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. system-wide configuration file (/etc/ssh/ssh_config)
13 For each parameter, the first obtained value will be used. The configu‐
15 ration files contain sections separated by Host specifications, and that
16 section is only applied for hosts that match one of the patterns given in
17 the specification. The matched host name is usually the one given on the
18 command line (see the CanonicalizeHostname option for exceptions).
19 Since the first obtained value for each parameter is used, more host-spe‐
21 cific declarations should be given near the beginning of the file, and
22 general defaults at the end.
23 The file contains keyword-argument pairs, one per line. Lines starting
25 with ‘#’ and empty lines are interpreted as comments. Arguments may op‐
26 tionally be enclosed in double quotes (") in order to represent arguments
27 containing spaces. Configuration options may be separated by whitespace
28 or optional whitespace and exactly one ‘=’; the latter format is useful
29 to avoid the need to quote whitespace when specifying configuration op‐
30 tions using the ssh, scp, and sftp -o option.
31 The possible keywords and their meanings are as follows (note that key‐
33 words are case-insensitive and arguments are case-sensitive):
34 Host Restricts the following declarations (up to the next Host or
36 Match keyword) to be only for those hosts that match one of the
37 patterns given after the keyword. If more than one pattern is
38 provided, they should be separated by whitespace. A single ‘*’
39 as a pattern can be used to provide global defaults for all
40 hosts. The host is usually the hostname argument given on the
41 command line (see the CanonicalizeHostname keyword for excep‐
42 tions).
43 A pattern entry may be negated by prefixing it with an exclama‐
45 tion mark (‘!’). If a negated entry is matched, then the Host
46 entry is ignored, regardless of whether any other patterns on the
47 line match. Negated matches are therefore useful to provide ex‐
48 ceptions for wildcard matches.
49 See PATTERNS for more information on patterns.
51 Match Restricts the following declarations (up to the next Host or
53 Match keyword) to be used only when the conditions following the
54 Match keyword are satisfied. Match conditions are specified us‐
55 ing one or more criteria or the single token all which always
56 matches. The available criteria keywords are: canonical, final,
57 exec, host, originalhost, user, and localuser. The all criteria
58 must appear alone or immediately after canonical or final. Other
59 criteria may be combined arbitrarily. All criteria but all,
60 canonical, and final require an argument. Criteria may be
61 negated by prepending an exclamation mark (‘!’).
62 The canonical keyword matches only when the configuration file is
64 being re-parsed after hostname canonicalization (see the
65 CanonicalizeHostname option). This may be useful to specify con‐
66 ditions that work with canonical host names only.
67 The final keyword requests that the configuration be re-parsed
69 (regardless of whether CanonicalizeHostname is enabled), and
70 matches only during this final pass. If CanonicalizeHostname is
71 enabled, then canonical and final match during the same pass.
72 The exec keyword executes the specified command under the user's
74 shell. If the command returns a zero exit status then the condi‐
75 tion is considered true. Commands containing whitespace charac‐
76 ters must be quoted. Arguments to exec accept the tokens de‐
77 scribed in the TOKENS section.
78 The other keywords' criteria must be single entries or comma-sep‐
80 arated lists and may use the wildcard and negation operators de‐
81 scribed in the PATTERNS section. The criteria for the host key‐
82 word are matched against the target hostname, after any substitu‐
83 tion by the Hostname or CanonicalizeHostname options. The
84 originalhost keyword matches against the hostname as it was spec‐
85 ified on the command-line. The user keyword matches against the
86 target username on the remote host. The localuser keyword
87 matches against the name of the local user running ssh(1) (this
88 keyword may be useful in system-wide ssh_config files).
89 AddKeysToAgent
91 Specifies whether keys should be automatically added to a running
92 ssh-agent(1). If this option is set to yes and a key is loaded
93 from a file, the key and its passphrase are added to the agent
94 with the default lifetime, as if by ssh-add(1). If this option
95 is set to ask, ssh(1) will require confirmation using the
96 SSH_ASKPASS program before adding a key (see ssh-add(1) for de‐
97 tails). If this option is set to confirm, each use of the key
98 must be confirmed, as if the -c option was specified to
99 ssh-add(1). If this option is set to no, no keys are added to
100 the agent. Alternately, this option may be specified as a time
101 interval using the format described in the TIME FORMATS section
102 of sshd_config(5) to specify the key's lifetime in ssh-agent(1),
103 after which it will automatically be removed. The argument must
104 be no (the default), yes, confirm (optionally followed by a time
105 interval), ask or a time interval.
106 AddressFamily
108 Specifies which address family to use when connecting. Valid ar‐
109 guments are any (the default), inet (use IPv4 only), or inet6
110 (use IPv6 only).
111 BatchMode
113 If set to yes, user interaction such as password prompts and host
114 key confirmation requests will be disabled. This option is use‐
115 ful in scripts and other batch jobs where no user is present to
116 interact with ssh(1). The argument must be yes or no (the de‐
117 fault).
118 BindAddress
120 Use the specified address on the local machine as the source ad‐
121 dress of the connection. Only useful on systems with more than
122 one address.
123 BindInterface
125 Use the address of the specified interface on the local machine
126 as the source address of the connection.
127 CanonicalDomains
129 When CanonicalizeHostname is enabled, this option specifies the
130 list of domain suffixes in which to search for the specified des‐
131 tination host.
132 CanonicalizeFallbackLocal
134 Specifies whether to fail with an error when hostname canonical‐
135 ization fails. The default, yes, will attempt to look up the un‐
136 qualified hostname using the system resolver's search rules. A
137 value of no will cause ssh(1) to fail instantly if
138 CanonicalizeHostname is enabled and the target hostname cannot be
139 found in any of the domains specified by CanonicalDomains.
140 CanonicalizeHostname
142 Controls whether explicit hostname canonicalization is performed.
143 The default, no, is not to perform any name rewriting and let the
144 system resolver handle all hostname lookups. If set to yes then,
145 for connections that do not use a ProxyCommand or ProxyJump,
146 ssh(1) will attempt to canonicalize the hostname specified on the
147 command line using the CanonicalDomains suffixes and
148 CanonicalizePermittedCNAMEs rules. If CanonicalizeHostname is
149 set to always, then canonicalization is applied to proxied con‐
150 nections too.
151 If this option is enabled, then the configuration files are pro‐
153 cessed again using the new target name to pick up any new config‐
154 uration in matching Host and Match stanzas.
155 CanonicalizeMaxDots
157 Specifies the maximum number of dot characters in a hostname be‐
158 fore canonicalization is disabled. The default, 1, allows a sin‐
159 gle dot (i.e. hostname.subdomain).
160 CanonicalizePermittedCNAMEs
162 Specifies rules to determine whether CNAMEs should be followed
163 when canonicalizing hostnames. The rules consist of one or more
164 arguments of source_domain_list:target_domain_list, where
165 source_domain_list is a pattern-list of domains that may follow
166 CNAMEs in canonicalization, and target_domain_list is a pattern-
167 list of domains that they may resolve to.
