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 list
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 list begins with a ‘-’ character, then the specified
212 ciphers (including wildcards) will be removed from the default
213 set instead of replacing them. If the specified list begins with
214 a ‘^’ character, then the specified ciphers will be placed at the
215 head of the default set.
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 modify 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 timeout is applied both to establishing the connection and
258 to performing the initial SSH protocol handshake and key
259 exchange.
260 ControlMaster
262 Enables the sharing of multiple sessions over a single network
263 connection. When set to yes, ssh(1) will listen for connections
264 on a control socket specified using the ControlPath argument.
265 Additional sessions can connect to this socket using the same
266 ControlPath with ControlMaster set to no (the default). These
267 sessions will try to reuse the master instance's network connec‐
268 tion rather than initiating new ones, but will fall back to con‐
269 necting normally if the control socket does not exist, or is not
270 listening.
271 Setting this to ask will cause ssh(1) to listen for control con‐
273 nections, but require confirmation using ssh-askpass(1). If the
274 ControlPath cannot be opened, ssh(1) will continue without con‐
275 necting to a master instance.
276 X11 and ssh-agent(1) forwarding is supported over these multi‐
278 plexed connections, however the display and agent forwarded will
279 be the one belonging to the master connection i.e. it is not pos‐
280 sible to forward multiple displays or agents.
281 Two additional options allow for opportunistic multiplexing: try
283 to use a master connection but fall back to creating a new one if
284 one does not already exist. These options are: auto and autoask.
285 The latter requires confirmation like the ask option.
286 ControlPath
288 Specify the path to the control socket used for connection shar‐
289 ing as described in the ControlMaster section above or the string
290 none to disable connection sharing. Arguments to ControlPath may
291 use the tilde syntax to refer to a user's home directory or the
292 tokens described in the TOKENS section. It is recommended that
293 any ControlPath used for opportunistic connection sharing include
294 at least %h, %p, and %r (or alternatively %C) and be placed in a
295 directory that is not writable by other users. This ensures that
296 shared connections are uniquely identified.
297 ControlPersist
299 When used in conjunction with ControlMaster, specifies that the
300 master connection should remain open in the background (waiting
301 for future client connections) after the initial client connec‐
302 tion has been closed. If set to no, then the master connection
303 will not be placed into the background, and will close as soon as
304 the initial client connection is closed. If set to yes or 0,
305 then the master connection will remain in the background indefi‐
306 nitely (until killed or closed via a mechanism such as the "ssh
307 -O exit"). If set to a time in seconds, or a time in any of the
308 formats documented in sshd_config(5), then the backgrounded mas‐
309 ter connection will automatically terminate after it has remained
310 idle (with no client connections) for the specified time.
311 DynamicForward
313 Specifies that a TCP port on the local machine be forwarded over
314 the secure channel, and the application protocol is then used to
315 determine where to connect to from the remote machine.
316 The argument must be [bind_address:]port. IPv6 addresses can be
318 specified by enclosing addresses in square brackets. By default,
319 the local port is bound in accordance with the GatewayPorts set‐
320 ting. However, an explicit bind_address may be used to bind the
321 connection to a specific address. The bind_address of localhost
322 indicates that the listening port be bound for local use only,
323 while an empty address or ‘*’ indicates that the port should be
324 available from all interfaces.
325 Currently the SOCKS4 and SOCKS5 protocols are supported, and
327 ssh(1) will act as a SOCKS server. Multiple forwardings may be
328 specified, and additional forwardings can be given on the command
329 line. Only the superuser can forward privileged ports.
330 EnableSSHKeysign
332 Setting this option to yes in the global client configuration
333 file /etc/ssh/ssh_config enables the use of the helper program
334 ssh-keysign(8) during HostbasedAuthentication. The argument must
335 be yes or no (the default). This option should be placed in the
336 non-hostspecific section. See ssh-keysign(8) for more informa‐
337 tion.
338 EscapeChar
340 Sets the escape character (default: ‘~’). The escape character
341 can also be set on the command line. The argument should be a
342 single character, ‘^’ followed by a letter, or none to disable
343 the escape character entirely (making the connection transparent
344 for binary data).
345 ExitOnForwardFailure
347 Specifies whether ssh(1) should terminate the connection if it
348 cannot set up all requested dynamic, tunnel, local, and remote
349 port forwardings, (e.g. if either end is unable to bind and lis‐
350 ten on a specified port). Note that ExitOnForwardFailure does
351 not apply to connections made over port forwardings and will not,
352 for example, cause ssh(1) to exit if TCP connections to the ulti‐
353 mate forwarding destination fail. The argument must be yes or no
354 (the default).
