Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.394
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.
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1.394 ! djm 36: .\" $OpenBSD: ssh_config.5,v 1.393 2024/01/10 06:33:13 jmc Exp $
! 37: .Dd $Mdocdate: January 10 2024 $
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
1.379 djm 59: Unless noted otherwise, for each parameter, the first obtained value
1.1 stevesk 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 ,
1.381 djm 144: .Cm localnetwork ,
1.169 djm 145: .Cm host ,
146: .Cm originalhost ,
1.394 ! djm 147: .Cm tagged ,
1.169 djm 148: .Cm user ,
149: and
150: .Cm localuser .
1.193 djm 151: The
152: .Cm all
153: criteria must appear alone or immediately after
1.287 djm 154: .Cm canonical
155: or
156: .Cm final .
1.193 djm 157: Other criteria may be combined arbitrarily.
158: All criteria but
1.288 jmc 159: .Cm all ,
160: .Cm canonical ,
1.193 djm 161: and
1.287 djm 162: .Cm final
1.193 djm 163: require an argument.
164: Criteria may be negated by prepending an exclamation mark
165: .Pq Sq !\& .
1.169 djm 166: .Pp
1.177 jmc 167: The
1.193 djm 168: .Cm canonical
1.210 dtucker 169: keyword matches only when the configuration file is being re-parsed
1.193 djm 170: after hostname canonicalization (see the
171: .Cm CanonicalizeHostname
1.288 jmc 172: option).
1.193 djm 173: This may be useful to specify conditions that work with canonical host
174: names only.
1.287 djm 175: .Pp
176: The
177: .Cm final
178: keyword requests that the configuration be re-parsed (regardless of whether
179: .Cm CanonicalizeHostname
180: is enabled), and matches only during this final pass.
181: If
182: .Cm CanonicalizeHostname
183: is enabled, then
184: .Cm canonical
185: and
186: .Cm final
187: match during the same pass.
188: .Pp
1.193 djm 189: The
1.176 djm 190: .Cm exec
1.177 jmc 191: keyword executes the specified command under the user's shell.
1.169 djm 192: If the command returns a zero exit status then the condition is considered true.
193: Commands containing whitespace characters must be quoted.
1.239 jmc 194: Arguments to
195: .Cm exec
196: accept the tokens described in the
197: .Sx TOKENS
198: section.
1.381 djm 199: .Pp
200: The
201: .Cm localnetwork
202: keyword matches the addresses of active local network interfaces against the
203: supplied list of networks in CIDR format.
204: This may be convenient for varying the effective configuration on devices that
205: roam between networks.
206: Note that network address is not a trustworthy criteria in many
207: situations (e.g. when the network is automatically configured using DHCP)
208: and so caution should be applied if using it to control security-sensitive
209: configuration.
1.169 djm 210: .Pp
211: The other keywords' criteria must be single entries or comma-separated
212: lists and may use the wildcard and negation operators described in the
213: .Sx PATTERNS
214: section.
215: The criteria for the
216: .Cm host
217: keyword are matched against the target hostname, after any substitution
218: by the
1.295 jmc 219: .Cm Hostname
1.193 djm 220: or
221: .Cm CanonicalizeHostname
222: options.
1.169 djm 223: The
224: .Cm originalhost
225: keyword matches against the hostname as it was specified on the command-line.
226: The
1.382 djm 227: .Cm tagged
228: keyword matches a tag name specified by a prior
229: .Cm Tag
230: directive or on the
231: .Xr ssh 1
232: command-line using the
233: .Fl P
234: flag.
235: The
1.169 djm 236: .Cm user
237: keyword matches against the target username on the remote host.
238: The
239: .Cm localuser
240: keyword matches against the name of the local user running
241: .Xr ssh 1
242: (this keyword may be useful in system-wide
243: .Nm
244: files).
1.222 jcs 245: .It Cm AddKeysToAgent
246: Specifies whether keys should be automatically added to a running
1.223 jmc 247: .Xr ssh-agent 1 .
1.222 jcs 248: If this option is set to
1.240 jmc 249: .Cm yes
1.222 jcs 250: and a key is loaded from a file, the key and its passphrase are added to
251: the agent with the default lifetime, as if by
252: .Xr ssh-add 1 .
253: If this option is set to
1.240 jmc 254: .Cm ask ,
255: .Xr ssh 1
1.222 jcs 256: will require confirmation using the
257: .Ev SSH_ASKPASS
258: program before adding a key (see
259: .Xr ssh-add 1
260: for details).
261: If this option is set to
1.240 jmc 262: .Cm confirm ,
1.222 jcs 263: each use of the key must be confirmed, as if the
264: .Fl c
265: option was specified to
266: .Xr ssh-add 1 .
267: If this option is set to
1.240 jmc 268: .Cm no ,
1.222 jcs 269: no keys are added to the agent.
1.332 djm 270: Alternately, this option may be specified as a time interval
271: using the format described in the
272: .Sx TIME FORMATS
273: section of
274: .Xr sshd_config 5
275: to specify the key's lifetime in
276: .Xr ssh-agent 1 ,
277: after which it will automatically be removed.
1.222 jcs 278: The argument must be
1.332 djm 279: .Cm no
280: (the default),
1.240 jmc 281: .Cm yes ,
1.332 djm 282: .Cm confirm
283: (optionally followed by a time interval),
284: .Cm ask
285: or a time interval.
1.10 djm 286: .It Cm AddressFamily
1.11 jmc 287: Specifies which address family to use when connecting.
288: Valid arguments are
1.240 jmc 289: .Cm any
290: (the default),
291: .Cm inet
1.84 jmc 292: (use IPv4 only), or
1.240 jmc 293: .Cm inet6
1.40 jmc 294: (use IPv6 only).
1.1 stevesk 295: .It Cm BatchMode
296: If set to
1.240 jmc 297: .Cm yes ,
1.318 djm 298: user interaction such as password prompts and host key confirmation requests
299: will be disabled.
1.1 stevesk 300: This option is useful in scripts and other batch jobs where no user
1.318 djm 301: is present to interact with
302: .Xr ssh 1 .
1.1 stevesk 303: The argument must be
1.240 jmc 304: .Cm yes
1.1 stevesk 305: or
1.240 jmc 306: .Cm no
307: (the default).
1.268 jmc 308: .It Cm BindAddress
309: Use the specified address on the local machine as the source address of
310: the connection.
311: Only useful on systems with more than one address.
312: .It Cm BindInterface
313: Use the address of the specified interface on the local machine as the
314: source address of the connection.
1.171 djm 315: .It Cm CanonicalDomains
1.172 jmc 316: When
1.173 djm 317: .Cm CanonicalizeHostname
1.171 djm 318: is enabled, this option specifies the list of domain suffixes in which to
319: search for the specified destination host.
1.173 djm 320: .It Cm CanonicalizeFallbackLocal
1.174 djm 321: Specifies whether to fail with an error when hostname canonicalization fails.
1.172 jmc 322: The default,
1.240 jmc 323: .Cm yes ,
1.172 jmc 324: will attempt to look up the unqualified hostname using the system resolver's
1.171 djm 325: search rules.
326: A value of
1.240 jmc 327: .Cm no
1.171 djm 328: will cause
329: .Xr ssh 1
330: to fail instantly if
1.173 djm 331: .Cm CanonicalizeHostname
1.171 djm 332: is enabled and the target hostname cannot be found in any of the domains
333: specified by
334: .Cm CanonicalDomains .
1.173 djm 335: .It Cm CanonicalizeHostname
1.174 djm 336: Controls whether explicit hostname canonicalization is performed.
1.172 jmc 337: The default,
1.240 jmc 338: .Cm no ,
1.171 djm 339: is not to perform any name rewriting and let the system resolver handle all
340: hostname lookups.
341: If set to
1.240 jmc 342: .Cm yes
1.171 djm 343: then, for connections that do not use a
1.284 djm 344: .Cm ProxyCommand
345: or
346: .Cm ProxyJump ,
1.171 djm 347: .Xr ssh 1
1.173 djm 348: will attempt to canonicalize the hostname specified on the command line
1.171 djm 349: using the
350: .Cm CanonicalDomains
351: suffixes and
1.173 djm 352: .Cm CanonicalizePermittedCNAMEs
1.171 djm 353: rules.
354: If
1.173 djm 355: .Cm CanonicalizeHostname
1.171 djm 356: is set to
1.240 jmc 357: .Cm always ,
1.174 djm 358: then canonicalization is applied to proxied connections too.
1.185 djm 359: .Pp
1.193 djm 360: If this option is enabled, then the configuration files are processed
361: again using the new target name to pick up any new configuration in matching
1.185 djm 362: .Cm Host
1.193 djm 363: and
364: .Cm Match
1.185 djm 365: stanzas.
1.361 dtucker 366: A value of
367: .Cm none
368: disables the use of a
369: .Cm ProxyJump
370: host.
1.173 djm 371: .It Cm CanonicalizeMaxDots
1.172 jmc 372: Specifies the maximum number of dot characters in a hostname before
1.174 djm 373: canonicalization is disabled.
1.240 jmc 374: The default, 1,
1.172 jmc 375: allows a single dot (i.e. hostname.subdomain).
1.173 djm 376: .It Cm CanonicalizePermittedCNAMEs
1.172 jmc 377: Specifies rules to determine whether CNAMEs should be followed when
1.173 djm 378: canonicalizing hostnames.
1.171 djm 379: The rules consist of one or more arguments of
1.172 jmc 380: .Ar source_domain_list : Ns Ar target_domain_list ,
1.171 djm 381: where
382: .Ar source_domain_list
1.174 djm 383: is a pattern-list of domains that may follow CNAMEs in canonicalization,
1.171 djm 384: and
385: .Ar target_domain_list
1.172 jmc 386: is a pattern-list of domains that they may resolve to.
1.171 djm 387: .Pp
388: For example,
1.240 jmc 389: .Qq *.a.example.com:*.b.example.com,*.c.example.com
1.171 djm 390: will allow hostnames matching
1.240 jmc 391: .Qq *.a.example.com
1.173 djm 392: to be canonicalized to names in the
1.240 jmc 393: .Qq *.b.example.com
1.171 djm 394: or
1.240 jmc 395: .Qq *.c.example.com
1.171 djm 396: domains.
1.365 djm 397: .Pp
398: A single argument of
399: .Qq none
400: causes no CNAMEs to be considered for canonicalization.
401: This is the default behaviour.
1.283 jmc 402: .It Cm CASignatureAlgorithms
403: Specifies which algorithms are allowed for signing of certificates
404: by certificate authorities (CAs).
405: The default is:
406: .Bd -literal -offset indent
1.362 djm 407: ssh-ed25519,ecdsa-sha2-nistp256,
408: ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
409: sk-ssh-ed25519@openssh.com,
410: sk-ecdsa-sha2-nistp256@openssh.com,
1.351 djm 411: rsa-sha2-512,rsa-sha2-256
1.283 jmc 412: .Ed
1.362 djm 413: .Pp
414: If the specified list begins with a
415: .Sq +
416: character, then the specified algorithms will be appended to the default set
417: instead of replacing them.
418: If the specified list begins with a
419: .Sq -
420: character, then the specified algorithms (including wildcards) will be removed
421: from the default set instead of replacing them.
1.283 jmc 422: .Pp
423: .Xr ssh 1
424: will not accept host certificates signed using algorithms other than those
425: specified.
1.221 djm 426: .It Cm CertificateFile
427: Specifies a file from which the user's certificate is read.
428: A corresponding private key must be provided separately in order
429: to use this certificate either
430: from an
431: .Cm IdentityFile
432: directive or
433: .Fl i
434: flag to
435: .Xr ssh 1 ,
436: via
437: .Xr ssh-agent 1 ,
438: or via a
1.305 naddy 439: .Cm PKCS11Provider
440: or
441: .Cm SecurityKeyProvider .
