1SSH_CONFIG(5) BSD File Formats Manual SSH_CONFIG(5)
2
4 ssh_config — OpenSSH SSH client configuration files
5
7 ssh(1) obtains configuration data from the following sources in the fol‐
8 lowing order:
9 1. command-line options
11 2. user's configuration file (~/.ssh/config)
12 3. GSSAPI configuration file ($HOME/.ssh/config.gssapi)
13 4. Kerberos configuration file ($HOME/.ssh/config.krb)
14 5. system-wide configuration file (/etc/gsissh/ssh_config)
15 For each parameter, the first obtained value will be used. The configu‐
17 ration files contain sections separated by Host specifications, and that
18 section is only applied for hosts that match one of the patterns given in
19 the specification. The matched host name is usually the one given on the
20 command line (see the CanonicalizeHostname option for exceptions).
21 Since the first obtained value for each parameter is used, more host-spe‐
23 cific declarations should be given near the beginning of the file, and
24 general defaults at the end.
25 The file contains keyword-argument pairs, one per line. Lines starting
27 with ‘#’ and empty lines are interpreted as comments. Arguments may
28 optionally be enclosed in double quotes (") in order to represent argu‐
29 ments containing spaces. Configuration options may be separated by
30 whitespace or optional whitespace and exactly one ‘=’; the latter format
31 is useful to avoid the need to quote whitespace when specifying configu‐
32 ration options using the ssh, scp, and sftp -o option.
33 The possible keywords and their meanings are as follows (note that key‐
35 words are case-insensitive and arguments are case-sensitive):
36 Host Restricts the following declarations (up to the next Host or
38 Match keyword) to be only for those hosts that match one of the
39 patterns given after the keyword. If more than one pattern is
40 provided, they should be separated by whitespace. A single ‘*’
41 as a pattern can be used to provide global defaults for all
42 hosts. The host is usually the hostname argument given on the
43 command line (see the CanonicalizeHostname keyword for excep‐
44 tions).
45 A pattern entry may be negated by prefixing it with an exclama‐
47 tion mark (‘!’). If a negated entry is matched, then the Host
48 entry is ignored, regardless of whether any other patterns on the
49 line match. Negated matches are therefore useful to provide
50 exceptions for wildcard matches.
51 See PATTERNS for more information on patterns.
53 Match Restricts the following declarations (up to the next Host or
55 Match keyword) to be used only when the conditions following the
56 Match keyword are satisfied. Match conditions are specified
57 using one or more criteria or the single token all which always
58 matches. The available criteria keywords are: canonical, final,
59 exec, host, originalhost, user, and localuser. The all criteria
60 must appear alone or immediately after canonical or final. Other
61 criteria may be combined arbitrarily. All criteria but all,
62 canonical, and final require an argument. Criteria may be
63 negated by prepending an exclamation mark (‘!’).
64 The canonical keyword matches only when the configuration file is
66 being re-parsed after hostname canonicalization (see the
67 CanonicalizeHostname option). This may be useful to specify con‐
68 ditions that work with canonical host names only.
69 The final keyword requests that the configuration be re-parsed
71 (regardless of whether CanonicalizeHostname is enabled), and
72 matches only during this final pass. If CanonicalizeHostname is
73 enabled, then canonical and final match during the same pass.
74 The exec keyword executes the specified command under the user's
76 shell. If the command returns a zero exit status then the condi‐
77 tion is considered true. Commands containing whitespace charac‐
78 ters must be quoted. Arguments to exec accept the tokens
79 described in the TOKENS section.
80 The other keywords' criteria must be single entries or comma-sep‐
82 arated lists and may use the wildcard and negation operators
83 described in the PATTERNS section. The criteria for the host
84 keyword are matched against the target hostname, after any sub‐
85 stitution by the Hostname or CanonicalizeHostname options. The
86 originalhost keyword matches against the hostname as it was spec‐
87 ified on the command-line. The user keyword matches against the
88 target username on the remote host. The localuser keyword
89 matches against the name of the local user running ssh(1) (this
90 keyword may be useful in system-wide ssh_config files).
91 AddKeysToAgent
93 Specifies whether keys should be automatically added to a running
94 ssh-agent(1). If this option is set to yes and a key is loaded
95 from a file, the key and its passphrase are added to the agent
96 with the default lifetime, as if by ssh-add(1). If this option
97 is set to ask, ssh(1) will require confirmation using the
98 SSH_ASKPASS program before adding a key (see ssh-add(1) for
99 details). If this option is set to confirm, each use of the key
100 must be confirmed, as if the -c option was specified to
101 ssh-add(1). If this option is set to no, no keys are added to
102 the agent. The argument must be yes, confirm, ask, or no (the
103 default).
104 AddressFamily
106 Specifies which address family to use when connecting. Valid
107 arguments are any (the default), inet (use IPv4 only), or inet6
108 (use IPv6 only).
109 BatchMode
111 If set to yes, passphrase/password querying will be disabled.
112 This option is useful in scripts and other batch jobs where no
113 user is present to supply the password. The argument must be yes
114 or no (the default).
115 BindAddress
117 Use the specified address on the local machine as the source
118 address of the connection. Only useful on systems with more than
119 one address.
120 BindInterface
122 Use the address of the specified interface on the local machine
123 as the source address of the connection.
124 CanonicalDomains
126 When CanonicalizeHostname is enabled, this option specifies the
127 list of domain suffixes in which to search for the specified des‐
128 tination host.
129 CanonicalizeFallbackLocal
131 Specifies whether to fail with an error when hostname canonical‐
132 ization fails. The default, yes, will attempt to look up the
133 unqualified hostname using the system resolver's search rules. A
134 value of no will cause ssh(1) to fail instantly if
135 CanonicalizeHostname is enabled and the target hostname cannot be
136 found in any of the domains specified by CanonicalDomains.
