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Chapter 14: Web, FTP, and Java Clients

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Chapter 14: Web, FTP, and Java Clients

Overview

Most Linux distributions will provide powerful Web and FTP clients for accessing the Internet. Many are installed automatically and are ready to use when you first start up your Linux system. Linux also includes full Java development support, letting you run and construct Java applets. This chapter will cover some of the more popular Web, Java, and FTP clients available on Linux.

Web and FTP clients connect to sites that run servers, using Web pages and FTP files to provide services to users. Sites are accessed using their Internet addresses. Local networks use the same addressing format. Though discussed in more detail in Chapter 38, a quick review is provided here. The Internet uses a set of network protocols called TCP/IP, which stands for Transmission Control Protocol/Internet Protocol. In a TCP/IP network, messages are broken into small components called datagrams, which are then transmitted through various interlocking routes and delivered to their destination computers. Once received, the datagrams are reassembled into the original message. Datagrams are also referred to as packets. Sending messages as small components has proved far more reliable and faster than sending them as one large bulky transmission. With small components, if one is lost or damaged, only that component has to be resent, whereas if any part of a large transmission is corrupted or lost, the entire message must be resent .

On a TCP/IP network such as the Internet, each computer is given a unique address called an IP address. The IP address is used to identify and locate a particular host—a computer connected to the network. To make identifying a computer on the Internet easier, the Domain Name Service (DNS) was implemented. The DNS establishes a domain name address for each IP address. The domain name address is a series of names separated by periods. Whenever you use a domain name address, it is automatically converted to an IP address, which is then used to identify that Internet host. The domain name address is far easier to use than its corresponding IP address.

A domain name address needs to be registered with an Internet domain name registry such as the American Registry for Internet Numbers (ARIN) so that each computer on the Internet can have a unique name (see www.iana.org for more information). Creating a name follows specified naming conventions. The domain name address consists of the hostname, the name you gave to your computer; a domain name, the name that identifies your network; and an extension that identifies the type of network you are on. Here is the syntax for domain addresses:


host-name

.

domain-name

.

extension

In the following example, the domain address references a computer called metalab on a network referred to as unc . It is part of an educational institution, as indicated by the extension edu .

metalab.unc.edu

With the whois command, you can obtain information for domain name servers about different networks and hosts connected to the Internet. Enter whois and the domain name address of the host or network, and whois displays information about the host, such as the street address and phone number, as well as contact persons.

$

whois


domain-address

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Web Clients

The World Wide Web (WWW, or the Web) is a hypertext database of different types of information, distributed across many different sites on the Internet. A hypertext database consists of items linked to other items, which, in turn , may be linked to yet other items, and so on. Upon retrieving an item, you can use that item to retrieve any related items. For example, you could retrieve an article on the Amazon rain forest and then use it to retrieve a map or a picture of the rain forest. In this respect, a hypertext database is like a web of interconnected data you can trace from one data item to another. Information is displayed in pages known as Web pages. On a Web page, certain keywords or graphics are highlighted that form links to other Web pages or to items, such as pictures, articles, or files.

To access the Web, you use a Web browser. You can choose from many different Web browsers. On your Linux system, you can choose from several Web browsers, including Mozilla and Lynx. Mozilla is an X Window System–based browser that provides full picture, sound, and video display capabilities. Most distributions also include the Lynx browser, a line-mode browser that displays only lines of text. The K Desktop incorporates Web browser capabilities into its file manager, letting a directory window operate as a Web browser. GNOME-based browsers, such as Express and Mnemonic, are also designed to be easily enhanced.

Web browsers and FTP clients are commonly used to conduct secure transactions such as logging into remote sites, ordering items, or transferring files. Such operations are currently secured by encryption methods provided by the Secure Sockets Layer (SSL). See Chapters 18 and 22 for more information about SSL and its counterpart , SSH, the Secure Shell. If you use a browser for secure transactions, it should be SSL enabled. Most browsers such as Mozilla and Links include SSL support. For FTP operations, you can use the SSH version of ftp, sftp, or the Kerberos 5 version (see Chapter 22). Linux distributions include SSL as part of a standard installation.

URL Addresses

An Internet resource is accessed using a Universal Resource Locator (URL). A URL is composed of three elements: the transfer protocol, the hostname, and the pathname. The transfer protocol and the hostname are separated by a colon and two slashes , :// . The pathname always begins with a single slash:


transfer-protocol

://

host-

name


/


path

-name

The transfer protocol is usually HTTP (Hypertext Transfer Protocol), indicating a Web page. Other possible values for transfer protocols are gopher , ftp , and file . As their names suggest, gopher and ftp initiate Gopher and FTP sessions, whereas file displays a local file on your own system, such as a text or HTML file. Table 14-1 lists the various transfer protocols.

