Native Compression Formats for Ubuntu Linux Initramfs

This article explains the compression formats supported by the Linux kernel for initramfs, specifically within the Ubuntu environment. It covers the default settings, available options, and how the kernel handles decompression during the boot process.

Primary Supported Format

The Linux kernel natively supports multiple compression formats for initramfs, but gzip is the most universally recognized and default standard. While the kernel can handle various algorithms, gzip ensures the widest compatibility across different hardware configurations and bootloader versions.

Additional Supported Formats

Besides gzip, the kernel can natively decompress several other formats if enabled during kernel compilation. These include bzip2, lzma, xz, lzo, lz4, and zstd. Support for these formats depends on the specific kernel configuration flags set by the distribution maintainer.

Ubuntu Default Configuration

In Ubuntu, the initramfs-tools package typically defaults to gzip compression. This choice balances compression ratio and decompression speed, ensuring maximum compatibility across different hardware and bootloaders without requiring additional modules during the early boot stage.

Changing Compression Settings

Users can modify the compression method by editing the configuration files within the initramfs-tools package. Specifically, setting the INITRAMFS_COMPRESSION variable allows administrators to switch between supported formats like xz or zstd to optimize for space or boot speed.