137 CanonicalizeHostname
139 Controls whether explicit hostname canonicalization is performed.
140 The default, no, is not to perform any name rewriting and let the
141 system resolver handle all hostname lookups. If set to yes then,
142 for connections that do not use a ProxyCommand or ProxyJump,
143 ssh(1) will attempt to canonicalize the hostname specified on the
144 command line using the CanonicalDomains suffixes and
145 CanonicalizePermittedCNAMEs rules. If CanonicalizeHostname is
146 set to always, then canonicalization is applied to proxied con‐
147 nections too.
148 If this option is enabled, then the configuration files are pro‐
150 cessed again using the new target name to pick up any new config‐
151 uration in matching Host and Match stanzas.
152 CanonicalizeMaxDots
154 Specifies the maximum number of dot characters in a hostname
155 before canonicalization is disabled. The default, 1, allows a
156 single dot (i.e. hostname.subdomain).
157 CanonicalizePermittedCNAMEs
159 Specifies rules to determine whether CNAMEs should be followed
160 when canonicalizing hostnames. The rules consist of one or more
161 arguments of source_domain_list:target_domain_list, where
162 source_domain_list is a pattern-list of domains that may follow
163 CNAMEs in canonicalization, and target_domain_list is a pattern-
164 list of domains that they may resolve to.
165 For example, "*.a.example.com:*.b.example.com,*.c.example.com"
167 will allow hostnames matching "*.a.example.com" to be canonical‐
168 ized to names in the "*.b.example.com" or "*.c.example.com"
169 domains.
170 CASignatureAlgorithms
172 Specifies which algorithms are allowed for signing of certifi‐
173 cates by certificate authorities (CAs). The default is:
174 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
176 ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
177 ssh(1) will not accept host certificates signed using algorithms
179 other than those specified.
180 CertificateFile
182 Specifies a file from which the user's certificate is read. A
183 corresponding private key must be provided separately in order to
184 use this certificate either from an IdentityFile directive or -i
185 flag to ssh(1), via ssh-agent(1), or via a PKCS11Provider.
186 Arguments to CertificateFile may use the tilde syntax to refer to
188 a user's home directory or the tokens described in the TOKENS
189 section.
190 It is possible to have multiple certificate files specified in
192 configuration files; these certificates will be tried in
193 sequence. Multiple CertificateFile directives will add to the
194 list of certificates used for authentication.
195 ChallengeResponseAuthentication
197 Specifies whether to use challenge-response authentication. The
198 argument to this keyword must be yes (the default) or no.
199 CheckHostIP
201 If set to yes (the default), ssh(1) will additionally check the
202 host IP address in the known_hosts file. This allows it to
203 detect if a host key changed due to DNS spoofing and will add
204 addresses of destination hosts to ~/.ssh/known_hosts in the
205 process, regardless of the setting of StrictHostKeyChecking. If
206 the option is set to no, the check will not be executed.
207 Ciphers
209 Specifies the ciphers allowed and their order of preference.
210 Multiple ciphers must be comma-separated. If the specified list
211 begins with a ‘+’ character, then the specified ciphers will be
212 appended to the default set instead of replacing them. If the
213 specified list begins with a ‘-’ character, then the specified
214 ciphers (including wildcards) will be removed from the default
215 set instead of replacing them. If the specified list begins with
216 a ‘^’ character, then the specified ciphers will be placed at the
217 head of the default set.
218 The supported ciphers are:
220 3des-cbc
222 aes128-cbc
223 aes192-cbc
224 aes256-cbc
225 aes128-ctr
226 aes192-ctr
227 aes256-ctr
228 aes128-gcm@openssh.com
229 aes256-gcm@openssh.com
230 chacha20-poly1305@openssh.com
231 The default is handled system-wide by crypto-policies(7). To see
233 the defaults and how to modify this default, see manual page
234 update-crypto-policies(8).
235 The list of available ciphers may also be obtained using "ssh -Q
237 cipher".
238 ClearAllForwardings
240 Specifies that all local, remote, and dynamic port forwardings
241 specified in the configuration files or on the command line be
242 cleared. This option is primarily useful when used from the
243 ssh(1) command line to clear port forwardings set in configura‐
244 tion files, and is automatically set by scp(1) and sftp(1). The
245 argument must be yes or no (the default).
246 Compression
248 Specifies whether to use compression. The argument must be yes
249 or no (the default).
250 ConnectionAttempts
252 Specifies the number of tries (one per second) to make before
253 exiting. The argument must be an integer. This may be useful in
254 scripts if the connection sometimes fails. The default is 1.
255 ConnectTimeout
257 Specifies the timeout (in seconds) used when connecting to the
258 SSH server, instead of using the default system TCP timeout.
259 This timeout is applied both to establishing the connection and
260 to performing the initial SSH protocol handshake and key
261 exchange.
262 ControlMaster
264 Enables the sharing of multiple sessions over a single network
265 connection. When set to yes, ssh(1) will listen for connections
266 on a control socket specified using the ControlPath argument.
267 Additional sessions can connect to this socket using the same
268 ControlPath with ControlMaster set to no (the default). These
269 sessions will try to reuse the master instance's network connec‐
270 tion rather than initiating new ones, but will fall back to con‐
271 necting normally if the control socket does not exist, or is not
272 listening.
273 Setting this to ask will cause ssh(1) to listen for control con‐
275 nections, but require confirmation using ssh-askpass(1). If the
276 ControlPath cannot be opened, ssh(1) will continue without con‐
277 necting to a master instance.
278 X11 and ssh-agent(1) forwarding is supported over these multi‐
280 plexed connections, however the display and agent forwarded will
281 be the one belonging to the master connection i.e. it is not pos‐
282 sible to forward multiple displays or agents.
283 Two additional options allow for opportunistic multiplexing: try
285 to use a master connection but fall back to creating a new one if
286 one does not already exist. These options are: auto and autoask.
287 The latter requires confirmation like the ask option.
288 ControlPath
290 Specify the path to the control socket used for connection shar‐
291 ing as described in the ControlMaster section above or the string
292 none to disable connection sharing. Arguments to ControlPath may
293 use the tilde syntax to refer to a user's home directory or the
294 tokens described in the TOKENS section. It is recommended that
295 any ControlPath used for opportunistic connection sharing include
296 at least %h, %p, and %r (or alternatively %C) and be placed in a
297 directory that is not writable by other users. This ensures that
298 shared connections are uniquely identified.
