Annotation of src/usr.bin/ssh/ssh.1, Revision 1.270
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: .\"
1.270 ! jmc 37: .\" $OpenBSD: ssh.1,v 1.269 2007/06/12 11:15:17 djm Exp $
1.269 djm 38: .Dd $Mdocdate: June 7 2007 $
1.2 deraadt 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
1.270 ! jmc 46: .Op Fl 1246AaCfgKkMNnqsTtVvXxY
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).
1.269 djm 318: .It Fl K
319: Enables GSSAPI-based authentication and forwarding (delegation) of GSSAPI
320: credentials to the server.
1.218 jmc 321: .It Fl k
322: Disables forwarding (delegation) of GSSAPI credentials to the server.
323: .It Fl L Xo
324: .Sm off
325: .Oo Ar bind_address : Oc
326: .Ar port : host : hostport
327: .Sm on
328: .Xc
329: Specifies that the given port on the local (client) host is to be
330: forwarded to the given host and port on the remote side.
331: This works by allocating a socket to listen to
332: .Ar port
333: on the local side, optionally bound to the specified
334: .Ar bind_address .
335: Whenever a connection is made to this port, the
336: connection is forwarded over the secure channel, and a connection is
337: made to
338: .Ar host
339: port
340: .Ar hostport
341: from the remote machine.
342: Port forwardings can also be specified in the configuration file.
343: IPv6 addresses can be specified with an alternative syntax:
344: .Sm off
345: .Xo
346: .Op Ar bind_address No /
347: .Ar port No / Ar host No /
348: .Ar hostport
349: .Xc
350: .Sm on
351: or by enclosing the address in square brackets.
352: Only the superuser can forward privileged ports.
353: By default, the local port is bound in accordance with the
354: .Cm GatewayPorts
355: setting.
356: However, an explicit
357: .Ar bind_address
358: may be used to bind the connection to a specific address.
1.2 deraadt 359: The
1.218 jmc 360: .Ar bind_address
361: of
362: .Dq localhost
363: indicates that the listening port be bound for local use only, while an
364: empty address or
365: .Sq *
366: indicates that the port should be available from all interfaces.
367: .It Fl l Ar login_name
368: Specifies the user to log in as on the remote machine.
369: This also may be specified on a per-host basis in the configuration file.
370: .It Fl M
371: Places the
372: .Nm
373: client into
374: .Dq master
375: mode for connection sharing.
1.231 stevesk 376: Multiple
377: .Fl M
378: options places
379: .Nm
380: into
381: .Dq master
382: mode with confirmation required before slave connections are accepted.
1.218 jmc 383: Refer to the description of
384: .Cm ControlMaster
385: in
386: .Xr ssh_config 5
387: for details.
388: .It Fl m Ar mac_spec
389: Additionally, for protocol version 2 a comma-separated list of MAC
390: (message authentication code) algorithms can
391: be specified in order of preference.
392: See the
393: .Cm MACs
394: keyword for more information.
395: .It Fl N
396: Do not execute a remote command.
397: This is useful for just forwarding ports
398: (protocol version 2 only).
399: .It Fl n
400: Redirects stdin from
401: .Pa /dev/null
402: (actually, prevents reading from stdin).
403: This must be used when
1.2 deraadt 404: .Nm
1.218 jmc 405: is run in the background.
406: A common trick is to use this to run X11 programs on a remote machine.
407: For example,
408: .Ic ssh -n shadows.cs.hut.fi emacs &
409: will start an emacs on shadows.cs.hut.fi, and the X11
410: connection will be automatically forwarded over an encrypted channel.
411: The
1.2 deraadt 412: .Nm
1.218 jmc 413: program will be put in the background.
414: (This does not work if
1.2 deraadt 415: .Nm
1.218 jmc 416: needs to ask for a password or passphrase; see also the
417: .Fl f
418: option.)
419: .It Fl O Ar ctl_cmd
420: Control an active connection multiplexing master process.
421: When the
422: .Fl O
423: option is specified, the
424: .Ar ctl_cmd
425: argument is interpreted and passed to the master process.
426: Valid commands are:
427: .Dq check
428: (check that the master process is running) and
429: .Dq exit
430: (request the master to exit).
431: .It Fl o Ar option
432: Can be used to give options in the format used in the configuration file.
433: This is useful for specifying options for which there is no separate
434: command-line flag.
435: For full details of the options listed below, and their possible values, see
436: .Xr ssh_config 5 .
