booster-um config file is located at /etc/booster-um.yaml. It is empty by default, but here is an example configuration:

sign_uki: true
sbsign: false
colors: true
efistub: true
microcode: true
low_memory: false
enable_splash: true
remove_leftovers: true
generate_fallback: true

cmdline: >
  root=LABEL=arch_root
  rw
  quiet
  loglevel=3
  udev.log_level=3
  sysrq_always_enabled=1

fallback_cmdline: >
  root=LABEL=arch_root
  rw
  sysrq_always_enabled=1

kernel_config:
  cmdline_per_kernel: false
  share_default_cmdline: false
  default_initramfs: [default, fallback]
  default_splash: /usr/share/systemd/bootctl/splash-arch.bmp
  linux:
    # splash:
    # cmdline:
    # fallback_cmdline:
    initramfs: [default]
    booster_config: |
      compression: zstd
      extra_files: busybox,fsck,fsck.ext4
  linux-lts:
    splash: false
    # cmdline:
    # fallback_cmdline:
    initramfs: [fallback]
  # linux-zen:

efistub_config:
  default_entry: linux
  append_entries: true

sbsign_config:
  pcr_banks: sha1,sha256,sha384,sha512
  pcr_private_key: /path/to/pcr-private-key.pem
  pcr_public_key: /path/to/pcr-public-key.pem
  secureboot_private_key: /path/to/DB.key
  secureboot_certificate: /path/to/DB.crt

sign_uki: true
sbsign: false
colors: true
efistub: true
microcode: true
low_memory: false
enable_splash: true
remove_leftovers: true
generate_fallback: true

cmdline: >
  root=LABEL=arch_root
  rw
  quiet

fallback_cmdline: "root=LABEL=arch_root rw"

• sign_uki manages the UKI signing. If enabled, sbctl (or sbsign), will sign generated UKI files. If it is not specified, its value is set to true

• sbsign manages UKI signing using the sbsign tool. If enabled, sbsign will be used instead of sbctl. After enabling this type of signing, the options in the sbsign_config node can be set arbitrarily. If it is not specified, its value is set to false

• colors colors the output of the booster-um. If it is not specified, its value is set to true

• efistub manages EFI entries. If enabled, booster-um will create a new EFI entry. If it is not specified, its value is set to false

• microcode manages the inclusion of the microcode images (intel-ucode and amd-ucode). If it is not specified, its value is set to true

• low_memory is an option that prevents high memory usage, especially when fallback images are generated. Instead of generating initramfs in parallel, booster-um will generate initramfs one by one. This is certainly slower, but takes up less memory. If it is not specified, its value is set to false

• enable_splash is an option that enables splash screen. If you want to disable splash for all specified or unspecified kernels under kernel_config node, set it to false. By default this option is enabled and /usr/share/systemd/bootctl/splash-arch.bmp splash will be used (you can change it with default_splash option under kernel_config node)

• remove_leftovers manages the removal of leftovers when generating the UKI files. Besides the vmlinuz and booster files, EFI entries, fallback images and kernel cmdlines are treated as leftovers, they will be removed if efistub, cmdline_per_kernel, generate_fallback options are disabled. If enabled, leftovers will always be removed after generating UKI files. Leftovers will always be removed if you manually delete the UKI for the specified kernel or all installed kernels (booster-um -r <package> or booster-um -R/booster-um -C). If it is not specified, its value is set to true

• generate_fallback manages the creation of fallback (universal) UKI files. Only fallback images will be generated if universal flag is enabled in the /etc/booster.yaml config. If it is not specified, its value is set to false

• cmdline is the default kernel cmdline and is used by all kernels. If cmdline is not defined here, booster-um will try to use the cmdline from /etc/kernel/cmdline file. If cmdline is not defined neither in the config nor in the /etc/kernel/cmdline file, the current cmdline from /proc/cmdline will be used. Kernel parameters can be written in multiple lines after the > sign. For example:

  cmdline: >
    root=LABEL=arch_root
    rw
    quiet

• fallback_cmdline is same as cmdline but for fallback kernel images. If it is not defined here, booster-um will try to use the cmdline from /etc/kernel/fallback-cmdline file. If cmdline is not defined neither in the config nor in the /etc/kernel/fallback-cmdline file, the current cmdline from /proc/cmdline will be used

 kernel_config:
   cmdline_per_kernel: false
   share_default_cmdline: false
   default_initramfs: [default, fallback]
   default_splash: /path/to/splash.bmp
   linux: 
     cmdline: >
       root=LABEL=arch_root
       rw
       quiet
     fallback_cmdline: "root=LABEL=arch_root rw"
     initramfs: [default]
     booster_config: |
       compression: zstd
       extra_files: busybox,fsck,fsck.ext4
   linux-lts:
     splash: false
     cmdline: "root=LABEL=arch_root rw quiet"
     fallback_cmdline: "root=LABEL=arch_root rw"
     initramfs: [fallback]

pkgbase = kernel package name (linux, linux-lts, linux-zen, etc.)

