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Reset the root password with ESX 3.x was quite simple, just because the service console was a partition writable a live CD… With ESX 4.x it was a little more complicated (the service console was basically a vmdk).
But with ESXi things are more complicated, due to the partition layout, that ESXi works in RAM and that all configurations files are stored in the banks it special archive files. The file containing the password hashes is called “shadow” and it is is contained in a nested structure of archives inside the state.tgz file.
So, in order to change the root password (or other password) you need to work with several compressed tar files, as well explained on this post:
- How to reset the root password of VMware ESXi 4.1 and 5.0
- ESXi: reset the root password
- Changing a forgotten ESXi 5 root password
Although you have detailed instructions on the web on how to “reset” to password, I still prefer to simple re-install the host and keep existing VMFS datastores: with ESXi 5.0 you can select “Install ESXi, preserve VMFS datatore” after selecting the installation disk. Also, to be sure to do not “touch” the existing disks, you can install ESXi on a USB keys or flash card (just in case that you need to access to some VMs).
Note that the host reinstallation is also the only supported way, as described in the KB1317898 (Changing a forgotten root password on an ESX/ESXi host).