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.
157 CanonicalizeMaxDots
159 Specifies the maximum number of dot characters in a hostname be‐
160 fore canonicalization is disabled. The default, 1, allows a sin‐
161 gle dot (i.e. hostname.subdomain).
162 CanonicalizePermittedCNAMEs
164 Specifies rules to determine whether CNAMEs should be followed
165 when canonicalizing hostnames. The rules consist of one or more
166 arguments of source_domain_list:target_domain_list, where
167 source_domain_list is a pattern-list of domains that may follow
168 CNAMEs in canonicalization, and target_domain_list is a pattern-
169 list of domains that they may resolve to.
170 For example, "*.a.example.com:*.b.example.com,*.c.example.com"
172 will allow hostnames matching "*.a.example.com" to be canonical‐
173 ized to names in the "*.b.example.com" or "*.c.example.com" do‐
174 mains.
175 CASignatureAlgorithms
177 The default is handled system-wide by crypto-policies(7). To see
178 the defaults and how to modify this default, see manual page
179 update-crypto-policies(8).
180 Specifies which algorithms are allowed for signing of certifi‐
182 cates by certificate authorities (CAs). ssh(1) will not accept
183 host certificates signed using algorithms other than those speci‐
184 fied.
185 CertificateFile
187 Specifies a file from which the user's certificate is read. A
188 corresponding private key must be provided separately in order to
189 use this certificate either from an IdentityFile directive or -i
190 flag to ssh(1), via ssh-agent(1), or via a PKCS11Provider or
191 SecurityKeyProvider.
192 Arguments to CertificateFile may use the tilde syntax to refer to
194 a user's home directory, the tokens described in the TOKENS sec‐
195 tion and environment variables as described in the ENVIRONMENT
196 VARIABLES section.
197 It is possible to have multiple certificate files specified in
199 configuration files; these certificates will be tried in se‐
200 quence. Multiple CertificateFile directives will add to the list
201 of certificates used for authentication.
202 ChallengeResponseAuthentication
204 Specifies whether to use challenge-response authentication. The
205 argument to this keyword must be yes (the default) or no.
206 CheckHostIP
208 If set to yes [22mssh(1) will additionally check the host IP address
209 in the known_hosts file. This allows it to detect if a host key
210 changed due to DNS spoofing and will add addresses of destination
211 hosts to ~/.ssh/known_hosts in the process, regardless of the
212 setting of StrictHostKeyChecking. If the option is set to no
213 (the default), the check will not be executed.
214 Ciphers
216 The default is handled system-wide by crypto-policies(7). To see
217 the defaults and how to modify this default, see manual page
218 update-crypto-policies(8).
219 Specifies the ciphers allowed and their order of preference.
221 Multiple ciphers must be comma-separated. If the specified list
222 begins with a ‘+’ character, then the specified ciphers will be
223 appended to the built-in openssh default set instead of replacing
224 them. If the specified list begins with a ‘-’ character, then
225 the specified ciphers (including wildcards) will be removed from
226 the built-in openssh default set instead of replacing them. If
227 the specified list begins with a ‘^’ character, then the speci‐
228 fied ciphers will be placed at the head of the built-in openssh
229 default set.
230 The supported ciphers are:
232 3des-cbc
234 aes128-cbc
235 aes192-cbc
236 aes256-cbc
237 aes128-ctr
238 aes192-ctr
239 aes256-ctr
240 aes128-gcm@openssh.com
241 aes256-gcm@openssh.com
242 chacha20-poly1305@openssh.com
243 The list of available ciphers may also be obtained using "ssh -Q
245 cipher".
246 ClearAllForwardings
248 Specifies that all local, remote, and dynamic port forwardings
249 specified in the configuration files or on the command line be
250 cleared. This option is primarily useful when used from the
251 ssh(1) command line to clear port forwardings set in configura‐
252 tion files, and is automatically set by scp(1) and sftp(1). The
253 argument must be yes or no (the default).
254 Compression
256 Specifies whether to use compression. The argument must be yes
257 or no (the default).
258 ConnectionAttempts
260 Specifies the number of tries (one per second) to make before ex‐
261 iting. The argument must be an integer. This may be useful in
262 scripts if the connection sometimes fails. The default is 1.
263 ConnectTimeout
265 Specifies the timeout (in seconds) used when connecting to the
266 SSH server, instead of using the default system TCP timeout.
267 This timeout is applied both to establishing the connection and
268 to performing the initial SSH protocol handshake and key ex‐
269 change.
270 ControlMaster
272 Enables the sharing of multiple sessions over a single network
273 connection. When set to yes, ssh(1) will listen for connections
274 on a control socket specified using the ControlPath argument.
275 Additional sessions can connect to this socket using the same
276 ControlPath with ControlMaster set to no (the default). These
277 sessions will try to reuse the master instance's network connec‐
278 tion rather than initiating new ones, but will fall back to con‐
279 necting normally if the control socket does not exist, or is not
280 listening.
281 Setting this to ask will cause ssh(1) to listen for control con‐
283 nections, but require confirmation using ssh-askpass(1). If the
284 ControlPath cannot be opened, ssh(1) will continue without con‐
285 necting to a master instance.
286 X11 and ssh-agent(1) forwarding is supported over these multi‐
288 plexed connections, however the display and agent forwarded will
289 be the one belonging to the master connection i.e. it is not pos‐
290 sible to forward multiple displays or agents.
291 Two additional options allow for opportunistic multiplexing: try
293 to use a master connection but fall back to creating a new one if
294 one does not already exist. These options are: auto and autoask.
295 The latter requires confirmation like the ask option.
296 ControlPath
298 Specify the path to the control socket used for connection shar‐
299 ing as described in the ControlMaster section above or the string
300 none to disable connection sharing. Arguments to ControlPath may
301 use the tilde syntax to refer to a user's home directory, the to‐
302 kens described in the TOKENS section and environment variables as
303 described in the ENVIRONMENT VARIABLES section. It is recom‐
304 mended that any ControlPath used for opportunistic connection
305 sharing include at least %h, %p, and %r (or alternatively %C) and
306 be placed in a directory that is not writable by other users.
