Genkernel

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genkernel es una herramienta creada por Gentoo que se utiliza para automatizar el proceso de construcción del núcleo e initramfs. Algunas de las características generales incluyen:

• Configurar los ficheros fuente del núcleo.
• Construir el núcleo comprimido bzImage y copiarlo a /boot.
• Crear un initramfs y copiarlo a /boot.
• Crear enlaces simbólicos en /boot.
• Añadir código del usuario al initramfs tal como ficheros de cifrado, imágenes de inicio (spla.github.io/sh), módulos añadidos y demás.
• Comprimir el initramfs.
• Configurar el Gestor de arranque para arrancar el núcleo e initramfs recientemente creados.

Where options have only a negative effect, the no-, and its effect, which are not optional in this case, are figured without square brackets. }}

--config=/path/to/genkernel.conf

Points to the Genkernel configuration file to use (defaults to /etc/genkernel.conf).

--kernel-config=/path/to/kernel.config

Points to the kernel configuration file to use. To re-use the kernel configuration from the currently running kernel, it is possible to specify /proc/config.gz if it exists. By default, genkernel uses the config from the previous build of the same kernel version or a default kernel config if there isn't a previous config. Use the special value default to force usage of genkernel's generic kernel config. This location must not be /usr/src/linux/.config as it risks being lost or causing errors.

--[no-]menuconfig

Activates (or deactivates) the make menuconfig command (which invokes an interactive configuration menu) before building the kernel.

--gconfig

Provides a kernel configuration utility which depends on the GTK libraries. The advantage of this option is that most users find it easier and clearer to configure the kernel using this tool, since it relies on the X-windowing system. The disadvantage of this option is that the X-windowing system is required to use it, so it will not work on the command line.

--xconfig

Provides a kernel configuration utility which depends on the QT libraries. The advantage of this option is that most users find it easier and clearer to configure the kernel using this tool, since it relies on the X-windowing system. The disadvantage of this option is that the X-windowing system is needed to use it, so it will not work on the command line.

--[no-]save-config

Saves [or does not save] the kernel configuration to a file in the /etc/kernels directory for later use.

--kernel-append-localversion=-mycfg42

Allows the modification of kernel's LOCALVERSION value which will affect kernel's and and initramfs' filename in /boot and modules in /lib/modules/ directory. This is especially helpful to build a new independent revision with its own kernel binary, initramfs and modules. The example above, with =sys-kernel/gentoo-sources-5.4.2, would create /boot/vmlinuz-5.4.2-gentoo-x86_64-mycfg42, /boot/initramfs-5.4.2-gentoo-x86_64-mycfg42.img and /lib/modules/4.19.88-gentoo-x86_64-mycfg42 on amd64 with default settings.

Las opciones de configuración mostradas aquí, definen qué características podrán ser o no se activadas en el núcleo e initrd resultantes.

--[no-]splash

Activa (o desactiva) el soporte del framebuffer splash Fbsplash en la imagen initrd construida para el núcleo. Para utilizar un tema distinto del que se ofrece por defecto por fbsplash, utilice --splash=TemaPreferido (donde TemaPreferido es el título de uno de los directorios dentro del directorio /etc/splash).

--splash-res=ResoluciónPreferida

Esta opción permite seleccionar qué resoluciones de pantallas para splash se ofrecerán durante el arranque del sistema. Esto es útil por dos razones. En primer lugar se puede seleccionar únicamente la resolución o resoluciones de pantalla relevantes para el sistema. En segundo lugar se puede evitar el incremento innecesario del espacio en disco que se initrd necesita (ya que la imagen initrd no ofrece soporte para las resoluciones que no son relevantes para la configuración del sistema). Sin embargo, esta opción se omite en mejores situaciones, por ejemplo cuando se construye un núcleo para un CD de instalación, esto permite soporte de splash para todas las resoluciones posibles.

--do-keymap-auto

Forzar las selección del mapa del teclado durante el arranque.

--keymap

Habilita la selección de mapa del teclado en el inicio del sistema (por ejemplo, para la entrada de la contraseña de contenedores LUKS). El mapa del teclado deseado se puede pasar como opción de inicio en el valor de keymap (nombre del fichero de mapa del teclado sin .map). Los ficheros de mapa de teclado disponibles se pueden encontrar en /usr/share/genkernel/defaults/keymaps/.

