Annotation of src/crypto/external/bsd/openssh/dist/sshd_config.5, Revision 1.25.2.2
1.25.2.2! pgoyette 1: .\" $NetBSD: sshd_config.5,v 1.27 2018/08/26 07:46:37 christos Exp $
1.1 christos 2: .\" -*- nroff -*-
3: .\"
4: .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
5: .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
6: .\" All rights reserved
7: .\"
8: .\" As far as I am concerned, the code I have written for this software
9: .\" can be used freely for any purpose. Any derived versions of this
10: .\" software must be clearly marked as such, and if the derived work is
11: .\" incompatible with the protocol description in the RFC file, it must be
12: .\" called by a name other than "ssh" or "Secure Shell".
13: .\"
14: .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
15: .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
16: .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
17: .\"
18: .\" Redistribution and use in source and binary forms, with or without
19: .\" modification, are permitted provided that the following conditions
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21: .\" 1. Redistributions of source code must retain the above copyright
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23: .\" 2. Redistributions in binary form must reproduce the above copyright
24: .\" notice, this list of conditions and the following disclaimer in the
25: .\" documentation and/or other materials provided with the distribution.
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27: .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
28: .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
29: .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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1.25.2.2! pgoyette 38: .\" $OpenBSD: sshd_config.5,v 1.281 2018/07/20 05:01:10 djm Exp $
! 39: .Dd July 20 2018
1.1 christos 40: .Dt SSHD_CONFIG 5
41: .Os
42: .Sh NAME
43: .Nm sshd_config
44: .Nd OpenSSH SSH daemon configuration file
45: .Sh DESCRIPTION
46: .Xr sshd 8
47: reads configuration data from
48: .Pa /etc/ssh/sshd_config
49: (or the file specified with
50: .Fl f
51: on the command line).
52: The file contains keyword-argument pairs, one per line.
1.25.2.1 pgoyette 53: For each keyword, the first obtained value will be used.
1.1 christos 54: Lines starting with
55: .Ql #
56: and empty lines are interpreted as comments.
57: Arguments may optionally be enclosed in double quotes
58: .Pq \&"
59: in order to represent arguments containing spaces.
60: .Pp
61: The possible
62: keywords and their meanings are as follows (note that
63: keywords are case-insensitive and arguments are case-sensitive):
64: .Bl -tag -width Ds
65: .It Cm AcceptEnv
66: Specifies what environment variables sent by the client will be copied into
67: the session's
68: .Xr environ 7 .
69: See
70: .Cm SendEnv
1.25.2.2! pgoyette 71: and
! 72: .Cm SetEnv
1.1 christos 73: in
74: .Xr ssh_config 5
75: for how to configure the client.
1.21 christos 76: The
1.18 christos 77: .Ev TERM
1.25.2.2! pgoyette 78: environment variable is always accepted whenever the client
1.18 christos 79: requests a pseudo-terminal as it is required by the protocol.
1.1 christos 80: Variables are specified by name, which may contain the wildcard characters
81: .Ql *
82: and
83: .Ql \&? .
84: Multiple environment variables may be separated by whitespace or spread
85: across multiple
86: .Cm AcceptEnv
87: directives.
88: Be warned that some environment variables could be used to bypass restricted
89: user environments.
90: For this reason, care should be taken in the use of this directive.
91: The default is not to accept any environment variables.
92: .It Cm AddressFamily
93: Specifies which address family should be used by
94: .Xr sshd 8 .
95: Valid arguments are
1.23 christos 96: .Cm any
97: (the default),
98: .Cm inet
1.1 christos 99: (use IPv4 only), or
1.23 christos 100: .Cm inet6
1.1 christos 101: (use IPv6 only).
102: .It Cm AllowAgentForwarding
103: Specifies whether
104: .Xr ssh-agent 1
105: forwarding is permitted.
106: The default is
1.23 christos 107: .Cm yes .
1.1 christos 108: Note that disabling agent forwarding does not improve security
109: unless users are also denied shell access, as they can always install
110: their own forwarders.
111: .It Cm AllowGroups
112: This keyword can be followed by a list of group name patterns, separated
113: by spaces.
114: If specified, login is allowed only for users whose primary
115: group or supplementary group list matches one of the patterns.
116: Only group names are valid; a numerical group ID is not recognized.
117: By default, login is allowed for all groups.
118: The allow/deny directives are processed in the following order:
119: .Cm DenyUsers ,
120: .Cm AllowUsers ,
121: .Cm DenyGroups ,
122: and finally
123: .Cm AllowGroups .
124: .Pp
1.15 christos 125: See PATTERNS in
1.1 christos 126: .Xr ssh_config 5
127: for more information on patterns.
1.23 christos 128: .It Cm AllowStreamLocalForwarding
129: Specifies whether StreamLocal (Unix-domain socket) forwarding is permitted.
1.14 christos 130: The available options are
1.23 christos 131: .Cm yes
132: (the default)
1.14 christos 133: or
1.23 christos 134: .Cm all
135: to allow StreamLocal forwarding,
136: .Cm no
137: to prevent all StreamLocal forwarding,
138: .Cm local
1.14 christos 139: to allow local (from the perspective of
140: .Xr ssh 1 )
141: forwarding only or
1.23 christos 142: .Cm remote
1.14 christos 143: to allow remote forwarding only.
1.23 christos 144: Note that disabling StreamLocal forwarding does not improve security unless
1.1 christos 145: users are also denied shell access, as they can always install their
146: own forwarders.
1.23 christos 147: .It Cm AllowTcpForwarding
148: Specifies whether TCP forwarding is permitted.
1.16 christos 149: The available options are
1.23 christos 150: .Cm yes
151: (the default)
1.16 christos 152: or
1.23 christos 153: .Cm all
154: to allow TCP forwarding,
155: .Cm no
156: to prevent all TCP forwarding,
157: .Cm local
1.16 christos 158: to allow local (from the perspective of
159: .Xr ssh 1 )
160: forwarding only or
1.23 christos 161: .Cm remote
1.16 christos 162: to allow remote forwarding only.
1.23 christos 163: Note that disabling TCP forwarding does not improve security unless
1.16 christos 164: users are also denied shell access, as they can always install their
165: own forwarders.
1.1 christos 166: .It Cm AllowUsers
167: This keyword can be followed by a list of user name patterns, separated
168: by spaces.
169: If specified, login is allowed only for user names that
170: match one of the patterns.
171: Only user names are valid; a numerical user ID is not recognized.
172: By default, login is allowed for all users.
173: If the pattern takes the form USER@HOST then USER and HOST
174: are separately checked, restricting logins to particular
175: users from particular hosts.
1.22 christos 176: HOST criteria may additionally contain addresses to match in CIDR
177: address/masklen format.
1.1 christos 178: The allow/deny directives are processed in the following order:
179: .Cm DenyUsers ,
180: .Cm AllowUsers ,
181: .Cm DenyGroups ,
182: and finally
183: .Cm AllowGroups .
184: .Pp
1.15 christos 185: See PATTERNS in
1.1 christos 186: .Xr ssh_config 5
187: for more information on patterns.
1.14 christos 188: .It Cm AuthenticationMethods
189: Specifies the authentication methods that must be successfully completed
190: for a user to be granted access.
1.25.2.2! pgoyette 191: This option must be followed by one or more lists of comma-separated
1.22 christos 192: authentication method names, or by the single string
1.23 christos 193: .Cm any
1.22 christos 194: to indicate the default behaviour of accepting any single authentication
195: method.
1.23 christos 196: If the default is overridden, then successful authentication requires
1.22 christos 197: completion of every method in at least one of these lists.
1.14 christos 198: .Pp
1.23 christos 199: For example,
200: .Qq publickey,password publickey,keyboard-interactive
1.14 christos 201: would require the user to complete public key authentication, followed by
202: either password or keyboard interactive authentication.
203: Only methods that are next in one or more lists are offered at each stage,
1.23 christos 204: so for this example it would not be possible to attempt password or
1.14 christos 205: keyboard-interactive authentication before public key.
206: .Pp
1.15 christos 207: For keyboard interactive authentication it is also possible to
208: restrict authentication to a specific device by appending a
209: colon followed by the device identifier
1.23 christos 210: .Cm bsdauth ,
211: .Cm pam ,
1.15 christos 212: or
1.23 christos 213: .Cm skey ,
1.15 christos 214: depending on the server configuration.
215: For example,
1.23 christos 216: .Qq keyboard-interactive:bsdauth
1.15 christos 217: would restrict keyboard interactive authentication to the
1.23 christos 218: .Cm bsdauth
1.15 christos 219: device.
220: .Pp
1.23 christos 221: If the publickey method is listed more than once,
1.17 christos 222: .Xr sshd 8
223: verifies that keys that have been used successfully are not reused for
224: subsequent authentications.
1.23 christos 225: For example,
226: .Qq publickey,publickey
227: requires successful authentication using two different public keys.
1.17 christos 228: .Pp
1.14 christos 229: Note that each authentication method listed should also be explicitly enabled
230: in the configuration.
1.25 christos 231: .Pp
232: The available authentication methods are:
233: .Qq gssapi-with-mic ,
234: .Qq hostbased ,
235: .Qq keyboard-interactive ,
236: .Qq none
237: (used for access to password-less accounts when
1.25.2.2! pgoyette 238: .Cm PermitEmptyPasswords
1.25 christos 239: is enabled),
240: .Qq password
241: and
242: .Qq publickey .
