The problem can be related to address changes of Windows DLLs after a Windows update operation. That behaviour may create collisions for more static Cygwin DLLs, especially in a 32-bit environment. We suggest to reboot the system as a first measure. You may need to install Copssh again by using our recipe which allows to keep an existing configuration intact. Consider to install the 64-bit version (available only in the product edition) if the problem still persists.

Activating users/groups can be done in multiple ways:

• Using AllowUsers/AllowGroups directives globally - requires that user does have a Windows profile directory

• Create a match block for a specific user/group (you can use directory isolation to specify a specific directory instead of user profile directory)

Copying public key can be done via Tools → Copy public key. It uses the tool ssh-copy-id. You can use localhost to contact the copssh server.

In some situations, it may be necessary to make a clean install to make an upgrade work. You can do it by following steps below:

• Backup your host keys in etc directory (etc/ssh_host*)
• Uninstall the existing version of Copssh
• Remove remnants of the installation directory except home directories if they exist
• Make sure that the service account and the sshd account are removed if they exist
• Install new Copssh
• Restore host keys back to etc directory
• Start Copssh Control Panel and verify that the service is running
• Activate your users again and specify their existing home directories as the home directory during the activation

Copssh 8 syslog daemon writes log messages to /var/log/messages as default. You may need to introduce a log rotation scheme to keep growth of that file under control.

You can use the recipe below to use our free tool logwot8 for that purpose.

• Install logwot8 to a separate directory
• Edit the configuration file logwot8.conf according to your requirements. The example below will rotate the log file weekly by keeping last 12 weeks of log activity in compressed files. See documentation for more options.

# Remember cygwin path conventions: 'c:\work' becomes '/cygdrive/c/work'
compress
create

"/cygdrive/c/copssh_x64/var/log/messages {
    rotate 12
    weekly
}

• Create a Windows scheduled task running the batch file logwot8.cmd weekly.

Sometimes it may be necessary to see directly how the openssh daemon reacts to startup or connection requests, to be able to locate daemon-related problems.

• Stop OpenSSH SSHD (system name: OpenSSHServer) service
• Right click Start a Unix Bash Shell from Copssh start menu (assuming that you have admin privileges)
• Enter the following command from the bash prompt:
  /bin/sshd -p <listening port> -D -d -e

This will start openssh daemon in standalone debug mode and messages will be displayed on the screen. You may specify up to three -d for increased output verbosity.

• Try to initiate a putty session and watch messages at the server side.

• Start a bash shell, locally or remotely
• Change to the user's home directory if it is not already done
• Link a directory or network share to a local name by using ln command

Examples:

ln -s "/cygdrive/d/pub/" "pub"

creates a link from D:\pub to pub in the user's home directory.

ln -s "//myserver/netdata" "netdata"

creates a link from \\myserver\netdata to netdata in the user's home directory.

Now, the user can use pub and netdata to access D:\pub and/or \\myserver\netdata respectively.

Some recommendations (not all of them can be applicable in your case, no sorting by importance):

On domain-joined machines, Cygwin normally qualifies local SAM accounts with the machine’s NetBIOS name as a prefix (e.g. MYSERVER+john instead of john). This is done to avoid name collisions with same-named domain accounts. Some environments find this prefix inconvenient — for example when SSH keys, authorized_keys files, or scripts reference plain usernames.

Yes. A patched build of cygwin1.dll is available upon request. We maintain a custom build of cygwin1.dll with a patch that removes the MACHINE+ prefix for local SAM accounts on domain member machines, making them behave the same way as primary domain accounts. The plain username (e.g. john) is used directly.

The patch itself is publicly available at https://gist.github.com/tevkar/dab3fb32346f6899e11e374f254746e9 for review or independent builds.

To obtain the patched DLL, please open a support request.

Before requesting, please be aware of the following:

• Name collisions are not detected or warned about. If a local account and a domain account share the same username, the first one resolved by the system wins. This can cause unexpected behaviour with permissions and home directory mappings.
• This is only relevant on domain-joined machines. On standalone machines the behaviour is unchanged.
• Existing setups may need updating. Any authorized_keys files, scripts, or configurations that reference the prefixed form (e.g. MYSERVER+john) must be updated to use the plain username.
• This is an unsupported customisation relative to the standard Cygwin distribution. The change will need to be reapplied when cygwin1.dll is updated.

I am fond of fancy and short names :-)

Cygwin + OPENSSH is a qualified guess !!