On Windows 7, trying to execute a non-existent program as follows... OSProcess command: 'notepadXX.exe' ...causes an MNU in ExternalWindowsOSProcess>>value. This is due to writing to stderr where "self initialStdErr" returns nil, seemingly due to ExternalWindowsOSProcess missing the #initialize and #setDefaults of E xternalUnixOSProcess. Now I understand that stderr is problematic in general on Windows. The following statements... OSProcess thisOSProcess stdErr nextPutAll: 'test'. FileStream stderr nextPutAll: 'test'. ...both work fine on OSX, but fail on Windows with the error "FileWriteError: File stderr is closed" The result is the same on both Pharo 4 and Squeak 4.5. (Squeak also brings up a bottom message bar saying... "# To disable: F2 -> 'debug options' -> 'show console on errors' WARNING: Manufactured file handle detected!") Pharo has a workaround for the general issue by creating a disk file named 'stderr' as follows... FileStream class >> standardIOStreamNamed: moniker forWrite: forWrite self flag: #todo. "This is an ugly hack, while waiting for a real fix for windows. There several problems with this approach, but it allow us to run tests, etc." Smalltalk os isWin32 ifTrue: [ [ ^ MultiByteFileStream forceNewFileNamed: moniker asString ] on: CannotDeleteFileException do: [ "HACK: if the image is opened a second time windows barks about the already opened locked file" ^ MultiByteFileStream forceNewFileNamed: moniker asString, '_', (Random new nextInt: SmallInteger maxVal) asString ]]. So to address the MNU for OSProcess? 1. wrap the "self initialStdErr" with an #ifNil: check 2. Squeak adopt the Pharo workaround, then lean on that to define #initialize and #setDefaults for ExternalWindowsOSProcess 3. real fix for stderr (outside of OSProcess?) 4. wont fix 5. other? Note that this is not a burning issue for me. I am just cleaning out old issues that I logged in the Pharo bug tracker. If the answer if (4.) I'll just close the issue [1]. For both Squeak and Pharo, I loaded ConfigurationOfOSProcess-ThierryGoubier.33 from... MCHttpRepository location: 'http://smalltalkhub.com/mc/Pharo/MetaRepoForPharo40/main' (Perhaps someone with access can copy that to the main repo) cheers -ben [1] https://pharo.fogbugz.com/default.asp?11615