1.14 christos 243: .It Cm AuthorizedKeysCommand
244: Specifies a program to be used to look up the user's public keys.
1.18 christos 245: The program must be owned by root, not writable by group or others and
246: specified by an absolute path.
247: Arguments to
248: .Cm AuthorizedKeysCommand
1.23 christos 249: accept the tokens described in the
250: .Sx TOKENS
251: section.
252: If no arguments are specified then the username of the target user is used.
1.18 christos 253: .Pp
254: The program should produce on standard output zero or
1.23 christos 255: more lines of authorized_keys output (see
256: .Sx AUTHORIZED_KEYS
257: in
1.14 christos 258: .Xr sshd 8 ) .
1.23 christos 259: If a key supplied by
260: .Cm AuthorizedKeysCommand
261: does not successfully authenticate
1.14 christos 262: and authorize the user then public key authentication continues using the usual
263: .Cm AuthorizedKeysFile
264: files.
1.23 christos 265: By default, no
266: .Cm AuthorizedKeysCommand
267: is run.
1.14 christos 268: .It Cm AuthorizedKeysCommandUser
1.23 christos 269: Specifies the user under whose account the
270: .Cm AuthorizedKeysCommand
271: is run.
1.14 christos 272: It is recommended to use a dedicated user that has no other role on the host
273: than running authorized keys commands.
1.17 christos 274: If
275: .Cm AuthorizedKeysCommand
276: is specified but
277: .Cm AuthorizedKeysCommandUser
278: is not, then
279: .Xr sshd 8
280: will refuse to start.
1.1 christos 281: .It Cm AuthorizedKeysFile
1.23 christos 282: Specifies the file that contains the public keys used for user authentication.
1.6 adam 283: The format is described in the
1.23 christos 284: .Sx AUTHORIZED_KEYS FILE FORMAT
1.6 adam 285: section of
286: .Xr sshd 8 .
1.23 christos 287: Arguments to
1.1 christos 288: .Cm AuthorizedKeysFile
1.23 christos 289: accept the tokens described in the
290: .Sx TOKENS
291: section.
1.1 christos 292: After expansion,
293: .Cm AuthorizedKeysFile
294: is taken to be an absolute path or one relative to the user's home
295: directory.
1.11 christos 296: Multiple files may be listed, separated by whitespace.
1.21 christos 297: Alternately this option may be set to
1.23 christos 298: .Cm none
1.21 christos 299: to skip checking for user keys in files.
1.1 christos 300: The default is
1.23 christos 301: .Qq .ssh/authorized_keys .ssh/authorized_keys2 .
1.18 christos 302: .It Cm AuthorizedPrincipalsCommand
303: Specifies a program to be used to generate the list of allowed
304: certificate principals as per
305: .Cm AuthorizedPrincipalsFile .
306: The program must be owned by root, not writable by group or others and
307: specified by an absolute path.
308: Arguments to
309: .Cm AuthorizedPrincipalsCommand
1.23 christos 310: accept the tokens described in the
311: .Sx TOKENS
312: section.
313: If no arguments are specified then the username of the target user is used.
1.18 christos 314: .Pp
315: The program should produce on standard output zero or
316: more lines of
317: .Cm AuthorizedPrincipalsFile
318: output.
319: If either
320: .Cm AuthorizedPrincipalsCommand
321: or
322: .Cm AuthorizedPrincipalsFile
323: is specified, then certificates offered by the client for authentication
324: must contain a principal that is listed.
1.23 christos 325: By default, no
326: .Cm AuthorizedPrincipalsCommand
327: is run.
1.18 christos 328: .It Cm AuthorizedPrincipalsCommandUser
1.23 christos 329: Specifies the user under whose account the
330: .Cm AuthorizedPrincipalsCommand
331: is run.
1.18 christos 332: It is recommended to use a dedicated user that has no other role on the host
333: than running authorized principals commands.
334: If
335: .Cm AuthorizedPrincipalsCommand
336: is specified but
337: .Cm AuthorizedPrincipalsCommandUser
338: is not, then
339: .Xr sshd 8
340: will refuse to start.
1.6 adam 341: .It Cm AuthorizedPrincipalsFile
342: Specifies a file that lists principal names that are accepted for
343: certificate authentication.
344: When using certificates signed by a key listed in
345: .Cm TrustedUserCAKeys ,
346: this file lists names, one of which must appear in the certificate for it
347: to be accepted for authentication.
1.23 christos 348: Names are listed one per line preceded by key options (as described in
349: .Sx AUTHORIZED_KEYS FILE FORMAT
350: in
1.6 adam 351: .Xr sshd 8 ) .
352: Empty lines and comments starting with
353: .Ql #
354: are ignored.
355: .Pp
1.23 christos 356: Arguments to
1.6 adam 357: .Cm AuthorizedPrincipalsFile
1.23 christos 358: accept the tokens described in the
359: .Sx TOKENS
360: section.
1.6 adam 361: After expansion,
362: .Cm AuthorizedPrincipalsFile
1.23 christos 363: is taken to be an absolute path or one relative to the user's home directory.
1.13 christos 364: The default is
1.23 christos 365: .Cm none ,
1.13 christos 366: i.e. not to use a principals file \(en in this case, the username
1.6 adam 367: of the user must appear in a certificate's principals list for it to be
368: accepted.
1.23 christos 369: .Pp
1.6 adam 370: Note that
371: .Cm AuthorizedPrincipalsFile
372: is only used when authentication proceeds using a CA listed in
373: .Cm TrustedUserCAKeys
374: and is not consulted for certification authorities trusted via
375: .Pa ~/.ssh/authorized_keys ,
376: though the
377: .Cm principals=
378: key option offers a similar facility (see
379: .Xr sshd 8
380: for details).
1.1 christos 381: .It Cm Banner
382: The contents of the specified file are sent to the remote user before
383: authentication is allowed.
384: If the argument is
1.23 christos 385: .Cm none
1.1 christos 386: then no banner is displayed.
387: By default, no banner is displayed.
388: .It Cm ChallengeResponseAuthentication
389: Specifies whether challenge-response authentication is allowed.
390: All authentication styles from
391: .Xr login.conf 5
392: are supported.
393: The default is
1.23 christos 394: .Cm yes .
1.1 christos 395: .It Cm ChrootDirectory
1.6 adam 396: Specifies the pathname of a directory to
1.1 christos 397: .Xr chroot 2
398: to after authentication.
1.17 christos 399: At session startup
400: .Xr sshd 8
401: checks that all components of the pathname are root-owned directories
402: which are not writable by any other user or group.
1.3 christos 403: After the chroot,
404: .Xr sshd 8
405: changes the working directory to the user's home directory.
1.23 christos 406: Arguments to
407: .Cm ChrootDirectory
408: accept the tokens described in the
409: .Sx TOKENS
410: section.
1.1 christos 411: .Pp
412: The
413: .Cm ChrootDirectory
414: must contain the necessary files and directories to support the
1.3 christos 415: user's session.
1.1 christos 416: For an interactive session this requires at least a shell, typically
417: .Xr sh 1 ,
418: and basic
419: .Pa /dev
420: nodes such as
421: .Xr null 4 ,
422: .Xr zero 4 ,
423: .Xr stdin 4 ,
424: .Xr stdout 4 ,
425: .Xr stderr 4 ,
426: and
427: .Xr tty 4
428: devices.
1.23 christos 429: For file transfer sessions using SFTP
430: no additional configuration of the environment is necessary if the in-process
431: sftp-server is used,
1.16 christos 432: though sessions which use logging may require
1.3 christos 433: .Pa /dev/log
1.16 christos 434: inside the chroot directory on some operating systems (see
1.3 christos 435: .Xr sftp-server 8
1.1 christos 436: for details).
437: .Pp
1.17 christos 438: For safety, it is very important that the directory hierarchy be
439: prevented from modification by other processes on the system (especially
440: those outside the jail).
441: Misconfiguration can lead to unsafe environments which
442: .Xr sshd 8
443: cannot detect.
444: .Pp
1.21 christos 445: The default is
1.23 christos 446: .Cm none ,
1.21 christos 447: indicating not to
1.1 christos 448: .Xr chroot 2 .
449: .It Cm Ciphers
1.21 christos 450: Specifies the ciphers allowed.
1.1 christos 451: Multiple ciphers must be comma-separated.
1.19 christos 452: If the specified value begins with a
453: .Sq +
454: character, then the specified ciphers will be appended to the default set
455: instead of replacing them.
1.24 christos 456: If the specified value begins with a
457: .Sq -
458: character, then the specified ciphers (including wildcards) will be removed
459: from the default set instead of replacing them.
1.19 christos 460: .Pp
1.16 christos 461: The supported ciphers are:
462: .Pp
463: .Bl -item -compact -offset indent
464: .It
465: 3des-cbc
466: .It
467: aes128-cbc
468: .It
469: aes192-cbc
470: .It
471: aes256-cbc
472: .It
473: aes128-ctr
474: .It
475: aes192-ctr
476: .It
477: aes256-ctr
478: .It
479: aes128-gcm@openssh.com
480: .It
481: aes256-gcm@openssh.com
482: .It
483: chacha20-poly1305@openssh.com
484: .El
485: .Pp
1.1 christos 486: The default is:
1.16 christos 487: .Bd -literal -offset indent
1.20 christos 488: chacha20-poly1305@openssh.com,
1.16 christos 489: aes128-ctr,aes192-ctr,aes256-ctr,
1.20 christos 490: aes128-gcm@openssh.com,aes256-gcm@openssh.com
1.1 christos 491: .Ed
1.16 christos 492: .Pp
1.23 christos 493: The list of available ciphers may also be obtained using
494: .Qq ssh -Q cipher .
