signal.h

PROLOG
NAME
SYNOPSIS
DESCRIPTION
APPLICATION USAGE
RATIONALE
FUTURE DIRECTIONS
SEE ALSO
COPYRIGHT

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PROLOG

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

signal.h — signals

SYNOPSIS

#include

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 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 header shall define the pthread_t, size_t, and uid_t types as described in .

The header shall define the timespec structure as described in .

The 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 .

The header shall define the pthread_attr_t type as described in .

The 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 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 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 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):

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 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 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 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 header shall define the mcontext_t type through typedef.

The 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 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 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 .
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 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.

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:

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 header may make visible all symbols from the 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

, , ,

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 .

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