mkuki

mkuki builds a UEFI unified kernel image (UKI): it takes a PE/COFF EFI stub and appends the kernel, the initramfs, and the kernel command line to it as named PE sections, producing a single EFI binary that UEFI firmware boots directly. Where mkirf produces the initramfs image, mkuki is the step that wraps that image — together with a kernel and a command line — into one bootable artifact. The two are the two halves of Peios' Dynamic Boot system.

mkuki --kernel PATH --initramfs PATH (--cmdline TEXT | --cmdline-file PATH) --out PATH
      [--stub PATH] [--watch] [--debounce SECS]
mkuki --stub-info

The UKI section layout #

A UKI is an ordinary PE/COFF EFI executable — the stub — with three extra sections appended, which the stub reads at boot to find its payloads:

mkuki appends them in exactly that order. Each new section is marked as initialised, read-only data. The tool works at the PE level directly: it parses the stub's DOS/PE headers and section table, computes correctly-aligned virtual addresses and file offsets for the new sections, appends their data, updates the section count and the SizeOfImage/SizeOfHeaders fields, and — if the stub's header has no spare room for three more section entries — grows the header region and relocates the existing sections' file pointers to make space. A stub that is not a valid MZ/PE image, or whose optional header is malformed, is rejected.

The command line #

The command line is taken either literally from --cmdline or read from the file named by --cmdline-file (exactly one is required). Either way, mkuki trims trailing newlines and carriage returns and appends a single NUL terminator. A command line containing an embedded NUL byte is rejected.

The stub #

--stub names the EFI stub to append to. With no --stub, mkuki uses a stub bundled into the binary (the systemd EFI stub). mkuki --stub-info prints that bundled stub's provenance and exits, so you can see exactly what the default is without building anything.

Output and atomicity #

mkuki creates any missing parent directories of --out, writes the assembled image to a sibling temp file, and renames it into place, so an interrupted or failed build never leaves a half-written UKI behind. On success it prints the output path and byte size to stderr. Each of the three payloads must be non-empty; an empty .cmdline, .linux, or .initrd fails the build.

Watch mode #

With --watch, mkuki stays resident: it builds once up front, then rebuilds the UKI whenever an input changes — so the boot image tracks a new kernel, a freshly-repacked initramfs (mkirf's half of Dynamic Boot), or an edited command-line file with no manual step. Like mkirf's watch mode, it is a foreground loop that runs until killed; supervising it is a service manager's job, and a rebuild that fails (for example, a kernel caught mid-copy) is logged rather than fatal, so fixing the input recovers on the next change.

The watched inputs are --kernel, --initramfs, and — only if it is a --cmdline-file, since a literal --cmdline is static — the command-line file. mkuki watches each input's parent directory (non-recursively), not the file itself: this survives the atomic temp-and-rename writes that mkirf and mkuki both perform (which appear as a directory event a stale single-file watch would miss) and catches a versioned kernel being swapped in /boot. Because the watch is non-recursive, a write to an --out path nested deeper under a watched directory does not retrigger it — but an --out sitting directly in a watched input directory would, so mkuki refuses that invocation. The --debounce window (default 5 seconds) is the settle time before a rebuild.

Options #

Exactly one of --cmdline or --cmdline-file must be given: supplying both, or neither, is a usage error.

Exit status #

See also #

• mkirf — builds the .initrd payload mkuki wraps.
• The initramfs stage — what the bundled initramfs does once firmware boots the UKI.