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. system-wide configuration file (/etc/ssh/ssh_config)
13 For each parameter, the first obtained value will be used. The configu‐
15 ration files contain sections separated by Host specifications, and that
16 section is only applied for hosts that match one of the patterns given in
17 the specification. The matched host name is usually the one given on the
18 command line (see the CanonicalizeHostname option for exceptions).
19 Since the first obtained value for each parameter is used, more host-spe‐
21 cific declarations should be given near the beginning of the file, and
22 general defaults at the end.
23 The file contains keyword-argument pairs, one per line. Lines starting
25 with ‘#’ and empty lines are interpreted as comments. Arguments may
26 optionally be enclosed in double quotes (") in order to represent argu‐
27 ments containing spaces. Configuration options may be separated by
28 whitespace or optional whitespace and exactly one ‘=’; the latter format
29 is useful to avoid the need to quote whitespace when specifying configu‐
30 ration options using the ssh, scp, and sftp -o option.
31 The possible keywords and their meanings are as follows (note that key‐
33 words are case-insensitive and arguments are case-sensitive):
34 Host Restricts the following declarations (up to the next Host or
36 Match keyword) to be only for those hosts that match one of the
37 patterns given after the keyword. If more than one pattern is
38 provided, they should be separated by whitespace. A single ‘*’
39 as a pattern can be used to provide global defaults for all
40 hosts. The host is usually the hostname argument given on the
41 command line (see the CanonicalizeHostname keyword for excep‐
42 tions).
43 A pattern entry may be negated by prefixing it with an exclama‐
45 tion mark (‘!’). If a negated entry is matched, then the Host
46 entry is ignored, regardless of whether any other patterns on the
47 line match. Negated matches are therefore useful to provide
48 exceptions for wildcard matches.
49 See PATTERNS for more information on patterns.
51 Match Restricts the following declarations (up to the next Host or
53 Match keyword) to be used only when the conditions following the
54 Match keyword are satisfied. Match conditions are specified
55 using one or more criteria or the single token all which always
56 matches. The available criteria keywords are: canonical, final,
57 exec, host, originalhost, user, and localuser. The all criteria
58 must appear alone or immediately after canonical or final. Other
59 criteria may be combined arbitrarily. All criteria but all,
60 canonical, and final require an argument. Criteria may be
61 negated by prepending an exclamation mark (‘!’).
62 The canonical keyword matches only when the configuration file is
64 being re-parsed after hostname canonicalization (see the
65 CanonicalizeHostname option). This may be useful to specify con‐
66 ditions that work with canonical host names only.
67 The final keyword requests that the configuration be re-parsed
69 (regardless of whether CanonicalizeHostname is enabled), and
70 matches only during this final pass. If CanonicalizeHostname is
71 enabled, then canonical and final match during the same pass.
72 The exec keyword executes the specified command under the user's
74 shell. If the command returns a zero exit status then the condi‐
75 tion is considered true. Commands containing whitespace charac‐
76 ters must be quoted. Arguments to exec accept the tokens
77 described in the TOKENS section.
78 The other keywords' criteria must be single entries or comma-sep‐
80 arated lists and may use the wildcard and negation operators
81 described in the PATTERNS section. The criteria for the host
82 keyword are matched against the target hostname, after any sub‐
83 stitution by the Hostname or CanonicalizeHostname options. The
84 originalhost keyword matches against the hostname as it was spec‐
85 ified on the command-line. The user keyword matches against the
86 target username on the remote host. The localuser keyword
87 matches against the name of the local user running ssh(1) (this
88 keyword may be useful in system-wide ssh_config files).
89 AddKeysToAgent
91 Specifies whether keys should be automatically added to a running
92 ssh-agent(1). If this option is set to yes and a key is loaded
93 from a file, the key and its passphrase are added to the agent
94 with the default lifetime, as if by ssh-add(1). If this option
95 is set to ask, ssh(1) will require confirmation using the
96 SSH_ASKPASS program before adding a key (see ssh-add(1) for
97 details). If this option is set to confirm, each use of the key
98 must be confirmed, as if the -c option was specified to
99 ssh-add(1). If this option is set to no, no keys are added to
100 the agent. The argument must be yes, confirm, ask, or no (the
101 default).
102 AddressFamily
104 Specifies which address family to use when connecting. Valid
105 arguments are any (the default), inet (use IPv4 only), or inet6
106 (use IPv6 only).
107 BatchMode
109 If set to yes, passphrase/password querying will be disabled.
110 This option is useful in scripts and other batch jobs where no
111 user is present to supply the password. The argument must be yes
112 or no (the default).
113 BindAddress
115 Use the specified address on the local machine as the source
116 address of the connection. Only useful on systems with more than
117 one address.
118 BindInterface
120 Use the address of the specified interface on the local machine
121 as the source address of the connection.
122 CanonicalDomains
124 When CanonicalizeHostname is enabled, this option specifies the
125 list of domain suffixes in which to search for the specified des‐
126 tination host.
127 CanonicalizeFallbackLocal
129 Specifies whether to fail with an error when hostname canonical‐
130 ization fails. The default, yes, will attempt to look up the
131 unqualified hostname using the system resolver's search rules. A
132 value of no will cause ssh(1) to fail instantly if
133 CanonicalizeHostname is enabled and the target hostname cannot be
134 found in any of the domains specified by CanonicalDomains.
135 CanonicalizeHostname
137 Controls whether explicit hostname canonicalization is performed.
138 The default, no, is not to perform any name rewriting and let the
139 system resolver handle all hostname lookups. If set to yes then,
140 for connections that do not use a ProxyCommand or ProxyJump,
141 ssh(1) will attempt to canonicalize the hostname specified on the
142 command line using the CanonicalDomains suffixes and
143 CanonicalizePermittedCNAMEs rules. If CanonicalizeHostname is
144 set to always, then canonicalization is applied to proxied con‐
145 nections too.
