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 value
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 value begins with a ‘-’ character, then the specified
214 ciphers (including wildcards) will be removed from the default
215 set instead of replacing them.
216 The supported ciphers are:
218 3des-cbc
220 aes128-cbc
221 aes192-cbc
222 aes256-cbc
223 aes128-ctr
224 aes192-ctr
225 aes256-ctr
226 aes128-gcm@openssh.com
227 aes256-gcm@openssh.com
228 chacha20-poly1305@openssh.com
229 The default is handled system-wide by crypto-policies(7). To see
231 the defaults and how to modifuy this default, see manual page
232 update-crypto-policies(8).
233 The list of available ciphers may also be obtained using "ssh -Q
235 cipher".
236 ClearAllForwardings
238 Specifies that all local, remote, and dynamic port forwardings
239 specified in the configuration files or on the command line be
240 cleared. This option is primarily useful when used from the
241 ssh(1) command line to clear port forwardings set in configura‐
242 tion files, and is automatically set by scp(1) and sftp(1). The
243 argument must be yes or no (the default).
244 Compression
246 Specifies whether to use compression. The argument must be yes
247 or no (the default).
248 ConnectionAttempts
250 Specifies the number of tries (one per second) to make before
251 exiting. The argument must be an integer. This may be useful in
252 scripts if the connection sometimes fails. The default is 1.
253 ConnectTimeout
255 Specifies the timeout (in seconds) used when connecting to the
256 SSH server, instead of using the default system TCP timeout.
257 This value is used only when the target is down or really
258 unreachable, not when it refuses the connection.
259 ControlMaster
261 Enables the sharing of multiple sessions over a single network
262 connection. When set to yes, ssh(1) will listen for connections
263 on a control socket specified using the ControlPath argument.
264 Additional sessions can connect to this socket using the same
265 ControlPath with ControlMaster set to no (the default). These
266 sessions will try to reuse the master instance's network connec‐
267 tion rather than initiating new ones, but will fall back to con‐
268 necting normally if the control socket does not exist, or is not
269 listening.
270 Setting this to ask will cause ssh(1) to listen for control con‐
272 nections, but require confirmation using ssh-askpass(1). If the
273 ControlPath cannot be opened, ssh(1) will continue without con‐
274 necting to a master instance.
275 X11 and ssh-agent(1) forwarding is supported over these multi‐
277 plexed connections, however the display and agent forwarded will
278 be the one belonging to the master connection i.e. it is not pos‐
279 sible to forward multiple displays or agents.
280 Two additional options allow for opportunistic multiplexing: try
282 to use a master connection but fall back to creating a new one if
283 one does not already exist. These options are: auto and autoask.
284 The latter requires confirmation like the ask option.
285 ControlPath
287 Specify the path to the control socket used for connection shar‐
288 ing as described in the ControlMaster section above or the string
289 none to disable connection sharing. Arguments to ControlPath may
290 use the tilde syntax to refer to a user's home directory or the
291 tokens described in the TOKENS section. It is recommended that
292 any ControlPath used for opportunistic connection sharing include
293 at least %h, %p, and %r (or alternatively %C) and be placed in a
294 directory that is not writable by other users. This ensures that
295 shared connections are uniquely identified.
296 ControlPersist
298 When used in conjunction with ControlMaster, specifies that the
299 master connection should remain open in the background (waiting
300 for future client connections) after the initial client connec‐
301 tion has been closed. If set to no, then the master connection
302 will not be placed into the background, and will close as soon as
303 the initial client connection is closed. If set to yes or 0,
304 then the master connection will remain in the background indefi‐
305 nitely (until killed or closed via a mechanism such as the "ssh
306 -O exit"). If set to a time in seconds, or a time in any of the
307 formats documented in sshd_config(5), then the backgrounded mas‐
308 ter connection will automatically terminate after it has remained
309 idle (with no client connections) for the specified time.
310 DynamicForward
312 Specifies that a TCP port on the local machine be forwarded over
313 the secure channel, and the application protocol is then used to
314 determine where to connect to from the remote machine.
315 The argument must be [bind_address:]port. IPv6 addresses can be
317 specified by enclosing addresses in square brackets. By default,
318 the local port is bound in accordance with the GatewayPorts set‐
319 ting. However, an explicit bind_address may be used to bind the
320 connection to a specific address. The bind_address of localhost
321 indicates that the listening port be bound for local use only,
322 while an empty address or ‘*’ indicates that the port should be
323 available from all interfaces.
324 Currently the SOCKS4 and SOCKS5 protocols are supported, and
326 ssh(1) will act as a SOCKS server. Multiple forwardings may be
327 specified, and additional forwardings can be given on the command
328 line. Only the superuser can forward privileged ports.
