1SSH_CONFIG(5) BSD File Formats Manual SSH_CONFIG(5)
2
4 ssh_config — OpenSSH client configuration file
5
7 ssh(1) obtains configuration data from the following sources in the fol‐
8 lowing order:
9 1. command-line options
11 2. user's configuration file (~/.ssh/config)
12 3. GSSAPI configuration file ($HOME/.ssh/config.gssapi)
13 4. Kerberos configuration file ($HOME/.ssh/config.krb)
14 5. system-wide configuration file (/etc/gsissh/ssh_config)
15 For each parameter, the first obtained value will be used. The configu‐
17 ration files contain sections separated by Host specifications, and that
18 section is only applied for hosts that match one of the patterns given in
19 the specification. The matched host name is usually the one given on the
20 command line (see the CanonicalizeHostname option for exceptions).
21 Since the first obtained value for each parameter is used, more host-spe‐
23 cific declarations should be given near the beginning of the file, and
24 general defaults at the end.
25 The file contains keyword-argument pairs, one per line. Lines starting
27 with ‘#’ and empty lines are interpreted as comments. Arguments may op‐
28 tionally be enclosed in double quotes (") in order to represent arguments
29 containing spaces. Configuration options may be separated by whitespace
30 or optional whitespace and exactly one ‘=’; the latter format is useful
31 to avoid the need to quote whitespace when specifying configuration op‐
32 tions using the ssh, scp, and sftp -o option.
33 The possible keywords and their meanings are as follows (note that key‐
35 words are case-insensitive and arguments are case-sensitive):
36 Host Restricts the following declarations (up to the next Host or
38 Match keyword) to be only for those hosts that match one of the
39 patterns given after the keyword. If more than one pattern is
40 provided, they should be separated by whitespace. A single ‘*’
41 as a pattern can be used to provide global defaults for all
42 hosts. The host is usually the hostname argument given on the
43 command line (see the CanonicalizeHostname keyword for excep‐
44 tions).
45 A pattern entry may be negated by prefixing it with an exclama‐
47 tion mark (‘!’). If a negated entry is matched, then the Host
48 entry is ignored, regardless of whether any other patterns on the
49 line match. Negated matches are therefore useful to provide ex‐
50 ceptions for wildcard matches.
51 See PATTERNS for more information on patterns.
53 Match Restricts the following declarations (up to the next Host or
55 Match keyword) to be used only when the conditions following the
56 Match keyword are satisfied. Match conditions are specified us‐
57 ing one or more criteria or the single token all which always
58 matches. The available criteria keywords are: canonical, final,
59 exec, host, originalhost, user, and localuser. The all criteria
60 must appear alone or immediately after canonical or final. Other
61 criteria may be combined arbitrarily. All criteria but all,
62 canonical, and final require an argument. Criteria may be
63 negated by prepending an exclamation mark (‘!’).
64 The canonical keyword matches only when the configuration file is
66 being re-parsed after hostname canonicalization (see the
67 CanonicalizeHostname option). This may be useful to specify con‐
68 ditions that work with canonical host names only.
69 The final keyword requests that the configuration be re-parsed
71 (regardless of whether CanonicalizeHostname is enabled), and
72 matches only during this final pass. If CanonicalizeHostname is
73 enabled, then canonical and final match during the same pass.
74 The exec keyword executes the specified command under the user's
76 shell. If the command returns a zero exit status then the condi‐
77 tion is considered true. Commands containing whitespace charac‐
78 ters must be quoted. Arguments to exec accept the tokens de‐
79 scribed in the TOKENS section.
80 The other keywords' criteria must be single entries or comma-sep‐
82 arated lists and may use the wildcard and negation operators de‐
83 scribed in the PATTERNS section. The criteria for the host key‐
84 word are matched against the target hostname, after any substitu‐
85 tion by the Hostname or CanonicalizeHostname options. The
86 originalhost keyword matches against the hostname as it was spec‐
87 ified on the command-line. The user keyword matches against the
88 target username on the remote host. The localuser keyword
89 matches against the name of the local user running ssh(1) (this
90 keyword may be useful in system-wide ssh_config files).
91 AddKeysToAgent
93 Specifies whether keys should be automatically added to a running
94 ssh-agent(1). If this option is set to yes and a key is loaded
95 from a file, the key and its passphrase are added to the agent
96 with the default lifetime, as if by ssh-add(1). If this option
97 is set to ask, ssh(1) will require confirmation using the
98 SSH_ASKPASS program before adding a key (see ssh-add(1) for de‐
99 tails). If this option is set to confirm, each use of the key
100 must be confirmed, as if the -c option was specified to
101 ssh-add(1). If this option is set to no, no keys are added to
102 the agent. Alternately, this option may be specified as a time
103 interval using the format described in the TIME FORMATS section
104 of sshd_config(5) to specify the key's lifetime in ssh-agent(1),
105 after which it will automatically be removed. The argument must
106 be no (the default), yes, confirm (optionally followed by a time
107 interval), ask or a time interval.
108 AddressFamily
110 Specifies which address family to use when connecting. Valid ar‐
111 guments are any (the default), inet (use IPv4 only), or inet6
112 (use IPv6 only).
113 BatchMode
115 If set to yes, user interaction such as password prompts and host
116 key confirmation requests will be disabled. This option is use‐
117 ful in scripts and other batch jobs where no user is present to
118 interact with ssh(1). The argument must be yes or no (the de‐
119 fault).
120 BindAddress
122 Use the specified address on the local machine as the source ad‐
123 dress of the connection. Only useful on systems with more than
124 one address.
125 BindInterface
127 Use the address of the specified interface on the local machine
128 as the source address of the connection.
129 CanonicalDomains
131 When CanonicalizeHostname is enabled, this option specifies the
132 list of domain suffixes in which to search for the specified des‐
133 tination host.
134 CanonicalizeFallbackLocal
136 Specifies whether to fail with an error when hostname canonical‐
137 ization fails. The default, yes, will attempt to look up the un‐
138 qualified hostname using the system resolver's search rules. A
139 value of no will cause ssh(1) to fail instantly if
140 CanonicalizeHostname is enabled and the target hostname cannot be
141 found in any of the domains specified by CanonicalDomains.
142 CanonicalizeHostname
144 Controls whether explicit hostname canonicalization is performed.
145 The default, no, is not to perform any name rewriting and let the
146 system resolver handle all hostname lookups. If set to yes then,
147 for connections that do not use a ProxyCommand or ProxyJump,
148 ssh(1) will attempt to canonicalize the hostname specified on the
149 command line using the CanonicalDomains suffixes and
150 CanonicalizePermittedCNAMEs rules. If CanonicalizeHostname is
151 set to always, then canonicalization is applied to proxied con‐
152 nections too.
153 If this option is enabled, then the configuration files are pro‐
155 cessed again using the new target name to pick up any new config‐
156 uration in matching Host and Match stanzas. A value of none dis‐
157 ables the use of a ProxyJump host.
158 CanonicalizeMaxDots
160 Specifies the maximum number of dot characters in a hostname be‐
161 fore canonicalization is disabled. The default, 1, allows a sin‐
162 gle dot (i.e. hostname.subdomain).
