Annotation of src/usr.bin/ssh/ssh.1, Revision 1.266
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: .\"
1.266 ! markus 37: .\" $OpenBSD: ssh.1,v 1.265 2006/10/28 18:08:10 otto 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
1.263 markus 452: .It ExitOnForwardFailure
1.218 jmc 453: .It ForwardAgent
454: .It ForwardX11
455: .It ForwardX11Trusted
456: .It GatewayPorts
457: .It GlobalKnownHostsFile
458: .It GSSAPIAuthentication
459: .It GSSAPIDelegateCredentials
460: .It HashKnownHosts
461: .It Host
462: .It HostbasedAuthentication
463: .It HostKeyAlgorithms
464: .It HostKeyAlias
465: .It HostName
466: .It IdentityFile
467: .It IdentitiesOnly
468: .It KbdInteractiveDevices
469: .It LocalCommand
470: .It LocalForward
471: .It LogLevel
472: .It MACs
473: .It NoHostAuthenticationForLocalhost
474: .It NumberOfPasswordPrompts
475: .It PasswordAuthentication
476: .It PermitLocalCommand
477: .It Port
478: .It PreferredAuthentications
479: .It Protocol
480: .It ProxyCommand
481: .It PubkeyAuthentication
1.251 dtucker 482: .It RekeyLimit
1.218 jmc 483: .It RemoteForward
484: .It RhostsRSAAuthentication
485: .It RSAAuthentication
486: .It SendEnv
487: .It ServerAliveInterval
488: .It ServerAliveCountMax
489: .It SmartcardDevice
490: .It StrictHostKeyChecking
491: .It TCPKeepAlive
492: .It Tunnel
493: .It TunnelDevice
494: .It UsePrivilegedPort
495: .It User
496: .It UserKnownHostsFile
497: .It VerifyHostKeyDNS
498: .It XAuthLocation
499: .El
500: .It Fl p Ar port
501: Port to connect to on the remote host.
502: This can be specified on a
503: per-host basis in the configuration file.
504: .It Fl q
505: Quiet mode.
506: Causes all warning and diagnostic messages to be suppressed.
507: .It Fl R Xo
508: .Sm off
509: .Oo Ar bind_address : Oc
510: .Ar port : host : hostport
511: .Sm on
512: .Xc
513: Specifies that the given port on the remote (server) host is to be
514: forwarded to the given host and port on the local side.
515: This works by allocating a socket to listen to
516: .Ar port
517: on the remote side, and whenever a connection is made to this port, the
518: connection is forwarded over the secure channel, and a connection is
519: made to
520: .Ar host
521: port
522: .Ar hostport
523: from the local machine.
1.2 deraadt 524: .Pp
1.218 jmc 525: Port forwardings can also be specified in the configuration file.
526: Privileged ports can be forwarded only when
527: logging in as root on the remote machine.
528: IPv6 addresses can be specified by enclosing the address in square braces or
529: using an alternative syntax:
530: .Sm off
531: .Xo
532: .Op Ar bind_address No /
533: .Ar host No / Ar port No /
534: .Ar hostport
535: .Xc .
536: .Sm on
1.194 jakob 537: .Pp
1.218 jmc 538: By default, the listening socket on the server will be bound to the loopback
539: interface only.
540: This may be overriden by specifying a
541: .Ar bind_address .
542: An empty
543: .Ar bind_address ,
544: or the address
545: .Ql * ,
546: indicates that the remote socket should listen on all interfaces.
547: Specifying a remote
548: .Ar bind_address
549: will only succeed if the server's
550: .Cm GatewayPorts
551: option is enabled (see
552: .Xr sshd_config 5 ) .
553: .It Fl S Ar ctl_path
554: Specifies the location of a control socket for connection sharing.
555: Refer to the description of
556: .Cm ControlPath
557: and
558: .Cm ControlMaster
559: in
560: .Xr ssh_config 5
561: for details.
562: .It Fl s
563: May be used to request invocation of a subsystem on the remote system.
564: Subsystems are a feature of the SSH2 protocol which facilitate the use
565: of SSH as a secure transport for other applications (eg.\&
566: .Xr sftp 1 ) .
567: The subsystem is specified as the remote command.
568: .It Fl T
569: Disable pseudo-tty allocation.
570: .It Fl t
571: Force pseudo-tty allocation.
572: This can be used to execute arbitrary
573: screen-based programs on a remote machine, which can be very useful,
1.257 jmc 574: e.g. when implementing menu services.
1.218 jmc 575: Multiple
576: .Fl t
577: options force tty allocation, even if
1.194 jakob 578: .Nm
1.218 jmc 579: has no local tty.
580: .It Fl V
581: Display the version number and exit.
582: .It Fl v
583: Verbose mode.
584: Causes
1.176 jmc 585: .Nm
1.218 jmc 586: to print debugging messages about its progress.
