signal.h(1) signals

SYNOPSIS

#include <signal.h>

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 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.

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 shall be defined through typedef:

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 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:

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. 

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):

SignalDefault Action     Description   
SIGABRTA     Process abort signal.   
SIGALRMT     Alarm clock.   
SIGBUSA     Access to an undefined portion of a memory object.   
SIGCHLDI     Child process terminated, stopped,   
       or continued.   
SIGCONTC     Continue executing, if stopped.   
SIGFPEA     Erroneous arithmetic operation.   
SIGHUPT     Hangup.   
SIGILLA     Illegal instruction.   
SIGINTT     Terminal interrupt signal.   
SIGKILLT     Kill (cannot be caught or ignored).   
SIGPIPET     Write on a pipe with no one to read it.   
SIGQUITA     Terminal quit signal.   
SIGSEGVA     Invalid memory reference.   
SIGSTOPS     Stop executing (cannot be caught or ignored).   
SIGTERMT     Termination signal.   
SIGTSTPS     Terminal stop signal.   
SIGTTINS     Background process attempting read.   
SIGTTOUS     Background process attempting write.   
SIGUSR1T     User-defined signal 1.   
SIGUSR2T     User-defined signal 2.   
SIGPOLLT     Pollable event.   
SIGPROFT     Profiling timer expired.   
SIGSYSA     Bad system call.   
SIGTRAPA     Trace/breakpoint trap.   
SIGURGI     High bandwidth data is available at a socket.   
SIGVTALRMT     Virtual timer expired.   
SIGXCPUA     CPU time limit exceeded.   
SIGXFSZA     File size limit exceeded.   

The default actions are as follows:

T
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.
A
Abnormal termination of the process.
Additionally, implementation-defined abnormal termination actions, such as creation of a core file, may occur.
I
Ignore the signal.
S
Stop the process.
C
Continue the process, if it is stopped; otherwise, ignore the signal.

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:

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

SignalCode     Reason
SIGILLILL_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.
SIGFPEFPE_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.
SIGSEGVSEGV_MAPERR     Address not mapped to object.
 SEGV_ACCERR     Invalid permissions for mapped object.
SIGBUSBUS_ADRALN     Invalid address alignment.
 BUS_ADRERR     Nonexistent physical address.
 BUS_OBJERR     Object-specific hardware error.
SIGTRAPTRAP_BRKPT     Process breakpoint.
 TRAP_TRACE     Process trace trap.
SIGCHLDCLD_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.
SIGPOLLPOLL_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.
AnySI_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 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:

SignalMember    Value  
SIGILLvoid * si_addr    Address of faulting instruction.  
SIGFPE        
SIGSEGVvoid * si_addr    Address of faulting memory reference.  
SIGBUS        
SIGCHLDpid_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.  
SIGPOLLlong 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.

APPLICATION USAGE

None.

RATIONALE

None.

FUTURE DIRECTIONS

None.

COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 .