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. A value of none dis‐
155 ables the use of a ProxyJump host.
156 CanonicalizeMaxDots
158 Specifies the maximum number of dot characters in a hostname be‐
159 fore canonicalization is disabled. The default, 1, allows a sin‐
160 gle dot (i.e. hostname.subdomain).
161 CanonicalizePermittedCNAMEs
163 Specifies rules to determine whether CNAMEs should be followed
164 when canonicalizing hostnames. The rules consist of one or more
165 arguments of source_domain_list:target_domain_list, where
166 source_domain_list is a pattern-list of domains that may follow
167 CNAMEs in canonicalization, and target_domain_list is a pattern-
168 list of domains that they may resolve to.
169 For example, "*.a.example.com:*.b.example.com,*.c.example.com"
171 will allow hostnames matching "*.a.example.com" to be canonical‐
172 ized to names in the "*.b.example.com" or "*.c.example.com" do‐
173 mains.
174 CASignatureAlgorithms
176 The default is handled system-wide by crypto-policies(7). To see
177 the defaults and how to modify this default, see manual page
178 update-crypto-policies(8).
179 Specifies which algorithms are allowed for signing of certifi‐
181 cates by certificate authorities (CAs). If the specified list
182 begins with a ‘+’ character, then the specified algorithms will
183 be appended to the default set instead of replacing them. If the
184 specified list begins with a ‘-’ character, then the specified
185 algorithms (including wildcards) will be removed from the default
186 set instead of replacing them.
187 ssh(1) will not accept host certificates signed using algorithms
189 other than those specified.
190 CertificateFile
192 Specifies a file from which the user's certificate is read. A
193 corresponding private key must be provided separately in order to
194 use this certificate either from an IdentityFile directive or -i
195 flag to ssh(1), via ssh-agent(1), or via a PKCS11Provider or
196 SecurityKeyProvider.
197 Arguments to CertificateFile may use the tilde syntax to refer to
199 a user's home directory, the tokens described in the TOKENS sec‐
200 tion and environment variables as described in the ENVIRONMENT
201 VARIABLES section.
202 It is possible to have multiple certificate files specified in
204 configuration files; these certificates will be tried in se‐
205 quence. Multiple CertificateFile directives will add to the list
206 of certificates used for authentication.
207 CheckHostIP
209 If set to yes [22mssh(1) will additionally check the host IP address
210 in the known_hosts file. This allows it to detect if a host key
211 changed due to DNS spoofing and will add addresses of destination
212 hosts to ~/.ssh/known_hosts in the process, regardless of the
213 setting of StrictHostKeyChecking. If the option is set to no
214 (the default), the check will not be executed.
215 Ciphers
217 The default is handled system-wide by crypto-policies(7). To see
218 the defaults and how to modify this default, see manual page
219 update-crypto-policies(8).
220 Specifies the ciphers allowed and their order of preference.
222 Multiple ciphers must be comma-separated. If the specified list
223 begins with a ‘+’ character, then the specified ciphers will be
224 appended to the built-in openssh default set instead of replacing
225 them. If the specified list begins with a ‘-’ character, then
226 the specified ciphers (including wildcards) will be removed from
227 the built-in openssh default set instead of replacing them. If
228 the specified list begins with a ‘^’ character, then the speci‐
229 fied ciphers will be placed at the head of the built-in openssh
230 default set.
231 The supported ciphers are:
233 3des-cbc
235 aes128-cbc
236 aes192-cbc
237 aes256-cbc
238 aes128-ctr
239 aes192-ctr
240 aes256-ctr
241 aes128-gcm@openssh.com
242 aes256-gcm@openssh.com
243 chacha20-poly1305@openssh.com
244 The list of available ciphers may also be obtained using "ssh -Q
246 cipher".
247 ClearAllForwardings
249 Specifies that all local, remote, and dynamic port forwardings
250 specified in the configuration files or on the command line be
251 cleared. This option is primarily useful when used from the
252 ssh(1) command line to clear port forwardings set in configura‐
253 tion files, and is automatically set by scp(1) and sftp(1). The
254 argument must be yes or no (the default).
255 Compression
257 Specifies whether to use compression. The argument must be yes
258 or no (the default).
259 ConnectionAttempts
261 Specifies the number of tries (one per second) to make before ex‐
262 iting. The argument must be an integer. This may be useful in
263 scripts if the connection sometimes fails. The default is 1.
264 ConnectTimeout
266 Specifies the timeout (in seconds) used when connecting to the
267 SSH server, instead of using the default system TCP timeout.
268 This timeout is applied both to establishing the connection and
269 to performing the initial SSH protocol handshake and key ex‐
270 change.
271 ControlMaster
273 Enables the sharing of multiple sessions over a single network
274 connection. When set to yes, ssh(1) will listen for connections
275 on a control socket specified using the ControlPath argument.
276 Additional sessions can connect to this socket using the same
277 ControlPath with ControlMaster set to no (the default). These
278 sessions will try to reuse the master instance's network connec‐
279 tion rather than initiating new ones, but will fall back to con‐
280 necting normally if the control socket does not exist, or is not
281 listening.
282 Setting this to ask will cause ssh(1) to listen for control con‐
284 nections, but require confirmation using ssh-askpass(1). If the
285 ControlPath cannot be opened, ssh(1) will continue without con‐
286 necting to a master instance.
287 X11 and ssh-agent(1) forwarding is supported over these multi‐
289 plexed connections, however the display and agent forwarded will
290 be the one belonging to the master connection i.e. it is not pos‐
291 sible to forward multiple displays or agents.
292 Two additional options allow for opportunistic multiplexing: try
294 to use a master connection but fall back to creating a new one if
295 one does not already exist. These options are: auto and autoask.
296 The latter requires confirmation like the ask option.
297 ControlPath
299 Specify the path to the control socket used for connection shar‐
300 ing as described in the ControlMaster section above or the string
301 none to disable connection sharing. Arguments to ControlPath may
302 use the tilde syntax to refer to a user's home directory, the to‐
303 kens described in the TOKENS section and environment variables as
304 described in the ENVIRONMENT VARIABLES section. It is recom‐
305 mended that any ControlPath used for opportunistic connection
306 sharing include at least %h, %p, and %r (or alternatively %C) and
307 be placed in a directory that is not writable by other users.
