According to System.IO, handles are automatically closed once they are garbage-collected. This served me well for files so far, but for processes, it gives me a weird problem: If I don't prevent my stdErr handle from being garbage-collected, the exit code reported by getProcessExitCode is just wrong (for me, it's always ExitSuccess, no matter what the program does). I posted this into #haskell and some poeple could not reproduce it, so I wanted to ask the Cafe what happens if you run this and if you have an idea why it happens to me. Thank you Niklas The following code gives an example. (http://hpaste.org/73593) You can see the real exit code with "./test; echo $?". module Main where import Control.Concurrent (threadDelay) import System.Process import System.IO import System.Exit run :: FilePath -> [String] -> IO (Handle, Handle, Handle, ProcessHandle) run cmd args = do r@(i, o, e, p) <- runInteractiveProcess cmd args Nothing Nothing getProcessExitCode p >>= \me -> case me of Just (ExitFailure 127) -> error $ "command not found: " ++ show cmd _ -> do mapM_ (flip hSetBuffering LineBuffering) [i, o, e] return r main = do (i, o, e, p) <- run "./test" [] putStrLn "spawned" threadDelay 1100000 putStrLn "waited" print =<< getProcessExitCode p -- If you comment these away, the above always returns Just ExitSuccess -- print =<< hGetContents o -- print =<< hGetContents e {- test.c: #include <stdio.h> #include <unistd.h> int main(int argc, char const *argv[]) { sleep (1); printf ("some stdout\n"); fprintf (stderr, "some stderr\n"); fflush (stdout); fflush (stderr); return 2; } -}