FreePascal doesn't see the module 'graph'

[Abdourazak Osmanov <05rnan0ff@xxxxxxxxx>]

When I compile this code:

program radar;
>
> uses
>     crt, graph;
>
> var
>     DriverVar, ModeVar : integer;
>
> begin
>         DriverVar := Detect;
>         ModeVar := 2;
>         InitGraph(DriverVar, ModeVar,'');
>         SetColor(4);
>         LineTo(100,100);
> end.
>

I get an error message:

mao@mao-note-arch Pascal $ fpc radar.pas
> Free Pascal Compiler version 2.6.0 [2012/01/02] for x86_64
> Copyright (c) 1993-2011 by Florian Klaempfl and others
> Target OS: Linux for x86-64
> Compiling radar.pas
> Fatal: Can't find unit graph used by radar
> Fatal: Compilation aborted
> Error: /usr/bin/ppcx64 returned an error exitcode (normal if you did not
> specify a source file to be compiled)
>

Why is this happening?