Annotation of src/usr.bin/ssh/sshd.8, Revision 1.81
1.1 deraadt 1: .\" -*- nroff -*-
2: .\"
3: .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
4: .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5: .\" All rights reserved
6: .\"
1.64 deraadt 7: .\" As far as I am concerned, the code I have written for this software
8: .\" can be used freely for any purpose. Any derived versions of this
9: .\" software must be clearly marked as such, and if the derived work is
10: .\" incompatible with the protocol description in the RFC file, it must be
11: .\" called by a name other than "ssh" or "Secure Shell".
12: .\"
13: .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
14: .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
15: .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
16: .\"
17: .\" Redistribution and use in source and binary forms, with or without
18: .\" modification, are permitted provided that the following conditions
19: .\" are met:
20: .\" 1. Redistributions of source code must retain the above copyright
21: .\" notice, this list of conditions and the following disclaimer.
22: .\" 2. Redistributions in binary form must reproduce the above copyright
23: .\" notice, this list of conditions and the following disclaimer in the
24: .\" documentation and/or other materials provided with the distribution.
1.1 deraadt 25: .\"
1.64 deraadt 26: .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
27: .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
28: .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
29: .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
30: .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
31: .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
32: .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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34: .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
35: .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
1.1 deraadt 36: .\"
1.81 ! markus 37: .\" $OpenBSD: sshd.8,v 1.80 2001/01/08 22:29:05 markus Exp $
1.2 deraadt 38: .Dd September 25, 1999
39: .Dt SSHD 8
40: .Os
41: .Sh NAME
42: .Nm sshd
43: .Nd secure shell daemon
44: .Sh SYNOPSIS
45: .Nm sshd
1.74 markus 46: .Op Fl diqDQ46
1.2 deraadt 47: .Op Fl b Ar bits
48: .Op Fl f Ar config_file
49: .Op Fl g Ar login_grace_time
50: .Op Fl h Ar host_key_file
51: .Op Fl k Ar key_gen_time
52: .Op Fl p Ar port
1.61 markus 53: .Op Fl u Ar len
1.26 markus 54: .Op Fl V Ar client_protocol_id
1.40 aaron 55: .Sh DESCRIPTION
1.2 deraadt 56: .Nm
1.40 aaron 57: (Secure Shell Daemon) is the daemon program for
1.2 deraadt 58: .Xr ssh 1 .
1.42 hugh 59: Together these programs replace rlogin and rsh, and
1.1 deraadt 60: provide secure encrypted communications between two untrusted hosts
1.36 aaron 61: over an insecure network.
62: The programs are intended to be as easy to
1.1 deraadt 63: install and use as possible.
1.2 deraadt 64: .Pp
65: .Nm
1.36 aaron 66: is the daemon that listens for connections from clients.
1.40 aaron 67: It is normally started at boot from
1.2 deraadt 68: .Pa /etc/rc .
69: It forks a new
1.36 aaron 70: daemon for each incoming connection.
71: The forked daemons handle
1.1 deraadt 72: key exchange, encryption, authentication, command execution,
73: and data exchange.
1.49 markus 74: This implementation of
75: .Nm
76: supports both SSH protocol version 1 and 2 simultaneously.
1.2 deraadt 77: .Nm
1.36 aaron 78: works as follows.
1.49 markus 79: .Pp
80: .Ss SSH protocol version 1
81: .Pp
1.36 aaron 82: Each host has a host-specific RSA key
83: (normally 1024 bits) used to identify the host.
84: Additionally, when
1.1 deraadt 85: the daemon starts, it generates a server RSA key (normally 768 bits).
86: This key is normally regenerated every hour if it has been used, and
87: is never stored on disk.
1.2 deraadt 88: .Pp
1.42 hugh 89: Whenever a client connects the daemon responds with its public
90: host and server keys.
1.36 aaron 91: The client compares the
1.49 markus 92: RSA host key against its own database to verify that it has not changed.
1.36 aaron 93: The client then generates a 256 bit random number.
94: It encrypts this
1.1 deraadt 95: random number using both the host key and the server key, and sends
1.36 aaron 96: the encrypted number to the server.
1.42 hugh 97: Both sides then use this
1.1 deraadt 98: random number as a session key which is used to encrypt all further
1.36 aaron 99: communications in the session.
100: The rest of the session is encrypted
1.42 hugh 101: using a conventional cipher, currently Blowfish or 3DES, with 3DES
1.39 deraadt 102: being used by default.
1.36 aaron 103: The client selects the encryption algorithm
1.5 deraadt 104: to use from those offered by the server.
1.2 deraadt 105: .Pp
1.36 aaron 106: Next, the server and the client enter an authentication dialog.
107: The client tries to authenticate itself using
1.2 deraadt 108: .Pa .rhosts
109: authentication,
110: .Pa .rhosts
111: authentication combined with RSA host
1.1 deraadt 112: authentication, RSA challenge-response authentication, or password
113: based authentication.
1.2 deraadt 114: .Pp
1.1 deraadt 115: Rhosts authentication is normally disabled
116: because it is fundamentally insecure, but can be enabled in the server
1.36 aaron 117: configuration file if desired.
118: System security is not improved unless
1.2 deraadt 119: .Xr rshd 8 ,
120: .Xr rlogind 8 ,
121: .Xr rexecd 8 ,
122: and
123: .Xr rexd 8
1.1 deraadt 124: are disabled (thus completely disabling
1.2 deraadt 125: .Xr rlogin 1
1.1 deraadt 126: and
1.2 deraadt 127: .Xr rsh 1
1.42 hugh 128: into the machine).
1.2 deraadt 129: .Pp
1.49 markus 130: .Ss SSH protocol version 2
131: .Pp
1.58 deraadt 132: Version 2 works similarly:
1.49 markus 133: Each host has a host-specific DSA key used to identify the host.
134: However, when the daemon starts, it does not generate a server key.
135: Forward security is provided through a Diffie-Hellman key agreement.
136: This key agreement results in a shared session key.
137: The rest of the session is encrypted
138: using a symmetric cipher, currently
139: Blowfish, 3DES or CAST128 in CBC mode or Arcfour.
140: The client selects the encryption algorithm
141: to use from those offered by the server.