587: This is helpful in
588: debugging connection, authentication, and configuration problems.
589: Multiple
590: .Fl v
591: options increase the verbosity.
592: The maximum is 3.
1.261 stevesk 593: .It Fl w Xo
594: .Ar local_tun Ns Op : Ns Ar remote_tun
595: .Xc
596: Requests
597: tunnel
598: device forwarding with the specified
1.218 jmc 599: .Xr tun 4
1.261 stevesk 600: devices between the client
601: .Pq Ar local_tun
602: and the server
603: .Pq Ar remote_tun .
604: .Pp
1.228 jmc 605: The devices may be specified by numerical ID or the keyword
606: .Dq any ,
607: which uses the next available tunnel device.
1.261 stevesk 608: If
609: .Ar remote_tun
610: is not specified, it defaults to
611: .Dq any .
1.228 jmc 612: See also the
1.218 jmc 613: .Cm Tunnel
1.261 stevesk 614: and
615: .Cm TunnelDevice
616: directives in
1.218 jmc 617: .Xr ssh_config 5 .
1.261 stevesk 618: If the
619: .Cm Tunnel
620: directive is unset, it is set to the default tunnel mode, which is
621: .Dq point-to-point .
1.218 jmc 622: .It Fl X
623: Enables X11 forwarding.
1.54 markus 624: This can also be specified on a per-host basis in a configuration file.
1.165 stevesk 625: .Pp
1.218 jmc 626: X11 forwarding should be enabled with caution.
1.168 jmc 627: Users with the ability to bypass file permissions on the remote host
1.218 jmc 628: (for the user's X authorization database)
629: can access the local X11 display through the forwarded connection.
630: An attacker may then be able to perform activities such as keystroke monitoring.
631: .Pp
632: For this reason, X11 forwarding is subjected to X11 SECURITY extension
633: restrictions by default.
634: Please refer to the
635: .Nm
636: .Fl Y
637: option and the
638: .Cm ForwardX11Trusted
639: directive in
640: .Xr ssh_config 5
641: for more information.
642: .It Fl x
643: Disables X11 forwarding.
644: .It Fl Y
645: Enables trusted X11 forwarding.
646: Trusted X11 forwardings are not subjected to the X11 SECURITY extension
647: controls.
648: .El
1.224 jmc 649: .Pp
650: .Nm
651: may additionally obtain configuration data from
652: a per-user configuration file and a system-wide configuration file.
653: The file format and configuration options are described in
654: .Xr ssh_config 5 .
655: .Pp
656: .Nm
657: exits with the exit status of the remote command or with 255
658: if an error occurred.
1.222 jmc 659: .Sh AUTHENTICATION
1.249 jmc 660: The OpenSSH SSH client supports SSH protocols 1 and 2.
1.222 jmc 661: Protocol 2 is the default, with
662: .Nm
663: falling back to protocol 1 if it detects protocol 2 is unsupported.
664: These settings may be altered using the
665: .Cm Protocol
666: option in
667: .Xr ssh_config 5 ,
668: or enforced using the
669: .Fl 1
670: and
671: .Fl 2
672: options (see above).
673: Both protocols support similar authentication methods,
674: but protocol 2 is preferred since
675: it provides additional mechanisms for confidentiality
676: (the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour)
677: and integrity (hmac-md5, hmac-sha1, hmac-ripemd160).
678: Protocol 1 lacks a strong mechanism for ensuring the
679: integrity of the connection.
680: .Pp
681: The methods available for authentication are:
1.260 jmc 682: GSSAPI-based authentication,
1.222 jmc 683: host-based authentication,
684: public key authentication,
685: challenge-response authentication,
686: and password authentication.
687: Authentication methods are tried in the order specified above,
688: though protocol 2 has a configuration option to change the default order:
689: .Cm PreferredAuthentications .
690: .Pp
691: Host-based authentication works as follows:
1.218 jmc 692: If the machine the user logs in from is listed in
693: .Pa /etc/hosts.equiv
694: or
695: .Pa /etc/shosts.equiv
696: on the remote machine, and the user names are
697: the same on both sides, or if the files
698: .Pa ~/.rhosts
699: or
700: .Pa ~/.shosts
701: exist in the user's home directory on the
702: remote machine and contain a line containing the name of the client
703: machine and the name of the user on that machine, the user is
1.222 jmc 704: considered for login.
705: Additionally, the server
706: .Em must
707: be able to verify the client's
708: host key (see the description of
1.218 jmc 709: .Pa /etc/ssh/ssh_known_hosts
1.189 dtucker 710: and
1.222 jmc 711: .Pa ~/.ssh/known_hosts ,
712: below)
713: for login to be permitted.
1.218 jmc 714: This authentication method closes security holes due to IP
1.222 jmc 715: spoofing, DNS spoofing, and routing spoofing.
