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1SSH_CONFIG(5) File Formats Manual SSH_CONFIG(5)
2
3NAME
4 ssh_config M-bM-^@M-^S OpenSSH SSH client configuration files
5
6SYNOPSIS
7 ~/.ssh/config
8 /etc/ssh/ssh_config
9
10DESCRIPTION
11 ssh(1) obtains configuration data from the following sources in the
12 following order:
13
14 1. command-line options
15 2. user's configuration file (~/.ssh/config)
16 3. system-wide configuration file (/etc/ssh/ssh_config)
17
18 For each parameter, the first obtained value will be used. The
19 configuration files contain sections separated by M-bM-^@M-^\HostM-bM-^@M-^] specifications,
20 and that section is only applied for hosts that match one of the patterns
21 given in the specification. The matched host name is usually the one
22 given on the command line (see the CanonicalizeHostname option for
23 exceptions.)
24
25 Since the first obtained value for each parameter is used, more host-
26 specific declarations should be given near the beginning of the file, and
27 general defaults at the end.
28
29 The configuration file has the following format:
30
31 Empty lines and lines starting with M-bM-^@M-^X#M-bM-^@M-^Y are comments. Otherwise a line
32 is of the format M-bM-^@M-^\keyword argumentsM-bM-^@M-^]. Configuration options may be
33 separated by whitespace or optional whitespace and exactly one M-bM-^@M-^X=M-bM-^@M-^Y; the
34 latter format is useful to avoid the need to quote whitespace when
35 specifying configuration options using the ssh, scp, and sftp -o option.
36 Arguments may optionally be enclosed in double quotes (") in order to
37 represent arguments containing spaces.
38
39 The possible keywords and their meanings are as follows (note that
40 keywords are case-insensitive and arguments are case-sensitive):
41
42 Host Restricts the following declarations (up to the next Host or
43 Match keyword) to be only for those hosts that match one of the
44 patterns given after the keyword. If more than one pattern is
45 provided, they should be separated by whitespace. A single M-bM-^@M-^X*M-bM-^@M-^Y
46 as a pattern can be used to provide global defaults for all
47 hosts. The host is usually the hostname argument given on the
48 command line (see the CanonicalizeHostname option for
49 exceptions.)
50
51 A pattern entry may be negated by prefixing it with an
52 exclamation mark (M-bM-^@M-^X!M-bM-^@M-^Y). If a negated entry is matched, then the
53 Host entry is ignored, regardless of whether any other patterns
54 on the line match. Negated matches are therefore useful to
55 provide exceptions for wildcard matches.
56
57 See PATTERNS for more information on patterns.
58
59 Match Restricts the following declarations (up to the next Host or
60 Match keyword) to be used only when the conditions following the
61 Match keyword are satisfied. Match conditions are specified
62 using one or more criteria or the single token all which always
63 matches. The available criteria keywords are: canonical, exec,
64 host, originalhost, user, and localuser. The all criteria must
65 appear alone or immediately after canonical. Other criteria may
66 be combined arbitrarily. All criteria but all and canonical
67 require an argument. Criteria may be negated by prepending an
68 exclamation mark (M-bM-^@M-^X!M-bM-^@M-^Y).
69
70 The canonical keyword matches only when the configuration file is
71 being re-parsed after hostname canonicalization (see the
72 CanonicalizeHostname option.) This may be useful to specify
73 conditions that work with canonical host names only. The exec
74 keyword executes the specified command under the user's shell.
75 If the command returns a zero exit status then the condition is
76 considered true. Commands containing whitespace characters must
77 be quoted. The following character sequences in the command will
78 be expanded prior to execution: M-bM-^@M-^X%LM-bM-^@M-^Y will be substituted by the
79 first component of the local host name, M-bM-^@M-^X%lM-bM-^@M-^Y will be substituted
80 by the local host name (including any domain name), M-bM-^@M-^X%hM-bM-^@M-^Y will be
81 substituted by the target host name, M-bM-^@M-^X%nM-bM-^@M-^Y will be substituted by
82 the original target host name specified on the command-line, M-bM-^@M-^X%pM-bM-^@M-^Y
83 the destination port, M-bM-^@M-^X%rM-bM-^@M-^Y by the remote login username, and M-bM-^@M-^X%uM-bM-^@M-^Y
84 by the username of the user running ssh(1).
85
86 The other keywords' criteria must be single entries or comma-
87 separated lists and may use the wildcard and negation operators
88 described in the PATTERNS section. The criteria for the host
89 keyword are matched against the target hostname, after any
90 substitution by the Hostname or CanonicalizeHostname options.
91 The originalhost keyword matches against the hostname as it was
92 specified on the command-line. The user keyword matches against
93 the target username on the remote host. The localuser keyword
94 matches against the name of the local user running ssh(1) (this
95 keyword may be useful in system-wide ssh_config files).
96
97 AddKeysToAgent
98 Specifies whether keys should be automatically added to a running
99 ssh-agent(1). If this option is set to M-bM-^@M-^\yesM-bM-^@M-^] and a key is loaded
100 from a file, the key and its passphrase are added to the agent
101 with the default lifetime, as if by ssh-add(1). If this option
102 is set to M-bM-^@M-^\askM-bM-^@M-^], ssh will require confirmation using the
103 SSH_ASKPASS program before adding a key (see ssh-add(1) for
104 details). If this option is set to M-bM-^@M-^\confirmM-bM-^@M-^], each use of the
105 key must be confirmed, as if the -c option was specified to
106 ssh-add(1). If this option is set to M-bM-^@M-^\noM-bM-^@M-^], no keys are added to
107 the agent. The argument must be M-bM-^@M-^\yesM-bM-^@M-^], M-bM-^@M-^\confirmM-bM-^@M-^], M-bM-^@M-^\askM-bM-^@M-^], or
108 M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\noM-bM-^@M-^].
109
110 AddressFamily
111 Specifies which address family to use when connecting. Valid
112 arguments are M-bM-^@M-^\anyM-bM-^@M-^], M-bM-^@M-^\inetM-bM-^@M-^] (use IPv4 only), or M-bM-^@M-^\inet6M-bM-^@M-^] (use IPv6
113 only). The default is M-bM-^@M-^\anyM-bM-^@M-^].
114
115 BatchMode
116 If set to M-bM-^@M-^\yesM-bM-^@M-^], passphrase/password querying will be disabled.
117 This option is useful in scripts and other batch jobs where no
118 user is present to supply the password. The argument must be
119 M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\noM-bM-^@M-^].
120
121 BindAddress
122 Use the specified address on the local machine as the source
123 address of the connection. Only useful on systems with more than
124 one address. Note that this option does not work if
125 UsePrivilegedPort is set to M-bM-^@M-^\yesM-bM-^@M-^].
126
127 CanonicalDomains
128 When CanonicalizeHostname is enabled, this option specifies the
129 list of domain suffixes in which to search for the specified
130 destination host.
