Apologies for spamming but I think this fix needs to be automated in
ssh-host-config and updated in the cygwin FAQ.
Like many users I've been struggling with this obscure bug that allows one
to log on with ssh only as the priviledged user (cyg_server in my case).
Attempts under another user succeed in all modes of authentication (password,
RSA, DSA, whatever), but then get disconnected with the esoteric line:

/bin/bash: Operation not permitted

It turns out this has nothing to with bash, but rather with the usser
cyg_server needing specific NTSEC rights to allow logons as other users.

The fix was found here:

http://www.tux.org/~mayer/cygwin/cygwin_sshd.pdf

Specifically, ssh-host-config needs these following lines:
editrights -a SeAssignPrimaryTokenPrivilege -u cyg_server （cyg_server为服务启动用户）
editrights -a SeCreateTokenPrivilege -u cyg_server
editrights -a SeTcbPrivilege -u cyg_server
editrights -a SeServiceLogonRight -u cyg_server

#editrights -l -u cyg_server

然后重启cygwin服务生效
Francis Korning de Grandpre
enterprise software architect
fkorning at yahoo dot ca

cygwin 多用户 /bin/bash: Operation not permitted