Annotation of src/usr.bin/ssh/sshd_config.5, Revision 1.284
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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1.284 ! jmc 36: .\" $OpenBSD: sshd_config.5,v 1.283 2019/01/23 20:48:52 dtucker Exp $
! 37: .Dd $Mdocdate: January 23 2019 $
1.1 stevesk 38: .Dt SSHD_CONFIG 5
39: .Os
40: .Sh NAME
41: .Nm sshd_config
42: .Nd OpenSSH SSH daemon configuration file
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.
1.54 jmc 116: The allow/deny directives are processed in the following order:
117: .Cm DenyUsers ,
118: .Cm AllowUsers ,
119: .Cm DenyGroups ,
120: and finally
121: .Cm AllowGroups .
1.49 jmc 122: .Pp
1.161 jmc 123: See PATTERNS in
1.49 jmc 124: .Xr ssh_config 5
125: for more information on patterns.
1.231 jmc 126: .It Cm AllowStreamLocalForwarding
127: Specifies whether StreamLocal (Unix-domain socket) forwarding is permitted.
1.150 djm 128: The available options are
1.237 jmc 129: .Cm yes
130: (the default)
1.150 djm 131: or
1.237 jmc 132: .Cm all
1.231 jmc 133: to allow StreamLocal forwarding,
1.237 jmc 134: .Cm no
1.231 jmc 135: to prevent all StreamLocal forwarding,
1.237 jmc 136: .Cm local
1.150 djm 137: to allow local (from the perspective of
1.151 jmc 138: .Xr ssh 1 )
139: forwarding only or
1.237 jmc 140: .Cm remote
1.150 djm 141: to allow remote forwarding only.
1.231 jmc 142: Note that disabling StreamLocal forwarding does not improve security unless
1.1 stevesk 143: users are also denied shell access, as they can always install their
144: own forwarders.
1.231 jmc 145: .It Cm AllowTcpForwarding
146: Specifies whether TCP forwarding is permitted.
1.175 millert 147: The available options are
1.237 jmc 148: .Cm yes
149: (the default)
1.175 millert 150: or
1.237 jmc 151: .Cm all
1.231 jmc 152: to allow TCP forwarding,
1.237 jmc 153: .Cm no
1.231 jmc 154: to prevent all TCP forwarding,
1.237 jmc 155: .Cm local
1.175 millert 156: to allow local (from the perspective of
157: .Xr ssh 1 )
158: forwarding only or
1.237 jmc 159: .Cm remote
1.175 millert 160: to allow remote forwarding only.
1.231 jmc 161: Note that disabling TCP forwarding does not improve security unless
1.175 millert 162: users are also denied shell access, as they can always install their
163: own forwarders.
1.1 stevesk 164: .It Cm AllowUsers
165: This keyword can be followed by a list of user name patterns, separated
166: by spaces.
1.14 jmc 167: If specified, login is allowed only for user names that
1.1 stevesk 168: match one of the patterns.
169: Only user names are valid; a numerical user ID is not recognized.
170: By default, login is allowed for all users.
171: If the pattern takes the form USER@HOST then USER and HOST
172: are separately checked, restricting logins to particular
173: users from particular hosts.
1.222 jmc 174: HOST criteria may additionally contain addresses to match in CIDR
175: address/masklen format.
1.54 jmc 176: The allow/deny directives are processed in the following order:
177: .Cm DenyUsers ,
178: .Cm AllowUsers ,
179: .Cm DenyGroups ,
180: and finally
181: .Cm AllowGroups .
1.49 jmc 182: .Pp
1.161 jmc 183: See PATTERNS in
1.49 jmc 184: .Xr ssh_config 5
185: for more information on patterns.
1.149 djm 186: .It Cm AuthenticationMethods
187: Specifies the authentication methods that must be successfully completed
188: for a user to be granted access.
1.281 djm 189: This option must be followed by one or more lists of comma-separated
1.224 djm 190: authentication method names, or by the single string
1.237 jmc 191: .Cm any
1.224 djm 192: to indicate the default behaviour of accepting any single authentication
1.225 jmc 193: method.
1.237 jmc 194: If the default is overridden, then successful authentication requires
1.224 djm 195: completion of every method in at least one of these lists.
1.149 djm 196: .Pp
1.237 jmc 197: For example,
198: .Qq publickey,password publickey,keyboard-interactive
1.149 djm 199: would require the user to complete public key authentication, followed by
200: either password or keyboard interactive authentication.
201: Only methods that are next in one or more lists are offered at each stage,
1.237 jmc 202: so for this example it would not be possible to attempt password or
1.149 djm 203: keyboard-interactive authentication before public key.
1.157 markus 204: .Pp
205: For keyboard interactive authentication it is also possible to
206: restrict authentication to a specific device by appending a
207: colon followed by the device identifier
1.237 jmc 208: .Cm bsdauth ,
209: .Cm pam ,
1.157 markus 210: or
1.237 jmc 211: .Cm skey ,
1.157 markus 212: depending on the server configuration.
213: For example,
1.237 jmc 214: .Qq keyboard-interactive:bsdauth
1.157 markus 215: would restrict keyboard interactive authentication to the
1.237 jmc 216: .Cm bsdauth
1.157 markus 217: device.
1.185 djm 218: .Pp
1.237 jmc 219: If the publickey method is listed more than once,
1.185 djm 220: .Xr sshd 8
221: verifies that keys that have been used successfully are not reused for
222: subsequent authentications.
1.237 jmc 223: For example,
224: .Qq publickey,publickey
225: requires successful authentication using two different public keys.
1.181 djm 226: .Pp
1.149 djm 227: Note that each authentication method listed should also be explicitly enabled
228: in the configuration.
1.251 djm 229: .Pp
230: The available authentication methods are:
231: .Qq gssapi-with-mic ,
232: .Qq hostbased ,
233: .Qq keyboard-interactive ,
234: .Qq none
235: (used for access to password-less accounts when
1.266 jmc 236: .Cm PermitEmptyPasswords
1.251 djm 237: is enabled),
238: .Qq password
239: and
240: .Qq publickey .
1.146 djm 241: .It Cm AuthorizedKeysCommand
1.147 jmc 242: Specifies a program to be used to look up the user's public keys.
1.201 djm 243: The program must be owned by root, not writable by group or others and
244: specified by an absolute path.
245: Arguments to
246: .Cm AuthorizedKeysCommand
1.235 jmc 247: accept the tokens described in the
248: .Sx TOKENS
249: section.
250: If no arguments are specified then the username of the target user is used.
1.201 djm 251: .Pp
252: The program should produce on standard output zero or
1.235 jmc 253: more lines of authorized_keys output (see
254: .Sx AUTHORIZED_KEYS
255: in
1.147 jmc 256: .Xr sshd 8 ) .
1.235 jmc 257: If a key supplied by
258: .Cm AuthorizedKeysCommand
259: does not successfully authenticate
1.146 djm 260: and authorize the user then public key authentication continues using the usual
261: .Cm AuthorizedKeysFile
262: files.
1.237 jmc 263: By default, no
264: .Cm AuthorizedKeysCommand
265: is run.
1.146 djm 266: .It Cm AuthorizedKeysCommandUser
1.237 jmc 267: Specifies the user under whose account the
268: .Cm AuthorizedKeysCommand
269: is run.
1.146 djm 270: It is recommended to use a dedicated user that has no other role on the host
271: than running authorized keys commands.
1.186 djm 272: If
1.181 djm 273: .Cm AuthorizedKeysCommand
1.186 djm 274: is specified but
275: .Cm AuthorizedKeysCommandUser
276: is not, then
277: .Xr sshd 8
278: will refuse to start.
1.1 stevesk 279: .It Cm AuthorizedKeysFile
1.235 jmc 280: Specifies the file that contains the public keys used for user authentication.
1.124 djm 281: The format is described in the
1.235 jmc 282: .Sx AUTHORIZED_KEYS FILE FORMAT
1.124 djm 283: section of
284: .Xr sshd 8 .
1.235 jmc 285: Arguments to
1.1 stevesk 286: .Cm AuthorizedKeysFile
1.235 jmc 287: accept the tokens described in the
288: .Sx TOKENS
289: section.
1.1 stevesk 290: After expansion,
291: .Cm AuthorizedKeysFile
292: is taken to be an absolute path or one relative to the user's home
293: directory.
1.133 jmc 294: Multiple files may be listed, separated by whitespace.
1.212 djm 295: Alternately this option may be set to
1.237 jmc 296: .Cm none
1.212 djm 297: to skip checking for user keys in files.
1.133 jmc 298: The default is
1.237 jmc 299: .Qq .ssh/authorized_keys .ssh/authorized_keys2 .
1.202 djm 300: .It Cm AuthorizedPrincipalsCommand
301: Specifies a program to be used to generate the list of allowed
302: certificate principals as per
303: .Cm AuthorizedPrincipalsFile .
304: The program must be owned by root, not writable by group or others and
305: specified by an absolute path.
306: Arguments to
307: .Cm AuthorizedPrincipalsCommand
1.235 jmc 308: accept the tokens described in the
309: .Sx TOKENS
310: section.
311: If no arguments are specified then the username of the target user is used.
