Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.342
1.1 stevesk 1: .\"
2: .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
3: .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
4: .\" All rights reserved
5: .\"
6: .\" As far as I am concerned, the code I have written for this software
7: .\" can be used freely for any purpose. Any derived versions of this
8: .\" software must be clearly marked as such, and if the derived work is
9: .\" incompatible with the protocol description in the RFC file, it must be
10: .\" called by a name other than "ssh" or "Secure Shell".
11: .\"
12: .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
13: .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
14: .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
15: .\"
16: .\" Redistribution and use in source and binary forms, with or without
17: .\" modification, are permitted provided that the following conditions
18: .\" are met:
19: .\" 1. Redistributions of source code must retain the above copyright
20: .\" notice, this list of conditions and the following disclaimer.
21: .\" 2. Redistributions in binary form must reproduce the above copyright
22: .\" notice, this list of conditions and the following disclaimer in the
23: .\" documentation and/or other materials provided with the distribution.
24: .\"
25: .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
26: .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
27: .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
28: .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
29: .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
30: .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
31: .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
32: .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
33: .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
34: .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
35: .\"
1.342 ! rob 36: .\" $OpenBSD: ssh_config.5,v 1.341 2021/01/08 04:49:13 djm Exp $
! 37: .Dd $Mdocdate: January 8 2021 $
1.1 stevesk 38: .Dt SSH_CONFIG 5
39: .Os
40: .Sh NAME
41: .Nm ssh_config
1.310 jmc 42: .Nd OpenSSH client configuration file
1.1 stevesk 43: .Sh DESCRIPTION
1.84 jmc 44: .Xr ssh 1
1.1 stevesk 45: obtains configuration data from the following sources in
46: the following order:
1.79 jmc 47: .Pp
1.2 stevesk 48: .Bl -enum -offset indent -compact
49: .It
50: command-line options
51: .It
52: user's configuration file
1.50 djm 53: .Pq Pa ~/.ssh/config
1.2 stevesk 54: .It
55: system-wide configuration file
56: .Pq Pa /etc/ssh/ssh_config
57: .El
1.1 stevesk 58: .Pp
59: For each parameter, the first obtained value
60: will be used.
1.41 jmc 61: The configuration files contain sections separated by
1.240 jmc 62: .Cm Host
1.1 stevesk 63: specifications, and that section is only applied for hosts that
64: match one of the patterns given in the specification.
1.193 djm 65: The matched host name is usually the one given on the command line
66: (see the
67: .Cm CanonicalizeHostname
1.240 jmc 68: option for exceptions).
1.1 stevesk 69: .Pp
70: Since the first obtained value for each parameter is used, more
71: host-specific declarations should be given near the beginning of the
72: file, and general defaults at the end.
1.80 jmc 73: .Pp
1.240 jmc 74: The file contains keyword-argument pairs, one per line.
75: Lines starting with
1.1 stevesk 76: .Ql #
1.240 jmc 77: and empty lines are interpreted as comments.
78: Arguments may optionally be enclosed in double quotes
79: .Pq \&"
80: in order to represent arguments containing spaces.
1.1 stevesk 81: Configuration options may be separated by whitespace or
82: optional whitespace and exactly one
83: .Ql = ;
84: the latter format is useful to avoid the need to quote whitespace
85: when specifying configuration options using the
86: .Nm ssh ,
1.87 jmc 87: .Nm scp ,
1.1 stevesk 88: and
89: .Nm sftp
90: .Fl o
91: option.
92: .Pp
93: The possible
94: keywords and their meanings are as follows (note that
95: keywords are case-insensitive and arguments are case-sensitive):
96: .Bl -tag -width Ds
97: .It Cm Host
98: Restricts the following declarations (up to the next
99: .Cm Host
1.169 djm 100: or
101: .Cm Match
1.1 stevesk 102: keyword) to be only for those hosts that match one of the patterns
103: given after the keyword.
1.112 krw 104: If more than one pattern is provided, they should be separated by whitespace.
1.1 stevesk 105: A single
1.83 jmc 106: .Ql *
1.1 stevesk 107: as a pattern can be used to provide global
108: defaults for all hosts.
1.193 djm 109: The host is usually the
1.1 stevesk 110: .Ar hostname
1.193 djm 111: argument given on the command line
112: (see the
113: .Cm CanonicalizeHostname
1.240 jmc 114: keyword for exceptions).
1.148 djm 115: .Pp
116: A pattern entry may be negated by prefixing it with an exclamation mark
117: .Pq Sq !\& .
118: If a negated entry is matched, then the
119: .Cm Host
120: entry is ignored, regardless of whether any other patterns on the line
121: match.
122: Negated matches are therefore useful to provide exceptions for wildcard
123: matches.
1.81 jmc 124: .Pp
125: See
126: .Sx PATTERNS
127: for more information on patterns.
1.170 jmc 128: .It Cm Match
1.169 djm 129: Restricts the following declarations (up to the next
130: .Cm Host
131: or
132: .Cm Match
133: keyword) to be used only when the conditions following the
134: .Cm Match
135: keyword are satisfied.
1.220 sobrado 136: Match conditions are specified using one or more criteria
1.178 dtucker 137: or the single token
138: .Cm all
1.193 djm 139: which always matches.
140: The available criteria keywords are:
141: .Cm canonical ,
1.287 djm 142: .Cm final ,
1.176 djm 143: .Cm exec ,
1.169 djm 144: .Cm host ,
145: .Cm originalhost ,
146: .Cm user ,
147: and
148: .Cm localuser .
1.193 djm 149: The
150: .Cm all
151: criteria must appear alone or immediately after
1.287 djm 152: .Cm canonical
153: or
154: .Cm final .
1.193 djm 155: Other criteria may be combined arbitrarily.
156: All criteria but
1.288 jmc 157: .Cm all ,
158: .Cm canonical ,
1.193 djm 159: and
1.287 djm 160: .Cm final
1.193 djm 161: require an argument.
162: Criteria may be negated by prepending an exclamation mark
163: .Pq Sq !\& .
1.169 djm 164: .Pp
1.177 jmc 165: The
1.193 djm 166: .Cm canonical
1.210 dtucker 167: keyword matches only when the configuration file is being re-parsed
1.193 djm 168: after hostname canonicalization (see the
169: .Cm CanonicalizeHostname
1.288 jmc 170: option).
1.193 djm 171: This may be useful to specify conditions that work with canonical host
172: names only.
1.287 djm 173: .Pp
174: The
175: .Cm final
176: keyword requests that the configuration be re-parsed (regardless of whether
177: .Cm CanonicalizeHostname
178: is enabled), and matches only during this final pass.
179: If
180: .Cm CanonicalizeHostname
181: is enabled, then
182: .Cm canonical
183: and
184: .Cm final
185: match during the same pass.
186: .Pp
1.193 djm 187: The
1.176 djm 188: .Cm exec
1.177 jmc 189: keyword executes the specified command under the user's shell.
1.169 djm 190: If the command returns a zero exit status then the condition is considered true.
191: Commands containing whitespace characters must be quoted.
1.239 jmc 192: Arguments to
193: .Cm exec
194: accept the tokens described in the
195: .Sx TOKENS
196: section.
1.169 djm 197: .Pp
198: The other keywords' criteria must be single entries or comma-separated
199: lists and may use the wildcard and negation operators described in the
200: .Sx PATTERNS
201: section.
202: The criteria for the
203: .Cm host
204: keyword are matched against the target hostname, after any substitution
205: by the
1.295 jmc 206: .Cm Hostname
1.193 djm 207: or
208: .Cm CanonicalizeHostname
209: options.
1.169 djm 210: The
211: .Cm originalhost
212: keyword matches against the hostname as it was specified on the command-line.
213: The
214: .Cm user
215: keyword matches against the target username on the remote host.
216: The
217: .Cm localuser
218: keyword matches against the name of the local user running
219: .Xr ssh 1
220: (this keyword may be useful in system-wide
221: .Nm
222: files).
1.222 jcs 223: .It Cm AddKeysToAgent
224: Specifies whether keys should be automatically added to a running
1.223 jmc 225: .Xr ssh-agent 1 .
1.222 jcs 226: If this option is set to
1.240 jmc 227: .Cm yes
1.222 jcs 228: and a key is loaded from a file, the key and its passphrase are added to
229: the agent with the default lifetime, as if by
230: .Xr ssh-add 1 .
231: If this option is set to
1.240 jmc 232: .Cm ask ,
233: .Xr ssh 1
1.222 jcs 234: will require confirmation using the
235: .Ev SSH_ASKPASS
236: program before adding a key (see
237: .Xr ssh-add 1
238: for details).
239: If this option is set to
1.240 jmc 240: .Cm confirm ,
1.222 jcs 241: each use of the key must be confirmed, as if the
242: .Fl c
243: option was specified to
244: .Xr ssh-add 1 .
245: If this option is set to
1.240 jmc 246: .Cm no ,
1.222 jcs 247: no keys are added to the agent.
1.332 djm 248: Alternately, this option may be specified as a time interval
249: using the format described in the
250: .Sx TIME FORMATS
251: section of
252: .Xr sshd_config 5
253: to specify the key's lifetime in
254: .Xr ssh-agent 1 ,
255: after which it will automatically be removed.
1.222 jcs 256: The argument must be
1.332 djm 257: .Cm no
258: (the default),
1.240 jmc 259: .Cm yes ,
1.332 djm 260: .Cm confirm
261: (optionally followed by a time interval),
262: .Cm ask
263: or a time interval.
1.10 djm 264: .It Cm AddressFamily
1.11 jmc 265: Specifies which address family to use when connecting.
266: Valid arguments are
1.240 jmc 267: .Cm any
268: (the default),
269: .Cm inet
1.84 jmc 270: (use IPv4 only), or
1.240 jmc 271: .Cm inet6
1.40 jmc 272: (use IPv6 only).
1.1 stevesk 273: .It Cm BatchMode
274: If set to
1.240 jmc 275: .Cm yes ,
1.318 djm 276: user interaction such as password prompts and host key confirmation requests
277: will be disabled.
1.1 stevesk 278: This option is useful in scripts and other batch jobs where no user
1.318 djm 279: is present to interact with
280: .Xr ssh 1 .
1.1 stevesk 281: The argument must be
1.240 jmc 282: .Cm yes
1.1 stevesk 283: or
1.240 jmc 284: .Cm no
285: (the default).
1.268 jmc 286: .It Cm BindAddress
287: Use the specified address on the local machine as the source address of
288: the connection.
289: Only useful on systems with more than one address.
290: .It Cm BindInterface
291: Use the address of the specified interface on the local machine as the
292: source address of the connection.
1.171 djm 293: .It Cm CanonicalDomains
1.172 jmc 294: When
1.173 djm 295: .Cm CanonicalizeHostname
1.171 djm 296: is enabled, this option specifies the list of domain suffixes in which to
297: search for the specified destination host.