142: Additionally, session integrity is provided
1.51 hugh 143: through a cryptographic message authentication code
1.49 markus 144: (hmac-sha1 or hmac-md5).
145: .Pp
146: Protocol version 2 provides a public key based
1.72 markus 147: user authentication method (PubkeyAuthentication)
1.49 markus 148: and conventional password authentication.
149: .Pp
150: .Ss Command execution and data forwarding
151: .Pp
1.1 deraadt 152: If the client successfully authenticates itself, a dialog for
1.36 aaron 153: preparing the session is entered.
154: At this time the client may request
1.1 deraadt 155: things like allocating a pseudo-tty, forwarding X11 connections,
156: forwarding TCP/IP connections, or forwarding the authentication agent
157: connection over the secure channel.
1.2 deraadt 158: .Pp
1.1 deraadt 159: Finally, the client either requests a shell or execution of a command.
1.36 aaron 160: The sides then enter session mode.
161: In this mode, either side may send
1.1 deraadt 162: data at any time, and such data is forwarded to/from the shell or
163: command on the server side, and the user terminal in the client side.
1.2 deraadt 164: .Pp
1.1 deraadt 165: When the user program terminates and all forwarded X11 and other
166: connections have been closed, the server sends command exit status to
167: the client, and both sides exit.
1.2 deraadt 168: .Pp
169: .Nm
1.1 deraadt 170: can be configured using command-line options or a configuration
1.36 aaron 171: file.
172: Command-line options override values specified in the
1.1 deraadt 173: configuration file.
1.25 markus 174: .Pp
175: .Nm
176: rereads its configuration file when it receives a hangup signal,
177: .Dv SIGHUP .
1.18 aaron 178: .Pp
179: The options are as follows:
1.2 deraadt 180: .Bl -tag -width Ds
181: .It Fl b Ar bits
1.1 deraadt 182: Specifies the number of bits in the server key (default 768).
1.2 deraadt 183: .Pp
184: .It Fl d
1.36 aaron 185: Debug mode.
186: The server sends verbose debug output to the system
187: log, and does not put itself in the background.
188: The server also will not fork and will only process one connection.
189: This option is only intended for debugging for the server.
1.67 aaron 190: Multiple -d options increases the debugging level.
191: Maximum is 3.
1.2 deraadt 192: .It Fl f Ar configuration_file
1.36 aaron 193: Specifies the name of the configuration file.
194: The default is
1.2 deraadt 195: .Pa /etc/sshd_config .
1.16 markus 196: .Nm
197: refuses to start if there is no configuration file.
1.2 deraadt 198: .It Fl g Ar login_grace_time
1.1 deraadt 199: Gives the grace time for clients to authenticate themselves (default
1.77 markus 200: 600 seconds).
1.36 aaron 201: If the client fails to authenticate the user within
202: this many seconds, the server disconnects and exits.
203: A value of zero indicates no limit.
1.2 deraadt 204: .It Fl h Ar host_key_file
1.75 markus 205: Specifies the file from which the host key is read (default
1.2 deraadt 206: .Pa /etc/ssh_host_key ) .
1.7 markus 207: This option must be given if
208: .Nm
209: is not run as root (as the normal
1.1 deraadt 210: host file is normally not readable by anyone but root).
1.75 markus 211: It is possible to have multiple host key files for
212: the different protocol versions.
1.2 deraadt 213: .It Fl i
1.7 markus 214: Specifies that
215: .Nm
1.40 aaron 216: is being run from inetd.
1.7 markus 217: .Nm
218: is normally not run
1.1 deraadt 219: from inetd because it needs to generate the server key before it can
1.36 aaron 220: respond to the client, and this may take tens of seconds.
221: Clients would have to wait too long if the key was regenerated every time.
1.35 aaron 222: However, with small key sizes (e.g., 512) using
1.7 markus 223: .Nm
224: from inetd may
1.1 deraadt 225: be feasible.
1.2 deraadt 226: .It Fl k Ar key_gen_time
1.1 deraadt 227: Specifies how often the server key is regenerated (default 3600
1.36 aaron 228: seconds, or one hour).
229: The motivation for regenerating the key fairly
1.1 deraadt 230: often is that the key is not stored anywhere, and after about an hour,
231: it becomes impossible to recover the key for decrypting intercepted
232: communications even if the machine is cracked into or physically
1.36 aaron 233: seized.
234: A value of zero indicates that the key will never be regenerated.
1.2 deraadt 235: .It Fl p Ar port
1.1 deraadt 236: Specifies the port on which the server listens for connections
237: (default 22).
1.2 deraadt 238: .It Fl q
1.36 aaron 239: Quiet mode.
240: Nothing is sent to the system log.
241: Normally the beginning,
1.1 deraadt 242: authentication, and termination of each connection is logged.
1.61 markus 243: .It Fl u Ar len
244: This option is used to specify the size of the field
245: in the
246: .Li utmp
247: structure that holds the remote host name.
248: If the resolved host name is longer than
249: .Ar len ,
250: the dotted decimal value will be used instead.
251: This allows hosts with very long host names that
252: overflow this field to still be uniquely identified.
253: Specifying
254: .Fl u0
255: indicates that only dotted decimal addresses
256: should be put into the
257: .Pa utmp
258: file.
1.74 markus 259: .It Fl D
260: When this option is specified
261: .Nm
262: will not detach and does not become a daemon.
263: This allows easy monitoring of
1.76 markus 264: .Nm sshd .
1.18 aaron 265: .It Fl Q
266: Do not print an error message if RSA support is missing.
1.26 markus 267: .It Fl V Ar client_protocol_id
1.68 markus 268: SSH-2 compatibility mode.
1.42 hugh 269: When this option is specified
1.26 markus 270: .Nm
1.42 hugh 271: assumes the client has sent the supplied version string
1.26 markus 272: and skips the
273: Protocol Version Identification Exchange.
1.68 markus 274: This option is not intended to be called directly.
1.29 markus 275: .It Fl 4
276: Forces
277: .Nm
278: to use IPv4 addresses only.
279: .It Fl 6
280: Forces
281: .Nm
282: to use IPv6 addresses only.
1.2 deraadt 283: .El
284: .Sh CONFIGURATION FILE
285: .Nm
1.40 aaron 286: reads configuration data from
1.2 deraadt 287: .Pa /etc/sshd_config
288: (or the file specified with
289: .Fl f
1.36 aaron 290: on the command line).