1.221 djm 442: .Pp
1.239 jmc 443: Arguments to
444: .Cm CertificateFile
1.326 dtucker 445: may use the tilde syntax to refer to a user's home directory,
446: the tokens described in the
1.239 jmc 447: .Sx TOKENS
1.326 dtucker 448: section and environment variables as described in the
449: .Sx ENVIRONMENT VARIABLES
1.239 jmc 450: section.
1.221 djm 451: .Pp
452: It is possible to have multiple certificate files specified in
453: configuration files; these certificates will be tried in sequence.
454: Multiple
455: .Cm CertificateFile
456: directives will add to the list of certificates used for
457: authentication.
1.390 djm 458: .It Cm ChannelTimeout
459: Specifies whether and how quickly
460: .Xr ssh 1
461: should close inactive channels.
462: Timeouts are specified as one or more
463: .Dq type=interval
464: pairs separated by whitespace, where the
465: .Dq type
1.392 djm 466: must be the special keyword
467: .Dq global
468: or a channel type name from the list below, optionally containing
469: wildcard characters.
1.390 djm 470: .Pp
471: The timeout value
472: .Dq interval
473: is specified in seconds or may use any of the units documented in the
474: .Sx TIME FORMATS
475: section.
476: For example,
477: .Dq session=5m
1.392 djm 478: would cause interactive sessions to terminate after five minutes of
1.390 djm 479: inactivity.
480: Specifying a zero value disables the inactivity timeout.
481: .Pp
1.392 djm 482: The special timeout
483: .Dq global
1.393 jmc 484: applies to all active channels, taken together.
1.392 djm 485: Traffic on any active channel will reset the timeout, but when the timeout
486: expires then all open channels will be closed.
487: Note that this global timeout is not matched by wildcards and must be
488: specified explicitly.
489: .Pp
490: The available channel type names include:
1.390 djm 491: .Bl -tag -width Ds
492: .It Cm agent-connection
493: Open connections to
494: .Xr ssh-agent 1 .
495: .It Cm direct-tcpip , Cm direct-streamlocal@openssh.com
496: Open TCP or Unix socket (respectively) connections that have
497: been established from a
498: .Xr ssh 1
499: local forwarding, i.e.\&
500: .Cm LocalForward
501: or
502: .Cm DynamicForward .
503: .It Cm forwarded-tcpip , Cm forwarded-streamlocal@openssh.com
504: Open TCP or Unix socket (respectively) connections that have been
505: established to a
506: .Xr sshd 8
507: listening on behalf of a
508: .Xr ssh 1
509: remote forwarding, i.e.\&
510: .Cm RemoteForward .
511: .It Cm session
512: The interactive main session, including shell session, command execution,
513: .Xr scp 1 ,
514: .Xr sftp 1 ,
515: etc.
516: .It Cm tun-connection
517: Open
518: .Cm TunnelForward
519: connections.
520: .It Cm x11-connection
521: Open X11 forwarding sessions.
522: .El
523: .Pp
524: Note that in all the above cases, terminating an inactive session does not
525: guarantee to remove all resources associated with the session, e.g. shell
526: processes or X11 clients relating to the session may continue to execute.
527: .Pp
528: Moreover, terminating an inactive channel or session does not necessarily
529: close the SSH connection, nor does it prevent a client from
530: requesting another channel of the same type.
531: In particular, expiring an inactive forwarding session does not prevent
532: another identical forwarding from being subsequently created.
533: .Pp
534: The default is not to expire channels of any type for inactivity.
1.1 stevesk 535: .It Cm CheckHostIP
1.240 jmc 536: If set to
1.370 naddy 537: .Cm yes ,
1.84 jmc 538: .Xr ssh 1
539: will additionally check the host IP address in the
1.1 stevesk 540: .Pa known_hosts
541: file.
1.240 jmc 542: This allows it to detect if a host key changed due to DNS spoofing
1.211 djm 543: and will add addresses of destination hosts to
544: .Pa ~/.ssh/known_hosts
545: in the process, regardless of the setting of
546: .Cm StrictHostKeyChecking .
1.107 grunk 547: If the option is set to
1.341 djm 548: .Cm no
549: (the default),
1.1 stevesk 550: the check will not be executed.
551: .It Cm Ciphers
1.245 djm 552: Specifies the ciphers allowed and their order of preference.
1.1 stevesk 553: Multiple ciphers must be comma-separated.
1.299 kn 554: If the specified list begins with a
1.214 djm 555: .Sq +
556: character, then the specified ciphers will be appended to the default set
557: instead of replacing them.
1.299 kn 558: If the specified list begins with a
1.241 djm 559: .Sq -
560: character, then the specified ciphers (including wildcards) will be removed
561: from the default set instead of replacing them.
1.301 naddy 562: If the specified list begins with a
563: .Sq ^
564: character, then the specified ciphers will be placed at the head of the
565: default set.
1.214 djm 566: .Pp
1.180 djm 567: The supported ciphers are:
1.240 jmc 568: .Bd -literal -offset indent
1.186 naddy 569: 3des-cbc
570: aes128-cbc
571: aes192-cbc
572: aes256-cbc
573: aes128-ctr
574: aes192-ctr
575: aes256-ctr
576: aes128-gcm@openssh.com
577: aes256-gcm@openssh.com
578: chacha20-poly1305@openssh.com
1.240 jmc 579: .Ed
1.180 djm 580: .Pp
1.84 jmc 581: The default is:
1.186 naddy 582: .Bd -literal -offset indent
1.215 jmc 583: chacha20-poly1305@openssh.com,
1.186 naddy 584: aes128-ctr,aes192-ctr,aes256-ctr,
1.270 djm 585: aes128-gcm@openssh.com,aes256-gcm@openssh.com
1.1 stevesk 586: .Ed
1.180 djm 587: .Pp
1.240 jmc 588: The list of available ciphers may also be obtained using
589: .Qq ssh -Q cipher .
1.1 stevesk 590: .It Cm ClearAllForwardings
1.84 jmc 591: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 592: specified in the configuration files or on the command line be
1.7 jmc 593: cleared.
594: This option is primarily useful when used from the
1.84 jmc 595: .Xr ssh 1
1.1 stevesk 596: command line to clear port forwardings set in
597: configuration files, and is automatically set by
598: .Xr scp 1
599: and
600: .Xr sftp 1 .
601: The argument must be
1.240 jmc 602: .Cm yes
1.1 stevesk 603: or
1.240 jmc 604: .Cm no
605: (the default).
1.1 stevesk 606: .It Cm Compression
607: Specifies whether to use compression.
608: The argument must be
1.240 jmc 609: .Cm yes
1.1 stevesk 610: or
1.240 jmc 611: .Cm no
612: (the default).
1.247 naddy 613: .It Cm ConnectionAttempts
614: Specifies the number of tries (one per second) to make before exiting.
615: The argument must be an integer.
616: This may be useful in scripts if the connection sometimes fails.
617: The default is 1.
1.9 djm 618: .It Cm ConnectTimeout
1.84 jmc 619: Specifies the timeout (in seconds) used when connecting to the
620: SSH server, instead of using the default system TCP timeout.
1.302 djm 621: This timeout is applied both to establishing the connection and to performing
622: the initial SSH protocol handshake and key exchange.
1.36 djm 623: .It Cm ControlMaster
624: Enables the sharing of multiple sessions over a single network connection.
625: When set to
1.240 jmc 626: .Cm yes ,
1.84 jmc 627: .Xr ssh 1
1.36 djm 628: will listen for connections on a control socket specified using the
629: .Cm ControlPath
630: argument.
631: Additional sessions can connect to this socket using the same
632: .Cm ControlPath
633: with
634: .Cm ControlMaster
635: set to
1.240 jmc 636: .Cm no
1.38 jmc 637: (the default).
1.64 jmc 638: These sessions will try to reuse the master instance's network connection
1.63 djm 639: rather than initiating new ones, but will fall back to connecting normally
640: if the control socket does not exist, or is not listening.
641: .Pp
1.37 djm 642: Setting this to
1.240 jmc 643: .Cm ask
644: will cause
645: .Xr ssh 1
1.206 jmc 646: to listen for control connections, but require confirmation using
647: .Xr ssh-askpass 1 .
1.51 jakob 648: If the
649: .Cm ControlPath
1.84 jmc 650: cannot be opened,
1.240 jmc 651: .Xr ssh 1
652: will continue without connecting to a master instance.
1.58 djm 653: .Pp
654: X11 and
1.59 jmc 655: .Xr ssh-agent 1
1.58 djm 656: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 657: display and agent forwarded will be the one belonging to the master
1.59 jmc 658: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 659: .Pp
660: Two additional options allow for opportunistic multiplexing: try to use a
661: master connection but fall back to creating a new one if one does not already
662: exist.
663: These options are:
1.240 jmc 664: .Cm auto
1.56 djm 665: and
1.240 jmc 666: .Cm autoask .
1.56 djm 667: The latter requires confirmation like the
1.240 jmc 668: .Cm ask
1.56 djm 669: option.
1.36 djm 670: .It Cm ControlPath
1.55 djm 671: Specify the path to the control socket used for connection sharing as described
672: in the
1.36 djm 673: .Cm ControlMaster
1.57 djm 674: section above or the string
1.240 jmc 675: .Cm none
1.57 djm 676: to disable connection sharing.
1.239 jmc 677: Arguments to
678: .Cm ControlPath
1.326 dtucker 679: may use the tilde syntax to refer to a user's home directory,
680: the tokens described in the
1.239 jmc 681: .Sx TOKENS
1.326 dtucker 682: section and environment variables as described in the
683: .Sx ENVIRONMENT VARIABLES
1.239 jmc 684: section.
1.56 djm 685: It is recommended that any
686: .Cm ControlPath
687: used for opportunistic connection sharing include
1.195 djm 688: at least %h, %p, and %r (or alternatively %C) and be placed in a directory
689: that is not writable by other users.
1.56 djm 690: This ensures that shared connections are uniquely identified.
1.137 djm 691: .It Cm ControlPersist
692: When used in conjunction with
693: .Cm ControlMaster ,
694: specifies that the master connection should remain open
695: in the background (waiting for future client connections)
696: after the initial client connection has been closed.
697: If set to
1.314 naddy 698: .Cm no
699: (the default),
1.137 djm 700: then the master connection will not be placed into the background,
701: and will close as soon as the initial client connection is closed.
702: If set to
1.240 jmc 703: .Cm yes
704: or 0,
1.137 djm 705: then the master connection will remain in the background indefinitely
706: (until killed or closed via a mechanism such as the
1.240 jmc 707: .Qq ssh -O exit ) .
1.137 djm 708: If set to a time in seconds, or a time in any of the formats documented in
709: .Xr sshd_config 5 ,
710: then the backgrounded master connection will automatically terminate
711: after it has remained idle (with no client connections) for the
712: specified time.
1.38 jmc 713: .It Cm DynamicForward
1.74 jmc 714: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 715: over the secure channel, and the application
716: protocol is then used to determine where to connect to from the
717: remote machine.
1.62 djm 718: .Pp
719: The argument must be
720: .Sm off
721: .Oo Ar bind_address : Oc Ar port .
722: .Sm on
1.138 djm 723: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.62 djm 724: By default, the local port is bound in accordance with the
725: .Cm GatewayPorts
726: setting.
727: However, an explicit
728: .Ar bind_address
729: may be used to bind the connection to a specific address.
