[SOLVED] Why would a faulty(?) SD card prevent Debian from booting?

Hello,

After cleanly rebooting an appliance that runs Debian off a USB key drive, I proceeded to move the drive to a Linux workstation, and image it for the day when it dies and I need to build a new one fast.

This appliance also has an FAT32-formatted SD card that I use as an easy way to copy files to/from Windows. The whole Debian system lives on the USB key drive.

But when I slid the USB drive back into the appliance, the /boot partition loaded OK, but / didn't:

…
[  OK  ] Reached target Swap.
[  OK  ] Started File System Check on /dev/d…106d8-83af-47ab-bd56-bdfd2d4711f3.
         Mounting /boot...
[   13.925920] EXT4-fs (sda1): mounting ext2 file system using the ext4 subsystem
[   13.942175] EXT4-fs (sda1): mounted filesystem without journal. Opts: (null)
[  OK  ] Mounted /boot.
[ TIME ] Timed out waiting for device dev-disk-by\x2duuid-BF90\x2dFE5B.device.
[DEPEND] Dependency failed for /mnt/sdcard.
[DEPEND] Dependency failed for Local File Systems.
[  OK  ] Started ifup for eth0.
         Starting Raise network interfaces...
[  OK  ] Reached target Timers.
[  OK  ] Closed Syslog Socket.
[  OK  ] Reached target Login Prompts.
         Starting Create Volatile Files and Directories...
[  OK  ] Started Emergency Shell.
[  OK  ] Reached target Sockets.
[  OK  ] Reached target Emergency Mode.
[  OK  ] Started Create Volatile Files and Directories.
[  OK  ] Reached target System Time Synchronized.
         Starting Update UTMP about System Boot/Shutdown...
[  OK  ] Started Update UTMP about System Boot/Shutdown.
         Starting Update UTMP about System Runlevel Changes...
[  OK  ] Started Update UTMP about System Runlevel Changes.
[  OK  ] Started Raise network interfaces.
[  OK    102.699581] IPv6: ADDRCONF(NETDEV_UP): eth0: link is not ready
m] Reached target Network.
[  OK  ] Reached target Network is Online.

You are in emergGive root password for maintenance
(or press Control-D to continue): [  104.403462] mv643xx_eth_port mv643xx_eth_port.0 eth0: link u                  p, 
Give root password for maintenance
(or press Control-D to continue):

After a bit of head scratching, it appears the issue was not with the USB key drive's root filesystem, but with the SD card: After commenting it out in /etc/fstab and rebooting, Debian went up successfully.

Considering fsck says nothing and the whole Debian lives in the USB drive… why does the SD card prevent Debian from booting up?

~# cat /etc/fstab
UUID=2ef427a6-37b0-494a-9eda-5f627e2d633f /               ext4    errors=remount-ro 0       1
UUID=d71106d8-83af-47ab-bd56-bdfd2d4711f3 /boot           ext2    defaults        0       2
UUID=7d3971ad-2dca-4ae6-b67a-27b2190df289 none            swap    sw              0       0

#SD card
#UUID=BF90-FE5B /mnt/sdcard     vfat    dmask=000,fmask=0177,user       0       0
#Debian could start OK after I commented out the following line
#UUID=BF90-FE5B /mnt/sdcard     vfat    dmask=000,fmask=0111,user       0       0

~# fsck /dev/mmcblk0p1
fsck from util-linux 2.29.2
fsck.fat 4.1 (2017-01-24)
/dev/mmcblk0p1: 3 files, 18971/1952650 clusters

Thank you.

* dd if=/dev/sdc of=My.appliance.boot.image.dd conv=notrunc status=progress

This is not about a corrupted filesystem. The error is "Timed out waiting for device". My guess: The card reader has intermittent problems or takes too long to get activated.

EDIT: You could use options nofail or x-systemd.device-timeout. See https://www.freedesktop.org/software...emd.mount.html.

Thank you.

From (reading) your other threads, you have an ARM device, which uses a FAT partition to load the bootloader for the Arm processor, that then reads Debian from a Linux file system.

So, you should have /dev/mmcblk0p1 which will be FAT file system, & /dev/sda1 which is your ext2 Debian file system.
The FAT partition will be /boot, the ext2 partition is the rest of the Debian system (/).

EDIT: This is where your boot process is failing...
[ TIME ] Timed out waiting for device dev-disk-by\x2duuid-BF90\x2dFE5B.device.
[DEPEND] Dependency failed for /mnt/sdcard.
[DEPEND] Dependency failed for Local File Systems.

Not sure why it says /mnt/sdcard - likely this could be where you need to look.