Linux (GNU/Linux according to Stallman if you’re referring to a complete Linux distribution) is actually just the kernel of the operating system. The kernel is the core of the system, it handles access to all the harddrive, security mechanisms, networking and pretty much everything. It had better be secure or you are screwed.
In addition to this we have problems like the Pentium F00F bug and inherent problems with the TCP-IP protocol, the Linux kernel has it’s work cut out for it. Kernel versions are labeled as X.Y.Z, Z are minor revision numbers, Y define if the kernel is a test (odd number) or production (even number), and X defines the major revision (we have had 0, 1 and 2 so far). I would highly recommend running kernel 2.2.x, as of May 1999 this is 2.2.9. The .2.x series of kernel has major improvements over the 2.0.x series. Using the 2.2.x kernels also allows you access to newer features such as ipchains (instead of ipfwadm) and other advanced security features.
Upgrading and Compiling the Kernel
Upgrading the kernel consists of getting a new kernel and modules, editing /etc/lilo.conf, rerunning lilo to write a new MBR. The kernel will typically be placed into /boot, and the modules in /lib/modules/kernel.version.number/.
Getting a new kernel and modules can be accomplished 2 ways, by downloading the appropriate kernel package and installing it, or by downloading the source code from ftp://ftp.kernel.org/ (please use a mirror site), and compiling it.
Compiling a kernel is straightforward:
cd /usr/src
there should be a symlink called "linux" pointing to the directory containing the current kernel, remove it if there is, if there isn’t one no problem. You might want to ‘mv’ the linux directory to /usr/src/linux-kernel.version.number and create a link pointing /usr/src/linux at it.
Unpack the source code using tar and gzip as appropriate so that you now have a /usr/src/linux with about 50 megabytes of source code in it. The next step is to create the linux kernel configuration (/usr/src/linux.config), this can be achieved using "make config", "make menuconfig" or "make xconfig", my preferred method is "make menuconfig" (for this you will need ncurses and ncurses devel libraries). This is arguably the hardest step, there are hundreds options, which can be categorized into two main areas: hardware support, and service support. For hardware support make a list of hardware that this kernel will be running on (i.e. P166, Adaptec 2940 SCSI Controller, NE2000 ethernet card, etc.) and turn on the appropriate options. As for service support you will need to figure out which filesystems (fat, ext2, minix ,etc.) you plan to use, the same for networking (firewalling, etc.).
Once you have configured the kernel you need to compile it, the following commands makes dependencies ensuring that libraries and so forth get built in the right order, then cleans out any information from previous compiles, then builds a kernel, the modules and installs the modules.
make dep (makes dependencies)
make clean (cleans out previous cruft)
make bzImage (make zImage pukes if the kernel is to big, and 2.2.x kernels tend to be pretty big)
make modules (creates all the modules you specified)
make modules_install (installs the modules to /lib/modules/kernel.version.number/)
you then need to copy /usr/src/linux/arch/i386/boot/bzImage (zImage) to /boot/vmlinuz-kernel.version.number. Then edit /etc/lilo.conf, adding a new entry for the new kernel and setting it as the default image is the safest way (using the default=X command, otherwise it will boot the first kernel listed), if it fails you can reboot and go back to the previous working kernel. Run lilo, and reboot.
Kernel Versions
Currently we are in a stable kernel release series, 2.2.x. I would highly recommend running the latest stable kernel (currently 2.2.9 as of May 1999) as there are several nasty security problems (network attacks and denial of service attacks) that affect all kernels up to 2.0.35, 2.0.36 is patched, and the later 2.1.x test kernels to 2.2.3. Upgrading from the 2.0.x series of stable kernels to the 2.2.x series is relatively painless if you are careful and follow instructions (there are some minor issues but for most users it will go smoothly). Several software packages must be updated, libraries, ppp, modutils and others (they are covered in the kernel docs / rpm dependencies / etc.). Additionally keep the old working kernel, add an entry in lilo.conf for it as "linuxold" or something similar and you will be able to easily recover in the event 2.2.x doesn't work out as expected. Don't expect the 2.2.x series to be bug free, 2.2.9 will be found to contain flaws and will be obsoleted, like every piece of software in the world.
