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NAMEsignal - ANSI C signal handlingSYNOPSIS#include <signal.h>typedef void (*sighandler_t)(int); sighandler_t signal(int signum, sighandler_t handler); DESCRIPTIONThe signal() system call installs a new signal handler for the signal with number signum. The signal handler is set to sighandler which may be a user specified function, or either SIG_IGN or SIG_DFL.Upon arrival of a signal with number signum the following happens. If the corresponding handler is set to SIG_IGN, then the signal is ignored. If the handler is set to SIG_DFL, then the default action associated to the signal (see signal(7)) occurs. Finally, if the handler is set to a function sighandler then first either the handler is reset to SIG_DFL or an implementation-dependent blocking of the signal is performed and next sighandler is called with argument signum. Using a signal handler function for a signal is called "catching the signal". The signals SIGKILL and SIGSTOP cannot be caught or ignored. RETURN VALUEThe signal() function returns the previous value of the signal handler, or SIG_ERR on error.PORTABILITYThe original Unix signal() would reset the handler to SIG_DFL, and System V (and the Linux kernel and libc4,5) does the same. On the other hand, BSD does not reset the handler, but blocks new instances of this signal from occurring during a call of the handler. The glibc2 library follows the BSD behaviour.If one on a libc5 system includes <bsd/signal.h> instead of <signal.h> then signal is redefined as __bsd_signal and signal has the BSD semantics. This is not recommended. If one on a glibc2 system defines a feature test macro such as _XOPEN_SOURCE or uses a separate sysv_signal function, one obtains classical behaviour. This is not recommended. Trying to change the semantics of this call using defines and includes is not a good idea. It is better to avoid signal altogether, and use sigaction(2) instead. SEE ALSOkill(1), kill(2), killpg(2), pause(2), raise(3), sigaction(2), signal(7), sigsetops(3), sigvec(2), alarm(2)
Important: Use the man command (% man) to see how a command is used on your particular computer. |
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