1.2 deraadt 437: .Pp
1.218 jmc 438: .Bl -tag -width Ds -offset indent -compact
439: .It AddressFamily
440: .It BatchMode
441: .It BindAddress
442: .It ChallengeResponseAuthentication
443: .It CheckHostIP
444: .It Cipher
445: .It Ciphers
446: .It ClearAllForwardings
447: .It Compression
448: .It CompressionLevel
449: .It ConnectionAttempts
450: .It ConnectTimeout
451: .It ControlMaster
452: .It ControlPath
453: .It DynamicForward
454: .It EscapeChar
1.263 markus 455: .It ExitOnForwardFailure
1.218 jmc 456: .It ForwardAgent
457: .It ForwardX11
458: .It ForwardX11Trusted
459: .It GatewayPorts
460: .It GlobalKnownHostsFile
461: .It GSSAPIAuthentication
462: .It GSSAPIDelegateCredentials
463: .It HashKnownHosts
464: .It Host
465: .It HostbasedAuthentication
466: .It HostKeyAlgorithms
467: .It HostKeyAlias
468: .It HostName
469: .It IdentityFile
470: .It IdentitiesOnly
471: .It KbdInteractiveDevices
472: .It LocalCommand
473: .It LocalForward
474: .It LogLevel
475: .It MACs
476: .It NoHostAuthenticationForLocalhost
477: .It NumberOfPasswordPrompts
478: .It PasswordAuthentication
479: .It PermitLocalCommand
480: .It Port
481: .It PreferredAuthentications
482: .It Protocol
483: .It ProxyCommand
484: .It PubkeyAuthentication
1.251 dtucker 485: .It RekeyLimit
1.218 jmc 486: .It RemoteForward
487: .It RhostsRSAAuthentication
488: .It RSAAuthentication
489: .It SendEnv
490: .It ServerAliveInterval
491: .It ServerAliveCountMax
492: .It SmartcardDevice
493: .It StrictHostKeyChecking
494: .It TCPKeepAlive
495: .It Tunnel
496: .It TunnelDevice
497: .It UsePrivilegedPort
498: .It User
499: .It UserKnownHostsFile
500: .It VerifyHostKeyDNS
501: .It XAuthLocation
502: .El
503: .It Fl p Ar port
504: Port to connect to on the remote host.
505: This can be specified on a
506: per-host basis in the configuration file.
507: .It Fl q
508: Quiet mode.
509: Causes all warning and diagnostic messages to be suppressed.
510: .It Fl R Xo
511: .Sm off
512: .Oo Ar bind_address : Oc
513: .Ar port : host : hostport
514: .Sm on
515: .Xc
516: Specifies that the given port on the remote (server) host is to be
517: forwarded to the given host and port on the local side.
518: This works by allocating a socket to listen to
519: .Ar port
520: on the remote side, and whenever a connection is made to this port, the
521: connection is forwarded over the secure channel, and a connection is
522: made to
523: .Ar host
524: port
525: .Ar hostport
526: from the local machine.
1.2 deraadt 527: .Pp
1.218 jmc 528: Port forwardings can also be specified in the configuration file.
529: Privileged ports can be forwarded only when
530: logging in as root on the remote machine.
531: IPv6 addresses can be specified by enclosing the address in square braces or
532: using an alternative syntax:
533: .Sm off
534: .Xo
535: .Op Ar bind_address No /
536: .Ar host No / Ar port No /
537: .Ar hostport
538: .Xc .
539: .Sm on
1.194 jakob 540: .Pp
1.218 jmc 541: By default, the listening socket on the server will be bound to the loopback
542: interface only.
543: This may be overriden by specifying a
544: .Ar bind_address .
545: An empty
546: .Ar bind_address ,
547: or the address
548: .Ql * ,
549: indicates that the remote socket should listen on all interfaces.
550: Specifying a remote
551: .Ar bind_address
552: will only succeed if the server's
553: .Cm GatewayPorts
554: option is enabled (see
555: .Xr sshd_config 5 ) .
556: .It Fl S Ar ctl_path
557: Specifies the location of a control socket for connection sharing.
558: Refer to the description of
559: .Cm ControlPath
560: and
561: .Cm ControlMaster
562: in
563: .Xr ssh_config 5
564: for details.
565: .It Fl s
566: May be used to request invocation of a subsystem on the remote system.
567: Subsystems are a feature of the SSH2 protocol which facilitate the use
568: of SSH as a secure transport for other applications (eg.\&
569: .Xr sftp 1 ) .
570: The subsystem is specified as the remote command.
571: .It Fl T
572: Disable pseudo-tty allocation.
573: .It Fl t
574: Force pseudo-tty allocation.
575: This can be used to execute arbitrary
576: screen-based programs on a remote machine, which can be very useful,
1.257 jmc 577: e.g. when implementing menu services.
1.218 jmc 578: Multiple
579: .Fl t
580: options force tty allocation, even if
1.194 jakob 581: .Nm
1.218 jmc 582: has no local tty.
583: .It Fl V
584: Display the version number and exit.
585: .It Fl v
586: Verbose mode.
587: Causes
1.176 jmc 588: .Nm
1.218 jmc 589: to print debugging messages about its progress.
590: This is helpful in
591: debugging connection, authentication, and configuration problems.
592: Multiple
593: .Fl v
594: options increase the verbosity.
595: The maximum is 3.
1.261 stevesk 596: .It Fl w Xo
597: .Ar local_tun Ns Op : Ns Ar remote_tun
598: .Xc
599: Requests
600: tunnel
601: device forwarding with the specified
1.218 jmc 602: .Xr tun 4
1.261 stevesk 603: devices between the client
604: .Pq Ar local_tun
605: and the server
606: .Pq Ar remote_tun .
607: .Pp
1.228 jmc 608: The devices may be specified by numerical ID or the keyword
609: .Dq any ,
610: which uses the next available tunnel device.
1.261 stevesk 611: If
612: .Ar remote_tun
613: is not specified, it defaults to
614: .Dq any .
1.228 jmc 615: See also the
1.218 jmc 616: .Cm Tunnel
1.261 stevesk 617: and
618: .Cm TunnelDevice
619: directives in
1.218 jmc 620: .Xr ssh_config 5 .
1.261 stevesk 621: If the
622: .Cm Tunnel
623: directive is unset, it is set to the default tunnel mode, which is
624: .Dq point-to-point .