291: The file contains keyword-value pairs, one per line.
292: Lines starting with
1.2 deraadt 293: .Ql #
1.1 deraadt 294: and empty lines are interpreted as comments.
1.2 deraadt 295: .Pp
1.1 deraadt 296: The following keywords are possible.
1.2 deraadt 297: .Bl -tag -width Ds
298: .It Cm AFSTokenPassing
1.36 aaron 299: Specifies whether an AFS token may be forwarded to the server.
300: Default is
1.2 deraadt 301: .Dq yes .
1.11 markus 302: .It Cm AllowGroups
303: This keyword can be followed by a number of group names, separated
1.36 aaron 304: by spaces.
305: If specified, login is allowed only for users whose primary
1.81 ! markus 306: group or supplementary group list matches one of the patterns.
1.11 markus 307: .Ql \&*
308: and
309: .Ql ?
310: can be used as
1.36 aaron 311: wildcards in the patterns.
1.58 deraadt 312: Only group names are valid; a numerical group ID isn't recognized.
1.81 ! markus 313: By default login is allowed regardless of the group list.
1.3 dugsong 314: .Pp
1.69 markus 315: .It Cm AllowTcpForwarding
316: Specifies whether TCP forwarding is permitted.
317: The default is
318: .Dq yes .
319: Note that disabling TCP forwarding does not improve security unless
320: users are also denied shell access, as they can always install their
321: own forwarders.
322: .Pp
1.11 markus 323: .It Cm AllowUsers
324: This keyword can be followed by a number of user names, separated
1.36 aaron 325: by spaces.
326: If specified, login is allowed only for users names that
1.11 markus 327: match one of the patterns.
328: .Ql \&*
329: and
330: .Ql ?
331: can be used as
1.36 aaron 332: wildcards in the patterns.
1.58 deraadt 333: Only user names are valid; a numerical user ID isn't recognized.
1.36 aaron 334: By default login is allowed regardless of the user name.
1.80 markus 335: .Pp
336: .It Cm Banner
337: In some jurisdictions, sending a warning message before authentication
338: may be relevant for getting legal protection.
339: The contents of the specified file are sent to the remote user before
340: authentication is allowed.
341: This option is only available for protocol version 2.
1.11 markus 342: .Pp
1.41 markus 343: .It Cm Ciphers
344: Specifies the ciphers allowed for protocol version 2.
345: Multiple ciphers must be comma-separated.
346: The default is
1.78 djm 347: .Dq 3des-cbc,blowfish-cbc,cast128-cbc,arcfour,aes128-cbc .
1.8 markus 348: .It Cm CheckMail
349: Specifies whether
350: .Nm
351: should check for new mail for interactive logins.
352: The default is
353: .Dq no .
1.11 markus 354: .It Cm DenyGroups
355: This keyword can be followed by a number of group names, separated
1.36 aaron 356: by spaces.
1.81 ! markus 357: Users whose primary group or supplementary group list matches
! 358: one of the patterns aren't allowed to log in.
1.11 markus 359: .Ql \&*
360: and
361: .Ql ?
362: can be used as
1.36 aaron 363: wildcards in the patterns.
1.58 deraadt 364: Only group names are valid; a numerical group ID isn't recognized.
1.81 ! markus 365: By default login is allowed regardless of the group list.
1.11 markus 366: .Pp
367: .It Cm DenyUsers
368: This keyword can be followed by a number of user names, separated
1.36 aaron 369: by spaces.
370: Login is disallowed for user names that match one of the patterns.
1.11 markus 371: .Ql \&*
372: and
373: .Ql ?
1.36 aaron 374: can be used as wildcards in the patterns.
1.58 deraadt 375: Only user names are valid; a numerical user ID isn't recognized.
1.36 aaron 376: By default login is allowed regardless of the user name.
1.72 markus 377: .It Cm PubkeyAuthentication
378: Specifies whether public key authentication is allowed.
1.49 markus 379: The default is
380: .Dq yes .
381: Note that this option applies to protocol version 2 only.
1.47 markus 382: .It Cm GatewayPorts
383: Specifies whether remote hosts are allowed to connect to ports
384: forwarded for the client.
385: The argument must be
386: .Dq yes
387: or
388: .Dq no .
389: The default is
390: .Dq no .
1.2 deraadt 391: .It Cm HostKey
1.72 markus 392: Specifies the file containing the private host keys (default
1.46 markus 393: .Pa /etc/ssh_host_key )
1.72 markus 394: used by SSH protocol versions 1 and 2.
1.9 markus 395: Note that
396: .Nm
1.72 markus 397: if this file is group/world-accessible.
398: It is possible to have multiple host key files.
399: .Dq rsa1
400: keys are used for version 1 and
401: .Dq dsa
402: or
403: .Dq rsa
404: are used for version 2 of the SSH protocol.
1.2 deraadt 405: .It Cm IgnoreRhosts
1.34 markus 406: Specifies that
407: .Pa .rhosts
1.40 aaron 408: and
1.34 markus 409: .Pa .shosts
410: files will not be used in authentication.
1.2 deraadt 411: .Pa /etc/hosts.equiv
1.1 deraadt 412: and
1.40 aaron 413: .Pa /etc/shosts.equiv
1.36 aaron 414: are still used.
1.40 aaron 415: The default is
1.34 markus 416: .Dq yes .
1.24 markus 417: .It Cm IgnoreUserKnownHosts
418: Specifies whether
419: .Nm
420: should ignore the user's
421: .Pa $HOME/.ssh/known_hosts
1.45 markus 422: during
1.24 markus 423: .Cm RhostsRSAAuthentication .
424: The default is
1.2 deraadt 425: .Dq no .
426: .It Cm KeepAlive
1.1 deraadt 427: Specifies whether the system should send keepalive messages to the
1.36 aaron 428: other side.
429: If they are sent, death of the connection or crash of one
430: of the machines will be properly noticed.
431: However, this means that
1.1 deraadt 432: connections will die if the route is down temporarily, and some people
1.36 aaron 433: find it annoying.
1.51 hugh 434: On the other hand, if keepalives are not sent,
1.2 deraadt 435: sessions may hang indefinitely on the server, leaving
436: .Dq ghost
437: users and consuming server resources.
