Annotation of src/usr.bin/ssh/ssh.1, Revision 1.261
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: .\"
1.261 ! stevesk 37: .\" $OpenBSD: ssh.1,v 1.260 2006/05/29 16:13:23 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
1.261 ! stevesk 81: .Oo Fl w Ar local_tun Ns
! 82: .Op : Ns Ar remote_tun Oc
1.176 jmc 83: .Oo Ar user Ns @ Oc Ns Ar hostname
1.2 deraadt 84: .Op Ar command
1.216 jmc 85: .Ek
1.44 aaron 86: .Sh DESCRIPTION
1.2 deraadt 87: .Nm
1.96 deraadt 88: (SSH client) is a program for logging into a remote machine and for
1.40 aaron 89: executing commands on a remote machine.
1.176 jmc 90: It is intended to replace rlogin and rsh,
91: and provide secure encrypted communications between
1.40 aaron 92: two untrusted hosts over an insecure network.
1.247 jmc 93: X11 connections and arbitrary TCP ports
1.176 jmc 94: can also be forwarded over the secure channel.
1.2 deraadt 95: .Pp
96: .Nm
1.44 aaron 97: connects and logs into the specified
1.176 jmc 98: .Ar hostname
99: (with optional
100: .Ar user
101: name).
1.1 deraadt 102: The user must prove
1.49 markus 103: his/her identity to the remote machine using one of several methods
1.221 jmc 104: depending on the protocol version used (see below).
1.49 markus 105: .Pp
1.176 jmc 106: If
107: .Ar command
108: is specified,
1.219 jmc 109: it is executed on the remote host instead of a login shell.
1.2 deraadt 110: .Pp
1.218 jmc 111: The options are as follows:
112: .Bl -tag -width Ds
113: .It Fl 1
114: Forces
1.2 deraadt 115: .Nm
1.218 jmc 116: to try protocol version 1 only.
117: .It Fl 2
118: Forces
1.2 deraadt 119: .Nm
1.218 jmc 120: to try protocol version 2 only.
121: .It Fl 4
122: Forces
1.2 deraadt 123: .Nm
1.218 jmc 124: to use IPv4 addresses only.
125: .It Fl 6
126: Forces
1.2 deraadt 127: .Nm
1.218 jmc 128: to use IPv6 addresses only.
129: .It Fl A
130: Enables forwarding of the authentication agent connection.
131: This can also be specified on a per-host basis in a configuration file.
1.2 deraadt 132: .Pp
1.218 jmc 133: Agent forwarding should be enabled with caution.
134: Users with the ability to bypass file permissions on the remote host
135: (for the agent's Unix-domain socket)
136: can access the local agent through the forwarded connection.
137: An attacker cannot obtain key material from the agent,
138: however they can perform operations on the keys that enable them to
139: authenticate using the identities loaded into the agent.
140: .It Fl a
141: Disables forwarding of the authentication agent connection.
142: .It Fl b Ar bind_address
143: Use
144: .Ar bind_address
145: on the local machine as the source address
146: of the connection.
147: Only useful on systems with more than one address.
148: .It Fl C
149: Requests compression of all data (including stdin, stdout, stderr, and
1.247 jmc 150: data for forwarded X11 and TCP connections).
1.218 jmc 151: The compression algorithm is the same used by
152: .Xr gzip 1 ,
153: and the
154: .Dq level
155: can be controlled by the
156: .Cm CompressionLevel
157: option for protocol version 1.
158: Compression is desirable on modem lines and other
159: slow connections, but will only slow down things on fast networks.
160: The default value can be set on a host-by-host basis in the
161: configuration files; see the
162: .Cm Compression
163: option.
164: .It Fl c Ar cipher_spec
165: Selects the cipher specification for encrypting the session.
1.2 deraadt 166: .Pp
1.218 jmc 167: Protocol version 1 allows specification of a single cipher.
168: The supported values are
169: .Dq 3des ,
1.220 jmc 170: .Dq blowfish ,
1.218 jmc 171: and
172: .Dq des .
173: .Ar 3des
174: (triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
175: It is believed to be secure.
176: .Ar blowfish
177: is a fast block cipher; it appears very secure and is much faster than
178: .Ar 3des .
179: .Ar des
180: is only supported in the
1.2 deraadt 181: .Nm
1.218 jmc 182: client for interoperability with legacy protocol 1 implementations
183: that do not support the
184: .Ar 3des
185: cipher.
186: Its use is strongly discouraged due to cryptographic weaknesses.
187: The default is
188: .Dq 3des .
1.49 markus 189: .Pp
1.230 jmc 190: For protocol version 2,
1.218 jmc 191: .Ar cipher_spec
192: is a comma-separated list of ciphers
193: listed in order of preference.
1.230 jmc 194: The supported ciphers are:
195: 3des-cbc,
196: aes128-cbc,
197: aes192-cbc,
198: aes256-cbc,
199: aes128-ctr,
200: aes192-ctr,
201: aes256-ctr,
202: arcfour128,
203: arcfour256,
204: arcfour,
205: blowfish-cbc,
1.218 jmc 206: and
1.230 jmc 207: cast128-cbc.
1.220 jmc 208: The default is:
209: .Bd -literal -offset indent
210: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
211: arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
212: aes192-ctr,aes256-ctr
1.218 jmc 213: .Ed
214: .It Fl D Xo
215: .Sm off
216: .Oo Ar bind_address : Oc
217: .Ar port
218: .Sm on
219: .Xc
220: Specifies a local
221: .Dq dynamic
222: application-level port forwarding.
223: This works by allocating a socket to listen to
224: .Ar port
225: on the local side, optionally bound to the specified
226: .Ar bind_address .
227: Whenever a connection is made to this port, the
228: connection is forwarded over the secure channel, and the application
229: protocol is then used to determine where to connect to from the
230: remote machine.
231: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.107 markus 232: .Nm
1.218 jmc 233: will act as a SOCKS server.
234: Only root can forward privileged ports.
235: Dynamic port forwardings can also be specified in the configuration file.
1.49 markus 236: .Pp
1.218 jmc 237: IPv6 addresses can be specified with an alternative syntax:
238: .Sm off
239: .Xo
240: .Op Ar bind_address No /
241: .Ar port
242: .Xc
243: .Sm on
244: or by enclosing the address in square brackets.
245: Only the superuser can forward privileged ports.