146 If this option is enabled, then the configuration files are pro‐
148 cessed again using the new target name to pick up any new config‐
149 uration in matching Host and Match stanzas.
150 CanonicalizeMaxDots
152 Specifies the maximum number of dot characters in a hostname
153 before canonicalization is disabled. The default, 1, allows a
154 single dot (i.e. hostname.subdomain).
155 CanonicalizePermittedCNAMEs
157 Specifies rules to determine whether CNAMEs should be followed
158 when canonicalizing hostnames. The rules consist of one or more
159 arguments of source_domain_list:target_domain_list, where
160 source_domain_list is a pattern-list of domains that may follow
161 CNAMEs in canonicalization, and target_domain_list is a pattern-
162 list of domains that they may resolve to.
163 For example, "*.a.example.com:*.b.example.com,*.c.example.com"
165 will allow hostnames matching "*.a.example.com" to be canonical‐
166 ized to names in the "*.b.example.com" or "*.c.example.com"
167 domains.
168 CASignatureAlgorithms
170 Specifies which algorithms are allowed for signing of certifi‐
171 cates by certificate authorities (CAs). The default is:
172 ecdsa-sha2-nistp256.ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
174 ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
175 ssh(1) will not accept host certificates signed using algorithms
177 other than those specified.
178 CertificateFile
180 Specifies a file from which the user's certificate is read. A
181 corresponding private key must be provided separately in order to
182 use this certificate either from an IdentityFile directive or -i
183 flag to ssh(1), via ssh-agent(1), or via a PKCS11Provider.
184 Arguments to CertificateFile may use the tilde syntax to refer to
186 a user's home directory or the tokens described in the TOKENS
187 section.
188 It is possible to have multiple certificate files specified in
190 configuration files; these certificates will be tried in
191 sequence. Multiple CertificateFile directives will add to the
192 list of certificates used for authentication.
193 ChallengeResponseAuthentication
195 Specifies whether to use challenge-response authentication. The
196 argument to this keyword must be yes (the default) or no.
197 CheckHostIP
199 If set to yes (the default), ssh(1) will additionally check the
200 host IP address in the known_hosts file. This allows it to
201 detect if a host key changed due to DNS spoofing and will add
202 addresses of destination hosts to ~/.ssh/known_hosts in the
203 process, regardless of the setting of StrictHostKeyChecking. If
204 the option is set to no, the check will not be executed.
205 Ciphers
207 Specifies the ciphers allowed and their order of preference.
208 Multiple ciphers must be comma-separated. If the specified value
209 begins with a ‘+’ character, then the specified ciphers will be
210 appended to the default set instead of replacing them. If the
211 specified value begins with a ‘-’ character, then the specified
212 ciphers (including wildcards) will be removed from the default
213 set instead of replacing them.
214 The supported ciphers are:
216 3des-cbc
218 aes128-cbc
219 aes192-cbc
220 aes256-cbc
221 aes128-ctr
222 aes192-ctr
223 aes256-ctr
224 aes128-gcm@openssh.com
225 aes256-gcm@openssh.com
226 chacha20-poly1305@openssh.com
227 The default is handled system-wide by crypto-policies(7). To see
229 the defaults and how to modifuy this default, see manual page
230 update-crypto-policies(8).
231 The list of available ciphers may also be obtained using "ssh -Q
233 cipher".
234 ClearAllForwardings
236 Specifies that all local, remote, and dynamic port forwardings
237 specified in the configuration files or on the command line be
238 cleared. This option is primarily useful when used from the
239 ssh(1) command line to clear port forwardings set in configura‐
240 tion files, and is automatically set by scp(1) and sftp(1). The
241 argument must be yes or no (the default).
242 Compression
244 Specifies whether to use compression. The argument must be yes
245 or no (the default).
246 ConnectionAttempts
248 Specifies the number of tries (one per second) to make before
249 exiting. The argument must be an integer. This may be useful in
250 scripts if the connection sometimes fails. The default is 1.
251 ConnectTimeout
253 Specifies the timeout (in seconds) used when connecting to the
254 SSH server, instead of using the default system TCP timeout.
255 This value is used only when the target is down or really
256 unreachable, not when it refuses the connection.
257 ControlMaster
259 Enables the sharing of multiple sessions over a single network
260 connection. When set to yes, ssh(1) will listen for connections
261 on a control socket specified using the ControlPath argument.
262 Additional sessions can connect to this socket using the same
263 ControlPath with ControlMaster set to no (the default). These
264 sessions will try to reuse the master instance's network connec‐
265 tion rather than initiating new ones, but will fall back to con‐
266 necting normally if the control socket does not exist, or is not
267 listening.
268 Setting this to ask will cause ssh(1) to listen for control con‐
270 nections, but require confirmation using ssh-askpass(1). If the
271 ControlPath cannot be opened, ssh(1) will continue without con‐
272 necting to a master instance.
273 X11 and ssh-agent(1) forwarding is supported over these multi‐
275 plexed connections, however the display and agent forwarded will
276 be the one belonging to the master connection i.e. it is not pos‐
277 sible to forward multiple displays or agents.
278 Two additional options allow for opportunistic multiplexing: try
280 to use a master connection but fall back to creating a new one if
281 one does not already exist. These options are: auto and autoask.
282 The latter requires confirmation like the ask option.
283 ControlPath
285 Specify the path to the control socket used for connection shar‐
286 ing as described in the ControlMaster section above or the string
287 none to disable connection sharing. Arguments to ControlPath may
288 use the tilde syntax to refer to a user's home directory or the
289 tokens described in the TOKENS section. It is recommended that
290 any ControlPath used for opportunistic connection sharing include
291 at least %h, %p, and %r (or alternatively %C) and be placed in a
292 directory that is not writable by other users. This ensures that
293 shared connections are uniquely identified.
