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 A single argument of "none" causes no CNAMEs to be considered for
176 canonicalization. This is the default behaviour.
177 CASignatureAlgorithms
179 The default is handled system-wide by crypto-policies(7). Infor‐
180 mation about defaults, how to modify the defaults and how to cus‐
181 tomize existing policies with sub-policies are present in manual
182 page update-crypto-policies(8).
183 Specifies which algorithms are allowed for signing of certifi‐
185 cates by certificate authorities (CAs). If the specified list
186 begins with a ‘+’ character, then the specified algorithms will
187 be appended to the default set instead of replacing them. If the
188 specified list begins with a ‘-’ character, then the specified
189 algorithms (including wildcards) will be removed from the default
190 set instead of replacing them.
191 ssh(1) will not accept host certificates signed using algorithms
193 other than those specified.
194 CertificateFile
196 Specifies a file from which the user's certificate is read. A
197 corresponding private key must be provided separately in order to
198 use this certificate either from an IdentityFile directive or -i
199 flag to ssh(1), via ssh-agent(1), or via a PKCS11Provider or
200 SecurityKeyProvider.
201 Arguments to CertificateFile may use the tilde syntax to refer to
203 a user's home directory, the tokens described in the TOKENS sec‐
204 tion and environment variables as described in the ENVIRONMENT
205 VARIABLES section.
206 It is possible to have multiple certificate files specified in
208 configuration files; these certificates will be tried in se‐
209 quence. Multiple CertificateFile directives will add to the list
210 of certificates used for authentication.
211 CheckHostIP
213 If set to yes, ssh(1) will additionally check the host IP address
214 in the known_hosts file. This allows it to detect if a host key
215 changed due to DNS spoofing and will add addresses of destination
216 hosts to ~/.ssh/known_hosts in the process, regardless of the
217 setting of StrictHostKeyChecking. If the option is set to no
218 (the default), the check will not be executed.
219 Ciphers
221 The default is handled system-wide by crypto-policies(7). Infor‐
222 mation about defaults, how to modify the defaults and how to cus‐
223 tomize existing policies with sub-policies are present in manual
224 page update-crypto-policies(8).
225 Specifies the ciphers allowed and their order of preference.
227 Multiple ciphers must be comma-separated. If the specified list
228 begins with a ‘+’ character, then the specified ciphers will be
229 appended to the built-in openssh default set instead of replacing
230 them. If the specified list begins with a ‘-’ character, then
231 the specified ciphers (including wildcards) will be removed from
232 the built-in openssh default set instead of replacing them. If
233 the specified list begins with a ‘^’ character, then the speci‐
234 fied ciphers will be placed at the head of the built-in openssh
235 default set.
236 The supported ciphers are:
238 3des-cbc
240 aes128-cbc
241 aes192-cbc
242 aes256-cbc
243 aes128-ctr
244 aes192-ctr
245 aes256-ctr
246 aes128-gcm@openssh.com
247 aes256-gcm@openssh.com
248 chacha20-poly1305@openssh.com
249 The list of available ciphers may also be obtained using "ssh -Q
251 cipher".
252 ClearAllForwardings
254 Specifies that all local, remote, and dynamic port forwardings
255 specified in the configuration files or on the command line be
256 cleared. This option is primarily useful when used from the
257 ssh(1) command line to clear port forwardings set in configura‐
258 tion files, and is automatically set by scp(1) and sftp(1). The
259 argument must be yes or no (the default).
260 Compression
262 Specifies whether to use compression. The argument must be yes
263 or no (the default).
264 ConnectionAttempts
266 Specifies the number of tries (one per second) to make before ex‐
267 iting. The argument must be an integer. This may be useful in
268 scripts if the connection sometimes fails. The default is 1.
269 ConnectTimeout
271 Specifies the timeout (in seconds) used when connecting to the
272 SSH server, instead of using the default system TCP timeout.
273 This timeout is applied both to establishing the connection and
274 to performing the initial SSH protocol handshake and key ex‐
275 change.
276 ControlMaster
278 Enables the sharing of multiple sessions over a single network
279 connection. When set to yes, ssh(1) will listen for connections
280 on a control socket specified using the ControlPath argument.
281 Additional sessions can connect to this socket using the same
282 ControlPath with ControlMaster set to no (the default). These
283 sessions will try to reuse the master instance's network connec‐
284 tion rather than initiating new ones, but will fall back to con‐
285 necting normally if the control socket does not exist, or is not
286 listening.
287 Setting this to ask will cause ssh(1) to listen for control con‐
289 nections, but require confirmation using ssh-askpass(1). If the
290 ControlPath cannot be opened, ssh(1) will continue without con‐
291 necting to a master instance.
292 X11 and ssh-agent(1) forwarding is supported over these multi‐
294 plexed connections, however the display and agent forwarded will
295 be the one belonging to the master connection i.e. it is not pos‐
296 sible to forward multiple displays or agents.
297 Two additional options allow for opportunistic multiplexing: try
299 to use a master connection but fall back to creating a new one if
300 one does not already exist. These options are: auto and autoask.
301 The latter requires confirmation like the ask option.
302 ControlPath
304 Specify the path to the control socket used for connection shar‐
305 ing as described in the ControlMaster section above or the string
306 none to disable connection sharing. Arguments to ControlPath may
307 use the tilde syntax to refer to a user's home directory, the to‐
308 kens described in the TOKENS section and environment variables as
309 described in the ENVIRONMENT VARIABLES section. It is recom‐
310 mended that any ControlPath used for opportunistic connection
311 sharing include at least %h, %p, and %r (or alternatively %C) and
312 be placed in a directory that is not writable by other users.
313 This ensures that shared connections are uniquely identified.
314 ControlPersist
316 When used in conjunction with ControlMaster, specifies that the
317 master connection should remain open in the background (waiting
318 for future client connections) after the initial client connec‐
319 tion has been closed. If set to no (the default), then the mas‐
320 ter connection will not be placed into the background, and will
321 close as soon as the initial client connection is closed. If set
322 to yes or 0, then the master connection will remain in the back‐
323 ground indefinitely (until killed or closed via a mechanism such
324 as the "ssh -O exit"). If set to a time in seconds, or a time in
325 any of the formats documented in sshd_config(5), then the back‐
326 grounded master connection will automatically terminate after it
327 has remained idle (with no client connections) for the specified
328 time.
