Annotation of src/usr.bin/ssh/sshd_config.5, Revision 1.288
1.1 stevesk 1: .\"
2: .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
3: .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
4: .\" All rights reserved
5: .\"
6: .\" As far as I am concerned, the code I have written for this software
7: .\" can be used freely for any purpose. Any derived versions of this
8: .\" software must be clearly marked as such, and if the derived work is
9: .\" incompatible with the protocol description in the RFC file, it must be
10: .\" called by a name other than "ssh" or "Secure Shell".
11: .\"
12: .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
13: .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
14: .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
15: .\"
16: .\" Redistribution and use in source and binary forms, with or without
17: .\" modification, are permitted provided that the following conditions
18: .\" are met:
19: .\" 1. Redistributions of source code must retain the above copyright
20: .\" notice, this list of conditions and the following disclaimer.
21: .\" 2. Redistributions in binary form must reproduce the above copyright
22: .\" notice, this list of conditions and the following disclaimer in the
23: .\" documentation and/or other materials provided with the distribution.
24: .\"
25: .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
26: .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
27: .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
28: .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
29: .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
30: .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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1.288 ! dtucker 36: .\" $OpenBSD: sshd_config.5,v 1.287 2019/07/23 23:06:57 dtucker Exp $
! 37: .Dd $Mdocdate: July 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.
1.285 schwarze 281: The format is described in the AUTHORIZED_KEYS FILE FORMAT section of
1.124 djm 282: .Xr sshd 8 .
1.235 jmc 283: Arguments to
1.1 stevesk 284: .Cm AuthorizedKeysFile
1.235 jmc 285: accept the tokens described in the
286: .Sx TOKENS
287: section.
1.1 stevesk 288: After expansion,
289: .Cm AuthorizedKeysFile
290: is taken to be an absolute path or one relative to the user's home
291: directory.
1.133 jmc 292: Multiple files may be listed, separated by whitespace.
1.212 djm 293: Alternately this option may be set to
1.237 jmc 294: .Cm none
1.212 djm 295: to skip checking for user keys in files.
1.133 jmc 296: The default is
1.237 jmc 297: .Qq .ssh/authorized_keys .ssh/authorized_keys2 .
1.202 djm 298: .It Cm AuthorizedPrincipalsCommand
299: Specifies a program to be used to generate the list of allowed
300: certificate principals as per
301: .Cm AuthorizedPrincipalsFile .
302: The program must be owned by root, not writable by group or others and
303: specified by an absolute path.
304: Arguments to
305: .Cm AuthorizedPrincipalsCommand
1.235 jmc 306: accept the tokens described in the
307: .Sx TOKENS
308: section.
309: If no arguments are specified then the username of the target user is used.
1.202 djm 310: .Pp
311: The program should produce on standard output zero or
312: more lines of
313: .Cm AuthorizedPrincipalsFile
314: output.
315: If either
316: .Cm AuthorizedPrincipalsCommand
317: or
318: .Cm AuthorizedPrincipalsFile
319: is specified, then certificates offered by the client for authentication
320: must contain a principal that is listed.
1.235 jmc 321: By default, no
322: .Cm AuthorizedPrincipalsCommand
323: is run.
1.202 djm 324: .It Cm AuthorizedPrincipalsCommandUser
1.235 jmc 325: Specifies the user under whose account the
326: .Cm AuthorizedPrincipalsCommand
327: is run.
1.202 djm 328: It is recommended to use a dedicated user that has no other role on the host
329: than running authorized principals commands.
330: If
331: .Cm AuthorizedPrincipalsCommand
332: is specified but
333: .Cm AuthorizedPrincipalsCommandUser
334: is not, then
335: .Xr sshd 8
336: will refuse to start.
1.121 djm 337: .It Cm AuthorizedPrincipalsFile
338: Specifies a file that lists principal names that are accepted for
339: certificate authentication.
340: When using certificates signed by a key listed in
341: .Cm TrustedUserCAKeys ,
342: this file lists names, one of which must appear in the certificate for it
343: to be accepted for authentication.
1.235 jmc 344: Names are listed one per line preceded by key options (as described in
345: .Sx AUTHORIZED_KEYS FILE FORMAT
346: in
1.125 jmc 347: .Xr sshd 8 ) .
1.124 djm 348: Empty lines and comments starting with
1.121 djm 349: .Ql #
350: are ignored.
351: .Pp
1.235 jmc 352: Arguments to
1.121 djm 353: .Cm AuthorizedPrincipalsFile
1.235 jmc 354: accept the tokens described in the
355: .Sx TOKENS
356: section.
1.121 djm 357: After expansion,
358: .Cm AuthorizedPrincipalsFile
1.235 jmc 359: is taken to be an absolute path or one relative to the user's home directory.
1.138 djm 360: The default is
1.237 jmc 361: .Cm none ,
1.138 djm 362: i.e. not to use a principals file \(en in this case, the username
1.121 djm 363: of the user must appear in a certificate's principals list for it to be
364: accepted.
1.235 jmc 365: .Pp
1.121 djm 366: Note that
367: .Cm AuthorizedPrincipalsFile
368: is only used when authentication proceeds using a CA listed in
369: .Cm TrustedUserCAKeys
370: and is not consulted for certification authorities trusted via
371: .Pa ~/.ssh/authorized_keys ,
372: though the
373: .Cm principals=
374: key option offers a similar facility (see
375: .Xr sshd 8
376: for details).
1.1 stevesk 377: .It Cm Banner
378: The contents of the specified file are sent to the remote user before
379: authentication is allowed.
1.78 djm 380: If the argument is
1.237 jmc 381: .Cm none
1.78 djm 382: then no banner is displayed.
1.1 stevesk 383: By default, no banner is displayed.
1.282 djm 384: .It Cm CASignatureAlgorithms
385: Specifies which algorithms are allowed for signing of certificates
386: by certificate authorities (CAs).
387: The default is:
388: .Bd -literal -offset indent
1.287 dtucker 389: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.282 djm 390: ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
391: .Ed
392: .Pp
393: Certificates signed using other algorithms will not be accepted for
394: public key or host-based authentication.
1.1 stevesk 395: .It Cm ChallengeResponseAuthentication
1.50 jmc 396: Specifies whether challenge-response authentication is allowed.
1.1 stevesk 397: All authentication styles from
398: .Xr login.conf 5
399: are supported.
400: The default is
1.237 jmc 401: .Cm yes .
1.80 djm 402: .It Cm ChrootDirectory
1.113 stevesk 403: Specifies the pathname of a directory to
1.80 djm 404: .Xr chroot 2
405: to after authentication.
1.190 deraadt 406: At session startup
407: .Xr sshd 8
408: checks that all components of the pathname are root-owned directories
409: which are not writable by any other user or group.
1.106 stevesk 410: After the chroot,
411: .Xr sshd 8
412: changes the working directory to the user's home directory.
1.235 jmc 413: Arguments to
414: .Cm ChrootDirectory
415: accept the tokens described in the
416: .Sx TOKENS
417: section.
1.80 djm 418: .Pp
419: The
420: .Cm ChrootDirectory
421: must contain the necessary files and directories to support the
1.103 stevesk 422: user's session.
1.80 djm 423: For an interactive session this requires at least a shell, typically
424: .Xr sh 1 ,
425: and basic
426: .Pa /dev
427: nodes such as
428: .Xr null 4 ,
429: .Xr zero 4 ,
430: .Xr stdin 4 ,
431: .Xr stdout 4 ,
432: .Xr stderr 4 ,
1.180 jmc 433: and
1.80 djm 434: .Xr tty 4
435: devices.
1.237 jmc 436: For file transfer sessions using SFTP
437: no additional configuration of the environment is necessary if the in-process
438: sftp-server is used,
1.176 schwarze 439: though sessions which use logging may require
1.104 stevesk 440: .Pa /dev/log
1.176 schwarze 441: inside the chroot directory on some operating systems (see
1.104 stevesk 442: .Xr sftp-server 8
1.81 jmc 443: for details).
1.190 deraadt 444: .Pp
1.191 jmc 445: For safety, it is very important that the directory hierarchy be
1.190 deraadt 446: prevented from modification by other processes on the system (especially
447: those outside the jail).
448: Misconfiguration can lead to unsafe environments which
449: .Xr sshd 8
450: cannot detect.
