Linux hub suddenly got restarted.
When looking at hub.log, here is some error message regarding file descriptor.
hub: FATAL: CTRL <HUB> caused hub to reach max file descriptors
hub any version running in Linux platform.
In release older than hub 7.96, there was an internal hard-coded limit at 999 for opened file descriptors.
So if the number of file descriptor (opened by hub) reaches 999, hub then undergo self-restart automatically.
This hard-coded limit has been eliminated with hub 7.96.
*** Important note ***
Starting with hub 7.96 it can consume as many file descriptors as Operating System allows.
However, in most Linux distributions, maximum number of file descriptors per process is 1024.
So with the default OS settings, hub can not open more than 1024 file descriptors.
Enhancing OS side (to increase max file descriptor per process) is required for hub to use open more than 1024 file descriptors.