329 DynamicForward
331 Specifies that a TCP port on the local machine be forwarded over
332 the secure channel, and the application protocol is then used to
333 determine where to connect to from the remote machine.
334 The argument must be [bind_address:]port. IPv6 addresses can be
336 specified by enclosing addresses in square brackets. By default,
337 the local port is bound in accordance with the GatewayPorts set‐
338 ting. However, an explicit bind_address may be used to bind the
339 connection to a specific address. The bind_address of localhost
340 indicates that the listening port be bound for local use only,
341 while an empty address or ‘*’ indicates that the port should be
342 available from all interfaces.
343 Currently the SOCKS4 and SOCKS5 protocols are supported, and
345 ssh(1) will act as a SOCKS server. Multiple forwardings may be
346 specified, and additional forwardings can be given on the command
347 line. Only the superuser can forward privileged ports.
348 EnableSSHKeysign
350 Setting this option to yes in the global client configuration
351 file /etc/ssh/ssh_config enables the use of the helper program
352 ssh-keysign(8) during HostbasedAuthentication. The argument must
353 be yes or no (the default). This option should be placed in the
354 non-hostspecific section. See ssh-keysign(8) for more informa‐
355 tion.
356 EscapeChar
358 Sets the escape character (default: ‘~’). The escape character
359 can also be set on the command line. The argument should be a
360 single character, ‘^’ followed by a letter, or none to disable
361 the escape character entirely (making the connection transparent
362 for binary data).
363 ExitOnForwardFailure
365 Specifies whether ssh(1) should terminate the connection if it
366 cannot set up all requested dynamic, tunnel, local, and remote
367 port forwardings, (e.g. if either end is unable to bind and lis‐
368 ten on a specified port). Note that ExitOnForwardFailure does
369 not apply to connections made over port forwardings and will not,
370 for example, cause ssh(1) to exit if TCP connections to the ulti‐
371 mate forwarding destination fail. The argument must be yes or no
372 (the default).
373 FingerprintHash
375 Specifies the hash algorithm used when displaying key finger‐
376 prints. Valid options are: md5 and sha256 (the default).
377 ForkAfterAuthentication
379 Requests ssh to go to background just before command execution.
380 This is useful if ssh is going to ask for passwords or
381 passphrases, but the user wants it in the background. This im‐
382 plies the StdinNull configuration option being set to “yes”. The
383 recommended way to start X11 programs at a remote site is with
384 something like ssh -f host xterm, which is the same as ssh host
385 xterm if the ForkAfterAuthentication configuration option is set
386 to “yes”.
387 If the ExitOnForwardFailure configuration option is set to “yes”,
389 then a client started with the ForkAfterAuthentication configura‐
390 tion option being set to “yes” will wait for all remote port for‐
391 wards to be successfully established before placing itself in the
392 background. The argument to this keyword must be yes (same as
393 the -f option) or no (the default).
394 ForwardAgent
396 Specifies whether the connection to the authentication agent (if
397 any) will be forwarded to the remote machine. The argument may
398 be yes, no (the default), an explicit path to an agent socket or
399 the name of an environment variable (beginning with ‘$’) in which
400 to find the path.
401 Agent forwarding should be enabled with caution. Users with the
403 ability to bypass file permissions on the remote host (for the
404 agent's Unix-domain socket) can access the local agent through
405 the forwarded connection. An attacker cannot obtain key material
406 from the agent, however they can perform operations on the keys
407 that enable them to authenticate using the identities loaded into
408 the agent.
409 ForwardX11
411 Specifies whether X11 connections will be automatically redi‐
412 rected over the secure channel and DISPLAY set. The argument
413 must be yes or no (the default).
414 X11 forwarding should be enabled with caution. Users with the
416 ability to bypass file permissions on the remote host (for the
417 user's X11 authorization database) can access the local X11 dis‐
418 play through the forwarded connection. An attacker may then be
419 able to perform activities such as keystroke monitoring if the
420 ForwardX11Trusted option is also enabled.
421 ForwardX11Timeout
423 Specify a timeout for untrusted X11 forwarding using the format
424 described in the TIME FORMATS section of sshd_config(5). X11
425 connections received by ssh(1) after this time will be refused.
426 Setting ForwardX11Timeout to zero will disable the timeout and
427 permit X11 forwarding for the life of the connection. The de‐
428 fault is to disable untrusted X11 forwarding after twenty minutes
429 has elapsed.
430 ForwardX11Trusted
432 If this option is set to yes, remote X11 clients will have full
433 access to the original X11 display.
434 If this option is set to no (the default), remote X11 clients
436 will be considered untrusted and prevented from stealing or tam‐
437 pering with data belonging to trusted X11 clients. Furthermore,
438 the xauth(1) token used for the session will be set to expire af‐
439 ter 20 minutes. Remote clients will be refused access after this
440 time.
441 See the X11 SECURITY extension specification for full details on
443 the restrictions imposed on untrusted clients.
444 GatewayPorts
446 Specifies whether remote hosts are allowed to connect to local
447 forwarded ports. By default, ssh(1) binds local port forwardings
448 to the loopback address. This prevents other remote hosts from
449 connecting to forwarded ports. GatewayPorts can be used to spec‐
450 ify that ssh should bind local port forwardings to the wildcard
451 address, thus allowing remote hosts to connect to forwarded
452 ports. The argument must be yes or no (the default).
453 GlobalKnownHostsFile
455 Specifies one or more files to use for the global host key data‐
456 base, separated by whitespace. The default is
457 /etc/ssh/ssh_known_hosts, /etc/ssh/ssh_known_hosts2.
458 GSSAPIAuthentication
460 Specifies whether user authentication based on GSSAPI is allowed.
461 The default is no.
462 GSSAPIClientIdentity
464 If set, specifies the GSSAPI client identity that ssh should use
465 when connecting to the server. The default is unset, which means
466 that the default identity will be used.
467 GSSAPIDelegateCredentials
469 Forward (delegate) credentials to the server. The default is no.
470 GSSAPIKeyExchange
472 Specifies whether key exchange based on GSSAPI may be used. When
473 using GSSAPI key exchange the server need not have a host key.