1.1 christos 495: .It Cm ClientAliveCountMax
1.23 christos 496: Sets the number of client alive messages which may be sent without
1.1 christos 497: .Xr sshd 8
498: receiving any messages back from the client.
499: If this threshold is reached while client alive messages are being sent,
500: sshd will disconnect the client, terminating the session.
501: It is important to note that the use of client alive messages is very
502: different from
1.23 christos 503: .Cm TCPKeepAlive .
1.1 christos 504: The client alive messages are sent through the encrypted channel
505: and therefore will not be spoofable.
506: The TCP keepalive option enabled by
507: .Cm TCPKeepAlive
508: is spoofable.
509: The client alive mechanism is valuable when the client or
510: server depend on knowing when a connection has become inactive.
511: .Pp
512: The default value is 3.
513: If
514: .Cm ClientAliveInterval
1.23 christos 515: is set to 15, and
1.1 christos 516: .Cm ClientAliveCountMax
517: is left at the default, unresponsive SSH clients
518: will be disconnected after approximately 45 seconds.
519: .It Cm ClientAliveInterval
520: Sets a timeout interval in seconds after which if no data has been received
521: from the client,
522: .Xr sshd 8
523: will send a message through the encrypted
524: channel to request a response from the client.
525: The default
526: is 0, indicating that these messages will not be sent to the client.
527: .It Cm Compression
1.23 christos 528: Specifies whether compression is enabled after
1.1 christos 529: the user has authenticated successfully.
530: The argument must be
1.23 christos 531: .Cm yes ,
532: .Cm delayed
533: (a legacy synonym for
534: .Cm yes )
1.1 christos 535: or
1.23 christos 536: .Cm no .
1.1 christos 537: The default is
1.23 christos 538: .Cm yes .
1.1 christos 539: .It Cm DenyGroups
540: This keyword can be followed by a list of group name patterns, separated
541: by spaces.
542: Login is disallowed for users whose primary group or supplementary
543: group list matches one of the patterns.
544: Only group names are valid; a numerical group ID is not recognized.
545: By default, login is allowed for all groups.
546: The allow/deny directives are processed in the following order:
547: .Cm DenyUsers ,
548: .Cm AllowUsers ,
549: .Cm DenyGroups ,
550: and finally
551: .Cm AllowGroups .
552: .Pp
1.15 christos 553: See PATTERNS in
1.1 christos 554: .Xr ssh_config 5
555: for more information on patterns.
556: .It Cm DenyUsers
557: This keyword can be followed by a list of user name patterns, separated
558: by spaces.
559: Login is disallowed for user names that match one of the patterns.
560: Only user names are valid; a numerical user ID is not recognized.
561: By default, login is allowed for all users.
562: If the pattern takes the form USER@HOST then USER and HOST
563: are separately checked, restricting logins to particular
564: users from particular hosts.
1.22 christos 565: HOST criteria may additionally contain addresses to match in CIDR
566: address/masklen format.
1.1 christos 567: The allow/deny directives are processed in the following order:
568: .Cm DenyUsers ,
569: .Cm AllowUsers ,
570: .Cm DenyGroups ,
571: and finally
572: .Cm AllowGroups .
573: .Pp
1.15 christos 574: See PATTERNS in
1.1 christos 575: .Xr ssh_config 5
576: for more information on patterns.
1.23 christos 577: .It Cm DisableForwarding
578: Disables all forwarding features, including X11,
579: .Xr ssh-agent 1 ,
580: TCP and StreamLocal.
581: This option overrides all other forwarding-related options and may
582: simplify restricted configurations.
1.25 christos 583: .It Cm ExposeAuthInfo
584: Writes a temporary file containing a list of authentication methods and
585: public credentials (e.g. keys) used to authenticate the user.
586: The location of the file is exposed to the user session through the
587: .Ev SSH_USER_AUTH
588: environment variable.
589: The default is
590: .Cm no .
1.17 christos 591: .It Cm FingerprintHash
592: Specifies the hash algorithm used when logging key fingerprints.
593: Valid options are:
1.23 christos 594: .Cm md5
1.17 christos 595: and
1.23 christos 596: .Cm sha256 .
1.17 christos 597: The default is
1.23 christos 598: .Cm sha256 .
1.1 christos 599: .It Cm ForceCommand
600: Forces the execution of the command specified by
601: .Cm ForceCommand ,
602: ignoring any command supplied by the client and
603: .Pa ~/.ssh/rc
604: if present.
605: The command is invoked by using the user's login shell with the -c option.
606: This applies to shell, command, or subsystem execution.
607: It is most useful inside a
608: .Cm Match
609: block.
610: The command originally supplied by the client is available in the
611: .Ev SSH_ORIGINAL_COMMAND
612: environment variable.
613: Specifying a command of
1.23 christos 614: .Cm internal-sftp
615: will force the use of an in-process SFTP server that requires no support
1.1 christos 616: files when used with
617: .Cm ChrootDirectory .
1.21 christos 618: The default is
1.23 christos 619: .Cm none .
1.1 christos 620: .It Cm GatewayPorts
621: Specifies whether remote hosts are allowed to connect to ports
622: forwarded for the client.
623: By default,
624: .Xr sshd 8
625: binds remote port forwardings to the loopback address.
626: This prevents other remote hosts from connecting to forwarded ports.
627: .Cm GatewayPorts
628: can be used to specify that sshd
629: should allow remote port forwardings to bind to non-loopback addresses, thus
630: allowing other hosts to connect.
631: The argument may be
1.23 christos 632: .Cm no
1.1 christos 633: to force remote port forwardings to be available to the local host only,
1.23 christos 634: .Cm yes
1.1 christos 635: to force remote port forwardings to bind to the wildcard address, or
1.23 christos 636: .Cm clientspecified
1.1 christos 637: to allow the client to select the address to which the forwarding is bound.
638: The default is
1.23 christos 639: .Cm no .
1.1 christos 640: .It Cm GSSAPIAuthentication
641: Specifies whether user authentication based on GSSAPI is allowed.
642: The default is
1.23 christos 643: .Cm no .
1.1 christos 644: .It Cm GSSAPICleanupCredentials
645: Specifies whether to automatically destroy the user's credentials cache
646: on logout.
647: The default is
1.23 christos 648: .Cm yes .
1.18 christos 649: .It Cm GSSAPIStrictAcceptorCheck
650: Determines whether to be strict about the identity of the GSSAPI acceptor
651: a client authenticates against.
652: If set to
1.23 christos 653: .Cm yes
654: then the client must authenticate against the host
1.18 christos 655: service on the current hostname.
656: If set to
1.23 christos 657: .Cm no
1.18 christos 658: then the client may authenticate against any service key stored in the
659: machine's default store.
660: This facility is provided to assist with operation on multi homed machines.
661: The default is
1.23 christos 662: .Cm yes .
1.17 christos 663: .It Cm HostbasedAcceptedKeyTypes
664: Specifies the key types that will be accepted for hostbased authentication
1.25.2.2! pgoyette 665: as a list of comma-separated patterns.
1.19 christos 666: Alternately if the specified value begins with a
667: .Sq +
668: character, then the specified key types will be appended to the default set
669: instead of replacing them.
1.24 christos 670: If the specified value begins with a
671: .Sq -
672: character, then the specified key types (including wildcards) will be removed
673: from the default set instead of replacing them.
1.19 christos 674: The default for this option is:
675: .Bd -literal -offset 3n
676: ecdsa-sha2-nistp256-cert-v01@openssh.com,
677: ecdsa-sha2-nistp384-cert-v01@openssh.com,
678: ecdsa-sha2-nistp521-cert-v01@openssh.com,
679: ssh-ed25519-cert-v01@openssh.com,
1.25.2.2! pgoyette 680: rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,
1.19 christos 681: ssh-rsa-cert-v01@openssh.com,
682: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.25.2.2! pgoyette 683: ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.19 christos 684: .Ed
685: .Pp
1.23 christos 686: The list of available key types may also be obtained using
687: .Qq ssh -Q key .
1.1 christos 688: .It Cm HostbasedAuthentication
689: Specifies whether rhosts or /etc/hosts.equiv authentication together
690: with successful public key client host authentication is allowed
691: (host-based authentication).
692: The default is
1.23 christos 693: .Cm no .
1.1 christos 694: .It Cm HostbasedUsesNameFromPacketOnly
695: Specifies whether or not the server will attempt to perform a reverse
696: name lookup when matching the name in the
697: .Pa ~/.shosts ,
698: .Pa ~/.rhosts ,
699: and
700: .Pa /etc/hosts.equiv
701: files during
702: .Cm HostbasedAuthentication .
703: A setting of
1.23 christos 704: .Cm yes
1.1 christos 705: means that
706: .Xr sshd 8
707: uses the name supplied by the client rather than
708: attempting to resolve the name from the TCP connection itself.
