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I have a block device. It is removed from the system and later added again. How can I verify that it is exactly the same device?

The device will always be a mass storage device (which I'm not planning to write to and will only mount read-only).

I could md5sum both devices and verify that the hashes match, but this is time consuming for large storage devices.

Is there a quicker method?

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  • What kind of devices are you thinking of? The identification can be different depending of the kind of device. Mass storage devices (HDD, SSD, USB pendrive memory card), or also other devices, that are seen as block devices? Must the identification be fully automatic and 100 % reliable, or can you check/verify manually, so the automatic identification is only a help tool?
    – sudodus
    Commented Jun 15, 2018 at 13:47
  • @sudodus It will always be a mass storage device, and the identification has to be fully automatic and generally reliable (knowing it "might be a different device" and having to verify manually is okay if it means the automated method is fast, compared to 100% reliability but really slow). Commented Jun 15, 2018 at 13:59

3 Answers 3

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The output of fdisk -l $device includes a line starting 'Disk identifier:' with some detail from the device that is usually unique and persistent for it. Illustration:

# fdisk -l /dev/sda | grep 'Disk identifier:'
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You could use the devices UUID. lsblk -f or blkid .

UUID can be set (with tune2fs) but for most use cases it should be unique enough.

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Hardcoded unique(?) ID

Most mass storage devices (maybe not all) have a hardcoded unique ID, that is seen at /dev/disk/by-id. The following command line will show this ID,

sudo ls -l /dev/disk/by-id|grep -v '[1-9]$'|tr -s ' ' '\t'|cut -f 9- | sed 's#../../#/dev/#'

and also show which block device it is represented by, '-> /dev/sdx'

Example (my working computer with three USB pendrives connected),

$ sudo ls -l /dev/disk/by-id|grep -v '[1-9]$'|tr -s ' ' '\t'|cut -f 9- | sed 's#../../#/dev/#'

ata-HL-DT-STDVD+-RW_GSA-H21L    ->  /dev/sr0
ata-KINGSTON_SKC300S37A120G_50026B724703BCA8    ->  /dev/sda
ata-WDC_WD4002FYYZ-01B7CB1_K3GWHAEB ->  /dev/sdb
usb-Corsair_Voyager_GT_3.0_070883862E1B9719-0:0 ->  /dev/sdc
usb-SanDisk_Cruzer_Blade_200429068118E7C2CFFD-0:0   ->  /dev/sde
usb-SanDisk_Cruzer_Blade_200429068118F440A09E-0:0   ->  /dev/sdd
wwn-0x5000cca25ccc7f97  ->  /dev/sdb
wwn-0x50026b724703bca8  ->  /dev/sda

UUID of file system(s)

If there are partitions with file systems, there are also UUIDs for each file system, and these are often but not always unique, depending on if they were created individually or cloned from some common original file system or image file. The UUIDs can be shown by blkid and by lsblkvia the following command line,

lsblk -l -o name,size,UUID,model

Example (my working computer with three USB pendrives connected),

$ lsblk -l -o name,size,UUID,model
NAME   SIZE UUID                                 MODEL
sda  111,8G                                      KINGSTON SKC300S
sda1 106,9G 0ac1cb43-1609-4fc3-8c69-3e21299729bc 
sda2     5G 6d54c49d-31ac-45fe-917c-2335bcfe7399 
sdb    3,7T                                      WDC WD4002FYYZ-0
sdb1   510M 9F05-5B18                            
sdb2     5G 08b7164f-8852-451b-9624-63b16a66359a 
sdb3    10G fa242ddd-90f8-4603-af5c-c89f4b71ac70 
sdb4    15G 491a6a2b-4867-44d5-94d8-082f79066a5a 
sdb5     1M                                      
sdb6   100G 44156f43-0958-4ea1-800d-b02afbc7d306 
sdb7   3,5T 862210fd-a6fd-4fe3-913c-e18e1448ef36 
sdb8     5G 6958d86a-57a9-4e40-8376-1e41258e5810 
sdc   29,5G                                      Voyager GT 3.0  
sdc1   9,1G 38028BF9184E3FB4                     
sdc2     1M                                      
sdc3   244M 4299-B748                            
sdc4   1,8G 2018-04-26-18-43-51-00               
sdc5  18,4G 033ffb75-518d-4335-89cb-ef7d159cf20b 
sdd    3,7G 2016-08-24-07-06-03-00               Cruzer Blade    
sdd1   1,3G 2016-08-24-07-06-03-00               
sde    3,7G 2016-07-19-21-27-51-00               Cruzer Blade    
sde1   1,4G 2016-07-19-21-27-51-00               
sde2   2,3M 0F7B-9366                            
sr0   1024M                                      DVD+-RW GSA-H21L

These methods are enough to help me identify the connected mass storage devices after a quick manual inspection.

It is possible to use the hardcoded ID and/or the UUIDs automatically. For example, you can create a corresponding md5sum for every mass storage device that you have, and store the md5sums in variables in a shellscript, where you can check for matches.

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