NAME

signal.h — signals

SYNOPSIS

#include <signal.h>

DESCRIPTION

The <signal.h> header defines the following symbolic constants, each of which expands to a distinct constant expression of the type:

void (*)(int)

whose value matches no declarable function.

SIG_DFL: Request for default signal handling.
SIG_ERR: Return value from signal(3) in case of error.
SIG_HOLD: Request that signal be held.
SIG_IGN: Request that signal be ignored.

The following data types are defined through typedef:

sig_atomic_t: Integral type of an object that can be accessed as an atomic entity, even in the presence of asynchronous interrupts
sigset_t: Integral or structure type of an object used to represent sets of signals.
pid_t: As described in <sys/types.h> .

The <signal.h> header defines 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 are defined:

SIGEV_NONE: No asynchronous notification will be delivered when the event of interest occurs.
SIGEV_SIGNAL: A queued signal, with an application-defined value, will be generated when the event of interest occurs.
SIGEV_THREAD: A notification function will be called to perform notification.

The sigval union is defined as: int sival_int integer signal value void* sival_ptr pointer signal value

This header also declares the macros SIGRTMIN and SIGRTMAX, which evaluate to integral expressions and, if the Realtime Signals Extension option is supported, specify a range of signal numbers that are reserved for application use and for which the realtime signal behaviour specified in this specification 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 includes at least RTSIG_MAX signal numbers.

It is implementation-dependent whether realtime signal behaviour 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 integral values. The value 0 is reserved for use as the null signal (see kill()). Additional implementation-dependent signals may occur in the system.

The following signals are supported on all implementations (default actions are explained below the table):

Signal	Default Action	Description
SIGABRT	ii	Process abort signal.
SIGALRM	i	Alarm clock.
SIGFPE	ii	Erroneous arithmetic operation.
SIGHUP	i	Hangup.
SIGILL	ii	Illegal instruction.
SIGINT	i	Terminal interrupt signal.
SIGKILL	i	Kill (cannot be caught or ignored).
SIGPIPE	i	Write on a pipe with no one to read it.
SIGQUIT	ii	Terminal quit signal.
SIGSEGV	ii	Invalid memory reference.
SIGTERM	i	Termination signal.
SIGUSR1	i	User-defined signal 1.
SIGUSR2	i	User-defined signal 2.
SIGCHLD	iii	Child process terminated or stopped.
SIGCONT	v	Continue executing, if stopped.
SIGSTOP	iv	Stop executing (cannot be caught or ignored).
SIGTSTP	iv	Terminal stop signal.
SIGTTIN	iv	Background process attempting read.
SIGTTOU	iv	Background process attempting write.
SIGBUS	ii	Access to an undefined portion of a memory object.
SIGPOLL	i	Pollable event.
SIGPROF	i	Profiling timer expired.
SIGSYS	ii	Bad system call.
SIGTRAP	ii	Trace/breakpoint trap.
SIGURG	iii	High bandwidth data is available at a socket.
SIGVTALRM	i	Virtual timer expired.
SIGXCPU	ii	CPU time limit exceeded.
SIGXFSZ	ii	File size limit exceeded.

The default actions are as follows:

i: Abnormal termination of the process. The process is terminated with all the consequences of _exit(3) except that the status made available to wait(3) and waitpid(3) indicates abnormal termination by the specified signal.
ii: Abnormal termination of the process. Additionally, implementation-dependent abnormal termination actions, such as creation of a core file, may occur.
iii: Ignore the signal.
iv: Stop the process.
v: Continue the process, if it is stopped; otherwise ignore the signal.

The header provides a declaration of struct sigaction, including at least the following members: void (*sa_handler)(int) what to do on receipt of signal sigset_t sa_mask set of signals to be blocked during execution of the signal handling function int sa_flags special flags void (*)(int, siginfo_t *, void *) sa_sigaction pointer to signal handler function or one of the macros SIG_IGN or SIG_DFL

The storage occupied by sa_handler and sa_sigaction may overlap, and a portable program must not use both simultaneously.

The following are declared as constants:

SA_NOCLDSTOP: Do not generate SIGCHLD when children stop.
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 .
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 on child death.
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 ucontext_t structure is defined through typedef as described in <ucontext.h>.

The <signal.h> header defines 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 defines 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 defines 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 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	non-existent 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
	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 will 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 will be available:

Signal	Member	Value
SIGILL SIGFPE	void * si_addr	address of faulting instruction
SIGSEGV SIGBUS	void * si_addr	address of faulting memory reference
SIGCHLD	pid_t si_pid int si_status uid_t si_uid	child process ID exit value or signal 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 are 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 *, struct sigaction *); int sigaddset(sigset_t *, int); int sigaltstack(const stack_t *, stack_t *); 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 *, sigset_t *); int sigqueue(pid_t, int, const union sigval); int sigrelse(int); void (*sigset(int, void (*)(int)))(int); int sigstack(struct sigstack *ss, struct sigstack *oss); (LEGACY) int sigsuspend(const sigset_t *); int sigtimedwait(const sigset_t *, siginfo_t *, const struct timespec *); int sigwait(const sigset_t *set, int *sig); int sigwaitinfo(const sigset_t *, siginfo_t *);

APPLICATION USAGE

None.

FUTURE DIRECTIONS