131
132 CanonicalizeFallbackLocal
133 Specifies whether to fail with an error when hostname
134 canonicalization fails. The default, M-bM-^@M-^\yesM-bM-^@M-^], will attempt to look
135 up the unqualified hostname using the system resolver's search
136 rules. A value of M-bM-^@M-^\noM-bM-^@M-^] will cause ssh(1) to fail instantly if
137 CanonicalizeHostname is enabled and the target hostname cannot be
138 found in any of the domains specified by CanonicalDomains.
139
140 CanonicalizeHostname
141 Controls whether explicit hostname canonicalization is performed.
142 The default, M-bM-^@M-^\noM-bM-^@M-^], is not to perform any name rewriting and let
143 the system resolver handle all hostname lookups. If set to M-bM-^@M-^\yesM-bM-^@M-^]
144 then, for connections that do not use a ProxyCommand, ssh(1) will
145 attempt to canonicalize the hostname specified on the command
146 line using the CanonicalDomains suffixes and
147 CanonicalizePermittedCNAMEs rules. If CanonicalizeHostname is
148 set to M-bM-^@M-^\alwaysM-bM-^@M-^], then canonicalization is applied to proxied
149 connections too.
150
151 If this option is enabled, then the configuration files are
152 processed again using the new target name to pick up any new
153 configuration in matching Host and Match stanzas.
154
155 CanonicalizeMaxDots
156 Specifies the maximum number of dot characters in a hostname
157 before canonicalization is disabled. The default, M-bM-^@M-^\1M-bM-^@M-^], allows a
158 single dot (i.e. hostname.subdomain).
159
160 CanonicalizePermittedCNAMEs
161 Specifies rules to determine whether CNAMEs should be followed
162 when canonicalizing hostnames. The rules consist of one or more
163 arguments of source_domain_list:target_domain_list, where
164 source_domain_list is a pattern-list of domains that may follow
165 CNAMEs in canonicalization, and target_domain_list is a pattern-
166 list of domains that they may resolve to.
167
168 For example, M-bM-^@M-^\*.a.example.com:*.b.example.com,*.c.example.comM-bM-^@M-^]
169 will allow hostnames matching M-bM-^@M-^\*.a.example.comM-bM-^@M-^] to be
170 canonicalized to names in the M-bM-^@M-^\*.b.example.comM-bM-^@M-^] or
171 M-bM-^@M-^\*.c.example.comM-bM-^@M-^] domains.
172
173 CertificateFile
174 Specifies a file from which the user's certificate is read. A
175 corresponding private key must be provided separately in order to
176 use this certificate either from an IdentityFile directive or -i
177 flag to ssh(1), via ssh-agent(1), or via a PKCS11Provider.
178
179 The file name may use the tilde syntax to refer to a user's home
180 directory or one of the following escape characters: M-bM-^@M-^X%dM-bM-^@M-^Y (local
181 user's home directory), M-bM-^@M-^X%uM-bM-^@M-^Y (local user name), M-bM-^@M-^X%lM-bM-^@M-^Y (local host
182 name), M-bM-^@M-^X%hM-bM-^@M-^Y (remote host name) or M-bM-^@M-^X%rM-bM-^@M-^Y (remote user name).
183
184 It is possible to have multiple certificate files specified in
185 configuration files; these certificates will be tried in
186 sequence. Multiple CertificateFile directives will add to the
187 list of certificates used for authentication.
188
189 ChallengeResponseAuthentication
190 Specifies whether to use challenge-response authentication. The
191 argument to this keyword must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is
192 M-bM-^@M-^\yesM-bM-^@M-^].
193
194 CheckHostIP
195 If this flag is set to M-bM-^@M-^\yesM-bM-^@M-^], ssh(1) will additionally check the
196 host IP address in the known_hosts file. This allows ssh to
197 detect if a host key changed due to DNS spoofing and will add
198 addresses of destination hosts to ~/.ssh/known_hosts in the
199 process, regardless of the setting of StrictHostKeyChecking. If
200 the option is set to M-bM-^@M-^\noM-bM-^@M-^], the check will not be executed. The
201 default is M-bM-^@M-^\yesM-bM-^@M-^].
202
203 Cipher Specifies the cipher to use for encrypting the session in
204 protocol version 1. Currently, M-bM-^@M-^\blowfishM-bM-^@M-^], M-bM-^@M-^\3desM-bM-^@M-^], and M-bM-^@M-^\desM-bM-^@M-^] are
205 supported. des is only supported in the ssh(1) client for
206 interoperability with legacy protocol 1 implementations that do
207 not support the 3des cipher. Its use is strongly discouraged due
208 to cryptographic weaknesses. The default is M-bM-^@M-^\3desM-bM-^@M-^].
209
210 Ciphers
211 Specifies the ciphers allowed for protocol version 2 in order of
212 preference. Multiple ciphers must be comma-separated. If the
213 specified value begins with a M-bM-^@M-^X+M-bM-^@M-^Y character, then the specified
214 ciphers will be appended to the default set instead of replacing
215 them.
216
217 The supported ciphers are:
218
219 3des-cbc
220 aes128-cbc
221 aes192-cbc
222 aes256-cbc
223 aes128-ctr
224 aes192-ctr
225 aes256-ctr
226 aes128-gcm@openssh.com
227 aes256-gcm@openssh.com
228 arcfour
229 arcfour128
230 arcfour256
231 blowfish-cbc
232 cast128-cbc
233 chacha20-poly1305@openssh.com
234
235 The default is:
236
237 chacha20-poly1305@openssh.com,
238 aes128-ctr,aes192-ctr,aes256-ctr,
239 aes128-gcm@openssh.com,aes256-gcm@openssh.com,
240 aes128-cbc,aes192-cbc,aes256-cbc,3des-cbc
241
242 The list of available ciphers may also be obtained using the -Q
243 option of ssh(1) with an argument of M-bM-^@M-^\cipherM-bM-^@M-^].
244
245 ClearAllForwardings
246 Specifies that all local, remote, and dynamic port forwardings
247 specified in the configuration files or on the command line be
248 cleared. This option is primarily useful when used from the
249 ssh(1) command line to clear port forwardings set in
250 configuration files, and is automatically set by scp(1) and
251 sftp(1). The argument must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is
252 M-bM-^@M-^\noM-bM-^@M-^].
253
254 Compression
255 Specifies whether to use compression. The argument must be M-bM-^@M-^\yesM-bM-^@M-^]
256 or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\noM-bM-^@M-^].
257
258 CompressionLevel
259 Specifies the compression level to use if compression is enabled.
260 The argument must be an integer from 1 (fast) to 9 (slow, best).
261 The default level is 6, which is good for most applications. The
262 meaning of the values is the same as in gzip(1). Note that this
263 option applies to protocol version 1 only.
