Java keytool quick tips

Creating a keystore from an SSL key and cert

To store an SSL key for Jetty or other Java based webserver, you usually use keytool. You'll first need to convert the key to pkcs12 (we're calling the output file jetty.pkcs12) format like so (we're assuming your key is generated with openssl or something similar - also, we're in the same directory as the keys):

Convert mykey,key and mykey.crt to a pkcs12  format using openssl
( I highly recommend using a passphrase on the key)


openssl pkcs12 -inkey ./mykey.key -in ./mykey.crt -export -out ./jetty.pkcs12

Let's take that pkcs12 key and convert it into a Java keystore (we're calling the keystore mykeystore)




keytool -importkeystore -srckeystore jetty.pkcs12 -srcstoretype pkcs12 -destkeystore mykeystore

Let's list the contents of this keystore:

keytool -list -storename mykeystore


Add an CA certificate to the default java CA cert keystore

Java keeps its own CA cert repo - which can be frustrating if you don't update java on your server frequently. To add a new CA cert (let's assume you just bought an SSL cert online and your cert CA's certificates were created recently)

1. Find cacerts for your installation - note that many commercial java programs like to install their own java. If you're looking at the default java location, try:

find /usr -name cacerts

1b. If you're trying to find the cacerts for an application you installed, figure out where java is being called from:

ps wwaux | grep java

(you'll likely see a path for java - i.e., /opt/java/bin/java  or something similar)

Now, find the cacerts,  
 find /opt -name cacerts

2. Add the CA cert to your cacerts file:

keytool -import -trustcacerts -alias MyCAsName -file /path/to/ca-certificatec -keystore /path/to/keystore

Cisco ASA to Juniper ScreenOS to Juniper JunOS Reference Cheat Sheet

Here is a basic reference sheet for looking up equivalent commands between a Cisco ASA and a Juniper ScreenOS (or Netscreen) SSG and a Juniper JunOS SRX firewall.

Cisco ASA	Juniper ScreenOS (SSG)	Juniper JunOS (SRX)
show log	get event	show log messages show log messages | last 20 (see the 20 most recent logs)
show ip	get interface	show interface terse
show failover	get nsrp	show chassist cluster status
no failover active	exec nsrp vsd [vsd] mode backup	request chassis cluster failover redundancy-group [group] node
show route	get route	show route
show connections	get session	show security flow session
show clock	get clock	show system uptime
show version (to get uptime)	get system	show system uptime
show running-config	get config	show config
show version (to get serial number)	get chassis	show chassis hardware detail
show access-list	get policy	show security policies
show crypto isakmp sa	get ike cookie	show security ike security-associations
show crypto ipsec sa	get sa	show security ipsec security-associations
clear crypto isakmp sa	clear ike cookie	clear security ike security-associations
clear crypto ipsec sa	clear sa	clear security ipsec security-associations
show cpu	get perf cpu	show chassis routing-engine
show proc cpu-usage		show system processes extensive
show int (for i/o of bytes)	get counter statistics
ssh x.x.x.0 y.y.y.0 inside	set admin manager-ip x.x.x.0 y.y.y.0 set ssh enable
show run [cry isakmp|tunnel-group]?	get ike gateway
interface Ethernet1 shutdown	set interface ethernet0/0 phy link-down
interface Ethernet1 no shutdown	unset interface ethernet0/0 phy link-down
show failover	get nsrp
route outside 1.1.1.0 255.255.255.0 1.1.1.2	set route 1.1.1.0/24 interface bgroup3/0 gateway 1.1.1.2
logging host INSIDE 1.1.1.1 logging trap notification	set syslog config 172.16.200.200 facilities local5 set syslog src-interface ethernet1/0 set syslog enable
ntp server 1.1.1.1 source OUTSIDE	set ntp server 1.1.1.1 set ntp server src-interface ethernet3/0 set clock ntp exec ntp update
capture CAP1 match ip host 1.1.1.1 host 2.2.2.2	clear db set console dbuf set ffilter src-ip 1.1.1.1 dst-ip 2.2.2.2 debug flow basic — OR — snoop filter ip src-ip 1.1.1.1 dst-ip 2.2.2.2 direction both clear dbuf snoop	edit security flow traceoptions set file TSHOOT set flag basic-datapath set packet-filter IN-TO-OUT source-prefix 10.1.1.100/32 destination-prefix 10.2.0.3/32
show capture CAP1	get dbuf stream	show log TSHOOT
clear capture CAP1	undebug all unset ffilter — OR — snoop filter delete	deactivate security flow traceoptions delete security flow traceoptions

