Simple bash script to create a Bootable ISO from macOS Catalina Install Image from Mac App Store

create-iso.sh

#!/usr/bin/env bash
#===========================================================================
# Works only with the official image available in the Mac App Store.
# Make sure you download the official installer before running this script.
#===========================================================================

hdiutil create -o /tmp/Catalina.cdr -size 9000m -layout SPUD -fs HFS+J
hdiutil attach /tmp/Catalina.cdr.dmg -noverify -mountpoint /Volumes/install_build
sudo /Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia  --volume /Volumes/install_build --nointeraction
hdiutil detach "/Volumes/Install macOS Catalina"
hdiutil convert /tmp/Catalina.cdr.dmg -format UDTO -o /tmp/Catalina.iso
mv /tmp/Catalina.iso.cdr ~/Desktop/Catalina.iso
rm /tmp/Catalina.cdr.dmg

can't speak for others but generally i want an image as small as possible when storing it for later usage

I do aim for the same. This is why I lowered the size back down again when I saw that 9000m was fitting. But maybe today is no more because of security patches and such. So 9200m sound plausible to me.

Tested it with the Big Sur installer from Apple, making the obvious naming and sizing adjustments (12700m worked for me) and it also works fine, thank you.

I've created the relative script for Big Sur and you can find it if you're interested: https://gist.github.com/julianxhokaxhiu/286017b9872474d2c9b9fa090f6802bf

Glad you made it up yourself :) Cheers

Instead of specifying the size, I tried -type SPARSE and was able to have the ISO be the perfect size:

>hdiutil create -o /tmp/Catalina.cdr -type SPARSE -layout SPUD -fs HFS+J

I haven't been able to boot into it yet, but don't think it's because of -type SPARSE

Logically the parameter makes sense, if someone could please test the resulting ISO I'd be happy to update the script. Thank you for looking into this.