Golden Image Generator — Documentation

Part 1: Real Ubuntu ISO — File & Folder Structure

When you download a stock Ubuntu Server ISO and open it, this is what you find inside:

.disk/info

Contains a unique identifier and metadata (version, codename, arch) for the ISO. This ID is read by the initrd at boot time to confirm the correct disc is inserted.

casper/

The live-boot directory — everything needed to boot Ubuntu from the ISO lives here. The kernel, initrd, and squashfs root filesystems are all inside this folder.

casper/vmlinuz

The compressed Linux kernel image that gets loaded into memory at boot. GRUB points to this file; it decompresses itself and starts the kernel.

casper/initrd

The initial RAM disk — a tiny temporary filesystem loaded before the real root. It contains just enough tools (busybox, udev, casper scripts) to find and mount the squashfs.

casper/filesystem.squashfs (or ubuntu-server-minimal.squashfs)

The compressed root filesystem of the live Ubuntu system, packed into a single file. unsquashfs unpacks it into a real directory tree; mksquashfs repacks it back.

casper/filesystem.manifest

A plain-text list of every installed package and its version inside the squashfs. Ubuntu's installer reads this to know what packages came pre-installed.

casper/filesystem.size