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9.2.3. Configuring the Kernel
The next step consists of configuring the kernel according to your needs. The exact procedure depends on the goals.
The kernel build depends on a kernel configuration file. In most cases, you will most likely keep as close as possible to that proposed by Kali, which, like all Linux distributions, is installed in the
/boot directory. In this case, rather than reconfiguring everything from scratch, it is sufficient to make a copy of the /boot/config-version file. (The version should be the same as that version of the kernel currently used, which can be found with the uname -r command.) Place the copy into a .config file in the directory containing the kernel sources.
$ cp /boot/config-4.9.0-kali1-amd64 ~/kernel/linux-source-4.9/.config
$ cp /boot/config-4.9.0-kali1-amd64 ~/kernel/linux-source-4.9/.config
Alternatively, since the kernel provides default configurations in arch/arch/configs/*_ defconfig, you can put your selected configuration in place with a command like make x86_64_defconfig (in the case of a 64-bit PC) or make i386_defconfig (in the case of a 32-bit PC).
Unless you need to change the configuration, you can stop here and skip to section 9.2.4, “Com- piling and Building the Package” [page 236]. If you need to make changes or if you decide to reconfigure everything from scratch, you must take the time to configure your kernel. There are various dedicated interfaces in the kernel source directory that can be used by calling the make target command, where target is one of the values described below.
make menuconfig compiles and launches a text-mode kernel configuration interface (this is where the libncurses5-dev package is required), which allows navigating the many available ker- nel options in a hierarchical structure. Pressing the Space key changes the value of the selected option, and Enter validates the button selected at the bottom of the screen; Select returns to the selected sub-menu; Exit closes the current screen and moves back up in the hierarchy; Help will display more detailed information on the role of the selected option. The arrow keys allow mov- ing within the list of options and buttons. To exit the configuration program, choose Exit from the main menu. The program then offers to save the changes that you have made; accept if you are satisfied with your choices.
Other interfaces have similar features but they work within more modern graphical interfaces, such as make xconfig, which uses a Qt graphical interface, and make gconfig, which uses GTK+. The former requires libqt4-dev, while the latter depends on libglade2-dev and libgtk2.0-dev.
Dealing with Outdated When you provide a .config file that has been generated with another (usually older)
.config Files kernel version, you will have to update it. You can do so with make oldconfig, which will interactively ask you the questions corresponding to the new configuration op- tions. If you want to use the default answer to all those questions, you can use make olddefconfig. With make oldnoconfig, it will assume a negative answer to all ques- tions.
Dealing with Outdated When you provide a .config file that has been generated with another (usually older)
.config Files kernel version, you will have to update it. You can do so with make oldconfig, which will interactively ask you the questions corresponding to the new configuration op- tions. If you want to use the default answer to all those questions, you can use make olddefconfig. With make oldnoconfig, it will assume a negative answer to all ques- tions.