User:Immolo/Sandbox/kernel part duex

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Warning
Readers should not try to follow instructions directly from the Handbook:Parts namespace (which is THIS page!). The sections displayed below are used as a skeleton for transcluding information into the computer architecture specific handbooks and are therefore lacking critical information.

Please visit the Handbook list to read instructions for a relevant computer architecture.


Immolo Handbook
Installation
About the installation
Choosing the media
Configuring the network
Preparing the disks
The stage file
Installing base system
Configuring the kernel
Configuring the system
Installing tools
Configuring the bootloader
Finalizing
Working with Gentoo
Portage introduction
USE flags
Portage features
Initscript system
Environment variables
Working with Portage
Files and directories
Variables
Mixing software branches
Additional tools
Custom package repository
Advanced features
OpenRC network configuration
Getting started
Advanced configuration
Modular networking
Wireless
Adding functionality
Dynamic management


Optional: Installing firmware and/or microcode

Firmware

Suggested: Linux Firmware

On many systems, non-FOSS firmware is required for certain hardware to function. The sys-kernel/linux-firmware package contains firmware for many, but not all, devices.

Tip
Most wireless cards and GPUs require firmware to function.
root #emerge --ask sys-kernel/linux-firmware
Note
Installing certain firmware packages often requires accepting the associated firmware licenses. If necessary, visit the license handling section of the Handbook for help on accepting licenses.
Firmware Loading

Firmware files are typically loaded when the associated kernel module is loaded. This means the firmware must be built into the kernel using CONFIG_EXTRA_FIRMWARE if the kernel module is set to Y instead of M. In most cases, building-in a module which required firmware can complicate or break loading.

Handbook:Immolo/Blocks/Firmware

{{#switch: {{Handbook Variable|architecture}} | amd64 | x86 =

Microcode

In addition to discrete graphics hardware and network interfaces, CPUs also can require firmware updates. Typically this kind of firmware is referred to as microcode. Newer revisions of microcode are sometimes necessary to patch instability, security concerns, or other miscellaneous bugs in CPU hardware.

Microcode updates for AMD CPUs are distributed within the aforementioned sys-kernel/linux-firmware package. Microcode for Intel CPUs can be found within the sys-firmware/intel-microcode package, which will need to be installed separately. See the Microcode article for more information on how to apply microcode updates. }}

sys-kernel/installkernel

Installkernel may be used to automate the kernel installation, initramfs generation, unified kernel image generation and/or bootloader configuration among other things. sys-kernel/installkernel implements two paths of achieving this: the traditional installkernel originating from Debian and systemd's kernel-install. Which one to choose depends, among other things, on the system's bootloader. By default, systemd's kernel-install is used on systemd profiles, while the traditional installkernel is the default for other profiles.

Bootloader

Now is the time to think about which bootloader the user wants for the system, if unsure, follow the 'Traditional layout' subsection below.

GRUB

Users of GRUB can use either systemd's kernel-install or the traditional Debian installkernel. The systemd USE flag switches between these implementations. To automatically run grub-mkconfig when installing the kernel, enable the grub USE flag.

FILE /etc/portage/package.use/installkernel
sys-kernel/installkernel grub
root #emerge --ask sys-kernel/installkernel

{{#switch: {{Handbook Variable|architecture}} | amd64 | arm64 | arm | loong | riscv | x86 =

systemd-boot

When using systemd-boot (formerly gummiboot) as the bootloader, systemd's kernel-install must be used. Therefore ensure the systemd and the systemd-boot USE flags are enabled on sys-kernel/installkernel, and then install the relevant package for systemd-boot.

