Thursday, June 17, 2010

Resetting the original administrator account password

Follow these steps to reset a password when there is only one administrator account on the computer, or if the original administrator account needs a password reset. "Original" administrator account refers to the one that was created immediately after installing Mac OS X. If the original administrator password is known, that administrator account may be used to reset the passwords of other administrator accounts using the steps described above. These steps require an optical drive; if your Mac does not have an optical drive and you have a Mac OS X v10.6 Install disc, see below.
  1. Start up from a Mac OS X Install disc (one whose version is closest to the version of Mac OS X installed).  Usually, you can start from the disc by putting it in your computer, restarting, and holding the C key. Or, put it in the computer and click the Install or Restore icon you see in the disc's main window (after which the computer will start from the disc without you needing to hold C). Or, you can use Startup Manager or the Startup Disk preference pane to select the Install disc.
     
  2. Choose a language, click the arrow button to continue,
  3. Mac OS X v10.6 or later: Choose Password Reset from the Utilities menu.
    Mac OS X v10.5 or v10.4: Choose Reset Password from the Utilities menu.
    Mac OS X v10.3: Choose Reset Password from the Installer menu.

    Tip: If you don't see this menu or menu choice, you're probably not started from the disc yet.

    Note
    : The default keyboard layout is U.S. English while started from the installation disc. If you use a keyboard layout other than U.S English, use the Input menu (the flag icon on the right side of the menu bar) to select the desired layout before typing a new password.
     
  4. Select your Mac OS X hard disk volume.
  5. Select the user name of your original administrator account.

    Important: Do not select "System Administrator (root)". This is actually the root user. You should not confuse it with a normal administrator account.

  6. Enter a new password.
  7. Click Save.
  8. Click the red button in the upper left corner to quit the application.
  9. Choose Quit Mac OS X Installer... from the Mac OS X Installer menu.
  10. Click Restart.

How do KVM switches work?

    1. What is the difference between a mechanical KVM switch and an electronic KVM switch?There are two main types of KVM switches, mechanical and electronic. Mechanical switches use no electronics or intelligent circuitry. You must physically turn a rotary switch to the channel through which you want to pass information. These switches cannot communicate with the computers at the end of each closed channel or interpret the information that passes through the switch. For example, to turn on the computers attached to the KVM switch, you must manually turn the rotary switch to each computer port individually. While the rotary switch is at a particular computer port, you can turn that computer on. You must wait for it to boot before going to the next computer. NTI does offer a selection of mechanical switches for customers who prefer this low-cost option. Electronics switches operate on the same principle as mechanical switches, but can communicate with the user and maintain continuous contact with all the attached computers. NTI's advanced KVM electronic switches will fully emulate the mouse and keyboard connections for each computer, even when that computer is not selected. They do this by dedicating a microprocessor to each computer attached to the KVM console. This ensures that all attached computers can boot and maintain connections. As a result, switching is seamless and you can even reboot servers through the switch. 2. How are Electronic KVM switches controlled?NTI KVM switches can be controlled from the front panel buttons or by using "hot keys." Some models are also offered with optional On Screen Display (OSD), Liquid Crystal Display (LCD), Wired Remote Control, and RS232 control options. For information on which options are available for specific models, click on the Options icon at the bottom of the appropriate product description page on this website, or contact Customer Service at 800-742-8324. Click on the Options link for further Options FAQs. 3. How do the hot keys work?Enter the command mode by hitting CNTL` (Control Key + tick mark located on same key as tilde~) and set your options. To exit you hit the Escape key.

How to Hide Files Inside JPEG/GIF/PNG Images

Author: Himanshu

We discussed various methods for hiding files inside your computer. Methods include super secure Truecrypt which offers military level security and handy MyLockbox to lock any folder. But all these methods require installation of software on your PC which is obviously visible to others.
We are now going to talk about a unique method of hiding files that’s kinda sneaky and doesn’t require a third-party tool. This technique involves hiding  files inside JPEG, GIF or PNG images. Sounds cool, right? Lets see how it is done.
1. Create a folder in C drive. Give it a name, lets say Testfile. It’s location should be C:\Testfile.
2. Now move all the files you want to hide inside this folder. Also move the image file in which you want to hide those files. Let’s say the files which I want to hide are FileA.txt and FileB.txt, and the image file is Image.jpg. We are taking .txt files as an example. You can take files of any format (.mp3, .doc, .divx, .flv etc.) and any number of files.
hide file inside image
3. Select both the files you want to hide (FileA.txt and FileB.txt in this case), right click and select “Add to Archive”. Make sure that you’ve got a file compression tool like WinZip or ZipGenius installed.
testfile image
4. Give it a name. I have given Compressed.rar. You can give it any name.
compressed files
5. Click on “Start” button. Type cmd in the search box. Press Enter.
cmd
6. A command prompt window will open.
command-prompt
7. Type cd \ and press Enter to get to the root directory.
command-prompt1
8. Now type cd Testfile to enter in the newly created directory.
command-prompt2
9. Type copy /b Image.png + Compressed.rar Secretimage.png and press Enter.
command-prompt3
10. When you look up at Testfile folder, you will find a new image file called SecretImage.png. This image file is created in previous step with the help of command. Secretimage is just a name given to the new image. You could give any name and extension (like xyz.jpg or xyz.png).
Both the files FileA.txt and FileB.txt are hidden inside this image file. You can delete rest of the files now.
image-file

How to get our Files back from the image

That’s easy too. Just right click on the image (SecretImage.png) and open it with Winrar/Winzip/ZipGenius. You will see both the hidden files. Extract them anywhere on your computer.
Update: From comments I came to know that few users are facing problem while opening image file in Winrar application. They can change the file extension of secret image file in which all the other files are hidden from .jpg to .RAR. (In the above case SecretImage.png to Secretimage.RAR) and then open it with the help of Winrar.

Wednesday, June 16, 2010

Wi-Fi Working Concepts

here are three most important items which makes Wi-Fi working in your laptop or desktop. These are:
  • Radio Signals
  • Wi-Fi Card which fits in your laptop or computer.
  • Hotspots which create Wi-Fi Network.


    Radio Signals:

    Radio Signals are the keys which make WiFi networking possible. These radio signals transmitted from Wi-Fi antennas are picked up by WiFi receivers such as computers and cell phones that are equipped with WiFi cards. Whenever a computer receives any of the signals within the range of a WiFi network which is usually 300 - 500 feet for antennas, the WiFi card will read the signals and thus create an internet connection between the user and the network without the use of a cord.
    Access points which consist of antennas and routers are the main source which transmit and receive radio waves.
    Antennas work stronger and have a longer radio transmission with a radius of 300-500 feet which are used in public areas while the weaker yet effective router is more suitable for homes with a radio transmission of 100-150 feet.

    Wi-Fi Cards:

    You can think WiFi card as being an invisible cord that connects your computer to the antenna for a direct connection to the internet.
    WiFi cards can be external or internal, meaning that if a WiFi card is not installed in your computer, you may purchase a USB antenna attachment and have it externally connect to your USB port, or have an antenna-equipped expansion card installed directly to the computer. For laptops, this card will be a PCMCIA card in which you insert to the PCMCIA slot on the laptop.

    Wi-Fi Hotspots:

    A Wi-Fi hotspot is created by installing an access point to an internet connection. The access point transmits a wireless signal over a short distance . typically covering around 300 feet. When a Wi-Fi .enabled device, such as a Pocket PC, encounters a hotspot, the device can then connect to that network wirelessly.
    Most hotspots are located in places that are readily accessible to the public, like airports, coffee shops, hotels, book stores and campus environments. 802.11b is the most common specification for hotspots worldwide. The 802.11g standard is backwards compatible with .11b but .11a uses a different frequency range and requires separate hardware such as an a, a/g, or a/b/g adapter. The largest public Wi-Fi networks are provided by private internet service providers (ISPs) that charge a fee for users to connect to the internet.
    Hotspots are increasingly developing around the world. In fact, T-mobile USA controls more than 4,100 hotspots located in public locations such as Starbucks, Borders, Kinko.s, and the airline clubs of Delta, United, and US Airways. Even select McDonald.s restaurants now feature Wi-Fi hotspot access.
    Any notebook computer with integrated wireless, a wireless adapter attached to the motherboard by the manufacturer, or a wireless adapter such as a PCMCIA card can access a wireless network. Furthermore, all Pocket PCs or Palm units with Compact Flash, SD I/O support, or built-in Wi-Fi, can access hotspots.
    Some Hotspots require WEP key to connect that is the connection is considered to be private or secure. As for open connections, anyone with a WiFi card can gain access to that hotspot. So in order for a user to gain access to the internet under WEP, the user must input the WEP key code.