Additional reading material regarding Juniper SSG and ScreenOS commands: http://www.juniper.net/techpubs/software/screenos/screenos6.2.0/index.html

Tomcat with apache-mod_jk configuration in Linux

Few years back I was working for a project which have given me a chance to work around Apache and tomcat,there are a few reasons why we’d want to configure Tomcat to run with Apache. For me the most important is security and the fact that I’d like to run my web servers on port 80. In order to run Tomcat on port 80 it has to run as root which is not safe and absolutely not recommended. I am going to show you how to configure your Apache to run and pass connections to Tomcat.
What I normally like to do in such situation is to compile Apache instead of installing from repositories, install and configure Java and Tomcat, and then complile mod_jk to provide Tomcat/Apache connector. Basically all steps will be manual. Perhaps all this can be done using repositories too, but this way I can keep things updated as they updates come out by the developers, not when they become available in repositories.
To simplify the solution and make it a universal tutorial, I am going to refer to each product by its name. Therefore we will be renaming all extracted folders to their generic names. For instance, latest versions of Apache, Tomcat, Java and mod_jk are 2.2.11, 6.0.18, 6u11 and 1.2.27 respectively (Jan 09), but we are going to refer to them as just Apache, Tomcat, Java and mod_jk. I have actually renamed them right after they were extracted before I placed them onto their permanent directories. I am going to use /opt  as my installation directory but you can place them in /opt or any other directory you wish.
Most steps are performed under a non-root account. I will let you know when to use the root account.
Installing Apache:

1. Log on with your non-root account.
2. Download Apache tar package from http://www.apache.org and extract. This directory will be called “apache” from this point forward.
3. Change directory to apache ‘cd apache’.

Prepare the product to compile:

1. In apache directory:

   ./configure --prefix=/opt/apache

2. make
3. Change to root user: su
4. make install

Once it’s complete run apache:

/opt/apache/bin/apachectl start

test installation by browsing the target address. If it’s running then stop the process:

/opt/apache/bin/apachectl stop

Install Java (I’m using jdk):

1. Download Java self-extracting package from http://www.java.com. Whatever this file is, we call it java.bin.
2. Make it executable:
   chmod +x java.bin
3. Execute:
   ./java.bin
4. Once you’re done with the installation you will have a directory jre1xxxxx. We will refer to this directory as “java”.
5. Become root: su (to move directory to /opt)
   
6. Move the directory to its final resting place. Mine sits in /opt:
   mv java /opt

Install Tomcat:

1. Download Tomcat from http://tomcat.apache.org and extract the tar ball. We will call this directory “tomcat” from now on.
2. Become root: su (to move directory to /opt)
   
3. Move this directory to /opt:
   mv tomcat /opt

Now it’s time to configure our paths. Edit your .bash_profile:
STOP: This is local to the user running Tomcat. Each user who’ll be running Tomcat should have a bash_profile in their own home directory.
nano ~/.bash_profile
and add the following lines:

export JRE_HOME=/opt/java
export JAVA_HOME=/opt/java
export CATALINA_HOME=/opt/tomcat

Save and exit, then execute the following command:
source ~/.bash_profile
Now test your Tomcat: as non-root user:

/opt/tomcat/bin/startup.sh

browse to http://localhost:8080. If it’s working then shut it down:

/opt/tomcat/bin/shutdown.sh

Installing connector (mod_jk):

1. Download mod_jk connector from http://tomcat.apache.org/download-connectors.cgi and extract. We will call this new directory “connector”.
2. Go to connector/native.
3. To prepare:

   ./configure --with-apxs=/opt/apache/bin/apxs

4. make
   
5. Become root and:
   make install
6. Check to see if mod_jk.so is in /opt/apache/modules. If it’s there then you’ve so far been successful.