1.202 djm 312: .Pp
313: The program should produce on standard output zero or
314: more lines of
315: .Cm AuthorizedPrincipalsFile
316: output.
317: If either
318: .Cm AuthorizedPrincipalsCommand
319: or
320: .Cm AuthorizedPrincipalsFile
321: is specified, then certificates offered by the client for authentication
322: must contain a principal that is listed.
1.235 jmc 323: By default, no
324: .Cm AuthorizedPrincipalsCommand
325: is run.
1.202 djm 326: .It Cm AuthorizedPrincipalsCommandUser
1.235 jmc 327: Specifies the user under whose account the
328: .Cm AuthorizedPrincipalsCommand
329: is run.
1.202 djm 330: It is recommended to use a dedicated user that has no other role on the host
331: than running authorized principals commands.
332: If
333: .Cm AuthorizedPrincipalsCommand
334: is specified but
335: .Cm AuthorizedPrincipalsCommandUser
336: is not, then
337: .Xr sshd 8
338: will refuse to start.
1.121 djm 339: .It Cm AuthorizedPrincipalsFile
340: Specifies a file that lists principal names that are accepted for
341: certificate authentication.
342: When using certificates signed by a key listed in
343: .Cm TrustedUserCAKeys ,
344: this file lists names, one of which must appear in the certificate for it
345: to be accepted for authentication.
1.235 jmc 346: Names are listed one per line preceded by key options (as described in
347: .Sx AUTHORIZED_KEYS FILE FORMAT
348: in
1.125 jmc 349: .Xr sshd 8 ) .
1.124 djm 350: Empty lines and comments starting with
1.121 djm 351: .Ql #
352: are ignored.
353: .Pp
1.235 jmc 354: Arguments to
1.121 djm 355: .Cm AuthorizedPrincipalsFile
1.235 jmc 356: accept the tokens described in the
357: .Sx TOKENS
358: section.
1.121 djm 359: After expansion,
360: .Cm AuthorizedPrincipalsFile
1.235 jmc 361: is taken to be an absolute path or one relative to the user's home directory.
1.138 djm 362: The default is
1.237 jmc 363: .Cm none ,
1.138 djm 364: i.e. not to use a principals file \(en in this case, the username
1.121 djm 365: of the user must appear in a certificate's principals list for it to be
366: accepted.
1.235 jmc 367: .Pp
1.121 djm 368: Note that
369: .Cm AuthorizedPrincipalsFile
370: is only used when authentication proceeds using a CA listed in
371: .Cm TrustedUserCAKeys
372: and is not consulted for certification authorities trusted via
373: .Pa ~/.ssh/authorized_keys ,
374: though the
375: .Cm principals=
376: key option offers a similar facility (see
377: .Xr sshd 8
378: for details).
1.1 stevesk 379: .It Cm Banner
380: The contents of the specified file are sent to the remote user before
381: authentication is allowed.
1.78 djm 382: If the argument is
1.237 jmc 383: .Cm none
1.78 djm 384: then no banner is displayed.
1.1 stevesk 385: By default, no banner is displayed.
1.282 djm 386: .It Cm CASignatureAlgorithms
387: Specifies which algorithms are allowed for signing of certificates
388: by certificate authorities (CAs).
389: The default is:
390: .Bd -literal -offset indent
391: ecdsa-sha2-nistp256.ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
392: ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
393: .Ed
394: .Pp
395: Certificates signed using other algorithms will not be accepted for
396: public key or host-based authentication.
1.1 stevesk 397: .It Cm ChallengeResponseAuthentication
1.50 jmc 398: Specifies whether challenge-response authentication is allowed.
1.1 stevesk 399: All authentication styles from
400: .Xr login.conf 5
401: are supported.
402: The default is
1.237 jmc 403: .Cm yes .
1.80 djm 404: .It Cm ChrootDirectory
1.113 stevesk 405: Specifies the pathname of a directory to
1.80 djm 406: .Xr chroot 2
407: to after authentication.
1.190 deraadt 408: At session startup
409: .Xr sshd 8
410: checks that all components of the pathname are root-owned directories
411: which are not writable by any other user or group.
1.106 stevesk 412: After the chroot,
413: .Xr sshd 8
414: changes the working directory to the user's home directory.
1.235 jmc 415: Arguments to
416: .Cm ChrootDirectory
417: accept the tokens described in the
418: .Sx TOKENS
419: section.
1.80 djm 420: .Pp
421: The
422: .Cm ChrootDirectory
423: must contain the necessary files and directories to support the
1.103 stevesk 424: user's session.
1.80 djm 425: For an interactive session this requires at least a shell, typically
426: .Xr sh 1 ,
427: and basic
428: .Pa /dev
429: nodes such as
430: .Xr null 4 ,
431: .Xr zero 4 ,
432: .Xr stdin 4 ,
433: .Xr stdout 4 ,
434: .Xr stderr 4 ,
1.180 jmc 435: and
1.80 djm 436: .Xr tty 4
437: devices.
1.237 jmc 438: For file transfer sessions using SFTP
439: no additional configuration of the environment is necessary if the in-process
440: sftp-server is used,
1.176 schwarze 441: though sessions which use logging may require
1.104 stevesk 442: .Pa /dev/log
1.176 schwarze 443: inside the chroot directory on some operating systems (see
1.104 stevesk 444: .Xr sftp-server 8
1.81 jmc 445: for details).
1.190 deraadt 446: .Pp
1.191 jmc 447: For safety, it is very important that the directory hierarchy be
1.190 deraadt 448: prevented from modification by other processes on the system (especially
449: those outside the jail).
450: Misconfiguration can lead to unsafe environments which
451: .Xr sshd 8
452: cannot detect.
1.80 djm 453: .Pp
1.215 djm 454: The default is
1.237 jmc 455: .Cm none ,
1.215 djm 456: indicating not to
1.80 djm 457: .Xr chroot 2 .
1.1 stevesk 458: .It Cm Ciphers
1.219 jmc 459: Specifies the ciphers allowed.
1.1 stevesk 460: Multiple ciphers must be comma-separated.
1.208 djm 461: If the specified value begins with a
462: .Sq +
463: character, then the specified ciphers will be appended to the default set
464: instead of replacing them.
1.242 djm 465: If the specified value begins with a
466: .Sq -
467: character, then the specified ciphers (including wildcards) will be removed
468: from the default set instead of replacing them.
1.208 djm 469: .Pp
1.167 djm 470: The supported ciphers are:
471: .Pp
1.173 naddy 472: .Bl -item -compact -offset indent
473: .It
474: 3des-cbc
475: .It
476: aes128-cbc
477: .It
478: aes192-cbc
479: .It
480: aes256-cbc
481: .It
482: aes128-ctr
483: .It
484: aes192-ctr
485: .It
486: aes256-ctr
487: .It
488: aes128-gcm@openssh.com
489: .It
490: aes256-gcm@openssh.com
491: .It
492: chacha20-poly1305@openssh.com
493: .El
1.167 djm 494: .Pp
1.52 jmc 495: The default is:
1.173 naddy 496: .Bd -literal -offset indent
1.211 jmc 497: chacha20-poly1305@openssh.com,
1.173 naddy 498: aes128-ctr,aes192-ctr,aes256-ctr,
1.211 jmc 499: aes128-gcm@openssh.com,aes256-gcm@openssh.com
1.1 stevesk 500: .Ed
1.167 djm 501: .Pp
1.237 jmc 502: The list of available ciphers may also be obtained using
503: .Qq ssh -Q cipher .
1.1 stevesk 504: .It Cm ClientAliveCountMax
1.237 jmc 505: Sets the number of client alive messages which may be sent without
1.52 jmc 506: .Xr sshd 8
1.17 jmc 507: receiving any messages back from the client.
508: If this threshold is reached while client alive messages are being sent,
1.52 jmc 509: sshd will disconnect the client, terminating the session.
1.17 jmc 510: It is important to note that the use of client alive messages is very
511: different from
1.237 jmc 512: .Cm TCPKeepAlive .
1.17 jmc 513: The client alive messages are sent through the encrypted channel
514: and therefore will not be spoofable.
515: The TCP keepalive option enabled by
1.27 markus 516: .Cm TCPKeepAlive
1.17 jmc 517: is spoofable.
518: The client alive mechanism is valuable when the client or
1.1 stevesk 519: server depend on knowing when a connection has become inactive.
520: .Pp
1.17 jmc 521: The default value is 3.
522: If
1.1 stevesk 523: .Cm ClientAliveInterval
1.237 jmc 524: is set to 15, and
1.1 stevesk 525: .Cm ClientAliveCountMax
1.52 jmc 526: is left at the default, unresponsive SSH clients
1.1 stevesk 527: will be disconnected after approximately 45 seconds.
1.42 djm 528: .It Cm ClientAliveInterval
529: Sets a timeout interval in seconds after which if no data has been received
530: from the client,
1.52 jmc 531: .Xr sshd 8
1.42 djm 532: will send a message through the encrypted
533: channel to request a response from the client.
534: The default
535: is 0, indicating that these messages will not be sent to the client.