Working Principle of Bluetooth Technology

Bluetooth was the brainchild of the SIG (Special Interest Group). This SIG included Intel, Toshiba, Nokia, IBM, Compaq, Dell, Motorola, HP, Lucent, and Samsung to name a few. They all came together to set up a short frequency wireless technology for transferring data.
Bluetooth is a communication protocol. It is a like a language that devices use to wirelessly communicate between each other. It is in fact based on a Master/Slave operation format. Pico net is a term used to describe a network formed by one device and all other devices detected in its range. In single coverage are around 10 Pico nets can co-exist. A master can connect to more than one slave simultaneously. In reality, the master keeps switching between slaves. Bluetooth links two Pico nets to form a larger network. This works over a short range and can be used to establish connections between PDAs, mobile phones, laptops, digital cameras, printers, scanner, and many other electronic gadgets.
Establishing a connection using Bluetooth is a complicated process. Initially, the device stays in a "Passive state", i.e. it is just in contact with the network, but not performing any activity. Next the connection establishment process begins with the inquiry process. "Inquiry" is a request sent by the master to all the devices found in its range. Whichever devices receive this inquiry send a response with their respective addresses. Now the master chooses one address and synchronises with its access point. This process known as the "Paging technique" involves alignment of its clock and frequency with that of the access point.
Next in line is the "Service Discovery" phase, wherein a link is established and the master device enters the access point using the Service Discovery Protocol. As a result of linking, a "Communication Channel" is to be created. Sometimes the access point may include a security mechanism and you may need to know the encryption key or in common terms the PIN. Once the PIN is sent and received and confirmed a communication is established. Finally the master and slave can use the communication channel to transfer data and information.
Thus Bluetooth is neither a broadband nor a long distance networking technique. It is a Personal Area Networking technology that can be used in a number of important applications. First of all, Bluetooth technology uses the same frequency range as the Wi-Fi system. It only requires a careful coordination of the various frequencies with the perfect transmit and receive timings between various devices. Finally, the enhanced version of Bluetooth is expected to use Ultra-Wide Band frequencies that contributes increased data rate and improved signal strength.

Saturday, June 12, 2010

How VoIP Works

If you've never heard of VoIP, get ready to change the way you think about long-distance phone calls. VoIP, or Voice over Internet Protocol, is a method for taking analog audio signals, like the kind you hear when you talk on the phone, and turning them into digital data that can be transmitted over the Internet.
How is this useful? VoIP can turn a standard Internet connection into a way to place free phone calls. The practical upshot of this is that by using some of the free VoIP software that is available to make Internet phone calls, you're bypassing the phone company (and its charges) entirely.

VoIP is a revolutionary technology that has the potential to completely rework the world's phone systems. VoIP providers like Vonage have already been around for a while and are growing steadily. Major carriers like AT&T are already setting up VoIP calling plans in several markets around the United States, and the FCC is looking seriously at the potential ramifications of VoIP service.
Above all else, VoIP is basically a clever "reinvention of the wheel." In this article, we'll explore the principles behind VoIP, its applications and the potential of this emerging technology, which will more than likely one day replace the traditional phone system entirely.
The interesting thing about VoIP is that there is not just one way to place a call. There are three different "flavors" of VoIP service in common use today:
  • ATA -- The simplest and most common way is through the use of a device called an ATA (analog telephone adaptor). The ATA allows you to connect a standard phone to your computer or your Internet connection for use with VoIP. The ATA is an analog-to-digital converter. It takes the analog signal from your traditional phone and converts it into digital data for transmission over the Internet. Providers like Vonage and AT&T CallVantage are bundling ATAs free with their service. You simply crack the ATA out of the box, plug the cable from your phone that would normally go in the wall socket into the ATA, and you're ready to make VoIP calls. Some ATAs may ship with additional software that is loaded onto the host computer to configure it; but in any case, it's a very straightforward setup.
  • IP Phones -- These specialized phones look just like normal phones with a handset, cradle and buttons. But instead of having the standard RJ-11 phone connectors, IP phones have an RJ-45 Ethernet connector. IP phones connect directly to your router and have all the hardware and software necessary right onboard to handle the IP call. Wi-Fi phones allow subscribing callers to make VoIP calls from any Wi-Fi hot spot.
  • Computer-to-computer -- This is certainly the easiest way to use VoIP. You don't even have to pay for long-distance calls. There are several companies offering free or very low-cost software that you can use for this type of VoIP. All you need is the software, a microphone, speakers, a sound card and an Internet connection, preferably a fast one like you would get through a cable or DSL modem. Except for your normal monthly ISP fee, there is usually no charge for computer-to-computer calls, no matter the distance.
If you're interested in trying VoIP, then you should check out some of the free VoIP software available on the Internet. You should be able to download and set it up in about three to five minutes. Get a friend to download the software, too, and you can start tinkering with VoIP to get a feel for how it works.

Using VoIP

Chances are good you're already making VoIP calls any time you place a long-distance call. Phone companies use VoIP to streamline their networks. By routing thousands of phone calls through a circuit switch and into an IP gateway, they can seriously reduce the bandwidth they're using for the long haul. Once the call is received by a gateway on the other side of the call, it's decompressed, reassembled and routed to a local circuit switch.
Although it will take some time, you can be sure that eventually all of the current circuit-switched networks will be replaced with packet-switching technology (more on packet switching and circuit switching later). IP telephony just makes sense, in terms of both economics and infrastructure requirements. More and more businesses are installing VoIP systems, and the technology will continue to grow in popularity as it makes its way into our homes. Perhaps the biggest draws to VoIP for the home users that are making the switch are price and flexibility.
With VoIP, you can make a call from anywhere you have broadband connectivity. Since the IP phones or ATAs broadcast their info over the Internet, they can be administered by the provider anywhere there's a connection. So business travelers can take their phones or ATAs with them on trips and always have access to their home phone. Another alternative is the softphone. A softphone is client software that loads the VoIP service onto your desktop or laptop. The Vonage softphone has an interface on your screen that looks like a traditional telephone. As long as you have a headset/microphone, you can place calls from your laptop anywhere in the broadband-connected world.
Most VoIP companies are offering minute-rate plans structured like cell phone bills for as little as $30 per month. On the higher end, some offer unlimited plans for $79. With the elimination of unregulated charges and the suite of free features that are included with these plans, it can be quite a savings.
Most VoIP companies provide the features that normal phone companies charge extra for when they are added to your service plan. VoIP includes:
  • Caller ID
  • Call waiting
  • Call transfer
  • Repeat dial
  • Return call
  • Three-way calling
There are also advanced call-filtering options available from some carriers. These features use caller ID information to allow you make a choice about how calls from a particular number are handled. You can:
  • Forward the call to a particular number
  • Send the call directly to voice mail
  • Give the caller a busy signal
  • Play a "not-in-service" message
  • Send the caller to a funny rejection hotline
With many VoIP services, you can also check voice mail via the Web or attach messages to an e-mail that is sent to your computer or handheld. Not all VoIP services offer all of the features above. Prices and services vary, so if you're interested, it's best to do a little shopping.
Now that we've looked at VoIP in a general sense, let's look more closely at the components that make the system work. To understand how VoIP really works and why it's an improvement over the traditional phone system, it helps to first understand how a traditional phone system works.