730: The
731: .Ar bind_address
732: of
1.240 jmc 733: .Cm localhost
1.62 djm 734: indicates that the listening port be bound for local use only, while an
735: empty address or
736: .Sq *
737: indicates that the port should be available from all interfaces.
738: .Pp
1.38 jmc 739: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 740: .Xr ssh 1
1.38 jmc 741: will act as a SOCKS server.
742: Multiple forwardings may be specified, and
743: additional forwardings can be given on the command line.
744: Only the superuser can forward privileged ports.
1.376 djm 745: .It Cm EnableEscapeCommandline
746: Enables the command line option in the
747: .Cm EscapeChar
748: menu for interactive sessions (default
749: .Ql ~C ) .
750: By default, the command line is disabled.
1.14 markus 751: .It Cm EnableSSHKeysign
752: Setting this option to
1.240 jmc 753: .Cm yes
1.14 markus 754: in the global client configuration file
755: .Pa /etc/ssh/ssh_config
756: enables the use of the helper program
757: .Xr ssh-keysign 8
758: during
759: .Cm HostbasedAuthentication .
760: The argument must be
1.240 jmc 761: .Cm yes
1.14 markus 762: or
1.240 jmc 763: .Cm no
764: (the default).
1.23 jmc 765: This option should be placed in the non-hostspecific section.
1.14 markus 766: See
767: .Xr ssh-keysign 8
768: for more information.
1.1 stevesk 769: .It Cm EscapeChar
770: Sets the escape character (default:
771: .Ql ~ ) .
772: The escape character can also
773: be set on the command line.
774: The argument should be a single character,
775: .Ql ^
776: followed by a letter, or
1.240 jmc 777: .Cm none
1.1 stevesk 778: to disable the escape
779: character entirely (making the connection transparent for binary
780: data).
1.96 markus 781: .It Cm ExitOnForwardFailure
782: Specifies whether
783: .Xr ssh 1
784: should terminate the connection if it cannot set up all requested
1.216 djm 785: dynamic, tunnel, local, and remote port forwardings, (e.g.\&
1.217 jmc 786: if either end is unable to bind and listen on a specified port).
1.216 djm 787: Note that
788: .Cm ExitOnForwardFailure
789: does not apply to connections made over port forwardings and will not,
790: for example, cause
791: .Xr ssh 1
792: to exit if TCP connections to the ultimate forwarding destination fail.
1.96 markus 793: The argument must be
1.240 jmc 794: .Cm yes
1.96 markus 795: or
1.240 jmc 796: .Cm no
797: (the default).
1.197 djm 798: .It Cm FingerprintHash
799: Specifies the hash algorithm used when displaying key fingerprints.
800: Valid options are:
1.240 jmc 801: .Cm md5
1.197 djm 802: and
1.240 jmc 803: .Cm sha256
1.359 djm 804: (the default).
805: .It Cm ForkAfterAuthentication
806: Requests
807: .Nm ssh
808: to go to background just before command execution.
809: This is useful if
810: .Nm ssh
811: is going to ask for passwords or passphrases, but the user
812: wants it in the background.
813: This implies the
814: .Cm StdinNull
815: configuration option being set to
816: .Dq yes .
817: The recommended way to start X11 programs at a remote site is with
818: something like
819: .Ic ssh -f host xterm ,
820: which is the same as
821: .Ic ssh host xterm
822: if the
823: .Cm ForkAfterAuthentication
824: configuration option is set to
825: .Dq yes .
826: .Pp
827: If the
828: .Cm ExitOnForwardFailure
829: configuration option is set to
830: .Dq yes ,
831: then a client started with the
832: .Cm ForkAfterAuthentication
833: configuration option being set to
834: .Dq yes
835: will wait for all remote port forwards to be successfully established
836: before placing itself in the background.
837: The argument to this keyword must be
838: .Cm yes
839: (same as the
840: .Fl f
841: option) or
842: .Cm no
1.240 jmc 843: (the default).
1.1 stevesk 844: .It Cm ForwardAgent
845: Specifies whether the connection to the authentication agent (if any)
846: will be forwarded to the remote machine.
1.312 djm 847: The argument may be
848: .Cm yes ,
1.240 jmc 849: .Cm no
1.312 djm 850: (the default),
851: an explicit path to an agent socket or the name of an environment variable
852: (beginning with
853: .Sq $ )
854: in which to find the path.
1.3 stevesk 855: .Pp
1.7 jmc 856: Agent forwarding should be enabled with caution.
857: Users with the ability to bypass file permissions on the remote host
858: (for the agent's Unix-domain socket)
859: can access the local agent through the forwarded connection.
860: An attacker cannot obtain key material from the agent,
1.3 stevesk 861: however they can perform operations on the keys that enable them to
862: authenticate using the identities loaded into the agent.
1.1 stevesk 863: .It Cm ForwardX11
864: Specifies whether X11 connections will be automatically redirected
865: over the secure channel and
866: .Ev DISPLAY
867: set.
868: The argument must be
1.240 jmc 869: .Cm yes
1.1 stevesk 870: or
1.240 jmc 871: .Cm no
872: (the default).
1.3 stevesk 873: .Pp
1.7 jmc 874: X11 forwarding should be enabled with caution.
875: Users with the ability to bypass file permissions on the remote host
1.22 markus 876: (for the user's X11 authorization database)
1.7 jmc 877: can access the local X11 display through the forwarded connection.
1.22 markus 878: An attacker may then be able to perform activities such as keystroke monitoring
879: if the
880: .Cm ForwardX11Trusted
881: option is also enabled.
1.134 djm 882: .It Cm ForwardX11Timeout
1.135 jmc 883: Specify a timeout for untrusted X11 forwarding
884: using the format described in the
1.240 jmc 885: .Sx TIME FORMATS
886: section of
1.134 djm 887: .Xr sshd_config 5 .
888: X11 connections received by
889: .Xr ssh 1
890: after this time will be refused.
1.285 djm 891: Setting
892: .Cm ForwardX11Timeout
893: to zero will disable the timeout and permit X11 forwarding for the life
894: of the connection.
1.134 djm 895: The default is to disable untrusted X11 forwarding after twenty minutes has
896: elapsed.
1.22 markus 897: .It Cm ForwardX11Trusted
1.34 jmc 898: If this option is set to
1.240 jmc 899: .Cm yes ,
1.84 jmc 900: remote X11 clients will have full access to the original X11 display.
1.42 djm 901: .Pp
1.22 markus 902: If this option is set to
1.240 jmc 903: .Cm no
904: (the default),
1.84 jmc 905: remote X11 clients will be considered untrusted and prevented
1.22 markus 906: from stealing or tampering with data belonging to trusted X11
907: clients.
1.42 djm 908: Furthermore, the
909: .Xr xauth 1
910: token used for the session will be set to expire after 20 minutes.
911: Remote clients will be refused access after this time.
1.22 markus 912: .Pp
913: See the X11 SECURITY extension specification for full details on
914: the restrictions imposed on untrusted clients.
1.1 stevesk 915: .It Cm GatewayPorts
916: Specifies whether remote hosts are allowed to connect to local
917: forwarded ports.
918: By default,
1.84 jmc 919: .Xr ssh 1
1.7 jmc 920: binds local port forwardings to the loopback address.
921: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 922: .Cm GatewayPorts
1.84 jmc 923: can be used to specify that ssh
1.1 stevesk 924: should bind local port forwardings to the wildcard address,
925: thus allowing remote hosts to connect to forwarded ports.
926: The argument must be
1.240 jmc 927: .Cm yes
1.1 stevesk 928: or
1.240 jmc 929: .Cm no
930: (the default).
1.1 stevesk 931: .It Cm GlobalKnownHostsFile
1.151 djm 932: Specifies one or more files to use for the global
933: host key database, separated by whitespace.
934: The default is
935: .Pa /etc/ssh/ssh_known_hosts ,
936: .Pa /etc/ssh/ssh_known_hosts2 .
1.18 markus 937: .It Cm GSSAPIAuthentication
1.27 markus 938: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 939: The default is
1.240 jmc 940: .Cm no .
1.18 markus 941: .It Cm GSSAPIDelegateCredentials
942: Forward (delegate) credentials to the server.
943: The default is
1.240 jmc 944: .Cm no .
1.44 djm 945: .It Cm HashKnownHosts
946: Indicates that
1.84 jmc 947: .Xr ssh 1
1.44 djm 948: should hash host names and addresses when they are added to
1.50 djm 949: .Pa ~/.ssh/known_hosts .
1.44 djm 950: These hashed names may be used normally by
1.84 jmc 951: .Xr ssh 1
1.44 djm 952: and
1.84 jmc 953: .Xr sshd 8 ,
1.316 djm 954: but they do not visually reveal identifying information if the
955: file's contents are disclosed.
1.44 djm 956: The default is
1.240 jmc 957: .Cm no .
1.97 jmc 958: Note that existing names and addresses in known hosts files
959: will not be converted automatically,
960: but may be manually hashed using
1.45 djm 961: .Xr ssh-keygen 1 .
1.344 dtucker 962: .It Cm HostbasedAcceptedAlgorithms
1.348 djm 963: Specifies the signature algorithms that will be used for hostbased
964: authentication as a comma-separated list of patterns.
1.300 naddy 965: Alternately if the specified list begins with a
1.214 djm 966: .Sq +
1.348 djm 967: character, then the specified signature algorithms will be appended
968: to the default set instead of replacing them.
1.300 naddy 969: If the specified list begins with a
1.241 djm 970: .Sq -
1.348 djm 971: character, then the specified signature algorithms (including wildcards)
972: will be removed from the default set instead of replacing them.
1.301 naddy 973: If the specified list begins with a
974: .Sq ^
1.348 djm 975: character, then the specified signature algorithms will be placed
976: at the head of the default set.
1.213 markus 977: The default for this option is:
978: .Bd -literal -offset 3n
1.333 djm 979: ssh-ed25519-cert-v01@openssh.com,
1.213 markus 980: ecdsa-sha2-nistp256-cert-v01@openssh.com,
981: ecdsa-sha2-nistp384-cert-v01@openssh.com,
982: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.333 djm 983: sk-ssh-ed25519-cert-v01@openssh.com,
1.311 naddy 984: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.305 naddy 985: rsa-sha2-512-cert-v01@openssh.com,
986: rsa-sha2-256-cert-v01@openssh.com,
1.333 djm 987: ssh-ed25519,
1.213 markus 988: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.333 djm 989: sk-ssh-ed25519@openssh.com,
1.311 naddy 990: sk-ecdsa-sha2-nistp256@openssh.com,
1.366 kn 991: rsa-sha2-512,rsa-sha2-256
1.213 markus 992: .Ed
993: .Pp
1.202 djm 994: The
995: .Fl Q
996: option of
997: .Xr ssh 1
1.348 djm 998: may be used to list supported signature algorithms.
1.344 dtucker 999: This was formerly named HostbasedKeyTypes.
1.345 naddy 1000: .It Cm HostbasedAuthentication
1001: Specifies whether to try rhosts based authentication with public key
1002: authentication.
1003: The argument must be
1004: .Cm yes
1005: or
1006: .Cm no
1007: (the default).
1.1 stevesk 1008: .It Cm HostKeyAlgorithms
1.348 djm 1009: Specifies the host key signature algorithms
1.1 stevesk 1010: that the client wants to use in order of preference.
1.300 naddy 1011: Alternately if the specified list begins with a
1.214 djm 1012: .Sq +
1.348 djm 1013: character, then the specified signature algorithms will be appended to
1014: the default set instead of replacing them.
1.300 naddy 1015: If the specified list begins with a
1.241 djm 1016: .Sq -
1.348 djm 1017: character, then the specified signature algorithms (including wildcards)
1018: will be removed from the default set instead of replacing them.