On OpenRC systems:

FILE /etc/portage/package.use/systemd-boot
sys-apps/systemd-utils boot kernel-install
sys-kernel/installkernel systemd systemd-boot
root #emerge --ask sys-apps/systemd-utils sys-kernel/installkernel

On systemd systems:

FILE /etc/portage/package.use/systemd
sys-apps/systemd boot
sys-kernel/installkernel systemd-boot
root #emerge --ask sys-apps/systemd sys-kernel/installkernel

The kernel command line to use for new kernels should be specified in /etc/kernel/cmdline, for example:

FILE /etc/kernel/cmdline
quiet splash

}}

{{#switch: {{Handbook Variable|architecture}} | amd64 | arm64 | arm | x86 =

EFI stub

UEFI-based computer systems technically do not need secondary bootloaders in order to boot kernels. Secondary bootloaders exist to extend the functionality of UEFI firmware during the boot process. That being said, using a secondary bootloader is typically easier and more robust because it offers a more flexible approach for quickly modifying kernel parameters at boot time. Note also that UEFI implentations strongly differ between vendors and between models and there is no guarantee that a given firmware follows the UEFI specification. Therefore, EFI Stub booting is not guaranteed to work on every UEFI-based system, and hence the USE flag is stable masked and testing keywords must be accepted for installkernel to use this feature.

FILE /etc/portage/package.accept_keywords/installkernel
sys-kernel/installkernel
sys-boot/uefi-mkconfig
app-emulation/virt-firmware
FILE /etc/portage/package.use/installkernel
sys-kernel/installkernel efistub
root #emerge --ask sys-kernel/installkernel
root #mkdir -p

}}

Traditional layout, other bootloaders (e.g. (e)lilo, syslinux, etc.)

The traditional /boot layout (for e.g. (e)LILO, syslinux, etc.) is used by default if the grub, systemd-boot, efistub and uki USE flags are not enabled. No further action is required.

Initramfs

An initial ram-based file system, or initramfs, may be required for a system to boot. A wide of variety of cases may necessitate one, but common cases include:

  • Kernels where storage/filesystem drivers are modules.
  • Layouts with /usr/ or /var/ on separate partitions.
  • Encrypted root filesystems.
Tip
Distribution kernels are designed to be used with an initramfs, as many storage and filesystem drivers are built as modules.

In addition to mounting the root filesystem, an initramfs may also perform other tasks such as:

  • Running file system consistency check fsck, a tool to check and repair consistency of a file system in such events of uncleanly shutdown a system.
  • Providing a recovery environment in the event of late-boot failures.

Installkernel can automatically generate an initramfs when installing the kernel if the dracut or ugrd USE flag is enabled:

FILE /etc/portage/package.use/installkernel
sys-kernel/installkernel dracut
root #emerge --ask sys-kernel/installkernel

{{#switch: {{Handbook Variable|architecture}} | amd64 | arm64 | x86 =

Optional: Unified Kernel Image

A Unified Kernel Image (UKI) combines, among other things, the kernel, the initramfs and the kernel command line into a single executable. Since the kernel command line is embedded into the unified kernel image, it should be specified before generating the unified kernel image (see below). Note that any kernel command line arguments supplied by the bootloader or firmware at boot are ignored when booting with secure boot enabled.

A unified kernel image requires a stub loader. Currently, the only one available is systemd-stub. To enable it:

For systemd systems:

FILE /etc/portage/package.use/uki
sys-apps/systemd boot
root #emerge --ask sys-apps/systemd

For OpenRC systems:

FILE /etc/portage/package.use/uki
sys-apps/systemd-utils boot kernel-install
root #emerge --ask sys-apps/systemd-utils

Installkernel can automatically generate a unified kernel image using either dracut or ukify by enabling the respective flag and the uki USE flag.

For dracut:

FILE /etc/portage/package.use/uki
sys-kernel/installkernel dracut uki
FILE /etc/dracut.conf.d/uki.conf
uefi="yes"
kernel_cmdline="some-kernel-command-line-arguments"
root #emerge --ask sys-kernel/installkernel

For ukify:

FILE /etc/portage/package.use/uki
sys-apps/systemd boot ukify                         # For systemd systems
sys-apps/systemd-utils kernel-install boot ukify    # For OpenRC systems
sys-kernel/installkernel dracut ukify uki
FILE /etc/kernel/cmdline
some-kernel-command-line-arguments
root #emerge --ask sys-kernel/installkernel

Note that while dracut can generate both an initramfs and a unified kernel image, ukify can only generate the latter and therefore the initramfs must be generated separately with dracut.

Important
In the above configuration examples (for both Dracut and ukify) it is important to specify at least an appropriate root= parameter for the kernel command line to ensure that the Unified Kernel Image can find the root partition. This is not required for systemd based systems following the Discoverable Partitions Specification (DPS), in that case the embedded initramfs will be able to dynamically find the root partition.

