initramfs-tools

Ben Hutchings

What is the initramfs for?

• Huge variety of disk drivers, net drivers and filesystems that may be needed to mount root
• Generic kernel shouldn't have all these built-in
• Root might also need RAID, LVM, dm-crypt, which generally need to be configured by userland
• Kernel needs a way to load modules and run scripts but it can't read them from the root filesystem
• Solution: boot loader provides a bundle of files (initramfs image) to the kernel

How the kernel uses an initramfs

• Kernel always mounts an initial root filesystem using either ramfs or tmpfs
• If the boot loader provides an initramfs image, kernel unpacks it into this filesystem, then runs /init
• The initramfs init system is then responsible for mounting the real root filesystem and running the real init
  • Although it is not required to hand over at all - e.g. debian-installer

Questions?

Credits

• Linux 'Tux' logo © Larry Ewing, Simon Budig.
  • Modified by Ben to add Debian open-ND logo
• Debian open-ND logo © Software in the Public Interest, Inc.
• Xzibit promotional photo © Retna, used for purpose of parody