I happened to stumble over the Cygwin section of the installation docs, and was surprised to see references to not entirely bleeding-edge Windows versions:
"The adduser command is not supported; use the appropriate user management application on Windows NT, 2000, or XP. Otherwise, skip this step." Not knowing the first thing about Cygwin I might be out cycling here; it does sound like it's about due for an update to reflect current versions of Windows, or is this just relevant for older versions? Skimming backwards we have, with various wordings, recommendeed against Cygwin since 8.0, the current wording going back to 8.4 more or less unchanged. cheers ./daniel