VoIP: Circuit Switching

Existing phone systems are driven by a very reliable but somewhat inefficient method for connecting calls called circuit switching.
Circuit switching is a very basic concept that has been used by telephone networks for more than 100 years. When a call is made between two parties, the connection is maintained for the duration of the call. Because you're connecting two points in both directions, the connection is called a circuit. This is the foundation of the Public Switched Telephone Network (PSTN).
Here's how a typical telephone call works:
  1. You pick up the receiver and listen for a dial tone. This lets you know that you have a connection to the local office of your telephone carrier.
  2. You dial the number of the party you wish to talk to.
  3. The call is routed through the switch at your local carrier to the party you are calling.
  4. A connection is made between your telephone and the other party's line using several interconnected switches along the way.
  5. The phone at the other end rings, and someone answers the call.
  6. The connection opens the circuit.
  7. You talk for a period of time and then hang up the receiver.
  8. When you hang up, the circuit is closed, freeing your line and all the lines in between.
Let's say you talk for 10 minutes. During this time, the circuit is continuously open between the two phones. In the early phone system, up until 1960 or so, every call had to have a dedicated wire stretching from one end of the call to the other for the duration of the call. So if you were in New York and you wanted to call Los Angeles, the switches between New York and Los Angeles would connect pieces of copper wire all the way across the United States. You would use all those pieces of wire just for your call for the full 10 minutes. You paid a lot for the call, because you actually owned a 3,000-mile-long copper wire for 10 minutes.
Telephone conversations over today's traditional phone network are somewhat more efficient and they cost a lot less. Your voice is digitized, and your voice along with thousands of others can be combined onto a single fiber optic cable for much of the journey (there's still a dedicated piece of copper wire going into your house, though). These calls are transmitted at a fixed rate of 64 kilobits per second (Kbps) in each direction, for a total transmission rate of 128 Kbps. Since there are 8 kilobits (Kb) in a kilobyte (KB), this translates to a transmission of 16 KB each second the circuit is open, and 960 KB every minute it's open. In a 10-minute conversation, the total transmission is 9,600 KB, which is roughly equal to 10 megabytes (check out How Bits and Bytes Work to learn about these conversions). If you look at a typical phone conversation, much of this transmitted data is wasted.

VoIP: Packet Switching

A packet-switched phone network is the alternative to circuit switching. It works like this: While you're talking, the other party is listening, which means that only half of the connection is in use at any given time. Based on that, we can surmise that we could cut the file in half, down to about 4.7 MB, for efficiency. Plus, a significant amount of the time in most conversations is dead air -- for seconds at a time, neither party is talking. If we could remove these silent intervals, the file would be even smaller. Then, instead of sending a continuous stream of bytes (both silent and noisy), what if we sent just the packets of noisy bytes when you created them?
Data networks do not use circuit switching. Your Internet connection would be a lot slower if it maintained a constant connection to the Web page you were viewing at any given time. Instead, data networks simply send and retrieve data as you need it. And, instead of routing the data over a dedicated line, the data packets flow through a chaotic network along thousands of possible paths. This is called packet switching.
While circuit switching keeps the connection open and constant, packet switching opens a brief connection -- just long enough to send a small chunk of data, called a packet, from one system to another. It works like this:
  • The sending computer chops data into small packets, with an address on each one telling the network devices where to send them.
  • Inside of each packet is a payload. The payload is a piece of the e-mail, a music file or whatever type of file is being transmitted inside the packet.
  • The sending computer sends the packet to a nearby router and forgets about it. The nearby router send the packet to another router that is closer to the recipient computer. That router sends the packet along to another, even closer router, and so on.
  • When the receiving computer finally gets the packets (which may have all taken completely different paths to get there), it uses instructions contained within the packets to reassemble the data into its original state.
Packet switching is very efficient. It lets the network route the packets along the least congested and cheapest lines. It also frees up the two computers communicating with each other so that they can accept information from other computers, as well.

Advantages of Using VoIP

VoIP technology uses the Internet's packet-switching capabilities to provide phone service. VoIP has several advantages over circuit switching. For example, packet switching allows several telephone calls to occupy the amount of space occupied by only one in a circuit-switched network. Using PSTN, that 10-minute phone call we talked about earlier consumed 10 full minutes of transmission time at a cost of 128 Kbps. With VoIP, that same call may have occupied only 3.5 minutes of transmission time at a cost of 64 Kbps, leaving another 64 Kbps free for that 3.5 minutes, plus an additional 128 Kbps for the remaining 6.5 minutes. Based on this simple estimate, another three or four calls could easily fit into the space used by a single call under the conventional system. And this example doesn't even factor in the use of data compression, which further reduces the size of each call.
Let's say that you and your friend both have service through a VoIP provider. You both have your analog phones hooked up to the service-provided ATAs. Let's take another look at that typical telephone call, but this time using VoIP over a packet-switched network:
  1. You pick up the receiver, which sends a signal to the ATA.
  2. The ATA receives the signal and sends a dial tone. This lets you know that you have a connection to the Internet.
  3. You dial the phone number of the party you wish to talk to. The tones are converted by the ATA into digital data and temporarily stored.
  4. The phone number data is sent in the form of a request to your VoIP company's call processor. The call processor checks it to ensure that it's in a valid format.
  5. The call processor determines to whom to map the phone number. In mapping, the phone number is translated to an IP address (more on this later). The soft switch connects the two devices on either end of the call. On the other end, a signal is sent to your friend's ATA, telling it to ask the connected phone to ring.
  6. Once your friend picks up the phone, a session is established between your computer and your friend's computer. This means that each system knows to expect packets of data from the other system. In the middle, the normal Internet infrastructure handles the call as if it were e-mail or a Web page. Each system must use the same protocol to communicate. The systems implement two channels, one for each direction, as part of the session.
  7. You talk for a period of time. During the conversation, your system and your friend's system transmit packets back and forth when there is data to be sent. The ATAs at each end translate these packets as they are received and convert them to the analog audio signal that you hear. Your ATA also keeps the circuit open between itself and your analog phone while it forwards packets to and from the IP host at the other end.
  8. You finish talking and hang up the receiver.
  9. When you hang up, the circuit is closed between your phone and the ATA.
  10. The ATA sends a signal to the soft switch connecting the call, terminating the session.
VoIP Terms
The central call processor is a piece of hardware running a specialized database/mapping program called a soft switch. See the "Soft Switches" section to learn more.
Probably one of the most compelling advantages of packet switching is that data networks already understand the technology. By migrating to this technology, telephone networks immediately gain the ability to communicate the way computers do.
It will still be at least a decade before communications companies can make the full switch over to VoIP. As with all emerging technologies, there are certain hurdles that have to be overcome.

Disadvantages of Using VoIP

The current Public Switched Telephone Network is a robust and fairly bulletproof system for delivering phone calls. Phones just work, and we've all come to depend on that. On the other hand, computers, e-mail and other related devices are still kind of flaky. Let's face it -- few people really panic when their e-mail goes down for 30 minutes. It's expected from time to time. On the other hand, a half hour of no dial tone can easily send people into a panic. So what the PSTN may lack in efficiency it more than makes up for in reliability. But the network that makes up the Internet is far more complex and therefore functions within a far greater margin of error. What this all adds up to is one of the major flaws in VoIP: reliability.
  • First of all, VoIP is dependant on wall power. Your current phone runs on phantom power that is provided over the line from the central office. Even if your power goes out, your phone (unless it is a cordless) still works. With VoIP, no power means no phone. A stable power source must be created for VoIP.
  • Another consideration is that many other systems in your home may be integrated into the phone line. Digital video recorders, digital subscription TV services and home security systems all use a standard phone line to do their thing. There's currently no way to integrate these products with VoIP. The related industries are going to have to get together to make this work.
  • Emergency 911 calls also become a challenge with VoIP. As stated before, VoIP uses IP-addressed phone numbers, not NANP phone numbers. There's no way to associate a geographic location with an IP address. So if the caller can't tell the 911 operator where he is located, then there's no way to know which call center to route the emergency call to and which EMS should respond. To fix this, perhaps geographical information could somehow be integrated into the packets.
  • Testing, Testing...
    Wondering if your broadband connection could support VoIP service? Brix Network offers a way to test your Internet connection to see how well it works.
  • Because VoIP uses an Internet connection, it's susceptible to all the hiccups normally associated with home broadband services. All of these factors affect call quality:
    • Latency
    • Jitter
    • Packet loss
    Phone conversations can become distorted, garbled or lost because of transmission errors. Some kind of stability in Internet data transfer needs to be guaranteed before VoIP could truly replace traditional phones.
  • VoIP is susceptible to worms, viruses and hacking, although this is very rare and VoIP developers are working on VoIP encryption to counter this.
  • Another issue associated with VoIP is having a phone system dependant on individual PCs of varying specifications and power. A call can be affected by processor drain. Let's say you are chatting away on your softphone, and you decide to open a program that saps your processor. Quality loss will become immediately evident. In a worst case scenario, your system could crash in the middle of an important call. In VoIP, all phone calls are subject to the limitations of normal computer issues.
One of the hurdles that was overcome some time ago was the conversion of the analog audio signal your phone receives into packets of data. How it is that analog audio is turned into packets for VoIP transmission? The answer is codecs.

