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S_CLIENT(1)                         OpenSSL                        S_CLIENT(1)

       s_client - SSL/TLS client program

       openssl s_client [-connect host:port] [-verify depth] [-cert filename] [-certform
       DER|PEM] [-key filename] [-keyform DER|PEM] [-pass arg] [-CApath directory]
       [-CAfile filename] [-trusted_first] [-krb5svc service] [-keytab filename]
       [-reconnect] [-pause] [-showcerts] [-debug] [-msg] [-nbio_test] [-state] [-nbio]
       [-crlf] [-ign_eof] [-no_ign_eof] [-quiet] [-ssl2] [-ssl3] [-tls1] [-tls1_1]
       [-tls1_2] [-dtls1] [-no_ssl2] [-no_ssl3] [-no_tls1] [-no_tls1_1] [-no_tls1_2]
       [-fallback_scsv] [-bugs] [-cipher cipherlist] [-starttls protocol] [-engine id]
       [-tlsextdebug] [-no_ticket] [-sess_out filename] [-sess_in filename] [-rand
       file(s)] [-nextprotoneg protocols]

       The s_client command implements a generic SSL/TLS client which connects to a remote
       host using SSL/TLS. It is a very useful diagnostic tool for SSL servers.

       -connect host:port
           This specifies the host and optional port to connect to. If not specified then
           an attempt is made to connect to the local host on port 4433.

       -cert certname
           The certificate to use, if one is requested by the server. The default is not
           to use a certificate.

       -certform format
           The certificate format to use: DER or PEM. PEM is the default.

       -key keyfile
           The private key to use. If not specified then the certificate file will be

       -keyform format
           The private format to use: DER or PEM. PEM is the default.

       -pass arg
           the private key password source. For more information about the format of arg
           see the PASS PHRASE ARGUMENTS section in openssl(1).

       -verify depth
           The verify depth to use. This specifies the maximum length of the server
           certificate chain and turns on server certificate verification.  Currently the
           verify operation continues after errors so all the problems with a certificate
           chain can be seen. As a side effect the connection will never fail due to a
           server certificate verify failure.

       -CApath directory
           The directory to use for server certificate verification. This directory must
           be in "hash format", see verify for more information. These are also used when
           building the client certificate chain.

       -CAfile file
           A file containing trusted certificates to use during server authentication and
           to use when attempting to build the client certificate chain.

       -purpose, -ignore_critical, -issuer_checks, -crl_check, -crl_check_all,
       -policy_check, -extended_crl, -x509_strict, -policy -check_ss_sig, -trusted_first
           Set various certificate chain valiadition option. See the verify manual page
           for details.

       -krb5svc service
           the Kerberos service name to use (default "host"). This means s_server will
           expect a ticket for the principal service/hostname@REALM, and will need keys
           for that principal in its keytab.

       -keytab filename
           the Kerberos "keytab" (key table) file, containing keys for the s_server
           service principal (Kerberos identity; see -krb5svc).

           reconnects to the same server 5 times using the same session ID, this can be
           used as a test that session caching is working.

           pauses 1 second between each read and write call.

           display the whole server certificate chain: normally only the server
           certificate itself is displayed.

           print session information when the program exits. This will always attempt to
           print out information even if the connection fails. Normally information will
           only be printed out once if the connection succeeds. This option is useful
           because the cipher in use may be renegotiated or the connection may fail
           because a client certificate is required or is requested only after an attempt
           is made to access a certain URL. Note: the output produced by this option is
           not always accurate because a connection might never have been established.

           prints out the SSL session states.

           print extensive debugging information including a hex dump of all traffic.

           show all protocol messages with hex dump.

           tests non-blocking I/O

           turns on non-blocking I/O

           this option translated a line feed from the terminal into CR+LF as required by
           some servers.

           inhibit shutting down the connection when end of file is reached in the input.

           shut down the connection when end of file is reached in the input. Can be used
           to override the implicit -ign_eof after -quiet.

           inhibit printing of session and certificate information.  This implicitly turns
           on -ign_eof as well.

       -psk_identity identity
           Use the PSK identity identity when using a PSK cipher suite.

       -psk key
           Use the PSK key key when using a PSK cipher suite. The key is given as a
           hexadecimal number without leading 0x, for example -psk 1a2b3c4d.