Si el mapa del teclado necesitado no está disponible en genkernel, se puede convertir uno de los mapas de sys-apps/kbd ya existentes (disponibles en /usr/share/genkernel/defaults/keymaps/) utilizando loadkeys --bkeymap. Leer la página del manual de loadkeys para más detalles.

--lvm

Incluye soporte para almacenamiento mediante gestión de volúmenes lógicos (LVM2) desde binarios estáticos si están disponibles en el sistema. Los binarios (estáticos) relevantes LVM2 se compilan si no están disponibles. Asegúrese de instalar el paquete sys-fs/lvm2 en el sistema (emerge sys-fs/lvm2) antes de habilitar esta opción, luego eche un vistazo al artículo sobre LVM en el wiki de Gentoo.

--dmraid

Incluye soporte para DMRAID, la utilidad que crea mapeos RAID utilizando el subsistema de mapeo de dispositivos del núcleo. DMRAID descubre, activa, desactiva y muestra las propiedades de conjuntos de software RAID (por ejemplo ATARAID) y particiones DOS contenidas.

--luks

Incluye soporte para la configuración de clave unificada Linux o LUKS. Esto permite utilizar un dispositivo cifrado por LUKS que contiene el sistema de ficheros. En el cargador de arranque, se configura un dispositivo cifrado en el valor de crypt_root (y root debería ser el dispositivo no cifrado que crea LUKS).

--disklabel

Añade soporte para etiquetas de discos y UUID support en la imagen initrd.

--iscsi

Añade soporte para iSCSI en la imagen initrd.

--multipath

Añade soporte para Multipath a la imagen initrd.

--linuxrc=/ruta/al/fichero/linuxrc

Especifica un archivo linuxrc creado por el usuario, un guión que se inicializa durante la fase de inicialización del núcleo antes de la propia fase de arranque. Se puede encontar un guión linuxrc por defecto en el directorio /usr/share/genkernel/. Este guión permite iniciar en un pequeño núcleo modular que intentará cargar la menor cantidad de controladores (como módulos) necesitados por el sistema.

--cachedir=/ruta/al/directorio/alternativo

Cambia la localización por defecto de la caché que se utiliza cuando se construye el núcleo.

--tempdir=/ruta/al/nuevo/directoriotemporal

Especifica la localización del directorio temporal utilizado por genkernel durante la construcción del núcleo.

--unionfs

Incluye soporte para el sistema de ficheros de unificación en la imagen initrd.

--mountboot

Detecta si se necesita montar o no el directorio /boot en una partición separada. Buscará instrucciones acerca de cómo montar la partición de inicio en un sistema de ficheros en el guión /etc/fstab (si es necesario).

--microcode

Crea un cpio temprano relleno con microcódigo para procesadores Intel/AMD processors para ofrecer soporte temprano para Xen y Linux.

--splash-res=PreferredResolution

This option allows to select which splash screen resolutions will be supported in the initrd during the start-up of the system. This is useful for two reasons. First, to be able to select only the splash screen resolution(s) relevant to the system. Second, to avoid the unnecessary increase in the disk space required by initrd (since the initrd does not have to support resolutions that are irrelevant for the system's configuration.) However, the option is best omitted if the kernel is being compiled for an Installation CD; this allows splash support for all possible resolutions.

--do-keymap-auto

Force keymap selection during the boot sequence.

--keymap

Enables keymap selection at boot (e.g. for LUKS container password input). The desired keymap can be passed in boot options as the value of keymap (name of the keymap file without .map). Available keymap files can be found in /usr/share/genkernel/defaults/keymaps/.

If a needed keymap is not available in genkernel, it is possible to convert one of the existing sys-apps/kbd keymaps (available in /usr/share/genkernel/defaults/keymaps/) using loadkeys --bkeymap. See loadkeys man page for details.

--lvm

Includes support for storage using via Logical Volume Management (LVM2) from static binaries, if available to the system. Relevant (static) LVM2 binaries are compiled when unavailable. Be sure to install the sys-fs/lvm2 package on the system (emerge sys-fs/lvm2) before enabling this option.

--dmraid

Includes support for DMRAID; the utility which creates RAID mappings using the kernel device-mapper subsystem. DMRAID discovers, activates, deactivates and displays properties of software RAID sets (ATARAID, for example) and contained DOS partitions.

