.\" This manpage is Copyright (C) 1992 Drew Eckhardt;

.\"             and Copyright (C) 1993 Michael Haardt, Ian Jackson.

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.\" Modified Wed Jul 21 19:42:57 1993 by Rik Faith <faith@cs.unc.edu>

.\" Modified Sun Jul 21 21:25:26 1996 by Andries Brouwer <aeb@cwi.nl>

.\" Modified Wed Nov  6 03:46:05 1996 by Eric S. Raymond <esr@thyrsus.com>

.\"

.TH ALARM 2 2017-05-03 "Linux" "Linux Programmer's Manual"

.SH NAME

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

.SH SYNOPSIS

.nf

.B #include <unistd.h>

.PP

.BI "unsigned int alarm(unsigned int " seconds );

.fi

.SH DESCRIPTION

.BR alarm ()

arranges for a

.B SIGALRM

signal to be delivered to the calling process in

.I seconds

seconds.

.PP

If

.I seconds

is zero, any pending alarm is canceled.

.PP

In any event any previously set

.BR alarm ()

is canceled.

.SH RETURN VALUE

.BR 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.

.SH CONFORMING TO

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

.SH NOTES

.BR alarm ()

and

.BR setitimer (2)

share the same timer; calls to one will interfere with use of the

other.

.PP

Alarms created by

.BR alarm ()

are preserved across

.BR execve (2)

and are not inherited by children created via

.BR fork (2).

.PP

.BR sleep (3)

may be implemented using

.BR SIGALRM ;

mixing calls to

.BR alarm ()

and

.BR sleep (3)

is a bad idea.

.PP

Scheduling delays can, as ever, cause the execution of the process to

be delayed by an arbitrary amount of time.

.SH SEE ALSO

.BR gettimeofday (2),

.BR pause (2),

.BR select (2),

.BR setitimer (2),

.BR sigaction (2),

.BR signal (2),

.BR timer_create (2),

.BR timerfd_create (2),

.BR sleep (3),

.BR time (7)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I man-pages

project.

A description of the project,

information about reporting bugs,

and the latest version of this page,

can be found at

\%https://www.kernel.org/doc/man\-pages/.