299 ControlPersist
301 When used in conjunction with ControlMaster, specifies that the
302 master connection should remain open in the background (waiting
303 for future client connections) after the initial client connec‐
304 tion has been closed. If set to no, then the master connection
305 will not be placed into the background, and will close as soon as
306 the initial client connection is closed. If set to yes or 0,
307 then the master connection will remain in the background indefi‐
308 nitely (until killed or closed via a mechanism such as the "ssh
309 -O exit"). If set to a time in seconds, or a time in any of the
310 formats documented in sshd_config(5), then the backgrounded mas‐
311 ter connection will automatically terminate after it has remained
312 idle (with no client connections) for the specified time.
313 DynamicForward
315 Specifies that a TCP port on the local machine be forwarded over
316 the secure channel, and the application protocol is then used to
317 determine where to connect to from the remote machine.
318 The argument must be [bind_address:]port. IPv6 addresses can be
320 specified by enclosing addresses in square brackets. By default,
321 the local port is bound in accordance with the GatewayPorts set‐
322 ting. However, an explicit bind_address may be used to bind the
323 connection to a specific address. The bind_address of localhost
324 indicates that the listening port be bound for local use only,
325 while an empty address or ‘*’ indicates that the port should be
326 available from all interfaces.
327 Currently the SOCKS4 and SOCKS5 protocols are supported, and
329 ssh(1) will act as a SOCKS server. Multiple forwardings may be
330 specified, and additional forwardings can be given on the command
331 line. Only the superuser can forward privileged ports.
332 EnableSSHKeysign
334 Setting this option to yes in the global client configuration
335 file /etc/gsissh/ssh_config enables the use of the helper program
336 ssh-keysign(8) during HostbasedAuthentication. The argument must
337 be yes or no (the default). This option should be placed in the
338 non-hostspecific section. See ssh-keysign(8) for more informa‐
339 tion.
340 EscapeChar
342 Sets the escape character (default: ‘~’). The escape character
343 can also be set on the command line. The argument should be a
344 single character, ‘^’ followed by a letter, or none to disable
345 the escape character entirely (making the connection transparent
346 for binary data).
347 ExitOnForwardFailure
349 Specifies whether ssh(1) should terminate the connection if it
350 cannot set up all requested dynamic, tunnel, local, and remote
351 port forwardings, (e.g. if either end is unable to bind and lis‐
352 ten on a specified port). Note that ExitOnForwardFailure does
353 not apply to connections made over port forwardings and will not,
354 for example, cause ssh(1) to exit if TCP connections to the ulti‐
355 mate forwarding destination fail. The argument must be yes or no
356 (the default).
357 FingerprintHash
359 Specifies the hash algorithm used when displaying key finger‐
360 prints. Valid options are: md5 and sha256 (the default).
361 ForwardAgent
363 Specifies whether the connection to the authentication agent (if
364 any) will be forwarded to the remote machine. The argument must
365 be yes or no (the default).
366 Agent forwarding should be enabled with caution. Users with the
368 ability to bypass file permissions on the remote host (for the
369 agent's Unix-domain socket) can access the local agent through
370 the forwarded connection. An attacker cannot obtain key material
371 from the agent, however they can perform operations on the keys
372 that enable them to authenticate using the identities loaded into
373 the agent.
374 ForwardX11
376 Specifies whether X11 connections will be automatically redi‐
377 rected over the secure channel and DISPLAY set. The argument
378 must be yes or no (the default).
379 X11 forwarding should be enabled with caution. Users with the
381 ability to bypass file permissions on the remote host (for the
382 user's X11 authorization database) can access the local X11 dis‐
383 play through the forwarded connection. An attacker may then be
384 able to perform activities such as keystroke monitoring if the
385 ForwardX11Trusted option is also enabled.
386 ForwardX11Timeout
388 Specify a timeout for untrusted X11 forwarding using the format
389 described in the TIME FORMATS section of sshd_config(5). X11
390 connections received by ssh(1) after this time will be refused.
391 Setting ForwardX11Timeout to zero will disable the timeout and
392 permit X11 forwarding for the life of the connection. The
393 default is to disable untrusted X11 forwarding after twenty min‐
394 utes has elapsed.
395 ForwardX11Trusted
397 If this option is set to yes, remote X11 clients will have full
398 access to the original X11 display.
399 If this option is set to no (the default), remote X11 clients
401 will be considered untrusted and prevented from stealing or tam‐
402 pering with data belonging to trusted X11 clients. Furthermore,
403 the xauth(1) token used for the session will be set to expire
404 after 20 minutes. Remote clients will be refused access after
405 this time.
406 See the X11 SECURITY extension specification for full details on
408 the restrictions imposed on untrusted clients.
409 GatewayPorts
411 Specifies whether remote hosts are allowed to connect to local
412 forwarded ports. By default, ssh(1) binds local port forwardings
413 to the loopback address. This prevents other remote hosts from
414 connecting to forwarded ports. GatewayPorts can be used to spec‐
415 ify that ssh should bind local port forwardings to the wildcard
416 address, thus allowing remote hosts to connect to forwarded
417 ports. The argument must be yes or no (the default).
418 GlobalKnownHostsFile
420 Specifies one or more files to use for the global host key data‐
421 base, separated by whitespace. The default is
422 /etc/gsissh/ssh_known_hosts, /etc/gsissh/ssh_known_hosts2.
423 GSSAPIAuthentication
425 Specifies whether user authentication based on GSSAPI is allowed.
426 The default is yes.
427 GSSAPIClientIdentity
429 If set, specifies the GSSAPI client identity that ssh should use
430 when connecting to the server. The default is unset, which means
431 that the default identity will be used.
432 GSSAPIDelegateCredentials
434 Forward (delegate) credentials to the server. The default is
435 yes.
436 GSSAPIKeyExchange
438 Specifies whether key exchange based on GSSAPI may be used. When
439 using GSSAPI key exchange the server need not have a host key.
