'\" et
.TH signal.h "0P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
signal.h
\(em signals
.SH SYNOPSIS
.LP
.nf
#include <signal.h>
.fi
.SH 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 POSIX.1\(hy2017,
.IR "Section 2.2" ", " "The Compilation Environment")
to enable the visibility of these symbols in this header.
.P
The
.IR <signal.h> 
header shall define the following macros, which shall expand to constant
expressions with distinct values that have a type compatible with the
second argument to, and the return value of, the
\fIsignal\fR()
function, and whose values shall compare unequal to the address of any
declarable function.
.IP SIG_DFL 14
Request for default signal handling.
.IP SIG_ERR 14
Return value from
\fIsignal\fR()
in case of error.
.IP SIG_HOLD 14
Request that signal be held.
.IP SIG_IGN 14
Request that signal be ignored.
.P
The
.IR <signal.h> 
header shall define the
.BR pthread_t ,
.BR size_t ,
and
.BR uid_t
types as described in
.IR <sys/types.h> .
.P
The
.IR <signal.h> 
header shall define the
.BR timespec
structure as described in
.IR <time.h> .
.P
The
.IR <signal.h> 
header shall define the following data types:
.IP "\fBsig_atomic_t\fP" 14
Possibly volatile-qualified integer type of an object that can be
accessed as an atomic entity, even in the presence of asynchronous
interrupts.
.IP "\fBsigset_t\fP" 14
Integer or structure type of an object used to represent sets of
signals.
.IP "\fBpid_t\fP" 14
As described in
.IR <sys/types.h> .
.P
The
.IR <signal.h> 
header shall define the
.BR pthread_attr_t
type as described in
.IR <sys/types.h> .
.P
The
.IR <signal.h> 
header shall define the
.BR sigevent
structure, which shall include at least the following members:
.sp
.RS 4
.nf

int              sigev_notify            \fRNotification type.\fP
int              sigev_signo             \fRSignal number.\fP
union sigval     sigev_value             \fRSignal value.\fP
void           (*sigev_notify_function)(union sigval)
                                         \fRNotification function.\fP
pthread_attr_t *sigev_notify_attributes  \fRNotification attributes.\fP
.fi
.P
.RE
.P
The
.IR <signal.h> 
header shall define the following symbolic constants for the values of
.IR sigev_notify :
.IP SIGEV_NONE 14
No asynchronous notification is delivered when the event of interest
occurs.
.IP SIGEV_SIGNAL 14
A queued signal, with an application-defined value, is generated when
the event of interest occurs.
.IP SIGEV_THREAD 14
A notification function is called to perform notification.
.br
.P
The
.BR sigval
union shall be defined as:
.sp
.RS 4
.nf

int    sival_int    \fRInteger signal value.\fP
void  *sival_ptr    \fRPointer signal value.\fP
.fi
.P
.RE
.P
The
.IR <signal.h> 
header shall declare the SIGRTMIN and SIGRTMAX macros,
which shall expand to positive integer expressions with type
.BR int ,
but which need not be constant expressions. These macros specify a
range of signal numbers that are reserved for application use and for
which the realtime signal behavior specified in this volume of POSIX.1\(hy2017 is supported. The
signal numbers in this range do not overlap any of the signals specified
in the following table.
.P
The range SIGRTMIN through SIGRTMAX inclusive shall include at least
{RTSIG_MAX}
signal numbers.
.P
It is implementation-defined whether realtime signal behavior is
supported for other signals.
.P
The
.IR <signal.h> 
header shall define the following macros that are used to refer to the
signals that occur in the system. Signals defined here begin with the
letters SIG followed by an uppercase letter. The macros shall expand to
positive integer constant expressions with type
.BR int
and distinct values. The value 0 is reserved for use as the null signal
(see
\fIkill\fR()).
Additional implementation-defined signals may occur in the system.
.P
The ISO\ C standard only requires the signal names SIGABRT, SIGFPE, SIGILL,
SIGINT, SIGSEGV, and SIGTERM to be defined. An implementation need
not generate any of these six signals, except as a result of
explicit use of interfaces that generate signals, such as
\fIraise\fR(),
\fIkill\fR(),
the General Terminal Interface (see
.IR "Section 11.1.9" ", " "Special Characters"),
and the
.IR kill
utility, unless otherwise stated (see, for example, the System Interfaces volume of POSIX.1\(hy2017,
.IR "Section 2.8.3.3" ", " "Memory Protection").
.P
The following signals shall be supported on all implementations
(default actions are explained below the table):
.TS
box center tab(!);
cB | cB | cB
l | n | lw(3.6i).
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,
!!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.
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.
SIGVTALRM!T!Virtual timer expired.
SIGXCPU!A!CPU time limit exceeded.
SIGXFSZ!A!File size limit exceeded.
.sp
.TE
.br
.P
The default actions are as follows:
.IP T 6
Abnormal termination of the process.
.IP A 6
Abnormal termination of the process
with additional actions.
.IP I 6
Ignore the signal.
.IP S 6
Stop the process.
.IP C 6
Continue the process, if it is stopped; otherwise, ignore the signal.
.P
The effects on the process in each case are described in the System Interfaces volume of POSIX.1\(hy2017,
.IR "Section 2.4.3" ", " "Signal Actions".
.P
The
.IR <signal.h> 
header shall declare the
.BR sigaction
structure, which shall include at least the following members:
.sp
.RS 4
.nf

