keep USB powered after shutdown [ubuntu 12.04LTS]

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http://www.linuxquestions.org – Hello everybody, my secondary PC has this specs MSI 870-g54 AMD X3 455 2x2GB DDR3 1600MHz ATi HD3650 PCIe Seasonic S12II-480w it is dualboot Windows 7 x64 SP1 (up to date) Ubuntu 12.04 LTS x64 (up to date, kernel 3.2.0-48) when I shutdown Windows 7 (proper shutdown, no sleep no hibernate) USB3 ports keep providing 5.0 voltage When I reboot into Ubuntu 12.04 and do shutdown, USB3 power is killed what I want to achieve? to keep usb3 powered even after shutting down Ubuntu because I am powering a 120mm fan that is cooling my router and raspberry pi and powering small portable Lenovo speakers (HowTos)