168 For example, "*.a.example.com:*.b.example.com,*.c.example.com"
170 will allow hostnames matching "*.a.example.com" to be canonical‐
171 ized to names in the "*.b.example.com" or "*.c.example.com" do‐
172 mains.
173 CASignatureAlgorithms
175 The default is handled system-wide by crypto-policies(7). To see
176 the defaults and how to modify this default, see manual page
177 update-crypto-policies(8).
178 Specifies which algorithms are allowed for signing of certifi‐
180 cates by certificate authorities (CAs). ssh(1) will not accept
181 host certificates signed using algorithms other than those speci‐
182 fied.
183 CertificateFile
185 Specifies a file from which the user's certificate is read. A
186 corresponding private key must be provided separately in order to
187 use this certificate either from an IdentityFile directive or -i
188 flag to ssh(1), via ssh-agent(1), or via a PKCS11Provider or
189 SecurityKeyProvider.
190 Arguments to CertificateFile may use the tilde syntax to refer to
192 a user's home directory, the tokens described in the TOKENS sec‐
193 tion and environment variables as described in the ENVIRONMENT
194 VARIABLES section.
195 It is possible to have multiple certificate files specified in
197 configuration files; these certificates will be tried in se‐
198 quence. Multiple CertificateFile directives will add to the list
199 of certificates used for authentication.
200 ChallengeResponseAuthentication
202 Specifies whether to use challenge-response authentication. The
203 argument to this keyword must be yes (the default) or no.
204 CheckHostIP
206 If set to yes [22mssh(1) will additionally check the host IP address
207 in the known_hosts file. This allows it to detect if a host key
208 changed due to DNS spoofing and will add addresses of destination
209 hosts to ~/.ssh/known_hosts in the process, regardless of the
210 setting of StrictHostKeyChecking. If the option is set to no
211 (the default), the check will not be executed.
212 Ciphers
214 The default is handled system-wide by crypto-policies(7). To see
215 the defaults and how to modify this default, see manual page
216 update-crypto-policies(8).
217 Specifies the ciphers allowed and their order of preference.
219 Multiple ciphers must be comma-separated. If the specified list
220 begins with a ‘+’ character, then the specified ciphers will be
221 appended to the built-in openssh default set instead of replacing
222 them. If the specified list begins with a ‘-’ character, then
223 the specified ciphers (including wildcards) will be removed from
224 the built-in openssh default set instead of replacing them. If
225 the specified list begins with a ‘^’ character, then the speci‐
226 fied ciphers will be placed at the head of the built-in openssh
227 default set.
228 The supported ciphers are:
230 3des-cbc
232 aes128-cbc
233 aes192-cbc
234 aes256-cbc
235 aes128-ctr
236 aes192-ctr
237 aes256-ctr
238 aes128-gcm@openssh.com
239 aes256-gcm@openssh.com
240 chacha20-poly1305@openssh.com
241 The list of available ciphers may also be obtained using "ssh -Q
243 cipher".
244 ClearAllForwardings
246 Specifies that all local, remote, and dynamic port forwardings
247 specified in the configuration files or on the command line be
248 cleared. This option is primarily useful when used from the
249 ssh(1) command line to clear port forwardings set in configura‐
250 tion files, and is automatically set by scp(1) and sftp(1). The
251 argument must be yes or no (the default).
252 Compression
254 Specifies whether to use compression. The argument must be yes
255 or no (the default).
256 ConnectionAttempts
258 Specifies the number of tries (one per second) to make before ex‐
259 iting. The argument must be an integer. This may be useful in
260 scripts if the connection sometimes fails. The default is 1.
261 ConnectTimeout
263 Specifies the timeout (in seconds) used when connecting to the
264 SSH server, instead of using the default system TCP timeout.
265 This timeout is applied both to establishing the connection and
266 to performing the initial SSH protocol handshake and key ex‐
267 change.
268 ControlMaster
270 Enables the sharing of multiple sessions over a single network
271 connection. When set to yes, ssh(1) will listen for connections
272 on a control socket specified using the ControlPath argument.
273 Additional sessions can connect to this socket using the same
274 ControlPath with ControlMaster set to no (the default). These
275 sessions will try to reuse the master instance's network connec‐
276 tion rather than initiating new ones, but will fall back to con‐
277 necting normally if the control socket does not exist, or is not
278 listening.
279 Setting this to ask will cause ssh(1) to listen for control con‐
281 nections, but require confirmation using ssh-askpass(1). If the
282 ControlPath cannot be opened, ssh(1) will continue without con‐
283 necting to a master instance.
284 X11 and ssh-agent(1) forwarding is supported over these multi‐
286 plexed connections, however the display and agent forwarded will
287 be the one belonging to the master connection i.e. it is not pos‐
288 sible to forward multiple displays or agents.
289 Two additional options allow for opportunistic multiplexing: try
291 to use a master connection but fall back to creating a new one if
292 one does not already exist. These options are: auto and autoask.
293 The latter requires confirmation like the ask option.
294 ControlPath
296 Specify the path to the control socket used for connection shar‐
297 ing as described in the ControlMaster section above or the string
298 none to disable connection sharing. Arguments to ControlPath may
299 use the tilde syntax to refer to a user's home directory, the to‐
300 kens described in the TOKENS section and environment variables as
301 described in the ENVIRONMENT VARIABLES section. It is recom‐
302 mended that any ControlPath used for opportunistic connection
303 sharing include at least %h, %p, and %r (or alternatively %C) and
304 be placed in a directory that is not writable by other users.
305 This ensures that shared connections are uniquely identified.
306 ControlPersist
308 When used in conjunction with ControlMaster, specifies that the
309 master connection should remain open in the background (waiting
310 for future client connections) after the initial client connec‐
311 tion has been closed. If set to no (the default), then the mas‐
312 ter connection will not be placed into the background, and will
313 close as soon as the initial client connection is closed. If set
314 to yes or 0, then the master connection will remain in the back‐
315 ground indefinitely (until killed or closed via a mechanism such
316 as the "ssh -O exit"). If set to a time in seconds, or a time in
317 any of the formats documented in sshd_config(5), then the back‐
318 grounded master connection will automatically terminate after it
319 has remained idle (with no client connections) for the specified
320 time.
321 DynamicForward
323 Specifies that a TCP port on the local machine be forwarded over
324 the secure channel, and the application protocol is then used to
325 determine where to connect to from the remote machine.
326 The argument must be [bind_address:]port. IPv6 addresses can be
328 specified by enclosing addresses in square brackets. By default,
329 the local port is bound in accordance with the GatewayPorts set‐
330 ting. However, an explicit bind_address may be used to bind the
331 connection to a specific address. The bind_address of localhost
332 indicates that the listening port be bound for local use only,
333 while an empty address or ‘*’ indicates that the port should be
334 available from all interfaces.