329 EnableSSHKeysign
331 Setting this option to yes in the global client configuration
332 file /etc/gsissh/ssh_config enables the use of the helper program
333 ssh-keysign(8) during HostbasedAuthentication. The argument must
334 be yes or no (the default). This option should be placed in the
335 non-hostspecific section. See ssh-keysign(8) for more informa‐
336 tion.
337 EscapeChar
339 Sets the escape character (default: ‘~’). The escape character
340 can also be set on the command line. The argument should be a
341 single character, ‘^’ followed by a letter, or none to disable
342 the escape character entirely (making the connection transparent
343 for binary data).
344 ExitOnForwardFailure
346 Specifies whether ssh(1) should terminate the connection if it
347 cannot set up all requested dynamic, tunnel, local, and remote
348 port forwardings, (e.g. if either end is unable to bind and lis‐
349 ten on a specified port). Note that ExitOnForwardFailure does
350 not apply to connections made over port forwardings and will not,
351 for example, cause ssh(1) to exit if TCP connections to the ulti‐
352 mate forwarding destination fail. The argument must be yes or no
353 (the default).
354 FingerprintHash
356 Specifies the hash algorithm used when displaying key finger‐
357 prints. Valid options are: md5 and sha256 (the default).
358 ForwardAgent
360 Specifies whether the connection to the authentication agent (if
361 any) will be forwarded to the remote machine. The argument must
362 be yes or no (the default).
363 Agent forwarding should be enabled with caution. Users with the
365 ability to bypass file permissions on the remote host (for the
366 agent's Unix-domain socket) can access the local agent through
367 the forwarded connection. An attacker cannot obtain key material
368 from the agent, however they can perform operations on the keys
369 that enable them to authenticate using the identities loaded into
370 the agent.
371 ForwardX11
373 Specifies whether X11 connections will be automatically redi‐
374 rected over the secure channel and DISPLAY set. The argument
375 must be yes or no (the default).
376 X11 forwarding should be enabled with caution. Users with the
378 ability to bypass file permissions on the remote host (for the
379 user's X11 authorization database) can access the local X11 dis‐
380 play through the forwarded connection. An attacker may then be
381 able to perform activities such as keystroke monitoring if the
382 ForwardX11Trusted option is also enabled.
383 ForwardX11Timeout
385 Specify a timeout for untrusted X11 forwarding using the format
386 described in the TIME FORMATS section of sshd_config(5). X11
387 connections received by ssh(1) after this time will be refused.
388 Setting ForwardX11Timeout to zero will disable the timeout and
389 permit X11 forwarding for the life of the connection. The
390 default is to disable untrusted X11 forwarding after twenty min‐
391 utes has elapsed.
392 ForwardX11Trusted
394 If this option is set to yes, remote X11 clients will have full
395 access to the original X11 display.
396 If this option is set to no (the default), remote X11 clients
398 will be considered untrusted and prevented from stealing or tam‐
399 pering with data belonging to trusted X11 clients. Furthermore,
400 the xauth(1) token used for the session will be set to expire
401 after 20 minutes. Remote clients will be refused access after
402 this time.
403 See the X11 SECURITY extension specification for full details on
405 the restrictions imposed on untrusted clients.
406 GatewayPorts
408 Specifies whether remote hosts are allowed to connect to local
409 forwarded ports. By default, ssh(1) binds local port forwardings
410 to the loopback address. This prevents other remote hosts from
411 connecting to forwarded ports. GatewayPorts can be used to spec‐
412 ify that ssh should bind local port forwardings to the wildcard
413 address, thus allowing remote hosts to connect to forwarded
414 ports. The argument must be yes or no (the default).
415 GlobalKnownHostsFile
417 Specifies one or more files to use for the global host key data‐
418 base, separated by whitespace. The default is
419 /etc/gsissh/ssh_known_hosts, /etc/gsissh/ssh_known_hosts2.
420 GSSAPIAuthentication
422 Specifies whether user authentication based on GSSAPI is allowed.
423 The default is yes.
424 GSSAPIClientIdentity
426 If set, specifies the GSSAPI client identity that ssh should use
427 when connecting to the server. The default is unset, which means
428 that the default identity will be used.
429 GSSAPIDelegateCredentials
431 Forward (delegate) credentials to the server. The default is
432 yes.
433 GSSAPIKeyExchange
435 Specifies whether key exchange based on GSSAPI may be used. When
436 using GSSAPI key exchange the server need not have a host key.
437 The default is “yes”.
438 GSSAPIRenewalForcesRekey
440 If set to “yes” then renewal of the client's GSSAPI credentials
441 will force the rekeying of the ssh connection. With a compatible
442 server, this will delegate the renewed credentials to a session
443 on the server.
444 Checks are made to ensure that credentials are only propagated
446 when the new credentials match the old ones on the originating
447 client and where the receiving server still has the old set in
448 its cache.
449 The default is “no”.
451 For this to work GSSAPIKeyExchange needs to be enabled in the
453 server and also used by the client.