355 FingerprintHash
357 Specifies the hash algorithm used when displaying key finger‐
358 prints. Valid options are: md5 and sha256 (the default).
359 ForwardAgent
361 Specifies whether the connection to the authentication agent (if
362 any) will be forwarded to the remote machine. The argument must
363 be yes or no (the default).
364 Agent forwarding should be enabled with caution. Users with the
366 ability to bypass file permissions on the remote host (for the
367 agent's Unix-domain socket) can access the local agent through
368 the forwarded connection. An attacker cannot obtain key material
369 from the agent, however they can perform operations on the keys
370 that enable them to authenticate using the identities loaded into
371 the agent.
372 ForwardX11
374 Specifies whether X11 connections will be automatically redi‐
375 rected over the secure channel and DISPLAY set. The argument
376 must be yes or no (the default).
377 X11 forwarding should be enabled with caution. Users with the
379 ability to bypass file permissions on the remote host (for the
380 user's X11 authorization database) can access the local X11 dis‐
381 play through the forwarded connection. An attacker may then be
382 able to perform activities such as keystroke monitoring if the
383 ForwardX11Trusted option is also enabled.
384 ForwardX11Timeout
386 Specify a timeout for untrusted X11 forwarding using the format
387 described in the TIME FORMATS section of sshd_config(5). X11
388 connections received by ssh(1) after this time will be refused.
389 Setting ForwardX11Timeout to zero will disable the timeout and
390 permit X11 forwarding for the life of the connection. The
391 default is to disable untrusted X11 forwarding after twenty min‐
392 utes has elapsed.
393 ForwardX11Trusted
395 If this option is set to yes, remote X11 clients will have full
396 access to the original X11 display.
397 If this option is set to no (the default), remote X11 clients
399 will be considered untrusted and prevented from stealing or tam‐
400 pering with data belonging to trusted X11 clients. Furthermore,
401 the xauth(1) token used for the session will be set to expire
402 after 20 minutes. Remote clients will be refused access after
403 this time.
404 See the X11 SECURITY extension specification for full details on
406 the restrictions imposed on untrusted clients.
407 GatewayPorts
409 Specifies whether remote hosts are allowed to connect to local
410 forwarded ports. By default, ssh(1) binds local port forwardings
411 to the loopback address. This prevents other remote hosts from
412 connecting to forwarded ports. GatewayPorts can be used to spec‐
413 ify that ssh should bind local port forwardings to the wildcard
414 address, thus allowing remote hosts to connect to forwarded
415 ports. The argument must be yes or no (the default).
416 GlobalKnownHostsFile
418 Specifies one or more files to use for the global host key data‐
419 base, separated by whitespace. The default is
420 /etc/ssh/ssh_known_hosts, /etc/ssh/ssh_known_hosts2.
421 GSSAPIAuthentication
423 Specifies whether user authentication based on GSSAPI is allowed.
424 The default is no.
425 GSSAPIClientIdentity
427 If set, specifies the GSSAPI client identity that ssh should use
428 when connecting to the server. The default is unset, which means
429 that the default identity will be used.
430 GSSAPIDelegateCredentials
432 Forward (delegate) credentials to the server. The default is no.
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 “no”.
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 modify this default, see manual page
481 update-crypto-policies(8). This option only applies to protocol
482 version 2 connections using GSSAPI.
483 HashKnownHosts
485 Indicates that ssh(1) should hash host names and addresses when
486 they are added to ~/.ssh/known_hosts. These hashed names may be
487 used normally by ssh(1) and sshd(8), but they do not reveal iden‐
488 tifying information should the file's contents be disclosed. The
489 default is no. Note that existing names and addresses in known
490 hosts files will not be converted automatically, but may be manu‐
491 ally hashed using ssh-keygen(1).
492 HostbasedAuthentication
494 Specifies whether to try rhosts based authentication with public
495 key authentication. The argument must be yes or no (the
496 default).