294 ControlPersist
296 When used in conjunction with ControlMaster, specifies that the
297 master connection should remain open in the background (waiting
298 for future client connections) after the initial client connec‐
299 tion has been closed. If set to no, then the master connection
300 will not be placed into the background, and will close as soon as
301 the initial client connection is closed. If set to yes or 0,
302 then the master connection will remain in the background indefi‐
303 nitely (until killed or closed via a mechanism such as the "ssh
304 -O exit"). If set to a time in seconds, or a time in any of the
305 formats documented in sshd_config(5), then the backgrounded mas‐
306 ter connection will automatically terminate after it has remained
307 idle (with no client connections) for the specified time.
308 DynamicForward
310 Specifies that a TCP port on the local machine be forwarded over
311 the secure channel, and the application protocol is then used to
312 determine where to connect to from the remote machine.
313 The argument must be [bind_address:]port. IPv6 addresses can be
315 specified by enclosing addresses in square brackets. By default,
316 the local port is bound in accordance with the GatewayPorts set‐
317 ting. However, an explicit bind_address may be used to bind the
318 connection to a specific address. The bind_address of localhost
319 indicates that the listening port be bound for local use only,
320 while an empty address or ‘*’ indicates that the port should be
321 available from all interfaces.
322 Currently the SOCKS4 and SOCKS5 protocols are supported, and
324 ssh(1) will act as a SOCKS server. Multiple forwardings may be
325 specified, and additional forwardings can be given on the command
326 line. Only the superuser can forward privileged ports.
327 EnableSSHKeysign
329 Setting this option to yes in the global client configuration
330 file /etc/ssh/ssh_config enables the use of the helper program
331 ssh-keysign(8) during HostbasedAuthentication. The argument must
332 be yes or no (the default). This option should be placed in the
333 non-hostspecific section. See ssh-keysign(8) for more informa‐
334 tion.
335 EscapeChar
337 Sets the escape character (default: ‘~’). The escape character
338 can also be set on the command line. The argument should be a
339 single character, ‘^’ followed by a letter, or none to disable
340 the escape character entirely (making the connection transparent
341 for binary data).
342 ExitOnForwardFailure
344 Specifies whether ssh(1) should terminate the connection if it
345 cannot set up all requested dynamic, tunnel, local, and remote
346 port forwardings, (e.g. if either end is unable to bind and lis‐
347 ten on a specified port). Note that ExitOnForwardFailure does
348 not apply to connections made over port forwardings and will not,
349 for example, cause ssh(1) to exit if TCP connections to the ulti‐
350 mate forwarding destination fail. The argument must be yes or no
351 (the default).
352 FingerprintHash
354 Specifies the hash algorithm used when displaying key finger‐
355 prints. Valid options are: md5 and sha256 (the default).
356 ForwardAgent
358 Specifies whether the connection to the authentication agent (if
359 any) will be forwarded to the remote machine. The argument must
360 be yes or no (the default).
361 Agent forwarding should be enabled with caution. Users with the
363 ability to bypass file permissions on the remote host (for the
364 agent's Unix-domain socket) can access the local agent through
365 the forwarded connection. An attacker cannot obtain key material
366 from the agent, however they can perform operations on the keys
367 that enable them to authenticate using the identities loaded into
368 the agent.
369 ForwardX11
371 Specifies whether X11 connections will be automatically redi‐
372 rected over the secure channel and DISPLAY set. The argument
373 must be yes or no (the default).
374 X11 forwarding should be enabled with caution. Users with the
376 ability to bypass file permissions on the remote host (for the
377 user's X11 authorization database) can access the local X11 dis‐
378 play through the forwarded connection. An attacker may then be
379 able to perform activities such as keystroke monitoring if the
380 ForwardX11Trusted option is also enabled.
381 ForwardX11Timeout
383 Specify a timeout for untrusted X11 forwarding using the format
384 described in the TIME FORMATS section of sshd_config(5). X11
385 connections received by ssh(1) after this time will be refused.
386 Setting ForwardX11Timeout to zero will disable the timeout and
387 permit X11 forwarding for the life of the connection. The
388 default is to disable untrusted X11 forwarding after twenty min‐
389 utes has elapsed.
390 ForwardX11Trusted
392 If this option is set to yes, remote X11 clients will have full
393 access to the original X11 display.
394 If this option is set to no (the default), remote X11 clients
396 will be considered untrusted and prevented from stealing or tam‐
397 pering with data belonging to trusted X11 clients. Furthermore,
398 the xauth(1) token used for the session will be set to expire
399 after 20 minutes. Remote clients will be refused access after
400 this time.
401 See the X11 SECURITY extension specification for full details on
403 the restrictions imposed on untrusted clients.
404 GatewayPorts
406 Specifies whether remote hosts are allowed to connect to local
407 forwarded ports. By default, ssh(1) binds local port forwardings
408 to the loopback address. This prevents other remote hosts from
409 connecting to forwarded ports. GatewayPorts can be used to spec‐
410 ify that ssh should bind local port forwardings to the wildcard
411 address, thus allowing remote hosts to connect to forwarded
412 ports. The argument must be yes or no (the default).
413 GlobalKnownHostsFile
415 Specifies one or more files to use for the global host key data‐
416 base, separated by whitespace. The default is
417 /etc/ssh/ssh_known_hosts, /etc/ssh/ssh_known_hosts2.
418 GSSAPIAuthentication
420 Specifies whether user authentication based on GSSAPI is allowed.
421 The default is no.
422 GSSAPIClientIdentity
424 If set, specifies the GSSAPI client identity that ssh should use
425 when connecting to the server. The default is unset, which means
426 that the default identity will be used.
427 GSSAPIDelegateCredentials
429 Forward (delegate) credentials to the server. The default is no.
430 GSSAPIKeyExchange
432 Specifies whether key exchange based on GSSAPI may be used. When
433 using GSSAPI key exchange the server need not have a host key.
434 The default is “no”.
435 GSSAPIRenewalForcesRekey
437 If set to “yes” then renewal of the client's GSSAPI credentials
438 will force the rekeying of the ssh connection. With a compatible
439 server, this will delegate the renewed credentials to a session
440 on the server.