163 CanonicalizePermittedCNAMEs
165 Specifies rules to determine whether CNAMEs should be followed
166 when canonicalizing hostnames. The rules consist of one or more
167 arguments of source_domain_list:target_domain_list, where
168 source_domain_list is a pattern-list of domains that may follow
169 CNAMEs in canonicalization, and target_domain_list is a pattern-
170 list of domains that they may resolve to.
171 For example, "*.a.example.com:*.b.example.com,*.c.example.com"
173 will allow hostnames matching "*.a.example.com" to be canonical‐
174 ized to names in the "*.b.example.com" or "*.c.example.com" do‐
175 mains.
176 CASignatureAlgorithms
178 The default is handled system-wide by crypto-policies(7). To see
179 the defaults and how to modify this default, see manual page
180 update-crypto-policies(8).
181 Specifies which algorithms are allowed for signing of certifi‐
183 cates by certificate authorities (CAs). If the specified list
184 begins with a ‘+’ character, then the specified algorithms will
185 be appended to the default set instead of replacing them. If the
186 specified list begins with a ‘-’ character, then the specified
187 algorithms (including wildcards) will be removed from the default
188 set instead of replacing them.
189 ssh(1) will not accept host certificates signed using algorithms
191 other than those specified.
192 CertificateFile
194 Specifies a file from which the user's certificate is read. A
195 corresponding private key must be provided separately in order to
196 use this certificate either from an IdentityFile directive or -i
197 flag to ssh(1), via ssh-agent(1), or via a PKCS11Provider or
198 SecurityKeyProvider.
199 Arguments to CertificateFile may use the tilde syntax to refer to
201 a user's home directory, the tokens described in the TOKENS sec‐
202 tion and environment variables as described in the ENVIRONMENT
203 VARIABLES section.
204 It is possible to have multiple certificate files specified in
206 configuration files; these certificates will be tried in se‐
207 quence. Multiple CertificateFile directives will add to the list
208 of certificates used for authentication.
209 CheckHostIP
211 If set to yes [22mssh(1) will additionally check the host IP address
212 in the known_hosts file. This allows it to detect if a host key
213 changed due to DNS spoofing and will add addresses of destination
214 hosts to ~/.ssh/known_hosts in the process, regardless of the
215 setting of StrictHostKeyChecking. If the option is set to no
216 (the default), the check will not be executed.
217 Ciphers
219 The default is handled system-wide by crypto-policies(7). To see
220 the defaults and how to modify this default, see manual page
221 update-crypto-policies(8).
222 Specifies the ciphers allowed and their order of preference.
224 Multiple ciphers must be comma-separated. If the specified list
225 begins with a ‘+’ character, then the specified ciphers will be
226 appended to the built-in openssh default set instead of replacing
227 them. If the specified list begins with a ‘-’ character, then
228 the specified ciphers (including wildcards) will be removed from
229 the built-in openssh default set instead of replacing them. If
230 the specified list begins with a ‘^’ character, then the speci‐
231 fied ciphers will be placed at the head of the built-in openssh
232 default set.
233 The supported ciphers are:
235 3des-cbc
237 aes128-cbc
238 aes192-cbc
239 aes256-cbc
240 aes128-ctr
241 aes192-ctr
242 aes256-ctr
243 aes128-gcm@openssh.com
244 aes256-gcm@openssh.com
245 chacha20-poly1305@openssh.com
246 The list of available ciphers may also be obtained using "ssh -Q
248 cipher".
249 ClearAllForwardings
251 Specifies that all local, remote, and dynamic port forwardings
252 specified in the configuration files or on the command line be
253 cleared. This option is primarily useful when used from the
254 ssh(1) command line to clear port forwardings set in configura‐
255 tion files, and is automatically set by scp(1) and sftp(1). The
256 argument must be yes or no (the default).
257 Compression
259 Specifies whether to use compression. The argument must be yes
260 or no (the default).
261 ConnectionAttempts
263 Specifies the number of tries (one per second) to make before ex‐
264 iting. The argument must be an integer. This may be useful in
265 scripts if the connection sometimes fails. The default is 1.
266 ConnectTimeout
268 Specifies the timeout (in seconds) used when connecting to the
269 SSH server, instead of using the default system TCP timeout.
270 This timeout is applied both to establishing the connection and
271 to performing the initial SSH protocol handshake and key ex‐
272 change.
273 ControlMaster
275 Enables the sharing of multiple sessions over a single network
276 connection. When set to yes, ssh(1) will listen for connections
277 on a control socket specified using the ControlPath argument.
278 Additional sessions can connect to this socket using the same
279 ControlPath with ControlMaster set to no (the default). These
280 sessions will try to reuse the master instance's network connec‐
281 tion rather than initiating new ones, but will fall back to con‐
282 necting normally if the control socket does not exist, or is not
283 listening.
284 Setting this to ask will cause ssh(1) to listen for control con‐
286 nections, but require confirmation using ssh-askpass(1). If the
287 ControlPath cannot be opened, ssh(1) will continue without con‐
288 necting to a master instance.
289 X11 and ssh-agent(1) forwarding is supported over these multi‐
291 plexed connections, however the display and agent forwarded will
292 be the one belonging to the master connection i.e. it is not pos‐
293 sible to forward multiple displays or agents.
294 Two additional options allow for opportunistic multiplexing: try
296 to use a master connection but fall back to creating a new one if
297 one does not already exist. These options are: auto and autoask.
298 The latter requires confirmation like the ask option.
299 ControlPath
301 Specify the path to the control socket used for connection shar‐
302 ing as described in the ControlMaster section above or the string
303 none to disable connection sharing. Arguments to ControlPath may
304 use the tilde syntax to refer to a user's home directory, the to‐
305 kens described in the TOKENS section and environment variables as
306 described in the ENVIRONMENT VARIABLES section. It is recom‐
307 mended that any ControlPath used for opportunistic connection
308 sharing include at least %h, %p, and %r (or alternatively %C) and
309 be placed in a directory that is not writable by other users.
310 This ensures that shared connections are uniquely identified.
311 ControlPersist
313 When used in conjunction with ControlMaster, specifies that the
314 master connection should remain open in the background (waiting
315 for future client connections) after the initial client connec‐
316 tion has been closed. If set to no (the default), then the mas‐
317 ter connection will not be placed into the background, and will
318 close as soon as the initial client connection is closed. If set
319 to yes or 0, then the master connection will remain in the back‐
320 ground indefinitely (until killed or closed via a mechanism such
321 as the "ssh -O exit"). If set to a time in seconds, or a time in
322 any of the formats documented in sshd_config(5), then the back‐
323 grounded master connection will automatically terminate after it
324 has remained idle (with no client connections) for the specified
325 time.
326 DynamicForward
328 Specifies that a TCP port on the local machine be forwarded over
329 the secure channel, and the application protocol is then used to
330 determine where to connect to from the remote machine.
331 The argument must be [bind_address:]port. IPv6 addresses can be
333 specified by enclosing addresses in square brackets. By default,
334 the local port is bound in accordance with the GatewayPorts set‐
335 ting. However, an explicit bind_address may be used to bind the
336 connection to a specific address. The bind_address of localhost
337 indicates that the listening port be bound for local use only,
338 while an empty address or ‘*’ indicates that the port should be
339 available from all interfaces.