264
265 ConnectionAttempts
266 Specifies the number of tries (one per second) to make before
267 exiting. The argument must be an integer. This may be useful in
268 scripts if the connection sometimes fails. The default is 1.
269
270 ConnectTimeout
271 Specifies the timeout (in seconds) used when connecting to the
272 SSH server, instead of using the default system TCP timeout.
273 This value is used only when the target is down or really
274 unreachable, not when it refuses the connection.
275
276 ControlMaster
277 Enables the sharing of multiple sessions over a single network
278 connection. When set to M-bM-^@M-^\yesM-bM-^@M-^], ssh(1) will listen for
279 connections on a control socket specified using the ControlPath
280 argument. Additional sessions can connect to this socket using
281 the same ControlPath with ControlMaster set to M-bM-^@M-^\noM-bM-^@M-^] (the
282 default). These sessions will try to reuse the master instance's
283 network connection rather than initiating new ones, but will fall
284 back to connecting normally if the control socket does not exist,
285 or is not listening.
286
287 Setting this to M-bM-^@M-^\askM-bM-^@M-^] will cause ssh to listen for control
288 connections, but require confirmation using ssh-askpass(1). If
289 the ControlPath cannot be opened, ssh will continue without
290 connecting to a master instance.
291
292 X11 and ssh-agent(1) forwarding is supported over these
293 multiplexed connections, however the display and agent forwarded
294 will be the one belonging to the master connection i.e. it is not
295 possible to forward multiple displays or agents.
296
297 Two additional options allow for opportunistic multiplexing: try
298 to use a master connection but fall back to creating a new one if
299 one does not already exist. These options are: M-bM-^@M-^\autoM-bM-^@M-^] and
300 M-bM-^@M-^\autoaskM-bM-^@M-^]. The latter requires confirmation like the M-bM-^@M-^\askM-bM-^@M-^]
301 option.
302
303 ControlPath
304 Specify the path to the control socket used for connection
305 sharing as described in the ControlMaster section above or the
306 string M-bM-^@M-^\noneM-bM-^@M-^] to disable connection sharing. In the path, M-bM-^@M-^X%LM-bM-^@M-^Y
307 will be substituted by the first component of the local host
308 name, M-bM-^@M-^X%lM-bM-^@M-^Y will be substituted by the local host name (including
309 any domain name), M-bM-^@M-^X%hM-bM-^@M-^Y will be substituted by the target host
310 name, M-bM-^@M-^X%nM-bM-^@M-^Y will be substituted by the original target host name
311 specified on the command line, M-bM-^@M-^X%pM-bM-^@M-^Y the destination port, M-bM-^@M-^X%rM-bM-^@M-^Y by
312 the remote login username, M-bM-^@M-^X%uM-bM-^@M-^Y by the username and M-bM-^@M-^X%iM-bM-^@M-^Y by the
313 numeric user ID (uid) of the user running ssh(1), and M-bM-^@M-^X%CM-bM-^@M-^Y by a
314 hash of the concatenation: %l%h%p%r. It is recommended that any
315 ControlPath used for opportunistic connection sharing include at
316 least %h, %p, and %r (or alternatively %C) and be placed in a
317 directory that is not writable by other users. This ensures that
318 shared connections are uniquely identified.
319
320 ControlPersist
321 When used in conjunction with ControlMaster, specifies that the
322 master connection should remain open in the background (waiting
323 for future client connections) after the initial client
324 connection has been closed. If set to M-bM-^@M-^\noM-bM-^@M-^], then the master
325 connection will not be placed into the background, and will close
326 as soon as the initial client connection is closed. If set to
327 M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\0M-bM-^@M-^], then the master connection will remain in the
328 background indefinitely (until killed or closed via a mechanism
329 such as the ssh(1) M-bM-^@M-^\-O exitM-bM-^@M-^] option). If set to a time in
330 seconds, or a time in any of the formats documented in
331 sshd_config(5), then the backgrounded master connection will
332 automatically terminate after it has remained idle (with no
333 client connections) for the specified time.
334
335 DynamicForward
336 Specifies that a TCP port on the local machine be forwarded over
337 the secure channel, and the application protocol is then used to
338 determine where to connect to from the remote machine.
339
340 The argument must be [bind_address:]port. IPv6 addresses can be
341 specified by enclosing addresses in square brackets. By default,
342 the local port is bound in accordance with the GatewayPorts
343 setting. However, an explicit bind_address may be used to bind
344 the connection to a specific address. The bind_address of
345 M-bM-^@M-^\localhostM-bM-^@M-^] indicates that the listening port be bound for local
346 use only, while an empty address or M-bM-^@M-^X*M-bM-^@M-^Y indicates that the port
347 should be available from all interfaces.
348
349 Currently the SOCKS4 and SOCKS5 protocols are supported, and
350 ssh(1) will act as a SOCKS server. Multiple forwardings may be
351 specified, and additional forwardings can be given on the command
352 line. Only the superuser can forward privileged ports.
353
354 EnableSSHKeysign
355 Setting this option to M-bM-^@M-^\yesM-bM-^@M-^] in the global client configuration
356 file /etc/ssh/ssh_config enables the use of the helper program
357 ssh-keysign(8) during HostbasedAuthentication. The argument must
358 be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\noM-bM-^@M-^]. This option should be
359 placed in the non-hostspecific section. See ssh-keysign(8) for
360 more information.
361
362 EscapeChar
363 Sets the escape character (default: M-bM-^@M-^X~M-bM-^@M-^Y). The escape character
364 can also be set on the command line. The argument should be a
365 single character, M-bM-^@M-^X^M-bM-^@M-^Y followed by a letter, or M-bM-^@M-^\noneM-bM-^@M-^] to disable
366 the escape character entirely (making the connection transparent
367 for binary data).
368
369 ExitOnForwardFailure
370 Specifies whether ssh(1) should terminate the connection if it
371 cannot set up all requested dynamic, tunnel, local, and remote
372 port forwardings, (e.g. if either end is unable to bind and
373 listen on a specified port). Note that ExitOnForwardFailure does
374 not apply to connections made over port forwardings and will not,
375 for example, cause ssh(1) to exit if TCP connections to the
376 ultimate forwarding destination fail. The argument must be M-bM-^@M-^\yesM-bM-^@M-^]
377 or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\noM-bM-^@M-^].
378
379 FingerprintHash
380 Specifies the hash algorithm used when displaying key
381 fingerprints. Valid options are: M-bM-^@M-^\md5M-bM-^@M-^] and M-bM-^@M-^\sha256M-bM-^@M-^]. The
382 default is M-bM-^@M-^\sha256M-bM-^@M-^].
383
384 ForwardAgent
385 Specifies whether the connection to the authentication agent (if
386 any) will be forwarded to the remote machine. The argument must
387 be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\noM-bM-^@M-^].
