[fpc-pascal] Truncate procedure unable to work under Linux, is this a bug?

[Géza Kovacs Géza]

Truncate procedure unable to work under Linux, is this a bug?
This code is unable to work under linux: the Truncate drops an error
message if the file is larger than 2 or 3 GB.
I tested it with Free Pascal 2.6.4 under Debian Jessie 64 bit.
It produce the same error message under Ubuntu 12.04 32 bit with Free
Pascal 2.4.4
Sometimes I did not get any error message but the file (which was 2 or
3 GB) will be only some hundred MB after truncate...
It operates correctly under Windows.

It produce the following error message:
An unhandled exception occurred at $<address>:
EPrivilege : Privileged instruction
$<address>

Program File_Trunc;
{$MODE OBJFPC} {$H+}
uses dos,sysutils;
var
	f : file of byte;
	fs : int64;
begin
	assign(f,paramstr(1));
	ReSet(f);
	fs := FileSize(f);
	WriteLn('Original file size: ',fs);
	fs := fs-3456789;
	WriteLn('File size after truncate: ',fs);
	Seek(f,fs);
	Truncate(f);
	Close(f);
end.
Best regards, Geza