246: By default, the local port is bound in accordance with the
247: .Cm GatewayPorts
248: setting.
249: However, an explicit
250: .Ar bind_address
251: may be used to bind the connection to a specific address.
252: The
253: .Ar bind_address
254: of
255: .Dq localhost
256: indicates that the listening port be bound for local use only, while an
257: empty address or
258: .Sq *
259: indicates that the port should be available from all interfaces.
1.229 jmc 260: .It Fl e Ar escape_char
1.218 jmc 261: Sets the escape character for sessions with a pty (default:
262: .Ql ~ ) .
263: The escape character is only recognized at the beginning of a line.
264: The escape character followed by a dot
265: .Pq Ql \&.
266: closes the connection;
267: followed by control-Z suspends the connection;
268: and followed by itself sends the escape character once.
269: Setting the character to
1.2 deraadt 270: .Dq none
1.218 jmc 271: disables any escapes and makes the session fully transparent.
272: .It Fl F Ar configfile
273: Specifies an alternative per-user configuration file.
274: If a configuration file is given on the command line,
275: the system-wide configuration file
276: .Pq Pa /etc/ssh/ssh_config
277: will be ignored.
278: The default for the per-user configuration file is
279: .Pa ~/.ssh/config .
280: .It Fl f
281: Requests
282: .Nm
283: to go to background just before command execution.
284: This is useful if
1.176 jmc 285: .Nm
1.218 jmc 286: is going to ask for passwords or passphrases, but the user
287: wants it in the background.
288: This implies
289: .Fl n .
290: The recommended way to start X11 programs at a remote site is with
291: something like
292: .Ic ssh -f host xterm .
293: .It Fl g
294: Allows remote hosts to connect to local forwarded ports.
295: .It Fl I Ar smartcard_device
1.229 jmc 296: Specify the device
1.176 jmc 297: .Nm
1.218 jmc 298: should use to communicate with a smartcard used for storing the user's
299: private RSA key.
1.229 jmc 300: This option is only available if support for smartcard devices
301: is compiled in (default is no support).
1.218 jmc 302: .It Fl i Ar identity_file
303: Selects a file from which the identity (private key) for
304: RSA or DSA authentication is read.
305: The default is
306: .Pa ~/.ssh/identity
307: for protocol version 1, and
308: .Pa ~/.ssh/id_rsa
1.149 jakob 309: and
1.218 jmc 310: .Pa ~/.ssh/id_dsa
311: for protocol version 2.
312: Identity files may also be specified on
313: a per-host basis in the configuration file.
314: It is possible to have multiple
315: .Fl i
316: options (and multiple identities specified in
317: configuration files).
318: .It Fl k
319: Disables forwarding (delegation) of GSSAPI credentials to the server.
320: .It Fl L Xo
321: .Sm off
322: .Oo Ar bind_address : Oc
323: .Ar port : host : hostport
324: .Sm on
325: .Xc
326: Specifies that the given port on the local (client) host is to be
327: forwarded to the given host and port on the remote side.
328: This works by allocating a socket to listen to
329: .Ar port
330: on the local side, optionally bound to the specified
331: .Ar bind_address .
332: Whenever a connection is made to this port, the
333: connection is forwarded over the secure channel, and a connection is
334: made to
335: .Ar host
336: port
337: .Ar hostport
338: from the remote machine.
339: Port forwardings can also be specified in the configuration file.
340: IPv6 addresses can be specified with an alternative syntax:
341: .Sm off
342: .Xo
343: .Op Ar bind_address No /
344: .Ar port No / Ar host No /
345: .Ar hostport
346: .Xc
347: .Sm on
348: or by enclosing the address in square brackets.
349: Only the superuser can forward privileged ports.
350: By default, the local port is bound in accordance with the
351: .Cm GatewayPorts
352: setting.
353: However, an explicit
354: .Ar bind_address
355: may be used to bind the connection to a specific address.
1.2 deraadt 356: The
1.218 jmc 357: .Ar bind_address
358: of
359: .Dq localhost
360: indicates that the listening port be bound for local use only, while an
361: empty address or
362: .Sq *
363: indicates that the port should be available from all interfaces.
364: .It Fl l Ar login_name
365: Specifies the user to log in as on the remote machine.
366: This also may be specified on a per-host basis in the configuration file.
367: .It Fl M
368: Places the
369: .Nm
370: client into
371: .Dq master
372: mode for connection sharing.
1.231 stevesk 373: Multiple
374: .Fl M
375: options places
376: .Nm
377: into
378: .Dq master
379: mode with confirmation required before slave connections are accepted.
1.218 jmc 380: Refer to the description of
381: .Cm ControlMaster
382: in
383: .Xr ssh_config 5
384: for details.
385: .It Fl m Ar mac_spec
386: Additionally, for protocol version 2 a comma-separated list of MAC
387: (message authentication code) algorithms can
388: be specified in order of preference.
389: See the
390: .Cm MACs
391: keyword for more information.
392: .It Fl N
393: Do not execute a remote command.
394: This is useful for just forwarding ports
395: (protocol version 2 only).
396: .It Fl n
397: Redirects stdin from
398: .Pa /dev/null
399: (actually, prevents reading from stdin).
400: This must be used when
1.2 deraadt 401: .Nm
1.218 jmc 402: is run in the background.
403: A common trick is to use this to run X11 programs on a remote machine.
404: For example,
405: .Ic ssh -n shadows.cs.hut.fi emacs &
406: will start an emacs on shadows.cs.hut.fi, and the X11
407: connection will be automatically forwarded over an encrypted channel.
408: The
1.2 deraadt 409: .Nm
1.218 jmc 410: program will be put in the background.
411: (This does not work if
1.2 deraadt 412: .Nm
1.218 jmc 413: needs to ask for a password or passphrase; see also the
414: .Fl f
415: option.)
416: .It Fl O Ar ctl_cmd
417: Control an active connection multiplexing master process.
418: When the
419: .Fl O
420: option is specified, the
421: .Ar ctl_cmd
422: argument is interpreted and passed to the master process.
423: Valid commands are:
424: .Dq check
425: (check that the master process is running) and
426: .Dq exit
427: (request the master to exit).
428: .It Fl o Ar option
429: Can be used to give options in the format used in the configuration file.
430: This is useful for specifying options for which there is no separate
431: command-line flag.