438: .Pp
439: The default is
440: .Dq yes
441: (to send keepalives), and the server will notice
1.36 aaron 442: if the network goes down or the client host reboots.
443: This avoids infinitely hanging sessions.
1.2 deraadt 444: .Pp
445: To disable keepalives, the value should be set to
446: .Dq no
447: in both the server and the client configuration files.
448: .It Cm KerberosAuthentication
1.36 aaron 449: Specifies whether Kerberos authentication is allowed.
450: This can be in the form of a Kerberos ticket, or if
1.7 markus 451: .Cm PasswordAuthentication
1.1 deraadt 452: is yes, the password provided by the user will be validated through
1.67 aaron 453: the Kerberos KDC.
454: To use this option, the server needs a
1.59 provos 455: Kerberos servtab which allows the verification of the KDC's identity.
1.36 aaron 456: Default is
1.60 provos 457: .Dq yes .
1.2 deraadt 458: .It Cm KerberosOrLocalPasswd
1.1 deraadt 459: If set then if password authentication through Kerberos fails then
460: the password will be validated via any additional local mechanism
1.2 deraadt 461: such as
1.66 markus 462: .Pa /etc/passwd .
1.36 aaron 463: Default is
1.20 dugsong 464: .Dq yes .
1.2 deraadt 465: .It Cm KerberosTgtPassing
1.1 deraadt 466: Specifies whether a Kerberos TGT may be forwarded to the server.
1.40 aaron 467: Default is
1.3 dugsong 468: .Dq no ,
469: as this only works when the Kerberos KDC is actually an AFS kaserver.
1.2 deraadt 470: .It Cm KerberosTicketCleanup
1.7 markus 471: Specifies whether to automatically destroy the user's ticket cache
1.36 aaron 472: file on logout.
473: Default is
1.3 dugsong 474: .Dq yes .
1.2 deraadt 475: .It Cm KeyRegenerationInterval
1.1 deraadt 476: The server key is automatically regenerated after this many seconds
1.36 aaron 477: (if it has been used).
478: The purpose of regeneration is to prevent
1.1 deraadt 479: decrypting captured sessions by later breaking into the machine and
1.36 aaron 480: stealing the keys.
481: The key is never stored anywhere.
482: If the value is 0, the key is never regenerated.
483: The default is 3600 (seconds).
1.7 markus 484: .It Cm ListenAddress
485: Specifies what local address
486: .Nm
487: should listen on.
488: The default is to listen to all local addresses.
1.28 markus 489: Multiple options of this type are permitted.
490: Additionally, the
491: .Cm Ports
492: options must precede this option.
1.2 deraadt 493: .It Cm LoginGraceTime
1.1 deraadt 494: The server disconnects after this time if the user has not
1.36 aaron 495: successfully logged in.
496: If the value is 0, there is no time limit.
1.1 deraadt 497: The default is 600 (seconds).
1.23 markus 498: .It Cm LogLevel
499: Gives the verbosity level that is used when logging messages from
500: .Nm sshd .
501: The possible values are:
1.79 markus 502: QUIET, FATAL, ERROR, NOTICE, VERBOSE and DEBUG.
503: The default is NOTICE.
1.23 markus 504: Logging with level DEBUG violates the privacy of users
505: and is not recommended.
1.55 markus 506: .It Cm MaxStartups
507: Specifies the maximum number of concurrent unauthenticated connections to the
508: .Nm
509: daemon.
510: Additional connections will be dropped until authentication succeeds or the
511: .Cm LoginGraceTime
512: expires for a connection.
513: The default is 10.
1.57 markus 514: .Pp
515: Alternatively, random early drop can be enabled by specifying
516: the three colon separated values
517: .Dq start:rate:full
1.67 aaron 518: (e.g., "10:30:60").
1.57 markus 519: .Nm
520: will refuse connection attempts with a probabillity of
521: .Dq rate/100
522: (30%)
523: if there are currently
524: .Dq start
525: (10)
526: unauthenticated connections.
527: The probabillity increases linearly and all connection attempts
528: are refused if the number of unauthenticated connections reaches
529: .Dq full
530: (60).
1.2 deraadt 531: .It Cm PasswordAuthentication
1.1 deraadt 532: Specifies whether password authentication is allowed.
1.2 deraadt 533: The default is
534: .Dq yes .
1.58 deraadt 535: Note that this option applies to both protocol versions 1 and 2.
1.2 deraadt 536: .It Cm PermitEmptyPasswords
1.1 deraadt 537: When password authentication is allowed, it specifies whether the
1.36 aaron 538: server allows login to accounts with empty password strings.
539: The default is
1.34 markus 540: .Dq no .
1.2 deraadt 541: .It Cm PermitRootLogin
1.1 deraadt 542: Specifies whether the root can log in using
1.2 deraadt 543: .Xr ssh 1 .
1.15 markus 544: The argument must be
545: .Dq yes ,
546: .Dq without-password
547: or
548: .Dq no .
1.2 deraadt 549: The default is
550: .Dq yes .
1.15 markus 551: If this options is set to
552: .Dq without-password
553: only password authentication is disabled for root.
1.2 deraadt 554: .Pp
555: Root login with RSA authentication when the
556: .Ar command
557: option has been
1.1 deraadt 558: specified will be allowed regardless of the value of this setting
559: (which may be useful for taking remote backups even if root login is
560: normally not allowed).
1.43 markus 561: .It Cm PidFile
562: Specifies the file that contains the process identifier of the
563: .Nm
564: daemon.
565: The default is
566: .Pa /var/run/sshd.pid .
1.2 deraadt 567: .It Cm Port
1.1 deraadt 568: Specifies the port number that
1.2 deraadt 569: .Nm
1.36 aaron 570: listens on.
571: The default is 22.
1.28 markus 572: Multiple options of this type are permitted.
1.2 deraadt 573: .It Cm PrintMotd
1.1 deraadt 574: Specifies whether
1.2 deraadt 575: .Nm
1.40 aaron 576: should print
1.2 deraadt 577: .Pa /etc/motd
1.36 aaron 578: when a user logs in interactively.
579: (On some systems it is also printed by the shell,
1.2 deraadt 580: .Pa /etc/profile ,
1.36 aaron 581: or equivalent.)