308 This ensures that shared connections are uniquely identified.
309 ControlPersist
311 When used in conjunction with ControlMaster, specifies that the
312 master connection should remain open in the background (waiting
313 for future client connections) after the initial client connec‐
314 tion has been closed. If set to no (the default), then the mas‐
315 ter connection will not be placed into the background, and will
316 close as soon as the initial client connection is closed. If set
317 to yes or 0, then the master connection will remain in the back‐
318 ground indefinitely (until killed or closed via a mechanism such
319 as the "ssh -O exit"). If set to a time in seconds, or a time in
320 any of the formats documented in sshd_config(5), then the back‐
321 grounded master connection will automatically terminate after it
322 has remained idle (with no client connections) for the specified
323 time.
324 DynamicForward
326 Specifies that a TCP port on the local machine be forwarded over
327 the secure channel, and the application protocol is then used to
328 determine where to connect to from the remote machine.
329 The argument must be [bind_address:]port. IPv6 addresses can be
331 specified by enclosing addresses in square brackets. By default,
332 the local port is bound in accordance with the GatewayPorts set‐
333 ting. However, an explicit bind_address may be used to bind the
334 connection to a specific address. The bind_address of localhost
335 indicates that the listening port be bound for local use only,
336 while an empty address or ‘*’ indicates that the port should be
337 available from all interfaces.
338 Currently the SOCKS4 and SOCKS5 protocols are supported, and
340 ssh(1) will act as a SOCKS server. Multiple forwardings may be
341 specified, and additional forwardings can be given on the command
342 line. Only the superuser can forward privileged ports.
343 EnableSSHKeysign
345 Setting this option to yes in the global client configuration
346 file /etc/ssh/ssh_config enables the use of the helper program
347 ssh-keysign(8) during HostbasedAuthentication. The argument must
348 be yes or no (the default). This option should be placed in the
349 non-hostspecific section. See ssh-keysign(8) for more informa‐
350 tion.
351 EscapeChar
353 Sets the escape character (default: ‘~’). The escape character
354 can also be set on the command line. The argument should be a
355 single character, ‘^’ followed by a letter, or none to disable
356 the escape character entirely (making the connection transparent
357 for binary data).
358 ExitOnForwardFailure
360 Specifies whether ssh(1) should terminate the connection if it
361 cannot set up all requested dynamic, tunnel, local, and remote
362 port forwardings, (e.g. if either end is unable to bind and lis‐
363 ten on a specified port). Note that ExitOnForwardFailure does
364 not apply to connections made over port forwardings and will not,
365 for example, cause ssh(1) to exit if TCP connections to the ulti‐
366 mate forwarding destination fail. The argument must be yes or no
367 (the default).
368 FingerprintHash
370 Specifies the hash algorithm used when displaying key finger‐
371 prints. Valid options are: md5 and sha256 (the default).
372 ForkAfterAuthentication
374 Requests ssh to go to background just before command execution.
375 This is useful if ssh is going to ask for passwords or
376 passphrases, but the user wants it in the background. This im‐
377 plies the StdinNull configuration option being set to “yes”. The
378 recommended way to start X11 programs at a remote site is with
379 something like ssh -f host xterm, which is the same as ssh host
380 xterm if the ForkAfterAuthentication configuration option is set
381 to “yes”.
382 If the ExitOnForwardFailure configuration option is set to “yes”,
384 then a client started with the ForkAfterAuthentication configura‐
385 tion option being set to “yes” will wait for all remote port for‐
386 wards to be successfully established before placing itself in the
387 background. The argument to this keyword must be yes (same as
388 the -f option) or no (the default).
389 ForwardAgent
391 Specifies whether the connection to the authentication agent (if
392 any) will be forwarded to the remote machine. The argument may
393 be yes, no (the default), an explicit path to an agent socket or
394 the name of an environment variable (beginning with ‘$’) in which
395 to find the path.
396 Agent forwarding should be enabled with caution. Users with the
398 ability to bypass file permissions on the remote host (for the
399 agent's Unix-domain socket) can access the local agent through
400 the forwarded connection. An attacker cannot obtain key material
401 from the agent, however they can perform operations on the keys
402 that enable them to authenticate using the identities loaded into
403 the agent.
404 ForwardX11
406 Specifies whether X11 connections will be automatically redi‐
407 rected over the secure channel and DISPLAY set. The argument
408 must be yes or no (the default).
409 X11 forwarding should be enabled with caution. Users with the
411 ability to bypass file permissions on the remote host (for the
412 user's X11 authorization database) can access the local X11 dis‐
413 play through the forwarded connection. An attacker may then be
414 able to perform activities such as keystroke monitoring if the
415 ForwardX11Trusted option is also enabled.
416 ForwardX11Timeout
418 Specify a timeout for untrusted X11 forwarding using the format
419 described in the TIME FORMATS section of sshd_config(5). X11
420 connections received by ssh(1) after this time will be refused.
421 Setting ForwardX11Timeout to zero will disable the timeout and
422 permit X11 forwarding for the life of the connection. The de‐
423 fault is to disable untrusted X11 forwarding after twenty minutes
424 has elapsed.
425 ForwardX11Trusted
427 If this option is set to yes, remote X11 clients will have full
428 access to the original X11 display.
429 If this option is set to no (the default), remote X11 clients
431 will be considered untrusted and prevented from stealing or tam‐
432 pering with data belonging to trusted X11 clients. Furthermore,
433 the xauth(1) token used for the session will be set to expire af‐
434 ter 20 minutes. Remote clients will be refused access after this
435 time.
436 See the X11 SECURITY extension specification for full details on
438 the restrictions imposed on untrusted clients.
439 GatewayPorts
441 Specifies whether remote hosts are allowed to connect to local
442 forwarded ports. By default, ssh(1) binds local port forwardings
443 to the loopback address. This prevents other remote hosts from
444 connecting to forwarded ports. GatewayPorts can be used to spec‐
445 ify that ssh should bind local port forwardings to the wildcard
446 address, thus allowing remote hosts to connect to forwarded
447 ports. The argument must be yes or no (the default).
448 GlobalKnownHostsFile
450 Specifies one or more files to use for the global host key data‐
451 base, separated by whitespace. The default is
452 /etc/ssh/ssh_known_hosts, /etc/ssh/ssh_known_hosts2.