1.173 djm 298: .It Cm CanonicalizeFallbackLocal
1.174 djm 299: Specifies whether to fail with an error when hostname canonicalization fails.
1.172 jmc 300: The default,
1.240 jmc 301: .Cm yes ,
1.172 jmc 302: will attempt to look up the unqualified hostname using the system resolver's
1.171 djm 303: search rules.
304: A value of
1.240 jmc 305: .Cm no
1.171 djm 306: will cause
307: .Xr ssh 1
308: to fail instantly if
1.173 djm 309: .Cm CanonicalizeHostname
1.171 djm 310: is enabled and the target hostname cannot be found in any of the domains
311: specified by
312: .Cm CanonicalDomains .
1.173 djm 313: .It Cm CanonicalizeHostname
1.174 djm 314: Controls whether explicit hostname canonicalization is performed.
1.172 jmc 315: The default,
1.240 jmc 316: .Cm no ,
1.171 djm 317: is not to perform any name rewriting and let the system resolver handle all
318: hostname lookups.
319: If set to
1.240 jmc 320: .Cm yes
1.171 djm 321: then, for connections that do not use a
1.284 djm 322: .Cm ProxyCommand
323: or
324: .Cm ProxyJump ,
1.171 djm 325: .Xr ssh 1
1.173 djm 326: will attempt to canonicalize the hostname specified on the command line
1.171 djm 327: using the
328: .Cm CanonicalDomains
329: suffixes and
1.173 djm 330: .Cm CanonicalizePermittedCNAMEs
1.171 djm 331: rules.
332: If
1.173 djm 333: .Cm CanonicalizeHostname
1.171 djm 334: is set to
1.240 jmc 335: .Cm always ,
1.174 djm 336: then canonicalization is applied to proxied connections too.
1.185 djm 337: .Pp
1.193 djm 338: If this option is enabled, then the configuration files are processed
339: again using the new target name to pick up any new configuration in matching
1.185 djm 340: .Cm Host
1.193 djm 341: and
342: .Cm Match
1.185 djm 343: stanzas.
1.173 djm 344: .It Cm CanonicalizeMaxDots
1.172 jmc 345: Specifies the maximum number of dot characters in a hostname before
1.174 djm 346: canonicalization is disabled.
1.240 jmc 347: The default, 1,
1.172 jmc 348: allows a single dot (i.e. hostname.subdomain).
1.173 djm 349: .It Cm CanonicalizePermittedCNAMEs
1.172 jmc 350: Specifies rules to determine whether CNAMEs should be followed when
1.173 djm 351: canonicalizing hostnames.
1.171 djm 352: The rules consist of one or more arguments of
1.172 jmc 353: .Ar source_domain_list : Ns Ar target_domain_list ,
1.171 djm 354: where
355: .Ar source_domain_list
1.174 djm 356: is a pattern-list of domains that may follow CNAMEs in canonicalization,
1.171 djm 357: and
358: .Ar target_domain_list
1.172 jmc 359: is a pattern-list of domains that they may resolve to.
1.171 djm 360: .Pp
361: For example,
1.240 jmc 362: .Qq *.a.example.com:*.b.example.com,*.c.example.com
1.171 djm 363: will allow hostnames matching
1.240 jmc 364: .Qq *.a.example.com
1.173 djm 365: to be canonicalized to names in the
1.240 jmc 366: .Qq *.b.example.com
1.171 djm 367: or
1.240 jmc 368: .Qq *.c.example.com
1.171 djm 369: domains.
1.283 jmc 370: .It Cm CASignatureAlgorithms
371: Specifies which algorithms are allowed for signing of certificates
372: by certificate authorities (CAs).
373: The default is:
374: .Bd -literal -offset indent
1.333 djm 375: ssh-ed25519,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,
376: ecdsa-sha2-nistp521,rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.283 jmc 377: .Ed
378: .Pp
379: .Xr ssh 1
380: will not accept host certificates signed using algorithms other than those
381: specified.
1.221 djm 382: .It Cm CertificateFile
383: Specifies a file from which the user's certificate is read.
384: A corresponding private key must be provided separately in order
385: to use this certificate either
386: from an
387: .Cm IdentityFile
388: directive or
389: .Fl i
390: flag to
391: .Xr ssh 1 ,
392: via
393: .Xr ssh-agent 1 ,
394: or via a
1.305 naddy 395: .Cm PKCS11Provider
396: or
397: .Cm SecurityKeyProvider .
1.221 djm 398: .Pp
1.239 jmc 399: Arguments to
400: .Cm CertificateFile
1.326 dtucker 401: may use the tilde syntax to refer to a user's home directory,
402: the tokens described in the
1.239 jmc 403: .Sx TOKENS
1.326 dtucker 404: section and environment variables as described in the
405: .Sx ENVIRONMENT VARIABLES
1.239 jmc 406: section.
1.221 djm 407: .Pp
408: It is possible to have multiple certificate files specified in
409: configuration files; these certificates will be tried in sequence.
410: Multiple
411: .Cm CertificateFile
412: directives will add to the list of certificates used for
413: authentication.
1.1 stevesk 414: .It Cm ChallengeResponseAuthentication
1.82 jmc 415: Specifies whether to use challenge-response authentication.
1.1 stevesk 416: The argument to this keyword must be
1.240 jmc 417: .Cm yes
418: (the default)
1.1 stevesk 419: or
1.240 jmc 420: .Cm no .
1.1 stevesk 421: .It Cm CheckHostIP
1.240 jmc 422: If set to
423: .Cm yes
1.84 jmc 424: .Xr ssh 1
425: will additionally check the host IP address in the
1.1 stevesk 426: .Pa known_hosts
427: file.
1.240 jmc 428: This allows it to detect if a host key changed due to DNS spoofing
1.211 djm 429: and will add addresses of destination hosts to
430: .Pa ~/.ssh/known_hosts
431: in the process, regardless of the setting of
432: .Cm StrictHostKeyChecking .
1.107 grunk 433: If the option is set to
1.341 djm 434: .Cm no
435: (the default),
1.1 stevesk 436: the check will not be executed.
437: .It Cm Ciphers
1.245 djm 438: Specifies the ciphers allowed and their order of preference.
1.1 stevesk 439: Multiple ciphers must be comma-separated.
1.299 kn 440: If the specified list begins with a
1.214 djm 441: .Sq +
442: character, then the specified ciphers will be appended to the default set
443: instead of replacing them.
1.299 kn 444: If the specified list begins with a
1.241 djm 445: .Sq -
446: character, then the specified ciphers (including wildcards) will be removed
447: from the default set instead of replacing them.
1.301 naddy 448: If the specified list begins with a
449: .Sq ^
450: character, then the specified ciphers will be placed at the head of the
451: default set.
1.214 djm 452: .Pp
1.180 djm 453: The supported ciphers are:
1.240 jmc 454: .Bd -literal -offset indent
1.186 naddy 455: 3des-cbc
456: aes128-cbc
457: aes192-cbc
458: aes256-cbc
459: aes128-ctr
460: aes192-ctr
461: aes256-ctr
462: aes128-gcm@openssh.com
463: aes256-gcm@openssh.com
464: chacha20-poly1305@openssh.com
1.240 jmc 465: .Ed
1.180 djm 466: .Pp
1.84 jmc 467: The default is:
1.186 naddy 468: .Bd -literal -offset indent
1.215 jmc 469: chacha20-poly1305@openssh.com,
1.186 naddy 470: aes128-ctr,aes192-ctr,aes256-ctr,
1.270 djm 471: aes128-gcm@openssh.com,aes256-gcm@openssh.com
1.1 stevesk 472: .Ed
1.180 djm 473: .Pp
1.240 jmc 474: The list of available ciphers may also be obtained using
475: .Qq ssh -Q cipher .
1.1 stevesk 476: .It Cm ClearAllForwardings
1.84 jmc 477: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 478: specified in the configuration files or on the command line be
1.7 jmc 479: cleared.
480: This option is primarily useful when used from the
1.84 jmc 481: .Xr ssh 1
1.1 stevesk 482: command line to clear port forwardings set in
483: configuration files, and is automatically set by
484: .Xr scp 1
485: and
486: .Xr sftp 1 .
487: The argument must be
1.240 jmc 488: .Cm yes
1.1 stevesk 489: or
1.240 jmc 490: .Cm no
491: (the default).
1.1 stevesk 492: .It Cm Compression
493: Specifies whether to use compression.
494: The argument must be
1.240 jmc 495: .Cm yes
1.1 stevesk 496: or
1.240 jmc 497: .Cm no
498: (the default).
1.247 naddy 499: .It Cm ConnectionAttempts
500: Specifies the number of tries (one per second) to make before exiting.
501: The argument must be an integer.
502: This may be useful in scripts if the connection sometimes fails.
503: The default is 1.
1.9 djm 504: .It Cm ConnectTimeout
1.84 jmc 505: Specifies the timeout (in seconds) used when connecting to the
506: SSH server, instead of using the default system TCP timeout.
1.302 djm 507: This timeout is applied both to establishing the connection and to performing
508: the initial SSH protocol handshake and key exchange.
1.36 djm 509: .It Cm ControlMaster
510: Enables the sharing of multiple sessions over a single network connection.
511: When set to
1.240 jmc 512: .Cm yes ,
1.84 jmc 513: .Xr ssh 1
1.36 djm 514: will listen for connections on a control socket specified using the
515: .Cm ControlPath
516: argument.
517: Additional sessions can connect to this socket using the same
518: .Cm ControlPath
519: with
520: .Cm ControlMaster
521: set to
1.240 jmc 522: .Cm no
1.38 jmc 523: (the default).
1.64 jmc 524: These sessions will try to reuse the master instance's network connection
1.63 djm 525: rather than initiating new ones, but will fall back to connecting normally
526: if the control socket does not exist, or is not listening.
527: .Pp
1.37 djm 528: Setting this to
1.240 jmc 529: .Cm ask
530: will cause
531: .Xr ssh 1
1.206 jmc 532: to listen for control connections, but require confirmation using
533: .Xr ssh-askpass 1 .
1.51 jakob 534: If the
535: .Cm ControlPath
1.84 jmc 536: cannot be opened,
1.240 jmc 537: .Xr ssh 1
538: will continue without connecting to a master instance.
1.58 djm 539: .Pp
540: X11 and
1.59 jmc 541: .Xr ssh-agent 1
1.58 djm 542: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 543: display and agent forwarded will be the one belonging to the master
1.59 jmc 544: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 545: .Pp
546: Two additional options allow for opportunistic multiplexing: try to use a
547: master connection but fall back to creating a new one if one does not already
548: exist.
549: These options are:
1.240 jmc 550: .Cm auto
1.56 djm 551: and
1.240 jmc 552: .Cm autoask .