454 GSSAPIServerIdentity
456 If set, specifies the GSSAPI server identity that ssh should
457 expect when connecting to the server. The default is unset, which
458 means that the expected GSSAPI server identity will be determined
459 from the target hostname.
460 GSSAPITrustDns
462 Set to “yes” to indicate that the DNS is trusted to securely
463 canonicalize the name of the host being connected to. If “no”,
464 the hostname entered on the command line will be passed untouched
465 to the GSSAPI library. The default is “no”.
466 GSSAPIKexAlgorithms
468 The list of key exchange algorithms that are offered for GSSAPI
469 key exchange. Possible values are
470 gss-gex-sha1-,
472 gss-group1-sha1-,
473 gss-group14-sha1-,
474 gss-group14-sha256-,
475 gss-group16-sha512-,
476 gss-nistp256-sha256-,
477 gss-curve25519-sha256-
478 The default is handled system-wide by crypto-policies(7). To see
480 the defaults and how to modifuy this default, see manual page
481 update-crypto-policies(8).
482 HashKnownHosts
484 Indicates that ssh(1) should hash host names and addresses when
485 they are added to ~/.ssh/known_hosts. These hashed names may be
486 used normally by ssh(1) and sshd(8), but they do not reveal iden‐
487 tifying information should the file's contents be disclosed. The
488 default is no. Note that existing names and addresses in known
489 hosts files will not be converted automatically, but may be manu‐
490 ally hashed using ssh-keygen(1).
491 HostbasedAuthentication
493 Specifies whether to try rhosts based authentication with public
494 key authentication. The argument must be yes or no (the
495 default).
496 HostbasedKeyTypes
498 Specifies the key types that will be used for hostbased authenti‐
499 cation as a comma-separated list of patterns. Alternately if the
500 specified value begins with a ‘+’ character, then the specified
501 key types will be appended to the default set instead of replac‐
502 ing them. If the specified value begins with a ‘-’ character,
503 then the specified key types (including wildcards) will be
504 removed from the default set instead of replacing them. The
505 default for this option is:
506 ecdsa-sha2-nistp256-cert-v01@openssh.com,
508 ecdsa-sha2-nistp384-cert-v01@openssh.com,
509 ecdsa-sha2-nistp521-cert-v01@openssh.com,
510 ssh-ed25519-cert-v01@openssh.com,
511 rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,
512 ssh-rsa-cert-v01@openssh.com,
513 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
514 ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
515 The -Q option of ssh(1) may be used to list supported key types.
517 HostKeyAlgorithms
519 Specifies the host key algorithms that the client wants to use in
520 order of preference. Alternately if the specified value begins
521 with a ‘+’ character, then the specified key types will be
522 appended to the default set instead of replacing them. If the
523 specified value begins with a ‘-’ character, then the specified
524 key types (including wildcards) will be removed from the default
525 set instead of replacing them. The default for this option is:
526 ecdsa-sha2-nistp256-cert-v01@openssh.com,
528 ecdsa-sha2-nistp384-cert-v01@openssh.com,
529 ecdsa-sha2-nistp521-cert-v01@openssh.com,
530 ssh-ed25519-cert-v01@openssh.com,
531 rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,
532 ssh-rsa-cert-v01@openssh.com,
533 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
534 ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
535 If hostkeys are known for the destination host then this default
537 is modified to prefer their algorithms.
538 The list of available key types may also be obtained using "ssh
540 -Q key".
541 HostKeyAlias
543 Specifies an alias that should be used instead of the real host
544 name when looking up or saving the host key in the host key data‐
545 base files and when validating host certificates. This option is
546 useful for tunneling SSH connections or for multiple servers run‐
547 ning on a single host.
548 HostName
550 Specifies the real host name to log into. This can be used to
551 specify nicknames or abbreviations for hosts. Arguments to
552 HostName accept the tokens described in the TOKENS section.
553 Numeric IP addresses are also permitted (both on the command line
554 and in HostName specifications). The default is the name given
555 on the command line.
556 IdentitiesOnly
558 Specifies that ssh(1) should only use the authentication identity
559 and certificate files explicitly configured in the ssh_config
560 files or passed on the ssh(1) command-line, even if ssh-agent(1)
561 or a PKCS11Provider offers more identities. The argument to this
562 keyword must be yes or no (the default). This option is intended
563 for situations where ssh-agent offers many different identities.
564 IdentityAgent
566 Specifies the UNIX-domain socket used to communicate with the
567 authentication agent.
568 This option overrides the SSH_AUTH_SOCK environment variable and
570 can be used to select a specific agent. Setting the socket name
571 to none disables the use of an authentication agent. If the
572 string "SSH_AUTH_SOCK" is specified, the location of the socket
573 will be read from the SSH_AUTH_SOCK environment variable. Other‐
574 wise if the specified value begins with a ‘$’ character, then it
575 will be treated as an environment variable containing the loca‐
576 tion of the socket.