582: The default is
1.2 deraadt 583: .Dq yes .
1.41 markus 584: .It Cm Protocol
585: Specifies the protocol versions
586: .Nm
587: should support.
588: The possible values are
589: .Dq 1
590: and
591: .Dq 2 .
592: Multiple versions must be comma-separated.
593: The default is
594: .Dq 1 .
1.2 deraadt 595: .It Cm RandomSeed
1.36 aaron 596: Obsolete.
597: Random number generation uses other techniques.
1.2 deraadt 598: .It Cm RhostsAuthentication
1.1 deraadt 599: Specifies whether authentication using rhosts or /etc/hosts.equiv
1.36 aaron 600: files is sufficient.
601: Normally, this method should not be permitted because it is insecure.
1.7 markus 602: .Cm RhostsRSAAuthentication
603: should be used
1.1 deraadt 604: instead, because it performs RSA-based host authentication in addition
605: to normal rhosts or /etc/hosts.equiv authentication.
1.2 deraadt 606: The default is
607: .Dq no .
608: .It Cm RhostsRSAAuthentication
1.1 deraadt 609: Specifies whether rhosts or /etc/hosts.equiv authentication together
1.36 aaron 610: with successful RSA host authentication is allowed.
611: The default is
1.34 markus 612: .Dq no .
1.2 deraadt 613: .It Cm RSAAuthentication
1.36 aaron 614: Specifies whether pure RSA authentication is allowed.
615: The default is
1.2 deraadt 616: .Dq yes .
1.49 markus 617: Note that this option applies to protocol version 1 only.
1.2 deraadt 618: .It Cm ServerKeyBits
1.36 aaron 619: Defines the number of bits in the server key.
620: The minimum value is 512, and the default is 768.
1.7 markus 621: .It Cm SkeyAuthentication
622: Specifies whether
1.40 aaron 623: .Xr skey 1
1.36 aaron 624: authentication is allowed.
625: The default is
1.7 markus 626: .Dq yes .
627: Note that s/key authentication is enabled only if
628: .Cm PasswordAuthentication
629: is allowed, too.
1.2 deraadt 630: .It Cm StrictModes
1.12 markus 631: Specifies whether
632: .Nm
633: should check file modes and ownership of the
1.36 aaron 634: user's files and home directory before accepting login.
635: This is normally desirable because novices sometimes accidentally leave their
636: directory or files world-writable.
637: The default is
1.7 markus 638: .Dq yes .
1.54 jakob 639: .It Cm Subsystem
1.67 aaron 640: Configures an external subsystem (e.g., file transfer daemon).
641: Arguments should be a subsystem name and a command to execute upon subsystem
642: request.
1.63 markus 643: The command
644: .Xr sftp-server 8
645: implements the
646: .Dq sftp
647: file transfer subsystem.
1.54 jakob 648: By default no subsystems are defined.
649: Note that this option applies to protocol version 2 only.
1.2 deraadt 650: .It Cm SyslogFacility
1.1 deraadt 651: Gives the facility code that is used when logging messages from
1.2 deraadt 652: .Nm sshd .
1.1 deraadt 653: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1.36 aaron 654: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
655: The default is AUTH.
1.10 markus 656: .It Cm UseLogin
657: Specifies whether
658: .Xr login 1
1.53 markus 659: is used for interactive login sessions.
660: Note that
661: .Xr login 1
1.58 deraadt 662: is never used for remote command execution.
1.36 aaron 663: The default is
1.10 markus 664: .Dq no .
1.6 aaron 665: .It Cm X11DisplayOffset
666: Specifies the first display number available for
667: .Nm sshd Ns 's
1.36 aaron 668: X11 forwarding.
669: This prevents
1.6 aaron 670: .Nm
671: from interfering with real X11 servers.
1.34 markus 672: The default is 10.
1.30 markus 673: .It Cm X11Forwarding
1.36 aaron 674: Specifies whether X11 forwarding is permitted.
675: The default is
1.34 markus 676: .Dq no .
1.30 markus 677: Note that disabling X11 forwarding does not improve security in any
678: way, as users can always install their own forwarders.
1.52 markus 679: .It Cm XAuthLocation
680: Specifies the location of the
681: .Xr xauth 1
682: program.
683: The default is
684: .Pa /usr/X11R6/bin/xauth .
1.2 deraadt 685: .El
686: .Sh LOGIN PROCESS
1.1 deraadt 687: When a user successfully logs in,
1.2 deraadt 688: .Nm
1.1 deraadt 689: does the following:
1.2 deraadt 690: .Bl -enum -offset indent
691: .It
1.1 deraadt 692: If the login is on a tty, and no command has been specified,
1.40 aaron 693: prints last login time and
1.2 deraadt 694: .Pa /etc/motd
1.1 deraadt 695: (unless prevented in the configuration file or by
1.2 deraadt 696: .Pa $HOME/.hushlogin ;
697: see the
1.40 aaron 698: .Sx FILES
1.2 deraadt 699: section).
700: .It
1.1 deraadt 701: If the login is on a tty, records login time.
1.2 deraadt 702: .It
703: Checks
704: .Pa /etc/nologin ;
705: if it exists, prints contents and quits
1.1 deraadt 706: (unless root).
1.2 deraadt 707: .It
1.1 deraadt 708: Changes to run with normal user privileges.
1.2 deraadt 709: .It
1.1 deraadt 710: Sets up basic environment.
1.2 deraadt 711: .It
712: Reads
713: .Pa $HOME/.ssh/environment
714: if it exists.
715: .It
1.1 deraadt 716: Changes to user's home directory.
1.2 deraadt 717: .It
718: If
719: .Pa $HOME/.ssh/rc
720: exists, runs it; else if
721: .Pa /etc/sshrc
722: exists, runs
1.36 aaron 723: it; otherwise runs xauth.
724: The
1.2 deraadt 725: .Dq rc
726: files are given the X11
1.1 deraadt 727: authentication protocol and cookie in standard input.
1.2 deraadt 728: .It
1.1 deraadt 729: Runs user's shell or command.