474 The default is “no”.
475 GSSAPIRenewalForcesRekey
477 If set to “yes” then renewal of the client's GSSAPI credentials
478 will force the rekeying of the ssh connection. With a compatible
479 server, this will delegate the renewed credentials to a session
480 on the server.
481 Checks are made to ensure that credentials are only propagated
483 when the new credentials match the old ones on the originating
484 client and where the receiving server still has the old set in
485 its cache.
486 The default is “no”.
488 For this to work GSSAPIKeyExchange needs to be enabled in the
490 server and also used by the client.
491 GSSAPIServerIdentity
493 If set, specifies the GSSAPI server identity that ssh should ex‐
494 pect when connecting to the server. The default is unset, which
495 means that the expected GSSAPI server identity will be determined
496 from the target hostname.
497 GSSAPITrustDns
499 Set to “yes” to indicate that the DNS is trusted to securely
500 canonicalize the name of the host being connected to. If “no”,
501 the hostname entered on the command line will be passed untouched
502 to the GSSAPI library. The default is “no”.
503 GSSAPIKexAlgorithms
505 The default is handled system-wide by crypto-policies(7). Infor‐
506 mation about defaults, how to modify the defaults and how to cus‐
507 tomize existing policies with sub-policies are present in manual
508 page update-crypto-policies(8).
509 The list of key exchange algorithms that are offered for GSSAPI
511 key exchange. Possible values are
512 gss-gex-sha1-,
514 gss-group1-sha1-,
515 gss-group14-sha1-,
516 gss-group14-sha256-,
517 gss-group16-sha512-,
518 gss-nistp256-sha256-,
519 gss-curve25519-sha256-
520 This option only applies to connections using GSSAPI.
522 HashKnownHosts
524 Indicates that ssh(1) should hash host names and addresses when
525 they are added to ~/.ssh/known_hosts. These hashed names may be
526 used normally by ssh(1) and sshd(8), but they do not visually re‐
527 veal identifying information if the file's contents are dis‐
528 closed. The default is no. Note that existing names and ad‐
529 dresses in known hosts files will not be converted automatically,
530 but may be manually hashed using ssh-keygen(1).
531 HostbasedAcceptedAlgorithms
533 The default is handled system-wide by crypto-policies(7). Infor‐
534 mation about defaults, how to modify the defaults and how to cus‐
535 tomize existing policies with sub-policies are present in manual
536 page update-crypto-policies(8).
537 Specifies the signature algorithms that will be used for host‐
539 based authentication as a comma-separated list of patterns. Al‐
540 ternately if the specified list begins with a ‘+’ character, then
541 the specified signature algorithms will be appended to the built-
542 in openssh default set instead of replacing them. If the speci‐
543 fied list begins with a ‘-’ character, then the specified signa‐
544 ture algorithms (including wildcards) will be removed from the
545 built-in openssh default set instead of replacing them. If the
546 specified list begins with a ‘^’ character, then the specified
547 signature algorithms will be placed at the head of the built-in
548 openssh default set.
549 The -Q option of ssh(1) may be used to list supported signature
551 algorithms. This was formerly named HostbasedKeyTypes.
552 HostbasedAuthentication
554 Specifies whether to try rhosts based authentication with public
555 key authentication. The argument must be yes or no (the de‐
556 fault).
557 HostKeyAlgorithms
559 Specifies the host key signature algorithms that the client wants
560 to use in order of preference. Alternately if the specified list
561 begins with a ‘+’ character, then the specified signature algo‐
562 rithms will be appended to the default set instead of replacing
563 them. If the specified list begins with a ‘-’ character, then
564 the specified signature algorithms (including wildcards) will be
565 removed from the default set instead of replacing them. If the
566 specified list begins with a ‘^’ character, then the specified
567 signature algorithms will be placed at the head of the default
568 set. The default for this option is:
569 ssh-ed25519-cert-v01@openssh.com,
571 ecdsa-sha2-nistp256-cert-v01@openssh.com,
572 ecdsa-sha2-nistp384-cert-v01@openssh.com,
573 ecdsa-sha2-nistp521-cert-v01@openssh.com,
574 sk-ssh-ed25519-cert-v01@openssh.com,
575 sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
576 rsa-sha2-512-cert-v01@openssh.com,
577 rsa-sha2-256-cert-v01@openssh.com,
578 ssh-ed25519,
579 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
580 sk-ecdsa-sha2-nistp256@openssh.com,
581 sk-ssh-ed25519@openssh.com,
582 rsa-sha2-512,rsa-sha2-256
583 If hostkeys are known for the destination host then this default
585 is modified to prefer their algorithms.
586 The list of available signature algorithms may also be obtained
588 using "ssh -Q HostKeyAlgorithms".
589 HostKeyAlias
591 Specifies an alias that should be used instead of the real host
592 name when looking up or saving the host key in the host key data‐
593 base files and when validating host certificates. This option is
594 useful for tunneling SSH connections or for multiple servers run‐
595 ning on a single host.
596 Hostname
598 Specifies the real host name to log into. This can be used to
599 specify nicknames or abbreviations for hosts. Arguments to
600 Hostname accept the tokens described in the TOKENS section. Nu‐
601 meric IP addresses are also permitted (both on the command line
602 and in Hostname specifications). The default is the name given
603 on the command line.
604 IdentitiesOnly
606 Specifies that ssh(1) should only use the configured authentica‐
607 tion identity and certificate files (either the default files, or
608 those explicitly configured in the ssh_config files or passed on
609 the ssh(1) command-line), even if ssh-agent(1) or a
610 PKCS11Provider or SecurityKeyProvider offers more identities.
611 The argument to this keyword must be yes or no (the default).
612 This option is intended for situations where ssh-agent offers
613 many different identities.
614 IdentityAgent
616 Specifies the UNIX-domain socket used to communicate with the au‐
617 thentication agent.
618 This option overrides the SSH_AUTH_SOCK environment variable and
620 can be used to select a specific agent. Setting the socket name
621 to none disables the use of an authentication agent. If the
622 string "SSH_AUTH_SOCK" is specified, the location of the socket
623 will be read from the SSH_AUTH_SOCK environment variable. Other‐
624 wise if the specified value begins with a ‘$’ character, then it
625 will be treated as an environment variable containing the loca‐
626 tion of the socket.