335 Currently the SOCKS4 and SOCKS5 protocols are supported, and
337 ssh(1) will act as a SOCKS server. Multiple forwardings may be
338 specified, and additional forwardings can be given on the command
339 line. Only the superuser can forward privileged ports.
340 EnableSSHKeysign
342 Setting this option to yes in the global client configuration
343 file /etc/ssh/ssh_config enables the use of the helper program
344 ssh-keysign(8) during HostbasedAuthentication. The argument must
345 be yes or no (the default). This option should be placed in the
346 non-hostspecific section. See ssh-keysign(8) for more informa‐
347 tion.
348 EscapeChar
350 Sets the escape character (default: ‘~’). The escape character
351 can also be set on the command line. The argument should be a
352 single character, ‘^’ followed by a letter, or none to disable
353 the escape character entirely (making the connection transparent
354 for binary data).
355 ExitOnForwardFailure
357 Specifies whether ssh(1) should terminate the connection if it
358 cannot set up all requested dynamic, tunnel, local, and remote
359 port forwardings, (e.g. if either end is unable to bind and lis‐
360 ten on a specified port). Note that ExitOnForwardFailure does
361 not apply to connections made over port forwardings and will not,
362 for example, cause ssh(1) to exit if TCP connections to the ulti‐
363 mate forwarding destination fail. The argument must be yes or no
364 (the default).
365 FingerprintHash
367 Specifies the hash algorithm used when displaying key finger‐
368 prints. Valid options are: md5 and sha256 (the default).
369 ForwardAgent
371 Specifies whether the connection to the authentication agent (if
372 any) will be forwarded to the remote machine. The argument may
373 be yes, no (the default), an explicit path to an agent socket or
374 the name of an environment variable (beginning with ‘$’) in which
375 to find the path.
376 Agent forwarding should be enabled with caution. Users with the
378 ability to bypass file permissions on the remote host (for the
379 agent's Unix-domain socket) can access the local agent through
380 the forwarded connection. An attacker cannot obtain key material
381 from the agent, however they can perform operations on the keys
382 that enable them to authenticate using the identities loaded into
383 the agent.
384 ForwardX11
386 Specifies whether X11 connections will be automatically redi‐
387 rected over the secure channel and DISPLAY set. The argument
388 must be yes or no (the default).
389 X11 forwarding should be enabled with caution. Users with the
391 ability to bypass file permissions on the remote host (for the
392 user's X11 authorization database) can access the local X11 dis‐
393 play through the forwarded connection. An attacker may then be
394 able to perform activities such as keystroke monitoring if the
395 ForwardX11Trusted option is also enabled.
396 ForwardX11Timeout
398 Specify a timeout for untrusted X11 forwarding using the format
399 described in the TIME FORMATS section of sshd_config(5). X11
400 connections received by ssh(1) after this time will be refused.
401 Setting ForwardX11Timeout to zero will disable the timeout and
402 permit X11 forwarding for the life of the connection. The de‐
403 fault is to disable untrusted X11 forwarding after twenty minutes
404 has elapsed.
405 ForwardX11Trusted
407 If this option is set to yes, remote X11 clients will have full
408 access to the original X11 display.
409 If this option is set to no (the default), remote X11 clients
411 will be considered untrusted and prevented from stealing or tam‐
412 pering with data belonging to trusted X11 clients. Furthermore,
413 the xauth(1) token used for the session will be set to expire af‐
414 ter 20 minutes. Remote clients will be refused access after this
415 time.
416 See the X11 SECURITY extension specification for full details on
418 the restrictions imposed on untrusted clients.
419 GatewayPorts
421 Specifies whether remote hosts are allowed to connect to local
422 forwarded ports. By default, ssh(1) binds local port forwardings
423 to the loopback address. This prevents other remote hosts from
424 connecting to forwarded ports. GatewayPorts can be used to spec‐
425 ify that ssh should bind local port forwardings to the wildcard
426 address, thus allowing remote hosts to connect to forwarded
427 ports. The argument must be yes or no (the default).
428 GlobalKnownHostsFile
430 Specifies one or more files to use for the global host key data‐
431 base, separated by whitespace. The default is
432 /etc/ssh/ssh_known_hosts, /etc/ssh/ssh_known_hosts2.
433 GSSAPIAuthentication
435 Specifies whether user authentication based on GSSAPI is allowed.
436 The default is no.
437 GSSAPIClientIdentity
439 If set, specifies the GSSAPI client identity that ssh should use
440 when connecting to the server. The default is unset, which means
441 that the default identity will be used.
442 GSSAPIDelegateCredentials
444 Forward (delegate) credentials to the server. The default is no.
445 GSSAPIKeyExchange
447 Specifies whether key exchange based on GSSAPI may be used. When
448 using GSSAPI key exchange the server need not have a host key.
449 The default is “no”.
450 GSSAPIRenewalForcesRekey
452 If set to “yes” then renewal of the client's GSSAPI credentials
453 will force the rekeying of the ssh connection. With a compatible
454 server, this will delegate the renewed credentials to a session
455 on the server.
456 Checks are made to ensure that credentials are only propagated
458 when the new credentials match the old ones on the originating
459 client and where the receiving server still has the old set in
460 its cache.
461 The default is “no”.
463 For this to work GSSAPIKeyExchange needs to be enabled in the
465 server and also used by the client.
466 GSSAPIServerIdentity
468 If set, specifies the GSSAPI server identity that ssh should ex‐
469 pect when connecting to the server. The default is unset, which
470 means that the expected GSSAPI server identity will be determined
471 from the target hostname.
472 GSSAPITrustDns
474 Set to “yes” to indicate that the DNS is trusted to securely
475 canonicalize the name of the host being connected to. If “no”,
476 the hostname entered on the command line will be passed untouched
477 to the GSSAPI library. The default is “no”.
478 GSSAPIKexAlgorithms
480 The default is handled system-wide by crypto-policies(7). To see
481 the defaults and how to modify this default, see manual page
482 update-crypto-policies(8).
483 The list of key exchange algorithms that are offered for GSSAPI
485 key exchange. Possible values are
486 gss-gex-sha1-,
488 gss-group1-sha1-,
489 gss-group14-sha1-,
490 gss-group14-sha256-,
491 gss-group16-sha512-,
492 gss-nistp256-sha256-,
493 gss-curve25519-sha256-
494 This option only applies to connections using GSSAPI.
496 HashKnownHosts
498 Indicates that ssh(1) should hash host names and addresses when
499 they are added to ~/.ssh/known_hosts. These hashed names may be
500 used normally by ssh(1) and sshd(8), but they do not visually re‐
501 veal identifying information if the file's contents are dis‐
502 closed. The default is no. Note that existing names and ad‐
503 dresses in known hosts files will not be converted automatically,
504 but may be manually hashed using ssh-keygen(1).
