1S_CLIENT(1) OpenSSL S_CLIENT(1)
2
6 s_client - SSL/TLS client program
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9 openssl s_client [-connect host:port] [-servername name] [-verify
10 depth] [-verify_return_error] [-cert filename] [-certform DER|PEM]
11 [-key filename] [-keyform DER|PEM] [-pass arg] [-CApath directory]
12 [-CAfile filename] [-trusted_first] [-no_alt_chains] [-reconnect]
13 [-pause] [-showcerts] [-debug] [-msg] [-nbio_test] [-state] [-nbio]
14 [-crlf] [-ign_eof] [-no_ign_eof] [-quiet] [-ssl3] [-tls1] [-tls1_1]
15 [-tls1_2] [-dtls1] [-no_ssl3] [-no_tls1] [-no_tls1_1] [-no_tls1_2]
16 [-fallback_scsv] [-bugs] [-cipher cipherlist] [-krb5svc service]
17 [-serverpref] [-starttls protocol] [-xmpphost hostname] [-name
18 hostname] [-engine id] [-tlsextdebug] [-no_ticket] [-sess_out filename]
19 [-sess_in filename] [-rand file(s)] [-serverinfo types] [-status]
20 [-alpn protocols] [-nextprotoneg protocols]
21
23 The s_client command implements a generic SSL/TLS client which connects
24 to a remote host using SSL/TLS. It is a very useful diagnostic tool for
25 SSL servers.
26
28 -connect host:port
29 This specifies the host and optional port to connect to. If not
30 specified then an attempt is made to connect to the local host on
31 port 4433.
32 -servername name
34 Set the TLS SNI (Server Name Indication) extension in the
35 ClientHello message.
36 -cert certname
38 The certificate to use, if one is requested by the server. The
39 default is not to use a certificate.
40 -certform format
42 The certificate format to use: DER or PEM. PEM is the default.
43 -key keyfile
45 The private key to use. If not specified then the certificate file
46 will be used.
47 -keyform format
49 The private format to use: DER or PEM. PEM is the default.
50 -pass arg
52 the private key password source. For more information about the
53 format of arg see the PASS PHRASE ARGUMENTS section in openssl(1).
54 -verify depth
56 The verify depth to use. This specifies the maximum length of the
57 server certificate chain and turns on server certificate
58 verification. Currently the verify operation continues after
59 errors so all the problems with a certificate chain can be seen. As
60 a side effect the connection will never fail due to a server
61 certificate verify failure.
62 -verify_return_error
64 Return verification errors instead of continuing. This will
65 typically abort the handshake with a fatal error.
66 -CApath directory
68 The directory to use for server certificate verification. This
69 directory must be in "hash format", see verify for more
70 information. These are also used when building the client
71 certificate chain.
72 -CAfile file
74 A file containing trusted certificates to use during server
75 authentication and to use when attempting to build the client
76 certificate chain.
77 -purpose, -ignore_critical, -issuer_checks, -crl_check, -crl_check_all,
79 -policy_check, -extended_crl, -x509_strict, -policy -check_ss_sig,
80 -trusted_first -no_alt_chains
81 Set various certificate chain valiadition option. See the verify
82 manual page for details.
83 -reconnect
85 reconnects to the same server 5 times using the same session ID,
86 this can be used as a test that session caching is working.
87 -pause
89 pauses 1 second between each read and write call.
90 -showcerts
92 display the whole server certificate chain: normally only the
93 server certificate itself is displayed.
94 -prexit
96 print session information when the program exits. This will always
97 attempt to print out information even if the connection fails.
98 Normally information will only be printed out once if the
99 connection succeeds. This option is useful because the cipher in
100 use may be renegotiated or the connection may fail because a client
101 certificate is required or is requested only after an attempt is
102 made to access a certain URL. Note: the output produced by this
103 option is not always accurate because a connection might never have
104 been established.
105 -state
107 prints out the SSL session states.
108 -debug
110 print extensive debugging information including a hex dump of all
111 traffic.
112 -msg
114 show all protocol messages with hex dump.
115 -nbio_test
117 tests non-blocking I/O
118 -nbio
120 turns on non-blocking I/O
121 -crlf
123 this option translated a line feed from the terminal into CR+LF as
124 required by some servers.
125 -ign_eof
127 inhibit shutting down the connection when end of file is reached in
128 the input.
129 -quiet
131 inhibit printing of session and certificate information. This
132 implicitly turns on -ign_eof as well.
133 -no_ign_eof
135 shut down the connection when end of file is reached in the input.
136 Can be used to override the implicit -ign_eof after -quiet.
137 -psk_identity identity
139 Use the PSK identity identity when using a PSK cipher suite.
140 -psk key
142 Use the PSK key key when using a PSK cipher suite. The key is given
143 as a hexadecimal number without leading 0x, for example -psk
144 1a2b3c4d.
145 -ssl3, -tls1, -tls1_1, -tls1_2, -dtls1, -no_ssl3, -no_tls1, -no_tls1_1,
147 -no_tls1_2
148 These options require or disable the use of the specified SSL or
149 TLS protocols. By default the initial handshake uses a version-
150 flexible method which will negotiate the highest mutually supported
151 protocol version.
152 -fallback_scsv
154 Send TLS_FALLBACK_SCSV in the ClientHello.
155 -bugs
157 there are several known bug in SSL and TLS implementations. Adding
158 this option enables various workarounds.
159 -cipher cipherlist
161 this allows the cipher list sent by the client to be modified.