void   (*sa_handler)(int)  \fRPointer to a signal-catching function\fR
                           \fRor one of the SIG_IGN or SIG_DFL.\fR
sigset_t sa_mask           \fRSet of signals to be blocked during execution\fR
                           \fRof the signal handling function.\fR
int      sa_flags          \fRSpecial flags.\fR
void   (*sa_sigaction)(int, siginfo_t *, void *)
                           \fRPointer to a signal-catching function.\fR
.fi
.P
.RE
.P
The storage occupied by
.IR sa_handler
and
.IR sa_sigaction
may overlap, and a conforming application shall not use both
simultaneously.
.P
The
.IR <signal.h> 
header shall define the following macros which shall expand to
integer constant expressions that need not be usable in
.BR #if
preprocessing directives:
.IP SIG_BLOCK 14
The resulting set is the union of the current set and the signal set
pointed to by the argument
.IR set .
.IP SIG_UNBLOCK 14
The resulting set is the intersection of the current set and the
complement of the signal set pointed to by the argument
.IR set .
.IP SIG_SETMASK 14
The resulting set is the signal set pointed to by the argument
.IR set .
.P
The
.IR <signal.h> 
header shall also define the following symbolic constants:
.IP SA_NOCLDSTOP 14
Do not generate SIGCHLD when children stop
.br
or stopped children continue.
.IP SA_ONSTACK 14
Causes signal delivery to occur on an alternate stack.
.IP SA_RESETHAND 14
Causes signal dispositions to be set to SIG_DFL on entry to signal
handlers.
.IP SA_RESTART 14
Causes certain functions to become restartable.
.IP SA_SIGINFO 14
Causes extra information to be passed to signal handlers at the time of
receipt of a signal.
.IP SA_NOCLDWAIT 14
Causes implementations not to create zombie processes or status
information on child termination. See
.IR "\fIsigaction\fR\^(\|)".
.IP SA_NODEFER 14
Causes signal not to be automatically blocked on entry to signal handler.
.IP SS_ONSTACK 14
Process is executing on an alternate signal stack.
.IP SS_DISABLE 14
Alternate signal stack is disabled.
.IP MINSIGSTKSZ 14
Minimum stack size for a signal handler.
.IP SIGSTKSZ 14
Default size in bytes for the alternate signal stack.
.P
The
.IR <signal.h> 
header shall define the
.BR mcontext_t
type through
.BR typedef .
.P
The
.IR <signal.h> 
header shall define the
.BR ucontext_t
type as a structure that shall include at least the following members:
.sp
.RS 4
.nf

ucontext_t *uc_link     \fRPointer to the context that is resumed\fR
                        \fRwhen this context returns.\fR
sigset_t    uc_sigmask  \fRThe set of signals that are blocked when this\fR
                        \fRcontext is active.\fR
stack_t     uc_stack    \fRThe stack used by this context.\fR
mcontext_t  uc_mcontext \fRA machine-specific representation of the saved\fR
                        \fRcontext.\fR
.fi
.P
.RE
.P
The
.IR <signal.h> 
header shall define the
.BR stack_t
type as a structure, which shall include at least the following members:
.sp
.RS 4
.nf

void     *ss_sp       \fRStack base or pointer.\fR
size_t    ss_size     \fRStack size.\fR
int       ss_flags    \fRFlags.\fR
.fi
.P
.RE
.P
The
.IR <signal.h> 
header shall define the
.BR siginfo_t
type as a structure, which shall include at least the following members:
.sp
.RS 4
.nf