388
389 Agent forwarding should be enabled with caution. Users with the
390 ability to bypass file permissions on the remote host (for the
391 agent's Unix-domain socket) can access the local agent through
392 the forwarded connection. An attacker cannot obtain key material
393 from the agent, however they can perform operations on the keys
394 that enable them to authenticate using the identities loaded into
395 the agent.
396
397 ForwardX11
398 Specifies whether X11 connections will be automatically
399 redirected over the secure channel and DISPLAY set. The argument
400 must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\noM-bM-^@M-^].
401
402 X11 forwarding should be enabled with caution. Users with the
403 ability to bypass file permissions on the remote host (for the
404 user's X11 authorization database) can access the local X11
405 display through the forwarded connection. An attacker may then
406 be able to perform activities such as keystroke monitoring if the
407 ForwardX11Trusted option is also enabled.
408
409 ForwardX11Timeout
410 Specify a timeout for untrusted X11 forwarding using the format
411 described in the TIME FORMATS section of sshd_config(5). X11
412 connections received by ssh(1) after this time will be refused.
413 The default is to disable untrusted X11 forwarding after twenty
414 minutes has elapsed.
415
416 ForwardX11Trusted
417 If this option is set to M-bM-^@M-^\yesM-bM-^@M-^], remote X11 clients will have full
418 access to the original X11 display.
419
420 If this option is set to M-bM-^@M-^\noM-bM-^@M-^], remote X11 clients will be
421 considered untrusted and prevented from stealing or tampering
422 with data belonging to trusted X11 clients. Furthermore, the
423 xauth(1) token used for the session will be set to expire after
424 20 minutes. Remote clients will be refused access after this
425 time.
426
427 The default is M-bM-^@M-^\noM-bM-^@M-^].
428
429 See the X11 SECURITY extension specification for full details on
430 the restrictions imposed on untrusted clients.
431
432 GatewayPorts
433 Specifies whether remote hosts are allowed to connect to local
434 forwarded ports. By default, ssh(1) binds local port forwardings
435 to the loopback address. This prevents other remote hosts from
436 connecting to forwarded ports. GatewayPorts can be used to
437 specify that ssh should bind local port forwardings to the
438 wildcard address, thus allowing remote hosts to connect to
439 forwarded ports. The argument must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The
440 default is M-bM-^@M-^\noM-bM-^@M-^].
441
442 GlobalKnownHostsFile
443 Specifies one or more files to use for the global host key
444 database, separated by whitespace. The default is
445 /etc/ssh/ssh_known_hosts, /etc/ssh/ssh_known_hosts2.
446
447 GSSAPIAuthentication
448 Specifies whether user authentication based on GSSAPI is allowed.
449 The default is M-bM-^@M-^\noM-bM-^@M-^].
450
451 GSSAPIDelegateCredentials
452 Forward (delegate) credentials to the server. The default is
453 M-bM-^@M-^\noM-bM-^@M-^].
454
455 HashKnownHosts
456 Indicates that ssh(1) should hash host names and addresses when
457 they are added to ~/.ssh/known_hosts. These hashed names may be
458 used normally by ssh(1) and sshd(8), but they do not reveal
459 identifying information should the file's contents be disclosed.
460 The default is M-bM-^@M-^\noM-bM-^@M-^]. Note that existing names and addresses in
461 known hosts files will not be converted automatically, but may be
462 manually hashed using ssh-keygen(1).
463
464 HostbasedAuthentication
465 Specifies whether to try rhosts based authentication with public
466 key authentication. The argument must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The
467 default is M-bM-^@M-^\noM-bM-^@M-^].
468
469 HostbasedKeyTypes
470 Specifies the key types that will be used for hostbased
471 authentication as a comma-separated pattern list. Alternately if
472 the specified value begins with a M-bM-^@M-^X+M-bM-^@M-^Y character, then the
473 specified key types will be appended to the default set instead
474 of replacing them. The default for this option is:
475
476 ecdsa-sha2-nistp256-cert-v01@openssh.com,
477 ecdsa-sha2-nistp384-cert-v01@openssh.com,
478 ecdsa-sha2-nistp521-cert-v01@openssh.com,
479 ssh-ed25519-cert-v01@openssh.com,
480 ssh-rsa-cert-v01@openssh.com,
481 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
482 ssh-ed25519,ssh-rsa
483
484 The -Q option of ssh(1) may be used to list supported key types.
485
486 HostKeyAlgorithms
487 Specifies the host key algorithms that the client wants to use in
488 order of preference. Alternately if the specified value begins
489 with a M-bM-^@M-^X+M-bM-^@M-^Y character, then the specified key types will be
490 appended to the default set instead of replacing them. The
491 default for this option is:
492
493 ecdsa-sha2-nistp256-cert-v01@openssh.com,
494 ecdsa-sha2-nistp384-cert-v01@openssh.com,
495 ecdsa-sha2-nistp521-cert-v01@openssh.com,
496 ssh-ed25519-cert-v01@openssh.com,
497 ssh-rsa-cert-v01@openssh.com,
498 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
499 ssh-ed25519,ssh-rsa
500
501 If hostkeys are known for the destination host then this default
502 is modified to prefer their algorithms.
503
504 The list of available key types may also be obtained using the -Q
505 option of ssh(1) with an argument of M-bM-^@M-^\keyM-bM-^@M-^].
506
507 HostKeyAlias
508 Specifies an alias that should be used instead of the real host
509 name when looking up or saving the host key in the host key
510 database files. This option is useful for tunneling SSH
511 connections or for multiple servers running on a single host.
512
513 HostName
514 Specifies the real host name to log into. This can be used to
515 specify nicknames or abbreviations for hosts. If the hostname
516 contains the character sequence M-bM-^@M-^X%hM-bM-^@M-^Y, then this will be replaced
517 with the host name specified on the command line (this is useful
518 for manipulating unqualified names). The character sequence M-bM-^@M-^X%%M-bM-^@M-^Y
519 will be replaced by a single M-bM-^@M-^X%M-bM-^@M-^Y character, which may be used
520 when specifying IPv6 link-local addresses.
521
522 The default is the name given on the command line. Numeric IP
523 addresses are also permitted (both on the command line and in
524 HostName specifications).
525
526 IdentitiesOnly
527 Specifies that ssh(1) should only use the authentication identity
528 and certificate files explicitly configured in the ssh_config
529 files or passed on the ssh(1) command-line, even if ssh-agent(1)
530 or a PKCS11Provider offers more identities. The argument to this
531 keyword must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. This option is intended for
532 situations where ssh-agent offers many different identities. The
533 default is M-bM-^@M-^\noM-bM-^@M-^].
534
535 IdentityFile
536 Specifies a file from which the user's DSA, ECDSA, Ed25519 or RSA
537 authentication identity is read. The default is ~/.ssh/identity
538 for protocol version 1, and ~/.ssh/id_dsa, ~/.ssh/id_ecdsa,
539 ~/.ssh/id_ed25519 and ~/.ssh/id_rsa for protocol version 2.
