complete collection from basics installation to working with examples for Opnet simulations

Video tutorials for opnet study :

Opnet Collections for opnet modeler 14.0 tuotrials , working and examples

1.collection tutors for opnet learning - begining from basics 1
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IT Guru Academic LAb experiments with screenshots

IT Guru enables one to create a virtual network consisting of relevant hardware, protocols, and application software (OPNET Corporation, Slide 2 of “IT Guru QuickStart”, PowerPoint Presentation, 2004). This network is a purely software entity that can run on an individual workstation. Routers, switches, web servers – almost anything found in real networks – can be duplicated in an IT Guru virtual network. It can be scaled from just a network of two workstations to one representing tens of thousands running in a WAN.

Once a virtual network is created it can be manipulated in various ways – for instance routers can be added or subtracted, protocols switched around or altered, web servers added or discarded – any permutation imaginable. The effects of various alterations and diverse configurations can then be usefully and quantifiably examined and analyzed. Importantly IT Guru allows one to study and gather useful statistics about a virtual network built from it. IT Guru permits not only the building of a virtual network in software but also provides tools for dynamically investigating the thus engendered network. (OPNET corporation, Slide 17 of “IT Guru QuickStart”, PowerPoint Presentation, 2004).

The following high level architectural rendering of IT Guru is an ideal place to get started. It shows IT Guru and its major modules: Source: OPNET Corporation, Slide 377 of “IT Guru QuickStart”, PowerPoint Presentation, 2004.

The virtual network environment represents a network. It can have a slew of components in every salient category. Opnet defines a topology as a “collection of links, nodes and configuration.” (OPNET Corporation, Slide 203 of “IT Guru QuickStart”, PowerPoint Presentation, 2004) By “nodes” Opnet means to include networking hardware of all kinds (routers, workstations, switches, hubs etc). By “links” the underlying connectivity technology (Ethernet, ATM, etc) and relevant characteristics (latency, bandwidth) are meant. In “configuration” things like routing protocols, addressing, whether VPN, are included. Some combination of nodes, links, and configuration makes up a VNE. (OPNET Corporation, Slide 203 of “IT Guru QuickStart”, PowerPoint Presentation, 2004)

As the diagram shows there are several different ways of creating an OPNET virtual network environment (VNE). The most straightforward is by using OPNET’s GUI interface for that purpose. One can select from a list of choices for all aspects of a network. The general procedure is to select appropriate hardware elements such as workstations, servers, routers, switches, hubs, then connect them together according to the desired topology. OPNET provides models of the major popular brands of network communication hardware – Cisco for instance is well represented with its family of routers and switches available in the relevant OPNET IT Guru menus. (OPNET Corporation, Slide 205, Slides 221-223 of “IT Guru QuickStart”, PowerPoint Presentation, 2004).

The GUI method works well in many contexts surely but it can be tedious if the network being modeled is elaborate and complex. OPNET has made it possible to automate VNE creation via the VNE Server technology. The VNE Server works in conjunction with OPNET VNE clients to gather user specified network data. It then has the ability to feed that data into IT Guru, producing a virtual representation of the network. Clearly this is a highly powerful method of engendering a VNE. It has the added advantage of sidestepping user errors that are possible in a manual VNE creation process.

Actually VNE server is powerful enough to process network topology data from not only OPNET clients but also industry standard network mapping and monitoring agents. For instance VNE server can interface with HP Openview NNM, Cisco Netflow Collector in addition to having the capacHTTP, FTP, E-Mail, Database, etcity to gather information directly from various Cisco, Juniper and Nortel switches and routers. It can also read from SNMP MIBs and in the worst-case scenario perhaps ASCII files containing sundry topology related information. (OPNET Corporation, Slide 207 of “IT Guru QuickStart”, PowerPoint Presentation, 2004)

IT Guru can also utilize network device configuration file information to create a VNE. Routers, for instance, have associated configuration files that contain commands to the router OS. Such files can be fed into IT Guru and IT Guru can in turn generate topology information from them. The restriction is that only Cisco and Juniper devices are currently supported. (OPNET Corporation, Slide 208 of “IT Guru QuickStart”, PowerPoint Presentation, 2004)


Opnet has devoted an entire specialized module called Application Characterization Environment (ACE) for modeling and analyzing the behavior of programs that reside above and are primarily users of the network. In other words, these are above the topology layer – they use network services but are not themselves strictly speaking, part of the topology. Consider a web browser, or a video conferencing client. Or a database query tool that talks to a database over the network. Any and all such applications can be modeled in IT Guru – one can make custom virtual representations of such program and populate them inside a VNE. Not only can IT Guru simulate network topology in the VNE but also any high level application that runs on the network.


One must hasten to clarify that it is not that the entire application’s logic and functionality will be duplicated inside the VNE. Rather ACE (using appropriate Opnet agents) captures an application’s communications and interactions with the underlying network topology. This sort of snapshot of an application’s network communications is called an application’s “trace”. As an illustration of how ACE could be used, suppose there is a new web application that remote users access on a DSL connection. However they are experiencing more than expected latency and delay. Suppose that ACE traces have been captured both at the client and server. Now ACE, working in conjunction with IT Guru, has the ability to simulate and analyze the entire client server interaction here. The transactions between client and server here can be simulated inside the appropriately constructed VNE. ACE and IT Guru gives one the ability to conduct detailed studies that would hopefully pin-point what the trouble may be (or at the very least rule out problem spots). For instance, it may be that the server is behaving correctly but the client is firing requests at too rapid a rate or in a redundant fashion. Such behavior, upon uncovering, may be fixed by re-configuring or re-programming the client appropriately. (OPNET Corporation, Slides 46-59, 176-178 of “IT Guru QuickStart”, PowerPoint Presentation, 2004)


Flow Analysis, Net Doctor and Discrete Event Simulation (DES) are IT Guru modules for all kinds of analysis and study of a constructed VNE. In other words, these modules assist with appropriately scrutinizing and playing with a virtual network. They are not tools for generating a topology and associated applications – rather they help in the further study of a given VNE. They are the analysis arms of IT Guru. IT Guru enables one to not only simulate a network but also to investigate such a simulation in depth. The preceding modules are each designed to probe different aspects of a VNE.

The Flow Analysis module enables conducting studies on network traffic flows. In particular Opnet showcases report generation on IP flows and ATM flows in permanent network connection (PVC) scenarios. The module is capable of reporting on throughput, and routing algorithm and traffic flow behaviors. Connection failures are recognized and reported on. Flow Analysis would be very useful in investigating what sort of impact changing network configuration may have on general traffic flow in a network. (OPNET Corporation, Slide 261 of “IT Guru QuickStart”, PowerPoint Presentation, 2004)

The Net Doctor module can be used to check the configuration of various nodes in a network model. For instance suppose that a network’s routers are all supposed to behave a certain way. After one captures this network into a VNE (possibly via the VNE server) one can run Net Doctor to verify router configuration. If Net Doctor says that the VNE routers are not working as they ought to then that suggests that the real routers in the network are not behaving as they ought to. Net Doctor can find issues in routing, security, addressing and the like – one can program Net Doctor with how things ought to look like and Net Doctor can tell if things are as they should be in the VNE. Assuming that the VNE is an accurate rendering of the relevant real network, chances are that if there are problems with the VNE there are problems in the real network. One can modify the VNE in various ways to try and fix the issues – and then Net Doctor can be run again. The final network configuration that passes Net Doctor’s tests can then be implemented into the real network. (OPNET Corporation, Slide 236-37 of “IT Guru QuickStart”, PowerPoint Presentation, 2004)

