Annotation of src/usr.bin/ssh/ssh.1, Revision 1.229
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: .\"
1.59 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: .\"
1.93 deraadt 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.
1.59 deraadt 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: .\"
1.59 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
33: .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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: .\"
1.229 ! jmc 37: .\" $OpenBSD: ssh.1,v 1.228 2005/12/22 11:23:42 jmc Exp $
1.2 deraadt 38: .Dd September 25, 1999
39: .Dt SSH 1
40: .Os
41: .Sh NAME
42: .Nm ssh
1.96 deraadt 43: .Nd OpenSSH SSH client (remote login program)
1.2 deraadt 44: .Sh SYNOPSIS
45: .Nm ssh
1.191 djm 46: .Op Fl 1246AaCfgkMNnqsTtVvXxY
1.108 markus 47: .Op Fl b Ar bind_address
1.51 markus 48: .Op Fl c Ar cipher_spec
1.210 djm 49: .Oo Fl D\ \&
50: .Sm off
51: .Oo Ar bind_address : Oc
52: .Ar port
53: .Sm on
54: .Oc
1.2 deraadt 55: .Op Fl e Ar escape_char
1.176 jmc 56: .Op Fl F Ar configfile
1.211 jmc 57: .Bk -words
1.2 deraadt 58: .Op Fl i Ar identity_file
1.211 jmc 59: .Ek
1.202 jmc 60: .Oo Fl L\ \&
1.12 aaron 61: .Sm off
1.200 djm 62: .Oo Ar bind_address : Oc
1.202 jmc 63: .Ar port : host : hostport
1.12 aaron 64: .Sm on
65: .Oc
1.211 jmc 66: .Bk -words
1.176 jmc 67: .Op Fl l Ar login_name
1.211 jmc 68: .Ek
1.176 jmc 69: .Op Fl m Ar mac_spec
1.198 djm 70: .Op Fl O Ar ctl_cmd
1.176 jmc 71: .Op Fl o Ar option
72: .Op Fl p Ar port
1.202 jmc 73: .Oo Fl R\ \&
1.12 aaron 74: .Sm off
1.200 djm 75: .Oo Ar bind_address : Oc
1.202 jmc 76: .Ar port : host : hostport
1.12 aaron 77: .Sm on
78: .Oc
1.198 djm 79: .Op Fl S Ar ctl_path
1.216 jmc 80: .Bk -words
81: .Op Fl w Ar tunnel : Ns Ar tunnel
1.176 jmc 82: .Oo Ar user Ns @ Oc Ns Ar hostname
1.2 deraadt 83: .Op Ar command
1.216 jmc 84: .Ek
1.44 aaron 85: .Sh DESCRIPTION
1.2 deraadt 86: .Nm
1.96 deraadt 87: (SSH client) is a program for logging into a remote machine and for
1.40 aaron 88: executing commands on a remote machine.
1.176 jmc 89: It is intended to replace rlogin and rsh,
90: and provide secure encrypted communications between
1.40 aaron 91: two untrusted hosts over an insecure network.
1.176 jmc 92: X11 connections and arbitrary TCP/IP ports
93: can also be forwarded over the secure channel.
1.2 deraadt 94: .Pp
95: .Nm
1.44 aaron 96: connects and logs into the specified
1.176 jmc 97: .Ar hostname
98: (with optional
99: .Ar user
100: name).
1.1 deraadt 101: The user must prove
1.49 markus 102: his/her identity to the remote machine using one of several methods
1.221 jmc 103: depending on the protocol version used (see below).
1.49 markus 104: .Pp
1.176 jmc 105: If
106: .Ar command
107: is specified,
1.219 jmc 108: it is executed on the remote host instead of a login shell.
1.2 deraadt 109: .Pp
1.218 jmc 110: The options are as follows:
111: .Bl -tag -width Ds
112: .It Fl 1
113: Forces
1.2 deraadt 114: .Nm
1.218 jmc 115: to try protocol version 1 only.
116: .It Fl 2
117: Forces
1.2 deraadt 118: .Nm
1.218 jmc 119: to try protocol version 2 only.
120: .It Fl 4
121: Forces
1.2 deraadt 122: .Nm
1.218 jmc 123: to use IPv4 addresses only.
124: .It Fl 6
125: Forces
1.2 deraadt 126: .Nm
1.218 jmc 127: to use IPv6 addresses only.
128: .It Fl A
129: Enables forwarding of the authentication agent connection.
130: This can also be specified on a per-host basis in a configuration file.
1.2 deraadt 131: .Pp
1.218 jmc 132: Agent forwarding should be enabled with caution.
133: Users with the ability to bypass file permissions on the remote host
134: (for the agent's Unix-domain socket)
135: can access the local agent through the forwarded connection.
136: An attacker cannot obtain key material from the agent,
137: however they can perform operations on the keys that enable them to
138: authenticate using the identities loaded into the agent.
139: .It Fl a
140: Disables forwarding of the authentication agent connection.
141: .It Fl b Ar bind_address
142: Use
143: .Ar bind_address
144: on the local machine as the source address
145: of the connection.
146: Only useful on systems with more than one address.
147: .It Fl C
148: Requests compression of all data (including stdin, stdout, stderr, and
149: data for forwarded X11 and TCP/IP connections).
150: The compression algorithm is the same used by
151: .Xr gzip 1 ,
152: and the
153: .Dq level
154: can be controlled by the
155: .Cm CompressionLevel
156: option for protocol version 1.
157: Compression is desirable on modem lines and other
158: slow connections, but will only slow down things on fast networks.
159: The default value can be set on a host-by-host basis in the
160: configuration files; see the
161: .Cm Compression
162: option.
163: .It Fl c Ar cipher_spec
164: Selects the cipher specification for encrypting the session.
1.2 deraadt 165: .Pp
1.218 jmc 166: Protocol version 1 allows specification of a single cipher.
167: The supported values are
168: .Dq 3des ,
1.220 jmc 169: .Dq blowfish ,
1.218 jmc 170: and
171: .Dq des .
172: .Ar 3des
173: (triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
174: It is believed to be secure.
175: .Ar blowfish
176: is a fast block cipher; it appears very secure and is much faster than
177: .Ar 3des .
