[TriLUG] using parted to change the size of a loop mounted filesystem

[Robert Dale]

As parted implies, it works with partitions.  You could resize a
partition in a file, as if the file were a disk of partitions. I'm not
aware of it resizing filesystems directly in a file.

However, you don't need parted to do it!  You can resize a file with
dd and grow/shrink the fs accordingly.

Let's try it...

First create the file that will hold the filesystem...
# dd if=/dev/zero of=foo.part bs=1M count=100
100+0 records in
100+0 records out
104857600 bytes (105 MB) copied, 0.742415 s, 141 MB/s


# mkfs.ext3 foo.part
mke2fs 1.41.14 (22-Dec-2010)
foo.part is not a block special device.
Proceed anyway? (y,n) y
Filesystem label=
OS type: Linux
Block size=1024 (log=0)
Fragment size=1024 (log=0)
Stride=0 blocks, Stripe width=0 blocks
25688 inodes, 102400 blocks
5120 blocks (5.00%) reserved for the super user
First data block=1
Maximum filesystem blocks=67371008
13 block groups
8192 blocks per group, 8192 fragments per group
1976 inodes per group
Superblock backups stored on blocks:
	8193, 24577, 40961, 57345, 73729

Writing inode tables: done
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 38 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.

# mount -o loop foo.part /mnt
# df -h
Filesystem                        Size  Used Avail Use% Mounted on
/dev/loop0                         96M  4.1M   87M   5% /mnt

Note our 96M filesystem.  Now let's grow it!

# umount /mnt
# dd if=/dev/zero of=foo.part bs=1M count=100 seek=100
100+0 records in
100+0 records out
104857600 bytes (105 MB) copied, 0.152461 s, 688 MB/s

# resize2fs foo.part 180M
resize2fs 1.41.14 (22-Dec-2010)
Please run 'e2fsck -f foo.part' first.

# e2fsck -f foo.part
e2fsck 1.41.14 (22-Dec-2010)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
foo.part: 11/25688 files (0.0% non-contiguous), 8913/102400 blocks

# resize2fs foo.part 180M
resize2fs 1.41.14 (22-Dec-2010)
Resizing the filesystem on foo.part to 184320 (1k) blocks.
The filesystem on foo.part is now 184320 blocks long.

# mount -o loop foo.part /mnt
# df -h
Filesystem                        Size  Used Avail Use% Mounted on
/dev/loop0                        173M  4.2M  160M   3% /mnt

Now the filesystem is 173M. It worked!

To shrink, resize2fs first, then use dd or your favorite tool to
truncate the file.

Enjoy.

On Wed, Mar 14, 2012 at 10:28 PM, Joseph Mack NA3T <jmack at wm7d.net> wrote:
> parted can change the size of an unmounted partition carrying a filesystem.
>
> A file carrying a filesystem within it and which can be loop mounted, could
> have its size changed too. I expect doing so would be quite a different
> kettle of fish.
>
> google doesn't show anyone doing this at least with parted. Has it just not
> been implemented?
>
> (I could make a new file and copy everything from the old file to the file
> etc, but that seems so old fashioned. I'd hoped there was a better way)
>
> Thanks
> Joe
>
> --
> Joseph Mack NA3T EME(B,D), FM05lw North Carolina
> jmack (at) wm7d (dot) net - azimuthal equidistant map
> generator at http://www.wm7d.net/azproj.shtml
> Homepage http://www.austintek.com/ It's GNU/Linux!
> --
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-- 
Robert Dale