709: The default is
1.23 christos 710: .Cm no .
1.6 adam 711: .It Cm HostCertificate
712: Specifies a file containing a public host certificate.
713: The certificate's public key must match a private host key already specified
714: by
715: .Cm HostKey .
716: The default behaviour of
717: .Xr sshd 8
718: is not to load any certificates.
1.1 christos 719: .It Cm HostKey
720: Specifies a file containing a private host key
721: used by SSH.
1.23 christos 722: The defaults are
1.16 christos 723: .Pa /etc/ssh/ssh_host_ecdsa_key ,
724: .Pa /etc/ssh/ssh_host_ed25519_key
1.10 christos 725: and
1.23 christos 726: .Pa /etc/ssh/ssh_host_rsa_key .
1.19 christos 727: .Pp
1.1 christos 728: Note that
729: .Xr sshd 8
1.19 christos 730: will refuse to use a file if it is group/world-accessible
731: and that the
732: .Cm HostKeyAlgorithms
733: option restricts which of the keys are actually used by
734: .Xr sshd 8 .
735: .Pp
1.1 christos 736: It is possible to have multiple host key files.
1.15 christos 737: It is also possible to specify public host key files instead.
738: In this case operations on the private key will be delegated
739: to an
740: .Xr ssh-agent 1 .
741: .It Cm HostKeyAgent
742: Identifies the UNIX-domain socket used to communicate
743: with an agent that has access to the private host keys.
1.22 christos 744: If the string
1.23 christos 745: .Qq SSH_AUTH_SOCK
1.15 christos 746: is specified, the location of the socket will be read from the
747: .Ev SSH_AUTH_SOCK
748: environment variable.
1.19 christos 749: .It Cm HostKeyAlgorithms
1.21 christos 750: Specifies the host key algorithms
1.19 christos 751: that the server offers.
752: The default for this option is:
753: .Bd -literal -offset 3n
754: ecdsa-sha2-nistp256-cert-v01@openssh.com,
755: ecdsa-sha2-nistp384-cert-v01@openssh.com,
756: ecdsa-sha2-nistp521-cert-v01@openssh.com,
757: ssh-ed25519-cert-v01@openssh.com,
1.25.2.2! pgoyette 758: rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,
1.19 christos 759: ssh-rsa-cert-v01@openssh.com,
760: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.25.2.2! pgoyette 761: ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.19 christos 762: .Ed
763: .Pp
1.23 christos 764: The list of available key types may also be obtained using
765: .Qq ssh -Q key .
1.1 christos 766: .It Cm IgnoreRhosts
767: Specifies that
768: .Pa .rhosts
769: and
770: .Pa .shosts
771: files will not be used in
772: .Cm HostbasedAuthentication .
773: .Pp
774: .Pa /etc/hosts.equiv
775: and
776: .Pa /etc/shosts.equiv
777: are still used.
778: The default is
1.23 christos 779: .Cm yes .
1.1 christos 780: .It Cm IgnoreUserKnownHosts
781: Specifies whether
782: .Xr sshd 8
783: should ignore the user's
784: .Pa ~/.ssh/known_hosts
785: during
1.25.2.1 pgoyette 786: .Cm HostbasedAuthentication
787: and use only the system-wide known hosts file
788: .Pa /etc/ssh/known_hosts .
1.1 christos 789: The default is
1.23 christos 790: .Cm no .
1.10 christos 791: .It Cm IPQoS
792: Specifies the IPv4 type-of-service or DSCP class for the connection.
793: Accepted values are
1.23 christos 794: .Cm af11 ,
795: .Cm af12 ,
796: .Cm af13 ,
797: .Cm af21 ,
798: .Cm af22 ,
799: .Cm af23 ,
800: .Cm af31 ,
801: .Cm af32 ,
802: .Cm af33 ,
803: .Cm af41 ,
804: .Cm af42 ,
805: .Cm af43 ,
806: .Cm cs0 ,
807: .Cm cs1 ,
808: .Cm cs2 ,
809: .Cm cs3 ,
810: .Cm cs4 ,
811: .Cm cs5 ,
812: .Cm cs6 ,
813: .Cm cs7 ,
814: .Cm ef ,
815: .Cm lowdelay ,
816: .Cm throughput ,
817: .Cm reliability ,
1.25 christos 818: a numeric value, or
819: .Cm none
820: to use the operating system default.
1.10 christos 821: This option may take one or two arguments, separated by whitespace.
822: If one argument is specified, it is used as the packet class unconditionally.
823: If two values are specified, the first is automatically selected for
824: interactive sessions and the second for non-interactive sessions.
825: The default is
1.25.2.2! pgoyette 826: .Cm af21
! 827: (Low-Latency Data)
1.10 christos 828: for interactive sessions and
1.25.2.2! pgoyette 829: .Cm cs1
! 830: (Lower Effort)
1.10 christos 831: for non-interactive sessions.
1.16 christos 832: .It Cm KbdInteractiveAuthentication
833: Specifies whether to allow keyboard-interactive authentication.
834: The argument to this keyword must be
1.23 christos 835: .Cm yes
1.16 christos 836: or
1.23 christos 837: .Cm no .
1.16 christos 838: The default is to use whatever value
839: .Cm ChallengeResponseAuthentication
840: is set to
841: (by default
1.23 christos 842: .Cm yes ) .
1.1 christos 843: .It Cm KerberosAuthentication
844: Specifies whether the password provided by the user for
845: .Cm PasswordAuthentication
846: will be validated through the Kerberos KDC.
847: To use this option, the server needs a
848: Kerberos servtab which allows the verification of the KDC's identity.
849: The default is
1.23 christos 850: .Cm no .
1.1 christos 851: .It Cm KerberosGetAFSToken
852: If AFS is active and the user has a Kerberos 5 TGT, attempt to acquire
853: an AFS token before accessing the user's home directory.
854: The default is
1.23 christos 855: .Cm no .
1.1 christos 856: .It Cm KerberosOrLocalPasswd
857: If password authentication through Kerberos fails then
858: the password will be validated via any additional local mechanism
859: such as
860: .Pa /etc/passwd .
861: The default is
1.23 christos 862: .Cm yes .
1.1 christos 863: .It Cm KerberosTicketCleanup
864: Specifies whether to automatically destroy the user's ticket cache
865: file on logout.
866: The default is
1.23 christos 867: .Cm yes .
1.10 christos 868: .It Cm KexAlgorithms
869: Specifies the available KEX (Key Exchange) algorithms.
870: Multiple algorithms must be comma-separated.
1.19 christos 871: Alternately if the specified value begins with a
872: .Sq +
873: character, then the specified methods will be appended to the default set
874: instead of replacing them.
1.24 christos 875: If the specified value begins with a
876: .Sq -
877: character, then the specified methods (including wildcards) will be removed
878: from the default set instead of replacing them.
1.16 christos 879: The supported algorithms are:
880: .Pp
881: .Bl -item -compact -offset indent
882: .It
1.23 christos 883: curve25519-sha256
884: .It
1.16 christos 885: curve25519-sha256@libssh.org
886: .It
887: diffie-hellman-group1-sha1
888: .It
889: diffie-hellman-group14-sha1
890: .It
1.25.2.1 pgoyette 891: diffie-hellman-group14-sha256
892: .It
893: diffie-hellman-group16-sha512
894: .It
895: diffie-hellman-group18-sha512
896: .It
1.16 christos 897: diffie-hellman-group-exchange-sha1
898: .It
899: diffie-hellman-group-exchange-sha256
900: .It
901: ecdh-sha2-nistp256
902: .It
903: ecdh-sha2-nistp384
904: .It
905: ecdh-sha2-nistp521
906: .El
907: .Pp
908: The default is:
909: .Bd -literal -offset indent
1.23 christos 910: curve25519-sha256,curve25519-sha256@libssh.org,
1.16 christos 911: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
912: diffie-hellman-group-exchange-sha256,
1.25.2.1 pgoyette 913: diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,
914: diffie-hellman-group14-sha256,diffie-hellman-group14-sha1
1.16 christos 915: .Ed
1.17 christos 916: .Pp
1.23 christos 917: The list of available key exchange algorithms may also be obtained using
918: .Qq ssh -Q kex .
1.1 christos 919: .It Cm ListenAddress
920: Specifies the local addresses
921: .Xr sshd 8
922: should listen on.
923: The following forms may be used:
924: .Pp
925: .Bl -item -offset indent -compact
926: .It
927: .Cm ListenAddress
928: .Sm off
1.25.2.1 pgoyette 929: .Ar hostname | address
930: .Sm on
931: .Op Cm rdomain Ar domain
932: .It
933: .Cm ListenAddress
934: .Sm off
935: .Ar hostname : port
1.1 christos 936: .Sm on
1.25.2.1 pgoyette 937: .Op Cm rdomain Ar domain
1.1 christos 938: .It
939: .Cm ListenAddress
940: .Sm off
1.25.2.1 pgoyette 941: .Ar IPv4_address : port
1.1 christos 942: .Sm on
1.25.2.1 pgoyette 943: .Op Cm rdomain Ar domain
1.1 christos 944: .It
945: .Cm ListenAddress
946: .Sm off
1.25.2.1 pgoyette 947: .Oo Ar hostname | address Oc : Ar port
1.1 christos 948: .Sm on
1.25.2.1 pgoyette 949: .Op Cm rdomain Ar domain
1.1 christos 950: .El
951: .Pp
1.25.2.1 pgoyette 952: The optional
953: .Cm rdomain
954: qualifier requests
955: .Xr sshd 8
956: listen in an explicit routing domain.
