In my system the problem was a misconfiguration involving the hostname.

NOTE: The solution below applies to workstations using NetworkManager. This solution does not apply to servers which do not employ NetworkManager.

In a nushell, you have to guarantee that /etc/hostname and /etc/hosts agree on the same hostname.
Also, make sure that you are not defining more IP addresses to your machine than necessary.
For example: imagine that your machine is called "myself", your domain is "example.com" and your DHCP server gives you always the same IP 192.168.1.3.
You may be tempted to configure your fixed IP address in /etc/hosts, right? DO NOT DO THAT!

This is how /etc/hostname and /etc/hosts should look like:

Code: Select all

$ cat /etc/hostname
myself


Code: Select all

$ cat /etc/hosts
127.0.0.1 localhost.localdomain localhost

127.0.1.1 myself.example.com myself

192.168.1.1 router
192.168.1.2 mywife.example.com mywife
### 192.168.1.3 myself.example.com myself # COMMENT OUT THIS LINE
192.168.1.3 myson.example.com myson


So, make sure that you comment out the address the router delivers to you.
In my case I've copied /etc/hosts from another computer and forgot to comment out the line which contains my fixed IP in the LAN.
This mistake cost me a couple of hours trying to figure out why KDE was so sluggish when I was attempting to login.

I hope it helps,

-- Richard Gomes