mkinitramfs

mkinitramfs is a command-line utility used in Debian and its derivatives, such as Ubuntu, to generate an initial RAM filesystem, often referred to as an initramfs. The initramfs is a small archive that contains essential kernel modules and utilities needed to boot the main Linux system. When the Linux kernel starts, it first loads the initramfs into memory. The initramfs then takes over the initial boot process, mounts the root filesystem, and eventually hands over control to the real init system (like systemd or SysVinit) on the root partition.

The primary purpose of mkinitramfs is to bundle necessary drivers and tools that are required to access the root filesystem, especially if these are not built directly into the kernel. This is common when the root filesystem resides on hardware that requires specific modules to be loaded early in the boot process, such as certain storage controllers (SATA, NVMe, RAID controllers) or encrypted volumes. Without the correct modules in the initramfs, the kernel would be unable to find and mount the root filesystem, leading to a boot failure.

mkinitramfs is typically invoked automatically by the package management system (like apt) when kernel packages are installed or updated. It can also be run manually by administrators to regenerate the initramfs image, for example, after manually installing new kernel modules or making changes to boot configuration. The generated image is usually stored in directories like /boot, with filenames reflecting the kernel version.