Annotation of src/usr.bin/ssh/sshd_config.5, Revision 1.333
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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29: .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
30: .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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1.333 ! jmc 36: .\" $OpenBSD: sshd_config.5,v 1.332 2021/07/02 05:11:21 dtucker Exp $
! 37: .Dd $Mdocdate: July 2 2021 $
1.1 stevesk 38: .Dt SSHD_CONFIG 5
39: .Os
40: .Sh NAME
41: .Nm sshd_config
1.295 jmc 42: .Nd OpenSSH daemon configuration file
1.1 stevesk 43: .Sh DESCRIPTION
1.53 jmc 44: .Xr sshd 8
1.1 stevesk 45: reads configuration data from
46: .Pa /etc/ssh/sshd_config
47: (or the file specified with
48: .Fl f
49: on the command line).
50: The file contains keyword-argument pairs, one per line.
1.254 benno 51: For each keyword, the first obtained value will be used.
1.1 stevesk 52: Lines starting with
53: .Ql #
54: and empty lines are interpreted as comments.
1.56 dtucker 55: Arguments may optionally be enclosed in double quotes
56: .Pq \&"
57: in order to represent arguments containing spaces.
1.1 stevesk 58: .Pp
59: The possible
60: keywords and their meanings are as follows (note that
61: keywords are case-insensitive and arguments are case-sensitive):
62: .Bl -tag -width Ds
1.30 djm 63: .It Cm AcceptEnv
64: Specifies what environment variables sent by the client will be copied into
65: the session's
66: .Xr environ 7 .
67: See
68: .Cm SendEnv
1.273 djm 69: and
70: .Cm SetEnv
1.30 djm 71: in
72: .Xr ssh_config 5
73: for how to configure the client.
1.219 jmc 74: The
1.197 dtucker 75: .Ev TERM
1.275 djm 76: environment variable is always accepted whenever the client
1.204 djm 77: requests a pseudo-terminal as it is required by the protocol.
1.30 djm 78: Variables are specified by name, which may contain the wildcard characters
1.51 jmc 79: .Ql *
1.30 djm 80: and
81: .Ql \&? .
1.31 djm 82: Multiple environment variables may be separated by whitespace or spread
1.30 djm 83: across multiple
84: .Cm AcceptEnv
85: directives.
1.31 djm 86: Be warned that some environment variables could be used to bypass restricted
1.30 djm 87: user environments.
88: For this reason, care should be taken in the use of this directive.
89: The default is not to accept any environment variables.
1.37 djm 90: .It Cm AddressFamily
91: Specifies which address family should be used by
1.53 jmc 92: .Xr sshd 8 .
1.37 djm 93: Valid arguments are
1.237 jmc 94: .Cm any
95: (the default),
96: .Cm inet
1.52 jmc 97: (use IPv4 only), or
1.237 jmc 98: .Cm inet6
1.37 djm 99: (use IPv6 only).
1.89 jmc 100: .It Cm AllowAgentForwarding
101: Specifies whether
102: .Xr ssh-agent 1
103: forwarding is permitted.
104: The default is
1.237 jmc 105: .Cm yes .
1.89 jmc 106: Note that disabling agent forwarding does not improve security
107: unless users are also denied shell access, as they can always install
108: their own forwarders.
1.1 stevesk 109: .It Cm AllowGroups
110: This keyword can be followed by a list of group name patterns, separated
111: by spaces.
112: If specified, login is allowed only for users whose primary
113: group or supplementary group list matches one of the patterns.
114: Only group names are valid; a numerical group ID is not recognized.
115: By default, login is allowed for all groups.
1.301 djm 116: The allow/deny groups directives are processed in the following order:
1.54 jmc 117: .Cm DenyGroups ,
118: .Cm AllowGroups .
1.49 jmc 119: .Pp
1.161 jmc 120: See PATTERNS in
1.49 jmc 121: .Xr ssh_config 5
122: for more information on patterns.
1.231 jmc 123: .It Cm AllowStreamLocalForwarding
124: Specifies whether StreamLocal (Unix-domain socket) forwarding is permitted.
1.150 djm 125: The available options are
1.237 jmc 126: .Cm yes
127: (the default)
1.150 djm 128: or
1.237 jmc 129: .Cm all
1.231 jmc 130: to allow StreamLocal forwarding,
1.237 jmc 131: .Cm no
1.231 jmc 132: to prevent all StreamLocal forwarding,
1.237 jmc 133: .Cm local
1.150 djm 134: to allow local (from the perspective of
1.151 jmc 135: .Xr ssh 1 )
136: forwarding only or
1.237 jmc 137: .Cm remote
1.150 djm 138: to allow remote forwarding only.
1.231 jmc 139: Note that disabling StreamLocal forwarding does not improve security unless
1.1 stevesk 140: users are also denied shell access, as they can always install their
141: own forwarders.
1.231 jmc 142: .It Cm AllowTcpForwarding
143: Specifies whether TCP forwarding is permitted.
1.175 millert 144: The available options are
1.237 jmc 145: .Cm yes
146: (the default)
1.175 millert 147: or
1.237 jmc 148: .Cm all
1.231 jmc 149: to allow TCP forwarding,
1.237 jmc 150: .Cm no
1.231 jmc 151: to prevent all TCP forwarding,
1.237 jmc 152: .Cm local
1.175 millert 153: to allow local (from the perspective of
154: .Xr ssh 1 )
155: forwarding only or
1.237 jmc 156: .Cm remote
1.175 millert 157: to allow remote forwarding only.
1.231 jmc 158: Note that disabling TCP forwarding does not improve security unless
1.175 millert 159: users are also denied shell access, as they can always install their
160: own forwarders.
1.1 stevesk 161: .It Cm AllowUsers
162: This keyword can be followed by a list of user name patterns, separated
163: by spaces.
1.14 jmc 164: If specified, login is allowed only for user names that
1.1 stevesk 165: match one of the patterns.
166: Only user names are valid; a numerical user ID is not recognized.
167: By default, login is allowed for all users.
168: If the pattern takes the form USER@HOST then USER and HOST
169: are separately checked, restricting logins to particular
170: users from particular hosts.
1.222 jmc 171: HOST criteria may additionally contain addresses to match in CIDR
172: address/masklen format.
1.301 djm 173: The allow/deny users directives are processed in the following order:
1.54 jmc 174: .Cm DenyUsers ,
1.301 djm 175: .Cm AllowUsers .
1.49 jmc 176: .Pp
1.161 jmc 177: See PATTERNS in
1.49 jmc 178: .Xr ssh_config 5
179: for more information on patterns.
1.149 djm 180: .It Cm AuthenticationMethods
181: Specifies the authentication methods that must be successfully completed
182: for a user to be granted access.
1.281 djm 183: This option must be followed by one or more lists of comma-separated
1.224 djm 184: authentication method names, or by the single string
1.237 jmc 185: .Cm any
1.224 djm 186: to indicate the default behaviour of accepting any single authentication
1.225 jmc 187: method.
1.237 jmc 188: If the default is overridden, then successful authentication requires
1.224 djm 189: completion of every method in at least one of these lists.
1.149 djm 190: .Pp
1.237 jmc 191: For example,
192: .Qq publickey,password publickey,keyboard-interactive
1.149 djm 193: would require the user to complete public key authentication, followed by
194: either password or keyboard interactive authentication.
195: Only methods that are next in one or more lists are offered at each stage,
1.237 jmc 196: so for this example it would not be possible to attempt password or
1.149 djm 197: keyboard-interactive authentication before public key.
1.157 markus 198: .Pp
199: For keyboard interactive authentication it is also possible to
200: restrict authentication to a specific device by appending a
201: colon followed by the device identifier
1.237 jmc 202: .Cm bsdauth ,
203: .Cm pam ,
1.157 markus 204: or
1.237 jmc 205: .Cm skey ,
1.157 markus 206: depending on the server configuration.
207: For example,
1.237 jmc 208: .Qq keyboard-interactive:bsdauth
1.157 markus 209: would restrict keyboard interactive authentication to the
1.237 jmc 210: .Cm bsdauth
1.157 markus 211: device.
1.185 djm 212: .Pp
1.237 jmc 213: If the publickey method is listed more than once,
1.185 djm 214: .Xr sshd 8
215: verifies that keys that have been used successfully are not reused for
216: subsequent authentications.
1.237 jmc 217: For example,
218: .Qq publickey,publickey
219: requires successful authentication using two different public keys.
1.181 djm 220: .Pp
1.149 djm 221: Note that each authentication method listed should also be explicitly enabled
222: in the configuration.
1.251 djm 223: .Pp
224: The available authentication methods are:
225: .Qq gssapi-with-mic ,
226: .Qq hostbased ,
227: .Qq keyboard-interactive ,
228: .Qq none
229: (used for access to password-less accounts when
1.266 jmc 230: .Cm PermitEmptyPasswords
1.251 djm 231: is enabled),
232: .Qq password
233: and
234: .Qq publickey .
1.146 djm 235: .It Cm AuthorizedKeysCommand
1.147 jmc 236: Specifies a program to be used to look up the user's public keys.
1.201 djm 237: The program must be owned by root, not writable by group or others and
238: specified by an absolute path.
239: Arguments to
240: .Cm AuthorizedKeysCommand
1.235 jmc 241: accept the tokens described in the
242: .Sx TOKENS
243: section.
244: If no arguments are specified then the username of the target user is used.
1.201 djm 245: .Pp
246: The program should produce on standard output zero or
1.235 jmc 247: more lines of authorized_keys output (see
248: .Sx AUTHORIZED_KEYS
249: in
1.147 jmc 250: .Xr sshd 8 ) .
1.235 jmc 251: .Cm AuthorizedKeysCommand
1.310 djm 252: is tried after the usual
1.146 djm 253: .Cm AuthorizedKeysFile
1.310 djm 254: files and will not be executed if a matching key is found there.
1.237 jmc 255: By default, no
256: .Cm AuthorizedKeysCommand
257: is run.
1.146 djm 258: .It Cm AuthorizedKeysCommandUser
1.237 jmc 259: Specifies the user under whose account the
260: .Cm AuthorizedKeysCommand
261: is run.
1.146 djm 262: It is recommended to use a dedicated user that has no other role on the host
263: than running authorized keys commands.
1.186 djm 264: If
1.181 djm 265: .Cm AuthorizedKeysCommand
1.186 djm 266: is specified but
267: .Cm AuthorizedKeysCommandUser
268: is not, then
269: .Xr sshd 8
270: will refuse to start.