432: For full details of the options listed below, and their possible values, see
433: .Xr ssh_config 5 .
1.2 deraadt 434: .Pp
1.218 jmc 435: .Bl -tag -width Ds -offset indent -compact
436: .It AddressFamily
437: .It BatchMode
438: .It BindAddress
439: .It ChallengeResponseAuthentication
440: .It CheckHostIP
441: .It Cipher
442: .It Ciphers
443: .It ClearAllForwardings
444: .It Compression
445: .It CompressionLevel
446: .It ConnectionAttempts
447: .It ConnectTimeout
448: .It ControlMaster
449: .It ControlPath
450: .It DynamicForward
451: .It EscapeChar
452: .It ForwardAgent
453: .It ForwardX11
454: .It ForwardX11Trusted
455: .It GatewayPorts
456: .It GlobalKnownHostsFile
457: .It GSSAPIAuthentication
458: .It GSSAPIDelegateCredentials
459: .It HashKnownHosts
460: .It Host
461: .It HostbasedAuthentication
462: .It HostKeyAlgorithms
463: .It HostKeyAlias
464: .It HostName
465: .It IdentityFile
466: .It IdentitiesOnly
467: .It KbdInteractiveDevices
468: .It LocalCommand
469: .It LocalForward
470: .It LogLevel
471: .It MACs
472: .It NoHostAuthenticationForLocalhost
473: .It NumberOfPasswordPrompts
474: .It PasswordAuthentication
475: .It PermitLocalCommand
476: .It Port
477: .It PreferredAuthentications
478: .It Protocol
479: .It ProxyCommand
480: .It PubkeyAuthentication
1.251 dtucker 481: .It RekeyLimit
1.218 jmc 482: .It RemoteForward
483: .It RhostsRSAAuthentication
484: .It RSAAuthentication
485: .It SendEnv
486: .It ServerAliveInterval
487: .It ServerAliveCountMax
488: .It SmartcardDevice
489: .It StrictHostKeyChecking
490: .It TCPKeepAlive
491: .It Tunnel
492: .It TunnelDevice
493: .It UsePrivilegedPort
494: .It User
495: .It UserKnownHostsFile
496: .It VerifyHostKeyDNS
497: .It XAuthLocation
498: .El
499: .It Fl p Ar port
500: Port to connect to on the remote host.
501: This can be specified on a
502: per-host basis in the configuration file.
503: .It Fl q
504: Quiet mode.
505: Causes all warning and diagnostic messages to be suppressed.
506: .It Fl R Xo
507: .Sm off
508: .Oo Ar bind_address : Oc
509: .Ar port : host : hostport
510: .Sm on
511: .Xc
512: Specifies that the given port on the remote (server) host is to be
513: forwarded to the given host and port on the local side.
514: This works by allocating a socket to listen to
515: .Ar port
516: on the remote side, and whenever a connection is made to this port, the
517: connection is forwarded over the secure channel, and a connection is
518: made to
519: .Ar host
520: port
521: .Ar hostport
522: from the local machine.
1.2 deraadt 523: .Pp
1.218 jmc 524: Port forwardings can also be specified in the configuration file.
525: Privileged ports can be forwarded only when
526: logging in as root on the remote machine.
527: IPv6 addresses can be specified by enclosing the address in square braces or
528: using an alternative syntax:
529: .Sm off
530: .Xo
531: .Op Ar bind_address No /
532: .Ar host No / Ar port No /
533: .Ar hostport
534: .Xc .
535: .Sm on
1.194 jakob 536: .Pp
1.218 jmc 537: By default, the listening socket on the server will be bound to the loopback
538: interface only.
539: This may be overriden by specifying a
540: .Ar bind_address .
541: An empty
542: .Ar bind_address ,
543: or the address
544: .Ql * ,
545: indicates that the remote socket should listen on all interfaces.
546: Specifying a remote
547: .Ar bind_address
548: will only succeed if the server's
549: .Cm GatewayPorts
550: option is enabled (see
551: .Xr sshd_config 5 ) .
552: .It Fl S Ar ctl_path
553: Specifies the location of a control socket for connection sharing.
554: Refer to the description of
555: .Cm ControlPath
556: and
557: .Cm ControlMaster
558: in
559: .Xr ssh_config 5
560: for details.
561: .It Fl s
562: May be used to request invocation of a subsystem on the remote system.
563: Subsystems are a feature of the SSH2 protocol which facilitate the use
564: of SSH as a secure transport for other applications (eg.\&
565: .Xr sftp 1 ) .
566: The subsystem is specified as the remote command.
567: .It Fl T
568: Disable pseudo-tty allocation.
569: .It Fl t
570: Force pseudo-tty allocation.
571: This can be used to execute arbitrary
572: screen-based programs on a remote machine, which can be very useful,
1.257 jmc 573: e.g. when implementing menu services.
1.218 jmc 574: Multiple
575: .Fl t
576: options force tty allocation, even if
1.194 jakob 577: .Nm
1.218 jmc 578: has no local tty.
579: .It Fl V
580: Display the version number and exit.
581: .It Fl v
582: Verbose mode.
583: Causes
1.176 jmc 584: .Nm
1.218 jmc 585: to print debugging messages about its progress.
586: This is helpful in
587: debugging connection, authentication, and configuration problems.
588: Multiple
589: .Fl v
590: options increase the verbosity.
591: The maximum is 3.
1.261 ! stevesk 592: .It Fl w Xo
! 593: .Ar local_tun Ns Op : Ns Ar remote_tun
! 594: .Xc
! 595: Requests
! 596: tunnel
! 597: device forwarding with the specified
1.218 jmc 598: .Xr tun 4
1.261 ! stevesk 599: devices between the client
! 600: .Pq Ar local_tun
! 601: and the server
! 602: .Pq Ar remote_tun .
! 603: .Pp
1.228 jmc 604: The devices may be specified by numerical ID or the keyword
605: .Dq any ,
606: which uses the next available tunnel device.
1.261 ! stevesk 607: If
! 608: .Ar remote_tun
! 609: is not specified, it defaults to
! 610: .Dq any .
1.228 jmc 611: See also the
1.218 jmc 612: .Cm Tunnel
1.261 ! stevesk 613: and
! 614: .Cm TunnelDevice
! 615: directives in
1.218 jmc 616: .Xr ssh_config 5 .