1.218 jmc 625: .It Fl X
626: Enables X11 forwarding.
1.54 markus 627: This can also be specified on a per-host basis in a configuration file.
1.165 stevesk 628: .Pp
1.218 jmc 629: X11 forwarding should be enabled with caution.
1.168 jmc 630: Users with the ability to bypass file permissions on the remote host
1.218 jmc 631: (for the user's X authorization database)
632: can access the local X11 display through the forwarded connection.
633: An attacker may then be able to perform activities such as keystroke monitoring.
634: .Pp
635: For this reason, X11 forwarding is subjected to X11 SECURITY extension
636: restrictions by default.
637: Please refer to the
638: .Nm
639: .Fl Y
640: option and the
641: .Cm ForwardX11Trusted
642: directive in
643: .Xr ssh_config 5
644: for more information.
645: .It Fl x
646: Disables X11 forwarding.
647: .It Fl Y
648: Enables trusted X11 forwarding.
649: Trusted X11 forwardings are not subjected to the X11 SECURITY extension
650: controls.
651: .El
1.224 jmc 652: .Pp
653: .Nm
654: may additionally obtain configuration data from
655: a per-user configuration file and a system-wide configuration file.
656: The file format and configuration options are described in
657: .Xr ssh_config 5 .
658: .Pp
659: .Nm
660: exits with the exit status of the remote command or with 255
661: if an error occurred.
1.222 jmc 662: .Sh AUTHENTICATION
1.249 jmc 663: The OpenSSH SSH client supports SSH protocols 1 and 2.
1.222 jmc 664: Protocol 2 is the default, with
665: .Nm
666: falling back to protocol 1 if it detects protocol 2 is unsupported.
667: These settings may be altered using the
668: .Cm Protocol
669: option in
670: .Xr ssh_config 5 ,
671: or enforced using the
672: .Fl 1
673: and
674: .Fl 2
675: options (see above).
676: Both protocols support similar authentication methods,
677: but protocol 2 is preferred since
678: it provides additional mechanisms for confidentiality
679: (the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour)
1.268 pvalchev 680: and integrity (hmac-md5, hmac-sha1, umac-64, hmac-ripemd160).
1.222 jmc 681: Protocol 1 lacks a strong mechanism for ensuring the
682: integrity of the connection.
683: .Pp
684: The methods available for authentication are:
1.260 jmc 685: GSSAPI-based authentication,
1.222 jmc 686: host-based authentication,
687: public key authentication,
688: challenge-response authentication,
689: and password authentication.
690: Authentication methods are tried in the order specified above,
691: though protocol 2 has a configuration option to change the default order:
692: .Cm PreferredAuthentications .
693: .Pp
694: Host-based authentication works as follows:
1.218 jmc 695: If the machine the user logs in from is listed in
696: .Pa /etc/hosts.equiv
697: or
698: .Pa /etc/shosts.equiv
699: on the remote machine, and the user names are
700: the same on both sides, or if the files
701: .Pa ~/.rhosts
702: or
703: .Pa ~/.shosts
704: exist in the user's home directory on the
705: remote machine and contain a line containing the name of the client
706: machine and the name of the user on that machine, the user is
1.222 jmc 707: considered for login.
708: Additionally, the server
709: .Em must
710: be able to verify the client's
711: host key (see the description of
1.218 jmc 712: .Pa /etc/ssh/ssh_known_hosts
1.189 dtucker 713: and
1.222 jmc 714: .Pa ~/.ssh/known_hosts ,
715: below)
716: for login to be permitted.
1.218 jmc 717: This authentication method closes security holes due to IP
1.222 jmc 718: spoofing, DNS spoofing, and routing spoofing.
1.218 jmc 719: [Note to the administrator:
720: .Pa /etc/hosts.equiv ,
721: .Pa ~/.rhosts ,
722: and the rlogin/rsh protocol in general, are inherently insecure and should be
723: disabled if security is desired.]
1.189 dtucker 724: .Pp
1.222 jmc 725: Public key authentication works as follows:
726: The scheme is based on public-key cryptography,
727: using cryptosystems
728: where encryption and decryption are done using separate keys,
729: and it is unfeasible to derive the decryption key from the encryption key.
1.218 jmc 730: The idea is that each user creates a public/private
731: key pair for authentication purposes.
732: The server knows the public key, and only the user knows the private key.
1.222 jmc 733: .Nm
734: implements public key authentication protocol automatically,
735: using either the RSA or DSA algorithms.
736: Protocol 1 is restricted to using only RSA keys,
737: but protocol 2 may use either.
738: The
739: .Sx HISTORY
740: section of
741: .Xr ssl 8
742: contains a brief discussion of the two algorithms.
1.210 djm 743: .Pp
1.218 jmc 744: The file
745: .Pa ~/.ssh/authorized_keys
746: lists the public keys that are permitted for logging in.
747: When the user logs in, the
1.2 deraadt 748: .Nm
1.218 jmc 749: program tells the server which key pair it would like to use for
750: authentication.
1.222 jmc 751: The client proves that it has access to the private key
752: and the server checks that the corresponding public key
753: is authorized to accept the account.
1.218 jmc 754: .Pp
1.222 jmc 755: The user creates his/her key pair by running
1.218 jmc 756: .Xr ssh-keygen 1 .
