16.1 Why Reconfigure the Kernel?

   

Many times, SD-UX reconfigures your kernel automatically after installing software or a patch that requires modification to the kernel. In such a situation, SD-UX informs you before installing the software that a new kernel will be needed for the software. This is also done after installing patches related to kernel configuration. You also need to reconfigure your kernel if you perform one of the following tasks .

Adding or Removing Device Drivers

HP-UX communicates with all devices by using device drivers. Many of these device drivers are already built into the kernel. If you add a new device whose device driver is not present in the kernel, you need to rebuild the kernel to add the device driver for that device. Once the device driver is built into the kernel, you need to reboot your system so that the new kernel gets loaded into memory.

All device drivers occupy some space in memory as well as increase the size of your kernel. If you are not using some devices on your systems and their device drivers are present in the kernel, they are wasting memory. In systems where memory is constrained, this may become a performance-degrading issue. In such a case, it is better to remove all unwanted device drivers from the kernel to reduce its size and memory utilization. Once you remove any device driver from the kernel, you build a new kernel and install it. You always need to reboot the system after installing a new kernel.

Adding or Removing a Subsystem

HP-UX is divided into subsystems. A subsystem is a major part of HP-UX. An example of this is the network subsystem and the Logical Volume Manager (LVM) subsystem. In a standalone workstation, you don't need the network subsystem in the kernel. If this is built into your kernel, it is taking up memory without any utilization. You need to remove any unwanted subsystems from the kernel.

Similarly, if you are moving a standalone HP-UX system to a network, you need to have the network subsystem installed and built into your kernel. Any time you install or remove a subsystem, you reconfigure your kernel.

Changing Swap or Dump Devices

The primary swap location may be specified in the kernel configuration, although it is not necessary in the case where you use LVM or a whole-disk approach. A dump device is the place that is used to create a memory dump in case of problems with your system. These memory dumps can be used for troubleshooting later on. The dump location is usually the primary swap space. It may happen that your primary swap space is less than the amount of memory installed in your system, and you need to specify a separate dump space. In such a case, you will tell the kernel that you are using additional or alternate dump space and rebuild it.

Modifying System Parameters

The kernel contains system-specific information, which is represented by kernel parameters. Kernel parameters show how many users can access the system simultaneously , what the maximum number of open files and processes is, and other information particular to a specific installation of HP-UX. You may wish to change the values of these parameters depending on your local requirements. For example, if you have many users on the system who are accessing a lot of files, you may need to increase the number of files that can be opened simultaneously. Similarly, if many applications are installed and they create a lot of processes in memory, it may happen that the system process table becomes full. In this case, you will be required to increase the size of your process table by increasing the number of simultaneous processes.

Many vendors specify special kernel parameter value that they need to make sure their product functions properly. But if you have many applications, this will not be of much help and you will have to decide what the appropriate value for a system parameter will be.


   
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HP Certified
HP Certified: HP-UX System Administration
ISBN: 0130183741
EAN: 2147483647
Year: 2000
Pages: 390
Authors: Rafeeq Rehman

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