540 Additionally, any identities represented by the authentication
541 agent will be used for authentication unless IdentitiesOnly is
542 set. If no certificates have been explicitly specified by
543 CertificateFile, ssh(1) will try to load certificate information
544 from the filename obtained by appending -cert.pub to the path of
545 a specified IdentityFile.
546
547 The file name may use the tilde syntax to refer to a user's home
548 directory or one of the following escape characters: M-bM-^@M-^X%dM-bM-^@M-^Y (local
549 user's home directory), M-bM-^@M-^X%uM-bM-^@M-^Y (local user name), M-bM-^@M-^X%lM-bM-^@M-^Y (local host
550 name), M-bM-^@M-^X%hM-bM-^@M-^Y (remote host name) or M-bM-^@M-^X%rM-bM-^@M-^Y (remote user name).
551
552 It is possible to have multiple identity files specified in
553 configuration files; all these identities will be tried in
554 sequence. Multiple IdentityFile directives will add to the list
555 of identities tried (this behaviour differs from that of other
556 configuration directives).
557
558 IdentityFile may be used in conjunction with IdentitiesOnly to
559 select which identities in an agent are offered during
560 authentication. IdentityFile may also be used in conjunction
561 with CertificateFile in order to provide any certificate also
562 needed for authentication with the identity.
563
564 IgnoreUnknown
565 Specifies a pattern-list of unknown options to be ignored if they
566 are encountered in configuration parsing. This may be used to
567 suppress errors if ssh_config contains options that are
568 unrecognised by ssh(1). It is recommended that IgnoreUnknown be
569 listed early in the configuration file as it will not be applied
570 to unknown options that appear before it.
571
572 IPQoS Specifies the IPv4 type-of-service or DSCP class for connections.
573 Accepted values are M-bM-^@M-^\af11M-bM-^@M-^], M-bM-^@M-^\af12M-bM-^@M-^], M-bM-^@M-^\af13M-bM-^@M-^], M-bM-^@M-^\af21M-bM-^@M-^], M-bM-^@M-^\af22M-bM-^@M-^],
574 M-bM-^@M-^\af23M-bM-^@M-^], M-bM-^@M-^\af31M-bM-^@M-^], M-bM-^@M-^\af32M-bM-^@M-^], M-bM-^@M-^\af33M-bM-^@M-^], M-bM-^@M-^\af41M-bM-^@M-^], M-bM-^@M-^\af42M-bM-^@M-^], M-bM-^@M-^\af43M-bM-^@M-^], M-bM-^@M-^\cs0M-bM-^@M-^],
575 M-bM-^@M-^\cs1M-bM-^@M-^], M-bM-^@M-^\cs2M-bM-^@M-^], M-bM-^@M-^\cs3M-bM-^@M-^], M-bM-^@M-^\cs4M-bM-^@M-^], M-bM-^@M-^\cs5M-bM-^@M-^], M-bM-^@M-^\cs6M-bM-^@M-^], M-bM-^@M-^\cs7M-bM-^@M-^], M-bM-^@M-^\efM-bM-^@M-^],
576 M-bM-^@M-^\lowdelayM-bM-^@M-^], M-bM-^@M-^\throughputM-bM-^@M-^], M-bM-^@M-^\reliabilityM-bM-^@M-^], or a numeric value.
577 This option may take one or two arguments, separated by
578 whitespace. If one argument is specified, it is used as the
579 packet class unconditionally. If two values are specified, the
580 first is automatically selected for interactive sessions and the
581 second for non-interactive sessions. The default is M-bM-^@M-^\lowdelayM-bM-^@M-^]
582 for interactive sessions and M-bM-^@M-^\throughputM-bM-^@M-^] for non-interactive
583 sessions.
584
585 KbdInteractiveAuthentication
586 Specifies whether to use keyboard-interactive authentication.
587 The argument to this keyword must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default
588 is M-bM-^@M-^\yesM-bM-^@M-^].
589
590 KbdInteractiveDevices
591 Specifies the list of methods to use in keyboard-interactive
592 authentication. Multiple method names must be comma-separated.
593 The default is to use the server specified list. The methods
594 available vary depending on what the server supports. For an
595 OpenSSH server, it may be zero or more of: M-bM-^@M-^\bsdauthM-bM-^@M-^], M-bM-^@M-^\pamM-bM-^@M-^], and
596 M-bM-^@M-^\skeyM-bM-^@M-^].
597
598 KexAlgorithms
599 Specifies the available KEX (Key Exchange) algorithms. Multiple
600 algorithms must be comma-separated. Alternately if the specified
601 value begins with a M-bM-^@M-^X+M-bM-^@M-^Y character, then the specified methods
602 will be appended to the default set instead of replacing them.
603 The default is:
604
605 curve25519-sha256@libssh.org,
606 ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
607 diffie-hellman-group-exchange-sha256,
608 diffie-hellman-group-exchange-sha1,
609 diffie-hellman-group14-sha1
610
611 The list of available key exchange algorithms may also be
612 obtained using the -Q option of ssh(1) with an argument of M-bM-^@M-^\kexM-bM-^@M-^].
613
614 LocalCommand
615 Specifies a command to execute on the local machine after
616 successfully connecting to the server. The command string
617 extends to the end of the line, and is executed with the user's
618 shell. The following escape character substitutions will be
619 performed: M-bM-^@M-^X%dM-bM-^@M-^Y (local user's home directory), M-bM-^@M-^X%hM-bM-^@M-^Y (remote host
620 name), M-bM-^@M-^X%lM-bM-^@M-^Y (local host name), M-bM-^@M-^X%nM-bM-^@M-^Y (host name as provided on the
621 command line), M-bM-^@M-^X%pM-bM-^@M-^Y (remote port), M-bM-^@M-^X%rM-bM-^@M-^Y (remote user name) or
622 M-bM-^@M-^X%uM-bM-^@M-^Y (local user name) or M-bM-^@M-^X%CM-bM-^@M-^Y by a hash of the concatenation:
623 %l%h%p%r.
624
625 The command is run synchronously and does not have access to the
626 session of the ssh(1) that spawned it. It should not be used for
627 interactive commands.
628
629 This directive is ignored unless PermitLocalCommand has been
630 enabled.
631
632 LocalForward
633 Specifies that a TCP port on the local machine be forwarded over
634 the secure channel to the specified host and port from the remote
635 machine. The first argument must be [bind_address:]port and the
636 second argument must be host:hostport. IPv6 addresses can be
637 specified by enclosing addresses in square brackets. Multiple
638 forwardings may be specified, and additional forwardings can be
639 given on the command line. Only the superuser can forward
640 privileged ports. By default, the local port is bound in
641 accordance with the GatewayPorts setting. However, an explicit
642 bind_address may be used to bind the connection to a specific
643 address. The bind_address of M-bM-^@M-^\localhostM-bM-^@M-^] indicates that the
644 listening port be bound for local use only, while an empty
645 address or M-bM-^@M-^X*M-bM-^@M-^Y indicates that the port should be available from
646 all interfaces.
