Virtualization : Basic Concepts

Virtualization is the creation of a virtual (rather than actual) version of something, such as an operating system, a server, a storage device or network resources. e.g. hard drive into different partitions, a partition is the logical division of a hard disk drive to create, in effect, two separate hard drives.
Similarly, Operating system virtualization is the use of software to allow a piece of hardware to run multiple operating system images at the same time.

There are three areas of IT where virtualization is making head roads
a) Network virtualization
b) Storage virtualization
c) Server virtualization

Today, virtualization is in the forefront - helping businesses with scalability, security and management of their global IT infrastructure.

Virtualization can host multiple guest operating systems. Each guest operating system runs in its own domain, Virtualization schedules virtual CPUs within the virtual machines to make the best use of the available physical CPUs. Each guest operating systems handles its own applications. These guest operating systems schedule each application accordingly.

You can deploy Virtualization in one of two choices: full virtualization or Para virtualization.

Full virtualization provides total abstraction of the underlying physical system and creates a new virtual system in which the guest operating systems can run. No modifications are needed in the guest OS or application (the guest OS or application is not aware of the virtualized environment and runs normally).

Para virtualization requires user modification of the guest operating systems that run on the virtual machines (these guest operating systems are aware that they are running on a virtual machine) and provide near-native performance.

To know more on Virtualization:
Intro to Virtualization,
SearchServerVirtualization.com,
Red Hat Enterprise Linux Virtualization.

Change the default port for SSh user

Default port for SSH user is 22. But we can change the default port to some another port.
eg. I want to run ssh service on port 99 instead of 22.

Make the following change.

open files
#emacs /etc/ssh/ssh_config
#emacs /etc/ssh/sshd_config

search for port ie is default port = 22

make port = 99

or

You can run on any port, But make sure other service not running on that port.

web Based administration solution for Linux : webmin

Webmin is an open source web Based administration solution for Linux. The purpose of webmin is to gather the administration of many different tasks and services under a common web interface. The software is perl based and module based which make it adaptable. Most common tasks have a module to administer.

how To Install Webmin:
# cd /usr/src
# wget http://prdownloads.sourceforge.net/webadmin/webmin-1.340-1.noarch.rpm
# rpm -ivh webmin-1.340-1.noarch.rpm

steps to install virtualmin & configure it:
login to webmin: ipaddress:100000
1) webmin -> webmin configuration -> webmin modulesInstall module -> from ftp or http url ->virtual min url is: http://download.webmin.com/download/virtualmin/virtual-server-3.201.gpl.wbm.gz

2) Enable https:yum install mod_sslin virtualmin config enable ssl for websites.
Configuring virtualmin:Enabled the subverion and mysql moduledisabled webalizerPostgreSQL setup and configuration enabled? yes.

3) If this server is going to use PGsqlPostfix configuration from webmin:servers->postfix->virtual domain->domain mapping lookup table: hash:/etc/postfix/virtual General options: Network interface for receiving mail: all [make sure that the hostname is something like sys.abc.comg is you are going to run the acb system here.]

4) dovecot configuration from webmin:webmin -> servers -> dovecot -> user login options -> Password authentication source -> unix shadow filestart at boot: yes

5) Webmin -> webmin configuration -> Ports and addressesaccess the webmin system: and then configure the port (eg 100000) for webmin listen and udp packets.

6) Webmin -> webmin configuration -> ssl encryptionAlso make webmin run on ssh.Enable SSL if available? yesRedirect non-SSL requests to SSL mode? yes

Check your memory !

We all are always worry about memory weather it is main memory, secondary, or other swap
These are few command which help u to debug your memory.

Simple stat.
#free
#du -h
#df -h

Some complex stat.

#cat /proc/meminfo
#dmesg | grep -n kernel

This command give you files have more than 100M usages.

#find / -size +100M -fprintf /root/big.txt '%-10s %p\n'