497 HostbasedKeyTypes
499 Specifies the key types that will be used for hostbased authenti‐
500 cation as a comma-separated list of patterns. Alternately if the
501 specified list begins with a ‘+’ character, then the specified
502 key types will be appended to the default set instead of replac‐
503 ing them. If the specified list begins with a ‘-’ character,
504 then the specified key types (including wildcards) will be
505 removed from the default set instead of replacing them. If the
506 specified list begins with a ‘^’ character, then the specified
507 key types will be placed at the head of the default set. The
508 default for this option is:
509 ecdsa-sha2-nistp256-cert-v01@openssh.com,
511 ecdsa-sha2-nistp384-cert-v01@openssh.com,
512 ecdsa-sha2-nistp521-cert-v01@openssh.com,
513 ssh-ed25519-cert-v01@openssh.com,
514 rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,
515 ssh-rsa-cert-v01@openssh.com,
516 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
517 ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
518 The -Q option of ssh(1) may be used to list supported key types.
520 HostKeyAlgorithms
522 Specifies the host key algorithms that the client wants to use in
523 order of preference. Alternately if the specified list begins
524 with a ‘+’ character, then the specified key types will be
525 appended to the default set instead of replacing them. If the
526 specified list begins with a ‘-’ character, then the specified
527 key types (including wildcards) will be removed from the default
528 set instead of replacing them. If the specified list begins with
529 a ‘^’ character, then the specified key types will be placed at
530 the head of the default set. The default for this option is:
531 ecdsa-sha2-nistp256-cert-v01@openssh.com,
533 ecdsa-sha2-nistp384-cert-v01@openssh.com,
534 ecdsa-sha2-nistp521-cert-v01@openssh.com,
535 ssh-ed25519-cert-v01@openssh.com,
536 rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,
537 ssh-rsa-cert-v01@openssh.com,
538 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
539 ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
540 If hostkeys are known for the destination host then this default
542 is modified to prefer their algorithms.
543 The list of available key types may also be obtained using "ssh
545 -Q key".
546 HostKeyAlias
548 Specifies an alias that should be used instead of the real host
549 name when looking up or saving the host key in the host key data‐
550 base files and when validating host certificates. This option is
551 useful for tunneling SSH connections or for multiple servers run‐
552 ning on a single host.
553 Hostname
555 Specifies the real host name to log into. This can be used to
556 specify nicknames or abbreviations for hosts. Arguments to
557 Hostname accept the tokens described in the TOKENS section.
558 Numeric IP addresses are also permitted (both on the command line
559 and in Hostname specifications). The default is the name given
560 on the command line.
561 IdentitiesOnly
563 Specifies that ssh(1) should only use the configured authentica‐
564 tion identity and certificate files (either the default files, or
565 those explicitly configured in the ssh_config files or passed on
566 the ssh(1) command-line), even if ssh-agent(1) or a
567 PKCS11Provider offers more identities. The argument to this key‐
568 word must be yes or no (the default). This option is intended
569 for situations where ssh-agent offers many different identities.
570 IdentityAgent
572 Specifies the UNIX-domain socket used to communicate with the
573 authentication agent.
574 This option overrides the SSH_AUTH_SOCK environment variable and
576 can be used to select a specific agent. Setting the socket name
577 to none disables the use of an authentication agent. If the
578 string "SSH_AUTH_SOCK" is specified, the location of the socket
579 will be read from the SSH_AUTH_SOCK environment variable. Other‐
580 wise if the specified value begins with a ‘$’ character, then it
581 will be treated as an environment variable containing the loca‐
582 tion of the socket.
583 Arguments to IdentityAgent may use the tilde syntax to refer to a
585 user's home directory or the tokens described in the TOKENS sec‐
586 tion.
587 IdentityFile
589 Specifies a file from which the user's DSA, ECDSA, Ed25519 or RSA
590 authentication identity is read. The default is ~/.ssh/id_dsa,
591 ~/.ssh/id_ecdsa, ~/.ssh/id_ed25519 and ~/.ssh/id_rsa. Addition‐
592 ally, any identities represented by the authentication agent will
593 be used for authentication unless IdentitiesOnly is set. If no
594 certificates have been explicitly specified by CertificateFile,
595 ssh(1) will try to load certificate information from the filename
596 obtained by appending -cert.pub to the path of a specified
597 IdentityFile.
598 Arguments to IdentityFile may use the tilde syntax to refer to a
600 user's home directory or the tokens described in the TOKENS sec‐
601 tion.
602 It is possible to have multiple identity files specified in con‐
604 figuration files; all these identities will be tried in sequence.
605 Multiple IdentityFile directives will add to the list of identi‐
606 ties tried (this behaviour differs from that of other configura‐
607 tion directives).
608 IdentityFile may be used in conjunction with IdentitiesOnly to
610 select which identities in an agent are offered during authenti‐
611 cation. IdentityFile may also be used in conjunction with
612 CertificateFile in order to provide any certificate also needed
613 for authentication with the identity.
614 The authentication identity can be also specified in a form of
616 PKCS#11 URI starting with a string pkcs11:. There is supported a
617 subset of the PKCS#11 URI as defined in RFC 7512 (implemented
618 path arguments id, manufacturer, object, token and query argu‐
619 ments module-path and pin-value ). The URI can not be in quotes.
