So this was pretty cool. I have a Supermicro branch server running ESXi that I was trying to upgrade to ESXi 7.
The problem was that I could not remember the admin password to the baseboard management controller web interface (akin to HP iLO or Dell iDrac).
Because I couldnt access the server console I couldnt do the ESXi upgrade remotely.

Supermicro BMC uses the IPMI protocol, so I searched google for how to reset admin user password with ipmi cli tools.
This led me to a compiled version of the ipmitool for ESXi. This works because the ipmi tool is interfacing directly with the BMC via ESXi (on box).

Here are the steps to install the ipmitool and reset access to the bmc admin:
1. First off download the zip file from here and scp the vib file across to /tmp on your target esxi server.
2. Set vib to community support and install the ipmi cli tool:
esxcli software acceptance set --level=CommunitySupported
esxcli software vib install -v /tmp/ipmitool-1.8.11-2.x86_64.vib --no-sig-check

3. Check your sensors and bmc lan config:
/opt/ipmitool/ipmitool sensor
/opt/ipmitool/ipmitool lan print

4. Add a new admin user named ‘netadmin’ and set password:
/opt/ipmitool/ipmitool user set name 3 netadmin
/opt/ipmitool/ipmitool user set password 3
Password for user 3:
Password for user 3:

5. Enable the netadmin user and set channel access:
/opt/ipmitool/ipmitool user enable 3
/opt/ipmitool/ipmitool channel setaccess 1 3 link=on ipmi=on privilege=4

6. Verify channel access:
/opt/ipmitool/ipmitool channel getaccess 1
User ID : 2
User Name : ADMIN
Fixed Name : Yes
Access Available : callback
Link Authentication : enabled
IPMI Messaging : enabled
Privilege Level : ADMINISTRATOR
User ID : 3
User Name : netadmin
Fixed Name : No
Access Available : call-in / callback
Link Authentication : enabled
IPMI Messaging : enabled
Privilege Level : ADMINISTRATOR

6. Now you can login with the user ‘netadmin’ to the servers BMC interface and edit the admin user, or run an ESXi upgrade from console!

As a side note, if your admin user is disabled or locked out you can use the ipmitool on esxi above and re-enable the admin user – heres how:
/opt/ipmitool/ipmitool channel setaccess 1 2 link=on ipmi=on privilege=4
opt/ipmitool/ipmitool user enable 2