Discrete Event Simulation (DES) module is in an important sense near the heart of IT Guru. DES is the thing that fleshes out a VNE in an operational sense. DES is the component responsible for actually running a VNE in a live way. Once a VNE is set-up it simply sits there inertly. DES is the component responsible for actually running an appropriately configured VNE so that the VNE begins to hum with life. DES is the simulator and analyzer. As the traffic begins to flow around the VNE and all the virtual nodes come online, DES runs statistical analyses of various kinds on the VNE. The results of these analyses can be displayed in various forms including in highly graphical ways - charts, diagrams and so forth. Some examples are things like throughputs, latency at various nodes, traffic volumes and application response times – all sorts of relevant information about the operations of the virtual network can be gathered up for scrutiny. (OPNET Corporation, Slide 288-290 of “IT Guru QuickStart”, PowerPoint Presentation, 2004)

Chapter 4: OPNET IT Guru for Education

It should be obvious from the preceding that IT Guru is an industrial strength network simulation and analysis tool. And indeed that is how OPNET is marketing it – it is not particularly a product exclusively designed for use in the classroom. IT Guru In other words IT Guru is not intrinsically for education nor has it been created purely for classroom use. However OPNET supports the use of IT Guru in the classroom primarily by making IT Guru freely available for academic use. IT Guru’s role in the classroom extends beyond merely learning networking technologies. Learning IT Guru is itself a worthwhile classroom objective because IT Guru is industrial strength software with real world applications and career paths. It is sort of like Microsoft Visual Studio – it can be used in the classroom of course to teach programming with C# or C++. But learning Visual Studio is more than simply learning programming – in mastering it one is actually a step closer to being a real-world programming professional. And Visual Studio is hardly a tool designed purely for education.

Though IT Guru itself can be made the learning objective not very many schools can afford to offer a course exclusively on it. IT Guru’s educational potential will typically be that of teaching networking technologies. The question then is how best to use it to teach networking technologies.

It has numerous modules and several distinct methods of creating topologies. Which of these modules and methods of VNE creation and subsequent manipulation would work well for the purposes of pedagogy? Prima facie the simplest approach for the run of the mill course seems to be that of creating a VNE manually and manipulating it via DES. Mapping a topology via automated methods (for example with VNE server) might be too advanced for a regular course. If the context is that of distant education it is entirely unlikely that a distance education student would be able utilize VNE server – for such an individual typically sits at a single workstation possibly at home. In a non distance-learning context, however, ACE and VNE server might make for exciting components to an advanced level course.

For instance imagine advanced networking students generating the university’s topology using ACE and VNE server. They could then manipulate the model in various ways possibly in conjunction with the network administrative staff. There are surely many possibilities. At any rate since IT Guru is already adopted in some educational institutions it is appropriate to briefly review such use. At Murdoch University (Australia) IT Guru has been used in a network communications course to teach client-server solutions paradigm. In one lab students are asked to compare different client server topologies from the point of view of network performance – they start out with a 20 workstation network hooked to a single server machine running FTP, E-Mail and Database servers.


Then the FTP server is placed on a different machine by itself. Finally the FTP server is moved onto a separate wire. Via IT Guru’s Discrete Event Simulation performance statistics analysis students learn that the latter topology is the fastest. In another lab, more complicated, students have to come up with the best network configuration (hardware and software) for a small business, given various constraints like costs. Here they design a suitable VNE from scratch in IT Guru and run simulations with DES. They then factor in costs for various configurations and submit their final design along with all relevant work. (Dixon, McGill and Karlsson 72-73) At the Rochester Institute of Technology (New York) OPNET simulation products are deployed in the regular classroom to teach networking.

There are several different ways in which it is being used. In one type of lab students build token ring and Ethernet networks with Opnet and compare performance under various situations. In another, rather different, type of context they use Opnet to design suitable networks for non-profit organizations seeking to deploy networks for their organizational benefit. In other words students are formed into groups to consult for real world “clients” – these are typically nonprofits in need of network technology assistance – perhaps the client is looking to institute an important upgrade or even a new network from scratch. Instructors act as resources to the student groups and also review student work and recommendations. Students have to work with the client to come up with requirements, design, and finally implementation type documents. Student use OPNET to justify and model optimum solutions. (Perez-Hardy 94f) build


Neither of the above institutions mentioned appear to be using things like VNE server or even for that matter ACE. And they have deployed OPNET in the regular classroom and not in a distance format and so there is no issue of lack of lab resources for mounting a VNE server. But just because these perhaps advanced features of OPNET have not been utilized thus far does not imply that they should not be so used by some curriculum in the future. Certainly abroad – in Europe – some institutions have incorporated application trace capture exercises in their curricula. Recall that application traces can be imported via ACE and this is indeed what the students do – they capture traces of, say, their Usenet sessions, on their local computer. (J. Theunis, B. Van den Broeck et. al. 3)

Regardless, in the remaining part of this work - very much in line with current the majority general pedagogy - the focus will be on manual topology building and subsequent DES based simulation running using the topology. First a “getting started” type tutorial and later sample IT Guru labs that could be a starting point for a range of courses on networking.

Chapter 6: OPNET IT Guru Multimedia Quickstart and Labs

While it is possible to construct a tutorial with appropriate screen captures and the like it may be more helpful to literally demonstrate the basics of operating IT Guru using demonstration multimedia tools. This tutorial can be viewed opening the web page file called “SimpleSim.htm” – it is linked to a Flash file called “SimpleSim.swf.” It shows how to create and run (using DES) a very simple network topology – a single workstation hooked to a server. Version 10.5 is the version of IT Guru shown in the demo. OPNET Labs Once the decision is made to deploy IT Guru in support of a course – distance learning or otherwise – the issue of precisely how to leverage it arises. Given the sophistication of the tool the range of choices for using it are vast. A range of appropriate labs can be created on virtually any networking topic. In the textbook world there is even a lab manual available now – Computer Networks: Network Simulation Experiments Manual – by Emad Aboelela. In this excellent work Aboelela has hit a range of topics – from token ring to VPN – and the labs are exclusively for IT Guru. However it may be that the manual is a bit too sophisticated for the introductory to intermediate networking student and beginning user of IT Guru.


It is certainly not for the neophyte. In this paper a set of three labs is produced with appropriate screen captures from OPNET IT Guru Version 10.5. They are appropriate for someone who is at the introductory to intermediate level with networking technology. They provide a way of learning features of OPNET in addition to being hands on review of some aspects of standard networking theory. They are written in a generic way – they are intended to be worthwhile anywhere from advanced high-school curriculum to graduate school. It should be noted that IT Guru may be installed right on the student’s own machine (OPNET IT Guru 9.5 is downloadable free for educational use) or alternatively it may be mounted on a suitable server or lab to which the student is given access – either physically or online.


Lab 1: Hubs versus Switches in Small Business LAN

Goal : The goal of this lab is to compare performance of pure hub LAN with switched LAN in a tiny network.

Overview

We will create two scenarios. In one scenario there are five workstations that connect to a web server via a hub. Relevant performance statistics will be collected at both the workstations and the server. The same will be done in a second scenario except that instead of a hub it will be a switch facilitating the connection between server and workstations.

IT Guru Step by Step Procedure

Step 1. Launch IT Guru and create a new project – hub_switch_project.
Step 2. Create a scenario – hub_scenario. Later we will add another scenario into the same project - switch_scenario.
Step 3. Choose the default model library and default scenario dimensions.
Step 4. Drag five Ethernet workstations and a Server into the construction area and connect them up with the aid of a hub. The topology should look like the screen capture below:

 

 Step 5. Add profile and application nodes.
Step 6. Open the attributes window for application node and select “Default” for the Application Definitions row. This makes all standard network applications available for use in our topology – HTTP, FTP, E-Mail, Database, etc.
Step 7. We will create a custom profile – web application user profile – let us call the profile “web user.” To get there, go under the edit box – attributes window - for the profile. It looks as follows.