1.3 markus 536: .It Cm Compression
1.236 djm 537: Specifies whether compression is enabled after
1.44 markus 538: the user has authenticated successfully.
1.3 markus 539: The argument must be
1.237 jmc 540: .Cm yes ,
541: .Cm delayed
1.236 djm 542: (a legacy synonym for
1.237 jmc 543: .Cm yes )
1.3 markus 544: or
1.237 jmc 545: .Cm no .
1.3 markus 546: The default is
1.237 jmc 547: .Cm yes .
1.1 stevesk 548: .It Cm DenyGroups
549: This keyword can be followed by a list of group name patterns, separated
550: by spaces.
551: Login is disallowed for users whose primary group or supplementary
552: group list matches one of the patterns.
553: Only group names are valid; a numerical group ID is not recognized.
554: By default, login is allowed for all groups.
1.54 jmc 555: The allow/deny directives are processed in the following order:
556: .Cm DenyUsers ,
557: .Cm AllowUsers ,
558: .Cm DenyGroups ,
559: and finally
560: .Cm AllowGroups .
1.49 jmc 561: .Pp
1.161 jmc 562: See PATTERNS in
1.49 jmc 563: .Xr ssh_config 5
564: for more information on patterns.
1.1 stevesk 565: .It Cm DenyUsers
566: This keyword can be followed by a list of user name patterns, separated
567: by spaces.
568: Login is disallowed for user names that match one of the patterns.
569: Only user names are valid; a numerical user ID is not recognized.
570: By default, login is allowed for all users.
571: If the pattern takes the form USER@HOST then USER and HOST
572: are separately checked, restricting logins to particular
573: users from particular hosts.
1.222 jmc 574: HOST criteria may additionally contain addresses to match in CIDR
575: address/masklen format.
1.54 jmc 576: The allow/deny directives are processed in the following order:
577: .Cm DenyUsers ,
578: .Cm AllowUsers ,
579: .Cm DenyGroups ,
580: and finally
581: .Cm AllowGroups .
1.49 jmc 582: .Pp
1.161 jmc 583: See PATTERNS in
1.49 jmc 584: .Xr ssh_config 5
585: for more information on patterns.
1.239 djm 586: .It Cm DisableForwarding
587: Disables all forwarding features, including X11,
588: .Xr ssh-agent 1 ,
589: TCP and StreamLocal.
590: This option overrides all other forwarding-related options and may
591: simplify restricted configurations.
1.246 djm 592: .It Cm ExposeAuthInfo
1.253 jmc 593: Writes a temporary file containing a list of authentication methods and
1.246 djm 594: public credentials (e.g. keys) used to authenticate the user.
1.247 jmc 595: The location of the file is exposed to the user session through the
1.248 djm 596: .Ev SSH_USER_AUTH
1.247 jmc 597: environment variable.
1.253 jmc 598: The default is
599: .Cm no .
1.183 djm 600: .It Cm FingerprintHash
601: Specifies the hash algorithm used when logging key fingerprints.
602: Valid options are:
1.237 jmc 603: .Cm md5
1.183 djm 604: and
1.237 jmc 605: .Cm sha256 .
1.183 djm 606: The default is
1.237 jmc 607: .Cm sha256 .
1.67 dtucker 608: .It Cm ForceCommand
609: Forces the execution of the command specified by
610: .Cm ForceCommand ,
1.84 djm 611: ignoring any command supplied by the client and
612: .Pa ~/.ssh/rc
613: if present.
1.67 dtucker 614: The command is invoked by using the user's login shell with the -c option.
615: This applies to shell, command, or subsystem execution.
616: It is most useful inside a
617: .Cm Match
618: block.
619: The command originally supplied by the client is available in the
620: .Ev SSH_ORIGINAL_COMMAND
621: environment variable.
1.82 djm 622: Specifying a command of
1.237 jmc 623: .Cm internal-sftp
624: will force the use of an in-process SFTP server that requires no support
1.82 djm 625: files when used with
626: .Cm ChrootDirectory .
1.215 djm 627: The default is
1.237 jmc 628: .Cm none .
1.1 stevesk 629: .It Cm GatewayPorts
630: Specifies whether remote hosts are allowed to connect to ports
631: forwarded for the client.
632: By default,
1.52 jmc 633: .Xr sshd 8
1.15 jmc 634: binds remote port forwardings to the loopback address.
635: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 636: .Cm GatewayPorts
1.52 jmc 637: can be used to specify that sshd
1.39 djm 638: should allow remote port forwardings to bind to non-loopback addresses, thus
639: allowing other hosts to connect.
640: The argument may be
1.237 jmc 641: .Cm no
1.39 djm 642: to force remote port forwardings to be available to the local host only,
1.237 jmc 643: .Cm yes
1.39 djm 644: to force remote port forwardings to bind to the wildcard address, or
1.237 jmc 645: .Cm clientspecified
1.39 djm 646: to allow the client to select the address to which the forwarding is bound.
1.1 stevesk 647: The default is
1.237 jmc 648: .Cm no .
1.23 markus 649: .It Cm GSSAPIAuthentication
1.25 markus 650: Specifies whether user authentication based on GSSAPI is allowed.
1.26 djm 651: The default is
1.237 jmc 652: .Cm no .
1.23 markus 653: .It Cm GSSAPICleanupCredentials
654: Specifies whether to automatically destroy the user's credentials cache
655: on logout.
656: The default is
1.237 jmc 657: .Cm yes .
1.203 djm 658: .It Cm GSSAPIStrictAcceptorCheck
659: Determines whether to be strict about the identity of the GSSAPI acceptor
660: a client authenticates against.
661: If set to
1.237 jmc 662: .Cm yes
663: then the client must authenticate against the host
1.203 djm 664: service on the current hostname.
665: If set to
1.237 jmc 666: .Cm no
1.203 djm 667: then the client may authenticate against any service key stored in the
668: machine's default store.
669: This facility is provided to assist with operation on multi homed machines.
670: The default is
1.237 jmc 671: .Cm yes .
1.189 djm 672: .It Cm HostbasedAcceptedKeyTypes
673: Specifies the key types that will be accepted for hostbased authentication
1.280 djm 674: as a list of comma-separated patterns.
1.208 djm 675: Alternately if the specified value begins with a
676: .Sq +
677: character, then the specified key types will be appended to the default set
678: instead of replacing them.
1.242 djm 679: If the specified value begins with a
680: .Sq -
681: character, then the specified key types (including wildcards) will be removed
682: from the default set instead of replacing them.
1.206 markus 683: The default for this option is:
684: .Bd -literal -offset 3n
685: ecdsa-sha2-nistp256-cert-v01@openssh.com,
686: ecdsa-sha2-nistp384-cert-v01@openssh.com,
687: ecdsa-sha2-nistp521-cert-v01@openssh.com,
688: ssh-ed25519-cert-v01@openssh.com,
1.279 djm 689: rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,
1.206 markus 690: ssh-rsa-cert-v01@openssh.com,
691: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.279 djm 692: ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.206 markus 693: .Ed
694: .Pp
1.237 jmc 695: The list of available key types may also be obtained using
696: .Qq ssh -Q key .
1.1 stevesk 697: .It Cm HostbasedAuthentication
698: Specifies whether rhosts or /etc/hosts.equiv authentication together
699: with successful public key client host authentication is allowed
1.50 jmc 700: (host-based authentication).
1.70 dtucker 701: The default is
1.237 jmc 702: .Cm no .
1.70 dtucker 703: .It Cm HostbasedUsesNameFromPacketOnly
704: Specifies whether or not the server will attempt to perform a reverse
705: name lookup when matching the name in the
706: .Pa ~/.shosts ,
707: .Pa ~/.rhosts ,
708: and
709: .Pa /etc/hosts.equiv
710: files during
711: .Cm HostbasedAuthentication .
712: A setting of
1.237 jmc 713: .Cm yes
1.70 dtucker 714: means that
715: .Xr sshd 8
716: uses the name supplied by the client rather than
717: attempting to resolve the name from the TCP connection itself.
1.1 stevesk 718: The default is
1.237 jmc 719: .Cm no .
1.117 djm 720: .It Cm HostCertificate
721: Specifies a file containing a public host certificate.
722: The certificate's public key must match a private host key already specified
723: by
724: .Cm HostKey .
725: The default behaviour of
726: .Xr sshd 8
727: is not to load any certificates.
1.1 stevesk 728: .It Cm HostKey
729: Specifies a file containing a private host key
730: used by SSH.
1.229 naddy 731: The defaults are
1.169 naddy 732: .Pa /etc/ssh/ssh_host_ecdsa_key ,
733: .Pa /etc/ssh/ssh_host_ed25519_key
1.126 djm 734: and
1.229 naddy 735: .Pa /etc/ssh/ssh_host_rsa_key .
1.206 markus 736: .Pp
1.1 stevesk 737: Note that
1.52 jmc 738: .Xr sshd 8
1.206 markus 739: will refuse to use a file if it is group/world-accessible
740: and that the
741: .Cm HostKeyAlgorithms
742: option restricts which of the keys are actually used by
743: .Xr sshd 8 .
744: .Pp
1.1 stevesk 745: It is possible to have multiple host key files.
1.162 markus 746: It is also possible to specify public host key files instead.
