issue 1841/S15: place the fallback kernel's boot entry from the loader the machine booted with
ADR 0508 §9 and §10: systemd-boot gets an entry from the booted command line, GRUB a regenerated menu only when its kernels change, a found kernel-copying hook is taken over, a full boot partition fails loudly.
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# Module kernel, novox/hq ADR 0508 §9, issue 1841. After a kernel image is installed, upgraded or removed, the
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# fallback kernel's boot entry (or the GRUB menu) is placed again. Written by the mesh; change the module.
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[Trigger]
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Operation = Install
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Operation = Upgrade
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Operation = Remove
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Type = Path
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Target = usr/lib/modules/*/vmlinuz
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[Action]
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Description = Placing the fallback kernel on the boot menu
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When = PostTransaction
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Exec = ${dir:state}/boot-entries run
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#!/bin/sh
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# The fallback kernel's place on this machine's boot menu (module kernel, novox/hq ADR 0508 §9 and §10,
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# issue 1841). Written by the mesh and run as root by mesh-kernel-boot-entries.service at boot and when the
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# module is applied, and by the pacman hook 90-mesh-kernel-boot-entries.hook after a kernel is installed,
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# upgraded or removed. Replaced on every push; change the module, never this file.
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#
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# boot-entries run [<root> [<this module's state> [<room needed in /boot, KiB>]]]
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#
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# The three are arguments only so the module's tests can run this against a stand-in tree.
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#
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# It reads from the machine which loader booted it, never from a setting:
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# systemd-boot the EFI variable LoaderEntrySelected is present: the entry mesh-linux-lts.conf is written
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# from the command line the machine booted with.
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# GRUB /boot/grub/grub.cfg exists and that variable does not: the menu is generated again, only
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# when the set of kernels in /boot differs from the menu's.
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# neither it fails loudly. The default entry is never touched.
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# And a pacman hook of someone else's that copies kernel images to one fixed name in /boot is moved into this
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# module's state first (ADR 0508 §10): it would put the fallback kernel in the default kernel's place.
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set -eu
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root=/
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state='${dir:state}'
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[ $# -ge 2 ] && root=$(printf '%s' "$2" | sed 's|/$||')
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[ $# -ge 3 ] && state=$3
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boot=$root/boot
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hooks=$root/etc/pacman.d/hooks
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efivar=$root/sys/firmware/efi/efivars/LoaderEntrySelected-4a67b082-0a4c-41cf-b6c7-440b29bb8c4f
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ours=90-mesh-kernel-boot-entries.hook
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# The fallback kernel and its initramfs are about 72 MB in /boot (issue 1836): less room fails the unit
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# before a package writes half of them.
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need_kib=98304
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[ $# -ge 4 ] && need_kib=$4
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[ $# -ge 1 ] && [ "$1" = run ] || {
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echo "usage: boot-entries run [<root> [<state directory> [<KiB needed>]]]" >&2
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exit 2
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}
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# A hook that is not ours, triggered by kernel images, whose action copies to one fixed name in /boot.
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copies_kernels() {
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grep -Eqi '^[[:space:]]*Target[[:space:]]*=.*(vmlinuz|usr/lib/modules)' "$1" &&
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grep -Eq '^[[:space:]]*Exec[[:space:]]*=.*(cp|install|ln|rsync)[[:space:]].*/boot/[A-Za-z0-9._+-]+([^A-Za-z0-9._+/%$*-]|$)' "$1"
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}
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if [ -d "$hooks" ]; then
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for hook in "$hooks"/*.hook; do
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[ -f "$hook" ] || continue
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[ "$(basename "$hook")" = "$ours" ] && continue
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copies_kernels "$hook" || continue
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mkdir -p "$state/taken-over"
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mv -f "$hook" "$state/taken-over/$(basename "$hook")"
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echo "taken over: the pacman hook $(basename "$hook") copied kernel images to one fixed name in /boot; moved to $state/taken-over/ so each kernel keeps its own package's name"
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done
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fi
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if [ -e "$efivar" ]; then
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loader=systemd-boot
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elif [ -f "$boot/grub/grub.cfg" ]; then
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loader=grub
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else
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echo "no boot loader found: the machine was not booted by systemd-boot (no LoaderEntrySelected variable) and there is no $boot/grub/grub.cfg; the fallback kernel has no menu to be placed on" >&2
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exit 1
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fi
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# Room first, only while the fallback kernel is not in /boot yet.