Generic Unified Kernel Image

The prebuilt sys-kernel/gentoo-kernel-bin can optionally install a prebuilt generic unified kernel image containing a generic initramfs that is able to boot most systemd based systems. It can be installed by enabling the generic-uki USE flag, and configuring installkernel to not generate a custom initramfs or unified kernel image:

FILE /etc/portage/package.use/uki
sys-apps/systemd boot                          # For systemd systems
sys-apps/systemd-utils kernel-install boot     # For OpenRC systems
sys-kernel/gentoo-kernel-bin generic-uki
sys-kernel/installkernel -dracut -ukify -ugrd uki

Secure Boot

Warning
If following this section and manually compiling your own kernel, then make sure to follow the steps outlined in Signing the kernel

The generic Unified Kernel Image optionally distributed by sys-kernel/gentoo-kernel-bin is already pre-signed. How to sign a locally generated unified kernel image depends on whether dracut or ukify is used. Note that the location of the key and certificate should be the same as the SECUREBOOT_SIGN_KEY and SECUREBOOT_SIGN_CERT as specified in /etc/portage/make.conf.

For dracut:

FILE /etc/dracut.conf.d/uki.conf
uefi="yes"
kernel_cmdline="some-kernel-command-line-arguments"
uefi_secureboot_key="/path/to/kernel_key.pem"
uefi_secureboot_cert="/path/to/kernel_key.pem"

For ukify:

FILE /etc/kernel/uki.conf
[UKI]
SecureBootPrivateKey=/path/to/kernel_key.pem
SecureBootCertificate=/path/to/kernel_key.pem

}}

Kernel configuration and compilation

Tip
It's can be a wise move to use the dist-kernel on the first boot as it provides a very simple method to rule out system issues and kernel config issues. Always having a known working kernel to fallback on can speed up debugging and alleviate anxiety when updating that your system will no longer boot.

Now it is time to configure and compile the kernel sources. For the purposes of the installation, three approaches to kernel management will be presented, however at any point post-installation a new approach can be employed.

Ranked from least involved to most involved:

{{#switch: {{Handbook Variable|architecture}} | amd64 | arm64 | hppa | ppc | ppc64 | sparc | x86 =

Full automation approach: Distribution kernels
A Distribution Kernel is used to configure, automatically build, and install the Linux kernel, its associated modules, and (optionally, but enabled by default) an initramfs file. Future kernel updates are fully automated since they are handled through the package manager, just like any other system package. It is possible provide a custom kernel configuration file if customization is necessary. This is the least involved process and is perfect for new Gentoo users due to it working out-of-the-box and offering minimal involvement from the system administrator.

}}

Full manual approach
New kernel sources are installed via the system package manager. The kernel is manually configured, built, and installed using the eselect kernel and a slew of make commands. Future kernel updates repeat the manual process of configuring, building, and installing the kernel files. This is the most involved process, but offers maximum control over the kernel update process.
Hybrid approach: Genkernel
We use the term hybrid here but, do note that the dist-kernel and manual sources, both include methods to achieve the same goal. New kernel sources are installed via the system package manager. System administrators may use Gentoo's genkernel tool to configure, build, and install the Linux kernel, its associated modules, and (optionally, but not enabled by default) an initramfs file. It is possible provide a custom kernel configuration file if customization is necessary. Future kernel configuration, compilation, and installation require the system administrator's involvement in the form of running eselect kernel, genkernel, and potentially other commands for each update. This option should only considered for users that know they have a need for genkernel

The core around which all distributions are built is the Linux kernel. It is the layer between the user's programs and the system hardware. Although the handbook provides its users several possible kernel sources, a more comprehensive listing with more detailed descriptions is available at the Kernel overview page.

Tip
Kernel installation tasks such as copying the kernel image to /boot or the EFI System Partition, generating an initramfs and/or Unified Kernel Image, updating bootloader configuration, can be automated with installkernel. Users may wish to configure and install sys-kernel/installkernel before proceeding. See the Kernel installation section below for more more information.

