Hi, after many test I found out that System.Process.runInteractiveProcess leaks memory while runInteractiveCommand does. The issue of memory leaks related to running external program was raised here: http://www.haskell.org/pipermail/haskell-cafe/2007-June/027234.html and Bryan noted that after a while the process hits a steady state: http://www.haskell.org/pipermail/haskell-cafe/2007-June/027278.html This is true for runInteractiveCommand, but not for runInceractiveProcess, even though, both relay on the same foreign C imported function. I think this is a ghc bug, but before reporting it I'd like to have someone to confirm it. I wrote this code that demonstrate my point. Could you please have a look? Thanks for you kind attention. Andrea here's the code.: module Main where import System.Process import System.Posix.IO import System.IO import Control.Concurrent readOutput rh = do str <- hGetLine rh return str runWith c f = do (i,o,e,p) <- f c exit <- waitForProcess p str <- readOutput o putStrLn str cHandles i o e threadDelay $ 100000 * 1 runWith c f runRunIntProcess c = do (inp,out,err,p) <- runInteractiveProcess c [] Nothing Nothing return (inp,out,err,p) runRunIntCommand c = do (inp,out,err,p) <- runInteractiveCommand c return (inp,out,err,p) cHandles i o e = do hClose i hClose o hClose e -- this does not leaks -- this reaches a steady state after a while: --virt --5528 3404 668 S 6.6 0.7 13:07.48 procRunInComm main = runWith "date" runRunIntProcess -- this keep on growing --10548 8436 676 S 8.6 1.6 13:15.24 procRunInProc main' = runWith "date" runRunIntCommand