Provided by: systemd-ukify_256.5-2ubuntu3.1_all 
NAME
ukify - Combine components into a signed Unified Kernel Image for UEFI systems
SYNOPSIS
ukify [OPTIONS...] build
ukify [OPTIONS...] genkey
ukify [OPTIONS...] inspect FILE...
DESCRIPTION
ukify is a tool whose primary purpose is to combine components (usually a kernel, an initrd, and 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.
COMMANDS
The following commands are understood:
build
This command creates a Unified Kernel Image. The two primary options that should be specified for the
build verb are Linux=/--linux=, and Initrd=/--initrd=. Initrd= accepts multiple whitespace-separated
paths and --initrd= can be specified multiple times.
Additional sections will be inserted into the UKI, either automatically or only if a specific option is
provided. See the discussions of Microcode=/--microcode=, Cmdline=/--cmdline=, OSRelease=/--os-release=,
DeviceTree=/--devicetree=, Splash=/--splash=, PCRPKey=/--pcrpkey=, Uname=/--uname=, SBAT=/--sbat=, and
--section= below.
ukify can also be used to assemble a PE binary that is not executable but contains auxiliary data, for
example additional kernel command line entries.
If PCR signing keys are provided via the PCRPrivateKey=/--pcr-private-key= and
PCRPublicKey=/--pcr-public-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 the
Phases=/--phases= option. If not specified, the default provided by systemd-measure is used. It is also
possible to specify the PCRPrivateKey=/--pcr-private-key=, PCRPublicKey=/--pcr-public-key=, and
Phases=/--phases= arguments more than once. Signatures will then be performed with each of the specified
keys. On the command line, 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. In the config file,
PCRPrivateKey=, PCRPublicKey=, and Phases= are grouped into separate sections, describing separate boot
phases. If SigningEngine=/--signing-engine= is specified, then the private keys arguments will be passed
verbatim to OpenSSL as URIs, and the public key arguments will be loaded as X.509 certificates, so that
signing can be performed with an OpenSSL engine.
If a SecureBoot signing key is provided via the SecureBootPrivateKey=/--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).
If the stub and/or the kernel contain ".sbat" sections they will be merged in the UKI so that revocation
updates affecting either are considered when the UKI is loaded by Shim. For more information on SBAT see
Shim documentation[2].
genkey
This command creates the keys for PCR signing and the key and certificate used for SecureBoot signing.
The same configuration options that determine what keys and in which paths will be needed for signing
when build is used, here determine which keys will be created. See the discussion of
PCRPrivateKey=/--pcr-private-key=, PCRPublicKey=/--pcr-public-key=, and
SecureBootPrivateKey=/--secureboot-private-key= below.
The output files must not exist.
inspect
Display information about the sections in a given binary or binaries. If --all is given, all sections are
shown. Otherwise, if --section= option is specified at least once, only those sections are shown.
Otherwise, well-known sections that are typically included in an UKI are shown. For each section, its
name, size, and sha256-digest is printed. For text sections, the contents are printed.
Also see the description of -j/--json= and --section=.
Other tools that may be useful for inspect UKIs: llvm-objdump(1) -p and pe-inspect.
CONFIGURATION SETTINGS
Settings can appear in configuration files (the syntax with SomeSetting=value) and on the command line
(the syntax with --some-setting=value). For some command line parameters, a single-letter shortcut is
also allowed. In the configuration files, the setting must be in the appropriate section, so the
descriptions are grouped by section below. When the same setting appears in the configuration file and on
the command line, generally the command line setting has higher priority and overwrites the config file
setting completely. If some setting behaves differently, this is described below.
If no config file is provided via the option --config=PATH, ukify will try to look for a default
configuration file in the following paths in this order: /etc/systemd/ukify.conf,
/run/systemd/ukify.conf, /usr/local/lib/systemd/ukify.conf, and /usr/lib/systemd/ukify.conf, and then
load the first one found. ukify will proceed normally if no configuration file is specified and no
default one is found.
The LINUX and INITRD positional arguments, or the equivalent Linux= and Initrd= settings, are optional.
If more than one initrd 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 and settings are understood:
Command line-only options
--config=PATH
Load configuration from the given config file. In general, settings specified in the config file have
lower precedence than the settings specified via options. In cases where the command line option does
not fully override the config file setting are explicitly mentioned in the descriptions of individual
options.
Added in version 254.
--measure, --no-measure
Enable or disable a call to systemd-measure(1) to print pre-calculated PCR values. Defaults to false.
Added in version 253.
--section=NAME:TEXT|@PATH, --section=NAME:text|binary[@PATH]
For all verbs except inspect, the first syntax is used. Specify an arbitrary additional section
"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.
For the inspect verb, the second syntax is used. The section NAME will be inspected (if found). If
the second argument is "text", the contents will be printed. If the third argument is given, the
contents will be saved to file PATH.
Note that the name is used as-is, and if the section name should start with a dot, it must be
included in NAME.
Added in version 253.
--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.
Added in version 253.
--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.
Added in version 253.
