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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

       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 numbers.

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

       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

       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

              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

              Causes signal not to be automatically blocked on entry to signal

              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

       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

       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

              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 .