1.261 ! stevesk 617: If the
! 618: .Cm Tunnel
! 619: directive is unset, it is set to the default tunnel mode, which is
! 620: .Dq point-to-point .
1.218 jmc 621: .It Fl X
622: Enables X11 forwarding.
1.54 markus 623: This can also be specified on a per-host basis in a configuration file.
1.165 stevesk 624: .Pp
1.218 jmc 625: X11 forwarding should be enabled with caution.
1.168 jmc 626: Users with the ability to bypass file permissions on the remote host
1.218 jmc 627: (for the user's X authorization database)
628: can access the local X11 display through the forwarded connection.
629: An attacker may then be able to perform activities such as keystroke monitoring.
630: .Pp
631: For this reason, X11 forwarding is subjected to X11 SECURITY extension
632: restrictions by default.
633: Please refer to the
634: .Nm
635: .Fl Y
636: option and the
637: .Cm ForwardX11Trusted
638: directive in
639: .Xr ssh_config 5
640: for more information.
641: .It Fl x
642: Disables X11 forwarding.
643: .It Fl Y
644: Enables trusted X11 forwarding.
645: Trusted X11 forwardings are not subjected to the X11 SECURITY extension
646: controls.
647: .El
1.224 jmc 648: .Pp
649: .Nm
650: may additionally obtain configuration data from
651: a per-user configuration file and a system-wide configuration file.
652: The file format and configuration options are described in
653: .Xr ssh_config 5 .
654: .Pp
655: .Nm
656: exits with the exit status of the remote command or with 255
657: if an error occurred.
1.222 jmc 658: .Sh AUTHENTICATION
1.249 jmc 659: The OpenSSH SSH client supports SSH protocols 1 and 2.
1.222 jmc 660: Protocol 2 is the default, with
661: .Nm
662: falling back to protocol 1 if it detects protocol 2 is unsupported.
663: These settings may be altered using the
664: .Cm Protocol
665: option in
666: .Xr ssh_config 5 ,
667: or enforced using the
668: .Fl 1
669: and
670: .Fl 2
671: options (see above).
672: Both protocols support similar authentication methods,
673: but protocol 2 is preferred since
674: it provides additional mechanisms for confidentiality
675: (the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour)
676: and integrity (hmac-md5, hmac-sha1, hmac-ripemd160).
677: Protocol 1 lacks a strong mechanism for ensuring the
678: integrity of the connection.
679: .Pp
680: The methods available for authentication are:
1.260 jmc 681: GSSAPI-based authentication,
1.222 jmc 682: host-based authentication,
683: public key authentication,
684: challenge-response authentication,
685: and password authentication.
686: Authentication methods are tried in the order specified above,
687: though protocol 2 has a configuration option to change the default order:
688: .Cm PreferredAuthentications .
689: .Pp
690: Host-based authentication works as follows:
1.218 jmc 691: If the machine the user logs in from is listed in
692: .Pa /etc/hosts.equiv
693: or
694: .Pa /etc/shosts.equiv
695: on the remote machine, and the user names are
696: the same on both sides, or if the files
697: .Pa ~/.rhosts
698: or
699: .Pa ~/.shosts
700: exist in the user's home directory on the
701: remote machine and contain a line containing the name of the client
702: machine and the name of the user on that machine, the user is
1.222 jmc 703: considered for login.
704: Additionally, the server
705: .Em must
706: be able to verify the client's
707: host key (see the description of
1.218 jmc 708: .Pa /etc/ssh/ssh_known_hosts
1.189 dtucker 709: and
1.222 jmc 710: .Pa ~/.ssh/known_hosts ,
711: below)
712: for login to be permitted.
1.218 jmc 713: This authentication method closes security holes due to IP
1.222 jmc 714: spoofing, DNS spoofing, and routing spoofing.
1.218 jmc 715: [Note to the administrator:
716: .Pa /etc/hosts.equiv ,
717: .Pa ~/.rhosts ,
718: and the rlogin/rsh protocol in general, are inherently insecure and should be
719: disabled if security is desired.]
1.189 dtucker 720: .Pp
1.222 jmc 721: Public key authentication works as follows:
722: The scheme is based on public-key cryptography,
723: using cryptosystems
724: where encryption and decryption are done using separate keys,
725: and it is unfeasible to derive the decryption key from the encryption key.
1.218 jmc 726: The idea is that each user creates a public/private
727: key pair for authentication purposes.
728: The server knows the public key, and only the user knows the private key.
1.222 jmc 729: .Nm
730: implements public key authentication protocol automatically,
731: using either the RSA or DSA algorithms.
732: Protocol 1 is restricted to using only RSA keys,
733: but protocol 2 may use either.
734: The
735: .Sx HISTORY
736: section of
737: .Xr ssl 8
738: contains a brief discussion of the two algorithms.
1.210 djm 739: .Pp
1.218 jmc 740: The file
741: .Pa ~/.ssh/authorized_keys
742: lists the public keys that are permitted for logging in.
743: When the user logs in, the
1.2 deraadt 744: .Nm
1.218 jmc 745: program tells the server which key pair it would like to use for
746: authentication.
1.222 jmc 747: The client proves that it has access to the private key
748: and the server checks that the corresponding public key
749: is authorized to accept the account.
1.218 jmc 750: .Pp
1.222 jmc 751: The user creates his/her key pair by running
1.218 jmc 752: .Xr ssh-keygen 1 .
753: This stores the private key in
1.207 djm 754: .Pa ~/.ssh/identity
1.222 jmc 755: (protocol 1),
756: .Pa ~/.ssh/id_dsa
757: (protocol 2 DSA),
758: or
759: .Pa ~/.ssh/id_rsa
760: (protocol 2 RSA)
1.218 jmc 761: and stores the public key in
762: .Pa ~/.ssh/identity.pub
1.222 jmc 763: (protocol 1),
764: .Pa ~/.ssh/id_dsa.pub
765: (protocol 2 DSA),
766: or
767: .Pa ~/.ssh/id_rsa.pub
768: (protocol 2 RSA)
1.218 jmc 769: in the user's home directory.
1.222 jmc 770: The user should then copy the public key
1.218 jmc 771: to
772: .Pa ~/.ssh/authorized_keys
1.222 jmc 773: in his/her home directory on the remote machine.
774: The
1.218 jmc 775: .Pa authorized_keys
776: file corresponds to the conventional
777: .Pa ~/.rhosts
778: file, and has one key
1.222 jmc 779: per line, though the lines can be very long.