757: This stores the private key in
1.207 djm 758: .Pa ~/.ssh/identity
1.222 jmc 759: (protocol 1),
760: .Pa ~/.ssh/id_dsa
761: (protocol 2 DSA),
762: or
763: .Pa ~/.ssh/id_rsa
764: (protocol 2 RSA)
1.218 jmc 765: and stores the public key in
766: .Pa ~/.ssh/identity.pub
1.222 jmc 767: (protocol 1),
768: .Pa ~/.ssh/id_dsa.pub
769: (protocol 2 DSA),
770: or
771: .Pa ~/.ssh/id_rsa.pub
772: (protocol 2 RSA)
1.218 jmc 773: in the user's home directory.
1.222 jmc 774: The user should then copy the public key
1.218 jmc 775: to
776: .Pa ~/.ssh/authorized_keys
1.222 jmc 777: in his/her home directory on the remote machine.
778: The
1.218 jmc 779: .Pa authorized_keys
780: file corresponds to the conventional
781: .Pa ~/.rhosts
782: file, and has one key
1.222 jmc 783: per line, though the lines can be very long.
1.218 jmc 784: After this, the user can log in without giving the password.
785: .Pp
1.222 jmc 786: The most convenient way to use public key authentication may be with an
1.218 jmc 787: authentication agent.
788: See
789: .Xr ssh-agent 1
790: for more information.
791: .Pp
1.222 jmc 792: Challenge-response authentication works as follows:
793: The server sends an arbitrary
794: .Qq challenge
795: text, and prompts for a response.
796: Protocol 2 allows multiple challenges and responses;
797: protocol 1 is restricted to just one challenge/response.
798: Examples of challenge-response authentication include
799: BSD Authentication (see
800: .Xr login.conf 5 )
801: and PAM (some non-OpenBSD systems).
802: .Pp
803: Finally, if other authentication methods fail,
1.218 jmc 804: .Nm
805: prompts the user for a password.
806: The password is sent to the remote
807: host for checking; however, since all communications are encrypted,
808: the password cannot be seen by someone listening on the network.
1.232 jmc 809: .Pp
810: .Nm
811: automatically maintains and checks a database containing
812: identification for all hosts it has ever been used with.
813: Host keys are stored in
814: .Pa ~/.ssh/known_hosts
815: in the user's home directory.
816: Additionally, the file
817: .Pa /etc/ssh/ssh_known_hosts
818: is automatically checked for known hosts.
819: Any new hosts are automatically added to the user's file.
820: If a host's identification ever changes,
821: .Nm
822: warns about this and disables password authentication to prevent
823: server spoofing or man-in-the-middle attacks,
824: which could otherwise be used to circumvent the encryption.
825: The
826: .Cm StrictHostKeyChecking
827: option can be used to control logins to machines whose
828: host key is not known or has changed.
829: .Pp
1.218 jmc 830: When the user's identity has been accepted by the server, the server
831: either executes the given command, or logs into the machine and gives
832: the user a normal shell on the remote machine.
833: All communication with
834: the remote command or shell will be automatically encrypted.
835: .Pp
836: If a pseudo-terminal has been allocated (normal login session), the
837: user may use the escape characters noted below.
838: .Pp
839: If no pseudo-tty has been allocated,
840: the session is transparent and can be used to reliably transfer binary data.
841: On most systems, setting the escape character to
842: .Dq none
843: will also make the session transparent even if a tty is used.
844: .Pp
845: The session terminates when the command or shell on the remote
1.247 jmc 846: machine exits and all X11 and TCP connections have been closed.
1.223 jmc 847: .Sh ESCAPE CHARACTERS
1.218 jmc 848: When a pseudo-terminal has been requested,
1.2 deraadt 849: .Nm
1.218 jmc 850: supports a number of functions through the use of an escape character.
851: .Pp
852: A single tilde character can be sent as
853: .Ic ~~
854: or by following the tilde by a character other than those described below.
855: The escape character must always follow a newline to be interpreted as
856: special.
857: The escape character can be changed in configuration files using the
858: .Cm EscapeChar
859: configuration directive or on the command line by the
860: .Fl e
861: option.
862: .Pp
863: The supported escapes (assuming the default
864: .Ql ~ )
865: are:
866: .Bl -tag -width Ds
867: .It Cm ~.
868: Disconnect.
869: .It Cm ~^Z
870: Background
1.234 jmc 871: .Nm .
1.218 jmc 872: .It Cm ~#
873: List forwarded connections.
874: .It Cm ~&
875: Background
1.2 deraadt 876: .Nm
1.218 jmc 877: at logout when waiting for forwarded connection / X11 sessions to terminate.
878: .It Cm ~?
879: Display a list of escape characters.
880: .It Cm ~B
881: Send a BREAK to the remote system
882: (only useful for SSH protocol version 2 and if the peer supports it).
883: .It Cm ~C
884: Open command line.
885: Currently this allows the addition of port forwardings using the
886: .Fl L
887: and
888: .Fl R
1.225 jmc 889: options (see above).
1.218 jmc 890: It also allows the cancellation of existing remote port-forwardings
891: using
1.262 stevesk 892: .Sm off
893: .Fl KR Oo Ar bind_address : Oc Ar port .
894: .Sm on
1.218 jmc 895: .Ic !\& Ns Ar command
896: allows the user to execute a local command if the
897: .Ic PermitLocalCommand
898: option is enabled in
1.176 jmc 899: .Xr ssh_config 5 .
1.218 jmc 900: Basic help is available, using the
901: .Fl h
902: option.
