While the systemd integration effectively requires /sysroot, it will
help people trying to use OSTree with other initramfs systems
(e.g. initramfs-tools) if we don't hardcode that requirement in this
tool.
See https://wiki.gnome.org/OSTree/DeploymentModel2
This is a major rework of the on-disk filesystem layout, and the boot
process. OSTree now explicitly supports upgrading kernels, and these
upgrades are also atomic.
The core concept of the new model is the "deployment list", which is
an ordered list of bootable operating system trees. The deployment
list is reflected in the bootloader configuration; which has a kernel
argument that tells the initramfs (dracut) which operating system root
to use.
Invidiual notable changes that come along with this:
1) Operating systems should now come with their etc in usr/etc; OSTree
will perform a 3-way merge at deployment time, and place etc in
the actual root. This avoids the need for a bind mount, and is
just a lot cleaner.
2) OSTree no longer bind mounts /root, /home, and /tmp. It is expected
that the the OS/ has these as symbolic links into /var.
At the moment, OSTree only supports managing syslinux; other
bootloader backends will follow.
Linux creates a copy of the soure mount flags when creating a bind
mount; if the source is read-only, then the bind mount is.
The problem is that systemd will remount the rootfs read/write, but
each mount (/home, /var etc.) will still be read-only. We need to
remount every bind mount except for /usr to read-write too.
This only "worked" with the old ostree-switch-root because it
effectively force mounted the rootfs read-write always, ignoring the
"ro" flag.
Rather than attempting to hack up the "switch-root" functionality of
systemd, this binary allows us to simply prepare the root before we
switch into it.
The real vision of OSTree is to "multiple versions of multiple
operating systems". Up until now, it's worked to install gnome-ostree
inside a host distribution, but several things don't work quite right
if you try to do completely different systems.
In the new model, there's the concept of an "osname" which encompasses
a few properties:
1) Its own /var
2) A set of trees deployed in /ostree/deploy/OSNAME/
3) Its own "current" and "previous" links.
Now it no longer really makes sense to boot with "ostree=current".
Instead, you specify e.g. "ostree=gnome/current".
This is an incompatible change to the deployment code - you will need
to run init-os gnome and redeploy.
All "ostree admin" subcommands now take an OSNAME argument.
First, move deployments to /ostree/deploy. Having them in the
toplevel clutters the filesystem layout too much.
When we deploy a tree like /ostree/deploy/NAME, there is now also a
writable directory /ostree/deploy/NAME-etc. This is mounted as
read-write inside the system.
On an initial install, that directory is copied from
/ostree/deploy/NAME/etc. On subsequent deployments, we find any
changes made in the current deployment's /etc, and apply that set of
changes to the new deployment's /etc.
See https://live.gnome.org/OSTree/EverythingInEtcIsABug
The ostree-switch-root tool expects three arguments (argc=4): new root, OS
tree target, and init(8) binary to launch inside it. Also, the error message
when not enough arguments are passed now tells about the second argument
being the target OS tree.
Reviewed-by: Colin Walters <walters@verbum.org>
Merge the code from ostree-init; now that we're back to targeting an
initramfs (dracut), we don't need to statically link the binary, so
there's no strong reason to have a separate module.
Colin Walters
Adrian Perez