1.218 jmc 780: After this, the user can log in without giving the password.
781: .Pp
1.222 jmc 782: The most convenient way to use public key authentication may be with an
1.218 jmc 783: authentication agent.
784: See
785: .Xr ssh-agent 1
786: for more information.
787: .Pp
1.222 jmc 788: Challenge-response authentication works as follows:
789: The server sends an arbitrary
790: .Qq challenge
791: text, and prompts for a response.
792: Protocol 2 allows multiple challenges and responses;
793: protocol 1 is restricted to just one challenge/response.
794: Examples of challenge-response authentication include
795: BSD Authentication (see
796: .Xr login.conf 5 )
797: and PAM (some non-OpenBSD systems).
798: .Pp
799: Finally, if other authentication methods fail,
1.218 jmc 800: .Nm
801: prompts the user for a password.
802: The password is sent to the remote
803: host for checking; however, since all communications are encrypted,
804: the password cannot be seen by someone listening on the network.
1.232 jmc 805: .Pp
806: .Nm
807: automatically maintains and checks a database containing
808: identification for all hosts it has ever been used with.
809: Host keys are stored in
810: .Pa ~/.ssh/known_hosts
811: in the user's home directory.
812: Additionally, the file
813: .Pa /etc/ssh/ssh_known_hosts
814: is automatically checked for known hosts.
815: Any new hosts are automatically added to the user's file.
816: If a host's identification ever changes,
817: .Nm
818: warns about this and disables password authentication to prevent
819: server spoofing or man-in-the-middle attacks,
820: which could otherwise be used to circumvent the encryption.
821: The
822: .Cm StrictHostKeyChecking
823: option can be used to control logins to machines whose
824: host key is not known or has changed.
825: .Pp
1.218 jmc 826: When the user's identity has been accepted by the server, the server
827: either executes the given command, or logs into the machine and gives
828: the user a normal shell on the remote machine.
829: All communication with
830: the remote command or shell will be automatically encrypted.
831: .Pp
832: If a pseudo-terminal has been allocated (normal login session), the
833: user may use the escape characters noted below.
834: .Pp
835: If no pseudo-tty has been allocated,
836: the session is transparent and can be used to reliably transfer binary data.
837: On most systems, setting the escape character to
838: .Dq none
839: will also make the session transparent even if a tty is used.
840: .Pp
841: The session terminates when the command or shell on the remote
1.247 jmc 842: machine exits and all X11 and TCP connections have been closed.
1.223 jmc 843: .Sh ESCAPE CHARACTERS
1.218 jmc 844: When a pseudo-terminal has been requested,
1.2 deraadt 845: .Nm
1.218 jmc 846: supports a number of functions through the use of an escape character.
847: .Pp
848: A single tilde character can be sent as
849: .Ic ~~
850: or by following the tilde by a character other than those described below.
851: The escape character must always follow a newline to be interpreted as
852: special.
853: The escape character can be changed in configuration files using the
854: .Cm EscapeChar
855: configuration directive or on the command line by the
856: .Fl e
857: option.
858: .Pp
859: The supported escapes (assuming the default
860: .Ql ~ )
861: are:
862: .Bl -tag -width Ds
863: .It Cm ~.
864: Disconnect.
865: .It Cm ~^Z
866: Background
1.234 jmc 867: .Nm .
1.218 jmc 868: .It Cm ~#
869: List forwarded connections.
870: .It Cm ~&
871: Background
1.2 deraadt 872: .Nm
1.218 jmc 873: at logout when waiting for forwarded connection / X11 sessions to terminate.
874: .It Cm ~?
875: Display a list of escape characters.
876: .It Cm ~B
877: Send a BREAK to the remote system
878: (only useful for SSH protocol version 2 and if the peer supports it).
879: .It Cm ~C
880: Open command line.
881: Currently this allows the addition of port forwardings using the
882: .Fl L
883: and
884: .Fl R
1.225 jmc 885: options (see above).
1.218 jmc 886: It also allows the cancellation of existing remote port-forwardings
887: using
888: .Fl KR Ar hostport .
889: .Ic !\& Ns Ar command
890: allows the user to execute a local command if the
891: .Ic PermitLocalCommand
892: option is enabled in
1.176 jmc 893: .Xr ssh_config 5 .
1.218 jmc 894: Basic help is available, using the
895: .Fl h
896: option.
897: .It Cm ~R
898: Request rekeying of the connection
899: (only useful for SSH protocol version 2 and if the peer supports it).
1.176 jmc 900: .El
1.246 jmc 901: .Sh TCP FORWARDING
902: Forwarding of arbitrary TCP connections over the secure channel can
903: be specified either on the command line or in a configuration file.
904: One possible application of TCP forwarding is a secure connection to a
905: mail server; another is going through firewalls.
906: .Pp
907: In the example below, we look at encrypting communication between
908: an IRC client and server, even though the IRC server does not directly
909: support encrypted communications.
910: This works as follows:
911: the user connects to the remote host using
912: .Nm ,
913: specifying a port to be used to forward connections
914: to the remote server.
915: After that it is possible to start the service which is to be encrypted
916: on the client machine,
917: connecting to the same local port,
918: and
919: .Nm
920: will encrypt and forward the connection.
921: .Pp
922: The following example tunnels an IRC session from client machine
923: .Dq 127.0.0.1
924: (localhost)
925: to remote server
926: .Dq server.example.com :
927: .Bd -literal -offset 4n
928: $ ssh -f -L 1234:localhost:6667 server.example.com sleep 10
929: $ irc -c '#users' -p 1234 pinky 127.0.0.1
930: .Ed
931: .Pp
932: This tunnels a connection to IRC server
933: .Dq server.example.com ,
934: joining channel
935: .Dq #users ,
936: nickname
937: .Dq pinky ,
938: using port 1234.
939: It doesn't matter which port is used,
940: as long as it's greater than 1023
941: (remember, only root can open sockets on privileged ports)
942: and doesn't conflict with any ports already in use.
943: The connection is forwarded to port 6667 on the remote server,
944: since that's the standard port for IRC services.
945: .Pp
946: The
947: .Fl f
948: option backgrounds
949: .Nm
950: and the remote command
951: .Dq sleep 10
952: is specified to allow an amount of time
953: (10 seconds, in the example)
954: to start the service which is to be tunnelled.