505 HostbasedAcceptedAlgorithms
507 Specifies the signature algorithms that will be used for host‐
508 based authentication as a comma-separated list of patterns. Al‐
509 ternately if the specified list begins with a ‘+’ character, then
510 the specified signature algorithms will be appended to the de‐
511 fault set instead of replacing them. If the specified list be‐
512 gins with a ‘-’ character, then the specified signature algo‐
513 rithms (including wildcards) will be removed from the default set
514 instead of replacing them. If the specified list begins with a
515 ‘^’ character, then the specified signature algorithms will be
516 placed at the head of the default set. The default for this op‐
517 tion is:
518 ssh-ed25519-cert-v01@openssh.com,
520 ecdsa-sha2-nistp256-cert-v01@openssh.com,
521 ecdsa-sha2-nistp384-cert-v01@openssh.com,
522 ecdsa-sha2-nistp521-cert-v01@openssh.com,
523 sk-ssh-ed25519-cert-v01@openssh.com,
524 sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
525 rsa-sha2-512-cert-v01@openssh.com,
526 rsa-sha2-256-cert-v01@openssh.com,
527 ssh-rsa-cert-v01@openssh.com,
528 ssh-ed25519,
529 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
530 sk-ssh-ed25519@openssh.com,
531 sk-ecdsa-sha2-nistp256@openssh.com,
532 rsa-sha2-512,rsa-sha2-256,ssh-rsa
533 The -Q option of ssh(1) may be used to list supported signature
535 algorithms. This was formerly named HostbasedKeyTypes.
536 HostbasedAuthentication
538 Specifies whether to try rhosts based authentication with public
539 key authentication. The argument must be yes or no (the de‐
540 fault).
541 HostKeyAlgorithms
543 Specifies the host key signature algorithms that the client wants
544 to use in order of preference. Alternately if the specified list
545 begins with a ‘+’ character, then the specified signature algo‐
546 rithms will be appended to the default set instead of replacing
547 them. If the specified list begins with a ‘-’ character, then
548 the specified signature algorithms (including wildcards) will be
549 removed from the default set instead of replacing them. If the
550 specified list begins with a ‘^’ character, then the specified
551 signature algorithms will be placed at the head of the default
552 set. The default for this option is:
553 ssh-ed25519-cert-v01@openssh.com,
555 ecdsa-sha2-nistp256-cert-v01@openssh.com,
556 ecdsa-sha2-nistp384-cert-v01@openssh.com,
557 ecdsa-sha2-nistp521-cert-v01@openssh.com,
558 sk-ssh-ed25519-cert-v01@openssh.com,
559 sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
560 rsa-sha2-512-cert-v01@openssh.com,
561 rsa-sha2-256-cert-v01@openssh.com,
562 ssh-rsa-cert-v01@openssh.com,
563 ssh-ed25519,
564 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
565 sk-ecdsa-sha2-nistp256@openssh.com,
566 sk-ssh-ed25519@openssh.com,
567 rsa-sha2-512,rsa-sha2-256,ssh-rsa
568 If hostkeys are known for the destination host then this default
570 is modified to prefer their algorithms.
571 The list of available signature algorithms may also be obtained
573 using "ssh -Q HostKeyAlgorithms".
574 HostKeyAlias
576 Specifies an alias that should be used instead of the real host
577 name when looking up or saving the host key in the host key data‐
578 base files and when validating host certificates. This option is
579 useful for tunneling SSH connections or for multiple servers run‐
580 ning on a single host.
581 Hostname
583 Specifies the real host name to log into. This can be used to
584 specify nicknames or abbreviations for hosts. Arguments to
585 Hostname accept the tokens described in the TOKENS section. Nu‐
586 meric IP addresses are also permitted (both on the command line
587 and in Hostname specifications). The default is the name given
588 on the command line.
589 IdentitiesOnly
591 Specifies that ssh(1) should only use the configured authentica‐
592 tion identity and certificate files (either the default files, or
593 those explicitly configured in the ssh_config files or passed on
594 the ssh(1) command-line), even if ssh-agent(1) or a
595 PKCS11Provider or SecurityKeyProvider offers more identities.
596 The argument to this keyword must be yes or no (the default).
597 This option is intended for situations where ssh-agent offers
598 many different identities.
599 IdentityAgent
601 Specifies the UNIX-domain socket used to communicate with the au‐
602 thentication agent.
603 This option overrides the SSH_AUTH_SOCK environment variable and
605 can be used to select a specific agent. Setting the socket name
606 to none disables the use of an authentication agent. If the
607 string "SSH_AUTH_SOCK" is specified, the location of the socket
608 will be read from the SSH_AUTH_SOCK environment variable. Other‐
609 wise if the specified value begins with a ‘$’ character, then it
610 will be treated as an environment variable containing the loca‐
611 tion of the socket.
612 Arguments to IdentityAgent may use the tilde syntax to refer to a
614 user's home directory, the tokens described in the TOKENS section
615 and environment variables as described in the ENVIRONMENT
616 VARIABLES section.
617 IdentityFile
619 Specifies a file from which the user's DSA, ECDSA, authenticator-
620 hosted ECDSA, Ed25519, authenticator-hosted Ed25519 or RSA au‐
621 thentication identity is read. The default is ~/.ssh/id_dsa,
622 ~/.ssh/id_ecdsa, ~/.ssh/id_ecdsa_sk, ~/.ssh/id_ed25519,
623 ~/.ssh/id_ed25519_sk and ~/.ssh/id_rsa. Additionally, any iden‐
624 tities represented by the authentication agent will be used for
625 authentication unless IdentitiesOnly is set. If no certificates
626 have been explicitly specified by CertificateFile, ssh(1) will
627 try to load certificate information from the filename obtained by
628 appending -cert.pub to the path of a specified IdentityFile.
629 Arguments to IdentityFile may use the tilde syntax to refer to a
631 user's home directory or the tokens described in the TOKENS sec‐
632 tion.
633 It is possible to have multiple identity files specified in con‐
635 figuration files; all these identities will be tried in sequence.
636 Multiple IdentityFile directives will add to the list of identi‐
637 ties tried (this behaviour differs from that of other configura‐
638 tion directives).
639 IdentityFile may be used in conjunction with IdentitiesOnly to
641 select which identities in an agent are offered during authenti‐
642 cation. IdentityFile may also be used in conjunction with
643 CertificateFile in order to provide any certificate also needed
644 for authentication with the identity.
645 The authentication identity can be also specified in a form of
647 PKCS#11 URI starting with a string pkcs11:. There is supported a
648 subset of the PKCS#11 URI as defined in RFC 7512 (implemented
649 path arguments id, manufacturer, object, token and query argu‐
650 ments module-path and pin-value ). The URI can not be in quotes.
651 IgnoreUnknown
653 Specifies a pattern-list of unknown options to be ignored if they
654 are encountered in configuration parsing. This may be used to
655 suppress errors if ssh_config contains options that are unrecog‐
656 nised by ssh(1). It is recommended that IgnoreUnknown be listed
657 early in the configuration file as it will not be applied to un‐
658 known options that appear before it.