--luks

Includes support for Linux Unified Key Setup. This will allow to use a device encrypted by LUKS which contains the root filesystem. On the bootloader, set that encrypted device as the value of crypt_root, and root shall be the unencrypted device LUKS creates ( i.e /dev/mapper/root will be path to mount, and proper boot parameters line will look, like this: GRUB_CMDLINE_LINUX="... crypt_root=UUID=<crypto_LUKS uuid> root=/dev/mapper/root ...").

--iscsi

Adds support for iSCSI to the initrd.

--multipath

Adds support for Multipath to the initrd.

--linuxrc=/path/to/the/linuxrc_file

Specifies a user-created linuxrc — a script that is initialized during the start-up stage of the kernel, prior to the actual boot process. A default linuxrc script can be found in the /usr/share/genkernel/ directory. This script allows booting into a small, modularized kernel; it tries to load the minimum amount of drivers that are needed (as modules) by the system.

--cachedir=/path/to/alt/dir

Overrides the default cache location used while compiling the kernel.

--tmpdir=/path/to/new/tempdir

Specifies the location of the temporary directory used by genkernel while compiling the kernel.

--unionfs

Includes support for the Unification File System in the initrd image.

--mountboot

Detects whether or not the /boot directory needs to be mounted on a separate partition. It will check /etc/fstab script for instructions on how to mount the boot partition on a file system (if needed).

--microcode

Creates an early cpio filled with microcode for Intel/AMD processors for Linux early microcode support.

Las siguientes opciones están soportadas por genkernel y se pasan a las aplicaciones relevantes mientras se ensambla el núcleo. Estas opciones afectan a las herramientas de compilación utilizadas en el proceso de compilación del núcleo aunque a un nivel mucho más bajo.

--kernel-cc=someCompiler

Specifies the compiler employed during the kernel compilation process.

--kernel-ld=someLinker

Specifies the linker employed during the kernel compilation process.

--kernel-as=someAssembler

Specifies the assembler employed during the kernel compilation process.

--kernel-make=someMake

Specifies an alternative to the GNU make utility employed during the kernel compilation process.

--utils-cc=someCompiler

Specifies the compiler employed during the compilation of support utilities.

--utils-ld=someLinker

Specifies the linker employed during the compilation of support utilities.

--utils-as=someAssembler

Specifies the assembler employed during the compilation of support utilities.

--utils-make=someMake

Specifies an alternative to the GNU make utility employed during the compilation of support utilities.

--makeopts=-jX

Specifies the number of concurrent threads that the make utility can implement while the kernel (and utilities) are being compiled. The variable X is a number to be freely chosen, although the most common values are obtained by adding one (1) to the number of cores used by the system, or just use the number of cores on the system. So, for a system with one core, most common option values are -j2 or -j1; a system with two cores most likely uses the -j3 or -j2 options, and so on. (A system with one processor that supports Hyper-ThreadingTM (HT) Technology can be assumed to have 2 cores, provided Symmetric Multi-Processing (SMP) support is enabled in the kernel.)

--kerneldir=/path/to/sources/

Specifies an alternative kernel source location, rather than the default /usr/src/linux/ location.

--kernel-config=/path/to/config-file

Specifies which kernel configuration will be used. By default, genkernel will determine kernel version found in --kerneldir and look for kernel config (KV) in /etc/kernels/kernel-config-$KV. If no kernel configuration was found, genkernel will look for a generic kernel configuration in /usr/share/genkernel/$ARCH. A special value default can be used to force usage of genkernel's generic kernel configuration.

Consejo
Use --kernel-config=/proc/config.gz to start building a new kernel based on kernel configuration from currently running kernel.
Note: This will only work if current active kernel was built with CONFIG_IKCONFIG=y which is normally the case.

--module-prefix=/path/to/prefix-directory/

Specifies a prefix to the directory where kernel modules will be installed (default path is the /lib/modules directory.)

--[no-]clean

Activates (or deactivates) the make clean command before compiling the kernel. The make clean command removes all object files and dependencies from the kernel's source tree.

--[no-]mrproper

Activates (or deactivates) the make mrproper command before kernel compilation. Like the make clean command listed above, make mrproper removes all object files and dependencies from the kernel's source tree. However, any previous configuration files (in /path/to/sources/.config or /path/to/sources/.config.old) will also be purged from the kernel's source tree. If it is undesirable that the kernel's .config file keeps disappearing, be sure to disable this option!