453 GSSAPIAuthentication
455 Specifies whether user authentication based on GSSAPI is allowed.
456 The default is no.
457 GSSAPIClientIdentity
459 If set, specifies the GSSAPI client identity that ssh should use
460 when connecting to the server. The default is unset, which means
461 that the default identity will be used.
462 GSSAPIDelegateCredentials
464 Forward (delegate) credentials to the server. The default is no.
465 GSSAPIKeyExchange
467 Specifies whether key exchange based on GSSAPI may be used. When
468 using GSSAPI key exchange the server need not have a host key.
469 The default is “no”.
470 GSSAPIRenewalForcesRekey
472 If set to “yes” then renewal of the client's GSSAPI credentials
473 will force the rekeying of the ssh connection. With a compatible
474 server, this will delegate the renewed credentials to a session
475 on the server.
476 Checks are made to ensure that credentials are only propagated
478 when the new credentials match the old ones on the originating
479 client and where the receiving server still has the old set in
480 its cache.
481 The default is “no”.
483 For this to work GSSAPIKeyExchange needs to be enabled in the
485 server and also used by the client.
486 GSSAPIServerIdentity
488 If set, specifies the GSSAPI server identity that ssh should ex‐
489 pect when connecting to the server. The default is unset, which
490 means that the expected GSSAPI server identity will be determined
491 from the target hostname.
492 GSSAPITrustDns
494 Set to “yes” to indicate that the DNS is trusted to securely
495 canonicalize the name of the host being connected to. If “no”,
496 the hostname entered on the command line will be passed untouched
497 to the GSSAPI library. The default is “no”.
498 GSSAPIKexAlgorithms
500 The default is handled system-wide by crypto-policies(7). To see
501 the defaults and how to modify this default, see manual page
502 update-crypto-policies(8).
503 The list of key exchange algorithms that are offered for GSSAPI
505 key exchange. Possible values are
506 gss-gex-sha1-,
508 gss-group1-sha1-,
509 gss-group14-sha1-,
510 gss-group14-sha256-,
511 gss-group16-sha512-,
512 gss-nistp256-sha256-,
513 gss-curve25519-sha256-
514 This option only applies to connections using GSSAPI.
516 HashKnownHosts
518 Indicates that ssh(1) should hash host names and addresses when
519 they are added to ~/.ssh/known_hosts. These hashed names may be
520 used normally by ssh(1) and sshd(8), but they do not visually re‐
521 veal identifying information if the file's contents are dis‐
522 closed. The default is no. Note that existing names and ad‐
523 dresses in known hosts files will not be converted automatically,
524 but may be manually hashed using ssh-keygen(1).
525 HostbasedAcceptedAlgorithms
527 Specifies the signature algorithms that will be used for host‐
528 based authentication as a comma-separated list of patterns. Al‐
529 ternately if the specified list begins with a ‘+’ character, then
530 the specified signature algorithms will be appended to the de‐
531 fault set instead of replacing them. If the specified list be‐
532 gins with a ‘-’ character, then the specified signature algo‐
533 rithms (including wildcards) will be removed from the default set
534 instead of replacing them. If the specified list begins with a
535 ‘^’ character, then the specified signature algorithms will be
536 placed at the head of the default set. The default for this op‐
537 tion is:
538 ssh-ed25519-cert-v01@openssh.com,
540 ecdsa-sha2-nistp256-cert-v01@openssh.com,
541 ecdsa-sha2-nistp384-cert-v01@openssh.com,
542 ecdsa-sha2-nistp521-cert-v01@openssh.com,
543 sk-ssh-ed25519-cert-v01@openssh.com,
544 sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
545 rsa-sha2-512-cert-v01@openssh.com,
546 rsa-sha2-256-cert-v01@openssh.com,
547 ssh-rsa-cert-v01@openssh.com,
548 ssh-ed25519,
549 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
550 sk-ssh-ed25519@openssh.com,
551 sk-ecdsa-sha2-nistp256@openssh.com,
552 rsa-sha2-512,rsa-sha2-256,ssh-rsa
553 The -Q option of ssh(1) may be used to list supported signature
555 algorithms. This was formerly named HostbasedKeyTypes.
556 HostbasedAuthentication
558 Specifies whether to try rhosts based authentication with public
559 key authentication. The argument must be yes or no (the de‐
560 fault).
561 HostKeyAlgorithms
563 Specifies the host key signature algorithms that the client wants
564 to use in order of preference. Alternately if the specified list
565 begins with a ‘+’ character, then the specified signature algo‐
566 rithms will be appended to the default set instead of replacing
567 them. If the specified list begins with a ‘-’ character, then
568 the specified signature algorithms (including wildcards) will be
569 removed from the default set instead of replacing them. If the
570 specified list begins with a ‘^’ character, then the specified
571 signature algorithms will be placed at the head of the default
572 set. The default for this option is:
573 ssh-ed25519-cert-v01@openssh.com,
575 ecdsa-sha2-nistp256-cert-v01@openssh.com,
576 ecdsa-sha2-nistp384-cert-v01@openssh.com,
577 ecdsa-sha2-nistp521-cert-v01@openssh.com,
578 sk-ssh-ed25519-cert-v01@openssh.com,
579 sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
580 rsa-sha2-512-cert-v01@openssh.com,
581 rsa-sha2-256-cert-v01@openssh.com,
582 ssh-rsa-cert-v01@openssh.com,
583 ssh-ed25519,
584 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
585 sk-ecdsa-sha2-nistp256@openssh.com,
586 sk-ssh-ed25519@openssh.com,
587 rsa-sha2-512,rsa-sha2-256,ssh-rsa
588 If hostkeys are known for the destination host then this default
590 is modified to prefer their algorithms.
591 The list of available signature algorithms may also be obtained
593 using "ssh -Q HostKeyAlgorithms".
594 HostKeyAlias
596 Specifies an alias that should be used instead of the real host
597 name when looking up or saving the host key in the host key data‐
598 base files and when validating host certificates. This option is
599 useful for tunneling SSH connections or for multiple servers run‐
600 ning on a single host.
601 Hostname
603 Specifies the real host name to log into. This can be used to
604 specify nicknames or abbreviations for hosts. Arguments to
605 Hostname accept the tokens described in the TOKENS section. Nu‐
606 meric IP addresses are also permitted (both on the command line
607 and in Hostname specifications). The default is the name given
608 on the command line.
