Rebuilding the kernel sounds like a pastime for hackers, but it is an important skill for any system administrator. First, you should rebuild the kernel on your system to eliminate the device drivers you don’t need. This reduces the amount of memory used by the kernel itself, as described in Section 6.2. The kernel is always present in memory, and the memory it uses cannot be reclaimed for use by programs if necessary.
You also need to occasionally upgrade your kernel to a newer version. As with any piece of your system, if you know of important bug fixes or new features in a kernel release, you may want to upgrade to pick them up. Those people who are actively developing kernel code will also need to keep their kernel up-to-date in case changes are made to the code they are working on. Sometimes, it is necessary to upgrade your kernel to use a new version of the compiler or libraries. Some applications (such as the X Window System) require a certain kernel version to run.
You can find out what kernel version you are running through the command uname -a. This should produce something like:
uname -aLinux owl 2.4.19-64GB-SMP #2 SMP Fri Aug 9 21:46:03 CEST 2002 i686 unknown
Here, we see a machine running Version 2.4.19 of the kernel (configured for a machine with more than one processor [SMP] and a maximum of 64 GB RAM), which was last compiled on August 9. We see other information as well, such as the hostname of the machine, the number of times ...