178: .Ar des
179: is only supported in the
1.2 deraadt 180: .Nm
1.218 jmc 181: client for interoperability with legacy protocol 1 implementations
182: that do not support the
183: .Ar 3des
184: cipher.
185: Its use is strongly discouraged due to cryptographic weaknesses.
186: The default is
187: .Dq 3des .
1.49 markus 188: .Pp
1.218 jmc 189: For protocol version 2
190: .Ar cipher_spec
191: is a comma-separated list of ciphers
192: listed in order of preference.
193: The supported ciphers are
194: .Dq 3des-cbc ,
195: .Dq aes128-cbc ,
196: .Dq aes192-cbc ,
197: .Dq aes256-cbc ,
198: .Dq aes128-ctr ,
199: .Dq aes192-ctr ,
200: .Dq aes256-ctr ,
201: .Dq arcfour128 ,
202: .Dq arcfour256 ,
203: .Dq arcfour ,
204: .Dq blowfish-cbc ,
205: and
206: .Dq cast128-cbc .
1.220 jmc 207: The default is:
208: .Bd -literal -offset indent
209: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
210: arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
211: aes192-ctr,aes256-ctr
1.218 jmc 212: .Ed
213: .It Fl D Xo
214: .Sm off
215: .Oo Ar bind_address : Oc
216: .Ar port
217: .Sm on
218: .Xc
219: Specifies a local
220: .Dq dynamic
221: application-level port forwarding.
222: This works by allocating a socket to listen to
223: .Ar port
224: on the local side, optionally bound to the specified
225: .Ar bind_address .
226: Whenever a connection is made to this port, the
227: connection is forwarded over the secure channel, and the application
228: protocol is then used to determine where to connect to from the
229: remote machine.
230: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.107 markus 231: .Nm
1.218 jmc 232: will act as a SOCKS server.
233: Only root can forward privileged ports.
234: Dynamic port forwardings can also be specified in the configuration file.
1.49 markus 235: .Pp
1.218 jmc 236: IPv6 addresses can be specified with an alternative syntax:
237: .Sm off
238: .Xo
239: .Op Ar bind_address No /
240: .Ar port
241: .Xc
242: .Sm on
243: or by enclosing the address in square brackets.
244: Only the superuser can forward privileged ports.
245: By default, the local port is bound in accordance with the
246: .Cm GatewayPorts
247: setting.
248: However, an explicit
249: .Ar bind_address
250: may be used to bind the connection to a specific address.
251: The
252: .Ar bind_address
253: of
254: .Dq localhost
255: indicates that the listening port be bound for local use only, while an
256: empty address or
257: .Sq *
258: indicates that the port should be available from all interfaces.
1.229 ! jmc 259: .It Fl e Ar escape_char
1.218 jmc 260: Sets the escape character for sessions with a pty (default:
261: .Ql ~ ) .
262: The escape character is only recognized at the beginning of a line.
263: The escape character followed by a dot
264: .Pq Ql \&.
265: closes the connection;
266: followed by control-Z suspends the connection;
267: and followed by itself sends the escape character once.
268: Setting the character to
1.2 deraadt 269: .Dq none
1.218 jmc 270: disables any escapes and makes the session fully transparent.
271: .It Fl F Ar configfile
272: Specifies an alternative per-user configuration file.
273: If a configuration file is given on the command line,
274: the system-wide configuration file
275: .Pq Pa /etc/ssh/ssh_config
276: will be ignored.
277: The default for the per-user configuration file is
278: .Pa ~/.ssh/config .
279: .It Fl f
280: Requests
281: .Nm
282: to go to background just before command execution.
283: This is useful if
1.176 jmc 284: .Nm
1.218 jmc 285: is going to ask for passwords or passphrases, but the user
286: wants it in the background.
287: This implies
288: .Fl n .
289: The recommended way to start X11 programs at a remote site is with
290: something like
291: .Ic ssh -f host xterm .
292: .It Fl g
293: Allows remote hosts to connect to local forwarded ports.
294: .It Fl I Ar smartcard_device
1.229 ! jmc 295: Specify the device
1.176 jmc 296: .Nm
1.218 jmc 297: should use to communicate with a smartcard used for storing the user's
298: private RSA key.
1.229 ! jmc 299: This option is only available if support for smartcard devices
! 300: is compiled in (default is no support).
1.218 jmc 301: .It Fl i Ar identity_file
302: Selects a file from which the identity (private key) for
303: RSA or DSA authentication is read.
304: The default is
305: .Pa ~/.ssh/identity
306: for protocol version 1, and
307: .Pa ~/.ssh/id_rsa
1.149 jakob 308: and
1.218 jmc 309: .Pa ~/.ssh/id_dsa
310: for protocol version 2.
311: Identity files may also be specified on
312: a per-host basis in the configuration file.
313: It is possible to have multiple
314: .Fl i
315: options (and multiple identities specified in
316: configuration files).
317: .It Fl k
318: Disables forwarding (delegation) of GSSAPI credentials to the server.
319: .It Fl L Xo
320: .Sm off
321: .Oo Ar bind_address : Oc
322: .Ar port : host : hostport
323: .Sm on
324: .Xc
325: Specifies that the given port on the local (client) host is to be
326: forwarded to the given host and port on the remote side.
327: This works by allocating a socket to listen to
328: .Ar port
329: on the local side, optionally bound to the specified
330: .Ar bind_address .
331: Whenever a connection is made to this port, the
332: connection is forwarded over the secure channel, and a connection is
333: made to
334: .Ar host
335: port
336: .Ar hostport
337: from the remote machine.
338: Port forwardings can also be specified in the configuration file.
339: IPv6 addresses can be specified with an alternative syntax:
340: .Sm off
341: .Xo
342: .Op Ar bind_address No /
343: .Ar port No / Ar host No /
344: .Ar hostport
345: .Xc
346: .Sm on
347: or by enclosing the address in square brackets.
348: Only the superuser can forward privileged ports.
349: By default, the local port is bound in accordance with the
350: .Cm GatewayPorts
351: setting.
352: However, an explicit
353: .Ar bind_address
354: may be used to bind the connection to a specific address.
