When a new Virtual Machine, or Virtual PC, is setup in Virtualbox for Ubuntu, or another Linux flavor, the screen size and screen resolution may be fixed smaller than your maximum resolution setting. This problem can be fixed by installing Guest Additions.

Guest Additions comes with Virtualbox, but is installed after you setup your Virtual Machine, or Guest OS, to add features such as increased screen size or screen resolution. On the test PC for this example the maximum resolution is 1280 x 1024. After loading Ubuntu under Virtualbox bring up the Display Preference by going into System -> Preferences -> Display. The maximum resolution option listed is 800 x 600.

Installing Guest Additions from Gnome Desktop

To get a bigger screen resolution we will need to install Guest Additions. On the Virtualbox File Menu click on Devices -> Install Guest Additions.

You should now see a vboxadditions_x file now located on your Ubuntu desktop.

To open the vboxadditions file either double click on the file, or right-click and then click Open.

Now double click the autorun.sh file. The vboxadditions file contains installation choices for a few different Linux versions including both 32 bit and 64 bit versions. By using the autorun.sh file you allow the script to automatically detect, and install the right software for your OS.

Now click Run.

The autorun.sh will open a Shell window and begin installing the files.

Once the autorun.sh file has completed installing the Guest Additions software all you have to do is hit Enter to close the Window.

Now reboot Ubuntu for the new files to load properly.

After you return to the Ubuntu desktop click System -> Preferences -> Display.

Under Display Preferences you will see the resolution is at 1152 x 864, which is still not the maximum resolution.

On the Virtualbox File Menu click on Machine -> Fullscreen Mode.

Once in Fullscreen Mode go to System -> Preferences -> Display again, and you will now see the maximum screen resolution is 1280 x 1024.

Installing Guest Additions from the Command Line Terminal Window

To install Guest Addtions from the Terminal window Command Line in Ubuntu click Applications -> Accessories -> Terminal.

At the Bash prompt ($) type:

cd /media/cdrom0

Hit Enter.

Now type:

dir

Hit Enter. This will give you a listing of all the files in the vboxadditions file directory. We want to run the autorun.sh so that script can install the right files for us.

Type:

sudo sh autorun.sh

Hit Enter.

The autorun.sh file should automatically change the proper permissions to run and install the vboxadditions file that will work on your OS.

The autorun.sh will open a Shell window and begin installing the files. Once the autorun.sh file has completed installing the Guest Additions software all you have to do is hit Enter to close the Window.

© Copyright NerdGrind 2009. All Rights Reserved.

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Whether you’re trying to destroy or erase data from your hard drives when the FBI knocks on your door, or just want to securely, and permanently do emergency data destruction to protect yourself from identity theft, before you sell or recycle your computer, there’s an easy solution.

The free open-source boot disk utility, called Darik’s Boot and Nuke (DBAN), automatically and completely deletes the content of every hard disk it can find on, or connected to, your computer when you run it.

The bootable DBAN can run from CDs, DVDs, thumb drives, and floppy disks.

The process is easy:

How to automatically wipe all hard drives

WARNING: THIS WILL PERMANENTLY ERASE ALL DATA ON ALL HARD DRIVE HOOKED TO THE PC!!!

1. Boot from the DBAN floppy or CD image.
2. Enter ‘autonuke’ at the boot prompt.

Darik’s Boot and Nuke website is here.

Click here to download the exe to write the image to a floppy disk.

Click here if you don’t have a floppy disk, and would like to create a DBAN CD image instead.

Keep the disk in a safe place. If it falls into the wrong hands your system could be toast, or just a big toaster.

© Copyright NerdGrind 2009. All Rights Reserved.

Related posts:

• Share Files and Folders and Printers Over a Network
• Clone or Copy My Hard Drive with Norton Ghost
• Share a Printer Files and Folders Over a Wired or Wireless Network Through a Firewall
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This step-by-step tutorial shows how to set up Network Address Translation (NAT) with Open Source Linux operating system and iptables firewall. This will allow your system to act as gateway and to provide Internet access to multiple hosts in Local Area Network (LAN) using a single public IP address.