1.1 stevesk 271: .It Cm AuthorizedKeysFile
1.235 jmc 272: Specifies the file that contains the public keys used for user authentication.
1.285 schwarze 273: The format is described in the AUTHORIZED_KEYS FILE FORMAT section of
1.124 djm 274: .Xr sshd 8 .
1.235 jmc 275: Arguments to
1.1 stevesk 276: .Cm AuthorizedKeysFile
1.235 jmc 277: accept the tokens described in the
278: .Sx TOKENS
279: section.
1.1 stevesk 280: After expansion,
281: .Cm AuthorizedKeysFile
282: is taken to be an absolute path or one relative to the user's home
283: directory.
1.133 jmc 284: Multiple files may be listed, separated by whitespace.
1.212 djm 285: Alternately this option may be set to
1.237 jmc 286: .Cm none
1.212 djm 287: to skip checking for user keys in files.
1.133 jmc 288: The default is
1.237 jmc 289: .Qq .ssh/authorized_keys .ssh/authorized_keys2 .
1.202 djm 290: .It Cm AuthorizedPrincipalsCommand
291: Specifies a program to be used to generate the list of allowed
292: certificate principals as per
293: .Cm AuthorizedPrincipalsFile .
294: The program must be owned by root, not writable by group or others and
295: specified by an absolute path.
296: Arguments to
297: .Cm AuthorizedPrincipalsCommand
1.235 jmc 298: accept the tokens described in the
299: .Sx TOKENS
300: section.
301: If no arguments are specified then the username of the target user is used.
1.202 djm 302: .Pp
303: The program should produce on standard output zero or
304: more lines of
305: .Cm AuthorizedPrincipalsFile
306: output.
307: If either
308: .Cm AuthorizedPrincipalsCommand
309: or
310: .Cm AuthorizedPrincipalsFile
311: is specified, then certificates offered by the client for authentication
312: must contain a principal that is listed.
1.235 jmc 313: By default, no
314: .Cm AuthorizedPrincipalsCommand
315: is run.
1.202 djm 316: .It Cm AuthorizedPrincipalsCommandUser
1.235 jmc 317: Specifies the user under whose account the
318: .Cm AuthorizedPrincipalsCommand
319: is run.
1.202 djm 320: It is recommended to use a dedicated user that has no other role on the host
321: than running authorized principals commands.
322: If
323: .Cm AuthorizedPrincipalsCommand
324: is specified but
325: .Cm AuthorizedPrincipalsCommandUser
326: is not, then
327: .Xr sshd 8
328: will refuse to start.
1.121 djm 329: .It Cm AuthorizedPrincipalsFile
330: Specifies a file that lists principal names that are accepted for
331: certificate authentication.
332: When using certificates signed by a key listed in
333: .Cm TrustedUserCAKeys ,
334: this file lists names, one of which must appear in the certificate for it
335: to be accepted for authentication.
1.235 jmc 336: Names are listed one per line preceded by key options (as described in
337: .Sx AUTHORIZED_KEYS FILE FORMAT
338: in
1.125 jmc 339: .Xr sshd 8 ) .
1.124 djm 340: Empty lines and comments starting with
1.121 djm 341: .Ql #
342: are ignored.
343: .Pp
1.235 jmc 344: Arguments to
1.121 djm 345: .Cm AuthorizedPrincipalsFile
1.235 jmc 346: accept the tokens described in the
347: .Sx TOKENS
348: section.
1.121 djm 349: After expansion,
350: .Cm AuthorizedPrincipalsFile
1.235 jmc 351: is taken to be an absolute path or one relative to the user's home directory.
1.138 djm 352: The default is
1.237 jmc 353: .Cm none ,
1.138 djm 354: i.e. not to use a principals file \(en in this case, the username
1.121 djm 355: of the user must appear in a certificate's principals list for it to be
356: accepted.
1.235 jmc 357: .Pp
1.121 djm 358: Note that
359: .Cm AuthorizedPrincipalsFile
360: is only used when authentication proceeds using a CA listed in
361: .Cm TrustedUserCAKeys
362: and is not consulted for certification authorities trusted via
363: .Pa ~/.ssh/authorized_keys ,
364: though the
365: .Cm principals=
366: key option offers a similar facility (see
367: .Xr sshd 8
368: for details).
1.1 stevesk 369: .It Cm Banner
370: The contents of the specified file are sent to the remote user before
371: authentication is allowed.
1.78 djm 372: If the argument is
1.237 jmc 373: .Cm none
1.78 djm 374: then no banner is displayed.
1.1 stevesk 375: By default, no banner is displayed.
1.282 djm 376: .It Cm CASignatureAlgorithms
377: Specifies which algorithms are allowed for signing of certificates
378: by certificate authorities (CAs).
379: The default is:
380: .Bd -literal -offset indent
1.330 djm 381: ssh-ed25519,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.331 jmc 382: sk-ssh-ed25519@openssh.com,sk-ecdsa-sha2-nistp256@openssh.com,
1.330 djm 383: rsa-sha2-512,rsa-sha2-256
1.282 djm 384: .Ed
385: .Pp
386: Certificates signed using other algorithms will not be accepted for
387: public key or host-based authentication.
1.80 djm 388: .It Cm ChrootDirectory
1.113 stevesk 389: Specifies the pathname of a directory to
1.80 djm 390: .Xr chroot 2
391: to after authentication.
1.190 deraadt 392: At session startup
393: .Xr sshd 8
394: checks that all components of the pathname are root-owned directories
395: which are not writable by any other user or group.
1.106 stevesk 396: After the chroot,
397: .Xr sshd 8
398: changes the working directory to the user's home directory.
1.235 jmc 399: Arguments to
400: .Cm ChrootDirectory
401: accept the tokens described in the
402: .Sx TOKENS
403: section.
1.80 djm 404: .Pp
405: The
406: .Cm ChrootDirectory
407: must contain the necessary files and directories to support the
1.103 stevesk 408: user's session.
1.80 djm 409: For an interactive session this requires at least a shell, typically
410: .Xr sh 1 ,
411: and basic
412: .Pa /dev
413: nodes such as
414: .Xr null 4 ,
415: .Xr zero 4 ,
416: .Xr stdin 4 ,
417: .Xr stdout 4 ,
418: .Xr stderr 4 ,
1.180 jmc 419: and
1.80 djm 420: .Xr tty 4
421: devices.
1.237 jmc 422: For file transfer sessions using SFTP
423: no additional configuration of the environment is necessary if the in-process
424: sftp-server is used,
1.176 schwarze 425: though sessions which use logging may require
1.104 stevesk 426: .Pa /dev/log
1.176 schwarze 427: inside the chroot directory on some operating systems (see
1.104 stevesk 428: .Xr sftp-server 8
1.81 jmc 429: for details).
1.190 deraadt 430: .Pp
1.191 jmc 431: For safety, it is very important that the directory hierarchy be
1.190 deraadt 432: prevented from modification by other processes on the system (especially
433: those outside the jail).
434: Misconfiguration can lead to unsafe environments which
435: .Xr sshd 8
436: cannot detect.
1.80 djm 437: .Pp
1.215 djm 438: The default is
1.237 jmc 439: .Cm none ,
1.215 djm 440: indicating not to
1.80 djm 441: .Xr chroot 2 .
1.1 stevesk 442: .It Cm Ciphers
1.219 jmc 443: Specifies the ciphers allowed.
1.1 stevesk 444: Multiple ciphers must be comma-separated.
1.289 naddy 445: If the specified list begins with a
1.208 djm 446: .Sq +
447: character, then the specified ciphers will be appended to the default set
448: instead of replacing them.
1.289 naddy 449: If the specified list begins with a
1.242 djm 450: .Sq -
451: character, then the specified ciphers (including wildcards) will be removed
452: from the default set instead of replacing them.
1.290 naddy 453: If the specified list begins with a
454: .Sq ^
455: character, then the specified ciphers will be placed at the head of the
456: default set.
1.208 djm 457: .Pp
1.167 djm 458: The supported ciphers are:
459: .Pp
1.173 naddy 460: .Bl -item -compact -offset indent
461: .It
462: 3des-cbc
463: .It
464: aes128-cbc
465: .It
466: aes192-cbc
467: .It
468: aes256-cbc
469: .It
470: aes128-ctr
471: .It
472: aes192-ctr
473: .It
474: aes256-ctr
475: .It
476: aes128-gcm@openssh.com
477: .It
478: aes256-gcm@openssh.com
479: .It
480: chacha20-poly1305@openssh.com
481: .El
1.167 djm 482: .Pp
1.52 jmc 483: The default is:
1.173 naddy 484: .Bd -literal -offset indent
1.211 jmc 485: chacha20-poly1305@openssh.com,
1.173 naddy 486: aes128-ctr,aes192-ctr,aes256-ctr,
1.211 jmc 487: aes128-gcm@openssh.com,aes256-gcm@openssh.com
1.1 stevesk 488: .Ed
1.167 djm 489: .Pp
1.237 jmc 490: The list of available ciphers may also be obtained using
491: .Qq ssh -Q cipher .
1.1 stevesk 492: .It Cm ClientAliveCountMax
1.237 jmc 493: Sets the number of client alive messages which may be sent without
1.52 jmc 494: .Xr sshd 8
1.17 jmc 495: receiving any messages back from the client.
496: If this threshold is reached while client alive messages are being sent,
1.52 jmc 497: sshd will disconnect the client, terminating the session.
1.17 jmc 498: It is important to note that the use of client alive messages is very
499: different from
1.237 jmc 500: .Cm TCPKeepAlive .
1.17 jmc 501: The client alive messages are sent through the encrypted channel
502: and therefore will not be spoofable.
503: The TCP keepalive option enabled by
1.27 markus 504: .Cm TCPKeepAlive
1.17 jmc 505: is spoofable.
506: The client alive mechanism is valuable when the client or
1.288 dtucker 507: server depend on knowing when a connection has become unresponsive.
1.1 stevesk 508: .Pp
1.17 jmc 509: The default value is 3.
510: If
1.1 stevesk 511: .Cm ClientAliveInterval
1.237 jmc 512: is set to 15, and
1.1 stevesk 513: .Cm ClientAliveCountMax
1.52 jmc 514: is left at the default, unresponsive SSH clients
1.1 stevesk 515: will be disconnected after approximately 45 seconds.