307 This ensures that shared connections are uniquely identified.
308 ControlPersist
310 When used in conjunction with ControlMaster, specifies that the
311 master connection should remain open in the background (waiting
312 for future client connections) after the initial client connec‐
313 tion has been closed. If set to no (the default), then the mas‐
314 ter connection will not be placed into the background, and will
315 close as soon as the initial client connection is closed. If set
316 to yes or 0, then the master connection will remain in the back‐
317 ground indefinitely (until killed or closed via a mechanism such
318 as the "ssh -O exit"). If set to a time in seconds, or a time in
319 any of the formats documented in sshd_config(5), then the back‐
320 grounded master connection will automatically terminate after it
321 has remained idle (with no client connections) for the specified
322 time.
323 DynamicForward
325 Specifies that a TCP port on the local machine be forwarded over
326 the secure channel, and the application protocol is then used to
327 determine where to connect to from the remote machine.
328 The argument must be [bind_address:]port. IPv6 addresses can be
330 specified by enclosing addresses in square brackets. By default,
331 the local port is bound in accordance with the GatewayPorts set‐
332 ting. However, an explicit bind_address may be used to bind the
333 connection to a specific address. The bind_address of localhost
334 indicates that the listening port be bound for local use only,
335 while an empty address or ‘*’ indicates that the port should be
336 available from all interfaces.
337 Currently the SOCKS4 and SOCKS5 protocols are supported, and
339 ssh(1) will act as a SOCKS server. Multiple forwardings may be
340 specified, and additional forwardings can be given on the command
341 line. Only the superuser can forward privileged ports.
342 EnableSSHKeysign
344 Setting this option to yes in the global client configuration
345 file /etc/gsissh/ssh_config enables the use of the helper program
346 ssh-keysign(8) during HostbasedAuthentication. The argument must
347 be yes or no (the default). This option should be placed in the
348 non-hostspecific section. See ssh-keysign(8) for more informa‐
349 tion.
350 EscapeChar
352 Sets the escape character (default: ‘~’). The escape character
353 can also be set on the command line. The argument should be a
354 single character, ‘^’ followed by a letter, or none to disable
355 the escape character entirely (making the connection transparent
356 for binary data).
357 ExitOnForwardFailure
359 Specifies whether ssh(1) should terminate the connection if it
360 cannot set up all requested dynamic, tunnel, local, and remote
361 port forwardings, (e.g. if either end is unable to bind and lis‐
362 ten on a specified port). Note that ExitOnForwardFailure does
363 not apply to connections made over port forwardings and will not,
364 for example, cause ssh(1) to exit if TCP connections to the ulti‐
365 mate forwarding destination fail. The argument must be yes or no
366 (the default).
367 FingerprintHash
369 Specifies the hash algorithm used when displaying key finger‐
370 prints. Valid options are: md5 and sha256 (the default).
371 ForwardAgent
373 Specifies whether the connection to the authentication agent (if
374 any) will be forwarded to the remote machine. The argument may
375 be yes, no (the default), an explicit path to an agent socket or
376 the name of an environment variable (beginning with ‘$’) in which
377 to find the path.
378 Agent forwarding should be enabled with caution. Users with the
380 ability to bypass file permissions on the remote host (for the
381 agent's Unix-domain socket) can access the local agent through
382 the forwarded connection. An attacker cannot obtain key material
383 from the agent, however they can perform operations on the keys
384 that enable them to authenticate using the identities loaded into
385 the agent.
386 ForwardX11
388 Specifies whether X11 connections will be automatically redi‐
389 rected over the secure channel and DISPLAY set. The argument
390 must be yes or no (the default).
391 X11 forwarding should be enabled with caution. Users with the
393 ability to bypass file permissions on the remote host (for the
394 user's X11 authorization database) can access the local X11 dis‐
395 play through the forwarded connection. An attacker may then be
396 able to perform activities such as keystroke monitoring if the
397 ForwardX11Trusted option is also enabled.
398 ForwardX11Timeout
400 Specify a timeout for untrusted X11 forwarding using the format
401 described in the TIME FORMATS section of sshd_config(5). X11
402 connections received by ssh(1) after this time will be refused.
403 Setting ForwardX11Timeout to zero will disable the timeout and
404 permit X11 forwarding for the life of the connection. The de‐
405 fault is to disable untrusted X11 forwarding after twenty minutes
406 has elapsed.
407 ForwardX11Trusted
409 If this option is set to yes, remote X11 clients will have full
410 access to the original X11 display.
411 If this option is set to no (the default), remote X11 clients
413 will be considered untrusted and prevented from stealing or tam‐
414 pering with data belonging to trusted X11 clients. Furthermore,
415 the xauth(1) token used for the session will be set to expire af‐
416 ter 20 minutes. Remote clients will be refused access after this
417 time.
418 See the X11 SECURITY extension specification for full details on
420 the restrictions imposed on untrusted clients.
421 GatewayPorts
423 Specifies whether remote hosts are allowed to connect to local
424 forwarded ports. By default, ssh(1) binds local port forwardings
425 to the loopback address. This prevents other remote hosts from
426 connecting to forwarded ports. GatewayPorts can be used to spec‐
427 ify that ssh should bind local port forwardings to the wildcard
428 address, thus allowing remote hosts to connect to forwarded
429 ports. The argument must be yes or no (the default).
430 GlobalKnownHostsFile
432 Specifies one or more files to use for the global host key data‐
433 base, separated by whitespace. The default is
434 /etc/gsissh/ssh_known_hosts, /etc/gsissh/ssh_known_hosts2.
435 GSSAPIAuthentication
437 Specifies whether user authentication based on GSSAPI is allowed.
438 The default is yes.
439 GSSAPIClientIdentity
441 If set, specifies the GSSAPI client identity that ssh should use
442 when connecting to the server. The default is unset, which means
443 that the default identity will be used.
444 GSSAPIDelegateCredentials
446 Forward (delegate) credentials to the server. The default is
447 yes.
448 GSSAPIKeyExchange
450 Specifies whether key exchange based on GSSAPI may be used. When
451 using GSSAPI key exchange the server need not have a host key.
