Initrdrewrite

The current incarnation of mkinitrd sucks for a variety of reasons. This page documents some of the plans to replace it with something better. This is not yet a feature, it's currently just a playground to try some things out

Planning

Initial ideas

• One initrd to rule them all - Instead of one for the livecd, one for the installer, one for the distro
• Death to nash - The bits of nash that don't currently exist in other tools need factoring out and putting into util-linux or similar packages.
• Same bits - Use the same bits the rest of the distro uses instead of custom functionality. No custom udev, just use the regular one etc.
• Diagnostics - Include a shell for diagnostic/debugging purposes.
• Probe at runtime instead of buildtime - Include all drivers, not just the drivers necessary for the hardware being run. (For storage, the common ones will be built-in to the kernel anyway)
• The initrd will be usable on other distros. - The idea being that it can be included in the upstream kernel, and changed when kernel interfaces change etc to prevent breaking distros.

Major Cases

The first cut of this will just support the simple case of root on a hard disk. Eventually we want to support the numerous esoteric cases the existing initrd supports. Namely root on..

• Disk based devices
  • -on-lvm
  • -on-dm-crypt
  • -on-dmraid
  • -on-mdraid
  • -on-multi-path
• Network based devices
  • -on-iSCSI
  • -on-nfs
  • -on-nbd
• Special cases to revisit later:
  • livecd (/ on dm-snapshot over ext3 on squashfs on iso9660)
  • installer
  • kdump

Other tasks performed by the initrd other than mounting rootfs

• restore from hibernate
• start 'pretty' plymouth
• kdump
• Loading initial SELinux policy.

Utilities to include in the initrd

• libc
• udev
• switchroot
• bash (no nash!)
  • If you can manage without bashisms (sometimes it's hard), consider dash or posh as much smaller POSIX shells.

Other stuff

• The code in the kernel for creating minimal initramfs's (scripts/gen_initramfs_list.sh & usr/*) is kind of useless. It's probably for the best if this just goes away and gets replaced by something useful.

Future Enhancement Requests

Note that our main concern, especially right now, is proving viability of some of the ideas and then showing it with the things that we already support. If things work out, then it should be doable to start putting in support for new things that we don't already have support for. Nothing in this list is guaranteed but if people have ideas about new things, put them here and they'll at least be considered.

• run ssh server to enter crypto password or perform debugging (supported by debian)
• Make it possible to easily extend the initramfs, e.g. by packages that provide additional features to the initramfs, e.g. an ssh server (partly? supported by initramfs-tools in debian. e.g. with /etc/initramfs-tools/hooks)
• Hook in overlay filesystem like aufs/unionfs (debian, ubuntu, etc.)
• switchroot without re-running daemons like udev again (not sure if this is possible)

Bits

Repository is currently available at git://fedorapeople.org/~katzj/dracut.git which works for some simple (and not so simple) cases. The goal is to get to dogfood-able in the very near future. Read the README, TODO and HACKING files for more information

There is also an initramfs@vger.kernel.org mailing list for discussion