Re: W3DJS Raspberry Pi Ham Radio Distribution v2.0 Released

Ray Wells


I feel some misinformation is starting to emerge re dd, img files and xz compression that needs clarification, especially since many individuals on this list are "feeling" their way and don't need the wrong information.

Big snips to remove ballast and, no names, no pack drill!

1.    "Because 'HamPi_v1.0.img.xz' is a proprietary compressed format,"

xz is not proprietary, all source code is released into the public domain, with xz Utils being subject to various version of GPL.
Also, binaries are available for FreeBSD, Linux systems, Microsoft Windows (since v 5.0), and FreeDOS. A complete list of supported OSs (including Mac OSX), and all licensing information can be found here

2.    "In this scenario, 'dd' will not work as it is expecting an image (.img), not a 'compressed disk image' (.xz). "

dd isn't expecting or rejecting any file type, it does an exact bit for bit copy of any file type, or entire disk partition(s). It's a cloning tool that produces an exact duplicate of the source. Remember, if you clone <name>.img.xz to another device (SD Card, etc) you will still have <name>.img.xz - dd does not uncompress, that's not its job. If you want dd to create an SD Card containing the OS image you need to uncompress first with "unxz <name>.img.xz" (or use tar with appropriate command line options), and then use dd. For Linux you may have to first install xz-utils with sudo apt-get install xz-utils. Non-Linux users should obtain a binary for their OS, see the project site, above. As previously stated elsewhere, Balena Etcher uncompresses a xz file as a transparent step in creating the image.

3.    "I would be careful with assuming dd will work in macOS."

Evidence suggests that dd does work with the Mac OS, and being that it uses a variant of BSD (another 'Nix OS) that's not surprising, but I'm not a Mac OS user.  Here's the man page for dd on Mac OS

HTH somebody.

Ray vk2tv

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