609 IdentitiesOnly
611 Specifies that ssh(1) should only use the configured authentica‐
612 tion identity and certificate files (either the default files, or
613 those explicitly configured in the ssh_config files or passed on
614 the ssh(1) command-line), even if ssh-agent(1) or a
615 PKCS11Provider or SecurityKeyProvider offers more identities.
616 The argument to this keyword must be yes or no (the default).
617 This option is intended for situations where ssh-agent offers
618 many different identities.
619 IdentityAgent
621 Specifies the UNIX-domain socket used to communicate with the au‐
622 thentication agent.
623 This option overrides the SSH_AUTH_SOCK environment variable and
625 can be used to select a specific agent. Setting the socket name
626 to none disables the use of an authentication agent. If the
627 string "SSH_AUTH_SOCK" is specified, the location of the socket
628 will be read from the SSH_AUTH_SOCK environment variable. Other‐
629 wise if the specified value begins with a ‘$’ character, then it
630 will be treated as an environment variable containing the loca‐
631 tion of the socket.
632 Arguments to IdentityAgent may use the tilde syntax to refer to a
634 user's home directory, the tokens described in the TOKENS section
635 and environment variables as described in the ENVIRONMENT
636 VARIABLES section.
637 IdentityFile
639 Specifies a file from which the user's DSA, ECDSA, authenticator-
640 hosted ECDSA, Ed25519, authenticator-hosted Ed25519 or RSA au‐
641 thentication identity is read. The default is ~/.ssh/id_dsa,
642 ~/.ssh/id_ecdsa, ~/.ssh/id_ecdsa_sk, ~/.ssh/id_ed25519,
643 ~/.ssh/id_ed25519_sk and ~/.ssh/id_rsa. Additionally, any iden‐
644 tities represented by the authentication agent will be used for
645 authentication unless IdentitiesOnly is set. If no certificates
646 have been explicitly specified by CertificateFile, ssh(1) will
647 try to load certificate information from the filename obtained by
648 appending -cert.pub to the path of a specified IdentityFile.
649 Arguments to IdentityFile may use the tilde syntax to refer to a
651 user's home directory or the tokens described in the TOKENS sec‐
652 tion.
653 It is possible to have multiple identity files specified in con‐
655 figuration files; all these identities will be tried in sequence.
656 Multiple IdentityFile directives will add to the list of identi‐
657 ties tried (this behaviour differs from that of other configura‐
658 tion directives).
659 IdentityFile may be used in conjunction with IdentitiesOnly to
661 select which identities in an agent are offered during authenti‐
662 cation. IdentityFile may also be used in conjunction with
663 CertificateFile in order to provide any certificate also needed
664 for authentication with the identity.
665 The authentication identity can be also specified in a form of
667 PKCS#11 URI starting with a string pkcs11:. There is supported a
668 subset of the PKCS#11 URI as defined in RFC 7512 (implemented
669 path arguments id, manufacturer, object, token and query argu‐
670 ments module-path and pin-value ). The URI can not be in quotes.
671 IgnoreUnknown
673 Specifies a pattern-list of unknown options to be ignored if they
674 are encountered in configuration parsing. This may be used to
675 suppress errors if ssh_config contains options that are unrecog‐
676 nised by ssh(1). It is recommended that IgnoreUnknown be listed
677 early in the configuration file as it will not be applied to un‐
678 known options that appear before it.
679 Include
681 Include the specified configuration file(s). Multiple pathnames
682 may be specified and each pathname may contain glob(7) wildcards
683 and, for user configurations, shell-like ‘~’ references to user
684 home directories. Wildcards will be expanded and processed in
685 lexical order. Files without absolute paths are assumed to be in
686 ~/.ssh if included in a user configuration file or /etc/ssh if
687 included from the system configuration file. Include directive
688 may appear inside a Match or Host block to perform conditional
689 inclusion.
690 IPQoS Specifies the IPv4 type-of-service or DSCP class for connections.
692 Accepted values are af11, af12, af13, af21, af22, af23, af31,
693 af32, af33, af41, af42, af43, cs0, cs1, cs2, cs3, cs4, cs5, cs6,
694 cs7, ef, le, lowdelay, throughput, reliability, a numeric value,
695 or none to use the operating system default. This option may
696 take one or two arguments, separated by whitespace. If one argu‐
697 ment is specified, it is used as the packet class uncondition‐
698 ally. If two values are specified, the first is automatically
699 selected for interactive sessions and the second for non-interac‐
700 tive sessions. The default is af21 (Low-Latency Data) for inter‐
701 active sessions and cs1 (Lower Effort) for non-interactive ses‐
702 sions.
703 KbdInteractiveAuthentication
705 Specifies whether to use keyboard-interactive authentication.
706 The argument to this keyword must be yes (the default) or no.
707 ChallengeResponseAuthentication is a deprecated alias for this.
708 KbdInteractiveDevices
710 Specifies the list of methods to use in keyboard-interactive au‐
711 thentication. Multiple method names must be comma-separated.
712 The default is to use the server specified list. The methods
713 available vary depending on what the server supports. For an
714 OpenSSH server, it may be zero or more of: bsdauth and pam.
715 KexAlgorithms
717 The default is handled system-wide by crypto-policies(7). To see
718 the defaults and how to modify this default, see manual page
719 update-crypto-policies(8).
720 Specifies the available KEX (Key Exchange) algorithms. Multiple
722 algorithms must be comma-separated. If the specified list begins
723 with a ‘+’ character, then the specified methods will be appended
724 to the built-in openssh default set instead of replacing them.
725 If the specified list begins with a ‘-’ character, then the spec‐
726 ified methods (including wildcards) will be removed from the
727 built-in openssh default set instead of replacing them. If the
728 specified list begins with a ‘^’ character, then the specified
729 methods will be placed at the head of the built-in openssh de‐
730 fault set.
731 The list of available key exchange algorithms may also be ob‐
733 tained using "ssh -Q kex".
734 KnownHostsCommand
736 Specifies a command to use to obtain a list of host keys, in ad‐
737 dition to those listed in UserKnownHostsFile and
738 GlobalKnownHostsFile. This command is executed after the files
739 have been read. It may write host key lines to standard output
740 in identical format to the usual files (described in the
741 VERIFYING HOST KEYS section in ssh(1)). Arguments to
742 KnownHostsCommand accept the tokens described in the TOKENS sec‐
743 tion. The command may be invoked multiple times per connection:
744 once when preparing the preference list of host key algorithms to
745 use, again to obtain the host key for the requested host name
746 and, if CheckHostIP is enabled, one more time to obtain the host
747 key matching the server's address. If the command exits abnor‐
748 mally or returns a non-zero exit status then the connection is
749 terminated.
