Interacting with customers on a daily basis, I often encounter misconceptions about keeping XenServer up to date. Most people believe that upgrading to the newest version is keeping XenServer up to date. Applying hotfixes is the way to keep your version of XenServer up to date. The important thing to remember, is that hotfixes do need to be applied in sequential order. If you have held off on hotfixes, and then a hotfix number 8 comes out, you will be busy applying hotfixes 1 through 7, with each requiring a reboot. This would also require XenMotion to move VMs off of a host to update it. Your whole pool also needs to be updated before moving to the next hotfix.

Common issues involving hotfixes:

1. Applying hotfixes out of order (would require a host to be ejected from the pool, XenServer reinstalled, applied in order, and then host can be rejoined to pool).

2. Applying hotfixes to only one host in a pool (pool needs to run the same version of software).

The greatest benefit of applying hotfixes is avoiding an issue before it occurs. Keeping your XenServer secure. In most situations, this is called preventative maintenance.

Below are updates (in order) for XenServer 5.6 SP2:

Hotfix 1 – http://support.citrix.com/article/CTX129767
Hotfix 2 – http://support.citrix.com/article/CTX130294
Hotfix 3 – http://support.citrix.com/article/CTX130355
Hotfix 4 – http://support.citrix.com/article/CTX130845
Hotfix 5 – http://support.citrix.com/article/CTX131108
Hotfix 6 – http://support.citrix.com/article/CTX131303
Hotfix 7 – http://support.citrix.com/article/CTX131639

Below are updates (in order) for XenServer 6:

Hotfix 1 – http://support.citrix.com/article/CTX131214
Hotfix 2 – http://support.citrix.com/article/CTX131400
Hotfix 3 – http://support.citrix.com/article/CTX131745
Hotfix 4 – http://support.citrix.com/article/CTX131673

NOTE: Often there are gaps between hotfixes as a hotifx is updated and then re-released as a higher number.  An example of this would be XenServer 5.6 FP1:

Hotfix XS56EFP1003 – http://support.citrix.com/article/CTX128416
Hotfix XS56EFP1006 – http://support.citrix.com/article/CTX129267 NOTE: This hotfix includes and supersedes Hotfix XS56EFP1005
Hotfix XS56EFP1007 – http://support.citrix.com/article/CTX129479 NOTE: This hotfix includes and supersedes Hotfix XS56EFP1004
Hotfix XS56EFP1008 – http://support.citrix.com/article/CTX130293