Requirements

1. Hardware server with 2 (two) network interface cards (NICs).
2. Any Linux distribution (get more information at DistroWatch.com).
3. Linux kernel with networking and iptables support.
4. iptables package (you can find latest release at NetFilter’s Download page).

Basic definitions

aa.aa.aa.aa is Wide Area Network (WAN) IP address (bb.bb.bb.bb is WAN netmask).
cc.cc.cc.cc is LAN IP address (e.g. 192.168.0.1 or 10.0.0.1), dd.dd.dd.dd is LAN netmask (e.g. 255.255.255.0).
ee.ee.ee.ee is default gateway for Internet connection.

eth0 is hardware name of the NIC connected to WAN base.
eth1 is name of LAN connected NIC.

Step-by-step set up

1. Apply two NICs to hardware server.
2. Verify that both NICs are recognized by Linux well and are fully workable:

dmesg | grep eth0
dmesg | grep eth1

the output may vary but in most cases it would be like following one:

eth1: RealTek RTL8139 at 0xe0830000, 00:30:4f:3b:af:45, IRQ 19
eth1:  Identified 8139 chip type ’RTL-8100B/8139D’
eth0: link up, 100Mbps, full-duplex, lpa 0x41E1

Similar output should be for eth0 NIC.

To verify that NICs are recognized by Linux as networking devices use the following commands:

ifconfig eth0
ifconfig eth1

In case of success the output will be as follows:

eth0      Link encap:Ethernet  HWaddr 00:50:56:C0:00:08
          inet6 addr: fe80::250:56ff:fec0:8/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:41 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)

You can find full manual page for ifconfig command here.

3. Configure WAN interface (eth0) to get Internet connection:

ifconfig eth0 aa.aa.aa.aa netmask bb.bb.bb.bb

e.g.

ifconfig eth0 123.45.67.89 netmask 255.255.255.248

WAN IP address and netmask should be provided by your ISP.

4. Set up WAN NIC settings to apply after server start up.

Configuration files containing NIC settings may have different syntax and location in various distributions. For such distributions as RedHat, Fedora, Centos and similar ones eth0 configuration file is at /etc/sysconfig/network-scripts/ifcfg-eth0. In Debian, Ubuntu NIC settings are located at single file /etc/network/interfaces.

To edit configuration files use any preferred text editor like vim, GNU nano or any other.

After editing /etc/sysconfig/network-scripts/ifcfg-eth0 should look as follows:

DEVICE=eth0
ONBOOT=yes
BOOTPROTO=static
IPADDR=aa.aa.aa.aa        # e.g. 123.45.67.89
NETMASK=bb.bb.bb.bb       # e.g. 255.255.255.0
GATEWAY=ee.ee.ee.ee       # e.g. 123.45.67.1
HWADDR=00:30:4f:3b:af:45  # MAC address (optional entry)

After making changes to /etc/network/interfaces section regarding eth0 NIC should looks like:

auto eth0
iface eth0 inet static
address aa.aa.aa.aa
netmask bb.bb.bb.bb
gateway ee.ee.ee.ee

Related links: detailed syntax description of /etc/sysconfig/network-scripts/ifcfg-ethN, manual page of /etc/network/interfaces.

5. Set up LAN NIC settings to apply after server start up. This step requires operations similar to previous step.

Edit /etc/sysconfig/network-scripts/ifcfg-eth1 and make sure that it looks like:

DEVICE=eth1
ONBOOT=yes
BOOTPROTO=static
IPADDR=cc.cc.cc.cc       # e.g. 192.168.0.1
NETMASK=dd.dd.dd.dd      # e.g. 255.255.255.0
HWADDR=00:50:8d:d1:24:db # MAC address of LAN NIC (optional entry)

If you are using Debian or related Linux distribution, edit /etc/network/interfaces (see previous step):

auto eth1
iface eth1 inet static
address cc.cc.cc.cc
netmask dd.dd.dd.dd

6. Set up Domain Name System servers IP addresses by editing /etc/resolv.conf:

nameserver 203.145.184.13
nameserver 203.145.184.12

7. Enable IP Forwarding:

echo 1 > /proc/sys/net/ipv4/ip_forward

8. Set up NAT with iptables:

To delete existing rules from every iptables table, execute the following commands:

iptables -F
iptables -t nat -F
iptables -t mangle -F

Related links: official iptables documentation.