903: .It Cm ~R
904: Request rekeying of the connection
905: (only useful for SSH protocol version 2 and if the peer supports it).
1.176 jmc 906: .El
1.246 jmc 907: .Sh TCP FORWARDING
908: Forwarding of arbitrary TCP connections over the secure channel can
909: be specified either on the command line or in a configuration file.
910: One possible application of TCP forwarding is a secure connection to a
911: mail server; another is going through firewalls.
912: .Pp
913: In the example below, we look at encrypting communication between
914: an IRC client and server, even though the IRC server does not directly
915: support encrypted communications.
916: This works as follows:
917: the user connects to the remote host using
918: .Nm ,
919: specifying a port to be used to forward connections
920: to the remote server.
921: After that it is possible to start the service which is to be encrypted
922: on the client machine,
923: connecting to the same local port,
924: and
925: .Nm
926: will encrypt and forward the connection.
927: .Pp
928: The following example tunnels an IRC session from client machine
929: .Dq 127.0.0.1
930: (localhost)
931: to remote server
932: .Dq server.example.com :
933: .Bd -literal -offset 4n
934: $ ssh -f -L 1234:localhost:6667 server.example.com sleep 10
935: $ irc -c '#users' -p 1234 pinky 127.0.0.1
936: .Ed
937: .Pp
938: This tunnels a connection to IRC server
939: .Dq server.example.com ,
940: joining channel
941: .Dq #users ,
942: nickname
943: .Dq pinky ,
944: using port 1234.
945: It doesn't matter which port is used,
946: as long as it's greater than 1023
947: (remember, only root can open sockets on privileged ports)
948: and doesn't conflict with any ports already in use.
949: The connection is forwarded to port 6667 on the remote server,
950: since that's the standard port for IRC services.
951: .Pp
952: The
953: .Fl f
954: option backgrounds
955: .Nm
956: and the remote command
957: .Dq sleep 10
958: is specified to allow an amount of time
959: (10 seconds, in the example)
960: to start the service which is to be tunnelled.
961: If no connections are made within the time specified,
962: .Nm
963: will exit.
964: .Sh X11 FORWARDING
1.218 jmc 965: If the
966: .Cm ForwardX11
967: variable is set to
968: .Dq yes
969: (or see the description of the
1.227 jmc 970: .Fl X ,
971: .Fl x ,
1.218 jmc 972: and
1.227 jmc 973: .Fl Y
1.226 jmc 974: options above)
1.218 jmc 975: and the user is using X11 (the
976: .Ev DISPLAY
977: environment variable is set), the connection to the X11 display is
978: automatically forwarded to the remote side in such a way that any X11
979: programs started from the shell (or command) will go through the
980: encrypted channel, and the connection to the real X server will be made
1.176 jmc 981: from the local machine.
1.218 jmc 982: The user should not manually set
983: .Ev DISPLAY .
984: Forwarding of X11 connections can be
985: configured on the command line or in configuration files.
986: .Pp
987: The
988: .Ev DISPLAY
989: value set by
990: .Nm
991: will point to the server machine, but with a display number greater than zero.
992: This is normal, and happens because
993: .Nm
994: creates a
995: .Dq proxy
996: X server on the server machine for forwarding the
997: connections over the encrypted channel.
1.200 djm 998: .Pp
1.218 jmc 999: .Nm
1000: will also automatically set up Xauthority data on the server machine.
1001: For this purpose, it will generate a random authorization cookie,
1002: store it in Xauthority on the server, and verify that any forwarded
1003: connections carry this cookie and replace it by the real cookie when
1004: the connection is opened.
1005: The real authentication cookie is never
1006: sent to the server machine (and no cookies are sent in the plain).
1.200 djm 1007: .Pp
1.218 jmc 1008: If the
1009: .Cm ForwardAgent
1010: variable is set to
1011: .Dq yes
1012: (or see the description of the
1013: .Fl A
1.191 djm 1014: and
1.218 jmc 1015: .Fl a
1.226 jmc 1016: options above) and
1.218 jmc 1017: the user is using an authentication agent, the connection to the agent
1018: is automatically forwarded to the remote side.
1.252 jmc 1019: .Sh VERIFYING HOST KEYS
1020: When connecting to a server for the first time,
1021: a fingerprint of the server's public key is presented to the user
1022: (unless the option
1023: .Cm StrictHostKeyChecking
1024: has been disabled).
1025: Fingerprints can be determined using
1026: .Xr ssh-keygen 1 :
1027: .Pp
1028: .Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key
1029: .Pp
1030: If the fingerprint is already known,
1031: it can be matched and verified,
1032: and the key can be accepted.
1033: If the fingerprint is unknown,
1034: an alternative method of verification is available:
1035: SSH fingerprints verified by DNS.
1036: An additional resource record (RR),
1037: SSHFP,
1038: is added to a zonefile
1039: and the connecting client is able to match the fingerprint
1040: with that of the key presented.
1041: .Pp
1042: In this example, we are connecting a client to a server,
1043: .Dq host.example.com .
1044: The SSHFP resource records should first be added to the zonefile for
1045: host.example.com:
1046: .Bd -literal -offset indent
1.259 jakob 1047: $ ssh-keygen -r host.example.com.
1.252 jmc 1048: .Ed
1049: .Pp
1050: The output lines will have to be added to the zonefile.