440 The default is “yes”.
441 GSSAPIRenewalForcesRekey
443 If set to “yes” then renewal of the client's GSSAPI credentials
444 will force the rekeying of the ssh connection. With a compatible
445 server, this will delegate the renewed credentials to a session
446 on the server.
447 Checks are made to ensure that credentials are only propagated
449 when the new credentials match the old ones on the originating
450 client and where the receiving server still has the old set in
451 its cache.
452 The default is “no”.
454 For this to work GSSAPIKeyExchange needs to be enabled in the
456 server and also used by the client.
457 GSSAPIServerIdentity
459 If set, specifies the GSSAPI server identity that ssh should
460 expect when connecting to the server. The default is unset, which
461 means that the expected GSSAPI server identity will be determined
462 from the target hostname.
463 GSSAPITrustDns
465 Set to “yes” to indicate that the DNS is trusted to securely
466 canonicalize the name of the host being connected to. If “no”,
467 the hostname entered on the command line will be passed untouched
468 to the GSSAPI library. The default is “no”.
469 GSSAPIKexAlgorithms
471 The list of key exchange algorithms that are offered for GSSAPI
472 key exchange. Possible values are
473 gss-gex-sha1-,
475 gss-group1-sha1-,
476 gss-group14-sha1-,
477 gss-group14-sha256-,
478 gss-group16-sha512-,
479 gss-nistp256-sha256-,
480 gss-curve25519-sha256-
481 The default is handled system-wide by crypto-policies(7). To see
483 the defaults and how to modify this default, see manual page
484 update-crypto-policies(8).
485 HashKnownHosts
487 Indicates that ssh(1) should hash host names and addresses when
488 they are added to ~/.ssh/known_hosts. These hashed names may be
489 used normally by ssh(1) and sshd(8), but they do not reveal iden‐
490 tifying information should the file's contents be disclosed. The
491 default is no. Note that existing names and addresses in known
492 hosts files will not be converted automatically, but may be manu‐
493 ally hashed using ssh-keygen(1).
494 HostbasedAuthentication
496 Specifies whether to try rhosts based authentication with public
497 key authentication. The argument must be yes or no (the
498 default).
499 HostbasedKeyTypes
501 Specifies the key types that will be used for hostbased authenti‐
502 cation as a comma-separated list of patterns. Alternately if the
503 specified list begins with a ‘+’ character, then the specified
504 key types will be appended to the default set instead of replac‐
505 ing them. If the specified list begins with a ‘-’ character,
506 then the specified key types (including wildcards) will be
507 removed from the default set instead of replacing them. If the
508 specified list begins with a ‘^’ character, then the specified
509 key types will be placed at the head of the default set. The
510 default for this option is:
511 ecdsa-sha2-nistp256-cert-v01@openssh.com,
513 ecdsa-sha2-nistp384-cert-v01@openssh.com,
514 ecdsa-sha2-nistp521-cert-v01@openssh.com,
515 ssh-ed25519-cert-v01@openssh.com,
516 rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,
517 ssh-rsa-cert-v01@openssh.com,
518 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
519 ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
520 The -Q option of ssh(1) may be used to list supported key types.
522 HostKeyAlgorithms
524 Specifies the host key algorithms that the client wants to use in
525 order of preference. Alternately if the specified list begins
526 with a ‘+’ character, then the specified key types will be
527 appended to the default set instead of replacing them. If the
528 specified list begins with a ‘-’ character, then the specified
529 key types (including wildcards) will be removed from the default
530 set instead of replacing them. If the specified list begins with
531 a ‘^’ character, then the specified key types will be placed at
532 the head of the default set. The default for this option is:
533 ecdsa-sha2-nistp256-cert-v01@openssh.com,
535 ecdsa-sha2-nistp384-cert-v01@openssh.com,
536 ecdsa-sha2-nistp521-cert-v01@openssh.com,
537 ssh-ed25519-cert-v01@openssh.com,
538 rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,
539 ssh-rsa-cert-v01@openssh.com,
540 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
541 ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
542 If hostkeys are known for the destination host then this default
544 is modified to prefer their algorithms.
545 The list of available key types may also be obtained using "ssh
547 -Q key".
548 HostKeyAlias
550 Specifies an alias that should be used instead of the real host
551 name when looking up or saving the host key in the host key data‐
552 base files and when validating host certificates. This option is
553 useful for tunneling SSH connections or for multiple servers run‐
554 ning on a single host.
555 Hostname
557 Specifies the real host name to log into. This can be used to
558 specify nicknames or abbreviations for hosts. Arguments to
559 Hostname accept the tokens described in the TOKENS section.
560 Numeric IP addresses are also permitted (both on the command line
561 and in Hostname specifications). The default is the name given
562 on the command line.
563 IdentitiesOnly
565 Specifies that ssh(1) should only use the configured authentica‐
566 tion identity and certificate files (either the default files, or
567 those explicitly configured in the ssh_config files or passed on
568 the ssh(1) command-line), even if ssh-agent(1) or a
569 PKCS11Provider offers more identities. The argument to this key‐
570 word must be yes or no (the default). This option is intended
571 for situations where ssh-agent offers many different identities.
572 IdentityAgent
574 Specifies the UNIX-domain socket used to communicate with the
575 authentication agent.
576 This option overrides the SSH_AUTH_SOCK environment variable and
578 can be used to select a specific agent. Setting the socket name
579 to none disables the use of an authentication agent. If the
580 string "SSH_AUTH_SOCK" is specified, the location of the socket
581 will be read from the SSH_AUTH_SOCK environment variable. Other‐
582 wise if the specified value begins with a ‘$’ character, then it
583 will be treated as an environment variable containing the loca‐
584 tion of the socket.
585 Arguments to IdentityAgent may use the tilde syntax to refer to a
587 user's home directory or the tokens described in the TOKENS sec‐
588 tion.