{{#switch: {{Handbook Variable|architecture}} | amd64 | arm64 | hppa | ppc | ppc64 | sparc | x86 =

Distribution kernels

Distribution Kernels are ebuilds that cover the complete process of unpacking, configuring, compiling, and installing the kernel. The primary advantage of this method is that the kernels are updated to new versions by the package manager as part of @world upgrade. This requires no more involvement than running an emerge command. Distribution kernels default to a configuration supporting the majority of hardware, however two mechanisms are offered for customization: savedconfig and config snippets. See the project page for more details on configuration.

Optional: Signed kernel modules

The kernel modules in the prebuilt distribution kernel (sys-kernel/gentoo-kernel-bin) are already signed. To sign the modules of kernels built from source enable the modules-sign USE flag, and optionally specify which key to use for signing in /etc/portage/make.conf:

FILE /etc/portage/make.confEnable module signing
USE="modules-sign"

# Optionally, to use custom signing keys.
MODULES_SIGN_KEY="/path/to/kernel_key.pem"
MODULES_SIGN_CERT="/path/to/kernel_key.pem" # Only required if the MODULES_SIGN_KEY does not also contain the certificate.
MODULES_SIGN_HASH="sha512" # Defaults to sha512.

If MODULES_SIGN_KEY is not specified the kernel build system will generate a key, it will be stored in /usr/src/linux-x.y.z/certs. It is recommended to manually generate a key to ensure that it will be the same for each kernel release. A key may be generated with:

root #openssl req -new -nodes -utf8 -sha256 -x509 -outform PEM -out kernel_key.pem -keyout kernel_key.pem
Note
The MODULES_SIGN_KEY and MODULES_SIGN_CERT may be different files. For this example the pem file generated by OpenSSL includes both the key and the accompanying certificate, and thus both variables are set to the same value.

OpenSSL will ask some questions about the user generating the key, it is recommended to fill in these questions as detailed as possible.

Store the key in a safe location, at the very least the key should be readable only by the root user. Verify this with:

root #ls -l kernel_key.pem
 -r-------- 1 root root 3164 Jan  4 10:38 kernel_key.pem 

If this outputs anything other then the above, correct the permissions with:

root #chown root:root kernel_key.pem
root #chmod 400 kernel_key.pem


Installing a distribution kernel

To build a kernel with Gentoo patches from source, type:

root #emerge --ask sys-kernel/gentoo-kernel

System administrators who want to avoid compiling the kernel sources locally can instead use precompiled kernel images:

root #emerge --ask sys-kernel/gentoo-kernel-bin
Important
Distribution Kernels, such as sys-kernel/gentoo-kernel and sys-kernel/gentoo-kernel-bin, by default, expect to be installed alongside an initramfs. Before running emerge to install the kernel users should ensure that sys-kernel/installkernel has been configured to utilize an initramfs generator (for example Dracut) as described in the installkernel section.

Upgrading and cleaning up

Once the kernel is installed, the package manager will automatically update it to newer versions. The previous versions will be kept until the package manager is requested to clean up stale packages. To reclaim disk space, stale packages can be trimmed by periodically running emerge with the --depclean option:

root #emerge --depclean

Alternatively, to specifically clean up old kernel versions:

root #emerge --prune sys-kernel/gentoo-kernel sys-kernel/gentoo-kernel-bin
Tip
By design, emerge only removes the kernel build directory. It does not actually remove the kernel modules, nor the installed kernel image. To completely clean-up old kernels, the app-admin/eclean-kernel tool may be used.

Post-install/upgrade tasks

An upgrade of a distribution kernel is capable of triggering an automatic rebuild for external kernel modules installed by other packages (for example: sys-fs/zfs-kmod or x11-drivers/nvidia-drivers). This automated behaviour is enabled by enabling the dist-kernel USE flag. When required, this same flag will also trigger re-generation of the initramfs.

