You've probably heard people talking about compiling the kernel or building a kernel, but what exactly is the kernel and what does it do? The kernel is the center of your computer. It is the foundation for the entire operating system. The kernel acts as a bridge between the hardware and the applications. This means that the kernel is (usually) the sole piece of software responsible for ordering around the hardware components of your computer. It is the kernel that instructs the hard drive to search for a certain data stream. It is the kernel that instructs your network card to transmit rapid changes in voltage. The kernel also listens to hardware as well. When the network card detects a remote computer sending information, it forwards that information to the kernel. This makes the kernel both the single most important piece of software on your computer and the most complex.

The complexity of a modern linux kernel is staggering. The source code for the kernel weighs in at nearly 400MB uncompressed. There are thousands of developers, hundreds of options, and if everything were built together, the kernel would soon pass 100MB in size itself. In order to keep the size of the kernel down (as well as the amount of RAM needed for the kernel), most of the kernel options are built as modules. You can think of these modules as device drivers which can be inserted or removed from a running kernel at will. In truth, many of them aren't device drivers at all, but contain support for things such as network protocols, security measures, and even filesystems. In short, nearly any piece of the linux kernel can be built as a loadable module. It's important to realize that Slackware will automatically handle loading most modules for you. When your system boots, udevd(8) is started and begins to probe your system's hardware. For each device it finds, it loads the proper module and created a device node in /dev. This usually means that you will not need to load any modules in order to use your computer, but occasionally this is necessary. So what modules are currently loaded on your computer and how do we load and unload them? Fortunately we have a full suite of tools for handling this. As you might have guessed, the tool for listing modules is lsmod(8). darkstar:~# lsmod Module Size Used by nls_utf8 1952 1 cifs 240600 2 i915 168584 2 drm 168128 3 i915 i2c_algo_bit 6468 1 i915 tun 12740 1 ... many more lines ommitted ... In addition to showing you what modules are loaded, it displays the size of each module and tells you what other modules are using it. There are two applications for loading modules: insmod(8) and modprobe(8). Both will load modules and report any errors (such as loading a module for a device that isn't present in your system), but modprobe is preferred because it can load any module dependencies. Using either is straight-forward. darkstar:~# insmod ext3 darkstar:~# modprobe ext4 darkstar:~# lsmod | grep ext ext4 239928 1 jbd2 59088 1 ext4 crc16 1984 1 ext4 ext3 139408 0 jbd 48520 1 ext3 mbcache 8068 2 ext4,ext3 Removing modules can be a tricky process, and once again we have two programs for removing them: rmmod(8) and modprobe. In order to remove a module with modprobe, you'll need to use the -r argument. darkstar:~# rmmod ext3 darkstar:~# modprobe -r ext4 darkstar:~# lsmod | grep ext

Most Slackware users will never need to compile a kernel. The huge and generic kernels contain virtually all the support you will need. However, some users may need to compile a kernel. If your computer contains bleeding edge hardware, a newer kernel may offer improved support. Sometimes a kernel patch my be available that corrects a problem you are experiencing. In these cases a kernel compile is probably warranted.