1.56 djm 553: The latter requires confirmation like the
1.240 jmc 554: .Cm ask
1.56 djm 555: option.
1.36 djm 556: .It Cm ControlPath
1.55 djm 557: Specify the path to the control socket used for connection sharing as described
558: in the
1.36 djm 559: .Cm ControlMaster
1.57 djm 560: section above or the string
1.240 jmc 561: .Cm none
1.57 djm 562: to disable connection sharing.
1.239 jmc 563: Arguments to
564: .Cm ControlPath
1.326 dtucker 565: may use the tilde syntax to refer to a user's home directory,
566: the tokens described in the
1.239 jmc 567: .Sx TOKENS
1.326 dtucker 568: section and environment variables as described in the
569: .Sx ENVIRONMENT VARIABLES
1.239 jmc 570: section.
1.56 djm 571: It is recommended that any
572: .Cm ControlPath
573: used for opportunistic connection sharing include
1.195 djm 574: at least %h, %p, and %r (or alternatively %C) and be placed in a directory
575: that is not writable by other users.
1.56 djm 576: This ensures that shared connections are uniquely identified.
1.137 djm 577: .It Cm ControlPersist
578: When used in conjunction with
579: .Cm ControlMaster ,
580: specifies that the master connection should remain open
581: in the background (waiting for future client connections)
582: after the initial client connection has been closed.
583: If set to
1.314 naddy 584: .Cm no
585: (the default),
1.137 djm 586: then the master connection will not be placed into the background,
587: and will close as soon as the initial client connection is closed.
588: If set to
1.240 jmc 589: .Cm yes
590: or 0,
1.137 djm 591: then the master connection will remain in the background indefinitely
592: (until killed or closed via a mechanism such as the
1.240 jmc 593: .Qq ssh -O exit ) .
1.137 djm 594: If set to a time in seconds, or a time in any of the formats documented in
595: .Xr sshd_config 5 ,
596: then the backgrounded master connection will automatically terminate
597: after it has remained idle (with no client connections) for the
598: specified time.
1.38 jmc 599: .It Cm DynamicForward
1.74 jmc 600: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 601: over the secure channel, and the application
602: protocol is then used to determine where to connect to from the
603: remote machine.
1.62 djm 604: .Pp
605: The argument must be
606: .Sm off
607: .Oo Ar bind_address : Oc Ar port .
608: .Sm on
1.138 djm 609: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.62 djm 610: By default, the local port is bound in accordance with the
611: .Cm GatewayPorts
612: setting.
613: However, an explicit
614: .Ar bind_address
615: may be used to bind the connection to a specific address.
616: The
617: .Ar bind_address
618: of
1.240 jmc 619: .Cm localhost
1.62 djm 620: indicates that the listening port be bound for local use only, while an
621: empty address or
622: .Sq *
623: indicates that the port should be available from all interfaces.
624: .Pp
1.38 jmc 625: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 626: .Xr ssh 1
1.38 jmc 627: will act as a SOCKS server.
628: Multiple forwardings may be specified, and
629: additional forwardings can be given on the command line.
630: Only the superuser can forward privileged ports.
1.14 markus 631: .It Cm EnableSSHKeysign
632: Setting this option to
1.240 jmc 633: .Cm yes
1.14 markus 634: in the global client configuration file
635: .Pa /etc/ssh/ssh_config
636: enables the use of the helper program
637: .Xr ssh-keysign 8
638: during
639: .Cm HostbasedAuthentication .
640: The argument must be
1.240 jmc 641: .Cm yes
1.14 markus 642: or
1.240 jmc 643: .Cm no
644: (the default).
1.23 jmc 645: This option should be placed in the non-hostspecific section.
1.14 markus 646: See
647: .Xr ssh-keysign 8
648: for more information.
1.1 stevesk 649: .It Cm EscapeChar
650: Sets the escape character (default:
651: .Ql ~ ) .
652: The escape character can also
653: be set on the command line.
654: The argument should be a single character,
655: .Ql ^
656: followed by a letter, or
1.240 jmc 657: .Cm none
1.1 stevesk 658: to disable the escape
659: character entirely (making the connection transparent for binary
660: data).
1.96 markus 661: .It Cm ExitOnForwardFailure
662: Specifies whether
663: .Xr ssh 1
664: should terminate the connection if it cannot set up all requested
1.216 djm 665: dynamic, tunnel, local, and remote port forwardings, (e.g.\&
1.217 jmc 666: if either end is unable to bind and listen on a specified port).
1.216 djm 667: Note that
668: .Cm ExitOnForwardFailure
669: does not apply to connections made over port forwardings and will not,
670: for example, cause
671: .Xr ssh 1
672: to exit if TCP connections to the ultimate forwarding destination fail.
1.96 markus 673: The argument must be
1.240 jmc 674: .Cm yes
1.96 markus 675: or
1.240 jmc 676: .Cm no
677: (the default).
1.197 djm 678: .It Cm FingerprintHash
679: Specifies the hash algorithm used when displaying key fingerprints.
680: Valid options are:
1.240 jmc 681: .Cm md5
1.197 djm 682: and
1.240 jmc 683: .Cm sha256
684: (the default).
1.1 stevesk 685: .It Cm ForwardAgent
686: Specifies whether the connection to the authentication agent (if any)
687: will be forwarded to the remote machine.
1.312 djm 688: The argument may be
689: .Cm yes ,
1.240 jmc 690: .Cm no
1.312 djm 691: (the default),
692: an explicit path to an agent socket or the name of an environment variable
693: (beginning with
694: .Sq $ )
695: in which to find the path.
1.3 stevesk 696: .Pp
1.7 jmc 697: Agent forwarding should be enabled with caution.
698: Users with the ability to bypass file permissions on the remote host
699: (for the agent's Unix-domain socket)
700: can access the local agent through the forwarded connection.
701: An attacker cannot obtain key material from the agent,
1.3 stevesk 702: however they can perform operations on the keys that enable them to
703: authenticate using the identities loaded into the agent.
1.1 stevesk 704: .It Cm ForwardX11
705: Specifies whether X11 connections will be automatically redirected
706: over the secure channel and
707: .Ev DISPLAY
708: set.
709: The argument must be
1.240 jmc 710: .Cm yes
1.1 stevesk 711: or
1.240 jmc 712: .Cm no
713: (the default).
1.3 stevesk 714: .Pp
1.7 jmc 715: X11 forwarding should be enabled with caution.
716: Users with the ability to bypass file permissions on the remote host
1.22 markus 717: (for the user's X11 authorization database)
1.7 jmc 718: can access the local X11 display through the forwarded connection.
1.22 markus 719: An attacker may then be able to perform activities such as keystroke monitoring
720: if the
721: .Cm ForwardX11Trusted
722: option is also enabled.
1.134 djm 723: .It Cm ForwardX11Timeout
1.135 jmc 724: Specify a timeout for untrusted X11 forwarding
725: using the format described in the
1.240 jmc 726: .Sx TIME FORMATS
727: section of
1.134 djm 728: .Xr sshd_config 5 .
729: X11 connections received by
730: .Xr ssh 1
731: after this time will be refused.
1.285 djm 732: Setting
733: .Cm ForwardX11Timeout
734: to zero will disable the timeout and permit X11 forwarding for the life
735: of the connection.
1.134 djm 736: The default is to disable untrusted X11 forwarding after twenty minutes has
737: elapsed.
1.22 markus 738: .It Cm ForwardX11Trusted
1.34 jmc 739: If this option is set to
1.240 jmc 740: .Cm yes ,
1.84 jmc 741: remote X11 clients will have full access to the original X11 display.
1.42 djm 742: .Pp
1.22 markus 743: If this option is set to
1.240 jmc 744: .Cm no
745: (the default),
1.84 jmc 746: remote X11 clients will be considered untrusted and prevented
1.22 markus 747: from stealing or tampering with data belonging to trusted X11
748: clients.
1.42 djm 749: Furthermore, the
750: .Xr xauth 1
751: token used for the session will be set to expire after 20 minutes.
752: Remote clients will be refused access after this time.
1.22 markus 753: .Pp
754: See the X11 SECURITY extension specification for full details on
755: the restrictions imposed on untrusted clients.
1.1 stevesk 756: .It Cm GatewayPorts
757: Specifies whether remote hosts are allowed to connect to local
758: forwarded ports.
759: By default,
1.84 jmc 760: .Xr ssh 1
1.7 jmc 761: binds local port forwardings to the loopback address.
762: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 763: .Cm GatewayPorts
1.84 jmc 764: can be used to specify that ssh
1.1 stevesk 765: should bind local port forwardings to the wildcard address,
766: thus allowing remote hosts to connect to forwarded ports.
767: The argument must be
1.240 jmc 768: .Cm yes
1.1 stevesk 769: or
1.240 jmc 770: .Cm no
771: (the default).
1.1 stevesk 772: .It Cm GlobalKnownHostsFile
1.151 djm 773: Specifies one or more files to use for the global
774: host key database, separated by whitespace.
775: The default is
776: .Pa /etc/ssh/ssh_known_hosts ,
777: .Pa /etc/ssh/ssh_known_hosts2 .
1.18 markus 778: .It Cm GSSAPIAuthentication
1.27 markus 779: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 780: The default is
1.240 jmc 781: .Cm no .
1.18 markus 782: .It Cm GSSAPIDelegateCredentials
783: Forward (delegate) credentials to the server.
784: The default is
1.240 jmc 785: .Cm no .
1.44 djm 786: .It Cm HashKnownHosts
787: Indicates that
1.84 jmc 788: .Xr ssh 1
1.44 djm 789: should hash host names and addresses when they are added to
1.50 djm 790: .Pa ~/.ssh/known_hosts .
1.44 djm 791: These hashed names may be used normally by
1.84 jmc 792: .Xr ssh 1
1.44 djm 793: and
1.84 jmc 794: .Xr sshd 8 ,
1.316 djm 795: but they do not visually reveal identifying information if the
796: file's contents are disclosed.
1.44 djm 797: The default is
1.240 jmc 798: .Cm no .
1.97 jmc 799: Note that existing names and addresses in known hosts files
800: will not be converted automatically,
801: but may be manually hashed using
1.45 djm 802: .Xr ssh-keygen 1 .
1.1 stevesk 803: .It Cm HostbasedAuthentication
804: Specifies whether to try rhosts based authentication with public key
805: authentication.
806: The argument must be
1.240 jmc 807: .Cm yes
1.1 stevesk 808: or
1.240 jmc 809: .Cm no
810: (the default).
1.202 djm 811: .It Cm HostbasedKeyTypes
812: Specifies the key types that will be used for hostbased authentication
1.279 djm 813: as a comma-separated list of patterns.
1.300 naddy 814: Alternately if the specified list begins with a
1.214 djm 815: .Sq +
816: character, then the specified key types will be appended to the default set
817: instead of replacing them.