452 The default is “yes”.
453 GSSAPIRenewalForcesRekey
455 If set to “yes” then renewal of the client's GSSAPI credentials
456 will force the rekeying of the ssh connection. With a compatible
457 server, this will delegate the renewed credentials to a session
458 on the server.
459 Checks are made to ensure that credentials are only propagated
461 when the new credentials match the old ones on the originating
462 client and where the receiving server still has the old set in
463 its cache.
464 The default is “no”.
466 For this to work GSSAPIKeyExchange needs to be enabled in the
468 server and also used by the client.
469 GSSAPIServerIdentity
471 If set, specifies the GSSAPI server identity that ssh should ex‐
472 pect when connecting to the server. The default is unset, which
473 means that the expected GSSAPI server identity will be determined
474 from the target hostname.
475 GSSAPITrustDns
477 Set to “yes” to indicate that the DNS is trusted to securely
478 canonicalize the name of the host being connected to. If “no”,
479 the hostname entered on the command line will be passed untouched
480 to the GSSAPI library. The default is “no”.
481 GSSAPIKexAlgorithms
483 The default is handled system-wide by crypto-policies(7). To see
484 the defaults and how to modify this default, see manual page
485 update-crypto-policies(8).
486 The list of key exchange algorithms that are offered for GSSAPI
488 key exchange. Possible values are
489 gss-gex-sha1-,
491 gss-group1-sha1-,
492 gss-group14-sha1-,
493 gss-group14-sha256-,
494 gss-group16-sha512-,
495 gss-nistp256-sha256-,
496 gss-curve25519-sha256-
497 This option only applies to connections using GSSAPI.
499 HashKnownHosts
501 Indicates that ssh(1) should hash host names and addresses when
502 they are added to ~/.ssh/known_hosts. These hashed names may be
503 used normally by ssh(1) and sshd(8), but they do not visually re‐
504 veal identifying information if the file's contents are dis‐
505 closed. The default is no. Note that existing names and ad‐
506 dresses in known hosts files will not be converted automatically,
507 but may be manually hashed using ssh-keygen(1).
508 HostbasedAcceptedAlgorithms
510 Specifies the signature algorithms that will be used for host‐
511 based authentication as a comma-separated list of patterns. Al‐
512 ternately if the specified list begins with a ‘+’ character, then
513 the specified signature algorithms will be appended to the de‐
514 fault set instead of replacing them. If the specified list be‐
515 gins with a ‘-’ character, then the specified signature algo‐
516 rithms (including wildcards) will be removed from the default set
517 instead of replacing them. If the specified list begins with a
518 ‘^’ character, then the specified signature algorithms will be
519 placed at the head of the default set. The default for this op‐
520 tion is:
521 ssh-ed25519-cert-v01@openssh.com,
523 ecdsa-sha2-nistp256-cert-v01@openssh.com,
524 ecdsa-sha2-nistp384-cert-v01@openssh.com,
525 ecdsa-sha2-nistp521-cert-v01@openssh.com,
526 sk-ssh-ed25519-cert-v01@openssh.com,
527 sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
528 rsa-sha2-512-cert-v01@openssh.com,
529 rsa-sha2-256-cert-v01@openssh.com,
530 ssh-rsa-cert-v01@openssh.com,
531 ssh-ed25519,
532 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
533 sk-ssh-ed25519@openssh.com,
534 sk-ecdsa-sha2-nistp256@openssh.com,
535 rsa-sha2-512,rsa-sha2-256,ssh-rsa
536 The -Q option of ssh(1) may be used to list supported signature
538 algorithms. This was formerly named HostbasedKeyTypes.
539 HostbasedAuthentication
541 Specifies whether to try rhosts based authentication with public
542 key authentication. The argument must be yes or no (the de‐
543 fault).
544 HostKeyAlgorithms
546 Specifies the host key signature algorithms that the client wants
547 to use in order of preference. Alternately if the specified list
548 begins with a ‘+’ character, then the specified signature algo‐
549 rithms will be appended to the default set instead of replacing
550 them. If the specified list begins with a ‘-’ character, then
551 the specified signature algorithms (including wildcards) will be
552 removed from the default set instead of replacing them. If the
553 specified list begins with a ‘^’ character, then the specified
554 signature algorithms will be placed at the head of the default
555 set. The default for this option is:
556 ssh-ed25519-cert-v01@openssh.com,
558 ecdsa-sha2-nistp256-cert-v01@openssh.com,
559 ecdsa-sha2-nistp384-cert-v01@openssh.com,
560 ecdsa-sha2-nistp521-cert-v01@openssh.com,
561 sk-ssh-ed25519-cert-v01@openssh.com,
562 sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
563 rsa-sha2-512-cert-v01@openssh.com,
564 rsa-sha2-256-cert-v01@openssh.com,
565 ssh-rsa-cert-v01@openssh.com,
566 ssh-ed25519,
567 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
568 sk-ecdsa-sha2-nistp256@openssh.com,
569 sk-ssh-ed25519@openssh.com,
570 rsa-sha2-512,rsa-sha2-256,ssh-rsa
571 If hostkeys are known for the destination host then this default
573 is modified to prefer their algorithms.
574 The list of available signature algorithms may also be obtained
576 using "ssh -Q HostKeyAlgorithms".
577 HostKeyAlias
579 Specifies an alias that should be used instead of the real host
580 name when looking up or saving the host key in the host key data‐
581 base files and when validating host certificates. This option is
582 useful for tunneling SSH connections or for multiple servers run‐
583 ning on a single host.
584 Hostname
586 Specifies the real host name to log into. This can be used to
587 specify nicknames or abbreviations for hosts. Arguments to
588 Hostname accept the tokens described in the TOKENS section. Nu‐
589 meric IP addresses are also permitted (both on the command line
590 and in Hostname specifications). The default is the name given
591 on the command line.
592 IdentitiesOnly
594 Specifies that ssh(1) should only use the configured authentica‐
595 tion identity and certificate files (either the default files, or
596 those explicitly configured in the ssh_config files or passed on
597 the ssh(1) command-line), even if ssh-agent(1) or a
598 PKCS11Provider or SecurityKeyProvider offers more identities.
599 The argument to this keyword must be yes or no (the default).
600 This option is intended for situations where ssh-agent offers
601 many different identities.