577 Arguments to IdentityAgent may use the tilde syntax to refer to a
579 user's home directory or the tokens described in the TOKENS sec‐
580 tion.
581 IdentityFile
583 Specifies a file from which the user's DSA, ECDSA, Ed25519 or RSA
584 authentication identity is read. The default is ~/.ssh/id_dsa,
585 ~/.ssh/id_ecdsa, ~/.ssh/id_ed25519 and ~/.ssh/id_rsa. Addition‐
586 ally, any identities represented by the authentication agent will
587 be used for authentication unless IdentitiesOnly is set. If no
588 certificates have been explicitly specified by CertificateFile,
589 ssh(1) will try to load certificate information from the filename
590 obtained by appending -cert.pub to the path of a specified
591 IdentityFile.
592 Arguments to IdentityFile may use the tilde syntax to refer to a
594 user's home directory or the tokens described in the TOKENS sec‐
595 tion.
596 It is possible to have multiple identity files specified in con‐
598 figuration files; all these identities will be tried in sequence.
599 Multiple IdentityFile directives will add to the list of identi‐
600 ties tried (this behaviour differs from that of other configura‐
601 tion directives).
602 IdentityFile may be used in conjunction with IdentitiesOnly to
604 select which identities in an agent are offered during authenti‐
605 cation. IdentityFile may also be used in conjunction with
606 CertificateFile in order to provide any certificate also needed
607 for authentication with the identity.
608 The authentication identity can be also specified in a form of
610 PKCS#11 URI starting with a string pkcs11:. There is supported a
611 subset of the PKCS#11 URI as defined in RFC 7512 (implemented
612 path arguments id, manufacturer, object, token and query argu‐
613 ments module-path and pin-value ). The URI can not be in quotes.
614 IgnoreUnknown
616 Specifies a pattern-list of unknown options to be ignored if they
617 are encountered in configuration parsing. This may be used to
618 suppress errors if ssh_config contains options that are unrecog‐
619 nised by ssh(1). It is recommended that IgnoreUnknown be listed
620 early in the configuration file as it will not be applied to
621 unknown options that appear before it.
622 Include
624 Include the specified configuration file(s). Multiple pathnames
625 may be specified and each pathname may contain glob(7) wildcards
626 and, for user configurations, shell-like ‘~’ references to user
627 home directories. Files without absolute paths are assumed to be
628 in ~/.ssh if included in a user configuration file or /etc/ssh if
629 included from the system configuration file. Include directive
630 may appear inside a Match or Host block to perform conditional
631 inclusion.
632 IPQoS Specifies the IPv4 type-of-service or DSCP class for connections.
634 Accepted values are af11, af12, af13, af21, af22, af23, af31,
635 af32, af33, af41, af42, af43, cs0, cs1, cs2, cs3, cs4, cs5, cs6,
636 cs7, ef, lowdelay, throughput, reliability, a numeric value, or
637 none to use the operating system default. This option may take
638 one or two arguments, separated by whitespace. If one argument
639 is specified, it is used as the packet class unconditionally. If
640 two values are specified, the first is automatically selected for
641 interactive sessions and the second for non-interactive sessions.
642 The default is af21 (Low-Latency Data) for interactive sessions
643 and cs1 (Lower Effort) for non-interactive sessions.
644 KbdInteractiveAuthentication
646 Specifies whether to use keyboard-interactive authentication.
647 The argument to this keyword must be yes (the default) or no.
648 KbdInteractiveDevices
650 Specifies the list of methods to use in keyboard-interactive
651 authentication. Multiple method names must be comma-separated.
652 The default is to use the server specified list. The methods
653 available vary depending on what the server supports. For an
654 OpenSSH server, it may be zero or more of: bsdauth and pam.
655 KexAlgorithms
657 Specifies the available KEX (Key Exchange) algorithms. Multiple
658 algorithms must be comma-separated. Alternately if the specified
659 value begins with a ‘+’ character, then the specified methods
660 will be appended to the default set instead of replacing them.
661 If the specified value begins with a ‘-’ character, then the
662 specified methods (including wildcards) will be removed from the
663 default set instead of replacing them. The default is handled
664 system-wide by crypto-policies(7). To see the defaults and how
665 to modifuy this default, see manual page
666 update-crypto-policies(8).
667 The list of available key exchange algorithms may also be
669 obtained using "ssh -Q kex".
670 LocalCommand
672 Specifies a command to execute on the local machine after suc‐
673 cessfully connecting to the server. The command string extends
674 to the end of the line, and is executed with the user's shell.
675 Arguments to LocalCommand accept the tokens described in the
676 TOKENS section.
677 The command is run synchronously and does not have access to the
679 session of the ssh(1) that spawned it. It should not be used for
680 interactive commands.
681 This directive is ignored unless PermitLocalCommand has been
683 enabled.
