85 lines
3.0 KiB
Plaintext
85 lines
3.0 KiB
Plaintext
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= Booting Citadel
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[topic]
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@link[guide >index#internals]
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== Disk Layout
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When Citadel is installed two disk partitions are created on the target disk.
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[screen]
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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
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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.
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[screen]
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[[[
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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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]]]
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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'.
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[screen sh]
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# 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
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=== Bootloader
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==== LUKS
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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).
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[screen sh]
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# cat /etc/crypttab
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luks UUID=683a17fc-4457-42cc-a946-cde67195a101 - discard
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==== Mounting rootfs
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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:
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[screen]
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citadel/meta-citadel/recipes-initrd/citadel-initramfs
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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:
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[screen]
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citadel-rootfs-mount.path
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citadel-rootfs-mount.service
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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
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[screen]
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ConditionPathExists=/dev/mapper/citadel-rootfsA
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ConditionPathExists=/dev/mapper/citadel-rootfsB
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ConditionPathExists=/dev/mapper/citadel-storage
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