1.218 jmc 716: [Note to the administrator:
717: .Pa /etc/hosts.equiv ,
718: .Pa ~/.rhosts ,
719: and the rlogin/rsh protocol in general, are inherently insecure and should be
720: disabled if security is desired.]
1.189 dtucker 721: .Pp
1.222 jmc 722: Public key authentication works as follows:
723: The scheme is based on public-key cryptography,
724: using cryptosystems
725: where encryption and decryption are done using separate keys,
726: and it is unfeasible to derive the decryption key from the encryption key.
1.218 jmc 727: The idea is that each user creates a public/private
728: key pair for authentication purposes.
729: The server knows the public key, and only the user knows the private key.
1.222 jmc 730: .Nm
731: implements public key authentication protocol automatically,
732: using either the RSA or DSA algorithms.
733: Protocol 1 is restricted to using only RSA keys,
734: but protocol 2 may use either.
735: The
736: .Sx HISTORY
737: section of
738: .Xr ssl 8
739: contains a brief discussion of the two algorithms.
1.210 djm 740: .Pp
1.218 jmc 741: The file
742: .Pa ~/.ssh/authorized_keys
743: lists the public keys that are permitted for logging in.
744: When the user logs in, the
1.2 deraadt 745: .Nm
1.218 jmc 746: program tells the server which key pair it would like to use for
747: authentication.
1.222 jmc 748: The client proves that it has access to the private key
749: and the server checks that the corresponding public key
750: is authorized to accept the account.
1.218 jmc 751: .Pp
1.222 jmc 752: The user creates his/her key pair by running
1.218 jmc 753: .Xr ssh-keygen 1 .
754: This stores the private key in
1.207 djm 755: .Pa ~/.ssh/identity
1.222 jmc 756: (protocol 1),
757: .Pa ~/.ssh/id_dsa
758: (protocol 2 DSA),
759: or
760: .Pa ~/.ssh/id_rsa
761: (protocol 2 RSA)
1.218 jmc 762: and stores the public key in
763: .Pa ~/.ssh/identity.pub
1.222 jmc 764: (protocol 1),
765: .Pa ~/.ssh/id_dsa.pub
766: (protocol 2 DSA),
767: or
768: .Pa ~/.ssh/id_rsa.pub
769: (protocol 2 RSA)
1.218 jmc 770: in the user's home directory.
1.222 jmc 771: The user should then copy the public key
1.218 jmc 772: to
773: .Pa ~/.ssh/authorized_keys
1.222 jmc 774: in his/her home directory on the remote machine.
775: The
1.218 jmc 776: .Pa authorized_keys
777: file corresponds to the conventional
778: .Pa ~/.rhosts
779: file, and has one key
1.222 jmc 780: per line, though the lines can be very long.
1.218 jmc 781: After this, the user can log in without giving the password.
782: .Pp
1.222 jmc 783: The most convenient way to use public key authentication may be with an
1.218 jmc 784: authentication agent.
785: See
786: .Xr ssh-agent 1
787: for more information.
788: .Pp
1.222 jmc 789: Challenge-response authentication works as follows:
790: The server sends an arbitrary
791: .Qq challenge
792: text, and prompts for a response.
793: Protocol 2 allows multiple challenges and responses;
794: protocol 1 is restricted to just one challenge/response.
795: Examples of challenge-response authentication include
796: BSD Authentication (see
797: .Xr login.conf 5 )
798: and PAM (some non-OpenBSD systems).
799: .Pp
800: Finally, if other authentication methods fail,
1.218 jmc 801: .Nm
802: prompts the user for a password.
803: The password is sent to the remote
804: host for checking; however, since all communications are encrypted,
805: the password cannot be seen by someone listening on the network.
1.232 jmc 806: .Pp
807: .Nm
808: automatically maintains and checks a database containing
809: identification for all hosts it has ever been used with.
810: Host keys are stored in
811: .Pa ~/.ssh/known_hosts
812: in the user's home directory.
813: Additionally, the file
814: .Pa /etc/ssh/ssh_known_hosts
815: is automatically checked for known hosts.
816: Any new hosts are automatically added to the user's file.
817: If a host's identification ever changes,
818: .Nm
819: warns about this and disables password authentication to prevent
820: server spoofing or man-in-the-middle attacks,
821: which could otherwise be used to circumvent the encryption.
822: The
823: .Cm StrictHostKeyChecking
824: option can be used to control logins to machines whose
825: host key is not known or has changed.
826: .Pp
1.218 jmc 827: When the user's identity has been accepted by the server, the server
828: either executes the given command, or logs into the machine and gives
829: the user a normal shell on the remote machine.
830: All communication with
831: the remote command or shell will be automatically encrypted.
832: .Pp
833: If a pseudo-terminal has been allocated (normal login session), the
834: user may use the escape characters noted below.