Enable NAT by commands:

iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
iptables -A FORWARD -i eth1 -j ACCEPT

8. Configure LAN clients to access Internet via described gateway:

Use clients’ operating system tools to set up the following TCP/IP settings:

IP address: from the same network as cc.cc.cc.cc (you can use IP/Subnet calculator to get it)
Netmask: dd.dd.dd.dd
DNS: ff.ff.ff.ff
Gateway: cc.cc.cc.cc

Example:

IP address: 192.168.0.7
Netmask: 255.255.255.0
DNS: 209.160.67.13
Gateway: 192.168.0.1

Setting all this up can be a lot easier if you’re using a control panel rather than the command line, but I’ll save that for another article.

© Copyright NerdGrind 2009. All Rights Reserved.

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The variety of options for home networking can make buying decisions difficult. Before you decide what hardware to get, you should decide what type of network technology (the way computers in a network connect to or communicate with one another) to use. This article describes and compares the most common network technologies and lists hardware requirements for each.

Note: This information could be applied to almost any operating system.

Network technologies

The most common types of network technology are wireless, Ethernet, and HPNA (home phone line). When choosing a network technology, consider the location of your computers, desired speed of your network, and how much you want to spend. The sections below compare these three technologies.

Wireless

Wireless networks use radio waves to send information between computers. The three most common wireless network standards are 802.11b, 802.11g, and 802.11a.

Speed

• 802.11b: transfers data at a maximum rate of 11 megabits per second (Mbps)
• 802.11g: transfers data at a maximum rate of 54 Mbps
• 802.11a: transfers data at a maximum rate of 54 Mbps

(For example, downloading a 10 megabyte [MB] photo from the Internet under optimal conditions takes about 7 seconds on an 802.11b network and about 1.5 seconds on an 802.11g or 802.11a network.)

Cost

Wireless network adapters and routers can cost three or four times as much as Ethernet cable adapters and hubs or switches. 802.11b products are the least expensive; 802.11a products are the most expensive. 802.11g products are priced in the middle and offer a greater signal range than 802.11b and 802.11a products.

Pros

• It’s easy to move computers around because there are no cables.
• Wireless networks are usually easier to install than Ethernet.

Cons

• Wireless is more expensive and often slower than Ethernet or HPNA.
• Wireless can be affected by interference from things such as walls, large metal objects, and pipes. Also, many cordless phones and microwave ovens can interfere with wireless networks when they’re in use.
• Wireless networks are typically about half as fast as their rated speed under all but ideal conditions.

Ethernet

Ethernet networks use Ethernet cables to send information between computers.

Speed

Ethernet transfers data at either 10, 100, or 1000 Mbps, depending on the type of cables used. Gigabit Ethernet is the fastest, with a transfer rate of 1 gigabit per second (or 1000 Mbps).

(For example, downloading a 10 megabyte [MB] photo from the Internet under optimal conditions takes about 8 seconds on a 10 Mbps network, about 1 second on a 100 Mbps network, and less than a second on a 1000 Mbps network.)

Cost

Ethernet cables, hubs, and switches are very inexpensive and many computers come with Ethernet adapters installed. Adding a hub, switch, or router to your network will be most of the cost.

Pros

• Ethernet is a proven and reliable technology.
• Ethernet networks are inexpensive and fast.

Cons

• Ethernet cables must be run between each computer and to a hub, switch, or router, which can be time-consuming and difficult when the computers are in different rooms.
• Gigabit Ethernet is expensive.

HPNA

HPNA networks use existing home telephone wires to send information between computers.

Speed

HPNA 2.0 transfers data at 10 Mbps. HPNA 3.0 transfers data at 128 Mbps.

(For example, downloading a 10 megabyte [MB] photo from the Internet under optimal conditions takes about 8 seconds on an HPNA 2.0 network and about 1 second on an HPNA 3.0 network.)