1.302 djm 516: Setting a zero
517: .Cm ClientAliveCountMax
518: disables connection termination.
1.42 djm 519: .It Cm ClientAliveInterval
520: Sets a timeout interval in seconds after which if no data has been received
521: from the client,
1.52 jmc 522: .Xr sshd 8
1.42 djm 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.
1.3 markus 527: .It Cm Compression
1.236 djm 528: Specifies whether compression is enabled after
1.44 markus 529: the user has authenticated successfully.
1.3 markus 530: The argument must be
1.237 jmc 531: .Cm yes ,
532: .Cm delayed
1.236 djm 533: (a legacy synonym for
1.237 jmc 534: .Cm yes )
1.3 markus 535: or
1.237 jmc 536: .Cm no .
1.3 markus 537: The default is
1.237 jmc 538: .Cm yes .
1.1 stevesk 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.
1.301 djm 546: The allow/deny groups directives are processed in the following order:
1.54 jmc 547: .Cm DenyGroups ,
548: .Cm AllowGroups .
1.49 jmc 549: .Pp
1.161 jmc 550: See PATTERNS in
1.49 jmc 551: .Xr ssh_config 5
552: for more information on patterns.
1.1 stevesk 553: .It Cm DenyUsers
554: This keyword can be followed by a list of user name patterns, separated
555: by spaces.
556: Login is disallowed for user names that match one of the patterns.
557: Only user names are valid; a numerical user ID is not recognized.
558: By default, login is allowed for all users.
559: If the pattern takes the form USER@HOST then USER and HOST
560: are separately checked, restricting logins to particular
561: users from particular hosts.
1.222 jmc 562: HOST criteria may additionally contain addresses to match in CIDR
563: address/masklen format.
1.301 djm 564: The allow/deny users directives are processed in the following order:
1.54 jmc 565: .Cm DenyUsers ,
1.301 djm 566: .Cm AllowUsers .
1.49 jmc 567: .Pp
1.161 jmc 568: See PATTERNS in
1.49 jmc 569: .Xr ssh_config 5
570: for more information on patterns.
1.239 djm 571: .It Cm DisableForwarding
572: Disables all forwarding features, including X11,
573: .Xr ssh-agent 1 ,
574: TCP and StreamLocal.
575: This option overrides all other forwarding-related options and may
576: simplify restricted configurations.
1.246 djm 577: .It Cm ExposeAuthInfo
1.253 jmc 578: Writes a temporary file containing a list of authentication methods and
1.246 djm 579: public credentials (e.g. keys) used to authenticate the user.
1.247 jmc 580: The location of the file is exposed to the user session through the
1.248 djm 581: .Ev SSH_USER_AUTH
1.247 jmc 582: environment variable.
1.253 jmc 583: The default is
584: .Cm no .
1.183 djm 585: .It Cm FingerprintHash
586: Specifies the hash algorithm used when logging key fingerprints.
587: Valid options are:
1.237 jmc 588: .Cm md5
1.183 djm 589: and
1.237 jmc 590: .Cm sha256 .
1.183 djm 591: The default is
1.237 jmc 592: .Cm sha256 .
1.67 dtucker 593: .It Cm ForceCommand
594: Forces the execution of the command specified by
595: .Cm ForceCommand ,
1.84 djm 596: ignoring any command supplied by the client and
597: .Pa ~/.ssh/rc
598: if present.
1.67 dtucker 599: The command is invoked by using the user's login shell with the -c option.
600: This applies to shell, command, or subsystem execution.
601: It is most useful inside a
602: .Cm Match
603: block.
604: The command originally supplied by the client is available in the
605: .Ev SSH_ORIGINAL_COMMAND
606: environment variable.
1.82 djm 607: Specifying a command of
1.237 jmc 608: .Cm internal-sftp
609: will force the use of an in-process SFTP server that requires no support
1.82 djm 610: files when used with
611: .Cm ChrootDirectory .
1.215 djm 612: The default is
1.237 jmc 613: .Cm none .
1.1 stevesk 614: .It Cm GatewayPorts
615: Specifies whether remote hosts are allowed to connect to ports
616: forwarded for the client.
617: By default,
1.52 jmc 618: .Xr sshd 8
1.15 jmc 619: binds remote port forwardings to the loopback address.
620: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 621: .Cm GatewayPorts
1.52 jmc 622: can be used to specify that sshd
1.39 djm 623: should allow remote port forwardings to bind to non-loopback addresses, thus
624: allowing other hosts to connect.
625: The argument may be
1.237 jmc 626: .Cm no
1.39 djm 627: to force remote port forwardings to be available to the local host only,
1.237 jmc 628: .Cm yes
1.39 djm 629: to force remote port forwardings to bind to the wildcard address, or
1.237 jmc 630: .Cm clientspecified
1.39 djm 631: to allow the client to select the address to which the forwarding is bound.
1.1 stevesk 632: The default is
1.237 jmc 633: .Cm no .
1.23 markus 634: .It Cm GSSAPIAuthentication
1.25 markus 635: Specifies whether user authentication based on GSSAPI is allowed.
1.26 djm 636: The default is
1.237 jmc 637: .Cm no .
1.23 markus 638: .It Cm GSSAPICleanupCredentials
639: Specifies whether to automatically destroy the user's credentials cache
640: on logout.
641: The default is
1.237 jmc 642: .Cm yes .
1.203 djm 643: .It Cm GSSAPIStrictAcceptorCheck
644: Determines whether to be strict about the identity of the GSSAPI acceptor
645: a client authenticates against.
646: If set to
1.237 jmc 647: .Cm yes
648: then the client must authenticate against the host
1.203 djm 649: service on the current hostname.
650: If set to
1.237 jmc 651: .Cm no
1.203 djm 652: then the client may authenticate against any service key stored in the
653: machine's default store.
654: This facility is provided to assist with operation on multi homed machines.
655: The default is
1.237 jmc 656: .Cm yes .
1.325 dtucker 657: .It Cm HostbasedAcceptedAlgorithms
1.327 djm 658: Specifies the signature algorithms that will be accepted for hostbased
659: authentication as a list of comma-separated patterns.
1.289 naddy 660: Alternately if the specified list begins with a
1.208 djm 661: .Sq +
1.327 djm 662: character, then the specified signature algorithms will be appended to
663: the default set instead of replacing them.
1.289 naddy 664: If the specified list begins with a
1.242 djm 665: .Sq -
1.327 djm 666: character, then the specified signature algorithms (including wildcards)
667: will be removed from the default set instead of replacing them.
1.290 naddy 668: If the specified list begins with a
669: .Sq ^
1.327 djm 670: character, then the specified signature algorithms will be placed at
671: the head of the default set.
1.206 markus 672: The default for this option is:
673: .Bd -literal -offset 3n
1.316 djm 674: ssh-ed25519-cert-v01@openssh.com,
1.206 markus 675: ecdsa-sha2-nistp256-cert-v01@openssh.com,
676: ecdsa-sha2-nistp384-cert-v01@openssh.com,
677: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.316 djm 678: sk-ssh-ed25519-cert-v01@openssh.com,
1.296 naddy 679: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.291 naddy 680: rsa-sha2-512-cert-v01@openssh.com,
681: rsa-sha2-256-cert-v01@openssh.com,
1.206 markus 682: ssh-rsa-cert-v01@openssh.com,
1.316 djm 683: ssh-ed25519,
1.206 markus 684: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.316 djm 685: sk-ssh-ed25519@openssh.com,
1.296 naddy 686: sk-ecdsa-sha2-nistp256@openssh.com,
687: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.206 markus 688: .Ed
689: .Pp
1.327 djm 690: The list of available signature algorithms may also be obtained using
1.325 dtucker 691: .Qq ssh -Q HostbasedAcceptedAlgorithms .
692: This was formerly named HostbasedAcceptedKeyTypes.
1.1 stevesk 693: .It Cm HostbasedAuthentication
694: Specifies whether rhosts or /etc/hosts.equiv authentication together
695: with successful public key client host authentication is allowed
1.50 jmc 696: (host-based authentication).
1.70 dtucker 697: The default is
1.237 jmc 698: .Cm no .
1.70 dtucker 699: .It Cm HostbasedUsesNameFromPacketOnly
700: Specifies whether or not the server will attempt to perform a reverse
701: name lookup when matching the name in the
702: .Pa ~/.shosts ,
703: .Pa ~/.rhosts ,
704: and
705: .Pa /etc/hosts.equiv
706: files during
707: .Cm HostbasedAuthentication .
708: A setting of
1.237 jmc 709: .Cm yes
1.70 dtucker 710: means that
711: .Xr sshd 8
712: uses the name supplied by the client rather than
713: attempting to resolve the name from the TCP connection itself.
1.1 stevesk 714: The default is
1.237 jmc 715: .Cm no .
1.117 djm 716: .It Cm HostCertificate
717: Specifies a file containing a public host certificate.
718: The certificate's public key must match a private host key already specified
719: by
720: .Cm HostKey .
721: The default behaviour of
722: .Xr sshd 8
723: is not to load any certificates.
1.1 stevesk 724: .It Cm HostKey
725: Specifies a file containing a private host key
726: used by SSH.
1.229 naddy 727: The defaults are
1.169 naddy 728: .Pa /etc/ssh/ssh_host_ecdsa_key ,
729: .Pa /etc/ssh/ssh_host_ed25519_key
1.126 djm 730: and
1.229 naddy 731: .Pa /etc/ssh/ssh_host_rsa_key .
1.206 markus 732: .Pp
1.1 stevesk 733: Note that
1.52 jmc 734: .Xr sshd 8
1.206 markus 735: will refuse to use a file if it is group/world-accessible
736: and that the
737: .Cm HostKeyAlgorithms
738: option restricts which of the keys are actually used by
739: .Xr sshd 8 .
740: .Pp
1.1 stevesk 741: It is possible to have multiple host key files.
1.162 markus 742: It is also possible to specify public host key files instead.
743: In this case operations on the private key will be delegated
744: to an
745: .Xr ssh-agent 1 .
746: .It Cm HostKeyAgent
747: Identifies the UNIX-domain socket used to communicate
748: with an agent that has access to the private host keys.
1.223 markus 749: If the string
1.237 jmc 750: .Qq SSH_AUTH_SOCK
1.162 markus 751: is specified, the location of the socket will be read from the
752: .Ev SSH_AUTH_SOCK
753: environment variable.