The hostname is the computer on which a particular Web site is located. You can think of this as the address of the Web site. By convention, most hostnames begin with www . In the next example, the URL locates a Web page called guides.html on the www.kernel.org Web site in the LDP directory:

http://www.kernel.org/LDP/guides.html

If you do not want to access a particular Web page, you can leave the file reference out, and then you automatically access the Web site's home page. To access a Web site directly, use its hostname. If no home page is specified for a Web site, the file index.html in the top directory is often used as the home page. In the next example, the user brings up the Red Hat home page:

http://www.redhat.com/

The pathname specifies the directory where the resource can be found on the host system, as well as the name of the resource's file. For example, /pub/Linux/newdat.html references an HTML document called newdat located in the /pub/Linux directory. As you move to other Web pages on a site, you may move more deeply into the directory tree. In the following example, the user accesses the FAQ.html document in the directory support/docs/faqs/rhl_general_faq/FAQ.html/ :

http://www.redhat.com/support/docs/faqs/rhl_general_faq/FAQ.html

The resource file's extension indicates the type of action to be taken on it. A picture has a .gif or .jpeg extension and is converted for display. A sound file has an .au or .wav extension and is played . The following URL references a .gif file. Instead of displaying a Web page, your browser invokes a graphics viewer to display the picture. Table 14-2 provides a list of the different file extensions.

http://www.train.com/engine/engine1.gif

Table 14-1: Web Protocols
Protocol	Description
http	Uses Hypertext Transfer Protocol for Web site access
gopher	Accesses Gopher site
ftp	Uses File Transfer Protocol for anonymous FTP connections
telnet	Makes a telnet connection
news	Reads Usenet news; uses Network News Transfer Protocol (NNTP)

Table 14-2: Web File Types
File Type	Description
.html	Web page document formatted using HTML, the Hypertext Markup Language
Graphics Files
.gif	Graphics, using GIF compression
.jpeg	Graphics, using JPEG compression
Sound Files
.au	Sun (Unix) sound file
.wav	Microsoft Windows sound file
.aiff	Macintosh sound file
Video Files
.QT	QuickTime video file, multiplatform
.mpeg	Video file
.avi	Microsoft Windows video file

Web Browsers

Most Web browsers are designed to access several different kinds of information. Web browsers can access a Web page on a remote Web site or a file on your own system. Some browsers can also access a remote news server or an FTP site. The type of information for a site is specified by the keyword http for Web sites, nntp for news servers, ftp for FTP sites, and file for files on your own system. As noted previously, several popular browsers are available for Linux. Three distinctive ones are described here: Mozilla, Konqueror, and Lynx. Mozilla is an X Window System–based Web browser capable of displaying graphics, video, and sound, as well as operating as a newsreader and mailer. Konqueror is the K Desktop file manager. KDE has integrated full Web-browsing capability into the Konqueror file manager, letting you seamlessly access the Web and your file system with the same application. Lynx and Links are command line–based browsers with no graphics capabilities, but in every other respect are fully functional Web browsers.

To search for files on FTP sites, you can use search engines provided by Web sites, such as Yahoo!, Excite, Google, AltaVista, or Lycos. These usually search for both Web pages and FTP files. To find a particular Web page you want on the Internet, you can use any of these search engines or perform searches from any number of Web portals. Web searches have become a standard service of most Web sites. Searches carried out on documents within a Web site may use local search indexes set up and maintained by indexing programs like ht:/Dig. Sites using ht:/Dig use a standard Web page search interface.

Mozilla

Hypertext databases are designed to access any kind of data, whether it is text, graphics, sound, or even video. Whether you can actually access such data depends to a large extent on the type of browser you use. Mozilla is a browser based on the Netscape core source code known as mozilla. In 1998, Netscape made this source code freely available under the Netscape Public License (NPL). The Mozilla Project, based at www.mozilla.org , has developed a commercial-level browser based on mozilla source code. Mozilla is developed on an open source model much like Linux, KDE, and GNOME. Developers can submit modifications and additions over the Internet to the Mozilla Web site. Mozilla releases are referred to as Milestones. Mozilla is currently released under both the NPL license for modifications of mozilla code and the MPL license (Mozilla Public License) for new additions. In current releases, Red Hat will use Mozilla as its primary browser, in place of Netscape.

Mozilla is an X Window System application you operate from your desktop. Red Hat has a Mozilla entry in the desktop's Internet menu. Mozilla displays an area at the top of the screen for entering a URL address and a series of buttons for various Web page operations. Drop-down menus provide access to Mozilla features. To access a Web site, you enter its address in the URL area and press ENTER. The icon bar across the top of the browser holds buttons for moving from one page to another and performing other operations (see Figure 14-1).

click to expand
Figure 14-1: Mozilla Web browser

Mozilla refers to the URLs of Web pages you want to keep as bookmarks, marking pages you want to access directly. The Bookmarks menu enables you to add your favorite Web pages. You can then view your bookmarks and select one to view. You can also edit your list of bookmarks, adding new ones or removing old ones. History is a list of previous URLs you have accessed. If you want to return to a Web page you did not save as a bookmark, you can find it in the History list. Additionally, you can use Mozilla to receive and send mail, as well as to access Usenet newsgroups. Mozilla also supports advanced features like cookie, form, image, and password management. You can elect to suppress cookies from sites, automatically fill in forms, not display site images, and set up login information such as usernames and passwords for selected sites.