441 Checks are made to ensure that credentials are only propagated
443 when the new credentials match the old ones on the originating
444 client and where the receiving server still has the old set in
445 its cache.
446 The default is “no”.
448 For this to work GSSAPIKeyExchange needs to be enabled in the
450 server and also used by the client.
451 GSSAPIServerIdentity
453 If set, specifies the GSSAPI server identity that ssh should
454 expect when connecting to the server. The default is unset, which
455 means that the expected GSSAPI server identity will be determined
456 from the target hostname.
457 GSSAPITrustDns
459 Set to “yes” to indicate that the DNS is trusted to securely
460 canonicalize the name of the host being connected to. If “no”,
461 the hostname entered on the command line will be passed untouched
462 to the GSSAPI library. The default is “no”.
463 GSSAPIKexAlgorithms
465 The list of key exchange algorithms that are offered for GSSAPI
466 key exchange. Possible values are
467 gss-gex-sha1-,
469 gss-group1-sha1-,
470 gss-group14-sha1-,
471 gss-group14-sha256-,
472 gss-group16-sha512-,
473 gss-nistp256-sha256-,
474 gss-curve25519-sha256-
475 The default is handled system-wide by crypto-policies(7). To see
477 the defaults and how to modifuy this default, see manual page
478 update-crypto-policies(8). This option only applies to protocol
479 version 2 connections using GSSAPI.
480 HashKnownHosts
482 Indicates that ssh(1) should hash host names and addresses when
483 they are added to ~/.ssh/known_hosts. These hashed names may be
484 used normally by ssh(1) and sshd(8), but they do not reveal iden‐
485 tifying information should the file's contents be disclosed. The
486 default is no. Note that existing names and addresses in known
487 hosts files will not be converted automatically, but may be manu‐
488 ally hashed using ssh-keygen(1).
489 HostbasedAuthentication
491 Specifies whether to try rhosts based authentication with public
492 key authentication. The argument must be yes or no (the
493 default).
494 HostbasedKeyTypes
496 Specifies the key types that will be used for hostbased authenti‐
497 cation as a comma-separated list of patterns. Alternately if the
498 specified value begins with a ‘+’ character, then the specified
499 key types will be appended to the default set instead of replac‐
500 ing them. If the specified value begins with a ‘-’ character,
501 then the specified key types (including wildcards) will be
502 removed from the default set instead of replacing them. The
503 default for this option is:
504 ecdsa-sha2-nistp256-cert-v01@openssh.com,
506 ecdsa-sha2-nistp384-cert-v01@openssh.com,
507 ecdsa-sha2-nistp521-cert-v01@openssh.com,
508 ssh-ed25519-cert-v01@openssh.com,
509 rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,
510 ssh-rsa-cert-v01@openssh.com,
511 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
512 ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
513 The -Q option of ssh(1) may be used to list supported key types.
515 HostKeyAlgorithms
517 Specifies the host key algorithms that the client wants to use in
518 order of preference. Alternately if the specified value begins
519 with a ‘+’ character, then the specified key types will be
520 appended to the default set instead of replacing them. If the
521 specified value begins with a ‘-’ character, then the specified
522 key types (including wildcards) will be removed from the default
523 set instead of replacing them. The default for this option is:
524 ecdsa-sha2-nistp256-cert-v01@openssh.com,
526 ecdsa-sha2-nistp384-cert-v01@openssh.com,
527 ecdsa-sha2-nistp521-cert-v01@openssh.com,
528 ssh-ed25519-cert-v01@openssh.com,
529 rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,
530 ssh-rsa-cert-v01@openssh.com,
531 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
532 ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
533 If hostkeys are known for the destination host then this default
535 is modified to prefer their algorithms.
536 The list of available key types may also be obtained using "ssh
538 -Q key".
539 HostKeyAlias
541 Specifies an alias that should be used instead of the real host
542 name when looking up or saving the host key in the host key data‐
543 base files and when validating host certificates. This option is
544 useful for tunneling SSH connections or for multiple servers run‐
545 ning on a single host.
546 HostName
548 Specifies the real host name to log into. This can be used to
549 specify nicknames or abbreviations for hosts. Arguments to
550 HostName accept the tokens described in the TOKENS section.
551 Numeric IP addresses are also permitted (both on the command line
552 and in HostName specifications). The default is the name given
553 on the command line.
554 IdentitiesOnly
556 Specifies that ssh(1) should only use the authentication identity
557 and certificate files explicitly configured in the ssh_config
558 files or passed on the ssh(1) command-line, even if ssh-agent(1)
559 or a PKCS11Provider offers more identities. The argument to this
560 keyword must be yes or no (the default). This option is intended
561 for situations where ssh-agent offers many different identities.
562 IdentityAgent
564 Specifies the UNIX-domain socket used to communicate with the
565 authentication agent.
566 This option overrides the SSH_AUTH_SOCK environment variable and
568 can be used to select a specific agent. Setting the socket name
569 to none disables the use of an authentication agent. If the
570 string "SSH_AUTH_SOCK" is specified, the location of the socket
571 will be read from the SSH_AUTH_SOCK environment variable. Other‐
572 wise if the specified value begins with a ‘$’ character, then it
573 will be treated as an environment variable containing the loca‐
574 tion of the socket.
575 Arguments to IdentityAgent may use the tilde syntax to refer to a
577 user's home directory or the tokens described in the TOKENS sec‐
578 tion.
579 IdentityFile
581 Specifies a file from which the user's DSA, ECDSA, Ed25519 or RSA
582 authentication identity is read. The default is ~/.ssh/id_dsa,
583 ~/.ssh/id_ecdsa, ~/.ssh/id_ed25519 and ~/.ssh/id_rsa. Addition‐
584 ally, any identities represented by the authentication agent will
585 be used for authentication unless IdentitiesOnly is set. If no
586 certificates have been explicitly specified by CertificateFile,
587 ssh(1) will try to load certificate information from the filename
588 obtained by appending -cert.pub to the path of a specified
589 IdentityFile.
590 Arguments to IdentityFile may use the tilde syntax to refer to a
592 user's home directory or the tokens described in the TOKENS sec‐
593 tion.
