Rollback an ESXi after an update

Upgrading and updating your ESXi hosts is necessary to be safe:) . Updates contain bug fixes, security updates, new features or improvements, and drivers. With VUM this can be quite easy. However, sometimes you want to rollback after an update. How do we perform a rollback on ESXi hosts within vSphere?
Well, the awesome thing is, that the ESXi hosts maintains an alternative altbootbank besides his regular bootbank. As you can see here in the screenshot below.

 

 

After an upgrade the previous build is stored in the altbootbank. So we need to trigger the host to start from that bank, but how do we do that.
Well actually this is quite simple. Close down VUM, cause you’re not gonna find it there.
First, put your host in maintenance mode and give it a reboot. Open up the console on the host with an out-of-band Management tool like ILO, IDRAC, IPMI, etcetera, or hook up a computer screen on the host. Wait until until you see the screen where it is loading the hypervisor. You should see a screen something like this.

 

 

During the Hypervisor will in Boot Phase press “Shift+R” on your keyboard.
This will open up the following menu.

 

As you see, the menu shows 2 different built. In this case the menu shows that my current build is 6.5.0-2.03.130004031, since it shows that is the “(Default)”. This is your bootbank. The other build “6.5.0-5969303” is the one that resides at my altbootbank. Which is the build that I had before I updated from 6.5u1 towards 6.5u2. As you see in the bottom left, you can simply perform a rollback by pressing “Y”.
In a few minutes the hypervisor will start the previous build (without a reboot) and you’re back as you were before the update.