620 IgnoreUnknown
622 Specifies a pattern-list of unknown options to be ignored if they
623 are encountered in configuration parsing. This may be used to
624 suppress errors if ssh_config contains options that are unrecog‐
625 nised by ssh(1). It is recommended that IgnoreUnknown be listed
626 early in the configuration file as it will not be applied to
627 unknown options that appear before it.
628 Include
630 Include the specified configuration file(s). Multiple pathnames
631 may be specified and each pathname may contain glob(7) wildcards
632 and, for user configurations, shell-like ‘~’ references to user
633 home directories. Files without absolute paths are assumed to be
634 in ~/.ssh if included in a user configuration file or /etc/ssh if
635 included from the system configuration file. Include directive
636 may appear inside a Match or Host block to perform conditional
637 inclusion.
638 IPQoS Specifies the IPv4 type-of-service or DSCP class for connections.
640 Accepted values are af11, af12, af13, af21, af22, af23, af31,
641 af32, af33, af41, af42, af43, cs0, cs1, cs2, cs3, cs4, cs5, cs6,
642 cs7, ef, lowdelay, throughput, reliability, a numeric value, or
643 none to use the operating system default. This option may take
644 one or two arguments, separated by whitespace. If one argument
645 is specified, it is used as the packet class unconditionally. If
646 two values are specified, the first is automatically selected for
647 interactive sessions and the second for non-interactive sessions.
648 The default is af21 (Low-Latency Data) for interactive sessions
649 and cs1 (Lower Effort) for non-interactive sessions.
650 KbdInteractiveAuthentication
652 Specifies whether to use keyboard-interactive authentication.
653 The argument to this keyword must be yes (the default) or no.
654 KbdInteractiveDevices
656 Specifies the list of methods to use in keyboard-interactive
657 authentication. Multiple method names must be comma-separated.
658 The default is to use the server specified list. The methods
659 available vary depending on what the server supports. For an
660 OpenSSH server, it may be zero or more of: bsdauth and pam.
661 KexAlgorithms
663 Specifies the available KEX (Key Exchange) algorithms. Multiple
664 algorithms must be comma-separated. If the specified list begins
665 with a ‘+’ character, then the specified methods will be appended
666 to the default set instead of replacing them. If the specified
667 list begins with a ‘-’ character, then the specified methods
668 (including wildcards) will be removed from the default set
669 instead of replacing them. If the specified list begins with a
670 ‘^’ character, then the specified methods will be placed at the
671 head of the default set. The default is handled system-wide by
672 crypto-policies(7). To see the defaults and how to modify this
673 default, see manual page update-crypto-policies(8).
674 The list of available key exchange algorithms may also be
676 obtained using "ssh -Q kex".
677 LocalCommand
679 Specifies a command to execute on the local machine after suc‐
680 cessfully connecting to the server. The command string extends
681 to the end of the line, and is executed with the user's shell.
682 Arguments to LocalCommand accept the tokens described in the
683 TOKENS section.
684 The command is run synchronously and does not have access to the
686 session of the ssh(1) that spawned it. It should not be used for
687 interactive commands.
688 This directive is ignored unless PermitLocalCommand has been
690 enabled.
691 LocalForward
693 Specifies that a TCP port on the local machine be forwarded over
694 the secure channel to the specified host and port from the remote
695 machine. The first argument must be [bind_address:]port and the
696 second argument must be host:hostport. IPv6 addresses can be
697 specified by enclosing addresses in square brackets. Multiple
698 forwardings may be specified, and additional forwardings can be
699 given on the command line. Only the superuser can forward privi‐
700 leged ports. By default, the local port is bound in accordance
701 with the GatewayPorts setting. However, an explicit bind_address
702 may be used to bind the connection to a specific address. The
703 bind_address of localhost indicates that the listening port be
704 bound for local use only, while an empty address or ‘*’ indicates
705 that the port should be available from all interfaces.
706 LogLevel
708 Gives the verbosity level that is used when logging messages from
709 ssh(1). The possible values are: QUIET, FATAL, ERROR, INFO, VER‐
710 BOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO.
711 DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify
712 higher levels of verbose output.
713 MACs Specifies the MAC (message authentication code) algorithms in
715 order of preference. The MAC algorithm is used for data
716 integrity protection. Multiple algorithms must be comma-sepa‐
717 rated. If the specified list begins with a ‘+’ character, then
718 the specified algorithms will be appended to the default set
719 instead of replacing them. If the specified list begins with a
720 ‘-’ character, then the specified algorithms (including wild‐
721 cards) will be removed from the default set instead of replacing
722 them. If the specified list begins with a ‘^’ character, then
723 the specified algorithms will be placed at the head of the
724 default set.
