Jun

7

Debian: Naming USB devices with uDev

June 7, 2009 | 1 Comment

I use three different small backup drives as three backup volumes. I turn them on on sunday, the backup scripts runs overnight, and I turn them off on monday morning. I’ve shared the backup script in a previous post.

The problem is that the backup script  starts by mounting the backup drives. It expects them to have the same device name in /dev everytime. For example, it expects backup1 to be /dev/sde1. It turns out that these assigned device names can randomly change. Sometimes, backup1 appears as /dev/sdh1. The solution, in this case, is to assign a persistent name to each device. That is what udev is for. Udev will be called when a drive is plugged. If the plugged drive match a udev rule, it will be assigned the name defined in the rule.

The first step is to find criterias that will allow to identify a single drive and then create a rule for it.

Run the following command for the drives you need to name (replace sde1 by what you need):

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udevinfo -a -p $(udevinfo -q path -n /dev/sde1)

In my case, I get the following result:

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 looking at device '/block/sde/sde1':
KERNEL=="sde1"
<strong> SUBSYSTEM=="block"</strong>
DRIVER==""
ATTR{start}=="63"
ATTR{size}=="2930272002"
ATTR{stat}=="      48     1558     3506      228       19        0       38      248        0      156      476"looking at parent device '/block/sde':
KERNELS=="sde"
<strong> SUBSYSTEMS=="block"</strong>
DRIVERS==""
ATTRS{range}=="16"
ATTRS{removable}=="0"
ATTRS{size}=="2930277168"
ATTRS{capability}=="12"
ATTRS{stat}=="      60     1573     3722      504       19        0       38      248        0      348      752"looking at parent device '/devices/pci0000:00/0000:00:02.1/usb2/2-4/2-4:1.0/host4/target4:0:0/4:0:0:1':
KERNELS=="4:0:0:1"
<strong> SUBSYSTEMS=="scsi"</strong>
DRIVERS=="sd"
ATTRS{device_blocked}=="0"
ATTRS{type}=="0"
ATTRS{scsi_level}=="3"
<strong><code> ATTRS{vendor}=="ST315003"
ATTRS{model}=="41AS            "

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ATTRS{rev}=="    "
ATTRS{state}=="running"
ATTRS{timeout}=="30"
ATTRS{iocounterbits}=="32"
ATTRS{iorequest_cnt}=="0x57"
ATTRS{iodone_cnt}=="0x57"
ATTRS{ioerr_cnt}=="0x0"
ATTRS{modalias}=="scsi:t-0x00"
ATTRS{evt_media_change}=="0"
ATTRS{queue_depth}=="1"
ATTRS{queue_type}=="none"
ATTRS{max_sectors}=="240"
...

I have outlined the unique values and criterias that will allow me to identify backup1. I also outlined the subsystem lines that will be used in the udev rule.

The rule that will match this drive is:

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SUBSYSTEM=="block", SUBSYSTEMS=="block", SUBSYSTEMS=="scsi", ATTRS{vendor}=="ST315003", ATTRS{model}=="41AaS", NAME="backup1"

More information about udev rules can be found online.

That done, you can test our rule by launching the following command:

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udevadm test $(udevinfo -q path -n /dev/sde1) --force

If the rule matched the drive, you can ls /dev/disk/by-label and find backup1 in the list.

You can now edit the backup script and replace mount /dev/sde1 by mount /dev/disk/by-label/backup1. The latter should always refer to the right drive.

Thanks to the authors of the following two guides that lead me to this solution:

Filed under: Computing, Debian, Système

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1 Comment to "Debian: Naming USB devices with uDev"

  1. Trackback on samantha on June 7, 2009 at 8:12 pm

    Debian: Naming USB devices with uDev http://tinyurl.com/of6kyq

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  • About Me


    photo of Samantha Halfon Samantha Halfon
    Software Engineer
    blueKiwi software
    Paris, France
    I enjoy playing with my computer(s), listening to Bob Dylan (and related artists) and watching movies (especially if they were directed by Martin Scorsese or John Cassavetes). Sometimes, I play a little guitar... If not doing any of the above, I am either riding a small red bike around Paris, or, making videos. About my videomaking please check out World Wide Angle and its blog.