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.
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SIG_DFL
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Request for default signal handling.
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SIG_ERR
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Return value from signal() in case of error.
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SIG_HOLD
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Request that signal be held.
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SIG_IGN
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Request that signal be ignored.
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The following data types shall be defined through typedef:
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sig_atomic_t
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Possibly volatile-qualified integer type of an object that can be
accessed as an atomic entity, even in the presence of
asynchronous interrupts.
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sigset_t
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Integer or structure type of an object used to represent sets of signals.
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pid_t
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As
described in <sys/types.h> .
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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:
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SIGEV_NONE
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No asynchronous notification is delivered when the event of interest
occurs.
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SIGEV_SIGNAL
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A queued signal, with an application-defined value, is generated when
the event of interest occurs.
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SIGEV_THREAD
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A notification function is called to perform notification.
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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
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| SIGABRT | A | Process abort signal.
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| SIGALRM | T | Alarm clock.
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| SIGBUS | A | Access to an undefined portion of a memory object.
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| SIGCHLD | I | Child process terminated, stopped,
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| | | or continued.
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| SIGCONT | C | Continue executing, if stopped.
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| SIGFPE | A | Erroneous arithmetic operation.
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| SIGHUP | T | Hangup.
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| SIGILL | A | Illegal instruction.
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| SIGINT | T | Terminal interrupt signal.
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| SIGKILL | T | Kill (cannot be caught or ignored).
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| SIGPIPE | T | Write on a pipe with no one to read it.
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| SIGQUIT | A | Terminal quit signal.
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| SIGSEGV | A | Invalid memory reference.
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| SIGSTOP | S | Stop executing (cannot be caught or ignored).
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| SIGTERM | T | Termination signal.
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| SIGTSTP | S | Terminal stop signal.
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| SIGTTIN | S | Background process attempting read.
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| SIGTTOU | S | Background process attempting write.
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| SIGUSR1 | T | User-defined signal 1.
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| SIGUSR2 | T | User-defined signal 2.
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| SIGPOLL | T | Pollable event.
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| SIGPROF | T | Profiling timer expired.
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| SIGSYS | A | Bad system call.
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| SIGTRAP | A | Trace/breakpoint trap.
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| SIGURG | I | High bandwidth data is available at a socket.
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| SIGVTALRM | T | Virtual timer expired.
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| SIGXCPU | A | CPU time limit exceeded.
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| SIGXFSZ | A | File size limit exceeded.
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The default actions are as follows:
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T
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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.
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A
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Abnormal termination of the process.
Additionally, implementation-defined abnormal termination actions,
such as creation of a core file, may occur.
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I
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Ignore the signal.
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S
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Stop the process.
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C
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Continue the process, if it is stopped; otherwise, ignore the signal.
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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:
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SA_NOCLDSTOP
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Do
not generate SIGCHLD when children stop
or
stopped children continue.
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SIG_BLOCK
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The resulting set is the union of the current set and the signal set
pointed to by the argument set.
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SIG_UNBLOCK
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The resulting set is the intersection of the current set and the complement
of the signal set pointed to by the argument
set.
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SIG_SETMASK
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The resulting set is the signal set pointed to by the argument set.
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SA_ONSTACK
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Causes signal delivery to occur on an alternate stack.
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SA_RESETHAND
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Causes signal dispositions to be set to SIG_DFL on entry to signal
handlers.
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SA_RESTART
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Causes certain functions to become restartable.
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SA_SIGINFO
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Causes extra information to be passed to signal handlers at the time
of receipt of a signal.
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SA_NOCLDWAIT
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Causes implementations not to create zombie processes on child death.
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SA_NODEFER
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Causes signal not to be automatically blocked on entry to signal handler.
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SS_ONSTACK
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Process is executing on an alternate signal stack.
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SS_DISABLE
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Alternate signal stack is disabled.
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MINSIGSTKSZ
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Minimum stack size for a signal handler.
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SIGSTKSZ
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Default size in bytes for the alternate signal stack.
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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
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| SIGILL | ILL_ILLOPC | Illegal opcode.
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| | ILL_ILLOPN | Illegal operand.
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| | ILL_ILLADR | Illegal addressing mode.
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| | ILL_ILLTRP | Illegal trap.
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| | ILL_PRVOPC | Privileged opcode.
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| | ILL_PRVREG | Privileged register.
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| | ILL_COPROC | Coprocessor error.
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| | ILL_BADSTK | Internal stack error.
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| SIGFPE | FPE_INTDIV | Integer divide by zero.
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| | FPE_INTOVF | Integer overflow.
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| | FPE_FLTDIV | Floating-point divide by zero.
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| | FPE_FLTOVF | Floating-point overflow.
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| | FPE_FLTUND | Floating-point underflow.
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| | FPE_FLTRES | Floating-point inexact result.
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| | FPE_FLTINV | Invalid floating-point operation.
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| | FPE_FLTSUB | Subscript out of range.
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| SIGSEGV | SEGV_MAPERR | Address not mapped to object.
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| | SEGV_ACCERR | Invalid permissions for mapped object.
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| SIGBUS | BUS_ADRALN | Invalid address alignment.
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| | BUS_ADRERR | Nonexistent physical address.
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| | BUS_OBJERR | Object-specific hardware error.
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| SIGTRAP | TRAP_BRKPT | Process breakpoint.
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| | TRAP_TRACE | Process trace trap.
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| SIGCHLD | CLD_EXITED | Child has exited.
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| | CLD_KILLED | Child has terminated abnormally and did not create a core file.
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| | CLD_DUMPED | Child has terminated abnormally and created a core file.
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| | CLD_TRAPPED | Traced child has trapped.
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| | CLD_STOPPED | Child has stopped.
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| | CLD_CONTINUED | Stopped child has continued.
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| SIGPOLL | POLL_IN | Data input available.
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| | POLL_OUT | Output buffers available.
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| | POLL_MSG | Input message available.
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| | POLL_ERR | I/O error.
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| | POLL_PRI | High priority input available.
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| | POLL_HUP | Device disconnected.
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| Any | SI_USER | Signal sent by kill().
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| | SI_QUEUE | Signal sent by the sigqueue().
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| | SI_TIMER | Signal generated by expiration of a timer set by timer_settime().
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| | SI_ASYNCIO | Signal generated by completion of an asynchronous I/O request.
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| | SI_MESGQ | Signal generated by arrival of a message on an empty message queue.
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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 | 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()