1.80 djm 451: .Pp
1.215 djm 452: The default is
1.237 jmc 453: .Cm none ,
1.215 djm 454: indicating not to
1.80 djm 455: .Xr chroot 2 .
1.1 stevesk 456: .It Cm Ciphers
1.219 jmc 457: Specifies the ciphers allowed.
1.1 stevesk 458: Multiple ciphers must be comma-separated.
1.208 djm 459: If the specified value begins with a
460: .Sq +
461: character, then the specified ciphers will be appended to the default set
462: instead of replacing them.
1.242 djm 463: If the specified value begins with a
464: .Sq -
465: character, then the specified ciphers (including wildcards) will be removed
466: from the default set instead of replacing them.
1.208 djm 467: .Pp
1.167 djm 468: The supported ciphers are:
469: .Pp
1.173 naddy 470: .Bl -item -compact -offset indent
471: .It
472: 3des-cbc
473: .It
474: aes128-cbc
475: .It
476: aes192-cbc
477: .It
478: aes256-cbc
479: .It
480: aes128-ctr
481: .It
482: aes192-ctr
483: .It
484: aes256-ctr
485: .It
486: aes128-gcm@openssh.com
487: .It
488: aes256-gcm@openssh.com
489: .It
490: chacha20-poly1305@openssh.com
491: .El
1.167 djm 492: .Pp
1.52 jmc 493: The default is:
1.173 naddy 494: .Bd -literal -offset indent
1.211 jmc 495: chacha20-poly1305@openssh.com,
1.173 naddy 496: aes128-ctr,aes192-ctr,aes256-ctr,
1.211 jmc 497: aes128-gcm@openssh.com,aes256-gcm@openssh.com
1.1 stevesk 498: .Ed
1.167 djm 499: .Pp
1.237 jmc 500: The list of available ciphers may also be obtained using
501: .Qq ssh -Q cipher .
1.1 stevesk 502: .It Cm ClientAliveCountMax
1.237 jmc 503: Sets the number of client alive messages which may be sent without
1.52 jmc 504: .Xr sshd 8
1.17 jmc 505: receiving any messages back from the client.
506: If this threshold is reached while client alive messages are being sent,
1.52 jmc 507: sshd will disconnect the client, terminating the session.
1.17 jmc 508: It is important to note that the use of client alive messages is very
509: different from
1.237 jmc 510: .Cm TCPKeepAlive .
1.17 jmc 511: The client alive messages are sent through the encrypted channel
512: and therefore will not be spoofable.
513: The TCP keepalive option enabled by
1.27 markus 514: .Cm TCPKeepAlive
1.17 jmc 515: is spoofable.
516: The client alive mechanism is valuable when the client or
1.288 ! dtucker 517: server depend on knowing when a connection has become unresponsive.
1.1 stevesk 518: .Pp
1.17 jmc 519: The default value is 3.
520: If
1.1 stevesk 521: .Cm ClientAliveInterval
1.237 jmc 522: is set to 15, and
1.1 stevesk 523: .Cm ClientAliveCountMax
1.52 jmc 524: is left at the default, unresponsive SSH clients
1.1 stevesk 525: will be disconnected after approximately 45 seconds.
1.42 djm 526: .It Cm ClientAliveInterval
527: Sets a timeout interval in seconds after which if no data has been received
528: from the client,
1.52 jmc 529: .Xr sshd 8
1.42 djm 530: will send a message through the encrypted
531: channel to request a response from the client.
532: The default
533: is 0, indicating that these messages will not be sent to the client.
1.3 markus 534: .It Cm Compression
1.236 djm 535: Specifies whether compression is enabled after
1.44 markus 536: the user has authenticated successfully.
1.3 markus 537: The argument must be
1.237 jmc 538: .Cm yes ,
539: .Cm delayed
1.236 djm 540: (a legacy synonym for
1.237 jmc 541: .Cm yes )
1.3 markus 542: or
1.237 jmc 543: .Cm no .
1.3 markus 544: The default is
1.237 jmc 545: .Cm yes .
1.1 stevesk 546: .It Cm DenyGroups
547: This keyword can be followed by a list of group name patterns, separated
548: by spaces.
549: Login is disallowed for users whose primary group or supplementary
550: group list matches one of the patterns.
551: Only group names are valid; a numerical group ID is not recognized.
552: By default, login is allowed for all groups.
1.54 jmc 553: The allow/deny directives are processed in the following order:
554: .Cm DenyUsers ,
555: .Cm AllowUsers ,
556: .Cm DenyGroups ,
557: and finally
558: .Cm AllowGroups .
1.49 jmc 559: .Pp
1.161 jmc 560: See PATTERNS in
1.49 jmc 561: .Xr ssh_config 5
562: for more information on patterns.
1.1 stevesk 563: .It Cm DenyUsers
564: This keyword can be followed by a list of user name patterns, separated
565: by spaces.
566: Login is disallowed for user names that match one of the patterns.
567: Only user names are valid; a numerical user ID is not recognized.
568: By default, login is allowed for all users.
569: If the pattern takes the form USER@HOST then USER and HOST
570: are separately checked, restricting logins to particular
571: users from particular hosts.
1.222 jmc 572: HOST criteria may additionally contain addresses to match in CIDR
573: address/masklen format.
1.54 jmc 574: The allow/deny directives are processed in the following order:
575: .Cm DenyUsers ,
576: .Cm AllowUsers ,
577: .Cm DenyGroups ,
578: and finally
579: .Cm AllowGroups .
1.49 jmc 580: .Pp
1.161 jmc 581: See PATTERNS in
1.49 jmc 582: .Xr ssh_config 5
583: for more information on patterns.
1.239 djm 584: .It Cm DisableForwarding
585: Disables all forwarding features, including X11,
586: .Xr ssh-agent 1 ,
587: TCP and StreamLocal.
588: This option overrides all other forwarding-related options and may
589: simplify restricted configurations.
1.246 djm 590: .It Cm ExposeAuthInfo
1.253 jmc 591: Writes a temporary file containing a list of authentication methods and
1.246 djm 592: public credentials (e.g. keys) used to authenticate the user.
1.247 jmc 593: The location of the file is exposed to the user session through the
1.248 djm 594: .Ev SSH_USER_AUTH
1.247 jmc 595: environment variable.
1.253 jmc 596: The default is
597: .Cm no .
1.183 djm 598: .It Cm FingerprintHash
599: Specifies the hash algorithm used when logging key fingerprints.
600: Valid options are:
1.237 jmc 601: .Cm md5
1.183 djm 602: and
1.237 jmc 603: .Cm sha256 .
1.183 djm 604: The default is
1.237 jmc 605: .Cm sha256 .
1.67 dtucker 606: .It Cm ForceCommand
607: Forces the execution of the command specified by
608: .Cm ForceCommand ,
1.84 djm 609: ignoring any command supplied by the client and
610: .Pa ~/.ssh/rc
611: if present.
1.67 dtucker 612: The command is invoked by using the user's login shell with the -c option.
613: This applies to shell, command, or subsystem execution.
614: It is most useful inside a
615: .Cm Match
616: block.
617: The command originally supplied by the client is available in the
618: .Ev SSH_ORIGINAL_COMMAND
619: environment variable.
1.82 djm 620: Specifying a command of
1.237 jmc 621: .Cm internal-sftp
622: will force the use of an in-process SFTP server that requires no support
1.82 djm 623: files when used with
624: .Cm ChrootDirectory .
1.215 djm 625: The default is
1.237 jmc 626: .Cm none .
1.1 stevesk 627: .It Cm GatewayPorts
628: Specifies whether remote hosts are allowed to connect to ports
629: forwarded for the client.
630: By default,
1.52 jmc 631: .Xr sshd 8
1.15 jmc 632: binds remote port forwardings to the loopback address.
633: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 634: .Cm GatewayPorts
1.52 jmc 635: can be used to specify that sshd
1.39 djm 636: should allow remote port forwardings to bind to non-loopback addresses, thus
637: allowing other hosts to connect.
638: The argument may be
1.237 jmc 639: .Cm no
1.39 djm 640: to force remote port forwardings to be available to the local host only,
1.237 jmc 641: .Cm yes
1.39 djm 642: to force remote port forwardings to bind to the wildcard address, or
1.237 jmc 643: .Cm clientspecified
1.39 djm 644: to allow the client to select the address to which the forwarding is bound.
1.1 stevesk 645: The default is
1.237 jmc 646: .Cm no .
