kexec-iso-init: improve hybrid ISO detection and boot param handling#2083
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tlaurion wants to merge 4 commits intolinuxboot:masterfrom
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kexec-iso-init: improve hybrid ISO detection and boot param handling#2083tlaurion wants to merge 4 commits intolinuxboot:masterfrom
tlaurion wants to merge 4 commits intolinuxboot:masterfrom
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Pull request overview
Adds ISO-on-USB boot compatibility detection and improved UX/logging around kexec-based booting, including documentation of supported ISO behaviors.
Changes:
- Add initrd/GRUB scanning and USB filesystem compatibility checks for ISO-file boot, with user warnings on likely failures.
- Improve boot option selection UX and display of applied kernel parameter add/remove operations.
- Log the final kernel command line in debug output and document the ISO boot flow + compatibility matrix.
Reviewed changes
Copilot reviewed 1 out of 4 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
| initrd/bin/kexec-select-boot.sh | Simplifies menu display and improves confirmation/add/remove parameter UX. |
| initrd/bin/kexec-iso-init.sh | Adds ISO boot-method detection, USB FS probing, initrd capability heuristics, and broader distro parameter support. |
| initrd/bin/kexec-boot.sh | Refactors option parsing and adds debug logging of the final kernel cmdline. |
| doc/boot-process.md | Documents “Stage 2b” ISO-on-USB boot flow and known compatibility results. |
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- Add check_hybrid_iso() using MBR signature at offset 510 (0x55AA) - Add detect_iso_boot_method() to extract boot params from initrd via strings - Add inspect_iso_boot_config() to extract boot params from GRUB configs - Simplify header to document Dracut vs Anaconda boot methods - Use DEBUG level for NOTE/WARN/STATUS spam per logging.md - Change terminal prompts to [Y,d] style with Enter defaulting to yes - Remove Anaconda blocking - let user attempt boot (Qubes R4.3 works) - Keep combined boot params approach (let ISO initrd pick what it needs) Tested with Qubes R4.3 on Q35 QEMU (works). Ref: linuxboot#2083, linuxboot#2008
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Add resolve_grub_vars() to substitute GRUB variables like ${iso_path}
and ${isofile} with the actual ISO path when extracting boot params
from GRUB configs.
Fixes boot failure where iso-scan/filename=${iso_path} wasn't being
resolved to the actual ISO path.
Ref: linuxboot#2083
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Apr 13, 2026
Add resolve_grub_vars() to substitute GRUB variables like ${iso_path}
and ${isofile} with the actual ISO path when extracting boot params
from GRUB configs.
Fixes boot failure where iso-scan/filename=${iso_path} wasn't being
resolved to the actual ISO path.
Ref: linuxboot#2083
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Add TRACE/DEBUG to understand how boot parameters flow through kexec-boot.sh, especially the cmdline and cmdadd parameters. Ref: linuxboot#2083
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This was referenced Apr 13, 2026
- Add check_hybrid_iso() using MBR signature at offset 510 (0x55AA) - Add detect_iso_boot_method() to extract boot params from initrd via strings - Add inspect_iso_boot_config() to extract boot params from GRUB configs - Simplify header to document Dracut vs Anaconda boot methods - Use DEBUG level for NOTE/WARN/STATUS spam per logging.md - Change terminal prompts to [Y,d] style with Enter defaulting to yes - Remove Anaconda blocking - let user attempt boot (Qubes R4.3 works) - Keep combined boot params approach (let ISO initrd pick what it needs) Tested with Qubes R4.3 on Q35 QEMU (works). Ref: linuxboot#2083, linuxboot#2008 Signed-off-by: Thierry Laurion <insurgo@riseup.net>
Add resolve_grub_vars() to substitute GRUB variables like ${iso_path}
and ${isofile} with the actual ISO path when extracting boot params
from GRUB configs.
Fixes boot failure where iso-scan/filename=${iso_path} wasn't being
resolved to the actual ISO path.
Ref: linuxboot#2083
Signed-off-by: Thierry Laurion <insurgo@riseup.net>
Add TRACE/DEBUG to understand how boot parameters flow through kexec-boot.sh, especially the cmdline and cmdadd parameters. Ref: linuxboot#2083 Signed-off-by: Thierry Laurion <insurgo@riseup.net>
Fixes linuxboot#2008 - boot hybrid ISOs (PureOS, Ubuntu, Tails, NixOS, Kicksecure, etc.) directly from ISO file on USB without needing to dd the ISO to a raw USB device. Key fixes (TESTED): - kexec-parse-boot: check_path() no longer fails on ISO-mounted files (which exist via FUSE but not at kernel level during initrd execution) - kexec-parse-boot: fix TAB-indented GRUB configs and leading whitespace stripping (sed 's/^[[:space:]]*//' before extracting cmd/val) - kexec-parse-boot: fix case \$trimcmd -> case \$cmd in syslinux_entry (trimcmd includes full line; cmd is just the command word) - kexec-parse-boot: strip GRUB '---' bootloader marker from append params - kexec-parse-boot: syslinux_end handles initrd= via \${param#initrd=} - kexec-parse-boot: fix set -e exits on normal conditions (grep -q, etc.) - kexec-parse-bls.sh: same TAB/whitespace/trim fixes - functions.sh: skip EFI boot configs (irrelevant on coreboot platforms) - unpack_initramfs.sh: handle set -e exits from grep/blkid - kexec-boot.sh: fix cmdadd append ordering in adjust_cmd_line() - kexec-select-boot.sh: fix initrd path detection Key fixes (UNTESTED - needs QEMU/hardware boot test): - kexec-iso-init: inject casper-premount script into ISO initrd (mounts ISO as loopback at /run/initramfs/iso_mount/ before casper runs) - kexec-iso-init: fix subshell isolation via /run/initramfs/livemedia.env (casper's run_scripts runs scripts in subshells; export doesn't propagate) - kexec-iso-init: patch casper to source livemedia.env after premount - kexec-iso-init: create casper-premount/ORDER so run_scripts executes script - kexec-iso-init: pass live-media=\$MOUNTED_ISO_PATH (ISO file path) - kexec-iso-init: pass iso-scan/auto=true Signed-off-by: Thierry Laurion <insurgo@riseup.net>
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Summary
Fixes #2008 - boot hybrid ISOs (PureOS, Ubuntu, Tails, NixOS, Kicksecure, etc.) directly from ISO file on USB without needing to dd the ISO to a raw USB device.
Changes
Tested (works in QEMU/Heads):
check_path()no longer fails on ISO-mounted files (FUSE-visible but not kernel-level)case $trimcmd→case $cmdin syslinux_entry---bootloader marker stripped from append paramssyslinux_endhandles initrd= via${param#initrd=}set -eexits on normal conditions fixed (grep -q, blkid, etc.)Untested (needs QEMU/hardware boot test):
/run/initramfs/iso_mount/before casper runs/run/initramfs/livemedia.envcasper-premount/ORDERso run_scripts executes the scriptlive-media=$MOUNTED_ISO_PATH(ISO file path)iso-scan/auto=trueTesting
Parser test harness at
tests/iso-parser-test.shvalidates all 13 ISOs parse correctly.Live boot test pending: PureOS 10.3 GNOME on QEMU/Heads — verify these logs:
DEBUG: Successfully injected casper-premount/iso_mount into initrdRunning /scripts/casper-premount→iso_mountscript