UKIFY(1)

NAME
ukify - Combine kernel and initrd into a signed Unified Kernel Image

SYNOPSIS

/usr/lib/systemd/ukify LINUX INITRD... [OPTIONS...]

DESCRIPTION

Note: this command is experimental for now. While it is intended to become a regular component of systemd, it might still change in behaviour and interface.

ukify is a tool that combines a kernel and an initrd with a UEFI boot stub to create a Unified Kernel Image (UKI)[1] — a PE binary that can be executed by the firmware to start the embedded linux kernel. See systemd-stub(7) for details about the stub.

Additional sections will be inserted into the UKI, either automatically or only if a specific option is provided. See the discussions of --cmdline=, --os-release=, --devicetree=, --splash=, --pcrpkey=, --uname=, and --section= below.

If PCR signing keys are provided via the --pcr-public-key= and --pcr-private-key= options, PCR values that will be seen after booting with the given kernel, initrd, and other sections, will be calculated, signed, and embedded in the UKI. systemd-measure(1) is used to perform this calculation and signing.

The calculation of PCR values is done for specific boot phase paths. Those can be specified with --phases= option. If not specified, the default provided by systemd-measure is used. It is also possible to specify the --pcr-private-key=, --pcr-public-key=, and --phases= arguments more than once. Signatures will be then performed with each of the specified keys. When both --phases= and --pcr-private-key= are used, they must be specified the same number of times, and then the n-th boot phase path set will be signed by the n-th key. This can be used to build different trust policies for different phases of the boot.

If a SecureBoot signing key is provided via the --secureboot-private-key= option, the resulting PE binary will be signed as a whole, allowing the resulting UKI to be trusted by SecureBoot. Also see the discussion of automatic enrollment in systemd-boot(7).

OPTIONS

Note that the LINUX positional argument is mandatory. The INITRD positional arguments are optional. If more than one is specified, they will all be combined into a single PE section. This is useful to for example prepend microcode before the actual initrd.

The following options are understood:

--cmdline=TEXT|@PATH
    Specify the kernel command line (the ".cmdline" section). The argument may be a literal string, or "@" followed by a path name. If not specified, no command line will be embedded.

--os-release=TEXT|@PATH
    Specify the os-release description (the ".osrel" section). The argument may be a literal string, or "@" followed by a path name. If not specified, the os-release(5) file will be picked up from the host system.

--devicetree=PATH
    Specify the devicetree description (the ".dtb" section). The argument is a path to a compiled binary DeviceTree file. If not specified, the section will not be present.

--splash=PATH
    Specify a picture to display during boot (the ".splash" section). The argument is a path to a BMP file. If not specified, the section will not be present.

--pcrpkey=PATH
    Specify a path to a public key to embed in the ".pcrpkey" section. If not specified, and there's exactly one --pcr-public-key= argument, that key will be used. Otherwise, the section will not be present.

--uname=VERSION
    Specify the kernel version (as in uname -r, the ".uname" section). If not specified, an attempt will be made to extract the version string from the kernel image. It is recommended to pass this explicitly if known, because the extraction is based on heuristics and not very reliable. If not specified and extraction fails, the section will not be present.

--section=NAME:TEXT|@PATH
    Specify an arbitrary additional section "NAME". Note that the name is used as-is, and if the section name should start with a dot, it must be included in NAME. The argument may be a literal string, or "@" followed by a path name. This option may be specified more than once. Any sections specified in this fashion will be inserted (in order) before the ".linux" section which is always last.

--pcr-private-key=PATH
    Specify a private key to use for signing PCR policies. This option may be specified more than once, in which case multiple signatures will be made.

--pcr-public-key=PATH
    Specify a public key to use for signing PCR policies. This option may be specified more than once, similarly to the --pcr-private-key= option. If not present, the public keys will be extracted from the private keys. If present, the this option must be specified the same number of times as the --pcr-private-key= option.