747: In this case operations on the private key will be delegated
748: to an
749: .Xr ssh-agent 1 .
750: .It Cm HostKeyAgent
751: Identifies the UNIX-domain socket used to communicate
752: with an agent that has access to the private host keys.
1.223 markus 753: If the string
1.237 jmc 754: .Qq SSH_AUTH_SOCK
1.162 markus 755: is specified, the location of the socket will be read from the
756: .Ev SSH_AUTH_SOCK
757: environment variable.
1.206 markus 758: .It Cm HostKeyAlgorithms
1.219 jmc 759: Specifies the host key algorithms
1.206 markus 760: that the server offers.
761: The default for this option is:
762: .Bd -literal -offset 3n
763: ecdsa-sha2-nistp256-cert-v01@openssh.com,
764: ecdsa-sha2-nistp384-cert-v01@openssh.com,
765: ecdsa-sha2-nistp521-cert-v01@openssh.com,
766: ssh-ed25519-cert-v01@openssh.com,
1.279 djm 767: rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,
1.206 markus 768: ssh-rsa-cert-v01@openssh.com,
769: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.279 djm 770: ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.206 markus 771: .Ed
772: .Pp
1.237 jmc 773: The list of available key types may also be obtained using
774: .Qq ssh -Q key .
1.1 stevesk 775: .It Cm IgnoreRhosts
776: Specifies that
777: .Pa .rhosts
778: and
779: .Pa .shosts
780: files will not be used in
781: .Cm HostbasedAuthentication .
782: .Pp
783: .Pa /etc/hosts.equiv
784: and
785: .Pa /etc/shosts.equiv
786: are still used.
787: The default is
1.237 jmc 788: .Cm yes .
1.1 stevesk 789: .It Cm IgnoreUserKnownHosts
790: Specifies whether
1.52 jmc 791: .Xr sshd 8
1.1 stevesk 792: should ignore the user's
1.41 djm 793: .Pa ~/.ssh/known_hosts
1.1 stevesk 794: during
1.261 djm 795: .Cm HostbasedAuthentication
796: and use only the system-wide known hosts file
797: .Pa /etc/ssh/known_hosts .
1.1 stevesk 798: The default is
1.237 jmc 799: .Cm no .
1.129 djm 800: .It Cm IPQoS
801: Specifies the IPv4 type-of-service or DSCP class for the connection.
802: Accepted values are
1.237 jmc 803: .Cm af11 ,
804: .Cm af12 ,
805: .Cm af13 ,
806: .Cm af21 ,
807: .Cm af22 ,
808: .Cm af23 ,
809: .Cm af31 ,
810: .Cm af32 ,
811: .Cm af33 ,
812: .Cm af41 ,
813: .Cm af42 ,
814: .Cm af43 ,
815: .Cm cs0 ,
816: .Cm cs1 ,
817: .Cm cs2 ,
818: .Cm cs3 ,
819: .Cm cs4 ,
820: .Cm cs5 ,
821: .Cm cs6 ,
822: .Cm cs7 ,
823: .Cm ef ,
824: .Cm lowdelay ,
825: .Cm throughput ,
826: .Cm reliability ,
1.250 djm 827: a numeric value, or
828: .Cm none
829: to use the operating system default.
1.131 djm 830: This option may take one or two arguments, separated by whitespace.
1.129 djm 831: If one argument is specified, it is used as the packet class unconditionally.
832: If two values are specified, the first is automatically selected for
833: interactive sessions and the second for non-interactive sessions.
834: The default is
1.264 job 835: .Cm af21
1.265 jmc 836: (Low-Latency Data)
1.129 djm 837: for interactive sessions and
1.264 job 838: .Cm cs1
1.265 jmc 839: (Lower Effort)
1.129 djm 840: for non-interactive sessions.
1.171 jmc 841: .It Cm KbdInteractiveAuthentication
842: Specifies whether to allow keyboard-interactive authentication.
843: The argument to this keyword must be
1.237 jmc 844: .Cm yes
1.171 jmc 845: or
1.237 jmc 846: .Cm no .
1.171 jmc 847: The default is to use whatever value
848: .Cm ChallengeResponseAuthentication
849: is set to
850: (by default
1.237 jmc 851: .Cm yes ) .
1.1 stevesk 852: .It Cm KerberosAuthentication
1.24 markus 853: Specifies whether the password provided by the user for
1.1 stevesk 854: .Cm PasswordAuthentication
1.24 markus 855: will be validated through the Kerberos KDC.
1.1 stevesk 856: To use this option, the server needs a
857: Kerberos servtab which allows the verification of the KDC's identity.
1.52 jmc 858: The default is
1.237 jmc 859: .Cm no .
1.29 dtucker 860: .It Cm KerberosGetAFSToken
1.45 djm 861: If AFS is active and the user has a Kerberos 5 TGT, attempt to acquire
1.29 dtucker 862: an AFS token before accessing the user's home directory.
1.52 jmc 863: The default is
1.237 jmc 864: .Cm no .
1.1 stevesk 865: .It Cm KerberosOrLocalPasswd
1.52 jmc 866: If password authentication through Kerberos fails then
1.1 stevesk 867: the password will be validated via any additional local mechanism
868: such as
869: .Pa /etc/passwd .
1.52 jmc 870: The default is
1.237 jmc 871: .Cm yes .
1.1 stevesk 872: .It Cm KerberosTicketCleanup
873: Specifies whether to automatically destroy the user's ticket cache
874: file on logout.
1.52 jmc 875: The default is
1.237 jmc 876: .Cm yes .
1.127 djm 877: .It Cm KexAlgorithms
878: Specifies the available KEX (Key Exchange) algorithms.
879: Multiple algorithms must be comma-separated.
1.208 djm 880: Alternately if the specified value begins with a
881: .Sq +
882: character, then the specified methods will be appended to the default set
883: instead of replacing them.
1.242 djm 884: If the specified value begins with a
885: .Sq -
886: character, then the specified methods (including wildcards) will be removed
887: from the default set instead of replacing them.
1.173 naddy 888: The supported algorithms are:
889: .Pp
890: .Bl -item -compact -offset indent
891: .It
1.234 djm 892: curve25519-sha256
893: .It
1.173 naddy 894: curve25519-sha256@libssh.org
895: .It
896: diffie-hellman-group1-sha1
897: .It
898: diffie-hellman-group14-sha1
899: .It
1.263 djm 900: diffie-hellman-group14-sha256
901: .It
902: diffie-hellman-group16-sha512
903: .It
904: diffie-hellman-group18-sha512
905: .It
1.173 naddy 906: diffie-hellman-group-exchange-sha1
907: .It
908: diffie-hellman-group-exchange-sha256
909: .It
910: ecdh-sha2-nistp256
911: .It
912: ecdh-sha2-nistp384
913: .It
914: ecdh-sha2-nistp521
915: .El
916: .Pp
917: The default is:
1.170 dtucker 918: .Bd -literal -offset indent
1.234 djm 919: curve25519-sha256,curve25519-sha256@libssh.org,
1.170 dtucker 920: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
921: diffie-hellman-group-exchange-sha256,
1.263 djm 922: diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,
923: diffie-hellman-group14-sha256,diffie-hellman-group14-sha1
1.170 dtucker 924: .Ed
1.188 djm 925: .Pp
1.237 jmc 926: The list of available key exchange algorithms may also be obtained using
927: .Qq ssh -Q kex .
1.1 stevesk 928: .It Cm ListenAddress
929: Specifies the local addresses
1.52 jmc 930: .Xr sshd 8
1.1 stevesk 931: should listen on.
932: The following forms may be used:
933: .Pp
934: .Bl -item -offset indent -compact
935: .It
936: .Cm ListenAddress
937: .Sm off
1.259 jmc 938: .Ar hostname | address
1.1 stevesk 939: .Sm on
1.260 jmc 940: .Op Cm rdomain Ar domain
1.1 stevesk 941: .It
942: .Cm ListenAddress
943: .Sm off
1.259 jmc 944: .Ar hostname : port
1.1 stevesk 945: .Sm on
1.260 jmc 946: .Op Cm rdomain Ar domain
1.256 djm 947: .It
948: .Cm ListenAddress
949: .Sm off
1.259 jmc 950: .Ar IPv4_address : port
1.256 djm 951: .Sm on
1.260 jmc 952: .Op Cm rdomain Ar domain
1.1 stevesk 953: .It
954: .Cm ListenAddress
955: .Sm off
1.259 jmc 956: .Oo Ar hostname | address Oc : Ar port
1.1 stevesk 957: .Sm on
1.260 jmc 958: .Op Cm rdomain Ar domain
1.1 stevesk 959: .El
960: .Pp
1.256 djm 961: The optional
962: .Cm rdomain
963: qualifier requests
964: .Xr sshd 8
965: listen in an explicit routing domain.
1.1 stevesk 966: If
967: .Ar port
968: is not specified,
1.200 dtucker 969: sshd will listen on the address and all
1.1 stevesk 970: .Cm Port
1.17 jmc 971: options specified.
1.256 djm 972: The default is to listen on all local addresses on the current default
973: routing domain.