Go to profile configuration – it is highlighted above – and select “edit”. A new mini-window opens up – profile configuration table window – select row #1. It should look as follows:

Now under Profile Name change the name to “Web User”. Change the entry under Repeatability column to “unlimited”. Under Applications select edit and a new window pops out – this is the Applications Table window. Here we will select an application that will be associated with the Web User profile. Select row 1 and pick “web browsing heavy.” It should look as follows:

Close all open windows. At this stage we have created a new profile called “Web User” and this profile can be applied in our topology.

Step 8. Apply the profile “Web User” to all the workstations. This can be conveniently done by holding the control key down and selecting all five workstations and then making the appropriate change in the attribute window of any ONE workstation. One must make sure that the “Apply changes to selected objects” is checked on however in the attribute window of the workstation. The profile is applied by first opening the Applications tree. In the row entry for Application Supported Profiles select edit. A new window opens – Supported Profiles window – here go to row 1 and select Web User. It should look something like the following:

Step 9. Proceed to configuring the server. Select edit attributes, open the Applications tree and go to the Application Supported Services row. Select edit. A new window – the Applications Services Table window – opens up. Select row 1 and choose web browsing heavy. Essentially a generic HTTP server is set up on this machine at this stage. It may look as follows:

Step 10. Choose the statistics that ought to be collected during a simulation run. Under the DES menu bar select “choose individual statistics.” In the resulting window select the tree for “node statistics”. There are a number of options. Of particular interest for the purpose of this lab may be:

Under Client HTTP: Object Response Time, Page Response Time, Traffic Sent and Traffic Received, User Cancelled Connections. Under Server HTTP: Load, Traffic Received, and Traffic Sent. Under TCP: Connection Aborts, Delay and Retransmission count. A screen capture of the DES statistics window looks like this:

Step 11. Run the simulation by choosing “Configure/Run DES simulation” under the DES menu.
Step 12. Examine the results by selecting DES menu -> results -> view statistics. The statistics window might look as follows:

Step 13. To find a useful contrast let us now create another scenario within the same project. It is convenient to duplicate the entire topology for the hub scenario into the work area of the new scenario and subsequently make changes to the copy. Go under the scenario menu and select duplicate scenario. Name it “switch scenario.” A new work area opens up with a duplicate of the hub scenario. Select an Ethernet switch from the objects window (click on the open object palette button if it is not visible) and place it in lieu of the hub. Step 14. Run the switch scenario with the same statistics that were selected for the hub scenario. It is possible to compare the two statistics simultaneously – view it on the same graph – by selecting the All Scenarios option in the drop down list. Different colors are used for the different data. Examine all the performance data and answer the following questions.

Lab Observations and Questions

(1) In which scenario is there greater page loading delay? Explain why.
(2) Are there any worthwhile differences in any of the other statistics that were collected? Explain why one would expect differences or identical results.
(3) Collect more statistics of your choice.

Lab Concluding Remarks

The lab should show that when there is a very small client/server network switches are worse than hubs from a performance point of view. This is explained due to latency involved in the switching process. The figure below is a screen capture showing page delay (points in red are from the switched scenario):

Lab 2: Hubs versus switches in medium scale LAN

Goal: The objective is to contrast the performance of hubs and switches in a medium scale LAN.

Overview
We will construct two scenarios – call them - hub_scenario and switch_scenario - under a new project called “medium_hub_switch”. The number of workstations will be at the medium scale – about 120 machines – each running web user profiles connecting to a web server. In one scenario the machines are hooked up exclusively to a hierarchy of hubs and bridges while in another a couple of switches come into play.

IT Guru Step by Step Procedure

Step 1. Create a new project called medium_hub_switch. Create an empty scenario called “hub_scenario.”
Step 2. Choose a different model library than the default one by going to the object palate window and selecting the Ethernet model library from the drop down list. A new list of objects should appear.
Step 3. We will create a subnet. Drag the subnet icon into the workspace. It should look as follows:

Step 4. Double click on the subnet icon – this will open up a new window – the subnet window for the subnet.
Step 5. Create a new topology for the subnet using rapid network configuration. Go under the topology menu and select rapid configuration. Choose star. Choose Ethernet hub for the “center” and Ethernet workstations for the periphery. Make them 14 workstations. Select the 100 Base T connectivity link. It should look as follows:

Step 6. Click OK and IT Guru should automatically generate 14 workstations linked in star shape to a hub.
Step 7. Create another 14 workstation linked to a hub topology in the subnet and place them alongside each other. (This can be done either by copying and pasting or by going through the rapid configuration menu again.)
Step 8. Add an application profile icon to the workspace and create a profile called Web User (see Lab 1 for review of how to do this). Apply this profile to all the workstations in the subnet.
Step 9. Drag in a bridge into the workspace and connect the two central hubs to the bridge. The result should look as follows:

Step 10. Return to the parent subnet window by clicking on the ‘Go to Parent Subnet’ button.
Step 11. Copy the subnet icon that was just created and paste it at least three to four times – approximately 80-120 workstations in total now from all subnets.
Step 12. Drag in a hub into the workspace and hook up the subnets to the hub via 100 Base T connections. During this process make sure to hook the hub to the bridge node in the subnet. In other words the link should be between the bridge in each subnet to the hub.
Step 13. Link the hub to an Ethernet server. (Make sure the server acts as a HTTP server – drag in an application profile icon into the workspace to facilitate this – review Lab 1 for details.)
Step 14. From DES menu select choose statistics and pick the page delay statistic for client HTTP. This is the key statistic for performance comparison between hubs versus switches. However in addition select any other statistic that may be of interest. Close the screen when done. The screen should look something like the following at this stage:

Step 15. Run the scenario. It may take several minutes under default settings.
Step 16. There may be a number of warnings generated in the simulation log file to the effect that TCP connections were timed out. Changing the TCP parameter in the workstations to allow more than 3 reconnect attempts (the default) may dispel some warnings on a subsequent run of the simulation. However the underlying problem is network congestion!
Step 17. Review the statistics collected. A number of nodes should have might have failed to secure connections with the server. There might be page delays running into the 10 seconds to 50 seconds range!
Step 18. Duplicate the current scenario into a new scenario called switch_scenario.
Step 19. Replace the bridges under each subnet with a switch.
Step 20. Replace the hub in the top-level network with again a switch. The top level may look as follows – the center entity is the switch below:

Step 21. Select the same statistics as in hub_scenario – the client HTTP page delay statistic and run the simulation. It may take several minutes to run.
Step 22. View the results. Compare the results. The red dots represent the switched scenario while the blue ones the hub/bridge scenario. A screenshot of the comparison is given below:

Lab Observation Questions and Mini-Labs for Further Study

(1) In which scenario is there greater page loading delay? Explain why.
(2) Are there any worthwhile differences in any of the other statistics that were (optionally) collected? Explain why one would expect differences or identical results.
(3) Re-run the switch_scenario by replacing switches in the subnets with bridges in all the subnets. What happens to the performance then – to the page delay statistic?
(4) Re-run the hub_scenario by replacing the central hub in the top-level network with a bridge. What happens to the performance then – to the page delay statistic?
(5) Re-run the switch_scenario by replacing the top-level switch with a hub but retaining the switches in all subnets. What happens to the performance then – to the page delay statistic?
(6) Write a report tabulating the different possible permutations. Extra Credit (7): Speculate on performance when the network scale increases to a 1000+ workstations. Build appropriate networks in IT Guru using techniques learned in this lab to test hypotheses.
Lab Concluding Remarks
Clearly as the number of workstations increases towards the 100 range the performance of hubs drops sharply – even when joined with bridges at the subnet level. But a bridge at the toplevel (instead of the hub) improves performance dramatically. Switching on the other hand is effective in all configurations.


