Kernel Configuration Tools

You can configure the kernel using one of several available configuration tools: config, menuconfig, xconfig, and with the 2.6 kernel, gconfig. You can also edit the configuration file directly. These tools perform the same configuration tasks but use different interfaces. The config tool is a simple configure script providing line-based prompts for different configuration options. The menuconfig tool provides a cursor-based menu, which you can still run from the command line. Menu entries exist for different configuration categories, and you can pick and choose the ones you want. To mark a feature for inclusion in the kernel, move to it and press the SPACEBAR. An asterisk appears in the empty parentheses to the left of the entry. If you want to make it a module, press M and an M appears in the parentheses. The xconfig tool runs on a window manager and provides a window interface with buttons and menus. You can use your mouse to select entries. A menu consists of configuration categories that are listed as buttons you can click. The 2.6 kernel's gconfig tool uses a GNOME interface to provide expandable menu trees, selectable panels, and help windows. Selectable features include check buttons you can click. All these tools save their settings to the .config file in the kernel source's directory. If you want to remove a configuration entirely, you can use the mrproper option to remove the .config file and any binary files, starting over from scratch.

make mrproper

You start a configuration tool by preceding it with the make command. Be sure you are in the /usr/src/linux-version directory. The process of starting a configuration tool is a make operation that uses the Linux kernel makefile. The xconfig tool should be started from a terminal window on your window manager. The menuconfig and config tools are started on a shell command line. The following example lists commands to start xconfig, menuconfig, and config:

make xconfig
make menuconfig
make config

xconfig

The xconfig tool opens a Linux Kernel Configuration window listing the different configuration categories. Figure 33-1 shows the configuration categories for the 2.4 kernel. Buttons at the right of the screen are used to save the configuration or to copy it to a file, as well as to quit. Clicking an entry opens a window that lists different features you can include. Three check boxes to the left of each entry enable you to choose to have a feature compiled directly into the kernel, created as a separate module that can be loaded at runtime, or not included at all. As a rule, features in continual use, such as network and file system support, should be compiled directly into the kernel. Features that could easily change, such as sound cards, or features used less frequently, should be compiled as modules. Otherwise, your kernel image file may become too large and slower to run.

Figure 33-1: The xconfig Linux Kernel Configuration tool, kernel 2.4

gconfig (Kernel 2.6)

The gconfig tool opens a Linux Kernel Configuration window listing the different configuration categories. Figure 33-2 shows the configuration categories for the 2.6 kernel. You will notice that there are fewer categories than for the 2.4 kernel. Many categories have been reorganized into a few major headings, with many now included under the Device Drivers menu. The Load and Save buttons and File menu entries can be used to save the configuration or to copy it to a file. Single, Split, and Full view buttons let you display menus in one window, in a display panel with another panel containing an expandable tree to select entries, or as a single expandable tree of entries. The Expand button will expand all headings and subheadings, whereas the Collapse button will let you expand only those you want displayed. Use the down and side triangles for each entry to expand or collapse subentries.

Figure 33-2: The gconfig Linux Kernel Configuration tool, kernel 2.6

Clicking an entry opens a window that lists different features you can include. Entries are arranged in columns listing the option, its actual name, its range (yes, module, or no), and its data (yes, no, or module status). Entries in the Options menu let you determine what columns to display: Name for the actual module name; Range for the selectable yes, no, and module entries; and Data for the option status, titled as Value.

The Range entries are titled N, M, and Y and are used to select whether or not to include an option (N), to load it as a module (M), or to compile it directly into the kernel (Y). Entries that you can select will display an underscore. Clicking the underscore will change its entry to Y for module or direct kernel inclusion, and N for no inclusion. The Value column will show what is currently selected.

The Options column will include a status showing whether the option is included directly (check mark), included as a module (line mark), or not included at all (empty). To quickly select or deselect an entry, double-click the option name in the Options field. You will see its check box checked, lined (module), or empty. Corresponding N, M, and Y entries for no inclusion, module, or kernel inclusion are selected. The default preference for either module or direct kernel inclusion for that option is selected automatically. You can change it manually if you wish.