Hello antonioking,
Command ‘su <user_name>’ should result in changing current user with the one passed to command. If it’s not possible for you to authenticate using this command, it’s likely that authentication issue is unrelated
to NoMachine.
This command: ‘grep nxexec /var/log/system.log > nxexec.log’ will generate nxexec.log file in current directory.
You can create archive of your log files by running from terminal (as root):
tar -zcf mac_os_server.tar.gz /Library/Application Support/NoMachine/var/log’
This should generate mac_os_server.tar.gz in current directory.