684 LocalForward
686 Specifies that a TCP port on the local machine be forwarded over
687 the secure channel to the specified host and port from the remote
688 machine. The first argument must be [bind_address:]port and the
689 second argument must be host:hostport. IPv6 addresses can be
690 specified by enclosing addresses in square brackets. Multiple
691 forwardings may be specified, and additional forwardings can be
692 given on the command line. Only the superuser can forward privi‐
693 leged ports. By default, the local port is bound in accordance
694 with the GatewayPorts setting. However, an explicit bind_address
695 may be used to bind the connection to a specific address. The
696 bind_address of localhost indicates that the listening port be
697 bound for local use only, while an empty address or ‘*’ indicates
698 that the port should be available from all interfaces.
699 LogLevel
701 Gives the verbosity level that is used when logging messages from
702 ssh(1). The possible values are: QUIET, FATAL, ERROR, INFO, VER‐
703 BOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO.
704 DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify
705 higher levels of verbose output.
706 MACs Specifies the MAC (message authentication code) algorithms in
708 order of preference. The MAC algorithm is used for data
709 integrity protection. Multiple algorithms must be comma-sepa‐
710 rated. If the specified value begins with a ‘+’ character, then
711 the specified algorithms will be appended to the default set
712 instead of replacing them. If the specified value begins with a
713 ‘-’ character, then the specified algorithms (including wild‐
714 cards) will be removed from the default set instead of replacing
715 them.
716 The algorithms that contain "-etm" calculate the MAC after
718 encryption (encrypt-then-mac). These are considered safer and
719 their use recommended.
720 The default is handled system-wide by crypto-policies(7). To see
722 the defaults and how to modifuy this default, see manual page
723 update-crypto-policies(8).
724 The list of available MAC algorithms may also be obtained using
726 "ssh -Q mac".
727 NoHostAuthenticationForLocalhost
729 Disable host authentication for localhost (loopback addresses).
730 The argument to this keyword must be yes or no (the default).
731 NumberOfPasswordPrompts
733 Specifies the number of password prompts before giving up. The
734 argument to this keyword must be an integer. The default is 3.
735 PasswordAuthentication
737 Specifies whether to use password authentication. The argument
738 to this keyword must be yes (the default) or no.
739 PermitLocalCommand
741 Allow local command execution via the LocalCommand option or
742 using the !command escape sequence in ssh(1). The argument must
743 be yes or no (the default).
744 PKCS11Provider
746 Specifies which PKCS#11 provider to use or none to indicate that
747 no provider should be used (the default). The argument to this
748 keyword is a path to the PKCS#11 shared library ssh(1) should use
749 to communicate with a PKCS#11 token providing keys for user
750 authentication.
751 Port Specifies the port number to connect on the remote host. The
753 default is 22.
754 PreferredAuthentications
756 Specifies the order in which the client should try authentication
757 methods. This allows a client to prefer one method (e.g.
758 keyboard-interactive) over another method (e.g. password). The
759 default is:
760 gssapi-keyex,gssapi-with-mic,hostbased,publickey,
762 keyboard-interactive,password
763 ProxyCommand
765 Specifies the command to use to connect to the server. The com‐
766 mand string extends to the end of the line, and is executed using
767 the user's shell ‘exec’ directive to avoid a lingering shell
768 process.
769 Arguments to ProxyCommand accept the tokens described in the
771 TOKENS section. The command can be basically anything, and
772 should read from its standard input and write to its standard
773 output. It should eventually connect an sshd(8) server running
774 on some machine, or execute sshd -i somewhere. Host key manage‐
775 ment will be done using the HostName of the host being connected
776 (defaulting to the name typed by the user). Setting the command
777 to none disables this option entirely. Note that CheckHostIP is
778 not available for connects with a proxy command.
779 This directive is useful in conjunction with nc(1) and its proxy
781 support. For example, the following directive would connect via
782 an HTTP proxy at 192.0.2.0:
783 ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
785 ProxyJump
787 Specifies one or more jump proxies as either [user@]host[:port]
788 or an ssh URI. Multiple proxies may be separated by comma char‐
789 acters and will be visited sequentially. Setting this option
790 will cause ssh(1) to connect to the target host by first making a
791 ssh(1) connection to the specified ProxyJump host and then estab‐
792 lishing a TCP forwarding to the ultimate target from there.
793 Note that this option will compete with the ProxyCommand option -
795 whichever is specified first will prevent later instances of the
796 other from taking effect.
797 Note also that the configuration for the destination host (either
799 supplied via the command-line or the configuration file) is not
800 generally applied to jump hosts. ~/.ssh/config should be used if
801 specific configuration is required for jump hosts.
802 ProxyUseFdpass
804 Specifies that ProxyCommand will pass a connected file descriptor
805 back to ssh(1) instead of continuing to execute and pass data.