kernel_config node provides kernel configuration:

• cmdline_per_kernel manages the creation of the cmdline per kernel. If this option is enabled, each kernel will use a separate cmdline which can be defined under pkgbase node within the cmdline option. If it is not specified, its value is set to false

• share_default_cmdline allows default cmdline to be shared with the cmdline of the specified kernel pkgbase under the kernel_config node. The default cmdline cmdline, fallback_cmdline or /etc/kernel/cmdline, /etc/kernel/fallback-cmdline files will be used as a shared cmdline for all kernels. That means that the kernel cmdline specified under pkgbase node, will be added to the default cmdline. This option only takes effect if the cmdline_per_kernel option is enabled. By default this option is set to false

• default_initramfs array provides initramfs type configuration for all other unspecified kernels. You can specify up to two types, default and fallback. if not defined, its values ​​will be default and fallback

Note: If you specified fallback type, you must enable generate_fallback, otherwise it will generate default images only

• default_splash a picture to display during boot. This is the default splash for all unspecified kernels under kernel_config node. The argument is a path to a BMP file. The default /usr/share/systemd/bootctl/splash-arch.bmp picture will be used if this path is invalid or not specified. To disable splash screen for all unspecified pkgbases under kernel_config node, simply set this option to false or leave it blank, for example:

    # valid options
    kernel_config:
      default_splash:
      default_splash: ''
      default_splash: ""
      default_splash: false

• pkgbase (kernel package name, below as $pkgbase) node provides additional configuration for specified kernel package name:

  • splash a picture to display during boot for the specified kernel. To disable splash screen for specified kernel pkgbase, simply set this option to false or leave it blank. If splash is not defined, the default_splash option outside the $pkgbase node, will be used

  • cmdline is the cmdline for the specified kernel. This cmdline will be applied if the cmdline_per_kernel option is enabled. If cmdline is not defined here, booster-um will try to use the cmdline from /etc/kernel/$pkgbase.cmdline file. If cmdline is not defined neither in the config nor in the /etc/kernel/$pkgbase.cmdline, booster-um will try to use the default cmdline outside the kernel_config node

  • fallback_cmdline is same as cmdline but for fallback kernel images. If it is not defined here, booster-um will try to use the cmdline from /etc/kernel/$pkgbase-fallback.cmdline file. If cmdline is not defined neither in the config nor in the /etc/kernel/$pkgbase-fallback.cmdline, booster-um will try to use the default fallback_cmdline outside the kernel_config node

  • initramfs provides initramfs type configuration for specified kernel. Here you can specify up to two types, default and fallback. If it is not defined, the default_initramfs will be used

  • booster_config provides additional booster configuration for specified kernel. Booster configuration can be written in multiple lines after the | sign. You can read here about booster configuration. For example:

    booster_config: |
     compression: lz4
     extra_files: busybox,fsck,fsck.ext4

  Note: If you enable universal flag here, booster-um will only create a fallback UKI for the specified kernel even if generate_fallback is disabled, or initramfs (default_initramfs) has the fallback type specified.

efistub_config:
 default_entry: linux
 append_entries: true

• efistub_config node provides additional efistub configuration:
  • default_entry makes sure that the EFI entry of the specified kernel is the first in the EFI boot order. If fallback UKI is generated for the specified kernel, its EFI entry will be added after the default entry. After changing its value, it is enough to regenerate all images (booster-um -G)
  • append_entries takes care of where new EFI entries will be added to the boot order. If enabled , newly created EFI entries will be added to the end of the boot order, otherwise they will be added to the beginning. If it is not specified, its value is set to true

 sbsign_config:
   pcr_banks: sha1,sha256,sha384,sha512
   pcr_private_key: /path/to/pcr-private-key.pem
   pcr_public_key: /path/to/pcr-public-key.pem
   secureboot_private_key: /path/to/DB.key
   secureboot_certificate: /path/to/DB.crt

• sbsign_config node provides sbsign configuration:
  • pcr_banks a comma separated list of PCR banks to sign a policy for
  • pcr_private_key a path to a private key to use for signing PCR policies
  • pcr_public_key a path to public key to use for signing PCR policies
  • secureboot_private_key a path to a private key to use for signing of the UKI file
  • secureboot_certificate a path to a certificate to use for signing of UKI file