1.1 christos 957: If
958: .Ar port
959: is not specified,
1.18 christos 960: sshd will listen on the address and all
1.1 christos 961: .Cm Port
962: options specified.
1.25.2.1 pgoyette 963: The default is to listen on all local addresses on the current default
964: routing domain.
1.1 christos 965: Multiple
966: .Cm ListenAddress
967: options are permitted.
1.25.2.1 pgoyette 968: For more information on routing domains, see
969: .Xr rdomain 4 .
1.1 christos 970: .It Cm LoginGraceTime
971: The server disconnects after this time if the user has not
972: successfully logged in.
973: If the value is 0, there is no time limit.
1.8 enami 974: The default is 120 seconds but the default
975: .Pa /etc/ssh/sshd_config
976: overwrites it to 600 seconds.
1.1 christos 977: .It Cm LogLevel
978: Gives the verbosity level that is used when logging messages from
979: .Xr sshd 8 .
980: The possible values are:
981: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
982: The default is INFO.
983: DEBUG and DEBUG1 are equivalent.
984: DEBUG2 and DEBUG3 each specify higher levels of debugging output.
985: Logging with a DEBUG level violates the privacy of users and is not recommended.
986: .It Cm MACs
987: Specifies the available MAC (message authentication code) algorithms.
1.21 christos 988: The MAC algorithm is used for data integrity protection.
1.1 christos 989: Multiple algorithms must be comma-separated.
1.19 christos 990: If the specified value begins with a
991: .Sq +
992: character, then the specified algorithms will be appended to the default set
993: instead of replacing them.
1.24 christos 994: If the specified value begins with a
995: .Sq -
996: character, then the specified algorithms (including wildcards) will be removed
997: from the default set instead of replacing them.
1.19 christos 998: .Pp
1.14 christos 999: The algorithms that contain
1.23 christos 1000: .Qq -etm
1.14 christos 1001: calculate the MAC after encryption (encrypt-then-mac).
1002: These are considered safer and their use recommended.
1.16 christos 1003: The supported MACs are:
1004: .Pp
1005: .Bl -item -compact -offset indent
1006: .It
1007: hmac-md5
1008: .It
1009: hmac-md5-96
1010: .It
1011: hmac-sha1
1012: .It
1013: hmac-sha1-96
1014: .It
1015: hmac-sha2-256
1016: .It
1017: hmac-sha2-512
1018: .It
1019: umac-64@openssh.com
1020: .It
1021: umac-128@openssh.com
1022: .It
1023: hmac-md5-etm@openssh.com
1024: .It
1025: hmac-md5-96-etm@openssh.com
1026: .It
1027: hmac-sha1-etm@openssh.com
1028: .It
1029: hmac-sha1-96-etm@openssh.com
1030: .It
1031: hmac-sha2-256-etm@openssh.com
1032: .It
1033: hmac-sha2-512-etm@openssh.com
1034: .It
1035: umac-64-etm@openssh.com
1036: .It
1037: umac-128-etm@openssh.com
1038: .El
1039: .Pp
1.1 christos 1040: The default is:
1041: .Bd -literal -offset indent
1.14 christos 1042: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
1043: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
1.21 christos 1044: hmac-sha1-etm@openssh.com,
1.16 christos 1045: umac-64@openssh.com,umac-128@openssh.com,
1.21 christos 1046: hmac-sha2-256,hmac-sha2-512,hmac-sha1
1.1 christos 1047: .Ed
1.17 christos 1048: .Pp
1.23 christos 1049: The list of available MAC algorithms may also be obtained using
1050: .Qq ssh -Q mac .
1.1 christos 1051: .It Cm Match
1052: Introduces a conditional block.
1053: If all of the criteria on the
1054: .Cm Match
1055: line are satisfied, the keywords on the following lines override those
1056: set in the global section of the config file, until either another
1057: .Cm Match
1058: line or the end of the file.
1.16 christos 1059: If a keyword appears in multiple
1060: .Cm Match
1.17 christos 1061: blocks that are satisfied, only the first instance of the keyword is
1.16 christos 1062: applied.
1.1 christos 1063: .Pp
1064: The arguments to
1065: .Cm Match
1.16 christos 1066: are one or more criteria-pattern pairs or the single token
1067: .Cm All
1068: which matches all criteria.
1.1 christos 1069: The available criteria are
1070: .Cm User ,
1071: .Cm Group ,
1072: .Cm Host ,
1.13 christos 1073: .Cm LocalAddress ,
1074: .Cm LocalPort ,
1.25.2.1 pgoyette 1075: .Cm RDomain ,
1.1 christos 1076: and
1.25.2.1 pgoyette 1077: .Cm Address
1078: (with
1079: .Cm RDomain
1080: representing the
1081: .Xr rdomain 4
1082: on which the connection was received.)
1083: .Pp
1.1 christos 1084: The match patterns may consist of single entries or comma-separated
1085: lists and may use the wildcard and negation operators described in the
1.23 christos 1086: .Sx PATTERNS
1087: section of
1.1 christos 1088: .Xr ssh_config 5 .
1089: .Pp
1090: The patterns in an
1091: .Cm Address
1092: criteria may additionally contain addresses to match in CIDR
1.23 christos 1093: address/masklen format,
1094: such as 192.0.2.0/24 or 2001:db8::/32.
1.1 christos 1095: Note that the mask length provided must be consistent with the address -
1096: it is an error to specify a mask length that is too long for the address
1097: or one with bits set in this host portion of the address.
1.23 christos 1098: For example, 192.0.2.0/33 and 192.0.2.0/8, respectively.
1.1 christos 1099: .Pp
1100: Only a subset of keywords may be used on the lines following a
1101: .Cm Match
1102: keyword.
1103: Available keywords are
1.13 christos 1104: .Cm AcceptEnv ,
1.1 christos 1105: .Cm AllowAgentForwarding ,
1.13 christos 1106: .Cm AllowGroups ,
1.17 christos 1107: .Cm AllowStreamLocalForwarding ,
1.1 christos 1108: .Cm AllowTcpForwarding ,
1.13 christos 1109: .Cm AllowUsers ,
1.14 christos 1110: .Cm AuthenticationMethods ,
1111: .Cm AuthorizedKeysCommand ,
1112: .Cm AuthorizedKeysCommandUser ,
1.6 adam 1113: .Cm AuthorizedKeysFile ,
1.21 christos 1114: .Cm AuthorizedPrincipalsCommand ,
1115: .Cm AuthorizedPrincipalsCommandUser ,
1.6 adam 1116: .Cm AuthorizedPrincipalsFile ,
1.1 christos 1117: .Cm Banner ,
1118: .Cm ChrootDirectory ,
1.23 christos 1119: .Cm ClientAliveCountMax ,
1120: .Cm ClientAliveInterval ,
1.13 christos 1121: .Cm DenyGroups ,
1122: .Cm DenyUsers ,
1.1 christos 1123: .Cm ForceCommand ,
1124: .Cm GatewayPorts ,
1125: .Cm GSSAPIAuthentication ,
1.17 christos 1126: .Cm HostbasedAcceptedKeyTypes ,
1.1 christos 1127: .Cm HostbasedAuthentication ,
1.6 adam 1128: .Cm HostbasedUsesNameFromPacketOnly ,
1.17 christos 1129: .Cm IPQoS ,
1.1 christos 1130: .Cm KbdInteractiveAuthentication ,
1131: .Cm KerberosAuthentication ,
1.25 christos 1132: .Cm LogLevel ,
1.1 christos 1133: .Cm MaxAuthTries ,
1134: .Cm MaxSessions ,
1135: .Cm PasswordAuthentication ,
1136: .Cm PermitEmptyPasswords ,
1.25.2.2! pgoyette 1137: .Cm PermitListen ,
1.1 christos 1138: .Cm PermitOpen ,
1139: .Cm PermitRootLogin ,
1.16 christos 1140: .Cm PermitTTY ,
1.6 adam 1141: .Cm PermitTunnel ,
1.16 christos 1142: .Cm PermitUserRC ,
1.17 christos 1143: .Cm PubkeyAcceptedKeyTypes ,
1.6 adam 1144: .Cm PubkeyAuthentication ,
1.15 christos 1145: .Cm RekeyLimit ,
1.17 christos 1146: .Cm RevokedKeys ,
1.25.2.1 pgoyette 1147: .Cm RDomain ,
1.25.2.2! pgoyette 1148: .Cm SetEnv ,
1.17 christos 1149: .Cm StreamLocalBindMask ,
1150: .Cm StreamLocalBindUnlink ,
1151: .Cm TrustedUserCAKeys ,
1.1 christos 1152: .Cm X11DisplayOffset ,
1153: .Cm X11Forwarding
1154: and
1155: .Cm X11UseLocalHost .
1156: .It Cm MaxAuthTries
1157: Specifies the maximum number of authentication attempts permitted per
1158: connection.
1159: Once the number of failures reaches half this value,
1160: additional failures are logged.
1161: The default is 6.
1162: .It Cm MaxSessions
1.21 christos 1163: Specifies the maximum number of open shell, login or subsystem (e.g. sftp)
1164: sessions permitted per network connection.
