NAME

       ostree-prepare-root - Change the view of a mounted root filesystem to an ostree deployment

SYNOPSIS

       ostree prepare-root {TARGET}

DESCRIPTION

       At its core, ostree operates on an existing mounted filesystem. Tooling such as ostree
       admin deploy will create a new directory that can be used as a bootable target. This tool
       is designed to run in an initramfs and set up "remapping" mounts as a view into that
       filesystem.

       As of more recently, this tool also has optional support for composefs, which creates a
       distinct mount point layered on top of the underlying filesystem.

       The most common pattern today is to use systemd in an initramfs. The systemd unit shipped
       upstream is ordered in this way: After=sysroot.mount and Before=initrd-root-fs.target

       When it runs, the mounted filesystem at the provided TARGET (usually /sysroot) will be
       changed such that what appears at /sysroot is actually the "deployment root" - i.e. a
       particular versioned subdirectory. What was formerly the "physical root" i.e. the real
       root of the filesystem will appear as /sysroot/sysroot.

       For /var, by default a bind mount is created from the deployment root to /sysroot/var.

       A read-only bind mount is created over /sysroot/usr. The immutable bit is set on the
       deployment root, so this provides basic protection for filesystem mutation. If the
       sysroot.readonly option is enabled, instead a writable bind mount for /sysroot/etc, and
       everything else is mounted read-only.

       Finally, when higher level tooling such as systemd performs a switch-root operation, what
       was /sysroot becomes / and after the transition into the real root, the system will be
       booted into the "deployment", which is a versioned immutable filesystem tree. The ostree
       tooling running in the real root thereafter performs further changes by operating on
       /sysroot which is now the "physical root".

CONFIGURATION

       The /usr/lib/ostree/prepare-root.conf (or /etc/ostree/prepare-root.conf) config file is
       parsed by ostree-prepare-root. This file must be present in the initramfs. The default
       dracut module will copy it from the real root if present.

       sysroot.readonly
           A boolean value; the default is false. If this is set to true, then the /sysroot mount
           point is mounted read-only.

       composefs.enabled
           This can be yes, no.  maybe or signed. The default is maybe. If set to yes or signed,
           then composefs is always used, and the boot fails if it is not available. Additionally
           if set to signed, boot will fail if the image cannot be validated by a public key. If
           set to maybe, then composefs is used if supported.

       composefs.keypath
           Path to a file with Ed25519 public keys in the initramfs, used if composefs.enabled is
           set to signed. The default value for this is /etc/ostree/initramfs-root-binding.key.
           For a valid signed boot the target OSTree commit must be signed by at least one public
           key in this file, and the commitfs digest listed in the commit must match the target
           composefs image.

SYSTEMD

       As mentioned above, this tool comes with a systemd unit file ostree-prepare-root.service
       and it is primarily expected to be invoked this way.

COMPOSEFS

       The default for ostree is to create a plain hardlinked filesystem tree. composefs support
       is currently experimental; see the upstream doc/composefs.md for more information on using
       it.