Linux – How to reconnect a logically disconnected USB device

linuxusbusb-drive

It is possible for a USB storage device to become logically disconnected: the device is still plugged in, but is invisible from the operating system (e.g. it's not listed under /proc/bus/usb). Maybe this can happen to other kinds of USB or other removable devices as well. This can happen for example:

after Nautilus has unmounted a USB storage device;
after VirtualBox has claimed a USB storage device (the device disappears from the Linux host when it is attached in the guest, and does not automatically reappear if it is detached from the guest).

What is going on in the driver or in the hardware, and most importantly, (how) can the device be logically reconnected (without physically plugging it out and back in)?

Note that this question is not about mounting. In the “logically disconnected” state, the kernel believes there is nothing on the USB bus (and so of course there is no entry under /dev).

Best Answer

It is sometimes possible to do a power cycle on branch of the USB bus where the device is plugged :

# echo suspend > /sys/bus/usb/devices/1-1/power/level
# echo auto > /sys/bus/usb/devices/1-1/power/level

The 1-1 should be adjusted to your configuration. You can see to which part of the USB tree your device is plugged by running lsusb -t before ejecting it.

You can find detailed information on the linux-usb mailing-list, this thread for example.

Related Solutions

Ubuntu – Auto reconnect to wifi once disconnected

You can get the state of wlan1 from /sys/class/net/wlan1/carrier , this is a sample script to check the state of your wifi interface every 2 seconds , then reconnecting ( replace sleep 2 to check the connectivity every n seconds):

while true
     do
     i=$(cat /sys/class/net/wlan1/carrier)
if [ $i == 1 ]
then
       echo "connected"

else
       echo "reconnecting"
       killall wpa_supplicant
       modprobe -rv rt2800usb
       modprobe -v rt2800usb
       wpa_supplicant -i wlan1 -c/etc/wpa_supplicant.conf -B
       dhclient wlan1
       echo "reconnected successfully"
       fi
sleep 2
done

testing the script

Run this script then open a new terminal and run killall wpa_supplicant, you will be reconnected again.

Linux – How to Logically Eject and Reattach a USB Device

Many answers found on the Internet (including those in TNW's comment) rely on /sys/bus/usb/devices/2-2/power/level or /sys/bus/usb/devices/2-2/power/control which are both deprecated since 2.6.something kernel. For newer kernels, the suggested procedure is to unbind and rebind its driver, which usually results in a power cycle:

# Find out which driver to unbind
tree /sys/bus/usb/devices/2-2.1 | grep driver
|-- driver -> ../../../../../../bus/usb/drivers/whatever

# Unbind the driver
echo 2-2.1 > /sys/bus/usb/drivers/whatever/unbind

# Rebind the driver
echo 2-2.1 > /sys/bus/usb/drivers/whatever/bind

Best Answer

Related Solutions

Ubuntu – Auto reconnect to wifi once disconnected

Linux – How to Logically Eject and Reattach a USB Device

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