1.300 naddy 818: If the specified list begins with a
1.241 djm 819: .Sq -
820: character, then the specified key types (including wildcards) will be removed
821: from the default set instead of replacing them.
1.301 naddy 822: If the specified list begins with a
823: .Sq ^
824: character, then the specified key types will be placed at the head of the
825: default set.
1.213 markus 826: The default for this option is:
827: .Bd -literal -offset 3n
1.333 djm 828: ssh-ed25519-cert-v01@openssh.com,
1.213 markus 829: ecdsa-sha2-nistp256-cert-v01@openssh.com,
830: ecdsa-sha2-nistp384-cert-v01@openssh.com,
831: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.333 djm 832: sk-ssh-ed25519-cert-v01@openssh.com,
1.311 naddy 833: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.305 naddy 834: rsa-sha2-512-cert-v01@openssh.com,
835: rsa-sha2-256-cert-v01@openssh.com,
1.213 markus 836: ssh-rsa-cert-v01@openssh.com,
1.333 djm 837: ssh-ed25519,
1.213 markus 838: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.333 djm 839: sk-ssh-ed25519@openssh.com,
1.311 naddy 840: sk-ecdsa-sha2-nistp256@openssh.com,
841: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.213 markus 842: .Ed
843: .Pp
1.202 djm 844: The
845: .Fl Q
846: option of
847: .Xr ssh 1
848: may be used to list supported key types.
1.1 stevesk 849: .It Cm HostKeyAlgorithms
1.226 jmc 850: Specifies the host key algorithms
1.1 stevesk 851: that the client wants to use in order of preference.
1.300 naddy 852: Alternately if the specified list begins with a
1.214 djm 853: .Sq +
854: character, then the specified key types will be appended to the default set
855: instead of replacing them.
1.300 naddy 856: If the specified list begins with a
1.241 djm 857: .Sq -
858: character, then the specified key types (including wildcards) will be removed
859: from the default set instead of replacing them.
1.301 naddy 860: If the specified list begins with a
861: .Sq ^
862: character, then the specified key types will be placed at the head of the
863: default set.
1.1 stevesk 864: The default for this option is:
1.139 djm 865: .Bd -literal -offset 3n
1.333 djm 866: ssh-ed25519-cert-v01@openssh.com,
1.139 djm 867: ecdsa-sha2-nistp256-cert-v01@openssh.com,
868: ecdsa-sha2-nistp384-cert-v01@openssh.com,
869: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.333 djm 870: sk-ssh-ed25519-cert-v01@openssh.com,
1.311 naddy 871: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.305 naddy 872: rsa-sha2-512-cert-v01@openssh.com,
873: rsa-sha2-256-cert-v01@openssh.com,
1.213 markus 874: ssh-rsa-cert-v01@openssh.com,
1.333 djm 875: ssh-ed25519,
1.139 djm 876: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.311 naddy 877: sk-ecdsa-sha2-nistp256@openssh.com,
1.333 djm 878: sk-ssh-ed25519@openssh.com,
1.311 naddy 879: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.139 djm 880: .Ed
1.145 djm 881: .Pp
882: If hostkeys are known for the destination host then this default is modified
883: to prefer their algorithms.
1.198 djm 884: .Pp
1.240 jmc 885: The list of available key types may also be obtained using
1.322 dtucker 886: .Qq ssh -Q HostKeyAlgorithms .
1.1 stevesk 887: .It Cm HostKeyAlias
888: Specifies an alias that should be used instead of the
889: real host name when looking up or saving the host key
1.251 djm 890: in the host key database files and when validating host certificates.
1.84 jmc 891: This option is useful for tunneling SSH connections
1.1 stevesk 892: or for multiple servers running on a single host.
1.295 jmc 893: .It Cm Hostname
1.1 stevesk 894: Specifies the real host name to log into.
895: This can be used to specify nicknames or abbreviations for hosts.
1.239 jmc 896: Arguments to
1.295 jmc 897: .Cm Hostname
1.239 jmc 898: accept the tokens described in the
899: .Sx TOKENS
900: section.
1.1 stevesk 901: Numeric IP addresses are also permitted (both on the command line and in
1.295 jmc 902: .Cm Hostname
1.1 stevesk 903: specifications).
1.239 jmc 904: The default is the name given on the command line.
1.29 markus 905: .It Cm IdentitiesOnly
906: Specifies that
1.84 jmc 907: .Xr ssh 1
1.304 djm 908: should only use the configured authentication identity and certificate files
909: (either the default files, or those explicitly configured in the
1.31 jmc 910: .Nm
1.221 djm 911: files
912: or passed on the
913: .Xr ssh 1
1.304 djm 914: command-line),
1.84 jmc 915: even if
916: .Xr ssh-agent 1
1.159 djm 917: or a
918: .Cm PKCS11Provider
1.305 naddy 919: or
920: .Cm SecurityKeyProvider
1.29 markus 921: offers more identities.
922: The argument to this keyword must be
1.240 jmc 923: .Cm yes
1.29 markus 924: or
1.240 jmc 925: .Cm no
926: (the default).
1.84 jmc 927: This option is intended for situations where ssh-agent
1.29 markus 928: offers many different identities.
1.231 markus 929: .It Cm IdentityAgent
930: Specifies the
931: .Ux Ns -domain
932: socket used to communicate with the authentication agent.
933: .Pp
934: This option overrides the
1.240 jmc 935: .Ev SSH_AUTH_SOCK
1.231 markus 936: environment variable and can be used to select a specific agent.
937: Setting the socket name to
1.240 jmc 938: .Cm none
1.231 markus 939: disables the use of an authentication agent.
1.232 markus 940: If the string
1.240 jmc 941: .Qq SSH_AUTH_SOCK
1.232 markus 942: is specified, the location of the socket will be read from the
943: .Ev SSH_AUTH_SOCK
944: environment variable.
1.286 djm 945: Otherwise if the specified value begins with a
946: .Sq $
947: character, then it will be treated as an environment variable containing
948: the location of the socket.
1.231 markus 949: .Pp
1.239 jmc 950: Arguments to
951: .Cm IdentityAgent
1.326 dtucker 952: may use the tilde syntax to refer to a user's home directory,
953: the tokens described in the
1.239 jmc 954: .Sx TOKENS
1.326 dtucker 955: section and environment variables as described in the
956: .Sx ENVIRONMENT VARIABLES
1.239 jmc 957: section.
1.67 jmc 958: .It Cm IdentityFile
1.313 naddy 959: Specifies a file from which the user's DSA, ECDSA, authenticator-hosted ECDSA,
960: Ed25519, authenticator-hosted Ed25519 or RSA authentication identity is read.
1.67 jmc 961: The default is
1.139 djm 962: .Pa ~/.ssh/id_dsa ,
1.183 naddy 963: .Pa ~/.ssh/id_ecdsa ,
1.305 naddy 964: .Pa ~/.ssh/id_ecdsa_sk ,
1.308 naddy 965: .Pa ~/.ssh/id_ed25519 ,
966: .Pa ~/.ssh/id_ed25519_sk
1.139 djm 967: and
1.245 djm 968: .Pa ~/.ssh/id_rsa .
1.67 jmc 969: Additionally, any identities represented by the authentication agent
1.165 djm 970: will be used for authentication unless
971: .Cm IdentitiesOnly
972: is set.
1.221 djm 973: If no certificates have been explicitly specified by
974: .Cm CertificateFile ,
1.129 djm 975: .Xr ssh 1
976: will try to load certificate information from the filename obtained by
977: appending
978: .Pa -cert.pub
979: to the path of a specified
980: .Cm IdentityFile .
1.90 djm 981: .Pp
1.239 jmc 982: Arguments to
983: .Cm IdentityFile
984: may use the tilde syntax to refer to a user's home directory
985: or the tokens described in the
986: .Sx TOKENS
987: section.
1.90 djm 988: .Pp
1.67 jmc 989: It is possible to have
990: multiple identity files specified in configuration files; all these
991: identities will be tried in sequence.
1.152 djm 992: Multiple
993: .Cm IdentityFile
994: directives will add to the list of identities tried (this behaviour
995: differs from that of other configuration directives).
1.165 djm 996: .Pp
997: .Cm IdentityFile
998: may be used in conjunction with
999: .Cm IdentitiesOnly
1000: to select which identities in an agent are offered during authentication.
1.221 djm 1001: .Cm IdentityFile
1002: may also be used in conjunction with
1003: .Cm CertificateFile
1004: in order to provide any certificate also needed for authentication with
1005: the identity.
1.164 jmc 1006: .It Cm IgnoreUnknown
1007: Specifies a pattern-list of unknown options to be ignored if they are
1008: encountered in configuration parsing.
1009: This may be used to suppress errors if
1010: .Nm
1011: contains options that are unrecognised by
1012: .Xr ssh 1 .
1013: It is recommended that
1014: .Cm IgnoreUnknown
1015: be listed early in the configuration file as it will not be applied
1016: to unknown options that appear before it.
1.229 djm 1017: .It Cm Include
1018: Include the specified configuration file(s).
1.230 jmc 1019: Multiple pathnames may be specified and each pathname may contain
1.281 kn 1020: .Xr glob 7
1.229 djm 1021: wildcards and, for user configurations, shell-like
1.240 jmc 1022: .Sq ~
1.229 djm 1023: references to user home directories.
1.327 djm 1024: Wildcards will be expanded and processed in lexical order.
1.229 djm 1025: Files without absolute paths are assumed to be in
1026: .Pa ~/.ssh
1.230 jmc 1027: if included in a user configuration file or
1.229 djm 1028: .Pa /etc/ssh
1029: if included from the system configuration file.
1030: .Cm Include
1031: directive may appear inside a
1032: .Cm Match
1033: or
1034: .Cm Host
1035: block
1036: to perform conditional inclusion.
1.143 djm 1037: .It Cm IPQoS
1038: Specifies the IPv4 type-of-service or DSCP class for connections.
1039: Accepted values are
1.240 jmc 1040: .Cm af11 ,
1041: .Cm af12 ,
1042: .Cm af13 ,
1043: .Cm af21 ,
1044: .Cm af22 ,
1045: .Cm af23 ,
1046: .Cm af31 ,
1047: .Cm af32 ,
1048: .Cm af33 ,
1049: .Cm af41 ,
1050: .Cm af42 ,
1051: .Cm af43 ,
1052: .Cm cs0 ,
1053: .Cm cs1 ,
1054: .Cm cs2 ,
1055: .Cm cs3 ,
1056: .Cm cs4 ,
1057: .Cm cs5 ,
1058: .Cm cs6 ,
1059: .Cm cs7 ,
1060: .Cm ef ,
1.319 djm 1061: .Cm le ,
1.240 jmc 1062: .Cm lowdelay ,
1063: .Cm throughput ,
1064: .Cm reliability ,
1.253 djm 1065: a numeric value, or
1066: .Cm none
1067: to use the operating system default.