647
648 LogLevel
649 Gives the verbosity level that is used when logging messages from
650 ssh(1). The possible values are: QUIET, FATAL, ERROR, INFO,
651 VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO.
652 DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify
653 higher levels of verbose output.
654
655 MACs Specifies the MAC (message authentication code) algorithms in
656 order of preference. The MAC algorithm is used for data
657 integrity protection. Multiple algorithms must be comma-
658 separated. If the specified value begins with a M-bM-^@M-^X+M-bM-^@M-^Y character,
659 then the specified algorithms will be appended to the default set
660 instead of replacing them.
661
662 The algorithms that contain M-bM-^@M-^\-etmM-bM-^@M-^] calculate the MAC after
663 encryption (encrypt-then-mac). These are considered safer and
664 their use recommended.
665
666 The default is:
667
668 umac-64-etm@openssh.com,umac-128-etm@openssh.com,
669 hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
670 hmac-sha1-etm@openssh.com,
671 umac-64@openssh.com,umac-128@openssh.com,
672 hmac-sha2-256,hmac-sha2-512,hmac-sha1
673
674 The list of available MAC algorithms may also be obtained using
675 the -Q option of ssh(1) with an argument of M-bM-^@M-^\macM-bM-^@M-^].
676
677 NoHostAuthenticationForLocalhost
678 This option can be used if the home directory is shared across
679 machines. In this case localhost will refer to a different
680 machine on each of the machines and the user will get many
681 warnings about changed host keys. However, this option disables
682 host authentication for localhost. The argument to this keyword
683 must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is to check the host key for
684 localhost.
685
686 NumberOfPasswordPrompts
687 Specifies the number of password prompts before giving up. The
688 argument to this keyword must be an integer. The default is 3.
689
690 PasswordAuthentication
691 Specifies whether to use password authentication. The argument
692 to this keyword must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\yesM-bM-^@M-^].
693
694 PermitLocalCommand
695 Allow local command execution via the LocalCommand option or
696 using the !command escape sequence in ssh(1). The argument must
697 be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\noM-bM-^@M-^].
698
699 PKCS11Provider
700 Specifies which PKCS#11 provider to use. The argument to this
701 keyword is the PKCS#11 shared library ssh(1) should use to
702 communicate with a PKCS#11 token providing the user's private RSA
703 key.
704
705 Port Specifies the port number to connect on the remote host. The
706 default is 22.
707
708 PreferredAuthentications
709 Specifies the order in which the client should try authentication
710 methods. This allows a client to prefer one method (e.g.
711 keyboard-interactive) over another method (e.g. password). The
712 default is:
713
714 gssapi-with-mic,hostbased,publickey,
715 keyboard-interactive,password
716
717 Protocol
718 Specifies the protocol versions ssh(1) should support in order of
719 preference. The possible values are M-bM-^@M-^X1M-bM-^@M-^Y and M-bM-^@M-^X2M-bM-^@M-^Y. Multiple
720 versions must be comma-separated. When this option is set to
721 M-bM-^@M-^\2,1M-bM-^@M-^] ssh will try version 2 and fall back to version 1 if
722 version 2 is not available. The default is M-bM-^@M-^X2M-bM-^@M-^Y. Protocol 1
723 suffers from a number of cryptographic weaknesses and should not
724 be used. It is only offered to support legacy devices.
725
726 ProxyCommand
727 Specifies the command to use to connect to the server. The
728 command string extends to the end of the line, and is executed
729 using the user's shell M-bM-^@M-^XexecM-bM-^@M-^Y directive to avoid a lingering
730 shell process.
731
732 In the command string, any occurrence of M-bM-^@M-^X%hM-bM-^@M-^Y will be substituted
733 by the host name to connect, M-bM-^@M-^X%pM-bM-^@M-^Y by the port, and M-bM-^@M-^X%rM-bM-^@M-^Y by the
734 remote user name. The command can be basically anything, and
735 should read from its standard input and write to its standard
736 output. It should eventually connect an sshd(8) server running
737 on some machine, or execute sshd -i somewhere. Host key
738 management will be done using the HostName of the host being
739 connected (defaulting to the name typed by the user). Setting
740 the command to M-bM-^@M-^\noneM-bM-^@M-^] disables this option entirely. Note that
741 CheckHostIP is not available for connects with a proxy command.
742
743 This directive is useful in conjunction with nc(1) and its proxy
744 support. For example, the following directive would connect via
745 an HTTP proxy at 192.0.2.0:
746
747 ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
748
749 ProxyUseFdpass
750 Specifies that ProxyCommand will pass a connected file descriptor
751 back to ssh(1) instead of continuing to execute and pass data.
752 The default is M-bM-^@M-^\noM-bM-^@M-^].
753
754 PubkeyAcceptedKeyTypes
755 Specifies the key types that will be used for public key
756 authentication as a comma-separated pattern list. Alternately if
757 the specified value begins with a M-bM-^@M-^X+M-bM-^@M-^Y character, then the key
758 types after it will be appended to the default instead of
759 replacing it. The default for this option is:
760
761 ecdsa-sha2-nistp256-cert-v01@openssh.com,
762 ecdsa-sha2-nistp384-cert-v01@openssh.com,
763 ecdsa-sha2-nistp521-cert-v01@openssh.com,
764 ssh-ed25519-cert-v01@openssh.com,
765 ssh-rsa-cert-v01@openssh.com,
766 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
767 ssh-ed25519,ssh-rsa
768
769 The -Q option of ssh(1) may be used to list supported key types.
770
771 PubkeyAuthentication
772 Specifies whether to try public key authentication. The argument
773 to this keyword must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\yesM-bM-^@M-^].
774
775 RekeyLimit
776 Specifies the maximum amount of data that may be transmitted
777 before the session key is renegotiated, optionally followed a
778 maximum amount of time that may pass before the session key is
779 renegotiated. The first argument is specified in bytes and may
780 have a suffix of M-bM-^@M-^XKM-bM-^@M-^Y, M-bM-^@M-^XMM-bM-^@M-^Y, or M-bM-^@M-^XGM-bM-^@M-^Y to indicate Kilobytes,
781 Megabytes, or Gigabytes, respectively. The default is between
782 M-bM-^@M-^X1GM-bM-^@M-^Y and M-bM-^@M-^X4GM-bM-^@M-^Y, depending on the cipher. The optional second
783 value is specified in seconds and may use any of the units
784 documented in the TIME FORMATS section of sshd_config(5). The
785 default value for RekeyLimit is M-bM-^@M-^\default noneM-bM-^@M-^], which means that
786 rekeying is performed after the cipher's default amount of data
787 has been sent or received and no time based rekeying is done.
