signal.h(0P) | POSIX Programmer's Manual | signal.h(0P) |
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.
signal.h — signals
#include <signal.h>
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.1‐2017, Section 2.2, The Compilation Environment) to enable the visibility of these symbols in this header.
The <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 signal() function, and whose values shall compare unequal to the address of any declarable function.
The <signal.h> header shall define the pthread_t, size_t, and uid_t types as described in <sys/types.h>.
The <signal.h> header shall define the timespec structure as described in <time.h>.
The <signal.h> header shall define the following data types:
The <signal.h> header shall define the pthread_attr_t type as described in <sys/types.h>.
The <signal.h> header shall define the sigevent structure, which shall include at least the following members:
int sigev_notify Notification type. int sigev_signo Signal number. union sigval sigev_value Signal value. void (*sigev_notify_function)(union sigval)
Notification function. pthread_attr_t *sigev_notify_attributes Notification attributes.
The <signal.h> header shall define the following symbolic constants for the values of sigev_notify:
The sigval union shall be defined as:
int sival_int Integer signal value. void *sival_ptr Pointer signal value.
The <signal.h> header shall declare the SIGRTMIN and SIGRTMAX macros, which shall expand to positive integer expressions with type 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.1‐2017 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.
The <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 int and distinct 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. An implementation need not generate any of these six signals, except as a result of explicit use of interfaces that generate signals, such as raise(), kill(), the General Terminal Interface (see Section 11.1.9, Special Characters), and the kill utility, unless otherwise stated (see, for example, the System Interfaces volume of POSIX.1‐2017, Section 2.8.3.3, Memory Protection).
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, |
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. |
The default actions are as follows:
The effects on the process in each case are described in the System Interfaces volume of POSIX.1‐2017, Section 2.4.3, Signal Actions.
The <signal.h> header shall declare the sigaction structure, which shall include at least the following members:
void (*sa_handler)(int) Pointer to a signal-catching function
or one of the 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 <signal.h> header shall define the following macros which shall expand to integer constant expressions that need not be usable in #if preprocessing directives:
The <signal.h> header shall also define the following symbolic constants:
The <signal.h> header shall define the mcontext_t type through typedef.
The <signal.h> header shall define the ucontext_t type as a structure that shall include at least the following members:
ucontext_t *uc_link Pointer to the context that is resumed
when this context returns. sigset_t uc_sigmask The set of signals that are blocked when this
context is active. stack_t uc_stack The stack used by this context. mcontext_t uc_mcontext A machine-specific representation of the saved
context.
The <signal.h> header shall define the stack_t type as a structure, which shall include 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 siginfo_t type as a structure, which shall include at least the following members:
int si_signo Signal number. int si_code Signal code. int si_errno If non-zero, an errno value associated with
this signal, as described 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. union sigval si_value Signal value.
The <signal.h> header shall define the symbolic constants in the Code column of the following table for use as values of si_code that are signal-specific or non-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 | 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. | |
Any | SI_USER | Signal sent by kill(). |
SI_QUEUE | Signal sent by 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:
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 | If si_code is equal to CLD_EXITED, then 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 si_status shall be equal to the full exit value (that is, the value passed to _exit(), _Exit(), or exit(), or returned from main()); it shall not be limited to the least significant eight bits of the value. | |
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. Function prototypes shall be provided.
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);
Inclusion of the <signal.h> header may make visible all symbols from the <time.h> header.
The following sections are informative.
On systems not supporting the XSI option, the si_pid and si_uid members of siginfo_t are only required to be valid when si_code is SI_USER or SI_QUEUE. On XSI-conforming systems, they are also valid for all 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 si_code has the value SI_USER or SI_QUEUE or is less than or equal to 0 to tell whether si_pid and si_uid are valid.
None.
The SIGPOLL and SIGPROF signals may be removed in a future version.
<errno.h>, <stropts.h>, <sys_types.h>, <time.h>
The System Interfaces volume of POSIX.1‐2017, Section 2.2, The Compilation Environment, alarm(), ioctl(), kill(), killpg(), psiginfo(), pthread_kill(), pthread_sigmask(), raise(), sigaction(), sigaddset(), sigaltstack(), sigdelset(), sigemptyset(), sigfillset(), sighold(), siginterrupt(), sigismember(), signal(), sigpending(), sigqueue(), sigsuspend(), sigtimedwait(), sigwait(), timer_create(), wait(), waitid()
The Shell and Utilities volume of POSIX.1‐2017, kill
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 .
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 .
2017 | IEEE/The Open Group |