1.146 djm 1068: This option may take one or two arguments, separated by whitespace.
1.143 djm 1069: If one argument is specified, it is used as the packet class unconditionally.
1070: If two values are specified, the first is automatically selected for
1071: interactive sessions and the second for non-interactive sessions.
1072: The default is
1.269 job 1073: .Cm af21
1.272 jmc 1074: (Low-Latency Data)
1.143 djm 1075: for interactive sessions and
1.269 job 1076: .Cm cs1
1.272 jmc 1077: (Lower Effort)
1.143 djm 1078: for non-interactive sessions.
1.103 djm 1079: .It Cm KbdInteractiveAuthentication
1080: Specifies whether to use keyboard-interactive authentication.
1081: The argument to this keyword must be
1.240 jmc 1082: .Cm yes
1083: (the default)
1.103 djm 1084: or
1.240 jmc 1085: .Cm no .
1.39 djm 1086: .It Cm KbdInteractiveDevices
1087: Specifies the list of methods to use in keyboard-interactive authentication.
1088: Multiple method names must be comma-separated.
1089: The default is to use the server specified list.
1.85 jmc 1090: The methods available vary depending on what the server supports.
1091: For an OpenSSH server,
1092: it may be zero or more of:
1.240 jmc 1093: .Cm bsdauth ,
1094: .Cm pam ,
1.85 jmc 1095: and
1.240 jmc 1096: .Cm skey .
1.140 djm 1097: .It Cm KexAlgorithms
1098: Specifies the available KEX (Key Exchange) algorithms.
1099: Multiple algorithms must be comma-separated.
1.299 kn 1100: If the specified list begins with a
1.214 djm 1101: .Sq +
1102: character, then the specified methods will be appended to the default set
1103: instead of replacing them.
1.299 kn 1104: If the specified list begins with a
1.241 djm 1105: .Sq -
1106: character, then the specified methods (including wildcards) will be removed
1107: from the default set instead of replacing them.
1.301 naddy 1108: If the specified list begins with a
1109: .Sq ^
1110: character, then the specified methods will be placed at the head of the
1111: default set.
1.141 jmc 1112: The default is:
1113: .Bd -literal -offset indent
1.238 djm 1114: curve25519-sha256,curve25519-sha256@libssh.org,
1.141 jmc 1115: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
1116: diffie-hellman-group-exchange-sha256,
1.266 djm 1117: diffie-hellman-group16-sha512,
1118: diffie-hellman-group18-sha512,
1.317 tedu 1119: diffie-hellman-group14-sha256
1.141 jmc 1120: .Ed
1.198 djm 1121: .Pp
1.240 jmc 1122: The list of available key exchange algorithms may also be obtained using
1123: .Qq ssh -Q kex .
1.339 djm 1124: .It Cm KnownHostsCommand
1.340 jmc 1125: Specifies a command to use to obtain a list of host keys, in addition to
1.339 djm 1126: those listed in
1127: .Cm UserKnownHostsFile
1128: and
1129: .Cm GlobalKnownHostsFile .
1130: This command is executed after the files have been read.
1.340 jmc 1131: It may write host key lines to standard output in identical format to the
1.339 djm 1132: usual files (described in the
1133: .Sx VERIFYING HOST KEYS
1134: section in
1135: .Xr ssh 1 ) .
1136: Arguments to
1137: .Cm KnownHostsCommand
1138: accept the tokens described in the
1139: .Sx TOKENS
1140: section.
1.340 jmc 1141: The command may be invoked multiple times per connection: once when preparing
1.339 djm 1142: the preference list of host key algorithms to use, again to obtain the
1143: host key for the requested host name and, if
1144: .Cm CheckHostIP
1145: is enabled, one more time to obtain the host key matching the server's
1146: address.
1147: If the command exits abnormally or returns a non-zero exit status then the
1148: connection is terminated.
1.65 reyk 1149: .It Cm LocalCommand
1150: Specifies a command to execute on the local machine after successfully
1151: connecting to the server.
1152: The command string extends to the end of the line, and is executed with
1.105 jmc 1153: the user's shell.
1.239 jmc 1154: Arguments to
1155: .Cm LocalCommand
1156: accept the tokens described in the
1157: .Sx TOKENS
1158: section.
1.123 djm 1159: .Pp
1160: The command is run synchronously and does not have access to the
1161: session of the
1162: .Xr ssh 1
1163: that spawned it.
1164: It should not be used for interactive commands.
1165: .Pp
1.65 reyk 1166: This directive is ignored unless
1167: .Cm PermitLocalCommand
1168: has been enabled.
1.1 stevesk 1169: .It Cm LocalForward
1.74 jmc 1170: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 1171: the secure channel to the specified host and port from the remote machine.
1.324 dtucker 1172: The first argument specifies the listener and may be
1.43 djm 1173: .Sm off
1.49 jmc 1174: .Oo Ar bind_address : Oc Ar port
1.43 djm 1175: .Sm on
1.324 dtucker 1176: or a Unix domain socket path.
1177: The second argument is the destination and may be
1178: .Ar host : Ns Ar hostport
1179: or a Unix domain socket path if the remote host supports it.
1180: .Pp
1.138 djm 1181: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.46 jmc 1182: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 1183: given on the command line.
1.1 stevesk 1184: Only the superuser can forward privileged ports.
1.43 djm 1185: By default, the local port is bound in accordance with the
1186: .Cm GatewayPorts
1187: setting.
1188: However, an explicit
1189: .Ar bind_address
1190: may be used to bind the connection to a specific address.
1191: The
1192: .Ar bind_address
1193: of
1.240 jmc 1194: .Cm localhost
1.46 jmc 1195: indicates that the listening port be bound for local use only, while an
1196: empty address or
1197: .Sq *
1.43 djm 1198: indicates that the port should be available from all interfaces.
1.326 dtucker 1199: Unix domain socket paths may use the tokens described in the
1.324 dtucker 1200: .Sx TOKENS
1.326 dtucker 1201: section and environment variables as described in the
1202: .Sx ENVIRONMENT VARIABLES
1.324 dtucker 1203: section.
1.1 stevesk 1204: .It Cm LogLevel
1205: Gives the verbosity level that is used when logging messages from
1.84 jmc 1206: .Xr ssh 1 .
1.1 stevesk 1207: The possible values are:
1.84 jmc 1208: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 1209: The default is INFO.
1210: DEBUG and DEBUG1 are equivalent.
1211: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.337 djm 1212: .It Cm LogVerbose
1213: Specify one or more overrides to LogLevel.
1214: An override consists of a pattern lists that matches the source file, function
1215: and line number to force detailed logging for.
1216: For example, an override pattern of:
1217: .Bd -literal -offset indent
1218: kex.c:*:1000,*:kex_exchange_identification():*,packet.c:*
1219: .Ed
1220: .Pp
1221: would enable detailed logging for line 1000 of
1.338 jmc 1222: .Pa kex.c ,
1.337 djm 1223: everything in the
1224: .Fn kex_exchange_identification
1225: function, and all code in the
1226: .Pa packet.c
1227: file.
1228: This option is intended for debugging and no overrides are enabled by default.
1.1 stevesk 1229: .It Cm MACs
1230: Specifies the MAC (message authentication code) algorithms
1231: in order of preference.
1.226 jmc 1232: The MAC algorithm is used for data integrity protection.
1.1 stevesk 1233: Multiple algorithms must be comma-separated.
1.299 kn 1234: If the specified list begins with a
1.214 djm 1235: .Sq +
1236: character, then the specified algorithms will be appended to the default set
1237: instead of replacing them.
1.299 kn 1238: If the specified list begins with a
1.241 djm 1239: .Sq -
1240: character, then the specified algorithms (including wildcards) will be removed
1241: from the default set instead of replacing them.
1.301 naddy 1242: If the specified list begins with a
1243: .Sq ^
1244: character, then the specified algorithms will be placed at the head of the
1245: default set.
1.214 djm 1246: .Pp
1.160 markus 1247: The algorithms that contain
1.240 jmc 1248: .Qq -etm
1.160 markus 1249: calculate the MAC after encryption (encrypt-then-mac).
1250: These are considered safer and their use recommended.
1.214 djm 1251: .Pp
1.84 jmc 1252: The default is:
1.101 jmc 1253: .Bd -literal -offset indent
1.160 markus 1254: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
1255: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
1.224 djm 1256: hmac-sha1-etm@openssh.com,
1.186 naddy 1257: umac-64@openssh.com,umac-128@openssh.com,
1.224 djm 1258: hmac-sha2-256,hmac-sha2-512,hmac-sha1
1.101 jmc 1259: .Ed
1.198 djm 1260: .Pp
1.240 jmc 1261: The list of available MAC algorithms may also be obtained using
1262: .Qq ssh -Q mac .
1.1 stevesk 1263: .It Cm NoHostAuthenticationForLocalhost
1.264 djm 1264: Disable host authentication for localhost (loopback addresses).
1.1 stevesk 1265: The argument to this keyword must be
1.240 jmc 1266: .Cm yes
1.1 stevesk 1267: or
1.242 jmc 1268: .Cm no
1.240 jmc 1269: (the default).
1.1 stevesk 1270: .It Cm NumberOfPasswordPrompts
1271: Specifies the number of password prompts before giving up.
1272: The argument to this keyword must be an integer.
1.84 jmc 1273: The default is 3.
1.1 stevesk 1274: .It Cm PasswordAuthentication
1275: Specifies whether to use password authentication.
1276: The argument to this keyword must be
1.240 jmc 1277: .Cm yes
1278: (the default)
1.1 stevesk 1279: or
1.240 jmc 1280: .Cm no .
1.65 reyk 1281: .It Cm PermitLocalCommand
1282: Allow local command execution via the
1283: .Ic LocalCommand
1284: option or using the
1.66 jmc 1285: .Ic !\& Ns Ar command
1.65 reyk 1286: escape sequence in
1287: .Xr ssh 1 .
1288: The argument must be
1.240 jmc 1289: .Cm yes
1.65 reyk 1290: or
1.240 jmc 1291: .Cm no
1292: (the default).
1.127 markus 1293: .It Cm PKCS11Provider
1.292 djm 1294: Specifies which PKCS#11 provider to use or
1295: .Cm none
1296: to indicate that no provider should be used (the default).
1297: The argument to this keyword is a path to the PKCS#11 shared library
1.127 markus 1298: .Xr ssh 1
1.292 djm 1299: should use to communicate with a PKCS#11 token providing keys for user
1300: authentication.
1.67 jmc 1301: .It Cm Port
1302: Specifies the port number to connect on the remote host.
1.84 jmc 1303: The default is 22.