725 The algorithms that contain "-etm" calculate the MAC after
727 encryption (encrypt-then-mac). These are considered safer and
728 their use recommended.
729 The default is handled system-wide by crypto-policies(7). To see
731 the defaults and how to modify this default, see manual page
732 update-crypto-policies(8).
733 The list of available MAC algorithms may also be obtained using
735 "ssh -Q mac".
736 NoHostAuthenticationForLocalhost
738 Disable host authentication for localhost (loopback addresses).
739 The argument to this keyword must be yes or no (the default).
740 NumberOfPasswordPrompts
742 Specifies the number of password prompts before giving up. The
743 argument to this keyword must be an integer. The default is 3.
744 PasswordAuthentication
746 Specifies whether to use password authentication. The argument
747 to this keyword must be yes (the default) or no.
748 PermitLocalCommand
750 Allow local command execution via the LocalCommand option or
751 using the !command escape sequence in ssh(1). The argument must
752 be yes or no (the default).
753 PKCS11Provider
755 Specifies which PKCS#11 provider to use or none to indicate that
756 no provider should be used (the default). The argument to this
757 keyword is a path to the PKCS#11 shared library ssh(1) should use
758 to communicate with a PKCS#11 token providing keys for user
759 authentication.
760 Port Specifies the port number to connect on the remote host. The
762 default is 22.
763 PreferredAuthentications
765 Specifies the order in which the client should try authentication
766 methods. This allows a client to prefer one method (e.g.
767 keyboard-interactive) over another method (e.g. password). The
768 default is:
769 gssapi-with-mic,hostbased,publickey,
771 keyboard-interactive,password
772 ProxyCommand
774 Specifies the command to use to connect to the server. The com‐
775 mand string extends to the end of the line, and is executed using
776 the user's shell ‘exec’ directive to avoid a lingering shell
777 process.
778 Arguments to ProxyCommand accept the tokens described in the
780 TOKENS section. The command can be basically anything, and
781 should read from its standard input and write to its standard
782 output. It should eventually connect an sshd(8) server running
783 on some machine, or execute sshd -i somewhere. Host key manage‐
784 ment will be done using the Hostname of the host being connected
785 (defaulting to the name typed by the user). Setting the command
786 to none disables this option entirely. Note that CheckHostIP is
787 not available for connects with a proxy command.
788 This directive is useful in conjunction with nc(1) and its proxy
790 support. For example, the following directive would connect via
791 an HTTP proxy at 192.0.2.0:
792 ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
794 ProxyJump
796 Specifies one or more jump proxies as either [user@]host[:port]
797 or an ssh URI. Multiple proxies may be separated by comma char‐
798 acters and will be visited sequentially. Setting this option
799 will cause ssh(1) to connect to the target host by first making a
800 ssh(1) connection to the specified ProxyJump host and then estab‐
801 lishing a TCP forwarding to the ultimate target from there.
802 Note that this option will compete with the ProxyCommand option -
804 whichever is specified first will prevent later instances of the
805 other from taking effect.
806 Note also that the configuration for the destination host (either
808 supplied via the command-line or the configuration file) is not
809 generally applied to jump hosts. ~/.ssh/config should be used if
810 specific configuration is required for jump hosts.
811 ProxyUseFdpass
813 Specifies that ProxyCommand will pass a connected file descriptor
814 back to ssh(1) instead of continuing to execute and pass data.
815 The default is no.
816 PubkeyAcceptedKeyTypes
818 Specifies the key types that will be used for public key authen‐
819 tication as a comma-separated list of patterns. If the specified
820 list begins with a ‘+’ character, then the key types after it
821 will be appended to the default instead of replacing it. If the
822 specified list begins with a ‘-’ character, then the specified
823 key types (including wildcards) will be removed from the default
824 set instead of replacing them. If the specified list begins with
825 a ‘^’ character, then the specified key types will be placed at
826 the head of the default set. The default is handled system-wide
827 by crypto-policies(7). To see the defaults and how to modify
828 this default, see manual page update-crypto-policies(8).
829 The list of available key types may also be obtained using "ssh
831 -Q key".
832 PubkeyAuthentication
834 Specifies whether to try public key authentication. The argument
835 to this keyword must be yes (the default) or no.
