alarm(2)

NAME
alarm - set an alarm clock for delivery of a signal

LIBRARY
Standard C library (libc, -lc)

SYNOPSIS
#include <unistd.h>

unsigned int alarm(unsigned int seconds);

DESCRIPTION
alarm() arranges for a SIGALRM signal to be delivered to the calling process in seconds seconds.

If seconds is zero, any pending alarm is canceled.

In any event any previously set alarm() is canceled.

RETURN VALUE
alarm() returns the number of seconds remaining until any previously scheduled alarm was due to be delivered, or zero if there was no previously scheduled alarm.

STANDARDS
POSIX.1-2024.

HISTORY
4.3BSD, SVr4, POSIX.1-1988.

NOTES
alarm() and setitimer(2) share the same timer; calls to one will interfere with use of the other.

Alarms created by alarm() are preserved across execve(2) and are not inherited by children created via fork(2).

sleep(3) may be implemented using SIGALRM; mixing calls to alarm() and sleep(3) is a bad idea.

Scheduling delays can, as ever, cause the execution of the process to be delayed by an arbitrary amount of time.

SEE ALSO
gettimeofday(2), pause(2), select(2), setitimer(2), sigaction(2), signal(2), timer_create(2), timerfd_create(2), sleep(3), time(7)