--summary
Print a summary of loaded config and exit. This is useful to check how the options from the
configuration file and the command line are combined.
Added in version 254.
--all
Print all sections (with inspect verb).
Added in version 255.
--json
Generate JSON output (with inspect verb).
Added in version 255.
-h, --help
Print a short help text and exit.
--version
Print a short version string and exit.
[UKI] section
Linux=LINUX, --linux=LINUX
A path to the kernel binary.
Added in version 254.
Initrd=INITRD..., --initrd=LINUX
Zero or more initrd paths. In the configuration file, items are separated by whitespace. The initrds
are combined in the order of specification, with the initrds specified in the config file first.
Added in version 254.
Microcode=UCODE, --microcode=UCODE
Path to initrd containing microcode updates. If not specified, the section will not be present.
Added in version 256.
Cmdline=TEXT|@PATH, --cmdline=TEXT|@PATH
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.
Added in version 253.
OSRelease=TEXT|@PATH, --os-release=TEXT|@PATH
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.
Added in version 253.
DeviceTree=PATH, --devicetree=PATH
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.
Added in version 253.
Splash=PATH, --splash=PATH
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.
Added in version 253.
PCRPKey=PATH, --pcrpkey=PATH
A path to a public key to embed in the ".pcrpkey" section. If not specified, and there's exactly one
PCRPublicKey=/--pcr-public-key= argument, that key will be used. Otherwise, the section will not be
present.
Added in version 253.
Uname=VERSION, --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.
Added in version 253.
PCRBanks=PATH, --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.
Added in version 253.
SecureBootSigningTool=SIGNER, --signtool=SIGNER
Whether to use "sbsign" or "pesign". Depending on this choice, different parameters are required in
order to sign an image. Defaults to "sbsign".
Added in version 254.
SecureBootPrivateKey=SB_KEY, --secureboot-private-key=SB_KEY
A path to a private key to use for signing of the resulting binary. If the
SigningEngine=/--signing-engine= option is used, this may also be an engine-specific designation.
This option is required by SecureBootSigningTool=sbsign/--signtool=sbsign.
Added in version 253.
SecureBootCertificate=SB_CERT, --secureboot-certificate=SB_CERT
A path to a certificate to use for signing of the resulting binary. If the
SigningEngine=/--signing-engine= option is used, this may also be an engine-specific designation.
This option is required by SecureBootSigningTool=sbsign/--signtool=sbsign.
Added in version 253.
SecureBootCertificateDir=SB_PATH, --secureboot-certificate-dir=SB_PATH
A path to a nss certificate database directory to use for signing of the resulting binary. Takes
effect when SecureBootSigningTool=pesign/--signtool=pesign is used. Defaults to /etc/pki/pesign.
Added in version 254.
SecureBootCertificateName=SB_CERTNAME, --secureboot-certificate-name=SB_CERTNAME
The name of the nss certificate database entry to use for signing of the resulting binary. This
option is required by SecureBootSigningTool=pesign/--signtool=pesign.
Added in version 254.
SecureBootCertificateValidity=DAYS, --secureboot-certificate-validity=DAYS
Period of validity (in days) for a certificate created by genkey. Defaults to 3650, i.e. 10 years.
Added in version 254.
SigningEngine=ENGINE, --signing-engine=ENGINE
An "engine" for signing of the resulting binary. This option is currently passed verbatim to the
--engine= option of sbsign(1).
Added in version 253.
SignKernel=BOOL, --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
SecureBootPrivateKey=/--secureboot-private-key= option and the binary has not already been signed. If
SignKernel=/--sign-kernel is true, and the binary has already been signed, the signature will be
appended anyway.
Added in version 253.
SBAT=TEXT|@PATH, --sbat=TEXT|@PATH
SBAT metadata associated with the UKI or addon. SBAT policies are useful to revoke whole groups of
UKIs or addons with a single, static policy update that does not take space in DBX/MOKX. If not
specified manually, a default metadata entry consisting of
"uki,1,UKI,uki,1,https://uapi-group.org/specifications/specs/unified_kernel_image/" for UKIs and
"uki-addon,1,UKI
Addon,addon,1,https://www.freedesktop.org/software/systemd/man/latest/systemd-stub.html" for addons
will be used, to ensure it is always possible to revoke them. For more information on SBAT see Shim
documentation[2].
Added in version 254.
[PCRSignature:NAME] section
In the config file, those options are grouped by section. On the command line, they must be specified in
the same order. The sections specified in both sources are combined.
PCRPrivateKey=PATH, --pcr-private-key=PATH
A private key to use for signing PCR policies. On the command line, this option may be specified more
than once, in which case multiple signatures will be made.
Added in version 253.
PCRPublicKey=PATH, --pcr-public-key=PATH
A public key to use for signing PCR policies.
On the command line, 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. On the command line,
if present, this option must be specified the same number of times as the --pcr-private-key= option.
Added in version 253.
Phases=LIST, --phases=LIST
A comma or space-separated list of colon-separated phase paths to sign a policy for. Each set of boot
phase paths will be signed with the corresponding private key. If not present, the default of
systemd-measure(1) will be used.
