Information
Set a timeout to automatically terminate idle ESXi Shell and SSH sessions.
If a user forgets to log out of their SSH session, the idle connection will remains open indefinitely, increasing the potential for someone to gain privileged access to the host. The ESXiShellInteractiveTimeOut allows you to automatically terminate idle shell sessions.
http://pubs.vmware.com/vsphere-60/topic/com.vmware.vsphere.security.doc/GUID-94F0C54F-05E3-4E16-8027-0280B9ED1009.html
http://kb.vmware.com/kb/2004746
Solution
# Set UserVars.ESXiShellInteractiveTimeOut to 900 on all hosts -
Get-VMHost | Foreach { Set-VMHostAdvancedConfiguration -VMHost $_ -Name UserVars.ESXiShellInteractiveTimeOut -Value 900 }