--oldconfig

Issues the make oldconfig command, which attempts to collect configuration information for the system's architecture from a generic script in /usr/share/genkernel. This is a non-interactive process; no user input is entertained. Also, if --oldconfig is used in conjunction with --clean, the latter option is negated, resulting in the activation of the --no-clean option.

--[no-]module-rebuild

Runs, or does not run emerge @module-rebuild to build out-of-tree modules after kernel and kernel modules have been built. This option is enabled by default.

--callback="echo hello"

Calls the specified arguments (echo hello, in this case) after the kernel and the relevant modules have been built, but before building the initramfs.

Nota
Before genkernel-4, this callback was used to trigger rebuild of out-of-tree modules. Since genkernel-4, a dedicated command-line parameter --module-rebuild was introduced, see above.

--[no-]install

Activates (or deactivates) the make install command, which installs the new kernel image, configuration file, initrd image and system map onto the boot partition. Any compiled modules will be installed as well. By default genkernel will attempt mount /boot if it is on a separate partition before running the install command.

--no-ramdisk-modules

Refrains from copying any modules to the genkernel-created initrd image. This option is an exception to the rule about the no- prefix; omission of this prefix creates an invalid genkernel option.

--all-ramdisk-modules

Copies all available modules to the genkernel-created initrd image.

--genzimage

Creates the initrd image, prior to the kernel image (this hack currently applies only to PPC Pegasos systems).

--loglevel=<0|1|2|3|4|5>

Controls the level of verbosity for information printed by genkernel. The variable LOGLEVEL is an integer between 0 and 5. The level '0' represents minimal output (=no output), while '5' provides as much information as possible about genkernel's activities during the kernel compilation and initramfs assemble process.

Nota
Genkernel will always log complete output to /var/log/genkernel.log by default. --loglevel only controls output shown on screen.

--logfile=/path/to/output_file

Log file where genkernel outputs to by default. Defaults to /var/log/genkernel.log.

--[no-]color

Activates (or deactivates) colored output.

--[no-]cleanup

Activates (or deactivates) the full post-run cleanup for debug purposes.

La operación descrita arriba provoca que genkernel cree un núcleo con pantalla una pantalla de bienvenida (--splash) que se deberá instalar de forma manual (--no-install). Mientras se prepara el árbol de fuentes del núcleo, genkernel evitará eliminar cualquiera de los archivos objeto preexistentes en el árbol de los fuentes (--no-clean). Se ofrecerá al usuario una herramienta de configuración basada en menús para seleccionar qué módulos se construirán en el sistema (--menuconfig).

Changing the boot directory to /efi

It is now recommended to mount the UEFI system boot partition (ESP) under /efi instead of /boot.

By default, the kernel is written to /boot, which used to be the ESP in certain configurations, but is now on the root partition. Reasons to write the kernel to /efi include:

• Secure Boot expecting a hard coded ESP kernel path
• Making GRUB2 independent of the root partition for stability or security
• GRUB2 not supporting the root file-system (bcachefs)
• Using a grub.cfg not generated by grub-mkconfig

To point genkernel to /efi, either add --bootdir=/efi to the genkernel command or BOOTDIR="/efi" to /etc/genkernel.conf.

# ¿Se lanza 'make menuconfig' antes de compilar este núcleo?
MENUCONFIG="yes"

Después de lanzar la orden emerge -u gentoo-sources, siempre que los nuevos fuentes estén disponibles, se creará un nuevo directorio de ficheros fuente del núcleo en /usr/src/ para almacenarlos. Normalmente los fuentes activos del núcleo se definen con el enlace simbólico /usr/src/linux.

Si ya se ha realizado una construcción del núcleo con los fuentes activos, debería aparecer un fichero dentro del directorio /etc/kernels que contiene al configuración del núcleo que se ha aplicado mientras se creó la última bzimage del núcleo. Este fichero se llama, por ejemplo, kernel-config-x86_64-3.7.9-gentoo-r1 donde x86_64 sería el nombre de la arquitectura del sistema, 3.7.9 sería la versión de los ficheros fuente utilizados, y r1 la revisión de los fuentes.

Es este fichero kernel-config-x86_64-3.7.9-gentoo-r1 el que se utiliza como configuración cuando se lanza genkernel --menuconfig all.

