Python Network - Telnet

Telnet is a type of network protocol which allows a user in one computer to logon to another computer which also belongs to the same network. The telnet command is used along with the host name and then the user credentials are entered. Upon successful login the remote user can access the applications and data in a way similar to the regular user of the system. Of course some privileges can be controlled by the administrator of the system who sets up and maintains the system.

In Python telnet is implemented by the module telnetlib which has the Telnet class which has the required methods to establish the connection. In the below example we also use the getpass module to handle the password prompt as part of the login process. Also we assume the connection is made to a unix host. The various methods from telnetlib. Telnet class used in the program are explained below.

• Telnet.read_until − Read until a given string, expected, is encountered or until timeout seconds have passed.

• Telnet.write − Write a string to the socket, doubling any IAC characters. This can block if the connection is blocked. May raise socket.error if the connection is closed.

• Telnet.read_all() − Read all data until EOF; block until connection closed.

Example - Using Telnet Programming

import getpass
import telnetlib

HOST = "http://localhost:8000/"
user = raw_input("Enter your remote account: ")
password = getpass.getpass()

tn = telnetlib.Telnet(HOST)

tn.read_until("login: ")
tn.write(user + "\n")
if password:
    tn.read_until("Password: ")
    tn.write(password + "\n")

tn.write("ls\n")
tn.write("exit\n")

print(tn.read_all())

Output

When we run the above program, we get the following output −

- lrwxrwxrwx    1 0        0               1 Nov 13  2012 ftp -> .
- lrwxrwxrwx    1 0        0               3 Nov 13  2012 mirror -> pub
- drwxr-xr-x   23 0        0            4096 Nov 27  2017 pub
- drwxr-sr-x   88 0        450          4096 May 04 19:30 site
- drwxr-xr-x    9 0        0            4096 Jan 23  2014 vol

Please note that this output is specific to the remote computer whose details are submitted when the program is run.