835: .Pp
836: If no pseudo-tty has been allocated,
837: the session is transparent and can be used to reliably transfer binary data.
838: On most systems, setting the escape character to
839: .Dq none
840: will also make the session transparent even if a tty is used.
841: .Pp
842: The session terminates when the command or shell on the remote
1.247 jmc 843: machine exits and all X11 and TCP connections have been closed.
1.223 jmc 844: .Sh ESCAPE CHARACTERS
1.218 jmc 845: When a pseudo-terminal has been requested,
1.2 deraadt 846: .Nm
1.218 jmc 847: supports a number of functions through the use of an escape character.
848: .Pp
849: A single tilde character can be sent as
850: .Ic ~~
851: or by following the tilde by a character other than those described below.
852: The escape character must always follow a newline to be interpreted as
853: special.
854: The escape character can be changed in configuration files using the
855: .Cm EscapeChar
856: configuration directive or on the command line by the
857: .Fl e
858: option.
859: .Pp
860: The supported escapes (assuming the default
861: .Ql ~ )
862: are:
863: .Bl -tag -width Ds
864: .It Cm ~.
865: Disconnect.
866: .It Cm ~^Z
867: Background
1.234 jmc 868: .Nm .
1.218 jmc 869: .It Cm ~#
870: List forwarded connections.
871: .It Cm ~&
872: Background
1.2 deraadt 873: .Nm
1.218 jmc 874: at logout when waiting for forwarded connection / X11 sessions to terminate.
875: .It Cm ~?
876: Display a list of escape characters.
877: .It Cm ~B
878: Send a BREAK to the remote system
879: (only useful for SSH protocol version 2 and if the peer supports it).
880: .It Cm ~C
881: Open command line.
882: Currently this allows the addition of port forwardings using the
883: .Fl L
884: and
885: .Fl R
1.225 jmc 886: options (see above).
1.218 jmc 887: It also allows the cancellation of existing remote port-forwardings
888: using
1.262 stevesk 889: .Sm off
890: .Fl KR Oo Ar bind_address : Oc Ar port .
891: .Sm on
1.218 jmc 892: .Ic !\& Ns Ar command
893: allows the user to execute a local command if the
894: .Ic PermitLocalCommand
895: option is enabled in
1.176 jmc 896: .Xr ssh_config 5 .
1.218 jmc 897: Basic help is available, using the
898: .Fl h
899: option.
900: .It Cm ~R
901: Request rekeying of the connection
902: (only useful for SSH protocol version 2 and if the peer supports it).
1.176 jmc 903: .El
1.246 jmc 904: .Sh TCP FORWARDING
905: Forwarding of arbitrary TCP connections over the secure channel can
906: be specified either on the command line or in a configuration file.
907: One possible application of TCP forwarding is a secure connection to a
908: mail server; another is going through firewalls.
909: .Pp
910: In the example below, we look at encrypting communication between
911: an IRC client and server, even though the IRC server does not directly
912: support encrypted communications.
913: This works as follows:
914: the user connects to the remote host using
915: .Nm ,
916: specifying a port to be used to forward connections
917: to the remote server.
918: After that it is possible to start the service which is to be encrypted
919: on the client machine,
920: connecting to the same local port,
921: and
922: .Nm
923: will encrypt and forward the connection.
924: .Pp
925: The following example tunnels an IRC session from client machine
926: .Dq 127.0.0.1
927: (localhost)
928: to remote server
929: .Dq server.example.com :
930: .Bd -literal -offset 4n
931: $ ssh -f -L 1234:localhost:6667 server.example.com sleep 10
932: $ irc -c '#users' -p 1234 pinky 127.0.0.1
933: .Ed
934: .Pp
935: This tunnels a connection to IRC server
936: .Dq server.example.com ,
937: joining channel
938: .Dq #users ,
939: nickname
940: .Dq pinky ,
941: using port 1234.
942: It doesn't matter which port is used,
943: as long as it's greater than 1023
944: (remember, only root can open sockets on privileged ports)
945: and doesn't conflict with any ports already in use.
946: The connection is forwarded to port 6667 on the remote server,
947: since that's the standard port for IRC services.
948: .Pp
949: The
950: .Fl f
951: option backgrounds
952: .Nm
953: and the remote command
954: .Dq sleep 10
955: is specified to allow an amount of time
956: (10 seconds, in the example)
957: to start the service which is to be tunnelled.
958: If no connections are made within the time specified,
959: .Nm
960: will exit.
961: .Sh X11 FORWARDING
1.218 jmc 962: If the
963: .Cm ForwardX11
964: variable is set to
965: .Dq yes
966: (or see the description of the
1.227 jmc 967: .Fl X ,
968: .Fl x ,
1.218 jmc 969: and
1.227 jmc 970: .Fl Y
1.226 jmc 971: options above)
1.218 jmc 972: and the user is using X11 (the
973: .Ev DISPLAY
974: environment variable is set), the connection to the X11 display is
975: automatically forwarded to the remote side in such a way that any X11
976: programs started from the shell (or command) will go through the
977: encrypted channel, and the connection to the real X server will be made
1.176 jmc 978: from the local machine.