750 LocalCommand
752 Specifies a command to execute on the local machine after suc‐
753 cessfully connecting to the server. The command string extends
754 to the end of the line, and is executed with the user's shell.
755 Arguments to LocalCommand accept the tokens described in the
756 TOKENS section.
757 The command is run synchronously and does not have access to the
759 session of the ssh(1) that spawned it. It should not be used for
760 interactive commands.
761 This directive is ignored unless PermitLocalCommand has been en‐
763 abled.
764 LocalForward
766 Specifies that a TCP port on the local machine be forwarded over
767 the secure channel to the specified host and port from the remote
768 machine. The first argument specifies the listener and may be
769 [bind_address:]port or a Unix domain socket path. The second ar‐
770 gument is the destination and may be host:hostport or a Unix do‐
771 main socket path if the remote host supports it.
772 IPv6 addresses can be specified by enclosing addresses in square
774 brackets. Multiple forwardings may be specified, and additional
775 forwardings can be given on the command line. Only the superuser
776 can forward privileged ports. By default, the local port is
777 bound in accordance with the GatewayPorts setting. However, an
778 explicit bind_address may be used to bind the connection to a
779 specific address. The bind_address of localhost indicates that
780 the listening port be bound for local use only, while an empty
781 address or ‘*’ indicates that the port should be available from
782 all interfaces. Unix domain socket paths may use the tokens de‐
783 scribed in the TOKENS section and environment variables as de‐
784 scribed in the ENVIRONMENT VARIABLES section.
785 LogLevel
787 Gives the verbosity level that is used when logging messages from
788 ssh(1). The possible values are: QUIET, FATAL, ERROR, INFO, VER‐
789 BOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO.
790 DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify
791 higher levels of verbose output.
792 LogVerbose
794 Specify one or more overrides to LogLevel. An override consists
795 of a pattern lists that matches the source file, function and
796 line number to force detailed logging for. For example, an over‐
797 ride pattern of:
798 kex.c:*:1000,*:kex_exchange_identification():*,packet.c:*
800 would enable detailed logging for line 1000 of kex.c, everything
802 in the kex_exchange_identification() function, and all code in
803 the packet.c file. This option is intended for debugging and no
804 overrides are enabled by default.
805 MACs The default is handled system-wide by crypto-policies(7). To see
807 the defaults and how to modify this default, see manual page
808 update-crypto-policies(8).
809 Specifies the MAC (message authentication code) algorithms in or‐
811 der of preference. The MAC algorithm is used for data integrity
812 protection. Multiple algorithms must be comma-separated. If the
813 specified list begins with a ‘+’ character, then the specified
814 algorithms will be appended to the built-in openssh default set
815 instead of replacing them. If the specified list begins with a
816 ‘-’ character, then the specified algorithms (including wild‐
817 cards) will be removed from the built-in openssh default set in‐
818 stead of replacing them. If the specified list begins with a ‘^’
819 character, then the specified algorithms will be placed at the
820 head of the built-in openssh default set.
821 The algorithms that contain "-etm" calculate the MAC after en‐
823 cryption (encrypt-then-mac). These are considered safer and
824 their use recommended.
825 The list of available MAC algorithms may also be obtained using
827 "ssh -Q mac".
828 NoHostAuthenticationForLocalhost
830 Disable host authentication for localhost (loopback addresses).
831 The argument to this keyword must be yes or no (the default).
832 NumberOfPasswordPrompts
834 Specifies the number of password prompts before giving up. The
835 argument to this keyword must be an integer. The default is 3.
836 PasswordAuthentication
838 Specifies whether to use password authentication. The argument
839 to this keyword must be yes (the default) or no.
840 PermitLocalCommand
842 Allow local command execution via the LocalCommand option or us‐
843 ing the !command escape sequence in ssh(1). The argument must be
844 yes or no (the default).
845 PermitRemoteOpen
847 Specifies the destinations to which remote TCP port forwarding is
848 permitted when RemoteForward is used as a SOCKS proxy. The for‐
849 warding specification must be one of the following forms:
850 PermitRemoteOpen host:port
852 PermitRemoteOpen IPv4_addr:port
853 PermitRemoteOpen [IPv6_addr]:port
854 Multiple forwards may be specified by separating them with white‐
856 space. An argument of any can be used to remove all restrictions
857 and permit any forwarding requests. An argument of none can be
858 used to prohibit all forwarding requests. The wildcard ‘*’ can
859 be used for host or port to allow all hosts or ports respec‐
860 tively. Otherwise, no pattern matching or address lookups are
861 performed on supplied names.
862 PKCS11Provider
864 Specifies which PKCS#11 provider to use or none to indicate that
865 no provider should be used (the default). The argument to this
866 keyword is a path to the PKCS#11 shared library ssh(1) should use
867 to communicate with a PKCS#11 token providing keys for user au‐
868 thentication.
869 Port Specifies the port number to connect on the remote host. The de‐
871 fault is 22.
872 PreferredAuthentications
874 Specifies the order in which the client should try authentication
875 methods. This allows a client to prefer one method (e.g.
876 keyboard-interactive) over another method (e.g. password). The
877 default is:
878 gssapi-with-mic,hostbased,publickey,
880 keyboard-interactive,password
881 ProxyCommand
883 Specifies the command to use to connect to the server. The com‐
884 mand string extends to the end of the line, and is executed using
885 the user's shell ‘exec’ directive to avoid a lingering shell
886 process.
887 Arguments to ProxyCommand accept the tokens described in the
889 TOKENS section. The command can be basically anything, and
890 should read from its standard input and write to its standard
891 output. It should eventually connect an sshd(8) server running
892 on some machine, or execute sshd -i somewhere. Host key manage‐
893 ment will be done using the Hostname of the host being connected
894 (defaulting to the name typed by the user). Setting the command
895 to none disables this option entirely. Note that CheckHostIP is
896 not available for connects with a proxy command.