1.2 deraadt 355: The
1.218 jmc 356: .Ar bind_address
357: of
358: .Dq localhost
359: indicates that the listening port be bound for local use only, while an
360: empty address or
361: .Sq *
362: indicates that the port should be available from all interfaces.
363: .It Fl l Ar login_name
364: Specifies the user to log in as on the remote machine.
365: This also may be specified on a per-host basis in the configuration file.
366: .It Fl M
367: Places the
368: .Nm
369: client into
370: .Dq master
371: mode for connection sharing.
372: Refer to the description of
373: .Cm ControlMaster
374: in
375: .Xr ssh_config 5
376: for details.
377: .It Fl m Ar mac_spec
378: Additionally, for protocol version 2 a comma-separated list of MAC
379: (message authentication code) algorithms can
380: be specified in order of preference.
381: See the
382: .Cm MACs
383: keyword for more information.
384: .It Fl N
385: Do not execute a remote command.
386: This is useful for just forwarding ports
387: (protocol version 2 only).
388: .It Fl n
389: Redirects stdin from
390: .Pa /dev/null
391: (actually, prevents reading from stdin).
392: This must be used when
1.2 deraadt 393: .Nm
1.218 jmc 394: is run in the background.
395: A common trick is to use this to run X11 programs on a remote machine.
396: For example,
397: .Ic ssh -n shadows.cs.hut.fi emacs &
398: will start an emacs on shadows.cs.hut.fi, and the X11
399: connection will be automatically forwarded over an encrypted channel.
400: The
1.2 deraadt 401: .Nm
1.218 jmc 402: program will be put in the background.
403: (This does not work if
1.2 deraadt 404: .Nm
1.218 jmc 405: needs to ask for a password or passphrase; see also the
406: .Fl f
407: option.)
408: .It Fl O Ar ctl_cmd
409: Control an active connection multiplexing master process.
410: When the
411: .Fl O
412: option is specified, the
413: .Ar ctl_cmd
414: argument is interpreted and passed to the master process.
415: Valid commands are:
416: .Dq check
417: (check that the master process is running) and
418: .Dq exit
419: (request the master to exit).
420: .It Fl o Ar option
421: Can be used to give options in the format used in the configuration file.
422: This is useful for specifying options for which there is no separate
423: command-line flag.
424: For full details of the options listed below, and their possible values, see
425: .Xr ssh_config 5 .
1.2 deraadt 426: .Pp
1.218 jmc 427: .Bl -tag -width Ds -offset indent -compact
428: .It AddressFamily
429: .It BatchMode
430: .It BindAddress
431: .It ChallengeResponseAuthentication
432: .It CheckHostIP
433: .It Cipher
434: .It Ciphers
435: .It ClearAllForwardings
436: .It Compression
437: .It CompressionLevel
438: .It ConnectionAttempts
439: .It ConnectTimeout
440: .It ControlMaster
441: .It ControlPath
442: .It DynamicForward
443: .It EscapeChar
444: .It ForwardAgent
445: .It ForwardX11
446: .It ForwardX11Trusted
447: .It GatewayPorts
448: .It GlobalKnownHostsFile
449: .It GSSAPIAuthentication
450: .It GSSAPIDelegateCredentials
451: .It HashKnownHosts
452: .It Host
453: .It HostbasedAuthentication
454: .It HostKeyAlgorithms
455: .It HostKeyAlias
456: .It HostName
457: .It IdentityFile
458: .It IdentitiesOnly
459: .It KbdInteractiveDevices
460: .It LocalCommand
461: .It LocalForward
462: .It LogLevel
463: .It MACs
464: .It NoHostAuthenticationForLocalhost
465: .It NumberOfPasswordPrompts
466: .It PasswordAuthentication
467: .It PermitLocalCommand
468: .It Port
469: .It PreferredAuthentications
470: .It Protocol
471: .It ProxyCommand
472: .It PubkeyAuthentication
473: .It RemoteForward
474: .It RhostsRSAAuthentication
475: .It RSAAuthentication
476: .It SendEnv
477: .It ServerAliveInterval
478: .It ServerAliveCountMax
479: .It SmartcardDevice
480: .It StrictHostKeyChecking
481: .It TCPKeepAlive
482: .It Tunnel
483: .It TunnelDevice
484: .It UsePrivilegedPort
485: .It User
486: .It UserKnownHostsFile
487: .It VerifyHostKeyDNS
488: .It XAuthLocation
489: .El
490: .It Fl p Ar port
491: Port to connect to on the remote host.
492: This can be specified on a
493: per-host basis in the configuration file.
494: .It Fl q
495: Quiet mode.
496: Causes all warning and diagnostic messages to be suppressed.
497: .It Fl R Xo
498: .Sm off
499: .Oo Ar bind_address : Oc
500: .Ar port : host : hostport
501: .Sm on
502: .Xc
503: Specifies that the given port on the remote (server) host is to be
504: forwarded to the given host and port on the local side.
505: This works by allocating a socket to listen to
506: .Ar port
507: on the remote side, and whenever a connection is made to this port, the
508: connection is forwarded over the secure channel, and a connection is
509: made to
510: .Ar host
511: port
512: .Ar hostport
513: from the local machine.
1.2 deraadt 514: .Pp
1.218 jmc 515: Port forwardings can also be specified in the configuration file.
516: Privileged ports can be forwarded only when
517: logging in as root on the remote machine.
518: IPv6 addresses can be specified by enclosing the address in square braces or
519: using an alternative syntax:
520: .Sm off
521: .Xo
522: .Op Ar bind_address No /
523: .Ar host No / Ar port No /
524: .Ar hostport
525: .Xc .
526: .Sm on
1.194 jakob 527: .Pp
1.218 jmc 528: By default, the listening socket on the server will be bound to the loopback
529: interface only.
530: This may be overriden by specifying a
531: .Ar bind_address .
532: An empty
533: .Ar bind_address ,
534: or the address
535: .Ql * ,
536: indicates that the remote socket should listen on all interfaces.
537: Specifying a remote
538: .Ar bind_address
539: will only succeed if the server's
540: .Cm GatewayPorts
541: option is enabled (see
542: .Xr sshd_config 5 ) .
543: .It Fl S Ar ctl_path
544: Specifies the location of a control socket for connection sharing.
545: Refer to the description of
546: .Cm ControlPath
547: and
548: .Cm ControlMaster
549: in
550: .Xr ssh_config 5
551: for details.
