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.

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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.

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.

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.

Technology	Hardware	How Many
Ethernet	Ethernet network adapter	One for each computer on your network
	Ethernet hub or switch (only needed if you want to connect more than two computers)	One (a 10/100 hub or switch is best and should have enough ports to accommodate all computers on your network)
	Ethernet router (only needed if you want to connect more than two computers and share an Internet connection)	One (you don’t need a hub or switch if you have a router because it has ports on it for your computers)
	Ethernet cables	One for each computer connected to the network hub or switch (10/100 Cat 5e cables are best)
	Crossover cable (only needed if you want to connect two computers directly to each other and not use a hub, switch, or router)	One
HPNA	Home phoneline network adapter (HPNA)	One for each computer on your network (USB-to-phoneline network adapters are best)
	Telephone cables	One for each computer on your network (use a standard telephone cable to plug each computer into a phone jack)
Wireless	Wireless network adapter	One for each computer on your network
	Wireless access point or router (recommended)	One

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.

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.

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