340 Currently the SOCKS4 and SOCKS5 protocols are supported, and
342 ssh(1) will act as a SOCKS server. Multiple forwardings may be
343 specified, and additional forwardings can be given on the command
344 line. Only the superuser can forward privileged ports.
345 EnableSSHKeysign
347 Setting this option to yes in the global client configuration
348 file /etc/gsissh/ssh_config enables the use of the helper program
349 ssh-keysign(8) during HostbasedAuthentication. The argument must
350 be yes or no (the default). This option should be placed in the
351 non-hostspecific section. See ssh-keysign(8) for more informa‐
352 tion.
353 EscapeChar
355 Sets the escape character (default: ‘~’). The escape character
356 can also be set on the command line. The argument should be a
357 single character, ‘^’ followed by a letter, or none to disable
358 the escape character entirely (making the connection transparent
359 for binary data).
360 ExitOnForwardFailure
362 Specifies whether ssh(1) should terminate the connection if it
363 cannot set up all requested dynamic, tunnel, local, and remote
364 port forwardings, (e.g. if either end is unable to bind and lis‐
365 ten on a specified port). Note that ExitOnForwardFailure does
366 not apply to connections made over port forwardings and will not,
367 for example, cause ssh(1) to exit if TCP connections to the ulti‐
368 mate forwarding destination fail. The argument must be yes or no
369 (the default).
370 FingerprintHash
372 Specifies the hash algorithm used when displaying key finger‐
373 prints. Valid options are: md5 and sha256 (the default).
374 ForkAfterAuthentication
376 Requests ssh to go to background just before command execution.
377 This is useful if ssh is going to ask for passwords or
378 passphrases, but the user wants it in the background. This im‐
379 plies the StdinNull configuration option being set to “yes”. The
380 recommended way to start X11 programs at a remote site is with
381 something like ssh -f host xterm, which is the same as ssh host
382 xterm if the ForkAfterAuthentication configuration option is set
383 to “yes”.
384 If the ExitOnForwardFailure configuration option is set to “yes”,
386 then a client started with the ForkAfterAuthentication configura‐
387 tion option being set to “yes” will wait for all remote port for‐
388 wards to be successfully established before placing itself in the
389 background. The argument to this keyword must be yes (same as
390 the -f option) or no (the default).
391 ForwardAgent
393 Specifies whether the connection to the authentication agent (if
394 any) will be forwarded to the remote machine. The argument may
395 be yes, no (the default), an explicit path to an agent socket or
396 the name of an environment variable (beginning with ‘$’) in which
397 to find the path.
398 Agent forwarding should be enabled with caution. Users with the
400 ability to bypass file permissions on the remote host (for the
401 agent's Unix-domain socket) can access the local agent through
402 the forwarded connection. An attacker cannot obtain key material
403 from the agent, however they can perform operations on the keys
404 that enable them to authenticate using the identities loaded into
405 the agent.
406 ForwardX11
408 Specifies whether X11 connections will be automatically redi‐
409 rected over the secure channel and DISPLAY set. The argument
410 must be yes or no (the default).
411 X11 forwarding should be enabled with caution. Users with the
413 ability to bypass file permissions on the remote host (for the
414 user's X11 authorization database) can access the local X11 dis‐
415 play through the forwarded connection. An attacker may then be
416 able to perform activities such as keystroke monitoring if the
417 ForwardX11Trusted option is also enabled.
418 ForwardX11Timeout
420 Specify a timeout for untrusted X11 forwarding using the format
421 described in the TIME FORMATS section of sshd_config(5). X11
422 connections received by ssh(1) after this time will be refused.
423 Setting ForwardX11Timeout to zero will disable the timeout and
424 permit X11 forwarding for the life of the connection. The de‐
425 fault is to disable untrusted X11 forwarding after twenty minutes
426 has elapsed.
427 ForwardX11Trusted
429 If this option is set to yes, remote X11 clients will have full
430 access to the original X11 display.
431 If this option is set to no (the default), remote X11 clients
433 will be considered untrusted and prevented from stealing or tam‐
434 pering with data belonging to trusted X11 clients. Furthermore,
435 the xauth(1) token used for the session will be set to expire af‐
436 ter 20 minutes. Remote clients will be refused access after this
437 time.
438 See the X11 SECURITY extension specification for full details on
440 the restrictions imposed on untrusted clients.
441 GatewayPorts
443 Specifies whether remote hosts are allowed to connect to local
444 forwarded ports. By default, ssh(1) binds local port forwardings
445 to the loopback address. This prevents other remote hosts from
446 connecting to forwarded ports. GatewayPorts can be used to spec‐
447 ify that ssh should bind local port forwardings to the wildcard
448 address, thus allowing remote hosts to connect to forwarded
449 ports. The argument must be yes or no (the default).
450 GlobalKnownHostsFile
452 Specifies one or more files to use for the global host key data‐
453 base, separated by whitespace. The default is
454 /etc/gsissh/ssh_known_hosts, /etc/gsissh/ssh_known_hosts2.
455 GSSAPIAuthentication
457 Specifies whether user authentication based on GSSAPI is allowed.
458 The default is yes.
459 GSSAPIClientIdentity
461 If set, specifies the GSSAPI client identity that ssh should use
462 when connecting to the server. The default is unset, which means
463 that the default identity will be used.
464 GSSAPIDelegateCredentials
466 Forward (delegate) credentials to the server. The default is
467 yes.
468 GSSAPIKeyExchange
470 Specifies whether key exchange based on GSSAPI may be used. When
471 using GSSAPI key exchange the server need not have a host key.
472 The default is “yes”.
473 GSSAPIRenewalForcesRekey
475 If set to “yes” then renewal of the client's GSSAPI credentials
476 will force the rekeying of the ssh connection. With a compatible
477 server, this will delegate the renewed credentials to a session
478 on the server.
479 Checks are made to ensure that credentials are only propagated
481 when the new credentials match the old ones on the originating
482 client and where the receiving server still has the old set in
483 its cache.
484 The default is “no”.
486 For this to work GSSAPIKeyExchange needs to be enabled in the
488 server and also used by the client.
489 GSSAPIServerIdentity
491 If set, specifies the GSSAPI server identity that ssh should ex‐
492 pect when connecting to the server. The default is unset, which
493 means that the expected GSSAPI server identity will be determined
494 from the target hostname.
495 GSSAPITrustDns
497 Set to “yes” to indicate that the DNS is trusted to securely
498 canonicalize the name of the host being connected to. If “no”,
499 the hostname entered on the command line will be passed untouched
500 to the GSSAPI library. The default is “no”.
501 GSSAPIKexAlgorithms
503 The default is handled system-wide by crypto-policies(7). To see
504 the defaults and how to modify this default, see manual page
505 update-crypto-policies(8).