552: .It Fl s
553: May be used to request invocation of a subsystem on the remote system.
554: Subsystems are a feature of the SSH2 protocol which facilitate the use
555: of SSH as a secure transport for other applications (eg.\&
556: .Xr sftp 1 ) .
557: The subsystem is specified as the remote command.
558: .It Fl T
559: Disable pseudo-tty allocation.
560: .It Fl t
561: Force pseudo-tty allocation.
562: This can be used to execute arbitrary
563: screen-based programs on a remote machine, which can be very useful,
564: e.g., when implementing menu services.
565: Multiple
566: .Fl t
567: options force tty allocation, even if
1.194 jakob 568: .Nm
1.218 jmc 569: has no local tty.
570: .It Fl V
571: Display the version number and exit.
572: .It Fl v
573: Verbose mode.
574: Causes
1.176 jmc 575: .Nm
1.218 jmc 576: to print debugging messages about its progress.
577: This is helpful in
578: debugging connection, authentication, and configuration problems.
579: Multiple
580: .Fl v
581: options increase the verbosity.
582: The maximum is 3.
583: .It Fl w Ar tunnel : Ns Ar tunnel
584: Requests a
585: .Xr tun 4
1.228 jmc 586: device on the client
587: (first
588: .Ar tunnel
589: arg)
590: and server
591: (second
592: .Ar tunnel
593: arg).
594: The devices may be specified by numerical ID or the keyword
595: .Dq any ,
596: which uses the next available tunnel device.
597: See also the
1.218 jmc 598: .Cm Tunnel
599: directive in
600: .Xr ssh_config 5 .
601: .It Fl X
602: Enables X11 forwarding.
1.54 markus 603: This can also be specified on a per-host basis in a configuration file.
1.165 stevesk 604: .Pp
1.218 jmc 605: X11 forwarding should be enabled with caution.
1.168 jmc 606: Users with the ability to bypass file permissions on the remote host
1.218 jmc 607: (for the user's X authorization database)
608: can access the local X11 display through the forwarded connection.
609: An attacker may then be able to perform activities such as keystroke monitoring.
610: .Pp
611: For this reason, X11 forwarding is subjected to X11 SECURITY extension
612: restrictions by default.
613: Please refer to the
614: .Nm
615: .Fl Y
616: option and the
617: .Cm ForwardX11Trusted
618: directive in
619: .Xr ssh_config 5
620: for more information.
621: .It Fl x
622: Disables X11 forwarding.
623: .It Fl Y
624: Enables trusted X11 forwarding.
625: Trusted X11 forwardings are not subjected to the X11 SECURITY extension
626: controls.
627: .El
1.224 jmc 628: .Pp
629: .Nm
630: may additionally obtain configuration data from
631: a per-user configuration file and a system-wide configuration file.
632: The file format and configuration options are described in
633: .Xr ssh_config 5 .
634: .Pp
635: .Nm
636: exits with the exit status of the remote command or with 255
637: if an error occurred.
1.222 jmc 638: .Sh AUTHENTICATION
639: The OpenSSH SSH client supports OpenSSH protocols 1 and 2.
640: Protocol 2 is the default, with
641: .Nm
642: falling back to protocol 1 if it detects protocol 2 is unsupported.
643: These settings may be altered using the
644: .Cm Protocol
645: option in
646: .Xr ssh_config 5 ,
647: or enforced using the
648: .Fl 1
649: and
650: .Fl 2
651: options (see above).
652: Both protocols support similar authentication methods,
653: but protocol 2 is preferred since
654: it provides additional mechanisms for confidentiality
655: (the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour)
656: and integrity (hmac-md5, hmac-sha1, hmac-ripemd160).
657: Protocol 1 lacks a strong mechanism for ensuring the
658: integrity of the connection.
659: .Pp
660: The methods available for authentication are:
661: host-based authentication,
662: public key authentication,
663: challenge-response authentication,
664: and password authentication.
665: Authentication methods are tried in the order specified above,
666: though protocol 2 has a configuration option to change the default order:
667: .Cm PreferredAuthentications .
668: .Pp
669: Host-based authentication works as follows:
1.218 jmc 670: If the machine the user logs in from is listed in
671: .Pa /etc/hosts.equiv
672: or
673: .Pa /etc/shosts.equiv
674: on the remote machine, and the user names are
675: the same on both sides, or if the files
676: .Pa ~/.rhosts
677: or
678: .Pa ~/.shosts
679: exist in the user's home directory on the
680: remote machine and contain a line containing the name of the client
681: machine and the name of the user on that machine, the user is
1.222 jmc 682: considered for login.
683: Additionally, the server
684: .Em must
685: be able to verify the client's
686: host key (see the description of
1.218 jmc 687: .Pa /etc/ssh/ssh_known_hosts
1.189 dtucker 688: and
1.222 jmc 689: .Pa ~/.ssh/known_hosts ,
690: below)
691: for login to be permitted.
1.218 jmc 692: This authentication method closes security holes due to IP
1.222 jmc 693: spoofing, DNS spoofing, and routing spoofing.
1.218 jmc 694: [Note to the administrator:
695: .Pa /etc/hosts.equiv ,
696: .Pa ~/.rhosts ,
697: and the rlogin/rsh protocol in general, are inherently insecure and should be
698: disabled if security is desired.]
1.189 dtucker 699: .Pp
1.222 jmc 700: Public key authentication works as follows:
701: The scheme is based on public-key cryptography,
702: using cryptosystems
703: where encryption and decryption are done using separate keys,
704: and it is unfeasible to derive the decryption key from the encryption key.
1.218 jmc 705: The idea is that each user creates a public/private
706: key pair for authentication purposes.
707: The server knows the public key, and only the user knows the private key.
1.222 jmc 708: .Nm
709: implements public key authentication protocol automatically,
710: using either the RSA or DSA algorithms.
711: Protocol 1 is restricted to using only RSA keys,
712: but protocol 2 may use either.
713: The
714: .Sx HISTORY
715: section of
716: .Xr ssl 8
717: contains a brief discussion of the two algorithms.
1.210 djm 718: .Pp
1.218 jmc 719: The file
720: .Pa ~/.ssh/authorized_keys
721: lists the public keys that are permitted for logging in.