int           si_signo  \fRSignal number.\fR
int           si_code   \fRSignal code.\fR
int           si_errno  \fRIf non-zero, an \fIerrno\fR value associated with\fR
                        \fRthis signal, as described in \fB<errno.h>\fR.\fR
pid_t         si_pid    \fRSending process ID.\fR
uid_t         si_uid    \fRReal user ID of sending process.\fR
void         *si_addr   \fRAddress of faulting instruction.\fR
int           si_status \fRExit value or signal.\fR
long          si_band   \fRBand event for SIGPOLL.\fR
union sigval  si_value  \fRSignal value.\fR
.fi
.P
.RE
.P
The
.IR <signal.h> 
header shall define the symbolic constants in the
.BR Code
column of the following table for use as values of
.IR si_code
that are signal-specific or non-signal-specific reasons why the
signal was generated.
.TS
box center tab(!);
cB | cB | cB
l1 | l1 | l.
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!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 \fBcore\fP file.
!CLD_DUMPED!Child has terminated abnormally and created a \fBcore\fP 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.
_
Any!SI_USER!Signal sent by \fIkill\fP\^(\|).
!SI_QUEUE!Signal sent by \fIsigqueue\fP\^(\|).
!SI_TIMER!Signal generated by expiration of a timer set by \fItimer_settime\fP\^(\|).
!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.
.TE
.P
Implementations may support additional
.IR 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.
.br
.P
In addition, the following signal-specific information shall be
available:
.TS
box center tab(!);
cB | cB | cB
l | lB | lw(3.9i).
Signal!Member!Value
_
SIGILL!void * \fIsi_addr\fP!Address of faulting instruction.
SIGFPE
_
SIGSEGV!void * \fIsi_addr\fP!Address of faulting memory reference.
SIGBUS
_
SIGCHLD!pid_t \fIsi_pid\fP!Child process ID.
!int \fIsi_status\fP!T{
If
.IR si_code
is equal to CLD_EXITED, then
.IR si_status
holds the exit value of the process; otherwise, it is equal to the
signal that caused the process to change state. The exit value in
.IR si_status
shall be equal to the full exit value (that is, the value passed to
\fI_exit\fR(),
\fI_Exit\fR(),
or
\fIexit\fR(),
or returned from
\fImain\fR());
it shall not be limited to the least significant eight bits of the value.
T}
!uid_t \fIsi_uid\fP!Real user ID of the process that sent the signal.
_
SIGPOLL!long \fIsi_band\fP!Band event for POLL_IN, POLL_OUT, or POLL_MSG.
.TE
.P
For some implementations, the value of \fIsi_addr\fR may be inaccurate.
.P
The following shall be declared as functions and may also be defined as
macros. Function prototypes shall be provided.
.sp
.RS 4
.nf

int    kill(pid_t, int);
int    killpg(pid_t, int);
void   psiginfo(const siginfo_t *, const char *);
void   psignal(int, const char *);
int    pthread_kill(pthread_t, int);
int    pthread_sigmask(int, const sigset_t *restrict,
           sigset_t *restrict);
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, 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);
.fi
.P
.RE
.P
Inclusion of the
.IR <signal.h> 
header may make visible all symbols from the
.IR <time.h> 
header.
.LP
.IR "The following sections are informative."
.SH "APPLICATION USAGE"
On systems not supporting the XSI option, the
.IR si_pid
and
.IR si_uid
members of
.BR siginfo_t
are only required to be valid when
.IR si_code
is SI_USER or SI_QUEUE. On XSI-conforming systems, they are also
valid for all
.IR si_code
values less than or equal to 0; however, it is unspecified whether
SI_USER and SI_QUEUE have values less than or equal to zero, and
therefore XSI applications should check whether
.IR si_code
has the value SI_USER or SI_QUEUE or is less than or equal to 0
to tell whether
.IR si_pid
and
.IR si_uid
are valid.
.SH RATIONALE
None.
.SH "FUTURE DIRECTIONS"
The SIGPOLL and SIGPROF signals may be removed in a future version.
.SH "SEE ALSO"
.IR "\fB<errno.h>\fP",
.IR "\fB<stropts.h>\fP",
.IR "\fB<sys_types.h>\fP",
.IR "\fB<time.h>\fP"
.P
.ad l
The System Interfaces volume of POSIX.1\(hy2017,
.IR "Section 2.2" ", " "The Compilation Environment",
.IR "\fIalarm\fR\^(\|)",
.IR "\fIioctl\fR\^(\|)",
.IR "\fIkill\fR\^(\|)",
.IR "\fIkillpg\fR\^(\|)",
.IR "\fIpsiginfo\fR\^(\|)",
.IR "\fIpthread_kill\fR\^(\|)",
.IR "\fIpthread_sigmask\fR\^(\|)",
.IR "\fIraise\fR\^(\|)",
.IR "\fIsigaction\fR\^(\|)",
.IR "\fIsigaddset\fR\^(\|)",
.IR "\fIsigaltstack\fR\^(\|)",
.IR "\fIsigdelset\fR\^(\|)",
.IR "\fIsigemptyset\fR\^(\|)",
.IR "\fIsigfillset\fR\^(\|)",
.IR "\fIsighold\fR\^(\|)",
.IR "\fIsiginterrupt\fR\^(\|)",
.IR "\fIsigismember\fR\^(\|)",
.IR "\fIsignal\fR\^(\|)",
.IR "\fIsigpending\fR\^(\|)",
.IR "\fIsigqueue\fR\^(\|)",
.IR "\fIsigsuspend\fR\^(\|)",
.IR "\fIsigtimedwait\fR\^(\|)",
.IR "\fIsigwait\fR\^(\|)",
.IR "\fItimer_create\fR\^(\|)",
.IR "\fIwait\fR\^(\|)",
.IR "\fIwaitid\fR\^(\|)"
.ad b
.P
The Shell and Utilities volume of POSIX.1\(hy2017,
.IR "\fIkill\fR\^"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 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 .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .