Welcome!

Linux Containers Authors: Elizabeth White, Zakia Bouachraoui, Liz McMillan, Yeshim Deniz, Pat Romanski

Related Topics: Linux Containers

Linux Containers: Article

Alternative Ways to Download Files with Linux

A sneak peek

Fedora Core (http://fedora.redhat.com) is one of the world's most popular Linux distributions in part from support by Red Hat and a strong community of users. It also has been a proving ground for Red Hat to develop technologies that will eventually make their way into Red Hat Enterprise Linux.

Recently Red Hat has spun off the Fedora Core Project into its own organization in much the same way that the Mozilla project was spun out of Netscape back in the late 1990s. Both Fedora and Red Hat Enterprise Linux have proven to be raging successes in their own right for both Red Hat and Linux users who choose to pursue a do-it-yourself approach to Linux. For those of you looking for additional resources to learn more about these distributions, you could consider the Red Hat Fedora and Enterprise Linux 4 Bible written by Christopher Negaus.

Christopher Negus has been working with UNIX systems, the Internet, and (most recently) Linux systems for more than two decades at AT&T Bell Laboratories, UNIX System Laboratories, and Novell, helping to develop the UNIX operating system. Features from many of the UNIX projects Chris worked on at AT&T have found their way into Red Hat Enterprise Linux, Fedora, and other Linux systems. Chris has written several books on UNIX and the Internet; his latest book is the Red Hat Fedora and Enterprise Linux 4 Bible (excerpted below) and released in July 2005. It discusses the features and capabilities of both operating systems. His book is written as a resource for users trying to adopt either of these technologies.

With your Fedora Core system connected to the Internet, you can take advantage of dozens of tools for browsing the Web, downloading files, getting e-mail, and communicating live with your friends. In most cases, you have several choices of GUI and command-line applications for using Internet services from your Linux desktop or shell. However, there are some utilities you may not be familiar with like wget, scp, and sftp.

Excerpt from Chapter 9...

Getting Files with wget
If you already know where a file is on the network, there are more efficient ways of downloading that file than opening an FTP session, moving around the FTP server, and running the get command. The wget command is a simple, efficient tool for doing non-interactive downloads of files over the Internet.

If there is a file you want to download from an FTP site or Web server (HTTP), and you know exactly where the file is, wget is a good way to download. The wget command is very useful if you want to copy a whole site, recursively, from one computer to another (for example, containing user home directories). When downloading from FTP sites, wget can let you just download as the anonymous user or add your own user name and password to the command line.

Downloading a File with User Name and Password
If you are doing an FTP file copy and need to log in as a user other than anonymous, you can add that information to the command line or to a .netrc file in your home directory (type man netrc to see the format of that file). Here is an example of adding the password to the command line:

$ wget ftp://joe:[email protected]/memol.doc .

CAUTION: Adding a password to a command line leaves the password exposed to onlookers. This practice is generally discouraged, except in cases where no one can see your monitor or your history files.

In the previous example, the user logs in as joe with the password my67chevy. The wget then copies the file memo1.doc from the current directory on the host computer named ftp.handsonhistory.com. That current directory is most likely /home/joe.

Downloading a Whole Web Site
Using wget, you can download a large number of files from Web servers as well. The wget command downloads files using the http protocol, if file addresses begin with http://. Downloading a single file, you would use the same form as you would for an FTP file (for example: wget http://host/file.). The best wget option for HTTP downloads is -r (recursive).

A recursive download lets you choose a point at a Web site and download all content below that point. Here is an example of a recursive download used to download the contents of the www.example.com Web site.

$ wget -r http://www.example.com

In this example, the HTML pages, images, and other content on the www.example.com Web site are copied below the current directory in the directory www.example.com. This is useful if you want to gather the contents of a Web site but don't have login access to that site. Because content is taken by following links, if there is content in a directory at the Web site that isn't in a link, it won't be downloaded.

Downloading an entire Web site can result in a massive amount of data being downloaded. If you want only part of a Web site, start from a point lower in the site's structure. Or, as an alternative, you can limit the number levels the wget will go down the site structure. Using the -l option (l as in level), the following example gets two levels of HTML content:

$ wget -r -l 2 http://www.example.com

To mirror a site, you can use the -m option instead of -r. With wget -m http://site, it is like asking to download an infinite number of levels recursively (-r -l inf), keep current time stamps (-N), and keep FTP directory listings (-nr).

Continuing a Download
In the old days, if you were downloading a particularly large file (such as an ISO image of a CD or DVD), if the download stopped for some reason (a disconnected network or errant reboot), you needed to start all over. With wget, you can choose to restart a download and have it continue right where it left off. This has been a lifesaver for me on many occasions.

Let's say that you were downloading a 4GB DVD ISO image named mydvd.iso from the site ftp://ftp.example.com and you killed the wget process by mistake after about 3GB of download. Make sure that your current directory is the one that contains the partially downloaded ISO. Then run the same wget command you did originally, adding the -c (continue) option as follows:

$ wget -c ftp://ftp.example.com/mydvd.iso

If you had not used the -c option, in this case, a new download would have started using the file name mydvd.iso.1 to download to.

NOTE: Another command that you might be interested in, similar to wget, is the curl command. Like wget, curl can download files using the ftp or http protocols. Curl can also do multiple file transfers on the same connection.

# ssh [email protected] "tail -f /var/log/messages"
[email protected]'s password:

After you typed the password in the preceding case, the last several lines of the /var/log/messages file on the remote computer would be displayed. As messages were received, they would continue to be displayed until you decided to exit (press Ctrl+C to exit the tail command).

NOTE: Find out more about the ssh command from the SSH Web site (www.openssh.org).

Using scp for Remote File Copy
The scp command is a simple yet secure way of copying files among Linux systems. It uses the underlying ssh facility, so if ssh is enabled, so is scp. Here is an example of using scp to copy a file from one computer to another:

# scp myfile toys.linuxtoys.net:/home/chris
[email protected]'s password: ******

In this example, the file myfile is copied to the computer named toys.linuxtoys.net in the /home/chris directory. If you don't provide a user name (as is the case here), scp assumes you are using the current user name. Unlike some tools that provide remote login, scp and ssh do allow you to login as root user over the network, by default. (Many people turn off this feature for security reasons.)

To use scp with a different user name, you can append the user name with an @ character. For example, [email protected]:/home/chris would attempt to log in as the user named chris to do the file copy.

The first time you connect to a remote computer using scp or ssh, those commands try to establish the authenticity of the remote host. If it cannot establish the host's authenticity, it will display the RSA key fingerprint and ask you if you want to continue. If you type yes, scp will not question the authenticity of that computer again for subsequent scp commands.

However, if the RSA key fingerprint should change in the future for the remote computer (which will happen if, for example, the operating system is reinstalled on that computer), scp will refuse to let you connect to that remote computer. To override that refusal, you need to edit your $HOME/.ssh/known_hosts file and delete the entry for the remote computer. You can then verify the authenticity of the remote computer and continue to use scp.

The sftp command, which also communicates using secure ssh protocols, is a command for copying files from an FTP server. It is considered a more secure way of getting files from an FTP server that has an sshd server running.

.  .  . 

You can receive more helpful tips on using Fedora and Red Hat Enterprise Linux 4 in Chris's book, Red Hat Fedora and Enterprise Linux 4 Bible available at your local retailer.

More Stories By Mark R. Hinkle

Mark Hinkle is the Senior Director, Open Soure Solutions at Citrix. He also is along-time open source expert and advocate. He is a co-founder of both the Open Source Management Consortium and the Desktop Linux Consortium. He has served as Editor-in-Chief for both LinuxWorld Magazine and Enterprise Open Source Magazine. Hinkle is also the author of the book, "Windows to Linux Business Desktop Migration" (Thomson, 2006). His blog on open source, technology, and new media can be found at http://www.socializedsoftware.com.

Comments (0)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


IoT & Smart Cities Stories
In his general session at 19th Cloud Expo, Manish Dixit, VP of Product and Engineering at Dice, discussed how Dice leverages data insights and tools to help both tech professionals and recruiters better understand how skills relate to each other and which skills are in high demand using interactive visualizations and salary indicator tools to maximize earning potential. Manish Dixit is VP of Product and Engineering at Dice. As the leader of the Product, Engineering and Data Sciences team at D...
Bill Schmarzo, Tech Chair of "Big Data | Analytics" of upcoming CloudEXPO | DXWorldEXPO New York (November 12-13, 2018, New York City) today announced the outline and schedule of the track. "The track has been designed in experience/degree order," said Schmarzo. "So, that folks who attend the entire track can leave the conference with some of the skills necessary to get their work done when they get back to their offices. It actually ties back to some work that I'm doing at the University of San...
When talking IoT we often focus on the devices, the sensors, the hardware itself. The new smart appliances, the new smart or self-driving cars (which are amalgamations of many ‘things'). When we are looking at the world of IoT, we should take a step back, look at the big picture. What value are these devices providing. IoT is not about the devices, its about the data consumed and generated. The devices are tools, mechanisms, conduits. This paper discusses the considerations when dealing with the...
Bill Schmarzo, author of "Big Data: Understanding How Data Powers Big Business" and "Big Data MBA: Driving Business Strategies with Data Science," is responsible for setting the strategy and defining the Big Data service offerings and capabilities for EMC Global Services Big Data Practice. As the CTO for the Big Data Practice, he is responsible for working with organizations to help them identify where and how to start their big data journeys. He's written several white papers, is an avid blogge...
Dynatrace is an application performance management software company with products for the information technology departments and digital business owners of medium and large businesses. Building the Future of Monitoring with Artificial Intelligence. Today we can collect lots and lots of performance data. We build beautiful dashboards and even have fancy query languages to access and transform the data. Still performance data is a secret language only a couple of people understand. The more busine...
If a machine can invent, does this mean the end of the patent system as we know it? The patent system, both in the US and Europe, allows companies to protect their inventions and helps foster innovation. However, Artificial Intelligence (AI) could be set to disrupt the patent system as we know it. This talk will examine how AI may change the patent landscape in the years to come. Furthermore, ways in which companies can best protect their AI related inventions will be examined from both a US and...
Enterprises have taken advantage of IoT to achieve important revenue and cost advantages. What is less apparent is how incumbent enterprises operating at scale have, following success with IoT, built analytic, operations management and software development capabilities - ranging from autonomous vehicles to manageable robotics installations. They have embraced these capabilities as if they were Silicon Valley startups.
Chris Matthieu is the President & CEO of Computes, inc. He brings 30 years of experience in development and launches of disruptive technologies to create new market opportunities as well as enhance enterprise product portfolios with emerging technologies. His most recent venture was Octoblu, a cross-protocol Internet of Things (IoT) mesh network platform, acquired by Citrix. Prior to co-founding Octoblu, Chris was founder of Nodester, an open-source Node.JS PaaS which was acquired by AppFog and ...
The deluge of IoT sensor data collected from connected devices and the powerful AI required to make that data actionable are giving rise to a hybrid ecosystem in which cloud, on-prem and edge processes become interweaved. Attendees will learn how emerging composable infrastructure solutions deliver the adaptive architecture needed to manage this new data reality. Machine learning algorithms can better anticipate data storms and automate resources to support surges, including fully scalable GPU-c...
Cloud-enabled transformation has evolved from cost saving measure to business innovation strategy -- one that combines the cloud with cognitive capabilities to drive market disruption. Learn how you can achieve the insight and agility you need to gain a competitive advantage. Industry-acclaimed CTO and cloud expert, Shankar Kalyana presents. Only the most exceptional IBMers are appointed with the rare distinction of IBM Fellow, the highest technical honor in the company. Shankar has also receive...