722: When the user logs in, the
1.2 deraadt 723: .Nm
1.218 jmc 724: program tells the server which key pair it would like to use for
725: authentication.
1.222 jmc 726: The client proves that it has access to the private key
727: and the server checks that the corresponding public key
728: is authorized to accept the account.
1.218 jmc 729: .Pp
1.222 jmc 730: The user creates his/her key pair by running
1.218 jmc 731: .Xr ssh-keygen 1 .
732: This stores the private key in
1.207 djm 733: .Pa ~/.ssh/identity
1.222 jmc 734: (protocol 1),
735: .Pa ~/.ssh/id_dsa
736: (protocol 2 DSA),
737: or
738: .Pa ~/.ssh/id_rsa
739: (protocol 2 RSA)
1.218 jmc 740: and stores the public key in
741: .Pa ~/.ssh/identity.pub
1.222 jmc 742: (protocol 1),
743: .Pa ~/.ssh/id_dsa.pub
744: (protocol 2 DSA),
745: or
746: .Pa ~/.ssh/id_rsa.pub
747: (protocol 2 RSA)
1.218 jmc 748: in the user's home directory.
1.222 jmc 749: The user should then copy the public key
1.218 jmc 750: to
751: .Pa ~/.ssh/authorized_keys
1.222 jmc 752: in his/her home directory on the remote machine.
753: The
1.218 jmc 754: .Pa authorized_keys
755: file corresponds to the conventional
756: .Pa ~/.rhosts
757: file, and has one key
1.222 jmc 758: per line, though the lines can be very long.
1.218 jmc 759: After this, the user can log in without giving the password.
760: .Pp
1.222 jmc 761: The most convenient way to use public key authentication may be with an
1.218 jmc 762: authentication agent.
763: See
764: .Xr ssh-agent 1
765: for more information.
766: .Pp
1.222 jmc 767: Challenge-response authentication works as follows:
768: The server sends an arbitrary
769: .Qq challenge
770: text, and prompts for a response.
771: Protocol 2 allows multiple challenges and responses;
772: protocol 1 is restricted to just one challenge/response.
773: Examples of challenge-response authentication include
774: BSD Authentication (see
775: .Xr login.conf 5 )
776: and PAM (some non-OpenBSD systems).
777: .Pp
778: Finally, if other authentication methods fail,
1.218 jmc 779: .Nm
780: prompts the user for a password.
781: The password is sent to the remote
782: host for checking; however, since all communications are encrypted,
783: the password cannot be seen by someone listening on the network.
1.223 jmc 784: .Sh LOGIN SESSION AND REMOTE EXECUTION
1.218 jmc 785: When the user's identity has been accepted by the server, the server
786: either executes the given command, or logs into the machine and gives
787: the user a normal shell on the remote machine.
788: All communication with
789: the remote command or shell will be automatically encrypted.
790: .Pp
791: If a pseudo-terminal has been allocated (normal login session), the
792: user may use the escape characters noted below.
793: .Pp
794: If no pseudo-tty has been allocated,
795: the session is transparent and can be used to reliably transfer binary data.
796: On most systems, setting the escape character to
797: .Dq none
798: will also make the session transparent even if a tty is used.
799: .Pp
800: The session terminates when the command or shell on the remote
801: machine exits and all X11 and TCP/IP connections have been closed.
1.223 jmc 802: .Sh ESCAPE CHARACTERS
1.218 jmc 803: When a pseudo-terminal has been requested,
1.2 deraadt 804: .Nm
1.218 jmc 805: supports a number of functions through the use of an escape character.
806: .Pp
807: A single tilde character can be sent as
808: .Ic ~~
809: or by following the tilde by a character other than those described below.
810: The escape character must always follow a newline to be interpreted as
811: special.
812: The escape character can be changed in configuration files using the
813: .Cm EscapeChar
814: configuration directive or on the command line by the
815: .Fl e
816: option.
817: .Pp
818: The supported escapes (assuming the default
819: .Ql ~ )
820: are:
821: .Bl -tag -width Ds
822: .It Cm ~.
823: Disconnect.
824: .It Cm ~^Z
825: Background
826: .Nm ssh .
827: .It Cm ~#
828: List forwarded connections.
829: .It Cm ~&
830: Background
1.2 deraadt 831: .Nm
1.218 jmc 832: at logout when waiting for forwarded connection / X11 sessions to terminate.
833: .It Cm ~?
834: Display a list of escape characters.
835: .It Cm ~B
836: Send a BREAK to the remote system
837: (only useful for SSH protocol version 2 and if the peer supports it).
838: .It Cm ~C
839: Open command line.
840: Currently this allows the addition of port forwardings using the
841: .Fl L
842: and
843: .Fl R
1.225 jmc 844: options (see above).
1.218 jmc 845: It also allows the cancellation of existing remote port-forwardings
846: using
847: .Fl KR Ar hostport .
848: .Ic !\& Ns Ar command
849: allows the user to execute a local command if the
850: .Ic PermitLocalCommand
851: option is enabled in
1.176 jmc 852: .Xr ssh_config 5 .
1.218 jmc 853: Basic help is available, using the
854: .Fl h
855: option.
856: .It Cm ~R
857: Request rekeying of the connection
858: (only useful for SSH protocol version 2 and if the peer supports it).
1.176 jmc 859: .El
1.223 jmc 860: .Sh X11 AND TCP FORWARDING
1.218 jmc 861: If the
862: .Cm ForwardX11
863: variable is set to
864: .Dq yes
865: (or see the description of the
1.227 jmc 866: .Fl X ,
867: .Fl x ,
1.218 jmc 868: and
1.227 jmc 869: .Fl Y
1.226 jmc 870: options above)
1.218 jmc 871: and the user is using X11 (the
872: .Ev DISPLAY
873: environment variable is set), the connection to the X11 display is
874: automatically forwarded to the remote side in such a way that any X11
875: programs started from the shell (or command) will go through the
876: encrypted channel, and the connection to the real X server will be made
1.176 jmc 877: from the local machine.
1.218 jmc 878: The user should not manually set
879: .Ev DISPLAY .
880: Forwarding of X11 connections can be
881: configured on the command line or in configuration files.
