Edit: For anyone reading this in the future ECMA-119 is freely distributable and seems to conform to ISO 9660. ECMA also have versions of some of the specs referenced by ISO 9660. (ECMA-6, ECMA-35, ECMA-43)

Will do. I was gonna start by reading ISO 9660 and I found out it costs 200 dollars from standards.iso.org. Which is a shame because there's a bunch of other ISO standards referenced in 9660 which would cost even more money to read. I always heard people reference these standards but I had no idea they were so inaccessible to regular users. But I think I found some kind of annotated copy of the spec to read,

Thanks. I see the word boot is referenced 200 times on the related manual page. So I suspect a thorough read through of that page will help me.

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Alright thanks. Well if you know of any good resources for xorriso particularly with the -b (boot) flag I'd like to read them.

Google has been mostly serving me 15 year old SO posts that aren't relevant to modern Linux anymore.

So eggs is great for Debian with my Gnome stuff.

As for xorriso I have a LFS dir that very much resembles a Linux root dir (without a DE or any distro specific software) and I can chroot into it mounting /dev, /sys, /run, /proc from my host system.

I would like to compress that LFS dir into an iso combined with a boot loader.

That LFS dir is on a separate partition and does have a boot loader installed on that partition's hard drive. But I'd rather boot it in a virtual machine and I didn't want to give the vm raw hard drive access.

I hope that helps but I'm happy to answer more questions.

Booting into a live CD isn't a hard requirement because I can probably just use eggs after I get it to boot in a vm.

Edit: also thanks for the insight about xorriso I had real trouble finding much info about the differences between the three.

Edit 2: I'm going to run LFS on the exact same hardware it compiled on so I can probably use grub installed on my host system.

That said I did try using grub-mkimage on my host system and when passing that iso into mkisofs -b I still couldn't get a boot. (No bootable medium found.)

Going to try the penguins-eggs method you posted. I would love to be able to turn a virtual box environment into an installable medium to make my own version of debian with all my gnome tweaks.

I would also love a solution that doesn't require booting into the OS first. So that I can take a root dir and turn it into a bootable iso. I tried a bunch of old tutorials for making a boot.iso and linking it into mkisofs with -b but it never worked.

I am willing to learn/use any free tooling. Not picky at all.

I've been struggling to make a bootable iso. I did Linux from scratch and I wanted to boot it in virtual box. I found a sparse amount of info about mkisofs/genisofimage but I couldn't actually get a successful boot after following a few tutorials.

I have to imagine there are more modern tools for something like this but I didn't have any luck googling.

Sorry to hijack but it sounds like you might have an answer I need. I just want a way to put together an iso with a bootloader that works in virtual machines. (I'm good with 32bit grub but I'd work with uefi too).