627 Arguments to IdentityAgent may use the tilde syntax to refer to a
629 user's home directory, the tokens described in the TOKENS section
630 and environment variables as described in the ENVIRONMENT
631 VARIABLES section.
632 IdentityFile
634 Specifies a file from which the user's DSA, ECDSA, authenticator-
635 hosted ECDSA, Ed25519, authenticator-hosted Ed25519 or RSA au‐
636 thentication identity is read. The default is ~/.ssh/id_rsa,
637 ~/.ssh/id_ecdsa, ~/.ssh/id_ecdsa_sk, ~/.ssh/id_ed25519,
638 ~/.ssh/id_ed25519_sk and ~/.ssh/id_dsa. Additionally, any iden‐
639 tities represented by the authentication agent will be used for
640 authentication unless IdentitiesOnly is set. If no certificates
641 have been explicitly specified by CertificateFile, ssh(1) will
642 try to load certificate information from the filename obtained by
643 appending -cert.pub to the path of a specified IdentityFile.
644 Arguments to IdentityFile may use the tilde syntax to refer to a
646 user's home directory or the tokens described in the TOKENS sec‐
647 tion.
648 It is possible to have multiple identity files specified in con‐
650 figuration files; all these identities will be tried in sequence.
651 Multiple IdentityFile directives will add to the list of identi‐
652 ties tried (this behaviour differs from that of other configura‐
653 tion directives).
654 IdentityFile may be used in conjunction with IdentitiesOnly to
656 select which identities in an agent are offered during authenti‐
657 cation. IdentityFile may also be used in conjunction with
658 CertificateFile in order to provide any certificate also needed
659 for authentication with the identity.
660 The authentication identity can be also specified in a form of
662 PKCS#11 URI starting with a string pkcs11:. There is supported a
663 subset of the PKCS#11 URI as defined in RFC 7512 (implemented
664 path arguments id, manufacturer, object, token and query argu‐
665 ments module-path and pin-value ). The URI can not be in quotes.
666 IgnoreUnknown
668 Specifies a pattern-list of unknown options to be ignored if they
669 are encountered in configuration parsing. This may be used to
670 suppress errors if ssh_config contains options that are unrecog‐
671 nised by ssh(1). It is recommended that IgnoreUnknown be listed
672 early in the configuration file as it will not be applied to un‐
673 known options that appear before it.
674 Include
676 Include the specified configuration file(s). Multiple pathnames
677 may be specified and each pathname may contain glob(7) wildcards
678 and, for user configurations, shell-like ‘~’ references to user
679 home directories. Wildcards will be expanded and processed in
680 lexical order. Files without absolute paths are assumed to be in
681 ~/.ssh if included in a user configuration file or /etc/ssh if
682 included from the system configuration file. Include directive
683 may appear inside a Match or Host block to perform conditional
684 inclusion.
685 IPQoS Specifies the IPv4 type-of-service or DSCP class for connections.
687 Accepted values are af11, af12, af13, af21, af22, af23, af31,
688 af32, af33, af41, af42, af43, cs0, cs1, cs2, cs3, cs4, cs5, cs6,
689 cs7, ef, le, lowdelay, throughput, reliability, a numeric value,
690 or none to use the operating system default. This option may
691 take one or two arguments, separated by whitespace. If one argu‐
692 ment is specified, it is used as the packet class uncondition‐
693 ally. If two values are specified, the first is automatically
694 selected for interactive sessions and the second for non-interac‐
695 tive sessions. The default is af21 (Low-Latency Data) for inter‐
696 active sessions and cs1 (Lower Effort) for non-interactive ses‐
697 sions.
698 KbdInteractiveAuthentication
700 Specifies whether to use keyboard-interactive authentication.
701 The argument to this keyword must be yes (the default) or no.
702 ChallengeResponseAuthentication is a deprecated alias for this.
703 KbdInteractiveDevices
705 Specifies the list of methods to use in keyboard-interactive au‐
706 thentication. Multiple method names must be comma-separated.
707 The default is to use the server specified list. The methods
708 available vary depending on what the server supports. For an
709 OpenSSH server, it may be zero or more of: bsdauth and pam.
710 KexAlgorithms
712 The default is handled system-wide by crypto-policies(7). Infor‐
713 mation about defaults, how to modify the defaults and how to cus‐
714 tomize existing policies with sub-policies are present in manual
715 page update-crypto-policies(8).
716 Specifies the available KEX (Key Exchange) algorithms. Multiple
718 algorithms must be comma-separated. If the specified list begins
719 with a ‘+’ character, then the specified methods will be appended
720 to the built-in openssh default set instead of replacing them.
721 If the specified list begins with a ‘-’ character, then the spec‐
722 ified algorithms (including wildcards) will be removed from the
723 built-in openssh default set instead of replacing them. If the
724 specified list begins with a ‘^’ character, then the specified
725 algorithms will be placed at the head of the built-in openssh de‐
726 fault set.
727 The list of available key exchange algorithms may also be ob‐
729 tained using "ssh -Q kex".
730 KnownHostsCommand
732 Specifies a command to use to obtain a list of host keys, in ad‐
733 dition to those listed in UserKnownHostsFile and
734 GlobalKnownHostsFile. This command is executed after the files
735 have been read. It may write host key lines to standard output
736 in identical format to the usual files (described in the
737 VERIFYING HOST KEYS section in ssh(1)). Arguments to
738 KnownHostsCommand accept the tokens described in the TOKENS sec‐
739 tion. The command may be invoked multiple times per connection:
740 once when preparing the preference list of host key algorithms to
741 use, again to obtain the host key for the requested host name
742 and, if CheckHostIP is enabled, one more time to obtain the host
743 key matching the server's address. If the command exits abnor‐
744 mally or returns a non-zero exit status then the connection is
745 terminated.
746 LocalCommand
748 Specifies a command to execute on the local machine after suc‐
749 cessfully connecting to the server. The command string extends
750 to the end of the line, and is executed with the user's shell.
751 Arguments to LocalCommand accept the tokens described in the
752 TOKENS section.
753 The command is run synchronously and does not have access to the
755 session of the ssh(1) that spawned it. It should not be used for
756 interactive commands.
757 This directive is ignored unless PermitLocalCommand has been en‐
759 abled.