1.23 markus 647: .It Cm GSSAPIAuthentication
1.25 markus 648: Specifies whether user authentication based on GSSAPI is allowed.
1.26 djm 649: The default is
1.237 jmc 650: .Cm no .
1.23 markus 651: .It Cm GSSAPICleanupCredentials
652: Specifies whether to automatically destroy the user's credentials cache
653: on logout.
654: The default is
1.237 jmc 655: .Cm yes .
1.203 djm 656: .It Cm GSSAPIStrictAcceptorCheck
657: Determines whether to be strict about the identity of the GSSAPI acceptor
658: a client authenticates against.
659: If set to
1.237 jmc 660: .Cm yes
661: then the client must authenticate against the host
1.203 djm 662: service on the current hostname.
663: If set to
1.237 jmc 664: .Cm no
1.203 djm 665: then the client may authenticate against any service key stored in the
666: machine's default store.
667: This facility is provided to assist with operation on multi homed machines.
668: The default is
1.237 jmc 669: .Cm yes .
1.189 djm 670: .It Cm HostbasedAcceptedKeyTypes
671: Specifies the key types that will be accepted for hostbased authentication
1.280 djm 672: as a list of comma-separated patterns.
1.208 djm 673: Alternately if the specified value begins with a
674: .Sq +
675: character, then the specified key types will be appended to the default set
676: instead of replacing them.
1.242 djm 677: If the specified value begins with a
678: .Sq -
679: character, then the specified key types (including wildcards) will be removed
680: from the default set instead of replacing them.
1.206 markus 681: The default for this option is:
682: .Bd -literal -offset 3n
683: ecdsa-sha2-nistp256-cert-v01@openssh.com,
684: ecdsa-sha2-nistp384-cert-v01@openssh.com,
685: ecdsa-sha2-nistp521-cert-v01@openssh.com,
686: ssh-ed25519-cert-v01@openssh.com,
1.279 djm 687: rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,
1.206 markus 688: ssh-rsa-cert-v01@openssh.com,
689: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.279 djm 690: ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.206 markus 691: .Ed
692: .Pp
1.237 jmc 693: The list of available key types may also be obtained using
694: .Qq ssh -Q key .
1.1 stevesk 695: .It Cm HostbasedAuthentication
696: Specifies whether rhosts or /etc/hosts.equiv authentication together
697: with successful public key client host authentication is allowed
1.50 jmc 698: (host-based authentication).
1.70 dtucker 699: The default is
1.237 jmc 700: .Cm no .
1.70 dtucker 701: .It Cm HostbasedUsesNameFromPacketOnly
702: Specifies whether or not the server will attempt to perform a reverse
703: name lookup when matching the name in the
704: .Pa ~/.shosts ,
705: .Pa ~/.rhosts ,
706: and
707: .Pa /etc/hosts.equiv
708: files during
709: .Cm HostbasedAuthentication .
710: A setting of
1.237 jmc 711: .Cm yes
1.70 dtucker 712: means that
713: .Xr sshd 8
714: uses the name supplied by the client rather than
715: attempting to resolve the name from the TCP connection itself.
1.1 stevesk 716: The default is
1.237 jmc 717: .Cm no .
1.117 djm 718: .It Cm HostCertificate
719: Specifies a file containing a public host certificate.
720: The certificate's public key must match a private host key already specified
721: by
722: .Cm HostKey .
723: The default behaviour of
724: .Xr sshd 8
725: is not to load any certificates.
1.1 stevesk 726: .It Cm HostKey
727: Specifies a file containing a private host key
728: used by SSH.
1.229 naddy 729: The defaults are
1.169 naddy 730: .Pa /etc/ssh/ssh_host_ecdsa_key ,
731: .Pa /etc/ssh/ssh_host_ed25519_key
1.126 djm 732: and
1.229 naddy 733: .Pa /etc/ssh/ssh_host_rsa_key .
1.206 markus 734: .Pp
1.1 stevesk 735: Note that
1.52 jmc 736: .Xr sshd 8
1.206 markus 737: will refuse to use a file if it is group/world-accessible
738: and that the
739: .Cm HostKeyAlgorithms
740: option restricts which of the keys are actually used by
741: .Xr sshd 8 .
742: .Pp
1.1 stevesk 743: It is possible to have multiple host key files.
1.162 markus 744: It is also possible to specify public host key files instead.
745: In this case operations on the private key will be delegated
746: to an
747: .Xr ssh-agent 1 .
748: .It Cm HostKeyAgent
749: Identifies the UNIX-domain socket used to communicate
750: with an agent that has access to the private host keys.
1.223 markus 751: If the string
1.237 jmc 752: .Qq SSH_AUTH_SOCK
1.162 markus 753: is specified, the location of the socket will be read from the
754: .Ev SSH_AUTH_SOCK
755: environment variable.
1.206 markus 756: .It Cm HostKeyAlgorithms
1.219 jmc 757: Specifies the host key algorithms
1.206 markus 758: that the server offers.
759: The default for this option is:
760: .Bd -literal -offset 3n
761: ecdsa-sha2-nistp256-cert-v01@openssh.com,
762: ecdsa-sha2-nistp384-cert-v01@openssh.com,
763: ecdsa-sha2-nistp521-cert-v01@openssh.com,
764: ssh-ed25519-cert-v01@openssh.com,
1.279 djm 765: rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,
1.206 markus 766: ssh-rsa-cert-v01@openssh.com,
767: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.279 djm 768: ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.206 markus 769: .Ed
770: .Pp
1.237 jmc 771: The list of available key types may also be obtained using
772: .Qq ssh -Q key .
1.1 stevesk 773: .It Cm IgnoreRhosts
774: Specifies that
775: .Pa .rhosts
776: and
777: .Pa .shosts
778: files will not be used in
779: .Cm HostbasedAuthentication .
780: .Pp
781: .Pa /etc/hosts.equiv
782: and
783: .Pa /etc/shosts.equiv
784: are still used.
785: The default is
1.237 jmc 786: .Cm yes .
1.1 stevesk 787: .It Cm IgnoreUserKnownHosts
788: Specifies whether
1.52 jmc 789: .Xr sshd 8
1.1 stevesk 790: should ignore the user's
1.41 djm 791: .Pa ~/.ssh/known_hosts
1.1 stevesk 792: during
1.261 djm 793: .Cm HostbasedAuthentication
794: and use only the system-wide known hosts file
795: .Pa /etc/ssh/known_hosts .
1.1 stevesk 796: The default is
1.237 jmc 797: .Cm no .
1.129 djm 798: .It Cm IPQoS
799: Specifies the IPv4 type-of-service or DSCP class for the connection.
800: Accepted values are
1.237 jmc 801: .Cm af11 ,
802: .Cm af12 ,
803: .Cm af13 ,
804: .Cm af21 ,
805: .Cm af22 ,
806: .Cm af23 ,
807: .Cm af31 ,
808: .Cm af32 ,
809: .Cm af33 ,
810: .Cm af41 ,
811: .Cm af42 ,
812: .Cm af43 ,
813: .Cm cs0 ,
814: .Cm cs1 ,
815: .Cm cs2 ,
816: .Cm cs3 ,
817: .Cm cs4 ,
818: .Cm cs5 ,
819: .Cm cs6 ,
820: .Cm cs7 ,
821: .Cm ef ,
822: .Cm lowdelay ,
823: .Cm throughput ,
824: .Cm reliability ,
1.250 djm 825: a numeric value, or
826: .Cm none
827: to use the operating system default.
1.131 djm 828: This option may take one or two arguments, separated by whitespace.
1.129 djm 829: If one argument is specified, it is used as the packet class unconditionally.
830: If two values are specified, the first is automatically selected for
831: interactive sessions and the second for non-interactive sessions.
832: The default is
1.264 job 833: .Cm af21
1.265 jmc 834: (Low-Latency Data)
1.129 djm 835: for interactive sessions and
1.264 job 836: .Cm cs1
1.265 jmc 837: (Lower Effort)
1.129 djm 838: for non-interactive sessions.
1.171 jmc 839: .It Cm KbdInteractiveAuthentication
840: Specifies whether to allow keyboard-interactive authentication.
841: The argument to this keyword must be
1.237 jmc 842: .Cm yes
1.171 jmc 843: or
1.237 jmc 844: .Cm no .