1.2 deraadt 730: .El
731: .Sh AUTHORIZED_KEYS FILE FORMAT
1.40 aaron 732: The
1.2 deraadt 733: .Pa $HOME/.ssh/authorized_keys
1.1 deraadt 734: file lists the RSA keys that are
1.44 deraadt 735: permitted for RSA authentication in SSH protocols 1.3 and 1.5
1.51 hugh 736: Similarly, the
1.44 deraadt 737: .Pa $HOME/.ssh/authorized_keys2
1.75 markus 738: file lists the DSA and RSA keys that are
739: permitted for public key authentication (PubkeyAuthentication)
740: in SSH protocol 2.0.
741: .Pp
1.36 aaron 742: Each line of the file contains one
1.2 deraadt 743: key (empty lines and lines starting with a
744: .Ql #
745: are ignored as
1.36 aaron 746: comments).
1.75 markus 747: Each RSA public key consists of the following fields, separated by
1.36 aaron 748: spaces: options, bits, exponent, modulus, comment.
1.75 markus 749: Each protocol version 2 public key consists of:
750: options, keytype, base64 encoded key, comment.
751: The options fields
752: are optional; its presence is determined by whether the line starts
1.1 deraadt 753: with a number or not (the option field never starts with a number).
1.75 markus 754: The bits, exponent, modulus and comment fields give the RSA key for
755: protocol version 1; the
1.1 deraadt 756: comment field is not used for anything (but may be convenient for the
757: user to identify the key).
1.75 markus 758: For protocol version 2 the keytype is
759: .Dq ssh-dss
760: or
761: .Dq ssh-rsa .
1.2 deraadt 762: .Pp
1.1 deraadt 763: Note that lines in this file are usually several hundred bytes long
1.36 aaron 764: (because of the size of the RSA key modulus).
765: You don't want to type them in; instead, copy the
1.2 deraadt 766: .Pa identity.pub
1.75 markus 767: or the
768: .Pa id_dsa.pub
1.1 deraadt 769: file and edit it.
1.2 deraadt 770: .Pp
1.58 deraadt 771: The options (if present) consist of comma-separated option
1.36 aaron 772: specifications.
773: No spaces are permitted, except within double quotes.
1.1 deraadt 774: The following option specifications are supported:
1.2 deraadt 775: .Bl -tag -width Ds
776: .It Cm from="pattern-list"
1.1 deraadt 777: Specifies that in addition to RSA authentication, the canonical name
778: of the remote host must be present in the comma-separated list of
1.36 aaron 779: patterns
780: .Pf ( Ql *
781: and
782: .Ql ?
783: serve as wildcards).
784: The list may also contain
785: patterns negated by prefixing them with
786: .Ql ! ;
787: if the canonical host name matches a negated pattern, the key is not accepted.
788: The purpose
1.1 deraadt 789: of this option is to optionally increase security: RSA authentication
790: by itself does not trust the network or name servers or anything (but
791: the key); however, if somebody somehow steals the key, the key
1.36 aaron 792: permits an intruder to log in from anywhere in the world.
793: This additional option makes using a stolen key more difficult (name
1.1 deraadt 794: servers and/or routers would have to be compromised in addition to
795: just the key).
1.2 deraadt 796: .It Cm command="command"
1.1 deraadt 797: Specifies that the command is executed whenever this key is used for
1.36 aaron 798: authentication.
799: The command supplied by the user (if any) is ignored.
1.1 deraadt 800: The command is run on a pty if the connection requests a pty;
1.36 aaron 801: otherwise it is run without a tty.
802: A quote may be included in the command by quoting it with a backslash.
803: This option might be useful
804: to restrict certain RSA keys to perform just a specific operation.
805: An example might be a key that permits remote backups but nothing else.
1.51 hugh 806: Note that the client may specify TCP/IP and/or X11
807: forwarding unless they are explicitly prohibited.
1.2 deraadt 808: .It Cm environment="NAME=value"
1.1 deraadt 809: Specifies that the string is to be added to the environment when
1.36 aaron 810: logging in using this key.
811: Environment variables set this way
812: override other default environment values.
813: Multiple options of this type are permitted.
1.2 deraadt 814: .It Cm no-port-forwarding
1.1 deraadt 815: Forbids TCP/IP forwarding when this key is used for authentication.
1.36 aaron 816: Any port forward requests by the client will return an error.
817: This might be used, e.g., in connection with the
1.2 deraadt 818: .Cm command
1.1 deraadt 819: option.
1.2 deraadt 820: .It Cm no-X11-forwarding
1.1 deraadt 821: Forbids X11 forwarding when this key is used for authentication.
822: Any X11 forward requests by the client will return an error.
1.2 deraadt 823: .It Cm no-agent-forwarding
1.1 deraadt 824: Forbids authentication agent forwarding when this key is used for
825: authentication.
1.2 deraadt 826: .It Cm no-pty
1.1 deraadt 827: Prevents tty allocation (a request to allocate a pty will fail).
1.2 deraadt 828: .El
829: .Ss Examples
1.1 deraadt 830: 1024 33 12121.\|.\|.\|312314325 ylo@foo.bar
1.2 deraadt 831: .Pp
1.1 deraadt 832: from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula
1.2 deraadt 833: .Pp
1.1 deraadt 834: command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi
1.2 deraadt 835: .Sh SSH_KNOWN_HOSTS FILE FORMAT
1.40 aaron 836: The
1.44 deraadt 837: .Pa /etc/ssh_known_hosts ,
838: .Pa /etc/ssh_known_hosts2 ,
839: .Pa $HOME/.ssh/known_hosts ,
1.40 aaron 840: and
1.44 deraadt 841: .Pa $HOME/.ssh/known_hosts2
1.36 aaron 842: files contain host public keys for all known hosts.
843: The global file should
1.37 brad 844: be prepared by the administrator (optional), and the per-user file is
1.58 deraadt 845: maintained automatically: whenever the user connects from an unknown host
1.36 aaron 846: its key is added to the per-user file.
1.2 deraadt 847: .Pp
1.1 deraadt 848: Each line in these files contains the following fields: hostnames,
1.36 aaron 849: bits, exponent, modulus, comment.
850: The fields are separated by spaces.
1.2 deraadt 851: .Pp
1.1 deraadt 852: Hostnames is a comma-separated list of patterns ('*' and '?' act as
853: wildcards); each pattern in turn is matched against the canonical host
854: name (when authenticating a client) or against the user-supplied
1.36 aaron 855: name (when authenticating a server).
