How to: Install and Setup XEN Virtualization Software on CentOS Linux 5

Posted on in Categories CentOS, High performance computing, Howto, Linux, Linux Virtualization, RedHat/Fedora Linux, xen last updated October 18, 2007

Xen is a free open source software virtual machine monitor for Intel / PowerPC architectures. It is software that runs on a host operating system and allows several guest operating systems to be run on top of the host on the same computer hardware at the same time (just like VMWare software). Luckily Installing and managing XEN is quite easy under CentOS 5 Linux.

How to: Upgrade VMWARE Server under Linux

Posted on in Categories CentOS, Howto, Linux Virtualization, RedHat/Fedora Linux, Suse Linux, Tips last updated September 25, 2007

Build 56528 is a release build of VMware Server 1.0.4. It is a maintenance bug fix release to address security issues. Upgrading VMWare server is a piece of cake under Redhat Enterprise Linux / CentOS Linux version 5.0.

Please note that following instructions are tested on RHEL 4.5, 5.0 and CentOS Linux 5.0 only. You can use tar ball based package to upgrade vmware under Debian Linux.

Find out current VMware server version

First find out current vmware server version, enter:
# vmware -v
Output:

VMware Server 1.0.3 build-44356

You can download the latest version from official site.

Shutdown all VMWARE guest oses / vps

Login to each running VM and bring down (halt) guest operating system. You can also use vmware server console or web based interface for the same purpose.
Stop VMWARE Server:
# /etc/init.d/vmware stop
Output:

Stopping VMware services:
   Virtual machine monitor                                 [  OK  ]
   Bridged networking on /dev/vmnet0                       [  OK  ]
   Virtual ethernet                                        [  OK  ]

Stop VMWARE Webbased interface:
# /etc/init.d/httpd.vmware stop
Output:

   Shutting down http.vmware:                              [  OK  ]

Download VMWARE Server

Use wget the ultimate command line downloader
# cd /tmp
# wget http://download3.vmware.com/software/vmserver/VMware-server-1.0.4-56528.i386.rpm
# wget http://download3.vmware.com/software/vmserver/VMware-mui-1.0.4-56528.tar.gz

Upgrade VMWARE server

Use rpm command to upgrade VMWARE server, enter:
# rpm -Uvh VMware-server-1.0.4-56528.i386.rpm
Output:

Preparing...                ########################################### [100%]
   1:VMware-server          ########################################### [100%]

Reconfigure VMWARE Server

Just reconfigure Vmware server with old values/options:
# vmware-config.pl
Just accept accept the End User License Agreement and press CTRL+C. Now configure server with old values:
# vmware-config.pl -d
Output:

aking sure services for VMware Server are stopped.

Stopping VMware services:
   Virtual machine monitor                                 [  OK  ]
   Bridged networking on /dev/vmnet0                       [  OK  ]
   Virtual ethernet                                        [  OK  ]

Configuring fallback GTK+ 2.4 libraries.

In which directory do you want to install the mime type icons?
[/usr/share/icons]

What directory contains your desktop menu entry files? These files have a
.desktop file extension. [/usr/share/applications]

In which directory do you want to install the application's icon?
[/usr/share/pixmaps]

Trying to find a suitable vmmon module for your running kernel.
...........
...
.....
*** Output truncated ***

Upgrade VMware Server Web-based management interface

The VMware Server Web-based management interface. Install on your VMware Server system to enable control from a Web browser. Untar and install the same:
# tar -zxvf VMware-mui-1.0.4-56528.tar.gz
# cd vmware-mui-distrib/
# perl vmware-install.pl

Just follow on screen instructions to install Web-based management interface. Finally just start all guest oses.

Force BIND DNS Server to take full advantage of Dual Core Multiple Intel / AMD Cpu

Posted on in Categories CentOS, Debian Linux, Gentoo Linux, Howto, Linux, RedHat/Fedora Linux, Sys admin, Tips, Troubleshooting, Tuning, Ubuntu Linux, UNIX last updated September 7, 2007

One of my client runs dedicated NS1 and NS2 to host more than 3000+ domains. Recently they upgraded their servers to latest Dual Core Dual AMD server with CentOS 5.0 and BIND server.