589 IdentityFile
591 Specifies a file from which the user's DSA, ECDSA, Ed25519 or RSA
592 authentication identity is read. The default is ~/.ssh/id_dsa,
593 ~/.ssh/id_ecdsa, ~/.ssh/id_ed25519 and ~/.ssh/id_rsa. Addition‐
594 ally, any identities represented by the authentication agent will
595 be used for authentication unless IdentitiesOnly is set. If no
596 certificates have been explicitly specified by CertificateFile,
597 ssh(1) will try to load certificate information from the filename
598 obtained by appending -cert.pub to the path of a specified
599 IdentityFile.
600 Arguments to IdentityFile may use the tilde syntax to refer to a
602 user's home directory or the tokens described in the TOKENS sec‐
603 tion.
604 It is possible to have multiple identity files specified in con‐
606 figuration files; all these identities will be tried in sequence.
607 Multiple IdentityFile directives will add to the list of identi‐
608 ties tried (this behaviour differs from that of other configura‐
609 tion directives).
610 IdentityFile may be used in conjunction with IdentitiesOnly to
612 select which identities in an agent are offered during authenti‐
613 cation. IdentityFile may also be used in conjunction with
614 CertificateFile in order to provide any certificate also needed
615 for authentication with the identity.
616 The authentication identity can be also specified in a form of
618 PKCS#11 URI starting with a string pkcs11:. There is supported a
619 subset of the PKCS#11 URI as defined in RFC 7512 (implemented
620 path arguments id, manufacturer, object, token and query argu‐
621 ments module-path and pin-value ). The URI can not be in quotes.
622 IgnoreUnknown
624 Specifies a pattern-list of unknown options to be ignored if they
625 are encountered in configuration parsing. This may be used to
626 suppress errors if ssh_config contains options that are unrecog‐
627 nised by ssh(1). It is recommended that IgnoreUnknown be listed
628 early in the configuration file as it will not be applied to
629 unknown options that appear before it.
630 Include
632 Include the specified configuration file(s). Multiple pathnames
633 may be specified and each pathname may contain glob(7) wildcards
634 and, for user configurations, shell-like ‘~’ references to user
635 home directories. Files without absolute paths are assumed to be
636 in ~/.ssh if included in a user configuration file or /etc/ssh if
637 included from the system configuration file. Include directive
638 may appear inside a Match or Host block to perform conditional
639 inclusion.
640 IPQoS Specifies the IPv4 type-of-service or DSCP class for connections.
642 Accepted values are af11, af12, af13, af21, af22, af23, af31,
643 af32, af33, af41, af42, af43, cs0, cs1, cs2, cs3, cs4, cs5, cs6,
644 cs7, ef, lowdelay, throughput, reliability, a numeric value, or
645 none to use the operating system default. This option may take
646 one or two arguments, separated by whitespace. If one argument
647 is specified, it is used as the packet class unconditionally. If
648 two values are specified, the first is automatically selected for
649 interactive sessions and the second for non-interactive sessions.
650 The default is af21 (Low-Latency Data) for interactive sessions
651 and cs1 (Lower Effort) for non-interactive sessions.
652 KbdInteractiveAuthentication
654 Specifies whether to use keyboard-interactive authentication.
655 The argument to this keyword must be yes (the default) or no.
656 KbdInteractiveDevices
658 Specifies the list of methods to use in keyboard-interactive
659 authentication. Multiple method names must be comma-separated.
660 The default is to use the server specified list. The methods
661 available vary depending on what the server supports. For an
662 OpenSSH server, it may be zero or more of: bsdauth and pam.
663 KexAlgorithms
665 Specifies the available KEX (Key Exchange) algorithms. Multiple
666 algorithms must be comma-separated. If the specified list begins
667 with a ‘+’ character, then the specified methods will be appended
668 to the default set instead of replacing them. If the specified
669 list begins with a ‘-’ character, then the specified methods
670 (including wildcards) will be removed from the default set
671 instead of replacing them. If the specified list begins with a
672 ‘^’ character, then the specified methods will be placed at the
673 head of the default set. The default is handled system-wide by
674 crypto-policies(7). To see the defaults and how to modify this
675 default, see manual page update-crypto-policies(8).
676 The list of available key exchange algorithms may also be
678 obtained using "ssh -Q kex".
679 LocalCommand
681 Specifies a command to execute on the local machine after suc‐
682 cessfully connecting to the server. The command string extends
683 to the end of the line, and is executed with the user's shell.
684 Arguments to LocalCommand accept the tokens described in the
685 TOKENS section.
686 The command is run synchronously and does not have access to the
688 session of the ssh(1) that spawned it. It should not be used for
689 interactive commands.
690 This directive is ignored unless PermitLocalCommand has been
692 enabled.
693 LocalForward
695 Specifies that a TCP port on the local machine be forwarded over
696 the secure channel to the specified host and port from the remote
697 machine. The first argument must be [bind_address:]port and the
698 second argument must be host:hostport. IPv6 addresses can be
699 specified by enclosing addresses in square brackets. Multiple
700 forwardings may be specified, and additional forwardings can be
701 given on the command line. Only the superuser can forward privi‐
702 leged ports. By default, the local port is bound in accordance
703 with the GatewayPorts setting. However, an explicit bind_address
704 may be used to bind the connection to a specific address. The
705 bind_address of localhost indicates that the listening port be
706 bound for local use only, while an empty address or ‘*’ indicates
707 that the port should be available from all interfaces.
708 LogLevel
710 Gives the verbosity level that is used when logging messages from
711 ssh(1). The possible values are: QUIET, FATAL, ERROR, INFO, VER‐
712 BOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO.
713 DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify
714 higher levels of verbose output.
715 MACs Specifies the MAC (message authentication code) algorithms in
717 order of preference. The MAC algorithm is used for data
718 integrity protection. Multiple algorithms must be comma-sepa‐
719 rated. If the specified list begins with a ‘+’ character, then
720 the specified algorithms will be appended to the default set
721 instead of replacing them. If the specified list begins with a
722 ‘-’ character, then the specified algorithms (including wild‐
723 cards) will be removed from the default set instead of replacing
724 them. If the specified list begins with a ‘^’ character, then
725 the specified algorithms will be placed at the head of the
726 default set.
