NAME

alarm — schedule SIGALRM delivery

SYNOPSIS

#include <unistd.h>

unsigned int
alarm(unsigned int seconds);

DESCRIPTION

The alarm() function schedules the SIGALRM signal for delivery to the calling process after the given number of seconds have elapsed.

If an alarm is already pending, another call to alarm() will supersede the prior call.

If seconds is zero, any pending alarm is cancelled.

RETURN VALUES

alarm() returns the number of seconds remaining until the pending alarm would have expired. If the alarm has already expired, the alarm was cancelled, or no alarm was ever scheduled, alarm() returns zero.

SEE ALSO

setitimer(2), sigaction(2), sigsuspend(2), signal(3), sleep(3), ualarm(3)

STANDARDS

The alarm() function conforms to IEEE Std 1003.1-2008 (“POSIX.1”).

HISTORY

An alarm() system call appeared in the Programmer's Workbench (PWB/UNIX) and was ported to Version 7 AT&T UNIX. For 4.1cBSD, it was reimplemented as a wrapper around the setitimer(2) system call.

CAVEATS

The alarm() function is implemented with the per-process ITIMER_REAL timer described in setitimer(2). Use of both alarm() and setitimer(2) in the same program may yield confusing behavior.