659 Include
661 Include the specified configuration file(s). Multiple pathnames
662 may be specified and each pathname may contain glob(7) wildcards
663 and, for user configurations, shell-like ‘~’ references to user
664 home directories. Wildcards will be expanded and processed in
665 lexical order. Files without absolute paths are assumed to be in
666 ~/.ssh if included in a user configuration file or /etc/ssh if
667 included from the system configuration file. Include directive
668 may appear inside a Match or Host block to perform conditional
669 inclusion.
670 IPQoS Specifies the IPv4 type-of-service or DSCP class for connections.
672 Accepted values are af11, af12, af13, af21, af22, af23, af31,
673 af32, af33, af41, af42, af43, cs0, cs1, cs2, cs3, cs4, cs5, cs6,
674 cs7, ef, le, lowdelay, throughput, reliability, a numeric value,
675 or none to use the operating system default. This option may
676 take one or two arguments, separated by whitespace. If one argu‐
677 ment is specified, it is used as the packet class uncondition‐
678 ally. If two values are specified, the first is automatically
679 selected for interactive sessions and the second for non-interac‐
680 tive sessions. The default is af21 (Low-Latency Data) for inter‐
681 active sessions and cs1 (Lower Effort) for non-interactive ses‐
682 sions.
683 KbdInteractiveAuthentication
685 Specifies whether to use keyboard-interactive authentication.
686 The argument to this keyword must be yes (the default) or no.
687 KbdInteractiveDevices
689 Specifies the list of methods to use in keyboard-interactive au‐
690 thentication. Multiple method names must be comma-separated.
691 The default is to use the server specified list. The methods
692 available vary depending on what the server supports. For an
693 OpenSSH server, it may be zero or more of: bsdauth and pam.
694 KexAlgorithms
696 The default is handled system-wide by crypto-policies(7). To see
697 the defaults and how to modify this default, see manual page
698 update-crypto-policies(8).
699 Specifies the available KEX (Key Exchange) algorithms. Multiple
701 algorithms must be comma-separated. If the specified list begins
702 with a ‘+’ character, then the specified methods will be appended
703 to the built-in openssh default set instead of replacing them.
704 If the specified list begins with a ‘-’ character, then the spec‐
705 ified methods (including wildcards) will be removed from the
706 built-in openssh default set instead of replacing them. If the
707 specified list begins with a ‘^’ character, then the specified
708 methods will be placed at the head of the built-in openssh de‐
709 fault set.
710 The list of available key exchange algorithms may also be ob‐
712 tained using "ssh -Q kex".
713 KnownHostsCommand
715 Specifies a command to use to obtain a list of host keys, in ad‐
716 dition to those listed in UserKnownHostsFile and
717 GlobalKnownHostsFile. This command is executed after the files
718 have been read. It may write host key lines to standard output
719 in identical format to the usual files (described in the
720 VERIFYING HOST KEYS section in ssh(1)). Arguments to
721 KnownHostsCommand accept the tokens described in the TOKENS sec‐
722 tion. The command may be invoked multiple times per connection:
723 once when preparing the preference list of host key algorithms to
724 use, again to obtain the host key for the requested host name
725 and, if CheckHostIP is enabled, one more time to obtain the host
726 key matching the server's address. If the command exits abnor‐
727 mally or returns a non-zero exit status then the connection is
728 terminated.
729 LocalCommand
731 Specifies a command to execute on the local machine after suc‐
732 cessfully connecting to the server. The command string extends
733 to the end of the line, and is executed with the user's shell.
734 Arguments to LocalCommand accept the tokens described in the
735 TOKENS section.
736 The command is run synchronously and does not have access to the
738 session of the ssh(1) that spawned it. It should not be used for
739 interactive commands.
740 This directive is ignored unless PermitLocalCommand has been en‐
742 abled.
743 LocalForward
745 Specifies that a TCP port on the local machine be forwarded over
746 the secure channel to the specified host and port from the remote
747 machine. The first argument specifies the listener and may be
748 [bind_address:]port or a Unix domain socket path. The second ar‐
749 gument is the destination and may be host:hostport or a Unix do‐
750 main socket path if the remote host supports it.
751 IPv6 addresses can be specified by enclosing addresses in square
753 brackets. Multiple forwardings may be specified, and additional
754 forwardings can be given on the command line. Only the superuser
755 can forward privileged ports. By default, the local port is
756 bound in accordance with the GatewayPorts setting. However, an
757 explicit bind_address may be used to bind the connection to a
758 specific address. The bind_address of localhost indicates that
759 the listening port be bound for local use only, while an empty
760 address or ‘*’ indicates that the port should be available from
761 all interfaces. Unix domain socket paths may use the tokens de‐
762 scribed in the TOKENS section and environment variables as de‐
763 scribed in the ENVIRONMENT VARIABLES section.
764 LogLevel
766 Gives the verbosity level that is used when logging messages from
767 ssh(1). The possible values are: QUIET, FATAL, ERROR, INFO, VER‐
768 BOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO.
769 DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify
770 higher levels of verbose output.
771 LogVerbose
773 Specify one or more overrides to LogLevel. An override consists
774 of a pattern lists that matches the source file, function and
775 line number to force detailed logging for. For example, an over‐
776 ride pattern of:
777 kex.c:*:1000,*:kex_exchange_identification():*,packet.c:*
779 would enable detailed logging for line 1000 of kex.c, everything
781 in the kex_exchange_identification() function, and all code in
782 the packet.c file. This option is intended for debugging and no
783 overrides are enabled by default.
784 MACs The default is handled system-wide by crypto-policies(7). To see
786 the defaults and how to modify this default, see manual page
787 update-crypto-policies(8).
788 Specifies the MAC (message authentication code) algorithms in or‐
790 der of preference. The MAC algorithm is used for data integrity
791 protection. Multiple algorithms must be comma-separated. If the
792 specified list begins with a ‘+’ character, then the specified
793 algorithms will be appended to the built-in openssh default set
794 instead of replacing them. If the specified list begins with a
795 ‘-’ character, then the specified algorithms (including wild‐
796 cards) will be removed from the built-in openssh default set in‐
797 stead of replacing them. If the specified list begins with a ‘^’
798 character, then the specified algorithms will be placed at the
799 head of the built-in openssh default set.
800 The algorithms that contain "-etm" calculate the MAC after en‐
802 cryption (encrypt-then-mac). These are considered safer and
803 their use recommended.
804 The list of available MAC algorithms may also be obtained using
806 "ssh -Q mac".
807 NoHostAuthenticationForLocalhost
809 Disable host authentication for localhost (loopback addresses).
810 The argument to this keyword must be yes or no (the default).
811 NumberOfPasswordPrompts
813 Specifies the number of password prompts before giving up. The
814 argument to this keyword must be an integer. The default is 3.
815 PasswordAuthentication
817 Specifies whether to use password authentication. The argument
818 to this keyword must be yes (the default) or no.
