Running rebaseall on Cygwin

Try invoking ash by giving its full pathname. For example, if you installed Cygwin into C:\cygwin\, then you would type this into the Start/Run dialog box:

C:\cygwin\bin\ash.exe

This should start the ash shell, within which you can then invoke /bin/rebaseall.

If you are running Cygwin-X make sure the X is closed, not just the xterms.

Expanding on this comment, using Win 10 and Msys2 from PortableApps, I went to Task Manager.

Given the large number of running processes, I sorted the list by the column "Command line". There I found my ssh-agent (/usr/bin/ssh-pageant) from Msys2 still running. I killed it, and then I could rebaseall .