67 lines
3.4 KiB
Plaintext
67 lines
3.4 KiB
Plaintext
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<?xml version="1.0" encoding="utf-8"?>
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<page xmlns="http://projectmallard.org/1.0/" type="topic" id="boot">
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<info>
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<link type="guide" xref="index#internals"/>
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</info>
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<title>Booting Citadel </title>
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<section>
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<title>Disk Layout</title>
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<p>When Citadel is installed two disk partitions are created on the target disk.</p>
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<screen>sda 8:0 0 477G 0 disk
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├─sda1 8:1 0 511M 0 part
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└─sda2 8:2 0 476.5G 0 part</screen>
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<p>The first partition is an EFI boot partition and the second partition is LUKS encrypted
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and contains multiple LVM volumes when decrypted.</p>
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<screen>
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/dev/sda1 /dev/sda2
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[EFI ESP Boot partition] [ LUKS encrypted partition filling remainder of disk ]
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. .
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. .
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. | .
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. | .
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. V .
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. .
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[ rootfsA ] [ rootfsB ] [ citadel-storage ]
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</screen>
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<p>There are three logical volumes. Two root filesystem partitions so that one partition
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can be updated while the other one is in use, and the remaining space is contained
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in a volume called 'storage'.</p>
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<screen type="sh"># lvs
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LV VG Attr LSize
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rootfsA citadel -wi-a----- 2.00g
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rootfsB citadel -wi-ao---- 2.00g
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storage citadel -wi-ao---- 472.43g</screen>
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<section>
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<title>Bootloader</title>
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<section>
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<title>LUKS</title>
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<p>The kernel initramfs has an /etc/crypttab file which guides the discovery of the LUKS partition.
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The UUID of the LUKS partition is hardcoded to the value listed below. If citadel is installed
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on more than one device on the system, the intended LUKS partition may not be chosen correctly.
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This problem can be addressed by changing the UUID of other citadel LUKS partitions and passing
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the UUID on kernel commandline to override /etc/crypttab. See systemd-cryptsetup-generator(8).</p>
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<screen type="sh"># cat /etc/crypttab
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luks UUID=683a17fc-4457-42cc-a946-cde67195a101 - discard</screen>
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</section>
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<section>
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<title>Mounting rootfs</title>
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<p>The initramfs boot stage is orchestrated by various systemd unit files which can be found
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in the citadel source tree at:</p>
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<screen>citadel/meta-citadel/recipes-initrd/citadel-initramfs</screen>
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<p>The same kernel and initramfs is used for the installer image. One task of these unit files
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is to set up a live mode boot when a certain kernel command line option is set. For a regular
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boot, a pair of unit files will attempt to mount the root filesystem partition when it becomes
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available:</p>
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<screen>citadel-rootfs-mount.path
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citadel-rootfs-mount.service</screen>
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<p>The .path unit triggers every time /dev/mapper changes and the corresponding .service unit is
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activated only when all of the LVM volumes inside</p>
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<screen>ConditionPathExists=/dev/mapper/citadel-rootfsA
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ConditionPathExists=/dev/mapper/citadel-rootfsB
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ConditionPathExists=/dev/mapper/citadel-storage</screen>
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</section>
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</section>
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</section>
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</page>
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