760 LocalForward
762 Specifies that a TCP port on the local machine be forwarded over
763 the secure channel to the specified host and port from the remote
764 machine. The first argument specifies the listener and may be
765 [bind_address:]port or a Unix domain socket path. The second ar‐
766 gument is the destination and may be host:hostport or a Unix do‐
767 main socket path if the remote host supports it.
768 IPv6 addresses can be specified by enclosing addresses in square
770 brackets. Multiple forwardings may be specified, and additional
771 forwardings can be given on the command line. Only the superuser
772 can forward privileged ports. By default, the local port is
773 bound in accordance with the GatewayPorts setting. However, an
774 explicit bind_address may be used to bind the connection to a
775 specific address. The bind_address of localhost indicates that
776 the listening port be bound for local use only, while an empty
777 address or ‘*’ indicates that the port should be available from
778 all interfaces. Unix domain socket paths may use the tokens de‐
779 scribed in the TOKENS section and environment variables as de‐
780 scribed in the ENVIRONMENT VARIABLES section.
781 LogLevel
783 Gives the verbosity level that is used when logging messages from
784 ssh(1). The possible values are: QUIET, FATAL, ERROR, INFO, VER‐
785 BOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO.
786 DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify
787 higher levels of verbose output.
788 LogVerbose
790 Specify one or more overrides to LogLevel. An override consists
791 of a pattern lists that matches the source file, function and
792 line number to force detailed logging for. For example, an over‐
793 ride pattern of:
794 kex.c:*:1000,*:kex_exchange_identification():*,packet.c:*
796 would enable detailed logging for line 1000 of kex.c, everything
798 in the kex_exchange_identification() function, and all code in
799 the packet.c file. This option is intended for debugging and no
800 overrides are enabled by default.
801 MACs The default is handled system-wide by crypto-policies(7). Infor‐
803 mation about defaults, how to modify the defaults and how to cus‐
804 tomize existing policies with sub-policies are present in manual
805 page update-crypto-policies(8).
806 Specifies the MAC (message authentication code) algorithms in or‐
808 der of preference. The MAC algorithm is used for data integrity
809 protection. Multiple algorithms must be comma-separated. If the
810 specified list begins with a ‘+’ character, then the specified
811 algorithms will be appended to the built-in openssh default set
812 instead of replacing them. If the specified list begins with a
813 ‘-’ character, then the specified algorithms (including wild‐
814 cards) will be removed from the built-in openssh default set in‐
815 stead of replacing them. If the specified list begins with a ‘^’
816 character, then the specified algorithms will be placed at the
817 head of the built-in openssh default set.
818 The algorithms that contain "-etm" calculate the MAC after en‐
820 cryption (encrypt-then-mac). These are considered safer and
821 their use recommended.
822 The list of available MAC algorithms may also be obtained using
824 "ssh -Q mac".
825 NoHostAuthenticationForLocalhost
827 Disable host authentication for localhost (loopback addresses).
828 The argument to this keyword must be yes or no (the default).
829 NumberOfPasswordPrompts
831 Specifies the number of password prompts before giving up. The
832 argument to this keyword must be an integer. The default is 3.
833 PasswordAuthentication
835 Specifies whether to use password authentication. The argument
836 to this keyword must be yes (the default) or no.
837 PermitLocalCommand
839 Allow local command execution via the LocalCommand option or us‐
840 ing the !command escape sequence in ssh(1). The argument must be
841 yes or no (the default).
842 PermitRemoteOpen
844 Specifies the destinations to which remote TCP port forwarding is
845 permitted when RemoteForward is used as a SOCKS proxy. The for‐
846 warding specification must be one of the following forms:
847 PermitRemoteOpen host:port
849 PermitRemoteOpen IPv4_addr:port
850 PermitRemoteOpen [IPv6_addr]:port
851 Multiple forwards may be specified by separating them with white‐
853 space. An argument of any can be used to remove all restrictions
854 and permit any forwarding requests. An argument of none can be
855 used to prohibit all forwarding requests. The wildcard ‘*’ can
856 be used for host or port to allow all hosts or ports respec‐
857 tively. Otherwise, no pattern matching or address lookups are
858 performed on supplied names.
859 PKCS11Provider
861 Specifies which PKCS#11 provider to use or none to indicate that
862 no provider should be used (the default). The argument to this
863 keyword is a path to the PKCS#11 shared library ssh(1) should use
864 to communicate with a PKCS#11 token providing keys for user au‐
865 thentication.
866 Port Specifies the port number to connect on the remote host. The de‐
868 fault is 22.
869 PreferredAuthentications
871 Specifies the order in which the client should try authentication
872 methods. This allows a client to prefer one method (e.g.
873 keyboard-interactive) over another method (e.g. password). The
874 default is:
875 gssapi-with-mic,hostbased,publickey,
877 keyboard-interactive,password
878 ProxyCommand
880 Specifies the command to use to connect to the server. The com‐
881 mand string extends to the end of the line, and is executed using
882 the user's shell ‘exec’ directive to avoid a lingering shell
883 process.
884 Arguments to ProxyCommand accept the tokens described in the
886 TOKENS section. The command can be basically anything, and
887 should read from its standard input and write to its standard
888 output. It should eventually connect an sshd(8) server running
889 on some machine, or execute sshd -i somewhere. Host key manage‐
890 ment will be done using the Hostname of the host being connected
891 (defaulting to the name typed by the user). Setting the command
892 to none disables this option entirely. Note that CheckHostIP is
893 not available for connects with a proxy command.
894 This directive is useful in conjunction with nc(1) and its proxy
896 support. For example, the following directive would connect via
897 an HTTP proxy at 192.0.2.0:
898 ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
900 ProxyJump
902 Specifies one or more jump proxies as either [user@]host[:port]
903 or an ssh URI. Multiple proxies may be separated by comma char‐
904 acters and will be visited sequentially. Setting this option
905 will cause ssh(1) to connect to the target host by first making a
906 ssh(1) connection to the specified ProxyJump host and then estab‐
907 lishing a TCP forwarding to the ultimate target from there. Set‐
908 ting the host to none disables this option entirely.
909 Note that this option will compete with the ProxyCommand option -
911 whichever is specified first will prevent later instances of the
912 other from taking effect.
913 Note also that the configuration for the destination host (either
915 supplied via the command-line or the configuration file) is not
916 generally applied to jump hosts. ~/.ssh/config should be used if
917 specific configuration is required for jump hosts.
