HP-UX System Administrator's Guide: Overview HP-UX 11i v3 (B3921-90011, September 2010)

3 Major Components of HP-UX
Operating systems are complex pieces of software designed to control the many resources of a
computer so that many users and processes can use those resources cooperatively and efficiently.
HP-UX 11i, a version of the UNIX operating system, is comprised of many components that work
together to control the resources of HP Integrity Servers, HP 9000 servers, and others.
This chapter describes the main components of HP-UX, what they do, and how they relate to
each other.
The HP-UX Kernel
The kernel is the central part of the HP-UX operating system; everything else around it depends
on and interacts with. When you start up (boot) HP-UX, it is the kernel that is copied from disk
into memory by the boot loader and initiated.
The kernel is made up of many subcomponents. In the case of an HP-UX kernel, these
subcomponents are called kernel modules and kernel tunables.
Kernel Modules
Kernel modules are sections of kernel code dedicated to specific purposes, such as memory
management, class drivers, or interface drivers.
Adding/Removing Kernel Modules
Many kernel modules are configured into the kernel when it is built and are always present in
the kernel whenever it is running. Other modules are added when they are needed, and some
can be removed when not needed.
The kernel modules that are only required some of the time fall into two categories:
• Modules that can be added to, or removed from, the kernel while it is running
• Modules that require a reboot to be added to, or removed from, the kernel
You can use the Modules tool in the Kernel Configuration toolbox in the System
Management Homepage, or the kcmodule command from a shell command line, to:
• view the current list of modules in the kernel,
• view the state of specific modules in the kernel,
• determine whether modules require a reboot to be added to or removed from the kernel,
• change the state of a module, either currently (if supported by the module) or at the next
boot.
For details about kernel configuration, see: “Configuring the Kernel” in HP-UX System
Administrator’s Guide: Configuration Management.
Kernel Tunables
Kernel tunables are settings that determine things like how many processes can simultaneously
be active or how much memory can be allocated for certain data structures within the kernel.
For more information on kernel tunables, what they are, and how to adjust them, see the HP-UX
System Administrator’s Guide: Configuration Management.
The HP-UX Kernel 39