897 This directive is useful in conjunction with nc(1) and its proxy
899 support. For example, the following directive would connect via
900 an HTTP proxy at 192.0.2.0:
901 ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
903 ProxyJump
905 Specifies one or more jump proxies as either [user@]host[:port]
906 or an ssh URI. Multiple proxies may be separated by comma char‐
907 acters and will be visited sequentially. Setting this option
908 will cause ssh(1) to connect to the target host by first making a
909 ssh(1) connection to the specified ProxyJump host and then estab‐
910 lishing a TCP forwarding to the ultimate target from there. Set‐
911 ting the host to none disables this option entirely.
912 Note that this option will compete with the ProxyCommand option -
914 whichever is specified first will prevent later instances of the
915 other from taking effect.
916 Note also that the configuration for the destination host (either
918 supplied via the command-line or the configuration file) is not
919 generally applied to jump hosts. ~/.ssh/config should be used if
920 specific configuration is required for jump hosts.
921 ProxyUseFdpass
923 Specifies that ProxyCommand will pass a connected file descriptor
924 back to ssh(1) instead of continuing to execute and pass data.
925 The default is no.
926 PubkeyAcceptedAlgorithms
928 The default is handled system-wide by crypto-policies(7). To see
929 the defaults and how to modify this default, see manual page
930 update-crypto-policies(8).
931 Specifies the signature algorithms that will be used for public
933 key authentication as a comma-separated list of patterns. If the
934 specified list begins with a ‘+’ character, then the algorithms
935 after it will be appended to the built-in openssh default instead
936 of replacing it. If the specified list begins with a ‘-’ charac‐
937 ter, then the specified algorithms (including wildcards) will be
938 removed from the built-in openssh default set instead of replac‐
939 ing them. If the specified list begins with a ‘^’ character,
940 then the specified algorithms will be placed at the head of the
941 built-in openssh default set.
942 The list of available signature algorithms may also be obtained
944 using "ssh -Q PubkeyAcceptedAlgorithms".
945 PubkeyAuthentication
947 Specifies whether to try public key authentication. The argument
948 to this keyword must be yes (the default) or no.
949 RekeyLimit
951 Specifies the maximum amount of data that may be transmitted be‐
952 fore the session key is renegotiated, optionally followed by a
953 maximum amount of time that may pass before the session key is
954 renegotiated. The first argument is specified in bytes and may
955 have a suffix of ‘K’, ‘M’, or ‘G’ to indicate Kilobytes,
956 Megabytes, or Gigabytes, respectively. The default is between
957 ‘1G’ and ‘4G’, depending on the cipher. The optional second
958 value is specified in seconds and may use any of the units docu‐
959 mented in the TIME FORMATS section of sshd_config(5). The de‐
960 fault value for RekeyLimit is default none, which means that
961 rekeying is performed after the cipher's default amount of data
962 has been sent or received and no time based rekeying is done.
963 RemoteCommand
965 Specifies a command to execute on the remote machine after suc‐
966 cessfully connecting to the server. The command string extends
967 to the end of the line, and is executed with the user's shell.
968 Arguments to RemoteCommand accept the tokens described in the
969 TOKENS section.
970 RemoteForward
972 Specifies that a TCP port on the remote machine be forwarded over
973 the secure channel. The remote port may either be forwarded to a
974 specified host and port from the local machine, or may act as a
975 SOCKS 4/5 proxy that allows a remote client to connect to arbi‐
976 trary destinations from the local machine. The first argument is
977 the listening specification and may be [bind_address:]port or, if
978 the remote host supports it, a Unix domain socket path. If for‐
979 warding to a specific destination then the second argument must
980 be host:hostport or a Unix domain socket path, otherwise if no
981 destination argument is specified then the remote forwarding will
982 be established as a SOCKS proxy. When acting as a SOCKS proxy
983 the destination of the connection can be restricted by
984 PermitRemoteOpen.
985 IPv6 addresses can be specified by enclosing addresses in square
987 brackets. Multiple forwardings may be specified, and additional
988 forwardings can be given on the command line. Privileged ports
989 can be forwarded only when logging in as root on the remote ma‐
990 chine. Unix domain socket paths may use the tokens described in
991 the TOKENS section and environment variables as described in the
992 ENVIRONMENT VARIABLES section.
993 If the port argument is 0, the listen port will be dynamically
995 allocated on the server and reported to the client at run time.
996 If the bind_address is not specified, the default is to only bind
998 to loopback addresses. If the bind_address is ‘*’ or an empty
999 string, then the forwarding is requested to listen on all inter‐
1000 faces. Specifying a remote bind_address will only succeed if the
1001 server's GatewayPorts option is enabled (see sshd_config(5)).
1002 RequestTTY
1004 Specifies whether to request a pseudo-tty for the session. The
1005 argument may be one of: no (never request a TTY), yes (always re‐
1006 quest a TTY when standard input is a TTY), force (always request
1007 a TTY) or auto (request a TTY when opening a login session).
1008 This option mirrors the -t and -T flags for ssh(1).
1009 RevokedHostKeys
1011 Specifies revoked host public keys. Keys listed in this file
1012 will be refused for host authentication. Note that if this file
1013 does not exist or is not readable, then host authentication will
1014 be refused for all hosts. Keys may be specified as a text file,
1015 listing one public key per line, or as an OpenSSH Key Revocation
1016 List (KRL) as generated by ssh-keygen(1). For more information
1017 on KRLs, see the KEY REVOCATION LISTS section in ssh-keygen(1).
1018 SecurityKeyProvider
1020 Specifies a path to a library that will be used when loading any
1021 FIDO authenticator-hosted keys, overriding the default of using
1022 the built-in USB HID support.
1023 If the specified value begins with a ‘$’ character, then it will
1025 be treated as an environment variable containing the path to the
1026 library.
1027 SendEnv
1029 Specifies what variables from the local environ(7) should be sent
1030 to the server. The server must also support it, and the server
1031 must be configured to accept these environment variables. Note
1032 that the TERM environment variable is always sent whenever a
1033 pseudo-terminal is requested as it is required by the protocol.
1034 Refer to AcceptEnv in sshd_config(5) for how to configure the
1035 server. Variables are specified by name, which may contain wild‐
1036 card characters. Multiple environment variables may be separated
1037 by whitespace or spread across multiple SendEnv directives.
1038 See PATTERNS for more information on patterns.
1040 It is possible to clear previously set SendEnv variable names by
1042 prefixing patterns with -. The default is not to send any envi‐
1043 ronment variables.