Create the connector:
Create a file called “connector.conf” in apache/conf directory:

vi /opt/apache/conf/connector.conf

and copy/paste the following lines in that file, save and exit:

workers.tomcat_home=/opt/tomcat
workers.java_home=/opt/java
ps=/
worker.list=myworker
worker.myworker.port=8009
worker.myworker.host=localhost
worker.myworker.type=ajp13
worker.myworker.lbfactor=1

Add the following lines to httpd.conf:

LoadModule jk_module modules/mod_jk.so
JkWorkersFile conf/connector.conf
JkLogFile logs/mod_jk.log
JkLogLevel error
JkLogStampFormat "[%a %b %d %H:%M:%S %Y]"
JkOptions +ForwardKeySize +ForwardURICompat -ForwardDirectories
JkRequestLogFormat "%w %V %T"
JkMount /*.jsp myworker
JkMount /* myworker

Now, start both Apache and Tomcat. You should be able to view the Tomcat default page in http://localhost AND http://localhost:8080. This means that the connector is working. To increase security disable http access to Tomcat through port 8080.
Note: Apache will automatically start after reboot, but you will have to add Tomcat to your startup script manually. Here is a startup script you can copy to your /etc/init.d and make it executable to start/stop your server. I don’t remember where I got this script from, but just so you know, it’s not mine. Good thing about this script is that even if you run this as root, it will run your Tomcat server as user specified in line 6.
Note: become root to run Apache. If you use the following script for your Tomcat, you may also run it as root. It will switch to specified user once it’s executed. I don’t use the script, however, what I do is to add it to my root crontab and have run it as non-root user. This is the command I use:

su - <username> -c /opt/tomcat/bin/startup.sh

Here is the script to run Tomcat (not mine, I found it in a mailing list):

#!/bin/sh
# Tomcat Startup Script

TOMCAT_OWNER=<user who will run tomcat>; export TOMCAT_OWNER

start() {
        echo -n "Starting Tomcat: "
        su $TOMCAT_OWNER -c $CATALINA_HOME/bin/startup.sh
        sleep 2
}
stop() {
        echo -n "Stopping Tomcat: "
        su $TOMCAT_OWNER -c $CATALINA_HOME/bin/shutdown.sh
}

# See how we were called.
case "$1" in
start)
        start
        ;;
stop)
        stop
        ;;
restart)
        stop
        start
        ;;
*)
        echo $"Usage: tomcat {start|stop|restart}"
        exit
esac

Data dictionaries for FIX Protocol

1) Fiximate

Fiximate is an online FIX reference application provided by fixprotocol.org. I found Fiximate quite easy to use and there description of fix message types, fix tags and other fix protocol related stuff quite helpful. Currently Fiximate is running with version 3.0 and supports FIX.4.0, FIX.4.1, FIX.4.2, FIX.4.3, FIX.4.4, FIX.5.0 and FIX.5.0.SP1 and SP2. You can search here by fix message type, by fix tag number or by tag name. You can even use regular expression while searching. It also has section on various abbreviation used in fix protocol, fix data type and fix fields and component.

2) Fixionary

Fixionary is another fix protocol data dictionary which you can download on your machine. Fixionary is one of the oldest fix data dictionaries available and has good description of all fix protocol information including fix messages, fix tags and fix concepts. There description of fix session and admin message is also very good in order to understand fix protocol concepts.

3) Transacttools

Transact tool also provide online fix reference guide. Which you can use to refer for getting details on any fix message, fix tag etc. transactool is also a leading provider of commercial fix engines along with NYFIX whose Appia fix engine is one of the most popular commercial fix engines on industry.

4) Fixopaedia

Fixopaedia is a fix data dictionary from btobits another commercial fix engine vendor. Fixopadedia is available online and you can access it with the link provided here. This fix data dictionary supports almost all version of fix protocol include fix.4.2, fix.44, FIX 5.0 SP1 AND fix5.0sp. Fixopaedia also has nice documentation around component block, message names, message types, field name and field types. Btobits also provides some next generation fix protocol tools which helps in development and fix protocol certification.