727 The algorithms that contain "-etm" calculate the MAC after
729 encryption (encrypt-then-mac). These are considered safer and
730 their use recommended.
731 The default is handled system-wide by crypto-policies(7). To see
733 the defaults and how to modify this default, see manual page
734 update-crypto-policies(8).
735 The list of available MAC algorithms may also be obtained using
737 "ssh -Q mac".
738 NoHostAuthenticationForLocalhost
740 Disable host authentication for localhost (loopback addresses).
741 The argument to this keyword must be yes or no (the default).
742 NumberOfPasswordPrompts
744 Specifies the number of password prompts before giving up. The
745 argument to this keyword must be an integer. The default is 3.
746 PasswordAuthentication
748 Specifies whether to use password authentication. The argument
749 to this keyword must be yes (the default) or no.
750 PermitLocalCommand
752 Allow local command execution via the LocalCommand option or
753 using the !command escape sequence in ssh(1). The argument must
754 be yes or no (the default).
755 PKCS11Provider
757 Specifies which PKCS#11 provider to use or none to indicate that
758 no provider should be used (the default). The argument to this
759 keyword is a path to the PKCS#11 shared library ssh(1) should use
760 to communicate with a PKCS#11 token providing keys for user
761 authentication.
762 Port Specifies the port number to connect on the remote host. The
764 default is 22.
765 PreferredAuthentications
767 Specifies the order in which the client should try authentication
768 methods. This allows a client to prefer one method (e.g.
769 keyboard-interactive) over another method (e.g. password). The
770 default is:
771 gssapi-keyex,gssapi-with-mic,hostbased,publickey,
773 keyboard-interactive,password
774 ProxyCommand
776 Specifies the command to use to connect to the server. The com‐
777 mand string extends to the end of the line, and is executed using
778 the user's shell ‘exec’ directive to avoid a lingering shell
779 process.
780 Arguments to ProxyCommand accept the tokens described in the
782 TOKENS section. The command can be basically anything, and
783 should read from its standard input and write to its standard
784 output. It should eventually connect an sshd(8) server running
785 on some machine, or execute sshd -i somewhere. Host key manage‐
786 ment will be done using the Hostname of the host being connected
787 (defaulting to the name typed by the user). Setting the command
788 to none disables this option entirely. Note that CheckHostIP is
789 not available for connects with a proxy command.
790 This directive is useful in conjunction with nc(1) and its proxy
792 support. For example, the following directive would connect via
793 an HTTP proxy at 192.0.2.0:
794 ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
796 ProxyJump
798 Specifies one or more jump proxies as either [user@]host[:port]
799 or an ssh URI. Multiple proxies may be separated by comma char‐
800 acters and will be visited sequentially. Setting this option
801 will cause ssh(1) to connect to the target host by first making a
802 ssh(1) connection to the specified ProxyJump host and then estab‐
803 lishing a TCP forwarding to the ultimate target from there.
804 Note that this option will compete with the ProxyCommand option -
806 whichever is specified first will prevent later instances of the
807 other from taking effect.
808 Note also that the configuration for the destination host (either
810 supplied via the command-line or the configuration file) is not
811 generally applied to jump hosts. ~/.ssh/config should be used if
812 specific configuration is required for jump hosts.
813 ProxyUseFdpass
815 Specifies that ProxyCommand will pass a connected file descriptor
816 back to ssh(1) instead of continuing to execute and pass data.
817 The default is no.
818 PubkeyAcceptedKeyTypes
820 Specifies the key types that will be used for public key authen‐
821 tication as a comma-separated list of patterns. If the specified
822 list begins with a ‘+’ character, then the key types after it
823 will be appended to the default instead of replacing it. If the
824 specified list begins with a ‘-’ character, then the specified
825 key types (including wildcards) will be removed from the default
826 set instead of replacing them. If the specified list begins with
827 a ‘^’ character, then the specified key types will be placed at
828 the head of the default set. The default is handled system-wide
829 by crypto-policies(7). To see the defaults and how to modify
830 this default, see manual page update-crypto-policies(8).
831 The list of available key types may also be obtained using "ssh
833 -Q key".
834 PubkeyAuthentication
836 Specifies whether to try public key authentication. The argument
837 to this keyword must be yes (the default) or no.
838 RekeyLimit
840 Specifies the maximum amount of data that may be transmitted
841 before the session key is renegotiated, optionally followed a
842 maximum amount of time that may pass before the session key is
843 renegotiated. The first argument is specified in bytes and may
844 have a suffix of ‘K’, ‘M’, or ‘G’ to indicate Kilobytes,
845 Megabytes, or Gigabytes, respectively. The default is between
846 ‘1G’ and ‘4G’, depending on the cipher. The optional second
847 value is specified in seconds and may use any of the units docu‐
848 mented in the TIME FORMATS section of sshd_config(5). The
849 default value for RekeyLimit is default none, which means that
850 rekeying is performed after the cipher's default amount of data
851 has been sent or received and no time based rekeying is done.
852 RemoteCommand
854 Specifies a command to execute on the remote machine after suc‐
855 cessfully connecting to the server. The command string extends
856 to the end of the line, and is executed with the user's shell.
857 Arguments to RemoteCommand accept the tokens described in the
858 TOKENS section.
859 RemoteForward
861 Specifies that a TCP port on the remote machine be forwarded over
862 the secure channel. The remote port may either be forwarded to a
863 specified host and port from the local machine, or may act as a
864 SOCKS 4/5 proxy that allows a remote client to connect to arbi‐
865 trary destinations from the local machine. The first argument
866 must be [bind_address:]port If forwarding to a specific destina‐
867 tion then the second argument must be host:hostport, otherwise if
868 no destination argument is specified then the remote forwarding
869 will be established as a SOCKS proxy.
870 IPv6 addresses can be specified by enclosing addresses in square
872 brackets. Multiple forwardings may be specified, and additional
873 forwardings can be given on the command line. Privileged ports
874 can be forwarded only when logging in as root on the remote
875 machine.
876 If the port argument is 0, the listen port will be dynamically
878 allocated on the server and reported to the client at run time.
