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signal(3) [netbsd man page]

SIGNAL(3)						   BSD Library Functions Manual 						 SIGNAL(3)

signal -- simplified software signal facilities LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <signal.h> void (* signal(int sig, void (*func)(int)))(int); DESCRIPTION
This signal() facility is a simplified interface to the more general sigaction(2) facility. Signals allow the manipulation of a process from outside its domain as well as allowing the process to manipulate itself or copies of itself (children). There are two general types of signals: those that cause termination of a process and those that do not. Signals which cause termination of a program might result from an irrecoverable error or might be the result of a user at a terminal typing the `interrupt' char- acter. Signals are used when a process is stopped because it wishes to access its control terminal while in the background (see tty(4)). Signals are optionally generated when a process resumes after being stopped, when the status of child processes changes, or when input is ready at the control terminal. Most signals result in the termination of the process receiving them if no action is taken; some signals instead cause the process receiving them to be stopped, or are simply discarded if the process has not requested otherwise. Except for the SIGKILL and SIGSTOP signals, the signal() function allows for a signal to be caught, to be ignored, or to generate an interrupt. See signal(7) for comprehensive list of supported signals. The func procedure allows a user to choose the action upon receipt of a signal. To set the default action of the signal to occur as listed above, func should be SIG_DFL. A SIG_DFL resets the default action. To ignore the signal func should be SIG_IGN. This will cause subse- quent instances of the signal to be ignored and pending instances to be discarded. If SIG_IGN is not used, further occurrences of the signal are automatically blocked and func is called. The handled signal is unblocked when the function returns and the process continues from where it left off when the signal occurred. Unlike previous signal facilities, the handler func() remains installed after a signal has been delivered. For some system calls, if a signal is caught while the call is executing and the call is prematurely terminated, the call is automatically restarted. (The handler is installed using the SA_RESTART flag with sigaction(2)). The affected system calls include read(2), write(2), sendto(2), recvfrom(2), sendmsg(2) and recvmsg(2) on a communications channel or a low speed device and during a ioctl(2) or wait(2). How- ever, calls that have already committed are not restarted, but instead return a partial success (for example, a short read count). When a process which has installed signal handlers forks, the child process inherits the signals. All caught signals may be reset to their default action by a call to the execve(2) function; ignored signals remain ignored. Only functions that are async-signal-safe can safely be used in signal handlers, see signal(7) for a complete list. RETURN VALUES
The previous action is returned on a successful call. Otherwise, SIG_ERR is returned and the global variable errno is set to indicate the error. ERRORS
signal() will fail and no action will take place if one of the following occur: [EINVAL] Specified sig is not a valid signal number. [EINVAL] An attempt is made to ignore or supply a handler for SIGKILL or SIGSTOP. SEE ALSO
kill(1), kill(2), ptrace(2), sigaction(2), sigaltstack(2), sigprocmask(2), sigsuspend(2), psignal(3), setjmp(3), strsignal(3), tty(4), signal(7) HISTORY
This signal() facility appeared in 4.0BSD. BSD
June 11, 2004 BSD

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sigset(3C)																sigset(3C)

sigset(), sighold(), sigrelse(), sigignore() - signal management SYNOPSIS
The system defines a set of signals that can be delivered to a process. The set of signals is defined in signal(5), along with the meaning and side effects of each signal. An alternate mechanism for handling these signals is defined here. The facilities described here should not be used in conjunction with the other facilities described under signal(2) and sigspace(2). allows the calling process to choose one of four ways to handle the receipt of a specific signal. sig specifies the signal and func speci- fies the action handler. sig can be any one of the signals described under signal(5) except or func is assigned one of four values: or a function address. The actions prescribed by and are described under signal(5). The action pre- scribed by and function address are described below: Hold signal. The signal sig is held upon receipt. Any pending signal of this signal type remains held. Only one signal of each type is held. Note: the signals and cannot be held. function address Catch signal. func must be a pointer to a function, the signal-catching handler, that is called when signal sig occurs. specifies that the process calls this function upon receipt of signal sig. Any pending signal of this type is released. This handler address is retained across calls to the other signal management functions listed here. Upon receipt of signal sig, the receiving process executes the signal-catching function pointed to by func as described under signal(5) with the follow- ing differences: Before calling the signal-catching handler, the defined action of sig is set to During a normal return from the signal- catching handler, the defined action is restored to func and any held signal of this type is released. If a non-local goto (longjmp(3C)) is taken, must be called to restore the defined action to func and release any held signal of this type. holds the signal sig. restores the defined action of sig to that specified previously by and are used to establish critical regions of code. is analogous to raising the priority level and deferring or holding a signal until the priority is lowered by sets the action for signal sig to (see signal(5)). RETURN VALUE
Upon successful completion, returns the previous value of the defined action for the specified signal sig. Otherwise, a value of is returned and is set to indicate the error. is defined in For the other functions, a 0 value indicates that the call succeeded. A -1 return value indicates an error occurred and is set to indicate the reason. ERRORS
fails and the defined action for sig is not changed if any of the following occur: The func argument points to memory that is not a valid part of the process address space. Reliable detection of this error is implementation dependent. and and fail and the defined action for sig is not changed if any of the following occur: sig is not a valid signal number. An attempt is made to ignore, hold, or supply a handler for a signal that cannot be ignored, held, or caught; see signal(5). WARNINGS
These signal facilities should not be used in conjunction with signal(2) and sigspace(2). SEE ALSO
kill(1), kill(2), pause(2), signal(2), sigspace(2), wait(2), abort(3C), setjmp(3C), sigpause(3C), signal(5). STANDARDS CONFORMANCE
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