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docs/atomic-rollbacks: Add a section on rollbacks
Describing how different types of rollbacks work. Signed-off-by: Eric Curtin <ecurtin@redhat.com>
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Eric Curtin
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nav_order: 19
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nav_order: 190
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# Contributing
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---
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nav_order: 990
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title: Historical OSTree README
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nav_order: 70
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---
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# Adapting existing mainstream distributions
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176
docs/atomic-rollbacks.md
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176
docs/atomic-rollbacks.md
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---
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nav_order: 60
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---
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# Atomic Rollbacks
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{: .no_toc }
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1. TOC
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{:toc}
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## Automatic rollbacks
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See [greenboot](https://github.com/fedora-iot/greenboot/blob/main/README.md) for information on automatic rollbacks and how to integrate
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without your bootloader.
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## Manual rollbacks
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Ostree writes bootloader entries that are interpreted by the bootloader. To
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manually rollback, for bootloaders such as GRUB and syslinux that have an
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interactive UI, it is possible to select a previous boot entry. In the case of
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an Android bootloader, a slot switch may be triggererd using an AB switching
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tool. This may be useful for testing purposes.
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## Rollbacks
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```
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+------------------------------------------------+
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+------------------+ | |
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| | | (ostree:0) latest (multi-user.target) |
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| Bootloader |--->+ root |
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| | | (ostree:1) latest - 1 (multi-user.target) |
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+------------------+ | |
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+------------------------------------------------+
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```
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Bootloaders have multiple boot entries to choose from after upgrade. On
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rollback, the bootloader will boot the "latest - 1" version, rather than the
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latest version of the OS.
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## Alternate rollback techniques
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Below is an alternate technique to traditional AB switching that can be used.
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On rollback, an alternative boot target is used, rather than booting as
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default.target.
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```
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+------------------------------------------------+
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+------------------+ | |
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| | | (ostree:0) latest (multi-user.target) |
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| Bootloader |--->+ root |
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| | | (ostree:1) latest - 1 (rescue.target) |
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+------------------+ | |
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+------------------------------------------------+
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```
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In this case, instead of rolling back to an older version, we also boot
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into an alternate systemd boot target. Here we will describe how you can put
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togther an alternate systemd boot target, using the built-in rescue.target as
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an example.
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Below is a rescue.service file, it essentially executes systemd-sulogin-shell
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rescue when this service is activated.
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rescue.service:
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```
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# SPDX-License-Identifier: LGPL-2.1-or-later
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#
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# This file is part of systemd.
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#
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# systemd is free software; you can redistribute it and/or modify it
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# under the terms of the GNU Lesser General Public License as published by
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# the Free Software Foundation; either version 2.1 of the License, or
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# (at your option) any later version.
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[Unit]
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Description=Rescue Shell
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Documentation=man:sulogin(8)
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DefaultDependencies=no
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Conflicts=shutdown.target
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After=sysinit.target plymouth-start.service
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Before=shutdown.target
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[Service]
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Environment=HOME=/root
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WorkingDirectory=-/root
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ExecStartPre=-/usr/bin/plymouth --wait quit
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ExecStart=-/usr/lib/systemd/systemd-sulogin-shell rescue
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Type=idle
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StandardInput=tty-force
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StandardOutput=inherit
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StandardError=inherit
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KillMode=process
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IgnoreSIGPIPE=no
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SendSIGHUP=yes
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```
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Below is a rescue.target file, it is reached once rescue.service is complete.
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rescue.target:
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```
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# SPDX-License-Identifier: LGPL-2.1-or-later
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#
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# This file is part of systemd.
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#
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# systemd is free software; you can redistribute it and/or modify it
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# under the terms of the GNU Lesser General Public License as published by
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# the Free Software Foundation; either version 2.1 of the License, or
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# (at your option) any later version.
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[Unit]
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Description=Rescue Mode
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Documentation=man:systemd.special(7)
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Requires=sysinit.target rescue.service
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After=sysinit.target rescue.service
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AllowIsolate=yes
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```
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This is a simple bash script, it checks whether `ostree admin status -D` is
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`not-default` and if it is, it notifies systemd to alternatively boot into
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rescue.target.
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In the happy path, when we have booted the latest version
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`ostree admin status -D` would output `default`.
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ostree-rollback-to-rescue:
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```
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#!/usr/bin/bash
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set -euo pipefail
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if [ "$(ostree admin status -D)" = "not-default" ]; then
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exec systemctl --no-block isolate rescue.target
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fi
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```
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This is a systemd service file that runs ostree-rollback-to-rescue early in the
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boot sequence, it is essential that this service is run early to ensure we
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don't execute a full boot sequence, hence options `DefaultDependencies=no` and
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`Before=` are used.
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ostree-rollback-to-rescue.service
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```
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[Unit]
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Description=OSTree rollback to rescue
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DefaultDependencies=no
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OnFailure=emergency.target
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OnFailureJobMode=replace-irreversibly
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After=initrd-root-fs.target initrd-fs.target initrd.target boot.mount
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Before=cryptsetup.target integritysetup.target remote-fs.target slices.target swap.target veritysetup.target
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[Service]
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Type=oneshot
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ExecStart=/usr/sbin/ostree-rollback-to-rescue
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[Install]
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WantedBy=sysinit.target
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```
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###### Licensing for this document:
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`SPDX-License-Identifier: (CC-BY-SA-3.0 OR GFDL-1.3-or-later)`
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@ -1,5 +1,5 @@
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---
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nav_order: 5
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nav_order: 50
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---
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# Atomic Upgrades
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---
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nav_order: 9
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nav_order: 100
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---
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# Handling access to authenticated remote repositories
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@ -1,5 +1,5 @@
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---
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nav_order: 11
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nav_order: 120
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---
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# Bootloaders
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---
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nav_order: 8
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nav_order: 90
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---
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# Writing a buildsystem and managing repositories
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---
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nav_order: 10
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nav_order: 110
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---
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# Using composefs with OSTree
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@ -1,5 +1,5 @@
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---
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nav_order: 20
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nav_order: 200
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---
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# OSTree Contributing Tutorial
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@ -1,5 +1,5 @@
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---
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nav_order: 4
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nav_order: 40
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---
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# Deployments
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---
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nav_order: 7
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nav_order: 80
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---
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# OSTree data formats
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@ -1,5 +1,5 @@
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---
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nav_order: 10
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nav_order: 110
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---
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# Using Linux IMA with OSTree
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@ -1,5 +1,5 @@
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---
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nav_order: 1
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nav_order: 10
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---
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# libostree
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@ -1,5 +1,5 @@
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---
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nav_order: 2
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nav_order: 20
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---
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# OSTree Overview
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@ -1,5 +1,5 @@
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---
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nav_order: 10
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nav_order: 110
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---
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# Related Projects
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---
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nav_order: 3
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nav_order: 30
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---
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# Anatomy of an OSTree repository
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@ -1,5 +1,5 @@
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---
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nav_order: 9
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nav_order: 100
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---
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# Managing content in OSTree repositories
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@ -1,5 +1,5 @@
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---
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nav_order: 6
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nav_order: 70
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---
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# OSTree and /var handling
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