1.301 naddy 1019: If the specified list begins with a
1020: .Sq ^
1.348 djm 1021: character, then the specified signature algorithms will be placed
1022: at the head of the default set.
1.1 stevesk 1023: The default for this option is:
1.139 djm 1024: .Bd -literal -offset 3n
1.333 djm 1025: ssh-ed25519-cert-v01@openssh.com,
1.139 djm 1026: ecdsa-sha2-nistp256-cert-v01@openssh.com,
1027: ecdsa-sha2-nistp384-cert-v01@openssh.com,
1028: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.333 djm 1029: sk-ssh-ed25519-cert-v01@openssh.com,
1.311 naddy 1030: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.305 naddy 1031: rsa-sha2-512-cert-v01@openssh.com,
1032: rsa-sha2-256-cert-v01@openssh.com,
1.333 djm 1033: ssh-ed25519,
1.139 djm 1034: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.311 naddy 1035: sk-ecdsa-sha2-nistp256@openssh.com,
1.333 djm 1036: sk-ssh-ed25519@openssh.com,
1.366 kn 1037: rsa-sha2-512,rsa-sha2-256
1.139 djm 1038: .Ed
1.145 djm 1039: .Pp
1040: If hostkeys are known for the destination host then this default is modified
1041: to prefer their algorithms.
1.198 djm 1042: .Pp
1.348 djm 1043: The list of available signature algorithms may also be obtained using
1.322 dtucker 1044: .Qq ssh -Q HostKeyAlgorithms .
1.1 stevesk 1045: .It Cm HostKeyAlias
1046: Specifies an alias that should be used instead of the
1047: real host name when looking up or saving the host key
1.251 djm 1048: in the host key database files and when validating host certificates.
1.84 jmc 1049: This option is useful for tunneling SSH connections
1.1 stevesk 1050: or for multiple servers running on a single host.
1.295 jmc 1051: .It Cm Hostname
1.1 stevesk 1052: Specifies the real host name to log into.
1053: This can be used to specify nicknames or abbreviations for hosts.
1.239 jmc 1054: Arguments to
1.295 jmc 1055: .Cm Hostname
1.239 jmc 1056: accept the tokens described in the
1057: .Sx TOKENS
1058: section.
1.1 stevesk 1059: Numeric IP addresses are also permitted (both on the command line and in
1.295 jmc 1060: .Cm Hostname
1.1 stevesk 1061: specifications).
1.239 jmc 1062: The default is the name given on the command line.
1.29 markus 1063: .It Cm IdentitiesOnly
1064: Specifies that
1.84 jmc 1065: .Xr ssh 1
1.304 djm 1066: should only use the configured authentication identity and certificate files
1067: (either the default files, or those explicitly configured in the
1.31 jmc 1068: .Nm
1.221 djm 1069: files
1070: or passed on the
1071: .Xr ssh 1
1.304 djm 1072: command-line),
1.84 jmc 1073: even if
1074: .Xr ssh-agent 1
1.159 djm 1075: or a
1076: .Cm PKCS11Provider
1.305 naddy 1077: or
1078: .Cm SecurityKeyProvider
1.29 markus 1079: offers more identities.
1080: The argument to this keyword must be
1.240 jmc 1081: .Cm yes
1.29 markus 1082: or
1.240 jmc 1083: .Cm no
1084: (the default).
1.84 jmc 1085: This option is intended for situations where ssh-agent
1.29 markus 1086: offers many different identities.
1.231 markus 1087: .It Cm IdentityAgent
1088: Specifies the
1089: .Ux Ns -domain
1090: socket used to communicate with the authentication agent.
1091: .Pp
1092: This option overrides the
1.240 jmc 1093: .Ev SSH_AUTH_SOCK
1.231 markus 1094: environment variable and can be used to select a specific agent.
1095: Setting the socket name to
1.240 jmc 1096: .Cm none
1.231 markus 1097: disables the use of an authentication agent.
1.232 markus 1098: If the string
1.240 jmc 1099: .Qq SSH_AUTH_SOCK
1.232 markus 1100: is specified, the location of the socket will be read from the
1101: .Ev SSH_AUTH_SOCK
1102: environment variable.
1.286 djm 1103: Otherwise if the specified value begins with a
1104: .Sq $
1105: character, then it will be treated as an environment variable containing
1106: the location of the socket.
1.231 markus 1107: .Pp
1.239 jmc 1108: Arguments to
1109: .Cm IdentityAgent
1.326 dtucker 1110: may use the tilde syntax to refer to a user's home directory,
1111: the tokens described in the
1.239 jmc 1112: .Sx TOKENS
1.326 dtucker 1113: section and environment variables as described in the
1114: .Sx ENVIRONMENT VARIABLES
1.239 jmc 1115: section.
1.67 jmc 1116: .It Cm IdentityFile
1.313 naddy 1117: Specifies a file from which the user's DSA, ECDSA, authenticator-hosted ECDSA,
1118: Ed25519, authenticator-hosted Ed25519 or RSA authentication identity is read.
1.375 dtucker 1119: You can also specify a public key file to use the corresponding
1120: private key that is loaded in
1121: .Xr ssh-agent 1
1122: when the private key file is not present locally.
1.67 jmc 1123: The default is
1.368 dtucker 1124: .Pa ~/.ssh/id_rsa ,
1.183 naddy 1125: .Pa ~/.ssh/id_ecdsa ,
1.305 naddy 1126: .Pa ~/.ssh/id_ecdsa_sk ,
1.308 naddy 1127: .Pa ~/.ssh/id_ed25519 ,
1128: .Pa ~/.ssh/id_ed25519_sk
1.139 djm 1129: and
1.368 dtucker 1130: .Pa ~/.ssh/id_dsa .
1.67 jmc 1131: Additionally, any identities represented by the authentication agent
1.165 djm 1132: will be used for authentication unless
1133: .Cm IdentitiesOnly
1134: is set.
1.221 djm 1135: If no certificates have been explicitly specified by
1136: .Cm CertificateFile ,
1.129 djm 1137: .Xr ssh 1
1138: will try to load certificate information from the filename obtained by
1139: appending
1140: .Pa -cert.pub
1141: to the path of a specified
1142: .Cm IdentityFile .
1.90 djm 1143: .Pp
1.239 jmc 1144: Arguments to
1145: .Cm IdentityFile
1146: may use the tilde syntax to refer to a user's home directory
1147: or the tokens described in the
1148: .Sx TOKENS
1149: section.
1.389 djm 1150: Alternately an argument of
1151: .Cm none
1152: may be used to indicate no identity files should be loaded.
1.90 djm 1153: .Pp
1.67 jmc 1154: It is possible to have
1155: multiple identity files specified in configuration files; all these
1156: identities will be tried in sequence.
1.152 djm 1157: Multiple
1158: .Cm IdentityFile
1159: directives will add to the list of identities tried (this behaviour
1160: differs from that of other configuration directives).
1.165 djm 1161: .Pp
1162: .Cm IdentityFile
1163: may be used in conjunction with
1164: .Cm IdentitiesOnly
1165: to select which identities in an agent are offered during authentication.
1.221 djm 1166: .Cm IdentityFile
1167: may also be used in conjunction with
1168: .Cm CertificateFile
1169: in order to provide any certificate also needed for authentication with
1170: the identity.
1.164 jmc 1171: .It Cm IgnoreUnknown
1172: Specifies a pattern-list of unknown options to be ignored if they are
1173: encountered in configuration parsing.
1174: This may be used to suppress errors if
1175: .Nm
1176: contains options that are unrecognised by
1177: .Xr ssh 1 .
1178: It is recommended that
1179: .Cm IgnoreUnknown
1180: be listed early in the configuration file as it will not be applied
1181: to unknown options that appear before it.
1.229 djm 1182: .It Cm Include
1183: Include the specified configuration file(s).
1.230 jmc 1184: Multiple pathnames may be specified and each pathname may contain
1.281 kn 1185: .Xr glob 7
1.229 djm 1186: wildcards and, for user configurations, shell-like
1.240 jmc 1187: .Sq ~
1.229 djm 1188: references to user home directories.
1.327 djm 1189: Wildcards will be expanded and processed in lexical order.
1.229 djm 1190: Files without absolute paths are assumed to be in
1191: .Pa ~/.ssh
1.230 jmc 1192: if included in a user configuration file or
1.229 djm 1193: .Pa /etc/ssh
1194: if included from the system configuration file.
1195: .Cm Include
1196: directive may appear inside a
1197: .Cm Match
1198: or
1199: .Cm Host
1200: block
1201: to perform conditional inclusion.
1.143 djm 1202: .It Cm IPQoS
1203: Specifies the IPv4 type-of-service or DSCP class for connections.
1204: Accepted values are
1.240 jmc 1205: .Cm af11 ,
1206: .Cm af12 ,
1207: .Cm af13 ,
1208: .Cm af21 ,
1209: .Cm af22 ,
1210: .Cm af23 ,
1211: .Cm af31 ,
1212: .Cm af32 ,
1213: .Cm af33 ,
1214: .Cm af41 ,
1215: .Cm af42 ,
1216: .Cm af43 ,
1217: .Cm cs0 ,
1218: .Cm cs1 ,
1219: .Cm cs2 ,
1220: .Cm cs3 ,
1221: .Cm cs4 ,
1222: .Cm cs5 ,
1223: .Cm cs6 ,
1224: .Cm cs7 ,
1225: .Cm ef ,
1.319 djm 1226: .Cm le ,
1.240 jmc 1227: .Cm lowdelay ,
1228: .Cm throughput ,
1229: .Cm reliability ,
1.253 djm 1230: a numeric value, or
1231: .Cm none
1232: to use the operating system default.
1.146 djm 1233: This option may take one or two arguments, separated by whitespace.
1.143 djm 1234: If one argument is specified, it is used as the packet class unconditionally.
1235: If two values are specified, the first is automatically selected for
1236: interactive sessions and the second for non-interactive sessions.
1237: The default is
1.269 job 1238: .Cm af21
1.272 jmc 1239: (Low-Latency Data)
1.143 djm 1240: for interactive sessions and
1.269 job 1241: .Cm cs1
1.272 jmc 1242: (Lower Effort)
1.143 djm 1243: for non-interactive sessions.
1.103 djm 1244: .It Cm KbdInteractiveAuthentication
1245: Specifies whether to use keyboard-interactive authentication.
1246: The argument to this keyword must be
1.240 jmc 1247: .Cm yes
1248: (the default)
1.103 djm 1249: or
1.240 jmc 1250: .Cm no .
1.355 dtucker 1251: .Cm ChallengeResponseAuthentication
1252: is a deprecated alias for this.
1.39 djm 1253: .It Cm KbdInteractiveDevices
1254: Specifies the list of methods to use in keyboard-interactive authentication.
1255: Multiple method names must be comma-separated.
1256: The default is to use the server specified list.
1.85 jmc 1257: The methods available vary depending on what the server supports.
1258: For an OpenSSH server,
1259: it may be zero or more of:
1.240 jmc 1260: .Cm bsdauth ,
1261: .Cm pam ,
1.85 jmc 1262: and
1.240 jmc 1263: .Cm skey .
1.140 djm 1264: .It Cm KexAlgorithms
1265: Specifies the available KEX (Key Exchange) algorithms.
1266: Multiple algorithms must be comma-separated.
1.299 kn 1267: If the specified list begins with a
1.214 djm 1268: .Sq +
1.363 dtucker 1269: character, then the specified algorithms will be appended to the default set
1.214 djm 1270: instead of replacing them.
1.299 kn 1271: If the specified list begins with a
1.241 djm 1272: .Sq -
1.363 dtucker 1273: character, then the specified algorithms (including wildcards) will be removed
1.241 djm 1274: from the default set instead of replacing them.