1044 ServerAliveCountMax
1046 Sets the number of server alive messages (see below) which may be
1047 sent without ssh(1) receiving any messages back from the server.
1048 If this threshold is reached while server alive messages are be‐
1049 ing sent, ssh will disconnect from the server, terminating the
1050 session. It is important to note that the use of server alive
1051 messages is very different from TCPKeepAlive (below). The server
1052 alive messages are sent through the encrypted channel and there‐
1053 fore will not be spoofable. The TCP keepalive option enabled by
1054 TCPKeepAlive is spoofable. The server alive mechanism is valu‐
1055 able when the client or server depend on knowing when a connec‐
1056 tion has become unresponsive.
1057 The default value is 3. If, for example, ServerAliveInterval
1059 (see below) is set to 15 and ServerAliveCountMax is left at the
1060 default, if the server becomes unresponsive, ssh will disconnect
1061 after approximately 45 seconds.
1062 ServerAliveInterval
1064 Sets a timeout interval in seconds after which if no data has
1065 been received from the server, ssh(1) will send a message through
1066 the encrypted channel to request a response from the server. The
1067 default is 0, indicating that these messages will not be sent to
1068 the server.
1069 SessionType
1071 May be used to either request invocation of a subsystem on the
1072 remote system, or to prevent the execution of a remote command at
1073 all. The latter is useful for just forwarding ports. The argu‐
1074 ment to this keyword must be none (same as the -N option),
1075 subsystem (same as the -s option) or default (shell or command
1076 execution).
1077 SetEnv Directly specify one or more environment variables and their con‐
1079 tents to be sent to the server. Similarly to SendEnv, with the
1080 exception of the TERM variable, the server must be prepared to
1081 accept the environment variable.
1082 StdinNull
1084 Redirects stdin from /dev/null (actually, prevents reading from
1085 stdin). Either this or the equivalent -n option must be used
1086 when ssh is run in the background. The argument to this keyword
1087 must be yes (same as the -n option) or no (the default).
1088 StreamLocalBindMask
1090 Sets the octal file creation mode mask (umask) used when creating
1091 a Unix-domain socket file for local or remote port forwarding.
1092 This option is only used for port forwarding to a Unix-domain
1093 socket file.
1094 The default value is 0177, which creates a Unix-domain socket
1096 file that is readable and writable only by the owner. Note that
1097 not all operating systems honor the file mode on Unix-domain
1098 socket files.
1099 StreamLocalBindUnlink
1101 Specifies whether to remove an existing Unix-domain socket file
1102 for local or remote port forwarding before creating a new one.
1103 If the socket file already exists and StreamLocalBindUnlink is
1104 not enabled, ssh will be unable to forward the port to the Unix-
1105 domain socket file. This option is only used for port forwarding
1106 to a Unix-domain socket file.
1107 The argument must be yes or no (the default).
1109 StrictHostKeyChecking
1111 If this flag is set to yes, ssh(1) will never automatically add
1112 host keys to the ~/.ssh/known_hosts file, and refuses to connect
1113 to hosts whose host key has changed. This provides maximum pro‐
1114 tection against man-in-the-middle (MITM) attacks, though it can
1115 be annoying when the /etc/ssh/ssh_known_hosts file is poorly
1116 maintained or when connections to new hosts are frequently made.
1117 This option forces the user to manually add all new hosts.
1118 If this flag is set to “accept-new” then ssh will automatically
1120 add new host keys to the user's known_hosts file, but will not
1121 permit connections to hosts with changed host keys. If this flag
1122 is set to “no” or “off”, ssh will automatically add new host keys
1123 to the user known hosts files and allow connections to hosts with
1124 changed hostkeys to proceed, subject to some restrictions. If
1125 this flag is set to ask (the default), new host keys will be
1126 added to the user known host files only after the user has con‐
1127 firmed that is what they really want to do, and ssh will refuse
1128 to connect to hosts whose host key has changed. The host keys of
1129 known hosts will be verified automatically in all cases.
1130 SyslogFacility
1132 Gives the facility code that is used when logging messages from
1133 ssh(1). The possible values are: DAEMON, USER, AUTH, LOCAL0, LO‐
1134 CAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. The de‐
1135 fault is USER.
1136 TCPKeepAlive
1138 Specifies whether the system should send TCP keepalive messages
1139 to the other side. If they are sent, death of the connection or
1140 crash of one of the machines will be properly noticed. However,
1141 this means that connections will die if the route is down tempo‐
1142 rarily, and some people find it annoying.
1143 The default is yes (to send TCP keepalive messages), and the
1145 client will notice if the network goes down or the remote host
1146 dies. This is important in scripts, and many users want it too.
1147 To disable TCP keepalive messages, the value should be set to no.
1149 See also ServerAliveInterval for protocol-level keepalives.
1150 Tunnel Request tun(4) device forwarding between the client and the
1152 server. The argument must be yes, point-to-point (layer 3),
1153 ethernet (layer 2), or no (the default). Specifying yes requests
1154 the default tunnel mode, which is point-to-point.
1155 TunnelDevice
1157 Specifies the tun(4) devices to open on the client (local_tun)
1158 and the server (remote_tun).
1159 The argument must be local_tun[:remote_tun]. The devices may be
1161 specified by numerical ID or the keyword any, which uses the next
1162 available tunnel device. If remote_tun is not specified, it de‐
1163 faults to any. The default is any:any.
1164 UpdateHostKeys
1166 Specifies whether ssh(1) should accept notifications of addi‐
1167 tional hostkeys from the server sent after authentication has
1168 completed and add them to UserKnownHostsFile. The argument must
1169 be yes, no or ask. This option allows learning alternate
1170 hostkeys for a server and supports graceful key rotation by al‐
1171 lowing a server to send replacement public keys before old ones
1172 are removed.
1173 Additional hostkeys are only accepted if the key used to authen‐
1175 ticate the host was already trusted or explicitly accepted by the
1176 user, the host was authenticated via UserKnownHostsFile (i.e. not
1177 GlobalKnownHostsFile) and the host was authenticated using a
1178 plain key and not a certificate.
1179 UpdateHostKeys is enabled by default if the user has not overrid‐
1181 den the default UserKnownHostsFile setting and has not enabled
1182 VerifyHostKeyDNS, otherwise UpdateHostKeys will be set to no.
1183 If UpdateHostKeys is set to ask, then the user is asked to con‐
1185 firm the modifications to the known_hosts file. Confirmation is
1186 currently incompatible with ControlPersist, and will be disabled
1187 if it is enabled.