VoIP: Codecs

A codec, which stands for coder-decoder, converts an audio signal into compressed digital form for transmission and then back into an uncompressed audio signal for replay. It's the essence of VoIP.
Codecs accomplish the conversion by sampling the audio signal several thousand times per second. For instance, a G.711 codec samples the audio at 64,000 times a second. It converts each tiny sample into digitized data and compresses it for transmission. When the 64,000 samples are reassembled, the pieces of audio missing between each sample are so small that to the human ear, it sounds like one continuous second of audio signal. There are different sampling rates in VoIP depending on the codec being used:
  • 64,000 times per second
  • 32,000 times per second
  • 8,000 times per second
A G.729A codec has a sampling rate of 8,000 times per second and is the most commonly used codec in VoIP.
Codecs use advanced algorithms to help sample, sort, compress and packetize audio data. The CS-ACELP algorithm (CS-ACELP = conjugate-structure algebraic-code-excited linear prediction) is one of the most prevalent algorithms in VoIP. CS-ACELP organizes and streamlines the available bandwidth. Annex B is an aspect of CS-ACELP that creates the transmission rule, which basically states "if no one is talking, don't send any data." The efficiency created by this rule is one of the greatest ways in which packet switching is superior to circuit switching. It's Annex B in the CS-ACELP algorithm that's responsible for that aspect of the VoIP call.
The codec works with the algorithm to convert and sort everything out, but it's not any good without knowing where to send the data. In VoIP, that task is handled by soft switches.
E.164 is the name given to the standard for the North American Numbering Plan (NANP). This is the numbering system that phone networks use to know where to route a call based on the dialed numbers. A phone number is like an address:
    (313) 555-1212 313 = State 555 = City 1212 = Street address
The switches use "313" to route the phone call to the area code's region. The "555" prefix sends the call to a central office, and the network routes the call using the last four digits, which are associated with a specific location. Based on that system, no matter where you're in the world, the number combination "(313) 555" always puts you in the same central office, which has a switch that knows which phone is associated with "1212."
The challenge with VoIP is that IP-based networks don't read phone numbers based on NANP. They look for IP addresses, which look like this:
    192.158.10.7
IP addresses correspond to a particular device on the network like a computer, a router, a switch, a gateway or a telephone. However, IP addresses are not always static. They're assigned by a DHCP server on the network and change with each new connection. VoIP's challenge is translating NANP phone numbers to IP addresses and then finding out the current IP address of the requested number. This mapping process is handled by a central call processor running a soft switch.
The central call processor is hardware that runs a specialized database/mapping program called a soft switch. Think of the user and the phone or computer as one package -- man and machine. That package is called the endpoint. The soft switch connects endpoints.
Soft switches know:
  • Where the network's endpoint is
  • What phone number is associated with that endpoint
  • The endpoint's current IP address

VoIP: Soft Switches and Protocols

The soft switch contains a database of users and phone numbers. If it doesn't have the information it needs, it hands off the request downstream to other soft switches until it finds one that can answer the request. Once it finds the user, it locates the current IP address of the device associated with that user in a similar series of requests. It sends back all the relevant information to the softphone or IP phone, allowing the exchange of data between the two endpoints.
Soft switches work in tandem with network devices to make VoIP possible. For all these devices to work together, they must communicate in the same way. This communication is one of the most important aspects that will have to be refined for VoIP to take off.


Protocols
As we've seen, on each end of a VoIP call we can have any combination of an analog, soft or IP phone as acting as a user interface, ATAs or client software working with a codec to handle the digital-to-analog conversion, and soft switches mapping the calls. How do you get all of these completely different pieces of hardware and software to communicate efficiently to pull all of this off? The answer is protocols.
There are several protocols currently used for VoIP. These protocols define ways in which devices like codecs connect to each other and to the network using VoIP. They also include specifications for audio codecs. The most widely used protocol is H.323, a standard created by the International Telecommunication Union (ITU). H.323 is a comprehensive and very complex protocol that was originally designed for video conferencing. It provides specifications for real-time, interactive videoconferencing, data sharing and audio applications such as VoIP. Actually a suite of protocols, H.323 incorporates many individual protocols that have been developed for specific applications.


H.323 Protocol Suite

Video

Audio

Data

Transport

H.261
H.263

G.711
G.722
G.723.1
G.728
G.729

T.122
T.124
T.125
T.126
T.127

H.225
H.235
H.245
H.450.1
H.450.2
H.450.3
RTP
X.224.0

As you can see, H.323 is a large collection of protocols and specifications. That's what allows it to be used for so many applications. The problem with H.323 is that it's not specifically tailored to VoIP.
An alternative to H.323 emerged with the development of Session Initiation Protocol (SIP). SIP is a more streamlined protocol, developed specifically for VoIP applications. Smaller and more efficient than H.323, SIP takes advantage of existing protocols to handle certain parts of the process. Media Gateway Control Protocol (MGCP) is a third commonly used VoIP protocol that focuses on endpoint control. MGCP is geared toward features like call waiting. You can learn more about the architecture of these protocols at Protocols.com: Voice Over IP.
One of the challenges facing the worldwide use of VoIP is that these three protocols are not always compatible. VoIP calls going between several networks may run into a snag if they hit conflicting protocols. Since VoIP is a relatively new technology, this compatibility issue will continue to be a problem until a governing body creates a standard universal protocol for VoIP.
VoIP is a vast improvement over the current phone system in efficiency, cost and flexibility. Like any emerging technology, VoIP has some challenges to overcome, but it's clear that developers will keep refining this technology until it eventually replaces the current phone system.

VoIP Call Monitoring

VoIP has its distinct advantages and disadvantages. The greatest advantage of VoIP is price and the greatest disadvantage is call quality. For businesses who deploy VoIP phone networks -- particularly those who operate busy call centers (customer service, tech support, telemarketing, et cetera) -- call quality issues are both inevitable and unacceptable. To analyze and fix call quality issues, most of these businesses use a technique called VoIP call monitoring.
VoIP call monitoring, also known as quality monitoring (QM), uses hardware and software solutions to test, analyze and rate the overall quality of calls made over a VoIP phone network [source: ManageEngine]. Call monitoring is a key component of a business's overall quality of service (QoS) plan.
Call monitoring hardware and software uses various mathematical algorithms to measure the quality of a VoIP call and generate a score. The most common score is called the mean opinion score (MOS). The MOS is measured on a scale of one to five, although 4.4 is technically the highest score possible on a VoIP network [source: TestYourVoIP.com]. An MOS of 3.5 or above is considered a "good call" [source: ManageEngine].
To come up with the MOS, call monitoring hardware and software analyzes several different call quality parameters, the most common being:
  • Latency -- This is the time delay between two ends of a VoIP phone conversation. It can be measured either one-way or round trip. Round-trip latency contributes to the "talk-over effect" experienced during bad VoIP calls, where people end up talking over each other because they think the other person has stopped speaking. A round-trip latency of over 300 millisecond is considered poor [source: TestYourVoIP.com].
  • Jitter -- Jitter is latency caused by packets arriving late or in the wrong order [source: SearchVoIP.com]. Most VoIP networks try to get rid of jitter with something called a jitter buffer that collects packets in small groups, puts them in the right order and delivers them to the end user all at once. VoIP callers will notice a jitter of 50 msec or greater [source: TestYourVoIP.com].
  • Packet loss -- Part of the problem with a jitter buffer is that sometimes it gets overloaded and late-arriving packets get "dropped" or lost [source: TestYourVoIP.com]. Sometimes the packets will get lost sporadically throughout a conversation (random loss) and sometimes whole sentences will get dropped (bursty loss) [source: TestYourVoIP.com]. Packet loss is measured as a percentage of lost packets to received packets.
There are two different types of call monitoring: active and passive. Active (or subjective) call monitoring happens before a company deploys its VoIP network. Active monitoring is often done by equipment manufacturers and network specialists who use a company's VoIP network exclusively for testing purposes [source: VoIP Troubleshooter.com]. Active testing can't occur once a VoIP network is deployed and employees are already using the system.
Passive call monitoring analyzes VoIP calls in real-time while they're being made by actual users [source: VoIP Troubleshooter.com]. Passive call monitoring can detect network traffic problems, buffer overloads and other glitches that network administrators can fix in network down time.
Another method for call monitoring is recording VoIP phone calls for later analysis. This type of analysis is limited, however, to what can be heard during the call, not what's happening on the actual network. This type of monitoring is usually done by human beings, not computers, and is called quality assurance.

