Telnet Basics

Telnet is a simple client/server application. Telnet allows you to log onto a remote machine and access almost like you are physically there. The remote machine MUST be running a telnet server and you must have a logon and password. This is how you will access some of core features of your webserver. Setting file permissions, compiling programs, setting passwords, and running programs are some of the things you will be able to do. For this tutorial I am assuming that the telnet server resides on a UNIX type machine.

Most current computers come with a telnet client. On Windows 95/98/NT you can simply click on the Start button and select run, then you will type telnet www.yourserver.com. This will now attempt to connect to port 23 on your domain. **note** if for some reason your webserver is using something other than port 23 you will have to specify is like this: telnet www.yourserver.com 123 where we will try to connect to port 123 on yourserver.com. Now once you are connect to the server you will have to adher to the conventions of that computer. What this means is if the remote computer is a 'UNIX' type computer you will have to remember that things are case sensitive. Filea is different that FiLea. You will also have to use '/' instead of a '\' when dealing with directories.

Once you login into your account you will be presented with a prompt. Depending on the shell your provider is using this prompt will vary a little. One of the first commands your will probably want to use is the "ls" command. This is the list command. If you type "ls" your will see a listing something like this:

filea.htm fileb.php3 directorya/

These are the files in the directory you are in.

The 'ls' command has many switches. A switch is usually prefixed with a '-' . The most common one is -l . This gives you a long listing of your current directory. So 'ls -l' will give you something like this:

drwxrwxrwx somename root /directorya

-rw-rw-rw- somename user filea.htm

-rw-rw-rw- somename user fileb.htm

This listing gives us a lot of useful information about our files. First, the leftmost column is the file permissions area. The next column is the owner, the next is the owner's group, and the last is the name. The permissions are 10 positions. They are broken up like this:

Pos 1 can be: D for directory, L for link, - regular file

rwx stand for read, write, and execute

Pos 2-4 these are the owner permissions

Pos 5-7 these are the group permissions

Pos 8-10 these are the world permissions

These permissions determine what a particular user can do to a file.

Another switch of note is the -a switch. This switch displays all files in a directory. So, 'ls -a' will dislay the same as the first example above plus all the hidden files such as the "dot" files. The "dot" files are the current directory ("."), the parent directory (".."), and any file that begins with a ".". One of the "dot" files that is important to you will be probably be the ".htaccess" file. This file can limit what can be viewed by the outside world. It also controls things such as whether Server Side Includes will work on your site.

You may also combine switches. This will apply to most commands in the system. So if you want to display the contents of the current directory in long format showing all the files you would type 'ls -al'.

By now you are probably ready to move around the filesystem. You probably need a little background on how a UNIX filesytems is organized. Everything is based upon a root ('/') directory. There aren't any drive letters to speak of. Every harddrive, cdrom, or floppy drive is given a subdirectory. So you may have a filesystem that looks like this:

/

/floppy0

/harddrive1

/cdrom

/bin

/etc

To see what is located in one of these directories we use the 'cd' command. Type 'cd /floppy0' to change to the floppy disk drive. This is akin to typing 'a:' on a Dos/Windows system. If you type 'cd' then press enter this will take you to your home directory. In order to change to a subdirectory you will type 'cd subdirname' or 'cd subdirname/alowerdir'. The first one will take you into a directory called 'subdirname' and the second one will take you into a directory name 'aloweredir' which is located underneath 'subdirname'. Typing 'cd /' will take you to the root directory. If you were to type 'cd /mydir' this would look for a directory called 'mydir' off of the root directory. Typing 'cd mydir' will look for 'mydir' in the current directory. So this means 'cd /home' will have different results than 'cd home'. That is of course if you are not located in the root directory. At anytime you can type 'pwd' (present working directory) to see something like this:

/home/gelfius/

To create a subdirectory you use the 'mkdir' command. This will create a directory underneath the current directory. To remove this directory you use 'rmdir'. A subdirectory is very useful in organizing files. It's a very nice to keep your program source away from the program executables.

To copy files from one place to another use the 'cp' command. Type 'cp file [location]/name'. This will create another copy of file and place it [locaiton]/name. If you want to delete a file use the 'rm' command. If you want to move the file to another location use the 'mv' command' The format for all three of the commands is very simular. See the man page on the command for further details.

Editing files through telnet can be a little tricky. Depending on the operating system you may or may not have a full page editor. I personally use 'pico' to edit files through telnet. Another useful editor is 'vi' . Vi is more cumberson; but is a very power editor once you master it.

Remembering all the switches and operands of all these commands can be a little tricky. So the 'man' command is provided. Man will give you a manual like page for the command you specify. So, 'man cp' will give you all the optional parameters for the copy command. Most commands in the system will have a man page.

The last very useful command is 'chmod'. This a very powerful command with a lot of security implications associated with. The 'chmod' (pronouced change mode) command lets you set the permissions on the files. This is what you would use to change whether a directory can be viewed everyone or only the creator.