Lab 3: Viewing Simulation Routing Tables (Parts of this lab were inspired by the RIP Lab from: Aboelela, 77-88)

Goal: The objective in this lab is to simulate routing in a small WAN setting. Routing tables generated by the simulation will be exported to a file for viewing. The routing protocol in effect is RIP.

Overview
The idea is to set-up a campus LAN/WAN linked together by routers. The routers will run RIP. The routing table of a router will be exported to a file for examination.

IT Guru Step by Step Procedures

Step 1. Create a new project named “router_project”. Accept the default name for the scenario. Make sure to select “campus” for the scenario topology.
Step 2. Drag in four “Ethernet4_slip8_gty” routers into the workspace (this is a model in the object palette called “internet toolbox” the default model palette.
Step 3. Connect each router to the other in a ring using ppp_ds3 link. As in the following screen capture:

Step 4. Drag in the 100-T LAN icons into the workspace – there may be two for each router. Each router connects to two LANs – possibly in a separate building somewhere in campus. Each LAN icon represents a LAN – by default each contains 10 workstations – it may be configured at will by opening the relevant attribute window. It may look as follows (this topology is from Aboelela 80):

Step 5. Open the edit attributes window of any one router and expand Reports. In the RIP routing table export row select “Once at End of Simulation.” It may look as below:

Step 6. Run the simulation.
Step 7. Open the results window and select the Discrete Events Table tab. Open up the tree node hierarchy until the routing table appears for the router. It may look as follows:

Lab Observation Questions and Mini-Labs for Further Study

(1) What is the maximum hop count? Why?
(2) What is the minimum hop count? Why?
(3) Re-run the scenario after erasing one of the links from one router to another. What happens to the hop count?
Lab Concluding Remarks
In this lab we observed how a router running RIP generates routing tables. More advanced work along the same lines is possible by changing the router topology in various ways and by possibly failing links and routers mid-way during the simulation.

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3.collection tutors for opnet learning - IT guru opnet Part 3
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9.collection tutors for opnet learning - IT guru opnet Part 8

Featured Textbooks and Lab Materials

For IT Guru Academic Edition

• Business Data Communications--Sixth Edition by William Stallings(textbook)
• Business Data Communications and Networking--11th Edition by Jerry Fitzgerald & Alan Dennis (textbook|online lab manual)
• Business Data Networks and Telecommunications--Fourth Edition by Raymond R. Panko (textbook | online lab manual)
• Computer Networks - A Systems Approach--Third Edition by Larry L. Peterson & Bruce S. Davie (textbook)
• Data and Computer Communications--Seventh Edition by William Stallings (textbook)
• OPNET IT Guru Academic Edition – A Tool for Networking Education - Regis University, USA (online lab manual)
• Security Labs in IT Guru Academic Edition – Universitat Ramon Llull, Spain (online lab manual)
• Simulacao Computacional para Redes de Computadores - First edition by Paulo Dias de Alecrim (textbook)

For OPNET Modeler®

• OPNET Modeler® User Manual - Technical University of Catalonia, Spain (online lab manual)
• OPNET Modeler® Tutorial - INATEL, Brazil (online lab manual)
• Lab Exercises Based on OPNET Modeler® - Blekinge Institute of Technology, Sweden (online lab manual)

Proceedings from OPNETWORK 2011 Academic Session

• Session 1020: Academic Instruction Using OPNET software

How to download files (video, mp3, mp4, avi,pdf etc) on Linux open terminal usig command (ubuntu 12.10)

How to download files (video, mp3, mp4, avi,pdf etc) on Linux open terminal using command (ubuntu 12.10)


CTRL+ALT+T to open terminal
example:
vina@vinay:/media/backup$ wget -r -l0 wapmint.com/datas/load/Games/Nokia%20Games/Java%20Games%20Collection/PipeDream.jar

Linux / Unix Command: wget
Command Library

Action     Command
Download file     wget http://link-to-file
Resumable Downloads     wget -c http://link-to-file
Download Entire Website     wget -r http://link-to-site
Download Only PDFs from a page     wget -A.pdf -r -l1 -nd --no-parent http://link-to-webpage
Download Only mp3 files from a page     wget -A.mp3 -r -l1 -nd --no-parent http://link-to-webpage
Donot Download mp3 files from a page     wget -R.mp3 -r -l1 -nd --no-parent http://link-to-webpage
Ignore robots.txt     wget -erobots=off http://link-to-fileordirectory
Limit download Speed in kbps     wget --limit-rate=20 http://url-to-fileorwebsite
Mask as firefox or act as firefox     wget -U Mozilla http://your-link-to/file



NAME
wget - GNU Wget Manual
SYNOPSIS
wget [option]... [URL]...
EXAMPLES
DESCRIPTION
GNU Wget is a free utility for non-interactive download of files from the Web. It supports HTTP, HTTPS, and FTP protocols, as well as retrieval through HTTP proxies.

Wget is non-interactive, meaning that it can work in the background, while the user is not logged on. This allows you to start a retrieval and disconnect from the system, letting Wget finish the work. By contrast, most of the Web browsers require constant user's presence, which can be a great hindrance when transferring a lot of data.

Wget can follow links in HTML pages and create local versions of remote web sites, fully recreating the directory structure of the original site. This is sometimes referred to as ``recursive downloading.'' While doing that, Wget respects the Robot Exclusion Standard (/robots.txt). Wget can be instructed to convert the links in downloaded HTML files to the local files for offline viewing.

Wget has been designed for robustness over slow or unstable network connections; if a download fails due to a network problem, it will keep retrying until the whole file has been retrieved. If the server supports regetting, it will instruct the server to continue the download from where it left off.
-V
--version
    Display the version of Wget.
-h
--help
    Print a help message describing all of Wget's command-line options.
-b
--background
    Go to background immediately after startup. If no output file is specified via the -o, output is redirected to wget-log.
-e command
--execute command
    Execute command as if it were a part of .wgetrc. A command thus invoked will be executed after the commands in .wgetrc, thus taking precedence over them.

Logging and Input File Options

-o logfile
--output-file=logfile
    Log all messages to logfile. The messages are normally reported to standard error.
-a logfile
--append-output=logfile
    Append to logfile. This is the same as -o, only it appends to logfile instead of overwriting the old log file. If logfile does not exist, a new file is created.
-d
--debug
    Turn on debug output, meaning various information important to the developers of Wget if it does not work properly. Your system administrator may have chosen to compile Wget without debug support, in which case -d will not work. Please note that compiling with debug support is always safe---Wget compiled with the debug support will not print any debug info unless requested with -d.
-q
--quiet
    Turn off Wget's output.
-v
--verbose
    Turn on verbose output, with all the available data. The default output is verbose.
-nv
--non-verbose
    Non-verbose output---turn off verbose without being completely quiet (use -q for that), which means that error messages and basic information still get printed.
-i file
--input-file=file
    Read URLs from file, in which case no URLs need to be on the command line. If there are URLs both on the command line and in an input file, those on the command lines will be the first ones to be retrieved. The file need not be an HTML document (but no harm if it is)---it is enough if the URLs are just listed sequentially.

    However, if you specify --force-html, the document will be regarded as html. In that case you may have problems with relative links, which you can solve either by adding "" to the documents or by specifying --base=url on the command line.
-F
--force-html
    When input is read from a file, force it to be treated as an HTML file. This enables you to retrieve relative links from existing HTML files on your local disk, by adding "" to HTML, or using the --base command-line option.
-B URL
--base=URL
    When used in conjunction with -F, prepends URL to relative links in the file specified by -i.

