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


signal.h - signals


#include <signal.h>


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.

Request for default signal handling.
Return value from signal() in case of error.
Request that signal be held.
Request that signal be ignored.

The following data types are defined through typedef:

Integral type of an object that can be accessed as an atomic entity, even in the presence of asynchronous interrupts
Integral or structure type of an object used to represent sets of signals.
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:

No asynchronous notification will be delivered when the event of interest occurs.
A queued signal, with an application-defined value, will be generated when the event of interest occurs.
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:

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.
Abnormal termination of the process. Additionally, implementation-dependent abnormal termination actions, such as creation of a core file, may occur.
Ignore the signal.
Stop the process.
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:

Do not generate SIGCHLD when children stop.
The resulting set is the union of the current set and the signal set pointed to by the argument set.
The resulting set is the intersection of the current set and the complement of the signal set pointed to by the argument set.
The resulting set is the signal set pointed to by the argument set.
Causes signal delivery to occur on an alternate stack.
Causes signal dispositions to be set to SIG_DFL on entry to signal handlers.
Causes certain functions to become restartable.
Causes extra information to be passed to signal handlers at the time of receipt of a signal.
Causes implementations not to create zombie processes on child death.
Causes signal not to be automatically blocked on entry to signal handler.
Process is executing on an alternate signal stack.
Alternate signal stack is disabled.
Minimum stack size for a signal handler.
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
void * si_addr address of faulting instruction
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 *);






alarm(), bsd_signal(), ioctl(), kill(), killpg(), raise(), sigaction(), sigaddset(), sigaltstack(), sigdelset(), sigemptyset(), sigfillset(), siginterrupt(), sigismember(), signal(), sigpending(), sigprocmask(), sigqueue(), sigsuspend(), sigwaitinfo(), wait(), waitid(), <errno.h>, <stropts.h>, <sys/types.h>, <ucontext.h>.

UNIX ® is a registered Trademark of The Open Group.
Copyright © 1997 The Open Group
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