Support creating an installer from `InstallOS.pkg`

[madsmtm]

The macOS 10.12 link (and probably the others) on Apple's official download page ends up downloading InstallOS.dmg, which in turn contains InstallOS.pkg, which is fairly troublesome to convert to the Install macOS Sierra.app that createinstalliso expects.

What's the recommended approach for these?

From my own testing, I ended up being able to create the iso after following the steps below (though not sure it actually runs yet):

1. Open InstallOS.dmg to get access to InstallOS.pkg
2. Unpack InstallOS.pkg and then InstallOS.pkg/Payload using instructions in https://stackoverflow.com/questions/11298855/how-to-unpack-and-pack-pkg-file (or maybe just pkgutil --expand-full?)
3. Copy InstallESD.dmg to Install XXX.app/Contents/SharedSupport
4. Run xattr -cr Install XXX.app to allow codesign to work
5. Run ./createinstalliso

[jgrisham]

Can you just skip steps 3-5 and just directly use the InstallESD.dmg image? (Iirc, it is bootable EFI-compatible ISO and can be burned to a DVD or a USB drive.)

Using Windows 11 and 7-Zip, for example, simply re-naming InstallOS.pkg to InstallOS.xar allowed opening it directly in 7-Zip, which then allowed extracting the InstallESD.dmg file. (The InstallOS.pkg file itself was obtainable from the downloaded disk image file using HFSExplorer and OpenJDK.)

• On macOS, an application such as Suspicious Package would also get this done.
• Linux and macOS Terminal methods should also be farily straightforward.

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Tl;dr:

Renaming InstallESD.dmg to InstallESD.iso should allow it to be used directly with a much wider array of software.

[madsmtm]

I had no idea what InstallESD.dmg was, but cool!

Are you sure that it's not necessary to invoke createinstallmedia?