1.301 naddy 1275: If the specified list begins with a
1276: .Sq ^
1.363 dtucker 1277: character, then the specified algorithms will be placed at the head of the
1.301 naddy 1278: default set.
1.141 jmc 1279: The default is:
1280: .Bd -literal -offset indent
1.371 naddy 1281: sntrup761x25519-sha512@openssh.com,
1.238 djm 1282: curve25519-sha256,curve25519-sha256@libssh.org,
1.141 jmc 1283: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
1284: diffie-hellman-group-exchange-sha256,
1.266 djm 1285: diffie-hellman-group16-sha512,
1286: diffie-hellman-group18-sha512,
1.317 tedu 1287: diffie-hellman-group14-sha256
1.141 jmc 1288: .Ed
1.198 djm 1289: .Pp
1.240 jmc 1290: The list of available key exchange algorithms may also be obtained using
1291: .Qq ssh -Q kex .
1.339 djm 1292: .It Cm KnownHostsCommand
1.340 jmc 1293: Specifies a command to use to obtain a list of host keys, in addition to
1.339 djm 1294: those listed in
1295: .Cm UserKnownHostsFile
1296: and
1297: .Cm GlobalKnownHostsFile .
1298: This command is executed after the files have been read.
1.340 jmc 1299: It may write host key lines to standard output in identical format to the
1.339 djm 1300: usual files (described in the
1301: .Sx VERIFYING HOST KEYS
1302: section in
1303: .Xr ssh 1 ) .
1304: Arguments to
1305: .Cm KnownHostsCommand
1306: accept the tokens described in the
1307: .Sx TOKENS
1308: section.
1.340 jmc 1309: The command may be invoked multiple times per connection: once when preparing
1.339 djm 1310: the preference list of host key algorithms to use, again to obtain the
1311: host key for the requested host name and, if
1312: .Cm CheckHostIP
1313: is enabled, one more time to obtain the host key matching the server's
1314: address.
1315: If the command exits abnormally or returns a non-zero exit status then the
1316: connection is terminated.
1.65 reyk 1317: .It Cm LocalCommand
1318: Specifies a command to execute on the local machine after successfully
1319: connecting to the server.
1320: The command string extends to the end of the line, and is executed with
1.105 jmc 1321: the user's shell.
1.239 jmc 1322: Arguments to
1323: .Cm LocalCommand
1324: accept the tokens described in the
1325: .Sx TOKENS
1326: section.
1.123 djm 1327: .Pp
1328: The command is run synchronously and does not have access to the
1329: session of the
1330: .Xr ssh 1
1331: that spawned it.
1332: It should not be used for interactive commands.
1333: .Pp
1.65 reyk 1334: This directive is ignored unless
1335: .Cm PermitLocalCommand
1336: has been enabled.
1.1 stevesk 1337: .It Cm LocalForward
1.74 jmc 1338: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 1339: the secure channel to the specified host and port from the remote machine.
1.324 dtucker 1340: The first argument specifies the listener and may be
1.43 djm 1341: .Sm off
1.49 jmc 1342: .Oo Ar bind_address : Oc Ar port
1.43 djm 1343: .Sm on
1.324 dtucker 1344: or a Unix domain socket path.
1345: The second argument is the destination and may be
1346: .Ar host : Ns Ar hostport
1347: or a Unix domain socket path if the remote host supports it.
1348: .Pp
1.138 djm 1349: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.46 jmc 1350: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 1351: given on the command line.
1.1 stevesk 1352: Only the superuser can forward privileged ports.
1.43 djm 1353: By default, the local port is bound in accordance with the
1354: .Cm GatewayPorts
1355: setting.
1356: However, an explicit
1357: .Ar bind_address
1358: may be used to bind the connection to a specific address.
1359: The
1360: .Ar bind_address
1361: of
1.240 jmc 1362: .Cm localhost
1.46 jmc 1363: indicates that the listening port be bound for local use only, while an
1364: empty address or
1365: .Sq *
1.43 djm 1366: indicates that the port should be available from all interfaces.
1.326 dtucker 1367: Unix domain socket paths may use the tokens described in the
1.324 dtucker 1368: .Sx TOKENS
1.326 dtucker 1369: section and environment variables as described in the
1370: .Sx ENVIRONMENT VARIABLES
1.324 dtucker 1371: section.
1.1 stevesk 1372: .It Cm LogLevel
1373: Gives the verbosity level that is used when logging messages from
1.84 jmc 1374: .Xr ssh 1 .
1.1 stevesk 1375: The possible values are:
1.84 jmc 1376: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 1377: The default is INFO.
1378: DEBUG and DEBUG1 are equivalent.
1379: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.337 djm 1380: .It Cm LogVerbose
1381: Specify one or more overrides to LogLevel.
1382: An override consists of a pattern lists that matches the source file, function
1383: and line number to force detailed logging for.
1384: For example, an override pattern of:
1385: .Bd -literal -offset indent
1386: kex.c:*:1000,*:kex_exchange_identification():*,packet.c:*
1387: .Ed
1388: .Pp
1389: would enable detailed logging for line 1000 of
1.338 jmc 1390: .Pa kex.c ,
1.337 djm 1391: everything in the
1392: .Fn kex_exchange_identification
1393: function, and all code in the
1394: .Pa packet.c
1395: file.
1396: This option is intended for debugging and no overrides are enabled by default.
1.1 stevesk 1397: .It Cm MACs
1398: Specifies the MAC (message authentication code) algorithms
1399: in order of preference.
1.226 jmc 1400: The MAC algorithm is used for data integrity protection.
1.1 stevesk 1401: Multiple algorithms must be comma-separated.
1.299 kn 1402: If the specified list begins with a
1.214 djm 1403: .Sq +
1404: character, then the specified algorithms will be appended to the default set
1405: instead of replacing them.
1.299 kn 1406: If the specified list begins with a
1.241 djm 1407: .Sq -
1408: character, then the specified algorithms (including wildcards) will be removed
1409: from the default set instead of replacing them.
1.301 naddy 1410: If the specified list begins with a
1411: .Sq ^
1412: character, then the specified algorithms will be placed at the head of the
1413: default set.
1.214 djm 1414: .Pp
1.160 markus 1415: The algorithms that contain
1.240 jmc 1416: .Qq -etm
1.160 markus 1417: calculate the MAC after encryption (encrypt-then-mac).
1418: These are considered safer and their use recommended.
1.214 djm 1419: .Pp
1.84 jmc 1420: The default is:
1.101 jmc 1421: .Bd -literal -offset indent
1.160 markus 1422: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
1423: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
1.224 djm 1424: hmac-sha1-etm@openssh.com,
1.186 naddy 1425: umac-64@openssh.com,umac-128@openssh.com,
1.224 djm 1426: hmac-sha2-256,hmac-sha2-512,hmac-sha1
1.101 jmc 1427: .Ed
1.198 djm 1428: .Pp
1.240 jmc 1429: The list of available MAC algorithms may also be obtained using
1430: .Qq ssh -Q mac .
1.1 stevesk 1431: .It Cm NoHostAuthenticationForLocalhost
1.264 djm 1432: Disable host authentication for localhost (loopback addresses).
1.1 stevesk 1433: The argument to this keyword must be
1.240 jmc 1434: .Cm yes
1.1 stevesk 1435: or
1.242 jmc 1436: .Cm no
1.240 jmc 1437: (the default).
1.1 stevesk 1438: .It Cm NumberOfPasswordPrompts
1439: Specifies the number of password prompts before giving up.
1440: The argument to this keyword must be an integer.
1.84 jmc 1441: The default is 3.
1.384 djm 1442: .It Cm ObscureKeystrokeTiming
1443: Specifies whether
1444: .Xr ssh 1
1445: should try to obscure inter-keystroke timings from passive observers of
1446: network traffic.
1447: If enabled, then for interactive sessions,
1448: .Xr ssh 1
1449: will send keystrokes at fixed intervals of a few tens of milliseconds
1450: and will send fake keystroke packets for some time after typing ceases.
1451: The argument to this keyword must be
1452: .Cm yes ,
1453: .Cm no
1454: or an interval specifier of the form
1455: .Cm interval:milliseconds
1456: (e.g.\&
1.386 djm 1457: .Cm interval:80
1458: for 80 milliseconds).
1.384 djm 1459: The default is to obscure keystrokes using a 20ms packet interval.
1460: Note that smaller intervals will result in higher fake keystroke packet rates.
1.1 stevesk 1461: .It Cm PasswordAuthentication
1462: Specifies whether to use password authentication.
1463: The argument to this keyword must be
1.240 jmc 1464: .Cm yes
1465: (the default)
1.1 stevesk 1466: or
1.240 jmc 1467: .Cm no .
1.65 reyk 1468: .It Cm PermitLocalCommand
1469: Allow local command execution via the
1470: .Ic LocalCommand
1471: option or using the
1.66 jmc 1472: .Ic !\& Ns Ar command
1.65 reyk 1473: escape sequence in
1474: .Xr ssh 1 .
1475: The argument must be
1.240 jmc 1476: .Cm yes
1.65 reyk 1477: or
1.240 jmc 1478: .Cm no
1479: (the default).
1.347 markus 1480: .It Cm PermitRemoteOpen
1481: Specifies the destinations to which remote TCP port forwarding is permitted when
1482: .Cm RemoteForward
1483: is used as a SOCKS proxy.
1484: The forwarding specification must be one of the following forms:
1485: .Pp
1486: .Bl -item -offset indent -compact
1487: .It
1488: .Cm PermitRemoteOpen
1489: .Sm off
1490: .Ar host : port
1491: .Sm on
1492: .It
1493: .Cm PermitRemoteOpen
1494: .Sm off
1495: .Ar IPv4_addr : port
1496: .Sm on
1497: .It
1498: .Cm PermitRemoteOpen
1499: .Sm off
1500: .Ar \&[ IPv6_addr \&] : port
1501: .Sm on
1502: .El
1503: .Pp
1504: Multiple forwards may be specified by separating them with whitespace.
1505: An argument of
1506: .Cm any
1507: can be used to remove all restrictions and permit any forwarding requests.
1508: An argument of
1509: .Cm none
1510: can be used to prohibit all forwarding requests.
1511: The wildcard
1512: .Sq *
1513: can be used for host or port to allow all hosts or ports respectively.
1514: Otherwise, no pattern matching or address lookups are performed on supplied
1515: names.
1.127 markus 1516: .It Cm PKCS11Provider
1.292 djm 1517: Specifies which PKCS#11 provider to use or
1518: .Cm none
1519: to indicate that no provider should be used (the default).
1520: The argument to this keyword is a path to the PKCS#11 shared library
1.127 markus 1521: .Xr ssh 1
1.292 djm 1522: should use to communicate with a PKCS#11 token providing keys for user
1523: authentication.
1.67 jmc 1524: .It Cm Port
1525: Specifies the port number to connect on the remote host.
1.84 jmc 1526: The default is 22.
1.1 stevesk 1527: .It Cm PreferredAuthentications
1.226 jmc 1528: Specifies the order in which the client should try authentication methods.
1.48 jmc 1529: This allows a client to prefer one method (e.g.\&
1.1 stevesk 1530: .Cm keyboard-interactive )
1.48 jmc 1531: over another method (e.g.\&
1.131 jmc 1532: .Cm password ) .
1533: The default is:
1534: .Bd -literal -offset indent
1535: gssapi-with-mic,hostbased,publickey,
1536: keyboard-interactive,password
1537: .Ed
1.1 stevesk 1538: .It Cm ProxyCommand
1539: Specifies the command to use to connect to the server.
1540: The command
1.190 djm 1541: string extends to the end of the line, and is executed
1542: using the user's shell
1543: .Ql exec
1544: directive to avoid a lingering shell process.
