With Mike’s excellent post, I was able to update my esxi install from Update 1 to Update 2 via the command line.
Summary:
esxcli network firewall ruleset set -e true -r httpClient
esxcli software profile update -d https://hostupdate.vmware.com/software/VUM/PRODUCTION/main/vmw-depot-index.xml -p ESXi-5.5.0-20140902001-standard
esxcli network firewall ruleset set -e false -r httpClient
reboot
To get the list of updates:
esxcli software sources profile list -d https://hostupdate.vmware.com/software/VUM/PRODUCTION/main/vmw-depot-index.xml