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.Dd $Mdocdate: June 18 2021 $ .Dt ALARM 3 .Os .Sh NAME .Nm alarm .Nd schedule SIGALRM delivery .Sh SYNOPSIS n unistd.h .Ft unsigned int .Fn alarm "unsigned int seconds" .Sh DESCRIPTION f -symbolic This is a simplified interface to .Xr setitimer 2 . .Ef
p The .Fn alarm function schedules the .Dv SIGALRM signal for delivery to the calling process after the given number of .Fa seconds have elapsed.
p If an alarm is already pending, another call to .Fn alarm will supersede the prior call.
p 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 first appeared outside of Bell Labs in the .Dq 50 changes tape for .At v6 . It was first officially released with PWB/UNIX 1.0. For x 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.