Issues when Upgrading from vSphere 4.1 to vSphere 5.x

Lately I had a little project where I had to upgrade a VMware Infrastructure from 4.1 to 5.x along all went well, I did vCenter then the vSphere Client and finally I went for the ESX hosts.
For product manageability purposes I did both via update manager and did an in place upgrade directly while being at the console.
The upgrade went straight forward without any _apparent_ issues, recently I was contacted by the customer and he informed that he can’t access the ESXi hosts using the credentials he had defined for each employee.
After troubleshooting and a lot of digging into the changed files on the ESXi hosts I found out that all users gets wiped out and only the root user gets preserved, along I’ve gathered a little list of what gets migrated and what not, its not comprehensive and I am sure if you contact VMware support they can provide you with a comprehensive listing.

Note Migrated:

/etc/logrotate.conf as ESXi log rotation is incompatible with prior versions.
/etc/localtime sadky timezones are not supported in ESXi.
/etc/syslog.conf
/etc/sysconfig/i18n this is not supported in ESXi.
/etc/hosts.allow
/etc/hosts.deny
/etc/sudoers yep sudo is not supported in ESXi.
/etc/vmware/vmware.lic thats why when you’re done you have to put the license again.
/etc/passwd and etc/shadow  we can say that these get partially migrated because root gets preserved.

Migrated:

/etc/sysconfig/network  as the service console virtual NICs (vswif) will be converted to ESXi virtual NICs (vmk).
/etc/ssh  as OpenSSH is supported/included in ESXi 5.

Hopefully this helps people whom faced the issues I have =).
Abdullah^2