alarm man page

alarm — set an alarm clock for delivery of a signal


#include <unistd.h>

unsigned int alarm(unsigned int seconds);


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.

Conforming to

POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.


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), sleep(3), time(7)

Referenced By

fork(2), getitimer(2), ObjCmdWrite(3), seccomp(2), signal(2), signal(7), sleep(3), snmp_alarm(3), syscalls(2), time(7), tload(1), ualarm(3), usleep(3).

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