signal.h(0p) — Linux manual page


signal.h(0P)            POSIX Programmer's Manual           signal.h(0P)

PROLOG         top

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

NAME         top

       signal.h — signals

SYNOPSIS         top

       #include <signal.h>

DESCRIPTION         top

       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

       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, 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

       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

       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

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

       SA_ONSTACK    Causes signal delivery to occur on an alternate

       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(3p).

       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

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

       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

       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
│ 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.


       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         top



       The SIGPOLL and SIGPROF signals may be removed in a future

SEE ALSO         top

       errno.h(0p), stropts.h(0p), sys_types.h(0p), time.h(0p)

       The System Interfaces volume of POSIX.1‐2017, Section 2.2, The
       Compilation Environment, alarm(3p), ioctl(3p), kill(3p),
       killpg(3p), psiginfo(3p), pthread_kill(3p), pthread_sigmask(3p),
       raise(3p), sigaction(3p), sigaddset(3p), sigaltstack(3p),
       sigdelset(3p), sigemptyset(3p), sigfillset(3p), sighold(3p),
       siginterrupt(3p), sigismember(3p), signal(3p), sigpending(3p),
       sigqueue(3p), sigsuspend(3p), sigtimedwait(3p), sigwait(3p),
       timer_create(3p), wait(3p), waitid(3p)

       The Shell and Utilities volume of POSIX.1‐2017, kill(1p)

COPYRIGHT         top

       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 .

       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 .

IEEE/The Open Group               2017                      signal.h(0P)

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