Si es la primera vez que se lanza genkernel con los nuevos fuentes del núcleo o si no se ha guardado el resultado previo este fichero se sustituye por un fichero de configuración por defecto que se encuentra en usr/share/genkernel/arch/x86_64/kernel-config donde hay que sustituir x86_64 por la arquitectura en la que se está trabajando.

• El segundo parámetro le indica a genkernel que guarde la configuración del núcleo que se ha compilado en /etc/kernels.

extlinux

TODO

GRUB Legacy

• Añadir real_root=/dev/sdaN, a los parámetros del núcleo que se pasan a la imagen, donde /dev/sdaN apunta a la partición raíz (N es el número de partición si ésta existe).
• Si está utilizando la pantalla de presentación de arranque (splash), se debe añadir una línea moda adecuada, como por ejemplo pasar vga=0x317 a los parámetros del núcleo y también splash=verbose o splash=silent dependiendo del nivel de detalle que desee a lo largo del proceso de arranque.
• Añadir la información sobre initrd que requiera la configuración del gestor de arranque. Consulte el capítulo de configuración del cargador de arranque del manual de Gentoo para obtener detallas sobre la configuración del gestor de arranque con initrd.

GRUB

TODO

systemd-boot

TODO

• El segundo aspecto importante es conservar las imágenes del núcleo e initramfs que arrancan correctamente. La forma de realizar esto depende del contexto:

1. Si el último núcleo que se construyó arranca correctamente, al lanzar genkernel se cambiará el nombre a la imagen este núcleo (y de igual forma al initramfs) a kernel-genkernel-ARCH-X.Y.Z-gentoo-rx.old y se creará un nuevo kernel-genkernel-ARCH-X.Y.Z-gentoo-rx. Esto implica que, en caso de que el nuevo núcleo no arranque, los usuarios siempre podrán arrancar con el antiguo.
2. Si el último núcleo que se construyó no arranca y los ficheros fuente no han cambiado desde que el usuario construyó un nuevo núcleo, antes de lanzar genkernel, se deberá eliminar la nueva imagen del núcleo y quitar el sufijo .old del último núcleo que arrancara. Si no se hace esto y el nuevo núcleo construido no arranca en la segunda ocasión, el núcleo arrancable kernel-genkernel-ARCH-X.Y.Z-gentoo-rx.old será sustituido por el núcleo kernel-genkernel-ARCH-X.Y.Z-gentoo-rx que no arranca, por lo que usuario no podrá arrancar su sistema. Para initramfs se emplea el mismo razonamiento.

Comprobar que initramfs incluye las herramientas necesarias antes de arrancar

Antes de arrancar el sistema, es recomendable comprobar que initramfs incluye las herramientas necesarias. Por ejemplo, si falta cryptsetup se producirá un error de pánico en el núcleo cuando se arranque con LUKS. Este artículo utiliza el siguiente procedimiento para comprobar que initramfs incluye cryptsetup:

Using lsinitrd

Since genkernel-4, created initramfs can be processed using the lsinitrd command from the sys-kernel/dracut package:

The output above shows the e1000.ko file for an Intel NIC, the dropbear executable (usr/bin/dropbearmulti), and the cryptsetup (sbin/cryptsetup) executable have been embedded into the initramfs file.

Manual extraction

To extract a generated initramfs to inspect its content:

Microcode loading

For microcode (ucode) updates, kernel must support (early-)microcode loading and microcode updates must be present early at boot. See Microcode article for more details.

Microcode loading support in kernel

By default, genkernel will enable microcode loading support in kernel for both, AMD and Intel processors. This behavior can be controlled through MICROCODE option in /etc/genkernel.conf or by using the --microcode=(no|all|amd|intel) command-line parameter during invocation.

Embedding microcode updates into initramfs

To embed microcode (ucode) updates into initramfs, MICROCODE_INITRAMFS must be enabled in /etc/genkernel.conf or command-line parameter --microcode-initramfs must be passed at invocation. This will cause genkernel to prepend microcode(s) for selected processor (see --microcode option above) to initramfs in case sys-firmware/intel-microcode with the split-ucode USE flag for Intel processors and/or sys-kernel/linux-firmware for AMD processors is installed.

Firmware loading

Specific firmware files can be added to genkernel's automatically generated initramfs when listed, with relative paths, in the variable FIRMWARE_FILES in /etc/genkernel.conf. When sys-kernel/genkernel is installed with USE="firmware" it will prefer firmware files from /lib/firmware.

