deploy: one-shot boot without the bootloader's help (terra runs Limine)
`install <config> localhost` assumed systemd-boot. terra's CachyOS boots
Limine, so it stopped at "/boot/loader/entries doesn't exist" — the check
added in e538788 doing its job, but with nowhere to go.
Limine cannot help here at all: `bootctl status` lists it as
`✗ One-shot entry control`, and CachyOS's pacman hooks regenerate
limine.conf regardless. So drop below the bootloader entirely and use the
firmware's own BootNext, pointing at a temporary UEFI entry that
EFI-stub-boots the installer kernel straight off the ESP. That keeps the
property which makes this safe to attempt: BootNext is spent by that one
boot, so a failed try still comes back on the normal bootloader.
- picked at runtime: systemd-boot loader entry when $BOOT/loader/entries
exists, else arm_efi_bootnext(). jupiter/neptun and terra-after-install
keep the systemd-boot path.
- `efibootmgr --create-only`, NOT `--create`: the latter pushes the entry
to the front of BootOrder, which would make a wiped installer the
permanent default if the install died halfway.
- the EFI stub loads initrd= from the volume it was loaded from, so this
mode stages on --print-esp-path rather than --print-boot-path.
- stale entries from an earlier attempt are removed before adding one, and
homelab-auto-install.service deletes the entry as soon as it boots, so
nothing lingers in NVRAM pointing at a reformatted partition.
- label matching is EXACT ("Homelab Installer"); a prefix match would have
deleted this box's Windows or Limine entry.
Verified against terra's real NVRAM (read-only): the label parser picks out
Limine/UEFI OS/Windows by exact name and rejects prefixes, and both branches
run end-to-end under stubs — BootNext mode emits the right --disk/--part,
loader path and initrd= cmdline, systemd-boot mode still writes its entry and
never calls efibootmgr.
README/CLAUDE.md corrected: terra runs Limine, not systemd-boot.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
This commit is contained in:
Claude Opus 4.8
+105
-11
@@ -132,6 +132,72 @@ disks_backing() {
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lsblk -rnso NAME,TYPE "$1" 2>/dev/null | awk '$2 == "disk" { print "/dev/" $1 }'
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}
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# Label of the temporary UEFI boot entry arm_efi_bootnext() creates. Also the
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# key the ISO uses to delete it again once it has booted (see flake.nix).
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EFI_LABEL="Homelab Installer"
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# Boot numbers of every UEFI entry with exactly this label, one per line.
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# efibootmgr prints `Boot0002* Limine<TAB>HD(1,GPT,...)/\EFI\...`, so the
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# label runs from past the "Boot####* " prefix up to the first TAB.
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# (Character classes spelled out rather than {4}: mawk predates ERE intervals.)
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efi_entries_named() {
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efibootmgr 2>/dev/null | awk -v want="$1" '
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/^Boot[0-9A-Fa-f][0-9A-Fa-f][0-9A-Fa-f][0-9A-Fa-f]/ {
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num = substr($0, 5, 4)
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rest = substr($0, 9)
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sub(/^\*/, "", rest); sub(/^ +/, "", rest)
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split(rest, parts, "\t")
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if (parts[1] == want) print num
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}'
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}
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# Arm a genuine one-shot boot of the staged installer WITHOUT any help from the
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# bootloader: create a UEFI boot entry that EFI-stub-boots the kernel straight
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# off the ESP, and point BootNext at it.
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#
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# Needed because "boot this once, then go back to normal" is not something
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# every bootloader can do. systemd-boot has it; terra's CachyOS runs Limine,
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# which reports `One-shot entry control: ✗` and has no equivalent, and whose
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# limine.conf is regenerated by pacman hooks anyway. BootNext is a firmware
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# feature, so it works underneath all of them — and the firmware clears it
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# after that one boot, which is what keeps the "a failed attempt still comes
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# back on the normal bootloader" property that makes this safe to try.
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arm_efi_bootnext() {
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local esp="$1" cmdline="$2"
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local esp_src esp_disk esp_part num n
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need efibootmgr
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esp_src="$(findmnt -no SOURCE --nofsroot --target "$esp")" \
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|| die "couldn't resolve $esp to a device"
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esp_disk="$(disks_backing "$esp_src" | head -1 || true)"
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esp_part="$(cat "/sys/class/block/$(basename "$esp_src")/partition" 2>/dev/null || true)"
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{ [ -n "$esp_disk" ] && [ -n "$esp_part" ]; } \
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|| die "couldn't work out the disk + partition number of the ESP ($esp -> $esp_src)"
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# Clear anything left by an earlier attempt first, so repeated runs don't
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# slowly fill NVRAM with dead entries pointing at a wiped partition.
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for n in $(efi_entries_named "$EFI_LABEL"); do
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echo ">> removing stale UEFI entry Boot$n ($EFI_LABEL)"
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efibootmgr -q -B -b "$n"
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done
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# --create-only, NOT --create: the latter also pushes the entry to the front
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# of BootOrder, which would make a wiped installer the permanent default if
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# anything went wrong. This way the entry is reachable through BootNext and
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# nothing else, i.e. exactly once.
