What can I use OpenSSL "s_client" command for? What are options supported by the "s_client" command?

OpenSSL "s_client" command implements a generic SSL/TLS client which can establish a transparent connection to a remote server speaking SSL/TLS. It's intended for testing purposes only and provides only rudimentary interface functionality but internally uses mostly all functionality of the OpenSSL ssl library.

Here are options supported by the "s_client" command:

C:\Users\fyicenter>\local\openssl\openssl.exe

OpenSSL> s_client -h
unknown option -h
usage: s_client args

 -host host     - use -connect instead
 -port port     - use -connect instead
 -connect host:port - who to connect to (default is localhost:4433)
 -verify depth - turn on peer certificate verification
 -cert arg     - certificate file to use, PEM format assumed
 -certform arg - certificate format (PEM or DER) PEM default
 -key arg      - Private key file to use, in cert file if
                 not specified but cert file is.
 -keyform arg  - key format (PEM or DER) PEM default
 -pass arg     - private key file pass phrase source
 -CApath arg   - PEM format directory of CA's
 -CAfile arg   - PEM format file of CA's
 -reconnect    - Drop and re-make the connection with the same Session-ID
 -pause        - sleep(1) after each read(2) and write(2) system call
 -showcerts    - show all certificates in the chain
 -debug        - extra output
 -msg          - Show protocol messages
 -nbio_test    - more ssl protocol testing
 -state        - print the 'ssl' states
 -nbio         - Run with non-blocking IO
 -crlf         - convert LF from terminal into CRLF
 -quiet        - no s_client output
 -ign_eof      - ignore input eof (default when -quiet)
 -ssl2         - just use SSLv2
 -ssl3         - just use SSLv3
 -tls1         - just use TLSv1
 -dtls1        - just use DTLSv1
 -mtu          - set the MTU
 -no_tls1/-no_ssl3/-no_ssl2 - turn off that protocol
 -bugs         - Switch on all SSL implementation bug workarounds
 -serverpref   - Use server's cipher preferences (only SSLv2)
 -cipher       - preferred cipher to use, use the 'openssl ciphers'
                 command to see what is available
 -starttls prot - use the STARTTLS command before starting TLS
                 for those protocols that support it, where
                 'prot' defines which one to assume.  Currently,
                 only "smtp", "pop3", "imap", and "ftp" are supported.
 -engine id    - Initialise and use the specified engine
 -rand file;file;...
 -sess_out arg - file to write SSL session to
 -sess_in arg  - file to read SSL session from
error in s_client

⇒ OpenSSL "s_client -connect" - Connect to HTTPS Web Site

⇐ OpenSSL "s_client" Command

⇑ OpenSSL "s_client" Command

⇑⇑ OpenSSL Tutorials