836 RekeyLimit
838 Specifies the maximum amount of data that may be transmitted
839 before the session key is renegotiated, optionally followed a
840 maximum amount of time that may pass before the session key is
841 renegotiated. The first argument is specified in bytes and may
842 have a suffix of ‘K’, ‘M’, or ‘G’ to indicate Kilobytes,
843 Megabytes, or Gigabytes, respectively. The default is between
844 ‘1G’ and ‘4G’, depending on the cipher. The optional second
845 value is specified in seconds and may use any of the units docu‐
846 mented in the TIME FORMATS section of sshd_config(5). The
847 default value for RekeyLimit is default none, which means that
848 rekeying is performed after the cipher's default amount of data
849 has been sent or received and no time based rekeying is done.
850 RemoteCommand
852 Specifies a command to execute on the remote machine after suc‐
853 cessfully connecting to the server. The command string extends
854 to the end of the line, and is executed with the user's shell.
855 Arguments to RemoteCommand accept the tokens described in the
856 TOKENS section.
857 RemoteForward
859 Specifies that a TCP port on the remote machine be forwarded over
860 the secure channel. The remote port may either be forwarded to a
861 specified host and port from the local machine, or may act as a
862 SOCKS 4/5 proxy that allows a remote client to connect to arbi‐
863 trary destinations from the local machine. The first argument
864 must be [bind_address:]port If forwarding to a specific destina‐
865 tion then the second argument must be host:hostport, otherwise if
866 no destination argument is specified then the remote forwarding
867 will be established as a SOCKS proxy.
868 IPv6 addresses can be specified by enclosing addresses in square
870 brackets. Multiple forwardings may be specified, and additional
871 forwardings can be given on the command line. Privileged ports
872 can be forwarded only when logging in as root on the remote
873 machine.
874 If the port argument is 0, the listen port will be dynamically
876 allocated on the server and reported to the client at run time.
877 If the bind_address is not specified, the default is to only bind
879 to loopback addresses. If the bind_address is ‘*’ or an empty
880 string, then the forwarding is requested to listen on all inter‐
881 faces. Specifying a remote bind_address will only succeed if the
882 server's GatewayPorts option is enabled (see sshd_config(5)).
883 RequestTTY
885 Specifies whether to request a pseudo-tty for the session. The
886 argument may be one of: no (never request a TTY), yes (always
887 request a TTY when standard input is a TTY), force (always
888 request a TTY) or auto (request a TTY when opening a login ses‐
889 sion). This option mirrors the -t and -T flags for ssh(1).
890 RevokedHostKeys
892 Specifies revoked host public keys. Keys listed in this file
893 will be refused for host authentication. Note that if this file
894 does not exist or is not readable, then host authentication will
895 be refused for all hosts. Keys may be specified as a text file,
896 listing one public key per line, or as an OpenSSH Key Revocation
897 List (KRL) as generated by ssh-keygen(1). For more information
898 on KRLs, see the KEY REVOCATION LISTS section in ssh-keygen(1).
899 SendEnv
901 Specifies what variables from the local environ(7) should be sent
902 to the server. The server must also support it, and the server
903 must be configured to accept these environment variables. Note
904 that the TERM environment variable is always sent whenever a
905 pseudo-terminal is requested as it is required by the protocol.
906 Refer to AcceptEnv in sshd_config(5) for how to configure the
907 server. Variables are specified by name, which may contain wild‐
908 card characters. Multiple environment variables may be separated
909 by whitespace or spread across multiple SendEnv directives.
910 See PATTERNS for more information on patterns.
912 It is possible to clear previously set SendEnv variable names by
914 prefixing patterns with -. The default is not to send any envi‐
915 ronment variables.
916 ServerAliveCountMax
918 Sets the number of server alive messages (see below) which may be
919 sent without ssh(1) receiving any messages back from the server.
920 If this threshold is reached while server alive messages are
921 being sent, ssh will disconnect from the server, terminating the
922 session. It is important to note that the use of server alive
923 messages is very different from TCPKeepAlive (below). The server
924 alive messages are sent through the encrypted channel and there‐
925 fore will not be spoofable. The TCP keepalive option enabled by
926 TCPKeepAlive is spoofable. The server alive mechanism is valu‐
927 able when the client or server depend on knowing when a connec‐
928 tion has become unresponsive.
929 The default value is 3. If, for example, ServerAliveInterval
931 (see below) is set to 15 and ServerAliveCountMax is left at the
932 default, if the server becomes unresponsive, ssh will disconnect
933 after approximately 45 seconds.
934 ServerAliveInterval
936 Sets a timeout interval in seconds after which if no data has
937 been received from the server, ssh(1) will send a message through
938 the encrypted channel to request a response from the server. The
939 default is 0, indicating that these messages will not be sent to
940 the server.