506 The list of key exchange algorithms that are offered for GSSAPI
508 key exchange. Possible values are
509 gss-gex-sha1-,
511 gss-group1-sha1-,
512 gss-group14-sha1-,
513 gss-group14-sha256-,
514 gss-group16-sha512-,
515 gss-nistp256-sha256-,
516 gss-curve25519-sha256-
517 This option only applies to connections using GSSAPI.
519 HashKnownHosts
521 Indicates that ssh(1) should hash host names and addresses when
522 they are added to ~/.ssh/known_hosts. These hashed names may be
523 used normally by ssh(1) and sshd(8), but they do not visually re‐
524 veal identifying information if the file's contents are dis‐
525 closed. The default is no. Note that existing names and ad‐
526 dresses in known hosts files will not be converted automatically,
527 but may be manually hashed using ssh-keygen(1).
528 HostbasedAcceptedAlgorithms
530 Specifies the signature algorithms that will be used for host‐
531 based authentication as a comma-separated list of patterns. Al‐
532 ternately if the specified list begins with a ‘+’ character, then
533 the specified signature algorithms will be appended to the de‐
534 fault set instead of replacing them. If the specified list be‐
535 gins with a ‘-’ character, then the specified signature algo‐
536 rithms (including wildcards) will be removed from the default set
537 instead of replacing them. If the specified list begins with a
538 ‘^’ character, then the specified signature algorithms will be
539 placed at the head of the default set. The default for this op‐
540 tion is:
541 ssh-ed25519-cert-v01@openssh.com,
543 ecdsa-sha2-nistp256-cert-v01@openssh.com,
544 ecdsa-sha2-nistp384-cert-v01@openssh.com,
545 ecdsa-sha2-nistp521-cert-v01@openssh.com,
546 sk-ssh-ed25519-cert-v01@openssh.com,
547 sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
548 rsa-sha2-512-cert-v01@openssh.com,
549 rsa-sha2-256-cert-v01@openssh.com,
550 ssh-rsa-cert-v01@openssh.com,
551 ssh-ed25519,
552 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
553 sk-ssh-ed25519@openssh.com,
554 sk-ecdsa-sha2-nistp256@openssh.com,
555 rsa-sha2-512,rsa-sha2-256,ssh-rsa
556 The -Q option of ssh(1) may be used to list supported signature
558 algorithms. This was formerly named HostbasedKeyTypes.
559 HostbasedAuthentication
561 Specifies whether to try rhosts based authentication with public
562 key authentication. The argument must be yes or no (the de‐
563 fault).
564 HostKeyAlgorithms
566 Specifies the host key signature algorithms that the client wants
567 to use in order of preference. Alternately if the specified list
568 begins with a ‘+’ character, then the specified signature algo‐
569 rithms will be appended to the default set instead of replacing
570 them. If the specified list begins with a ‘-’ character, then
571 the specified signature algorithms (including wildcards) will be
572 removed from the default set instead of replacing them. If the
573 specified list begins with a ‘^’ character, then the specified
574 signature algorithms will be placed at the head of the default
575 set. The default for this option is:
576 ssh-ed25519-cert-v01@openssh.com,
578 ecdsa-sha2-nistp256-cert-v01@openssh.com,
579 ecdsa-sha2-nistp384-cert-v01@openssh.com,
580 ecdsa-sha2-nistp521-cert-v01@openssh.com,
581 sk-ssh-ed25519-cert-v01@openssh.com,
582 sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
583 rsa-sha2-512-cert-v01@openssh.com,
584 rsa-sha2-256-cert-v01@openssh.com,
585 ssh-rsa-cert-v01@openssh.com,
586 ssh-ed25519,
587 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
588 sk-ecdsa-sha2-nistp256@openssh.com,
589 sk-ssh-ed25519@openssh.com,
590 rsa-sha2-512,rsa-sha2-256,ssh-rsa
591 If hostkeys are known for the destination host then this default
593 is modified to prefer their algorithms.
594 The list of available signature algorithms may also be obtained
596 using "ssh -Q HostKeyAlgorithms".
597 HostKeyAlias
599 Specifies an alias that should be used instead of the real host
600 name when looking up or saving the host key in the host key data‐
601 base files and when validating host certificates. This option is
602 useful for tunneling SSH connections or for multiple servers run‐
603 ning on a single host.
604 Hostname
606 Specifies the real host name to log into. This can be used to
607 specify nicknames or abbreviations for hosts. Arguments to
608 Hostname accept the tokens described in the TOKENS section. Nu‐
609 meric IP addresses are also permitted (both on the command line
610 and in Hostname specifications). The default is the name given
611 on the command line.
612 IdentitiesOnly
614 Specifies that ssh(1) should only use the configured authentica‐
615 tion identity and certificate files (either the default files, or
616 those explicitly configured in the ssh_config files or passed on
617 the ssh(1) command-line), even if ssh-agent(1) or a
618 PKCS11Provider or SecurityKeyProvider offers more identities.
619 The argument to this keyword must be yes or no (the default).
620 This option is intended for situations where ssh-agent offers
621 many different identities.
622 IdentityAgent
624 Specifies the UNIX-domain socket used to communicate with the au‐
625 thentication agent.
626 This option overrides the SSH_AUTH_SOCK environment variable and
628 can be used to select a specific agent. Setting the socket name
629 to none disables the use of an authentication agent. If the
630 string "SSH_AUTH_SOCK" is specified, the location of the socket
631 will be read from the SSH_AUTH_SOCK environment variable. Other‐
632 wise if the specified value begins with a ‘$’ character, then it
633 will be treated as an environment variable containing the loca‐
634 tion of the socket.
635 Arguments to IdentityAgent may use the tilde syntax to refer to a
637 user's home directory, the tokens described in the TOKENS section
638 and environment variables as described in the ENVIRONMENT
639 VARIABLES section.
640 IdentityFile
642 Specifies a file from which the user's DSA, ECDSA, authenticator-
643 hosted ECDSA, Ed25519, authenticator-hosted Ed25519 or RSA au‐
644 thentication identity is read. The default is ~/.ssh/id_dsa,
645 ~/.ssh/id_ecdsa, ~/.ssh/id_ecdsa_sk, ~/.ssh/id_ed25519,
646 ~/.ssh/id_ed25519_sk and ~/.ssh/id_rsa. Additionally, any iden‐
647 tities represented by the authentication agent will be used for
648 authentication unless IdentitiesOnly is set. If no certificates
649 have been explicitly specified by CertificateFile, ssh(1) will
650 try to load certificate information from the filename obtained by
651 appending -cert.pub to the path of a specified IdentityFile.
652 Arguments to IdentityFile may use the tilde syntax to refer to a
654 user's home directory or the tokens described in the TOKENS sec‐
655 tion.
656 It is possible to have multiple identity files specified in con‐
658 figuration files; all these identities will be tried in sequence.
659 Multiple IdentityFile directives will add to the list of identi‐
660 ties tried (this behaviour differs from that of other configura‐
661 tion directives).
662 IdentityFile may be used in conjunction with IdentitiesOnly to
664 select which identities in an agent are offered during authenti‐
665 cation. IdentityFile may also be used in conjunction with
666 CertificateFile in order to provide any certificate also needed
667 for authentication with the identity.
668 The authentication identity can be also specified in a form of
670 PKCS#11 URI starting with a string pkcs11:. There is supported a
671 subset of the PKCS#11 URI as defined in RFC 7512 (implemented
672 path arguments id, manufacturer, object, token and query argu‐
673 ments module-path and pin-value ). The URI can not be in quotes.
