NAME

alarm — set signal timer alarm

SYNOPSIS

#include <unistd.h>

unsigned int
alarm(unsigned int seconds);

DESCRIPTION

The alarm() function waits a count of seconds before asserting the terminating signal SIGALRM. When the signal has successfully been caught, alarm() returns the amount of time left on the clock. The maximum number of seconds allowed is 100000000.

If an alarm has been set with alarm(), another call to alarm() will supersede the prior call. The request alarm(0) voids the current alarm.

RETURN VALUES

If the call succeeds, any time left remaining from a previous call is returned. If an error occurs, the value -1 is returned, and a more precise error code is placed in the global variable errno.

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.