It is highly recommended to enable this flag globally via /etc/portage/make.conf when using a distribution kernel:

FILE /etc/portage/make.confEnabling USE=dist-kernel
USE="dist-kernel"
Manually rebuilding the initramfs or Unified Kernel Image

If required, manually trigger such rebuilds by, after a kernel upgrade, executing:

root #emerge --ask @module-rebuild

If any kernel modules (e.g. ZFS) are needed at early boot, rebuild the initramfs afterward via:

root #emerge --config sys-kernel/gentoo-kernel
root #emerge --config sys-kernel/gentoo-kernel-bin
}}

Installing the kernel sources

When installing and compiling the kernel for -based systems, Gentoo recommends the sys-kernel/ package.

Choose an appropriate kernel source and install it using emerge:

root #emerge --ask sys-kernel/

This will install the Linux kernel sources in /usr/src/ using the specific kernel version in the path. It will not create a symbolic link by itself without the symlink USE flag being enabled on the chosen kernel sources package.

It is conventional for a /usr/src/linux symlink to be maintained, such that it refers to whichever sources correspond with the currently running kernel. However, this symbolic link will not be created by default. An easy way to create the symbolic link is to utilize eselect's kernel module.

For further information regarding the purpose of the symlink, and how to manage it, please refer to Kernel/Upgrade.

First, list all installed kernels:

root #eselect kernel list
Available kernel symlink targets:
  [1]   linux-

In order to create a symbolic link called linux, use:

root #eselect kernel set 1
root #ls -l /usr/src/linux
lrwxrwxrwx    1 root   root    12 Oct 13 11:04 /usr/src/linux -> linux-

Alternative: Manual configuration

Note
In case it was missed, this section requires the kernel sources to be installed. Be sure to obtain the relevant kernel sources, then return here for the rest of section.

Manually configuring a kernel is commonly seen as one of the most difficult procedures a system administrator has to perform. Nothing is less true - after configuring a few kernels no one remembers that it was difficult! There are two ways for a Gentoo user to manage a manual kernel system, both of which are listed below:

Modprobed-db process

A very easy way to manage the kernel is to first install sys-kernel/gentoo-kernel-bin and use the sys-kernel/modprobed-db to collect information about what the system requires. modprobed-db is a tool which monitors the system via crontab to add all modules of all devices over the system's life to make sure it everything a user needs is supported. For example, if an Xbox controller is added after installation, then modprobed-db will add the modules to be built next time the kernel is rebuilt. More on this topic can be found in the Modprobed-db article.

Manual process

This method allows a user to have full control of how their kernel is built with as minimal help from outside tools as they wish. Some could consider this as making it hard for the sake of it.

However, with this choice one thing is true: it is vital to know the system when a kernel is configured manually. Most information can be gathered by emerging sys-apps/pciutils which contains the lspci command:

root #emerge --ask sys-apps/pciutils
Note
Inside the chroot, it is safe to ignore any pcilib warnings (like pcilib: cannot open /sys/bus/pci/devices) that lspci might throw out.

Another source of system information is to run lsmod to see what kernel modules the installation CD uses as it might provide a nice hint on what to enable.

Now go to the kernel source directory.

root #cd /usr/src/linux

The kernel has a method of autodetecting the modules currently being used on the installcd which will give a great starting point to allow a user to configure their own. This can be called by using:

root #make localmodconfig

It's now time to configure using nconfig:

root #make nconfig

The Linux kernel configuration has many, many sections. Let's first list some options that must be activated (otherwise Gentoo will not function, or not function properly without additional tweaks). We also have a Gentoo kernel configuration guide on the Gentoo wiki that might help out further.

Enabling required options

When using sys-kernel/gentoo-sources, it is strongly recommend the Gentoo-specific configuration options be enabled. These ensure that a minimum of kernel features required for proper functioning is available:

KERNEL Enabling Gentoo-specific options
Gentoo Linux --->
  Generic Driver Options --->
    [*] Gentoo Linux support
    [*]   Linux dynamic and persistent device naming (userspace devfs) support
    [*]   Select options required by Portage features
        Support for init systems, system and service managers  --->
          [*] OpenRC, runit and other script based systems and managers
          [*] systemd

Naturally the choice in the last two lines depends on the selected init system (OpenRC vs. systemd). It does not hurt to have support for both init systems enabled.

When using sys-kernel/vanilla-sources, the additional selections for init systems will be unavailable. Enabling support is possible, but goes beyond the scope of the handbook.

