tailieunhanh - Chapter-33-Custom kernels

A custom kernel often uses less memory. The kernel is the one system component that must always be present in memory, so unused code ties up memory that would otherwise be available to the virtual memory system. On a system with limited RAM, you can save some memory by building a custom kernel, but don’t overestimate the savings: a minimal kernel might save 500 kB over the GENERIC kernel supplied with the system. | 2 April 2003 17 00 47 The Complete FreeBSD page 599 In this chapter Building a new kernel Configuring I O devices The kernel build directory The configuration file Preparing for upgrades Building and installing the new kernel Making device nodes Kernel loadable modules sysctl Living with FreeBSD-CURRENT Analyzing kernel crash dumps 33 Custom kernels So far everything we ve done has been with the standard GENERIC kernel distributed with FreeBSD. You may find it an advantage to install a custom kernel As we saw in Chapter 2 GENERIC doesn t support everything that FreeBSD knows about. For example if you want to install a Yoyodyne frobulator you ll need to install special support for It will take less time to boot because it does not have to spend time probing for hardware that you do not have. A custom kernel often uses less memory. The kernel is the one system component that must always be present in memory so unused code ties up memory that would otherwise be available to the virtual memory system. On a system with limited RAM you can save some memory by building a custom kernel but don t overestimate the savings a minimal kernel might save 500 kB over the GENERIC kernel supplied with the system. In addition there are several kernel options that you can tune to fit your needs. Finally on page 613 we ll look at things to think about if you want to run the -CURRENT version of FreeBSD. In older releases of BSD you needed to build a new kernel for just about anything you wanted to change even things as simple as a different IRQ for a device. FreeBSD has evolved quite a bit since then and it s becoming increasingly less necessary to build a custom kernel. You will certainly need to do so if you want to enable kernel-wide 1. In fact the developer working on the Yoyodyne has defected to the Free Software Foundation. See the GNU General Public License for further details. v 2003 04 02 06 30 12 599 2 April 2003 17 00 47 The Complete FreeBSD