5) Onixs fix data dictionary

This is another online fix data dictionary, my personal favorite because of nice site layout and quality information related to fix messages and tags. You can browse FIX Dictionary by FIX Protocol version, by MsgType, and by Tag number and tag Name. This fix data dictionary not only serves as online fix reference but also a good fix protocol tutorial for beginners and advanced developers.

Linux networking basics for FIX Connections

Knowledge of networking basics are extremely important if you are dealing with FIX connection , FIX stands for Financial Information Exchange protocol and its the most popular protocol for electronic trading and supported by many brokers , exchanges etc.

  I would like discuss few important network related information which is quite useful for FIX connection establishment.


VPN (Virtual Private Network)
------------------------------
VPN uses a technique known as tunneling to transfer data securely on the Internet to a remote server on your workplace network. Using a VPN helps you save money by using the public Internet instead of using costlier leased lines. VPN provides security at network layer unlike HTTPS which provide security at application layer.
most of clients and broker used VPN to connect there FIX Engines and allow trading.

before setup of VPN some contracts needs to be sorted out by both party
e.g.
1) Encryption key
2) Protocol used
3) VPN Connector IP

once your VPN connection got setup you can connect to your brokers trading system on there respective IP/Port.

DMZ (Demilitarized Zone)
--------------------------------
Its host on any network which is used to connect Corporate network to public network e.g. external exchange connection.
Firewall rules are relaxed for this zone , also if security of DMZ is compromised then also intruder won’t get access to corporate network.

Normally client connection or exchange/broker connection originates and terminates in DMZ.

.

How to use Regular Expression

One of the most powerful tools available to sysadmins/programers  are Regular Expressions, if you are good with regular expressions you can solve many day to day problem extremely quickly e.g. find all the lines with ERROR in log file , find count of any particular ID in log file , find exceptions etc.

regular expression is generic concept which has implemented on many different language and many different tools including Java, here is some of the tools and languages which use regular expression.

• The vi editor which comes standard with the Unix/Linux operating system.
• Any decent programmer's editor e.g. EditPlus,Notepad ++
• The grep command found standard on many operating systems including Unix/Linux. 
• Sed command can be found in Unix/Linux
• The Perl programming language.  
• The PHP programming language. 

Regular Even if you feel regular expression is complex and hard to learn I would suggest to familiarize with atleast basic set of regex and try to use it as much as possible and later you will only want to learn more and more to do the stuff quickly.

Here are some of the basic regex and there examples:

1) you want to find ERROR in log file in linux ?    

grep ERROR logfile

2) If you want to find lines starts with ERROR ?

grep ^ERROR logfile     (^ is used to find for startswith)

3) If you want to find lines ends with ERROR ?

grep ERROR$ logfile     ($ is used to find for endswith)

4) If you want to find empty lines in log file ?

grep ^$ logfile

5) If  you want to match upper or lower case ERROR ?

grep [Ee]RROR logfile               ([] is used to include letters]

6)If you want find all lines that contains Error or Exception ?

egrep ERROR|Exception logfile   ( | is used for OR condition)

7) Match the letter E when it appears at least 3 times in a row but possibly 4 or more times in a row: E {3,} 

8) Match the letter E when it appears 3 times in a row or 6 times in a row or anything in between. E{3,6}

9)Match E when it appears 1 or more times in a row.

E+ 

10) (E+ and E{1,} mean exactly the same thing!)

openstack installation in Linux

This is the Exmaple of building Cloud Computing infrastracture by OpenStack
Please learn simply description about OpenStack below before building.

