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TELNET TUTORIAL

A nice telnet program, Easyterm, can be found at http://www.arachnoid.com.

Telnet was big back in the old days (1994). Most isp's offered TELNET/SHELL access as a standard feature in a webhosting package.  Gradually this has began to disappear because it takes a lot more monitoring of web servers to maintain security on servers where users have REAL (non-virtual) accounts.  This cuts into ISP profits and thus today you have many huge, generic ISP clones that rely on software as their only means of security and have substituted weak interfaces such as web-shells and cgi-wrappers for the real thing.  This is about like confusing a garden burger for a filet mingon.  Telnet is by far the MOST POWERFUL interface you can have into a web server.  Telnet is not available for NT users but is available on some of the better hosting companies. 

Whenever you CONNECT to a server you use what is called a PROTOCOL.  There are SEVERAL protocols.  Some of which you are already familiar with.  Here is a list of the ones you will be concerned with:

  • http - or HYPTERTEXT TRANSFER PROTOCOL
  • ftp - or FILE TRANSFER PROTOCOL
  • nntp - or NEWS TRANSFER PROTOCOL
  • telnet - this is just like logging into the server from the console

Each PROTOCOL uses a UNIQUE PORT and has a UNIQUE interface to CONNECT.  When you use http you use a browser to connect.   It generally requires NO LOGIN which is why you usually never have to enter a username and password when you get a webpage.  However you can change this.  All of the other protocols generally REQUIRE usernames and passwords.  Telnet is nice because you can DIRECTLY exectute and debug programs during a session.  Telnet is kind of like DOS.

Telnet allows you to login to a remote computer and work there as if you were resident at one of that machine's terminals. To use telnet you must have a telnet program ( a telnet client) resident on your local machine.   You will need to get a TELNET APPLICATION to login to your host.  You can download one by clicking here for windows or search SHAREWARE.COM for other operating systems.

EXECUTING COMMANDS DURING A TELNET SESSION

Most servers accessed through telnet will be using the unix operating system. This section contains a sub set of unix commands useful for navigating the system and managing files. The command descriptions use the following format

command - use

invocation with arguments and useful options

Examples

cd - change directory

cd directory

Changes current directory to a new directory.

cd
This returns you to your home directory.
cd ..
This moves you up one level in the directory hierarchy.
cd work
This moves you to the subdirectory work within the current directory.
cd ~/mystuff
This moves you to a subdirectory mystuff within your home directory.
cd /usr/users/joe/stuff
This moves you to a subdirectory stuff in Joe's home directory..


chmod - change access permission (mode) of a file

chmod mode filename

Changes the file-access permission for the specified file(s) to the specified permission(mode).

There are two ways to change permissions: through symbolic or numeric form. Numeric form is described here. A file is assigned a numeric "mode" that is the sum of all modes associated with the file. The modes are as follows:

400 - owner has read permission
200 - owner has write permission
100 - owner has execute permission
040 - group has read permission
020 - group has write permission
010 - group has execute permission
004 - world has read permission
002 - world has write permission
001 - world has execute permission

The lowest possible mode value is 000 - which means no one can read, write, or execute the file. The highest possible value is 777 - which means everyone can read, write and execute the file.

chmod 777 notes
The owner can read, write and execute notes. The files specified group and all other users may only read the file.


ls - list files

ls options directory

Lists the contents of the specified directory. If no directory is specified, the contents of the current directory are listed.

ls
Lists the contents of the current directory.
ls -l
Lists the contents of the current directory in long form - shows file-access permissons, owner, etc.
ls -a
Lists the contents of the current directory including hidden ( dot files like .htaccess) files.
ls -al
Lists the contents of the current directory in long form including hidden files.
ls -t /user/user/joe
Lists the contents of the Joe's directory by time stamp.


mkdir - make directory

mkdir options directory

Creates a new directory.

mkdir test
Creates a new directory called test.
mkdir -m 744 work
Creates a new directory called work with permissions set to 744.


perl - invoke perl

perl filename
perl testscript.pl
Invokes the perl interpreter for the file testscripts.pl.
/usr/local/bin/perl testscript.pl
Invokes the perl interpreter located at /usr/local/bin/perl for the file testscripts.pl.


pwd - print working directory

pwd

Prints the full path of the current working directory.


rm - remove file

rm options files

Removes files, providing you are the owner of the file or have write permission to the directory containing the file. This command can also be used to delete directories.

Note: Use this command with caution. When a file is removed, it is really gone. It does not go to a recycle bin or waste basket.

rm test
Removes the file named test.
rm *
Removes all files in the current directory.
rm -r stuff
Removes a directory named stuff and all it's contents, including files and subdirectories.
rm -i
Removes files after verification from user.


tar - archive/dearchive files

tar function options file

Writes files to an archive or extracts files from an archive depending on how the command is configured. Technically tar stands for tape archiver because originally most archives were stored to tape. However, tar writes to and extracts from hard disks and diskettes as well as tape. The archive referred to by tar is, in fact, a file itself, similar to a zip file.

Note that tar is slightly different than other unix commands because it has two sets of options - a function option followed by another set of options. The most often used functions are:

c - create a new tar archive
x - extract files from within a tar archive

The most commonly used options are:

v - verbose mode
f - specify device (or file) to archive to or extract from.

tar xvf codegame.tar
Extracts all of the files in the archive codegame.tar using verbose mode (prints a record).
tar cf backup.tar /user/users/joe
Creates a new archive named backup.tar of all the files in the directory /user/users/joe.


which - which file corresponds to a command

which command

List which file corresponds to the specified command.

which perl5
Displays the file path to perl5. i.e: /usr/bin/perl
 

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