1.206 markus 754: .It Cm HostKeyAlgorithms
1.327 djm 755: Specifies the host key signature algorithms
1.206 markus 756: that the server offers.
757: The default for this option is:
758: .Bd -literal -offset 3n
1.316 djm 759: ssh-ed25519-cert-v01@openssh.com,
1.206 markus 760: ecdsa-sha2-nistp256-cert-v01@openssh.com,
761: ecdsa-sha2-nistp384-cert-v01@openssh.com,
762: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.316 djm 763: sk-ssh-ed25519-cert-v01@openssh.com,
1.296 naddy 764: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.291 naddy 765: rsa-sha2-512-cert-v01@openssh.com,
766: rsa-sha2-256-cert-v01@openssh.com,
1.206 markus 767: ssh-rsa-cert-v01@openssh.com,
1.316 djm 768: ssh-ed25519,
1.206 markus 769: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.316 djm 770: sk-ssh-ed25519@openssh.com,
1.296 naddy 771: sk-ecdsa-sha2-nistp256@openssh.com,
772: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.206 markus 773: .Ed
774: .Pp
1.327 djm 775: The list of available signature algorithms may also be obtained using
1.307 dtucker 776: .Qq ssh -Q HostKeyAlgorithms .
1.1 stevesk 777: .It Cm IgnoreRhosts
1.309 djm 778: Specifies whether to ignore per-user
1.1 stevesk 779: .Pa .rhosts
780: and
781: .Pa .shosts
1.309 djm 782: files during
1.1 stevesk 783: .Cm HostbasedAuthentication .
1.309 djm 784: The system-wide
1.1 stevesk 785: .Pa /etc/hosts.equiv
786: and
787: .Pa /etc/shosts.equiv
1.309 djm 788: are still used regardless of this setting.
789: .Pp
790: Accepted values are
791: .Cm yes
792: (the default) to ignore all per-user files,
793: .Cm shosts-only
794: to allow the use of
795: .Pa .shosts
796: but to ignore
797: .Pa .rhosts
798: or
799: .Cm no
800: to allow both
801: .Pa .shosts
802: and
1.311 jmc 803: .Pa rhosts .
1.1 stevesk 804: .It Cm IgnoreUserKnownHosts
805: Specifies whether
1.52 jmc 806: .Xr sshd 8
1.1 stevesk 807: should ignore the user's
1.41 djm 808: .Pa ~/.ssh/known_hosts
1.1 stevesk 809: during
1.261 djm 810: .Cm HostbasedAuthentication
811: and use only the system-wide known hosts file
812: .Pa /etc/ssh/known_hosts .
1.1 stevesk 813: The default is
1.304 djm 814: .Dq no .
815: .It Cm Include
816: Include the specified configuration file(s).
1.305 jmc 817: Multiple pathnames may be specified and each pathname may contain
1.304 djm 818: .Xr glob 7
1.312 djm 819: wildcards that will be expanded and processed in lexical order.
1.304 djm 820: Files without absolute paths are assumed to be in
821: .Pa /etc/ssh .
1.305 jmc 822: An
1.304 djm 823: .Cm Include
824: directive may appear inside a
825: .Cm Match
826: block
827: to perform conditional inclusion.
1.129 djm 828: .It Cm IPQoS
829: Specifies the IPv4 type-of-service or DSCP class for the connection.
830: Accepted values are
1.237 jmc 831: .Cm af11 ,
832: .Cm af12 ,
833: .Cm af13 ,
834: .Cm af21 ,
835: .Cm af22 ,
836: .Cm af23 ,
837: .Cm af31 ,
838: .Cm af32 ,
839: .Cm af33 ,
840: .Cm af41 ,
841: .Cm af42 ,
842: .Cm af43 ,
843: .Cm cs0 ,
844: .Cm cs1 ,
845: .Cm cs2 ,
846: .Cm cs3 ,
847: .Cm cs4 ,
848: .Cm cs5 ,
849: .Cm cs6 ,
850: .Cm cs7 ,
851: .Cm ef ,
1.303 djm 852: .Cm le ,
1.237 jmc 853: .Cm lowdelay ,
854: .Cm throughput ,
855: .Cm reliability ,
1.250 djm 856: a numeric value, or
857: .Cm none
858: to use the operating system default.
1.131 djm 859: This option may take one or two arguments, separated by whitespace.
1.129 djm 860: If one argument is specified, it is used as the packet class unconditionally.
861: If two values are specified, the first is automatically selected for
862: interactive sessions and the second for non-interactive sessions.
863: The default is
1.264 job 864: .Cm af21
1.265 jmc 865: (Low-Latency Data)
1.129 djm 866: for interactive sessions and
1.264 job 867: .Cm cs1
1.265 jmc 868: (Lower Effort)
1.129 djm 869: for non-interactive sessions.
1.171 jmc 870: .It Cm KbdInteractiveAuthentication
871: Specifies whether to allow keyboard-interactive authentication.
1.332 dtucker 872: All authentication styles from
873: .Xr login.conf 5
874: are supported.
875: The default is
876: .Cm yes .
1.171 jmc 877: The argument to this keyword must be
1.237 jmc 878: .Cm yes
1.171 jmc 879: or
1.237 jmc 880: .Cm no .
1.171 jmc 881: .Cm ChallengeResponseAuthentication
1.332 dtucker 882: is a deprecated alias for this.
1.1 stevesk 883: .It Cm KerberosAuthentication
1.24 markus 884: Specifies whether the password provided by the user for
1.1 stevesk 885: .Cm PasswordAuthentication
1.24 markus 886: will be validated through the Kerberos KDC.
1.1 stevesk 887: To use this option, the server needs a
888: Kerberos servtab which allows the verification of the KDC's identity.
1.52 jmc 889: The default is
1.237 jmc 890: .Cm no .
1.29 dtucker 891: .It Cm KerberosGetAFSToken
1.45 djm 892: If AFS is active and the user has a Kerberos 5 TGT, attempt to acquire
1.29 dtucker 893: an AFS token before accessing the user's home directory.
1.52 jmc 894: The default is
1.237 jmc 895: .Cm no .
1.1 stevesk 896: .It Cm KerberosOrLocalPasswd
1.52 jmc 897: If password authentication through Kerberos fails then
1.1 stevesk 898: the password will be validated via any additional local mechanism
899: such as
900: .Pa /etc/passwd .
1.52 jmc 901: The default is
1.237 jmc 902: .Cm yes .
1.1 stevesk 903: .It Cm KerberosTicketCleanup
904: Specifies whether to automatically destroy the user's ticket cache
905: file on logout.
1.52 jmc 906: The default is
1.237 jmc 907: .Cm yes .
1.127 djm 908: .It Cm KexAlgorithms
909: Specifies the available KEX (Key Exchange) algorithms.
910: Multiple algorithms must be comma-separated.
1.289 naddy 911: Alternately if the specified list begins with a
1.208 djm 912: .Sq +
913: character, then the specified methods will be appended to the default set
914: instead of replacing them.
1.289 naddy 915: If the specified list begins with a
1.242 djm 916: .Sq -
917: character, then the specified methods (including wildcards) will be removed
918: from the default set instead of replacing them.
1.290 naddy 919: If the specified list begins with a
920: .Sq ^
921: character, then the specified methods will be placed at the head of the
922: default set.
1.173 naddy 923: The supported algorithms are:
924: .Pp
925: .Bl -item -compact -offset indent
926: .It
1.234 djm 927: curve25519-sha256
928: .It
1.173 naddy 929: curve25519-sha256@libssh.org
930: .It
931: diffie-hellman-group1-sha1
932: .It
933: diffie-hellman-group14-sha1
934: .It
1.263 djm 935: diffie-hellman-group14-sha256
936: .It
937: diffie-hellman-group16-sha512
938: .It
939: diffie-hellman-group18-sha512
940: .It
1.173 naddy 941: diffie-hellman-group-exchange-sha1
942: .It
943: diffie-hellman-group-exchange-sha256
944: .It
945: ecdh-sha2-nistp256
946: .It
947: ecdh-sha2-nistp384
948: .It
949: ecdh-sha2-nistp521
1.298 dtucker 950: .It
1.319 djm 951: sntrup761x25519-sha512@openssh.com
1.173 naddy 952: .El
953: .Pp
954: The default is:
1.170 dtucker 955: .Bd -literal -offset indent
1.234 djm 956: curve25519-sha256,curve25519-sha256@libssh.org,
1.170 dtucker 957: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
958: diffie-hellman-group-exchange-sha256,
1.263 djm 959: diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,
1.300 tedu 960: diffie-hellman-group14-sha256
1.170 dtucker 961: .Ed
1.188 djm 962: .Pp
1.237 jmc 963: The list of available key exchange algorithms may also be obtained using
1.307 dtucker 964: .Qq ssh -Q KexAlgorithms .
1.1 stevesk 965: .It Cm ListenAddress
966: Specifies the local addresses
1.52 jmc 967: .Xr sshd 8
1.1 stevesk 968: should listen on.
969: The following forms may be used:
970: .Pp
971: .Bl -item -offset indent -compact
972: .It
973: .Cm ListenAddress
974: .Sm off
1.259 jmc 975: .Ar hostname | address
1.1 stevesk 976: .Sm on
1.260 jmc 977: .Op Cm rdomain Ar domain
1.1 stevesk 978: .It
979: .Cm ListenAddress
980: .Sm off
1.259 jmc 981: .Ar hostname : port
1.1 stevesk 982: .Sm on
1.260 jmc 983: .Op Cm rdomain Ar domain
1.256 djm 984: .It
985: .Cm ListenAddress
986: .Sm off
1.259 jmc 987: .Ar IPv4_address : port
1.256 djm 988: .Sm on
1.260 jmc 989: .Op Cm rdomain Ar domain
1.1 stevesk 990: .It
991: .Cm ListenAddress
992: .Sm off
1.259 jmc 993: .Oo Ar hostname | address Oc : Ar port
1.1 stevesk 994: .Sm on
1.260 jmc 995: .Op Cm rdomain Ar domain
1.1 stevesk 996: .El
997: .Pp
1.256 djm 998: The optional
999: .Cm rdomain
1000: qualifier requests
1001: .Xr sshd 8
1002: listen in an explicit routing domain.
1.1 stevesk 1003: If
1004: .Ar port
1005: is not specified,
1.200 dtucker 1006: sshd will listen on the address and all
1.1 stevesk 1007: .Cm Port
1.17 jmc 1008: options specified.
