If you are debugging a SSH connection, you may need to run sshd by hand (instead of as a service) and enable debugging output. Doing so allows you to track exactly why a connection is failing to establish. However, if you try to run sshd by hand, you may get the following message.

% cygrunsrv.exe --stop sshd
% /usr/sbin/sshd.exe -D
Could not load host key: /etc/ssh_host_ecdsa_key
/var/empty must be owned by root and not group or world-writable.

To fix this, make the user starting the sshd service the owner of /var/empty.

% ls -ld /var/empty
drwxr-xr-x+ 1 cyg_server root 0 May  7  2010 empty
% chown <user> /var/empty

Now, start sshd again.

% /usr/sbin/sshd.exe -D

When you are done debugging and are ready to run sshd again as a service, change the owner of /var/empty to cyg_server.

% chown cyg_server /var/empty
% cygrunsrv.exe --start sshd

Note: you must have administrator privileges to run cygrunsrv.exe.