Cost

HPNA adapters cost a little more than Ethernet adapters but are usually less expensive than wireless adapters.

Pros

• HPNA uses the existing telephone wiring in your home.
• You don’t need hubs or switches to connect more than two computers in an HPNA network.

Cons

• You need a phone jack in each room where you want to have a computer, and all jacks must be on the same phone line.

Hardware requirements

There are several kinds of hardware used in home networks.

• Network adapters: These adapters (also called network interface cards, or NICs) connect computers to a network so that they can communicate. A network adapter can be connected to the USB port on your computer or installed inside your computer in an available Peripheral Component Interconnect (PCI) expansion slot.

Wireless, Ethernet, and HPNA network adapters

• Network hubs and switches: Hubs and switches connect two or more computers to an Ethernet network. A switch costs a little more than a hub, but it speeds up the transfer rate of information.

Ethernet hub

• Routers and access points: Routers connect computers and networks to each other (for example, a router can connect your home network to the Internet). Routers also enable you to share a single Internet connection among several computers. Routers can be wired or wireless. You don’t need to use a router for a wired network but we recommend it if you want to share an Internet connection. Access points turn wired Ethernet networks into wireless networks. If you want to share an Internet connection over a wireless network, you will need a wireless router or an access point.

Access point (left); wired router (center); wireless router (right)

• Modems: Computers use modems to send and receive information over telephone or cable lines. You will need a modem if you want to connect to the Internet.

Cable modem

• Network cables (Ethernet and HPNA only): Network cables connect computers to each other and to other related hardware, such as hubs and routers.

Ethernet and HPNA cables

The table below shows the hardware that you need for each type of network technology.

It’s a good idea to find out what kind of network adapters your computers have, if any. You might decide to go with a certain technology because you already have most of the hardware, or you might decide to upgrade your hardware. Most people find that a combination of technologies works best for their environment. For recommended layouts and information about assembling your network, see Setting Up a Home Network.

© Copyright NerdGrind 2009. All Rights Reserved.

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• Clone or Copy My Hard Drive with Norton Ghost
• Share a Printer Files and Folders Over a Wired or Wireless Network Through a Firewall
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• How to Enable Administrative Tools

Many web site owners have a hosting or co-location plan that limits the amount of bandwidth their web site can use each month. With the proliferation of user spaces on sites such as MySpace, Facebook, etc, people using those services, as well as other web site owners, copy the code for an image from your web site, and put it into a page on their site. This means that each time that person’s page loads for a reader, the image comes from your server, and uses your bandwidth to serve it. This practice is called hotlinking. The bandwidth you purchase can get chewed up in a hurry if too many people do this to you. Fortunately there is a solution.

This tutorial applies to Apache web server only.

There are two ways to block hotlinking. First by using the httpd.conf file, and second by using the .htaccess file.

Option 1:

Using the main httpd.conf file for Apache uses fewer resources, and will be applied to all web sites on the server, so we’ll start there. Using a bash shell type:

vi /etc/httpd/conf/httpd.conf

First be sure your httpd.conf contains the following line with no # sign in front of it. The line should look like the one below:

LoadModule setenvif_module modules/mod_setenvif.so

Rather than using your arrow key you can page down in vi, you can use ctrl + d to reach the end of the httpd.conf file. At the end of your config file you’ll need to add the following code.

<VirtualHost *:80>
SetEnvIfNoCase Referer "mydomain’.com" local_ref=1
<FilesMatch "’.(gif|jpg|jpeg|png|swf|mpg|avi|flv)">
Order Allow,Deny
Allow from env=local_ref
</FilesMatch>
</VirtualHost>

The new VirtualHost container should look something like this:

<VirtualHost *:80>
ServerName www.mydomain.com
ServerAlias mydomain.com
DocumentRoot /var/www/mysitedirectory
ServerPath /mysitedirectory
SetEnvIfNoCase Referer "mydomain’.com" local_ref=1
<FilesMatch "’.(gif|jpg|jpeg|png|swf|mpg|avi|flv)">
Order Allow,Deny
Allow from env=local_ref
</FilesMatch>
</VirtualHost>

You can add as many different file types to the list as you want. Just be sure each file is separated by a pipe |. To close and save the changes made by vi type:

:wq

and hit enter.