1165: Multiple sessions may be established by clients that support connection
1166: multiplexing.
1167: Setting
1168: .Cm MaxSessions
1169: to 1 will effectively disable session multiplexing, whereas setting it to 0
1170: will prevent all shell, login and subsystem sessions while still permitting
1171: forwarding.
1.1 christos 1172: The default is 10.
1173: .It Cm MaxStartups
1174: Specifies the maximum number of concurrent unauthenticated connections to the
1175: SSH daemon.
1176: Additional connections will be dropped until authentication succeeds or the
1177: .Cm LoginGraceTime
1178: expires for a connection.
1.14 christos 1179: The default is 10:30:100.
1.1 christos 1180: .Pp
1181: Alternatively, random early drop can be enabled by specifying
1182: the three colon separated values
1.23 christos 1183: start:rate:full (e.g. "10:30:60").
1.1 christos 1184: .Xr sshd 8
1.23 christos 1185: will refuse connection attempts with a probability of rate/100 (30%)
1186: if there are currently start (10) unauthenticated connections.
1.1 christos 1187: The probability increases linearly and all connection attempts
1.23 christos 1188: are refused if the number of unauthenticated connections reaches full (60).
1.1 christos 1189: .It Cm PasswordAuthentication
1190: Specifies whether password authentication is allowed.
1191: The default is
1.23 christos 1192: .Cm yes .
1.1 christos 1193: .It Cm PermitEmptyPasswords
1194: When password authentication is allowed, it specifies whether the
1195: server allows login to accounts with empty password strings.
1196: The default is
1.23 christos 1197: .Cm no .
1.25.2.2! pgoyette 1198: .It Cm PermitListen
! 1199: Specifies the addresses/ports on which a remote TCP port forwarding may listen.
! 1200: The listen specification must be one of the following forms:
! 1201: .Pp
! 1202: .Bl -item -offset indent -compact
! 1203: .It
! 1204: .Cm PermitListen
! 1205: .Sm off
! 1206: .Ar port
! 1207: .Sm on
! 1208: .It
! 1209: .Cm PermitListen
! 1210: .Sm off
! 1211: .Ar host : port
! 1212: .Sm on
! 1213: .El
! 1214: .Pp
! 1215: Multiple permissions may be specified by separating them with whitespace.
! 1216: An argument of
! 1217: .Cm any
! 1218: can be used to remove all restrictions and permit any listen requests.
! 1219: An argument of
! 1220: .Cm none
! 1221: can be used to prohibit all listen requests.
! 1222: The host name may contain wildcards as described in the PATTERNS section in
! 1223: .Xr ssh_config 5 .
! 1224: The wildcard
! 1225: .Sq *
! 1226: can also be used in place of a port number to allow all ports.
! 1227: By default all port forwarding listen requests are permitted.
! 1228: Note that the
! 1229: .Cm GatewayPorts
! 1230: option may further restrict which addresses may be listened on.
! 1231: Note also that
! 1232: .Xr ssh 1
! 1233: will request a listen host of
! 1234: .Dq localhost
! 1235: if no listen host was specifically requested, and this this name is
! 1236: treated differently to explicit localhost addresses of
! 1237: .Dq 127.0.0.1
! 1238: and
! 1239: .Dq ::1 .
1.1 christos 1240: .It Cm PermitOpen
1241: Specifies the destinations to which TCP port forwarding is permitted.
1242: The forwarding specification must be one of the following forms:
1243: .Pp
1244: .Bl -item -offset indent -compact
1245: .It
1246: .Cm PermitOpen
1247: .Sm off
1248: .Ar host : port
1249: .Sm on
1250: .It
1251: .Cm PermitOpen
1252: .Sm off
1253: .Ar IPv4_addr : port
1254: .Sm on
1255: .It
1256: .Cm PermitOpen
1257: .Sm off
1258: .Ar \&[ IPv6_addr \&] : port
1259: .Sm on
1260: .El
1261: .Pp
1262: Multiple forwards may be specified by separating them with whitespace.
1263: An argument of
1.23 christos 1264: .Cm any
1.1 christos 1265: can be used to remove all restrictions and permit any forwarding requests.
1.13 christos 1266: An argument of
1.23 christos 1267: .Cm none
1.13 christos 1268: can be used to prohibit all forwarding requests.
1.22 christos 1269: The wildcard
1.23 christos 1270: .Sq *
1.22 christos 1271: can be used for host or port to allow all hosts or ports, respectively.
1.1 christos 1272: By default all port forwarding requests are permitted.
1273: .It Cm PermitRootLogin
1274: Specifies whether root can log in using
1275: .Xr ssh 1 .
1276: The argument must be
1.23 christos 1277: .Cm yes ,
1278: .Cm prohibit-password ,
1279: .Cm forced-commands-only ,
1.1 christos 1280: or
1.23 christos 1281: .Cm no .
1.1 christos 1282: The default is
1.23 christos 1283: .Cm prohibit-password .
1.1 christos 1284: .Pp
1285: If this option is set to
1.23 christos 1286: .Cm prohibit-password
1.25.2.1 pgoyette 1287: (or its deprecated alias,
1288: .Cm without-password ) ,
1.19 christos 1289: password and keyboard-interactive authentication are disabled for root.
1.1 christos 1290: .Pp
1291: If this option is set to
1.23 christos 1292: .Cm forced-commands-only ,
1.1 christos 1293: root login with public key authentication will be allowed,
1294: but only if the
1295: .Ar command
1296: option has been specified
1297: (which may be useful for taking remote backups even if root login is
1298: normally not allowed).
1299: All other authentication methods are disabled for root.
1300: .Pp
1301: If this option is set to
1.23 christos 1302: .Cm no ,
1.1 christos 1303: root is not allowed to log in.
1.23 christos 1304: .It Cm PermitTTY
1305: Specifies whether
1306: .Xr pty 4
1307: allocation is permitted.
1308: The default is
1309: .Cm yes .
1.1 christos 1310: .It Cm PermitTunnel
1311: Specifies whether
1312: .Xr tun 4
1313: device forwarding is allowed.
1314: The argument must be
1.23 christos 1315: .Cm yes ,
1316: .Cm point-to-point
1.1 christos 1317: (layer 3),
1.23 christos 1318: .Cm ethernet
1.1 christos 1319: (layer 2), or
1.23 christos 1320: .Cm no .
1.1 christos 1321: Specifying
1.23 christos 1322: .Cm yes
1.1 christos 1323: permits both
1.23 christos 1324: .Cm point-to-point
1.1 christos 1325: and
1.23 christos 1326: .Cm ethernet .
1.1 christos 1327: The default is
1.23 christos 1328: .Cm no .
1.17 christos 1329: .Pp
1330: Independent of this setting, the permissions of the selected
1331: .Xr tun 4
1332: device must allow access to the user.
1.1 christos 1333: .It Cm PermitUserEnvironment
1334: Specifies whether
1335: .Pa ~/.ssh/environment
1336: and
1337: .Cm environment=
1338: options in
1339: .Pa ~/.ssh/authorized_keys
1340: are processed by
1341: .Xr sshd 8 .
1.25.2.2! pgoyette 1342: Valid options are
! 1343: .Cm yes ,
! 1344: .Cm no
! 1345: or a pattern-list specifying which environment variable names to accept
! 1346: (for example
! 1347: .Qq LANG,LC_* ) .
1.1 christos 1348: The default is
1.23 christos 1349: .Cm no .
1.1 christos 1350: Enabling environment processing may enable users to bypass access
1351: restrictions in some configurations using mechanisms such as
1352: .Ev LD_PRELOAD .
1.16 christos 1353: .It Cm PermitUserRC
1354: Specifies whether any
1355: .Pa ~/.ssh/rc
1356: file is executed.
1357: The default is
1.23 christos 1358: .Cm yes .
1.1 christos 1359: .It Cm PidFile
1360: Specifies the file that contains the process ID of the
1.18 christos 1361: SSH daemon, or
1.23 christos 1362: .Cm none
1.18 christos 1363: to not write one.
1.1 christos 1364: The default is
1365: .Pa /var/run/sshd.pid .
1366: .It Cm Port
1367: Specifies the port number that
1368: .Xr sshd 8
1369: listens on.
1370: The default is 22.
1371: Multiple options of this type are permitted.
1372: See also
1373: .Cm ListenAddress .
1374: .It Cm PrintLastLog
1375: Specifies whether
1376: .Xr sshd 8
1377: should print the date and time of the last user login when a user logs
1378: in interactively.
1379: The default is
1.23 christos 1380: .Cm yes .
1.1 christos 1381: .It Cm PrintMotd
1382: Specifies whether
1383: .Xr sshd 8
1384: should print
1385: .Pa /etc/motd
1386: when a user logs in interactively.
1387: (On some systems it is also printed by the shell,
1388: .Pa /etc/profile ,
1389: or equivalent.)
1390: The default is
1.23 christos 1391: .Cm yes .
1.17 christos 1392: .It Cm PubkeyAcceptedKeyTypes
1393: Specifies the key types that will be accepted for public key authentication
1.25.2.2! pgoyette 1394: as a list of comma-separated patterns.
1.19 christos 1395: Alternately if the specified value begins with a
1396: .Sq +
1397: character, then the specified key types will be appended to the default set
1398: instead of replacing them.