On the command line, when this argument is present, it must appear the same number of times as the
--pcr-private-key= option.
Added in version 253.
EXAMPLES
Example 1. Minimal invocation
$ ukify build \
--linux=/lib/modules/6.0.9-300.fc37.x86_64/vmlinuz \
--initrd=/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
$ ukify build \
--linux=/lib/modules/6.0.9-300.fc37.x86_64/vmlinuz \
--initrd=early_cpio \
--initrd=/some/path/initramfs-6.0.9-300.fc37.x86_64.img \
--sbat='sbat,1,SBAT Version,sbat,1,https://github.com/rhboot/shim/blob/main/SBAT.md
uki.author.myimage,1,UKI for System,uki.author.myimage,1,https://uapi-group.org/specifications/specs/unified_kernel_image/' \
--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.
Example 3. All the bells and whistles, via a config file
This is the same as the previous example, but this time the configuration is stored in a file:
$ cat ukify.conf
[UKI]
Initrd=early_cpio
Cmdline=quiet rw rhgb
SecureBootPrivateKey=sb.key
SecureBootCertificate=sb.cert
SignKernel=yes
PCRBanks=sha384,sha512
[PCRSignature:initrd]
PCRPrivateKey=pcr-private-initrd-key.pem
PCRPublicKey=pcr-public-initrd-key.pem
Phases=enter-initrd
[PCRSignature:system]
PCRPrivateKey=pcr-private-system-key.pem
PCRPublicKey=pcr-public-system-key.pem
Phases=enter-initrd:leave-initrd
enter-initrd:leave-initrd:sysinit
enter-initrd:leave-initrd:sysinit:ready
$ ukify -c ukify.conf build \
--linux=/lib/modules/6.0.9-300.fc37.x86_64/vmlinuz \
--initrd=/some/path/initramfs-6.0.9-300.fc37.x86_64.img
One "initrd" (early_cpio) is specified in the config file, and the other initrd
(initramfs-6.0.9-300.fc37.x86_64.img) is specified on the command line. This may be useful for example
when the first initrd contains microcode for the CPU and does not need to be updated when the kernel
version changes, unlike the actual initrd.
Example 4. Kernel command line PE addon
ukify build \
--secureboot-private-key=sb.key \
--secureboot-certificate=sb.cert \
--cmdline='debug' \
--sbat='sbat,1,SBAT Version,sbat,1,https://github.com/rhboot/shim/blob/main/SBAT.md
uki-addon.author,1,UKI Addon for System,uki-addon.author,1,https://www.freedesktop.org/software/systemd/man/systemd-stub.html'
--output=debug.addon.efi
This creates a signed PE binary that contains the additional kernel command line parameter "debug" with
SBAT metadata referring to the owner of the addon.
Example 5. Decide signing policy, and create certificate and keys
First, let's create a configuration file that specifies what signatures shall be made:
# cat >/etc/kernel/uki.conf <<EOF
[UKI]
SecureBootPrivateKey=/etc/kernel/secure-boot.key.pem
SecureBootCertificate=/etc/kernel/secure-boot.cert.pem
[PCRSignature:initrd]
Phases=enter-initrd
PCRPrivateKey=/etc/kernel/pcr-initrd.key.pem
PCRPublicKey=/etc/kernel/pcr-initrd.pub.pem
[PCRSignature:system]
Phases=enter-initrd:leave-initrd enter-initrd:leave-initrd:sysinit
enter-initrd:leave-initrd:sysinit:ready
PCRPrivateKey=/etc/kernel/pcr-system.key.pem
PCRPublicKey=/etc/kernel/pcr-system.pub.pem
EOF
Next, we can generate the certificate and keys:
# ukify genkey --config=/etc/kernel/uki.conf
Writing SecureBoot private key to /etc/kernel/secure-boot.key.pem
Writing SecureBoot certificate to /etc/kernel/secure-boot.cert.pem
Writing private key for PCR signing to /etc/kernel/pcr-initrd.key.pem
Writing public key for PCR signing to /etc/kernel/pcr-initrd.pub.pem
Writing private key for PCR signing to /etc/kernel/pcr-system.key.pem
Writing public key for PCR signing to /etc/kernel/pcr-system.pub.pem
(Both operations need to be done as root to allow write access to /etc/kernel/.)
Subsequent invocations using the config file (ukify build --config=/etc/kernel/uki.conf) will use this
certificate and key files. Note that the kernel-install(8) plugin 60-ukify.install uses
/etc/kernel/uki.conf by default, so after this file has been created, installations of kernels that
create a UKI on the local machine using kernel-install will perform signing using this config.
SEE ALSO
systemd(1), systemd-stub(7), systemd-boot(7), systemd-measure(1), systemd-pcrphase.service(8)
NOTES
1. Unified Kernel Image (UKI)
https://uapi-group.org/specifications/specs/unified_kernel_image/
2. Shim documentation
https://github.com/rhboot/shim/blob/main/SBAT.md