788
789 RemoteForward
790 Specifies that a TCP port on the remote machine be forwarded over
791 the secure channel to the specified host and port from the local
792 machine. The first argument must be [bind_address:]port and the
793 second argument must be host:hostport. IPv6 addresses can be
794 specified by enclosing addresses in square brackets. Multiple
795 forwardings may be specified, and additional forwardings can be
796 given on the command line. Privileged ports can be forwarded
797 only when logging in as root on the remote machine.
798
799 If the port argument is M-bM-^@M-^X0M-bM-^@M-^Y, the listen port will be dynamically
800 allocated on the server and reported to the client at run time.
801
802 If the bind_address is not specified, the default is to only bind
803 to loopback addresses. If the bind_address is M-bM-^@M-^X*M-bM-^@M-^Y or an empty
804 string, then the forwarding is requested to listen on all
805 interfaces. Specifying a remote bind_address will only succeed
806 if the server's GatewayPorts option is enabled (see
807 sshd_config(5)).
808
809 RequestTTY
810 Specifies whether to request a pseudo-tty for the session. The
811 argument may be one of: M-bM-^@M-^\noM-bM-^@M-^] (never request a TTY), M-bM-^@M-^\yesM-bM-^@M-^] (always
812 request a TTY when standard input is a TTY), M-bM-^@M-^\forceM-bM-^@M-^] (always
813 request a TTY) or M-bM-^@M-^\autoM-bM-^@M-^] (request a TTY when opening a login
814 session). This option mirrors the -t and -T flags for ssh(1).
815
816 RevokedHostKeys
817 Specifies revoked host public keys. Keys listed in this file
818 will be refused for host authentication. Note that if this file
819 does not exist or is not readable, then host authentication will
820 be refused for all hosts. Keys may be specified as a text file,
821 listing one public key per line, or as an OpenSSH Key Revocation
822 List (KRL) as generated by ssh-keygen(1). For more information
823 on KRLs, see the KEY REVOCATION LISTS section in ssh-keygen(1).
824
825 RhostsRSAAuthentication
826 Specifies whether to try rhosts based authentication with RSA
827 host authentication. The argument must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The
828 default is M-bM-^@M-^\noM-bM-^@M-^]. This option applies to protocol version 1 only
829 and requires ssh(1) to be setuid root.
830
831 RSAAuthentication
832 Specifies whether to try RSA authentication. The argument to
833 this keyword must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. RSA authentication will only
834 be attempted if the identity file exists, or an authentication
835 agent is running. The default is M-bM-^@M-^\yesM-bM-^@M-^]. Note that this option
836 applies to protocol version 1 only.
837
838 SendEnv
839 Specifies what variables from the local environ(7) should be sent
840 to the server. The server must also support it, and the server
841 must be configured to accept these environment variables. Note
842 that the TERM environment variable is always sent whenever a
843 pseudo-terminal is requested as it is required by the protocol.
844 Refer to AcceptEnv in sshd_config(5) for how to configure the
845 server. Variables are specified by name, which may contain
846 wildcard characters. Multiple environment variables may be
847 separated by whitespace or spread across multiple SendEnv
848 directives. The default is not to send any environment
849 variables.
850
851 See PATTERNS for more information on patterns.
852
853 ServerAliveCountMax
854 Sets the number of server alive messages (see below) which may be
855 sent without ssh(1) receiving any messages back from the server.
856 If this threshold is reached while server alive messages are
857 being sent, ssh will disconnect from the server, terminating the
858 session. It is important to note that the use of server alive
859 messages is very different from TCPKeepAlive (below). The server
860 alive messages are sent through the encrypted channel and
861 therefore will not be spoofable. The TCP keepalive option
862 enabled by TCPKeepAlive is spoofable. The server alive mechanism
863 is valuable when the client or server depend on knowing when a
864 connection has become inactive.
865
866 The default value is 3. If, for example, ServerAliveInterval
867 (see below) is set to 15 and ServerAliveCountMax is left at the
868 default, if the server becomes unresponsive, ssh will disconnect
869 after approximately 45 seconds.
870
871 ServerAliveInterval
872 Sets a timeout interval in seconds after which if no data has
873 been received from the server, ssh(1) will send a message through
874 the encrypted channel to request a response from the server. The
875 default is 0, indicating that these messages will not be sent to
876 the server.
877
878 StreamLocalBindMask
879 Sets the octal file creation mode mask (umask) used when creating
880 a Unix-domain socket file for local or remote port forwarding.
881 This option is only used for port forwarding to a Unix-domain
882 socket file.
883
884 The default value is 0177, which creates a Unix-domain socket
885 file that is readable and writable only by the owner. Note that
886 not all operating systems honor the file mode on Unix-domain
887 socket files.
888
889 StreamLocalBindUnlink
890 Specifies whether to remove an existing Unix-domain socket file
891 for local or remote port forwarding before creating a new one.
892 If the socket file already exists and StreamLocalBindUnlink is
893 not enabled, ssh will be unable to forward the port to the Unix-
894 domain socket file. This option is only used for port forwarding
895 to a Unix-domain socket file.
896
897 The argument must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\noM-bM-^@M-^].
898
899 StrictHostKeyChecking
900 If this flag is set to M-bM-^@M-^\yesM-bM-^@M-^], ssh(1) will never automatically add
901 host keys to the ~/.ssh/known_hosts file, and refuses to connect
902 to hosts whose host key has changed. This provides maximum
903 protection against trojan horse attacks, though it can be
904 annoying when the /etc/ssh/ssh_known_hosts file is poorly
905 maintained or when connections to new hosts are frequently made.
906 This option forces the user to manually add all new hosts. If
907 this flag is set to M-bM-^@M-^\noM-bM-^@M-^], ssh will automatically add new host
908 keys to the user known hosts files. If this flag is set to
909 M-bM-^@M-^\askM-bM-^@M-^], new host keys will be added to the user known host files
910 only after the user has confirmed that is what they really want
911 to do, and ssh will refuse to connect to hosts whose host key has
912 changed. The host keys of known hosts will be verified
913 automatically in all cases. The argument must be M-bM-^@M-^\yesM-bM-^@M-^], M-bM-^@M-^\noM-bM-^@M-^], or
914 M-bM-^@M-^\askM-bM-^@M-^]. The default is M-bM-^@M-^\askM-bM-^@M-^].
915
916 TCPKeepAlive
917 Specifies whether the system should send TCP keepalive messages
918 to the other side. If they are sent, death of the connection or
919 crash of one of the machines will be properly noticed. However,
920 this means that connections will die if the route is down
921 temporarily, and some people find it annoying.
922
923 The default is M-bM-^@M-^\yesM-bM-^@M-^] (to send TCP keepalive messages), and the
924 client will notice if the network goes down or the remote host
925 dies. This is important in scripts, and many users want it too.