1.171 jmc 845: The default is to use whatever value
846: .Cm ChallengeResponseAuthentication
847: is set to
848: (by default
1.237 jmc 849: .Cm yes ) .
1.1 stevesk 850: .It Cm KerberosAuthentication
1.24 markus 851: Specifies whether the password provided by the user for
1.1 stevesk 852: .Cm PasswordAuthentication
1.24 markus 853: will be validated through the Kerberos KDC.
1.1 stevesk 854: To use this option, the server needs a
855: Kerberos servtab which allows the verification of the KDC's identity.
1.52 jmc 856: The default is
1.237 jmc 857: .Cm no .
1.29 dtucker 858: .It Cm KerberosGetAFSToken
1.45 djm 859: If AFS is active and the user has a Kerberos 5 TGT, attempt to acquire
1.29 dtucker 860: an AFS token before accessing the user's home directory.
1.52 jmc 861: The default is
1.237 jmc 862: .Cm no .
1.1 stevesk 863: .It Cm KerberosOrLocalPasswd
1.52 jmc 864: If password authentication through Kerberos fails then
1.1 stevesk 865: the password will be validated via any additional local mechanism
866: such as
867: .Pa /etc/passwd .
1.52 jmc 868: The default is
1.237 jmc 869: .Cm yes .
1.1 stevesk 870: .It Cm KerberosTicketCleanup
871: Specifies whether to automatically destroy the user's ticket cache
872: file on logout.
1.52 jmc 873: The default is
1.237 jmc 874: .Cm yes .
1.127 djm 875: .It Cm KexAlgorithms
876: Specifies the available KEX (Key Exchange) algorithms.
877: Multiple algorithms must be comma-separated.
1.208 djm 878: Alternately if the specified value begins with a
879: .Sq +
880: character, then the specified methods will be appended to the default set
881: instead of replacing them.
1.242 djm 882: If the specified value begins with a
883: .Sq -
884: character, then the specified methods (including wildcards) will be removed
885: from the default set instead of replacing them.
1.173 naddy 886: The supported algorithms are:
887: .Pp
888: .Bl -item -compact -offset indent
889: .It
1.234 djm 890: curve25519-sha256
891: .It
1.173 naddy 892: curve25519-sha256@libssh.org
893: .It
894: diffie-hellman-group1-sha1
895: .It
896: diffie-hellman-group14-sha1
897: .It
1.263 djm 898: diffie-hellman-group14-sha256
899: .It
900: diffie-hellman-group16-sha512
901: .It
902: diffie-hellman-group18-sha512
903: .It
1.173 naddy 904: diffie-hellman-group-exchange-sha1
905: .It
906: diffie-hellman-group-exchange-sha256
907: .It
908: ecdh-sha2-nistp256
909: .It
910: ecdh-sha2-nistp384
911: .It
912: ecdh-sha2-nistp521
913: .El
914: .Pp
915: The default is:
1.170 dtucker 916: .Bd -literal -offset indent
1.234 djm 917: curve25519-sha256,curve25519-sha256@libssh.org,
1.170 dtucker 918: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
919: diffie-hellman-group-exchange-sha256,
1.263 djm 920: diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,
921: diffie-hellman-group14-sha256,diffie-hellman-group14-sha1
1.170 dtucker 922: .Ed
1.188 djm 923: .Pp
1.237 jmc 924: The list of available key exchange algorithms may also be obtained using
925: .Qq ssh -Q kex .
1.1 stevesk 926: .It Cm ListenAddress
927: Specifies the local addresses
1.52 jmc 928: .Xr sshd 8
1.1 stevesk 929: should listen on.
930: The following forms may be used:
931: .Pp
932: .Bl -item -offset indent -compact
933: .It
934: .Cm ListenAddress
935: .Sm off
1.259 jmc 936: .Ar hostname | address
1.1 stevesk 937: .Sm on
1.260 jmc 938: .Op Cm rdomain Ar domain
1.1 stevesk 939: .It
940: .Cm ListenAddress
941: .Sm off
1.259 jmc 942: .Ar hostname : port
1.1 stevesk 943: .Sm on
1.260 jmc 944: .Op Cm rdomain Ar domain
1.256 djm 945: .It
946: .Cm ListenAddress
947: .Sm off
1.259 jmc 948: .Ar IPv4_address : port
1.256 djm 949: .Sm on
1.260 jmc 950: .Op Cm rdomain Ar domain
1.1 stevesk 951: .It
952: .Cm ListenAddress
953: .Sm off
1.259 jmc 954: .Oo Ar hostname | address Oc : Ar port
1.1 stevesk 955: .Sm on
1.260 jmc 956: .Op Cm rdomain Ar domain
1.1 stevesk 957: .El
958: .Pp
1.256 djm 959: The optional
960: .Cm rdomain
961: qualifier requests
962: .Xr sshd 8
963: listen in an explicit routing domain.
1.1 stevesk 964: If
965: .Ar port
966: is not specified,
1.200 dtucker 967: sshd will listen on the address and all
1.1 stevesk 968: .Cm Port
1.17 jmc 969: options specified.
1.256 djm 970: The default is to listen on all local addresses on the current default
971: routing domain.
1.15 jmc 972: Multiple
1.1 stevesk 973: .Cm ListenAddress
1.17 jmc 974: options are permitted.
1.256 djm 975: For more information on routing domains, see
1.259 jmc 976: .Xr rdomain 4 .
1.1 stevesk 977: .It Cm LoginGraceTime
978: The server disconnects after this time if the user has not
979: successfully logged in.
980: If the value is 0, there is no time limit.
1.12 stevesk 981: The default is 120 seconds.
1.1 stevesk 982: .It Cm LogLevel
983: Gives the verbosity level that is used when logging messages from
1.53 jmc 984: .Xr sshd 8 .
1.1 stevesk 985: The possible values are:
1.52 jmc 986: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.15 jmc 987: The default is INFO.
988: DEBUG and DEBUG1 are equivalent.
989: DEBUG2 and DEBUG3 each specify higher levels of debugging output.
990: Logging with a DEBUG level violates the privacy of users and is not recommended.
1.1 stevesk 991: .It Cm MACs
992: Specifies the available MAC (message authentication code) algorithms.
1.219 jmc 993: The MAC algorithm is used for data integrity protection.
1.1 stevesk 994: Multiple algorithms must be comma-separated.
1.208 djm 995: If the specified value begins with a
996: .Sq +
997: character, then the specified algorithms will be appended to the default set
998: instead of replacing them.
1.242 djm 999: If the specified value begins with a
1000: .Sq -
1001: character, then the specified algorithms (including wildcards) will be removed
1002: from the default set instead of replacing them.
1.208 djm 1003: .Pp
1.152 markus 1004: The algorithms that contain
1.237 jmc 1005: .Qq -etm
1.152 markus 1006: calculate the MAC after encryption (encrypt-then-mac).
1007: These are considered safer and their use recommended.
1.173 naddy 1008: The supported MACs are:
1009: .Pp
1010: .Bl -item -compact -offset indent
1011: .It
1012: hmac-md5
1013: .It
1014: hmac-md5-96
1015: .It
1016: hmac-sha1
1017: .It
1018: hmac-sha1-96
1019: .It
1020: hmac-sha2-256
1021: .It
1022: hmac-sha2-512
1023: .It
1024: umac-64@openssh.com
1025: .It
1026: umac-128@openssh.com
1027: .It
1028: hmac-md5-etm@openssh.com
1029: .It
1030: hmac-md5-96-etm@openssh.com
1031: .It
1032: hmac-sha1-etm@openssh.com
1033: .It
1034: hmac-sha1-96-etm@openssh.com
1035: .It
1036: hmac-sha2-256-etm@openssh.com
1037: .It
1038: hmac-sha2-512-etm@openssh.com
1039: .It
1040: umac-64-etm@openssh.com
1041: .It
1042: umac-128-etm@openssh.com
1043: .El
1044: .Pp
1.52 jmc 1045: The default is:
1.77 jmc 1046: .Bd -literal -offset indent
1.152 markus 1047: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
1048: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
1.217 djm 1049: hmac-sha1-etm@openssh.com,
1.173 naddy 1050: umac-64@openssh.com,umac-128@openssh.com,
1.217 djm 1051: hmac-sha2-256,hmac-sha2-512,hmac-sha1
1.77 jmc 1052: .Ed
1.188 djm 1053: .Pp
1.237 jmc 1054: The list of available MAC algorithms may also be obtained using
1055: .Qq ssh -Q mac .