918 ProxyUseFdpass
920 Specifies that ProxyCommand will pass a connected file descriptor
921 back to ssh(1) instead of continuing to execute and pass data.
922 The default is no.
923 PubkeyAcceptedAlgorithms
925 The default is handled system-wide by crypto-policies(7). Infor‐
926 mation about defaults, how to modify the defaults and how to cus‐
927 tomize existing policies with sub-policies are present in manual
928 page update-crypto-policies(8).
929 Specifies the signature algorithms that will be used for public
931 key authentication as a comma-separated list of patterns. If the
932 specified list begins with a ‘+’ character, then the algorithms
933 after it will be appended to the built-in openssh default instead
934 of replacing it. If the specified list begins with a ‘-’ charac‐
935 ter, then the specified algorithms (including wildcards) will be
936 removed from the built-in openssh default set instead of replac‐
937 ing them. If the specified list begins with a ‘^’ character,
938 then the specified algorithms will be placed at the head of the
939 built-in openssh default set.
940 The list of available signature algorithms may also be obtained
942 using "ssh -Q PubkeyAcceptedAlgorithms".
943 PubkeyAuthentication
945 Specifies whether to try public key authentication. The argument
946 to this keyword must be yes (the default), no, unbound or
947 host-bound. The final two options enable public key authentica‐
948 tion while respectively disabling or enabling the OpenSSH host-
949 bound authentication protocol extension required for restricted
950 ssh-agent(1) forwarding.
951 RekeyLimit
953 Specifies the maximum amount of data that may be transmitted be‐
954 fore the session key is renegotiated, optionally followed by a
955 maximum amount of time that may pass before the session key is
956 renegotiated. The first argument is specified in bytes and may
957 have a suffix of ‘K’, ‘M’, or ‘G’ to indicate Kilobytes,
958 Megabytes, or Gigabytes, respectively. The default is between
959 ‘1G’ and ‘4G’, depending on the cipher. The optional second
960 value is specified in seconds and may use any of the units docu‐
961 mented in the TIME FORMATS section of sshd_config(5). The de‐
962 fault value for RekeyLimit is default none, which means that
963 rekeying is performed after the cipher's default amount of data
964 has been sent or received and no time based rekeying is done.
965 RemoteCommand
967 Specifies a command to execute on the remote machine after suc‐
968 cessfully connecting to the server. The command string extends
969 to the end of the line, and is executed with the user's shell.
970 Arguments to RemoteCommand accept the tokens described in the
971 TOKENS section.
972 RemoteForward
974 Specifies that a TCP port on the remote machine be forwarded over
975 the secure channel. The remote port may either be forwarded to a
976 specified host and port from the local machine, or may act as a
977 SOCKS 4/5 proxy that allows a remote client to connect to arbi‐
978 trary destinations from the local machine. The first argument is
979 the listening specification and may be [bind_address:]port or, if
980 the remote host supports it, a Unix domain socket path. If for‐
981 warding to a specific destination then the second argument must
982 be host:hostport or a Unix domain socket path, otherwise if no
983 destination argument is specified then the remote forwarding will
984 be established as a SOCKS proxy. When acting as a SOCKS proxy,
985 the destination of the connection can be restricted by
986 PermitRemoteOpen.
987 IPv6 addresses can be specified by enclosing addresses in square
989 brackets. Multiple forwardings may be specified, and additional
990 forwardings can be given on the command line. Privileged ports
991 can be forwarded only when logging in as root on the remote ma‐
992 chine. Unix domain socket paths may use the tokens described in
993 the TOKENS section and environment variables as described in the
994 ENVIRONMENT VARIABLES section.
995 If the port argument is 0, the listen port will be dynamically
997 allocated on the server and reported to the client at run time.
998 If the bind_address is not specified, the default is to only bind
1000 to loopback addresses. If the bind_address is ‘*’ or an empty
1001 string, then the forwarding is requested to listen on all inter‐
1002 faces. Specifying a remote bind_address will only succeed if the
1003 server's GatewayPorts option is enabled (see sshd_config(5)).
1004 RequestTTY
1006 Specifies whether to request a pseudo-tty for the session. The
1007 argument may be one of: no (never request a TTY), yes (always re‐
1008 quest a TTY when standard input is a TTY), force (always request
1009 a TTY) or auto (request a TTY when opening a login session).
1010 This option mirrors the -t and -T flags for ssh(1).
1011 RequiredRSASize
1013 Specifies the minimum RSA key size (in bits) that ssh(1) will ac‐
1014 cept. User authentication keys smaller than this limit will be
1015 ignored. Servers that present host keys smaller than this limit
1016 will cause the connection to be terminated. The default is 1024
1017 bits. Note that this limit may only be raised from the default.
1018 RevokedHostKeys
1020 Specifies revoked host public keys. Keys listed in this file
1021 will be refused for host authentication. Note that if this file
1022 does not exist or is not readable, then host authentication will
1023 be refused for all hosts. Keys may be specified as a text file,
1024 listing one public key per line, or as an OpenSSH Key Revocation
1025 List (KRL) as generated by ssh-keygen(1). For more information
1026 on KRLs, see the KEY REVOCATION LISTS section in ssh-keygen(1).
1027 SecurityKeyProvider
1029 Specifies a path to a library that will be used when loading any
1030 FIDO authenticator-hosted keys, overriding the default of using
1031 the built-in USB HID support.
1032 If the specified value begins with a ‘$’ character, then it will
1034 be treated as an environment variable containing the path to the
1035 library.
1036 SendEnv
1038 Specifies what variables from the local environ(7) should be sent
1039 to the server. The server must also support it, and the server
1040 must be configured to accept these environment variables. Note
1041 that the TERM environment variable is always sent whenever a
1042 pseudo-terminal is requested as it is required by the protocol.
1043 Refer to AcceptEnv in sshd_config(5) for how to configure the
1044 server. Variables are specified by name, which may contain wild‐
1045 card characters. Multiple environment variables may be separated
1046 by whitespace or spread across multiple SendEnv directives.
1047 See PATTERNS for more information on patterns.
1049 It is possible to clear previously set SendEnv variable names by
1051 prefixing patterns with -. The default is not to send any envi‐
1052 ronment variables.
1053 ServerAliveCountMax
1055 Sets the number of server alive messages (see below) which may be
1056 sent without ssh(1) receiving any messages back from the server.