882: .Pp
883: The
884: .Ev DISPLAY
885: value set by
886: .Nm
887: will point to the server machine, but with a display number greater than zero.
888: This is normal, and happens because
889: .Nm
890: creates a
891: .Dq proxy
892: X server on the server machine for forwarding the
893: connections over the encrypted channel.
1.200 djm 894: .Pp
1.218 jmc 895: .Nm
896: will also automatically set up Xauthority data on the server machine.
897: For this purpose, it will generate a random authorization cookie,
898: store it in Xauthority on the server, and verify that any forwarded
899: connections carry this cookie and replace it by the real cookie when
900: the connection is opened.
901: The real authentication cookie is never
902: sent to the server machine (and no cookies are sent in the plain).
1.200 djm 903: .Pp
1.218 jmc 904: If the
905: .Cm ForwardAgent
906: variable is set to
907: .Dq yes
908: (or see the description of the
909: .Fl A
1.191 djm 910: and
1.218 jmc 911: .Fl a
1.226 jmc 912: options above) and
1.218 jmc 913: the user is using an authentication agent, the connection to the agent
914: is automatically forwarded to the remote side.
915: .Pp
916: Forwarding of arbitrary TCP/IP connections over the secure channel can
917: be specified either on the command line or in a configuration file.
918: One possible application of TCP/IP forwarding is a secure connection to an
919: electronic purse; another is going through firewalls.
1.223 jmc 920: .Sh SERVER AUTHENTICATION
1.73 markus 921: .Nm
1.218 jmc 922: automatically maintains and checks a database containing
923: identifications for all hosts it has ever been used with.
924: Host keys are stored in
925: .Pa ~/.ssh/known_hosts
926: in the user's home directory.
927: Additionally, the file
928: .Pa /etc/ssh/ssh_known_hosts
929: is automatically checked for known hosts.
930: Any new hosts are automatically added to the user's file.
931: If a host's identification ever changes,
1.2 deraadt 932: .Nm
1.218 jmc 933: warns about this and disables password authentication to prevent a
934: trojan horse from getting the user's password.
935: Another purpose of this mechanism is to prevent man-in-the-middle attacks
936: which could otherwise be used to circumvent the encryption.
937: The
938: .Cm StrictHostKeyChecking
939: option can be used to prevent logins to machines whose
940: host key is not known or has changed.
1.203 djm 941: .Pp
942: .Nm
1.218 jmc 943: can be configured to verify host identification using fingerprint resource
944: records (SSHFP) published in DNS.
945: The
946: .Cm VerifyHostKeyDNS
947: option can be used to control how DNS lookups are performed.
948: SSHFP resource records can be generated using
949: .Xr ssh-keygen 1 .
1.2 deraadt 950: .Sh ENVIRONMENT
951: .Nm
1.1 deraadt 952: will normally set the following environment variables:
1.176 jmc 953: .Bl -tag -width LOGNAME
1.2 deraadt 954: .It Ev DISPLAY
955: The
956: .Ev DISPLAY
1.40 aaron 957: variable indicates the location of the X11 server.
1.44 aaron 958: It is automatically set by
1.2 deraadt 959: .Nm
960: to point to a value of the form
961: .Dq hostname:n
962: where hostname indicates
1.176 jmc 963: the host where the shell runs, and n is an integer \*(Ge 1.
1.40 aaron 964: .Nm
965: uses this special value to forward X11 connections over the secure
966: channel.
1.107 markus 967: The user should normally not set
968: .Ev DISPLAY
969: explicitly, as that
1.1 deraadt 970: will render the X11 connection insecure (and will require the user to
971: manually copy any required authorization cookies).
1.2 deraadt 972: .It Ev HOME
1.1 deraadt 973: Set to the path of the user's home directory.
1.2 deraadt 974: .It Ev LOGNAME
975: Synonym for
1.12 aaron 976: .Ev USER ;
977: set for compatibility with systems that use this variable.
1.2 deraadt 978: .It Ev MAIL
1.129 stevesk 979: Set to the path of the user's mailbox.
1.40 aaron 980: .It Ev PATH
1.2 deraadt 981: Set to the default
982: .Ev PATH ,
983: as specified when compiling
1.12 aaron 984: .Nm ssh .
1.118 markus 985: .It Ev SSH_ASKPASS
986: If
987: .Nm
988: needs a passphrase, it will read the passphrase from the current
989: terminal if it was run from a terminal.
990: If
991: .Nm
992: does not have a terminal associated with it but
993: .Ev DISPLAY
994: and
995: .Ev SSH_ASKPASS
996: are set, it will execute the program specified by
997: .Ev SSH_ASKPASS
998: and open an X11 window to read the passphrase.
999: This is particularly useful when calling
1000: .Nm
1001: from a
1.196 jmc 1002: .Pa .xsession
1.118 markus 1003: or related script.
1004: (Note that on some machines it
1005: may be necessary to redirect the input from
1006: .Pa /dev/null
1007: to make this work.)
1.18 markus 1008: .It Ev SSH_AUTH_SOCK
1.129 stevesk 1009: Identifies the path of a unix-domain socket used to communicate with the
1.17 markus 1010: agent.
1.166 stevesk 1011: .It Ev SSH_CONNECTION
1012: Identifies the client and server ends of the connection.
1.40 aaron 1013: The variable contains
1.166 stevesk 1014: four space-separated values: client ip-address, client port number,
1015: server ip-address and server port number.
1.73 markus 1016: .It Ev SSH_ORIGINAL_COMMAND
1017: The variable contains the original command line if a forced command
1018: is executed.
1019: It can be used to extract the original arguments.
1.2 deraadt 1020: .It Ev SSH_TTY
1.1 deraadt 1021: This is set to the name of the tty (path to the device) associated
1.40 aaron 1022: with the current shell or command.
1023: If the current session has no tty,
1.1 deraadt 1024: this variable is not set.
1.2 deraadt 1025: .It Ev TZ
1.214 jmc 1026: This variable is set to indicate the present time zone if it
1.56 deraadt 1027: was set when the daemon was started (i.e., the daemon passes the value
1.1 deraadt 1028: on to new connections).
1.2 deraadt 1029: .It Ev USER
1.1 deraadt 1030: Set to the name of the user logging in.
