signal.h(3)                POSIX Programmer's Manual               signal.h(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NAME
       signal.h -- signals

SYNOPSIS
       #include <signal.h>

DESCRIPTION
       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 POSIX.1-2017, Section 2.2,
       The Compilation Environment) to enable the visibility of these symbols
       in this header.

       The <signal.h> header shall define the following macros, which shall
       expand to constant expressions with distinct values that have a type
       compatible with the second argument to, and the return value of, the
       signal() function, and whose values shall compare unequal to the
       address of any declarable function.

       SIG_DFL       Request for default signal handling.

       SIG_ERR       Return value from signal() in case of error.

       SIG_HOLD      Request that signal be held.

       SIG_IGN       Request that signal be ignored.

       The <signal.h> header shall define the pthread_t, size_t, and uid_t
       types as described in <sys/types.h>.

       The <signal.h> header shall define the timespec structure as described
       in <time.h>.

       The <signal.h> header shall define the following data types:

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

       sigset_t      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 pthread_attr_t type as described
       in <sys/types.h>.

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


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

       The <signal.h> header shall define the following symbolic constants for
       the values of sigev__notify:

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

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

       SIGEV_THREAD  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.

       The <signal.h> header shall declare the SIGRTMIN and SIGRTMAX macros,
       which shall expand to positive integer expressions with type int, but
       which need not be constant expressions. These macros specify a range of
       signal numbers that are reserved for application use and for which the
       realtime signal behavior specified in this volume of POSIX.1-2017 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.

       The <signal.h> header shall define the following macros that are used
       to refer to the signals that occur in the system. Signals defined here
       begin with the letters SIG followed by an uppercase letter. The macros
       shall expand to positive integer constant expressions with type int and
       distinct 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. An implementation
       need not generate any of these six signals, except as a result of
       explicit use of interfaces that generate signals, such as raise(),
       kill(), the General Terminal Interface (see Section 11.1.9, Special
       Characters), and the kill utility, unless otherwise stated (see, for
       example, the System Interfaces volume of POSIX.1-2017, Section 2.8.3.3,
       Memory Protection).

       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 ignored).      |
  |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 socket.      |
  |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.

       A     Abnormal termination of the process with additional actions.

       I     Ignore the signal.

       S     Stop the process.

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

       The effects on the process in each case are described in the System
       Interfaces volume of POSIX.1-2017, Section 2.4.3, Signal Actions.

       The <signal.h> header shall declare the sigaction structure, which
       shall include at least the following members:


           void   (*sa_handler)(int)  Pointer to a signal-catching function
                                      or one of the 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 <signal.h> header shall define the following macros which shall
       expand to integer constant expressions that need not be usable in #if
       preprocessing directives:

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

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

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

       The <signal.h> header shall also define the following symbolic
       constants:

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

       SA_ONSTACK    Causes signal delivery to occur on an alternate stack.

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

       SA_RESTART    Causes certain functions to become restartable.

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

       SA_NOCLDWAIT  Causes implementations not to create zombie processes or
                     status information on child termination. See sigaction().

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

       SS_ONSTACK    Process is executing on an alternate signal stack.

       SS_DISABLE    Alternate signal stack is disabled.

       MINSIGSTKSZ   Minimum stack size for a signal handler.

       SIGSTKSZ      Default size in bytes for the alternate signal stack.

       The <signal.h> header shall define the mcontext_t type through typedef.

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


           ucontext_t *uc_link     Pointer to the context that is resumed
                                   when this context returns.
           sigset_t    uc_sigmask  The set of signals that are blocked when this
                                   context is active.
           stack_t     uc_stack    The stack used by this context.
           mcontext_t  uc_mcontext A machine-specific representation of the saved
                                   context.

       The <signal.h> header shall define the stack_t type as a structure,
       which shall include 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 siginfo_t type as a structure,
       which shall include at least the following members:


           int           si_signo  Signal number.
           int           si_code   Signal code.
           int           si_errno  If non-zero, an errno value associated with
                                   this signal, as described in <errno.h>.
           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 <signal.h> header shall define the symbolic constants in the Code
       column of the following table 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 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.                  |
    |SIGFPE  |                |                                                   |
    +--------+----------------+---------------------------------------------------+
    |SIGSEGV | void ** si__addr | Address of faulting memory reference.             |
    |SIGBUS  |                |                                                   |
    +--------+----------------+---------------------------------------------------+
    |SIGCHLD | pid_t si__pid   | Child process ID.                                 |
    |        | int si__status  | If si__code is equal to CLD_EXITED, then si__status |
    |        |                | holds the exit value of the process; otherwise,   |
    |        |                | it is equal to the signal that caused the process |
    |        |                | to change state. The exit value in si__status      |
    |        |                | shall be equal to the full exit value (that is,   |
    |        |                | the value passed to __exit(), __Exit(), or exit(),  |
    |        |                | or returned from main()); it shall not be limited |
    |        |                | to the least significant eight bits of the value. |
    |        | 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. Function prototypes shall be provided.


           int    kill(pid_t, int);
           int    killpg(pid_t, int);
           void   psiginfo(const siginfo_t *, const char *);
           void   psignal(int, const char *);
           int    pthread_kill(pthread_t, int);
           int    pthread_sigmask(int, const sigset_t *restrict,
                      sigset_t *restrict);
           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, 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.

APPLICATION USAGE
       On systems not supporting the XSI option, the si__pid and si__uid members
       of siginfo_t are only required to be valid when si__code is SI_USER or
       SI_QUEUE. On XSI-conforming systems, they are also valid for all
       si__code values less than or equal to 0; however, it is unspecified
       whether SI_USER and SI_QUEUE have values less than or equal to zero,
       and therefore XSI applications should check whether si__code has the
       value SI_USER or SI_QUEUE or is less than or equal to 0 to tell whether
       si__pid and si__uid are valid.

RATIONALE
       None.

FUTURE DIRECTIONS
       The SIGPOLL and SIGPROF signals may be removed in a future version.

SEE ALSO
       <errno.h>, <stropts.h>, <sys_types.h>, <time.h>

       The System Interfaces volume of POSIX.1-2017, Section 2.2, The
       Compilation Environment, alarm(), ioctl(), kill(), killpg(),
       psiginfo(), pthread__kill(), pthread__sigmask(), raise(), sigaction(),
       sigaddset(), sigaltstack(), sigdelset(), sigemptyset(), sigfillset(),
       sighold(), siginterrupt(), sigismember(), signal(), sigpending(),
       sigqueue(), sigsuspend(), sigtimedwait(), sigwait(), timer__create(),
       wait(), waitid()

       The Shell and Utilities volume of POSIX.1-2017, kill

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                          signal.h(3)