674 IgnoreUnknown
676 Specifies a pattern-list of unknown options to be ignored if they
677 are encountered in configuration parsing. This may be used to
678 suppress errors if ssh_config contains options that are unrecog‐
679 nised by ssh(1). It is recommended that IgnoreUnknown be listed
680 early in the configuration file as it will not be applied to un‐
681 known options that appear before it.
682 Include
684 Include the specified configuration file(s). Multiple pathnames
685 may be specified and each pathname may contain glob(7) wildcards
686 and, for user configurations, shell-like ‘~’ references to user
687 home directories. Wildcards will be expanded and processed in
688 lexical order. Files without absolute paths are assumed to be in
689 ~/.ssh if included in a user configuration file or /etc/ssh if
690 included from the system configuration file. Include directive
691 may appear inside a Match or Host block to perform conditional
692 inclusion.
693 IPQoS Specifies the IPv4 type-of-service or DSCP class for connections.
695 Accepted values are af11, af12, af13, af21, af22, af23, af31,
696 af32, af33, af41, af42, af43, cs0, cs1, cs2, cs3, cs4, cs5, cs6,
697 cs7, ef, le, lowdelay, throughput, reliability, a numeric value,
698 or none to use the operating system default. This option may
699 take one or two arguments, separated by whitespace. If one argu‐
700 ment is specified, it is used as the packet class uncondition‐
701 ally. If two values are specified, the first is automatically
702 selected for interactive sessions and the second for non-interac‐
703 tive sessions. The default is af21 (Low-Latency Data) for inter‐
704 active sessions and cs1 (Lower Effort) for non-interactive ses‐
705 sions.
706 KbdInteractiveAuthentication
708 Specifies whether to use keyboard-interactive authentication.
709 The argument to this keyword must be yes (the default) or no.
710 ChallengeResponseAuthentication is a deprecated alias for this.
711 KbdInteractiveDevices
713 Specifies the list of methods to use in keyboard-interactive au‐
714 thentication. Multiple method names must be comma-separated.
715 The default is to use the server specified list. The methods
716 available vary depending on what the server supports. For an
717 OpenSSH server, it may be zero or more of: bsdauth and pam.
718 KexAlgorithms
720 The default is handled system-wide by crypto-policies(7). To see
721 the defaults and how to modify this default, see manual page
722 update-crypto-policies(8).
723 Specifies the available KEX (Key Exchange) algorithms. Multiple
725 algorithms must be comma-separated. If the specified list begins
726 with a ‘+’ character, then the specified methods will be appended
727 to the built-in openssh default set instead of replacing them.
728 If the specified list begins with a ‘-’ character, then the spec‐
729 ified methods (including wildcards) will be removed from the
730 built-in openssh default set instead of replacing them. If the
731 specified list begins with a ‘^’ character, then the specified
732 methods will be placed at the head of the built-in openssh de‐
733 fault set.
734 The list of available key exchange algorithms may also be ob‐
736 tained using "ssh -Q kex".
737 KnownHostsCommand
739 Specifies a command to use to obtain a list of host keys, in ad‐
740 dition to those listed in UserKnownHostsFile and
741 GlobalKnownHostsFile. This command is executed after the files
742 have been read. It may write host key lines to standard output
743 in identical format to the usual files (described in the
744 VERIFYING HOST KEYS section in ssh(1)). Arguments to
745 KnownHostsCommand accept the tokens described in the TOKENS sec‐
746 tion. The command may be invoked multiple times per connection:
747 once when preparing the preference list of host key algorithms to
748 use, again to obtain the host key for the requested host name
749 and, if CheckHostIP is enabled, one more time to obtain the host
750 key matching the server's address. If the command exits abnor‐
751 mally or returns a non-zero exit status then the connection is
752 terminated.
753 LocalCommand
755 Specifies a command to execute on the local machine after suc‐
756 cessfully connecting to the server. The command string extends
757 to the end of the line, and is executed with the user's shell.
758 Arguments to LocalCommand accept the tokens described in the
759 TOKENS section.
760 The command is run synchronously and does not have access to the
762 session of the ssh(1) that spawned it. It should not be used for
763 interactive commands.
764 This directive is ignored unless PermitLocalCommand has been en‐
766 abled.
767 LocalForward
769 Specifies that a TCP port on the local machine be forwarded over
770 the secure channel to the specified host and port from the remote
771 machine. The first argument specifies the listener and may be
772 [bind_address:]port or a Unix domain socket path. The second ar‐
773 gument is the destination and may be host:hostport or a Unix do‐
774 main socket path if the remote host supports it.
775 IPv6 addresses can be specified by enclosing addresses in square
777 brackets. Multiple forwardings may be specified, and additional
778 forwardings can be given on the command line. Only the superuser
779 can forward privileged ports. By default, the local port is
780 bound in accordance with the GatewayPorts setting. However, an
781 explicit bind_address may be used to bind the connection to a
782 specific address. The bind_address of localhost indicates that
783 the listening port be bound for local use only, while an empty
784 address or ‘*’ indicates that the port should be available from
785 all interfaces. Unix domain socket paths may use the tokens de‐
786 scribed in the TOKENS section and environment variables as de‐
787 scribed in the ENVIRONMENT VARIABLES section.
788 LogLevel
790 Gives the verbosity level that is used when logging messages from
791 ssh(1). The possible values are: QUIET, FATAL, ERROR, INFO, VER‐
792 BOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO.
793 DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify
794 higher levels of verbose output.
795 LogVerbose
797 Specify one or more overrides to LogLevel. An override consists
798 of a pattern lists that matches the source file, function and
799 line number to force detailed logging for. For example, an over‐
800 ride pattern of:
801 kex.c:*:1000,*:kex_exchange_identification():*,packet.c:*
803 would enable detailed logging for line 1000 of kex.c, everything
805 in the kex_exchange_identification() function, and all code in
806 the packet.c file. This option is intended for debugging and no
807 overrides are enabled by default.
808 MACs The default is handled system-wide by crypto-policies(7). To see
810 the defaults and how to modify this default, see manual page
811 update-crypto-policies(8).
812 Specifies the MAC (message authentication code) algorithms in or‐
814 der of preference. The MAC algorithm is used for data integrity
815 protection. Multiple algorithms must be comma-separated. If the
816 specified list begins with a ‘+’ character, then the specified
817 algorithms will be appended to the built-in openssh default set
818 instead of replacing them. If the specified list begins with a
819 ‘-’ character, then the specified algorithms (including wild‐
820 cards) will be removed from the built-in openssh default set in‐
821 stead of replacing them. If the specified list begins with a ‘^’
822 character, then the specified algorithms will be placed at the
823 head of the built-in openssh default set.
824 The algorithms that contain "-etm" calculate the MAC after en‐
826 cryption (encrypt-then-mac). These are considered safer and
827 their use recommended.
828 The list of available MAC algorithms may also be obtained using
830 "ssh -Q mac".
831 NoHostAuthenticationForLocalhost
833 Disable host authentication for localhost (loopback addresses).
834 The argument to this keyword must be yes or no (the default).
835 NumberOfPasswordPrompts
837 Specifies the number of password prompts before giving up. The
838 argument to this keyword must be an integer. The default is 3.