955: If no connections are made within the time specified,
956: .Nm
957: will exit.
958: .Sh X11 FORWARDING
1.218 jmc 959: If the
960: .Cm ForwardX11
961: variable is set to
962: .Dq yes
963: (or see the description of the
1.227 jmc 964: .Fl X ,
965: .Fl x ,
1.218 jmc 966: and
1.227 jmc 967: .Fl Y
1.226 jmc 968: options above)
1.218 jmc 969: and the user is using X11 (the
970: .Ev DISPLAY
971: environment variable is set), the connection to the X11 display is
972: automatically forwarded to the remote side in such a way that any X11
973: programs started from the shell (or command) will go through the
974: encrypted channel, and the connection to the real X server will be made
1.176 jmc 975: from the local machine.
1.218 jmc 976: The user should not manually set
977: .Ev DISPLAY .
978: Forwarding of X11 connections can be
979: configured on the command line or in configuration files.
980: .Pp
981: The
982: .Ev DISPLAY
983: value set by
984: .Nm
985: will point to the server machine, but with a display number greater than zero.
986: This is normal, and happens because
987: .Nm
988: creates a
989: .Dq proxy
990: X server on the server machine for forwarding the
991: connections over the encrypted channel.
1.200 djm 992: .Pp
1.218 jmc 993: .Nm
994: will also automatically set up Xauthority data on the server machine.
995: For this purpose, it will generate a random authorization cookie,
996: store it in Xauthority on the server, and verify that any forwarded
997: connections carry this cookie and replace it by the real cookie when
998: the connection is opened.
999: The real authentication cookie is never
1000: sent to the server machine (and no cookies are sent in the plain).
1.200 djm 1001: .Pp
1.218 jmc 1002: If the
1003: .Cm ForwardAgent
1004: variable is set to
1005: .Dq yes
1006: (or see the description of the
1007: .Fl A
1.191 djm 1008: and
1.218 jmc 1009: .Fl a
1.226 jmc 1010: options above) and
1.218 jmc 1011: the user is using an authentication agent, the connection to the agent
1012: is automatically forwarded to the remote side.
1.252 jmc 1013: .Sh VERIFYING HOST KEYS
1014: When connecting to a server for the first time,
1015: a fingerprint of the server's public key is presented to the user
1016: (unless the option
1017: .Cm StrictHostKeyChecking
1018: has been disabled).
1019: Fingerprints can be determined using
1020: .Xr ssh-keygen 1 :
1021: .Pp
1022: .Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key
1023: .Pp
1024: If the fingerprint is already known,
1025: it can be matched and verified,
1026: and the key can be accepted.
1027: If the fingerprint is unknown,
1028: an alternative method of verification is available:
1029: SSH fingerprints verified by DNS.
1030: An additional resource record (RR),
1031: SSHFP,
1032: is added to a zonefile
1033: and the connecting client is able to match the fingerprint
1034: with that of the key presented.
1035: .Pp
1036: In this example, we are connecting a client to a server,
1037: .Dq host.example.com .
1038: The SSHFP resource records should first be added to the zonefile for
1039: host.example.com:
1040: .Bd -literal -offset indent
1.259 jakob 1041: $ ssh-keygen -r host.example.com.
1.252 jmc 1042: .Ed
1043: .Pp
1044: The output lines will have to be added to the zonefile.
1045: To check that the zone is answering fingerprint queries:
1046: .Pp
1047: .Dl $ dig -t SSHFP host.example.com
1048: .Pp
1049: Finally the client connects:
1050: .Bd -literal -offset indent
1051: $ ssh -o "VerifyHostKeyDNS ask" host.example.com
1052: [...]
1053: Matching host key fingerprint found in DNS.
1054: Are you sure you want to continue connecting (yes/no)?
1055: .Ed
1056: .Pp
1057: See the
1058: .Cm VerifyHostKeyDNS
1059: option in
1060: .Xr ssh_config 5
1061: for more information.
1.250 jmc 1062: .Sh SSH-BASED VIRTUAL PRIVATE NETWORKS
1063: .Nm
1064: contains support for Virtual Private Network (VPN) tunnelling
1065: using the
1066: .Xr tun 4
1067: network pseudo-device,
1068: allowing two networks to be joined securely.
1069: The
1070: .Xr sshd_config 5
1071: configuration option
1072: .Cm PermitTunnel
1073: controls whether the server supports this,
1074: and at what level (layer 2 or 3 traffic).
1075: .Pp
1076: The following example would connect client network 10.0.50.0/24
1077: with remote network 10.0.99.0/24, provided that the SSH server
1078: running on the gateway to the remote network,
1079: at 192.168.1.15, allows it:
1080: .Bd -literal -offset indent
1081: # ssh -f -w 0:1 192.168.1.15 true
1082: # ifconfig tun0 10.0.50.1 10.0.99.1 netmask 255.255.255.252
1083: .Ed
1084: .Pp
1085: Client access may be more finely tuned via the
1086: .Pa /root/.ssh/authorized_keys
1087: file (see below) and the
1088: .Cm PermitRootLogin
1089: server option.
1.255 jmc 1090: The following entry would permit connections on
1.250 jmc 1091: .Xr tun 4
1.255 jmc 1092: device 1 from user
1.250 jmc 1093: .Dq jane
1.255 jmc 1094: and on tun device 2 from user
1.250 jmc 1095: .Dq john ,
1096: if
1097: .Cm PermitRootLogin
1098: is set to
1099: .Dq forced-commands-only :
1100: .Bd -literal -offset 2n
1101: tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane
1.254 msf 1102: tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john
1.250 jmc 1103: .Ed
1104: .Pp
1105: Since a SSH-based setup entails a fair amount of overhead,
1106: it may be more suited to temporary setups,
1107: such as for wireless VPNs.
1108: More permanent VPNs are better provided by tools such as
1109: .Xr ipsecctl 8
1110: and
1111: .Xr isakmpd 8 .
1.2 deraadt 1112: .Sh ENVIRONMENT
1113: .Nm
1.1 deraadt 1114: will normally set the following environment variables:
1.237 jmc 1115: .Bl -tag -width "SSH_ORIGINAL_COMMAND"
1.2 deraadt 1116: .It Ev DISPLAY
1117: The
1118: .Ev DISPLAY
1.40 aaron 1119: variable indicates the location of the X11 server.
