ESXi (in this case version 6.7.0) can appear to hang / freeze during the boot up sequence at the following step:
dma_mapper_iommu loaded successfully
However the system is otherwise fully responsive (e.g., via vSphere). The root cause was that the video card used for displaying the local console had been enabled for passthrough.

When trying to update/upgrade ESXi 6.7.0 Update 1 to Update 2 (via software profile update command) you may run into the following error:

[InstallationError]
[Errno 28] No space left on device
vibs = VMware_locker_tools-light_10.3.5.10430147-12986307
Please refer to the log file for more details.

The solution is to manually install VMware_locker_tools package by following these steps via SSH on the host:

1. cd /tmp
2. wget http://hostupdate.vmware.com/software/VUM/PRODUCTION/main/esx/vmw/vib20/tools-light/VMware_locker_tools-light_10.3.5.10430147-12986307.vib
3. esxcli software vib install -f -v /tmp/VMware_locker_tools-light_10.3.5.10430147-12986307.vib
4. Once you receive verification that the locker tools package has been installed successfully, try the profile update command again to patch ESXi.
   Note – in some cases the installation of this VIB may be skipped by the server and you receive the message: Host is not changed.  If so then simply try the profile update command again and you should not receive Errno 28 related to the locker tools VIB.

When trying to update/upgrade ESXi 6.7 (via software profile update command) you may run into the following error message:

[OSError]
[Errno 28] No space left on device
Please refer to the log file for more details.

The solution is to set the host swap to use a datastore. In vSphere Web Access:

1. Navigate to Host->Manage->System->Swap. On a fresh install, the Datastore setting  is usually set to No.
2. Choose Edit Settings, select a valid Datastore in the drop down menu, then Save.
3. Now you are ready to issue the profile update command again to patch ESXi