1.218 jmc 979: The user should not manually set
980: .Ev DISPLAY .
981: Forwarding of X11 connections can be
982: configured on the command line or in configuration files.
983: .Pp
984: The
985: .Ev DISPLAY
986: value set by
987: .Nm
988: will point to the server machine, but with a display number greater than zero.
989: This is normal, and happens because
990: .Nm
991: creates a
992: .Dq proxy
993: X server on the server machine for forwarding the
994: connections over the encrypted channel.
1.200 djm 995: .Pp
1.218 jmc 996: .Nm
997: will also automatically set up Xauthority data on the server machine.
998: For this purpose, it will generate a random authorization cookie,
999: store it in Xauthority on the server, and verify that any forwarded
1000: connections carry this cookie and replace it by the real cookie when
1001: the connection is opened.
1002: The real authentication cookie is never
1003: sent to the server machine (and no cookies are sent in the plain).
1.200 djm 1004: .Pp
1.218 jmc 1005: If the
1006: .Cm ForwardAgent
1007: variable is set to
1008: .Dq yes
1009: (or see the description of the
1010: .Fl A
1.191 djm 1011: and
1.218 jmc 1012: .Fl a
1.226 jmc 1013: options above) and
1.218 jmc 1014: the user is using an authentication agent, the connection to the agent
1015: is automatically forwarded to the remote side.
1.252 jmc 1016: .Sh VERIFYING HOST KEYS
1017: When connecting to a server for the first time,
1018: a fingerprint of the server's public key is presented to the user
1019: (unless the option
1020: .Cm StrictHostKeyChecking
1021: has been disabled).
1022: Fingerprints can be determined using
1023: .Xr ssh-keygen 1 :
1024: .Pp
1025: .Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key
1026: .Pp
1027: If the fingerprint is already known,
1028: it can be matched and verified,
1029: and the key can be accepted.
1030: If the fingerprint is unknown,
1031: an alternative method of verification is available:
1032: SSH fingerprints verified by DNS.
1033: An additional resource record (RR),
1034: SSHFP,
1035: is added to a zonefile
1036: and the connecting client is able to match the fingerprint
1037: with that of the key presented.
1038: .Pp
1039: In this example, we are connecting a client to a server,
1040: .Dq host.example.com .
1041: The SSHFP resource records should first be added to the zonefile for
1042: host.example.com:
1043: .Bd -literal -offset indent
1.259 jakob 1044: $ ssh-keygen -r host.example.com.
1.252 jmc 1045: .Ed
1046: .Pp
1047: The output lines will have to be added to the zonefile.
1048: To check that the zone is answering fingerprint queries:
1049: .Pp
1050: .Dl $ dig -t SSHFP host.example.com
1051: .Pp
1052: Finally the client connects:
1053: .Bd -literal -offset indent
1054: $ ssh -o "VerifyHostKeyDNS ask" host.example.com
1055: [...]
1056: Matching host key fingerprint found in DNS.
1057: Are you sure you want to continue connecting (yes/no)?
1058: .Ed
1059: .Pp
1060: See the
1061: .Cm VerifyHostKeyDNS
1062: option in
1063: .Xr ssh_config 5
1064: for more information.
1.250 jmc 1065: .Sh SSH-BASED VIRTUAL PRIVATE NETWORKS
1066: .Nm
1067: contains support for Virtual Private Network (VPN) tunnelling
1068: using the
1069: .Xr tun 4
1070: network pseudo-device,
1071: allowing two networks to be joined securely.
1072: The
1073: .Xr sshd_config 5
1074: configuration option
1075: .Cm PermitTunnel
1076: controls whether the server supports this,
1077: and at what level (layer 2 or 3 traffic).
1078: .Pp
1079: The following example would connect client network 10.0.50.0/24
1.265 otto 1080: with remote network 10.0.99.0/24 using a point-to-point connection
1081: from 10.1.1.1 to 10.1.1.2,
1082: provided that the SSH server running on the gateway to the remote network,
1083: at 192.168.1.15, allows it.
1084: .Pp
1085: On the client:
1.250 jmc 1086: .Bd -literal -offset indent
1087: # ssh -f -w 0:1 192.168.1.15 true
1.265 otto 1088: # ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252
1089: # route add 10.0.99.0/24 10.1.1.2
1090: .Ed
1091: .Pp
1092: On the server:
1093: .Bd -literal -offset indent
1094: # ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252
1095: # route add 10.0.50.0/24 10.1.1.1
1.250 jmc 1096: .Ed
1097: .Pp
1098: Client access may be more finely tuned via the
1099: .Pa /root/.ssh/authorized_keys
1100: file (see below) and the
1101: .Cm PermitRootLogin
1102: server option.