1.15 jmc 974: Multiple
1.1 stevesk 975: .Cm ListenAddress
1.17 jmc 976: options are permitted.
1.256 djm 977: For more information on routing domains, see
1.259 jmc 978: .Xr rdomain 4 .
1.1 stevesk 979: .It Cm LoginGraceTime
980: The server disconnects after this time if the user has not
981: successfully logged in.
982: If the value is 0, there is no time limit.
1.12 stevesk 983: The default is 120 seconds.
1.1 stevesk 984: .It Cm LogLevel
985: Gives the verbosity level that is used when logging messages from
1.53 jmc 986: .Xr sshd 8 .
1.1 stevesk 987: The possible values are:
1.52 jmc 988: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.15 jmc 989: The default is INFO.
990: DEBUG and DEBUG1 are equivalent.
991: DEBUG2 and DEBUG3 each specify higher levels of debugging output.
992: Logging with a DEBUG level violates the privacy of users and is not recommended.
1.1 stevesk 993: .It Cm MACs
994: Specifies the available MAC (message authentication code) algorithms.
1.219 jmc 995: The MAC algorithm is used for data integrity protection.
1.1 stevesk 996: Multiple algorithms must be comma-separated.
1.208 djm 997: If the specified value begins with a
998: .Sq +
999: character, then the specified algorithms will be appended to the default set
1000: instead of replacing them.
1.242 djm 1001: If the specified value begins with a
1002: .Sq -
1003: character, then the specified algorithms (including wildcards) will be removed
1004: from the default set instead of replacing them.
1.208 djm 1005: .Pp
1.152 markus 1006: The algorithms that contain
1.237 jmc 1007: .Qq -etm
1.152 markus 1008: calculate the MAC after encryption (encrypt-then-mac).
1009: These are considered safer and their use recommended.
1.173 naddy 1010: The supported MACs are:
1011: .Pp
1012: .Bl -item -compact -offset indent
1013: .It
1014: hmac-md5
1015: .It
1016: hmac-md5-96
1017: .It
1018: hmac-sha1
1019: .It
1020: hmac-sha1-96
1021: .It
1022: hmac-sha2-256
1023: .It
1024: hmac-sha2-512
1025: .It
1026: umac-64@openssh.com
1027: .It
1028: umac-128@openssh.com
1029: .It
1030: hmac-md5-etm@openssh.com
1031: .It
1032: hmac-md5-96-etm@openssh.com
1033: .It
1034: hmac-sha1-etm@openssh.com
1035: .It
1036: hmac-sha1-96-etm@openssh.com
1037: .It
1038: hmac-sha2-256-etm@openssh.com
1039: .It
1040: hmac-sha2-512-etm@openssh.com
1041: .It
1042: umac-64-etm@openssh.com
1043: .It
1044: umac-128-etm@openssh.com
1045: .El
1046: .Pp
1.52 jmc 1047: The default is:
1.77 jmc 1048: .Bd -literal -offset indent
1.152 markus 1049: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
1050: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
1.217 djm 1051: hmac-sha1-etm@openssh.com,
1.173 naddy 1052: umac-64@openssh.com,umac-128@openssh.com,
1.217 djm 1053: hmac-sha2-256,hmac-sha2-512,hmac-sha1
1.77 jmc 1054: .Ed
1.188 djm 1055: .Pp
1.237 jmc 1056: The list of available MAC algorithms may also be obtained using
1057: .Qq ssh -Q mac .
1.60 dtucker 1058: .It Cm Match
1.61 jmc 1059: Introduces a conditional block.
1.65 dtucker 1060: If all of the criteria on the
1.60 dtucker 1061: .Cm Match
1.65 dtucker 1062: line are satisfied, the keywords on the following lines override those
1063: set in the global section of the config file, until either another
1.60 dtucker 1064: .Cm Match
1.65 dtucker 1065: line or the end of the file.
1.172 djm 1066: If a keyword appears in multiple
1067: .Cm Match
1.177 sobrado 1068: blocks that are satisfied, only the first instance of the keyword is
1.172 djm 1069: applied.
1.91 djm 1070: .Pp
1.61 jmc 1071: The arguments to
1.60 dtucker 1072: .Cm Match
1.163 dtucker 1073: are one or more criteria-pattern pairs or the single token
1074: .Cm All
1075: which matches all criteria.
1.60 dtucker 1076: The available criteria are
1077: .Cm User ,
1.69 dtucker 1078: .Cm Group ,
1.60 dtucker 1079: .Cm Host ,
1.139 dtucker 1080: .Cm LocalAddress ,
1081: .Cm LocalPort ,
1.258 djm 1082: .Cm RDomain ,
1.60 dtucker 1083: and
1.258 djm 1084: .Cm Address
1085: (with
1086: .Cm RDomain
1087: representing the
1088: .Xr rdomain 4
1.284 ! jmc 1089: on which the connection was received).
1.258 djm 1090: .Pp
1.91 djm 1091: The match patterns may consist of single entries or comma-separated
1092: lists and may use the wildcard and negation operators described in the
1.237 jmc 1093: .Sx PATTERNS
1094: section of
1.92 djm 1095: .Xr ssh_config 5 .
1.91 djm 1096: .Pp
1097: The patterns in an
1098: .Cm Address
1099: criteria may additionally contain addresses to match in CIDR
1.237 jmc 1100: address/masklen format,
1101: such as 192.0.2.0/24 or 2001:db8::/32.
1.91 djm 1102: Note that the mask length provided must be consistent with the address -
1103: it is an error to specify a mask length that is too long for the address
1.93 jmc 1104: or one with bits set in this host portion of the address.
1.237 jmc 1105: For example, 192.0.2.0/33 and 192.0.2.0/8, respectively.
1.91 djm 1106: .Pp
1.60 dtucker 1107: Only a subset of keywords may be used on the lines following a
1108: .Cm Match
1109: keyword.
1110: Available keywords are
1.142 jmc 1111: .Cm AcceptEnv ,
1.99 okan 1112: .Cm AllowAgentForwarding ,
1.142 jmc 1113: .Cm AllowGroups ,
1.193 djm 1114: .Cm AllowStreamLocalForwarding ,
1.62 dtucker 1115: .Cm AllowTcpForwarding ,
1.141 markus 1116: .Cm AllowUsers ,
1.149 djm 1117: .Cm AuthenticationMethods ,
1.146 djm 1118: .Cm AuthorizedKeysCommand ,
1119: .Cm AuthorizedKeysCommandUser ,
1.147 jmc 1120: .Cm AuthorizedKeysFile ,
1.214 djm 1121: .Cm AuthorizedPrincipalsCommand ,
1122: .Cm AuthorizedPrincipalsCommandUser ,
1.123 djm 1123: .Cm AuthorizedPrincipalsFile ,
1.72 dtucker 1124: .Cm Banner ,
1.85 djm 1125: .Cm ChrootDirectory ,
1.238 markus 1126: .Cm ClientAliveCountMax ,
1127: .Cm ClientAliveInterval ,
1.141 markus 1128: .Cm DenyGroups ,
1129: .Cm DenyUsers ,
1.67 dtucker 1130: .Cm ForceCommand ,
1.194 djm 1131: .Cm GatewayPorts ,
1.193 djm 1132: .Cm GSSAPIAuthentication ,
1.189 djm 1133: .Cm HostbasedAcceptedKeyTypes ,
1.87 djm 1134: .Cm HostbasedAuthentication ,
1.123 djm 1135: .Cm HostbasedUsesNameFromPacketOnly ,
1.193 djm 1136: .Cm IPQoS ,
1.74 jmc 1137: .Cm KbdInteractiveAuthentication ,
1.72 dtucker 1138: .Cm KerberosAuthentication ,
1.245 djm 1139: .Cm LogLevel ,
1.95 dtucker 1140: .Cm MaxAuthTries ,
1.94 dtucker 1141: .Cm MaxSessions ,
1.72 dtucker 1142: .Cm PasswordAuthentication ,
1.97 djm 1143: .Cm PermitEmptyPasswords ,
1.271 djm 1144: .Cm PermitListen ,
1.66 dtucker 1145: .Cm PermitOpen ,
1.79 dtucker 1146: .Cm PermitRootLogin ,
1.164 djm 1147: .Cm PermitTTY ,
1.123 djm 1148: .Cm PermitTunnel ,
1.174 djm 1149: .Cm PermitUserRC ,
1.189 djm 1150: .Cm PubkeyAcceptedKeyTypes ,
1.107 dtucker 1151: .Cm PubkeyAuthentication ,
1.159 dtucker 1152: .Cm RekeyLimit ,
1.193 djm 1153: .Cm RevokedKeys ,
1.257 djm 1154: .Cm RDomain ,
1.274 djm 1155: .Cm SetEnv ,
1.193 djm 1156: .Cm StreamLocalBindMask ,
1157: .Cm StreamLocalBindUnlink ,
1158: .Cm TrustedUserCAKeys ,
1.66 dtucker 1159: .Cm X11DisplayOffset ,
1.101 djm 1160: .Cm X11Forwarding
1.60 dtucker 1161: and
1.102 djm 1162: .Cm X11UseLocalHost .
