s_client - SSL/TLS client program
[-connect host:port] [-verify depth] [-cert filename] [-certform DER|PEM] [-key filename] [-keyform DER|PEM] [-pass arg] [-CApath directory] [-CAfile filename] [-reconnect] [-pause] [-showcerts] [-debug] [-msg] [-nbio_test] [-state] [-nbio] [-crlf] [-ign_eof] [-quiet] [-ssl2] [-ssl3] [-tls1] [-no_ssl2] [-no_ssl3] [-no_tls1] [-bugs] [-cipher cipherlist] [-starttls protocol] [-engine id] [-tlsextdebug] [-no_ticket] [-sess_out filename] [-sess_in filename] [-rand file(s)]
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.
In addition to the options below the s_client utility also supports the common and client only options documented in the
in the SSL_CONF_cmd(3)
- -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
- -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
Set various certificate chain valiadition option. See the
verify manual page for details.
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
prints out the SSL session states.
print extensive debugging information including a hex dump of all traffic.
show all protocol messages with hex dump.
show verbose trace output of protocol messages. OpenSSL needs to be
compiled with enable-ssl-trace for this option to work.
file to send output of -msg or -trace to, default standard output.
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
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, -no_ssl2, -no_ssl3, -no_tls1
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.
there are several known bug in SSL and TLS implementations. Adding this
option enables various workarounds.
only provide a brief summary of connection parameters instead of the normal
- -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 information.
- -starttls protocol
send the protocol-specific
message(s) to switch to TLS for
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 algorithms.
- -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.
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
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
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 simpler.
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)
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