Create bootable OSX ISO

osx_bootable_iso.sh

#!/bin/bash

# Use with care ...

# -----------------------------------------
# Mountain Lion, Mavericks, Yosemite ..
OS="El Capitan"
IMG_SIZE=8g
BUILD_MNT=/tmp/"$OS"_Build
INSTALL_MNT=/tmp/"$OS"_Install
INSTALL_DMG=/Applications/Install\ OS\ X\ "$OS".app/Contents/SharedSupport/InstallESD.dmg
OS_CDR=/tmp/"$OS"

# Mount the installer image
hdiutil attach "$INSTALL_DMG" -noverify -nobrowse -mountpoint "$INSTALL_MNT"

# Convert the boot image to a sparse bundle
hdiutil convert "$INSTALL_MNT"/BaseSystem.dmg -format UDSP -o "$OS_CDR"

# Increase the sparse bundle capacity to accommodate the packages
hdiutil resize -size $IMG_SIZE "$OS_CDR".sparseimage

# Mount the sparse bundle for package addition
hdiutil attach "$OS_CDR".sparseimage -noverify -nobrowse -mountpoint "$BUILD_MNT"

# Remove Package link and replace with actual files
rm -rf "$BUILD_MNT"/System/Installation/Packages
cp -rp "$INSTALL_MNT"/Packages "$BUILD_MNT"/System/Installation/

# Unmount the installer image
hdiutil detach "$BUILD_MNT"

# Unmount the sparse bundle
hdiutil detach "$INSTALL_MNT"

# Resize the partition in the sparse bundle to remove any free space
hdiutil resize -size `hdiutil resize -limits "$OS_CDR".sparseimage | tail -n 1 | awk '{print $ 1}' `b "$OS_CDR".sparseimage

# Convert the sparse bundle to ISO/CD master
hdiutil convert "$OS_CDR".sparseimage -format UDTO -o "$OS_CDR"

# Remove the sparse bundle
rm "$OS_CDR".sparseimage

# Rename the ISO and move it to the desktop
mv "$OS_CDR".cdr ~/Desktop/"$OS".iso