1.33 dtucker 1163: .It Cm MaxAuthTries
1164: Specifies the maximum number of authentication attempts permitted per
1.35 jmc 1165: connection.
1166: Once the number of failures reaches half this value,
1167: additional failures are logged.
1168: The default is 6.
1.90 djm 1169: .It Cm MaxSessions
1.216 djm 1170: Specifies the maximum number of open shell, login or subsystem (e.g. sftp)
1171: sessions permitted per network connection.
1172: Multiple sessions may be established by clients that support connection
1173: multiplexing.
1174: Setting
1175: .Cm MaxSessions
1176: to 1 will effectively disable session multiplexing, whereas setting it to 0
1177: will prevent all shell, login and subsystem sessions while still permitting
1178: forwarding.
1.90 djm 1179: The default is 10.
1.1 stevesk 1180: .It Cm MaxStartups
1181: Specifies the maximum number of concurrent unauthenticated connections to the
1.52 jmc 1182: SSH daemon.
1.1 stevesk 1183: Additional connections will be dropped until authentication succeeds or the
1184: .Cm LoginGraceTime
1185: expires for a connection.
1.156 dtucker 1186: The default is 10:30:100.
1.1 stevesk 1187: .Pp
1188: Alternatively, random early drop can be enabled by specifying
1189: the three colon separated values
1.237 jmc 1190: start:rate:full (e.g. "10:30:60").
1.53 jmc 1191: .Xr sshd 8
1.237 jmc 1192: will refuse connection attempts with a probability of rate/100 (30%)
1193: if there are currently start (10) unauthenticated connections.
1.1 stevesk 1194: The probability increases linearly and all connection attempts
1.237 jmc 1195: are refused if the number of unauthenticated connections reaches full (60).
1.1 stevesk 1196: .It Cm PasswordAuthentication
1197: Specifies whether password authentication is allowed.
1198: The default is
1.237 jmc 1199: .Cm yes .
1.1 stevesk 1200: .It Cm PermitEmptyPasswords
1201: When password authentication is allowed, it specifies whether the
1202: server allows login to accounts with empty password strings.
1203: The default is
1.237 jmc 1204: .Cm no .
1.271 djm 1205: .It Cm PermitListen
1206: Specifies the addresses/ports on which a remote TCP port forwarding may listen.
1207: The listen specification must be one of the following forms:
1208: .Pp
1209: .Bl -item -offset indent -compact
1210: .It
1211: .Cm PermitListen
1212: .Sm off
1.276 djm 1213: .Ar port
1.271 djm 1214: .Sm on
1215: .It
1216: .Cm PermitListen
1217: .Sm off
1.276 djm 1218: .Ar host : port
1.271 djm 1219: .Sm on
1220: .El
1221: .Pp
1222: Multiple permissions may be specified by separating them with whitespace.
1223: An argument of
1224: .Cm any
1225: can be used to remove all restrictions and permit any listen requests.
1226: An argument of
1227: .Cm none
1228: can be used to prohibit all listen requests.
1229: The host name may contain wildcards as described in the PATTERNS section in
1230: .Xr ssh_config 5 .
1231: The wildcard
1232: .Sq *
1233: can also be used in place of a port number to allow all ports.
1234: By default all port forwarding listen requests are permitted.
1.272 jmc 1235: Note that the
1.271 djm 1236: .Cm GatewayPorts
1237: option may further restrict which addresses may be listened on.
1.276 djm 1238: Note also that
1239: .Xr ssh 1
1240: will request a listen host of
1241: .Dq localhost
1.283 dtucker 1242: if no listen host was specifically requested, and this name is
1.277 jmc 1243: treated differently to explicit localhost addresses of
1.276 djm 1244: .Dq 127.0.0.1
1245: and
1246: .Dq ::1 .
1.62 dtucker 1247: .It Cm PermitOpen
1248: Specifies the destinations to which TCP port forwarding is permitted.
1249: The forwarding specification must be one of the following forms:
1250: .Pp
1251: .Bl -item -offset indent -compact
1252: .It
1253: .Cm PermitOpen
1254: .Sm off
1255: .Ar host : port
1256: .Sm on
1257: .It
1258: .Cm PermitOpen
1259: .Sm off
1260: .Ar IPv4_addr : port
1261: .Sm on
1262: .It
1263: .Cm PermitOpen
1264: .Sm off
1265: .Ar \&[ IPv6_addr \&] : port
1266: .Sm on
1267: .El
1268: .Pp
1.68 dtucker 1269: Multiple forwards may be specified by separating them with whitespace.
1.62 dtucker 1270: An argument of
1.237 jmc 1271: .Cm any
1.62 dtucker 1272: can be used to remove all restrictions and permit any forwarding requests.
1.140 dtucker 1273: An argument of
1.237 jmc 1274: .Cm none
1.140 dtucker 1275: can be used to prohibit all forwarding requests.
1.227 jmc 1276: The wildcard
1.237 jmc 1277: .Sq *
1.227 jmc 1278: can be used for host or port to allow all hosts or ports, respectively.
1.63 jmc 1279: By default all port forwarding requests are permitted.
1.1 stevesk 1280: .It Cm PermitRootLogin
1.38 jmc 1281: Specifies whether root can log in using
1.1 stevesk 1282: .Xr ssh 1 .
1283: The argument must be
1.237 jmc 1284: .Cm yes ,
1285: .Cm prohibit-password ,
1286: .Cm forced-commands-only ,
1.1 stevesk 1287: or
1.237 jmc 1288: .Cm no .
1.1 stevesk 1289: The default is
1.237 jmc 1290: .Cm prohibit-password .
1.1 stevesk 1291: .Pp
1292: If this option is set to
1.237 jmc 1293: .Cm prohibit-password
1.255 jmc 1294: (or its deprecated alias,
1295: .Cm without-password ) ,
1.210 deraadt 1296: password and keyboard-interactive authentication are disabled for root.
1.1 stevesk 1297: .Pp
1298: If this option is set to
1.237 jmc 1299: .Cm forced-commands-only ,
1.1 stevesk 1300: root login with public key authentication will be allowed,
1301: but only if the
1302: .Ar command
1303: option has been specified
1304: (which may be useful for taking remote backups even if root login is
1.17 jmc 1305: normally not allowed).
1306: All other authentication methods are disabled for root.
1.1 stevesk 1307: .Pp
1308: If this option is set to
1.237 jmc 1309: .Cm no ,
1.38 jmc 1310: root is not allowed to log in.
1.231 jmc 1311: .It Cm PermitTTY
1312: Specifies whether
1313: .Xr pty 4
1314: allocation is permitted.
1315: The default is
1.237 jmc 1316: .Cm yes .
1.46 reyk 1317: .It Cm PermitTunnel
1318: Specifies whether
1319: .Xr tun 4
1320: device forwarding is allowed.
1.47 reyk 1321: The argument must be
1.237 jmc 1322: .Cm yes ,
1323: .Cm point-to-point
1.58 stevesk 1324: (layer 3),
1.237 jmc 1325: .Cm ethernet
1.58 stevesk 1326: (layer 2), or
1.237 jmc 1327: .Cm no .
1.58 stevesk 1328: Specifying
1.237 jmc 1329: .Cm yes
1.58 stevesk 1330: permits both
1.237 jmc 1331: .Cm point-to-point
1.58 stevesk 1332: and
1.237 jmc 1333: .Cm ethernet .
1.46 reyk 1334: The default is
1.237 jmc 1335: .Cm no .
1.178 djm 1336: .Pp
1337: Independent of this setting, the permissions of the selected
1338: .Xr tun 4
1339: device must allow access to the user.
1.6 markus 1340: .It Cm PermitUserEnvironment
1341: Specifies whether
1342: .Pa ~/.ssh/environment
1.9 stevesk 1343: and
1.6 markus 1344: .Cm environment=
1345: options in
1346: .Pa ~/.ssh/authorized_keys
1.9 stevesk 1347: are processed by
1.52 jmc 1348: .Xr sshd 8 .
1.278 djm 1349: Valid options are
1350: .Cm yes ,
1351: .Cm no
1352: or a pattern-list specifying which environment variable names to accept
1353: (for example
1354: .Qq LANG,LC_* ) .
1.6 markus 1355: The default is
1.237 jmc 1356: .Cm no .
1.9 stevesk 1357: Enabling environment processing may enable users to bypass access
1358: restrictions in some configurations using mechanisms such as
1359: .Ev LD_PRELOAD .
1.174 djm 1360: .It Cm PermitUserRC
1361: Specifies whether any
1362: .Pa ~/.ssh/rc
1363: file is executed.
1364: The default is
1.237 jmc 1365: .Cm yes .
1.1 stevesk 1366: .It Cm PidFile
1.4 stevesk 1367: Specifies the file that contains the process ID of the
1.195 dtucker 1368: SSH daemon, or
1.237 jmc 1369: .Cm none
1.195 dtucker 1370: to not write one.
1.1 stevesk 1371: The default is
1372: .Pa /var/run/sshd.pid .
1373: .It Cm Port
1374: Specifies the port number that
1.52 jmc 1375: .Xr sshd 8
1.1 stevesk 1376: listens on.
1377: The default is 22.
1378: Multiple options of this type are permitted.