1051: To check that the zone is answering fingerprint queries:
1052: .Pp
1053: .Dl $ dig -t SSHFP host.example.com
1054: .Pp
1055: Finally the client connects:
1056: .Bd -literal -offset indent
1057: $ ssh -o "VerifyHostKeyDNS ask" host.example.com
1058: [...]
1059: Matching host key fingerprint found in DNS.
1060: Are you sure you want to continue connecting (yes/no)?
1061: .Ed
1062: .Pp
1063: See the
1064: .Cm VerifyHostKeyDNS
1065: option in
1066: .Xr ssh_config 5
1067: for more information.
1.250 jmc 1068: .Sh SSH-BASED VIRTUAL PRIVATE NETWORKS
1069: .Nm
1070: contains support for Virtual Private Network (VPN) tunnelling
1071: using the
1072: .Xr tun 4
1073: network pseudo-device,
1074: allowing two networks to be joined securely.
1075: The
1076: .Xr sshd_config 5
1077: configuration option
1078: .Cm PermitTunnel
1079: controls whether the server supports this,
1080: and at what level (layer 2 or 3 traffic).
1081: .Pp
1082: The following example would connect client network 10.0.50.0/24
1.265 otto 1083: with remote network 10.0.99.0/24 using a point-to-point connection
1084: from 10.1.1.1 to 10.1.1.2,
1085: provided that the SSH server running on the gateway to the remote network,
1086: at 192.168.1.15, allows it.
1087: .Pp
1088: On the client:
1.250 jmc 1089: .Bd -literal -offset indent
1090: # ssh -f -w 0:1 192.168.1.15 true
1.265 otto 1091: # ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252
1092: # route add 10.0.99.0/24 10.1.1.2
1093: .Ed
1094: .Pp
1095: On the server:
1096: .Bd -literal -offset indent
1097: # ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252
1098: # route add 10.0.50.0/24 10.1.1.1
1.250 jmc 1099: .Ed
1100: .Pp
1101: Client access may be more finely tuned via the
1102: .Pa /root/.ssh/authorized_keys
1103: file (see below) and the
1104: .Cm PermitRootLogin
1105: server option.
1.255 jmc 1106: The following entry would permit connections on
1.250 jmc 1107: .Xr tun 4
1.255 jmc 1108: device 1 from user
1.250 jmc 1109: .Dq jane
1.255 jmc 1110: and on tun device 2 from user
1.250 jmc 1111: .Dq john ,
1112: if
1113: .Cm PermitRootLogin
1114: is set to
1115: .Dq forced-commands-only :
1116: .Bd -literal -offset 2n
1117: tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane
1.254 msf 1118: tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john
1.250 jmc 1119: .Ed
1120: .Pp
1.264 ray 1121: Since an SSH-based setup entails a fair amount of overhead,
1.250 jmc 1122: it may be more suited to temporary setups,
1123: such as for wireless VPNs.
1124: More permanent VPNs are better provided by tools such as
1125: .Xr ipsecctl 8
1126: and
1127: .Xr isakmpd 8 .
1.2 deraadt 1128: .Sh ENVIRONMENT
1129: .Nm
1.1 deraadt 1130: will normally set the following environment variables:
1.237 jmc 1131: .Bl -tag -width "SSH_ORIGINAL_COMMAND"
1.2 deraadt 1132: .It Ev DISPLAY
1133: The
1134: .Ev DISPLAY
1.40 aaron 1135: variable indicates the location of the X11 server.
1.44 aaron 1136: It is automatically set by
1.2 deraadt 1137: .Nm
1138: to point to a value of the form
1.233 jmc 1139: .Dq hostname:n ,
1140: where
1141: .Dq hostname
1142: indicates the host where the shell runs, and
1143: .Sq n
1144: is an integer \*(Ge 1.
1.40 aaron 1145: .Nm
1146: uses this special value to forward X11 connections over the secure
1147: channel.
1.107 markus 1148: The user should normally not set
1149: .Ev DISPLAY
1150: explicitly, as that
1.1 deraadt 1151: will render the X11 connection insecure (and will require the user to
1152: manually copy any required authorization cookies).
1.2 deraadt 1153: .It Ev HOME
1.1 deraadt 1154: Set to the path of the user's home directory.
1.2 deraadt 1155: .It Ev LOGNAME
1156: Synonym for
1.12 aaron 1157: .Ev USER ;
1158: set for compatibility with systems that use this variable.
1.2 deraadt 1159: .It Ev MAIL
1.129 stevesk 1160: Set to the path of the user's mailbox.
1.40 aaron 1161: .It Ev PATH
1.2 deraadt 1162: Set to the default
1163: .Ev PATH ,
1164: as specified when compiling
1.234 jmc 1165: .Nm .
1.118 markus 1166: .It Ev SSH_ASKPASS
1167: If
1168: .Nm
1169: needs a passphrase, it will read the passphrase from the current
1170: terminal if it was run from a terminal.
1171: If
1172: .Nm
1173: does not have a terminal associated with it but
1174: .Ev DISPLAY
1175: and
1176: .Ev SSH_ASKPASS
1177: are set, it will execute the program specified by
1178: .Ev SSH_ASKPASS
1179: and open an X11 window to read the passphrase.
1180: This is particularly useful when calling
1181: .Nm
1182: from a
1.196 jmc 1183: .Pa .xsession
1.118 markus 1184: or related script.
1185: (Note that on some machines it
1186: may be necessary to redirect the input from
1187: .Pa /dev/null
1188: to make this work.)
