Hello, I started few days ago to make Buildbot under VxWorks run. I ported Python and made a few changes in Buildbot and Twisted to make everything run. I'm using Twisted 9.0.0 and Python 2.7.6 Twisted version is a bit old because its not complex as the 13.0.0 and it made the work under QNX for example. In Buildbot there are few possibilities to make a Step: * FileUpload * FileDownload * ShellCommand * MasterShellCommand MasterShellCommand doesnt make any difference here since its executed on the Master. FileUpload and FileDownload (filetransfer between Master and Slave) works fine. My Problem is the ShellCommand. It executes a command on the Slave. Im using the posix part on the Slave BUT fork() and exec() are not supported in VxWorks. So i changed for _fork methode in twisted/internet/process.py to avoid the fork()-part [self.pid = fork()]. I didnt change the exec part in Twisted. I did in the Python .. (in os.py i changed the exec methode to call another methode .. so i didnt made a huge change there). Now when i want to execute a ShellCommand, my buildbot/twisted/python crashes and i have an exception: remoteFailed: [Failure instance: Traceback (failure with no frames): <class 'twisted.spread.pb.PBConnectionLost'>: [Failure instance: Traceback (failure with no frames): <class 'twisted.internet.error.ConnectionDone'>: Connection was closed cleanly.] twisted.spread.pb.PBConnectionLost: [Failure instance: Traceback (failure with no frames): <class 'twisted.internet.error.ConnectionDone'>: Connection was closed cleanly. ] twisted.spread.pb.PBConnectionLost: [Failure instance: Traceback (failure with no frames): <class 'twisted.internet.error.ConnectionDone'>: Connection was closed cleanly. ] There are the two things i have. My question after writing 40 lines here: What could be the problem?  Why does it just crash without any "real" exception or error. Could someone point me to the right direction? Thanks. Best regards.