Cannot Complete Login Error
Just this week I ran into an interesting issue with a brand new ESXi server deployment. After installing 6.0 on a new host and setting up the Management Network from DCUI, any attempt to log in through vSphere client would yield ‘Cannot complete login’ error message.
Thinking highly of my reading comprehension, I assumed the problem was indeed a bad password.
Finding the Problem in DCUI
After logging into DCUI with the same password that just failed to let me into vSphere client, I was able to log in and turn on SSH. The SSH connection failed with an ‘Access Denied’ message as well. You’d think that the only situation this can take place in is if ‘Lockdown Mode’ was enabled—it was not, this system never touched a vCenter server.
Moving further into troubleshooting, I dug into DCUI and reviewed vmkernel.log and syslog.log and found the following entry:
Basically, something was trying to log into the IP address of the ESXi host 60,000 times per hour, causing the host to lock the ‘root’ account from remote access thus disabling SSH and thick client access.
The culprit turned out to be a badly behaved monitoring application that a previous admin had configured to use the root account, thus locking out remote access to the ESXi host and essentially performing a DOS attack on the host.