1.44 aaron 1120: It is automatically set by
1.2 deraadt 1121: .Nm
1122: to point to a value of the form
1.233 jmc 1123: .Dq hostname:n ,
1124: where
1125: .Dq hostname
1126: indicates the host where the shell runs, and
1127: .Sq n
1128: is an integer \*(Ge 1.
1.40 aaron 1129: .Nm
1130: uses this special value to forward X11 connections over the secure
1131: channel.
1.107 markus 1132: The user should normally not set
1133: .Ev DISPLAY
1134: explicitly, as that
1.1 deraadt 1135: will render the X11 connection insecure (and will require the user to
1136: manually copy any required authorization cookies).
1.2 deraadt 1137: .It Ev HOME
1.1 deraadt 1138: Set to the path of the user's home directory.
1.2 deraadt 1139: .It Ev LOGNAME
1140: Synonym for
1.12 aaron 1141: .Ev USER ;
1142: set for compatibility with systems that use this variable.
1.2 deraadt 1143: .It Ev MAIL
1.129 stevesk 1144: Set to the path of the user's mailbox.
1.40 aaron 1145: .It Ev PATH
1.2 deraadt 1146: Set to the default
1147: .Ev PATH ,
1148: as specified when compiling
1.234 jmc 1149: .Nm .
1.118 markus 1150: .It Ev SSH_ASKPASS
1151: If
1152: .Nm
1153: needs a passphrase, it will read the passphrase from the current
1154: terminal if it was run from a terminal.
1155: If
1156: .Nm
1157: does not have a terminal associated with it but
1158: .Ev DISPLAY
1159: and
1160: .Ev SSH_ASKPASS
1161: are set, it will execute the program specified by
1162: .Ev SSH_ASKPASS
1163: and open an X11 window to read the passphrase.
1164: This is particularly useful when calling
1165: .Nm
1166: from a
1.196 jmc 1167: .Pa .xsession
1.118 markus 1168: or related script.
1169: (Note that on some machines it
1170: may be necessary to redirect the input from
1171: .Pa /dev/null
1172: to make this work.)
1.18 markus 1173: .It Ev SSH_AUTH_SOCK
1.233 jmc 1174: Identifies the path of a
1175: .Ux Ns -domain
1176: socket used to communicate with the agent.
1.166 stevesk 1177: .It Ev SSH_CONNECTION
1178: Identifies the client and server ends of the connection.
1.40 aaron 1179: The variable contains
1.233 jmc 1180: four space-separated values: client IP address, client port number,
1181: server IP address, and server port number.
1.73 markus 1182: .It Ev SSH_ORIGINAL_COMMAND
1.233 jmc 1183: This variable contains the original command line if a forced command
1.73 markus 1184: is executed.
1185: It can be used to extract the original arguments.
1.2 deraadt 1186: .It Ev SSH_TTY
1.1 deraadt 1187: This is set to the name of the tty (path to the device) associated
1.40 aaron 1188: with the current shell or command.
1189: If the current session has no tty,
1.1 deraadt 1190: this variable is not set.
1.2 deraadt 1191: .It Ev TZ
1.214 jmc 1192: This variable is set to indicate the present time zone if it
1.257 jmc 1193: was set when the daemon was started (i.e. the daemon passes the value
1.1 deraadt 1194: on to new connections).
1.2 deraadt 1195: .It Ev USER
1.1 deraadt 1196: Set to the name of the user logging in.
1.2 deraadt 1197: .El
1198: .Pp
1.44 aaron 1199: Additionally,
1.2 deraadt 1200: .Nm
1.44 aaron 1201: reads
1.207 djm 1202: .Pa ~/.ssh/environment ,
1.2 deraadt 1203: and adds lines of the format
1204: .Dq VARNAME=value
1.233 jmc 1205: to the environment if the file exists and users are allowed to
1.161 marc 1206: change their environment.
1.176 jmc 1207: For more information, see the
1.161 marc 1208: .Cm PermitUserEnvironment
1.162 stevesk 1209: option in
1.161 marc 1210: .Xr sshd_config 5 .
1.2 deraadt 1211: .Sh FILES
1.236 jmc 1212: .Bl -tag -width Ds -compact
1213: .It ~/.rhosts
1.240 jmc 1214: This file is used for host-based authentication (see above).
1.92 markus 1215: On some machines this file may need to be
1.240 jmc 1216: world-readable if the user's home directory is on an NFS partition,
1.1 deraadt 1217: because
1.2 deraadt 1218: .Xr sshd 8
1.40 aaron 1219: reads it as root.
1220: Additionally, this file must be owned by the user,
1221: and must not have write permissions for anyone else.
1222: The recommended
1.1 deraadt 1223: permission for most machines is read/write for the user, and not
1224: accessible by others.
1.2 deraadt 1225: .Pp
1.236 jmc 1226: .It ~/.shosts
1.240 jmc 1227: This file is used in exactly the same way as
1228: .Pa .rhosts ,
1229: but allows host-based authentication without permitting login with
1230: rlogin/rsh.
1.236 jmc 1231: .Pp
1.238 jmc 1232: .It ~/.ssh/authorized_keys
1233: Lists the public keys (RSA/DSA) that can be used for logging in as this user.
1234: The format of this file is described in the
1235: .Xr sshd 8
1236: manual page.
1237: This file is not highly sensitive, but the recommended
1238: permissions are read/write for the user, and not accessible by others.
1239: .Pp
1240: .It ~/.ssh/config
1241: This is the per-user configuration file.
1242: The file format and configuration options are described in
1243: .Xr ssh_config 5 .
1244: Because of the potential for abuse, this file must have strict permissions:
1245: read/write for the user, and not accessible by others.
1246: .Pp
1247: .It ~/.ssh/environment
1.239 jmc 1248: Contains additional definitions for environment variables; see
1249: .Sx ENVIRONMENT ,
1.238 jmc 1250: above.
1251: .Pp
1252: .It ~/.ssh/identity
1253: .It ~/.ssh/id_dsa
1254: .It ~/.ssh/id_rsa
1255: Contains the private key for authentication.
1256: These files
1257: contain sensitive data and should be readable by the user but not
1258: accessible by others (read/write/execute).
1259: .Nm
1260: will simply ignore a private key file if it is accessible by others.