1379: See also
1380: .Cm ListenAddress .
1381: .It Cm PrintLastLog
1382: Specifies whether
1.52 jmc 1383: .Xr sshd 8
1.36 jaredy 1384: should print the date and time of the last user login when a user logs
1385: in interactively.
1.1 stevesk 1386: The default is
1.237 jmc 1387: .Cm yes .
1.1 stevesk 1388: .It Cm PrintMotd
1389: Specifies whether
1.52 jmc 1390: .Xr sshd 8
1.1 stevesk 1391: should print
1392: .Pa /etc/motd
1393: when a user logs in interactively.
1394: (On some systems it is also printed by the shell,
1395: .Pa /etc/profile ,
1396: or equivalent.)
1397: The default is
1.237 jmc 1398: .Cm yes .
1.189 djm 1399: .It Cm PubkeyAcceptedKeyTypes
1400: Specifies the key types that will be accepted for public key authentication
1.280 djm 1401: as a list of comma-separated patterns.
1.208 djm 1402: Alternately if the specified value begins with a
1403: .Sq +
1404: character, then the specified key types will be appended to the default set
1405: instead of replacing them.
1.242 djm 1406: If the specified value begins with a
1407: .Sq -
1408: character, then the specified key types (including wildcards) will be removed
1409: from the default set instead of replacing them.
1.206 markus 1410: The default for this option is:
1411: .Bd -literal -offset 3n
1412: ecdsa-sha2-nistp256-cert-v01@openssh.com,
1413: ecdsa-sha2-nistp384-cert-v01@openssh.com,
1414: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1415: ssh-ed25519-cert-v01@openssh.com,
1.279 djm 1416: rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,
1.206 markus 1417: ssh-rsa-cert-v01@openssh.com,
1418: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.279 djm 1419: ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.206 markus 1420: .Ed
1421: .Pp
1.237 jmc 1422: The list of available key types may also be obtained using
1423: .Qq ssh -Q key .
1.1 stevesk 1424: .It Cm PubkeyAuthentication
1425: Specifies whether public key authentication is allowed.
1426: The default is
1.237 jmc 1427: .Cm yes .
1.159 dtucker 1428: .It Cm RekeyLimit
1429: Specifies the maximum amount of data that may be transmitted before the
1430: session key is renegotiated, optionally followed a maximum amount of
1431: time that may pass before the session key is renegotiated.
1432: The first argument is specified in bytes and may have a suffix of
1433: .Sq K ,
1434: .Sq M ,
1435: or
1436: .Sq G
1437: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1438: The default is between
1439: .Sq 1G
1440: and
1441: .Sq 4G ,
1442: depending on the cipher.
1443: The optional second value is specified in seconds and may use any of the
1444: units documented in the
1445: .Sx TIME FORMATS
1.160 jmc 1446: section.
1.159 dtucker 1447: The default value for
1448: .Cm RekeyLimit
1449: is
1.237 jmc 1450: .Cm default none ,
1.159 dtucker 1451: which means that rekeying is performed after the cipher's default amount
1452: of data has been sent or received and no time based rekeying is done.
1.118 djm 1453: .It Cm RevokedKeys
1.195 dtucker 1454: Specifies revoked public keys file, or
1.237 jmc 1455: .Cm none
1.195 dtucker 1456: to not use one.
1.118 djm 1457: Keys listed in this file will be refused for public key authentication.
1458: Note that if this file is not readable, then public key authentication will
1459: be refused for all users.
1.154 djm 1460: Keys may be specified as a text file, listing one public key per line, or as
1461: an OpenSSH Key Revocation List (KRL) as generated by
1.155 jmc 1462: .Xr ssh-keygen 1 .
1.161 jmc 1463: For more information on KRLs, see the KEY REVOCATION LISTS section in
1.154 djm 1464: .Xr ssh-keygen 1 .
1.257 djm 1465: .It Cm RDomain
1466: Specifies an explicit routing domain that is applied after authentication
1467: has completed.
1.259 jmc 1468: The user session, as well and any forwarded or listening IP sockets,
1469: will be bound to this
1.257 djm 1470: .Xr rdomain 4 .
1471: If the routing domain is set to
1472: .Cm \&%D ,
1.259 jmc 1473: then the domain in which the incoming connection was received will be applied.
1.274 djm 1474: .It Cm SetEnv
1475: Specifies one or more environment variables to set in child sessions started
1476: by
1477: .Xr sshd 8
1478: as
1479: .Dq NAME=VALUE .
1480: The environment value may be quoted (e.g. if it contains whitespace
1481: characters).
1482: Environment variables set by
1483: .Cm SetEnv
1484: override the default environment and any variables specified by the user
1485: via
1486: .Cm AcceptEnv
1487: or
1488: .Cm PermitUserEnvironment .
1.175 millert 1489: .It Cm StreamLocalBindMask
1490: Sets the octal file creation mode mask
1491: .Pq umask
1492: used when creating a Unix-domain socket file for local or remote
1493: port forwarding.
1494: This option is only used for port forwarding to a Unix-domain socket file.
1495: .Pp
1496: The default value is 0177, which creates a Unix-domain socket file that is
1497: readable and writable only by the owner.
1498: Note that not all operating systems honor the file mode on Unix-domain
1499: socket files.
1500: .It Cm StreamLocalBindUnlink
1501: Specifies whether to remove an existing Unix-domain socket file for local
1502: or remote port forwarding before creating a new one.
1503: If the socket file already exists and
1504: .Cm StreamLocalBindUnlink
1505: is not enabled,
1506: .Nm sshd
1507: will be unable to forward the port to the Unix-domain socket file.
1508: This option is only used for port forwarding to a Unix-domain socket file.
1509: .Pp
1510: The argument must be
1.237 jmc 1511: .Cm yes
1.175 millert 1512: or
1.237 jmc 1513: .Cm no .
1.175 millert 1514: The default is
1.237 jmc 1515: .Cm no .
1.1 stevesk 1516: .It Cm StrictModes
1517: Specifies whether
1.52 jmc 1518: .Xr sshd 8
1.1 stevesk 1519: should check file modes and ownership of the
1520: user's files and home directory before accepting login.
1521: This is normally desirable because novices sometimes accidentally leave their
1522: directory or files world-writable.
1523: The default is
1.237 jmc 1524: .Cm yes .
1.112 djm 1525: Note that this does not apply to
1526: .Cm ChrootDirectory ,
1527: whose permissions and ownership are checked unconditionally.
1.1 stevesk 1528: .It Cm Subsystem
1.51 jmc 1529: Configures an external subsystem (e.g. file transfer daemon).
1.59 djm 1530: Arguments should be a subsystem name and a command (with optional arguments)
1531: to execute upon subsystem request.
1.80 djm 1532: .Pp
1.1 stevesk 1533: The command
1.237 jmc 1534: .Cm sftp-server
1535: implements the SFTP file transfer subsystem.
1.80 djm 1536: .Pp
1537: Alternately the name
1.237 jmc 1538: .Cm internal-sftp
1539: implements an in-process SFTP server.
1.80 djm 1540: This may simplify configurations using
1541: .Cm ChrootDirectory
1542: to force a different filesystem root on clients.
1543: .Pp
1.1 stevesk 1544: By default no subsystems are defined.
1545: .It Cm SyslogFacility
1546: Gives the facility code that is used when logging messages from
1.53 jmc 1547: .Xr sshd 8 .
1.1 stevesk 1548: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1549: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
1550: The default is AUTH.
1.27 markus 1551: .It Cm TCPKeepAlive
1552: Specifies whether the system should send TCP keepalive messages to the
1553: other side.
1554: If they are sent, death of the connection or crash of one
1555: of the machines will be properly noticed.
1556: However, this means that
1557: connections will die if the route is down temporarily, and some people
1558: find it annoying.
1559: On the other hand, if TCP keepalives are not sent,
1560: sessions may hang indefinitely on the server, leaving
1.237 jmc 1561: .Qq ghost
1.27 markus 1562: users and consuming server resources.
1563: .Pp
1564: The default is
1.237 jmc 1565: .Cm yes
1.27 markus 1566: (to send TCP keepalive messages), and the server will notice
1567: if the network goes down or the client host crashes.
1568: This avoids infinitely hanging sessions.
1569: .Pp
1570: To disable TCP keepalive messages, the value should be set to
1.237 jmc 1571: .Cm no .
1.118 djm 1572: .It Cm TrustedUserCAKeys
1573: Specifies a file containing public keys of certificate authorities that are
1.195 dtucker 1574: trusted to sign user certificates for authentication, or
1.237 jmc 1575: .Cm none
1.195 dtucker 1576: to not use one.
1.119 jmc 1577: Keys are listed one per line; empty lines and comments starting with
1.118 djm 1578: .Ql #
1579: are allowed.
1580: If a certificate is presented for authentication and has its signing CA key
1581: listed in this file, then it may be used for authentication for any user
1582: listed in the certificate's principals list.
1583: Note that certificates that lack a list of principals will not be permitted
1584: for authentication using
1585: .Cm TrustedUserCAKeys .
1.161 jmc 1586: For more details on certificates, see the CERTIFICATES section in
1.118 djm 1587: .Xr ssh-keygen 1 .
