archx86bootbzImage

arch/x86 boot bzImage, commonly referred to as bzImage, is the Linux kernel image format used to boot on x86 systems. It is the compressed kernel image produced by the build target make bzImage and is typically installed as a kernel image labeled vmlinuz or bzImage in boot directories. The arch/x86/boot portion of the kernel source contains the small real-mode bootstrap and the initial decompression code that prepares the system for the main kernel.

Structure and creation

A bzImage packages the compressed kernel alongside a minimal 16-bit bootstrap that runs when the image is loaded by a bootloader or BIOS. The kernel portion is compressed (by default with gzip) and preceded by a small header that communicates boot parameters and the decompression entry point. The size and layout are designed to allow the kernel to relocate and decompress itself into memory before transferring control to the main start-up code. While gzip is the common default, the kernel supports other compression formats depending on configuration.

Boot process

During boot, a bootloader loads the bzImage into memory, typically at a conventional address near 1 MiB. The real-mode bootstrap code then switches the processor to protected or long mode, relocates the kernel as needed, decompresses the image in place, and jumps to the kernel entry point. The kernel subsequently parses boot parameters (including command line and an optional initramfs/initrd provided by the bootloader) and proceeds with system initialization.

Usage notes

bzImage is the traditional x86 boot image and remains compatible with common bootloaders such as GRUB, Syslinux, and legacy chain loaders. In many distributions, the installed kernel image is presented as vmlinuz, a symlink to the bzImage. For UEFI boot, the image is loaded into memory by the firmware or a boot manager and handed to the kernel in a similar fashion.