Telnet is a tool for connecting to servers on a given port for troubleshooting connection issues.
One of the most common tasks that you can do via telnet – is connect to some web server and verify its health by checking the response code in HTTP header.
Or you can get the content of a whole web page via telnet if you need to analyze it deeper. (more…)
You can easily test a a website availability from the Linux command line and get the status codes from the web-server using commands like TELNET or CURL.
Execute the following command to check whether a web site is up, and what status message the web server is showing:
$ curl -Is http://www.shellhacks.com | head -1 HTTP/1.1 200 OK
Status code ‘200 OK’ means that the request has succeeded and a website is reachable.
Here is an another example that shows you how curl displays different status codes.
$ curl -Is http://shellhacks.com | head -n 1 HTTP/1.1 301 Moved Permanently
You’ll notice that if you visit: http://shellhacks.com you are redirected to http://www.shellhacks.com, because I prefer to have www in my site’s URL. I do this by implementing a 301 Redirect (Permanently moved) for any visitor who goes to http://shellhacks.com.
You can also check the availability of a particular page on the site:
$ curl -Is http://www.shellhacks.com/Bash-Colors | head -n 1 HTTP/1.1 200 OK
Read more: Status Code Definitions
You can also test website availability and get the response code using telnet command:
$ telnet www.shellhacks.com 80 Trying 91.206.200.119... Connected to www.shellhacks.com. Escape character is '^]'. HEAD / HTTP/1.0 HOST: www.shellhacks.com <PRESS ENTER> <PRESS ENTER>
You will get the output as follows:
HTTP/1.1 200 OK Server: nginx/1.1.10 Date: Sun, 26 May 2013 19:29:46 GMT ***
That also means that the website is OK.
The POP3 (Post Office Protocol Version 3) is an application-layer Internet standard protocol used by local Email clients to retrieve Email from a remote server over a TCP/IP connection.
This tutorial shows how to connect to POP3 mail server and manage incoming Email using the ‘telnet’ command.
Step 1: Open a connection from your computer to a POP3 mail server
$ telnet pop.domain.ext 110 Trying ???.???.???.???... Connected to pop.domain.ext. Escape character is '^]'. +OK ready
Step 2: Type your Login
> USER username +OK Password required for UserName.
Step 3: Type your Password
> PASS password +OK username has ? visible messages (? hidden) in ????? octets.
Here are the basic POP3 commands, that you can use to manage your incoming Email.
| Command | Description | Example |
|---|---|---|
| USER [username] | 1st login command | USER Stan +OK Please enter a password |
| PASS [password] | 2nd login command | PASS SeCrEt +OK valid logon |
| QUIT | Logs out and saves any changes | QUIT +OK Bye-bye. |
| STAT | Returns total number of messages and total size | STAT +OK 2 320 |
| LIST | Lists all messages | LIST +OK 2 messages (320 octets) 1 120 2 200 … LIST 2 +OK 2 200 |
| RETR [message] | Retrieves the whole message | RETR 1 +OK 120 octets follow. *** |
| DELE [message] | Deletes the specified message | DELE 2 +OK message deleted |
| NOOP | The POP3 server does nothing, it merely replies with a positive response. | NOOP +OK |
| RSET | Undelete the message if any marked for deletion | RSET +OK maildrop has 2 messages (320 octets) |
| TOP [message] [number] | Returns the headers and number of lines from the message | TOP 1 10 +OK *** |
The SMTP (Simple Mail Transfer Protocol) is an Internet standard for electronic mail (Email) transmission across Internet Protocol (IP) networks.
This tutorial shows how to connect to SMTP mail server and send an Email using the ‘telnet’ command.
Step 1: Open a connection from your computer to an SMTP mail server
$ telnet smtp.domain.ext 25 220 smtp.domain.ext ESMTP Sendmail ?version-number?; ?date+time+gmtoffset?
Step 2: Declare your domain name or IP-address
You can set local.domain.name or anything you want in ‘HELO’, because the server doesn’t check its authenticity, that is one of the drawbacks of this protocol.
> HELO local.domain.name 250 smtp.domain.ext Hello local.domain.name [xxx.xxx.xxx.xxx], pleased to meet you
Step 3: Set sender’s email
> MAIL FROM: sender@adress.ext 250 2.1.0 sender@adress.ext... Sender ok
Step 4: Set recipient’s email
> RCPT TO: recipient@adress.ext 250 2.1.5 recipient@adress.ext... Recipient ok
Step 5: To write the message, type DATA and press ‘Enter’
> DATA 354 Enter mail, end with "." on a line by itself
Step 6: On the first line type ‘SUBJECT: Your Subject’ and press ‘Enter’ twice
> SUBJECT: Test message
Step 7: Continue typing your message
Hello, this is a TEST message, please don't reply. Thank you.
Step 8: Put a single period (.) on a line by itself and press ‘Enter’ to send your message.
> . 250 2.0.0 ???????? Message accepted for delivery
Step 9: Close the connection
> QUIT 221 2.0.0 server.com closing connection