(1) Main Components of OpenStack

Service	Code Name	Description
Identity Service	Keystone	User Management
Compute Service	Nova	Virtual Machine Management
Image Service	Glance	Manages Virtual image like kernel image or disk image
Dashboard	Horizon	Provides GUI console via Web browser
Object Storage	Swift	Provides Cloud Storage
Block Storage	Cinder	Storage Management
Network Service	Quantum	Virtual Network Management

(2) Services which the components of OpenStack needs Type Software Which needs Virtualization libvirt ( KVM, Xen ), LXC, VMware nova-compute Database MySQL or PostgreSQL, SQLite keystone, glance, nova Web Server Apache HTTP, Nginx horizon Message Service RabbitMQ, Apache Qpid nova Cache Service memcached horizon

OpenStack is easily installed using a package called Packstack. Redhat is one of the primary contributors to packstack and this method  is similar to the installation of RDO, described here
 
The procedure is quite simple:
Install Redhat, Fedora or Centos on one or more x86 servers.
I installed the minimal Centos installation on a Dell OPTIPLEX 790
Install and configure NTP - network time protocol
# yum install ntp
# chkconfig ntpd on
# ntpdate pool.ntp.org
# /etc/init.d/ntpd start
Install the Fedora repo for grizzly
# yum install -y http://rdo.fedorapeople.org/openstack/openstack-grizzly/rdo-release-grizzly-2.noarch.rpm

CIO, CTO & Developer Resources

Install packstack
# yum install -y openstack-packstack
Generate an answer file
# packstack --gen-answer-file=/root/grizzly_openstack.cfg

please find grizzly_openstack.cfg

How to Minimize Skype to System Tray

Due to the new design behavior guideline for Windows Taskbar on Windows 7, more and more software application has now making its icon to locate and stick at Windows 7 Taskbar when minimized, instead of minimizing to system tray (notification area).
The most common example in Windows Live Messenger, and now Skype 4.2 (download Skype) follows the footstep.

In Skype 4.2 or any newer versions, Skype will be minimized to Taskbar, as an icon or button, when the Skype main window is closed. In previous versions, such as Skype 4.1, 4.0 and 3.0, Skype is typically minimized to system tray, which now known as notification area, right beside the clock on Windows Taskbar when the main window is closed.
Leaving the Skype program running on Windows Taskbar is not very useful to many users, especially notifications alert will pop up informing user when there is new incoming call, instant message (IM), files, contacts, events and etc. The Taskbar icon or button is prone to mistakenly or accidentally click and activate, and the Skype window is also subjected to rotation when user jumping around tasks with Alt+Tab or Win+Tab keyboard shortcuts.
In order to make Skype minimize and hide its icon into notification area or system tray when minimized, users can use the same trick to minimize Windows Live Messenger MSN Messenger to system tray in Windows 7. Here’s how to minimize Skype to notification tray on Windows 7.
Updated Skype Built-In Method

1. In Skype, go to Tools -> Options.
2. Then, click on Advanced tab to go to Advanced settings.
3. Uncheck and untick the Keep Skype in the taskbar while I’m signed in option.
4. Click Save button, and the Skype button or icon will be removed from Taskbar on minimize.

Note: You won’t see the option if the Skype is in compatibility mode.
Compatibility Mode Method

1. Exit or quit from Skype program.
2. Right click on Skype icon on Desktop or Skype shortcut in Start Menu, and select Properties.
3. Go to Compatibility tab.
4. Under “Compatibility Mode’ section, check and tick the checkbox for Run this program in compatibility mode for: option.
5. In the below drop-down box, select Windows Vista (Service Pack 2).  
6. Click OK.
7. Start the Skype program, and now it should minimize to system tray.

Linux shortcut keys

Linux / Unix Command prompt supports huge number of shortcut keys. If you familiar with the shortcut keys you can utilizes the command prompt very faster. The more practice on the shortcut keys will give you more speed in the command prompt. Below are the shortcut keys.


To move cursor one word backword

esc  +b 
   
To move cursor one word forward

esc  +f
   
To move cursor to the starting of the line

ctrl +a 

To move cursor one letter backword

ctrl +b      
 
Terminate foreground job

ctrl +c         

To Logout of the terminal

crrl +d  

To move cursor to the end of the line

ctrl +e


To move cursor forward

ctrl +f
     
To delete one letter backward like backspace

ctrl +h 

To delete contents from where the pointer to left side end

ctrl +u


To delete contents from where the pointer to Right side end.

ctrl +k       

To delete one word from where the pointer to one word on left side

crtl +w 
   
To move cursor one letter forward

ctrl +f


To display the previously executed Command

ctrl +p     

To display the next command when ctrl +p is used

ctrl +n    

To Clear the screen

ctrl +l


To execute a command like hitting ENTER

ctrl +j       

To execute a command like hitting ENTER

ctrl +o   

To pastes text previously erased (with Ctl-U or Ctl-W)

ctrl  +Y 

Short cut key to reverse search in the command history

ctrl +r

Lvm setup

What’s LVM? Why using Linux Logical Volume Manager or LVM? Well, these questions are not the scope here. But in brief, the most attractive feature of Logical Volume Manager is to make disk management easier in Linux!