819 PermitLocalCommand
821 Allow local command execution via the LocalCommand option or us‐
822 ing the !command escape sequence in ssh(1). The argument must be
823 yes or no (the default).
824 PermitRemoteOpen
826 Specifies the destinations to which remote TCP port forwarding is
827 permitted when RemoteForward is used as a SOCKS proxy. The for‐
828 warding specification must be one of the following forms:
829 PermitRemoteOpen host:port
831 PermitRemoteOpen IPv4_addr:port
832 PermitRemoteOpen [IPv6_addr]:port
833 Multiple forwards may be specified by separating them with white‐
835 space. An argument of any can be used to remove all restrictions
836 and permit any forwarding requests. An argument of none can be
837 used to prohibit all forwarding requests. The wildcard ‘*’ can
838 be used for host or port to allow all hosts or ports respec‐
839 tively. Otherwise, no pattern matching or address lookups are
840 performed on supplied names.
841 PKCS11Provider
843 Specifies which PKCS#11 provider to use or none to indicate that
844 no provider should be used (the default). The argument to this
845 keyword is a path to the PKCS#11 shared library ssh(1) should use
846 to communicate with a PKCS#11 token providing keys for user au‐
847 thentication.
848 Port Specifies the port number to connect on the remote host. The de‐
850 fault is 22.
851 PreferredAuthentications
853 Specifies the order in which the client should try authentication
854 methods. This allows a client to prefer one method (e.g.
855 keyboard-interactive) over another method (e.g. password). The
856 default is:
857 gssapi-with-mic,hostbased,publickey,
859 keyboard-interactive,password
860 ProxyCommand
862 Specifies the command to use to connect to the server. The com‐
863 mand string extends to the end of the line, and is executed using
864 the user's shell ‘exec’ directive to avoid a lingering shell
865 process.
866 Arguments to ProxyCommand accept the tokens described in the
868 TOKENS section. The command can be basically anything, and
869 should read from its standard input and write to its standard
870 output. It should eventually connect an sshd(8) server running
871 on some machine, or execute sshd -i somewhere. Host key manage‐
872 ment will be done using the Hostname of the host being connected
873 (defaulting to the name typed by the user). Setting the command
874 to none disables this option entirely. Note that CheckHostIP is
875 not available for connects with a proxy command.
876 This directive is useful in conjunction with nc(1) and its proxy
878 support. For example, the following directive would connect via
879 an HTTP proxy at 192.0.2.0:
880 ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
882 ProxyJump
884 Specifies one or more jump proxies as either [user@]host[:port]
885 or an ssh URI. Multiple proxies may be separated by comma char‐
886 acters and will be visited sequentially. Setting this option
887 will cause ssh(1) to connect to the target host by first making a
888 ssh(1) connection to the specified ProxyJump host and then estab‐
889 lishing a TCP forwarding to the ultimate target from there. Set‐
890 ting the host to none disables this option entirely.
891 Note that this option will compete with the ProxyCommand option -
893 whichever is specified first will prevent later instances of the
894 other from taking effect.
895 Note also that the configuration for the destination host (either
897 supplied via the command-line or the configuration file) is not
898 generally applied to jump hosts. ~/.ssh/config should be used if
899 specific configuration is required for jump hosts.
900 ProxyUseFdpass
902 Specifies that ProxyCommand will pass a connected file descriptor
903 back to ssh(1) instead of continuing to execute and pass data.
904 The default is no.
905 PubkeyAcceptedAlgorithms
907 The default is handled system-wide by crypto-policies(7). To see
908 the defaults and how to modify this default, see manual page
909 update-crypto-policies(8).
910 Specifies the signature algorithms that will be used for public
912 key authentication as a comma-separated list of patterns. If the
913 specified list begins with a ‘+’ character, then the algorithms
914 after it will be appended to the built-in openssh default instead
915 of replacing it. If the specified list begins with a ‘-’ charac‐
916 ter, then the specified algorithms (including wildcards) will be
917 removed from the built-in openssh default set instead of replac‐
918 ing them. If the specified list begins with a ‘^’ character,
919 then the specified algorithms will be placed at the head of the
920 built-in openssh default set.
921 The list of available signature algorithms may also be obtained
923 using "ssh -Q PubkeyAcceptedAlgorithms".
924 PubkeyAuthentication
926 Specifies whether to try public key authentication. The argument
927 to this keyword must be yes (the default) or no.
928 RekeyLimit
930 Specifies the maximum amount of data that may be transmitted be‐
931 fore the session key is renegotiated, optionally followed by a
932 maximum amount of time that may pass before the session key is
933 renegotiated. The first argument is specified in bytes and may
934 have a suffix of ‘K’, ‘M’, or ‘G’ to indicate Kilobytes,
935 Megabytes, or Gigabytes, respectively. The default is between
936 ‘1G’ and ‘4G’, depending on the cipher. The optional second
937 value is specified in seconds and may use any of the units docu‐
938 mented in the TIME FORMATS section of sshd_config(5). The de‐
939 fault value for RekeyLimit is default none, which means that
940 rekeying is performed after the cipher's default amount of data
941 has been sent or received and no time based rekeying is done.
942 RemoteCommand
944 Specifies a command to execute on the remote machine after suc‐
945 cessfully connecting to the server. The command string extends
946 to the end of the line, and is executed with the user's shell.
947 Arguments to RemoteCommand accept the tokens described in the
948 TOKENS section.
949 RemoteForward
951 Specifies that a TCP port on the remote machine be forwarded over
952 the secure channel. The remote port may either be forwarded to a
953 specified host and port from the local machine, or may act as a
954 SOCKS 4/5 proxy that allows a remote client to connect to arbi‐
955 trary destinations from the local machine. The first argument is
956 the listening specification and may be [bind_address:]port or, if
957 the remote host supports it, a Unix domain socket path. If for‐
958 warding to a specific destination then the second argument must
959 be host:hostport or a Unix domain socket path, otherwise if no
960 destination argument is specified then the remote forwarding will
961 be established as a SOCKS proxy. When acting as a SOCKS proxy
962 the destination of the connection can be restricted by
963 PermitRemoteOpen.
964 IPv6 addresses can be specified by enclosing addresses in square
966 brackets. Multiple forwardings may be specified, and additional
967 forwardings can be given on the command line. Privileged ports
968 can be forwarded only when logging in as root on the remote ma‐
969 chine. Unix domain socket paths may use the tokens described in
970 the TOKENS section and environment variables as described in the
971 ENVIRONMENT VARIABLES section.
972 If the port argument is 0, the listen port will be dynamically
974 allocated on the server and reported to the client at run time.
975 If the bind_address is not specified, the default is to only bind
977 to loopback addresses. If the bind_address is ‘*’ or an empty
978 string, then the forwarding is requested to listen on all inter‐
979 faces. Specifying a remote bind_address will only succeed if the
980 server's GatewayPorts option is enabled (see sshd_config(5)).
