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.Dd $Mdocdate: June 18 2021 $
.Dt ALARM 3
.Os
.Sh NAME
.Nm alarm
.Nd schedule SIGALRM delivery
.Sh SYNOPSIS
.In unistd.h
.Ft unsigned int
.Fn alarm "unsigned int seconds"
.Sh DESCRIPTION
.Bf -symbolic
This is a simplified interface to
.Xr setitimer 2 .
.Ef
.Pp
The
.Fn alarm
function schedules the
.Dv SIGALRM
signal for delivery to the calling process after the given number of
.Fa seconds
have elapsed.
.Pp
If an alarm is already pending,
another call to
.Fn alarm
will supersede the prior call.
.Pp
If
.Fa seconds
is zero,
any pending alarm is cancelled.
.Sh RETURN VALUES
.Fn alarm
returns the number of seconds remaining until the pending alarm would have
expired.
If the alarm has already expired,
the alarm was cancelled,
or no alarm was ever scheduled,
.Fn alarm
returns zero.
.Sh SEE ALSO
.Xr setitimer 2 ,
.Xr sigaction 2 ,
.Xr sigsuspend 2 ,
.Xr signal 3 ,
.Xr sleep 3 ,
.Xr ualarm 3
.Sh STANDARDS
The
.Fn alarm
function conforms to
.St -p1003.1-2008 .
.Sh HISTORY
An
.Fn alarm
system call appeared in the Programmer's Workbench (PWB/UNIX)
and was ported to
.At v7 .
For
.Bx 4.1c ,
it was reimplemented as a wrapper around the
.Xr setitimer 2
system call.
.Sh CAVEATS
The
.Fn alarm
function is implemented with the per-process
.Dv ITIMER_REAL
timer described in
.Xr setitimer 2 .
Use of both
.Fn alarm
and
.Xr setitimer 2
in the same program may yield confusing behavior.