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Manual Pages  — ALARM


alarm – set 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 after the specified number of seconds. 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() voids the current alarm and the signal SIGALRM will not be delivered.

Due to setitimer(2) restriction the maximum number of seconds allowed is 100000000.


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.


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


An alarm() function appeared in AT&T v7 .

ALARM (3) April 19, 1994

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Ken Thompson was once asked by a reporter what he would have changed about Unix if he had it all to do over again. His answer: “I would spell creat with an ‘e.'”