879 If the bind_address is not specified, the default is to only bind
881 to loopback addresses. If the bind_address is ‘*’ or an empty
882 string, then the forwarding is requested to listen on all inter‐
883 faces. Specifying a remote bind_address will only succeed if the
884 server's GatewayPorts option is enabled (see sshd_config(5)).
885 RequestTTY
887 Specifies whether to request a pseudo-tty for the session. The
888 argument may be one of: no (never request a TTY), yes (always
889 request a TTY when standard input is a TTY), force (always
890 request a TTY) or auto (request a TTY when opening a login ses‐
891 sion). This option mirrors the -t and -T flags for ssh(1).
892 RevokedHostKeys
894 Specifies revoked host public keys. Keys listed in this file
895 will be refused for host authentication. Note that if this file
896 does not exist or is not readable, then host authentication will
897 be refused for all hosts. Keys may be specified as a text file,
898 listing one public key per line, or as an OpenSSH Key Revocation
899 List (KRL) as generated by ssh-keygen(1). For more information
900 on KRLs, see the KEY REVOCATION LISTS section in ssh-keygen(1).
901 SendEnv
903 Specifies what variables from the local environ(7) should be sent
904 to the server. The server must also support it, and the server
905 must be configured to accept these environment variables. Note
906 that the TERM environment variable is always sent whenever a
907 pseudo-terminal is requested as it is required by the protocol.
908 Refer to AcceptEnv in sshd_config(5) for how to configure the
909 server. Variables are specified by name, which may contain wild‐
910 card characters. Multiple environment variables may be separated
911 by whitespace or spread across multiple SendEnv directives.
912 See PATTERNS for more information on patterns.
914 It is possible to clear previously set SendEnv variable names by
916 prefixing patterns with -. The default is not to send any envi‐
917 ronment variables.
918 ServerAliveCountMax
920 Sets the number of server alive messages (see below) which may be
921 sent without ssh(1) receiving any messages back from the server.
922 If this threshold is reached while server alive messages are
923 being sent, ssh will disconnect from the server, terminating the
924 session. It is important to note that the use of server alive
925 messages is very different from TCPKeepAlive (below). The server
926 alive messages are sent through the encrypted channel and there‐
927 fore will not be spoofable. The TCP keepalive option enabled by
928 TCPKeepAlive is spoofable. The server alive mechanism is valu‐
929 able when the client or server depend on knowing when a connec‐
930 tion has become unresponsive.
931 The default value is 3. If, for example, ServerAliveInterval
933 (see below) is set to 15 and ServerAliveCountMax is left at the
934 default, if the server becomes unresponsive, ssh will disconnect
935 after approximately 45 seconds.
936 ServerAliveInterval
938 Sets a timeout interval in seconds after which if no data has
939 been received from the server, ssh(1) will send a message through
940 the encrypted channel to request a response from the server. The
941 default is 0, indicating that these messages will not be sent to
942 the server.
943 SetEnv Directly specify one or more environment variables and their con‐
945 tents to be sent to the server. Similarly to SendEnv, the server
946 must be prepared to accept the environment variable.
947 StreamLocalBindMask
949 Sets the octal file creation mode mask (umask) used when creating
950 a Unix-domain socket file for local or remote port forwarding.
951 This option is only used for port forwarding to a Unix-domain
952 socket file.
953 The default value is 0177, which creates a Unix-domain socket
955 file that is readable and writable only by the owner. Note that
956 not all operating systems honor the file mode on Unix-domain
957 socket files.
958 StreamLocalBindUnlink
960 Specifies whether to remove an existing Unix-domain socket file
961 for local or remote port forwarding before creating a new one.
962 If the socket file already exists and StreamLocalBindUnlink is
963 not enabled, ssh will be unable to forward the port to the Unix-
964 domain socket file. This option is only used for port forwarding
965 to a Unix-domain socket file.
966 The argument must be yes or no (the default).
968 StrictHostKeyChecking
970 If this flag is set to yes, ssh(1) will never automatically add
971 host keys to the ~/.ssh/known_hosts file, and refuses to connect
972 to hosts whose host key has changed. This provides maximum pro‐
973 tection against man-in-the-middle (MITM) attacks, though it can
974 be annoying when the /etc/gsissh/ssh_known_hosts file is poorly
975 maintained or when connections to new hosts are frequently made.
976 This option forces the user to manually add all new hosts.
977 If this flag is set to “accept-new” then ssh will automatically
979 add new host keys to the user known hosts files, but will not
980 permit connections to hosts with changed host keys. If this flag
981 is set to “no” or “off”, ssh will automatically add new host keys
982 to the user known hosts files and allow connections to hosts with
983 changed hostkeys to proceed, subject to some restrictions. If
984 this flag is set to ask (the default), new host keys will be
985 added to the user known host files only after the user has con‐
986 firmed that is what they really want to do, and ssh will refuse
987 to connect to hosts whose host key has changed. The host keys of
988 known hosts will be verified automatically in all cases.
989 SyslogFacility
991 Gives the facility code that is used when logging messages from
992 ssh(1). The possible values are: DAEMON, USER, AUTH, LOCAL0,
993 LOCAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. The
994 default is USER.
995 TCPKeepAlive
997 Specifies whether the system should send TCP keepalive messages
998 to the other side. If they are sent, death of the connection or
999 crash of one of the machines will be properly noticed. However,
1000 this means that connections will die if the route is down tempo‐
1001 rarily, and some people find it annoying.
1002 The default is yes (to send TCP keepalive messages), and the
1004 client will notice if the network goes down or the remote host
1005 dies. This is important in scripts, and many users want it too.
1006 To disable TCP keepalive messages, the value should be set to no.
1008 See also ServerAliveInterval for protocol-level keepalives.
1009 Tunnel Request tun(4) device forwarding between the client and the
1011 server. The argument must be yes, point-to-point (layer 3),
1012 ethernet (layer 2), or no (the default). Specifying yes requests
1013 the default tunnel mode, which is point-to-point.
