<signal.h>

The Single UNIX ® Specification, Version 2
Copyright © 1997 The Open Group

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() 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() except that the status made available to wait() and waitpid() 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 *);

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.

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

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

APPLICATION USAGE

None.

FUTURE DIRECTIONS

None.

NAME

SYNOPSIS

DESCRIPTION

APPLICATION USAGE

FUTURE DIRECTIONS

SEE ALSO