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Chapter 10. Kernel boot command-line parameter reference [14]

There are three ways to pass options to the kernel and thus control its behavior:

  1. When building the kernel. Most of this book discusses these options.

  2. When starting the kernel. Usually, parameters are passed to the kernel when it is invoked from a boot file such as the GRUB or LILO configuration file.

  3. At run-time, by writing to files in the /proc and /sys directories.

This chapter describes the second method of passing options. The chapter breaks the boot-time options into different logical sections. A number of architecture-specific and individual driver options are not listed here. For a complete list of all known options, please see the file Documentation/kernel-parameters.txt in the kernel source tree and the individual architecture-specific documentation files.

Not all of the listed options are always available. Most are associated with subsystems, and work only if the kernel is configured with those subsystems built in. They also depend on the presence of the hardware with which they are associated.

All of these parameters are case-sensitive.

Module-specific options

In addition to the options listed in this chapter, parameters for modules that are built in to the kernel can also be passed on the command line. (Dynamically loaded modules, of course, are not in memory when the kernel boots and therefore cannot be passed parameters at boot time.) The syntax for passing parameters consisting of the module name followed by a dot (.) and the parameter.

For example, the usbcore module accepts the parameter blinkenlights to display flashing lights on all supported USB 2.0 hubs (don't ever say the kernel developers don't have a sense of humor). To set this parameter when loading the module dynamically, you would enter:

$ 
modprobe usbcore blinkenlights=1

But if the usbcore module is built into the kernel, you achieve the same effect by invoking the kernel with the following option:

usbcore.blinkenlights=1

Most module options for modules that are built into the kernel can also be changed at run time by writing to files in the subdirectory named after the module under the /sys/module/ directory. Thus, the blinkenlights option is represented by the file /sys/module/usbcore/blinkenlights. desired.



[14] The majority of this chapter is based on the in-kernel documentation for the different kernel boot command line reference options, which were written by the kernel developers and released under the GPL.


 
 
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