ESXi host that is disconnected or not responding in VMware vCenter Server

ESXi

ALT-F1 = Switches to the console
ALT-F2 = Switches to the DCUI

Restart the Management agents on an ESXi or ESX host

From the Local Console or SSH:

Log in to SSH or Local console as root.
Run these commands:

/etc/init.d/hostd restart
/etc/init.d/vpxa restart