28 December 2007

udev in Ubuntu

This post will be a recipe for configuring udev in Ubuntu so that if you plug in a USB storage device (like a flash drive, an MP3 player, etc.), it will get a consistent and predictable device name which you can attache as a non-root user to a fixed mount point. I'll be using my new Verbatim thumb drive as an example.

Plug in the flash drive, wait a few seconds, and type 'dmesg | tail'. The last few lines should show the USB system detecting the device and giving it the first available device name. In my case, the flash drive got /dev/sdd. Next, ask udevinfo for details about the device:
udevinfo -a -p $( udevinfo -q path -n /dev/sdd ) | less

Page through the output looking for the device's values for idVendor and idProduct. The udevinfo output for my thumb drive contained the following lines:


Next thing is to tell udev about the device. Create a udev rule file (I used /etc/udev/rules.d/99-thumb.rules) with something like the following:

SUBSYSTEMS=="usb", SYSFS{idVendor}=="13fe", SYSFS{idProduct}=="1e23", NAME="thumb", MODE="0660" OWNER="mbrisby" GROUP="mbrisby"

(Naturally, replace mbrisby with your username and group name.) You may need to run udevcontrol reload_rules to tell udev to read the new addition into its in-memory ruleset.

Now you can make a mount point:

$ sudo mkdir /media/thumb
$ sudo chown mbrisby.mbrisby /media/thumb

Finally, add the mount point to /etc/fstab:

/dev/thumb /media/thumb vfat user,noauto 0 0

And from now on, you should be able to plug in the thumb drive, wait a couple of seconds, type mount /media/thumb, and start accessing the files at /media/thumb.

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