1.60 dtucker 1056: .It Cm Match
1.61 jmc 1057: Introduces a conditional block.
1.65 dtucker 1058: If all of the criteria on the
1.60 dtucker 1059: .Cm Match
1.65 dtucker 1060: line are satisfied, the keywords on the following lines override those
1061: set in the global section of the config file, until either another
1.60 dtucker 1062: .Cm Match
1.65 dtucker 1063: line or the end of the file.
1.172 djm 1064: If a keyword appears in multiple
1065: .Cm Match
1.177 sobrado 1066: blocks that are satisfied, only the first instance of the keyword is
1.172 djm 1067: applied.
1.91 djm 1068: .Pp
1.61 jmc 1069: The arguments to
1.60 dtucker 1070: .Cm Match
1.163 dtucker 1071: are one or more criteria-pattern pairs or the single token
1072: .Cm All
1073: which matches all criteria.
1.60 dtucker 1074: The available criteria are
1075: .Cm User ,
1.69 dtucker 1076: .Cm Group ,
1.60 dtucker 1077: .Cm Host ,
1.139 dtucker 1078: .Cm LocalAddress ,
1079: .Cm LocalPort ,
1.258 djm 1080: .Cm RDomain ,
1.60 dtucker 1081: and
1.258 djm 1082: .Cm Address
1083: (with
1084: .Cm RDomain
1085: representing the
1086: .Xr rdomain 4
1.284 jmc 1087: on which the connection was received).
1.258 djm 1088: .Pp
1.91 djm 1089: The match patterns may consist of single entries or comma-separated
1090: lists and may use the wildcard and negation operators described in the
1.237 jmc 1091: .Sx PATTERNS
1092: section of
1.92 djm 1093: .Xr ssh_config 5 .
1.91 djm 1094: .Pp
1095: The patterns in an
1096: .Cm Address
1097: criteria may additionally contain addresses to match in CIDR
1.237 jmc 1098: address/masklen format,
1099: such as 192.0.2.0/24 or 2001:db8::/32.
1.91 djm 1100: Note that the mask length provided must be consistent with the address -
1101: it is an error to specify a mask length that is too long for the address
1.93 jmc 1102: or one with bits set in this host portion of the address.
1.237 jmc 1103: For example, 192.0.2.0/33 and 192.0.2.0/8, respectively.
1.91 djm 1104: .Pp
1.60 dtucker 1105: Only a subset of keywords may be used on the lines following a
1106: .Cm Match
1107: keyword.
1108: Available keywords are
1.142 jmc 1109: .Cm AcceptEnv ,
1.99 okan 1110: .Cm AllowAgentForwarding ,
1.142 jmc 1111: .Cm AllowGroups ,
1.193 djm 1112: .Cm AllowStreamLocalForwarding ,
1.62 dtucker 1113: .Cm AllowTcpForwarding ,
1.141 markus 1114: .Cm AllowUsers ,
1.149 djm 1115: .Cm AuthenticationMethods ,
1.146 djm 1116: .Cm AuthorizedKeysCommand ,
1117: .Cm AuthorizedKeysCommandUser ,
1.147 jmc 1118: .Cm AuthorizedKeysFile ,
1.214 djm 1119: .Cm AuthorizedPrincipalsCommand ,
1120: .Cm AuthorizedPrincipalsCommandUser ,
1.123 djm 1121: .Cm AuthorizedPrincipalsFile ,
1.72 dtucker 1122: .Cm Banner ,
1.85 djm 1123: .Cm ChrootDirectory ,
1.238 markus 1124: .Cm ClientAliveCountMax ,
1125: .Cm ClientAliveInterval ,
1.141 markus 1126: .Cm DenyGroups ,
1127: .Cm DenyUsers ,
1.67 dtucker 1128: .Cm ForceCommand ,
1.194 djm 1129: .Cm GatewayPorts ,
1.193 djm 1130: .Cm GSSAPIAuthentication ,
1.189 djm 1131: .Cm HostbasedAcceptedKeyTypes ,
1.87 djm 1132: .Cm HostbasedAuthentication ,
1.123 djm 1133: .Cm HostbasedUsesNameFromPacketOnly ,
1.193 djm 1134: .Cm IPQoS ,
1.74 jmc 1135: .Cm KbdInteractiveAuthentication ,
1.72 dtucker 1136: .Cm KerberosAuthentication ,
1.245 djm 1137: .Cm LogLevel ,
1.95 dtucker 1138: .Cm MaxAuthTries ,
1.94 dtucker 1139: .Cm MaxSessions ,
1.72 dtucker 1140: .Cm PasswordAuthentication ,
1.97 djm 1141: .Cm PermitEmptyPasswords ,
1.271 djm 1142: .Cm PermitListen ,
1.66 dtucker 1143: .Cm PermitOpen ,
1.79 dtucker 1144: .Cm PermitRootLogin ,
1.164 djm 1145: .Cm PermitTTY ,
1.123 djm 1146: .Cm PermitTunnel ,
1.174 djm 1147: .Cm PermitUserRC ,
1.189 djm 1148: .Cm PubkeyAcceptedKeyTypes ,
1.107 dtucker 1149: .Cm PubkeyAuthentication ,
1.159 dtucker 1150: .Cm RekeyLimit ,
1.193 djm 1151: .Cm RevokedKeys ,
1.257 djm 1152: .Cm RDomain ,
1.274 djm 1153: .Cm SetEnv ,
1.193 djm 1154: .Cm StreamLocalBindMask ,
1155: .Cm StreamLocalBindUnlink ,
1156: .Cm TrustedUserCAKeys ,
1.66 dtucker 1157: .Cm X11DisplayOffset ,
1.101 djm 1158: .Cm X11Forwarding
1.60 dtucker 1159: and
1.286 jmc 1160: .Cm X11UseLocalhost .
1.33 dtucker 1161: .It Cm MaxAuthTries
1162: Specifies the maximum number of authentication attempts permitted per
1.35 jmc 1163: connection.
1164: Once the number of failures reaches half this value,
1165: additional failures are logged.
1166: The default is 6.
1.90 djm 1167: .It Cm MaxSessions
1.216 djm 1168: Specifies the maximum number of open shell, login or subsystem (e.g. sftp)
1169: sessions permitted per network connection.
1170: Multiple sessions may be established by clients that support connection
1171: multiplexing.
1172: Setting
1173: .Cm MaxSessions
1174: to 1 will effectively disable session multiplexing, whereas setting it to 0
1175: will prevent all shell, login and subsystem sessions while still permitting
1176: forwarding.
1.90 djm 1177: The default is 10.
1.1 stevesk 1178: .It Cm MaxStartups
1179: Specifies the maximum number of concurrent unauthenticated connections to the
1.52 jmc 1180: SSH daemon.
1.1 stevesk 1181: Additional connections will be dropped until authentication succeeds or the
1182: .Cm LoginGraceTime
1183: expires for a connection.
1.156 dtucker 1184: The default is 10:30:100.
1.1 stevesk 1185: .Pp
1186: Alternatively, random early drop can be enabled by specifying
1187: the three colon separated values
1.237 jmc 1188: start:rate:full (e.g. "10:30:60").
1.53 jmc 1189: .Xr sshd 8
1.237 jmc 1190: will refuse connection attempts with a probability of rate/100 (30%)
1191: if there are currently start (10) unauthenticated connections.
1.1 stevesk 1192: The probability increases linearly and all connection attempts
1.237 jmc 1193: are refused if the number of unauthenticated connections reaches full (60).
1.1 stevesk 1194: .It Cm PasswordAuthentication
1195: Specifies whether password authentication is allowed.
1196: The default is
1.237 jmc 1197: .Cm yes .
1.1 stevesk 1198: .It Cm PermitEmptyPasswords
1199: When password authentication is allowed, it specifies whether the
1200: server allows login to accounts with empty password strings.
1201: The default is
1.237 jmc 1202: .Cm no .
1.271 djm 1203: .It Cm PermitListen
1204: Specifies the addresses/ports on which a remote TCP port forwarding may listen.