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if [ ! -e "$boot/vmlinuz-linux-lts" ]; then
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free=$(df -Pk "$boot" | awk 'NR==2 {print $4}')
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[ -n "$free" ] || free=0
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if [ "$free" -lt "$need_kib" ]; then
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echo "$boot has $free KiB free and the fallback kernel needs $need_kib KiB: free room there before the kernel is installed" >&2
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exit 1
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fi
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fi
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case "$loader" in
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systemd-boot)
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entries=$boot/loader/entries
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cmdline=$(sed -e 's/BOOT_IMAGE=[^ ]*//g' -e 's/initrd=[^ ]*//g' "$root/proc/cmdline" | tr -s ' \n' ' ' | sed -e 's/^ //' -e 's/ $//')
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[ -n "$cmdline" ] || {
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echo "$root/proc/cmdline holds no command line to boot the fallback kernel with" >&2
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exit 1
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}
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want=$(
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echo "title Arch Linux (linux-lts, fallback)"
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echo "linux /vmlinuz-linux-lts"
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for ucode in intel-ucode.img amd-ucode.img; do
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[ -e "$boot/$ucode" ] && echo "initrd /$ucode"
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done
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echo "initrd /initramfs-linux-lts.img"
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echo "options $cmdline"
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)
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mkdir -p "$entries"
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if [ "$(cat "$entries/mesh-linux-lts.conf" 2>/dev/null || true)" = "$want" ]; then
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echo "systemd-boot: mesh-linux-lts.conf, as it was"
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else
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printf '%s\n' "$want" >"$entries/mesh-linux-lts.conf"
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echo "systemd-boot: wrote $entries/mesh-linux-lts.conf from the command line the machine booted with; the default entry is as it was"
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fi
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;;
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grub)
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cfg=$boot/grub/grub.cfg
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menu=$(sed -n 's|^[[:space:]]*linux[[:space:]]*\(/boot\)\{0,1\}/\(vmlinuz-[^[:space:]]*\).*|\2|p' "$cfg" | sort -u)
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have=$(cd "$boot" && ls -d vmlinuz-* 2>/dev/null | sort -u || true)
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if [ "$menu" = "$have" ]; then
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echo "grub: the menu lists the kernels in /boot, left as it is"
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else
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grub-mkconfig -o "$cfg"
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echo "grub: the kernels in /boot changed ($(echo $have | tr '\n' ' ')); the menu is generated again; the default entry is as it was"
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fi
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;;
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esac
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@@ -0,0 +1,22 @@
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[Unit]
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Description=The fallback kernel's place on this machine's boot menu
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# Module kernel, novox/hq ADR 0508 §9, issue 1841. Starting this unit reads which loader booted the machine and
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# places the fallback kernel's boot entry (systemd-boot) or generates the menu again (GRUB); it fails, and says
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# why, when there is no loader or the boot partition has no room. The kernel packages are declared after this
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# unit, so the entry is in place before they are installed.
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After=local-fs.target
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Wants=local-fs.target
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[Service]
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Type=oneshot
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RemainAfterExit=yes
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ExecStart=${dir:state}/boot-entries run
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# It writes the boot partition, the pacman hook directory and its own state, and nothing else.
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ProtectSystem=strict
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ReadWritePaths=/boot ${dir:state} /etc/pacman.d/hooks
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ProtectHome=yes
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PrivateNetwork=yes
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NoNewPrivileges=yes
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[Install]
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WantedBy=multi-user.target
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