VoIP Cell Phones


VoIP-enabled cell phones are just entering the consumer market. In the United States, only T-Mobile's HotSpot@Home service allows customers to make cell phone calls over a VoIP network. HotSpot@Home relies on a device called a dual-mode cell phone.
Dual-mode cell phones contain both a regular cellular radio and a Wi-Fi (802.11 b/g) radio. The Wi-Fi radio enables the cell phone to connect to a wireless Internet network through a wireless router. If you have a wireless Internet router in your home, or if you're sitting at a Starbucks with wireless Internet access, you can use your cell phone to make VoIP calls. Here's how it works:
  1. When the cell phone is in range of a wireless Internet network, the phone automatically recognizes and connects to the network.
  2. Any calls you initiate on the wireless network are routed through the Internet as VoIP calls. With HotSpot@Home, all VoIP calls are free.
  3. If the phone is out of range of a wireless Internet signal, it automatically switches over to the regular cellular network and calls are charged as normal.
  4. Dual-mode phones can hand off seamlessly from Wi-Fi to cellular (and vice versa) in the middle of a call as you enter and exit Wi-Fi networks.
Similar to dual-mode cell phones are Wi-Fi phones. Wi-Fi phones aren't technically cell phones because they only have a Wi-Fi radio, not a cellular radio. Wi-Fi phones look like cell phones (small, lightweight handsets), but can only make calls when connected to a wireless Internet network. That means all Wi-Fi phone calls are VoIP calls.
Wi-Fi phones are useful in large companies and offices with their own extensive wireless networks. And could prove to be the next big thing, with the expanding market for municipal Wi-Fi. [source: Dr. Dobb's Portal]. Imagine that your entire city was covered by a high-speed wireless network. That means cheap (if not free) VoIP calls wherever you go.
In England, a company called Hutchinson 3G (or simply 3) has partnered with the popular VoIP service Skype to introduce the 3 Skypephone. The Skypephone allows users to make free cell phone calls to other Skype users. The phone can also make regular cell-phone calls to non-Skype users for the normal fees. Here's how it works:
  1. To make a Skype call using the 3 Skypephone, you have to be on 3's cellular network.
  2. To initiate a Skype call, find a Skype user in your phone's address book and press the big "Skype" button.
  3. The call first goes over 3's cellular GSM network to a fixed Internet line, which then connects the call to Skype [source: mobileSift].
  4. From your 3 Skypephone, you can make free VoIP calls to other Skype users whether they have a Skypephone or not. You can talk to Skype users on their PCs or using other Skype VoIP products.
The 3 Skypephone isn't currently available in the United States.

Use of VoIP in Amateur Radio

Think of amateur radio, or ham radio, as an early version of the Internet. Using a worldwide network of radio towers, antennas and transceivers, amateur radio enthusiasts are able to communicate with fellow hobbyists around the globe, sometimes by voice and sometimes by Morse code.
Amateur radio is limited by the distance that radio waves can travel. To send a signal to the other side of the world requires calculated timing and more than a little bit of luck. Every 11 years, for example, there's a peak in the number of sunspots produced by the sun, which increases the intensity of something called ionospheric propagation [source: International Solar Terrestrial Physics Program]. By bouncing radio signals high into the ionosphere, ham radio users can send long-distance messages. During off-peak years it's much more difficult.
Now amateur radio fans are using VoIP technology to link users around the globe. Here's how it works. Ham radio has always relied on FM repeaters, large radio towers that act as base stations for accessing the radio network from home. By attaching an Internet-connected PC to these repeater stations, people can communicate with the repeater using VoIP.
Several amateur radio fans have developed special software that helps connect home radio transceivers to the Internet. Users can connect their ham radio transceivers to their PC sound card and use the computer software to search for available repeater stations across the world [source: ARRL]. No longer are ham radio fans limited to the closest repeater station. If you live in Indiana, you can call into a repeater station in Mozambique and chat with local amateur radio aficionados instantly.
There are also software programs that allow you to communicate with other amateur radio users directly from your PC, without having an actual ham radio [source: ARRL]. Some ham radio purists wouldn't call this amateur radio, while others hope that this new technology will draw more young people into the hobby.

Related Articles


 

GNU Parted User Manual

Copyright © 1999-2010 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License”.
This document describes the use of GNU Parted, a program for creating, destroying, resizing, checking and copying hard drive partitions, and the file systems on them.
This document applies roughly to version 2.3 of GNU Parted.
The original version was written by Andrew Clausen in text format. Richard M. Kreuter translated it into Texinfo format in 2002, to be heavily edited by Leslie P. Polzer in 2006.

Short Contents

    GNU Parted User Manual1 Introduction2 Using Parted3 Related informationAppendix A Copying This ManualAppendix B This manual's historyIndex

1 Introduction


1.1 Overview of GNU Parted

GNU Parted is a program for creating, destroying, resizing, checking and copying partitions, and the file systems on them.
This is useful for creating space for new operating systems, for reorganizing disk usage, for copying data between hard disks and for “disk imaging” — replicating an installation on another computer.
This documentation is written with the assumption that the reader has some understanding of partitioning and file systems. If you want to learn more about these, the upcoming GNU Storage Guide is recommended reading.
GNU Parted was designed to minimize the chance of data loss. For example, it was designed to avoid data loss during interruptions (like power failure) and performs many safety checks. However, there could be bugs in GNU Parted, so you should back up your important files before running Parted. Also note that reiserfs support relies on libreiserfs, which does not fulfil the aforementioned requirement. The same holds for any external tools like ntfsresize.
The GNU Parted homepage is http://www.gnu.org/software/parted. The library and frontend themselves can be downloaded from ftp://ftp.gnu.org/gnu/parted. You can also find a listing of mailing lists, notes for contributing and more useful information on the web site.
Please send bug reports to bug-parted@gnu.org. When sending bug reports, please include the version of GNU Parted. Please include the output from these commands (for disk /dev/hda):
# parted /dev/hda print unit s print unit chs print
Feel free to ask for help on this list — just check that your question isn't answered here first. If you don't understand the documentation, please tell us, so we can explain it better. General philosophy is: if you need to ask for help, then something needs to be fixed so you (and others) don't need to ask for help.
Also, we'd love to hear your ideas :-)

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1.2 Software Required for the use of Parted

If you're installing or compiling Parted yourself, you'll need to have some other programs installed. If you are compiling Parted, you will need both the normal and devel packages of these programs installed:
  • libuuid, part of the e2fsprogs package. If you don't have this, you can get it from: http://web.mit.edu/tytso/www/linux/e2fsprogs.html
    If you want to compile Parted and e2fsprogs, note that you will need to make install and make install-libs e2fsprogs.
  • GNU Readline (optional), available from ftp://ftp.gnu.org/gnu/readline
    If you are compiling Parted, and you don't have readline, you can disable Parted's readline support with the --disable-readline option for configure.
  • GNU gettext (or compatible software) for compilation, if internationalisation support is desired. ftp://ftp.gnu.org/gnu/gettext
  • libreiserfs, if you want reiserfs support: http://reiserfs.osdn.org.ua
    Note that parted will automatically detect libreiserfs at runtime, and enable reiserfs support. libreiserfs is new, and hasn't been widely tested yet.

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1.3 Platforms on which GNU Parted runs

Hopefully, this list will grow a lot. If you do not have one of these platforms, then you can use a rescue disk and a static binary of GNU Parted. See Static binaries.
GNU/Linux
Linux versions 2.0 and up, on Alpha, x86 PCs, PC98, Macintosh PowerPC, Sun hardware.
GNU/Hurd
GNU libc 2.1 or higher is required. You can probably use older versions by using the ‘--disable-nls’ option. See Building GNU Parted. (Note: I think we have now dropped this requirement. TODO: check if libc 2.0 works!)

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1.4 Terms of distribution for GNU Parted

GNU Parted is free software, covered by the GNU General Public License Version 2. This should have been included with the Parted distribution, in the COPYING file. If not, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
Libparted is considered part of GNU Parted. It is covered by the GNU General Public License. It is NOT released under the GNU Lesser General Public License (LGPL).