1.256 djm 1009: The default is to listen on all local addresses on the current default
1010: routing domain.
1.15 jmc 1011: Multiple
1.1 stevesk 1012: .Cm ListenAddress
1.17 jmc 1013: options are permitted.
1.256 djm 1014: For more information on routing domains, see
1.259 jmc 1015: .Xr rdomain 4 .
1.1 stevesk 1016: .It Cm LoginGraceTime
1017: The server disconnects after this time if the user has not
1018: successfully logged in.
1019: If the value is 0, there is no time limit.
1.12 stevesk 1020: The default is 120 seconds.
1.1 stevesk 1021: .It Cm LogLevel
1022: Gives the verbosity level that is used when logging messages from
1.53 jmc 1023: .Xr sshd 8 .
1.1 stevesk 1024: The possible values are:
1.52 jmc 1025: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.15 jmc 1026: The default is INFO.
1027: DEBUG and DEBUG1 are equivalent.
1028: DEBUG2 and DEBUG3 each specify higher levels of debugging output.
1029: Logging with a DEBUG level violates the privacy of users and is not recommended.
1.317 djm 1030: .It Cm LogVerbose
1031: Specify one or more overrides to LogLevel.
1032: An override consists of a pattern lists that matches the source file, function
1033: and line number to force detailed logging for.
1034: For example, an override pattern of:
1035: .Bd -literal -offset indent
1036: kex.c:*:1000,*:kex_exchange_identification():*,packet.c:*
1037: .Ed
1038: .Pp
1039: would enable detailed logging for line 1000 of
1.318 jmc 1040: .Pa kex.c ,
1.317 djm 1041: everything in the
1042: .Fn kex_exchange_identification
1043: function, and all code in the
1044: .Pa packet.c
1045: file.
1046: This option is intended for debugging and no overrides are enabled by default.
1.1 stevesk 1047: .It Cm MACs
1048: Specifies the available MAC (message authentication code) algorithms.
1.219 jmc 1049: The MAC algorithm is used for data integrity protection.
1.1 stevesk 1050: Multiple algorithms must be comma-separated.
1.289 naddy 1051: If the specified list begins with a
1.208 djm 1052: .Sq +
1053: character, then the specified algorithms will be appended to the default set
1054: instead of replacing them.
1.289 naddy 1055: If the specified list begins with a
1.242 djm 1056: .Sq -
1057: character, then the specified algorithms (including wildcards) will be removed
1058: from the default set instead of replacing them.
1.290 naddy 1059: If the specified list begins with a
1060: .Sq ^
1061: character, then the specified algorithms will be placed at the head of the
1062: default set.
1.208 djm 1063: .Pp
1.152 markus 1064: The algorithms that contain
1.237 jmc 1065: .Qq -etm
1.152 markus 1066: calculate the MAC after encryption (encrypt-then-mac).
1067: These are considered safer and their use recommended.
1.173 naddy 1068: The supported MACs are:
1069: .Pp
1070: .Bl -item -compact -offset indent
1071: .It
1072: hmac-md5
1073: .It
1074: hmac-md5-96
1075: .It
1076: hmac-sha1
1077: .It
1078: hmac-sha1-96
1079: .It
1080: hmac-sha2-256
1081: .It
1082: hmac-sha2-512
1083: .It
1084: umac-64@openssh.com
1085: .It
1086: umac-128@openssh.com
1087: .It
1088: hmac-md5-etm@openssh.com
1089: .It
1090: hmac-md5-96-etm@openssh.com
1091: .It
1092: hmac-sha1-etm@openssh.com
1093: .It
1094: hmac-sha1-96-etm@openssh.com
1095: .It
1096: hmac-sha2-256-etm@openssh.com
1097: .It
1098: hmac-sha2-512-etm@openssh.com
1099: .It
1100: umac-64-etm@openssh.com
1101: .It
1102: umac-128-etm@openssh.com
1103: .El
1104: .Pp
1.52 jmc 1105: The default is:
1.77 jmc 1106: .Bd -literal -offset indent
1.152 markus 1107: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
1108: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
1.217 djm 1109: hmac-sha1-etm@openssh.com,
1.173 naddy 1110: umac-64@openssh.com,umac-128@openssh.com,
1.217 djm 1111: hmac-sha2-256,hmac-sha2-512,hmac-sha1
1.77 jmc 1112: .Ed
1.188 djm 1113: .Pp
1.237 jmc 1114: The list of available MAC algorithms may also be obtained using
1115: .Qq ssh -Q mac .
1.60 dtucker 1116: .It Cm Match
1.61 jmc 1117: Introduces a conditional block.
1.65 dtucker 1118: If all of the criteria on the
1.60 dtucker 1119: .Cm Match
1.65 dtucker 1120: line are satisfied, the keywords on the following lines override those
1121: set in the global section of the config file, until either another
1.60 dtucker 1122: .Cm Match
1.65 dtucker 1123: line or the end of the file.
1.172 djm 1124: If a keyword appears in multiple
1125: .Cm Match
1.177 sobrado 1126: blocks that are satisfied, only the first instance of the keyword is
1.172 djm 1127: applied.
1.91 djm 1128: .Pp
1.61 jmc 1129: The arguments to
1.60 dtucker 1130: .Cm Match
1.163 dtucker 1131: are one or more criteria-pattern pairs or the single token
1132: .Cm All
1133: which matches all criteria.
1.60 dtucker 1134: The available criteria are
1135: .Cm User ,
1.69 dtucker 1136: .Cm Group ,
1.60 dtucker 1137: .Cm Host ,
1.139 dtucker 1138: .Cm LocalAddress ,
1139: .Cm LocalPort ,
1.258 djm 1140: .Cm RDomain ,
1.60 dtucker 1141: and
1.258 djm 1142: .Cm Address
1143: (with
1144: .Cm RDomain
1145: representing the
1146: .Xr rdomain 4
1.284 jmc 1147: on which the connection was received).
1.258 djm 1148: .Pp
1.91 djm 1149: The match patterns may consist of single entries or comma-separated
1150: lists and may use the wildcard and negation operators described in the
1.237 jmc 1151: .Sx PATTERNS
1152: section of
1.92 djm 1153: .Xr ssh_config 5 .
1.91 djm 1154: .Pp
1155: The patterns in an
1156: .Cm Address
1157: criteria may additionally contain addresses to match in CIDR
1.237 jmc 1158: address/masklen format,
1159: such as 192.0.2.0/24 or 2001:db8::/32.
1.91 djm 1160: Note that the mask length provided must be consistent with the address -
1161: it is an error to specify a mask length that is too long for the address
1.93 jmc 1162: or one with bits set in this host portion of the address.
1.237 jmc 1163: For example, 192.0.2.0/33 and 192.0.2.0/8, respectively.
1.91 djm 1164: .Pp
1.60 dtucker 1165: Only a subset of keywords may be used on the lines following a
1166: .Cm Match
1167: keyword.
1168: Available keywords are
1.142 jmc 1169: .Cm AcceptEnv ,
1.99 okan 1170: .Cm AllowAgentForwarding ,
1.142 jmc 1171: .Cm AllowGroups ,
1.193 djm 1172: .Cm AllowStreamLocalForwarding ,
1.62 dtucker 1173: .Cm AllowTcpForwarding ,
1.141 markus 1174: .Cm AllowUsers ,
1.149 djm 1175: .Cm AuthenticationMethods ,
1.146 djm 1176: .Cm AuthorizedKeysCommand ,
1177: .Cm AuthorizedKeysCommandUser ,
1.147 jmc 1178: .Cm AuthorizedKeysFile ,
1.214 djm 1179: .Cm AuthorizedPrincipalsCommand ,
1180: .Cm AuthorizedPrincipalsCommandUser ,
1.123 djm 1181: .Cm AuthorizedPrincipalsFile ,
1.72 dtucker 1182: .Cm Banner ,
1.85 djm 1183: .Cm ChrootDirectory ,
1.238 markus 1184: .Cm ClientAliveCountMax ,
1185: .Cm ClientAliveInterval ,
1.141 markus 1186: .Cm DenyGroups ,
1187: .Cm DenyUsers ,
1.320 djm 1188: .Cm DisableForwarding ,
1.67 dtucker 1189: .Cm ForceCommand ,
1.194 djm 1190: .Cm GatewayPorts ,
1.193 djm 1191: .Cm GSSAPIAuthentication ,
1.325 dtucker 1192: .Cm HostbasedAcceptedAlgorithms ,
1.87 djm 1193: .Cm HostbasedAuthentication ,
1.123 djm 1194: .Cm HostbasedUsesNameFromPacketOnly ,
1.308 djm 1195: .Cm IgnoreRhosts ,
1.306 naddy 1196: .Cm Include ,
1.193 djm 1197: .Cm IPQoS ,
1.74 jmc 1198: .Cm KbdInteractiveAuthentication ,
1.72 dtucker 1199: .Cm KerberosAuthentication ,
1.245 djm 1200: .Cm LogLevel ,
1.95 dtucker 1201: .Cm MaxAuthTries ,
1.94 dtucker 1202: .Cm MaxSessions ,
1.72 dtucker 1203: .Cm PasswordAuthentication ,
1.97 djm 1204: .Cm PermitEmptyPasswords ,
1.271 djm 1205: .Cm PermitListen ,
1.66 dtucker 1206: .Cm PermitOpen ,
1.79 dtucker 1207: .Cm PermitRootLogin ,
1.164 djm 1208: .Cm PermitTTY ,
1.123 djm 1209: .Cm PermitTunnel ,
1.174 djm 1210: .Cm PermitUserRC ,
1.324 dtucker 1211: .Cm PubkeyAcceptedAlgorithms ,
1.107 dtucker 1212: .Cm PubkeyAuthentication ,
1.159 dtucker 1213: .Cm RekeyLimit ,
1.193 djm 1214: .Cm RevokedKeys ,
1.257 djm 1215: .Cm RDomain ,
1.274 djm 1216: .Cm SetEnv ,
1.193 djm 1217: .Cm StreamLocalBindMask ,
1218: .Cm StreamLocalBindUnlink ,
1219: .Cm TrustedUserCAKeys ,
1.66 dtucker 1220: .Cm X11DisplayOffset ,
1.101 djm 1221: .Cm X11Forwarding
1.60 dtucker 1222: and
1.286 jmc 1223: .Cm X11UseLocalhost .
