When you first install cygwin and run bash, it'll usually display this error message:
Your group is currently "mkpasswd". This indicates that the /etc/passwd (and possibly /etc/group) files should be rebuilt. See the man pages for mkpasswd and mkgroup then, for example, run mkpasswd -l [-d] > /etc/passwd mkgroup -l [-d] > /etc/group Note that the -d switch is necessary for domain users.
If you happen to be in a corporate environment with a huge active directory, then the
mkpasswd(1) command can take a very long time. A quicker way to fix this issue (provided only the current user uses cygwin on this machine, which is most likely) is to issue this command instead:
mkpasswd -l -c > /etc/passwd; mkgroup -l -d > /etc/group
mkgroup(1) command will still take a few minutes to complete, but typically there are much fewer groups than users, so it's bearable.