In case sys-kernel/gentoo-sources is installed with USE="experimental" and the kernel is configured with CONFIG_GENTOO_PRINT_FIRMWARE_INFO=y, the following command gets a comma-separated list of all currently loaded firmware files for the use in the FIRMWARE_FILES variable from /etc/genkernel.conf as illustrated above (the output is just an example):

It is also possible to incorporate the firmware into the kernel image directly, but be aware that CONFIG_EXTRA_FIRMWARE in the kernel configuration file .config (normally found in /usr/src/linux) requires a space-separated list (output example):

amdgpu/green_sardine_sdma.bin amdgpu/green_sardine_asd.bin amdgpu/green_sardine_ta.bin amdgpu/green_sardine_pfp.bin amdgpu/green_sardine_me.bin amdgpu/green_sardine_ce.bin amdgpu/green_sardine_rlc.bin amdgpu/green_sardine_mec.bin amdgpu/green_sardine_dmcub.bin amdgpu/green_sardine_vcn.bin regulatory.db regulatory.db.p7s rtw89/rtw8852a_fw.bin rtl_bt/rtl8852au_fw.bin rtl_bt/rtl8852au_config.bin rtl_nic/rtl8168h-2.fw

Remote rescue shell

genkernel can embed the net-misc/dropbear SSH daemon into the initramfs which will allow fixing certain things on boot remotely when initramfs is at least able to load. The most common used feature will be remote unlock capability for LUKS-encrypted root or swap devices or ZFS volumes.

Pre-requirement for SSH daemon support in initramfs

A authorized_keys file must exist before genkernel will be invoked. By default, genkernel will look for /etc/dropbear/authorized_keys. Command-line argument --ssh-authorized-keys-file=/path/to/custom/authorized_keys or genkernel configuration option SSH_AUTHORIZED_KEYS_FILE can be used to alter default value.

Adding SSH support to initramfs

To embed SSH daemon into genkernel's initramfs, run genkernel with --ssh command-line argument or set SSH="yes" in genkernel configuration file. Needless to mention that this feature will require working network at boot. The following example will just (re-)build initramfs with SSH daemon embedded:

Enabling SSH daemon on boot

Just adding SSH daemon to initramfs is not enough. Because exposing any network service could be a security risk, this feature must be enabled via the kernel command-line argument dosshd! See Configure Network for how to configure network in genkernel.

Remote unlock

There are two possibilities to unlock LUKS-encrypted root and/or swap volume: A manual way, through an SSH connection, run a command and will get prompted for passphrase(s) or an automatic way where user passes passphrase through SSH as command.

Manual unlock

Connect to the remote system through SSH and run the following commands:

Automatic unlock

It's basically the same like manual unlock just without the need to manually run resume-boot. In case user has both, encrypted root and swap volume, user must unlock swap volume first:

Device Drivers --->
 Networking Support --->
 Ethernet (10 or 100Mbit) --->
 [*] Ethernet (10 or 100Mbit)
 <*> El controlador o controladores para cada tarjeta de red

Device Drivers --->
 Networking Support --->
 Networking options [*]
 TCP/IP networking--->
 [*] IP: kernel level autoconfiguration
 [*] IP: DHCP support

Estas opciones le indican al núcleo que envíe una petición DHCP en el momento del arranque.

Adicionalmente, debería activar SquashFS ya que la mayoría de los CD de instalación actuales de Gentoo así lo requieren. El soporte para SquashFS no se incluye en el árbol genérico de fuentes del núcleo. Para activar SquashFS, debe aplicar los parches necesarios para las fuentes genéricas del núcleo o instalar el paquete gentoo-sources.

File systems--->
 Miscellaneous filesystems --->
 [*] SquashFS 2.X - Squashed file system support

# Aquí 192.168.1.2 es el servidor NFS y 192.168.1.10 será la dirección IP de la máquina que arranca por red
host netbootableMachine {
 hardware ethernet 11:22:33:44:55:66;
 fixed-address 192.168.1.10;
 option root-path "192.168.1.2:/nfs/livecd";
}

DEFAULT gentoo
TIMEOUT 40
PROMPT 1
LABEL gentoo
 KERNEL kernel-X.Y.Z
 APPEND initrd=initrd-X.Y.Z root=/dev/ram0 init=/linuxrc ip=dhcp

# Ejemplo para for GRUB 1.x
title Gentoo Linux
root (hd0,0)
kernel /vmlinuz root=/dev/md3 dolvm domdadm
initrd /initramfs-genkernel-x86_64-3.4.3

# Ejemplo para GRUB 1.x
title Gentoo Linux
root (hd0,0)
kernel /vmlinuz root=/dev/md3 init_opts=S
initrd /initramfs-genkernel-x86_64-3.4.3

Cross-compile support

To build kernel and/or initramfs for a different platform as genkernel is being executed on, kernel/initramfs must be cross-compiled.