By default BIND / named will try to determine the number of CPUs present and create one thread per CPU. If it is unable to determine the number of CPUs, a single worker thread will be created. However due to some reason the BIND server failed to automatically utilize all of the system’s available CPUs. So how do you force DNS Server to take advantage of multiple CPUs under CentOS Linux?

After a little investigation, named man page pointed out me in right direction ~ -n #CPU option, which creates #cpus worker threads to take advantage of multiple CPUs.

Force BIND DNS Server to take advantage of multiple CPUs

In order to enable multiple CPU open /etc/sysconfig/named file under CentOS / RHEL / Fedora Linux:
# vi /etc/sysconfig/named
To force bind to take advantage of 4 CPUs, add / modify as follows:
OPTIONS="-n 4"
Save and close the file. Restart named service:
# /etc/init.d/named restart

A note about Debian / Ubuntu Linux user

If you are a Debian / Ubuntu Linux modify /etc/defaults/bind9 file:
$ sudo vi /etc/defaults/bind9
Append config line:
OPTIONS="-n 4"
Please note append -n 4 to the end of other options (if any), for example:
OPTIONS="-4 -6 -n 4"
Save and close the file. Restart BIND server:
$ sudo /etc/init.d/bind9 restart

More more information read named man page.

How do I install Oracle database server on CentOS Enterprise Linux 5?

Posted on in Categories CentOS, Howto, Linux, Sys admin, Tips last updated May 1, 2007

This is a nice and step by step guide for installing Oracle database server under CentOS Linux. The guide has plenty of screenshots:

During OS install both GNOME and KDE desktops were selected as well as all components of all available groups except “Virtualisation”, “Clustering”, “Cluster Storage” KDE Session has been selected for system login. Firewall and SELINUX have been disabled.

Installing Oracle 10.2.0.1 on CentOS 5.0 (x86_64) [Oracle DBA Blog]

How to: Linux flush or remove all iptables rules

Posted on in Categories Debian Linux, Howto, Iptables, Linux, Networking, RedHat/Fedora Linux, Ubuntu Linux last updated June 20, 2005

Here is a small script that does this. Debian or Ubuntu GNU/Linux does not comes with any SYS V init script (located in /etc/init.d directory). You create a script as follows and use it to stop or flush the iptables rules. Please don’t type rules at the command prompt. Use the script to speed up work.

Warning: All the commands must be executed with root privileges.

Procedure for Debian / Ubuntu Linux (Generic method)

First, create /root/fw.stop script using text editor such as vi:

#!/bin/sh
echo "Stopping firewall and allowing everyone..."
ipt="/sbin/iptables"
## Failsafe - die if /sbin/iptables not found
[ ! -x "$ipt" ] && { echo "$0: \"${ipt}\" command not found."; exit 1; }
$ipt -P INPUT ACCEPT
$ipt -P FORWARD ACCEPT
$ipt -P OUTPUT ACCEPT
$ipt -F
$ipt -X
$ipt -t nat -F
$ipt -t nat -X
$ipt -t mangle -F
$ipt -t mangle -X
$ipt iptables -t raw -F
$ipt -t raw -X

Make sure you can execute the script:
# chmod +x /root/fw.stop

Run the script as root user:
# /root/fw.stop

How do I verify that my firewall rules are flushed out?

Type the following command:
# iptables -L -n -v
Sample outputs:

Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         
Chain FORWARD (policy ACCEPT 0 packets, 0 bytes) pkts bytes target prot opt in out source destination
Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes) pkts bytes target prot opt in out source destination

A note for RedHat (RHEL), CentOS and friends Linux user

Please note that RedHat Enterprise Linux (RHEL), Fedora and Centos Linux comes with pre-installed rc.d script, which can be used to stop the firewall, enter:
# /etc/init.d/iptables stop
OR
# service iptables stop
Sample outputs:

A note about firewalld on CentOS 7/Fedora (latest)/RedHat Enterprise Linux 7.x+ user

Type the following command to stop and flush all rules:
# systemctl stop firewalld