Download Options

--bind-address=ADDRESS
    When making client TCP/IP connections, "bind()" to ADDRESS on the local machine. ADDRESS may be specified as a hostname or IP address. This option can be useful if your machine is bound to multiple IPs.
-t number
--tries=number
    Set number of retries to number. Specify 0 or inf for infinite retrying.
-O file
--output-document=file
    The documents will not be written to the appropriate files, but all will be concatenated together and written to file. If file already exists, it will be overwritten. If the file is -, the documents will be written to standard output. Including this option automatically sets the number of tries to 1.
-nc
--no-clobber
    If a file is downloaded more than once in the same directory, Wget's behavior depends on a few options, including -nc. In certain cases, the local file will be clobbered, or overwritten, upon repeated download. In other cases it will be preserved.

    When running Wget without -N, -nc, or -r, downloading the same file in the same directory will result in the original copy of file being preserved and the second copy being named file.1. If that file is downloaded yet again, the third copy will be named file.2, and so on. When -nc is specified, this behavior is suppressed, and Wget will refuse to download newer copies of file. Therefore, ``"no-clobber"'' is actually a misnomer in this mode---it's not clobbering that's prevented (as the numeric suffixes were already preventing clobbering), but rather the multiple version saving that's prevented.

    When running Wget with -r, but without -N or -nc, re-downloading a file will result in the new copy simply overwriting the old. Adding -nc will prevent this behavior, instead causing the original version to be preserved and any newer copies on the server to be ignored.

    When running Wget with -N, with or without -r, the decision as to whether or not to download a newer copy of a file depends on the local and remote timestamp and size of the file. -nc may not be specified at the same time as -N.

    Note that when -nc is specified, files with the suffixes .html or (yuck) .htm will be loaded from the local disk and parsed as if they had been retrieved from the Web.
-c
--continue
    Continue getting a partially-downloaded file. This is useful when you want to finish up a download started by a previous instance of Wget, or by another program. For instance:

            wget -c ftp://sunsite.doc.ic.ac.uk/ls-lR.Z

    If there is a file named ls-lR.Z in the current directory, Wget will assume that it is the first portion of the remote file, and will ask the server to continue the retrieval from an offset equal to the length of the local file.

    Note that you don't need to specify this option if you just want the current invocation of Wget to retry downloading a file should the connection be lost midway through. This is the default behavior. -c only affects resumption of downloads started prior to this invocation of Wget, and whose local files are still sitting around.

    Without -c, the previous example would just download the remote file to ls-lR.Z.1, leaving the truncated ls-lR.Z file alone.

    Beginning with Wget 1.7, if you use -c on a non-empty file, and it turns out that the server does not support continued downloading, Wget will refuse to start the download from scratch, which would effectively ruin existing contents. If you really want the download to start from scratch, remove the file.

    Also beginning with Wget 1.7, if you use -c on a file which is of equal size as the one on the server, Wget will refuse to download the file and print an explanatory message. The same happens when the file is smaller on the server than locally (presumably because it was changed on the server since your last download attempt)---because ``continuing'' is not meaningful, no download occurs.

    On the other side of the coin, while using -c, any file that's bigger on the server than locally will be considered an incomplete download and only "(length(remote) - length(local))" bytes will be downloaded and tacked onto the end of the local file. This behavior can be desirable in certain cases---for instance, you can use wget -c to download just the new portion that's been appended to a data collection or log file.

    However, if the file is bigger on the server because it's been changed, as opposed to just appended to, you'll end up with a garbled file. Wget has no way of verifying that the local file is really a valid prefix of the remote file. You need to be especially careful of this when using -c in conjunction with -r, since every file will be considered as an ``incomplete download'' candidate.

    Another instance where you'll get a garbled file if you try to use -c is if you have a lame HTTP proxy that inserts a ``transfer interrupted'' string into the local file. In the future a ``rollback'' option may be added to deal with this case.

    Note that -c only works with FTP servers and with HTTP servers that support the "Range" header.
--progress=type
    Select the type of the progress indicator you wish to use. Legal indicators are ``dot'' and ``bar''.

    The ``bar'' indicator is used by default. It draws an ASCII progress bar graphics (a.k.a ``thermometer'' display) indicating the status of retrieval. If the output is not a TTY, the ``dot'' bar will be used by default.

    Use --progress=dot to switch to the ``dot'' display. It traces the retrieval by printing dots on the screen, each dot representing a fixed amount of downloaded data.

    When using the dotted retrieval, you may also set the style by specifying the type as dot:style. Different styles assign different meaning to one dot. With the "default" style each dot represents 1K, there are ten dots in a cluster and 50 dots in a line. The "binary" style has a more ``computer''-like orientation---8K dots, 16-dots clusters and 48 dots per line (which makes for 384K lines). The "mega" style is suitable for downloading very large files---each dot represents 64K retrieved, there are eight dots in a cluster, and 48 dots on each line (so each line contains 3M).

    Note that you can set the default style using the "progress" command in .wgetrc. That setting may be overridden from the command line. The exception is that, when the output is not a TTY, the ``dot'' progress will be favored over ``bar''. To force the bar output, use --progress=bar:force.
-N
--timestamping
    Turn on time-stamping.
-S
--server-response
    Print the headers sent by HTTP servers and responses sent by FTP servers.
--spider
    When invoked with this option, Wget will behave as a Web spider, which means that it will not download the pages, just check that they are there. You can use it to check your bookmarks, e.g. with:

            wget --spider --force-html -i bookmarks.html


    This feature needs much more work for Wget to get close to the functionality of real WWW spiders.
-T seconds
--timeout=seconds
    Set the read timeout to seconds seconds. Whenever a network read is issued, the file descriptor is checked for a timeout, which could otherwise leave a pending connection (uninterrupted read). The default timeout is 900 seconds (fifteen minutes). Setting timeout to 0 will disable checking for timeouts.

    Please do not lower the default timeout value with this option unless you know what you are doing.
--limit-rate=amount
    Limit the download speed to amount bytes per second. Amount may be expressed in bytes, kilobytes with the k suffix, or megabytes with the m suffix. For example, --limit-rate=20k will limit the retrieval rate to 20KB/s. This kind of thing is useful when, for whatever reason, you don't want Wget to consume the entire evailable bandwidth.

    Note that Wget implementeds the limiting by sleeping the appropriate amount of time after a network read that took less time than specified by the rate. Eventually this strategy causes the TCP transfer to slow down to approximately the specified rate. However, it takes some time for this balance to be achieved, so don't be surprised if limiting the rate doesn't work with very small files. Also, the ``sleeping'' strategy will misfire when an extremely small bandwidth, say less than 1.5KB/s, is specified.
-w seconds
--wait=seconds
    Wait the specified number of seconds between the retrievals. Use of this option is recommended, as it lightens the server load by making the requests less frequent. Instead of in seconds, the time can be specified in minutes using the "m" suffix, in hours using "h" suffix, or in days using "d" suffix.

    Specifying a large value for this option is useful if the network or the destination host is down, so that Wget can wait long enough to reasonably expect the network error to be fixed before the retry.
--waitretry=seconds
    If you don't want Wget to wait between every retrieval, but only between retries of failed downloads, you can use this option. Wget will use linear backoff, waiting 1 second after the first failure on a given file, then waiting 2 seconds after the second failure on that file, up to the maximum number of seconds you specify. Therefore, a value of 10 will actually make Wget wait up to (1 + 2 + ... + 10) = 55 seconds per file.