806 The default is no.
807 PubkeyAcceptedKeyTypes
809 Specifies the key types that will be used for public key authen‐
810 tication as a comma-separated list of patterns. Alternately if
811 the specified value begins with a ‘+’ character, then the key
812 types after it will be appended to the default instead of replac‐
813 ing it. If the specified value begins with a ‘-’ character, then
814 the specified key types (including wildcards) will be removed
815 from the default set instead of replacing them. The default is
816 handled system-wide by crypto-policies(7). To see the defaults
817 and how to modifuy this default, see manual page
818 update-crypto-policies(8).
819 The list of available key types may also be obtained using "ssh
821 -Q key".
822 PubkeyAuthentication
824 Specifies whether to try public key authentication. The argument
825 to this keyword must be yes (the default) or no.
826 RekeyLimit
828 Specifies the maximum amount of data that may be transmitted
829 before the session key is renegotiated, optionally followed a
830 maximum amount of time that may pass before the session key is
831 renegotiated. The first argument is specified in bytes and may
832 have a suffix of ‘K’, ‘M’, or ‘G’ to indicate Kilobytes,
833 Megabytes, or Gigabytes, respectively. The default is between
834 ‘1G’ and ‘4G’, depending on the cipher. The optional second
835 value is specified in seconds and may use any of the units docu‐
836 mented in the TIME FORMATS section of sshd_config(5). The
837 default value for RekeyLimit is default none, which means that
838 rekeying is performed after the cipher's default amount of data
839 has been sent or received and no time based rekeying is done.
840 RemoteCommand
842 Specifies a command to execute on the remote machine after suc‐
843 cessfully connecting to the server. The command string extends
844 to the end of the line, and is executed with the user's shell.
845 Arguments to RemoteCommand accept the tokens described in the
846 TOKENS section.
847 RemoteForward
849 Specifies that a TCP port on the remote machine be forwarded over
850 the secure channel. The remote port may either be forwarded to a
851 specified host and port from the local machine, or may act as a
852 SOCKS 4/5 proxy that allows a remote client to connect to arbi‐
853 trary destinations from the local machine. The first argument
854 must be [bind_address:]port If forwarding to a specific destina‐
855 tion then the second argument must be host:hostport, otherwise if
856 no destination argument is specified then the remote forwarding
857 will be established as a SOCKS proxy.
858 IPv6 addresses can be specified by enclosing addresses in square
860 brackets. Multiple forwardings may be specified, and additional
861 forwardings can be given on the command line. Privileged ports
862 can be forwarded only when logging in as root on the remote
863 machine.
864 If the port argument is 0, the listen port will be dynamically
866 allocated on the server and reported to the client at run time.
867 If the bind_address is not specified, the default is to only bind
869 to loopback addresses. If the bind_address is ‘*’ or an empty
870 string, then the forwarding is requested to listen on all inter‐
871 faces. Specifying a remote bind_address will only succeed if the
872 server's GatewayPorts option is enabled (see sshd_config(5)).
873 RequestTTY
875 Specifies whether to request a pseudo-tty for the session. The
876 argument may be one of: no (never request a TTY), yes (always
877 request a TTY when standard input is a TTY), force (always
878 request a TTY) or auto (request a TTY when opening a login ses‐
879 sion). This option mirrors the -t and -T flags for ssh(1).
880 RevokedHostKeys
882 Specifies revoked host public keys. Keys listed in this file
883 will be refused for host authentication. Note that if this file
884 does not exist or is not readable, then host authentication will
885 be refused for all hosts. Keys may be specified as a text file,
886 listing one public key per line, or as an OpenSSH Key Revocation
887 List (KRL) as generated by ssh-keygen(1). For more information
888 on KRLs, see the KEY REVOCATION LISTS section in ssh-keygen(1).
889 SendEnv
891 Specifies what variables from the local environ(7) should be sent
892 to the server. The server must also support it, and the server
893 must be configured to accept these environment variables. Note
894 that the TERM environment variable is always sent whenever a
895 pseudo-terminal is requested as it is required by the protocol.
896 Refer to AcceptEnv in sshd_config(5) for how to configure the
897 server. Variables are specified by name, which may contain wild‐
898 card characters. Multiple environment variables may be separated
899 by whitespace or spread across multiple SendEnv directives.
900 See PATTERNS for more information on patterns.
902 It is possible to clear previously set SendEnv variable names by
904 prefixing patterns with -. The default is not to send any envi‐
905 ronment variables.
906 ServerAliveCountMax
908 Sets the number of server alive messages (see below) which may be
909 sent without ssh(1) receiving any messages back from the server.
910 If this threshold is reached while server alive messages are
911 being sent, ssh will disconnect from the server, terminating the
912 session. It is important to note that the use of server alive
913 messages is very different from TCPKeepAlive (below). The server
914 alive messages are sent through the encrypted channel and there‐
915 fore will not be spoofable. The TCP keepalive option enabled by
916 TCPKeepAlive is spoofable. The server alive mechanism is valu‐
917 able when the client or server depend on knowing when a connec‐
918 tion has become inactive.