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1.5 Building GNU Parted

If you want to compile GNU Parted, this is generally done with:
$ ./configure
     $ make
However, there are a few options for configure:
--without-readline
turns off use of readline. This is useful for making rescue disks, etc., where few libraries are available.
--disable-debug
don't include assertions
--disable-dynamic-loading
disables dynamic loading of some libraries (only libreiserfs for now, although we hope to expand this). Dynamic loading is useful because it allows you to reuse libparted shared libraries even when you don't know if some libraries will be available. It has a small overhead (mainly linking with libdl), so it may be useful to disable it on bootdisks if you don't need the flexibility.
--disable-fs
disable all file system support
--disable-nls
turns off native language support. This is useful for use with old versions of glibc, or a trimmed down version of glibc suitable for rescue disks.
--disable-shared
turns off shared libraries. This may be necessary for use with old versions of GNU libc, if you get a compile error about a “spilled register”. Also useful for boot/rescue disks.
--disable-Werror
ignore warning messages in compilation
--enable-discover-only
support only reading/probing (reduces size considerably)
--enable-mtrace
enable malloc() debugging
--enable-read-only
disable writing (for debugging)

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1.6 Using static binaries of GNU Parted


1.6.1 Introduction

If you want to run GNU Parted on a machine without GNU/Linux installed, or you want to resize a root or boot partition, you will need to use a boot disk.
Special boot disk images for GNU Parted used to be available, but with the emergence of a plethora of rescue disks and Live CDs that all include GNU Parted this is no longer necessary. However, please note that these disks often ship with out-of-date versions of Parted. To compensate for this a static binary of the latest GNU Parted version is available, which you can use thus:

1.6.2 Creating the Parted disk

  1. Boot your system
  2. Download parted-static-VERSION.tgz from ftp://ftp.gnu.org/gnu/parted/static
  3. Unpack the tarball, resulting in a file called “parted.static".
  4. Insert a floppy.
  5. Do a low-level format on it (on GNU/Linux this can be achieved with the tool “fdformat" from the “util-linux" package. This is basically a sanity check because floppy disks often contain bad blocks.
  6. Create a file system. Example:
    $ parted /dev/fd0 mklabel loop mkpartfs ext2 0 1.4
  7. Mount the floppy disk, e.g.,
    $ mount -t ext2 /dev/fd0 /mnt/floppy
  8. Copy parted.static to the floppy, e.g.,
    $ cp parted.static /mnt/floppy
  9. Unmount the floppy, e.g.,
    $ umount /mnt/floppy

1.6.3 Using the Parted disk

  1. Choose a rescue disk that suits you.
  2. Boot off your rescue disk. Mount the disk you copied Parted onto.
  3. Run Parted. For example,
    # cd /mnt/floppy
              # ./parted-static

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2 Using Parted


2.1 Introduction to Partitioning

Unfortunately, partitioning your disk is rather complicated. This is because there are interactions between many different systems that need to be taken into consideration.
This manual used to introduce the reader to these systems and their working. This content has moved to the GNU Storage Guide.

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2.2 Using GNU Parted

Parted has two modes: command line and interactive. Parted should always be started with:
# parted device
where device is the hard disk device to edit. (If you're lazy and omit the DEVICE argument, Parted will attempt to guess which device you want.)
In command line mode, this is followed by one or more commands. For example:
# parted /dev/sda resize 1 52Mb 104Mb mkfs 2 fat16
Options (like --help) can only be specified on the command line.
In interactive mode, commands are entered one at a time at a prompt, and modify the disk immediately. For example:
(parted) resize 1 52.0005Mb 104.5Mb
     (parted) mkfs 2 fat16
Unambiguous abbreviations are allowed. For example, you can type “p” instead of “print”, and “resi” instead of “resize”. Commands can be typed either in English, or your native language (if your language has been translated). This may create ambiguities. Commands are case-insensitive.
Numbers indicating partition locations can be whole numbers or decimals. The suffix selects the unit, which may be one of those described in unit, except CHS and compact. If no suffix is given, then the default unit is assumed. Negative numbers count back from the end of the disk, with “-1s” indicating the end of the disk. Parted will compute sensible ranges for the locations you specify (e.g. a range of +/- 500 MB when you specify the location in “G”). Use the sector unit “s” to specify exact locations.
If you don't give a parameter to a command, Parted will prompt you for it. For example:
(parted) resize 1
     Start? 0Gb
     End? 40Gb
Parted will always warn you before doing something that is potentially dangerous, unless the command is one of those that is inherently dangerous (viz., rm, mklabel and mkfs). For example, if you attempt to shrink a partition “too much” (i.e., by more than the free space available), Parted will automatically reduce the shrinkage so that the partition is the smallest it can be without losing data. If this size is significantly different from the size requested, Parted will warn you. Since many partitioning systems have complicated constraints, Parted will usually do something slightly different to what you asked. (For example, create a partition starting at 10.352Mb, not 10.4Mb) If the calculated values differ too much, Parted will ask you for confirmation.
Currently ext3 filesystem functionality does not work. To manage ext3 type filesystems use tools like resize2fs or mke2fs. Note that the currently supported ext2 filesystem will be deprecated once ext3 support is finalized. Further note that ext3 support will have limited functionality that is yet to be defined. Use tools like resize2fs (8) and mke2fs (8) to manage these types of filesystems.

2.3 Command Line Options

When invoked from the command line, Parted supports the following syntax:
# parted [option] device [command [argument]]
Available options and commands follow. For detailed explanations of the use of Parted commands, see Command explanations. Options begin with a hyphen, commands do not:
Options:
-h
--help
display a help message
-s
--script
never prompt the user
-a alignment-type
--align alignment-type
Set alignment for newly created partitions, valid alignment types are: none, cylinder, minimal and optimal.
-v
--version
display the version

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2.4 Parted Session Commands

GNU Parted provides the following commands:

2.4.1 align-check


— Command: align-check align-type n
Determine whether the starting sector of partition n meets the disk's selected alignment criteria. align-type must be ‘minimal’, ‘optimal’ or an abbreviation. When in script mode, if the partition does not meet the alignment requirement, exit with status 1; otherwise (including on older kernels for which alignment data is not available), continue processing any remaining commands. Without --script, print either ‘N aligned’ or ‘N not aligned’.
Example:
(parted) align-check minimal 1
          1 aligned

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2.4.2 check


— Command: check number
Checks if the file system on partition number has any errors.
Example:
(parted) check 1
Check the file system on partition 1.

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2.4.3 cp


— Command: cp [from-device] from-number to-number
Copies the file system on the partition from-number to partition to-number, deleting the original contents of the destination partition.
An optional device parameter, from-device can be given, which specifies which device the source partition is on.
Supported file systems:
  • ext2 (provided the destination partition is larger than the source partition)
  • fat16, fat32
  • linux-swap (equivalent to mkswap on destination partition)
  • reiserfs (if libreiserfs is installed)
Example:
(parted) cp /dev/hdb 2 3
Copy partition 2 of /dev/hdb (i.e., /dev/hdb2) to partition on 3, on the device Parted was loaded with, destroying the original contents of partition 3.

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2.4.4 help


— Command: help [command]
Prints general help, or help on command.
Example:
(parted) help resize
Print help for the resize command.

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2.4.5 mklabel


— Command: mklabel label-type
Creates a new disk label, of type label-type. The new disk label will have no partitions. This command (normally) won't technically destroy your data, but it will make it basically unusable, and you will need to use the rescue command (see Related information) to recover any partitions. Parted works on all partition tables. 1
label-type must be one of these supported disk labels:
  • bsd
  • loop (raw disk access)
  • gpt
  • mac
  • msdos
  • pc98
  • sun
Example:
(parted) mklabel msdos
Create an MS-DOS disk label. This is still the most common disk label for PCs.

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2.4.6 mkfs


— Command: mkfs number fs-type
Makes a file system fs-type on partition number, destroying all data that resides on that partition.
Supported file systems:
  • ext2
  • fat16, fat32
  • linux-swap
  • reiserfs (if libreiserfs is installed)
Example:
(parted) mkfs 2 fat32
Make a fat32 file system on partition 2.

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2.4.7 mkpart


— Command: mkpart [part-type fs-type name] start end
Creates a new partition, without creating a new file system on that partition. This is useful for creating partitions for file systems (or LVM, etc.) that Parted doesn't support. You may specify a file system type, to set the appropriate partition code in the partition table for the new partition. fs-type is required for data partitions (i.e., non-extended partitions). start and end are the offset from the beginning of the disk, that is, the “distance” from the start of the disk.
part-type is one of ‘primary’, ‘extended’ or ‘logical’, and may be specified only with ‘msdos’ or ‘dvh’ partition tables. A name must be specified for a ‘gpt’ partition table. Neither part-type nor name may be used with a ‘sun’ partition table.
fs-type must be one of these supported file systems:
  • ext2
  • fat16, fat32
  • hfs, hfs+, hfsx
  • linux-swap
  • NTFS
  • reiserfs
  • ufs
Example:
(parted) mkpart logical 0.0 692.1
Create a logical partition that will contain an ext2 file system. The partition will start at the beginning of the disk, and end 692.1 megabytes into the disk.