    Note that this option is turned on by default in the global wgetrc file.
--random-wait
    Some web sites may perform log analysis to identify retrieval programs such as Wget by looking for statistically significant similarities in the time between requests. This option causes the time between requests to vary between 0 and 2 * wait seconds, where wait was specified using the -w or --wait options, in order to mask Wget's presence from such analysis.

    A recent article in a publication devoted to development on a popular consumer platform provided code to perform this analysis on the fly. Its author suggested blocking at the class C address level to ensure automated retrieval programs were blocked despite changing DHCP-supplied addresses.

    The --random-wait option was inspired by this ill-advised recommendation to block many unrelated users from a web site due to the actions of one.
-Y on/off
--proxy=on/off
    Turn proxy support on or off. The proxy is on by default if the appropriate environmental variable is defined.
-Q quota
--quota=quota
    Specify download quota for automatic retrievals. The value can be specified in bytes (default), kilobytes (with k suffix), or megabytes (with m suffix).

    Note that quota will never affect downloading a single file. So if you specify wget -Q10k ftp://wuarchive.wustl.edu/ls-lR.gz, all of the ls-lR.gz will be downloaded. The same goes even when several URLs are specified on the command-line. However, quota is respected when retrieving either recursively, or from an input file. Thus you may safely type wget -Q2m -i sites---download will be aborted when the quota is exceeded.

    Setting quota to 0 or to inf unlimits the download quota.

Directory Options

-nd
--no-directories
    Do not create a hierarchy of directories when retrieving recursively. With this option turned on, all files will get saved to the current directory, without clobbering (if a name shows up more than once, the filenames will get extensions .n).
-x
--force-directories
    The opposite of -nd---create a hierarchy of directories, even if one would not have been created otherwise. E.g. wget -x http://fly.srk.fer.hr/robots.txt will save the downloaded file to fly.srk.fer.hr/robots.txt.
-nH
--no-host-directories
    Disable generation of host-prefixed directories. By default, invoking Wget with -r http://fly.srk.fer.hr/ will create a structure of directories beginning with fly.srk.fer.hr/. This option disables such behavior.
--cut-dirs=number
    Ignore number directory components. This is useful for getting a fine-grained control over the directory where recursive retrieval will be saved.

    Take, for example, the directory at ftp://ftp.xemacs.org/pub/xemacs/. If you retrieve it with -r, it will be saved locally under ftp.xemacs.org/pub/xemacs/. While the -nH option can remove the ftp.xemacs.org/ part, you are still stuck with pub/xemacs. This is where --cut-dirs comes in handy; it makes Wget not ``see'' number remote directory components. Here are several examples of how --cut-dirs option works.

            No options        -> ftp.xemacs.org/pub/xemacs/
            -nH               -> pub/xemacs/
            -nH --cut-dirs=1  -> xemacs/
            -nH --cut-dirs=2  -> .


            --cut-dirs=1      -> ftp.xemacs.org/xemacs/
            ...


    If you just want to get rid of the directory structure, this option is similar to a combination of -nd and -P. However, unlike -nd, --cut-dirs does not lose with subdirectories---for instance, with -nH --cut-dirs=1, a beta/ subdirectory will be placed to xemacs/beta, as one would expect.
-P prefix
--directory-prefix=prefix
    Set directory prefix to prefix. The directory prefix is the directory where all other files and subdirectories will be saved to, i.e. the top of the retrieval tree. The default is . (the current directory).

HTTP Options

-E
--html-extension
    If a file of type text/html is downloaded and the URL does not end with the regexp \.[Hh][Tt][Mm][Ll]?, this option will cause the suffix .html to be appended to the local filename. This is useful, for instance, when you're mirroring a remote site that uses .asp pages, but you want the mirrored pages to be viewable on your stock Apache server. Another good use for this is when you're downloading the output of CGIs. A URL like http://site.com/article.cgi?25 will be saved as article.cgi?25.html.

    Note that filenames changed in this way will be re-downloaded every time you re-mirror a site, because Wget can't tell that the local X.html file corresponds to remote URL X (since it doesn't yet know that the URL produces output of type text/html. To prevent this re-downloading, you must use -k and -K so that the original version of the file will be saved as X.orig.
--http-user=user
--http-passwd=password
    Specify the username user and password password on an HTTP server. According to the type of the challenge, Wget will encode them using either the "basic" (insecure) or the "digest" authentication scheme.

    Another way to specify username and password is in the URL itself. Either method reveals your password to anyone who bothers to run "ps". To prevent the passwords from being seen, store them in .wgetrc or .netrc, and make sure to protect those files from other users with "chmod". If the passwords are really important, do not leave them lying in those files either---edit the files and delete them after Wget has started the download.

    For more information about security issues with Wget,
-C on/off
--cache=on/off
    When set to off, disable server-side cache. In this case, Wget will send the remote server an appropriate directive (Pragma: no-cache) to get the file from the remote service, rather than returning the cached version. This is especially useful for retrieving and flushing out-of-date documents on proxy servers.

    Caching is allowed by default.
--cookies=on/off
    When set to off, disable the use of cookies. Cookies are a mechanism for maintaining server-side state. The server sends the client a cookie using the "Set-Cookie" header, and the client responds with the same cookie upon further requests. Since cookies allow the server owners to keep track of visitors and for sites to exchange this information, some consider them a breach of privacy. The default is to use cookies; however, storing cookies is not on by default.
--load-cookies file
    Load cookies from file before the first HTTP retrieval. file is a textual file in the format originally used by Netscape's cookies.txt file.

    You will typically use this option when mirroring sites that require that you be logged in to access some or all of their content. The login process typically works by the web server issuing an HTTP cookie upon receiving and verifying your credentials. The cookie is then resent by the browser when accessing that part of the site, and so proves your identity.

    Mirroring such a site requires Wget to send the same cookies your browser sends when communicating with the site. This is achieved by --load-cookies---simply point Wget to the location of the cookies.txt file, and it will send the same cookies your browser would send in the same situation. Different browsers keep textual cookie files in different locations:

        Netscape 4.x.
            The cookies are in ~/.netscape/cookies.txt.
        Mozilla and Netscape 6.x.
            Mozilla's cookie file is also named cookies.txt, located somewhere under ~/.mozilla, in the directory of your profile. The full path usually ends up looking somewhat like ~/.mozilla/default/some-weird-string/cookies.txt.
        Internet Explorer.
            You can produce a cookie file Wget can use by using the File menu, Import and Export, Export Cookies. This has been tested with Internet Explorer 5; it is not guaranteed to work with earlier versions.
        Other browsers.
            If you are using a different browser to create your cookies, --load-cookies will only work if you can locate or produce a cookie file in the Netscape format that Wget expects.

        If you cannot use --load-cookies, there might still be an alternative. If your browser supports a ``cookie manager'', you can use it to view the cookies used when accessing the site you're mirroring. Write down the name and value of the cookie, and manually instruct Wget to send those cookies, bypassing the ``official'' cookie support:

                wget --cookies=off --header "Cookie: I=I"


--save-cookies file
    Save cookies from file at the end of session. Cookies whose expiry time is not specified, or those that have already expired, are not saved.
--ignore-length
    Unfortunately, some HTTP servers (CGI programs, to be more precise) send out bogus "Content-Length" headers, which makes Wget go wild, as it thinks not all the document was retrieved. You can spot this syndrome if Wget retries getting the same document again and again, each time claiming that the (otherwise normal) connection has closed on the very same byte.

    With this option, Wget will ignore the "Content-Length" header---as if it never existed.
--header=additional-header
    Define an additional-header to be passed to the HTTP servers. Headers must contain a : preceded by one or more non-blank characters, and must not contain newlines.