Suppose you wanted to add more trusted domains besides your own. You could add:

SetEnvIfNoCase Referer "trusted-domain’.com" trusted=yes
SetEnvIfNoCase Referer "another-trusted-domain’.com" trusted=yes
Allow from env=trusted

Your new code would then would include your own domain, and other trusted domains. The new code would look like the following below:

<VirtualHost *:80>
SetEnvIfNoCase Referer "mydomain’.com" local_ref=1
SetEnvIfNoCase Referer "trusted-domain’.com" trusted=yes
SetEnvIfNoCase Referer "another-trusted-domain’.com" trusted=yes
<FilesMatch "’.(gif|jpg|jpeg|png|swf|mpg|avi|flv)">
Order Allow,Deny
Allow from env=local_ref
Allow from env=trusted
</FilesMatch>
</VirtualHost>

Option 2:

The less efficient, but possibly more useful option is to use the use the .htaccess file. For Wordpress users you can access the .htaccess file from your administrative control panel by going to manage –> files –> .htaccess (for rewrite rules ). For others type the following into a bash shell:

vi /var/www/mysitedirectory/.htaccess

Add the following code:

<IfModule mod_rewrite.c>
RewriteEngine On
# Hotlink Protection with Feedburner Access Start
RewriteCond %{REQUEST_FILENAME} ’.(gif|jpg|jpeg|png|swf|mpg|avi|flv|mp3)$ [NC]
# Next line allows a blank or empty referrer to see images
# this includes people simply pasting the url to the image and going to it
# this line is necessary for some with firewalls, ISP firewalls, even AOL
# norton and mcafee personal firewall remove REFERER header
RewriteCond %{HTTP_REFERER} !^$ [NC]
RewriteCond %{HTTP_REFERER} !mydomain’.com [NC]
# The line below is a way to allow all of feedburner.com
# RewriteCond %{HTTP_REFERER} !feedburner’. [NC]
# It is better to only specify your direct feed
RewriteCond %{HTTP_REFERER} !^http://feeds.feedburner.com/mywebsite$ [NC]
RewriteCond %{HTTP_REFERER} !google’. [NC]
## RewriteCond %{HTTP_REFERER} !bloglines’. [NC]
RewriteRule ^(.*)$ http://www.mydomain.com/ [R=301,L]
</IfModule> # If this line is already present, as in Wordpress, then do NOT add
# Hotlink Protection with Feedburner Access End

To close and save the changes made by vi type:

:wq

and hit enter.

Whenever you see a # in, or at the start of, a line, anything after the # will not be read by Apache. Using # is referred to as commenting out the line or text. You can use more than one # to comment out a line. Wordpress already has </IfModule> at the end of the .htaccess file, so adding and extra </IfModule> could cause a problem.

If you make an error, and you get a 500 error instead of seeing your site type the following into your bash shell:

vi /var/www/mysitedirectory/.htaccess

Now type

dd

To erase each line of code you added. Remember to type :wq to close and save your work. Always make a backup of the .htaccess file before you start.

An easier way to access these files on a dedicated server is using an administrative control panel, which I will discuss in a later article.

Be sure to save your .htaccess file after make changes. Some plugins for Wordpress, as an example, can overwrite your .htaccess file. After making changes with a plugin, etc., it’s good practice to check and make sure your .htaccess file has not changed.

Some people serve another image that says NO HOTLINKING, but that is still using bandwidth, so my configuration serves nothing. On the thief’s end, readers will see a read X in Internet Explorer, but no image.

One last note, you cannot use option 1 and 2 together. You have to choose and use only option 1, or only option 2. Apache may not give you an error in the log, but it could drag down Apache’s performance with an incorrect configuration.

© Copyright NerdGrind 2009. All Rights Reserved.

Related posts:

• How to Increase Screen Size or Resolution in Virtualbox for Ubuntu or Linux
• Samsung Unveils Flexible OLED Concept Phone – Video
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