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2.4.8 mkpartfs


— Command: mkpartfs part-type fs-type start end
Creates a new partition of type part-type with a new file system of type fs-type on it. The new partition will start start megabytes, and end end megabytes from the beginning of the disk. Do not use this command to recover a deleted partition (use mkpart instead). Using this command is discouraged. Instead use mkpart to create an empty partition, and then use external tools like mke2fs (8) to create the filesystem.
part-type is one of: primary, extended, logical. Extended and logical are only used for msdos and dvh disk labels.
fs-type must be one of these supported file systems:
  • ext2
  • fat16, fat32
  • linux-swap
  • reiserfs (if libreiserfs is installed)
Example:
(parted) mkpartfs logical ext2 440 670
Make a logical partition and write an ext2 file system, starting 440 megabytes and ending 670 megabytes from the beginning of the disk.

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2.4.9 move


— Command: move number start end
Moves partition on the disk, by moving its beginning to start. You can't move a partition so that the old and new positions overlap. That is, you can only move partitions into free space. If you want to resize a partition in-place, use resize.
Move never changes the partition number.
Supported file systems:
  • ext2 (provided the destination partition is larger than the source partition)
  • fat16, fat32
  • linux-swap
  • reiserfs (if libreiserfs is installed)
Example:
(parted) move 2 150M 500M
Move the partition numbered 2 so that it begins 150 megabytes from the start of the disk, and ends 500 megabytes from the start.

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2.4.10 name


— Command: name number name
Sets the name for the partition number (GPT, Mac, MIPS and PC98 only). The name can be placed in quotes.
Example:
(parted) name 2 'Secret Documents'
Set the name of partition 2 to `Secret Documents'.

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2.4.11 print


— Command: print [number]
Displays the partition table on the device parted is editing, or detailed information about a particular partition.
Example:
(parted) print
          Disk geometry for /dev/hda: 0.000-2445.679 megabytes
          Disk label type: msdos
          Minor    Start       End     Type      Filesystem  Flags
          1          0.031    945.000  primary   fat32       boot, lba
          2        945.000   2358.562  primary   ext2
          3       2358.562   2445.187  primary   linux-swap
          (parted) print 1
          Minor: 1
          Flags: boot, lba
          File System: fat32
          Size:            945.000Mb (0%)
          Minimum size:     84.361Mb (0%)
          Maximum size:   2445.679Mb (100%)

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2.4.12 quit


— Command: quit
Quits Parted.
It is only after Parted exits that the Linux kernel knows about the changes Parted has made to the disks. However, the changes caused by typing your commands will probably be made to the disk immediately after typing a command. However, the operating system's cache and the disk's hardware cache may delay this.

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2.4.13 rescue


— Command: rescue start end
Rescue a lost partition that used to be located approximately between start and end. If such a partition is found, Parted will ask you if you want to create a partition for it. This is useful if you accidently deleted a partition with parted's rm command, for example.
Example:
(parted) print
          Disk geometry for /dev/hdc: 0.000-8063.507 megabytes
          Disk label type: msdos
          Minor    Start       End     Type      Filesystem  Flags
          1          0.031   8056.032  primary   ext3
          (parted) rm
          Partition number? 1
          (parted) print
          Disk geometry for /dev/hdc: 0.000-8063.507 megabytes
          Disk label type: msdos
          Minor    Start       End     Type      Filesystem  Flags
OUCH! We deleted our ext3 partition!!! Parted comes to the rescue...
(parted) rescue
          Start? 0
          End? 8056
          Information: A ext3 primary partition was found at 0.031MB ->
          8056.030MB.  Do you want to add it to the partition table?
          Yes/No/Cancel? y
          (parted) print
          Disk geometry for /dev/hdc: 0.000-8063.507 megabytes
          Disk label type: msdos
          Minor    Start       End     Type      Filesystem  Flags
          1          0.031   8056.032  primary   ext3
It's back! :)

Next: , Previous: rescue, Up: Command explanations

2.4.14 resize


— Command: resize number start end
Resizes the partition with number number. The partition will start start from the beginning of the disk, and end end from the beginning of the disk. resize never changes the partition number. Extended partitions can be resized only so long as the new extended partition completely contains all logical partitions.
Note that Parted can manipulate partitions whether or not they have been defragmented, so you do not need to defragment the disk before using Parted.
Supported file systems:
  • ext2 – restriction: the new start must be the same as the old start.
  • fat16, fat32
  • hfs, hfs+, hfsx – restriction: the new start must be the same as the old start and the new end must be smaller than the old end.
  • linux-swap
  • reiserfs (if libreiserfs is installed)
Example:
(parted) resize 3 200M 850M
Resize partition 3, so that it begins 200 megabytes and ends 850 megabytes from the beginning of the disk.

Next: , Previous: resize, Up: Command explanations

2.4.15 rm


— Command: rm number
Removes the partition with number number. If you accidently delete a partition with this command, use mkpart (not mkpartfs) to recover it. Also, you can use the gpart program (see Related information) to recover damaged disk labels.
Note for msdos disk labels: if you delete a logical partition, all logical partitions with a larger partition number will be renumbered. For example, if you delete a logical partition with a partition number of 6, then logical partitions that were number 7, 8 and 9 would be renumbered to 6, 7 and 8 respectively. This means, for example, that you have to update /etc/fstab on GNU/Linux systems.
Example:
(parted) rm 3
Remove partition 3.

Next: , Previous: rm, Up: Command explanations

2.4.16 select


— Command: select device
Selects the device, device, for Parted to edit. The device can be a Linux hard disk device, a partition, a software RAID device or LVM logical volume.
Example:
(parted) select /dev/hdb
Select /dev/hdb (the slave device on the first ide controller on Linux) as the device to edit.

Next: , Previous: select, Up: Command explanations

2.4.17 set


— Command: set number flag state
Changes a flag on the partition with number number. A flag can be either “on” or “off”. Some or all of these flags will be available, depending on what disk label you are using:
bios_grub
(GPT) - Enable this to record that the selected partition is a GRUB BIOS partition.
boot
(Mac, MS-DOS, PC98) - should be enabled if you want to boot off the partition. The semantics vary between disk labels. For MS-DOS disk labels, only one partition can be bootable. If you are installing LILO on a partition that partition must be bootable. For PC98 disk labels, all ext2 partitions must be bootable (this is enforced by Parted).
lba
(MS-DOS) - this flag can be enabled to tell MS DOS, MS Windows 9x and MS Windows ME based operating systems to use Linear (LBA) mode.
root
(Mac) - this flag should be enabled if the partition is the root device to be used by Linux.
swap
(Mac) - this flag should be enabled if the partition is the swap device to be used by Linux.
hidden
(MS-DOS, PC98) - this flag can be enabled to hide partitions from Microsoft operating systems.
raid
(MS-DOS) - this flag can be enabled to tell linux the partition is a software RAID partition.
LVM
(MS-DOS) - this flag can be enabled to tell linux the partition is a physical volume.
PALO
(MS-DOS) - this flag can be enabled so that the partition can be used by the Linux/PA-RISC boot loader, palo.
PREP
(MS-DOS) - this flag can be enabled so that the partition can be used as a PReP boot partition on PowerPC PReP or IBM RS6K/CHRP hardware.
DIAG
(MS-DOS) - Enable this to indicate that a partition can be used as a diagnostics / recovery partition.
The print command displays all enabled flags for each partition.
Example:
(parted) set 1 boot on
Set the ‘boot’ flag on partition 1.