1261: It is possible to specify a passphrase when
1262: generating the key which will be used to encrypt the
1263: sensitive part of this file using 3DES.
1264: .Pp
1265: .It ~/.ssh/identity.pub
1266: .It ~/.ssh/id_dsa.pub
1267: .It ~/.ssh/id_rsa.pub
1268: Contains the public key for authentication.
1269: These files are not
1270: sensitive and can (but need not) be readable by anyone.
1271: .Pp
1272: .It ~/.ssh/known_hosts
1.244 jmc 1273: Contains a list of host keys for all hosts the user has logged into
1274: that are not already in the systemwide list of known host keys.
1.238 jmc 1275: See
1.244 jmc 1276: .Xr sshd 8
1277: for further details of the format of this file.
1.238 jmc 1278: .Pp
1279: .It ~/.ssh/rc
1280: Commands in this file are executed by
1281: .Nm
1.245 jmc 1282: when the user logs in, just before the user's shell (or command) is
1.238 jmc 1283: started.
1284: See the
1285: .Xr sshd 8
1286: manual page for more information.
1287: .Pp
1.236 jmc 1288: .It /etc/hosts.equiv
1.240 jmc 1289: This file is for host-based authentication (see above).
1290: It should only be writable by root.
1.236 jmc 1291: .Pp
1292: .It /etc/shosts.equiv
1.240 jmc 1293: This file is used in exactly the same way as
1294: .Pa hosts.equiv ,
1295: but allows host-based authentication without permitting login with
1296: rlogin/rsh.
1.236 jmc 1297: .Pp
1.238 jmc 1298: .It Pa /etc/ssh/ssh_config
1299: Systemwide configuration file.
1300: The file format and configuration options are described in
1301: .Xr ssh_config 5 .
1302: .Pp
1303: .It /etc/ssh/ssh_host_key
1304: .It /etc/ssh/ssh_host_dsa_key
1305: .It /etc/ssh/ssh_host_rsa_key
1306: These three files contain the private parts of the host keys
1.245 jmc 1307: and are used for host-based authentication.
1308: If protocol version 1 is used,
1.238 jmc 1309: .Nm
1310: must be setuid root, since the host key is readable only by root.
1311: For protocol version 2,
1312: .Nm
1313: uses
1314: .Xr ssh-keysign 8
1.245 jmc 1315: to access the host keys,
1316: eliminating the requirement that
1.238 jmc 1317: .Nm
1.245 jmc 1318: be setuid root when host-based authentication is used.
1.238 jmc 1319: By default
1.2 deraadt 1320: .Nm
1.238 jmc 1321: is not setuid root.
1322: .Pp
1323: .It /etc/ssh/ssh_known_hosts
1324: Systemwide list of known host keys.
1325: This file should be prepared by the
1326: system administrator to contain the public host keys of all machines in the
1327: organization.
1.244 jmc 1328: It should be world-readable.
1329: See
1.238 jmc 1330: .Xr sshd 8
1.244 jmc 1331: for further details of the format of this file.
1.236 jmc 1332: .Pp
1.238 jmc 1333: .It /etc/ssh/sshrc
1.1 deraadt 1334: Commands in this file are executed by
1.2 deraadt 1335: .Nm
1.245 jmc 1336: when the user logs in, just before the user's shell (or command) is started.
1.44 aaron 1337: See the
1.2 deraadt 1338: .Xr sshd 8
1.1 deraadt 1339: manual page for more information.
1.58 itojun 1340: .El
1.2 deraadt 1341: .Sh SEE ALSO
1342: .Xr scp 1 ,
1.83 djm 1343: .Xr sftp 1 ,
1.2 deraadt 1344: .Xr ssh-add 1 ,
1345: .Xr ssh-agent 1 ,
1346: .Xr ssh-keygen 1 ,
1.242 jmc 1347: .Xr ssh-keyscan 1 ,
1.250 jmc 1348: .Xr tun 4 ,
1.176 jmc 1349: .Xr hosts.equiv 5 ,
1.159 stevesk 1350: .Xr ssh_config 5 ,
1.160 naddy 1351: .Xr ssh-keysign 8 ,
1.87 itojun 1352: .Xr sshd 8
1.106 markus 1353: .Rs
1.256 jmc 1354: .%R RFC 4250
1355: .%T "The Secure Shell (SSH) Protocol Assigned Numbers"
1356: .%D 2006
1357: .Re
1358: .Rs
1359: .%R RFC 4251
1360: .%T "The Secure Shell (SSH) Protocol Architecture"
1361: .%D 2006
1362: .Re
1363: .Rs
1364: .%R RFC 4252
1365: .%T "The Secure Shell (SSH) Authentication Protocol"
1366: .%D 2006
1367: .Re
1368: .Rs
1369: .%R RFC 4253
1370: .%T "The Secure Shell (SSH) Transport Layer Protocol"
1371: .%D 2006
1372: .Re
1373: .Rs
1374: .%R RFC 4254
1375: .%T "The Secure Shell (SSH) Connection Protocol"
1376: .%D 2006
1377: .Re
1378: .Rs
1379: .%R RFC 4255
1380: .%T "Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints"
1381: .%D 2006
1382: .Re
1383: .Rs
1384: .%R RFC 4256
1385: .%T "Generic Message Exchange Authentication for the Secure Shell Protocol (SSH)"
1386: .%D 2006
1387: .Re
1388: .Rs
1389: .%R RFC 4335
1390: .%T "The Secure Shell (SSH) Session Channel Break Extension"
1391: .%D 2006
1392: .Re
1393: .Rs
1394: .%R RFC 4344
1395: .%T "The Secure Shell (SSH) Transport Layer Encryption Modes"
1396: .%D 2006
1397: .Re
1398: .Rs
1399: .%R RFC 4345
1400: .%T "Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol"
1.258 djm 1401: .%D 2006
1402: .Re
1403: .Rs
1404: .%R RFC 4419
1405: .%T "Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol"
1.256 jmc 1406: .%D 2006
1.106 markus 1407: .Re
1.173 jmc 1408: .Sh AUTHORS
1409: OpenSSH is a derivative of the original and free
1410: ssh 1.2.12 release by Tatu Ylonen.
1411: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1412: Theo de Raadt and Dug Song
1413: removed many bugs, re-added newer features and
1414: created OpenSSH.
1415: Markus Friedl contributed the support for SSH
1416: protocol versions 1.5 and 2.0.