1.255 jmc 1103: The following entry would permit connections on
1.250 jmc 1104: .Xr tun 4
1.255 jmc 1105: device 1 from user
1.250 jmc 1106: .Dq jane
1.255 jmc 1107: and on tun device 2 from user
1.250 jmc 1108: .Dq john ,
1109: if
1110: .Cm PermitRootLogin
1111: is set to
1112: .Dq forced-commands-only :
1113: .Bd -literal -offset 2n
1114: tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane
1.254 msf 1115: tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john
1.250 jmc 1116: .Ed
1117: .Pp
1.264 ray 1118: Since an SSH-based setup entails a fair amount of overhead,
1.250 jmc 1119: it may be more suited to temporary setups,
1120: such as for wireless VPNs.
1121: More permanent VPNs are better provided by tools such as
1122: .Xr ipsecctl 8
1123: and
1124: .Xr isakmpd 8 .
1.2 deraadt 1125: .Sh ENVIRONMENT
1126: .Nm
1.1 deraadt 1127: will normally set the following environment variables:
1.237 jmc 1128: .Bl -tag -width "SSH_ORIGINAL_COMMAND"
1.2 deraadt 1129: .It Ev DISPLAY
1130: The
1131: .Ev DISPLAY
1.40 aaron 1132: variable indicates the location of the X11 server.
1.44 aaron 1133: It is automatically set by
1.2 deraadt 1134: .Nm
1135: to point to a value of the form
1.233 jmc 1136: .Dq hostname:n ,
1137: where
1138: .Dq hostname
1139: indicates the host where the shell runs, and
1140: .Sq n
1141: is an integer \*(Ge 1.
1.40 aaron 1142: .Nm
1143: uses this special value to forward X11 connections over the secure
1144: channel.
1.107 markus 1145: The user should normally not set
1146: .Ev DISPLAY
1147: explicitly, as that
1.1 deraadt 1148: will render the X11 connection insecure (and will require the user to
1149: manually copy any required authorization cookies).
1.2 deraadt 1150: .It Ev HOME
1.1 deraadt 1151: Set to the path of the user's home directory.
1.2 deraadt 1152: .It Ev LOGNAME
1153: Synonym for
1.12 aaron 1154: .Ev USER ;
1155: set for compatibility with systems that use this variable.
1.2 deraadt 1156: .It Ev MAIL
1.129 stevesk 1157: Set to the path of the user's mailbox.
1.40 aaron 1158: .It Ev PATH
1.2 deraadt 1159: Set to the default
1160: .Ev PATH ,
1161: as specified when compiling
1.234 jmc 1162: .Nm .
1.118 markus 1163: .It Ev SSH_ASKPASS
1164: If
1165: .Nm
1166: needs a passphrase, it will read the passphrase from the current
1167: terminal if it was run from a terminal.
1168: If
1169: .Nm
1170: does not have a terminal associated with it but
1171: .Ev DISPLAY
1172: and
1173: .Ev SSH_ASKPASS
1174: are set, it will execute the program specified by
1175: .Ev SSH_ASKPASS
1176: and open an X11 window to read the passphrase.
1177: This is particularly useful when calling
1178: .Nm
1179: from a
1.196 jmc 1180: .Pa .xsession
1.118 markus 1181: or related script.
1182: (Note that on some machines it
1183: may be necessary to redirect the input from
1184: .Pa /dev/null
1185: to make this work.)
1.18 markus 1186: .It Ev SSH_AUTH_SOCK
1.233 jmc 1187: Identifies the path of a
1188: .Ux Ns -domain
1189: socket used to communicate with the agent.
1.166 stevesk 1190: .It Ev SSH_CONNECTION
1191: Identifies the client and server ends of the connection.
1.40 aaron 1192: The variable contains
1.233 jmc 1193: four space-separated values: client IP address, client port number,
1194: server IP address, and server port number.
1.73 markus 1195: .It Ev SSH_ORIGINAL_COMMAND
1.233 jmc 1196: This variable contains the original command line if a forced command
1.73 markus 1197: is executed.
1198: It can be used to extract the original arguments.
1.2 deraadt 1199: .It Ev SSH_TTY
1.1 deraadt 1200: This is set to the name of the tty (path to the device) associated
1.40 aaron 1201: with the current shell or command.
1202: If the current session has no tty,
1.1 deraadt 1203: this variable is not set.
1.2 deraadt 1204: .It Ev TZ
1.214 jmc 1205: This variable is set to indicate the present time zone if it
1.257 jmc 1206: was set when the daemon was started (i.e. the daemon passes the value
1.1 deraadt 1207: on to new connections).
