"No space left on device" error when custom image is larger than source image.

[zsilet]

Background - I am using the pidock repo to create a raspi image that has a variety of development tools pre-installed. I came across the problem below during this process. Overall, I am very thankful that you put these scripts together. Even as part of debugging the issue I found, I learned quite a bit.

Please let me know if the proposed solution is acceptable and if I may push it to your repo on a branch. I would rather have it go to your mainline then to create yet another fork of your work.

Problem

When using the CUSTOM_IMG_SIZE option, the maximum image size is still limited by the size of the "source" image (raspbian.img). If subsequently the Dockerfile is used to install enough applications to exceed the "source" image size, the compose.sh step ends up failing with a "No space left on device" error during the step "sudo tar xf custom-root.tar -C /mnt --numeric-owner"

Root cause

The compose.sh step "sfdisk ${CUSTOM_IMG_NAME} < "${PT_FILENAME}" transfers the partition sizing from the "source" image to the destination. This means that even though the destination may have 4GB reserved by default, the new destination partition will be the size of the source partition, with free space left over.

Solution

Immediately after creating the two partitions from the partition_table.txt file, invoke sfdisk to expand partition 2 to use all available space on the destination image. The command to do this is

echo ", +" | sfdisk custom.img -N 2

where ", +" tells sfdisk that the second (partition size) argument "+" it is looking for as input should increase partition size to capacity. Alternately a number can be added to increase the partition by a specific size, but that seems unnecessary here.

Example output:

 dd if=/dev/zero of=./custom.img bs=1M count=4096
4096+0 records in
4096+0 records out
4294967296 bytes (4.3 GB, 4.0 GiB) copied, 6.59568 s, 651 MB/s
+ sfdisk custom.img
Checking that no-one is using this disk right now ... OK

Disk custom.img: 4 GiB, 4294967296 bytes, 8388608 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

>>> Script header accepted.
>>> Script header accepted.
>>> Script header accepted.
>>> Script header accepted.
>>> Script header accepted.
>>> Created a new DOS disklabel with disk identifier 0x43f6ece2.
custom.img1: Created a new partition 1 of type 'W95 FAT32 (LBA)' and of size 256 MiB.
custom.img2: Created a new partition 2 of type 'Linux' and of size 1.5 GiB.
custom.img3: Done.

New situation:
Disklabel type: dos
Disk identifier: 0x43f6ece2

Device      Boot  Start     End Sectors  Size Id Type
custom.img1        8192  532479  524288  256M  c W95 FAT32 (LBA)
custom.img2      532480 3686399 3153920  1.5G 83 Linux

The partition table has been altered.
Syncing disks.
+ echo ', +'
+ sfdisk custom.img -N 2
Checking that no-one is using this disk right now ... OK

Disk custom.img: 4 GiB, 4294967296 bytes, 8388608 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: 0x43f6ece2

Old situation:

Device      Boot  Start     End Sectors  Size Id Type
custom.img1        8192  532479  524288  256M  c W95 FAT32 (LBA)
custom.img2      532480 3686399 3153920  1.5G 83 Linux

custom.img2: 
New situation:
Disklabel type: dos
Disk identifier: 0x43f6ece2

Device      Boot  Start     End Sectors  Size Id Type
custom.img1        8192  532479  524288  256M  c W95 FAT32 (LBA)
custom.img2      532480 8388607 7856128  3.7G 83 Linux

The partition table has been altered.
Syncing disks.

Testing

Verified that with the addition of this command, a destination image is created which has more used disk space than the source image.

[zsilet]

I have a branch ready with a fix if you give me permission to push it up.

[eringr]

Thanks for addressing this and taking the time to upstream it. It was clunky about partition vs image sizes and this is a good fix. Push what you want and I'll merge

[zsilet]

Created PR #3