Basically, LVM allows users to dynamically extend or shrink Linux “partition” or file system in online mode! The LVM can resize volume groups (VG) online by adding new physical volumes (PV) or rejecting those existing PVs attached to VG.


^{A visualized concept diagram of the Linux Logical Volume Manager or LVM}

In this 3-minutes Linux LVM guide, let’s assume that

• The LVM is not currently configured or in used. Having say that, this is the LVM tutorial if you’re going to setup LVM from the ground up on a production Linux server with a new SATA / SCSI hard disk.
   
• Without a luxury server hardware, I tested this LVM tutorial on PC with the secondary hard disk dedicated for LVM setup. So, the Linux dev file of secondary IDE hard disk will be /dev/hdb (or /dev/sdb for SCSI hard disk).
   
• This guide is fully tested in Red Hat Enterprise Linux 4 with Logical Volume Manager 2 (LVM2) run-time environment (LVM version 2.00.31 2004-12-12, Library version 1.00.19-ioctl 2004-07-03, Driver version 4.1.0)!

How to setup Linux LVM in 3 minutes at command line?

1. Login with root user ID and try to avoid using sudo command for simplicity reason.
    
2. Using the whole secondary hard disk for LVM partition:
   fdisk /dev/hdb
   
   At the Linux fdisk command prompt,
   
   1. press n to create a new disk partition,
   2. press p to create a primary disk partition,
   3. press 1 to denote it as 1st disk partition,
   4. press ENTER twice to accept the default of 1st and last cylinder – to convert the whole secondary hard disk to a single disk partition,
   5. press t (will automatically select the only partition – partition 1) to change the default Linux partition type (0×83) to LVM partition type (0x8e),
   6. press L to list all the currently supported partition type,
   7. press 8e (as per the L listing) to change partition 1 to 8e, i.e. Linux LVM partition type,
   8. press p to display the secondary hard disk partition setup. Please take note that the first partition is denoted as /dev/hdb1 in Linux,
   9. press w to write the partition table and exit fdisk upon completion.
   
    
3. Next, this LVM command will create a LVM physical volume (PV) on a regular hard disk or partition:
   pvcreate /dev/hdb1
    
4. Now, another LVM command to create a LVM volume group (VG) called vg0 with a physical extent size (PE size) of 16MB:
   vgcreate -s 16M vg0 /dev/hdb1
   
   Be properly planning ahead of PE size before creating a volume group with vgcreate -s option!
    
5. Create a 400MB logical volume (LV) called lvol0 on volume group vg0:
   lvcreate -L 400M -n lvol0 vg0
   
   This lvcreate command will create a softlink /dev/vg0/lvol0 point to a correspondence block device file called /dev/mapper/vg0-lvol0.
    
6. The Linux LVM setup is almost done. Now is the time to format logical volume lvol0 to create a Red Hat Linux supported file system, i.e. EXT3 file system, with 1% reserved block count:
   mkfs -t ext3 -m 1 -v /dev/vg0/lvol0
    
7. Create a mount point before mounting the new EXT3 file system:
   mkdir /mnt/vfs
    
8. The last step of this LVM tutorial – mount the new EXT3 file system created on logical volume lvol0 of LVM to /mnt/vfs mount point:
   mount -t ext3 /dev/vg0/lvol0 /mnt/vfs

To confirm the LVM setup has been completed successfully, the df -h command should display these similar message:

/dev/mapper/vg0-lvol0 388M 11M 374M 3% /mnt/vfs

Some of the useful LVM commands reference:

vgdisplay vg0
 

To check or display volume group setting, such as physical size (PE Size), volume group name (VG name), maximum logical volumes (Max LV), maximum physical volume (Max PV), etc.
 

pvscan
 

To check or list all physical volumes (PV) created for volume group (VG) in the current system.
 

vgextend
 

To dynamically adding more physical volume (PV), i.e. through new hard disk or disk partition, to an existing volume group (VG) in online mode. You’ll have to manually execute vgextend after pvcreate command that create LVM physical volume (PV).