The Preferences menu in Mozilla enables you to set several different kinds of preferences for your browser. You can set preferences for mail and news, the network, and security, as well as general preferences. In general preferences, you can determine your home page and how you want the toolbar displayed. In the Mail/News Account Settings, you can enter the mail and news servers you use on the Internet. Mozilla can be set to access any number of news servers you subscribe to and that use the NNTP transfer protocols. You can switch from one news server to another if you want.

If you are on a network that connects to the Internet through a firewall, you must use the Proxies screen to enter the address of your network's firewall gateway computer. A firewall is a computer that operates as a controlled gateway to the Internet for your network. Several types of firewalls exist. One of the most restrictive uses programs called proxies, which receive Internet requests from users and then make those requests on their behalf . There is no direct connection to the Internet. From the Options menu, select Network and then choose the Proxies screen. Here, enter the IP address of your network's firewall gateway computer.

Note

The Privoxy Web proxy filters Web content to protect user privacy, intercepting unwanted advertising or blocking invasive cookies. Privoxy will execute rules listed in its action files, such as action.default, located in the /etc/privoxy directory. You can start Privoxy with the Services tool or the service command. To have your browser use Privoxy, configure it to use the host running Privoxy as a proxy.

K Desktop File Manager: Konqueror

If you are using the K Desktop, you can use a file manager window as a Web browser. The K Desktop's file manager is automatically configured to act as a Web browser. It can display Web pages, including graphics and links. The K Desktop's file manager supports standard Web page operation, such as moving forward and backward through accessed pages. Clicking a link accesses and displays the Web page referenced. In this respect, the Web becomes seamlessly integrated into the K Desktop.

GNOME Web Browsers: Nautilus and Epiphany

The new GNOME file manager, Nautilus, is a functional Web browser, just like Konqueror. In the Nautilus location box, you can enter a Web address and Nautilus will access and display that Web page. The file manager Forward and Backward buttons, as well as bookmarks, help you navigate through previously viewed pages. However, it is not a fully functional Web browser. Nautilus will display icons in its sidebar for dedicated Web browsers installed on your system. Click one to start using that Web browser instead of Nautilus.

Several other GNOME-based Web browsers are also available. Epiphany, Barque, and Atlantis support standard Web operations. Epiphany is a GNOME Web browser designed to be fast with a simple interface. You can find out more about Epiphany at epiphany.mozdev.org . Epiphany is included with Red Hat. For GNOME, you can also download numerous support tools, such as the GNOME News applet to display headlines from news sites and the GNOME Download Manager for controlling Web-based downloads.

Note

Epiphany has replaced Galeon in Fedora Linux, but you can download current versions of Galeon from galeon. sourceforge .net .

Lynx and Links: Line-Mode Browser

Lynx is a line-mode browser you can use without the X Window System. A Web page is displayed as text only. A text page can contain links to other Internet resources but does not display any graphics, video, or sound. Except for the display limitations, Lynx is a fully functional Web browser. You can use Lynx to download files or to make telnet connections. All information on the Web is still accessible to you. Because it does not require much of the overhead that graphics-based browsers need, Lynx can operate much faster, quickly displaying Web page text. To start the Lynx browser, you enter lynx on the command line and press ENTER.

Another useful text-based browser shipped with most distributions is Links. Links is a powerful screen-based browser that includes features such as frame, form, and table support. It also supports SSL secure encryption.

Creating Your Own Web Site

To create your own Web site, you need access to a Web server. Red Hat automatically installs the Apache Web server on its Linux systems. You can also rent Web page space on a remote server—a service many ISPs provide, some for free. On Red Hat systems, the directory set up by your Apache Web server for your Web site pages is /var/httpd/html . Other servers provide you with a directory for your home page. Place the Web pages you create in that directory. You place your home page here. You can make other subdirectories with their own Web pages to which these can link. Web pages are not difficult to create. Links from one page to another move users through your Web site. You can even create links to Web pages or resources on other sites. Many excellent texts are available on Web page creation and management.

Web pages are created using either HTML, the Hypertext Markup Language, or the newer extended version, XML, the Extended Markup Language. They are a subset of Standard Generalized Markup Language (SGML). Creating an HTML or XML document is a matter of inserting HTML or XML tags in a text file. In this respect, creating a Web page is as simple as using a tag-based word processor. You use the HTML tags to format text for display as a Web page. XML tags can include more detailed information about a particular connection such as object data or transaction characteristics. The Web page itself is a text file you can create using any text editor, such as Vi. If you are familiar with tag-based word processing on Unix systems, you will find it conceptually similar to nroff. Some HTML tags indicate headings, lists, and paragraphs, as well as links to reference Web resources.

Instead of manually entering HTML or XML code, you can use Web page composers. A Web page composer provides a graphical interface for constructing Web pages. Special Web page creation programs can easily help you create complex Web pages without ever having to type any HTML tags explicitly. Remember, though, no matter what tool you use to create your Web page, the Web page itself will be an HTML document.

Note

Many of the standard editors for the K Desktop and GNOME include Web page construction features. Many enable you to insert links or format headings. For example, the KEdit program supports basic text-based Web page components . You can add headings, links, or lines, but not graphics.

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