1.1 stevesk 1304: .It Cm PreferredAuthentications
1.226 jmc 1305: Specifies the order in which the client should try authentication methods.
1.48 jmc 1306: This allows a client to prefer one method (e.g.\&
1.1 stevesk 1307: .Cm keyboard-interactive )
1.48 jmc 1308: over another method (e.g.\&
1.131 jmc 1309: .Cm password ) .
1310: The default is:
1311: .Bd -literal -offset indent
1312: gssapi-with-mic,hostbased,publickey,
1313: keyboard-interactive,password
1314: .Ed
1.1 stevesk 1315: .It Cm ProxyCommand
1316: Specifies the command to use to connect to the server.
1317: The command
1.190 djm 1318: string extends to the end of the line, and is executed
1319: using the user's shell
1320: .Ql exec
1321: directive to avoid a lingering shell process.
1322: .Pp
1.239 jmc 1323: Arguments to
1324: .Cm ProxyCommand
1325: accept the tokens described in the
1326: .Sx TOKENS
1327: section.
1.1 stevesk 1328: The command can be basically anything,
1329: and should read from its standard input and write to its standard output.
1330: It should eventually connect an
1331: .Xr sshd 8
1332: server running on some machine, or execute
1333: .Ic sshd -i
1334: somewhere.
1335: Host key management will be done using the
1.296 jmc 1336: .Cm Hostname
1337: of the host being connected (defaulting to the name typed by the user).
1.7 jmc 1338: Setting the command to
1.240 jmc 1339: .Cm none
1.6 markus 1340: disables this option entirely.
1.1 stevesk 1341: Note that
1342: .Cm CheckHostIP
1343: is not available for connects with a proxy command.
1.52 djm 1344: .Pp
1345: This directive is useful in conjunction with
1346: .Xr nc 1
1347: and its proxy support.
1.53 jmc 1348: For example, the following directive would connect via an HTTP proxy at
1.52 djm 1349: 192.0.2.0:
1350: .Bd -literal -offset 3n
1351: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
1352: .Ed
1.233 djm 1353: .It Cm ProxyJump
1.260 millert 1354: Specifies one or more jump proxies as either
1.233 djm 1355: .Xo
1356: .Sm off
1.234 jmc 1357: .Op Ar user No @
1.233 djm 1358: .Ar host
1.234 jmc 1359: .Op : Ns Ar port
1.233 djm 1360: .Sm on
1.260 millert 1361: or an ssh URI
1.233 djm 1362: .Xc .
1.235 djm 1363: Multiple proxies may be separated by comma characters and will be visited
1.236 djm 1364: sequentially.
1.233 djm 1365: Setting this option will cause
1366: .Xr ssh 1
1367: to connect to the target host by first making a
1368: .Xr ssh 1
1369: connection to the specified
1370: .Cm ProxyJump
1371: host and then establishing a
1.234 jmc 1372: TCP forwarding to the ultimate target from there.
1.233 djm 1373: .Pp
1374: Note that this option will compete with the
1375: .Cm ProxyCommand
1376: option - whichever is specified first will prevent later instances of the
1377: other from taking effect.
1.289 djm 1378: .Pp
1379: Note also that the configuration for the destination host (either supplied
1380: via the command-line or the configuration file) is not generally applied
1381: to jump hosts.
1382: .Pa ~/.ssh/config
1383: should be used if specific configuration is required for jump hosts.
1.167 djm 1384: .It Cm ProxyUseFdpass
1.168 jmc 1385: Specifies that
1.167 djm 1386: .Cm ProxyCommand
1387: will pass a connected file descriptor back to
1.168 jmc 1388: .Xr ssh 1
1.167 djm 1389: instead of continuing to execute and pass data.
1390: The default is
1.240 jmc 1391: .Cm no .
1.213 markus 1392: .It Cm PubkeyAcceptedKeyTypes
1393: Specifies the key types that will be used for public key authentication
1.279 djm 1394: as a comma-separated list of patterns.
1.299 kn 1395: If the specified list begins with a
1.214 djm 1396: .Sq +
1397: character, then the key types after it will be appended to the default
1398: instead of replacing it.
1.299 kn 1399: If the specified list begins with a
1.241 djm 1400: .Sq -
1401: character, then the specified key types (including wildcards) will be removed
1402: from the default set instead of replacing them.
1.301 naddy 1403: If the specified list begins with a
1404: .Sq ^
1405: character, then the specified key types will be placed at the head of the
1406: default set.
1.213 markus 1407: The default for this option is:
1408: .Bd -literal -offset 3n
1.333 djm 1409: ssh-ed25519-cert-v01@openssh.com,
1.213 markus 1410: ecdsa-sha2-nistp256-cert-v01@openssh.com,
1411: ecdsa-sha2-nistp384-cert-v01@openssh.com,
1412: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.333 djm 1413: sk-ssh-ed25519-cert-v01@openssh.com,
1.311 naddy 1414: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.305 naddy 1415: rsa-sha2-512-cert-v01@openssh.com,
1416: rsa-sha2-256-cert-v01@openssh.com,
1.213 markus 1417: ssh-rsa-cert-v01@openssh.com,
1.333 djm 1418: ssh-ed25519,
1.311 naddy 1419: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.333 djm 1420: sk-ssh-ed25519@openssh.com,
1.305 naddy 1421: sk-ecdsa-sha2-nistp256@openssh.com,
1.311 naddy 1422: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.213 markus 1423: .Ed
1424: .Pp
1.240 jmc 1425: The list of available key types may also be obtained using
1.322 dtucker 1426: .Qq ssh -Q PubkeyAcceptedKeyTypes .
1.1 stevesk 1427: .It Cm PubkeyAuthentication
1428: Specifies whether to try public key authentication.
1429: The argument to this keyword must be
1.240 jmc 1430: .Cm yes
1431: (the default)
1.1 stevesk 1432: or
1.240 jmc 1433: .Cm no .
1.75 dtucker 1434: .It Cm RekeyLimit
1435: Specifies the maximum amount of data that may be transmitted before the
1.342 ! rob 1436: session key is renegotiated, optionally followed by a maximum amount of
1.162 dtucker 1437: time that may pass before the session key is renegotiated.
1438: The first argument is specified in bytes and may have a suffix of
1.76 jmc 1439: .Sq K ,
1440: .Sq M ,
1.75 dtucker 1441: or
1.76 jmc 1442: .Sq G
1.75 dtucker 1443: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1444: The default is between
1.84 jmc 1445: .Sq 1G
1.75 dtucker 1446: and
1.84 jmc 1447: .Sq 4G ,
1.75 dtucker 1448: depending on the cipher.
1.162 dtucker 1449: The optional second value is specified in seconds and may use any of the
1.293 schwarze 1450: units documented in the TIME FORMATS section of
1.162 dtucker 1451: .Xr sshd_config 5 .
1452: The default value for
1453: .Cm RekeyLimit
1454: is
1.240 jmc 1455: .Cm default none ,
1.162 dtucker 1456: which means that rekeying is performed after the cipher's default amount
1457: of data has been sent or received and no time based rekeying is done.
1.249 bluhm 1458: .It Cm RemoteCommand
1459: Specifies a command to execute on the remote machine after successfully
1460: connecting to the server.
1461: The command string extends to the end of the line, and is executed with
1462: the user's shell.
1.250 jmc 1463: Arguments to
1464: .Cm RemoteCommand
1465: accept the tokens described in the
1466: .Sx TOKENS
1467: section.
1.1 stevesk 1468: .It Cm RemoteForward
1.74 jmc 1469: Specifies that a TCP port on the remote machine be forwarded over
1.256 markus 1470: the secure channel.
1.273 djm 1471: The remote port may either be forwarded to a specified host and port
1.256 markus 1472: from the local machine, or may act as a SOCKS 4/5 proxy that allows a remote
1473: client to connect to arbitrary destinations from the local machine.
1.324 dtucker 1474: The first argument is the listening specification and may be
1.43 djm 1475: .Sm off
1.49 jmc 1476: .Oo Ar bind_address : Oc Ar port
1.43 djm 1477: .Sm on
1.324 dtucker 1478: or, if the remote host supports it, a Unix domain socket path.
1.256 markus 1479: If forwarding to a specific destination then the second argument must be
1.324 dtucker 1480: .Ar host : Ns Ar hostport
1481: or a Unix domain socket path,
1.256 markus 1482: otherwise if no destination argument is specified then the remote forwarding
1483: will be established as a SOCKS proxy.
1484: .Pp
1.138 djm 1485: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.1 stevesk 1486: Multiple forwardings may be specified, and additional
1487: forwardings can be given on the command line.
1.113 stevesk 1488: Privileged ports can be forwarded only when
1489: logging in as root on the remote machine.
1.326 dtucker 1490: Unix domain socket paths may use the tokens described in the
1.324 dtucker 1491: .Sx TOKENS
1.326 dtucker 1492: section and environment variables as described in the
1493: .Sx ENVIRONMENT VARIABLES
1.324 dtucker 1494: section.
1.118 jmc 1495: .Pp
1.117 djm 1496: If the
1497: .Ar port
1.240 jmc 1498: argument is 0,
1.117 djm 1499: the listen port will be dynamically allocated on the server and reported
1500: to the client at run time.
1.43 djm 1501: .Pp
1502: If the
1503: .Ar bind_address
1504: is not specified, the default is to only bind to loopback addresses.
1505: If the
1506: .Ar bind_address
1507: is
1508: .Ql *
1509: or an empty string, then the forwarding is requested to listen on all
1510: interfaces.
1511: Specifying a remote
1512: .Ar bind_address
1.46 jmc 1513: will only succeed if the server's
1514: .Cm GatewayPorts
1.43 djm 1515: option is enabled (see
1.46 jmc 1516: .Xr sshd_config 5 ) .
1.149 djm 1517: .It Cm RequestTTY
1518: Specifies whether to request a pseudo-tty for the session.
1519: The argument may be one of:
1.240 jmc 1520: .Cm no
1.149 djm 1521: (never request a TTY),
1.240 jmc 1522: .Cm yes
1.149 djm 1523: (always request a TTY when standard input is a TTY),
1.240 jmc 1524: .Cm force
1.149 djm 1525: (always request a TTY) or
1.240 jmc 1526: .Cm auto
1.149 djm 1527: (request a TTY when opening a login session).
1528: This option mirrors the
1529: .Fl t
1530: and
1531: .Fl T
1532: flags for
1533: .Xr ssh 1 .
1.196 djm 1534: .It Cm RevokedHostKeys
1535: Specifies revoked host public keys.
1536: Keys listed in this file will be refused for host authentication.
1537: Note that if this file does not exist or is not readable,
1538: then host authentication will be refused for all hosts.
1539: Keys may be specified as a text file, listing one public key per line, or as
1540: an OpenSSH Key Revocation List (KRL) as generated by
1541: .Xr ssh-keygen 1 .
