Unable to rollback ESXi Version as Bootbank and Altbootbank have the same build number

Products

VMware vSphere ESXi

Issue/Introduction

You are trying to roll back an ESXi host to an earlier version, following the steps outlined in Reverting to a previous version of ESXi 6.x, 7.x or 8.x

This fails, the ESXi still boots with the same version as before/

When comparing the boot configuration in /bootbank and in /altbootbank, you find that both have the same version. For example:

in /bootbank

$ less boot.cfg
bootstate=0
title=Loading VMware ESXi
timeout=5
prefix=
kernel=b.b00
kernelopt=autoPartition=FALSE
modules=jumpstrt.gz --- useropts.gz --- features.gz --- k.b00 --- uc_intel.b00 --- uc_amd.b00 --- uc_hygon.b00 --- procfs.b00 --- vmx.v00 --- vim.v00 --- tpm.v00
(...)
lsuv2_sm.v00 --- native_m.v00 --- trx.v00 --- vdfs.v00 --- vmware_e.v00 --- vmware_f.v00 --- vsan.v00 --- vsanheal.v00 --- vsanmgmt.v00 --- xorg.v00 --- gc.v00 --- imgdb.tgz --- basemisc.tgz --- state.tgz
build=7.0.3-0.125.23794027
updated=6

in /altbootbank

$ less boot.cfg
bootstate=0
title=Loading VMware ESXi
timeout=5
prefix=
kernel=b.b00
kernelopt=autoPartition=FALSE
modules=jumpstrt.gz --- useropts.gz --- features.gz --- k.b00 --- uc_intel.b00 --- uc_amd.b00 --- uc_hygon.b00 --- procfs.b00 --- vmx.v00 --- vim.v00 --- tpm.v00 -- (...)
lsuv2_sm.v00 --- native_m.v00 --- trx.v00 --- vdfs.v00 --- vmware_e.v00 --- vmware_f.v00 --- vsan.v00 --- vsanheal.v00 --- vsanmgmt.v00 --- xorg.v00 --- gc.v00 --- imgdb.tgz --- basemisc.tgz --- state.tgz
build=7.0.3-0.125.23794027
updated=7

Environment

VMware vSphere ESXi 6.x

VMware vSphere ESXi 7.0.x

VMware vSphere ESXi 8.0.x

Cause

As per design, at any given point rollback to only one previous state of ESXi is possible and this backup copy is placed in the altbootbank.

Actions such as ESXi upgrade/update, vib installation/removal will discard the older (n-2) copy in the altbootbank and only retain the (n-1) copy.
After the first reboot following a successful ESXi host upgrade, if any changes are made, such as installing VIBs (vSphere Installation Bundles) or Software VIB's that require another reboot, the option to roll back to the previous version will be lost.

Resolution

To confirm what changes are committed on the Host

run the following command:
```
# esxcli software profile get
```
review the vmksummary.log in /var/run/log/ and check if a reboot was initiated matching the Date time seen in "esxcli software profile get"

Example:

The host is successfully upgraded from Version-1 to Version-2 while in Maintenance Mode. After the first reboot, while still in Maintenance Mode, the bootbank will contain Version-2 (the upgraded version), and the altbootbank will still contain Version-1 (the previous version).
After removing the host from Maintenance Mode, if the host is part of an HA (High Availability) cluster, the FDM (Fault Domain Manager) VIB is installed on the host.
- Note: FDM VIB does not require a reboot.
The change will be updated in the bootbank, so it will reflect Version-2 with the FDM VIB.
- If the host is rebooted for any reason, the altbootbank will also be updated to Version-2, as the boot locations are swapped. After this reboot, Version-1 will no longer be available for rollback.

Conclusion

Any Installation requiring a Reboot of the Host will commit the changes to /bootbank and /altbootbank, hence rollback to previous version is no longer available.