1545: .Pp
1.239 jmc 1546: Arguments to
1547: .Cm ProxyCommand
1548: accept the tokens described in the
1549: .Sx TOKENS
1550: section.
1.1 stevesk 1551: The command can be basically anything,
1552: and should read from its standard input and write to its standard output.
1553: It should eventually connect an
1554: .Xr sshd 8
1555: server running on some machine, or execute
1556: .Ic sshd -i
1557: somewhere.
1558: Host key management will be done using the
1.296 jmc 1559: .Cm Hostname
1560: of the host being connected (defaulting to the name typed by the user).
1.7 jmc 1561: Setting the command to
1.240 jmc 1562: .Cm none
1.6 markus 1563: disables this option entirely.
1.1 stevesk 1564: Note that
1565: .Cm CheckHostIP
1566: is not available for connects with a proxy command.
1.52 djm 1567: .Pp
1568: This directive is useful in conjunction with
1569: .Xr nc 1
1570: and its proxy support.
1.53 jmc 1571: For example, the following directive would connect via an HTTP proxy at
1.52 djm 1572: 192.0.2.0:
1573: .Bd -literal -offset 3n
1574: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
1575: .Ed
1.233 djm 1576: .It Cm ProxyJump
1.260 millert 1577: Specifies one or more jump proxies as either
1.233 djm 1578: .Xo
1579: .Sm off
1.234 jmc 1580: .Op Ar user No @
1.233 djm 1581: .Ar host
1.234 jmc 1582: .Op : Ns Ar port
1.233 djm 1583: .Sm on
1.260 millert 1584: or an ssh URI
1.233 djm 1585: .Xc .
1.235 djm 1586: Multiple proxies may be separated by comma characters and will be visited
1.236 djm 1587: sequentially.
1.233 djm 1588: Setting this option will cause
1589: .Xr ssh 1
1590: to connect to the target host by first making a
1591: .Xr ssh 1
1592: connection to the specified
1593: .Cm ProxyJump
1594: host and then establishing a
1.234 jmc 1595: TCP forwarding to the ultimate target from there.
1.346 dlg 1596: Setting the host to
1597: .Cm none
1598: disables this option entirely.
1.233 djm 1599: .Pp
1600: Note that this option will compete with the
1601: .Cm ProxyCommand
1602: option - whichever is specified first will prevent later instances of the
1603: other from taking effect.
1.289 djm 1604: .Pp
1605: Note also that the configuration for the destination host (either supplied
1606: via the command-line or the configuration file) is not generally applied
1607: to jump hosts.
1608: .Pa ~/.ssh/config
1609: should be used if specific configuration is required for jump hosts.
1.167 djm 1610: .It Cm ProxyUseFdpass
1.168 jmc 1611: Specifies that
1.167 djm 1612: .Cm ProxyCommand
1613: will pass a connected file descriptor back to
1.168 jmc 1614: .Xr ssh 1
1.167 djm 1615: instead of continuing to execute and pass data.
1616: The default is
1.240 jmc 1617: .Cm no .
1.343 dtucker 1618: .It Cm PubkeyAcceptedAlgorithms
1619: Specifies the signature algorithms that will be used for public key
1620: authentication as a comma-separated list of patterns.
1.299 kn 1621: If the specified list begins with a
1.214 djm 1622: .Sq +
1.343 dtucker 1623: character, then the algorithms after it will be appended to the default
1.214 djm 1624: instead of replacing it.
1.299 kn 1625: If the specified list begins with a
1.241 djm 1626: .Sq -
1.343 dtucker 1627: character, then the specified algorithms (including wildcards) will be removed
1.241 djm 1628: from the default set instead of replacing them.
1.301 naddy 1629: If the specified list begins with a
1630: .Sq ^
1.343 dtucker 1631: character, then the specified algorithms will be placed at the head of the
1.301 naddy 1632: default set.
1.213 markus 1633: The default for this option is:
1634: .Bd -literal -offset 3n
1.333 djm 1635: ssh-ed25519-cert-v01@openssh.com,
1.213 markus 1636: ecdsa-sha2-nistp256-cert-v01@openssh.com,
1637: ecdsa-sha2-nistp384-cert-v01@openssh.com,
1638: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.333 djm 1639: sk-ssh-ed25519-cert-v01@openssh.com,
1.311 naddy 1640: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.305 naddy 1641: rsa-sha2-512-cert-v01@openssh.com,
1642: rsa-sha2-256-cert-v01@openssh.com,
1.333 djm 1643: ssh-ed25519,
1.311 naddy 1644: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.333 djm 1645: sk-ssh-ed25519@openssh.com,
1.305 naddy 1646: sk-ecdsa-sha2-nistp256@openssh.com,
1.366 kn 1647: rsa-sha2-512,rsa-sha2-256
1.213 markus 1648: .Ed
1649: .Pp
1.348 djm 1650: The list of available signature algorithms may also be obtained using
1.343 dtucker 1651: .Qq ssh -Q PubkeyAcceptedAlgorithms .
1.1 stevesk 1652: .It Cm PubkeyAuthentication
1653: Specifies whether to try public key authentication.
1654: The argument to this keyword must be
1.240 jmc 1655: .Cm yes
1.369 djm 1656: (the default),
1657: .Cm no ,
1658: .Cm unbound
1.1 stevesk 1659: or
1.369 djm 1660: .Cm host-bound .
1661: The final two options enable public key authentication while respectively
1662: disabling or enabling the OpenSSH host-bound authentication protocol
1663: extension required for restricted
1664: .Xr ssh-agent 1
1665: forwarding.
1.75 dtucker 1666: .It Cm RekeyLimit
1.373 djm 1667: Specifies the maximum amount of data that may be transmitted or received
1668: before the session key is renegotiated, optionally followed by a maximum
1669: amount of time that may pass before the session key is renegotiated.
1.162 dtucker 1670: The first argument is specified in bytes and may have a suffix of
1.76 jmc 1671: .Sq K ,
1672: .Sq M ,
1.75 dtucker 1673: or
1.76 jmc 1674: .Sq G
1.75 dtucker 1675: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1676: The default is between
1.84 jmc 1677: .Sq 1G
1.75 dtucker 1678: and
1.84 jmc 1679: .Sq 4G ,
1.75 dtucker 1680: depending on the cipher.
1.162 dtucker 1681: The optional second value is specified in seconds and may use any of the
1.293 schwarze 1682: units documented in the TIME FORMATS section of
1.162 dtucker 1683: .Xr sshd_config 5 .
1684: The default value for
1685: .Cm RekeyLimit
1686: is
1.240 jmc 1687: .Cm default none ,
1.162 dtucker 1688: which means that rekeying is performed after the cipher's default amount
1689: of data has been sent or received and no time based rekeying is done.
1.249 bluhm 1690: .It Cm RemoteCommand
1691: Specifies a command to execute on the remote machine after successfully
1692: connecting to the server.
1693: The command string extends to the end of the line, and is executed with
1694: the user's shell.
1.250 jmc 1695: Arguments to
1696: .Cm RemoteCommand
1697: accept the tokens described in the
1698: .Sx TOKENS
1699: section.
1.1 stevesk 1700: .It Cm RemoteForward
1.74 jmc 1701: Specifies that a TCP port on the remote machine be forwarded over
1.256 markus 1702: the secure channel.
1.273 djm 1703: The remote port may either be forwarded to a specified host and port
1.256 markus 1704: from the local machine, or may act as a SOCKS 4/5 proxy that allows a remote
1705: client to connect to arbitrary destinations from the local machine.
1.324 dtucker 1706: The first argument is the listening specification and may be
1.43 djm 1707: .Sm off
1.49 jmc 1708: .Oo Ar bind_address : Oc Ar port
1.43 djm 1709: .Sm on
1.324 dtucker 1710: or, if the remote host supports it, a Unix domain socket path.
1.256 markus 1711: If forwarding to a specific destination then the second argument must be
1.324 dtucker 1712: .Ar host : Ns Ar hostport
1713: or a Unix domain socket path,
1.256 markus 1714: otherwise if no destination argument is specified then the remote forwarding
1715: will be established as a SOCKS proxy.
1.370 naddy 1716: When acting as a SOCKS proxy, the destination of the connection can be
1.347 markus 1717: restricted by
1718: .Cm PermitRemoteOpen .
1.256 markus 1719: .Pp
1.138 djm 1720: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.1 stevesk 1721: Multiple forwardings may be specified, and additional
1722: forwardings can be given on the command line.
1.113 stevesk 1723: Privileged ports can be forwarded only when
1724: logging in as root on the remote machine.
1.326 dtucker 1725: Unix domain socket paths may use the tokens described in the
1.324 dtucker 1726: .Sx TOKENS
1.326 dtucker 1727: section and environment variables as described in the
1728: .Sx ENVIRONMENT VARIABLES
1.324 dtucker 1729: section.
1.118 jmc 1730: .Pp
1.117 djm 1731: If the
1732: .Ar port
1.240 jmc 1733: argument is 0,
1.117 djm 1734: the listen port will be dynamically allocated on the server and reported
1735: to the client at run time.
1.43 djm 1736: .Pp
1737: If the
1738: .Ar bind_address
1739: is not specified, the default is to only bind to loopback addresses.
1740: If the
1741: .Ar bind_address
1742: is
1743: .Ql *
1744: or an empty string, then the forwarding is requested to listen on all
1745: interfaces.
1746: Specifying a remote
1747: .Ar bind_address
1.46 jmc 1748: will only succeed if the server's
1749: .Cm GatewayPorts
1.43 djm 1750: option is enabled (see
1.46 jmc 1751: .Xr sshd_config 5 ) .
1.149 djm 1752: .It Cm RequestTTY
1753: Specifies whether to request a pseudo-tty for the session.
1754: The argument may be one of:
1.240 jmc 1755: .Cm no
1.149 djm 1756: (never request a TTY),
1.240 jmc 1757: .Cm yes
1.149 djm 1758: (always request a TTY when standard input is a TTY),
1.240 jmc 1759: .Cm force
1.149 djm 1760: (always request a TTY) or
1.240 jmc 1761: .Cm auto
1.149 djm 1762: (request a TTY when opening a login session).
1763: This option mirrors the
1764: .Fl t
1765: and
1766: .Fl T
1767: flags for
1768: .Xr ssh 1 .
1.374 djm 1769: .It Cm RequiredRSASize
1770: Specifies the minimum RSA key size (in bits) that
1771: .Xr ssh 1
1772: will accept.
1773: User authentication keys smaller than this limit will be ignored.
1774: Servers that present host keys smaller than this limit will cause the
1775: connection to be terminated.
1776: The default is
1777: .Cm 1024
1778: bits.
1779: Note that this limit may only be raised from the default.
1.196 djm 1780: .It Cm RevokedHostKeys
1781: Specifies revoked host public keys.
1782: Keys listed in this file will be refused for host authentication.
1783: Note that if this file does not exist or is not readable,
1784: then host authentication will be refused for all hosts.
1785: Keys may be specified as a text file, listing one public key per line, or as
1786: an OpenSSH Key Revocation List (KRL) as generated by
1787: .Xr ssh-keygen 1 .
1788: For more information on KRLs, see the KEY REVOCATION LISTS section in
1789: .Xr ssh-keygen 1 .
1.380 dtucker 1790: Arguments to
1791: .Cm RevokedHostKeys
1792: may use the tilde syntax to refer to a user's home directory,
1793: the tokens described in the
1794: .Sx TOKENS
1795: section and environment variables as described in the
1796: .Sx ENVIRONMENT VARIABLES
1797: section.