856: A pattern may also be preceded by
1.2 deraadt 857: .Ql !
858: to indicate negation: if the host name matches a negated
1.1 deraadt 859: pattern, it is not accepted (by that line) even if it matched another
860: pattern on the line.
1.2 deraadt 861: .Pp
1.49 markus 862: Bits, exponent, and modulus are taken directly from the RSA host key; they
1.2 deraadt 863: can be obtained, e.g., from
864: .Pa /etc/ssh_host_key.pub .
1.1 deraadt 865: The optional comment field continues to the end of the line, and is not used.
1.2 deraadt 866: .Pp
867: Lines starting with
868: .Ql #
869: and empty lines are ignored as comments.
870: .Pp
1.1 deraadt 871: When performing host authentication, authentication is accepted if any
1.36 aaron 872: matching line has the proper key.
873: It is thus permissible (but not
1.1 deraadt 874: recommended) to have several lines or different host keys for the same
1.36 aaron 875: names.
876: This will inevitably happen when short forms of host names
877: from different domains are put in the file.
878: It is possible
1.1 deraadt 879: that the files contain conflicting information; authentication is
880: accepted if valid information can be found from either file.
1.2 deraadt 881: .Pp
1.1 deraadt 882: Note that the lines in these files are typically hundreds of characters
883: long, and you definitely don't want to type in the host keys by hand.
1.6 aaron 884: Rather, generate them by a script
1.40 aaron 885: or by taking
1.2 deraadt 886: .Pa /etc/ssh_host_key.pub
1.1 deraadt 887: and adding the host names at the front.
1.2 deraadt 888: .Ss Examples
1.1 deraadt 889: closenet,closenet.hut.fi,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi
1.2 deraadt 890: .Sh FILES
891: .Bl -tag -width Ds
892: .It Pa /etc/sshd_config
1.1 deraadt 893: Contains configuration data for
1.2 deraadt 894: .Nm sshd .
1.1 deraadt 895: This file should be writable by root only, but it is recommended
896: (though not necessary) that it be world-readable.
1.2 deraadt 897: .It Pa /etc/ssh_host_key
1.7 markus 898: Contains the private part of the host key.
1.1 deraadt 899: This file should only be owned by root, readable only by root, and not
900: accessible to others.
1.14 markus 901: Note that
902: .Nm
903: does not start if this file is group/world-accessible.
1.2 deraadt 904: .It Pa /etc/ssh_host_key.pub
1.7 markus 905: Contains the public part of the host key.
906: This file should be world-readable but writable only by
1.36 aaron 907: root.
908: Its contents should match the private part.
909: This file is not
1.1 deraadt 910: really used for anything; it is only provided for the convenience of
911: the user so its contents can be copied to known hosts files.
1.7 markus 912: These two files are created using
913: .Xr ssh-keygen 1 .
1.73 provos 914: .It Pa /etc/primes
915: Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange".
1.2 deraadt 916: .It Pa /var/run/sshd.pid
917: Contains the process ID of the
918: .Nm
1.1 deraadt 919: listening for connections (if there are several daemons running
920: concurrently for different ports, this contains the pid of the one
1.36 aaron 921: started last).
1.58 deraadt 922: The content of this file is not sensitive; it can be world-readable.
1.2 deraadt 923: .It Pa $HOME/.ssh/authorized_keys
1.1 deraadt 924: Lists the RSA keys that can be used to log into the user's account.
925: This file must be readable by root (which may on some machines imply
926: it being world-readable if the user's home directory resides on an NFS
1.36 aaron 927: volume).
928: It is recommended that it not be accessible by others.
929: The format of this file is described above.
1.44 deraadt 930: Users will place the contents of their
931: .Pa identity.pub
932: files into this file, as described in
933: .Xr ssh-keygen 1 .
934: .It Pa $HOME/.ssh/authorized_keys2
935: Lists the DSA keys that can be used to log into the user's account.
936: This file must be readable by root (which may on some machines imply
937: it being world-readable if the user's home directory resides on an NFS
938: volume).
939: It is recommended that it not be accessible by others.
940: The format of this file is described above.
941: Users will place the contents of their
942: .Pa id_dsa.pub
943: files into this file, as described in
944: .Xr ssh-keygen 1 .
1.22 markus 945: .It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts"
946: These files are consulted when using rhosts with RSA host
1.36 aaron 947: authentication to check the public key of the host.
948: The key must be listed in one of these files to be accepted.
1.22 markus 949: The client uses the same files
1.58 deraadt 950: to verify that the remote host is the one it intended to connect.
1.36 aaron 951: These files should be writable only by root/the owner.
1.2 deraadt 952: .Pa /etc/ssh_known_hosts
953: should be world-readable, and
954: .Pa $HOME/.ssh/known_hosts
955: can but need not be world-readable.
1.6 aaron 956: .It Pa /etc/nologin
1.40 aaron 957: If this file exists,
1.2 deraadt 958: .Nm
1.36 aaron 959: refuses to let anyone except root log in.
960: The contents of the file
1.1 deraadt 961: are displayed to anyone trying to log in, and non-root connections are
1.36 aaron 962: refused.
963: The file should be world-readable.
1.19 dugsong 964: .It Pa /etc/hosts.allow, /etc/hosts.deny
965: If compiled with
966: .Sy LIBWRAP
967: support, tcp-wrappers access controls may be defined here as described in
968: .Xr hosts_access 5 .
1.6 aaron 969: .It Pa $HOME/.rhosts
1.1 deraadt 970: This file contains host-username pairs, separated by a space, one per
1.36 aaron 971: line.
972: The given user on the corresponding host is permitted to log in
973: without password.
974: The same file is used by rlogind and rshd.
1.6 aaron 975: The file must
1.1 deraadt 976: be writable only by the user; it is recommended that it not be
977: accessible by others.
1.2 deraadt 978: .Pp
1.36 aaron 979: If is also possible to use netgroups in the file.
980: Either host or user
1.1 deraadt 981: name may be of the form +@groupname to specify all hosts or all users
982: in the group.
1.2 deraadt 983: .It Pa $HOME/.shosts
984: For ssh,
985: this file is exactly the same as for
986: .Pa .rhosts .
987: However, this file is
988: not used by rlogin and rshd, so using this permits access using SSH only.