839 PasswordAuthentication
841 Specifies whether to use password authentication. The argument
842 to this keyword must be yes (the default) or no.
843 PermitLocalCommand
845 Allow local command execution via the LocalCommand option or us‐
846 ing the !command escape sequence in ssh(1). The argument must be
847 yes or no (the default).
848 PermitRemoteOpen
850 Specifies the destinations to which remote TCP port forwarding is
851 permitted when RemoteForward is used as a SOCKS proxy. The for‐
852 warding specification must be one of the following forms:
853 PermitRemoteOpen host:port
855 PermitRemoteOpen IPv4_addr:port
856 PermitRemoteOpen [IPv6_addr]:port
857 Multiple forwards may be specified by separating them with white‐
859 space. An argument of any can be used to remove all restrictions
860 and permit any forwarding requests. An argument of none can be
861 used to prohibit all forwarding requests. The wildcard ‘*’ can
862 be used for host or port to allow all hosts or ports respec‐
863 tively. Otherwise, no pattern matching or address lookups are
864 performed on supplied names.
865 PKCS11Provider
867 Specifies which PKCS#11 provider to use or none to indicate that
868 no provider should be used (the default). The argument to this
869 keyword is a path to the PKCS#11 shared library ssh(1) should use
870 to communicate with a PKCS#11 token providing keys for user au‐
871 thentication.
872 Port Specifies the port number to connect on the remote host. The de‐
874 fault is 22.
875 PreferredAuthentications
877 Specifies the order in which the client should try authentication
878 methods. This allows a client to prefer one method (e.g.
879 keyboard-interactive) over another method (e.g. password). The
880 default is:
881 gssapi-keyex,gssapi-with-mic,hostbased,publickey,
883 keyboard-interactive,password
884 ProxyCommand
886 Specifies the command to use to connect to the server. The com‐
887 mand string extends to the end of the line, and is executed using
888 the user's shell ‘exec’ directive to avoid a lingering shell
889 process.
890 Arguments to ProxyCommand accept the tokens described in the
892 TOKENS section. The command can be basically anything, and
893 should read from its standard input and write to its standard
894 output. It should eventually connect an sshd(8) server running
895 on some machine, or execute sshd -i somewhere. Host key manage‐
896 ment will be done using the Hostname of the host being connected
897 (defaulting to the name typed by the user). Setting the command
898 to none disables this option entirely. Note that CheckHostIP is
899 not available for connects with a proxy command.
900 This directive is useful in conjunction with nc(1) and its proxy
902 support. For example, the following directive would connect via
903 an HTTP proxy at 192.0.2.0:
904 ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
906 ProxyJump
908 Specifies one or more jump proxies as either [user@]host[:port]
909 or an ssh URI. Multiple proxies may be separated by comma char‐
910 acters and will be visited sequentially. Setting this option
911 will cause ssh(1) to connect to the target host by first making a
912 ssh(1) connection to the specified ProxyJump host and then estab‐
913 lishing a TCP forwarding to the ultimate target from there. Set‐
914 ting the host to none disables this option entirely.
915 Note that this option will compete with the ProxyCommand option -
917 whichever is specified first will prevent later instances of the
918 other from taking effect.
919 Note also that the configuration for the destination host (either
921 supplied via the command-line or the configuration file) is not
922 generally applied to jump hosts. ~/.ssh/config should be used if
923 specific configuration is required for jump hosts.
924 ProxyUseFdpass
926 Specifies that ProxyCommand will pass a connected file descriptor
927 back to ssh(1) instead of continuing to execute and pass data.
928 The default is no.
929 PubkeyAcceptedAlgorithms
931 The default is handled system-wide by crypto-policies(7). To see
932 the defaults and how to modify this default, see manual page
933 update-crypto-policies(8).
934 Specifies the signature algorithms that will be used for public
936 key authentication as a comma-separated list of patterns. If the
937 specified list begins with a ‘+’ character, then the algorithms
938 after it will be appended to the built-in openssh default instead
939 of replacing it. If the specified list begins with a ‘-’ charac‐
940 ter, then the specified algorithms (including wildcards) will be
941 removed from the built-in openssh default set instead of replac‐
942 ing them. If the specified list begins with a ‘^’ character,
943 then the specified algorithms will be placed at the head of the
944 built-in openssh default set.
945 The list of available signature algorithms may also be obtained
947 using "ssh -Q PubkeyAcceptedAlgorithms".
948 PubkeyAuthentication
950 Specifies whether to try public key authentication. The argument
951 to this keyword must be yes (the default) or no.
952 RekeyLimit
954 Specifies the maximum amount of data that may be transmitted be‐
955 fore the session key is renegotiated, optionally followed by a
956 maximum amount of time that may pass before the session key is
957 renegotiated. The first argument is specified in bytes and may
958 have a suffix of ‘K’, ‘M’, or ‘G’ to indicate Kilobytes,
959 Megabytes, or Gigabytes, respectively. The default is between
960 ‘1G’ and ‘4G’, depending on the cipher. The optional second
961 value is specified in seconds and may use any of the units docu‐
962 mented in the TIME FORMATS section of sshd_config(5). The de‐
963 fault value for RekeyLimit is default none, which means that
964 rekeying is performed after the cipher's default amount of data
965 has been sent or received and no time based rekeying is done.
966 RemoteCommand
968 Specifies a command to execute on the remote machine after suc‐
969 cessfully connecting to the server. The command string extends
970 to the end of the line, and is executed with the user's shell.
971 Arguments to RemoteCommand accept the tokens described in the
972 TOKENS section.
973 RemoteForward
975 Specifies that a TCP port on the remote machine be forwarded over
976 the secure channel. The remote port may either be forwarded to a
977 specified host and port from the local machine, or may act as a
978 SOCKS 4/5 proxy that allows a remote client to connect to arbi‐
979 trary destinations from the local machine. The first argument is
980 the listening specification and may be [bind_address:]port or, if
981 the remote host supports it, a Unix domain socket path. If for‐
982 warding to a specific destination then the second argument must
983 be host:hostport or a Unix domain socket path, otherwise if no
984 destination argument is specified then the remote forwarding will
985 be established as a SOCKS proxy. When acting as a SOCKS proxy
986 the destination of the connection can be restricted by
987 PermitRemoteOpen.
988 IPv6 addresses can be specified by enclosing addresses in square
990 brackets. Multiple forwardings may be specified, and additional
991 forwardings can be given on the command line. Privileged ports
992 can be forwarded only when logging in as root on the remote ma‐
993 chine. Unix domain socket paths may use the tokens described in
994 the TOKENS section and environment variables as described in the
995 ENVIRONMENT VARIABLES section.
996 If the port argument is 0, the listen port will be dynamically
998 allocated on the server and reported to the client at run time.
999 If the bind_address is not specified, the default is to only bind
1001 to loopback addresses. If the bind_address is ‘*’ or an empty
1002 string, then the forwarding is requested to listen on all inter‐
1003 faces. Specifying a remote bind_address will only succeed if the
1004 server's GatewayPorts option is enabled (see sshd_config(5)).
