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I'm trying to shrink a partition on a 64GB SD Card down so that I can fit it on a 32GB USB thumb drive, but I'm not having any success. I have the SD card plugged into a USB adapter, which is plugged into a Raspberry Pi running Raspbian.

Here is the output of fdisk -l:

Disk /dev/mmcblk0: 7948 MB, 7948206080 bytes
4 heads, 16 sectors/track, 242560 cylinders, total 15523840 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
Disk identifier: 0x0002c262

        Device Boot      Start         End      Blocks   Id  System
/dev/mmcblk0p1            8192      122879       57344    c  W95 FAT32 (LBA)
/dev/mmcblk0p2          122880    15523839     7700480   83  Linux

Disk /dev/sda: 63.9 GB, 63864569856 bytes
4 heads, 32 sectors/track, 974496 cylinders, total 124735488 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
Disk identifier: 0x000798a3

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1            4096      147455       71680    c  W95 FAT32 (LBA)
/dev/sda2          151552   124735487    62291968   83  Linux

It's /dev/sda2 that I want to shrink, but when I try resize2fs /dev/sda2 20G I get:

resize2fs 1.42.5 (29-Jul-2012)
resize2fs: Bad magic number in super-block while trying to open /dev/sda2
Couldn't find valid filesystem superblock.

I also tried shrinking the partition first via fdisk and then running resize2fs, but it failed with the same error message.

How can I shrink my partition?

PS. I have already imaged the card so I can restore should anything go wrong.

share|improve this question
Obviously it's not an ext[234] partition. Mount it and have a look at the output of mount. – Hauke Laging Feb 20 '14 at 8:18
It's f2fs, which helps explain why I was so confused because Raspbian doesn't seem to support it out of the box (if at all). I switched to booting into RaspBMC and can now mount. – me-- Feb 20 '14 at 9:21
up vote 1 down vote accepted

I don't understand the problem.

If the motivation for shrinking the partition is that you want to move it to another physical storage then the "shrinking magic" is:

  1. create the partition on the target storage

  2. format the new partition

  3. mount the partition (and the source partition)

  4. cp -a /path/to/source/. /path/to/target

Much faster, much easier, less dangerous, clean filesystem.

share|improve this answer
Thanks. I guess I was just over/under thinking it. I'm not very proficient in linux and just assumed imaging would be the safest way to ensure one takes a "perfect" backup. – me-- Feb 20 '14 at 10:42

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