926
927 To disable TCP keepalive messages, the value should be set to
928 M-bM-^@M-^\noM-bM-^@M-^].
929
930 Tunnel Request tun(4) device forwarding between the client and the
931 server. The argument must be M-bM-^@M-^\yesM-bM-^@M-^], M-bM-^@M-^\point-to-pointM-bM-^@M-^] (layer 3),
932 M-bM-^@M-^\ethernetM-bM-^@M-^] (layer 2), or M-bM-^@M-^\noM-bM-^@M-^]. Specifying M-bM-^@M-^\yesM-bM-^@M-^] requests the
933 default tunnel mode, which is M-bM-^@M-^\point-to-pointM-bM-^@M-^]. The default is
934 M-bM-^@M-^\noM-bM-^@M-^].
935
936 TunnelDevice
937 Specifies the tun(4) devices to open on the client (local_tun)
938 and the server (remote_tun).
939
940 The argument must be local_tun[:remote_tun]. The devices may be
941 specified by numerical ID or the keyword M-bM-^@M-^\anyM-bM-^@M-^], which uses the
942 next available tunnel device. If remote_tun is not specified, it
943 defaults to M-bM-^@M-^\anyM-bM-^@M-^]. The default is M-bM-^@M-^\any:anyM-bM-^@M-^].
944
945 UpdateHostKeys
946 Specifies whether ssh(1) should accept notifications of
947 additional hostkeys from the server sent after authentication has
948 completed and add them to UserKnownHostsFile. The argument must
949 be M-bM-^@M-^\yesM-bM-^@M-^], M-bM-^@M-^\noM-bM-^@M-^] (the default) or M-bM-^@M-^\askM-bM-^@M-^]. Enabling this option
950 allows learning alternate hostkeys for a server and supports
951 graceful key rotation by allowing a server to send replacement
952 public keys before old ones are removed. Additional hostkeys are
953 only accepted if the key used to authenticate the host was
954 already trusted or explicitly accepted by the user. If
955 UpdateHostKeys is set to M-bM-^@M-^\askM-bM-^@M-^], then the user is asked to confirm
956 the modifications to the known_hosts file. Confirmation is
957 currently incompatible with ControlPersist, and will be disabled
958 if it is enabled.
959
960 Presently, only sshd(8) from OpenSSH 6.8 and greater support the
961 M-bM-^@M-^\hostkeys@openssh.comM-bM-^@M-^] protocol extension used to inform the
962 client of all the server's hostkeys.
963
964 UsePrivilegedPort
965 Specifies whether to use a privileged port for outgoing
966 connections. The argument must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is
967 M-bM-^@M-^\noM-bM-^@M-^]. If set to M-bM-^@M-^\yesM-bM-^@M-^], ssh(1) must be setuid root. Note that
968 this option must be set to M-bM-^@M-^\yesM-bM-^@M-^] for RhostsRSAAuthentication with
969 older servers.
970
971 User Specifies the user to log in as. This can be useful when a
972 different user name is used on different machines. This saves
973 the trouble of having to remember to give the user name on the
974 command line.
975
976 UserKnownHostsFile
977 Specifies one or more files to use for the user host key
978 database, separated by whitespace. The default is
979 ~/.ssh/known_hosts, ~/.ssh/known_hosts2.
980
981 VerifyHostKeyDNS
982 Specifies whether to verify the remote key using DNS and SSHFP
983 resource records. If this option is set to M-bM-^@M-^\yesM-bM-^@M-^], the client
984 will implicitly trust keys that match a secure fingerprint from
985 DNS. Insecure fingerprints will be handled as if this option was
986 set to M-bM-^@M-^\askM-bM-^@M-^]. If this option is set to M-bM-^@M-^\askM-bM-^@M-^], information on
987 fingerprint match will be displayed, but the user will still need
988 to confirm new host keys according to the StrictHostKeyChecking
989 option. The argument must be M-bM-^@M-^\yesM-bM-^@M-^], M-bM-^@M-^\noM-bM-^@M-^], or M-bM-^@M-^\askM-bM-^@M-^]. The default
990 is M-bM-^@M-^\noM-bM-^@M-^].
991
992 See also VERIFYING HOST KEYS in ssh(1).
993
994 VisualHostKey
995 If this flag is set to M-bM-^@M-^\yesM-bM-^@M-^], an ASCII art representation of the
996 remote host key fingerprint is printed in addition to the
997 fingerprint string at login and for unknown host keys. If this
998 flag is set to M-bM-^@M-^\noM-bM-^@M-^], no fingerprint strings are printed at login
999 and only the fingerprint string will be printed for unknown host
1000 keys. The default is M-bM-^@M-^\noM-bM-^@M-^].
1001
1002 XAuthLocation
1003 Specifies the full pathname of the xauth(1) program. The default
1004 is /usr/X11R6/bin/xauth.
1005
1006PATTERNS
1007 A pattern consists of zero or more non-whitespace characters, M-bM-^@M-^X*M-bM-^@M-^Y (a
1008 wildcard that matches zero or more characters), or M-bM-^@M-^X?M-bM-^@M-^Y (a wildcard that
1009 matches exactly one character). For example, to specify a set of
1010 declarations for any host in the M-bM-^@M-^\.co.ukM-bM-^@M-^] set of domains, the following
1011 pattern could be used:
1012
1013 Host *.co.uk
1014
1015 The following pattern would match any host in the 192.168.0.[0-9] network
1016 range:
1017
1018 Host 192.168.0.?
1019
1020 A pattern-list is a comma-separated list of patterns. Patterns within
1021 pattern-lists may be negated by preceding them with an exclamation mark
1022 (M-bM-^@M-^X!M-bM-^@M-^Y). For example, to allow a key to be used from anywhere within an
1023 organization except from the M-bM-^@M-^\dialupM-bM-^@M-^] pool, the following entry (in
1024 authorized_keys) could be used:
1025
1026 from="!*.dialup.example.com,*.example.com"
1027
1028FILES
1029 ~/.ssh/config
1030 This is the per-user configuration file. The format of this file
1031 is described above. This file is used by the SSH client.
1032 Because of the potential for abuse, this file must have strict
1033 permissions: read/write for the user, and not accessible by
1034 others.
1035
1036 /etc/ssh/ssh_config
1037 Systemwide configuration file. This file provides defaults for
1038 those values that are not specified in the user's configuration
1039 file, and for those users who do not have a configuration file.
1040 This file must be world-readable.
1041
1042SEE ALSO
1043 ssh(1)
1044
1045AUTHORS
1046 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
1047 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
1048 de Raadt and Dug Song removed many bugs, re-added newer features and
1049 created OpenSSH. Markus Friedl contributed the support for SSH protocol
1050 versions 1.5 and 2.0.
1051
1052OpenBSD 5.9 February 20, 2016 OpenBSD 5.9
generated by cgit v1.2.3 (git 2.39.1) at 2024-06-29 08:36:47 +0000