I have recently decided to move from Microsoft ActiveDirectory (AD) to using OpenLDAP on my home network. My AD configuration included the use of kerberos. There is one more piece to my guestOS setup, I also automount user home directories via NFS. After making this transition, I noticed that several of my Ubuntu guest VMs were slow to log in. My once speedy login was now taking 18 or more seconds. After doing some “Googling”, I found [Bug # 1270445 - slow NFSv4 without Need_GSS=yes](https://bugs.launchpad.net/ubuntu/+source/nfs- utils/+bug/1270445) that fixed me up immediately.
Basically, I just needed to black list the rpcsec_gss_krb5 in /etc/modprobe.d/blacklist.conf. Making this change has restored my fast login times.