1.18 markus 1189: .It Ev SSH_AUTH_SOCK
1.233 jmc 1190: Identifies the path of a
1191: .Ux Ns -domain
1192: socket used to communicate with the agent.
1.166 stevesk 1193: .It Ev SSH_CONNECTION
1194: Identifies the client and server ends of the connection.
1.40 aaron 1195: The variable contains
1.233 jmc 1196: four space-separated values: client IP address, client port number,
1197: server IP address, and server port number.
1.73 markus 1198: .It Ev SSH_ORIGINAL_COMMAND
1.233 jmc 1199: This variable contains the original command line if a forced command
1.73 markus 1200: is executed.
1201: It can be used to extract the original arguments.
1.2 deraadt 1202: .It Ev SSH_TTY
1.1 deraadt 1203: This is set to the name of the tty (path to the device) associated
1.40 aaron 1204: with the current shell or command.
1205: If the current session has no tty,
1.1 deraadt 1206: this variable is not set.
1.2 deraadt 1207: .It Ev TZ
1.214 jmc 1208: This variable is set to indicate the present time zone if it
1.257 jmc 1209: was set when the daemon was started (i.e. the daemon passes the value
1.1 deraadt 1210: on to new connections).
1.2 deraadt 1211: .It Ev USER
1.1 deraadt 1212: Set to the name of the user logging in.
1.2 deraadt 1213: .El
1214: .Pp
1.44 aaron 1215: Additionally,
1.2 deraadt 1216: .Nm
1.44 aaron 1217: reads
1.207 djm 1218: .Pa ~/.ssh/environment ,
1.2 deraadt 1219: and adds lines of the format
1220: .Dq VARNAME=value
1.233 jmc 1221: to the environment if the file exists and users are allowed to
1.161 marc 1222: change their environment.
1.176 jmc 1223: For more information, see the
1.161 marc 1224: .Cm PermitUserEnvironment
1.162 stevesk 1225: option in
1.161 marc 1226: .Xr sshd_config 5 .
1.2 deraadt 1227: .Sh FILES
1.236 jmc 1228: .Bl -tag -width Ds -compact
1229: .It ~/.rhosts
1.240 jmc 1230: This file is used for host-based authentication (see above).
1.92 markus 1231: On some machines this file may need to be
1.240 jmc 1232: world-readable if the user's home directory is on an NFS partition,
1.1 deraadt 1233: because
1.2 deraadt 1234: .Xr sshd 8
1.40 aaron 1235: reads it as root.
1236: Additionally, this file must be owned by the user,
1237: and must not have write permissions for anyone else.
1238: The recommended
1.1 deraadt 1239: permission for most machines is read/write for the user, and not
1240: accessible by others.
1.2 deraadt 1241: .Pp
1.236 jmc 1242: .It ~/.shosts
1.240 jmc 1243: This file is used in exactly the same way as
1244: .Pa .rhosts ,
1245: but allows host-based authentication without permitting login with
1246: rlogin/rsh.
1.236 jmc 1247: .Pp
1.238 jmc 1248: .It ~/.ssh/authorized_keys
1249: Lists the public keys (RSA/DSA) that can be used for logging in as this user.
1250: The format of this file is described in the
1251: .Xr sshd 8
1252: manual page.
1253: This file is not highly sensitive, but the recommended
1254: permissions are read/write for the user, and not accessible by others.
1255: .Pp
1256: .It ~/.ssh/config
1257: This is the per-user configuration file.
1258: The file format and configuration options are described in
1259: .Xr ssh_config 5 .
1260: Because of the potential for abuse, this file must have strict permissions:
1261: read/write for the user, and not accessible by others.
1262: .Pp
1263: .It ~/.ssh/environment
1.239 jmc 1264: Contains additional definitions for environment variables; see
1265: .Sx ENVIRONMENT ,
1.238 jmc 1266: above.
1267: .Pp
1268: .It ~/.ssh/identity
1269: .It ~/.ssh/id_dsa
1270: .It ~/.ssh/id_rsa
1271: Contains the private key for authentication.
1272: These files
1273: contain sensitive data and should be readable by the user but not
1274: accessible by others (read/write/execute).
1275: .Nm
1276: will simply ignore a private key file if it is accessible by others.
1277: It is possible to specify a passphrase when
1278: generating the key which will be used to encrypt the
1279: sensitive part of this file using 3DES.
1280: .Pp
1281: .It ~/.ssh/identity.pub
1282: .It ~/.ssh/id_dsa.pub
1283: .It ~/.ssh/id_rsa.pub
1284: Contains the public key for authentication.
1285: These files are not
1286: sensitive and can (but need not) be readable by anyone.
1287: .Pp
1288: .It ~/.ssh/known_hosts
1.244 jmc 1289: Contains a list of host keys for all hosts the user has logged into
1290: that are not already in the systemwide list of known host keys.
1.238 jmc 1291: See
1.244 jmc 1292: .Xr sshd 8
1293: for further details of the format of this file.
1.238 jmc 1294: .Pp
1295: .It ~/.ssh/rc
1296: Commands in this file are executed by
1297: .Nm
1.245 jmc 1298: when the user logs in, just before the user's shell (or command) is
1.238 jmc 1299: started.
1300: See the
1301: .Xr sshd 8
1302: manual page for more information.
1303: .Pp
1.236 jmc 1304: .It /etc/hosts.equiv
1.240 jmc 1305: This file is for host-based authentication (see above).