1.33 dtucker 1224: .It Cm MaxAuthTries
1225: Specifies the maximum number of authentication attempts permitted per
1.35 jmc 1226: connection.
1227: Once the number of failures reaches half this value,
1228: additional failures are logged.
1229: The default is 6.
1.90 djm 1230: .It Cm MaxSessions
1.216 djm 1231: Specifies the maximum number of open shell, login or subsystem (e.g. sftp)
1232: sessions permitted per network connection.
1233: Multiple sessions may be established by clients that support connection
1234: multiplexing.
1235: Setting
1236: .Cm MaxSessions
1237: to 1 will effectively disable session multiplexing, whereas setting it to 0
1238: will prevent all shell, login and subsystem sessions while still permitting
1239: forwarding.
1.90 djm 1240: The default is 10.
1.1 stevesk 1241: .It Cm MaxStartups
1242: Specifies the maximum number of concurrent unauthenticated connections to the
1.52 jmc 1243: SSH daemon.
1.1 stevesk 1244: Additional connections will be dropped until authentication succeeds or the
1245: .Cm LoginGraceTime
1246: expires for a connection.
1.156 dtucker 1247: The default is 10:30:100.
1.1 stevesk 1248: .Pp
1249: Alternatively, random early drop can be enabled by specifying
1250: the three colon separated values
1.237 jmc 1251: start:rate:full (e.g. "10:30:60").
1.53 jmc 1252: .Xr sshd 8
1.237 jmc 1253: will refuse connection attempts with a probability of rate/100 (30%)
1254: if there are currently start (10) unauthenticated connections.
1.1 stevesk 1255: The probability increases linearly and all connection attempts
1.237 jmc 1256: are refused if the number of unauthenticated connections reaches full (60).
1.329 dtucker 1257: .It Cm ModuliFile
1258: Specifies the
1259: .Xr moduli 5
1260: file that contains the Diffie-Hellman groups used for the
1261: .Dq diffie-hellman-group-exchange-sha1
1262: and
1263: .Dq diffie-hellman-group-exchange-sha256
1264: key exchange methods.
1265: The default is
1266: .Pa /etc/moduli .
1.1 stevesk 1267: .It Cm PasswordAuthentication
1268: Specifies whether password authentication is allowed.
1269: The default is
1.237 jmc 1270: .Cm yes .
1.1 stevesk 1271: .It Cm PermitEmptyPasswords
1272: When password authentication is allowed, it specifies whether the
1273: server allows login to accounts with empty password strings.
1274: The default is
1.237 jmc 1275: .Cm no .
1.271 djm 1276: .It Cm PermitListen
1277: Specifies the addresses/ports on which a remote TCP port forwarding may listen.
1278: The listen specification must be one of the following forms:
1279: .Pp
1280: .Bl -item -offset indent -compact
1281: .It
1282: .Cm PermitListen
1283: .Sm off
1.276 djm 1284: .Ar port
1.271 djm 1285: .Sm on
1286: .It
1287: .Cm PermitListen
1288: .Sm off
1.276 djm 1289: .Ar host : port
1.271 djm 1290: .Sm on
1291: .El
1292: .Pp
1293: Multiple permissions may be specified by separating them with whitespace.
1294: An argument of
1295: .Cm any
1296: can be used to remove all restrictions and permit any listen requests.
1297: An argument of
1298: .Cm none
1299: can be used to prohibit all listen requests.
1300: The host name may contain wildcards as described in the PATTERNS section in
1301: .Xr ssh_config 5 .
1302: The wildcard
1303: .Sq *
1304: can also be used in place of a port number to allow all ports.
1305: By default all port forwarding listen requests are permitted.
1.272 jmc 1306: Note that the
1.271 djm 1307: .Cm GatewayPorts
1308: option may further restrict which addresses may be listened on.
1.276 djm 1309: Note also that
1310: .Xr ssh 1
1311: will request a listen host of
1312: .Dq localhost
1.283 dtucker 1313: if no listen host was specifically requested, and this name is
1.277 jmc 1314: treated differently to explicit localhost addresses of
1.276 djm 1315: .Dq 127.0.0.1
1316: and
1317: .Dq ::1 .
1.62 dtucker 1318: .It Cm PermitOpen
1319: Specifies the destinations to which TCP port forwarding is permitted.
1320: The forwarding specification must be one of the following forms:
1321: .Pp
1322: .Bl -item -offset indent -compact
1323: .It
1324: .Cm PermitOpen
1325: .Sm off
1326: .Ar host : port
1327: .Sm on
1328: .It
1329: .Cm PermitOpen
1330: .Sm off
1331: .Ar IPv4_addr : port
1332: .Sm on
1333: .It
1334: .Cm PermitOpen
1335: .Sm off
1336: .Ar \&[ IPv6_addr \&] : port
1337: .Sm on
1338: .El
1339: .Pp
1.68 dtucker 1340: Multiple forwards may be specified by separating them with whitespace.
1.62 dtucker 1341: An argument of
1.237 jmc 1342: .Cm any
1.62 dtucker 1343: can be used to remove all restrictions and permit any forwarding requests.
1.140 dtucker 1344: An argument of
1.237 jmc 1345: .Cm none
1.140 dtucker 1346: can be used to prohibit all forwarding requests.
1.227 jmc 1347: The wildcard
1.237 jmc 1348: .Sq *
1.299 djm 1349: can be used for host or port to allow all hosts or ports respectively.
1350: Otherwise, no pattern matching or address lookups are performed on supplied
1351: names.
1.63 jmc 1352: By default all port forwarding requests are permitted.
1.1 stevesk 1353: .It Cm PermitRootLogin
1.38 jmc 1354: Specifies whether root can log in using
1.1 stevesk 1355: .Xr ssh 1 .
1356: The argument must be
1.237 jmc 1357: .Cm yes ,
1358: .Cm prohibit-password ,
1359: .Cm forced-commands-only ,
1.1 stevesk 1360: or
1.237 jmc 1361: .Cm no .
1.1 stevesk 1362: The default is
1.237 jmc 1363: .Cm prohibit-password .
1.1 stevesk 1364: .Pp
1365: If this option is set to
1.237 jmc 1366: .Cm prohibit-password
1.255 jmc 1367: (or its deprecated alias,
1368: .Cm without-password ) ,
1.210 deraadt 1369: password and keyboard-interactive authentication are disabled for root.
1.1 stevesk 1370: .Pp
1371: If this option is set to
1.237 jmc 1372: .Cm forced-commands-only ,
1.1 stevesk 1373: root login with public key authentication will be allowed,
1374: but only if the
1375: .Ar command
1376: option has been specified
1377: (which may be useful for taking remote backups even if root login is
1.17 jmc 1378: normally not allowed).
1379: All other authentication methods are disabled for root.
1.1 stevesk 1380: .Pp
1381: If this option is set to
1.237 jmc 1382: .Cm no ,
1.38 jmc 1383: root is not allowed to log in.
1.231 jmc 1384: .It Cm PermitTTY
1385: Specifies whether
1386: .Xr pty 4
1387: allocation is permitted.
1388: The default is
1.237 jmc 1389: .Cm yes .
1.46 reyk 1390: .It Cm PermitTunnel
1391: Specifies whether
1392: .Xr tun 4
1393: device forwarding is allowed.
1.47 reyk 1394: The argument must be
1.237 jmc 1395: .Cm yes ,
1396: .Cm point-to-point
1.58 stevesk 1397: (layer 3),
1.237 jmc 1398: .Cm ethernet
1.58 stevesk 1399: (layer 2), or
1.237 jmc 1400: .Cm no .
1.58 stevesk 1401: Specifying
1.237 jmc 1402: .Cm yes
1.58 stevesk 1403: permits both
1.237 jmc 1404: .Cm point-to-point
1.58 stevesk 1405: and
1.237 jmc 1406: .Cm ethernet .
1.46 reyk 1407: The default is
1.237 jmc 1408: .Cm no .
1.178 djm 1409: .Pp
1410: Independent of this setting, the permissions of the selected
1411: .Xr tun 4
1412: device must allow access to the user.
1.6 markus 1413: .It Cm PermitUserEnvironment
1414: Specifies whether
1415: .Pa ~/.ssh/environment
1.9 stevesk 1416: and
1.6 markus 1417: .Cm environment=
1418: options in
1419: .Pa ~/.ssh/authorized_keys
1.9 stevesk 1420: are processed by
1.52 jmc 1421: .Xr sshd 8 .
1.278 djm 1422: Valid options are
1423: .Cm yes ,
1424: .Cm no
1425: or a pattern-list specifying which environment variable names to accept
1426: (for example
1427: .Qq LANG,LC_* ) .
1.6 markus 1428: The default is
1.237 jmc 1429: .Cm no .
1.9 stevesk 1430: Enabling environment processing may enable users to bypass access
1431: restrictions in some configurations using mechanisms such as
1432: .Ev LD_PRELOAD .
1.174 djm 1433: .It Cm PermitUserRC
1434: Specifies whether any
1435: .Pa ~/.ssh/rc
1436: file is executed.
1437: The default is
1.237 jmc 1438: .Cm yes .
1.321 dtucker 1439: .It Cm PerSourceMaxStartups
1440: Specifies the number of unauthenticated connections allowed from a
1441: given source address, or
1442: .Dq none
1443: if there is no limit.
1444: This limit is applied in addition to
1445: .Cm MaxStartups ,
1446: whichever is lower.
1447: The default is
1448: .Cm none .
1449: .It Cm PerSourceNetBlockSize
1450: Specifies the number of bits of source address that are grouped together
1451: for the purposes of applying PerSourceMaxStartups limits.
1452: Values for IPv4 and optionally IPv6 may be specified, separated by a colon.
1453: The default is
1.322 jmc 1454: .Cm 32:128 ,
1.321 dtucker 1455: which means each address is considered individually.
1.328 djm 1456: .It Cm PidFile
1457: Specifies the file that contains the process ID of the
1458: SSH daemon, or
1459: .Cm none
1460: to not write one.
1461: The default is
1462: .Pa /var/run/sshd.pid .
1.1 stevesk 1463: .It Cm Port
1464: Specifies the port number that
1.52 jmc 1465: .Xr sshd 8
1.1 stevesk 1466: listens on.
1467: The default is 22.
1468: Multiple options of this type are permitted.
1469: See also
1470: .Cm ListenAddress .
