Create bootable ISO from HighSierra Installer

highsierra_bootable.sh

# Generate a BaseSystem.dmg with 10.13 Install Packages
hdiutil attach /Applications/Install\ macOS\ 10.13\ Beta.app/Contents/SharedSupport/InstallESD.dmg -noverify -mountpoint /Volumes/highsierra
hdiutil create -o /tmp/HighSierraBase.cdr -size 7316m -layout SPUD -fs HFS+J
hdiutil attach /tmp/HighSierraBase.cdr.dmg -noverify -mountpoint /Volumes/install_build
asr restore -source /Applications/Install\ macOS\ 10.13\ Beta.app/Contents/SharedSupport/BaseSystem.dmg -target /Volumes/install_build -noprompt -noverify -erase
cp -R /Volumes/highsierra/Packages /Volumes/OS\ X\ Base\ System/System/Installation
hdiutil detach /Volumes/OS\ X\ Base\ System/
hdiutil detach /Volumes/highsierra/
mv /tmp/HighSierraBase.cdr.dmg /tmp/BaseSystem.dmg

# Restore the 10.13 Installer's BaseSystem.dmg into file system and place custom BaseSystem.dmg into the root
hdiutil create -o /tmp/HighSierra.cdr -size 8965m -layout SPUD -fs HFS+J
hdiutil attach /tmp/HighSierra.cdr.dmg -noverify -mountpoint /Volumes/install_build
asr restore -source /Applications/Install\ macOS\ 10.13\ Beta.app/Contents/SharedSupport/BaseSystem.dmg -target /Volumes/install_build -noprompt -noverify -erase
cp /tmp/BaseSystem.dmg /Volumes/OS\ X\ Base\ System

hdiutil detach /Volumes/OS\ X\ Base\ System/
hdiutil convert /tmp/HighSierra.cdr.dmg -format UDTO -o /tmp/HighSierra.iso
mv /tmp/HighSierra.iso.cdr ~/Desktop/HighSierra.iso
rm /tmp/HighSierra.cdr.dmg

When I try to follow @mwiesen steps from the Dec 26, 2017 comment, I hit the problem where creatinstallmedia fails trying to erase /Volumes/install_build. I get the same error as @stylemessiah:

$ sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/install_build
Password:
Ready to start.
To continue we need to erase the volume at /Volumes/install_build.
If you wish to continue type (Y) then press return: y
Erasing Disk: 0%... 10%...
Error erasing disk error number (22, 0)
A error occurred erasing the disk.

I'm trying to run this on 10.12.6 (Sierra). I haven't run the upgrade yet. The download in /Applications/Install macOS High Sierra.app looks ok, it is 4.9 GB, (4,968 MB). If I run createinstallmedia using a physical 8 GB USB thumb drive it succeeds.

@stylemessiah - were you able to figure it out?

Any ideas from anyone welcome.

Use "disk utility" to erase & format the /tmp/Catalina.dmg.

Wow thank you so much @maxmalta i've been trying from yesterday night to get an iso for high sierra and yours was clear, concise and worked perfectly! Thank you very much.

Guys if you are using catalina @maxmalta 's solution is the one to go to.

Generate ISO (New Method) Requires macOS Catalina+:

softwareupdate --fetch-full-installer --full-installer-version 10.13.6
sudo hdiutil create -o /tmp/HighSierra -size 16384m -volname HighSierra -layout SPUD -fs HFS+J
sudo hdiutil attach /tmp/HighSierra.dmg -noverify -mountpoint /Volumes/HighSierra
sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/HighSierra --nointeraction
hdiutil eject -force /Volumes/Install\ macOS\ High\ Sierra
hdiutil convert /tmp/HighSierra.dmg -format UDTO -o ~/Desktop/HighSierra
mv -v ~/Desktop/HighSierra.cdr ~/Desktop/HighSierra.iso
sudo rm -fv /tmp/HighSierra.dmg

You should end up with a High Sierra ISO File in your Desktop