1306: It should only be writable by root.
1.236 jmc 1307: .Pp
1308: .It /etc/shosts.equiv
1.240 jmc 1309: This file is used in exactly the same way as
1310: .Pa hosts.equiv ,
1311: but allows host-based authentication without permitting login with
1312: rlogin/rsh.
1.236 jmc 1313: .Pp
1.238 jmc 1314: .It Pa /etc/ssh/ssh_config
1315: Systemwide configuration file.
1316: The file format and configuration options are described in
1317: .Xr ssh_config 5 .
1318: .Pp
1319: .It /etc/ssh/ssh_host_key
1320: .It /etc/ssh/ssh_host_dsa_key
1321: .It /etc/ssh/ssh_host_rsa_key
1322: These three files contain the private parts of the host keys
1.245 jmc 1323: and are used for host-based authentication.
1324: If protocol version 1 is used,
1.238 jmc 1325: .Nm
1326: must be setuid root, since the host key is readable only by root.
1327: For protocol version 2,
1328: .Nm
1329: uses
1330: .Xr ssh-keysign 8
1.245 jmc 1331: to access the host keys,
1332: eliminating the requirement that
1.238 jmc 1333: .Nm
1.245 jmc 1334: be setuid root when host-based authentication is used.
1.238 jmc 1335: By default
1.2 deraadt 1336: .Nm
1.238 jmc 1337: is not setuid root.
1338: .Pp
1339: .It /etc/ssh/ssh_known_hosts
1340: Systemwide list of known host keys.
1341: This file should be prepared by the
1342: system administrator to contain the public host keys of all machines in the
1343: organization.
1.244 jmc 1344: It should be world-readable.
1345: See
1.238 jmc 1346: .Xr sshd 8
1.244 jmc 1347: for further details of the format of this file.
1.236 jmc 1348: .Pp
1.238 jmc 1349: .It /etc/ssh/sshrc
1.1 deraadt 1350: Commands in this file are executed by
1.2 deraadt 1351: .Nm
1.245 jmc 1352: when the user logs in, just before the user's shell (or command) is started.
1.44 aaron 1353: See the
1.2 deraadt 1354: .Xr sshd 8
1.1 deraadt 1355: manual page for more information.
1.58 itojun 1356: .El
1.2 deraadt 1357: .Sh SEE ALSO
1358: .Xr scp 1 ,
1.83 djm 1359: .Xr sftp 1 ,
1.2 deraadt 1360: .Xr ssh-add 1 ,
1361: .Xr ssh-agent 1 ,
1362: .Xr ssh-keygen 1 ,
1.242 jmc 1363: .Xr ssh-keyscan 1 ,
1.250 jmc 1364: .Xr tun 4 ,
1.176 jmc 1365: .Xr hosts.equiv 5 ,
1.159 stevesk 1366: .Xr ssh_config 5 ,
1.160 naddy 1367: .Xr ssh-keysign 8 ,
1.87 itojun 1368: .Xr sshd 8
1.106 markus 1369: .Rs
1.256 jmc 1370: .%R RFC 4250
1371: .%T "The Secure Shell (SSH) Protocol Assigned Numbers"
1372: .%D 2006
1373: .Re
1374: .Rs
1375: .%R RFC 4251
1376: .%T "The Secure Shell (SSH) Protocol Architecture"
1377: .%D 2006
1378: .Re
1379: .Rs
1380: .%R RFC 4252
1381: .%T "The Secure Shell (SSH) Authentication Protocol"
1382: .%D 2006
1383: .Re
1384: .Rs
1385: .%R RFC 4253
1386: .%T "The Secure Shell (SSH) Transport Layer Protocol"
1387: .%D 2006
1388: .Re
1389: .Rs
1390: .%R RFC 4254
1391: .%T "The Secure Shell (SSH) Connection Protocol"
1392: .%D 2006
1393: .Re
1394: .Rs
1395: .%R RFC 4255
1396: .%T "Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints"
1397: .%D 2006
1398: .Re
1399: .Rs
1400: .%R RFC 4256
1401: .%T "Generic Message Exchange Authentication for the Secure Shell Protocol (SSH)"
1402: .%D 2006
1403: .Re
1404: .Rs
1405: .%R RFC 4335
1406: .%T "The Secure Shell (SSH) Session Channel Break Extension"
1407: .%D 2006
1408: .Re
1409: .Rs
1410: .%R RFC 4344
1411: .%T "The Secure Shell (SSH) Transport Layer Encryption Modes"
1412: .%D 2006
1413: .Re
1414: .Rs
1415: .%R RFC 4345
1416: .%T "Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol"
1.258 djm 1417: .%D 2006
1418: .Re
1419: .Rs
1420: .%R RFC 4419
1421: .%T "Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol"
1.266 markus 1422: .%D 2006
1423: .Re
1424: .Rs
1425: .%R RFC 4716
1426: .%T "The Secure Shell (SSH) Public Key File Format"
1.256 jmc 1427: .%D 2006
1.106 markus 1428: .Re
1.173 jmc 1429: .Sh AUTHORS
1430: OpenSSH is a derivative of the original and free
1431: ssh 1.2.12 release by Tatu Ylonen.
1432: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1433: Theo de Raadt and Dug Song
1434: removed many bugs, re-added newer features and
1435: created OpenSSH.
1436: Markus Friedl contributed the support for SSH
1437: protocol versions 1.5 and 2.0.
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