1471: .It Cm PrintLastLog
1472: Specifies whether
1.52 jmc 1473: .Xr sshd 8
1.36 jaredy 1474: should print the date and time of the last user login when a user logs
1475: in interactively.
1.1 stevesk 1476: The default is
1.237 jmc 1477: .Cm yes .
1.1 stevesk 1478: .It Cm PrintMotd
1479: Specifies whether
1.52 jmc 1480: .Xr sshd 8
1.1 stevesk 1481: should print
1482: .Pa /etc/motd
1483: when a user logs in interactively.
1484: (On some systems it is also printed by the shell,
1485: .Pa /etc/profile ,
1486: or equivalent.)
1487: The default is
1.237 jmc 1488: .Cm yes .
1.324 dtucker 1489: .It Cm PubkeyAcceptedAlgorithms
1490: Specifies the signature algorithms that will be accepted for public key
1491: authentication as a list of comma-separated patterns.
1.289 naddy 1492: Alternately if the specified list begins with a
1.208 djm 1493: .Sq +
1.324 dtucker 1494: character, then the specified algorithms will be appended to the default set
1.208 djm 1495: instead of replacing them.
1.289 naddy 1496: If the specified list begins with a
1.242 djm 1497: .Sq -
1.324 dtucker 1498: character, then the specified algorithms (including wildcards) will be removed
1.242 djm 1499: from the default set instead of replacing them.
1.290 naddy 1500: If the specified list begins with a
1501: .Sq ^
1.324 dtucker 1502: character, then the specified algorithms will be placed at the head of the
1.290 naddy 1503: default set.
1.206 markus 1504: The default for this option is:
1505: .Bd -literal -offset 3n
1.316 djm 1506: ssh-ed25519-cert-v01@openssh.com,
1.206 markus 1507: ecdsa-sha2-nistp256-cert-v01@openssh.com,
1508: ecdsa-sha2-nistp384-cert-v01@openssh.com,
1509: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.316 djm 1510: sk-ssh-ed25519-cert-v01@openssh.com,
1.296 naddy 1511: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.291 naddy 1512: rsa-sha2-512-cert-v01@openssh.com,
1513: rsa-sha2-256-cert-v01@openssh.com,
1.206 markus 1514: ssh-rsa-cert-v01@openssh.com,
1.316 djm 1515: ssh-ed25519,
1.296 naddy 1516: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.316 djm 1517: sk-ssh-ed25519@openssh.com,
1.291 naddy 1518: sk-ecdsa-sha2-nistp256@openssh.com,
1.296 naddy 1519: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.206 markus 1520: .Ed
1521: .Pp
1.326 djm 1522: The list of available signature algorithms may also be obtained using
1.324 dtucker 1523: .Qq ssh -Q PubkeyAcceptedAlgorithms .
1.293 djm 1524: .It Cm PubkeyAuthOptions
1525: Sets one or more public key authentication options.
1.313 djm 1526: The supported keywords are:
1.294 jmc 1527: .Cm none
1.313 djm 1528: (the default; indicating no additional options are enabled),
1529: .Cm touch-required
1.293 djm 1530: and
1.313 djm 1531: .Cm verify-required .
1.293 djm 1532: .Pp
1533: The
1534: .Cm touch-required
1.297 naddy 1535: option causes public key authentication using a FIDO authenticator algorithm
1.294 jmc 1536: (i.e.\&
1.293 djm 1537: .Cm ecdsa-sk
1538: or
1539: .Cm ed25519-sk )
1540: to always require the signature to attest that a physically present user
1.297 naddy 1541: explicitly confirmed the authentication (usually by touching the authenticator).
1.293 djm 1542: By default,
1543: .Xr sshd 8
1.297 naddy 1544: requires user presence unless overridden with an authorized_keys option.
1.293 djm 1545: The
1546: .Cm touch-required
1547: flag disables this override.
1.313 djm 1548: .Pp
1549: The
1550: .Cm verify-required
1.315 jmc 1551: option requires a FIDO key signature attest that the user was verified,
1.314 jmc 1552: e.g. via a PIN.
1.313 djm 1553: .Pp
1554: Neither the
1555: .Cm touch-required
1556: or
1557: .Cm verify-required
1.314 jmc 1558: options have any effect for other, non-FIDO, public key types.
1.1 stevesk 1559: .It Cm PubkeyAuthentication
1560: Specifies whether public key authentication is allowed.
1561: The default is
1.237 jmc 1562: .Cm yes .
1.159 dtucker 1563: .It Cm RekeyLimit
1564: Specifies the maximum amount of data that may be transmitted before the
1.323 rob 1565: session key is renegotiated, optionally followed by a maximum amount of
1.159 dtucker 1566: time that may pass before the session key is renegotiated.
1567: The first argument is specified in bytes and may have a suffix of
1568: .Sq K ,
1569: .Sq M ,
1570: or
1571: .Sq G
1572: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1573: The default is between
1574: .Sq 1G
1575: and
1576: .Sq 4G ,
1577: depending on the cipher.
1578: The optional second value is specified in seconds and may use any of the
1579: units documented in the
1580: .Sx TIME FORMATS
1.160 jmc 1581: section.
1.159 dtucker 1582: The default value for
1583: .Cm RekeyLimit
1584: is
1.237 jmc 1585: .Cm default none ,
1.159 dtucker 1586: which means that rekeying is performed after the cipher's default amount
1587: of data has been sent or received and no time based rekeying is done.
1.118 djm 1588: .It Cm RevokedKeys
1.195 dtucker 1589: Specifies revoked public keys file, or
1.237 jmc 1590: .Cm none
1.195 dtucker 1591: to not use one.
1.118 djm 1592: Keys listed in this file will be refused for public key authentication.
1593: Note that if this file is not readable, then public key authentication will
1594: be refused for all users.
1.154 djm 1595: Keys may be specified as a text file, listing one public key per line, or as
1596: an OpenSSH Key Revocation List (KRL) as generated by
1.155 jmc 1597: .Xr ssh-keygen 1 .
1.161 jmc 1598: For more information on KRLs, see the KEY REVOCATION LISTS section in
1.154 djm 1599: .Xr ssh-keygen 1 .
1.257 djm 1600: .It Cm RDomain
1601: Specifies an explicit routing domain that is applied after authentication
1602: has completed.
1.333 ! jmc 1603: The user session, as well as any forwarded or listening IP sockets,
1.259 jmc 1604: will be bound to this
1.257 djm 1605: .Xr rdomain 4 .
1606: If the routing domain is set to
1607: .Cm \&%D ,
1.259 jmc 1608: then the domain in which the incoming connection was received will be applied.
1.296 naddy 1609: .It Cm SecurityKeyProvider
1.297 naddy 1610: Specifies a path to a library that will be used when loading
1611: FIDO authenticator-hosted keys, overriding the default of using
1612: the built-in USB HID support.
1.274 djm 1613: .It Cm SetEnv
1614: Specifies one or more environment variables to set in child sessions started
1615: by
1616: .Xr sshd 8
1617: as
1618: .Dq NAME=VALUE .
1619: The environment value may be quoted (e.g. if it contains whitespace
1620: characters).
1621: Environment variables set by
1622: .Cm SetEnv
1623: override the default environment and any variables specified by the user
1624: via
1625: .Cm AcceptEnv
1626: or
1627: .Cm PermitUserEnvironment .
1.175 millert 1628: .It Cm StreamLocalBindMask
1629: Sets the octal file creation mode mask
1630: .Pq umask
1631: used when creating a Unix-domain socket file for local or remote
1632: port forwarding.
1633: This option is only used for port forwarding to a Unix-domain socket file.
1634: .Pp
1635: The default value is 0177, which creates a Unix-domain socket file that is
1636: readable and writable only by the owner.
1637: Note that not all operating systems honor the file mode on Unix-domain
1638: socket files.
1639: .It Cm StreamLocalBindUnlink
1640: Specifies whether to remove an existing Unix-domain socket file for local
1641: or remote port forwarding before creating a new one.
1642: If the socket file already exists and
1643: .Cm StreamLocalBindUnlink
1644: is not enabled,
1645: .Nm sshd
1646: will be unable to forward the port to the Unix-domain socket file.
1647: This option is only used for port forwarding to a Unix-domain socket file.
1648: .Pp
1649: The argument must be
1.237 jmc 1650: .Cm yes
1.175 millert 1651: or
1.237 jmc 1652: .Cm no .
1.175 millert 1653: The default is
1.237 jmc 1654: .Cm no .
1.1 stevesk 1655: .It Cm StrictModes
1656: Specifies whether
1.52 jmc 1657: .Xr sshd 8
1.1 stevesk 1658: should check file modes and ownership of the
1659: user's files and home directory before accepting login.
1660: This is normally desirable because novices sometimes accidentally leave their
1661: directory or files world-writable.
1662: The default is
1.237 jmc 1663: .Cm yes .
1.112 djm 1664: Note that this does not apply to
1665: .Cm ChrootDirectory ,
1666: whose permissions and ownership are checked unconditionally.
1.1 stevesk 1667: .It Cm Subsystem
1.51 jmc 1668: Configures an external subsystem (e.g. file transfer daemon).
1.59 djm 1669: Arguments should be a subsystem name and a command (with optional arguments)
1670: to execute upon subsystem request.
1.80 djm 1671: .Pp
1.1 stevesk 1672: The command
1.237 jmc 1673: .Cm sftp-server
1674: implements the SFTP file transfer subsystem.
1.80 djm 1675: .Pp
1676: Alternately the name
1.237 jmc 1677: .Cm internal-sftp
1678: implements an in-process SFTP server.
1.80 djm 1679: This may simplify configurations using
1680: .Cm ChrootDirectory
1681: to force a different filesystem root on clients.
1682: .Pp
1.1 stevesk 1683: By default no subsystems are defined.
1684: .It Cm SyslogFacility
1685: Gives the facility code that is used when logging messages from
1.53 jmc 1686: .Xr sshd 8 .
1.1 stevesk 1687: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1688: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
1689: The default is AUTH.
1.27 markus 1690: .It Cm TCPKeepAlive
1691: Specifies whether the system should send TCP keepalive messages to the
1692: other side.
1693: If they are sent, death of the connection or crash of one
1694: of the machines will be properly noticed.
1695: However, this means that
1696: connections will die if the route is down temporarily, and some people
1697: find it annoying.