Optional: Signed kernel modules

To automatically sign the kernel modules enable CONFIG_MODULE_SIG_ALL:

KERNEL Sign kernel modules CONFIG_MODULE_SIG_ALL
[*] Enable loadable module support  
  -*-   Module signature verification    
    [*]     Automatically sign all modules    
    Which hash algorithm should modules be signed with? (Sign modules with SHA-512) --->

Optionally change the hash algorithm if desired.

To enforce that all modules are signed with a valid signature, enable CONFIG_MODULE_SIG_FORCE as well:

KERNEL Enforce signed kernel modules CONFIG_MODULE_SIG_FORCE
[*] Enable loadable module support  
  -*-   Module signature verification    
    [*]     Require modules to be validly signed
    [*]     Automatically sign all modules
    Which hash algorithm should modules be signed with? (Sign modules with SHA-512) --->

To use a custom key, specify the location of this key in CONFIG_MODULE_SIG_KEY. If unspecified, the kernel build system will generate a key. It is recommended to generate one manually instead. This can be done with:

root #openssl req -new -nodes -utf8 -sha256 -x509 -outform PEM -out kernel_key.pem -keyout kernel_key.pem

OpenSSL will ask some questions about the user generating the key, it is recommended to fill in these questions as detailed as possible.

Store the key in a safe location, at the very least the key should be readable only by the root user. Verify this with:

root #ls -l kernel_key.pem
 -r-------- 1 root root 3164 Jan  4 10:38 kernel_key.pem 

If this outputs anything other then the above, correct the permissions with:

root #chown root:root kernel_key.pem
root #chmod 400 kernel_key.pem
KERNEL Specify signing key CONFIG_MODULE_SIG_KEY
-*- Cryptographic API  ---> 
  Certificates for signature checking  --->  
    (/path/to/kernel_key.pem) File name or PKCS#11 URI of module signing key

To also sign external kernel modules installed by other packages via linux-mod-r1.eclass, enable the modules-sign USE flag globally:

FILE /etc/portage/make.confEnable module signing
USE="modules-sign"

# Optionally, when using custom signing keys.
MODULES_SIGN_KEY="/path/to/kernel_key.pem"
MODULES_SIGN_CERT="/path/to/kernel_key.pem" # Only required if the MODULES_SIGN_KEY does not also contain the certificate
MODULES_SIGN_HASH="sha512" # Defaults to sha512
Note
MODULES_SIGN_KEY and MODULES_SIGN_CERT may point to different files. For this example, the pem file generated by OpenSSL includes both the key and the accompanying certificate, and thus both variables are set to the same value.

{{#switch: {{Handbook Variable|architecture}} | amd64 | arm64 | riscv | x86 =

Optional: Signing the kernel image (Secure Boot)

When signing the kernel image (for use on systems with Secure Boot enabled) it is recommended to set the following kernel config options:

KERNEL Lockdown for secureboot
General setup  --->
  Kexec and crash features  --->   
    [*] Enable kexec system call                                                                                          
    [*] Enable kexec file based system call                                                                               
    [*]   Verify kernel signature during kexec_file_load() syscall                                                        
    [*]     Require a valid signature in kexec_file_load() syscall                                                        
    [*]     Enable ""image"" signature verification support  

[*] Enable loadable module support  
  -*-   Module signature verification    
    [*]     Require modules to be validly signed
    [*]     Automatically sign all modules
    Which hash algorithm should modules be signed with? (Sign modules with SHA-512) --->  

Security options  ---> 
[*] Integrity subsystem   
  [*] Basic module for enforcing kernel lockdown                                                                       
  [*]   Enable lockdown LSM early in init                                                                       
        Kernel default lockdown mode (Integrity)  --->            

  [*]   Digital signature verification using multiple keyrings                                                            
  [*]     Enable asymmetric keys support                                                                                     
  -*-       Require all keys on the integrity keyrings be signed                                                              
  [*]       Provide keyring for platform/firmware trusted keys                                                                
  [*]       Provide a keyring to which Machine Owner Keys may be added                                                        
  [ ]         Enforce Machine Keyring CA Restrictions

Where ""image"" is a placeholder for the architecture specific image name. These options, from the top to the bottom: enforces that the kernel image in a kexec call must be signed (kexec allows replacing the kernel in-place), enforces that kernel modules are signed, enables lockdown integrity mode (prevents modifying the kernel at runtime), and enables various keychains.