1188 Presently, only sshd(8) from OpenSSH 6.8 and greater support the
1190 "hostkeys@openssh.com" protocol extension used to inform the
1191 client of all the server's hostkeys.
1192 User Specifies the user to log in as. This can be useful when a dif‐
1194 ferent user name is used on different machines. This saves the
1195 trouble of having to remember to give the user name on the com‐
1196 mand line.
1197 UserKnownHostsFile
1199 Specifies one or more files to use for the user host key data‐
1200 base, separated by whitespace. Each filename may use tilde nota‐
1201 tion to refer to the user's home directory, the tokens described
1202 in the TOKENS section and environment variables as described in
1203 the ENVIRONMENT VARIABLES section. The default is
1204 ~/.ssh/known_hosts, ~/.ssh/known_hosts2.
1205 VerifyHostKeyDNS
1207 Specifies whether to verify the remote key using DNS and SSHFP
1208 resource records. If this option is set to yes, the client will
1209 implicitly trust keys that match a secure fingerprint from DNS.
1210 Insecure fingerprints will be handled as if this option was set
1211 to ask. If this option is set to ask, information on fingerprint
1212 match will be displayed, but the user will still need to confirm
1213 new host keys according to the StrictHostKeyChecking option. The
1214 default is no.
1215 See also VERIFYING HOST KEYS in ssh(1).
1217 VisualHostKey
1219 If this flag is set to yes, an ASCII art representation of the
1220 remote host key fingerprint is printed in addition to the finger‐
1221 print string at login and for unknown host keys. If this flag is
1222 set to no (the default), no fingerprint strings are printed at
1223 login and only the fingerprint string will be printed for unknown
1224 host keys.
1225 XAuthLocation
1227 Specifies the full pathname of the xauth(1) program. The default
1228 is /usr/bin/xauth.
1229
1231 A pattern consists of zero or more non-whitespace characters, ‘*’ (a
1232 wildcard that matches zero or more characters), or ‘?’ (a wildcard that
1233 matches exactly one character). For example, to specify a set of decla‐
1234 rations for any host in the ".co.uk" set of domains, the following pat‐
1235 tern could be used:
1236 Host *.co.uk
1238 The following pattern would match any host in the 192.168.0.[0-9] network
1240 range:
1241 Host 192.168.0.?
1243 A pattern-list is a comma-separated list of patterns. Patterns within
1245 pattern-lists may be negated by preceding them with an exclamation mark
1246 (‘!’). For example, to allow a key to be used from anywhere within an
1247 organization except from the "dialup" pool, the following entry (in au‐
1248 thorized_keys) could be used:
1249 from="!*.dialup.example.com,*.example.com"
1251 Note that a negated match will never produce a positive result by itself.
1253 For example, attempting to match "host3" against the following pattern-
1254 list will fail:
1255 from="!host1,!host2"
1257 The solution here is to include a term that will yield a positive match,
1259 such as a wildcard:
1260 from="!host1,!host2,*"
1262
1264 Arguments to some keywords can make use of tokens, which are expanded at
1265 runtime:
1266 %% A literal ‘%’.
1268 %C Hash of %l%h%p%r.
1269 %d Local user's home directory.
1270 %f The fingerprint of the server's host key.
1271 %H The known_hosts hostname or address that is being searched
1272 for.
1273 %h The remote hostname.
1274 %I A string describing the reason for a KnownHostsCommand execu‐
1275 tion: either ADDRESS when looking up a host by address (only
1276 when CheckHostIP is enabled), HOSTNAME when searching by
1277 hostname, or ORDER when preparing the host key algorithm
1278 preference list to use for the destination host.
1279 %i The local user ID.
1280 %K The base64 encoded host key.
1281 %k The host key alias if specified, otherwise the original re‐
1282 mote hostname given on the command line.
1283 %L The local hostname.
1284 %l The local hostname, including the domain name.
1285 %n The original remote hostname, as given on the command line.
1286 %p The remote port.
1287 %r The remote username.
1288 %T The local tun(4) or tap(4) network interface assigned if tun‐
1289 nel forwarding was requested, or "NONE" otherwise.
1290 %t The type of the server host key, e.g. ssh-ed25519.
1291 %u The local username.
1292 CertificateFile, ControlPath, IdentityAgent, IdentityFile,
1294 KnownHostsCommand, LocalForward, Match exec, RemoteCommand,
1295 RemoteForward, and UserKnownHostsFile accept the tokens %%, %C, %d, %h,
1296 %i, %k, %L, %l, %n, %p, %r, and %u.
1297 KnownHostsCommand additionally accepts the tokens %f, %H, %I, %K and %t.
1299 Hostname accepts the tokens %% and %h.
1301 LocalCommand accepts all tokens.
1303 ProxyCommand accepts the tokens %%, %h, %n, %p, and %r.
1305
1307 Arguments to some keywords can be expanded at runtime from environment
1308 variables on the client by enclosing them in ${}, for example
1309 ${HOME}/.ssh would refer to the user's .ssh directory. If a specified
1310 environment variable does not exist then an error will be returned and
1311 the setting for that keyword will be ignored.
1312 The keywords CertificateFile, ControlPath, IdentityAgent, IdentityFile,
1314 KnownHostsCommand, and UserKnownHostsFile support environment variables.
1315 The keywords LocalForward and RemoteForward support environment variables
1316 only for Unix domain socket paths.
1317
1319 ~/.ssh/config
1320 This is the per-user configuration file. The format of this file
1321 is described above. This file is used by the SSH client. Be‐
1322 cause of the potential for abuse, this file must have strict per‐
1323 missions: read/write for the user, and not writable by others.
1324 /etc/ssh/ssh_config
1326 Systemwide configuration file. This file provides defaults for
1327 those values that are not specified in the user's configuration
1328 file, and for those users who do not have a configuration file.
1329 This file must be world-readable.
1330
1332 ssh(1)
1333
1335 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
1336 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
1337 de Raadt and Dug Song removed many bugs, re-added newer features and cre‐
1338 ated OpenSSH. Markus Friedl contributed the support for SSH protocol
1339 versions 1.5 and 2.0.
1340BSD August 12, 2021 BSD