1542: For more information on KRLs, see the KEY REVOCATION LISTS section in
1543: .Xr ssh-keygen 1 .
1.305 naddy 1544: .It Cm SecurityKeyProvider
1.313 naddy 1545: Specifies a path to a library that will be used when loading any
1546: FIDO authenticator-hosted keys, overriding the default of using
1547: the built-in USB HID support.
1.309 naddy 1548: .Pp
1549: If the specified value begins with a
1550: .Sq $
1551: character, then it will be treated as an environment variable containing
1552: the path to the library.
1.32 djm 1553: .It Cm SendEnv
1554: Specifies what variables from the local
1555: .Xr environ 7
1556: should be sent to the server.
1.84 jmc 1557: The server must also support it, and the server must be configured to
1.33 djm 1558: accept these environment variables.
1.207 dtucker 1559: Note that the
1560: .Ev TERM
1.208 jmc 1561: environment variable is always sent whenever a
1.207 dtucker 1562: pseudo-terminal is requested as it is required by the protocol.
1.32 djm 1563: Refer to
1564: .Cm AcceptEnv
1565: in
1566: .Xr sshd_config 5
1567: for how to configure the server.
1.80 jmc 1568: Variables are specified by name, which may contain wildcard characters.
1.33 djm 1569: Multiple environment variables may be separated by whitespace or spread
1.32 djm 1570: across multiple
1571: .Cm SendEnv
1572: directives.
1.81 jmc 1573: .Pp
1574: See
1575: .Sx PATTERNS
1576: for more information on patterns.
1.271 djm 1577: .Pp
1.272 jmc 1578: It is possible to clear previously set
1.271 djm 1579: .Cm SendEnv
1580: variable names by prefixing patterns with
1581: .Pa - .
1582: The default is not to send any environment variables.
1.28 markus 1583: .It Cm ServerAliveCountMax
1.73 jmc 1584: Sets the number of server alive messages (see below) which may be
1.28 markus 1585: sent without
1.84 jmc 1586: .Xr ssh 1
1.28 markus 1587: receiving any messages back from the server.
1588: If this threshold is reached while server alive messages are being sent,
1.84 jmc 1589: ssh will disconnect from the server, terminating the session.
1.28 markus 1590: It is important to note that the use of server alive messages is very
1591: different from
1592: .Cm TCPKeepAlive
1593: (below).
1594: The server alive messages are sent through the encrypted channel
1595: and therefore will not be spoofable.
1596: The TCP keepalive option enabled by
1597: .Cm TCPKeepAlive
1598: is spoofable.
1599: The server alive mechanism is valuable when the client or
1.298 dtucker 1600: server depend on knowing when a connection has become unresponsive.
1.28 markus 1601: .Pp
1602: The default value is 3.
1603: If, for example,
1604: .Cm ServerAliveInterval
1.84 jmc 1605: (see below) is set to 15 and
1.28 markus 1606: .Cm ServerAliveCountMax
1.84 jmc 1607: is left at the default, if the server becomes unresponsive,
1608: ssh will disconnect after approximately 45 seconds.
1.67 jmc 1609: .It Cm ServerAliveInterval
1610: Sets a timeout interval in seconds after which if no data has been received
1611: from the server,
1.84 jmc 1612: .Xr ssh 1
1.67 jmc 1613: will send a message through the encrypted
1614: channel to request a response from the server.
1615: The default
1616: is 0, indicating that these messages will not be sent to the server.
1.277 jmc 1617: .It Cm SetEnv
1618: Directly specify one or more environment variables and their contents to
1619: be sent to the server.
1620: Similarly to
1621: .Cm SendEnv ,
1622: the server must be prepared to accept the environment variable.
1.191 millert 1623: .It Cm StreamLocalBindMask
1624: Sets the octal file creation mode mask
1625: .Pq umask
1626: used when creating a Unix-domain socket file for local or remote
1627: port forwarding.
1628: This option is only used for port forwarding to a Unix-domain socket file.
1629: .Pp
1630: The default value is 0177, which creates a Unix-domain socket file that is
1631: readable and writable only by the owner.
1632: Note that not all operating systems honor the file mode on Unix-domain
1633: socket files.
1634: .It Cm StreamLocalBindUnlink
1635: Specifies whether to remove an existing Unix-domain socket file for local
1636: or remote port forwarding before creating a new one.
1637: If the socket file already exists and
1638: .Cm StreamLocalBindUnlink
1639: is not enabled,
1640: .Nm ssh
1641: will be unable to forward the port to the Unix-domain socket file.
1642: This option is only used for port forwarding to a Unix-domain socket file.
1643: .Pp
1644: The argument must be
1.240 jmc 1645: .Cm yes
1.191 millert 1646: or
1.240 jmc 1647: .Cm no
1648: (the default).
1.1 stevesk 1649: .It Cm StrictHostKeyChecking
1650: If this flag is set to
1.240 jmc 1651: .Cm yes ,
1.84 jmc 1652: .Xr ssh 1
1.1 stevesk 1653: will never automatically add host keys to the
1.50 djm 1654: .Pa ~/.ssh/known_hosts
1.1 stevesk 1655: file, and refuses to connect to hosts whose host key has changed.
1.263 dtucker 1656: This provides maximum protection against man-in-the-middle (MITM) attacks,
1.84 jmc 1657: though it can be annoying when the
1.1 stevesk 1658: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 1659: file is poorly maintained or when connections to new hosts are
1.1 stevesk 1660: frequently made.
1661: This option forces the user to manually
1662: add all new hosts.
1.255 jmc 1663: .Pp
1.1 stevesk 1664: If this flag is set to
1.254 djm 1665: .Dq accept-new
1.255 jmc 1666: then ssh will automatically add new host keys to the user
1.254 djm 1667: known hosts files, but will not permit connections to hosts with
1668: changed host keys.
1669: If this flag is set to
1670: .Dq no
1671: or
1672: .Dq off ,
1.255 jmc 1673: ssh will automatically add new host keys to the user known hosts files
1674: and allow connections to hosts with changed hostkeys to proceed,
1675: subject to some restrictions.
1.1 stevesk 1676: If this flag is set to
1.240 jmc 1677: .Cm ask
1678: (the default),
1.1 stevesk 1679: new host keys
1680: will be added to the user known host files only after the user
1681: has confirmed that is what they really want to do, and
1.84 jmc 1682: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 1683: The host keys of
1684: known hosts will be verified automatically in all cases.
1.244 jmc 1685: .It Cm SyslogFacility
1686: Gives the facility code that is used when logging messages from
1687: .Xr ssh 1 .
1688: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1689: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
1690: The default is USER.
1.26 markus 1691: .It Cm TCPKeepAlive
1692: Specifies whether the system should send TCP keepalive messages to the
1693: other side.
1694: If they are sent, death of the connection or crash of one
1695: of the machines will be properly noticed.
1696: However, this means that
1697: connections will die if the route is down temporarily, and some people
1698: find it annoying.
1699: .Pp
1700: The default is
1.240 jmc 1701: .Cm yes
1.26 markus 1702: (to send TCP keepalive messages), and the client will notice
1703: if the network goes down or the remote host dies.
1704: This is important in scripts, and many users want it too.
1705: .Pp
1706: To disable TCP keepalive messages, the value should be set to
1.240 jmc 1707: .Cm no .
1.265 djm 1708: See also
1709: .Cm ServerAliveInterval
1710: for protocol-level keepalives.
1.65 reyk 1711: .It Cm Tunnel
1.95 stevesk 1712: Request
1.65 reyk 1713: .Xr tun 4
1.69 jmc 1714: device forwarding between the client and the server.
1.65 reyk 1715: The argument must be
1.240 jmc 1716: .Cm yes ,
1717: .Cm point-to-point
1.95 stevesk 1718: (layer 3),
1.240 jmc 1719: .Cm ethernet
1.95 stevesk 1720: (layer 2),
1.65 reyk 1721: or
1.240 jmc 1722: .Cm no
1723: (the default).
1.95 stevesk 1724: Specifying
1.240 jmc 1725: .Cm yes
1.95 stevesk 1726: requests the default tunnel mode, which is
1.240 jmc 1727: .Cm point-to-point .
1.65 reyk 1728: .It Cm TunnelDevice
1.95 stevesk 1729: Specifies the
1.65 reyk 1730: .Xr tun 4
1.95 stevesk 1731: devices to open on the client
1732: .Pq Ar local_tun
1733: and the server
1734: .Pq Ar remote_tun .
1735: .Pp
1736: The argument must be
1737: .Sm off
1738: .Ar local_tun Op : Ar remote_tun .
1739: .Sm on
1740: The devices may be specified by numerical ID or the keyword
1.240 jmc 1741: .Cm any ,
1.95 stevesk 1742: which uses the next available tunnel device.
1743: If
1744: .Ar remote_tun
1745: is not specified, it defaults to
1.240 jmc 1746: .Cm any .
1.95 stevesk 1747: The default is
1.240 jmc 1748: .Cm any:any .
1.201 djm 1749: .It Cm UpdateHostKeys
1.200 djm 1750: Specifies whether
1751: .Xr ssh 1
1752: should accept notifications of additional hostkeys from the server sent
1753: after authentication has completed and add them to
1754: .Cm UserKnownHostsFile .
1755: The argument must be
1.240 jmc 1756: .Cm yes ,
1757: .Cm no
1.320 djm 1758: or
1.240 jmc 1759: .Cm ask .
1.320 djm 1760: This option allows learning alternate hostkeys for a server
1.201 djm 1761: and supports graceful key rotation by allowing a server to send replacement
1762: public keys before old ones are removed.
1.336 djm 1763: .Pp
1.200 djm 1764: Additional hostkeys are only accepted if the key used to authenticate the
1.336 djm 1765: host was already trusted or explicitly accepted by the user, the host was
1766: authenticated via
1767: .Cm UserKnownHostsFile
1768: (i.e. not
1769: .Cm GlobalKnownHostsFile )
1770: and the host was authenticated using a plain key and not a certificate.
1.320 djm 1771: .Pp
1772: .Cm UpdateHostKeys
1.321 jmc 1773: is enabled by default if the user has not overridden the default
1.320 djm 1774: .Cm UserKnownHostsFile
1.335 djm 1775: setting and has not enabled
1776: .Cm VerifyHostKeyDNS ,
1777: otherwise
1.320 djm 1778: .Cm UpdateHostKeys
1779: will be set to
1.334 djm 1780: .Cm no .
1.320 djm 1781: .Pp
1.204 djm 1782: If
1783: .Cm UpdateHostKeys
1784: is set to
1.240 jmc 1785: .Cm ask ,
1.204 djm 1786: then the user is asked to confirm the modifications to the known_hosts file.
1.205 djm 1787: Confirmation is currently incompatible with
1788: .Cm ControlPersist ,
1789: and will be disabled if it is enabled.