1.305 naddy 1798: .It Cm SecurityKeyProvider
1.313 naddy 1799: Specifies a path to a library that will be used when loading any
1800: FIDO authenticator-hosted keys, overriding the default of using
1801: the built-in USB HID support.
1.309 naddy 1802: .Pp
1803: If the specified value begins with a
1804: .Sq $
1805: character, then it will be treated as an environment variable containing
1806: the path to the library.
1.32 djm 1807: .It Cm SendEnv
1808: Specifies what variables from the local
1809: .Xr environ 7
1810: should be sent to the server.
1.84 jmc 1811: The server must also support it, and the server must be configured to
1.33 djm 1812: accept these environment variables.
1.207 dtucker 1813: Note that the
1814: .Ev TERM
1.208 jmc 1815: environment variable is always sent whenever a
1.207 dtucker 1816: pseudo-terminal is requested as it is required by the protocol.
1.32 djm 1817: Refer to
1818: .Cm AcceptEnv
1819: in
1820: .Xr sshd_config 5
1821: for how to configure the server.
1.80 jmc 1822: Variables are specified by name, which may contain wildcard characters.
1.33 djm 1823: Multiple environment variables may be separated by whitespace or spread
1.32 djm 1824: across multiple
1825: .Cm SendEnv
1826: directives.
1.81 jmc 1827: .Pp
1828: See
1829: .Sx PATTERNS
1830: for more information on patterns.
1.271 djm 1831: .Pp
1.272 jmc 1832: It is possible to clear previously set
1.271 djm 1833: .Cm SendEnv
1834: variable names by prefixing patterns with
1835: .Pa - .
1836: The default is not to send any environment variables.
1.28 markus 1837: .It Cm ServerAliveCountMax
1.73 jmc 1838: Sets the number of server alive messages (see below) which may be
1.28 markus 1839: sent without
1.84 jmc 1840: .Xr ssh 1
1.28 markus 1841: receiving any messages back from the server.
1842: If this threshold is reached while server alive messages are being sent,
1.84 jmc 1843: ssh will disconnect from the server, terminating the session.
1.28 markus 1844: It is important to note that the use of server alive messages is very
1845: different from
1846: .Cm TCPKeepAlive
1847: (below).
1848: The server alive messages are sent through the encrypted channel
1849: and therefore will not be spoofable.
1850: The TCP keepalive option enabled by
1851: .Cm TCPKeepAlive
1852: is spoofable.
1853: The server alive mechanism is valuable when the client or
1.298 dtucker 1854: server depend on knowing when a connection has become unresponsive.
1.28 markus 1855: .Pp
1856: The default value is 3.
1857: If, for example,
1858: .Cm ServerAliveInterval
1.84 jmc 1859: (see below) is set to 15 and
1.28 markus 1860: .Cm ServerAliveCountMax
1.84 jmc 1861: is left at the default, if the server becomes unresponsive,
1862: ssh will disconnect after approximately 45 seconds.
1.67 jmc 1863: .It Cm ServerAliveInterval
1864: Sets a timeout interval in seconds after which if no data has been received
1865: from the server,
1.84 jmc 1866: .Xr ssh 1
1.67 jmc 1867: will send a message through the encrypted
1868: channel to request a response from the server.
1869: The default
1870: is 0, indicating that these messages will not be sent to the server.
1.357 jmc 1871: .It Cm SessionType
1872: May be used to either request invocation of a subsystem on the remote system,
1873: or to prevent the execution of a remote command at all.
1874: The latter is useful for just forwarding ports.
1875: The argument to this keyword must be
1876: .Cm none
1877: (same as the
1878: .Fl N
1879: option),
1880: .Cm subsystem
1881: (same as the
1882: .Fl s
1883: option) or
1884: .Cm default
1885: (shell or command execution).
1.277 jmc 1886: .It Cm SetEnv
1887: Directly specify one or more environment variables and their contents to
1888: be sent to the server.
1889: Similarly to
1890: .Cm SendEnv ,
1.354 djm 1891: with the exception of the
1892: .Ev TERM
1893: variable, the server must be prepared to accept the environment variable.
1.358 djm 1894: .It Cm StdinNull
1895: Redirects stdin from
1896: .Pa /dev/null
1897: (actually, prevents reading from stdin).
1898: Either this or the equivalent
1899: .Fl n
1900: option must be used when
1901: .Nm ssh
1902: is run in the background.
1903: The argument to this keyword must be
1904: .Cm yes
1905: (same as the
1906: .Fl n
1907: option) or
1908: .Cm no
1909: (the default).
1.191 millert 1910: .It Cm StreamLocalBindMask
1911: Sets the octal file creation mode mask
1912: .Pq umask
1913: used when creating a Unix-domain socket file for local or remote
1914: port forwarding.
1915: This option is only used for port forwarding to a Unix-domain socket file.
1916: .Pp
1917: The default value is 0177, which creates a Unix-domain socket file that is
1918: readable and writable only by the owner.
1919: Note that not all operating systems honor the file mode on Unix-domain
1920: socket files.
1921: .It Cm StreamLocalBindUnlink
1922: Specifies whether to remove an existing Unix-domain socket file for local
1923: or remote port forwarding before creating a new one.
1924: If the socket file already exists and
1925: .Cm StreamLocalBindUnlink
1926: is not enabled,
1927: .Nm ssh
1928: will be unable to forward the port to the Unix-domain socket file.
1929: This option is only used for port forwarding to a Unix-domain socket file.
1930: .Pp
1931: The argument must be
1.240 jmc 1932: .Cm yes
1.191 millert 1933: or
1.240 jmc 1934: .Cm no
1935: (the default).
1.1 stevesk 1936: .It Cm StrictHostKeyChecking
1937: If this flag is set to
1.240 jmc 1938: .Cm yes ,
1.84 jmc 1939: .Xr ssh 1
1.1 stevesk 1940: will never automatically add host keys to the
1.50 djm 1941: .Pa ~/.ssh/known_hosts
1.1 stevesk 1942: file, and refuses to connect to hosts whose host key has changed.
1.263 dtucker 1943: This provides maximum protection against man-in-the-middle (MITM) attacks,
1.84 jmc 1944: though it can be annoying when the
1.1 stevesk 1945: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 1946: file is poorly maintained or when connections to new hosts are
1.1 stevesk 1947: frequently made.
1948: This option forces the user to manually
1949: add all new hosts.
1.255 jmc 1950: .Pp
1.1 stevesk 1951: If this flag is set to
1.364 dtucker 1952: .Cm accept-new
1.360 jmc 1953: then ssh will automatically add new host keys to the user's
1954: .Pa known_hosts
1955: file, but will not permit connections to hosts with
1.254 djm 1956: changed host keys.
1957: If this flag is set to
1.364 dtucker 1958: .Cm no
1.254 djm 1959: or
1.364 dtucker 1960: .Cm off ,
1.255 jmc 1961: ssh will automatically add new host keys to the user known hosts files
1962: and allow connections to hosts with changed hostkeys to proceed,
1963: subject to some restrictions.
1.1 stevesk 1964: If this flag is set to
1.240 jmc 1965: .Cm ask
1966: (the default),
1.1 stevesk 1967: new host keys
1968: will be added to the user known host files only after the user
1969: has confirmed that is what they really want to do, and
1.84 jmc 1970: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 1971: The host keys of
1972: known hosts will be verified automatically in all cases.
1.244 jmc 1973: .It Cm SyslogFacility
1974: Gives the facility code that is used when logging messages from
1975: .Xr ssh 1 .
1976: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1977: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
1978: The default is USER.
1.26 markus 1979: .It Cm TCPKeepAlive
1980: Specifies whether the system should send TCP keepalive messages to the
1981: other side.
1982: If they are sent, death of the connection or crash of one
1983: of the machines will be properly noticed.
1984: However, this means that
1985: connections will die if the route is down temporarily, and some people
1986: find it annoying.
1987: .Pp
1988: The default is
1.240 jmc 1989: .Cm yes
1.26 markus 1990: (to send TCP keepalive messages), and the client will notice
1991: if the network goes down or the remote host dies.
1992: This is important in scripts, and many users want it too.
1993: .Pp
1994: To disable TCP keepalive messages, the value should be set to
1.240 jmc 1995: .Cm no .
1.265 djm 1996: See also
1997: .Cm ServerAliveInterval
1998: for protocol-level keepalives.
1.382 djm 1999: .It Cm Tag
2000: Specify a configuration tag name that may be later used by a
2001: .Cm Match
1.383 jsg 2002: directive to select a block of configuration.
1.65 reyk 2003: .It Cm Tunnel
1.95 stevesk 2004: Request
1.65 reyk 2005: .Xr tun 4
1.69 jmc 2006: device forwarding between the client and the server.
1.65 reyk 2007: The argument must be
1.240 jmc 2008: .Cm yes ,
2009: .Cm point-to-point
1.95 stevesk 2010: (layer 3),
1.240 jmc 2011: .Cm ethernet
1.95 stevesk 2012: (layer 2),
1.65 reyk 2013: or
1.240 jmc 2014: .Cm no
2015: (the default).
1.95 stevesk 2016: Specifying
1.240 jmc 2017: .Cm yes
1.95 stevesk 2018: requests the default tunnel mode, which is
1.240 jmc 2019: .Cm point-to-point .
1.65 reyk 2020: .It Cm TunnelDevice
1.95 stevesk 2021: Specifies the
1.65 reyk 2022: .Xr tun 4
1.95 stevesk 2023: devices to open on the client
2024: .Pq Ar local_tun
2025: and the server
2026: .Pq Ar remote_tun .
2027: .Pp
2028: The argument must be
2029: .Sm off
2030: .Ar local_tun Op : Ar remote_tun .
2031: .Sm on
2032: The devices may be specified by numerical ID or the keyword
1.240 jmc 2033: .Cm any ,
1.95 stevesk 2034: which uses the next available tunnel device.
2035: If
2036: .Ar remote_tun
2037: is not specified, it defaults to
1.240 jmc 2038: .Cm any .
1.95 stevesk 2039: The default is
1.240 jmc 2040: .Cm any:any .
1.201 djm 2041: .It Cm UpdateHostKeys
1.200 djm 2042: Specifies whether
2043: .Xr ssh 1
2044: should accept notifications of additional hostkeys from the server sent
2045: after authentication has completed and add them to
2046: .Cm UserKnownHostsFile .
2047: The argument must be
1.240 jmc 2048: .Cm yes ,
2049: .Cm no
1.320 djm 2050: or
1.240 jmc 2051: .Cm ask .
1.320 djm 2052: This option allows learning alternate hostkeys for a server
1.201 djm 2053: and supports graceful key rotation by allowing a server to send replacement
2054: public keys before old ones are removed.
1.336 djm 2055: .Pp
1.200 djm 2056: Additional hostkeys are only accepted if the key used to authenticate the
1.336 djm 2057: host was already trusted or explicitly accepted by the user, the host was
2058: authenticated via
2059: .Cm UserKnownHostsFile
2060: (i.e. not
2061: .Cm GlobalKnownHostsFile )
2062: and the host was authenticated using a plain key and not a certificate.
1.320 djm 2063: .Pp
2064: .Cm UpdateHostKeys
1.321 jmc 2065: is enabled by default if the user has not overridden the default
1.320 djm 2066: .Cm UserKnownHostsFile
1.335 djm 2067: setting and has not enabled
2068: .Cm VerifyHostKeyDNS ,
2069: otherwise
1.320 djm 2070: .Cm UpdateHostKeys
2071: will be set to
1.334 djm 2072: .Cm no .
1.320 djm 2073: .Pp
1.204 djm 2074: If
2075: .Cm UpdateHostKeys
2076: is set to
1.240 jmc 2077: .Cm ask ,
1.204 djm 2078: then the user is asked to confirm the modifications to the known_hosts file.
