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Linux Tuning The VM (memory) Subsystem

I've fast RAID-10 disk subsystem with multiple SCSI disks. Apps running under modern Linux kernel don't write directly to the disk. They write it to the file system cache which is managed by Linux kernel virtual memory manager. Since I've high performance RAID controller I need to decrease the number of flushes. How do I tune virtual memory subsystem under Linux operating systems for better performance?
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Bash Clear DNS Cache

How do I clear DNS cache using BASH shell prompt under UNIX like operating systems?
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Linux Error: Page Allocation Failure and Solution

Q. How do I get rid of an error message that read as - "Page allocation failure"?
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Q. I've followed your Xcache php 5.x opcode cacher installation under RHEL 5 for my vbulltin board. I see good boosting in performance. Now I've installed 2nd VB forum on the same server and I see all sub-forums hosted from 1st forum. So I had to disable Xcache. I want Xcache for both board on same host. How do I fix this mess?
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Q. Recently we made changes to our server hardware and swapped all IP address from old to a new server. However, 2 IP addresses are not get updated due to arp cache issues (IPs are cached on the router). They are going to other servers. How do I solve this problem under Redhat Enterprise Linux version 5.0 or any other Linux distribution?
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Q. I’m using CentOS Linux. I only have one processor (AMD 170 CPU) in my system, why does top command output report two processors?

A. You have a DUAL core CPU. A dual-core CPU combines two independent processors and their respective caches and cache controllers onto a single silicon chip, or integrated circuit. Some Intel P4 system comes with hyperthreading (HT) built into it.

This is not an error, it is a normal result of the hyperthreading and dual core CPU technology. This will improve system performance and will not harm any way to your server.

Various dual-core CPUs are being developed by companies such as Motorola, Intel and AMD. Following is the diagram of an Intel Core 2 dual core processor, with CPU-local Level 1 caches, and a shared, on-die Level 2 cache:
Why does top command shows two CPU when I have only one processor?
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