594 It is possible to have multiple identity files specified in con‐
596 figuration files; all these identities will be tried in sequence.
597 Multiple IdentityFile directives will add to the list of identi‐
598 ties tried (this behaviour differs from that of other configura‐
599 tion directives).
600 IdentityFile may be used in conjunction with IdentitiesOnly to
602 select which identities in an agent are offered during authenti‐
603 cation. IdentityFile may also be used in conjunction with
604 CertificateFile in order to provide any certificate also needed
605 for authentication with the identity.
606 The authentication identity can be also specified in a form of
608 PKCS#11 URI starting with a string pkcs11:. There is supported a
609 subset of the PKCS#11 URI as defined in RFC 7512 (implemented
610 path arguments id, manufacturer, object, token and query argu‐
611 ments module-path and pin-value ). The URI can not be in quotes.
612 IgnoreUnknown
614 Specifies a pattern-list of unknown options to be ignored if they
615 are encountered in configuration parsing. This may be used to
616 suppress errors if ssh_config contains options that are unrecog‐
617 nised by ssh(1). It is recommended that IgnoreUnknown be listed
618 early in the configuration file as it will not be applied to
619 unknown options that appear before it.
620 Include
622 Include the specified configuration file(s). Multiple pathnames
623 may be specified and each pathname may contain glob(7) wildcards
624 and, for user configurations, shell-like ‘~’ references to user
625 home directories. Files without absolute paths are assumed to be
626 in ~/.ssh if included in a user configuration file or /etc/ssh if
627 included from the system configuration file. Include directive
628 may appear inside a Match or Host block to perform conditional
629 inclusion.
630 IPQoS Specifies the IPv4 type-of-service or DSCP class for connections.
632 Accepted values are af11, af12, af13, af21, af22, af23, af31,
633 af32, af33, af41, af42, af43, cs0, cs1, cs2, cs3, cs4, cs5, cs6,
634 cs7, ef, lowdelay, throughput, reliability, a numeric value, or
635 none to use the operating system default. This option may take
636 one or two arguments, separated by whitespace. If one argument
637 is specified, it is used as the packet class unconditionally. If
638 two values are specified, the first is automatically selected for
639 interactive sessions and the second for non-interactive sessions.
640 The default is af21 (Low-Latency Data) for interactive sessions
641 and cs1 (Lower Effort) for non-interactive sessions.
642 KbdInteractiveAuthentication
644 Specifies whether to use keyboard-interactive authentication.
645 The argument to this keyword must be yes (the default) or no.
646 KbdInteractiveDevices
648 Specifies the list of methods to use in keyboard-interactive
649 authentication. Multiple method names must be comma-separated.
650 The default is to use the server specified list. The methods
651 available vary depending on what the server supports. For an
652 OpenSSH server, it may be zero or more of: bsdauth and pam.
653 KexAlgorithms
655 Specifies the available KEX (Key Exchange) algorithms. Multiple
656 algorithms must be comma-separated. Alternately if the specified
657 value begins with a ‘+’ character, then the specified methods
658 will be appended to the default set instead of replacing them.
659 If the specified value begins with a ‘-’ character, then the
660 specified methods (including wildcards) will be removed from the
661 default set instead of replacing them. The default is handled
662 system-wide by crypto-policies(7). To see the defaults and how
663 to modifuy this default, see manual page
664 update-crypto-policies(8).
665 The list of available key exchange algorithms may also be
667 obtained using "ssh -Q kex".
668 LocalCommand
670 Specifies a command to execute on the local machine after suc‐
671 cessfully connecting to the server. The command string extends
672 to the end of the line, and is executed with the user's shell.
673 Arguments to LocalCommand accept the tokens described in the
674 TOKENS section.
675 The command is run synchronously and does not have access to the
677 session of the ssh(1) that spawned it. It should not be used for
678 interactive commands.
679 This directive is ignored unless PermitLocalCommand has been
681 enabled.
682 LocalForward
684 Specifies that a TCP port on the local machine be forwarded over
685 the secure channel to the specified host and port from the remote
686 machine. The first argument must be [bind_address:]port and the
687 second argument must be host:hostport. IPv6 addresses can be
688 specified by enclosing addresses in square brackets. Multiple
689 forwardings may be specified, and additional forwardings can be
690 given on the command line. Only the superuser can forward privi‐
691 leged ports. By default, the local port is bound in accordance
692 with the GatewayPorts setting. However, an explicit bind_address
693 may be used to bind the connection to a specific address. The
694 bind_address of localhost indicates that the listening port be
695 bound for local use only, while an empty address or ‘*’ indicates
696 that the port should be available from all interfaces.
697 LogLevel
699 Gives the verbosity level that is used when logging messages from
700 ssh(1). The possible values are: QUIET, FATAL, ERROR, INFO, VER‐
701 BOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO.
702 DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify
703 higher levels of verbose output.
704 MACs Specifies the MAC (message authentication code) algorithms in
706 order of preference. The MAC algorithm is used for data
707 integrity protection. Multiple algorithms must be comma-sepa‐
708 rated. If the specified value begins with a ‘+’ character, then
709 the specified algorithms will be appended to the default set
710 instead of replacing them. If the specified value begins with a
711 ‘-’ character, then the specified algorithms (including wild‐
712 cards) will be removed from the default set instead of replacing
713 them.
714 The algorithms that contain "-etm" calculate the MAC after
716 encryption (encrypt-then-mac). These are considered safer and
717 their use recommended.
718 The default is handled system-wide by crypto-policies(7). To see
720 the defaults and how to modifuy this default, see manual page
721 update-crypto-policies(8).