    You may define more than one additional header by specifying --header more than once.

            wget --header='Accept-Charset: iso-8859-2' \
                 --header='Accept-Language: hr'        \
                   http://fly.srk.fer.hr/

    Specification of an empty string as the header value will clear all previous user-defined headers.
--proxy-user=user
--proxy-passwd=password
    Specify the username user and password password for authentication on a proxy server. Wget will encode them using the "basic" authentication scheme.

    Security considerations similar to those with --http-passwd pertain here as well.
--referer=url
    Include `Referer: url' header in HTTP request. Useful for retrieving documents with server-side processing that assume they are always being retrieved by interactive web browsers and only come out properly when Referer is set to one of the pages that point to them.
-s
--save-headers
    Save the headers sent by the HTTP server to the file, preceding the actual contents, with an empty line as the separator.
-U agent-string
--user-agent=agent-string
    Identify as agent-string to the HTTP server.

    The HTTP protocol allows the clients to identify themselves using a "User-Agent" header field. This enables distinguishing the WWW software, usually for statistical purposes or for tracing of protocol violations. Wget normally identifies as Wget/version, version being the current version number of Wget.

    However, some sites have been known to impose the policy of tailoring the output according to the "User-Agent"-supplied information. While conceptually this is not such a bad idea, it has been abused by servers denying information to clients other than "Mozilla" or Microsoft "Internet Explorer". This option allows you to change the "User-Agent" line issued by Wget. Use of this option is discouraged, unless you really know what you are doing.

FTP Options

-nr
--dont-remove-listing

Don't remove the temporary .listing files generated by FTP retrievals. Normally, these files contain the raw directory listings received from FTP servers. Not removing them can be useful for debugging purposes, or when you want to be able to easily check on the contents of remote server directories (e.g. to verify that a mirror you're running is complete).

Note that even though Wget writes to a known filename for this file, this is not a security hole in the scenario of a user making .listing a symbolic link to /etc/passwd or something and asking "root" to run Wget in his or her directory. Depending on the options used, either Wget will refuse to write to .listing, making the globbing/recursion/time-stamping operation fail, or the symbolic link will be deleted and replaced with the actual .listing file, or the listing will be written to a .listing.number file.

Even though this situation isn't a problem, though, "root" should never run Wget in a non-trusted user's directory. A user could do something as simple as linking index.html to /etc/passwd and asking "root" to run Wget with -N or -r so the file will be overwritten.
-g on/off
--glob=on/off
    Turn FTP globbing on or off. Globbing means you may use the shell-like special characters (wildcards), like *, ?, [ and ] to retrieve more than one file from the same directory at once, like:

            wget ftp://gnjilux.srk.fer.hr/*.msg

    By default, globbing will be turned on if the URL contains a globbing character. This option may be used to turn globbing on or off permanently.

    You may have to quote the URL to protect it from being expanded by your shell. Globbing makes Wget look for a directory listing, which is system-specific. This is why it currently works only with Unix FTP servers (and the ones emulating Unix "ls" output).
--passive-ftp
    Use the passive FTP retrieval scheme, in which the client initiates the data connection. This is sometimes required for FTP to work behind firewalls.
--retr-symlinks
    Usually, when retrieving FTP directories recursively and a symbolic link is encountered, the linked-to file is not downloaded. Instead, a matching symbolic link is created on the local filesystem. The pointed-to file will not be downloaded unless this recursive retrieval would have encountered it separately and downloaded it anyway.

    When --retr-symlinks is specified, however, symbolic links are traversed and the pointed-to files are retrieved. At this time, this option does not cause Wget to traverse symlinks to directories and recurse through them, but in the future it should be enhanced to do this.

    Note that when retrieving a file (not a directory) because it was specified on the commandline, rather than because it was recursed to, this option has no effect. Symbolic links are always traversed in this case.
    Recursive Retrieval Options

    -r
    --recursive
        Turn on recursive retrieving.
    -l depth
    --level=depth
        Specify recursion maximum depth level depth. The default maximum depth is 5.
    --delete-after
        This option tells Wget to delete every single file it downloads, after having done so. It is useful for pre-fetching popular pages through a proxy, e.g.:

                wget -r -nd --delete-after http://whatever.com/~popular/page/


        The -r option is to retrieve recursively, and -nd to not create directories.

        Note that --delete-after deletes files on the local machine. It does not issue the DELE command to remote FTP sites, for instance. Also note that when --delete-after is specified, --convert-links is ignored, so .orig files are simply not created in the first place.
    -k
    --convert-links
        After the download is complete, convert the links in the document to make them suitable for local viewing. This affects not only the visible hyperlinks, but any part of the document that links to external content, such as embedded images, links to style sheets, hyperlinks to non-HTML content, etc.

        Each link will be changed in one of the two ways:

            *
                The links to files that have been downloaded by Wget will be changed to refer to the file they point to as a relative link.

                Example: if the downloaded file /foo/doc.html links to /bar/img.gif, also downloaded, then the link in doc.html will be modified to point to ../bar/img.gif. This kind of transformation works reliably for arbitrary combinations of directories.
            *
                The links to files that have not been downloaded by Wget will be changed to include host name and absolute path of the location they point to.

                Example: if the downloaded file /foo/doc.html links to /bar/img.gif (or to ../bar/img.gif), then the link in doc.html will be modified to point to http://hostname/bar/img.gif.

            Because of this, local browsing works reliably: if a linked file was downloaded, the link will refer to its local name; if it was not downloaded, the link will refer to its full Internet address rather than presenting a broken link. The fact that the former links are converted to relative links ensures that you can move the downloaded hierarchy to another directory.

            Note that only at the end of the download can Wget know which links have been downloaded. Because of that, the work done by -k will be performed at the end of all the downloads.

    -K
    --backup-converted
        When converting a file, back up the original version with a .orig suffix. Affects the behavior of -N.
    -m
    --mirror
        Turn on options suitable for mirroring. This option turns on recursion and time-stamping, sets infinite recursion depth and keeps FTP directory listings. It is currently equivalent to -r -N -l inf -nr.
    -p
    --page-requisites
        This option causes Wget to download all the files that are necessary to properly display a given HTML page. This includes such things as inlined images, sounds, and referenced stylesheets.

        Ordinarily, when downloading a single HTML page, any requisite documents that may be needed to display it properly are not downloaded. Using -r together with -l can help, but since Wget does not ordinarily distinguish between external and inlined documents, one is generally left with ``leaf documents'' that are missing their requisites.

        For instance, say document 1.html contains an "< IMG >" tag referencing 1.gif and an "< A >" tag pointing to external document 2.html. Say that 2.html is similar but that its image is 2.gif and it links to 3.html. Say this continues up to some arbitrarily high number.

        If one executes the command:

                wget -r -l 2 http://I/1.html


        then 1.html, 1.gif, 2.html, 2.gif, and 3.html will be downloaded. As you can see, 3.html is without its requisite 3.gif because Wget is simply counting the number of hops (up to 2) away from 1.html in order to determine where to stop the recursion. However, with this command:

                wget -r -l 2 -p http://I/1.html


        all the above files and 3.html's requisite 3.gif will be downloaded. Similarly,

                wget -r -l 1 -p http://I/1.html


        will cause 1.html, 1.gif, 2.html, and 2.gif to be downloaded. One might think that:

                wget -r -l 0 -p http://I/1.html


        would download just 1.html and 1.gif, but unfortunately this is not the case, because -l 0 is equivalent to -l inf---that is, infinite recursion. To download a single HTML page (or a handful of them, all specified on the commandline or in a -i URL input file) and its (or their) requisites, simply leave off -r and -l:

                wget -p http://I/1.html


        Note that Wget will behave as if -r had been specified, but only that single page and its requisites will be downloaded. Links from that page to external documents will not be followed. Actually, to download a single page and all its requisites (even if they exist on separate websites), and make sure the lot displays properly locally, this author likes to use a few options in addition to -p:

                wget -E -H -k -K -p http://I/I

        To finish off this topic, it's worth knowing that Wget's idea of an external document link is any URL specified in an "< A >" tag, an "" tag, or a "" tag other than "".