162 Although the server determines which cipher suite is used it should
163 take the first supported cipher in the list sent by the client. See
164 the ciphers command for more information.
165 -serverpref
167 use the server's cipher preferences; only used for SSLV2.
168 -krb5svc service
170 the Kerberos service name to use (default "host"). This means
171 s_server will expect a ticket for the principal
172 service/hostname@REALM, and will need keys for that principal in
173 its keytab.
174 -starttls protocol
176 send the protocol-specific message(s) to switch to TLS for
177 communication. protocol is a keyword for the intended protocol.
178 Currently, the only supported keywords are "smtp", "pop3", "imap",
179 "ftp", "xmpp", "xmpp-server", "irc", "postgres", "lmtp", "nntp",
180 "sieve" and "ldap".
181 -xmpphost hostname
183 This option, when used with "-starttls xmpp" or "-starttls xmpp-
184 server", specifies the host for the "to" attribute of the stream
185 element. If this option is not specified, then the host specified
186 with "-connect" will be used.
187 -name hostname
189 the host name to use with "-starttls smtp". If this option is not
190 specified, the default "openssl.client.net" will be used.
191 -tlsextdebug
193 print out a hex dump of any TLS extensions received from the
194 server.
195 -no_ticket
197 disable RFC4507bis session ticket support.
198 -sess_out filename
200 output SSL session to filename
201 -sess_in sess.pem
203 load SSL session from filename. The client will attempt to resume a
204 connection from this session.
205 -engine id
207 specifying an engine (by its unique id string) will cause s_client
208 to attempt to obtain a functional reference to the specified
209 engine, thus initialising it if needed. The engine will then be set
210 as the default for all available algorithms.
211 -rand file(s)
213 a file or files containing random data used to seed the random
214 number generator, or an EGD socket (see RAND_egd(3)). Multiple
215 files can be specified separated by a OS-dependent character. The
216 separator is ; for MS-Windows, , for OpenVMS, and : for all others.
217 -serverinfo types
219 a list of comma-separated TLS Extension Types (numbers between 0
220 and 65535). Each type will be sent as an empty ClientHello TLS
221 Extension. The server's response (if any) will be encoded and
222 displayed as a PEM file.
223 -status
225 sends a certificate status request to the server (OCSP stapling).
226 The server response (if any) is printed out.
227 -alpn protocols, -nextprotoneg protocols
229 these flags enable the Enable the Application-Layer Protocol
230 Negotiation or Next Protocol Negotiation extension, respectively.
231 ALPN is the IETF standard and replaces NPN. The protocols list is
232 a comma-separated protocol names that the client should advertise
233 support for. The list should contain most wanted protocols first.
234 Protocol names are printable ASCII strings, for example "http/1.1"
235 or "spdy/3". Empty list of protocols is treated specially and will
236 cause the client to advertise support for the TLS extension but
237 disconnect just after reciving ServerHello with a list of server
238 supported protocols.
239
241 If a connection is established with an SSL server then any data
242 received from the server is displayed and any key presses will be sent
243 to the server. When used interactively (which means neither -quiet nor
244 -ign_eof have been given), the session will be renegotiated if the line
245 begins with an R, and if the line begins with a Q or if end of file is
246 reached, the connection will be closed down.
247
249 s_client can be used to debug SSL servers. To connect to an SSL HTTP
250 server the command:
251 openssl s_client -connect servername:443
253 would typically be used (https uses port 443). If the connection
255 succeeds then an HTTP command can be given such as "GET /" to retrieve
256 a web page.
257 If the handshake fails then there are several possible causes, if it is
259 nothing obvious like no client certificate then the -bugs, -ssl3,
260 -tls1, -no_ssl3, -no_tls1 options can be tried in case it is a buggy
261 server. In particular you should play with these options before
262 submitting a bug report to an OpenSSL mailing list.
263 A frequent problem when attempting to get client certificates working
265 is that a web client complains it has no certificates or gives an empty
266 list to choose from. This is normally because the server is not sending
267 the clients certificate authority in its "acceptable CA list" when it
268 requests a certificate. By using s_client the CA list can be viewed and
269 checked. However some servers only request client authentication after
270 a specific URL is requested. To obtain the list in this case it is
271 necessary to use the -prexit option and send an HTTP request for an
272 appropriate page.
273 If a certificate is specified on the command line using the -cert
275 option it will not be used unless the server specifically requests a
276 client certificate. Therefor merely including a client certificate on
277 the command line is no guarantee that the certificate works.
278 If there are problems verifying a server certificate then the
280 -showcerts option can be used to show the whole chain.
281 The s_client utility is a test tool and is designed to continue the
283 handshake after any certificate verification errors. As a result it
284 will accept any certificate chain (trusted or not) sent by the peer.
285 None test applications should not do this as it makes them vulnerable
286 to a MITM attack. This behaviour can be changed by with the
287 -verify_return_error option: any verify errors are then returned
288 aborting the handshake.
289
291 Because this program has a lot of options and also because some of the
292 techniques used are rather old, the C source of s_client is rather hard
293 to read and not a model of how things should be done. A typical SSL
294 client program would be much simpler.
295 The -prexit option is a bit of a hack. We should really report
297 information whenever a session is renegotiated.
298
300 sess_id(1), s_server(1), ciphers(1)
301
303 The -no_alt_chains options was first added to OpenSSL 1.0.2b.
3041.0.2k 2019-03-12 S_CLIENT(1)