602 IdentityAgent
604 Specifies the UNIX-domain socket used to communicate with the au‐
605 thentication agent.
606 This option overrides the SSH_AUTH_SOCK environment variable and
608 can be used to select a specific agent. Setting the socket name
609 to none disables the use of an authentication agent. If the
610 string "SSH_AUTH_SOCK" is specified, the location of the socket
611 will be read from the SSH_AUTH_SOCK environment variable. Other‐
612 wise if the specified value begins with a ‘$’ character, then it
613 will be treated as an environment variable containing the loca‐
614 tion of the socket.
615 Arguments to IdentityAgent may use the tilde syntax to refer to a
617 user's home directory, the tokens described in the TOKENS section
618 and environment variables as described in the ENVIRONMENT
619 VARIABLES section.
620 IdentityFile
622 Specifies a file from which the user's DSA, ECDSA, authenticator-
623 hosted ECDSA, Ed25519, authenticator-hosted Ed25519 or RSA au‐
624 thentication identity is read. The default is ~/.ssh/id_dsa,
625 ~/.ssh/id_ecdsa, ~/.ssh/id_ecdsa_sk, ~/.ssh/id_ed25519,
626 ~/.ssh/id_ed25519_sk and ~/.ssh/id_rsa. Additionally, any iden‐
627 tities represented by the authentication agent will be used for
628 authentication unless IdentitiesOnly is set. If no certificates
629 have been explicitly specified by CertificateFile, ssh(1) will
630 try to load certificate information from the filename obtained by
631 appending -cert.pub to the path of a specified IdentityFile.
632 Arguments to IdentityFile may use the tilde syntax to refer to a
634 user's home directory or the tokens described in the TOKENS sec‐
635 tion.
636 It is possible to have multiple identity files specified in con‐
638 figuration files; all these identities will be tried in sequence.
639 Multiple IdentityFile directives will add to the list of identi‐
640 ties tried (this behaviour differs from that of other configura‐
641 tion directives).
642 IdentityFile may be used in conjunction with IdentitiesOnly to
644 select which identities in an agent are offered during authenti‐
645 cation. IdentityFile may also be used in conjunction with
646 CertificateFile in order to provide any certificate also needed
647 for authentication with the identity.
648 The authentication identity can be also specified in a form of
650 PKCS#11 URI starting with a string pkcs11:. There is supported a
651 subset of the PKCS#11 URI as defined in RFC 7512 (implemented
652 path arguments id, manufacturer, object, token and query argu‐
653 ments module-path and pin-value ). The URI can not be in quotes.
654 IgnoreUnknown
656 Specifies a pattern-list of unknown options to be ignored if they
657 are encountered in configuration parsing. This may be used to
658 suppress errors if ssh_config contains options that are unrecog‐
659 nised by ssh(1). It is recommended that IgnoreUnknown be listed
660 early in the configuration file as it will not be applied to un‐
661 known options that appear before it.
662 Include
664 Include the specified configuration file(s). Multiple pathnames
665 may be specified and each pathname may contain glob(7) wildcards
666 and, for user configurations, shell-like ‘~’ references to user
667 home directories. Wildcards will be expanded and processed in
668 lexical order. Files without absolute paths are assumed to be in
669 ~/.ssh if included in a user configuration file or /etc/ssh if
670 included from the system configuration file. Include directive
671 may appear inside a Match or Host block to perform conditional
672 inclusion.
673 IPQoS Specifies the IPv4 type-of-service or DSCP class for connections.
675 Accepted values are af11, af12, af13, af21, af22, af23, af31,
676 af32, af33, af41, af42, af43, cs0, cs1, cs2, cs3, cs4, cs5, cs6,
677 cs7, ef, le, lowdelay, throughput, reliability, a numeric value,
678 or none to use the operating system default. This option may
679 take one or two arguments, separated by whitespace. If one argu‐
680 ment is specified, it is used as the packet class uncondition‐
681 ally. If two values are specified, the first is automatically
682 selected for interactive sessions and the second for non-interac‐
683 tive sessions. The default is af21 (Low-Latency Data) for inter‐
684 active sessions and cs1 (Lower Effort) for non-interactive ses‐
685 sions.
686 KbdInteractiveAuthentication
688 Specifies whether to use keyboard-interactive authentication.
689 The argument to this keyword must be yes (the default) or no.
690 KbdInteractiveDevices
692 Specifies the list of methods to use in keyboard-interactive au‐
693 thentication. Multiple method names must be comma-separated.
694 The default is to use the server specified list. The methods
695 available vary depending on what the server supports. For an
696 OpenSSH server, it may be zero or more of: bsdauth and pam.
697 KexAlgorithms
699 The default is handled system-wide by crypto-policies(7). To see
700 the defaults and how to modify this default, see manual page
701 update-crypto-policies(8).
702 Specifies the available KEX (Key Exchange) algorithms. Multiple
704 algorithms must be comma-separated. If the specified list begins
705 with a ‘+’ character, then the specified methods will be appended
706 to the built-in openssh default set instead of replacing them.
707 If the specified list begins with a ‘-’ character, then the spec‐
708 ified methods (including wildcards) will be removed from the
709 built-in openssh default set instead of replacing them. If the
710 specified list begins with a ‘^’ character, then the specified
711 methods will be placed at the head of the built-in openssh de‐
712 fault set.
713 The list of available key exchange algorithms may also be ob‐
715 tained using "ssh -Q kex".
716 KnownHostsCommand
718 Specifies a command to use to obtain a list of host keys, in ad‐
719 dition to those listed in UserKnownHostsFile and
720 GlobalKnownHostsFile. This command is executed after the files
721 have been read. It may write host key lines to standard output
722 in identical format to the usual files (described in the
723 VERIFYING HOST KEYS section in ssh(1)). Arguments to
724 KnownHostsCommand accept the tokens described in the TOKENS sec‐
725 tion. The command may be invoked multiple times per connection:
726 once when preparing the preference list of host key algorithms to
727 use, again to obtain the host key for the requested host name
728 and, if CheckHostIP is enabled, one more time to obtain the host
729 key matching the server's address. If the command exits abnor‐
730 mally or returns a non-zero exit status then the connection is
731 terminated.