    Recursive Accept/Reject Options

    -A acclist --accept acclist
    -R rejlist --reject rejlist
        Specify comma-separated lists of file name suffixes or patterns to accept or reject.
    -D domain-list
    --domains=domain-list
        Set domains to be followed. domain-list is a comma-separated list of domains. Note that it does not turn on -H.
    --exclude-domains domain-list
        Specify the domains that are not to be followed..
    --follow-ftp
        Follow FTP links from HTML documents. Without this option, Wget will ignore all the FTP links.
    --follow-tags=list
        Wget has an internal table of HTML tag / attribute pairs that it considers when looking for linked documents during a recursive retrieval. If a user wants only a subset of those tags to be considered, however, he or she should be specify such tags in a comma-separated list with this option.
    -G list
    --ignore-tags=list
        This is the opposite of the --follow-tags option. To skip certain HTML tags when recursively looking for documents to download, specify them in a comma-separated list.

        In the past, the -G option was the best bet for downloading a single page and its requisites, using a commandline like:

                wget -Ga,area -H -k -K -r http://I/I

        However, the author of this option came across a page with tags like "" and came to the realization that -G was not enough. One can't just tell Wget to ignore "", because then stylesheets will not be downloaded. Now the best bet for downloading a single page and its requisites is the dedicated --page-requisites option.
    -H
    --span-hosts
        Enable spanning across hosts when doing recursive retrieving.
    -L
    --relative
        Follow relative links only. Useful for retrieving a specific home page without any distractions, not even those from the same hosts.
    -I list
    --include-directories=list
        Specify a comma-separated list of directories you wish to follow when downloading Elements of list may contain wildcards.
    -X list
    --exclude-directories=list
        Specify a comma-separated list of directories you wish to exclude from download Elements of list may contain wildcards.
    -np
    --no-parent
        Do not ever ascend to the parent directory when retrieving recursively. This is a useful option, since it guarantees that only the files below a certain hierarchy will be downloaded.

    EXAMPLES
    The examples are divided into three sections loosely based on their complexity.
    Simple Usage

    *
        Say you want to download a URL. Just type:

                wget http://fly.srk.fer.hr/

    *
        But what will happen if the connection is slow, and the file is lengthy? The connection will probably fail before the whole file is retrieved, more than once. In this case, Wget will try getting the file until it either gets the whole of it, or exceeds the default number of retries (this being 20). It is easy to change the number of tries to 45, to insure that the whole file will arrive safely:

                wget --tries=45 http://fly.srk.fer.hr/jpg/flyweb.jpg

    *
        Now let's leave Wget to work in the background, and write its progress to log file log. It is tiring to type --tries, so we shall use -t.

                wget -t 45 -o log http://fly.srk.fer.hr/jpg/flyweb.jpg &

        The ampersand at the end of the line makes sure that Wget works in the background. To unlimit the number of retries, use -t inf.
    *
        The usage of FTP is as simple. Wget will take care of login and password.

                wget ftp://gnjilux.srk.fer.hr/welcome.msg

    *
        If you specify a directory, Wget will retrieve the directory listing, parse it and convert it to HTML. Try:

                wget ftp://prep.ai.mit.edu/pub/gnu/
                links index.html


    Advanced Usage

    *
        You have a file that contains the URLs you want to download? Use the -i switch:

                wget -i I

        If you specify - as file name, the URLs will be read from standard input.
    *
        Create a five levels deep mirror image of the GNU web site, with the same directory structure the original has, with only one try per document, saving the log of the activities to gnulog:

                wget -r http://www.gnu.org/ -o gnulog


    *
        The same as the above, but convert the links in the HTML files to point to local files, so you can view the documents off-line:

                wget --convert-links -r http://www.gnu.org/ -o gnulog


    *
        Retrieve only one HTML page, but make sure that all the elements needed for the page to be displayed, such as inline images and external style sheets, are also downloaded. Also make sure the downloaded page references the downloaded links.

                wget -p --convert-links http://www.server.com/dir/page.html


        The HTML page will be saved to www.server.com/dir/page.html, and the images, stylesheets, etc., somewhere under www.server.com/, depending on where they were on the remote server.
    *
        The same as the above, but without the www.server.com/ directory. In fact, I don't want to have all those random server directories anyway---just save all those files under a download/ subdirectory of the current directory.

                wget -p --convert-links -nH -nd -Pdownload \
                     http://www.server.com/dir/page.html

    *
        Retrieve the index.html of www.lycos.com, showing the original server headers:

                wget -S http://www.lycos.com/

    *
        Save the server headers with the file, perhaps for post-processing.

                wget -s http://www.lycos.com/
                more index.html


    *
        Retrieve the first two levels of wuarchive.wustl.edu, saving them to /tmp.

                wget -r -l2 -P/tmp ftp://wuarchive.wustl.edu/

    *
        You want to download all the GIFs from a directory on an HTTP server. You tried wget http://www.server.com/dir/*.gif, but that didn't work because HTTP retrieval does not support globbing. In that case, use:

                wget -r -l1 --no-parent -A.gif http://www.server.com/dir/

        More verbose, but the effect is the same. -r -l1 means to retrieve recursively, with maximum depth of 1. --no-parent means that references to the parent directory are ignored, and -A.gif means to download only the GIF files. -A ``*.gif'' would have worked too.
    *
        Suppose you were in the middle of downloading, when Wget was interrupted. Now you do not want to clobber the files already present. It would be:

                wget -nc -r http://www.gnu.org/

    *
        If you want to encode your own username and password to HTTP or FTP, use the appropriate URL syntax.

                wget ftp://hniksic:mypassword@unix.server.com/.emacs

        Note, however, that this usage is not advisable on multi-user systems because it reveals your password to anyone who looks at the output of "ps".
    *
        You would like the output documents to go to standard output instead of to files?

                wget -O - http://jagor.srce.hr/ http://www.srce.hr/

        You can also combine the two options and make pipelines to retrieve the documents from remote hotlists:

                wget -O - http://cool.list.com/ | wget --force-html -i -


    Very Advanced Usage

    *
        If you wish Wget to keep a mirror of a page (or FTP subdirectories), use --mirror (-m), which is the shorthand for -r -l inf -N. You can put Wget in the crontab file asking it to recheck a site each Sunday:

                crontab
                0 0 * * 0 wget --mirror http://www.gnu.org/ -o /home/me/weeklog


    *
        In addition to the above, you want the links to be converted for local viewing. But, after having read this manual, you know that link conversion doesn't play well with timestamping, so you also want Wget to back up the original HTML files before the conversion. Wget invocation would look like this:

                wget --mirror --convert-links --backup-converted  \
                     http://www.gnu.org/ -o /home/me/weeklog


    *
        But you've also noticed that local viewing doesn't work all that well when HTML files are saved under extensions other than .html, perhaps because they were served as index.cgi. So you'd like Wget to rename all the files served with content-type text/html to name.html.

                wget --mirror --convert-links --backup-converted \
                     --html-extension -o /home/me/weeklog        \
                     http://www.gnu.org/

        Or, with less typing:

                wget -m -k -K -E http://www.gnu.org/ -o /home/me/weeklog