On arches that do not natively support decompressing the kernel (e.g. arm64 and riscv), the kernel must be built with its own decompressor (zboot):

KERNEL zboot CONFIG_EFI_ZBOOT
Device Drivers --->                                                                                                                           
  Firmware Drivers --->                                                                                                                       
    EFI (Extensible Firmware Interface) Support --->                                                                                               
      [*] Enable the generic EFI decompressor

After compilation of the kernel, as explained in the next section, the kernel image must be signed. First install app-crypt/sbsigntools and then sign the kernel image:

root #emerge --ask app-crypt/sbsigntools
root #sbsign /usr/src/linux-x.y.z/path/to/kernel-image --cert /path/to/kernel_key.pem --key /path/to/kernel_key.pem --out /usr/src/linux-x.y.z/path/to/kernel-image
Note
For this example, the same key that was generated to sign the modules is used to sign the kernel image. It is also possible to generate and use a second separate key for signing the kernel image. The same OpenSSL command as in the previous section may be used again.

Then proceed with the installation.

To automatically sign EFI executables installed by other packages, enable the secureboot USE flag globally:

FILE /etc/portage/make.confEnable Secure Boot
USE="modules-sign secureboot"

# Optionally, to use custom signing keys.
MODULES_SIGN_KEY="/path/to/kernel_key.pem"
MODULES_SIGN_CERT="/path/to/kernel_key.pem" # Only required if the MODULES_SIGN_KEY does not also contain the certificate.
MODULES_SIGN_HASH="sha512" # Defaults to sha512

# Optionally, to boot with secureboot enabled, may be the same or different signing key.
SECUREBOOT_SIGN_KEY="/path/to/kernel_key.pem"
SECUREBOOT_SIGN_CERT="/path/to/kernel_key.pem"
Note
SECUREBOOT_SIGN_KEY and SECUREBOOT_SIGN_CERT may point to different files. For this example, the pem file generated by OpenSSL includes both the key and the accompanying certificate, and thus both variables are set to the same value.
Note
When generating an Unified Kernel Image with systemd's ukify the kernel image will be signed automatically before inclusion in the unified kernel image and it is not necessary to sign it manually.

}}

Handbook:Immolo/Blocks/Kernel

Deprecated: Genkernel

Genkernel should only be considered by users with a required need that only Genkernel can meet. For others, it is recommended to use the Distribution kernel or manually compile their own as it will make maintaining a Gentoo system a lot more simple. An example of why genkernel is more difficult to manage is the lack of integration with sys-kernel/installkernel. This means a user will not get the same level of automation as provided by the other methods; for example, Unified Kernel Images will need to be created manually when using Genkernel.

Users still wishing to use Genkernel should see the Genkernel article for more information.

Kernel modules

Listing available kernel modules

Note
Hardware modules are optional to be listed manually. udev will normally load all hardware modules that are detected to be connected in most cases. However, it is not harmful for modules that will be automatically loaded to be listed. Modules cannot be loaded twice; they are either loaded or unloaded. Sometimes exotic hardware requires help to load their drivers.

The modules that need to be loaded during each boot in can be added to /etc/modules-load.d/*.conf files in the format of one module per line. When extra options are needed for the modules, they should be set in /etc/modprobe.d/*.conf files instead.

To view all modules available for a specific kernel version, issue the following find command. Do not forget to substitute "<kernel version>" with the appropriate version of the kernel to search:

root #find /lib/modules/<kernel version>/ -type f -iname '*.o' -or -iname '*.ko' | less

Force loading particular kernel modules

To force load the kernel to load the 3c59x.ko module (which is the driver for a specific 3Com network card family), edit the /etc/modules-load.d/network.conf file and enter the module name within it.

root #mkdir -p /etc/modules-load.d
root #nano -w /etc/modules-load.d/network.conf

Note that the module's .ko file suffix is insignificant to the loading mechanism and left out of the configuration file:

FILE /etc/modules-load.d/network.confForce loading 3c59x module
3c59x

Continue the installation with Configuring the system.