Recently updated my Cygwin install on Windows 7 Ultimate x64 Workstation.
Tried to run
startxdmcp.bat and got a Cygwin X error – failed to activate core devices
Looking in /var/log/XWin.0.log showed nothing obvious as to why the X server failed to start.
Ran Cygwin Setup.exe to update it Cygwin and got error:
The procedure entry point rl_filename_rewrite_hook could not be located in the dynamic link library cygreadline7.dll
The fix was re-start Cygwin’s Setup.exe and choose to reinstall libreadline7 6.1.2-2
startxdmcp.bat command then worked as expected spawning a local X server and connecting to the remote Linux Servers display via xdmcp.
This could have been caused by a recent update that, from memory, gave an error stating that Cygwin couldn’t replace some files that were in use so perhaps the upgrade failed and left things inconsistant.