Kernel/Configuration

This article describes the manual configuration and setup of the Linux kernel. For an automatic method see the genkernel article.

Set symlink
The symlink should always point to the kernel sources that is currently being used. This can be done in one of three ways:


 * 1. Installing the kernel sources with active symlink USE flag
 * This will make the point to your newly installed kernel sources. If necessary, it can still be modified later with the following two methods:


 * 2. Setting the symlink with eselect:




 * This outputs the available kernel sources. The asterisk indicates the chosen sources. To change the kernel sources, e.g. to the second entry, do:




 * 3. Setting the symlink manually:



Configuration tools
The kernel offers several tools to configure itself:


 * make config
 * Text based configuration. The options are prompted one after another. All options need to be answered, and out-of-order access to former options is not possible.


 * make menuconfig
 * Graphical menu (only text input). You can navigate through the menu and change the options you want.


 * make nconfig
 * Graphical menu based on ncurses. Requires to be installed.


 * make xconfig
 * Graphical menu using Qt4. Requires to be installed.


 * make gconfig
 * Graphical menu using GTK+. Requires, and  to be installed.


 * make oldconfig
 * Review changes between kernel versions and update to create new .config for kernel.

There are also several scripts to create miscellaneous default configurations. See:

Configuration
This article describes the configuration using make menuconfig, but the procedure is similar for the other menus.

Usage
In the shown menu the blue bar indicates your position. With the arrow keys and  you can change the position. The arrow keys and  traverse the menu bar in the bottom and define, what happens, when you hit the  key. Select switches to a sub menu - the menu entries ending with ---> -, while Exit exits a sub menu. Alternative you can hit the key twice.

Menu entries, which start with brackets, are drivers or features which can be activated:


 * [ ], [*]
 * Options in square brackets can be activated or deactivated. The asterisk marks the menu entry as activated. You change the value with the key or press  (Yes) to activate or  (No) to deactivate the entry.
 * Is the option is activated, the chosen driver will be built into the kernel and will always be available at boot time.


 * < >, , <*>
 * Options in angle brackets can be activated or deactivated, but also activated as module (indicated by a M). You change the value as before and press key for activate as module.
 * See the Kernel Modules article for differentiation.


 * {M}, {*}
 * Options in curly brackets can be activated or activated as module but not be deactivated, because another driver needs this activated in either way.


 * -M-, -*-
 * Options between hyphens are activated in the shown way by another driver. There is no choice.

Furthermore some menu entries have a tag at the end:


 * (NEW)
 * This driver is new in the kernel and is maybe not stable enough.


 * (EXPERIMENTAL)
 * This driver is experimental and most likely not stable enough.


 * (DEPRECATED)
 * This driver is deprecated and not needed for most systems.


 * (OBSOLETE)
 * This driver is obsolete and should not be activated.

Most options have a description, which get by pressing the key or choose in the menu bar Help.

Driver selection
See the hardware detection article and the articles in the Hardware category.

Search modules
Within menuconfig, you can use to search modules by keyboards.

This is a new kernel configuration option only present in and other Kernel Project maintained kernels. It does nothing on its own, but sets various required configuration options for typical installations.

In order to boot Gentoo Linux a minimal set of config settings needs to be enabled in the kernel; to avoid the users from having to enable them manually as part of a Gentoo Linux installation or a new clean config, we enable these config settings by default for convenience.

Currently this only selects TMPFS, DEVTMPFS and their dependencies. TMPFS is enabled to maintain a tmpfs file system at /dev/shm, /run and /sys/fs/cgroup; DEVTMPFS to maintain a devtmpfs file system at /dev.

Some of these are critical files that need to be available early in the boot process; if not available, it causes sysfs and udev to malfunction.

To ensure Gentoo Linux boots, it is best to leave this option enabled; if you run a custom setup, you could consider whether to disable this.

Build
After configuring the kernel you have to compile the kernel:

If you have a processor with multiple cores, you can let all the cores do the work. For this add the parameter -j(NUMBER_CORES +1). For a dual core processor:

Setup
If activated drivers as modules, you have to install them:

The modules will be copied to a sub directory of.

To install the actual kernel:

This command executes /sbin/installkernel, which is part of the package. ''The new kernel is installed into. If a symbolic link already exists, it is refreshed by making a link from  to the new kernel, and the previously installed kernel is available as . (installkernel'' man page). The same for and  files. These symlinks are handy, because they point always to the newest kernel without changing the file path (e.g. you can use them in the bootloader configuration).

Bootloader
Change your bootloader configuration to pick up at boot the new kernel.

Finally restart your system with the new kernel.