941 SetEnv Directly specify one or more environment variables and their con‐
943 tents to be sent to the server. Similarly to SendEnv, the server
944 must be prepared to accept the environment variable.
945 StreamLocalBindMask
947 Sets the octal file creation mode mask (umask) used when creating
948 a Unix-domain socket file for local or remote port forwarding.
949 This option is only used for port forwarding to a Unix-domain
950 socket file.
951 The default value is 0177, which creates a Unix-domain socket
953 file that is readable and writable only by the owner. Note that
954 not all operating systems honor the file mode on Unix-domain
955 socket files.
956 StreamLocalBindUnlink
958 Specifies whether to remove an existing Unix-domain socket file
959 for local or remote port forwarding before creating a new one.
960 If the socket file already exists and StreamLocalBindUnlink is
961 not enabled, ssh will be unable to forward the port to the Unix-
962 domain socket file. This option is only used for port forwarding
963 to a Unix-domain socket file.
964 The argument must be yes or no (the default).
966 StrictHostKeyChecking
968 If this flag is set to yes, ssh(1) will never automatically add
969 host keys to the ~/.ssh/known_hosts file, and refuses to connect
970 to hosts whose host key has changed. This provides maximum pro‐
971 tection against man-in-the-middle (MITM) attacks, though it can
972 be annoying when the /etc/ssh/ssh_known_hosts file is poorly
973 maintained or when connections to new hosts are frequently made.
974 This option forces the user to manually add all new hosts.
975 If this flag is set to “accept-new” then ssh will automatically
977 add new host keys to the user known hosts files, but will not
978 permit connections to hosts with changed host keys. If this flag
979 is set to “no” or “off”, ssh will automatically add new host keys
980 to the user known hosts files and allow connections to hosts with
981 changed hostkeys to proceed, subject to some restrictions. If
982 this flag is set to ask (the default), new host keys will be
983 added to the user known host files only after the user has con‐
984 firmed that is what they really want to do, and ssh will refuse
985 to connect to hosts whose host key has changed. The host keys of
986 known hosts will be verified automatically in all cases.
987 SyslogFacility
989 Gives the facility code that is used when logging messages from
990 ssh(1). The possible values are: DAEMON, USER, AUTH, LOCAL0,
991 LOCAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. The
992 default is USER.
993 TCPKeepAlive
995 Specifies whether the system should send TCP keepalive messages
996 to the other side. If they are sent, death of the connection or
997 crash of one of the machines will be properly noticed. However,
998 this means that connections will die if the route is down tempo‐
999 rarily, and some people find it annoying.
1000 The default is yes (to send TCP keepalive messages), and the
1002 client will notice if the network goes down or the remote host
1003 dies. This is important in scripts, and many users want it too.
1004 To disable TCP keepalive messages, the value should be set to no.
1006 See also ServerAliveInterval for protocol-level keepalives.
1007 Tunnel Request tun(4) device forwarding between the client and the
1009 server. The argument must be yes, point-to-point (layer 3),
1010 ethernet (layer 2), or no (the default). Specifying yes requests
1011 the default tunnel mode, which is point-to-point.
1012 TunnelDevice
1014 Specifies the tun(4) devices to open on the client (local_tun)
1015 and the server (remote_tun).
1016 The argument must be local_tun[:remote_tun]. The devices may be
1018 specified by numerical ID or the keyword any, which uses the next
1019 available tunnel device. If remote_tun is not specified, it
1020 defaults to any. The default is any:any.
1021 UpdateHostKeys
1023 Specifies whether ssh(1) should accept notifications of addi‐
1024 tional hostkeys from the server sent after authentication has
1025 completed and add them to UserKnownHostsFile. The argument must
1026 be yes, no (the default) or ask. Enabling this option allows
1027 learning alternate hostkeys for a server and supports graceful
1028 key rotation by allowing a server to send replacement public keys
1029 before old ones are removed. Additional hostkeys are only
1030 accepted if the key used to authenticate the host was already
1031 trusted or explicitly accepted by the user. If UpdateHostKeys is
1032 set to ask, then the user is asked to confirm the modifications
1033 to the known_hosts file. Confirmation is currently incompatible
1034 with ControlPersist, and will be disabled if it is enabled.
1035 Presently, only sshd(8) from OpenSSH 6.8 and greater support the
1037 "hostkeys@openssh.com" protocol extension used to inform the
1038 client of all the server's hostkeys.
1039 User Specifies the user to log in as. This can be useful when a dif‐
1041 ferent user name is used on different machines. This saves the
1042 trouble of having to remember to give the user name on the com‐
1043 mand line.