1.2 deraadt 1031: .El
1032: .Pp
1.44 aaron 1033: Additionally,
1.2 deraadt 1034: .Nm
1.44 aaron 1035: reads
1.207 djm 1036: .Pa ~/.ssh/environment ,
1.2 deraadt 1037: and adds lines of the format
1038: .Dq VARNAME=value
1.161 marc 1039: to the environment if the file exists and if users are allowed to
1040: change their environment.
1.176 jmc 1041: For more information, see the
1.161 marc 1042: .Cm PermitUserEnvironment
1.162 stevesk 1043: option in
1.161 marc 1044: .Xr sshd_config 5 .
1.2 deraadt 1045: .Sh FILES
1.36 markus 1046: .Bl -tag -width Ds
1.207 djm 1047: .It Pa ~/.ssh/known_hosts
1.129 stevesk 1048: Records host keys for all hosts the user has logged into that are not
1.2 deraadt 1049: in
1.147 deraadt 1050: .Pa /etc/ssh/ssh_known_hosts .
1.2 deraadt 1051: See
1052: .Xr sshd 8 .
1.207 djm 1053: .It Pa ~/.ssh/identity, ~/.ssh/id_dsa, ~/.ssh/id_rsa
1.102 itojun 1054: Contains the authentication identity of the user.
1055: They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively.
1.48 markus 1056: These files
1057: contain sensitive data and should be readable by the user but not
1.15 markus 1058: accessible by others (read/write/execute).
1059: Note that
1060: .Nm
1.48 markus 1061: ignores a private key file if it is accessible by others.
1.15 markus 1062: It is possible to specify a passphrase when
1.1 deraadt 1063: generating the key; the passphrase will be used to encrypt the
1.8 deraadt 1064: sensitive part of this file using 3DES.
1.207 djm 1065: .It Pa ~/.ssh/identity.pub, ~/.ssh/id_dsa.pub, ~/.ssh/id_rsa.pub
1.1 deraadt 1066: Contains the public key for authentication (public part of the
1.40 aaron 1067: identity file in human-readable form).
1.48 markus 1068: The contents of the
1.207 djm 1069: .Pa ~/.ssh/identity.pub
1.176 jmc 1070: file should be added to the file
1.207 djm 1071: .Pa ~/.ssh/authorized_keys
1.2 deraadt 1072: on all machines
1.137 deraadt 1073: where the user wishes to log in using protocol version 1 RSA authentication.
1.48 markus 1074: The contents of the
1.207 djm 1075: .Pa ~/.ssh/id_dsa.pub
1.102 itojun 1076: and
1.207 djm 1077: .Pa ~/.ssh/id_rsa.pub
1.48 markus 1078: file should be added to
1.207 djm 1079: .Pa ~/.ssh/authorized_keys
1.48 markus 1080: on all machines
1.137 deraadt 1081: where the user wishes to log in using protocol version 2 DSA/RSA authentication.
1.48 markus 1082: These files are not
1.40 aaron 1083: sensitive and can (but need not) be readable by anyone.
1.48 markus 1084: These files are
1.84 markus 1085: never used automatically and are not necessary; they are only provided for
1.1 deraadt 1086: the convenience of the user.
1.207 djm 1087: .It Pa ~/.ssh/config
1.40 aaron 1088: This is the per-user configuration file.
1.158 stevesk 1089: The file format and configuration options are described in
1090: .Xr ssh_config 5 .
1.183 djm 1091: Because of the potential for abuse, this file must have strict permissions:
1092: read/write for the user, and not accessible by others.
1.207 djm 1093: .It Pa ~/.ssh/authorized_keys
1.115 markus 1094: Lists the public keys (RSA/DSA) that can be used for logging in as this user.
1.40 aaron 1095: The format of this file is described in the
1.2 deraadt 1096: .Xr sshd 8
1.40 aaron 1097: manual page.
1.176 jmc 1098: In the simplest form the format is the same as the
1099: .Pa .pub
1.116 markus 1100: identity files.
1.48 markus 1101: This file is not highly sensitive, but the recommended
1102: permissions are read/write for the user, and not accessible by others.
1.147 deraadt 1103: .It Pa /etc/ssh/ssh_known_hosts
1.40 aaron 1104: Systemwide list of known host keys.
1.116 markus 1105: This file should be prepared by the
1.1 deraadt 1106: system administrator to contain the public host keys of all machines in the
1.40 aaron 1107: organization.
1108: This file should be world-readable.
1109: This file contains
1.1 deraadt 1110: public keys, one per line, in the following format (fields separated
1.116 markus 1111: by spaces): system name, public key and optional comment field.
1.40 aaron 1112: When different names are used
1.1 deraadt 1113: for the same machine, all such names should be listed, separated by
1.40 aaron 1114: commas.
1.176 jmc 1115: The format is described in the
1.2 deraadt 1116: .Xr sshd 8
1.1 deraadt 1117: manual page.
1.2 deraadt 1118: .Pp
1.1 deraadt 1119: The canonical system name (as returned by name servers) is used by
1.2 deraadt 1120: .Xr sshd 8
1.1 deraadt 1121: to verify the client host when logging in; other names are needed because
1.2 deraadt 1122: .Nm
1.1 deraadt 1123: does not convert the user-supplied name to a canonical name before
1124: checking the key, because someone with access to the name servers
1125: would then be able to fool host authentication.
1.147 deraadt 1126: .It Pa /etc/ssh/ssh_config
1.40 aaron 1127: Systemwide configuration file.
1.158 stevesk 1128: The file format and configuration options are described in
1129: .Xr ssh_config 5 .
1.147 deraadt 1130: .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key
1.141 markus 1131: These three files contain the private parts of the host keys
1132: and are used for
1133: .Cm RhostsRSAAuthentication
1134: and
1135: .Cm HostbasedAuthentication .
1.155 stevesk 1136: If the protocol version 1
1137: .Cm RhostsRSAAuthentication
1.157 deraadt 1138: method is used,
1.155 stevesk 1139: .Nm
1140: must be setuid root, since the host key is readable only by root.
1141: For protocol version 2,
1142: .Nm
1143: uses
1144: .Xr ssh-keysign 8
1145: to access the host keys for
1146: .Cm HostbasedAuthentication .