1057 If this threshold is reached while server alive messages are be‐
1058 ing sent, ssh will disconnect from the server, terminating the
1059 session. It is important to note that the use of server alive
1060 messages is very different from TCPKeepAlive (below). The server
1061 alive messages are sent through the encrypted channel and there‐
1062 fore will not be spoofable. The TCP keepalive option enabled by
1063 TCPKeepAlive is spoofable. The server alive mechanism is valu‐
1064 able when the client or server depend on knowing when a connec‐
1065 tion has become unresponsive.
1066 The default value is 3. If, for example, ServerAliveInterval
1068 (see below) is set to 15 and ServerAliveCountMax is left at the
1069 default, if the server becomes unresponsive, ssh will disconnect
1070 after approximately 45 seconds.
1071 ServerAliveInterval
1073 Sets a timeout interval in seconds after which if no data has
1074 been received from the server, ssh(1) will send a message through
1075 the encrypted channel to request a response from the server. The
1076 default is 0, indicating that these messages will not be sent to
1077 the server.
1078 SessionType
1080 May be used to either request invocation of a subsystem on the
1081 remote system, or to prevent the execution of a remote command at
1082 all. The latter is useful for just forwarding ports. The argu‐
1083 ment to this keyword must be none (same as the -N option),
1084 subsystem (same as the -s option) or default (shell or command
1085 execution).
1086 SetEnv Directly specify one or more environment variables and their con‐
1088 tents to be sent to the server. Similarly to SendEnv, with the
1089 exception of the TERM variable, the server must be prepared to
1090 accept the environment variable.
1091 StdinNull
1093 Redirects stdin from /dev/null (actually, prevents reading from
1094 stdin). Either this or the equivalent -n option must be used
1095 when ssh is run in the background. The argument to this keyword
1096 must be yes (same as the -n option) or no (the default).
1097 StreamLocalBindMask
1099 Sets the octal file creation mode mask (umask) used when creating
1100 a Unix-domain socket file for local or remote port forwarding.
1101 This option is only used for port forwarding to a Unix-domain
1102 socket file.
1103 The default value is 0177, which creates a Unix-domain socket
1105 file that is readable and writable only by the owner. Note that
1106 not all operating systems honor the file mode on Unix-domain
1107 socket files.
1108 StreamLocalBindUnlink
1110 Specifies whether to remove an existing Unix-domain socket file
1111 for local or remote port forwarding before creating a new one.
1112 If the socket file already exists and StreamLocalBindUnlink is
1113 not enabled, ssh will be unable to forward the port to the Unix-
1114 domain socket file. This option is only used for port forwarding
1115 to a Unix-domain socket file.
1116 The argument must be yes or no (the default).
1118 StrictHostKeyChecking
1120 If this flag is set to yes, ssh(1) will never automatically add
1121 host keys to the ~/.ssh/known_hosts file, and refuses to connect
1122 to hosts whose host key has changed. This provides maximum pro‐
1123 tection against man-in-the-middle (MITM) attacks, though it can
1124 be annoying when the /etc/ssh/ssh_known_hosts file is poorly
1125 maintained or when connections to new hosts are frequently made.
1126 This option forces the user to manually add all new hosts.
1127 If this flag is set to accept-new then ssh will automatically add
1129 new host keys to the user's known_hosts file, but will not permit
1130 connections to hosts with changed host keys. If this flag is set
1131 to no or off, ssh will automatically add new host keys to the
1132 user known hosts files and allow connections to hosts with
1133 changed hostkeys to proceed, subject to some restrictions. If
1134 this flag is set to ask (the default), new host keys will be
1135 added to the user known host files only after the user has con‐
1136 firmed that is what they really want to do, and ssh will refuse
1137 to connect to hosts whose host key has changed. The host keys of
1138 known hosts will be verified automatically in all cases.
1139 SyslogFacility
1141 Gives the facility code that is used when logging messages from
1142 ssh(1). The possible values are: DAEMON, USER, AUTH, LOCAL0, LO‐
1143 CAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. The de‐
1144 fault is USER.
1145 TCPKeepAlive
1147 Specifies whether the system should send TCP keepalive messages
1148 to the other side. If they are sent, death of the connection or
1149 crash of one of the machines will be properly noticed. However,
1150 this means that connections will die if the route is down tempo‐
1151 rarily, and some people find it annoying.
1152 The default is yes (to send TCP keepalive messages), and the
1154 client will notice if the network goes down or the remote host
1155 dies. This is important in scripts, and many users want it too.
1156 To disable TCP keepalive messages, the value should be set to no.
1158 See also ServerAliveInterval for protocol-level keepalives.
1159 Tunnel Request tun(4) device forwarding between the client and the
1161 server. The argument must be yes, point-to-point (layer 3),
1162 ethernet (layer 2), or no (the default). Specifying yes requests
1163 the default tunnel mode, which is point-to-point.
1164 TunnelDevice
1166 Specifies the tun(4) devices to open on the client (local_tun)
1167 and the server (remote_tun).
1168 The argument must be local_tun[:remote_tun]. The devices may be
1170 specified by numerical ID or the keyword any, which uses the next
1171 available tunnel device. If remote_tun is not specified, it de‐
1172 faults to any. The default is any:any.
1173 UpdateHostKeys
1175 Specifies whether ssh(1) should accept notifications of addi‐
1176 tional hostkeys from the server sent after authentication has
1177 completed and add them to UserKnownHostsFile. The argument must
1178 be yes, no or ask. This option allows learning alternate
1179 hostkeys for a server and supports graceful key rotation by al‐
1180 lowing a server to send replacement public keys before old ones
1181 are removed.
1182 Additional hostkeys are only accepted if the key used to authen‐
1184 ticate the host was already trusted or explicitly accepted by the
1185 user, the host was authenticated via UserKnownHostsFile (i.e. not
1186 GlobalKnownHostsFile) and the host was authenticated using a
1187 plain key and not a certificate.
1188 UpdateHostKeys is enabled by default if the user has not overrid‐
1190 den the default UserKnownHostsFile setting and has not enabled
1191 VerifyHostKeyDNS, otherwise UpdateHostKeys will be set to no.
1192 If UpdateHostKeys is set to ask, then the user is asked to con‐
1194 firm the modifications to the known_hosts file. Confirmation is
1195 currently incompatible with ControlPersist, and will be disabled
1196 if it is enabled.