722 The list of available MAC algorithms may also be obtained using
724 "ssh -Q mac".
725 NoHostAuthenticationForLocalhost
727 Disable host authentication for localhost (loopback addresses).
728 The argument to this keyword must be yes or no (the default).
729 NumberOfPasswordPrompts
731 Specifies the number of password prompts before giving up. The
732 argument to this keyword must be an integer. The default is 3.
733 PasswordAuthentication
735 Specifies whether to use password authentication. The argument
736 to this keyword must be yes (the default) or no.
737 PermitLocalCommand
739 Allow local command execution via the LocalCommand option or
740 using the !command escape sequence in ssh(1). The argument must
741 be yes or no (the default).
742 PKCS11Provider
744 Specifies which PKCS#11 provider to use or none to indicate that
745 no provider should be used (the default). The argument to this
746 keyword is a path to the PKCS#11 shared library ssh(1) should use
747 to communicate with a PKCS#11 token providing keys for user
748 authentication.
749 Port Specifies the port number to connect on the remote host. The
751 default is 22.
752 PreferredAuthentications
754 Specifies the order in which the client should try authentication
755 methods. This allows a client to prefer one method (e.g.
756 keyboard-interactive) over another method (e.g. password). The
757 default is:
758 gssapi-with-mic,hostbased,publickey,
760 keyboard-interactive,password
761 ProxyCommand
763 Specifies the command to use to connect to the server. The com‐
764 mand string extends to the end of the line, and is executed using
765 the user's shell ‘exec’ directive to avoid a lingering shell
766 process.
767 Arguments to ProxyCommand accept the tokens described in the
769 TOKENS section. The command can be basically anything, and
770 should read from its standard input and write to its standard
771 output. It should eventually connect an sshd(8) server running
772 on some machine, or execute sshd -i somewhere. Host key manage‐
773 ment will be done using the HostName of the host being connected
774 (defaulting to the name typed by the user). Setting the command
775 to none disables this option entirely. Note that CheckHostIP is
776 not available for connects with a proxy command.
777 This directive is useful in conjunction with nc(1) and its proxy
779 support. For example, the following directive would connect via
780 an HTTP proxy at 192.0.2.0:
781 ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
783 ProxyJump
785 Specifies one or more jump proxies as either [user@]host[:port]
786 or an ssh URI. Multiple proxies may be separated by comma char‐
787 acters and will be visited sequentially. Setting this option
788 will cause ssh(1) to connect to the target host by first making a
789 ssh(1) connection to the specified ProxyJump host and then estab‐
790 lishing a TCP forwarding to the ultimate target from there.
791 Note that this option will compete with the ProxyCommand option -
793 whichever is specified first will prevent later instances of the
794 other from taking effect.
795 Note also that the configuration for the destination host (either
797 supplied via the command-line or the configuration file) is not
798 generally applied to jump hosts. ~/.ssh/config should be used if
799 specific configuration is required for jump hosts.
800 ProxyUseFdpass
802 Specifies that ProxyCommand will pass a connected file descriptor
803 back to ssh(1) instead of continuing to execute and pass data.
804 The default is no.
805 PubkeyAcceptedKeyTypes
807 Specifies the key types that will be used for public key authen‐
808 tication as a comma-separated list of patterns. Alternately if
809 the specified value begins with a ‘+’ character, then the key
810 types after it will be appended to the default instead of replac‐
811 ing it. If the specified value begins with a ‘-’ character, then
812 the specified key types (including wildcards) will be removed
813 from the default set instead of replacing them. The default is
814 handled system-wide by crypto-policies(7). To see the defaults
815 and how to modifuy this default, see manual page
816 update-crypto-policies(8).
817 The list of available key types may also be obtained using "ssh
819 -Q key".
820 PubkeyAuthentication
822 Specifies whether to try public key authentication. The argument
823 to this keyword must be yes (the default) or no.
824 RekeyLimit
826 Specifies the maximum amount of data that may be transmitted
827 before the session key is renegotiated, optionally followed a
828 maximum amount of time that may pass before the session key is
829 renegotiated. The first argument is specified in bytes and may
830 have a suffix of ‘K’, ‘M’, or ‘G’ to indicate Kilobytes,
831 Megabytes, or Gigabytes, respectively. The default is between
832 ‘1G’ and ‘4G’, depending on the cipher. The optional second
833 value is specified in seconds and may use any of the units docu‐
834 mented in the TIME FORMATS section of sshd_config(5). The
835 default value for RekeyLimit is default none, which means that
836 rekeying is performed after the cipher's default amount of data
837 has been sent or received and no time based rekeying is done.
838 RemoteCommand
840 Specifies a command to execute on the remote machine after suc‐
841 cessfully connecting to the server. The command string extends
842 to the end of the line, and is executed with the user's shell.
843 Arguments to RemoteCommand accept the tokens described in the
844 TOKENS section.
845 RemoteForward
847 Specifies that a TCP port on the remote machine be forwarded over
848 the secure channel. The remote port may either be forwarded to a
849 specified host and port from the local machine, or may act as a
850 SOCKS 4/5 proxy that allows a remote client to connect to arbi‐
851 trary destinations from the local machine. The first argument
852 must be [bind_address:]port If forwarding to a specific destina‐
853 tion then the second argument must be host:hostport, otherwise if
854 no destination argument is specified then the remote forwarding
855 will be established as a SOCKS proxy.
856 IPv6 addresses can be specified by enclosing addresses in square
858 brackets. Multiple forwardings may be specified, and additional
859 forwardings can be given on the command line. Privileged ports
860 can be forwarded only when logging in as root on the remote
861 machine.
862 If the port argument is 0, the listen port will be dynamically
864 allocated on the server and reported to the client at run time.
865 If the bind_address is not specified, the default is to only bind
867 to loopback addresses. If the bind_address is ‘*’ or an empty
868 string, then the forwarding is requested to listen on all inter‐
869 faces. Specifying a remote bind_address will only succeed if the
870 server's GatewayPorts option is enabled (see sshd_config(5)).
