updateinitramfs

update-initramfs is a command-line utility found on many Debian-based Linux distributions. It is used to create or update the initial RAM filesystem (initramfs) for the Linux kernel. The tool is provided by the initramfs-tools package and is invoked to ensure that the system can boot with the required kernel modules and early userspace utilities.

The initramfs is an archive that the kernel unpacks into memory during the boot process. It contains the necessary drivers and scripts to mount the root filesystem and start the real system. update-initramfs reads configuration from /etc/initramfs-tools and uses scripts located in /usr/share/initramfs-tools to assemble the image. The resulting images are stored in /boot, typically named with the kernel version, such as initrd.img-<version> or initramfs-<version>.img, depending on the distribution.

Common usage is to update the initramfs for the currently running kernel with update-initramfs -u. To create a new image for a specific kernel version, use update-initramfs -c -k <version>. To delete an existing image, use update-initramfs -d -k <version>. If the -k option is omitted, the operation applies to the running kernel by default. Additional options adjust verbosity or enable testing modes, and -v or -q can control console output.

After updating initramfs, systems with certain bootloaders may require a refresh of the boot configuration, such as running update-grub on some setups. While generally safe, changes to initramfs affect the boot process, so caution is advised and a known-good backup or recovery plan should be available.

In practice, update-initramfs is commonly used after kernel upgrades, adding new drivers, or changing early boot requirements that must be present in the initramfs. It is distinct from tools like dracut, which provide similar functionality on other distributions.