Linux file system without using partition DIRECTLY

How Can  we create a Linux file system without using partition DIRECTLY – sort of file system within file system management?

The answer is certainly YES we can do !

With a loopback device in Linux (a feature that’s not natively available in Windows Vista and its predecessors) one can easily create a Linux loopback file system on a regular disk file, and not directly using a disk partition!

How to create a Linux loopback file system with a regular disk file?
To complete this Linux tricks, you need to login with a root user ID for all the steps given below

1. Type dd if=/dev/zero of=/virtualfs bs=1024 count=30720 to create a 30MB disk file (zero-filled) called virtualfs in the root (/) directory
    
2. Type losetup /dev/loop0 to confirm that the current system is not using any loopback devices. Replace /dev/loop0 with /dev/loop1, /dev/loop2, etc, until a free Linux loopback device is found. In this case, let’s assume that /dev/loop0 is free for usage
    
3. Tpye losetup /dev/loop0 /virtualfs to attach the first Linux loopback device (/dev/loop0) with regular disk file (/virtualfs) created in step 1
    
4. Type echo $? to confirm the previous step is completed successfully without error – a zero will be returned to indicate success. Alternative, type losetup /dev/loop0 to confirm
    
5. Type mkfs -t ext3 -m 1 -v /dev/loop0 to create a Linux EXT3 file system with 1% reserved block count on the loopback device that’s currently associated with a regular disk file. Hence, we are creating a file system within file system, or creating a file system (mkfs) without using a disk partition directly
    
6. Type mkdir /mnt/vfs to create a directory (as mount point) in /mnt
    
7. Type mount -t ext3 /dev/loop0 /mnt/vfs to mount the loopback device (regular disk file) to /mnt/vfs as a “regular” Linux EXT3 file system! Now, all the Linux file system-related commands can be act on this unusual Linux file system. For example, you can type df -h to confirm its “disk usage”, type tune2fs -l /dev/loop0 to print its file system settings, create / remove files or directories, etc.
    
8. To un-mount the loopback file system, type umount /mnt/vfs follow with losetup -d /dev/loop0 to effectively remove the loopback file system and release loopback device subsequently.

How to install VNC in Linux

VNC server works similar to Telnet or SSH daemon, except that it allows VNC clients running on diverse OS platforms to remotely access Linux Desktop Manager of the server itself, rather than the TTY text-based console!

1. Locate the vnc-server-4.0-8.1.rpm package from the Red Hat Linux installation CD or download the latest free version of VNC server from Real VNC.
    
2. Install the rpm package of VNC server:
   rpm -Uvh vnc-server-4.0-8.1.rpm
    
3. VNC server is using different set of login authentication than the Linux /etc/passwd. Meaning that, you have to create VNC login password for individual Linux login accounts who are granted remote access with VNC client.
4. Run the command 'vncserver -geometry 1024x768' - if you know how to tweak this command then feel free. This command will give you a basic VNC server 
   5.) Note the number that it prints to console after you supply a password to use - example output:
   
   
   [15:23:10][Siva@Siva-pc:~]$ vncserver -geometry 1024x768

   
   

   You will require a password to access your desktops.

   
   

   Password:

   Verify:

   xauth:  creating new authority file /home/siva/.Xauthority

   xauth: (stdin):1:  bad display name "xxxxxxx:2" in "add" command

   
   

   New 'xxxxxxxxxxxxxxxxxxxxxxx:2 (Siva)' desktop is xxxxxxxxxxxxx:2

   
   

   Creating default startup script /home/siva/.vnc/xstartup

   Starting applications specified in /home/siva/.vnc/xstartup

   Log file is /home/siva/.vnc/xxxxxxxxxxxxxxx:2.log