--phases=LIST
    A comma or space-separated list of colon-separated phase paths to sign a policy for. If not present, the default of systemd-measure(1) will be used. When this argument is present, it must appear the same number of times as the --pcr-private-key= option. Each set of boot phase paths will be signed with the corresponding private key.

--pcr-banks=PATH
    A comma or space-separated list of PCR banks to sign a policy for. If not present, all known banks will be used ("sha1", "sha256", "sha384", "sha512"), which will fail if not supported by the system.

--secureboot-private-key=SB_KEY
    A path to a private key to use for signing of the resulting binary. If the --signing-engine= option is used, this may also be an engine-specific designation.

--secureboot-certificate=SB_CERT
    A path to a certificate to use for signing of the resulting binary. If the --signing-engine= option is used, this may also be an engine-specific designation.

--signing-engine=ENGINE
    An "engine" to for signing of the resulting binary. This option is currently passed verbatim to the --engine= option of sbsign(1).

--sign-kernel, --no-sign-kernel
    Override the detection of whether to sign the Linux binary itself before it is embedded in the combined image. If not specified, it will be signed if a SecureBoot signing key is provided via the --secureboot-private-key= option and the binary has not already been signed. If --sign-kernel is specified, and the binary has already been signed, the signature will be appended anyway.

--tools=DIRS
    Specify one or more directories with helper tools. ukify will look for helper tools in those directories first, and if not found, try to load them from $PATH in the usual fashion.

--measure, --no-measure
    Enable or disable a call to systemd-measure to print pre-calculated PCR values. Defaults to false.

--output=FILENAME
    The output filename. If not specified, the name of the LINUX argument, with the suffix ".unsigned.efi" or ".signed.efi" will be used, depending on whether signing for SecureBoot was performed.

-h, --help
    Print a short help text and exit.

--version
    Print a short version string and exit.

EXAMPLES

Example 1. Minimal invocation

    ukify \
          /lib/modules/6.0.9-300.fc37.x86_64/vmlinuz \
          /some/path/initramfs-6.0.9-300.fc37.x86_64.img \
          --cmdline='quiet rw'

This creates an unsigned UKI ./vmlinuz.unsigned.efi.

Example 2. All the bells and whistles

    /usr/lib/systemd/ukify \
          /lib/modules/6.0.9-300.fc37.x86_64/vmlinuz \
          early_cpio \
          /some/path/initramfs-6.0.9-300.fc37.x86_64.img \
          --pcr-private-key=pcr-private-initrd-key.pem \
          --pcr-public-key=pcr-public-initrd-key.pem \
          --phases='enter-initrd' \
          --pcr-private-key=pcr-private-system-key.pem \
          --pcr-public-key=pcr-public-system-key.pem \
          --phases='enter-initrd:leave-initrd enter-initrd:leave-initrd:sysinit \
                    enter-initrd:leave-initrd:sysinit:ready' \
          --pcr-banks=sha384,sha512 \
          --secureboot-private-key=sb.key \
          --secureboot-certificate=sb.cert \
          --sign-kernel \
          --cmdline='quiet rw rhgb'

This creates a signed UKI ./vmlinuz.signed.efi. The initrd section contains two concatenated parts, early_cpio and initramfs-6.0.9-300.fc37.x86_64.img. The policy embedded in the ".pcrsig" section will be signed for the initrd (the enter-initrd phase) with the key pcr-private-initrd-key.pem, and for the main system (phases leave-initrd, sysinit, ready) with the key pcr-private-system-key.pem. The Linux binary and the resulting combined image will be signed with the SecureBoot key sb.key.

SEE ALSO

systemd(1), systemd-stub(7), systemd-boot(7), objcopy(1), systemd-pcrphase.service(8)

NOTES

1.  Unified Kernel Image (UKI)
    https://uapi-group.org/specifications/specs/unified_kernel_image/