1197 Presently, only sshd(8) from OpenSSH 6.8 and greater support the
1199 "hostkeys@openssh.com" protocol extension used to inform the
1200 client of all the server's hostkeys.
1201 User Specifies the user to log in as. This can be useful when a dif‐
1203 ferent user name is used on different machines. This saves the
1204 trouble of having to remember to give the user name on the com‐
1205 mand line.
1206 UserKnownHostsFile
1208 Specifies one or more files to use for the user host key data‐
1209 base, separated by whitespace. Each filename may use tilde nota‐
1210 tion to refer to the user's home directory, the tokens described
1211 in the TOKENS section and environment variables as described in
1212 the ENVIRONMENT VARIABLES section. The default is
1213 ~/.ssh/known_hosts, ~/.ssh/known_hosts2.
1214 VerifyHostKeyDNS
1216 Specifies whether to verify the remote key using DNS and SSHFP
1217 resource records. If this option is set to yes, the client will
1218 implicitly trust keys that match a secure fingerprint from DNS.
1219 Insecure fingerprints will be handled as if this option was set
1220 to ask. If this option is set to ask, information on fingerprint
1221 match will be displayed, but the user will still need to confirm
1222 new host keys according to the StrictHostKeyChecking option. The
1223 default is no.
1224 See also VERIFYING HOST KEYS in ssh(1).
1226 VisualHostKey
1228 If this flag is set to yes, an ASCII art representation of the
1229 remote host key fingerprint is printed in addition to the finger‐
1230 print string at login and for unknown host keys. If this flag is
1231 set to no (the default), no fingerprint strings are printed at
1232 login and only the fingerprint string will be printed for unknown
1233 host keys.
1234 XAuthLocation
1236 Specifies the full pathname of the xauth(1) program. The default
1237 is /usr/bin/xauth.
1238
1240 A pattern consists of zero or more non-whitespace characters, ‘*’ (a
1241 wildcard that matches zero or more characters), or ‘?’ (a wildcard that
1242 matches exactly one character). For example, to specify a set of decla‐
1243 rations for any host in the ".co.uk" set of domains, the following pat‐
1244 tern could be used:
1245 Host *.co.uk
1247 The following pattern would match any host in the 192.168.0.[0-9] network
1249 range:
1250 Host 192.168.0.?
1252 A pattern-list is a comma-separated list of patterns. Patterns within
1254 pattern-lists may be negated by preceding them with an exclamation mark
1255 (‘!’). For example, to allow a key to be used from anywhere within an
1256 organization except from the "dialup" pool, the following entry (in au‐
1257 thorized_keys) could be used:
1258 from="!*.dialup.example.com,*.example.com"
1260 Note that a negated match will never produce a positive result by itself.
1262 For example, attempting to match "host3" against the following pattern-
1263 list will fail:
1264 from="!host1,!host2"
1266 The solution here is to include a term that will yield a positive match,
1268 such as a wildcard:
1269 from="!host1,!host2,*"
1271
1273 Arguments to some keywords can make use of tokens, which are expanded at
1274 runtime:
1275 %% A literal ‘%’.
1277 %C Hash of %l%h%p%r.
1278 %d Local user's home directory.
1279 %f The fingerprint of the server's host key.
1280 %H The known_hosts hostname or address that is being searched
1281 for.
1282 %h The remote hostname.
1283 %I A string describing the reason for a KnownHostsCommand execu‐
1284 tion: either ADDRESS when looking up a host by address (only
1285 when CheckHostIP is enabled), HOSTNAME when searching by
1286 hostname, or ORDER when preparing the host key algorithm
1287 preference list to use for the destination host.
1288 %i The local user ID.
1289 %K The base64 encoded host key.
1290 %k The host key alias if specified, otherwise the original re‐
1291 mote hostname given on the command line.
1292 %L The local hostname.
1293 %l The local hostname, including the domain name.
1294 %n The original remote hostname, as given on the command line.
1295 %p The remote port.
1296 %r The remote username.
1297 %T The local tun(4) or tap(4) network interface assigned if tun‐
1298 nel forwarding was requested, or "NONE" otherwise.
1299 %t The type of the server host key, e.g. ssh-ed25519.
1300 %u The local username.
1301 CertificateFile, ControlPath, IdentityAgent, IdentityFile,
1303 KnownHostsCommand, LocalForward, Match exec, RemoteCommand,
1304 RemoteForward, and UserKnownHostsFile accept the tokens %%, %C, %d, %h,
1305 %i, %k, %L, %l, %n, %p, %r, and %u.
1306 KnownHostsCommand additionally accepts the tokens %f, %H, %I, %K and %t.
1308 Hostname accepts the tokens %% and %h.
1310 LocalCommand accepts all tokens.
1312 ProxyCommand accepts the tokens %%, %h, %n, %p, and %r.
1314
1316 Arguments to some keywords can be expanded at runtime from environment
1317 variables on the client by enclosing them in ${}, for example
1318 ${HOME}/.ssh would refer to the user's .ssh directory. If a specified
1319 environment variable does not exist then an error will be returned and
1320 the setting for that keyword will be ignored.
1321 The keywords CertificateFile, ControlPath, IdentityAgent, IdentityFile,
1323 KnownHostsCommand, and UserKnownHostsFile support environment variables.
1324 The keywords LocalForward and RemoteForward support environment variables
1325 only for Unix domain socket paths.
1326
1328 ~/.ssh/config
1329 This is the per-user configuration file. The format of this file
1330 is described above. This file is used by the SSH client. Be‐
1331 cause of the potential for abuse, this file must have strict per‐
1332 missions: read/write for the user, and not writable by others.
1333 /etc/ssh/ssh_config
1335 Systemwide configuration file. This file provides defaults for
1336 those values that are not specified in the user's configuration
1337 file, and for those users who do not have a configuration file.
1338 This file must be world-readable.
1339
1341 ssh(1), crypto-policies(7), update-crypto-policies(8)
1342
1344 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
1345 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
1346 de Raadt and Dug Song removed many bugs, re-added newer features and cre‐
1347 ated OpenSSH. Markus Friedl contributed the support for SSH protocol
1348 versions 1.5 and 2.0.
1349BSD March 31, 2022 BSD