Updated: April 19, 2023

Driver for USB Mass Storage interface

Note: In order to start this driver, you must be logged in as root or have the right abilities, and the USB stack (io-usb-otg) needs to be running.


devb-umass [blk option[,option]...]
           [cam option[,option]...]
           [disk option[,option]...]
           [umass option[,option]...]
           [fs_type options]

Runs on:

QNX Neutrino


Note: Use commas (,) to separate the options. You can put the blk, cam, disk, and umass groups of options in any order.
blk options
The blk options control If specified, they must follow the blk keyword. For more information, see
cam options
The cam options control If specified, they must follow the cam keyword.
disk options
The disk options control the driver's interface to If specified, they must follow the disk keyword.
umass options
The umass options control the driver's interface to the USB device. If you've installed multiple devices, you can repeat these options for each device. Remember, however, to specify the umass keyword before each controller's set of options.
The bus number of the USB controller.
Specify the command timeout in ms. The default is 4 seconds.
The configuration number of the device.
Ignore the Command Status Wrapper. Some devices return invalid data for the CSW.
The USB address of the device.
The device ID of the device.
The particular interface number of the device.
Set the maximum number of bulk resets. The default is 0. Once we reach this, the device will be disabled.
Set the maximum number of consecutive medium errors for devices that need to tweak the medium sense error. Beyond this limit, medium errors will return. The default is 10.
Set the polling thread interval, where num is the normal polling interval in ms, fpoll is the polling interval to use during startup (a faster rate), and fnum is how many times to poll using the second parameter. You can either specify the first parameter (without fpoll and fnum), or specify all three parameters. If you don't specify this option, there's no polling thread.
Connect to the specified USB stack. The default is /dev/usb/io-usb-otg.
Set the priority of the processing thread. The default is 21.
Set the path name of the SCSI passthrough interface (default none).
The vendor ID of the device.
Wait num of seconds for the USB stack. The default is 60 seconds.
fs_type options
The fs_type options control any filesystem (fs-*.so) module being loaded. Here, fs_type is the filesystem type, such as qnx6 for the Power-Safe filesystem. For the list of supported filesystem options, see the reference for the corresponding shared object. For example, for qnx6, see


The devb-umass driver is the driver for a USB mass storage interface.


Assume a USB controller, and list all connected devices:

devb-umass &

Assume a USB controller, and list/wait for all connected devices:

devb-umass cam pnp &