981 RequestTTY
983 Specifies whether to request a pseudo-tty for the session. The
984 argument may be one of: no (never request a TTY), yes (always re‐
985 quest a TTY when standard input is a TTY), force (always request
986 a TTY) or auto (request a TTY when opening a login session).
987 This option mirrors the -t and -T flags for ssh(1).
988 RevokedHostKeys
990 Specifies revoked host public keys. Keys listed in this file
991 will be refused for host authentication. Note that if this file
992 does not exist or is not readable, then host authentication will
993 be refused for all hosts. Keys may be specified as a text file,
994 listing one public key per line, or as an OpenSSH Key Revocation
995 List (KRL) as generated by ssh-keygen(1). For more information
996 on KRLs, see the KEY REVOCATION LISTS section in ssh-keygen(1).
997 SecurityKeyProvider
999 Specifies a path to a library that will be used when loading any
1000 FIDO authenticator-hosted keys, overriding the default of using
1001 the built-in USB HID support.
1002 If the specified value begins with a ‘$’ character, then it will
1004 be treated as an environment variable containing the path to the
1005 library.
1006 SendEnv
1008 Specifies what variables from the local environ(7) should be sent
1009 to the server. The server must also support it, and the server
1010 must be configured to accept these environment variables. Note
1011 that the TERM environment variable is always sent whenever a
1012 pseudo-terminal is requested as it is required by the protocol.
1013 Refer to AcceptEnv in sshd_config(5) for how to configure the
1014 server. Variables are specified by name, which may contain wild‐
1015 card characters. Multiple environment variables may be separated
1016 by whitespace or spread across multiple SendEnv directives.
1017 See PATTERNS for more information on patterns.
1019 It is possible to clear previously set SendEnv variable names by
1021 prefixing patterns with -. The default is not to send any envi‐
1022 ronment variables.
1023 ServerAliveCountMax
1025 Sets the number of server alive messages (see below) which may be
1026 sent without ssh(1) receiving any messages back from the server.
1027 If this threshold is reached while server alive messages are be‐
1028 ing sent, ssh will disconnect from the server, terminating the
1029 session. It is important to note that the use of server alive
1030 messages is very different from TCPKeepAlive (below). The server
1031 alive messages are sent through the encrypted channel and there‐
1032 fore will not be spoofable. The TCP keepalive option enabled by
1033 TCPKeepAlive is spoofable. The server alive mechanism is valu‐
1034 able when the client or server depend on knowing when a connec‐
1035 tion has become unresponsive.
1036 The default value is 3. If, for example, ServerAliveInterval
1038 (see below) is set to 15 and ServerAliveCountMax is left at the
1039 default, if the server becomes unresponsive, ssh will disconnect
1040 after approximately 45 seconds.
1041 ServerAliveInterval
1043 Sets a timeout interval in seconds after which if no data has
1044 been received from the server, ssh(1) will send a message through
1045 the encrypted channel to request a response from the server. The
1046 default is 0, indicating that these messages will not be sent to
1047 the server.
1048 SetEnv Directly specify one or more environment variables and their con‐
1050 tents to be sent to the server. Similarly to SendEnv, the server
1051 must be prepared to accept the environment variable.
1052 StreamLocalBindMask
1054 Sets the octal file creation mode mask (umask) used when creating
1055 a Unix-domain socket file for local or remote port forwarding.
1056 This option is only used for port forwarding to a Unix-domain
1057 socket file.
1058 The default value is 0177, which creates a Unix-domain socket
1060 file that is readable and writable only by the owner. Note that
1061 not all operating systems honor the file mode on Unix-domain
1062 socket files.
1063 StreamLocalBindUnlink
1065 Specifies whether to remove an existing Unix-domain socket file
1066 for local or remote port forwarding before creating a new one.
1067 If the socket file already exists and StreamLocalBindUnlink is
1068 not enabled, ssh will be unable to forward the port to the Unix-
1069 domain socket file. This option is only used for port forwarding
1070 to a Unix-domain socket file.
1071 The argument must be yes or no (the default).
1073 StrictHostKeyChecking
1075 If this flag is set to yes, ssh(1) will never automatically add
1076 host keys to the ~/.ssh/known_hosts file, and refuses to connect
1077 to hosts whose host key has changed. This provides maximum pro‐
1078 tection against man-in-the-middle (MITM) attacks, though it can
1079 be annoying when the /etc/ssh/ssh_known_hosts file is poorly
1080 maintained or when connections to new hosts are frequently made.
1081 This option forces the user to manually add all new hosts.
1082 If this flag is set to “accept-new” then ssh will automatically
1084 add new host keys to the user known hosts files, but will not
1085 permit connections to hosts with changed host keys. If this flag
1086 is set to “no” or “off”, ssh will automatically add new host keys
1087 to the user known hosts files and allow connections to hosts with
1088 changed hostkeys to proceed, subject to some restrictions. If
1089 this flag is set to ask (the default), new host keys will be
1090 added to the user known host files only after the user has con‐
1091 firmed that is what they really want to do, and ssh will refuse
1092 to connect to hosts whose host key has changed. The host keys of
1093 known hosts will be verified automatically in all cases.
1094 SyslogFacility
1096 Gives the facility code that is used when logging messages from
1097 ssh(1). The possible values are: DAEMON, USER, AUTH, LOCAL0, LO‐
1098 CAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. The de‐
1099 fault is USER.
1100 TCPKeepAlive
1102 Specifies whether the system should send TCP keepalive messages
1103 to the other side. If they are sent, death of the connection or
1104 crash of one of the machines will be properly noticed. However,
1105 this means that connections will die if the route is down tempo‐
1106 rarily, and some people find it annoying.
1107 The default is yes (to send TCP keepalive messages), and the
1109 client will notice if the network goes down or the remote host
1110 dies. This is important in scripts, and many users want it too.
1111 To disable TCP keepalive messages, the value should be set to no.
1113 See also ServerAliveInterval for protocol-level keepalives.
1114 Tunnel Request tun(4) device forwarding between the client and the
1116 server. The argument must be yes, point-to-point (layer 3),
1117 ethernet (layer 2), or no (the default). Specifying yes requests
1118 the default tunnel mode, which is point-to-point.
1119 TunnelDevice
1121 Specifies the tun(4) devices to open on the client (local_tun)
1122 and the server (remote_tun).
1123 The argument must be local_tun[:remote_tun]. The devices may be
1125 specified by numerical ID or the keyword any, which uses the next
1126 available tunnel device. If remote_tun is not specified, it de‐
1127 faults to any. The default is any:any.
1128 UpdateHostKeys
1130 Specifies whether ssh(1) should accept notifications of addi‐
1131 tional hostkeys from the server sent after authentication has
1132 completed and add them to UserKnownHostsFile. The argument must
1133 be yes, no or ask. This option allows learning alternate
1134 hostkeys for a server and supports graceful key rotation by al‐
1135 lowing a server to send replacement public keys before old ones
1136 are removed.