1698: On the other hand, if TCP keepalives are not sent,
1699: sessions may hang indefinitely on the server, leaving
1.237 jmc 1700: .Qq ghost
1.27 markus 1701: users and consuming server resources.
1702: .Pp
1703: The default is
1.237 jmc 1704: .Cm yes
1.27 markus 1705: (to send TCP keepalive messages), and the server will notice
1706: if the network goes down or the client host crashes.
1707: This avoids infinitely hanging sessions.
1708: .Pp
1709: To disable TCP keepalive messages, the value should be set to
1.237 jmc 1710: .Cm no .
1.118 djm 1711: .It Cm TrustedUserCAKeys
1712: Specifies a file containing public keys of certificate authorities that are
1.195 dtucker 1713: trusted to sign user certificates for authentication, or
1.237 jmc 1714: .Cm none
1.195 dtucker 1715: to not use one.
1.119 jmc 1716: Keys are listed one per line; empty lines and comments starting with
1.118 djm 1717: .Ql #
1718: are allowed.
1719: If a certificate is presented for authentication and has its signing CA key
1720: listed in this file, then it may be used for authentication for any user
1721: listed in the certificate's principals list.
1722: Note that certificates that lack a list of principals will not be permitted
1723: for authentication using
1724: .Cm TrustedUserCAKeys .
1.161 jmc 1725: For more details on certificates, see the CERTIFICATES section in
1.118 djm 1726: .Xr ssh-keygen 1 .
1.18 markus 1727: .It Cm UseDNS
1728: Specifies whether
1.52 jmc 1729: .Xr sshd 8
1.207 djm 1730: should look up the remote host name, and to check that
1.18 markus 1731: the resolved host name for the remote IP address maps back to the
1732: very same IP address.
1.207 djm 1733: .Pp
1734: If this option is set to
1.237 jmc 1735: .Cm no
1.207 djm 1736: (the default) then only addresses and not host names may be used in
1.221 djm 1737: .Pa ~/.ssh/authorized_keys
1.207 djm 1738: .Cm from
1739: and
1.211 jmc 1740: .Nm
1.207 djm 1741: .Cm Match
1742: .Cm Host
1743: directives.
1.137 djm 1744: .It Cm VersionAddendum
1745: Optionally specifies additional text to append to the SSH protocol banner
1746: sent by the server upon connection.
1747: The default is
1.237 jmc 1748: .Cm none .
1.1 stevesk 1749: .It Cm X11DisplayOffset
1750: Specifies the first display number available for
1.52 jmc 1751: .Xr sshd 8 Ns 's
1.1 stevesk 1752: X11 forwarding.
1.52 jmc 1753: This prevents sshd from interfering with real X11 servers.
1.1 stevesk 1754: The default is 10.
1755: .It Cm X11Forwarding
1756: Specifies whether X11 forwarding is permitted.
1.13 stevesk 1757: The argument must be
1.237 jmc 1758: .Cm yes
1.13 stevesk 1759: or
1.237 jmc 1760: .Cm no .
1.1 stevesk 1761: The default is
1.237 jmc 1762: .Cm no .
1.13 stevesk 1763: .Pp
1764: When X11 forwarding is enabled, there may be additional exposure to
1765: the server and to client displays if the
1.52 jmc 1766: .Xr sshd 8
1.13 stevesk 1767: proxy display is configured to listen on the wildcard address (see
1.237 jmc 1768: .Cm X11UseLocalhost ) ,
1769: though this is not the default.
1.13 stevesk 1770: Additionally, the authentication spoofing and authentication data
1771: verification and substitution occur on the client side.
1772: The security risk of using X11 forwarding is that the client's X11
1.52 jmc 1773: display server may be exposed to attack when the SSH client requests
1.13 stevesk 1774: forwarding (see the warnings for
1775: .Cm ForwardX11
1776: in
1.19 jmc 1777: .Xr ssh_config 5 ) .
1.13 stevesk 1778: A system administrator may have a stance in which they want to
1779: protect clients that may expose themselves to attack by unwittingly
1780: requesting X11 forwarding, which can warrant a
1.237 jmc 1781: .Cm no
1.13 stevesk 1782: setting.
1783: .Pp
1784: Note that disabling X11 forwarding does not prevent users from
1785: forwarding X11 traffic, as users can always install their own forwarders.
1.1 stevesk 1786: .It Cm X11UseLocalhost
1787: Specifies whether
1.52 jmc 1788: .Xr sshd 8
1.1 stevesk 1789: should bind the X11 forwarding server to the loopback address or to
1.15 jmc 1790: the wildcard address.
1791: By default,
1.52 jmc 1792: sshd binds the forwarding server to the loopback address and sets the
1.1 stevesk 1793: hostname part of the
1794: .Ev DISPLAY
1795: environment variable to
1.237 jmc 1796: .Cm localhost .
1.8 stevesk 1797: This prevents remote hosts from connecting to the proxy display.
1.1 stevesk 1798: However, some older X11 clients may not function with this
1799: configuration.
1800: .Cm X11UseLocalhost
1801: may be set to
1.237 jmc 1802: .Cm no
1.1 stevesk 1803: to specify that the forwarding server should be bound to the wildcard
1804: address.
1805: The argument must be
1.237 jmc 1806: .Cm yes
1.1 stevesk 1807: or
1.237 jmc 1808: .Cm no .
1.1 stevesk 1809: The default is
1.237 jmc 1810: .Cm yes .
1.1 stevesk 1811: .It Cm XAuthLocation
1.11 stevesk 1812: Specifies the full pathname of the
1.1 stevesk 1813: .Xr xauth 1
1.195 dtucker 1814: program, or
1.237 jmc 1815: .Cm none
1.195 dtucker 1816: to not use one.
1.1 stevesk 1817: The default is
1818: .Pa /usr/X11R6/bin/xauth .
1819: .El
1.55 jmc 1820: .Sh TIME FORMATS
1.53 jmc 1821: .Xr sshd 8
1.1 stevesk 1822: command-line arguments and configuration file options that specify time
1823: may be expressed using a sequence of the form:
1824: .Sm off
1.7 stevesk 1825: .Ar time Op Ar qualifier ,
1.1 stevesk 1826: .Sm on
1827: where
1828: .Ar time
1829: is a positive integer value and
1830: .Ar qualifier
1831: is one of the following:
1832: .Pp
1833: .Bl -tag -width Ds -compact -offset indent
1.64 jmc 1834: .It Aq Cm none
1.1 stevesk 1835: seconds
1836: .It Cm s | Cm S
1837: seconds
1838: .It Cm m | Cm M
1839: minutes
1840: .It Cm h | Cm H
1841: hours
1842: .It Cm d | Cm D
1843: days
1844: .It Cm w | Cm W
1845: weeks
1846: .El
1847: .Pp
1848: Each member of the sequence is added together to calculate
1849: the total time value.
1850: .Pp
1851: Time format examples:
1852: .Pp
1853: .Bl -tag -width Ds -compact -offset indent
1854: .It 600
1855: 600 seconds (10 minutes)
1856: .It 10m
1857: 10 minutes
1858: .It 1h30m
1859: 1 hour 30 minutes (90 minutes)
1860: .El
1.235 jmc 1861: .Sh TOKENS
1862: Arguments to some keywords can make use of tokens,
1863: which are expanded at runtime:
1864: .Pp
1865: .Bl -tag -width XXXX -offset indent -compact
1866: .It %%
1867: A literal
1868: .Sq % .
1.257 djm 1869: .It \&%D
1870: The routing domain in which the incoming connection was received.
1.235 jmc 1871: .It %F
1872: The fingerprint of the CA key.
1873: .It %f
1874: The fingerprint of the key or certificate.
1875: .It %h
1876: The home directory of the user.
1877: .It %i
1878: The key ID in the certificate.
1879: .It %K
1880: The base64-encoded CA key.
1881: .It %k
1882: The base64-encoded key or certificate for authentication.
1883: .It %s
1884: The serial number of the certificate.
1885: .It \&%T
1886: The type of the CA key.
1887: .It %t
1888: The key or certificate type.
1.268 jmc 1889: .It \&%U
1890: The numeric user ID of the target user.
1.235 jmc 1891: .It %u
1892: The username.
1893: .El
1894: .Pp
1895: .Cm AuthorizedKeysCommand
1.270 jmc 1896: accepts the tokens %%, %f, %h, %k, %t, %U, and %u.
1.235 jmc 1897: .Pp
1898: .Cm AuthorizedKeysFile
1.270 jmc 1899: accepts the tokens %%, %h, %U, and %u.
1.235 jmc 1900: .Pp
1901: .Cm AuthorizedPrincipalsCommand
1.270 jmc 1902: accepts the tokens %%, %F, %f, %h, %i, %K, %k, %s, %T, %t, %U, and %u.
1.235 jmc 1903: .Pp
1904: .Cm AuthorizedPrincipalsFile
1.270 jmc 1905: accepts the tokens %%, %h, %U, and %u.
1.235 jmc 1906: .Pp
1907: .Cm ChrootDirectory
1.270 jmc 1908: accepts the tokens %%, %h, %U, and %u.
1.257 djm 1909: .Pp
1910: .Cm RoutingDomain
1911: accepts the token %D.
1.1 stevesk 1912: .Sh FILES
1913: .Bl -tag -width Ds
1914: .It Pa /etc/ssh/sshd_config
1915: Contains configuration data for
1.53 jmc 1916: .Xr sshd 8 .
1.1 stevesk 1917: This file should be writable by root only, but it is recommended
1918: (though not necessary) that it be world-readable.
1919: .El
1.19 jmc 1920: .Sh SEE ALSO
1.237 jmc 1921: .Xr sftp-server 8 ,
1.19 jmc 1922: .Xr sshd 8
1.1 stevesk 1923: .Sh AUTHORS
1.237 jmc 1924: .An -nosplit
1.1 stevesk 1925: OpenSSH is a derivative of the original and free
1.237 jmc 1926: ssh 1.2.12 release by
1927: .An Tatu Ylonen .
1928: .An Aaron Campbell , Bob Beck , Markus Friedl , Niels Provos ,
1929: .An Theo de Raadt
1930: and
1931: .An Dug Song
1.1 stevesk 1932: removed many bugs, re-added newer features and
1933: created OpenSSH.
1.237 jmc 1934: .An Markus Friedl
1935: contributed the support for SSH protocol versions 1.5 and 2.0.
1936: .An Niels Provos
1937: and
1938: .An Markus Friedl
1939: contributed support for privilege separation.
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