Manual browser: alarm(3)

ALARM(3) Library Functions Manual ALARM(3)


alarmset signal timer alarm


Standard C Library (libc, -lc)


#include <unistd.h>

unsigned int
alarm(unsigned int seconds);


This interface is made obsolete by setitimer(2).

The alarm() function sets a timer to deliver the signal SIGALRM to the calling process seconds after the call to alarm(). If an alarm has already been set with alarm() but has not been delivered, another call to alarm() will supersede the prior call. The request alarm(0) voids the current alarm and the signal SIGALRM will not be delivered. The maximum number of seconds allowed is 2147483647.

The return value of alarm() is the amount of time left on the timer from a previous call to alarm(). If no alarm is currently set, the return value is 0. If there is an error setting the timer, alarm() returns ((unsigned int) -1).


The alarm() function conforms to IEEE Std 1003.1-1990 (“POSIX.1”).


An alarm() function appeared in Version 7 AT&T UNIX.
April 19, 1994 NetBSD 7.0