This article applies only to NoMachine servers for Linux supporting virtual desktops session. It doesn't apply to NoMachine (free to download) and Enteprise Desktop.

On Fedora 20, not all system processes are correctly terminated when the NoMachine virtual desktop is closed. Left over processes may slow down the system and prevent any new virtual desktop from starting.

A description of the problem is available here:

https://bugzilla.redhat.com/show_bug.cgi?id=1047186

and the suggested solution is to update the whole Fedora 20 installation to the most recent version.

If this is not possible, you may also try to change the default configuration in the /etc/systemd/logind.conf file from:

KillUserProcesses=no

to:

KillUserProcesses=yes

This should help the system to terminate all user's processes when the NoMachine virtual desktop sessions are closed.