1205: The listen specification must be one of the following forms:
1206: .Pp
1207: .Bl -item -offset indent -compact
1208: .It
1209: .Cm PermitListen
1210: .Sm off
1.276 djm 1211: .Ar port
1.271 djm 1212: .Sm on
1213: .It
1214: .Cm PermitListen
1215: .Sm off
1.276 djm 1216: .Ar host : port
1.271 djm 1217: .Sm on
1218: .El
1219: .Pp
1220: Multiple permissions may be specified by separating them with whitespace.
1221: An argument of
1222: .Cm any
1223: can be used to remove all restrictions and permit any listen requests.
1224: An argument of
1225: .Cm none
1226: can be used to prohibit all listen requests.
1227: The host name may contain wildcards as described in the PATTERNS section in
1228: .Xr ssh_config 5 .
1229: The wildcard
1230: .Sq *
1231: can also be used in place of a port number to allow all ports.
1232: By default all port forwarding listen requests are permitted.
1.272 jmc 1233: Note that the
1.271 djm 1234: .Cm GatewayPorts
1235: option may further restrict which addresses may be listened on.
1.276 djm 1236: Note also that
1237: .Xr ssh 1
1238: will request a listen host of
1239: .Dq localhost
1.283 dtucker 1240: if no listen host was specifically requested, and this name is
1.277 jmc 1241: treated differently to explicit localhost addresses of
1.276 djm 1242: .Dq 127.0.0.1
1243: and
1244: .Dq ::1 .
1.62 dtucker 1245: .It Cm PermitOpen
1246: Specifies the destinations to which TCP port forwarding is permitted.
1247: The forwarding specification must be one of the following forms:
1248: .Pp
1249: .Bl -item -offset indent -compact
1250: .It
1251: .Cm PermitOpen
1252: .Sm off
1253: .Ar host : port
1254: .Sm on
1255: .It
1256: .Cm PermitOpen
1257: .Sm off
1258: .Ar IPv4_addr : port
1259: .Sm on
1260: .It
1261: .Cm PermitOpen
1262: .Sm off
1263: .Ar \&[ IPv6_addr \&] : port
1264: .Sm on
1265: .El
1266: .Pp
1.68 dtucker 1267: Multiple forwards may be specified by separating them with whitespace.
1.62 dtucker 1268: An argument of
1.237 jmc 1269: .Cm any
1.62 dtucker 1270: can be used to remove all restrictions and permit any forwarding requests.
1.140 dtucker 1271: An argument of
1.237 jmc 1272: .Cm none
1.140 dtucker 1273: can be used to prohibit all forwarding requests.
1.227 jmc 1274: The wildcard
1.237 jmc 1275: .Sq *
1.227 jmc 1276: can be used for host or port to allow all hosts or ports, respectively.
1.63 jmc 1277: By default all port forwarding requests are permitted.
1.1 stevesk 1278: .It Cm PermitRootLogin
1.38 jmc 1279: Specifies whether root can log in using
1.1 stevesk 1280: .Xr ssh 1 .
1281: The argument must be
1.237 jmc 1282: .Cm yes ,
1283: .Cm prohibit-password ,
1284: .Cm forced-commands-only ,
1.1 stevesk 1285: or
1.237 jmc 1286: .Cm no .
1.1 stevesk 1287: The default is
1.237 jmc 1288: .Cm prohibit-password .
1.1 stevesk 1289: .Pp
1290: If this option is set to
1.237 jmc 1291: .Cm prohibit-password
1.255 jmc 1292: (or its deprecated alias,
1293: .Cm without-password ) ,
1.210 deraadt 1294: password and keyboard-interactive authentication are disabled for root.
1.1 stevesk 1295: .Pp
1296: If this option is set to
1.237 jmc 1297: .Cm forced-commands-only ,
1.1 stevesk 1298: root login with public key authentication will be allowed,
1299: but only if the
1300: .Ar command
1301: option has been specified
1302: (which may be useful for taking remote backups even if root login is
1.17 jmc 1303: normally not allowed).
1304: All other authentication methods are disabled for root.
1.1 stevesk 1305: .Pp
1306: If this option is set to
1.237 jmc 1307: .Cm no ,
1.38 jmc 1308: root is not allowed to log in.
1.231 jmc 1309: .It Cm PermitTTY
1310: Specifies whether
1311: .Xr pty 4
1312: allocation is permitted.
1313: The default is
1.237 jmc 1314: .Cm yes .
1.46 reyk 1315: .It Cm PermitTunnel
1316: Specifies whether
1317: .Xr tun 4
1318: device forwarding is allowed.
1.47 reyk 1319: The argument must be
1.237 jmc 1320: .Cm yes ,
1321: .Cm point-to-point
1.58 stevesk 1322: (layer 3),
1.237 jmc 1323: .Cm ethernet
1.58 stevesk 1324: (layer 2), or
1.237 jmc 1325: .Cm no .
1.58 stevesk 1326: Specifying
1.237 jmc 1327: .Cm yes
1.58 stevesk 1328: permits both
1.237 jmc 1329: .Cm point-to-point
1.58 stevesk 1330: and
1.237 jmc 1331: .Cm ethernet .
1.46 reyk 1332: The default is
1.237 jmc 1333: .Cm no .
1.178 djm 1334: .Pp
1335: Independent of this setting, the permissions of the selected
1336: .Xr tun 4
1337: device must allow access to the user.
1.6 markus 1338: .It Cm PermitUserEnvironment
1339: Specifies whether
1340: .Pa ~/.ssh/environment
1.9 stevesk 1341: and
1.6 markus 1342: .Cm environment=
1343: options in
1344: .Pa ~/.ssh/authorized_keys
1.9 stevesk 1345: are processed by
1.52 jmc 1346: .Xr sshd 8 .
1.278 djm 1347: Valid options are
1348: .Cm yes ,
1349: .Cm no
1350: or a pattern-list specifying which environment variable names to accept
1351: (for example
1352: .Qq LANG,LC_* ) .
1.6 markus 1353: The default is
1.237 jmc 1354: .Cm no .
1.9 stevesk 1355: Enabling environment processing may enable users to bypass access
1356: restrictions in some configurations using mechanisms such as
1357: .Ev LD_PRELOAD .
1.174 djm 1358: .It Cm PermitUserRC
1359: Specifies whether any
1360: .Pa ~/.ssh/rc
1361: file is executed.
1362: The default is
1.237 jmc 1363: .Cm yes .
1.1 stevesk 1364: .It Cm PidFile
1.4 stevesk 1365: Specifies the file that contains the process ID of the
1.195 dtucker 1366: SSH daemon, or
1.237 jmc 1367: .Cm none
1.195 dtucker 1368: to not write one.
1.1 stevesk 1369: The default is
1370: .Pa /var/run/sshd.pid .
1371: .It Cm Port
1372: Specifies the port number that
1.52 jmc 1373: .Xr sshd 8
1.1 stevesk 1374: listens on.
1375: The default is 22.
1376: Multiple options of this type are permitted.
1377: See also
1378: .Cm ListenAddress .
1379: .It Cm PrintLastLog
1380: Specifies whether
1.52 jmc 1381: .Xr sshd 8
1.36 jaredy 1382: should print the date and time of the last user login when a user logs
1383: in interactively.
1.1 stevesk 1384: The default is
1.237 jmc 1385: .Cm yes .
1.1 stevesk 1386: .It Cm PrintMotd
1387: Specifies whether
1.52 jmc 1388: .Xr sshd 8
1.1 stevesk 1389: should print
1390: .Pa /etc/motd
1391: when a user logs in interactively.
1392: (On some systems it is also printed by the shell,
1393: .Pa /etc/profile ,
1394: or equivalent.)
1395: The default is
1.237 jmc 1396: .Cm yes .
1.189 djm 1397: .It Cm PubkeyAcceptedKeyTypes
1398: Specifies the key types that will be accepted for public key authentication
1.280 djm 1399: as a list of comma-separated patterns.
1.208 djm 1400: Alternately if the specified value begins with a
1401: .Sq +
1402: character, then the specified key types will be appended to the default set
1403: instead of replacing them.
1.242 djm 1404: If the specified value begins with a
1405: .Sq -
1406: character, then the specified key types (including wildcards) will be removed
1407: from the default set instead of replacing them.
1.206 markus 1408: The default for this option is:
1409: .Bd -literal -offset 3n
1410: ecdsa-sha2-nistp256-cert-v01@openssh.com,
1411: ecdsa-sha2-nistp384-cert-v01@openssh.com,
1412: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1413: ssh-ed25519-cert-v01@openssh.com,
1.279 djm 1414: rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,
1.206 markus 1415: ssh-rsa-cert-v01@openssh.com,
1416: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.279 djm 1417: ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.206 markus 1418: .Ed
1419: .Pp
1.237 jmc 1420: The list of available key types may also be obtained using
1421: .Qq ssh -Q key .