1147: This eliminates the requirement that
1148: .Nm
1149: be setuid root when that authentication method is used.
1150: By default
1.141 markus 1151: .Nm
1.155 stevesk 1152: is not setuid root.
1.207 djm 1153: .It Pa ~/.rhosts
1.2 deraadt 1154: This file is used in
1.195 markus 1155: .Cm RhostsRSAAuthentication
1156: and
1157: .Cm HostbasedAuthentication
1.2 deraadt 1158: authentication to list the
1.40 aaron 1159: host/user pairs that are permitted to log in.
1160: (Note that this file is
1.1 deraadt 1161: also used by rlogin and rsh, which makes using this file insecure.)
1162: Each line of the file contains a host name (in the canonical form
1163: returned by name servers), and then a user name on that host,
1.40 aaron 1164: separated by a space.
1.92 markus 1165: On some machines this file may need to be
1.1 deraadt 1166: world-readable if the user's home directory is on a NFS partition,
1167: because
1.2 deraadt 1168: .Xr sshd 8
1.40 aaron 1169: reads it as root.
1170: Additionally, this file must be owned by the user,
1171: and must not have write permissions for anyone else.
1172: The recommended
1.1 deraadt 1173: permission for most machines is read/write for the user, and not
1174: accessible by others.
1.2 deraadt 1175: .Pp
1.195 markus 1176: Note that
1.2 deraadt 1177: .Xr sshd 8
1.195 markus 1178: allows authentication only in combination with client host key
1179: authentication before permitting log in.
1.137 deraadt 1180: If the server machine does not have the client's host key in
1.147 deraadt 1181: .Pa /etc/ssh/ssh_known_hosts ,
1.137 deraadt 1182: it can be stored in
1.207 djm 1183: .Pa ~/.ssh/known_hosts .
1.2 deraadt 1184: The easiest way to do this is to
1.1 deraadt 1185: connect back to the client from the server machine using ssh; this
1.48 markus 1186: will automatically add the host key to
1.207 djm 1187: .Pa ~/.ssh/known_hosts .
1188: .It Pa ~/.shosts
1.2 deraadt 1189: This file is used exactly the same way as
1.176 jmc 1190: .Pa .rhosts .
1.2 deraadt 1191: The purpose for
1.195 markus 1192: having this file is to be able to use
1193: .Cm RhostsRSAAuthentication
1194: and
1195: .Cm HostbasedAuthentication
1196: authentication without permitting login with
1.176 jmc 1197: .Xr rlogin
1.2 deraadt 1198: or
1199: .Xr rsh 1 .
1200: .It Pa /etc/hosts.equiv
1201: This file is used during
1.195 markus 1202: .Cm RhostsRSAAuthentication
1203: and
1204: .Cm HostbasedAuthentication
1.173 jmc 1205: authentication.
1.40 aaron 1206: It contains
1.176 jmc 1207: canonical hosts names, one per line (the full format is described in the
1.2 deraadt 1208: .Xr sshd 8
1.40 aaron 1209: manual page).
1210: If the client host is found in this file, login is
1.1 deraadt 1211: automatically permitted provided client and server user names are the
1.40 aaron 1212: same.
1.195 markus 1213: Additionally, successful client host key authentication is required.
1.40 aaron 1214: This file should only be writable by root.
1.2 deraadt 1215: .It Pa /etc/shosts.equiv
1.44 aaron 1216: This file is processed exactly as
1.2 deraadt 1217: .Pa /etc/hosts.equiv .
1.1 deraadt 1218: This file may be useful to permit logins using
1.2 deraadt 1219: .Nm
1.1 deraadt 1220: but not using rsh/rlogin.
1.147 deraadt 1221: .It Pa /etc/ssh/sshrc
1.1 deraadt 1222: Commands in this file are executed by
1.2 deraadt 1223: .Nm
1.1 deraadt 1224: when the user logs in just before the user's shell (or command) is started.
1225: See the
1.2 deraadt 1226: .Xr sshd 8
1.1 deraadt 1227: manual page for more information.
1.207 djm 1228: .It Pa ~/.ssh/rc
1.1 deraadt 1229: Commands in this file are executed by
1.2 deraadt 1230: .Nm
1.1 deraadt 1231: when the user logs in just before the user's shell (or command) is
1232: started.
1.44 aaron 1233: See the
1.2 deraadt 1234: .Xr sshd 8
1.1 deraadt 1235: manual page for more information.
1.207 djm 1236: .It Pa ~/.ssh/environment
1.31 markus 1237: Contains additional definitions for environment variables, see section
1238: .Sx ENVIRONMENT
1239: above.
1.58 itojun 1240: .El
1.2 deraadt 1241: .Sh SEE ALSO
1.176 jmc 1242: .Xr gzip 1 ,
1.2 deraadt 1243: .Xr rsh 1 ,
1244: .Xr scp 1 ,
1.83 djm 1245: .Xr sftp 1 ,
1.2 deraadt 1246: .Xr ssh-add 1 ,
1247: .Xr ssh-agent 1 ,
1248: .Xr ssh-keygen 1 ,
1249: .Xr telnet 1 ,
1.176 jmc 1250: .Xr hosts.equiv 5 ,
1.159 stevesk 1251: .Xr ssh_config 5 ,
1.160 naddy 1252: .Xr ssh-keysign 8 ,
1.87 itojun 1253: .Xr sshd 8
1.106 markus 1254: .Rs
1255: .%A T. Ylonen
1256: .%A T. Kivinen
1257: .%A M. Saarinen
1258: .%A T. Rinne
1259: .%A S. Lehtinen
1260: .%T "SSH Protocol Architecture"
1.150 markus 1261: .%N draft-ietf-secsh-architecture-12.txt
1262: .%D January 2002
1.106 markus 1263: .%O work in progress material
1264: .Re
1.173 jmc 1265: .Sh AUTHORS
1266: OpenSSH is a derivative of the original and free
1267: ssh 1.2.12 release by Tatu Ylonen.
1268: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1269: Theo de Raadt and Dug Song
1270: removed many bugs, re-added newer features and
1271: created OpenSSH.
1272: Markus Friedl contributed the support for SSH
1273: protocol versions 1.5 and 2.0.
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