871 RequestTTY
873 Specifies whether to request a pseudo-tty for the session. The
874 argument may be one of: no (never request a TTY), yes (always
875 request a TTY when standard input is a TTY), force (always
876 request a TTY) or auto (request a TTY when opening a login ses‐
877 sion). This option mirrors the -t and -T flags for ssh(1).
878 RevokedHostKeys
880 Specifies revoked host public keys. Keys listed in this file
881 will be refused for host authentication. Note that if this file
882 does not exist or is not readable, then host authentication will
883 be refused for all hosts. Keys may be specified as a text file,
884 listing one public key per line, or as an OpenSSH Key Revocation
885 List (KRL) as generated by ssh-keygen(1). For more information
886 on KRLs, see the KEY REVOCATION LISTS section in ssh-keygen(1).
887 SendEnv
889 Specifies what variables from the local environ(7) should be sent
890 to the server. The server must also support it, and the server
891 must be configured to accept these environment variables. Note
892 that the TERM environment variable is always sent whenever a
893 pseudo-terminal is requested as it is required by the protocol.
894 Refer to AcceptEnv in sshd_config(5) for how to configure the
895 server. Variables are specified by name, which may contain wild‐
896 card characters. Multiple environment variables may be separated
897 by whitespace or spread across multiple SendEnv directives.
898 See PATTERNS for more information on patterns.
900 It is possible to clear previously set SendEnv variable names by
902 prefixing patterns with -. The default is not to send any envi‐
903 ronment variables.
904 ServerAliveCountMax
906 Sets the number of server alive messages (see below) which may be
907 sent without ssh(1) receiving any messages back from the server.
908 If this threshold is reached while server alive messages are
909 being sent, ssh will disconnect from the server, terminating the
910 session. It is important to note that the use of server alive
911 messages is very different from TCPKeepAlive (below). The server
912 alive messages are sent through the encrypted channel and there‐
913 fore will not be spoofable. The TCP keepalive option enabled by
914 TCPKeepAlive is spoofable. The server alive mechanism is valu‐
915 able when the client or server depend on knowing when a connec‐
916 tion has become inactive.
917 The default value is 3. If, for example, ServerAliveInterval
919 (see below) is set to 15 and ServerAliveCountMax is left at the
920 default, if the server becomes unresponsive, ssh will disconnect
921 after approximately 45 seconds.
922 ServerAliveInterval
924 Sets a timeout interval in seconds after which if no data has
925 been received from the server, ssh(1) will send a message through
926 the encrypted channel to request a response from the server. The
927 default is 0, indicating that these messages will not be sent to
928 the server.
929 SetEnv Directly specify one or more environment variables and their con‐
931 tents to be sent to the server. Similarly to SendEnv, the server
932 must be prepared to accept the environment variable.
933 StreamLocalBindMask
935 Sets the octal file creation mode mask (umask) used when creating
936 a Unix-domain socket file for local or remote port forwarding.
937 This option is only used for port forwarding to a Unix-domain
938 socket file.
939 The default value is 0177, which creates a Unix-domain socket
941 file that is readable and writable only by the owner. Note that
942 not all operating systems honor the file mode on Unix-domain
943 socket files.
944 StreamLocalBindUnlink
946 Specifies whether to remove an existing Unix-domain socket file
947 for local or remote port forwarding before creating a new one.
948 If the socket file already exists and StreamLocalBindUnlink is
949 not enabled, ssh will be unable to forward the port to the Unix-
950 domain socket file. This option is only used for port forwarding
951 to a Unix-domain socket file.
952 The argument must be yes or no (the default).
954 StrictHostKeyChecking
956 If this flag is set to yes, ssh(1) will never automatically add
957 host keys to the ~/.ssh/known_hosts file, and refuses to connect
958 to hosts whose host key has changed. This provides maximum pro‐
959 tection against man-in-the-middle (MITM) attacks, though it can
960 be annoying when the /etc/ssh/ssh_known_hosts file is poorly
961 maintained or when connections to new hosts are frequently made.
962 This option forces the user to manually add all new hosts.
963 If this flag is set to “accept-new” then ssh will automatically
965 add new host keys to the user known hosts files, but will not
966 permit connections to hosts with changed host keys. If this flag
967 is set to “no” or “off”, ssh will automatically add new host keys
968 to the user known hosts files and allow connections to hosts with
969 changed hostkeys to proceed, subject to some restrictions. If
970 this flag is set to ask (the default), new host keys will be
971 added to the user known host files only after the user has con‐
972 firmed that is what they really want to do, and ssh will refuse
973 to connect to hosts whose host key has changed. The host keys of
974 known hosts will be verified automatically in all cases.
975 SyslogFacility
977 Gives the facility code that is used when logging messages from
978 ssh(1). The possible values are: DAEMON, USER, AUTH, LOCAL0,
979 LOCAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. The
980 default is USER.
981 TCPKeepAlive
983 Specifies whether the system should send TCP keepalive messages
984 to the other side. If they are sent, death of the connection or
985 crash of one of the machines will be properly noticed. However,
986 this means that connections will die if the route is down tempo‐
987 rarily, and some people find it annoying.
988 The default is yes (to send TCP keepalive messages), and the
990 client will notice if the network goes down or the remote host
991 dies. This is important in scripts, and many users want it too.
992 To disable TCP keepalive messages, the value should be set to no.
994 See also ServerAliveInterval for protocol-level keepalives.
995 Tunnel Request tun(4) device forwarding between the client and the
997 server. The argument must be yes, point-to-point (layer 3),
998 ethernet (layer 2), or no (the default). Specifying yes requests
999 the default tunnel mode, which is point-to-point.
1000 TunnelDevice
1002 Specifies the tun(4) devices to open on the client (local_tun)
1003 and the server (remote_tun).