1137 Additional hostkeys are only accepted if the key used to authen‐
1139 ticate the host was already trusted or explicitly accepted by the
1140 user, the host was authenticated via UserKnownHostsFile (i.e. not
1141 GlobalKnownHostsFile) and the host was authenticated using a
1142 plain key and not a certificate.
1143 UpdateHostKeys is enabled by default if the user has not overrid‐
1145 den the default UserKnownHostsFile setting and has not enabled
1146 VerifyHostKeyDNS, otherwise UpdateHostKeys will be set to no.
1147 If UpdateHostKeys is set to ask, then the user is asked to con‐
1149 firm the modifications to the known_hosts file. Confirmation is
1150 currently incompatible with ControlPersist, and will be disabled
1151 if it is enabled.
1152 Presently, only sshd(8) from OpenSSH 6.8 and greater support the
1154 "hostkeys@openssh.com" protocol extension used to inform the
1155 client of all the server's hostkeys.
1156 User Specifies the user to log in as. This can be useful when a dif‐
1158 ferent user name is used on different machines. This saves the
1159 trouble of having to remember to give the user name on the com‐
1160 mand line.
1161 UserKnownHostsFile
1163 Specifies one or more files to use for the user host key data‐
1164 base, separated by whitespace. Each filename may use tilde nota‐
1165 tion to refer to the user's home directory, the tokens described
1166 in the TOKENS section and environment variables as described in
1167 the ENVIRONMENT VARIABLES section. The default is
1168 ~/.ssh/known_hosts, ~/.ssh/known_hosts2.
1169 VerifyHostKeyDNS
1171 Specifies whether to verify the remote key using DNS and SSHFP
1172 resource records. If this option is set to yes, the client will
1173 implicitly trust keys that match a secure fingerprint from DNS.
1174 Insecure fingerprints will be handled as if this option was set
1175 to ask. If this option is set to ask, information on fingerprint
1176 match will be displayed, but the user will still need to confirm
1177 new host keys according to the StrictHostKeyChecking option. The
1178 default is no.
1179 See also VERIFYING HOST KEYS in ssh(1).
1181 VisualHostKey
1183 If this flag is set to yes, an ASCII art representation of the
1184 remote host key fingerprint is printed in addition to the finger‐
1185 print string at login and for unknown host keys. If this flag is
1186 set to no (the default), no fingerprint strings are printed at
1187 login and only the fingerprint string will be printed for unknown
1188 host keys.
1189 XAuthLocation
1191 Specifies the full pathname of the xauth(1) program. The default
1192 is /usr/bin/xauth.
1193
1195 A pattern consists of zero or more non-whitespace characters, ‘*’ (a
1196 wildcard that matches zero or more characters), or ‘?’ (a wildcard that
1197 matches exactly one character). For example, to specify a set of decla‐
1198 rations for any host in the ".co.uk" set of domains, the following pat‐
1199 tern could be used:
1200 Host *.co.uk
1202 The following pattern would match any host in the 192.168.0.[0-9] network
1204 range:
1205 Host 192.168.0.?
1207 A pattern-list is a comma-separated list of patterns. Patterns within
1209 pattern-lists may be negated by preceding them with an exclamation mark
1210 (‘!’). For example, to allow a key to be used from anywhere within an
1211 organization except from the "dialup" pool, the following entry (in au‐
1212 thorized_keys) could be used:
1213 from="!*.dialup.example.com,*.example.com"
1215 Note that a negated match will never produce a positive result by itself.
1217 For example, attempting to match "host3" against the following pattern-
1218 list will fail:
1219 from="!host1,!host2"
1221 The solution here is to include a term that will yield a positive match,
1223 such as a wildcard:
1224 from="!host1,!host2,*"
1226
1228 Arguments to some keywords can make use of tokens, which are expanded at
1229 runtime:
1230 %% A literal ‘%’.
1232 %C Hash of %l%h%p%r.
1233 %d Local user's home directory.
1234 %f The fingerprint of the server's host key.
1235 %H The known_hosts hostname or address that is being searched
1236 for.
1237 %h The remote hostname.
1238 %I A string describing the reason for a KnownHostsCommand execu‐
1239 tion: either ADDRESS when looking up a host by address (only
1240 when CheckHostIP is enabled), HOSTNAME when searching by
1241 hostname, or ORDER when preparing the host key algorithm
1242 preference list to use for the destination host.
1243 %i The local user ID.
1244 %K The base64 encoded host key.
1245 %k The host key alias if specified, otherwise the original re‐
1246 mote hostname given on the command line.
1247 %L The local hostname.
1248 %l The local hostname, including the domain name.
1249 %n The original remote hostname, as given on the command line.
1250 %p The remote port.
1251 %r The remote username.
1252 %T The local tun(4) or tap(4) network interface assigned if tun‐
1253 nel forwarding was requested, or "NONE" otherwise.
1254 %t The type of the server host key, e.g. ssh-ed25519
1255 %u The local username.
1256 CertificateFile, ControlPath, IdentityAgent, IdentityFile,
1258 KnownHostsCommand, LocalForward, Match exec, RemoteCommand,
1259 RemoteForward, and UserKnownHostsFile accept the tokens %%, %C, %d, %h,
1260 %i, %k, %L, %l, %n, %p, %r, and %u.
1261 KnownHostsCommand additionally accepts the tokens %f, %H, %I, %K and %t.
1263 Hostname accepts the tokens %% and %h.
1265 LocalCommand accepts all tokens.
1267 ProxyCommand accepts the tokens %%, %h, %n, %p, and %r.
1269
1271 Arguments to some keywords can be expanded at runtime from environment
1272 variables on the client by enclosing them in ${}, for example
1273 ${HOME}/.ssh would refer to the user's .ssh directory. If a specified
1274 environment variable does not exist then an error will be returned and
1275 the setting for that keyword will be ignored.
1276 The keywords CertificateFile, ControlPath, IdentityAgent, IdentityFile,
1278 KnownHostsCommand, and UserKnownHostsFile support environment variables.
1279 The keywords LocalForward and RemoteForward support environment variables
1280 only for Unix domain socket paths.
1281
1283 ~/.ssh/config
1284 This is the per-user configuration file. The format of this file
1285 is described above. This file is used by the SSH client. Be‐
1286 cause of the potential for abuse, this file must have strict per‐
1287 missions: read/write for the user, and not writable by others.
1288 /etc/ssh/ssh_config
1290 Systemwide configuration file. This file provides defaults for
1291 those values that are not specified in the user's configuration
1292 file, and for those users who do not have a configuration file.
1293 This file must be world-readable.
1294
1296 ssh(1)
1297
1299 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
1300 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
1301 de Raadt and Dug Song removed many bugs, re-added newer features and cre‐
1302 ated OpenSSH. Markus Friedl contributed the support for SSH protocol
1303 versions 1.5 and 2.0.
1304BSD April 4, 2021 BSD