I've put together a simple test case for a rather annoying problem. I've got a program that drives other programs. For example, it can drive `cat`: :; Simple cat a-file When the file is a little bit greater than 135060 bytes, this program fails to produce any output at all -- I need to use ^C to get my console back. I have a similar program that encounters the same issue a little after 139192 bytes. The inconsistency is one baffling feature of this bug. If I remove the `hClose`, the example program just hangs, no matter the size of the input. It is entirely possible that I have overlooked some subtle feature of pipe semantics -- indeed, I hope that is the case. -- _jsn import Data.ByteString.Lazy import System.Process import System.Environment import System.IO (hClose) import Prelude hiding (writeFile, readFile) main = do exe:file:_ <- getArgs bytes <- readFile file foo <- simple exe bytes [] writeFile (file ++ ".foo") foo -- Manufactures a simple stream handler from a command line utility. simple :: String -> ByteString -> [String] -> IO ByteString simple exe bytes args = do (i, o, e, p) <- runInteractiveProcess exe args Nothing Nothing hPut i bytes s <- hGetContents o hClose i return s