1.1 stevesk 1422: .It Cm PubkeyAuthentication
1423: Specifies whether public key authentication is allowed.
1424: The default is
1.237 jmc 1425: .Cm yes .
1.159 dtucker 1426: .It Cm RekeyLimit
1427: Specifies the maximum amount of data that may be transmitted before the
1428: session key is renegotiated, optionally followed a maximum amount of
1429: time that may pass before the session key is renegotiated.
1430: The first argument is specified in bytes and may have a suffix of
1431: .Sq K ,
1432: .Sq M ,
1433: or
1434: .Sq G
1435: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1436: The default is between
1437: .Sq 1G
1438: and
1439: .Sq 4G ,
1440: depending on the cipher.
1441: The optional second value is specified in seconds and may use any of the
1442: units documented in the
1443: .Sx TIME FORMATS
1.160 jmc 1444: section.
1.159 dtucker 1445: The default value for
1446: .Cm RekeyLimit
1447: is
1.237 jmc 1448: .Cm default none ,
1.159 dtucker 1449: which means that rekeying is performed after the cipher's default amount
1450: of data has been sent or received and no time based rekeying is done.
1.118 djm 1451: .It Cm RevokedKeys
1.195 dtucker 1452: Specifies revoked public keys file, or
1.237 jmc 1453: .Cm none
1.195 dtucker 1454: to not use one.
1.118 djm 1455: Keys listed in this file will be refused for public key authentication.
1456: Note that if this file is not readable, then public key authentication will
1457: be refused for all users.
1.154 djm 1458: Keys may be specified as a text file, listing one public key per line, or as
1459: an OpenSSH Key Revocation List (KRL) as generated by
1.155 jmc 1460: .Xr ssh-keygen 1 .
1.161 jmc 1461: For more information on KRLs, see the KEY REVOCATION LISTS section in
1.154 djm 1462: .Xr ssh-keygen 1 .
1.257 djm 1463: .It Cm RDomain
1464: Specifies an explicit routing domain that is applied after authentication
1465: has completed.
1.259 jmc 1466: The user session, as well and any forwarded or listening IP sockets,
1467: will be bound to this
1.257 djm 1468: .Xr rdomain 4 .
1469: If the routing domain is set to
1470: .Cm \&%D ,
1.259 jmc 1471: then the domain in which the incoming connection was received will be applied.
1.274 djm 1472: .It Cm SetEnv
1473: Specifies one or more environment variables to set in child sessions started
1474: by
1475: .Xr sshd 8
1476: as
1477: .Dq NAME=VALUE .
1478: The environment value may be quoted (e.g. if it contains whitespace
1479: characters).
1480: Environment variables set by
1481: .Cm SetEnv
1482: override the default environment and any variables specified by the user
1483: via
1484: .Cm AcceptEnv
1485: or
1486: .Cm PermitUserEnvironment .
1.175 millert 1487: .It Cm StreamLocalBindMask
1488: Sets the octal file creation mode mask
1489: .Pq umask
1490: used when creating a Unix-domain socket file for local or remote
1491: port forwarding.
1492: This option is only used for port forwarding to a Unix-domain socket file.
1493: .Pp
1494: The default value is 0177, which creates a Unix-domain socket file that is
1495: readable and writable only by the owner.
1496: Note that not all operating systems honor the file mode on Unix-domain
1497: socket files.
1498: .It Cm StreamLocalBindUnlink
1499: Specifies whether to remove an existing Unix-domain socket file for local
1500: or remote port forwarding before creating a new one.
1501: If the socket file already exists and
1502: .Cm StreamLocalBindUnlink
1503: is not enabled,
1504: .Nm sshd
1505: will be unable to forward the port to the Unix-domain socket file.
1506: This option is only used for port forwarding to a Unix-domain socket file.
1507: .Pp
1508: The argument must be
1.237 jmc 1509: .Cm yes
1.175 millert 1510: or
1.237 jmc 1511: .Cm no .
1.175 millert 1512: The default is
1.237 jmc 1513: .Cm no .
1.1 stevesk 1514: .It Cm StrictModes
1515: Specifies whether
1.52 jmc 1516: .Xr sshd 8
1.1 stevesk 1517: should check file modes and ownership of the
1518: user's files and home directory before accepting login.
1519: This is normally desirable because novices sometimes accidentally leave their
1520: directory or files world-writable.
1521: The default is
1.237 jmc 1522: .Cm yes .
1.112 djm 1523: Note that this does not apply to
1524: .Cm ChrootDirectory ,
1525: whose permissions and ownership are checked unconditionally.
1.1 stevesk 1526: .It Cm Subsystem
1.51 jmc 1527: Configures an external subsystem (e.g. file transfer daemon).
1.59 djm 1528: Arguments should be a subsystem name and a command (with optional arguments)
1529: to execute upon subsystem request.
1.80 djm 1530: .Pp
1.1 stevesk 1531: The command
1.237 jmc 1532: .Cm sftp-server
1533: implements the SFTP file transfer subsystem.
1.80 djm 1534: .Pp
1535: Alternately the name
1.237 jmc 1536: .Cm internal-sftp
1537: implements an in-process SFTP server.
1.80 djm 1538: This may simplify configurations using
1539: .Cm ChrootDirectory
1540: to force a different filesystem root on clients.
1541: .Pp
1.1 stevesk 1542: By default no subsystems are defined.
1543: .It Cm SyslogFacility
1544: Gives the facility code that is used when logging messages from
1.53 jmc 1545: .Xr sshd 8 .
1.1 stevesk 1546: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1547: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
1548: The default is AUTH.
1.27 markus 1549: .It Cm TCPKeepAlive
1550: Specifies whether the system should send TCP keepalive messages to the
1551: other side.
1552: If they are sent, death of the connection or crash of one
1553: of the machines will be properly noticed.
1554: However, this means that
1555: connections will die if the route is down temporarily, and some people
1556: find it annoying.
1557: On the other hand, if TCP keepalives are not sent,
1558: sessions may hang indefinitely on the server, leaving
1.237 jmc 1559: .Qq ghost
1.27 markus 1560: users and consuming server resources.
1561: .Pp
1562: The default is
1.237 jmc 1563: .Cm yes
1.27 markus 1564: (to send TCP keepalive messages), and the server will notice
1565: if the network goes down or the client host crashes.
1566: This avoids infinitely hanging sessions.
1567: .Pp
1568: To disable TCP keepalive messages, the value should be set to
1.237 jmc 1569: .Cm no .
1.118 djm 1570: .It Cm TrustedUserCAKeys
1571: Specifies a file containing public keys of certificate authorities that are
1.195 dtucker 1572: trusted to sign user certificates for authentication, or
1.237 jmc 1573: .Cm none
1.195 dtucker 1574: to not use one.
1.119 jmc 1575: Keys are listed one per line; empty lines and comments starting with
1.118 djm 1576: .Ql #
1577: are allowed.
1578: If a certificate is presented for authentication and has its signing CA key
1579: listed in this file, then it may be used for authentication for any user
1580: listed in the certificate's principals list.
1581: Note that certificates that lack a list of principals will not be permitted
1582: for authentication using
1583: .Cm TrustedUserCAKeys .
1.161 jmc 1584: For more details on certificates, see the CERTIFICATES section in
1.118 djm 1585: .Xr ssh-keygen 1 .
1.18 markus 1586: .It Cm UseDNS
1587: Specifies whether
1.52 jmc 1588: .Xr sshd 8
1.207 djm 1589: should look up the remote host name, and to check that
1.18 markus 1590: the resolved host name for the remote IP address maps back to the
1591: very same IP address.
1.207 djm 1592: .Pp
1593: If this option is set to
1.237 jmc 1594: .Cm no
1.207 djm 1595: (the default) then only addresses and not host names may be used in
1.221 djm 1596: .Pa ~/.ssh/authorized_keys
1.207 djm 1597: .Cm from
1598: and
1.211 jmc 1599: .Nm
1.207 djm 1600: .Cm Match
1601: .Cm Host
1602: directives.