1005 RequestTTY
1007 Specifies whether to request a pseudo-tty for the session. The
1008 argument may be one of: no (never request a TTY), yes (always re‐
1009 quest a TTY when standard input is a TTY), force (always request
1010 a TTY) or auto (request a TTY when opening a login session).
1011 This option mirrors the -t and -T flags for ssh(1).
1012 RevokedHostKeys
1014 Specifies revoked host public keys. Keys listed in this file
1015 will be refused for host authentication. Note that if this file
1016 does not exist or is not readable, then host authentication will
1017 be refused for all hosts. Keys may be specified as a text file,
1018 listing one public key per line, or as an OpenSSH Key Revocation
1019 List (KRL) as generated by ssh-keygen(1). For more information
1020 on KRLs, see the KEY REVOCATION LISTS section in ssh-keygen(1).
1021 SecurityKeyProvider
1023 Specifies a path to a library that will be used when loading any
1024 FIDO authenticator-hosted keys, overriding the default of using
1025 the built-in USB HID support.
1026 If the specified value begins with a ‘$’ character, then it will
1028 be treated as an environment variable containing the path to the
1029 library.
1030 SendEnv
1032 Specifies what variables from the local environ(7) should be sent
1033 to the server. The server must also support it, and the server
1034 must be configured to accept these environment variables. Note
1035 that the TERM environment variable is always sent whenever a
1036 pseudo-terminal is requested as it is required by the protocol.
1037 Refer to AcceptEnv in sshd_config(5) for how to configure the
1038 server. Variables are specified by name, which may contain wild‐
1039 card characters. Multiple environment variables may be separated
1040 by whitespace or spread across multiple SendEnv directives.
1041 See PATTERNS for more information on patterns.
1043 It is possible to clear previously set SendEnv variable names by
1045 prefixing patterns with -. The default is not to send any envi‐
1046 ronment variables.
1047 ServerAliveCountMax
1049 Sets the number of server alive messages (see below) which may be
1050 sent without ssh(1) receiving any messages back from the server.
1051 If this threshold is reached while server alive messages are be‐
1052 ing sent, ssh will disconnect from the server, terminating the
1053 session. It is important to note that the use of server alive
1054 messages is very different from TCPKeepAlive (below). The server
1055 alive messages are sent through the encrypted channel and there‐
1056 fore will not be spoofable. The TCP keepalive option enabled by
1057 TCPKeepAlive is spoofable. The server alive mechanism is valu‐
1058 able when the client or server depend on knowing when a connec‐
1059 tion has become unresponsive.
1060 The default value is 3. If, for example, ServerAliveInterval
1062 (see below) is set to 15 and ServerAliveCountMax is left at the
1063 default, if the server becomes unresponsive, ssh will disconnect
1064 after approximately 45 seconds.
1065 ServerAliveInterval
1067 Sets a timeout interval in seconds after which if no data has
1068 been received from the server, ssh(1) will send a message through
1069 the encrypted channel to request a response from the server. The
1070 default is 0, indicating that these messages will not be sent to
1071 the server.
1072 SessionType
1074 May be used to either request invocation of a subsystem on the
1075 remote system, or to prevent the execution of a remote command at
1076 all. The latter is useful for just forwarding ports. The argu‐
1077 ment to this keyword must be none (same as the -N option),
1078 subsystem (same as the -s option) or default (shell or command
1079 execution).
1080 SetEnv Directly specify one or more environment variables and their con‐
1082 tents to be sent to the server. Similarly to SendEnv, with the
1083 exception of the TERM variable, the server must be prepared to
1084 accept the environment variable.
1085 StdinNull
1087 Redirects stdin from /dev/null (actually, prevents reading from
1088 stdin). Either this or the equivalent -n option must be used
1089 when ssh is run in the background. The argument to this keyword
1090 must be yes (same as the -n option) or no (the default).
1091 StreamLocalBindMask
1093 Sets the octal file creation mode mask (umask) used when creating
1094 a Unix-domain socket file for local or remote port forwarding.
1095 This option is only used for port forwarding to a Unix-domain
1096 socket file.
1097 The default value is 0177, which creates a Unix-domain socket
1099 file that is readable and writable only by the owner. Note that
1100 not all operating systems honor the file mode on Unix-domain
1101 socket files.
1102 StreamLocalBindUnlink
1104 Specifies whether to remove an existing Unix-domain socket file
1105 for local or remote port forwarding before creating a new one.
1106 If the socket file already exists and StreamLocalBindUnlink is
1107 not enabled, ssh will be unable to forward the port to the Unix-
1108 domain socket file. This option is only used for port forwarding
1109 to a Unix-domain socket file.
1110 The argument must be yes or no (the default).
1112 StrictHostKeyChecking
1114 If this flag is set to yes, ssh(1) will never automatically add
1115 host keys to the ~/.ssh/known_hosts file, and refuses to connect
1116 to hosts whose host key has changed. This provides maximum pro‐
1117 tection against man-in-the-middle (MITM) attacks, though it can
1118 be annoying when the /etc/gsissh/ssh_known_hosts file is poorly
1119 maintained or when connections to new hosts are frequently made.
1120 This option forces the user to manually add all new hosts.
1121 If this flag is set to “accept-new” then ssh will automatically
1123 add new host keys to the user's known_hosts file, but will not
1124 permit connections to hosts with changed host keys. If this flag
1125 is set to “no” or “off”, ssh will automatically add new host keys
1126 to the user known hosts files and allow connections to hosts with
1127 changed hostkeys to proceed, subject to some restrictions. If
1128 this flag is set to ask (the default), new host keys will be
1129 added to the user known host files only after the user has con‐
1130 firmed that is what they really want to do, and ssh will refuse
1131 to connect to hosts whose host key has changed. The host keys of
1132 known hosts will be verified automatically in all cases.
1133 SyslogFacility
1135 Gives the facility code that is used when logging messages from
1136 ssh(1). The possible values are: DAEMON, USER, AUTH, LOCAL0, LO‐
1137 CAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. The de‐
1138 fault is USER.
1139 TCPKeepAlive
1141 Specifies whether the system should send TCP keepalive messages
1142 to the other side. If they are sent, death of the connection or
1143 crash of one of the machines will be properly noticed. However,
1144 this means that connections will die if the route is down tempo‐
1145 rarily, and some people find it annoying.
1146 The default is yes (to send TCP keepalive messages), and the
1148 client will notice if the network goes down or the remote host
1149 dies. This is important in scripts, and many users want it too.
1150 To disable TCP keepalive messages, the value should be set to no.
1152 See also ServerAliveInterval for protocol-level keepalives.
1153 Tunnel Request tun(4) device forwarding between the client and the
1155 server. The argument must be yes, point-to-point (layer 3),
1156 ethernet (layer 2), or no (the default). Specifying yes requests
1157 the default tunnel mode, which is point-to-point.
1158 TunnelDevice
1160 Specifies the tun(4) devices to open on the client (local_tun)
1161 and the server (remote_tun).
1162 The argument must be local_tun[:remote_tun]. The devices may be
1164 specified by numerical ID or the keyword any, which uses the next
1165 available tunnel device. If remote_tun is not specified, it de‐
1166 faults to any. The default is any:any.
