Can't mount a USB Flash after using `dd`

Konst

10/28/23, 11:57 AM

i'm newbie in Linux. And i was practicing using dd with my USB flash. Here's what it looked like at the very beginning:

sdb 8:16 1 7.5G 0 disk
└─sdb1 8:17 1 7.5G 0 part /media/old/28B9-91AE

and

Disk /dev/sdb: 7.45 GiB, 8004304896 bytes, 15633408 sectors
Disk model: Cruzer Switch   
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x00000000
Device     Boot Start      End  Sectors  Size Id Type
/dev/sdb1          32 15633407 15633376  7.5G  b W95 FAT32

But after this command dd if=/dev/mapper/vgubuntu-root of=/dev/sdb1 status=progress flash was unmounted (still visible in lblk as before, but withount mountpoint) and i couldn't mount it back using mount /dev/sdb1 /media/old/usb, got this error:

mount: /media/old/usb: wrong fs type, bad option, bad superblock on /dev/sdb1, missing codepage or helper program, or other error.

dmesg showed me this:

[91674.360598]  sdb: sdb1
[91674.361844] sd 1:0:0:0: [sdb] Attached SCSI removable disk
[91674.554703] EXT4-fs (sdb1): bad geometry: block count 116137984 exceeds size of device (1954172 blocks)
[91678.031627] EXT4-fs (sdb1): bad geometry: block count 116137984 exceeds size of device (1954172 blocks)
[91754.132008] EXT4-fs (sdb1): bad geometry: block count 116137984 exceeds size of device (1954172 blocks)
[92587.188449] FAT-fs (sdb1): bogus number of reserved sectors
[92587.188457] FAT-fs (sdb1): Can't find a valid FAT filesystem
[92863.793347] EXT4-fs (sdb1): bad geometry: block count 116137984 exceeds size of device (1954172 blocks)

And since there were no important files there, i just formatted the flash to FAT. And that solved a problem. But i still can't figure out what was the mistake and how i could have avoided it.

0 + 2

usb

mount

Jos

10/28/23, 12:12 PM

You tried to copy a member of a volume group to a FAT32 filesystem. That is a different type of filesystem.

Konst

10/30/23, 2:36 PM

@Jos thank you a lot

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EN: Can't mount a USB Flash after using `dd`

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