732 LocalCommand
734 Specifies a command to execute on the local machine after suc‐
735 cessfully connecting to the server. The command string extends
736 to the end of the line, and is executed with the user's shell.
737 Arguments to LocalCommand accept the tokens described in the
738 TOKENS section.
739 The command is run synchronously and does not have access to the
741 session of the ssh(1) that spawned it. It should not be used for
742 interactive commands.
743 This directive is ignored unless PermitLocalCommand has been en‐
745 abled.
746 LocalForward
748 Specifies that a TCP port on the local machine be forwarded over
749 the secure channel to the specified host and port from the remote
750 machine. The first argument specifies the listener and may be
751 [bind_address:]port or a Unix domain socket path. The second ar‐
752 gument is the destination and may be host:hostport or a Unix do‐
753 main socket path if the remote host supports it.
754 IPv6 addresses can be specified by enclosing addresses in square
756 brackets. Multiple forwardings may be specified, and additional
757 forwardings can be given on the command line. Only the superuser
758 can forward privileged ports. By default, the local port is
759 bound in accordance with the GatewayPorts setting. However, an
760 explicit bind_address may be used to bind the connection to a
761 specific address. The bind_address of localhost indicates that
762 the listening port be bound for local use only, while an empty
763 address or ‘*’ indicates that the port should be available from
764 all interfaces. Unix domain socket paths may use the tokens de‐
765 scribed in the TOKENS section and environment variables as de‐
766 scribed in the ENVIRONMENT VARIABLES section.
767 LogLevel
769 Gives the verbosity level that is used when logging messages from
770 ssh(1). The possible values are: QUIET, FATAL, ERROR, INFO, VER‐
771 BOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO.
772 DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify
773 higher levels of verbose output.
774 LogVerbose
776 Specify one or more overrides to LogLevel. An override consists
777 of a pattern lists that matches the source file, function and
778 line number to force detailed logging for. For example, an over‐
779 ride pattern of:
780 kex.c:*:1000,*:kex_exchange_identification():*,packet.c:*
782 would enable detailed logging for line 1000 of kex.c, everything
784 in the kex_exchange_identification() function, and all code in
785 the packet.c file. This option is intended for debugging and no
786 overrides are enabled by default.
787 MACs The default is handled system-wide by crypto-policies(7). To see
789 the defaults and how to modify this default, see manual page
790 update-crypto-policies(8).
791 Specifies the MAC (message authentication code) algorithms in or‐
793 der of preference. The MAC algorithm is used for data integrity
794 protection. Multiple algorithms must be comma-separated. If the
795 specified list begins with a ‘+’ character, then the specified
796 algorithms will be appended to the built-in openssh default set
797 instead of replacing them. If the specified list begins with a
798 ‘-’ character, then the specified algorithms (including wild‐
799 cards) will be removed from the built-in openssh default set in‐
800 stead of replacing them. If the specified list begins with a ‘^’
801 character, then the specified algorithms will be placed at the
802 head of the built-in openssh default set.
803 The algorithms that contain "-etm" calculate the MAC after en‐
805 cryption (encrypt-then-mac). These are considered safer and
806 their use recommended.
807 The list of available MAC algorithms may also be obtained using
809 "ssh -Q mac".
810 NoHostAuthenticationForLocalhost
812 Disable host authentication for localhost (loopback addresses).
813 The argument to this keyword must be yes or no (the default).
814 NumberOfPasswordPrompts
816 Specifies the number of password prompts before giving up. The
817 argument to this keyword must be an integer. The default is 3.
818 PasswordAuthentication
820 Specifies whether to use password authentication. The argument
821 to this keyword must be yes (the default) or no.
822 PermitLocalCommand
824 Allow local command execution via the LocalCommand option or us‐
825 ing the !command escape sequence in ssh(1). The argument must be
826 yes or no (the default).
827 PermitRemoteOpen
829 Specifies the destinations to which remote TCP port forwarding is
830 permitted when RemoteForward is used as a SOCKS proxy. The for‐
831 warding specification must be one of the following forms:
832 PermitRemoteOpen host:port
834 PermitRemoteOpen IPv4_addr:port
835 PermitRemoteOpen [IPv6_addr]:port
836 Multiple forwards may be specified by separating them with white‐
838 space. An argument of any can be used to remove all restrictions
839 and permit any forwarding requests. An argument of none can be
840 used to prohibit all forwarding requests. The wildcard ‘*’ can
841 be used for host or port to allow all hosts or ports respec‐
842 tively. Otherwise, no pattern matching or address lookups are
843 performed on supplied names.
844 PKCS11Provider
846 Specifies which PKCS#11 provider to use or none to indicate that
847 no provider should be used (the default). The argument to this
848 keyword is a path to the PKCS#11 shared library ssh(1) should use
849 to communicate with a PKCS#11 token providing keys for user au‐
850 thentication.
851 Port Specifies the port number to connect on the remote host. The de‐
853 fault is 22.
854 PreferredAuthentications
856 Specifies the order in which the client should try authentication
857 methods. This allows a client to prefer one method (e.g.
858 keyboard-interactive) over another method (e.g. password). The
859 default is:
860 gssapi-keyex,gssapi-with-mic,hostbased,publickey,
862 keyboard-interactive,password
863 ProxyCommand
865 Specifies the command to use to connect to the server. The com‐
866 mand string extends to the end of the line, and is executed using
867 the user's shell ‘exec’ directive to avoid a lingering shell
868 process.
869 Arguments to ProxyCommand accept the tokens described in the
871 TOKENS section. The command can be basically anything, and
872 should read from its standard input and write to its standard
873 output. It should eventually connect an sshd(8) server running
874 on some machine, or execute sshd -i somewhere. Host key manage‐
875 ment will be done using the Hostname of the host being connected
876 (defaulting to the name typed by the user). Setting the command
877 to none disables this option entirely. Note that CheckHostIP is
878 not available for connects with a proxy command.