1.58 deraadt 989: .It Pa /etc/hosts.equiv
1.2 deraadt 990: This file is used during
991: .Pa .rhosts
1.36 aaron 992: authentication.
993: In the simplest form, this file contains host names, one per line.
994: Users on
1.1 deraadt 995: those hosts are permitted to log in without a password, provided they
1.36 aaron 996: have the same user name on both machines.
997: The host name may also be
1.1 deraadt 998: followed by a user name; such users are permitted to log in as
1.2 deraadt 999: .Em any
1.36 aaron 1000: user on this machine (except root).
1001: Additionally, the syntax
1.2 deraadt 1002: .Dq +@group
1.36 aaron 1003: can be used to specify netgroups.
1004: Negated entries start with
1.2 deraadt 1005: .Ql \&- .
1006: .Pp
1.1 deraadt 1007: If the client host/user is successfully matched in this file, login is
1008: automatically permitted provided the client and server user names are the
1.36 aaron 1009: same.
1010: Additionally, successful RSA host authentication is normally required.
1011: This file must be writable only by root; it is recommended
1.1 deraadt 1012: that it be world-readable.
1.2 deraadt 1013: .Pp
1.6 aaron 1014: .Sy "Warning: It is almost never a good idea to use user names in"
1.2 deraadt 1015: .Pa hosts.equiv .
1.1 deraadt 1016: Beware that it really means that the named user(s) can log in as
1.2 deraadt 1017: .Em anybody ,
1.1 deraadt 1018: which includes bin, daemon, adm, and other accounts that own critical
1.36 aaron 1019: binaries and directories.
1020: Using a user name practically grants the user root access.
1021: The only valid use for user names that I can think
1.1 deraadt 1022: of is in negative entries.
1.2 deraadt 1023: .Pp
1024: Note that this warning also applies to rsh/rlogin.
1025: .It Pa /etc/shosts.equiv
1.1 deraadt 1026: This is processed exactly as
1.2 deraadt 1027: .Pa /etc/hosts.equiv .
1.1 deraadt 1028: However, this file may be useful in environments that want to run both
1.2 deraadt 1029: rsh/rlogin and ssh.
1.6 aaron 1030: .It Pa $HOME/.ssh/environment
1.36 aaron 1031: This file is read into the environment at login (if it exists).
1032: It can only contain empty lines, comment lines (that start with
1.2 deraadt 1033: .Ql # ) ,
1.36 aaron 1034: and assignment lines of the form name=value.
1035: The file should be writable
1.6 aaron 1036: only by the user; it need not be readable by anyone else.
1.2 deraadt 1037: .It Pa $HOME/.ssh/rc
1.1 deraadt 1038: If this file exists, it is run with /bin/sh after reading the
1.36 aaron 1039: environment files but before starting the user's shell or command.
1040: If X11 spoofing is in use, this will receive the "proto cookie" pair in
1.2 deraadt 1041: standard input (and
1042: .Ev DISPLAY
1.36 aaron 1043: in environment).
1044: This must call
1.2 deraadt 1045: .Xr xauth 1
1046: in that case.
1047: .Pp
1.1 deraadt 1048: The primary purpose of this file is to run any initialization routines
1049: which may be needed before the user's home directory becomes
1050: accessible; AFS is a particular example of such an environment.
1.2 deraadt 1051: .Pp
1.1 deraadt 1052: This file will probably contain some initialization code followed by
1053: something similar to: "if read proto cookie; then echo add $DISPLAY
1054: $proto $cookie | xauth -q -; fi".
1.2 deraadt 1055: .Pp
1056: If this file does not exist,
1057: .Pa /etc/sshrc
1058: is run, and if that
1.1 deraadt 1059: does not exist either, xauth is used to store the cookie.
1.2 deraadt 1060: .Pp
1.1 deraadt 1061: This file should be writable only by the user, and need not be
1062: readable by anyone else.
1.2 deraadt 1063: .It Pa /etc/sshrc
1064: Like
1065: .Pa $HOME/.ssh/rc .
1066: This can be used to specify
1.36 aaron 1067: machine-specific login-time initializations globally.
1068: This file should be writable only by root, and should be world-readable.
1.56 aaron 1069: .El
1.71 aaron 1070: .Sh AUTHORS
1.17 deraadt 1071: OpenSSH
1.33 deraadt 1072: is a derivative of the original (free) ssh 1.2.12 release by Tatu Ylonen,
1.36 aaron 1073: but with bugs removed and newer features re-added.
1074: Rapidly after the
1.33 deraadt 1075: 1.2.12 release, newer versions of the original ssh bore successively
1076: more restrictive licenses, and thus demand for a free version was born.
1.48 markus 1077: .Pp
1.33 deraadt 1078: This version of OpenSSH
1.17 deraadt 1079: .Bl -bullet
1080: .It
1.32 aaron 1081: has all components of a restrictive nature (i.e., patents, see
1.17 deraadt 1082: .Xr ssl 8 )
1083: directly removed from the source code; any licensed or patented components
1084: are chosen from
1085: external libraries.
1086: .It
1.48 markus 1087: has been updated to support SSH protocol 1.5 and 2, making it compatible with
1088: all other SSH clients and servers.
1.17 deraadt 1089: .It
1.40 aaron 1090: contains added support for
1.17 deraadt 1091: .Xr kerberos 8
1092: authentication and ticket passing.
1093: .It
1094: supports one-time password authentication with
1095: .Xr skey 1 .
1096: .El
1.48 markus 1097: .Pp
1098: OpenSSH has been created by Aaron Campbell, Bob Beck, Markus Friedl,
1099: Niels Provos, Theo de Raadt, and Dug Song.
1100: .Pp
1101: The support for SSH protocol 2 was written by Markus Friedl.
1.2 deraadt 1102: .Sh SEE ALSO
1103: .Xr scp 1 ,
1.63 markus 1104: .Xr sftp-server 8 ,
1.2 deraadt 1105: .Xr ssh 1 ,
1.5 deraadt 1106: .Xr ssh-add 1 ,
1.2 deraadt 1107: .Xr ssh-agent 1 ,
1.5 deraadt 1108: .Xr ssh-keygen 1 ,
1.38 deraadt 1109: .Xr ssl 8 ,
1110: .Xr rlogin 1 ,
1111: .Xr rsh 1
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