The above command causes genkernel to create a kernel supporting MD raid and embed mdadm into initramfs (--mdadm), both kernel and initramfs will have to be manually installed (--no-install). The kernel and programs embedded into initramfs will run on arm64 (--cross-compile=aarch64-linux-gnu).

--cross-compile=<target triplet>

Target triple (i.e. aarch64-linux-gnu) to build for. Only needed when the system running genkernel has a different architecture like the system which should boot the created kernel/initramfs.

Initramfs kernel command-line parameters

root=<...>

Specifies the device node of the root filesystem to mount. I.e. root=/dev/sda3, root=UUID=a1e5968c-bd1b-41ee-bf08-2d0ed376fa83.

cdroot

This attempts to load livecd.squashfs and is used for loading live media.

crypt_root=<...>

This specifies the device encrypted by LUKS, which contains the root filesystem to mount. Supports same syntax like root kernel command-line parameter from above.

Nota
Will require that at least initramfs was built with --luks option set.

crypt_swap=<...>

This specifies the swap device encrypted by LUKS. For more details please see crypt_root kernel command-line parameter from above.

root_trim=(yes|no)

Enables TRIM support for a LUKS-based root device.

Nota
Will require that at least initramfs was built with --luks option set and is only useful for flash-based volumes.

ip=<dhcp,addr/cidr>

Normally used to tell the kernel that it should start a network interface which can be specified using gk.net.iface kernel parameter. By default, dhcp will be used. A specific IP address can be set using addr/CIDR notation, i.e. 1.2.3.4/24.

gk.net.dhcp.retries=<...>

Sends up to 3 DHCP discovery requests by default.

gk.net.iface=<interface,macaddr>

Use the interface named eth0 by default. Use this kernel parameter to specify another interface.
A MAC address (00:00:00:00:00:00 format) can be specified instead of an interface name.

gk.net.gw=<...>

Optional gateway. If ip is set to dhcp, this kernel parameter will be ignored.

gk.net.routes=<...>

Optional additional routes. If ip is set to dhcp, this kernel parameter will be ignored.

gk.net.timeout.dad=<...>

Wait up to 10 seconds by default for IPv6's DAD to complete. At the moment, only wait for DAD while bringing down an interface to prevent a race condition.

gk.net.timeout.deconfiguration=<...>

Wait up to 10 seconds by default while bringing down an interface to prevent a race condition.

gk.net.timeout.dhcp=<...>

Wait up to 10 seconds by default for a DHCP server reply.

gk.net.timeout.interface=<...>

Wait up to 10 seconds by default for interface to show up.

gk.prompt.timeout=<...>

By default a prompt within genkernel initramfs like shown when set root could not be found will never timeout. Use this option to set a timeout.

Nota
When dosshd is used, gk.prompt.timeout will be set to 30 seconds when not set. This will allow remote user to provide answer through GK_PROMPT_FILE which is set to /tmp/current_prompt by default.

dosshd

Will bring up an interface and start a SSH daemon within initramfs allowing to remotely unlock encrypted devices or just for debugging purpose. See ip option for how to configure network.

Nota
Will require that initramfs was built at least with --ssh option set.

gk.sshd.port=<...>

By default, sshd will listen on port 22.

gk.sshd.wait=<...>

Wait X seconds after setting up sshd. Useful for login (and thus pause boot process) before booting real system.

dolvm

Activate LVM volumes on bootup.

Nota
Will require that initramfs was built at least with --lvm option set.

lvmraid=<...>

Specify RAID devices to set up before the activation of LVM volumes. Implies option dolvm from above.

domdadm (Deprecated in Genkernel 4.2.0, udev rules now control MD assembly)

Scan for RAID arrays on bootup.

Nota
Will require that initramfs was built at least with --mdadm option set.

dozfs[=cache,force]

Scan for bootable ZFS pools on bootup. Optionally use cachefile or force import if necessary or perform both actions.

