Debug services

A common problem after installing a service is testing if it correctly works. This could be done using different command-line tools that sends data in raw mode allowing system administrator to see exactly what comes back.

This cheat-sheet shows how to use command-line tools to pinpoint the connection problems:

Port 21

How to login and execute commands on ftp server:

$ telnet domain.tld 21
Trying domain.tld...
Connected to domain.tld.
Escape character is '^]'.
220 ProFTPD 1.3.1 Server ready.
user username
331 Password required for username
pass password
230 User username logged in
help
214-The following commands are recognized (* =>'s unimplemented):
214-CWD     XCWD    CDUP    XCUP    SMNT*   QUIT    PORT    PASV
214-EPRT    EPSV    ALLO*   RNFR    RNTO    DELE    MDTM    RMD
214-XRMD    MKD     XMKD    PWD     XPWD    SIZE    SYST    HELP
214-NOOP    FEAT    OPTS    AUTH    CCC*    CONF*   ENC*    MIC*
214-PBSZ    PROT    TYPE    STRU    MODE    RETR    STOR    STOU
214-APPE    REST    ABOR    USER    PASS    ACCT*   REIN*   LIST
214-NLST    STAT    SITE
quit
221 Goodbye.

Port 25

How to send an email:

$ telnet domain.tld 25
Trying domain.tld...
Connected to domain.tld.
Escape character is '^]'.
220 localhost ESMTP Postfix (Ubuntu/GNU)
HELO domain.tld
250 localhost
MAIL FROM: root
250 2.1.0 Ok
RCPT TO: <email@domain.tld>
250 2.1.5 Ok
DATA
354 End data with .
Subject: Email from domain.tld
From: domain.tld

Test data
.
250 2.0.0 Ok: queued as 7C3F68464C1
quit
221 2.0.0 Bye

Port 80

How to retrieve a webpage:

telnet domain.tld 80
Trying domain.tld...
Connected to domain.tld.
Escape character is '^]'.
HEAD / HTTP/1.1
Host: domain.tld

HTTP/1.1 200 OK
Date: Thu, 12 Nov 2009 10:41:18 GMT
Server: Apache
Last-Modified: Wed, 01 Apr 2009 15:02:13 GMT
ETag: "b8c6a-73-4667f99bca740"
Accept-Ranges: bytes
Content-Length: 115
Vary: Accept-Encoding,User-Agent
Content-Type: text/html

Port 110

How to check email account for new messages:

$ telnet domain.tld 110
Trying domain.tld...
Connected to domain.tld.
+OK Hello There
user username
+OK Password required.
pass password
+OK Logged in.
stat
+OK a b
quit
+OK goodbye

Port 143

How to login to a IMAP server:

telnet domain.tld 143
Trying domain.tld...
Connected to domain.tld.
Escape character is '^]'.
* OK Dovecot ready.
a login email@domain.tld e
a OK Logged in.
a examine inbox
a logout
* BYE Logging out
a OK Logout completed.

Port 993

To debug IMAP over SSL:

openssl s_client -connect domain.tld:993

then use same commands as port 143 example.

Port 995

To debug POP3 over SSL:

openssl s_client -connect domain.tld:995

then use same commands as port 110 example.