919 The default value is 3. If, for example, ServerAliveInterval
921 (see below) is set to 15 and ServerAliveCountMax is left at the
922 default, if the server becomes unresponsive, ssh will disconnect
923 after approximately 45 seconds.
924 ServerAliveInterval
926 Sets a timeout interval in seconds after which if no data has
927 been received from the server, ssh(1) will send a message through
928 the encrypted channel to request a response from the server. The
929 default is 0, indicating that these messages will not be sent to
930 the server.
931 SetEnv Directly specify one or more environment variables and their con‐
933 tents to be sent to the server. Similarly to SendEnv, the server
934 must be prepared to accept the environment variable.
935 StreamLocalBindMask
937 Sets the octal file creation mode mask (umask) used when creating
938 a Unix-domain socket file for local or remote port forwarding.
939 This option is only used for port forwarding to a Unix-domain
940 socket file.
941 The default value is 0177, which creates a Unix-domain socket
943 file that is readable and writable only by the owner. Note that
944 not all operating systems honor the file mode on Unix-domain
945 socket files.
946 StreamLocalBindUnlink
948 Specifies whether to remove an existing Unix-domain socket file
949 for local or remote port forwarding before creating a new one.
950 If the socket file already exists and StreamLocalBindUnlink is
951 not enabled, ssh will be unable to forward the port to the Unix-
952 domain socket file. This option is only used for port forwarding
953 to a Unix-domain socket file.
954 The argument must be yes or no (the default).
956 StrictHostKeyChecking
958 If this flag is set to yes, ssh(1) will never automatically add
959 host keys to the ~/.ssh/known_hosts file, and refuses to connect
960 to hosts whose host key has changed. This provides maximum pro‐
961 tection against man-in-the-middle (MITM) attacks, though it can
962 be annoying when the /etc/gsissh/ssh_known_hosts file is poorly
963 maintained or when connections to new hosts are frequently made.
964 This option forces the user to manually add all new hosts.
965 If this flag is set to “accept-new” then ssh will automatically
967 add new host keys to the user known hosts files, but will not
968 permit connections to hosts with changed host keys. If this flag
969 is set to “no” or “off”, ssh will automatically add new host keys
970 to the user known hosts files and allow connections to hosts with
971 changed hostkeys to proceed, subject to some restrictions. If
972 this flag is set to ask (the default), new host keys will be
973 added to the user known host files only after the user has con‐
974 firmed that is what they really want to do, and ssh will refuse
975 to connect to hosts whose host key has changed. The host keys of
976 known hosts will be verified automatically in all cases.
977 SyslogFacility
979 Gives the facility code that is used when logging messages from
980 ssh(1). The possible values are: DAEMON, USER, AUTH, LOCAL0,
981 LOCAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. The
982 default is USER.
983 TCPKeepAlive
985 Specifies whether the system should send TCP keepalive messages
986 to the other side. If they are sent, death of the connection or
987 crash of one of the machines will be properly noticed. However,
988 this means that connections will die if the route is down tempo‐
989 rarily, and some people find it annoying.
990 The default is yes (to send TCP keepalive messages), and the
992 client will notice if the network goes down or the remote host
993 dies. This is important in scripts, and many users want it too.
994 To disable TCP keepalive messages, the value should be set to no.
996 See also ServerAliveInterval for protocol-level keepalives.
997 Tunnel Request tun(4) device forwarding between the client and the
999 server. The argument must be yes, point-to-point (layer 3),
1000 ethernet (layer 2), or no (the default). Specifying yes requests
1001 the default tunnel mode, which is point-to-point.
1002 TunnelDevice
1004 Specifies the tun(4) devices to open on the client (local_tun)
1005 and the server (remote_tun).
1006 The argument must be local_tun[:remote_tun]. The devices may be
1008 specified by numerical ID or the keyword any, which uses the next
1009 available tunnel device. If remote_tun is not specified, it
1010 defaults to any. The default is any:any.
1011 UpdateHostKeys
1013 Specifies whether ssh(1) should accept notifications of addi‐
1014 tional hostkeys from the server sent after authentication has
1015 completed and add them to UserKnownHostsFile. The argument must
1016 be yes, no (the default) or ask. Enabling this option allows
1017 learning alternate hostkeys for a server and supports graceful
1018 key rotation by allowing a server to send replacement public keys
1019 before old ones are removed. Additional hostkeys are only
1020 accepted if the key used to authenticate the host was already
1021 trusted or explicitly accepted by the user. If UpdateHostKeys is
1022 set to ask, then the user is asked to confirm the modifications
1023 to the known_hosts file. Confirmation is currently incompatible
1024 with ControlPersist, and will be disabled if it is enabled.
1025 Presently, only sshd(8) from OpenSSH 6.8 and greater support the
1027 "hostkeys@openssh.com" protocol extension used to inform the
1028 client of all the server's hostkeys.
