First, let us take a quick tour of the kernel build directory. All directories mentioned will be relative to the main /usr/src/sys directory, which is also accessible through /sys. There are a number of subdirectories here representing different parts of the kernel, but the most important, for our purposes, are arch/conf, where you will edit your custom kernel configuration, and compile, which is the staging area where your kernel will be built. arch represents either i386 or amd64, at this point in development. Everything inside a particular architecture's directory deals with that architecture only; the rest of the code is common to all platforms to which DragonFly could potentially be ported. Notice the logical organization of the directory structure, with each supported device, file system, and option in its own subdirectory.
Note: If there is not a /usr/src/sys directory on your system, then the kernel source has not been installed. The easiest way to do this is via cvsup.
Next, move to the arch/conf directory and copy the GENERIC configuration file to the name you want to give your kernel. For example:
# cd /usr/src/sys/i386/conf # cp GENERIC MYKERNEL
Traditionally, this name is in all capital letters and, if you are maintaining multiple DragonFly machines with different hardware, it is a good idea to name it after your machine's hostname. We will call it MYKERNEL for the purpose of this example.
Tip: Storing your kernel config file directly under /usr/src can be a bad idea. If you are experiencing problems it can be tempting to just delete /usr/src and start again. Five seconds after you do that you realize that you have deleted your custom kernel config file. Do not edit GENERIC directly, as it may get overwritten the next time you update your source tree, and your kernel modifications will be lost.
You might want to keep your kernel config file elsewhere, and then create a symbolic link to the file in the i386 directory.
For example:# cd /usr/src/sys/i386/conf # mkdir /root/kernels # cp GENERIC /root/kernels/MYKERNEL # ln -s /root/kernels/MYKERNEL
Note: You must execute these and all of the following commands under the root account or you will get permission denied errors.
Now, edit MYKERNEL with your favorite text editor. If you are just starting out, the only editor available will probably be vi, which is too complex to explain here, but is covered well in many books in the bibliography. However, DragonFly does offer an easier editor called ee which, if you are a beginner, should be your editor of choice. Feel free to change the comment lines at the top to reflect your configuration or the changes you have made to differentiate it from GENERIC.
If you have built a kernel under SunOS™ or some other BSD operating system, much of this file will be very familiar to you. If you are coming from some other operating system such as DOS, on the other hand, the GENERIC configuration file might seem overwhelming to you, so follow the descriptions in the Configuration File section slowly and carefully.
Note: Be sure to always check the file /usr/src/UPDATING, before you perform any update steps, in the case you sync your source tree with the latest sources of the DragonFly project. In this file all important issues with updating DragonFly are typed out. /usr/src/UPDATING always fits your version of the DragonFly source, and is therefore more accurate for new information than the handbook.
Building a Kernel
Change to the /usr/src directory.
# cd /usr/src
Compile the kernel.
# make buildkernel KERNCONF=MYKERNEL
Install the new kernel.
# make installkernel KERNCONF=MYKERNEL
If you have not upgraded your source tree in any way since the last time you successfully completed a buildworld-installworld cycle (you have not run CVSup), then it is safe to use the quickworld and quickkernel, buildworld, buildkernel sequence.
The new kernel will be copied to the root directory as /kernel and the old kernel will be moved to /kernel.old. Now, shutdown the system and reboot to use your new kernel. In case something goes wrong, there are some troubleshooting instructions at the end of this chapter. Be sure to read the section which explains how to recover in case your new kernel does not boot.
Note: If you have added any new devices (such as sound cards), you may have to add some device nodes to your /dev directory before you can use them. For more information, take a look at Making Device Nodes section later on in this chapter.
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