1.137 djm 1603: .It Cm VersionAddendum
1604: Optionally specifies additional text to append to the SSH protocol banner
1605: sent by the server upon connection.
1606: The default is
1.237 jmc 1607: .Cm none .
1.1 stevesk 1608: .It Cm X11DisplayOffset
1609: Specifies the first display number available for
1.52 jmc 1610: .Xr sshd 8 Ns 's
1.1 stevesk 1611: X11 forwarding.
1.52 jmc 1612: This prevents sshd from interfering with real X11 servers.
1.1 stevesk 1613: The default is 10.
1614: .It Cm X11Forwarding
1615: Specifies whether X11 forwarding is permitted.
1.13 stevesk 1616: The argument must be
1.237 jmc 1617: .Cm yes
1.13 stevesk 1618: or
1.237 jmc 1619: .Cm no .
1.1 stevesk 1620: The default is
1.237 jmc 1621: .Cm no .
1.13 stevesk 1622: .Pp
1623: When X11 forwarding is enabled, there may be additional exposure to
1624: the server and to client displays if the
1.52 jmc 1625: .Xr sshd 8
1.13 stevesk 1626: proxy display is configured to listen on the wildcard address (see
1.237 jmc 1627: .Cm X11UseLocalhost ) ,
1628: though this is not the default.
1.13 stevesk 1629: Additionally, the authentication spoofing and authentication data
1630: verification and substitution occur on the client side.
1631: The security risk of using X11 forwarding is that the client's X11
1.52 jmc 1632: display server may be exposed to attack when the SSH client requests
1.13 stevesk 1633: forwarding (see the warnings for
1634: .Cm ForwardX11
1635: in
1.19 jmc 1636: .Xr ssh_config 5 ) .
1.13 stevesk 1637: A system administrator may have a stance in which they want to
1638: protect clients that may expose themselves to attack by unwittingly
1639: requesting X11 forwarding, which can warrant a
1.237 jmc 1640: .Cm no
1.13 stevesk 1641: setting.
1642: .Pp
1643: Note that disabling X11 forwarding does not prevent users from
1644: forwarding X11 traffic, as users can always install their own forwarders.
1.1 stevesk 1645: .It Cm X11UseLocalhost
1646: Specifies whether
1.52 jmc 1647: .Xr sshd 8
1.1 stevesk 1648: should bind the X11 forwarding server to the loopback address or to
1.15 jmc 1649: the wildcard address.
1650: By default,
1.52 jmc 1651: sshd binds the forwarding server to the loopback address and sets the
1.1 stevesk 1652: hostname part of the
1653: .Ev DISPLAY
1654: environment variable to
1.237 jmc 1655: .Cm localhost .
1.8 stevesk 1656: This prevents remote hosts from connecting to the proxy display.
1.1 stevesk 1657: However, some older X11 clients may not function with this
1658: configuration.
1659: .Cm X11UseLocalhost
1660: may be set to
1.237 jmc 1661: .Cm no
1.1 stevesk 1662: to specify that the forwarding server should be bound to the wildcard
1663: address.
1664: The argument must be
1.237 jmc 1665: .Cm yes
1.1 stevesk 1666: or
1.237 jmc 1667: .Cm no .
1.1 stevesk 1668: The default is
1.237 jmc 1669: .Cm yes .
1.1 stevesk 1670: .It Cm XAuthLocation
1.11 stevesk 1671: Specifies the full pathname of the
1.1 stevesk 1672: .Xr xauth 1
1.195 dtucker 1673: program, or
1.237 jmc 1674: .Cm none
1.195 dtucker 1675: to not use one.
1.1 stevesk 1676: The default is
1677: .Pa /usr/X11R6/bin/xauth .
1678: .El
1.55 jmc 1679: .Sh TIME FORMATS
1.53 jmc 1680: .Xr sshd 8
1.1 stevesk 1681: command-line arguments and configuration file options that specify time
1682: may be expressed using a sequence of the form:
1683: .Sm off
1.7 stevesk 1684: .Ar time Op Ar qualifier ,
1.1 stevesk 1685: .Sm on
1686: where
1687: .Ar time
1688: is a positive integer value and
1689: .Ar qualifier
1690: is one of the following:
1691: .Pp
1692: .Bl -tag -width Ds -compact -offset indent
1.64 jmc 1693: .It Aq Cm none
1.1 stevesk 1694: seconds
1695: .It Cm s | Cm S
1696: seconds
1697: .It Cm m | Cm M
1698: minutes
1699: .It Cm h | Cm H
1700: hours
1701: .It Cm d | Cm D
1702: days
1703: .It Cm w | Cm W
1704: weeks
1705: .El
1706: .Pp
1707: Each member of the sequence is added together to calculate
1708: the total time value.
1709: .Pp
1710: Time format examples:
1711: .Pp
1712: .Bl -tag -width Ds -compact -offset indent
1713: .It 600
1714: 600 seconds (10 minutes)
1715: .It 10m
1716: 10 minutes
1717: .It 1h30m
1718: 1 hour 30 minutes (90 minutes)
1719: .El
1.235 jmc 1720: .Sh TOKENS
1721: Arguments to some keywords can make use of tokens,
1722: which are expanded at runtime:
1723: .Pp
1724: .Bl -tag -width XXXX -offset indent -compact
1725: .It %%
1726: A literal
1727: .Sq % .
1.257 djm 1728: .It \&%D
1729: The routing domain in which the incoming connection was received.
1.235 jmc 1730: .It %F
1731: The fingerprint of the CA key.
1732: .It %f
1733: The fingerprint of the key or certificate.
1734: .It %h
1735: The home directory of the user.
1736: .It %i
1737: The key ID in the certificate.
1738: .It %K
1739: The base64-encoded CA key.
1740: .It %k
1741: The base64-encoded key or certificate for authentication.
1742: .It %s
1743: The serial number of the certificate.
1744: .It \&%T
1745: The type of the CA key.
1746: .It %t
1747: The key or certificate type.
1.268 jmc 1748: .It \&%U
1749: The numeric user ID of the target user.
1.235 jmc 1750: .It %u
1751: The username.
1752: .El
1753: .Pp
1754: .Cm AuthorizedKeysCommand
1.270 jmc 1755: accepts the tokens %%, %f, %h, %k, %t, %U, and %u.
1.235 jmc 1756: .Pp
1757: .Cm AuthorizedKeysFile
1.270 jmc 1758: accepts the tokens %%, %h, %U, and %u.
1.235 jmc 1759: .Pp
1760: .Cm AuthorizedPrincipalsCommand
1.270 jmc 1761: accepts the tokens %%, %F, %f, %h, %i, %K, %k, %s, %T, %t, %U, and %u.
1.235 jmc 1762: .Pp
1763: .Cm AuthorizedPrincipalsFile
1.270 jmc 1764: accepts the tokens %%, %h, %U, and %u.
1.235 jmc 1765: .Pp
1766: .Cm ChrootDirectory
1.270 jmc 1767: accepts the tokens %%, %h, %U, and %u.
1.257 djm 1768: .Pp
1769: .Cm RoutingDomain
1770: accepts the token %D.
1.1 stevesk 1771: .Sh FILES
1772: .Bl -tag -width Ds
1773: .It Pa /etc/ssh/sshd_config
1774: Contains configuration data for
1.53 jmc 1775: .Xr sshd 8 .
1.1 stevesk 1776: This file should be writable by root only, but it is recommended
1777: (though not necessary) that it be world-readable.
1778: .El
1.19 jmc 1779: .Sh SEE ALSO
1.237 jmc 1780: .Xr sftp-server 8 ,
1.19 jmc 1781: .Xr sshd 8
1.1 stevesk 1782: .Sh AUTHORS
1.237 jmc 1783: .An -nosplit
1.1 stevesk 1784: OpenSSH is a derivative of the original and free
1.237 jmc 1785: ssh 1.2.12 release by
1786: .An Tatu Ylonen .
1787: .An Aaron Campbell , Bob Beck , Markus Friedl , Niels Provos ,
1788: .An Theo de Raadt
1789: and
1790: .An Dug Song
1.1 stevesk 1791: removed many bugs, re-added newer features and
1792: created OpenSSH.
1.237 jmc 1793: .An Markus Friedl
1794: contributed the support for SSH protocol versions 1.5 and 2.0.
1795: .An Niels Provos
1796: and
1797: .An Markus Friedl
1798: contributed support for privilege separation.
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