1029 User Specifies the user to log in as. This can be useful when a dif‐
1031 ferent user name is used on different machines. This saves the
1032 trouble of having to remember to give the user name on the com‐
1033 mand line.
1034 UserKnownHostsFile
1036 Specifies one or more files to use for the user host key data‐
1037 base, separated by whitespace. The default is
1038 ~/.ssh/known_hosts, ~/.ssh/known_hosts2.
1039 VerifyHostKeyDNS
1041 Specifies whether to verify the remote key using DNS and SSHFP
1042 resource records. If this option is set to yes, the client will
1043 implicitly trust keys that match a secure fingerprint from DNS.
1044 Insecure fingerprints will be handled as if this option was set
1045 to ask. If this option is set to ask, information on fingerprint
1046 match will be displayed, but the user will still need to confirm
1047 new host keys according to the StrictHostKeyChecking option. The
1048 default is no.
1049 See also VERIFYING HOST KEYS in ssh(1).
1051 VisualHostKey
1053 If this flag is set to yes, an ASCII art representation of the
1054 remote host key fingerprint is printed in addition to the finger‐
1055 print string at login and for unknown host keys. If this flag is
1056 set to no (the default), no fingerprint strings are printed at
1057 login and only the fingerprint string will be printed for unknown
1058 host keys.
1059 XAuthLocation
1061 Specifies the full pathname of the xauth(1) program. The default
1062 is /usr/bin/xauth.
1063
1065 A pattern consists of zero or more non-whitespace characters, ‘*’ (a
1066 wildcard that matches zero or more characters), or ‘?’ (a wildcard that
1067 matches exactly one character). For example, to specify a set of decla‐
1068 rations for any host in the ".co.uk" set of domains, the following pat‐
1069 tern could be used:
1070 Host *.co.uk
1072 The following pattern would match any host in the 192.168.0.[0-9] network
1074 range:
1075 Host 192.168.0.?
1077 A pattern-list is a comma-separated list of patterns. Patterns within
1079 pattern-lists may be negated by preceding them with an exclamation mark
1080 (‘!’). For example, to allow a key to be used from anywhere within an
1081 organization except from the "dialup" pool, the following entry (in
1082 authorized_keys) could be used:
1083 from="!*.dialup.example.com,*.example.com"
1085 Note that a negated match will never produce a positive result by itself.
1087 For example, attempting to match "host3" against the following pattern-
1088 list will fail:
1089 from="!host1,!host2"
1091 The solution here is to include a term that will yield a positive match,
1093 such as a wildcard:
1094 from="!host1,!host2,*"
1096
1098 Arguments to some keywords can make use of tokens, which are expanded at
1099 runtime:
1100 %% A literal ‘%’.
1102 %C Hash of %l%h%p%r.
1103 %d Local user's home directory.
1104 %h The remote hostname.
1105 %i The local user ID.
1106 %L The local hostname.
1107 %l The local hostname, including the domain name.
1108 %n The original remote hostname, as given on the command line.
1109 %p The remote port.
1110 %r The remote username.
1111 %T The local tun(4) or tap(4) network interface assigned if tun‐
1112 nel forwarding was requested, or "NONE" otherwise.
1113 %u The local username.
1114 Match exec accepts the tokens %%, %h, %i, %L, %l, %n, %p, %r, and %u.
1116 CertificateFile accepts the tokens %%, %d, %h, %i, %l, %r, and %u.
1118 ControlPath accepts the tokens %%, %C, %h, %i, %L, %l, %n, %p, %r, and
1120 %u.
1121 HostName accepts the tokens %% and %h.
1123 IdentityAgent and IdentityFile accept the tokens %%, %d, %h, %i, %l, %r,
1125 and %u.
1126 LocalCommand accepts the tokens %%, %C, %d, %h, %i, %l, %n, %p, %r, %T,
1128 and %u.
1129 ProxyCommand accepts the tokens %%, %h, %p, and %r.
1131 RemoteCommand accepts the tokens %%, %C, %d, %h, %i, %l, %n, %p, %r, and
1133 %u.
1134
1136 ~/.ssh/config
1137 This is the per-user configuration file. The format of this file
1138 is described above. This file is used by the SSH client.
1139 Because of the potential for abuse, this file must have strict
1140 permissions: read/write for the user, and not writable by others.
1141 /etc/gsissh/ssh_config
1143 Systemwide configuration file. This file provides defaults for
1144 those values that are not specified in the user's configuration
1145 file, and for those users who do not have a configuration file.
1146 This file must be world-readable.
1147
1149 ssh(1)
1150
1152 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
1153 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
1154 de Raadt and Dug Song removed many bugs, re-added newer features and cre‐
1155 ated OpenSSH. Markus Friedl contributed the support for SSH protocol
1156 versions 1.5 and 2.0.
1157BSD June 21, 2019 BSD