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#
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# The EFI stub loads `initrd=` off the volume it was itself loaded from, so
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# the path is relative to the ESP root and uses backslashes.
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efibootmgr -q --create-only --disk "$esp_disk" --part "$esp_part" \
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--label "$EFI_LABEL" \
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--loader '\homelab-installer\bzImage' \
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--unicode "initrd=\\homelab-installer\\initrd $cmdline"
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num="$(efi_entries_named "$EFI_LABEL" | head -1)"
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[ -n "$num" ] || die "efibootmgr did not create a '$EFI_LABEL' entry"
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efibootmgr -q --bootnext "$num"
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echo ">> UEFI BootNext -> Boot$num ($EFI_LABEL); BootOrder untouched"
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}
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# Sets tb / cpio / bbox — the kexec tarball plus the static cpio+gzip that
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# kexec-run.sh needs on PATH to rebuild its initrd.
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#
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@@ -194,15 +260,30 @@ local_install_prepare_and_reboot() {
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need stat
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need df
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# Where to stage the installer, and how to make the box boot it exactly once.
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#
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# systemd-boot keeps its entries on $BOOT — the XBOOTLDR partition when there
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# is one, the ESP otherwise — which is not always /boot. Hardcoding /boot on
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# a box that mounts its ESP elsewhere just creates a directory on the root
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# filesystem, and then reboots into an entry the firmware never sees.
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local boot
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boot="$(bootctl --print-boot-path 2>/dev/null)" \
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|| die "bootctl couldn't locate the boot partition — is systemd-boot installed here?"
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[ -d "$boot/loader/entries" ] \
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|| die "$boot/loader/entries doesn't exist — systemd-boot isn't installed on this box"
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# filesystem and then reboots into an entry the firmware never sees.
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#
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# No systemd-boot (terra's CachyOS runs Limine) means no `bootctl set-oneshot`,
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# so fall back to the firmware's own BootNext — see arm_efi_bootnext(). That
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# path EFI-stub-boots the kernel directly, which requires it to sit on the ESP
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# itself rather than on a separate XBOOTLDR.
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local boot boot_mode esp
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esp="$(bootctl --print-esp-path 2>/dev/null)" \
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|| die "bootctl couldn't locate the ESP — is this box actually UEFI-booted?"
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boot="$(bootctl --print-boot-path 2>/dev/null || echo "$esp")"
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if [ -d "$boot/loader/entries" ]; then
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boot_mode=systemd-boot
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else
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boot_mode=efi-bootnext
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boot="$esp"
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need efibootmgr
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echo ">> no systemd-boot entries at $boot/loader/entries — arming the firmware's"
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echo " own BootNext instead (bootloader in charge here: $(bootctl status 2>/dev/null | awk '/Product:/ {$1=""; print substr($0,2); exit}' || echo unknown))"
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fi
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# No default/auto-picked location — the wrong disk here is destroyed
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# mid-install (see the OS-disk check below), so this always asks rather
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@@ -273,7 +354,7 @@ local_install_prepare_and_reboot() {
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echo " -> $osdisk_real ** WIPED, unattended, after the reboot **"
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# Unquoted on purpose: collapses the one-per-line list onto one line.
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echo " staging: $stagedir (on $(echo $stage_disks))"
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echo " entry: $boot/loader/entries/homelab-installer.conf (one-shot)"
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echo " one-shot: $boot_mode"
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read -rp ">> type 'yes' to build the installer, reboot into it and wipe $osdisk_real: " ok
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[ "$ok" = yes ] || die "aborted"
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fi
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@@ -330,15 +411,28 @@ local_install_prepare_and_reboot() {
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mnt_point="$(findmnt -no TARGET --target "$stagedir")"
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iso_relpath="$(printf '/%s/%s' "${stagedir#"$mnt_point"}" homelab-installer.iso | tr -s /)"
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cat >"$boot/loader/entries/homelab-installer.conf" <<EOF
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# Identical either way — only the mechanism that gets the kernel booted with
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# it differs.
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local cmdline
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cmdline="nohibernate root=fstab loglevel=4 lsm=landlock,yama,bpf findiso=$iso_relpath homelab.install=$config homelab.keypart=$boot_partuuid"
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case "$boot_mode" in
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systemd-boot)
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cat >"$boot/loader/entries/homelab-installer.conf" <<EOF
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title Homelab Installer ($config, findiso)
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linux /homelab-installer/bzImage
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initrd /homelab-installer/initrd
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options nohibernate root=fstab loglevel=4 lsm=landlock,yama,bpf findiso=$iso_relpath homelab.install=$config homelab.keypart=$boot_partuuid
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options $cmdline
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EOF
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bootctl set-oneshot homelab-installer.conf
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echo ">> systemd-boot one-shot entry armed"
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;;
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efi-bootnext)
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arm_efi_bootnext "$boot" "$cmdline"
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;;
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esac
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echo ">> one-shot boot into the installer, then rebooting — it will finish this install itself"
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bootctl set-oneshot homelab-installer.conf
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echo ">> rebooting into the installer — it will finish this install itself"
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systemctl reboot
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}
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