879 This directive is useful in conjunction with nc(1) and its proxy
881 support. For example, the following directive would connect via
882 an HTTP proxy at 192.0.2.0:
883 ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
885 ProxyJump
887 Specifies one or more jump proxies as either [user@]host[:port]
888 or an ssh URI. Multiple proxies may be separated by comma char‐
889 acters and will be visited sequentially. Setting this option
890 will cause ssh(1) to connect to the target host by first making a
891 ssh(1) connection to the specified ProxyJump host and then estab‐
892 lishing a TCP forwarding to the ultimate target from there. Set‐
893 ting the host to none disables this option entirely.
894 Note that this option will compete with the ProxyCommand option -
896 whichever is specified first will prevent later instances of the
897 other from taking effect.
898 Note also that the configuration for the destination host (either
900 supplied via the command-line or the configuration file) is not
901 generally applied to jump hosts. ~/.ssh/config should be used if
902 specific configuration is required for jump hosts.
903 ProxyUseFdpass
905 Specifies that ProxyCommand will pass a connected file descriptor
906 back to ssh(1) instead of continuing to execute and pass data.
907 The default is no.
908 PubkeyAcceptedAlgorithms
910 The default is handled system-wide by crypto-policies(7). To see
911 the defaults and how to modify this default, see manual page
912 update-crypto-policies(8).
913 Specifies the signature algorithms that will be used for public
915 key authentication as a comma-separated list of patterns. If the
916 specified list begins with a ‘+’ character, then the algorithms
917 after it will be appended to the built-in openssh default instead
918 of replacing it. If the specified list begins with a ‘-’ charac‐
919 ter, then the specified algorithms (including wildcards) will be
920 removed from the built-in openssh default set instead of replac‐
921 ing them. If the specified list begins with a ‘^’ character,
922 then the specified algorithms will be placed at the head of the
923 built-in openssh default set.
924 The list of available signature algorithms may also be obtained
926 using "ssh -Q PubkeyAcceptedAlgorithms".
927 PubkeyAuthentication
929 Specifies whether to try public key authentication. The argument
930 to this keyword must be yes (the default) or no.
931 RekeyLimit
933 Specifies the maximum amount of data that may be transmitted be‐
934 fore the session key is renegotiated, optionally followed by a
935 maximum amount of time that may pass before the session key is
936 renegotiated. The first argument is specified in bytes and may
937 have a suffix of ‘K’, ‘M’, or ‘G’ to indicate Kilobytes,
938 Megabytes, or Gigabytes, respectively. The default is between
939 ‘1G’ and ‘4G’, depending on the cipher. The optional second
940 value is specified in seconds and may use any of the units docu‐
941 mented in the TIME FORMATS section of sshd_config(5). The de‐
942 fault value for RekeyLimit is default none, which means that
943 rekeying is performed after the cipher's default amount of data
944 has been sent or received and no time based rekeying is done.
945 RemoteCommand
947 Specifies a command to execute on the remote machine after suc‐
948 cessfully connecting to the server. The command string extends
949 to the end of the line, and is executed with the user's shell.
950 Arguments to RemoteCommand accept the tokens described in the
951 TOKENS section.
952 RemoteForward
954 Specifies that a TCP port on the remote machine be forwarded over
955 the secure channel. The remote port may either be forwarded to a
956 specified host and port from the local machine, or may act as a
957 SOCKS 4/5 proxy that allows a remote client to connect to arbi‐
958 trary destinations from the local machine. The first argument is
959 the listening specification and may be [bind_address:]port or, if
960 the remote host supports it, a Unix domain socket path. If for‐
961 warding to a specific destination then the second argument must
962 be host:hostport or a Unix domain socket path, otherwise if no
963 destination argument is specified then the remote forwarding will
964 be established as a SOCKS proxy. When acting as a SOCKS proxy
965 the destination of the connection can be restricted by
966 PermitRemoteOpen.
967 IPv6 addresses can be specified by enclosing addresses in square
969 brackets. Multiple forwardings may be specified, and additional
970 forwardings can be given on the command line. Privileged ports
971 can be forwarded only when logging in as root on the remote ma‐
972 chine. Unix domain socket paths may use the tokens described in
973 the TOKENS section and environment variables as described in the
974 ENVIRONMENT VARIABLES section.
975 If the port argument is 0, the listen port will be dynamically
977 allocated on the server and reported to the client at run time.
978 If the bind_address is not specified, the default is to only bind
980 to loopback addresses. If the bind_address is ‘*’ or an empty
981 string, then the forwarding is requested to listen on all inter‐
982 faces. Specifying a remote bind_address will only succeed if the
983 server's GatewayPorts option is enabled (see sshd_config(5)).
984 RequestTTY
986 Specifies whether to request a pseudo-tty for the session. The
987 argument may be one of: no (never request a TTY), yes (always re‐
988 quest a TTY when standard input is a TTY), force (always request
989 a TTY) or auto (request a TTY when opening a login session).
990 This option mirrors the -t and -T flags for ssh(1).
991 RevokedHostKeys
993 Specifies revoked host public keys. Keys listed in this file
994 will be refused for host authentication. Note that if this file
995 does not exist or is not readable, then host authentication will
996 be refused for all hosts. Keys may be specified as a text file,
997 listing one public key per line, or as an OpenSSH Key Revocation
998 List (KRL) as generated by ssh-keygen(1). For more information
999 on KRLs, see the KEY REVOCATION LISTS section in ssh-keygen(1).
1000 SecurityKeyProvider
1002 Specifies a path to a library that will be used when loading any
1003 FIDO authenticator-hosted keys, overriding the default of using
1004 the built-in USB HID support.
1005 If the specified value begins with a ‘$’ character, then it will
1007 be treated as an environment variable containing the path to the
1008 library.
1009 SendEnv
1011 Specifies what variables from the local environ(7) should be sent
1012 to the server. The server must also support it, and the server
1013 must be configured to accept these environment variables. Note
1014 that the TERM environment variable is always sent whenever a
1015 pseudo-terminal is requested as it is required by the protocol.
1016 Refer to AcceptEnv in sshd_config(5) for how to configure the
1017 server. Variables are specified by name, which may contain wild‐
1018 card characters. Multiple environment variables may be separated
1019 by whitespace or spread across multiple SendEnv directives.
