Error "Connection Refused 111" while connecting to session might be caused by wrong "/usr/NX/var/db/unknown" catalog owner (known as "/Library/Application Support/NoMachine/var/db/unknown/" on macOS).

Originally reported on Linux, it also affects all Mac versions.

Workaround

To check the owner of "/usr/NX/var/db/unknown" catalog, use the command "ls -ltr /usr/NX/var/db/ | grep unknown" in a system console.

If the owner is set to "root:root", it needs to be changed to "nx:root" with the command "chown nx:root /usr/NX/var/db/unknown".

To check if the problem is fixed, restart the server by running "/etc/NX/nxserver --restart".

All commands must be run with root privileges.