Citrix XenServer host in a pool showing "No interface present"

If a host in your pool is showing "No interface present", you can perform the following steps

1. Check if the host is in emergency mode

xe host-is-in-emergency-mode 

2. If the output is "True" then change it to "False" by running

xe pool-emergency-transition-to-master

3. Ensure host is no longer in emergency mode

4. Restart toolstack

xe-toolstack-restart

Applying updates on open source version of Citrix XenServer 6.2

Citrix XenServer 6.2 is now open source therefore for support and maintenance you will have to get the paid version which basically means buying a license for your XenServer.

Although all features are enable on the open source version of XenServer itself, some features are disabled when it comes to managing them using Citrix tools like XenCenter and one of the affected feature is the installation of patches. You will notice that the option to apply patches on your servers are greyed out.

You can however apply the patches manually. All your need to do is the get to the server console and run a few commands.

Before that, transfer the updates to the server or pool master using transfer tools like Filezilla and then run the following command

xe patch-upload file-name=‹filename location›

The command above will provide you with a UUID which you will use when you run the next command, if you are applying on a pool

xe patch-pool-apply uuid=‹UUID›

If you are applying for a single server, then you will need the host UUID which you can find through 
XenCenter. The command will then be

xe patch-apply uuid=‹UUID› host-uuid=‹host-UUID›

You can monitor the updates progress in XenCenter. If the server is showing the arrow down icon, the updates are being applied will turn back to a green circle icon once it is done. 

For can find more details here