1020 See PATTERNS for more information on patterns.
1022 It is possible to clear previously set SendEnv variable names by
1024 prefixing patterns with -. The default is not to send any envi‐
1025 ronment variables.
1026 ServerAliveCountMax
1028 Sets the number of server alive messages (see below) which may be
1029 sent without ssh(1) receiving any messages back from the server.
1030 If this threshold is reached while server alive messages are be‐
1031 ing sent, ssh will disconnect from the server, terminating the
1032 session. It is important to note that the use of server alive
1033 messages is very different from TCPKeepAlive (below). The server
1034 alive messages are sent through the encrypted channel and there‐
1035 fore will not be spoofable. The TCP keepalive option enabled by
1036 TCPKeepAlive is spoofable. The server alive mechanism is valu‐
1037 able when the client or server depend on knowing when a connec‐
1038 tion has become unresponsive.
1039 The default value is 3. If, for example, ServerAliveInterval
1041 (see below) is set to 15 and ServerAliveCountMax is left at the
1042 default, if the server becomes unresponsive, ssh will disconnect
1043 after approximately 45 seconds.
1044 ServerAliveInterval
1046 Sets a timeout interval in seconds after which if no data has
1047 been received from the server, ssh(1) will send a message through
1048 the encrypted channel to request a response from the server. The
1049 default is 0, indicating that these messages will not be sent to
1050 the server.
1051 SetEnv Directly specify one or more environment variables and their con‐
1053 tents to be sent to the server. Similarly to SendEnv, the server
1054 must be prepared to accept the environment variable.
1055 StreamLocalBindMask
1057 Sets the octal file creation mode mask (umask) used when creating
1058 a Unix-domain socket file for local or remote port forwarding.
1059 This option is only used for port forwarding to a Unix-domain
1060 socket file.
1061 The default value is 0177, which creates a Unix-domain socket
1063 file that is readable and writable only by the owner. Note that
1064 not all operating systems honor the file mode on Unix-domain
1065 socket files.
1066 StreamLocalBindUnlink
1068 Specifies whether to remove an existing Unix-domain socket file
1069 for local or remote port forwarding before creating a new one.
1070 If the socket file already exists and StreamLocalBindUnlink is
1071 not enabled, ssh will be unable to forward the port to the Unix-
1072 domain socket file. This option is only used for port forwarding
1073 to a Unix-domain socket file.
1074 The argument must be yes or no (the default).
1076 StrictHostKeyChecking
1078 If this flag is set to yes, ssh(1) will never automatically add
1079 host keys to the ~/.ssh/known_hosts file, and refuses to connect
1080 to hosts whose host key has changed. This provides maximum pro‐
1081 tection against man-in-the-middle (MITM) attacks, though it can
1082 be annoying when the /etc/gsissh/ssh_known_hosts file is poorly
1083 maintained or when connections to new hosts are frequently made.
1084 This option forces the user to manually add all new hosts.
1085 If this flag is set to “accept-new” then ssh will automatically
1087 add new host keys to the user known hosts files, but will not
1088 permit connections to hosts with changed host keys. If this flag
1089 is set to “no” or “off”, ssh will automatically add new host keys
1090 to the user known hosts files and allow connections to hosts with
1091 changed hostkeys to proceed, subject to some restrictions. If
1092 this flag is set to ask (the default), new host keys will be
1093 added to the user known host files only after the user has con‐
1094 firmed that is what they really want to do, and ssh will refuse
1095 to connect to hosts whose host key has changed. The host keys of
1096 known hosts will be verified automatically in all cases.
1097 SyslogFacility
1099 Gives the facility code that is used when logging messages from
1100 ssh(1). The possible values are: DAEMON, USER, AUTH, LOCAL0, LO‐
1101 CAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. The de‐
1102 fault is USER.
1103 TCPKeepAlive
1105 Specifies whether the system should send TCP keepalive messages
1106 to the other side. If they are sent, death of the connection or
1107 crash of one of the machines will be properly noticed. However,
1108 this means that connections will die if the route is down tempo‐
1109 rarily, and some people find it annoying.
1110 The default is yes (to send TCP keepalive messages), and the
1112 client will notice if the network goes down or the remote host
1113 dies. This is important in scripts, and many users want it too.
1114 To disable TCP keepalive messages, the value should be set to no.
1116 See also ServerAliveInterval for protocol-level keepalives.
1117 Tunnel Request tun(4) device forwarding between the client and the
1119 server. The argument must be yes, point-to-point (layer 3),
1120 ethernet (layer 2), or no (the default). Specifying yes requests
1121 the default tunnel mode, which is point-to-point.
1122 TunnelDevice
1124 Specifies the tun(4) devices to open on the client (local_tun)
1125 and the server (remote_tun).
1126 The argument must be local_tun[:remote_tun]. The devices may be
1128 specified by numerical ID or the keyword any, which uses the next
1129 available tunnel device. If remote_tun is not specified, it de‐
1130 faults to any. The default is any:any.
1131 UpdateHostKeys
1133 Specifies whether ssh(1) should accept notifications of addi‐
1134 tional hostkeys from the server sent after authentication has
1135 completed and add them to UserKnownHostsFile. The argument must
1136 be yes, no or ask. This option allows learning alternate
1137 hostkeys for a server and supports graceful key rotation by al‐
1138 lowing a server to send replacement public keys before old ones
1139 are removed.
1140 Additional hostkeys are only accepted if the key used to authen‐
1142 ticate the host was already trusted or explicitly accepted by the
1143 user, the host was authenticated via UserKnownHostsFile (i.e. not
1144 GlobalKnownHostsFile) and the host was authenticated using a
1145 plain key and not a certificate.
1146 UpdateHostKeys is enabled by default if the user has not overrid‐
1148 den the default UserKnownHostsFile setting and has not enabled
1149 VerifyHostKeyDNS, otherwise UpdateHostKeys will be set to no.
1150 If UpdateHostKeys is set to ask, then the user is asked to con‐
1152 firm the modifications to the known_hosts file. Confirmation is
1153 currently incompatible with ControlPersist, and will be disabled
1154 if it is enabled.