Nota
Will require that initramfs was built at least with --zfs option set.

gk.log.disabled=<...>

By default, any shown message and external command calls will be logged to /tmp/init.log in initramfs. Disables logging.

gk.log.keep=<...>

When set to a boolean value, genkernel will preserve /tmp/init.log, see above, and copy file to /genkernel-boot.log on root device (see root or real_root kernel command-line parameter above). Customize to a file like /root/my-genkernel-boot.log to copy the log.

Nota
The default file /genkernel-boot.log on root was chosen because genkernel's initramfs will only mount root filesystem by default. To store the log file at /var/log/genkernel-boot.log, the mount point must be accessible (see /etc/initramfs.mounts).

gk.hw.load-all=<...>

By default, genkernel loads various module groups (nvme, sata, scsi, pata, usb...) until block device specified in root parameter (see above) becomes available. This boolean option can be used to force loading of all module groups regardless whether root device is already available when set to yes.

Resolución de problemas

Can genkernel be used for systemd-based systems?

Yes.

Genkernel? Dracut?

sys-kernel/dracut in comparison to sys-kernel/genkernel is just a generic tool for creating an initramfs. It does not create a kernel like genkernel does. I.e. while both, genkernel and dracut supports booting from LUKS-encrypted root volume, only genkernel will ensure that kernel will have all required options set. It's also worthwhile to mention that genkernel will compile most packages (LVM, cryptsetup, mdadm, sshd...) used in initramfs on its own whereas dracut will copy binaries from host system which can be a problem for some setups. Thus, genkernel supports kernel/initramfs creation for another system (cross-compile) unlike dracut or genkernel-next.

Can a separate kernel/initramfs be created for tests?

The above command causes genkernel to build a new kernel and initramfs (all) based on config from current running kernel (--kernel-config=/proc/config.gz), invoke menuconfig (--menuconfig) allowing user to adjust configuration and will append -test42 to kernel's LOCALVERSION variable (--kernel-append-localversion=-test42) which will affect naming of kernel image, modules dir and initramfs by default.

How can external modules (such as xtables-addons, nvidia-drivers...) be rebuilt for a new kernel?

By default, genkernel will call emerge @module-rebuild when building a kernel to ensure that out-of-tree modules installed through the package manager are still present in new/rebuilt kernel. This feature can be toggled via --[no-]module-rebuild command-line argument or MODULEREBUILD in /etc/genkernel.conf.

How can additional commands be run after building the kernel?

Genkernel provides a callback for that (before version 4, callback was used to rebuild external modules). See CMD_CALLBACK in /etc/genkernel.conf for more details.

How can ccache or distcc be used with genkernel?

Set up ccache or distcc the normal way like for sys-apps/portage . Set --kernel-cc command-line parameter or adjust KERNEL_CC in /etc/genkernel.conf for the desired tool to use. Do the same for UTILS_CC (--utils-cc) and UTILS_CXX (--utils-cxx).

ERROR: compile_kernel(): compile_generic() failed to compile the "bzImage" target!

Check /var/log/genkernel.log first. In most cases, a root cause will appear like:

In other words: The system has run out of disk space (No space left on device) during compilation.

To guard against problems like this set CHECK_FREE_DISK_SPACE_BOOTDIR=50 and CHECK_FREE_DISK_SPACE_KERNELOUTPUTDIR=4000 in /etc/genkernel.conf in which case genkernel would fail early with a message like

Is the order of kernel command-line arguments important?

No.

Required kernel option 'CONFIG_MICROCODE_INTEL' or 'CONFIG_MICROCODE_AMD' which genkernel tried to set is missing!

Kernel v6.6 permanently applied the kernel config parameters (see this commit). This was fixed in version 4.3.10 of sys-kernel/genkernel .

Help! Something isn't working!

To report a problem, please always provide /var/log/genkernel.log (sometimes it maybe necessary to compress that file before sharing or attaching to bugs) which will help developers a lot. Even if the command is run with --loglevel=1 (default), the logfile will always contain complete output (no need to re-run with logging turned on) which will help developers to understand, reproduce and maybe fix a bug.

• Configuración manual del núcleo - Para cuando sea necesario hacer las cosas de forma manual.
• Dracut - Otro constructor de initramfs disponible en Gentoo.