1.24 christos 1399: If the specified value begins with a
1400: .Sq -
1401: character, then the specified key types (including wildcards) will be removed
1402: from the default set instead of replacing them.
1.19 christos 1403: The default for this option is:
1404: .Bd -literal -offset 3n
1405: ecdsa-sha2-nistp256-cert-v01@openssh.com,
1406: ecdsa-sha2-nistp384-cert-v01@openssh.com,
1407: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1408: ssh-ed25519-cert-v01@openssh.com,
1.25.2.2! pgoyette 1409: rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,
1.19 christos 1410: ssh-rsa-cert-v01@openssh.com,
1411: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.25.2.2! pgoyette 1412: ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.19 christos 1413: .Ed
1414: .Pp
1.23 christos 1415: The list of available key types may also be obtained using
1416: .Qq ssh -Q key .
1.1 christos 1417: .It Cm PubkeyAuthentication
1418: Specifies whether public key authentication is allowed.
1419: The default is
1.23 christos 1420: .Cm yes .
1.15 christos 1421: .It Cm RekeyLimit
1422: Specifies the maximum amount of data that may be transmitted before the
1423: session key is renegotiated, optionally followed a maximum amount of
1424: time that may pass before the session key is renegotiated.
1425: The first argument is specified in bytes and may have a suffix of
1426: .Sq K ,
1427: .Sq M ,
1428: or
1429: .Sq G
1430: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1431: The default is between
1432: .Sq 1G
1433: and
1434: .Sq 4G ,
1435: depending on the cipher.
1436: The optional second value is specified in seconds and may use any of the
1437: units documented in the
1438: .Sx TIME FORMATS
1439: section.
1440: The default value for
1441: .Cm RekeyLimit
1442: is
1.23 christos 1443: .Cm default none ,
1.15 christos 1444: which means that rekeying is performed after the cipher's default amount
1445: of data has been sent or received and no time based rekeying is done.
1.6 adam 1446: .It Cm RevokedKeys
1.18 christos 1447: Specifies revoked public keys file, or
1.23 christos 1448: .Cm none
1.18 christos 1449: to not use one.
1.6 adam 1450: Keys listed in this file will be refused for public key authentication.
1451: Note that if this file is not readable, then public key authentication will
1452: be refused for all users.
1.14 christos 1453: Keys may be specified as a text file, listing one public key per line, or as
1454: an OpenSSH Key Revocation List (KRL) as generated by
1455: .Xr ssh-keygen 1 .
1.15 christos 1456: For more information on KRLs, see the KEY REVOCATION LISTS section in
1.14 christos 1457: .Xr ssh-keygen 1 .
1.25.2.1 pgoyette 1458: .It Cm RDomain
1459: Specifies an explicit routing domain that is applied after authentication
1460: has completed.
1461: The user session, as well and any forwarded or listening IP sockets,
1462: will be bound to this
1463: .Xr rdomain 4 .
1464: If the routing domain is set to
1465: .Cm \&%D ,
1466: then the domain in which the incoming connection was received will be applied.
1.25.2.2! pgoyette 1467: .It Cm SetEnv
! 1468: Specifies one or more environment variables to set in child sessions started
! 1469: by
! 1470: .Xr sshd 8
! 1471: as
! 1472: .Dq NAME=VALUE .
! 1473: The environment value may be quoted (e.g. if it contains whitespace
! 1474: characters).
! 1475: Environment variables set by
! 1476: .Cm SetEnv
! 1477: override the default environment and any variables specified by the user
! 1478: via
! 1479: .Cm AcceptEnv
! 1480: or
! 1481: .Cm PermitUserEnvironment .
1.16 christos 1482: .It Cm StreamLocalBindMask
1483: Sets the octal file creation mode mask
1484: .Pq umask
1485: used when creating a Unix-domain socket file for local or remote
1486: port forwarding.
1487: This option is only used for port forwarding to a Unix-domain socket file.
1488: .Pp
1489: The default value is 0177, which creates a Unix-domain socket file that is
1490: readable and writable only by the owner.
1491: Note that not all operating systems honor the file mode on Unix-domain
1492: socket files.
1493: .It Cm StreamLocalBindUnlink
1494: Specifies whether to remove an existing Unix-domain socket file for local
1495: or remote port forwarding before creating a new one.
1496: If the socket file already exists and
1497: .Cm StreamLocalBindUnlink
1498: is not enabled,
1499: .Nm sshd
1500: will be unable to forward the port to the Unix-domain socket file.
1501: This option is only used for port forwarding to a Unix-domain socket file.
1502: .Pp
1503: The argument must be
1.23 christos 1504: .Cm yes
1.16 christos 1505: or
1.23 christos 1506: .Cm no .
1.16 christos 1507: The default is
1.23 christos 1508: .Cm no .
1.1 christos 1509: .It Cm StrictModes
1510: Specifies whether
1511: .Xr sshd 8
1512: should check file modes and ownership of the
1513: user's files and home directory before accepting login.
1514: This is normally desirable because novices sometimes accidentally leave their
1515: directory or files world-writable.
1516: The default is
1.23 christos 1517: .Cm yes .
1.6 adam 1518: Note that this does not apply to
1519: .Cm ChrootDirectory ,
1520: whose permissions and ownership are checked unconditionally.
1.1 christos 1521: .It Cm Subsystem
1522: Configures an external subsystem (e.g. file transfer daemon).
1523: Arguments should be a subsystem name and a command (with optional arguments)
1524: to execute upon subsystem request.
1525: .Pp
1526: The command
1.23 christos 1527: .Cm sftp-server
1528: implements the SFTP file transfer subsystem.
1.1 christos 1529: .Pp
1530: Alternately the name
1.23 christos 1531: .Cm internal-sftp
1532: implements an in-process SFTP server.
1.1 christos 1533: This may simplify configurations using
1534: .Cm ChrootDirectory
1535: to force a different filesystem root on clients.
1536: .Pp
1537: By default no subsystems are defined.
1538: .It Cm SyslogFacility
1539: Gives the facility code that is used when logging messages from
1540: .Xr sshd 8 .
1541: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1542: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
1543: The default is AUTH.
1544: .It Cm TCPKeepAlive
1545: Specifies whether the system should send TCP keepalive messages to the
1546: other side.
1547: If they are sent, death of the connection or crash of one
1548: of the machines will be properly noticed.
1549: However, this means that
1550: connections will die if the route is down temporarily, and some people
1551: find it annoying.
1552: On the other hand, if TCP keepalives are not sent,
1553: sessions may hang indefinitely on the server, leaving
1.23 christos 1554: .Qq ghost
1.1 christos 1555: users and consuming server resources.
1556: .Pp
1557: The default is
1.23 christos 1558: .Cm yes
1.1 christos 1559: (to send TCP keepalive messages), and the server will notice
1560: if the network goes down or the client host crashes.
1561: This avoids infinitely hanging sessions.
1562: .Pp
1563: To disable TCP keepalive messages, the value should be set to
1.23 christos 1564: .Cm no .
1.6 adam 1565: .It Cm TrustedUserCAKeys
1566: Specifies a file containing public keys of certificate authorities that are
1.18 christos 1567: trusted to sign user certificates for authentication, or
1.23 christos 1568: .Cm none
1.18 christos 1569: to not use one.
1.6 adam 1570: Keys are listed one per line; empty lines and comments starting with
1571: .Ql #
1572: are allowed.
1573: If a certificate is presented for authentication and has its signing CA key
1574: listed in this file, then it may be used for authentication for any user
1575: listed in the certificate's principals list.
1576: Note that certificates that lack a list of principals will not be permitted
1577: for authentication using
1578: .Cm TrustedUserCAKeys .
1.15 christos 1579: For more details on certificates, see the CERTIFICATES section in
1.6 adam 1580: .Xr ssh-keygen 1 .
1.1 christos 1581: .It Cm UseDNS
1582: Specifies whether
1583: .Xr sshd 8
1.19 christos 1584: should look up the remote host name, and to check that
1.1 christos 1585: the resolved host name for the remote IP address maps back to the
1586: very same IP address.
1.19 christos 1587: .Pp
1588: If this option is set to
1.23 christos 1589: .Cm no
1.19 christos 1590: (the default) then only addresses and not host names may be used in
1.22 christos 1591: .Pa ~/.ssh/authorized_keys
1.19 christos 1592: .Cm from
1593: and
1.20 christos 1594: .Nm
1.19 christos 1595: .Cm Match
1596: .Cm Host
1597: directives.
1.13 christos 1598: .It Cm VersionAddendum
1599: Optionally specifies additional text to append to the SSH protocol banner
1600: sent by the server upon connection.
1601: The default is
1.23 christos 1602: .Cm none .
1.1 christos 1603: .It Cm X11DisplayOffset
1604: Specifies the first display number available for
1605: .Xr sshd 8 Ns 's
1606: X11 forwarding.
1607: This prevents sshd from interfering with real X11 servers.
1608: The default is 10.
1609: .It Cm X11Forwarding
1610: Specifies whether X11 forwarding is permitted.
1611: The argument must be
1.23 christos 1612: .Cm yes
1.1 christos 1613: or
1.23 christos 1614: .Cm no .
1.1 christos 1615: The default is
1.23 christos 1616: .Cm no .
