Can't properly flash some micro SD cards

Question

I have a couple of Micro SD card here and it seems like only some of them can be flashed correctly. No errors during the flashing process, but only the boot partition turns out to be mountable on my Linux computer and so the RPi fails to boot it (Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(179,2)).
At first I assumed that the issue was just with a very old card that I had lying around (broken sectors or something like that).
But now I have bought a brand new 16GB MicroSD card (SanDisk 16GB 80MB/S), and I get the exact same result: Flashing seems to work, but only the boot partition becomes mountable.

I flashed using:

sudo dd bs=4M if=2017-08-16-raspbian-stretch.img of=/dev/mmcblk0 status=progress conv=fsync

4907335680 bytes (4.9 GB, 4.6 GiB) copied, 397.067 s, 12.4 MB/s
1170+1 records in
1170+1 records out
4907675648 bytes (4.9 GB, 4.6 GiB) copied, 452.665 s, 10.8 MB/s

and then I also I also tried:

sudo dd bs=1M if=2017-08-16-raspbian-stretch.img of=/dev/mmcblk0 status=progress conv=fsync

4906287104 bytes (4.9 GB, 4.6 GiB) copied, 399.06 s, 12.3 MB/s  
4680+1 records in
4680+1 records out
4907675648 bytes (4.9 GB, 4.6 GiB) copied, 451.091 s, 10.9 MB/s

Using the lite image instead didn't make a difference.

I also bought a new cheap Fujitsu card that only has 2GB and that card flashed just fine.

My Micro SD cards:

• A very old Vertatim 2GB card (flashing etc works fine)
• A very old SanDisk 8GB card (flashing etc doesn't work correctly)
• A new Fujitsu 2GB card (flashing etc works fine)
• A new SanDisk 16GB card (flashing etc doesn't work correctly)

It almost seems like there are issues with cards bigger than 2GB.

What am I doing wrong?

Edit: The output of sudo fdisk -l /dev/mmcblk0:

Disk /dev/mmcblk0: 14.9 GiB, 15931539456 bytes, 31116288 sectors
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: 0x242ad76d

Device         Boot Start     End Sectors  Size Id Type
/dev/mmcblk0p1       8192   93814   85623 41.8M  c W95 FAT32 (LBA)
/dev/mmcblk0p2      94208 9585303 9491096  4.5G 83 Linux

Edit 2:

Output of sudo cmp /dev/mmcblk0 2017-08-16-raspbian-stretch.img

/dev/mmcblk0 2017-08-16-raspbian-stretch.img differ: byte 4194370, line 1

Edit 3: I just bought another 8GB Micro SD card, this time from the brand 'Intenso'. - Same issue with that card.

Edit 4: Tried it with Etcher instead of dd. - Same results.

Edit 5: I tried it with dd on a different computer and it was able to correctly flash all my cards. But I still need this to work on my system...

Answer 1

To be sure that all writes are done after a dd, be sure to use the command sync. Once sync command brings back the prompt, you can then eject the SD card, never before. Some SD may takes more time to write their buffer and ejecting before all writes are done just corrupt it.

If you properly sync your SD card and still endure issue, this may be related to the hardware, maybe a faulty SD card. You can check if the kernel doesn't provide I/O error with sudo dmesg.

Answer 2

If you are executing those commands on a running RPi, you are writing to the running system (of=/dev/mmcblk0) unless I'm missing something in your explanation. I'd expect your command line to look like:

sudo dd bs=1M if=2017-08-16-raspbian-stretch.img of=/dev/sda status=progress conv=fsync

Targeting a card mounted in a reader at /dev/sda as the target for writing.

Answer 3

Check the image after writing it and see if it verifies.

Do your normal copy:

sudo dd bs=4M if=2017-08-16-raspbian-stretch.img of=/dev/mmcblk0 status=progress conv=fsync

4907335680 bytes (4.9 GB, 4.6 GiB) copied, 397.067 s, 12.4 MB/s
1170+1 records in
1170+1 records out
4907675648 bytes (4.9 GB, 4.6 GiB) copied, 452.665 s, 10.8 MB/s

Then see if the written image is the same as the download:

$ sudo cmp /dev/mmcblk0 2017-08-16-raspbian-stretch.img
cmp: EOF on 2017-08-16-raspbian-stretch.img

If you get the EOF message, then verification has succeeded and the image on the card seems to match the download. Normally I'd suggest verifying the image itself (checksum or such), but you are saying that writing the image to other cards works. So that seems to point to the image being okay.

If the card is having a problem, then you should get a message about the first location where there is a difference between the two.

Answer 4

I came here having similar problems: One card flashing fine, one failing repeatedly. It finally worked when I did

dd if=... of=...
sync

instead of

dd bs=4M if=... of=... conv=fsync

Answer 5

I just encountered the same problem and I finally succeed after using a microsd adapter to flash directly instead of using a sd to microsd adapter in between. Hope that helps!