1004 The argument must be local_tun[:remote_tun]. The devices may be
1006 specified by numerical ID or the keyword any, which uses the next
1007 available tunnel device. If remote_tun is not specified, it
1008 defaults to any. The default is any:any.
1009 UpdateHostKeys
1011 Specifies whether ssh(1) should accept notifications of addi‐
1012 tional hostkeys from the server sent after authentication has
1013 completed and add them to UserKnownHostsFile. The argument must
1014 be yes, no (the default) or ask. Enabling this option allows
1015 learning alternate hostkeys for a server and supports graceful
1016 key rotation by allowing a server to send replacement public keys
1017 before old ones are removed. Additional hostkeys are only
1018 accepted if the key used to authenticate the host was already
1019 trusted or explicitly accepted by the user. If UpdateHostKeys is
1020 set to ask, then the user is asked to confirm the modifications
1021 to the known_hosts file. Confirmation is currently incompatible
1022 with ControlPersist, and will be disabled if it is enabled.
1023 Presently, only sshd(8) from OpenSSH 6.8 and greater support the
1025 "hostkeys@openssh.com" protocol extension used to inform the
1026 client of all the server's hostkeys.
1027 User Specifies the user to log in as. This can be useful when a dif‐
1029 ferent user name is used on different machines. This saves the
1030 trouble of having to remember to give the user name on the com‐
1031 mand line.
1032 UserKnownHostsFile
1034 Specifies one or more files to use for the user host key data‐
1035 base, separated by whitespace. The default is
1036 ~/.ssh/known_hosts, ~/.ssh/known_hosts2.
1037 VerifyHostKeyDNS
1039 Specifies whether to verify the remote key using DNS and SSHFP
1040 resource records. If this option is set to yes, the client will
1041 implicitly trust keys that match a secure fingerprint from DNS.
1042 Insecure fingerprints will be handled as if this option was set
1043 to ask. If this option is set to ask, information on fingerprint
1044 match will be displayed, but the user will still need to confirm
1045 new host keys according to the StrictHostKeyChecking option. The
1046 default is no.
1047 See also VERIFYING HOST KEYS in ssh(1).
1049 VisualHostKey
1051 If this flag is set to yes, an ASCII art representation of the
1052 remote host key fingerprint is printed in addition to the finger‐
1053 print string at login and for unknown host keys. If this flag is
1054 set to no (the default), no fingerprint strings are printed at
1055 login and only the fingerprint string will be printed for unknown
1056 host keys.
1057 XAuthLocation
1059 Specifies the full pathname of the xauth(1) program. The default
1060 is /usr/bin/xauth.
1061
1063 A pattern consists of zero or more non-whitespace characters, ‘*’ (a
1064 wildcard that matches zero or more characters), or ‘?’ (a wildcard that
1065 matches exactly one character). For example, to specify a set of decla‐
1066 rations for any host in the ".co.uk" set of domains, the following pat‐
1067 tern could be used:
1068 Host *.co.uk
1070 The following pattern would match any host in the 192.168.0.[0-9] network
1072 range:
1073 Host 192.168.0.?
1075 A pattern-list is a comma-separated list of patterns. Patterns within
1077 pattern-lists may be negated by preceding them with an exclamation mark
1078 (‘!’). For example, to allow a key to be used from anywhere within an
1079 organization except from the "dialup" pool, the following entry (in
1080 authorized_keys) could be used:
1081 from="!*.dialup.example.com,*.example.com"
1083 Note that a negated match will never produce a positive result by itself.
1085 For example, attempting to match "host3" against the following pattern-
1086 list will fail:
1087 from="!host1,!host2"
1089 The solution here is to include a term that will yield a positive match,
1091 such as a wildcard:
1092 from="!host1,!host2,*"
1094
1096 Arguments to some keywords can make use of tokens, which are expanded at
1097 runtime:
1098 %% A literal ‘%’.
1100 %C Hash of %l%h%p%r.
1101 %d Local user's home directory.
1102 %h The remote hostname.
1103 %i The local user ID.
1104 %L The local hostname.
1105 %l The local hostname, including the domain name.
1106 %n The original remote hostname, as given on the command line.
1107 %p The remote port.
1108 %r The remote username.
1109 %T The local tun(4) or tap(4) network interface assigned if tun‐
1110 nel forwarding was requested, or "NONE" otherwise.
1111 %u The local username.
1112 Match exec accepts the tokens %%, %h, %i, %L, %l, %n, %p, %r, and %u.
1114 CertificateFile accepts the tokens %%, %d, %h, %i, %l, %r, and %u.
1116 ControlPath accepts the tokens %%, %C, %h, %i, %L, %l, %n, %p, %r, and
1118 %u.
1119 HostName accepts the tokens %% and %h.
1121 IdentityAgent and IdentityFile accept the tokens %%, %d, %h, %i, %l, %r,
1123 and %u.
1124 LocalCommand accepts the tokens %%, %C, %d, %h, %i, %l, %n, %p, %r, %T,
1126 and %u.
1127 ProxyCommand accepts the tokens %%, %h, %p, and %r.
1129 RemoteCommand accepts the tokens %%, %C, %d, %h, %i, %l, %n, %p, %r, and
1131 %u.
1132
1134 ~/.ssh/config
1135 This is the per-user configuration file. The format of this file
1136 is described above. This file is used by the SSH client.
1137 Because of the potential for abuse, this file must have strict
1138 permissions: read/write for the user, and not writable by others.
1139 /etc/ssh/ssh_config
1141 Systemwide configuration file. This file provides defaults for
1142 those values that are not specified in the user's configuration
1143 file, and for those users who do not have a configuration file.
1144 This file must be world-readable.
1145
1147 ssh(1)
1148
1150 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
1151 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
1152 de Raadt and Dug Song removed many bugs, re-added newer features and cre‐
1153 ated OpenSSH. Markus Friedl contributed the support for SSH protocol
1154 versions 1.5 and 2.0.
1155BSD June 22, 2019 BSD