1155 Presently, only sshd(8) from OpenSSH 6.8 and greater support the
1157 "hostkeys@openssh.com" protocol extension used to inform the
1158 client of all the server's hostkeys.
1159 User Specifies the user to log in as. This can be useful when a dif‐
1161 ferent user name is used on different machines. This saves the
1162 trouble of having to remember to give the user name on the com‐
1163 mand line.
1164 UserKnownHostsFile
1166 Specifies one or more files to use for the user host key data‐
1167 base, separated by whitespace. Each filename may use tilde nota‐
1168 tion to refer to the user's home directory, the tokens described
1169 in the TOKENS section and environment variables as described in
1170 the ENVIRONMENT VARIABLES section. The default is
1171 ~/.ssh/known_hosts, ~/.ssh/known_hosts2.
1172 VerifyHostKeyDNS
1174 Specifies whether to verify the remote key using DNS and SSHFP
1175 resource records. If this option is set to yes, the client will
1176 implicitly trust keys that match a secure fingerprint from DNS.
1177 Insecure fingerprints will be handled as if this option was set
1178 to ask. If this option is set to ask, information on fingerprint
1179 match will be displayed, but the user will still need to confirm
1180 new host keys according to the StrictHostKeyChecking option. The
1181 default is no.
1182 See also VERIFYING HOST KEYS in ssh(1).
1184 VisualHostKey
1186 If this flag is set to yes, an ASCII art representation of the
1187 remote host key fingerprint is printed in addition to the finger‐
1188 print string at login and for unknown host keys. If this flag is
1189 set to no (the default), no fingerprint strings are printed at
1190 login and only the fingerprint string will be printed for unknown
1191 host keys.
1192 XAuthLocation
1194 Specifies the full pathname of the xauth(1) program. The default
1195 is /usr/bin/xauth.
1196
1198 A pattern consists of zero or more non-whitespace characters, ‘*’ (a
1199 wildcard that matches zero or more characters), or ‘?’ (a wildcard that
1200 matches exactly one character). For example, to specify a set of decla‐
1201 rations for any host in the ".co.uk" set of domains, the following pat‐
1202 tern could be used:
1203 Host *.co.uk
1205 The following pattern would match any host in the 192.168.0.[0-9] network
1207 range:
1208 Host 192.168.0.?
1210 A pattern-list is a comma-separated list of patterns. Patterns within
1212 pattern-lists may be negated by preceding them with an exclamation mark
1213 (‘!’). For example, to allow a key to be used from anywhere within an
1214 organization except from the "dialup" pool, the following entry (in au‐
1215 thorized_keys) could be used:
1216 from="!*.dialup.example.com,*.example.com"
1218 Note that a negated match will never produce a positive result by itself.
1220 For example, attempting to match "host3" against the following pattern-
1221 list will fail:
1222 from="!host1,!host2"
1224 The solution here is to include a term that will yield a positive match,
1226 such as a wildcard:
1227 from="!host1,!host2,*"
1229
1231 Arguments to some keywords can make use of tokens, which are expanded at
1232 runtime:
1233 %% A literal ‘%’.
1235 %C Hash of %l%h%p%r.
1236 %d Local user's home directory.
1237 %f The fingerprint of the server's host key.
1238 %H The known_hosts hostname or address that is being searched
1239 for.
1240 %h The remote hostname.
1241 %I A string describing the reason for a KnownHostsCommand execu‐
1242 tion: either ADDRESS when looking up a host by address (only
1243 when CheckHostIP is enabled), HOSTNAME when searching by
1244 hostname, or ORDER when preparing the host key algorithm
1245 preference list to use for the destination host.
1246 %i The local user ID.
1247 %K The base64 encoded host key.
1248 %k The host key alias if specified, otherwise the original re‐
1249 mote hostname given on the command line.
1250 %L The local hostname.
1251 %l The local hostname, including the domain name.
1252 %n The original remote hostname, as given on the command line.
1253 %p The remote port.
1254 %r The remote username.
1255 %T The local tun(4) or tap(4) network interface assigned if tun‐
1256 nel forwarding was requested, or "NONE" otherwise.
1257 %t The type of the server host key, e.g. ssh-ed25519
1258 %u The local username.
1259 CertificateFile, ControlPath, IdentityAgent, IdentityFile,
1261 KnownHostsCommand, LocalForward, Match exec, RemoteCommand,
1262 RemoteForward, and UserKnownHostsFile accept the tokens %%, %C, %d, %h,
1263 %i, %k, %L, %l, %n, %p, %r, and %u.
1264 KnownHostsCommand additionally accepts the tokens %f, %H, %I, %K and %t.
1266 Hostname accepts the tokens %% and %h.
1268 LocalCommand accepts all tokens.
1270 ProxyCommand accepts the tokens %%, %h, %n, %p, and %r.
1272
1274 Arguments to some keywords can be expanded at runtime from environment
1275 variables on the client by enclosing them in ${}, for example
1276 ${HOME}/.ssh would refer to the user's .ssh directory. If a specified
1277 environment variable does not exist then an error will be returned and
1278 the setting for that keyword will be ignored.
1279 The keywords CertificateFile, ControlPath, IdentityAgent, IdentityFile,
1281 KnownHostsCommand, and UserKnownHostsFile support environment variables.
1282 The keywords LocalForward and RemoteForward support environment variables
1283 only for Unix domain socket paths.
1284
1286 ~/.ssh/config
1287 This is the per-user configuration file. The format of this file
1288 is described above. This file is used by the SSH client. Be‐
1289 cause of the potential for abuse, this file must have strict per‐
1290 missions: read/write for the user, and not writable by others.
1291 /etc/gsissh/ssh_config
1293 Systemwide configuration file. This file provides defaults for
1294 those values that are not specified in the user's configuration
1295 file, and for those users who do not have a configuration file.
1296 This file must be world-readable.
1297
1299 ssh(1)
1300
1302 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
1303 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
1304 de Raadt and Dug Song removed many bugs, re-added newer features and cre‐
1305 ated OpenSSH. Markus Friedl contributed the support for SSH protocol
1306 versions 1.5 and 2.0.
1307BSD April 4, 2021 BSD