1.2 deraadt 1208: .It Ev USER
1.1 deraadt 1209: Set to the name of the user logging in.
1.2 deraadt 1210: .El
1211: .Pp
1.44 aaron 1212: Additionally,
1.2 deraadt 1213: .Nm
1.44 aaron 1214: reads
1.207 djm 1215: .Pa ~/.ssh/environment ,
1.2 deraadt 1216: and adds lines of the format
1217: .Dq VARNAME=value
1.233 jmc 1218: to the environment if the file exists and users are allowed to
1.161 marc 1219: change their environment.
1.176 jmc 1220: For more information, see the
1.161 marc 1221: .Cm PermitUserEnvironment
1.162 stevesk 1222: option in
1.161 marc 1223: .Xr sshd_config 5 .
1.2 deraadt 1224: .Sh FILES
1.236 jmc 1225: .Bl -tag -width Ds -compact
1226: .It ~/.rhosts
1.240 jmc 1227: This file is used for host-based authentication (see above).
1.92 markus 1228: On some machines this file may need to be
1.240 jmc 1229: world-readable if the user's home directory is on an NFS partition,
1.1 deraadt 1230: because
1.2 deraadt 1231: .Xr sshd 8
1.40 aaron 1232: reads it as root.
1233: Additionally, this file must be owned by the user,
1234: and must not have write permissions for anyone else.
1235: The recommended
1.1 deraadt 1236: permission for most machines is read/write for the user, and not
1237: accessible by others.
1.2 deraadt 1238: .Pp
1.236 jmc 1239: .It ~/.shosts
1.240 jmc 1240: This file is used in exactly the same way as
1241: .Pa .rhosts ,
1242: but allows host-based authentication without permitting login with
1243: rlogin/rsh.
1.236 jmc 1244: .Pp
1.238 jmc 1245: .It ~/.ssh/authorized_keys
1246: Lists the public keys (RSA/DSA) that can be used for logging in as this user.
1247: The format of this file is described in the
1248: .Xr sshd 8
1249: manual page.
1250: This file is not highly sensitive, but the recommended
1251: permissions are read/write for the user, and not accessible by others.
1252: .Pp
1253: .It ~/.ssh/config
1254: This is the per-user configuration file.
1255: The file format and configuration options are described in
1256: .Xr ssh_config 5 .
1257: Because of the potential for abuse, this file must have strict permissions:
1258: read/write for the user, and not accessible by others.
1259: .Pp
1260: .It ~/.ssh/environment
1.239 jmc 1261: Contains additional definitions for environment variables; see
1262: .Sx ENVIRONMENT ,
1.238 jmc 1263: above.
1264: .Pp
1265: .It ~/.ssh/identity
1266: .It ~/.ssh/id_dsa
1267: .It ~/.ssh/id_rsa
1268: Contains the private key for authentication.
1269: These files
1270: contain sensitive data and should be readable by the user but not
1271: accessible by others (read/write/execute).
1272: .Nm
1273: will simply ignore a private key file if it is accessible by others.
1274: It is possible to specify a passphrase when
1275: generating the key which will be used to encrypt the
1276: sensitive part of this file using 3DES.
1277: .Pp
1278: .It ~/.ssh/identity.pub
1279: .It ~/.ssh/id_dsa.pub
1280: .It ~/.ssh/id_rsa.pub
1281: Contains the public key for authentication.
1282: These files are not
1283: sensitive and can (but need not) be readable by anyone.
1284: .Pp
1285: .It ~/.ssh/known_hosts
1.244 jmc 1286: Contains a list of host keys for all hosts the user has logged into
1287: that are not already in the systemwide list of known host keys.
1.238 jmc 1288: See
1.244 jmc 1289: .Xr sshd 8
1290: for further details of the format of this file.
1.238 jmc 1291: .Pp
1292: .It ~/.ssh/rc
1293: Commands in this file are executed by
1294: .Nm
1.245 jmc 1295: when the user logs in, just before the user's shell (or command) is
1.238 jmc 1296: started.
1297: See the
1298: .Xr sshd 8
1299: manual page for more information.
1300: .Pp
1.236 jmc 1301: .It /etc/hosts.equiv
1.240 jmc 1302: This file is for host-based authentication (see above).
1303: It should only be writable by root.
1.236 jmc 1304: .Pp
1305: .It /etc/shosts.equiv
1.240 jmc 1306: This file is used in exactly the same way as
1307: .Pa hosts.equiv ,
1308: but allows host-based authentication without permitting login with
1309: rlogin/rsh.
1.236 jmc 1310: .Pp
1.238 jmc 1311: .It Pa /etc/ssh/ssh_config
1312: Systemwide configuration file.
1313: The file format and configuration options are described in
1314: .Xr ssh_config 5 .
