Question 38382 in Ubuntu Question posted in
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How to specify SD card among multiple SD cards that don't have UUID – Ubuntu

Environment

  • Ubuntu-20.04 LTS
  • Bash shell

Question

How to define specific SD card to specific mount point when multiple SD card is inserted as same time and no UUID?

Background

I am working on a bash script which used to copy daily generated image from 2 cameras (front/rear-view) stored in coresponding SD card. The workflow would be somethings like this:

  1. Manually extract the SD cards from cameras (SD cards are labelled and assume they are inserted in correct order, e.g. front-camera always comes with the "A" SD card.)
  2. Insert to the SD card readers that already plugged into the host pc, ( /dev/sda and /dev/sdb )
  3. Automount to desired path , e.g. /media/user/front-sd-card and /media/user/rear-sd-card
  4. Run the script (which the source path is pre-defined as above) and start copying from source to dest

Challenge

I found that at this moment if I insert the rear-sd-card first, it will mount to /dev/sda/disk, and if I insert the front-sd-card first, it will mount to /dev/sda/disk. The next one would be /dev/sdb/disk1. So, which one is inserted first, which will be disk and the second one is disk1, this make human error possible…

Assume the operator insert to the correct card reader ( "A" sd card alwasys insert to sda card reader, and so to "B", this also generate human error if they dont follow).

I have run blkid and no UUID for both SD card, so I could not use UUID and set /etc/fstab to automount to correct mount directory.

Expectation

The "A" SD card and "B" SD card alwasys go to the desired mount point so that the script can pre-define the source path for copying to desired destination directory.

The copy task script is alredy ready and in use, but I want to minimise the human error due to the source pathing issue. So far is check manully before running the script.

I also think of adding a function to open a preview image of both Sd cards, and promot the user to answer yes/no, if the sequence is wrong, answer no and exit the script.

Any other suggestion of workflow also welcome.

Tags:

2

Answers


  1. 0

    If you are using those SD cards on an ongoing basis, you may as well bite the bullet and assign either a UUID or LABEL or both. Those operations are non-destructive to the content of the partition (they warn you that you should always do a backup before performing these operations), but the UUID/LABEL values are permanently changed and can be restored manually IF you kept track of what those values were before the operations.

    After you plugged in your SD card (I would do this one card at a time so you know which card is which),

    • enter mount -l to obtain the current details for mounted devices (specifically options for the SD card which may be required to create an fstab entry).
    • open ,
    • select the device from the drop-down menu at the upper-left,
    • then right-click on the line for the partition in question (there should be a "key" icon next to the /dev/${partition}, meaning locked on mounting),
    • then choose the unmount option.

    Now GParted will allow you to make changes to the SD card … so click and choose carefully! The little key icon should be gone.

    If you right-click on the partition again, you will now have options, including

    • Label File-system
    • New UUID

    enter image description here

    Option 1: UUID
    If you choose UUID, that will actually update the SD card with a new UUID (replace the previous UUID, or, add one where there was none before).

    Option 2: LABEL
    Your other option is to create a LABEL on your partition. If you choose that option, not only will it create a label, that operation also replaces any previously existing UUID with a new UUID to signify that the partition has been physically modified, namely a LABEL has now been assigned.

    So, basically, Option 2 is the better choice, unless you absolutely must keep the LABEL for code that uses that value.

    After that, setting up an fstab entry to perform mount based on UUID={…} or LABEL={…} is up to your preferences. Using UUID has become the standard approach for the most part but you might choose the LABEL approach for FRONT or BACK as labels.

    There are many examples available for details on how to do those various steps.

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  2. 0

    How to define specific SD card to specific mount point when multiple SD card is inserted as same time and no UUID?

    Detect with udev to which card reader the card was inserted and add a udev rule to mount it.

    This consist of watching udevadm monitor, inserting the card, then the second, watching the stream what values you can use for the rule. Then write a rule, which will look somewhere like https://github.com/crittermike/dotfiles/blob/master/udev/11-sd-cards-auto-mount.rules or and you can find many examples of udev rules online.

    See also See https://wiki.archlinux.org/title/persistent_block_device_naming .

    -l /dev/disk/by-path show something might be useful. pci-0000:00:14.0-usb-0:2.3:1.0-scsi-0:0:0:0-part1 for /sda1 and pci-0000:00:14.0-usb-0:2.4:1.0-scsi-0:0:0:0-part1 for /sdb1

    Great, so just mount /dev/disk/pci-0000:00:14.0-usb-0:2.3:1.0-scsi-0:0:0:0-part1 /where/you/want/to/mount/one/card and similar for the other one..

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