1.1 christos 1617: .Pp
1618: When X11 forwarding is enabled, there may be additional exposure to
1619: the server and to client displays if the
1620: .Xr sshd 8
1621: proxy display is configured to listen on the wildcard address (see
1.23 christos 1622: .Cm X11UseLocalhost ) ,
1623: though this is not the default.
1.1 christos 1624: Additionally, the authentication spoofing and authentication data
1625: verification and substitution occur on the client side.
1626: The security risk of using X11 forwarding is that the client's X11
1627: display server may be exposed to attack when the SSH client requests
1628: forwarding (see the warnings for
1629: .Cm ForwardX11
1630: in
1631: .Xr ssh_config 5 ) .
1632: A system administrator may have a stance in which they want to
1633: protect clients that may expose themselves to attack by unwittingly
1634: requesting X11 forwarding, which can warrant a
1.23 christos 1635: .Cm no
1.1 christos 1636: setting.
1637: .Pp
1638: Note that disabling X11 forwarding does not prevent users from
1639: forwarding X11 traffic, as users can always install their own forwarders.
1640: .It Cm X11UseLocalhost
1641: Specifies whether
1642: .Xr sshd 8
1643: should bind the X11 forwarding server to the loopback address or to
1644: the wildcard address.
1645: By default,
1646: sshd binds the forwarding server to the loopback address and sets the
1647: hostname part of the
1648: .Ev DISPLAY
1649: environment variable to
1.23 christos 1650: .Cm localhost .
1.1 christos 1651: This prevents remote hosts from connecting to the proxy display.
1652: However, some older X11 clients may not function with this
1653: configuration.
1654: .Cm X11UseLocalhost
1655: may be set to
1.23 christos 1656: .Cm no
1.1 christos 1657: to specify that the forwarding server should be bound to the wildcard
1658: address.
1659: The argument must be
1.23 christos 1660: .Cm yes
1.1 christos 1661: or
1.23 christos 1662: .Cm no .
1.1 christos 1663: The default is
1.23 christos 1664: .Cm yes .
1.1 christos 1665: .It Cm XAuthLocation
1666: Specifies the full pathname of the
1667: .Xr xauth 1
1.18 christos 1668: program, or
1.23 christos 1669: .Cm none
1.18 christos 1670: to not use one.
1.1 christos 1671: The default is
1672: .Pa /usr/X11R6/bin/xauth .
1.7 adam 1673: .It Cm UseLPK
1674: Specifies whether LDAP public key retrieval must be used or not. It allow
1675: an easy centralisation of public keys within an LDAP directory. The argument must be
1676: .Dq yes
1677: or
1678: .Dq no .
1679: .It Cm LpkLdapConf
1680: Specifies whether LDAP Public keys should parse the specified ldap.conf file
1681: instead of sshd_config Tokens. The argument must be a valid path to an ldap.conf
1682: file like
1683: .Pa /etc/ldap.conf
1684: .It Cm LpkServers
1685: Specifies LDAP one or more [:space:] separated server's url the following form may be used:
1686: .Pp
1687: LpkServers ldaps://127.0.0.1 ldap://127.0.0.2 ldap://127.0.0.3
1688: .It Cm LpkUserDN
1689: Specifies the LDAP user DN.
1690: .Pp
1691: LpkUserDN ou=users,dc=phear,dc=org
1692: .It Cm LpkGroupDN
1693: Specifies the LDAP groups DN.
1694: .Pp
1695: LpkGroupDN ou=groups,dc=phear,dc=org
1696: .It Cm LpkBindDN
1697: Specifies the LDAP bind DN to use if necessary.
1698: .Pp
1699: LpkBindDN cn=Manager,dc=phear,dc=org
1700: .It Cm LpkBindPw
1701: Specifies the LDAP bind credential.
1702: .Pp
1703: LpkBindPw secret
1704: .It Cm LpkServerGroup
1705: Specifies one or more [:space:] separated group the server is part of.
1706: .Pp
1707: LpkServerGroup unix mail prod
1708: .It Cm LpkFilter
1709: Specifies an additional LDAP filter to use for finding SSH keys
1710: .Pp
1711: LpkFilter (hostAccess=master.phear.org)
1712: .It Cm LpkForceTLS
1713: Specifies if the LDAP server connection must be tried, forced or not used. The argument must be
1714: .Dq yes
1715: or
1716: .Dq no
1717: or
1718: .Dq try .
1719: .It Cm LpkSearchTimelimit
1.9 agc 1720: Specifies the search time limit before the search is considered over. value is
1.7 adam 1721: in seconds.
1722: .Pp
1723: LpkSearchTimelimit 3
1724: .It Cm LpkBindTimelimit
1.9 agc 1725: Specifies the bind time limit before the connection is considered dead. value is
1.7 adam 1726: in seconds.
1727: .Pp
1728: LpkBindTimelimit 3
1.1 christos 1729: .El
1730: .Sh TIME FORMATS
1731: .Xr sshd 8
1732: command-line arguments and configuration file options that specify time
1733: may be expressed using a sequence of the form:
1734: .Sm off
1735: .Ar time Op Ar qualifier ,
1736: .Sm on
1737: where
1738: .Ar time
1739: is a positive integer value and
1740: .Ar qualifier
1741: is one of the following:
1742: .Pp
1743: .Bl -tag -width Ds -compact -offset indent
1744: .It Aq Cm none
1745: seconds
1746: .It Cm s | Cm S
1747: seconds
1748: .It Cm m | Cm M
1749: minutes
1750: .It Cm h | Cm H
1751: hours
1752: .It Cm d | Cm D
1753: days
1754: .It Cm w | Cm W
1755: weeks
1756: .El
1757: .Pp
1758: Each member of the sequence is added together to calculate
1759: the total time value.
1760: .Pp
1761: Time format examples:
1762: .Pp
1763: .Bl -tag -width Ds -compact -offset indent
1764: .It 600
1765: 600 seconds (10 minutes)
1766: .It 10m
1767: 10 minutes
1768: .It 1h30m
1769: 1 hour 30 minutes (90 minutes)
1770: .El
1.23 christos 1771: .Sh TOKENS
1772: Arguments to some keywords can make use of tokens,
1773: which are expanded at runtime:
1774: .Pp
1775: .Bl -tag -width XXXX -offset indent -compact
1776: .It %%
1777: A literal
1778: .Sq % .
1.25.2.1 pgoyette 1779: .It \&%D
1780: The routing domain in which the incoming connection was received.
1.23 christos 1781: .It %F
1782: The fingerprint of the CA key.
1783: .It %f
1784: The fingerprint of the key or certificate.
1785: .It %h
1786: The home directory of the user.
1787: .It %i
1788: The key ID in the certificate.
1789: .It %K
1790: The base64-encoded CA key.
1791: .It %k
1792: The base64-encoded key or certificate for authentication.
1793: .It %s
1794: The serial number of the certificate.
1795: .It \&%T
1796: The type of the CA key.
1797: .It %t
1798: The key or certificate type.
1.25.2.2! pgoyette 1799: .It \&%U
! 1800: The numeric user ID of the target user.
1.23 christos 1801: .It %u
1802: The username.
1803: .El
1804: .Pp
1805: .Cm AuthorizedKeysCommand
1.25.2.2! pgoyette 1806: accepts the tokens %%, %f, %h, %k, %t, %U, and %u.
1.23 christos 1807: .Pp
1808: .Cm AuthorizedKeysFile
1.25.2.2! pgoyette 1809: accepts the tokens %%, %h, %U, and %u.
1.23 christos 1810: .Pp
1811: .Cm AuthorizedPrincipalsCommand
1.25.2.2! pgoyette 1812: accepts the tokens %%, %F, %f, %h, %i, %K, %k, %s, %T, %t, %U, and %u.
1.23 christos 1813: .Pp
1814: .Cm AuthorizedPrincipalsFile
1.25.2.2! pgoyette 1815: accepts the tokens %%, %h, %U, and %u.
1.23 christos 1816: .Pp
1817: .Cm ChrootDirectory
1.25.2.2! pgoyette 1818: accepts the tokens %%, %h, %U, and %u.
1.25.2.1 pgoyette 1819: .Pp
1820: .Cm RoutingDomain
1821: accepts the token %D.
1.1 christos 1822: .Sh FILES
1823: .Bl -tag -width Ds
1824: .It Pa /etc/ssh/sshd_config
1825: Contains configuration data for
1826: .Xr sshd 8 .
1827: This file should be writable by root only, but it is recommended
1828: (though not necessary) that it be world-readable.
1829: .El
1830: .Sh SEE ALSO
1.23 christos 1831: .Xr sftp-server 8 ,
1.1 christos 1832: .Xr sshd 8
1833: .Sh AUTHORS
1.23 christos 1834: .An -nosplit
1.1 christos 1835: OpenSSH is a derivative of the original and free
1.23 christos 1836: ssh 1.2.12 release by
1837: .An Tatu Ylonen .
1838: .An Aaron Campbell , Bob Beck , Markus Friedl , Niels Provos ,
1839: .An Theo de Raadt
1840: and
1841: .An Dug Song
1.1 christos 1842: removed many bugs, re-added newer features and
1843: created OpenSSH.
1.23 christos 1844: .An Markus Friedl
1845: contributed the support for SSH protocol versions 1.5 and 2.0.
1846: .An Niels Provos
1847: and
1848: .An Markus Friedl
1849: contributed support for privilege separation.
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