Previous: set, Up: Command explanations

2.4.18 unit


— Command: unit unit
Selects the current default unit that Parted will use to display locations and capacities on the disk and to interpret those given by the user if they are not suffixed by an unit.
unit may be one of:
s
sector (n bytes depending on the sector size, often 512)
B
byte
kB
kilobyte (1000 bytes)
MB
megabyte (1000000 bytes)
GB
gigabyte (1000000000 bytes)
TB
terabyte (1000000000000 bytes)
%
percentage of the device (between 0 and 100)
cyl
cylinders (related to the BIOS CHS geometry)
chs
cylinders, heads, sectors addressing (related to the BIOS CHS geometry)
compact
This is a special unit that defaults to megabytes for input, and picks a unit that gives a compact human readable representation for output.
The default unit apply only for the output and when no unit is specified after an input number. Input numbers can be followed by an unit (without any space or other character between them), in which case this unit apply instead of the default unit for this particular number, but CHS and cylinder units are not supported as a suffix. If no suffix is given, then the default unit is assumed. Parted will compute sensible ranges for the locations you specify (e.g. a range of +/- 500 MB when you specify the location in “G”) and will select the nearest location in this range from the one you wrote that satisfies constraints from both the operation, the filesystem being worked on, the disk label, other partitions and so on. Use the sector unit “s” to specify exact locations (if they do not satisfy all constraints, Parted will ask you for the nearest solution). Note that negative numbers count back from the end of the disk, with “-1s” pointing to the end of the disk.
Example:
(parted) unit compact
          (parted) print
          Disk geometry for /dev/hda: 0kB - 123GB
          Disk label type: msdos
          Number  Start   End     Size    Type      File system  Flags
          1       32kB    1078MB  1077MB  primary   reiserfs     boot
          2       1078MB  2155MB  1078MB  primary   linux-swap
          3       2155MB  123GB   121GB   extended
          5       2155MB  7452MB  5297MB  logical   reiserfs
          (parted) unit chs print
          Disk geometry for /dev/hda: 0,0,0 - 14946,225,62
          BIOS cylinder,head,sector geometry: 14946,255,63.  Each cylinder
          is 8225kB.
          Disk label type: msdos
          Number  Start       End         Type      File system  Flags
          1       0,1,0       130,254,62  primary   reiserfs     boot
          2       131,0,0     261,254,62  primary   linux-swap
          3       262,0,0     14945,254,62 extended
          5       262,2,0     905,254,62  logical   reiserfs
          (parted) unit mb print
          Disk geometry for /dev/hda: 0MB - 122942MB
          Disk label type: msdos
          Number  Start   End     Size    Type      File system  Flags
          1       0MB     1078MB  1077MB  primary   reiserfs     boot
          2       1078MB  2155MB  1078MB  primary   linux-swap
          3       2155MB  122935MB 120780MB extended
          5       2155MB  7452MB  5297MB  logical   reiserfs

Next: , Previous: Using Parted, Up: Top

3 Related information

If you want to find out more information, please see the GNU Parted web site.
These files in the Parted distribution contain further information:
  • ABOUT-NLS - information about using Native Language Support, and the Free Translation Project.
  • AUTHORS - who wrote what.
  • ChangeLog - record of changes made to Parted.
  • COPYING - the GNU General Public License, the terms under which GNU Parted may be distributed.
  • COPYING.DOC - the GNU Free Documentation Licence, the term under which Parted's documentation may be distributed.
  • INSTALL — how to compile and install Parted, and most other free software

Next: , Previous: Related information, Up: Top

Appendix A Copying This Manual

A.1 GNU Free Documentation License


Version 1.1, March 2000
Copyright © 2000, 2009-2010 Free Software Foundation, Inc.
     51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
     
     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.
  1. PREAMBLE The purpose of this License is to make a manual, textbook, or other written document free in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.
    This License is a kind of “copyleft”, which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.
    We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.
  2. APPLICABILITY AND DEFINITIONS This License applies to any manual or other work that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. The “Document”, below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as “you”.
    A “Modified Version” of the Document means any work containing the Document or a portion of it, either copied verbatim, or with modifications and/or translated into another language.
    A “Secondary Section” is a named appendix or a front-matter section of the Document that deals exclusively with the relationship of the publishers or authors of the Document to the Document's overall subject (or to related matters) and contains nothing that could fall directly within that overall subject. (For example, if the Document is in part a textbook of mathematics, a Secondary Section may not explain any mathematics.) The relationship could be a matter of historical connection with the subject or with related matters, or of legal, commercial, philosophical, ethical or political position regarding them.
    The “Invariant Sections” are certain Secondary Sections whose titles are designated, as being those of Invariant Sections, in the notice that says that the Document is released under this License.
    The “Cover Texts” are certain short passages of text that are listed, as Front-Cover Texts or Back-Cover Texts, in the notice that says that the Document is released under this License.
    A “Transparent” copy of the Document means a machine-readable copy, represented in a format whose specification is available to the general public, whose contents can be viewed and edited directly and straightforwardly with generic text editors or (for images composed of pixels) generic paint programs or (for drawings) some widely available drawing editor, and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters. A copy made in an otherwise Transparent file format whose markup has been designed to thwart or discourage subsequent modification by readers is not Transparent. A copy that is not “Transparent” is called “Opaque”.
    Examples of suitable formats for Transparent copies include plain ascii without markup, Texinfo input format, LaTeX input format, SGML or XML using a publicly available DTD, and standard-conforming simple HTML designed for human modification. Opaque formats include PostScript, PDF, proprietary formats that can be read and edited only by proprietary word processors, SGML or XML for which the DTD and/or processing tools are not generally available, and the machine-generated HTML produced by some word processors for output purposes only.
    The “Title Page” means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, “Title Page” means the text near the most prominent appearance of the work's title, preceding the beginning of the body of the text.
  3. VERBATIM COPYING You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.
    You may also lend copies, under the same conditions stated above, and you may publicly display copies.
  4. COPYING IN QUANTITY If you publish printed copies of the Document numbering more than 100, and the Document's license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.
    If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.
    If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a publicly-accessible computer-network location containing a complete Transparent copy of the Document, free of added material, which the general network-using public has access to download anonymously at no charge using public-standard network protocols. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.
    It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document.
  5. MODIFICATIONS You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:
    1. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission.
    2. List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together with at least five of the principal authors of the Document (all of its principal authors, if it has less than five).
    3. State on the Title page the name of the publisher of the Modified Version, as the publisher.
    4. Preserve all the copyright notices of the Document.
    5. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.
    6. Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this License, in the form shown in the Addendum below.
    7. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document's license notice.
    8. Include an unaltered copy of this License.
    9. Preserve the section entitled “History”, and its title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section entitled “History” in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence.
    10. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the “History” section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission.
    11. In any section entitled “Acknowledgments” or “Dedications”, preserve the section's title, and preserve in the section all the substance and tone of each of the contributor acknowledgments and/or dedications given therein.
    12. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered part of the section titles.
    13. Delete any section entitled “Endorsements”. Such a section may not be included in the Modified Version.
    14. Do not retitle any existing section as “Endorsements” or to conflict in title with any Invariant Section.
    If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version's license notice. These titles must be distinct from any other section titles.
    You may add a section entitled “Endorsements”, provided it contains nothing but endorsements of your Modified Version by various parties—for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.
    You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.
    The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.
  6. COMBINING DOCUMENTS You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice.
    The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.
    In the combination, you must combine any sections entitled “History” in the various original documents, forming one section entitled “History”; likewise combine any sections entitled “Acknowledgments”, and any sections entitled “Dedications”. You must delete all sections entitled “Endorsements.”
  7. COLLECTIONS OF DOCUMENTS You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.
    You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.
  8. AGGREGATION WITH INDEPENDENT WORKS A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, does not as a whole count as a Modified Version of the Document, provided no compilation copyright is claimed for the compilation. Such a compilation is called an “aggregate”, and this License does not apply to the other self-contained works thus compiled with the Document, on account of their being thus compiled, if they are not themselves derivative works of the Document.
    If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one quarter of the entire aggregate, the Document's Cover Texts may be placed on covers that surround only the Document within the aggregate. Otherwise they must appear on covers around the whole aggregate.
  9. TRANSLATION Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License provided that you also include the original English version of this License. In case of a disagreement between the translation and the original English version of this License, the original English version will prevail.
  10. TERMINATION You may not copy, modify, sublicense, or distribute the Document except as expressly provided for under this License. Any other attempt to copy, modify, sublicense or distribute the Document is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.
  11. FUTURE REVISIONS OF THIS LICENSE The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See http://www.gnu.org/copyleft/.
    Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License “or any later version” applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation.

A.1.1 ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:
Copyright (C)  year  your name.
       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.3
       or any later version published by the Free Software Foundation;
       with the Invariant Sections being list their titles, with the
       Front-Cover Texts being list, and with the Back-Cover Texts being list.
       A copy of the license is included in the section entitled ``GNU
       Free Documentation License''.
If you have no Invariant Sections, write “with no Invariant Sections” instead of saying which ones are invariant. If you have no Front-Cover Texts, write “no Front-Cover Texts” instead of “Front-Cover Texts being list”; likewise for Back-Cover Texts.
If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.

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