1.21. Unix Networking and Communications
Generally speaking, a network lets two
or more computers communicate and work together. Partly because of
the open design of Unix, a lot of networking development has been
done in this operating system. Just as there are different versions
of Unix, there are different ways and programs to use networks from
There's an entire chapter devoted to Connectivity
(Chapter 46), but for now, here's
a quick review of the major networking components.
- The Internet
The Internet is a worldwide network of
computers. Internet users can transfer files, log into other
computers, and use a wide range of programs and services.
The World Wide Web is a set of information servers on the Internet.
The servers are linked into a hypertext web of documents, graphics,
sound, and more. Point-and-click browser
programs turn that hypertext into an easy-to-use Internet interface.
(For many people, the Web is the Internet. But
Unix lets you do much more.)
A Unix facility that's been around for years, long
before networking was common, is electronic mail. Users can send
electronic memos, usually called email messages,
between themselves. When you send email, your message waits for the
other user to start his own mail program. System programs can send
you mail to tell you about problems or give you information. You can
send mail to programs, asking them for information. Worldwide mailing
lists connect users into discussion groups.
The ftp program is
one way to transfer files between your computer and another computer
with TCP/IP, often over the Internet network, using the File Transfer
Unix-to-Unix Copy is a family of programs
uulog, and others) for transferring files and
email between computers. UUCP is usually used with modems over
telephone lines and has been mostly superceded by Internet-type
isn't exactly a network. It's a
collection of hundreds of thousands (millions?) of computers
worldwide that exchange files called news
articles. This "net
news" system has thousands of interactive discussion
groups -- electronic bulletin boards -- for discussing
everything from technical topics to erotic art.
logs you into a remote computer over a network (such as the Internet)
using TCP/IP. You can work on the remote computer as if it were your
local computer. The telnet program is available on
many operating systems; telnet can log you into
other operating systems from your Unix host and vice versa.
This starts a
shell" to run a command on a
remote system without needing to log in interactively. If you
don't give a command, rsh acts
like rlogin. This is often used to start remote
X Window System (Section 1.22) programs whose display opens on your local
system. Section 6.10 has examples -- as
well as details on problems you can have running
rsh for any application.
acts like rsh (and rlogin), but
it makes a secure encrypted connection to the remote computer. It
also can encrypt X Window System
(Section 1.22) connections, as well as other types of
connections, between hosts. The utility ssh-agent
allows remote logins without typing a passphrase.
We've included an entire chapter on
ssh (Chapter 51).
This is a
cp" program for copying files
between computers. It has the same command-line syntax as
cp except that hostnames are added to the remote
This is a secure version of
rcp that uses the ssh protocol.
ssh-agent works here, too.
a user utility. The Network FileSystem and related packages like NIS
(the Network Information Service) let your system administrator mount
remote computers' filesystems onto your local
computer. You can use the remote filesystem as easily as if it were
on your local computer.
messsages to another user's screen. Two users can
have a discussion with write.
sophisticated program than write,
talk splits the screen into two pieces and lets
users type at the same time if they wish. talk can
be used over networks, though not all versions of
talk can talk to one another.
Chat allows multiple users to carry on multiple discussions across
the Internet and other networks. One popular IRC
client is irc.
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