signal.h - signals
#include <signal.h>
[CX] 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
- [CX] 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
- [CX] Integer or structure type of an object used to represent sets of signals.
- pid_t
- [CX] As described in <sys/types.h>.
[RTS] 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.
[CX] 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):
Signal
Default Action
Description
SIGABRT
A
Process abort signal.
SIGALRM
T
Alarm clock.
SIGBUS
A
Access to an undefined portion of a memory object.
SIGCHLD
I
Child process terminated, stopped,
[XSI]
or continued.
SIGCONT
C
Continue executing, if stopped.
SIGFPE
A
Erroneous arithmetic operation.
SIGHUP
T
Hangup.
SIGILL
A
Illegal instruction.
SIGINT
T
Terminal interrupt signal.
SIGKILL
T
Kill (cannot be caught or ignored).
SIGPIPE
T
Write on a pipe with no one to read it.
SIGQUIT
A
Terminal quit signal.
SIGSEGV
A
Invalid memory reference.
SIGSTOP
S
Stop executing (cannot be caught or ignored).
SIGTERM
T
Termination signal.
SIGTSTP
S
Terminal stop signal.
SIGTTIN
S
Background process attempting read.
SIGTTOU
S
Background process attempting write.
SIGUSR1
T
User-defined signal 1.
SIGUSR2
T
User-defined signal 2.
[XSI] SIGPOLL
T
Pollable event.
SIGPROF
T
Profiling timer expired.
SIGSYS
A
Bad system call.
SIGTRAP
A
Trace/breakpoint trap.
SIGURG
I
High bandwidth data is available at a socket.
[XSI] SIGVTALRM
T
Virtual timer expired.
SIGXCPU
A
CPU time limit exceeded.
SIGXFSZ
A
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.
[XSI] 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.
[CX] 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.[XSI] 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
- [CX] Do not generate SIGCHLD when children stop
[XSI] or stopped children continue.- SIG_BLOCK
- [CX] The resulting set is the union of the current set and the signal set pointed to by the argument set.
- SIG_UNBLOCK
- [CX] 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
- [CX] The resulting set is the signal set pointed to by the argument set.
- SA_ONSTACK
- [XSI] Causes signal delivery to occur on an alternate stack.
- SA_RESETHAND
- [XSI] Causes signal dispositions to be set to SIG_DFL on entry to signal handlers.
- SA_RESTART
- [XSI] Causes certain functions to become restartable.
- SA_SIGINFO
- [XSI] Causes extra information to be passed to signal handlers at the time of receipt of a signal.
- SA_NOCLDWAIT
- [XSI] Causes implementations not to create zombie processes on child death.
- SA_NODEFER
- [XSI] Causes signal not to be automatically blocked on entry to signal handler.
- SS_ONSTACK
- [XSI] Process is executing on an alternate signal stack.
- SS_DISABLE
- [XSI] Alternate signal stack is disabled.
- MINSIGSTKSZ
- [XSI] Minimum stack size for a signal handler.
- SIGSTKSZ
- [XSI] Default size in bytes for the alternate signal stack.
[XSI] 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.[CX] The <signal.h> header shall define the siginfo_t type as a structure that includes at least the following members:
[CX] int si_signo Signal number. int si_code Signal code. [XSI] int si_errno If non-zero, an errno value associated with this signal, as defined in <errno.h>. 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. [RTS] 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 [XSI] signal-specific or non-signal-specific reasons why the signal was generated.
Signal
Code
Reason
[XSI] 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
Nonexistent 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.
[CX] Any
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.
[XSI] 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:
Signal
Member
Value
SIGILL
void * si_addr
Address of faulting instruction.
SIGFPE
SIGSEGV
void * si_addr
Address of faulting memory reference.
SIGBUS
SIGCHLD
pid_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.
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 shall be declared as functions and may also be defined as macros:
[XSI] void (*bsd_signal(int, void (*)(int)))(int); [CX] int kill(pid_t, int); [XSI] int killpg(pid_t, int); [THR] int pthread_kill(pthread_t, int); int pthread_sigmask(int, const sigset_t *, sigset_t *); int raise(int); [CX] int sigaction(int, const struct sigaction *restrict, struct sigaction *restrict); int sigaddset(sigset_t *, int); [XSI] int sigaltstack(const stack_t *restrict, stack_t *restrict); [CX] int sigdelset(sigset_t *, int); int sigemptyset(sigset_t *); int sigfillset(sigset_t *); [XSI] int sighold(int); int sigignore(int); int siginterrupt(int, int); [CX] int sigismember(const sigset_t *, int); void (*signal(int, void (*)(int)))(int); [XSI] int sigpause(int); [CX] int sigpending(sigset_t *); int sigprocmask(int, const sigset_t *restrict, sigset_t *restrict); [RTS] int sigqueue(pid_t, int, const union sigval); [XSI] int sigrelse(int); void (*sigset(int, void (*)(int)))(int); [CX] int sigsuspend(const sigset_t *); [RTS] int sigtimedwait(const sigset_t *restrict, siginfo_t *restrict, const struct timespec *restrict); [CX] int sigwait(const sigset_t *restrict, int *restrict); [RTS] int sigwaitinfo(const sigset_t *restrict, siginfo_t *restrict);[CX] Inclusion of the <signal.h> header may make visible all symbols from the <time.h> header.
None.
None.
None.
<errno.h>, <stropts.h>, <sys/types.h>, <time.h>, <ucontext.h>, the System Interfaces volume of IEEE Std 1003.1-2001, alarm(), bsd_signal(), ioctl(), kill(), killpg(), raise(), sigaction(), sigaddset(), sigaltstack(), sigdelset(), sigemptyset(), sigfillset(), siginterrupt(), sigismember(), signal(), sigpending(), sigprocmask(), sigqueue(), sigsuspend(), sigwaitinfo(), wait(), waitid()
First released in Issue 1.
The DESCRIPTION is updated for alignment with the POSIX Realtime Extension and the POSIX Threads Extension.
The default action for SIGURG is changed from i to iii. The function prototype for sigmask() is removed.
The Open Group Corrigendum U035/2 is applied. In the DESCRIPTION, the wording for abnormal termination is clarified.
The Open Group Corrigendum U028/8 is applied, correcting the prototype for the sigset() function.
The Open Group Corrigendum U026/3 is applied, correcting the type of the sigev_notify_function function member of the sigevent structure.
The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:
The SIGCHLD, SIGCONT, SIGSTOP, SIGTSTP, SIGTTIN, and SIGTTOU signals are now mandated. This is also a FIPS requirement.
The pid_t definition is mandated.
The RT markings are changed to RTS to denote that the semantics are part of the Realtime Signals Extension option.
The restrict keyword is added to the prototypes for sigaction(), sigaltstack(), sigprocmask(), sigtimedwait(), sigwait(), and sigwaitinfo().
IEEE PASC Interpretation 1003.1 #85 is applied, adding the statement that symbols from <time.h> may be made visible when <signal.h> is included.
Extensions beyond the ISO C standard are marked.
IEEE Std 1003.1-2001/Cor 1-2002, item XBD/TC1/D6/14 is applied, changing the descriptive text for members of struct sigaction.
IEEE Std 1003.1-2001/Cor 1-2002, item XBD/TC1/D6/15 is applied, correcting the definition of the sa_sigaction member of struct sigaction.
IEEE Std 1003.1-2001/Cor 2-2004, item XBD/TC2/D6/24 is applied, reworking the ordering of the siginfo_t type structure in the DESCRIPTION. This is an editorial change and no normative change is intended.