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Boot-partition mounts as msdos instead of vfat

December 01, 2022 — BarryK

If you click on the boot-partition of the usb-stick, it will mount and will show in the file manager, as expected; however, it has mounted as the title says, as an msdos filesystem instead of vfat.

Way back in the early days of the FAT filesystem, all files were "8.3", that is, maximum eight-character name and maximum three-character extension. Microsoft introduced an extension to allow longer filenames, and also to store upper-case and lower-case characters -- though FAT remained case-insensitive.

The old 8.3 is what we call the "msdos" filesystem, and the extension is "vfat". The problem that has mysteriously appeared is that when click on the boot-partition, it mounts as msdos.

To show the difference, first mount as vfat:

# busybox mount -t vfat /dev/sdc1 /mnt/sdc1


...and I have created a file with long name, with mix of upper and lower case characters. Now, unmount and remount as msdos:

# busybox mount -t msdos /dev/sdc1 /mnt/sdc1


...hmmm, it has been a very very long time since I have seen 8.3 files.

I am reporting the problem, don't know why it is happening. I only recall seeing it in about the last month. A change in the kernel FAT driver?

Trying to think what has changed in the last month or so... the kernel yes, but also changed from using busybox 'blkid' to the full 'blkid' utility. OK, comparing them, where sdb1 is the boot-partition on the 4.5.2 usb-stick:

# blkid /dev/sdb1
/dev/sdb1: SEC_TYPE="msdos" UUID="260A-C6D3" BLOCK_SIZE="512" TYPE="vfat" PARTUUID="03fa83c2-01"
# busybox blkid /dev/sdb1
/dev/sdb1: UUID="260A-C6D3" TYPE="vfat"

...interesting, what is that "SEC_TYPE" reported by the full 'blkid'?

One of the internal drives has a fat32 partition, sda2:

# blkid /dev/sda2
/dev/sda2: LABEL_FATBOOT="HDDESP" LABEL="HDDESP" UUID="9473-48E1" BLOCK_SIZE="512" TYPE="vfat" PARTUUID="90182abe-5fe0-4cf5-b2b5-ddb6b732f09c"
# busybox blkid /dev/sda2
/dev/sda2: LABEL="HDDESP" UUID="9473-48E1" TYPE="vfat" problem with that, mounts as vfat.

Just reporting the problem, as working on something else right now and don't want to break the train of thought.

A thought: fat12 is so ancient, might have to go up to fat16, but also will need to increase the size of the boot-partition.    

Tags: easy