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CentOS 7.0 - man page for alarm (centos section 2)

ALARM(2)						     Linux Programmer's Manual							  ALARM(2)

NAME
alarm - set an alarm clock for delivery of a signal
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 pre- viously scheduled alarm.
CONFORMING TO
SVr4, POSIX.1-2001, 4.3BSD.
NOTES
alarm() and setitimer(2) share the same timer; calls to one will interfere with use of the other. 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)
COLOPHON
This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. Linux 2013-04-18 ALARM(2)