code   Signal code.

              pid_t         si_pid    Sending process ID.
              uid_t         si_uid    Real user ID of sending process.
              void         *si_addr   Address of faulting instruction.
              int           si_status Exit value or signal.
              long          si_band   Band event for SIGPOLL.

              union sigval  si_value  Signal value.

       The  macros  specified  in  the  Code column of the following table are defined for use as
       values of si_code that are  signal-specific or  non-signal-specific reasons why the signal
       was generated.

                   Signal    Code            Reason
                   SIGILL    ILL_ILLOPC      Illegal opcode.
                             ILL_ILLOPN      Illegal operand.
                             ILL_ILLADR      Illegal addressing mode.

                             ILL_ILLTRP      Illegal trap.
                             ILL_PRVOPC      Privileged opcode.
                             ILL_PRVREG      Privileged register.
                             ILL_COPROC      Coprocessor error.
                             ILL_BADSTK      Internal stack error.
                   SIGFPE    FPE_INTDIV      Integer divide by zero.
                             FPE_INTOVF      Integer overflow.
                             FPE_FLTDIV      Floating-point divide by zero.
                             FPE_FLTOVF      Floating-point overflow.
                             FPE_FLTUND      Floating-point underflow.
                             FPE_FLTRES      Floating-point inexact result.
                             FPE_FLTINV      Invalid floating-point operation.
                             FPE_FLTSUB      Subscript out of range.
                   SIGSEGV   SEGV_MAPERR     Address not mapped to object.
                             SEGV_ACCERR     Invalid permissions for mapped object.
                   SIGBUS    BUS_ADRALN      Invalid address alignment.
                             BUS_ADRERR      Nonexistent physical address.
                             BUS_OBJERR      Object-specific hardware error.
                   SIGTRAP   TRAP_BRKPT      Process breakpoint.
                             TRAP_TRACE      Process trace trap.
                   SIGCHLD   CLD_EXITED      Child has exited.
                             CLD_KILLED      Child has terminated abnormally and did
                                             not create a core file.
                             CLD_DUMPED      Child has terminated abnormally and
                                             created a core file.
                             CLD_TRAPPED     Traced child has trapped.
                             CLD_STOPPED     Child has stopped.
                             CLD_CONTINUED   Stopped child has continued.
                   SIGPOLL   POLL_IN         Data input available.
                             POLL_OUT        Output buffers available.
                             POLL_MSG        Input message available.
                             POLL_ERR        I/O error.
                             POLL_PRI        High priority input available.
                             POLL_HUP        Device disconnected.
                   Any       SI_USER         Signal sent by kill().
                             SI_QUEUE        Signal sent by the sigqueue().
                             SI_TIMER        Signal generated by expiration of a
                                             timer set by timer_settime().
                             SI_ASYNCIO      Signal generated by completion of an
                                             asynchronous I/O request.
                             SI_MESGQ        Signal generated by arrival of a message
                                             on an empty message queue.

       Implementations may support additional si_code values  not  included  in  this  list,  may
       generate  values  included  in this list under circumstances other than those described in
       this list, and may contain extensions or limitations that prevent some values  from  being
       generated.  Implementations  do  not generate a different value from the ones described in
       this list for circumstances described in this list.

       In addition, the following signal-specific information shall be available:

                Signal  Member         Value
                SIGILL  void * si_addr Address of faulting instruction.
                SIGSEGV void * si_addr Address of faulting memory reference.
                SIGCHLD pid_t si_pid   Child process ID.
                        int si_status  Exit value or signal.
                        uid_t si_uid   Real user ID of the process that sent the signal.
                SIGPOLL long si_band   Band event for POLL_IN, POLL_OUT, or POLL_MSG.

       For some implementations, the value of si_addr may be inaccurate.

       The following shall be declared as functions and may also be defined as macros:

              void (*bsd_signal(int, void (*)(int)))(int);

              int    kill(pid_t, int);

              int    killpg(pid_t, int);

              int    pthread_kill(pthread_t, int);
              int    pthread_sigmask(int, const sigset_t *, sigset_t *);

              int    raise(int);

              int    sigaction(int, const struct sigaction *restrict,
                         struct sigaction *restrict);
              int    sigaddset(sigset_t *, int);

              int    sigaltstack(const stack_t *restrict, stack_t *restrict);

              int    sigdelset(sigset_t *, int);
              int    sigemptyset(sigset_t *);
              int    sigfillset(sigset_t *);

              int    sighold(int);
              int    sigignore(int);
              int    siginterrupt(int, int);

              int    sigismember(const sigset_t *, int);

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

              int    sigpause(int);

              int    sigpending(sigset_t *);
              int    sigprocmask(int, const sigset_t *restrict, sigset_t *restrict);

              int    sigqueue(pid_t, int, const union sigval);

              int    sigrelse(int);
              void (*sigset(int, void (*)(int)))(int);

              int    sigsuspend(const sigset_t *);

              int    sigtimedwait(const sigset_t *restrict, siginfo_t *restrict,
                         const struct timespec *restrict);

              int    sigwait(const sigset_t *restrict, int *restrict);

              int    sigwaitinfo(const sigset_t *restrict, siginfo_t *restrict);

       Inclusion of the <signal.h> header may make visible all symbols from the <time.h> header.

       The following sections are informative.








       <errno.h> , <stropts.h> , <sys/types.h> , <time.h> , <ucontext.h> , the System  Interfaces
       volume of IEEE Std 1003.1-2001, alarm(), bsd_signal(), ioctl(), kill(), killpg(), raise(),
       sigaction(),  sigaddset(),  sigaltstack(),   sigdelset(),   sigemptyset(),   sigfillset(),
       siginterrupt(),   sigismember(),   signal(),   sigpending(),   sigprocmask(),  sigqueue(),
       sigsuspend(), sigwaitinfo(), wait(), waitid()


       Portions of this text are reprinted and  reproduced  in  electronic  form  from  IEEE  Std
       1003.1,  2003  Edition,  Standard  for Information Technology -- Portable Operating System
       Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003  by
       the  Institute  of  Electrical  and  Electronics Engineers, Inc and The Open Group. In the
       event of any discrepancy between this version and the original IEEE  and  The  Open  Group
       Standard,  the  original  IEEE  and  The  Open Group Standard is the referee document. The
       original Standard can be obtained online at .