1167 UpdateHostKeys
1169 Specifies whether ssh(1) should accept notifications of addi‐
1170 tional hostkeys from the server sent after authentication has
1171 completed and add them to UserKnownHostsFile. The argument must
1172 be yes, no or ask. This option allows learning alternate
1173 hostkeys for a server and supports graceful key rotation by al‐
1174 lowing a server to send replacement public keys before old ones
1175 are removed.
1176 Additional hostkeys are only accepted if the key used to authen‐
1178 ticate the host was already trusted or explicitly accepted by the
1179 user, the host was authenticated via UserKnownHostsFile (i.e. not
1180 GlobalKnownHostsFile) and the host was authenticated using a
1181 plain key and not a certificate.
1182 UpdateHostKeys is enabled by default if the user has not overrid‐
1184 den the default UserKnownHostsFile setting and has not enabled
1185 VerifyHostKeyDNS, otherwise UpdateHostKeys will be set to no.
1186 If UpdateHostKeys is set to ask, then the user is asked to con‐
1188 firm the modifications to the known_hosts file. Confirmation is
1189 currently incompatible with ControlPersist, and will be disabled
1190 if it is enabled.
1191 Presently, only sshd(8) from OpenSSH 6.8 and greater support the
1193 "hostkeys@openssh.com" protocol extension used to inform the
1194 client of all the server's hostkeys.
1195 User Specifies the user to log in as. This can be useful when a dif‐
1197 ferent user name is used on different machines. This saves the
1198 trouble of having to remember to give the user name on the com‐
1199 mand line.
1200 UserKnownHostsFile
1202 Specifies one or more files to use for the user host key data‐
1203 base, separated by whitespace. Each filename may use tilde nota‐
1204 tion to refer to the user's home directory, the tokens described
1205 in the TOKENS section and environment variables as described in
1206 the ENVIRONMENT VARIABLES section. The default is
1207 ~/.ssh/known_hosts, ~/.ssh/known_hosts2.
1208 VerifyHostKeyDNS
1210 Specifies whether to verify the remote key using DNS and SSHFP
1211 resource records. If this option is set to yes, the client will
1212 implicitly trust keys that match a secure fingerprint from DNS.
1213 Insecure fingerprints will be handled as if this option was set
1214 to ask. If this option is set to ask, information on fingerprint
1215 match will be displayed, but the user will still need to confirm
1216 new host keys according to the StrictHostKeyChecking option. The
1217 default is no.
1218 See also VERIFYING HOST KEYS in ssh(1).
1220 VisualHostKey
1222 If this flag is set to yes, an ASCII art representation of the
1223 remote host key fingerprint is printed in addition to the finger‐
1224 print string at login and for unknown host keys. If this flag is
1225 set to no (the default), no fingerprint strings are printed at
1226 login and only the fingerprint string will be printed for unknown
1227 host keys.
1228 XAuthLocation
1230 Specifies the full pathname of the xauth(1) program. The default
1231 is /usr/bin/xauth.
1232
1234 A pattern consists of zero or more non-whitespace characters, ‘*’ (a
1235 wildcard that matches zero or more characters), or ‘?’ (a wildcard that
1236 matches exactly one character). For example, to specify a set of decla‐
1237 rations for any host in the ".co.uk" set of domains, the following pat‐
1238 tern could be used:
1239 Host *.co.uk
1241 The following pattern would match any host in the 192.168.0.[0-9] network
1243 range:
1244 Host 192.168.0.?
1246 A pattern-list is a comma-separated list of patterns. Patterns within
1248 pattern-lists may be negated by preceding them with an exclamation mark
1249 (‘!’). For example, to allow a key to be used from anywhere within an
1250 organization except from the "dialup" pool, the following entry (in au‐
1251 thorized_keys) could be used:
1252 from="!*.dialup.example.com,*.example.com"
1254 Note that a negated match will never produce a positive result by itself.
1256 For example, attempting to match "host3" against the following pattern-
1257 list will fail:
1258 from="!host1,!host2"
1260 The solution here is to include a term that will yield a positive match,
1262 such as a wildcard:
1263 from="!host1,!host2,*"
1265
1267 Arguments to some keywords can make use of tokens, which are expanded at
1268 runtime:
1269 %% A literal ‘%’.
1271 %C Hash of %l%h%p%r.
1272 %d Local user's home directory.
1273 %f The fingerprint of the server's host key.
1274 %H The known_hosts hostname or address that is being searched
1275 for.
1276 %h The remote hostname.
1277 %I A string describing the reason for a KnownHostsCommand execu‐
1278 tion: either ADDRESS when looking up a host by address (only
1279 when CheckHostIP is enabled), HOSTNAME when searching by
1280 hostname, or ORDER when preparing the host key algorithm
1281 preference list to use for the destination host.
1282 %i The local user ID.
1283 %K The base64 encoded host key.
1284 %k The host key alias if specified, otherwise the original re‐
1285 mote hostname given on the command line.
1286 %L The local hostname.
1287 %l The local hostname, including the domain name.
1288 %n The original remote hostname, as given on the command line.
1289 %p The remote port.
1290 %r The remote username.
1291 %T The local tun(4) or tap(4) network interface assigned if tun‐
1292 nel forwarding was requested, or "NONE" otherwise.
1293 %t The type of the server host key, e.g. ssh-ed25519.
1294 %u The local username.
1295 CertificateFile, ControlPath, IdentityAgent, IdentityFile,
1297 KnownHostsCommand, LocalForward, Match exec, RemoteCommand,
1298 RemoteForward, and UserKnownHostsFile accept the tokens %%, %C, %d, %h,
1299 %i, %k, %L, %l, %n, %p, %r, and %u.
1300 KnownHostsCommand additionally accepts the tokens %f, %H, %I, %K and %t.
1302 Hostname accepts the tokens %% and %h.
1304 LocalCommand accepts all tokens.
1306 ProxyCommand accepts the tokens %%, %h, %n, %p, and %r.
1308
1310 Arguments to some keywords can be expanded at runtime from environment
1311 variables on the client by enclosing them in ${}, for example
1312 ${HOME}/.ssh would refer to the user's .ssh directory. If a specified
1313 environment variable does not exist then an error will be returned and
1314 the setting for that keyword will be ignored.
1315 The keywords CertificateFile, ControlPath, IdentityAgent, IdentityFile,
1317 KnownHostsCommand, and UserKnownHostsFile support environment variables.
1318 The keywords LocalForward and RemoteForward support environment variables
1319 only for Unix domain socket paths.
1320
1322 ~/.ssh/config
1323 This is the per-user configuration file. The format of this file
1324 is described above. This file is used by the SSH client. Be‐
1325 cause of the potential for abuse, this file must have strict per‐
1326 missions: read/write for the user, and not writable by others.
1327 /etc/gsissh/ssh_config
1329 Systemwide configuration file. This file provides defaults for
1330 those values that are not specified in the user's configuration
1331 file, and for those users who do not have a configuration file.
1332 This file must be world-readable.
1333
1335 ssh(1)
1336
1338 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
1339 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
1340 de Raadt and Dug Song removed many bugs, re-added newer features and cre‐
1341 ated OpenSSH. Markus Friedl contributed the support for SSH protocol
1342 versions 1.5 and 2.0.
1343BSD August 12, 2021 BSD