1.200 djm 1790: .Pp
1791: Presently, only
1792: .Xr sshd 8
1793: from OpenSSH 6.8 and greater support the
1.240 jmc 1794: .Qq hostkeys@openssh.com
1.200 djm 1795: protocol extension used to inform the client of all the server's hostkeys.
1.1 stevesk 1796: .It Cm User
1797: Specifies the user to log in as.
1798: This can be useful when a different user name is used on different machines.
1799: This saves the trouble of
1800: having to remember to give the user name on the command line.
1801: .It Cm UserKnownHostsFile
1.151 djm 1802: Specifies one or more files to use for the user
1803: host key database, separated by whitespace.
1.329 dtucker 1804: Each filename may use tilde notation to refer to the user's home directory,
1805: the tokens described in the
1806: .Sx TOKENS
1807: section and environment variables as described in the
1808: .Sx ENVIRONMENT VARIABLES
1809: section.
1.151 djm 1810: The default is
1811: .Pa ~/.ssh/known_hosts ,
1812: .Pa ~/.ssh/known_hosts2 .
1.8 jakob 1813: .It Cm VerifyHostKeyDNS
1814: Specifies whether to verify the remote key using DNS and SSHFP resource
1815: records.
1.24 jakob 1816: If this option is set to
1.240 jmc 1817: .Cm yes ,
1.25 jmc 1818: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1819: from DNS.
1820: Insecure fingerprints will be handled as if this option was set to
1.240 jmc 1821: .Cm ask .
1.24 jakob 1822: If this option is set to
1.240 jmc 1823: .Cm ask ,
1.24 jakob 1824: information on fingerprint match will be displayed, but the user will still
1825: need to confirm new host keys according to the
1826: .Cm StrictHostKeyChecking
1827: option.
1.8 jakob 1828: The default is
1.240 jmc 1829: .Cm no .
1.84 jmc 1830: .Pp
1.240 jmc 1831: See also
1832: .Sx VERIFYING HOST KEYS
1833: in
1.84 jmc 1834: .Xr ssh 1 .
1.111 grunk 1835: .It Cm VisualHostKey
1836: If this flag is set to
1.240 jmc 1837: .Cm yes ,
1.111 grunk 1838: an ASCII art representation of the remote host key fingerprint is
1.197 djm 1839: printed in addition to the fingerprint string at login and
1.114 stevesk 1840: for unknown host keys.
1.111 grunk 1841: If this flag is set to
1.240 jmc 1842: .Cm no
1843: (the default),
1.114 stevesk 1844: no fingerprint strings are printed at login and
1.197 djm 1845: only the fingerprint string will be printed for unknown host keys.
1.1 stevesk 1846: .It Cm XAuthLocation
1.5 stevesk 1847: Specifies the full pathname of the
1.1 stevesk 1848: .Xr xauth 1
1849: program.
1850: The default is
1851: .Pa /usr/X11R6/bin/xauth .
1852: .El
1.86 jmc 1853: .Sh PATTERNS
1854: A
1855: .Em pattern
1856: consists of zero or more non-whitespace characters,
1857: .Sq *
1858: (a wildcard that matches zero or more characters),
1859: or
1860: .Sq ?\&
1861: (a wildcard that matches exactly one character).
1862: For example, to specify a set of declarations for any host in the
1.240 jmc 1863: .Qq .co.uk
1.86 jmc 1864: set of domains,
1865: the following pattern could be used:
1866: .Pp
1867: .Dl Host *.co.uk
1868: .Pp
1869: The following pattern
1870: would match any host in the 192.168.0.[0-9] network range:
1871: .Pp
1872: .Dl Host 192.168.0.?
1873: .Pp
1874: A
1875: .Em pattern-list
1876: is a comma-separated list of patterns.
1877: Patterns within pattern-lists may be negated
1878: by preceding them with an exclamation mark
1879: .Pq Sq !\& .
1880: For example,
1.174 djm 1881: to allow a key to be used from anywhere within an organization
1.86 jmc 1882: except from the
1.240 jmc 1883: .Qq dialup
1.86 jmc 1884: pool,
1885: the following entry (in authorized_keys) could be used:
1886: .Pp
1887: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.258 djm 1888: .Pp
1889: Note that a negated match will never produce a positive result by itself.
1890: For example, attempting to match
1891: .Qq host3
1892: against the following pattern-list will fail:
1893: .Pp
1894: .Dl from=\&"!host1,!host2\&"
1895: .Pp
1896: The solution here is to include a term that will yield a positive match,
1897: such as a wildcard:
1898: .Pp
1899: .Dl from=\&"!host1,!host2,*\&"
1.239 jmc 1900: .Sh TOKENS
1901: Arguments to some keywords can make use of tokens,
1902: which are expanded at runtime:
1903: .Pp
1904: .Bl -tag -width XXXX -offset indent -compact
1905: .It %%
1906: A literal
1907: .Sq % .
1908: .It \&%C
1.257 jmc 1909: Hash of %l%h%p%r.
1.239 jmc 1910: .It %d
1911: Local user's home directory.
1.339 djm 1912: .It %f
1913: The fingerprint of the server's host key.
1914: .It %H
1915: The
1916: .Pa known_hosts
1917: hostname or address that is being searched for.
1.239 jmc 1918: .It %h
1919: The remote hostname.
1.340 jmc 1920: .It \%%I
1.339 djm 1921: A string describing the reason for a
1922: .Cm KnownHostsCommand
1.340 jmc 1923: execution: either
1924: .Cm ADDRESS
1.339 djm 1925: when looking up a host by address (only when
1926: .Cm CheckHostIP
1927: is enabled),
1.340 jmc 1928: .Cm HOSTNAME
1929: when searching by hostname, or
1930: .Cm ORDER
1.339 djm 1931: when preparing the host key algorithm preference list to use for the
1932: destination host.
1.239 jmc 1933: .It %i
1934: The local user ID.
1.339 djm 1935: .It %K
1936: The base64 encoded host key.
1.330 dtucker 1937: .It %k
1938: The host key alias if specified, otherwise the orignal remote hostname given
1939: on the command line.
1.239 jmc 1940: .It %L
1941: The local hostname.
1942: .It %l
1943: The local hostname, including the domain name.
1944: .It %n
1945: The original remote hostname, as given on the command line.
1946: .It %p
1947: The remote port.
1948: .It %r
1949: The remote username.
1.261 djm 1950: .It \&%T
1951: The local
1952: .Xr tun 4
1953: or
1954: .Xr tap 4
1955: network interface assigned if
1.262 jmc 1956: tunnel forwarding was requested, or
1957: .Qq NONE
1.261 djm 1958: otherwise.
1.339 djm 1959: .It %t
1960: The type of the server host key, e.g.
1961: .Cm ssh-ed25519
1.239 jmc 1962: .It %u
1963: The local username.
1964: .El
1965: .Pp
1.323 dtucker 1966: .Cm CertificateFile ,
1967: .Cm ControlPath ,
1968: .Cm IdentityAgent ,
1969: .Cm IdentityFile ,
1.339 djm 1970: .Cm KnownHostsCommand ,
1.325 jmc 1971: .Cm LocalForward ,
1.324 dtucker 1972: .Cm Match exec ,
1973: .Cm RemoteCommand ,
1.329 dtucker 1974: .Cm RemoteForward ,
1.323 dtucker 1975: and
1.331 jmc 1976: .Cm UserKnownHostsFile
1.323 dtucker 1977: accept the tokens %%, %C, %d, %h, %i, %L, %l, %n, %p, %r, and %u.
1.239 jmc 1978: .Pp
1.339 djm 1979: .Cm KnownHostsCommand
1980: additionally accepts the tokens %f, %H, %I, %K and %t.
1981: .Pp
1.295 jmc 1982: .Cm Hostname
1.239 jmc 1983: accepts the tokens %% and %h.
1984: .Pp
1985: .Cm LocalCommand
1.323 dtucker 1986: accepts all tokens.
1.239 jmc 1987: .Pp
1988: .Cm ProxyCommand
1.303 djm 1989: accepts the tokens %%, %h, %n, %p, and %r.
1.326 dtucker 1990: .Sh ENVIRONMENT VARIABLES
1991: Arguments to some keywords can be expanded at runtime from environment
1992: variables on the client by enclosing them in
1993: .Ic ${} ,
1994: for example
1995: .Ic ${HOME}/.ssh
1996: would refer to the user's .ssh directory.
1997: If a specified environment variable does not exist then an error will be
1998: returned and the setting for that keyword will be ignored.
1999: .Pp
2000: The keywords
2001: .Cm CertificateFile ,
2002: .Cm ControlPath ,
1.329 dtucker 2003: .Cm IdentityAgent ,
2004: .Cm IdentityFile
1.339 djm 2005: .Cm KnownHostsCommand ,
1.326 dtucker 2006: and
1.329 dtucker 2007: .Cm UserKnownHostsFile
1.326 dtucker 2008: support environment variables.
2009: The keywords
2010: .Cm LocalForward
2011: and
2012: .Cm RemoteForward
2013: support environment variables only for Unix domain socket paths.
1.1 stevesk 2014: .Sh FILES
2015: .Bl -tag -width Ds
1.50 djm 2016: .It Pa ~/.ssh/config
1.1 stevesk 2017: This is the per-user configuration file.
2018: The format of this file is described above.
1.84 jmc 2019: This file is used by the SSH client.
1.30 djm 2020: Because of the potential for abuse, this file must have strict permissions:
1.290 jmc 2021: read/write for the user, and not writable by others.
1.1 stevesk 2022: .It Pa /etc/ssh/ssh_config
2023: Systemwide configuration file.
2024: This file provides defaults for those
2025: values that are not specified in the user's configuration file, and
2026: for those users who do not have a configuration file.
2027: This file must be world-readable.
2028: .El
1.13 jmc 2029: .Sh SEE ALSO
2030: .Xr ssh 1
1.1 stevesk 2031: .Sh AUTHORS
1.240 jmc 2032: .An -nosplit
1.1 stevesk 2033: OpenSSH is a derivative of the original and free
1.240 jmc 2034: ssh 1.2.12 release by
2035: .An Tatu Ylonen .
2036: .An Aaron Campbell , Bob Beck , Markus Friedl ,
2037: .An Niels Provos , Theo de Raadt
2038: and
2039: .An Dug Song
1.1 stevesk 2040: removed many bugs, re-added newer features and
2041: created OpenSSH.
1.240 jmc 2042: .An Markus Friedl
2043: contributed the support for SSH protocol versions 1.5 and 2.0.
![[BACK]](/icons/back.gif){kind=icon}
Return to ssh_config.5 CVS log ![[TXT]](/icons/text.gif){kind=icon}
![[DIR]](/icons/dir.gif){kind=icon}
Up to [local] / src / usr.bin / ssh