1315: .Pp
1316: .It /etc/ssh/ssh_host_key
1317: .It /etc/ssh/ssh_host_dsa_key
1318: .It /etc/ssh/ssh_host_rsa_key
1319: These three files contain the private parts of the host keys
1.245 jmc 1320: and are used for host-based authentication.
1321: If protocol version 1 is used,
1.238 jmc 1322: .Nm
1323: must be setuid root, since the host key is readable only by root.
1324: For protocol version 2,
1325: .Nm
1326: uses
1327: .Xr ssh-keysign 8
1.245 jmc 1328: to access the host keys,
1329: eliminating the requirement that
1.238 jmc 1330: .Nm
1.245 jmc 1331: be setuid root when host-based authentication is used.
1.238 jmc 1332: By default
1.2 deraadt 1333: .Nm
1.238 jmc 1334: is not setuid root.
1335: .Pp
1336: .It /etc/ssh/ssh_known_hosts
1337: Systemwide list of known host keys.
1338: This file should be prepared by the
1339: system administrator to contain the public host keys of all machines in the
1340: organization.
1.244 jmc 1341: It should be world-readable.
1342: See
1.238 jmc 1343: .Xr sshd 8
1.244 jmc 1344: for further details of the format of this file.
1.236 jmc 1345: .Pp
1.238 jmc 1346: .It /etc/ssh/sshrc
1.1 deraadt 1347: Commands in this file are executed by
1.2 deraadt 1348: .Nm
1.245 jmc 1349: when the user logs in, just before the user's shell (or command) is started.
1.44 aaron 1350: See the
1.2 deraadt 1351: .Xr sshd 8
1.1 deraadt 1352: manual page for more information.
1.58 itojun 1353: .El
1.2 deraadt 1354: .Sh SEE ALSO
1355: .Xr scp 1 ,
1.83 djm 1356: .Xr sftp 1 ,
1.2 deraadt 1357: .Xr ssh-add 1 ,
1358: .Xr ssh-agent 1 ,
1359: .Xr ssh-keygen 1 ,
1.242 jmc 1360: .Xr ssh-keyscan 1 ,
1.250 jmc 1361: .Xr tun 4 ,
1.176 jmc 1362: .Xr hosts.equiv 5 ,
1.159 stevesk 1363: .Xr ssh_config 5 ,
1.160 naddy 1364: .Xr ssh-keysign 8 ,
1.87 itojun 1365: .Xr sshd 8
1.106 markus 1366: .Rs
1.256 jmc 1367: .%R RFC 4250
1368: .%T "The Secure Shell (SSH) Protocol Assigned Numbers"
1369: .%D 2006
1370: .Re
1371: .Rs
1372: .%R RFC 4251
1373: .%T "The Secure Shell (SSH) Protocol Architecture"
1374: .%D 2006
1375: .Re
1376: .Rs
1377: .%R RFC 4252
1378: .%T "The Secure Shell (SSH) Authentication Protocol"
1379: .%D 2006
1380: .Re
1381: .Rs
1382: .%R RFC 4253
1383: .%T "The Secure Shell (SSH) Transport Layer Protocol"
1384: .%D 2006
1385: .Re
1386: .Rs
1387: .%R RFC 4254
1388: .%T "The Secure Shell (SSH) Connection Protocol"
1389: .%D 2006
1390: .Re
1391: .Rs
1392: .%R RFC 4255
1393: .%T "Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints"
1394: .%D 2006
1395: .Re
1396: .Rs
1397: .%R RFC 4256
1398: .%T "Generic Message Exchange Authentication for the Secure Shell Protocol (SSH)"
1399: .%D 2006
1400: .Re
1401: .Rs
1402: .%R RFC 4335
1403: .%T "The Secure Shell (SSH) Session Channel Break Extension"
1404: .%D 2006
1405: .Re
1406: .Rs
1407: .%R RFC 4344
1408: .%T "The Secure Shell (SSH) Transport Layer Encryption Modes"
1409: .%D 2006
1410: .Re
1411: .Rs
1412: .%R RFC 4345
1413: .%T "Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol"
1.258 djm 1414: .%D 2006
1415: .Re
1416: .Rs
1417: .%R RFC 4419
1418: .%T "Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol"
1.266 ! markus 1419: .%D 2006
! 1420: .Re
! 1421: .Rs
! 1422: .%R RFC 4716
! 1423: .%T "The Secure Shell (SSH) Public Key File Format"
1.256 jmc 1424: .%D 2006
1.106 markus 1425: .Re
1.173 jmc 1426: .Sh AUTHORS
1427: OpenSSH is a derivative of the original and free
1428: ssh 1.2.12 release by Tatu Ylonen.
1429: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1430: Theo de Raadt and Dug Song
1431: removed many bugs, re-added newer features and
1432: created OpenSSH.
1433: Markus Friedl contributed the support for SSH
1434: protocol versions 1.5 and 2.0.
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