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/path/to/directory/ is a path that points within an encrypted volume, to an arbitrary depth. In a bash script I need to determine if the block device related to this path is a removable device. I'm using Arch Linux.

I have looked at a lot of similar questions (such as these listed below and others) but did not find a suitable answer:

This is an example of what I'm working with:

findmnt -n -o SOURCE --target /path/to/directory/
/dev/mapper/luksdev[/@subvolume]

findmnt -D --target /path/to/directory
SOURCE                         FSTYPE  SIZE   USED AVAIL USE% TARGET
/dev/mapper/luksdev[/@subvolume] btrfs   4.5T 203.5G  4.3T   4% /path/to/directory

df -P /path/to/directory/ | awk 'END{print $1}'
/dev/mapper/luksdev

(The findmnt parameter --target seems to be required if the path is not the exact mountpoint.)

If the script can determine the block device (e.g., /dev/sda1) associated with /dev/mapper/luksdev, I get a step closer:

udevadm info --query=all --name=/dev/sda1 | grep ID_BUS | grep "=usb"
E: ID_BUS=usb

But I assume not all removable devices are usb, right?

By the way, I am OK with methods specific to BTRFS, if that makes this any easier. I did check:

btrfs - Find physical block device of root filesystem on an encrypted filesystem? - Unix & Linux Stack Exchange

EDIT: based on answer by Vojtech Trefny, here is what I have:

mapper_path=$(findmnt -n -o SOURCE --target /path/to/directory/ | cut -d [ -f 1)
mydev=$(lsblk -sl -o NAME /${mapper_path} | tail -n 1)
drive_name=$(udisksctl info -b /dev/${mydev} | grep "Drive:" | cut -d"'" -f2)
drive_name=$(echo $drive_name | sed -e 's|/org/freedesktop/UDisks2/drives/||')
udisksctl info -d ${drive_name} | grep "\sRemovable:" | cut -d":" -f2 | tr -d "[:blank:]"

1 Answer 1

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From the /dev/mapper path, the easiest way to get the disk name should be lsblk with -s to list devices in inverse order:

$ lsblk -sl -o NAME /dev/mapper/<name> | tail -1
sda

Easiest way from here is probably to check removable property from sysfs

$ cat /sys/block/sda/removable
0

but I'd recommend using UDisks here, it does some extra checks on top of the sysfs information so I assume sysfs can be wrong about some removable devices. You can either use busctl to communicate with UDisks over DBus or udisksctl and grep from the output.

$ busctl get-property org.freedesktop.UDisks2 /org/freedesktop/UDisks2/block_devices/sda org.freedesktop.UDisks2.Block Drive 
o "/org/freedesktop/UDisks2/drives/<drive_name>"

$ busctl get-property org.freedesktop.UDisks2 /org/freedesktop/UDisks2/drives/<drive_name> org.freedesktop.UDisks2.Drive Removable 
b false

or

$ udisksctl info -b /dev/sda | grep "Drive:" | cut -d"'" -f2
/org/freedesktop/UDisks2/drives/<drive_name>

$ udisksctl info -d <drive_name> | grep "\sRemovable:" | cut -d":" -f2 | tr -d "[:blank:]"
false
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  • Very helpful. Thank you. Unfortunately, when using either busctl or udisksctl I get the error Error looking up object for drive /org/freedesktop/UDisks2/drives/SanDisk_Cruzer_Blade_XYZ123456789. If I use /sys/block/sdX/removable it does give the expected value of 1 for USB sticks, but for a removable USB HDD (WD Elements) it reports 0.
    – MountainX
    Commented Oct 10, 2020 at 7:20
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    @MountainX that's because it's not removable. You can't the platter and change it with another ;-) What you're asking for is impossible. You can only make "educated" guesses (USB -> "removable", etc).
    – user313992
    Commented Oct 10, 2020 at 7:31
  • @MountainX realpath /sys/block/sda will tell you the full path to the device. Starting from there, you can make some guesses.
    – user313992
    Commented Oct 10, 2020 at 7:41
  • @MountainX Is the drive visible in udisksctl dump? If the sda object says the drive is /org/freedesktop/UDisks2/drives/SanDisk_Cruzer_Blade_XYZ123456789 and then the drive object is not there, that's a bug in UDisks, unfortunately. Commented Oct 10, 2020 at 7:47
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    @VojtechTrefny: I figured the issue out, and accepted your answer. See edit in my question for details.
    – MountainX
    Commented Oct 10, 2020 at 8:14

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