1.18 markus 1588: .It Cm UseDNS
1589: Specifies whether
1.52 jmc 1590: .Xr sshd 8
1.207 djm 1591: should look up the remote host name, and to check that
1.18 markus 1592: the resolved host name for the remote IP address maps back to the
1593: very same IP address.
1.207 djm 1594: .Pp
1595: If this option is set to
1.237 jmc 1596: .Cm no
1.207 djm 1597: (the default) then only addresses and not host names may be used in
1.221 djm 1598: .Pa ~/.ssh/authorized_keys
1.207 djm 1599: .Cm from
1600: and
1.211 jmc 1601: .Nm
1.207 djm 1602: .Cm Match
1603: .Cm Host
1604: directives.
1.137 djm 1605: .It Cm VersionAddendum
1606: Optionally specifies additional text to append to the SSH protocol banner
1607: sent by the server upon connection.
1608: The default is
1.237 jmc 1609: .Cm none .
1.1 stevesk 1610: .It Cm X11DisplayOffset
1611: Specifies the first display number available for
1.52 jmc 1612: .Xr sshd 8 Ns 's
1.1 stevesk 1613: X11 forwarding.
1.52 jmc 1614: This prevents sshd from interfering with real X11 servers.
1.1 stevesk 1615: The default is 10.
1616: .It Cm X11Forwarding
1617: Specifies whether X11 forwarding is permitted.
1.13 stevesk 1618: The argument must be
1.237 jmc 1619: .Cm yes
1.13 stevesk 1620: or
1.237 jmc 1621: .Cm no .
1.1 stevesk 1622: The default is
1.237 jmc 1623: .Cm no .
1.13 stevesk 1624: .Pp
1625: When X11 forwarding is enabled, there may be additional exposure to
1626: the server and to client displays if the
1.52 jmc 1627: .Xr sshd 8
1.13 stevesk 1628: proxy display is configured to listen on the wildcard address (see
1.237 jmc 1629: .Cm X11UseLocalhost ) ,
1630: though this is not the default.
1.13 stevesk 1631: Additionally, the authentication spoofing and authentication data
1632: verification and substitution occur on the client side.
1633: The security risk of using X11 forwarding is that the client's X11
1.52 jmc 1634: display server may be exposed to attack when the SSH client requests
1.13 stevesk 1635: forwarding (see the warnings for
1636: .Cm ForwardX11
1637: in
1.19 jmc 1638: .Xr ssh_config 5 ) .
1.13 stevesk 1639: A system administrator may have a stance in which they want to
1640: protect clients that may expose themselves to attack by unwittingly
1641: requesting X11 forwarding, which can warrant a
1.237 jmc 1642: .Cm no
1.13 stevesk 1643: setting.
1644: .Pp
1645: Note that disabling X11 forwarding does not prevent users from
1646: forwarding X11 traffic, as users can always install their own forwarders.
1.1 stevesk 1647: .It Cm X11UseLocalhost
1648: Specifies whether
1.52 jmc 1649: .Xr sshd 8
1.1 stevesk 1650: should bind the X11 forwarding server to the loopback address or to
1.15 jmc 1651: the wildcard address.
1652: By default,
1.52 jmc 1653: sshd binds the forwarding server to the loopback address and sets the
1.1 stevesk 1654: hostname part of the
1655: .Ev DISPLAY
1656: environment variable to
1.237 jmc 1657: .Cm localhost .
1.8 stevesk 1658: This prevents remote hosts from connecting to the proxy display.
1.1 stevesk 1659: However, some older X11 clients may not function with this
1660: configuration.
1661: .Cm X11UseLocalhost
1662: may be set to
1.237 jmc 1663: .Cm no
1.1 stevesk 1664: to specify that the forwarding server should be bound to the wildcard
1665: address.
1666: The argument must be
1.237 jmc 1667: .Cm yes
1.1 stevesk 1668: or
1.237 jmc 1669: .Cm no .
1.1 stevesk 1670: The default is
1.237 jmc 1671: .Cm yes .
1.1 stevesk 1672: .It Cm XAuthLocation
1.11 stevesk 1673: Specifies the full pathname of the
1.1 stevesk 1674: .Xr xauth 1
1.195 dtucker 1675: program, or
1.237 jmc 1676: .Cm none
1.195 dtucker 1677: to not use one.
1.1 stevesk 1678: The default is
1679: .Pa /usr/X11R6/bin/xauth .
1680: .El
1.55 jmc 1681: .Sh TIME FORMATS
1.53 jmc 1682: .Xr sshd 8
1.1 stevesk 1683: command-line arguments and configuration file options that specify time
1684: may be expressed using a sequence of the form:
1685: .Sm off
1.7 stevesk 1686: .Ar time Op Ar qualifier ,
1.1 stevesk 1687: .Sm on
1688: where
1689: .Ar time
1690: is a positive integer value and
1691: .Ar qualifier
1692: is one of the following:
1693: .Pp
1694: .Bl -tag -width Ds -compact -offset indent
1.64 jmc 1695: .It Aq Cm none
1.1 stevesk 1696: seconds
1697: .It Cm s | Cm S
1698: seconds
1699: .It Cm m | Cm M
1700: minutes
1701: .It Cm h | Cm H
1702: hours
1703: .It Cm d | Cm D
1704: days
1705: .It Cm w | Cm W
1706: weeks
1707: .El
1708: .Pp
1709: Each member of the sequence is added together to calculate
1710: the total time value.
1711: .Pp
1712: Time format examples:
1713: .Pp
1714: .Bl -tag -width Ds -compact -offset indent
1715: .It 600
1716: 600 seconds (10 minutes)
1717: .It 10m
1718: 10 minutes
1719: .It 1h30m
1720: 1 hour 30 minutes (90 minutes)
1721: .El
1.235 jmc 1722: .Sh TOKENS
1723: Arguments to some keywords can make use of tokens,
1724: which are expanded at runtime:
1725: .Pp
1726: .Bl -tag -width XXXX -offset indent -compact
1727: .It %%
1728: A literal
1729: .Sq % .
1.257 djm 1730: .It \&%D
1731: The routing domain in which the incoming connection was received.
1.235 jmc 1732: .It %F
1733: The fingerprint of the CA key.
1734: .It %f
1735: The fingerprint of the key or certificate.
1736: .It %h
1737: The home directory of the user.
1738: .It %i
1739: The key ID in the certificate.
1740: .It %K
1741: The base64-encoded CA key.
1742: .It %k
1743: The base64-encoded key or certificate for authentication.
1744: .It %s
1745: The serial number of the certificate.
1746: .It \&%T
1747: The type of the CA key.
1748: .It %t
1749: The key or certificate type.
1.268 jmc 1750: .It \&%U
1751: The numeric user ID of the target user.
1.235 jmc 1752: .It %u
1753: The username.
1754: .El
1755: .Pp
1756: .Cm AuthorizedKeysCommand
1.270 jmc 1757: accepts the tokens %%, %f, %h, %k, %t, %U, and %u.
1.235 jmc 1758: .Pp
1759: .Cm AuthorizedKeysFile
1.270 jmc 1760: accepts the tokens %%, %h, %U, and %u.
1.235 jmc 1761: .Pp
1762: .Cm AuthorizedPrincipalsCommand
1.270 jmc 1763: accepts the tokens %%, %F, %f, %h, %i, %K, %k, %s, %T, %t, %U, and %u.
1.235 jmc 1764: .Pp
1765: .Cm AuthorizedPrincipalsFile
1.270 jmc 1766: accepts the tokens %%, %h, %U, and %u.
1.235 jmc 1767: .Pp
1768: .Cm ChrootDirectory
1.270 jmc 1769: accepts the tokens %%, %h, %U, and %u.
1.257 djm 1770: .Pp
1771: .Cm RoutingDomain
1772: accepts the token %D.
1.1 stevesk 1773: .Sh FILES
1774: .Bl -tag -width Ds
1775: .It Pa /etc/ssh/sshd_config
1776: Contains configuration data for
1.53 jmc 1777: .Xr sshd 8 .
1.1 stevesk 1778: This file should be writable by root only, but it is recommended
1779: (though not necessary) that it be world-readable.
1780: .El
1.19 jmc 1781: .Sh SEE ALSO
1.237 jmc 1782: .Xr sftp-server 8 ,
1.19 jmc 1783: .Xr sshd 8
1.1 stevesk 1784: .Sh AUTHORS
1.237 jmc 1785: .An -nosplit
1.1 stevesk 1786: OpenSSH is a derivative of the original and free
1.237 jmc 1787: ssh 1.2.12 release by
1788: .An Tatu Ylonen .
1789: .An Aaron Campbell , Bob Beck , Markus Friedl , Niels Provos ,
1790: .An Theo de Raadt
1791: and
1792: .An Dug Song
1.1 stevesk 1793: removed many bugs, re-added newer features and
1794: created OpenSSH.
1.237 jmc 1795: .An Markus Friedl
1796: contributed the support for SSH protocol versions 1.5 and 2.0.
1797: .An Niels Provos
1798: and
1799: .An Markus Friedl
1800: contributed support for privilege separation.
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