1044 UserKnownHostsFile
1046 Specifies one or more files to use for the user host key data‐
1047 base, separated by whitespace. The default is
1048 ~/.ssh/known_hosts, ~/.ssh/known_hosts2.
1049 VerifyHostKeyDNS
1051 Specifies whether to verify the remote key using DNS and SSHFP
1052 resource records. If this option is set to yes, the client will
1053 implicitly trust keys that match a secure fingerprint from DNS.
1054 Insecure fingerprints will be handled as if this option was set
1055 to ask. If this option is set to ask, information on fingerprint
1056 match will be displayed, but the user will still need to confirm
1057 new host keys according to the StrictHostKeyChecking option. The
1058 default is no.
1059 See also VERIFYING HOST KEYS in ssh(1).
1061 VisualHostKey
1063 If this flag is set to yes, an ASCII art representation of the
1064 remote host key fingerprint is printed in addition to the finger‐
1065 print string at login and for unknown host keys. If this flag is
1066 set to no (the default), no fingerprint strings are printed at
1067 login and only the fingerprint string will be printed for unknown
1068 host keys.
1069 XAuthLocation
1071 Specifies the full pathname of the xauth(1) program. The default
1072 is /usr/bin/xauth.
1073
1075 A pattern consists of zero or more non-whitespace characters, ‘*’ (a
1076 wildcard that matches zero or more characters), or ‘?’ (a wildcard that
1077 matches exactly one character). For example, to specify a set of decla‐
1078 rations for any host in the ".co.uk" set of domains, the following pat‐
1079 tern could be used:
1080 Host *.co.uk
1082 The following pattern would match any host in the 192.168.0.[0-9] network
1084 range:
1085 Host 192.168.0.?
1087 A pattern-list is a comma-separated list of patterns. Patterns within
1089 pattern-lists may be negated by preceding them with an exclamation mark
1090 (‘!’). For example, to allow a key to be used from anywhere within an
1091 organization except from the "dialup" pool, the following entry (in
1092 authorized_keys) could be used:
1093 from="!*.dialup.example.com,*.example.com"
1095 Note that a negated match will never produce a positive result by itself.
1097 For example, attempting to match "host3" against the following pattern-
1098 list will fail:
1099 from="!host1,!host2"
1101 The solution here is to include a term that will yield a positive match,
1103 such as a wildcard:
1104 from="!host1,!host2,*"
1106
1108 Arguments to some keywords can make use of tokens, which are expanded at
1109 runtime:
1110 %% A literal ‘%’.
1112 %C Hash of %l%h%p%r.
1113 %d Local user's home directory.
1114 %h The remote hostname.
1115 %i The local user ID.
1116 %L The local hostname.
1117 %l The local hostname, including the domain name.
1118 %n The original remote hostname, as given on the command line.
1119 %p The remote port.
1120 %r The remote username.
1121 %T The local tun(4) or tap(4) network interface assigned if tun‐
1122 nel forwarding was requested, or "NONE" otherwise.
1123 %u The local username.
1124 Match exec accepts the tokens %%, %h, %i, %L, %l, %n, %p, %r, and %u.
1126 CertificateFile accepts the tokens %%, %d, %h, %i, %l, %r, and %u.
1128 ControlPath accepts the tokens %%, %C, %h, %i, %L, %l, %n, %p, %r, and
1130 %u.
1131 Hostname accepts the tokens %% and %h.
1133 IdentityAgent and IdentityFile accept the tokens %%, %d, %h, %i, %l, %r,
1135 and %u.
1136 LocalCommand accepts the tokens %%, %C, %d, %h, %i, %l, %n, %p, %r, %T,
1138 and %u.
1139 ProxyCommand accepts the tokens %%, %h, %n, %p, and %r.
1141 RemoteCommand accepts the tokens %%, %C, %d, %h, %i, %l, %n, %p, %r, and
1143 %u.
1144
1146 ~/.ssh/config
1147 This is the per-user configuration file. The format of this file
1148 is described above. This file is used by the SSH client.
1149 Because of the potential for abuse, this file must have strict
1150 permissions: read/write for the user, and not writable by others.
1151 /etc/ssh/ssh_config
1153 Systemwide configuration file. This file provides defaults for
1154 those values that are not specified in the user's configuration
1155 file, and for those users who do not have a configuration file.
1156 This file must be world-readable.
1157
1159 ssh(1)
1160
1162 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
1163 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
1164 de Raadt and Dug Song removed many bugs, re-added newer features and cre‐
1165 ated OpenSSH. Markus Friedl contributed the support for SSH protocol
1166 versions 1.5 and 2.0.
1167BSD December 31, 2019 BSD