1.205 djm 2079: Confirmation is currently incompatible with
2080: .Cm ControlPersist ,
2081: and will be disabled if it is enabled.
1.200 djm 2082: .Pp
2083: Presently, only
2084: .Xr sshd 8
2085: from OpenSSH 6.8 and greater support the
1.240 jmc 2086: .Qq hostkeys@openssh.com
1.200 djm 2087: protocol extension used to inform the client of all the server's hostkeys.
1.1 stevesk 2088: .It Cm User
2089: Specifies the user to log in as.
2090: This can be useful when a different user name is used on different machines.
2091: This saves the trouble of
2092: having to remember to give the user name on the command line.
2093: .It Cm UserKnownHostsFile
1.151 djm 2094: Specifies one or more files to use for the user
2095: host key database, separated by whitespace.
1.329 dtucker 2096: Each filename may use tilde notation to refer to the user's home directory,
2097: the tokens described in the
2098: .Sx TOKENS
2099: section and environment variables as described in the
2100: .Sx ENVIRONMENT VARIABLES
2101: section.
1.377 dtucker 2102: A value of
2103: .Cm none
2104: causes
2105: .Xr ssh 1
1.378 jmc 2106: to ignore any user-specific known hosts files.
1.151 djm 2107: The default is
2108: .Pa ~/.ssh/known_hosts ,
2109: .Pa ~/.ssh/known_hosts2 .
1.8 jakob 2110: .It Cm VerifyHostKeyDNS
2111: Specifies whether to verify the remote key using DNS and SSHFP resource
2112: records.
1.24 jakob 2113: If this option is set to
1.240 jmc 2114: .Cm yes ,
1.25 jmc 2115: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 2116: from DNS.
2117: Insecure fingerprints will be handled as if this option was set to
1.240 jmc 2118: .Cm ask .
1.24 jakob 2119: If this option is set to
1.240 jmc 2120: .Cm ask ,
1.24 jakob 2121: information on fingerprint match will be displayed, but the user will still
2122: need to confirm new host keys according to the
2123: .Cm StrictHostKeyChecking
2124: option.
1.8 jakob 2125: The default is
1.240 jmc 2126: .Cm no .
1.84 jmc 2127: .Pp
1.240 jmc 2128: See also
2129: .Sx VERIFYING HOST KEYS
2130: in
1.84 jmc 2131: .Xr ssh 1 .
1.111 grunk 2132: .It Cm VisualHostKey
2133: If this flag is set to
1.240 jmc 2134: .Cm yes ,
1.111 grunk 2135: an ASCII art representation of the remote host key fingerprint is
1.197 djm 2136: printed in addition to the fingerprint string at login and
1.114 stevesk 2137: for unknown host keys.
1.111 grunk 2138: If this flag is set to
1.240 jmc 2139: .Cm no
2140: (the default),
1.114 stevesk 2141: no fingerprint strings are printed at login and
1.197 djm 2142: only the fingerprint string will be printed for unknown host keys.
1.1 stevesk 2143: .It Cm XAuthLocation
1.5 stevesk 2144: Specifies the full pathname of the
1.1 stevesk 2145: .Xr xauth 1
2146: program.
2147: The default is
2148: .Pa /usr/X11R6/bin/xauth .
2149: .El
1.86 jmc 2150: .Sh PATTERNS
2151: A
2152: .Em pattern
2153: consists of zero or more non-whitespace characters,
2154: .Sq *
2155: (a wildcard that matches zero or more characters),
2156: or
2157: .Sq ?\&
2158: (a wildcard that matches exactly one character).
2159: For example, to specify a set of declarations for any host in the
1.240 jmc 2160: .Qq .co.uk
1.86 jmc 2161: set of domains,
2162: the following pattern could be used:
2163: .Pp
2164: .Dl Host *.co.uk
2165: .Pp
2166: The following pattern
2167: would match any host in the 192.168.0.[0-9] network range:
2168: .Pp
2169: .Dl Host 192.168.0.?
2170: .Pp
2171: A
2172: .Em pattern-list
2173: is a comma-separated list of patterns.
2174: Patterns within pattern-lists may be negated
2175: by preceding them with an exclamation mark
2176: .Pq Sq !\& .
2177: For example,
1.174 djm 2178: to allow a key to be used from anywhere within an organization
1.86 jmc 2179: except from the
1.240 jmc 2180: .Qq dialup
1.86 jmc 2181: pool,
2182: the following entry (in authorized_keys) could be used:
2183: .Pp
2184: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.258 djm 2185: .Pp
2186: Note that a negated match will never produce a positive result by itself.
2187: For example, attempting to match
2188: .Qq host3
2189: against the following pattern-list will fail:
2190: .Pp
2191: .Dl from=\&"!host1,!host2\&"
2192: .Pp
2193: The solution here is to include a term that will yield a positive match,
2194: such as a wildcard:
2195: .Pp
2196: .Dl from=\&"!host1,!host2,*\&"
1.239 jmc 2197: .Sh TOKENS
2198: Arguments to some keywords can make use of tokens,
2199: which are expanded at runtime:
2200: .Pp
2201: .Bl -tag -width XXXX -offset indent -compact
2202: .It %%
2203: A literal
2204: .Sq % .
2205: .It \&%C
1.391 djm 2206: Hash of %l%h%p%r%j.
1.239 jmc 2207: .It %d
2208: Local user's home directory.
1.339 djm 2209: .It %f
2210: The fingerprint of the server's host key.
2211: .It %H
2212: The
2213: .Pa known_hosts
2214: hostname or address that is being searched for.
1.239 jmc 2215: .It %h
2216: The remote hostname.
1.340 jmc 2217: .It \%%I
1.339 djm 2218: A string describing the reason for a
2219: .Cm KnownHostsCommand
1.340 jmc 2220: execution: either
2221: .Cm ADDRESS
1.339 djm 2222: when looking up a host by address (only when
2223: .Cm CheckHostIP
2224: is enabled),
1.340 jmc 2225: .Cm HOSTNAME
2226: when searching by hostname, or
2227: .Cm ORDER
1.339 djm 2228: when preparing the host key algorithm preference list to use for the
2229: destination host.
1.239 jmc 2230: .It %i
2231: The local user ID.
1.391 djm 2232: .It %j
2233: The contents of the ProxyJump option, or the empty string if this
2234: option is unset.
1.339 djm 2235: .It %K
2236: The base64 encoded host key.
1.330 dtucker 2237: .It %k
1.350 jsg 2238: The host key alias if specified, otherwise the original remote hostname given
1.330 dtucker 2239: on the command line.
1.239 jmc 2240: .It %L
2241: The local hostname.
2242: .It %l
2243: The local hostname, including the domain name.
2244: .It %n
2245: The original remote hostname, as given on the command line.
2246: .It %p
2247: The remote port.
2248: .It %r
2249: The remote username.
1.261 djm 2250: .It \&%T
2251: The local
2252: .Xr tun 4
2253: or
2254: .Xr tap 4
2255: network interface assigned if
1.262 jmc 2256: tunnel forwarding was requested, or
2257: .Qq NONE
1.261 djm 2258: otherwise.
1.339 djm 2259: .It %t
2260: The type of the server host key, e.g.
1.360 jmc 2261: .Cm ssh-ed25519 .
1.239 jmc 2262: .It %u
2263: The local username.
2264: .El
2265: .Pp
1.323 dtucker 2266: .Cm CertificateFile ,
2267: .Cm ControlPath ,
2268: .Cm IdentityAgent ,
2269: .Cm IdentityFile ,
1.339 djm 2270: .Cm KnownHostsCommand ,
1.325 jmc 2271: .Cm LocalForward ,
1.324 dtucker 2272: .Cm Match exec ,
2273: .Cm RemoteCommand ,
1.329 dtucker 2274: .Cm RemoteForward ,
1.380 dtucker 2275: .Cm RevokedHostKeys ,
1.323 dtucker 2276: and
1.331 jmc 2277: .Cm UserKnownHostsFile
1.391 djm 2278: accept the tokens %%, %C, %d, %h, %i, %j, %k, %L, %l, %n, %p, %r, and %u.
1.239 jmc 2279: .Pp
1.339 djm 2280: .Cm KnownHostsCommand
2281: additionally accepts the tokens %f, %H, %I, %K and %t.
2282: .Pp
1.295 jmc 2283: .Cm Hostname
1.239 jmc 2284: accepts the tokens %% and %h.
2285: .Pp
2286: .Cm LocalCommand
1.323 dtucker 2287: accepts all tokens.
1.239 jmc 2288: .Pp
2289: .Cm ProxyCommand
1.372 dtucker 2290: and
2291: .Cm ProxyJump
2292: accept the tokens %%, %h, %n, %p, and %r.
1.387 djm 2293: .Pp
2294: Note that some of these directives build commands for execution via the shell.
2295: Because
2296: .Xr ssh 1
2297: performs no filtering or escaping of characters that have special meaning in
1.388 jmc 2298: shell commands (e.g. quotes), it is the user's responsibility to ensure that
1.387 djm 2299: the arguments passed to
2300: .Xr ssh 1
2301: do not contain such characters and that tokens are appropriately quoted
2302: when used.
1.326 dtucker 2303: .Sh ENVIRONMENT VARIABLES
2304: Arguments to some keywords can be expanded at runtime from environment
2305: variables on the client by enclosing them in
2306: .Ic ${} ,
2307: for example
2308: .Ic ${HOME}/.ssh
2309: would refer to the user's .ssh directory.
2310: If a specified environment variable does not exist then an error will be
2311: returned and the setting for that keyword will be ignored.
2312: .Pp
2313: The keywords
2314: .Cm CertificateFile ,
2315: .Cm ControlPath ,
1.329 dtucker 2316: .Cm IdentityAgent ,
1.352 jmc 2317: .Cm IdentityFile ,
1.339 djm 2318: .Cm KnownHostsCommand ,
1.326 dtucker 2319: and
1.329 dtucker 2320: .Cm UserKnownHostsFile
1.326 dtucker 2321: support environment variables.
2322: The keywords
2323: .Cm LocalForward
2324: and
2325: .Cm RemoteForward
2326: support environment variables only for Unix domain socket paths.
1.1 stevesk 2327: .Sh FILES
2328: .Bl -tag -width Ds
1.50 djm 2329: .It Pa ~/.ssh/config
1.1 stevesk 2330: This is the per-user configuration file.
2331: The format of this file is described above.
1.84 jmc 2332: This file is used by the SSH client.
1.30 djm 2333: Because of the potential for abuse, this file must have strict permissions:
1.290 jmc 2334: read/write for the user, and not writable by others.
1.1 stevesk 2335: .It Pa /etc/ssh/ssh_config
2336: Systemwide configuration file.
2337: This file provides defaults for those
2338: values that are not specified in the user's configuration file, and
2339: for those users who do not have a configuration file.
2340: This file must be world-readable.
2341: .El
1.13 jmc 2342: .Sh SEE ALSO
2343: .Xr ssh 1
1.1 stevesk 2344: .Sh AUTHORS
1.240 jmc 2345: .An -nosplit
1.1 stevesk 2346: OpenSSH is a derivative of the original and free
1.240 jmc 2347: ssh 1.2.12 release by
2348: .An Tatu Ylonen .
2349: .An Aaron Campbell , Bob Beck , Markus Friedl ,
2350: .An Niels Provos , Theo de Raadt
2351: and
2352: .An Dug Song
1.1 stevesk 2353: removed many bugs, re-added newer features and
2354: created OpenSSH.
1.240 jmc 2355: .An Markus Friedl
2356: contributed the support for SSH protocol versions 1.5 and 2.0.
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