1014 TunnelDevice
1016 Specifies the tun(4) devices to open on the client (local_tun)
1017 and the server (remote_tun).
1018 The argument must be local_tun[:remote_tun]. The devices may be
1020 specified by numerical ID or the keyword any, which uses the next
1021 available tunnel device. If remote_tun is not specified, it
1022 defaults to any. The default is any:any.
1023 UpdateHostKeys
1025 Specifies whether ssh(1) should accept notifications of addi‐
1026 tional hostkeys from the server sent after authentication has
1027 completed and add them to UserKnownHostsFile. The argument must
1028 be yes, no (the default) or ask. Enabling this option allows
1029 learning alternate hostkeys for a server and supports graceful
1030 key rotation by allowing a server to send replacement public keys
1031 before old ones are removed. Additional hostkeys are only
1032 accepted if the key used to authenticate the host was already
1033 trusted or explicitly accepted by the user. If UpdateHostKeys is
1034 set to ask, then the user is asked to confirm the modifications
1035 to the known_hosts file. Confirmation is currently incompatible
1036 with ControlPersist, and will be disabled if it is enabled.
1037 Presently, only sshd(8) from OpenSSH 6.8 and greater support the
1039 "hostkeys@openssh.com" protocol extension used to inform the
1040 client of all the server's hostkeys.
1041 User Specifies the user to log in as. This can be useful when a dif‐
1043 ferent user name is used on different machines. This saves the
1044 trouble of having to remember to give the user name on the com‐
1045 mand line.
1046 UserKnownHostsFile
1048 Specifies one or more files to use for the user host key data‐
1049 base, separated by whitespace. The default is
1050 ~/.ssh/known_hosts, ~/.ssh/known_hosts2.
1051 VerifyHostKeyDNS
1053 Specifies whether to verify the remote key using DNS and SSHFP
1054 resource records. If this option is set to yes, the client will
1055 implicitly trust keys that match a secure fingerprint from DNS.
1056 Insecure fingerprints will be handled as if this option was set
1057 to ask. If this option is set to ask, information on fingerprint
1058 match will be displayed, but the user will still need to confirm
1059 new host keys according to the StrictHostKeyChecking option. The
1060 default is no.
1061 See also VERIFYING HOST KEYS in ssh(1).
1063 VisualHostKey
1065 If this flag is set to yes, an ASCII art representation of the
1066 remote host key fingerprint is printed in addition to the finger‐
1067 print string at login and for unknown host keys. If this flag is
1068 set to no (the default), no fingerprint strings are printed at
1069 login and only the fingerprint string will be printed for unknown
1070 host keys.
1071 XAuthLocation
1073 Specifies the full pathname of the xauth(1) program. The default
1074 is /usr/bin/xauth.
1075
1077 A pattern consists of zero or more non-whitespace characters, ‘*’ (a
1078 wildcard that matches zero or more characters), or ‘?’ (a wildcard that
1079 matches exactly one character). For example, to specify a set of decla‐
1080 rations for any host in the ".co.uk" set of domains, the following pat‐
1081 tern could be used:
1082 Host *.co.uk
1084 The following pattern would match any host in the 192.168.0.[0-9] network
1086 range:
1087 Host 192.168.0.?
1089 A pattern-list is a comma-separated list of patterns. Patterns within
1091 pattern-lists may be negated by preceding them with an exclamation mark
1092 (‘!’). For example, to allow a key to be used from anywhere within an
1093 organization except from the "dialup" pool, the following entry (in
1094 authorized_keys) could be used:
1095 from="!*.dialup.example.com,*.example.com"
1097 Note that a negated match will never produce a positive result by itself.
1099 For example, attempting to match "host3" against the following pattern-
1100 list will fail:
1101 from="!host1,!host2"
1103 The solution here is to include a term that will yield a positive match,
1105 such as a wildcard:
1106 from="!host1,!host2,*"
1108
1110 Arguments to some keywords can make use of tokens, which are expanded at
1111 runtime:
1112 %% A literal ‘%’.
1114 %C Hash of %l%h%p%r.
1115 %d Local user's home directory.
1116 %h The remote hostname.
1117 %i The local user ID.
1118 %L The local hostname.
1119 %l The local hostname, including the domain name.
1120 %n The original remote hostname, as given on the command line.
1121 %p The remote port.
1122 %r The remote username.
1123 %T The local tun(4) or tap(4) network interface assigned if tun‐
1124 nel forwarding was requested, or "NONE" otherwise.
1125 %u The local username.
1126 Match exec accepts the tokens %%, %h, %i, %L, %l, %n, %p, %r, and %u.
1128 CertificateFile accepts the tokens %%, %d, %h, %i, %l, %r, and %u.
1130 ControlPath accepts the tokens %%, %C, %h, %i, %L, %l, %n, %p, %r, and
1132 %u.
1133 Hostname accepts the tokens %% and %h.
1135 IdentityAgent and IdentityFile accept the tokens %%, %d, %h, %i, %l, %r,
1137 and %u.
1138 LocalCommand accepts the tokens %%, %C, %d, %h, %i, %l, %n, %p, %r, %T,
1140 and %u.
1141 ProxyCommand accepts the tokens %%, %h, %n, %p, and %r.
1143 RemoteCommand accepts the tokens %%, %C, %d, %h, %i, %l, %n, %p, %r, and
1145 %u.
1146
1148 ~/.ssh/config
1149 This is the per-user configuration file. The format of this file
1150 is described above. This file is used by the SSH client.
1151 Because of the potential for abuse, this file must have strict
1152 permissions: read/write for the user, and not writable by others.
1153 /etc/gsissh/ssh_config
1155 Systemwide configuration file. This file provides defaults for
1156 those values that are not specified in the user's configuration
1157 file, and for those users who do not have a configuration file.
1158 This file must be world-readable.
1159
1161 ssh(1)
1162
1164 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
1165 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
1166 de Raadt and Dug Song removed many bugs, re-added newer features and cre‐
1167 ated OpenSSH. Markus Friedl contributed the support for SSH protocol
1168 versions 1.5 and 2.0.
1169BSD December 31, 2019 BSD