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#bananapi → On how compressed files should be used

Submitted by gwolf on Thu, 09/25/2014 - 11:37

I am among the lucky people who got back home from DebConf with a brand new computer: a Banana Pi. Despite the name similarity, it is not affiliated with the very well known Raspberry Pi, although it is a very comparable (although much better) machine: A dual-core ARM A7 system with 1GB RAM, several more on-board connectors, and same form-factor.

I have not yet been able to get it to boot, even from the images distributed on their site (although I cannot complain, I have not devoted more than a hour or so to the process!), but I do have a gripe on how the images are distributed.

I downloaded some images to play with: Bananian, Raspbian, a Scratch distribution, and Lubuntu. I know I have a long way to learn in order to contribute to Debian's ARM port, but if I can learn by doing... ☻

So, what is my gripe? That the three images are downloaded as archive files:

  1. 0 gwolf@mosca『9』~/Download/banana$ ls -hl \
  2. > Lubuntu_For_BananaPi_v3.1.1.tgz Raspbian_For_BananaPi_v3.1.tgz \
  3. > Scratch_For_BananaPi_v1.0.tgz
  4. -rw-r--r-- 1 gwolf gwolf 222M Sep 25 09:52
  5. -rw-r--r-- 1 gwolf gwolf 823M Sep 25 10:02 Lubuntu_For_BananaPi_v3.1.1.tgz
  6. -rw-r--r-- 1 gwolf gwolf 1.3G Sep 25 10:01 Raspbian_For_BananaPi_v3.1.tgz
  7. -rw-r--r-- 1 gwolf gwolf 1.2G Sep 25 10:05 Scratch_For_BananaPi_v1.0.tgz

Now... that is quite an odd way to distribute image files! Specially when looking at their contents:

  1. 0 gwolf@mosca『14』~/Download/banana$ unzip -l
  2. Archive:
  3. Length Date Time Name
  4. --------- ---------- ----- ----
  5. 2032664576 2014-09-17 15:29 bananian-1409.img
  6. --------- -------
  7. 2032664576 1 file
  8. 0 gwolf@mosca『15』~/Download/banana$ for i in Lubuntu_For_BananaPi_v3.1.1.tgz \
  9. > Raspbian_For_BananaPi_v3.1.tgz Scratch_For_BananaPi_v1.0.tgz
  10. > do tar tzvf $i; done
  11. -rw-rw-r-- bananapi/bananapi 3670016000 2014-08-06 03:45 Lubuntu_1404_For_BananaPi_v3_1_1.img
  12. -rwxrwxr-x bananapi/bananapi 3670016000 2014-08-08 04:30 Raspbian_For_BananaPi_v3_1.img
  13. -rw------- bananapi/bananapi 3980394496 2014-05-27 01:54 Scratch_For_BananaPi_v1_0.img

And what is bad about them? That they force me to either have heaps of disk space available (2GB or 4GB for each image) or to spend valuable time extracting before recording the image each time.

Why not just compressing the image file without archiving it? That is,

  1. 0 gwolf@mosca『7』~/Download/banana$ tar xzf Lubuntu_For_BananaPi_v3.1.1.tgz
  2. 0 gwolf@mosca『8』~/Download/banana$ xz Lubuntu_1404_For_BananaPi_v3_1_1.img
  3. 0 gwolf@mosca『9』~/Download/banana$ ls -hl Lubun*
  4. -rw-r--r-- 1 gwolf gwolf 606M Aug 6 03:45 Lubuntu_1404_For_BananaPi_v3_1_1.img.xz
  5. -rw-r--r-- 1 gwolf gwolf 823M Sep 25 10:02 Lubuntu_For_BananaPi_v3.1.1.tgz

Now, wouldn't we need to decompress said files as well? Yes, but thanks to the magic of shell redirections, we can just do it on the fly. That is, instead of having 3×4GB+1×2GB files sitting on my hard drive, I just need to have several files ranging between 145M and I guess ~1GB. Then, it's as easy as doing:

  1. 0 gwolf@mosca『8』~/Download/banana$ dd if=<(xzcat bananian-1409.img.xz) of=/dev/sdd

And the result should be the same: A fresh new card with Bananian ready to fly. Right, right, people using these files need to have xz installed on their systems, but... As it stands now, I can suppose current prospective users of a Banana Pi won't fret about facing a standard Unix tool!

(Yes, I'll forward this rant to the Banana people, it's not just bashing on my blog :-P )

[update] Several people (thanks!) have contacted me stating that I use a bashism: The <(…) construct is specific to Bash. If you want to do this with any other shell, it can be done with a simple pipe:

  1. $ xzcat bananian-1409.img.xz | dd of=/dev/sdd

That allows for less piping to be done on the kernel, and is portable between different shells. Also, a possibility would be:

  1. $ xzcat bananian-1409.img.xz > /dev/sdd

Although that might not be desirable, as it avoids the block-by-block nature of dd. I'm not sure if it makes a realdifference, but it's worth saying :)

And yes, some alternatives for not unarchiving the file — Here in the blog, an anon commenter suggests (respectively, for zip and .tar.gz files):

  1. $ dd if=<(unzip -p of=/dev/sdd
  2. $ dd if=<(tar -xOf Lubuntu_For_BananaPi_v3.1.1.tgz) of=/dev/sdd

And a commenter by IRC suggests:

  1. $ paxtar -xOaf Raspbian_For_BananaPi_v3.1.tgz Raspbian_For_BananaPi_v3_1.img | sudo dd bs=262144 of=/dev/


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