       -ssl2, -ssl3, -tls1, -tls1_1, -tls1_2, -dtls1, -no_ssl2, -no_ssl3, -no_tls1,
       -no_tls1_1, -no_tls1_2
           these options disable the use of certain SSL or TLS protocols. By default the
           initial handshake uses a method which should be compatible with all servers and
           permit them to use SSL v3, SSL v2 or TLS as appropriate.

           Unfortunately there are a lot of ancient and broken servers in use which cannot
           handle this technique and will fail to connect. Some servers only work if TLS
           is turned off with the -no_tls option others will only support SSL v2 and may
           need the -ssl2 option.

           Send TLS_FALLBACK_SCSV in the ClientHello.

           there are several known bug in SSL and TLS implementations. Adding this option
           enables various workarounds.

       -cipher cipherlist
           this allows the cipher list sent by the client to be modified. Although the
           server determines which cipher suite is used it should take the first supported
           cipher in the list sent by the client. See the ciphers command for more

       -starttls protocol
           send the protocol-specific message(s) to switch to TLS for communication.
           protocol is a keyword for the intended protocol.  Currently, the only supported
           keywords are "smtp", "pop3", "imap", and "ftp".

           print out a hex dump of any TLS extensions received from the server.

           disable RFC4507bis session ticket support.

       -sess_out filename
           output SSL session to filename

       -sess_in sess.pem
           load SSL session from filename. The client will attempt to resume a connection
           from this session.

       -engine id
           specifying an engine (by its unique id string) will cause s_client to attempt
           to obtain a functional reference to the specified engine, thus initialising it
           if needed. The engine will then be set as the default for all available

       -rand file(s)
           a file or files containing random data used to seed the random number
           generator, or an EGD socket (see RAND_egd(3)).  Multiple files can be specified
           separated by a OS-dependent character.  The separator is ; for MS-Windows, ,
           for OpenVMS, and : for all others.

       -nextprotoneg protocols
           enable Next Protocol Negotiation TLS extension and provide a list of comma-
           separated protocol names that the client should advertise support for. The list
           should contain most wanted protocols first.  Protocol names are printable ASCII
           strings, for example "http/1.1" or "spdy/3".  Empty list of protocols is
           treated specially and will cause the client to advertise support for the TLS
           extension but disconnect just after reciving ServerHello with a list of server
           supported protocols.

       If a connection is established with an SSL server then any data received from the
       server is displayed and any key presses will be sent to the server. When used
       interactively (which means neither -quiet nor -ign_eof have been given), the
       session will be renegotiated if the line begins with an R, and if the line begins
       with a Q or if end of file is reached, the connection will be closed down.

       s_client can be used to debug SSL servers. To connect to an SSL HTTP server the

        openssl s_client -connect servername:443

       would typically be used (https uses port 443). If the connection succeeds then an
       HTTP command can be given such as "GET /" to retrieve a web page.

       If the handshake fails then there are several possible causes, if it is nothing
       obvious like no client certificate then the -bugs, -ssl2, -ssl3, -tls1, -no_ssl2,
       -no_ssl3, -no_tls1 options can be tried in case it is a buggy server. In particular
       you should play with these options before submitting a bug report to an OpenSSL
       mailing list.

       A frequent problem when attempting to get client certificates working is that a web
       client complains it has no certificates or gives an empty list to choose from. This
       is normally because the server is not sending the clients certificate authority in
       its "acceptable CA list" when it requests a certificate. By using s_client the CA
       list can be viewed and checked. However some servers only request client
       authentication after a specific URL is requested. To obtain the list in this case
       it is necessary to use the -prexit option and send an HTTP request for an
       appropriate page.

       If a certificate is specified on the command line using the -cert option it will
       not be used unless the server specifically requests a client certificate. Therefor
       merely including a client certificate on the command line is no guarantee that the
       certificate works.

       If there are problems verifying a server certificate then the -showcerts option can
       be used to show the whole chain.

       Since the SSLv23 client hello cannot include compression methods or extensions
       these will only be supported if its use is disabled, for example by using the
       -no_sslv2 option.

       Because this program has a lot of options and also because some of the techniques
       used are rather old, the C source of s_client is rather hard to read and not a
       model of how things should be done. A typical SSL client program would be much

       The -verify option should really exit if the server verification fails.

       The -prexit option is a bit of a hack. We should really report information whenever
       a session is renegotiated.

       sess_id(1), s_server(1), ciphers(1)

1.0.1e                            2017-03-22                       S_CLIENT(1)

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