I have a ESXi 5.5 (U1) host running off a USB stick on my HP Proliant Microserver (N40L). The host runs off the USB port directly attached to the M/B of the N40L.
Virtualised on the host are 3 VMs - FreeNAS, pfSense, and an Ubuntu 14.04 server. The only VM with a USB adapter attached is the Ubuntu one. Connected to the USB is an Apollo Line Interactive USB. Running on Ubuntu is NUT (Network UPS Tools) installed from packages. I have successfully configured NUT to see the UPS and to monitor and all seems well, initially.
The problem is that after a period of time - which varies (it can be a minute, it can be 20) - NUT appears to lose the USB. I can still see the device connected doing a lsusb, but I can't successfully start monitoring again unless I physically unplug and replug it, or if I reboot the VM, and then all is well again, for a short period of time.
If I try to simply restart the NUT driver that interrogates the UPS without unplugging the USB, I get a message that the device is in use, and the driver then fails to start. Does ESX do anything that could interfere with the ability of a process to bind to the USB? Has anyone come across a similar problem?