Annotation of src/usr.bin/ssh/ssh.1, Revision 1.283
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: .\"
1.283 ! jmc 37: .\" $OpenBSD: ssh.1,v 1.282 2009/02/12 03:44:25 djm Exp $
1.282 djm 38: .Dd $Mdocdate: February 12 2009 $
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
1.278 djm 46: .Op Fl 1246AaCfgKkMNnqsTtVvXxYy
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.
1.283 ! jmc 194: See the
! 195: .Cm Ciphers
! 196: keyword for more information.
1.218 jmc 197: .It Fl D Xo
198: .Sm off
199: .Oo Ar bind_address : Oc
200: .Ar port
201: .Sm on
202: .Xc
203: Specifies a local
204: .Dq dynamic
205: application-level port forwarding.
206: This works by allocating a socket to listen to
207: .Ar port
208: on the local side, optionally bound to the specified
209: .Ar bind_address .
210: Whenever a connection is made to this port, the
211: connection is forwarded over the secure channel, and the application
212: protocol is then used to determine where to connect to from the
213: remote machine.
214: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.107 markus 215: .Nm
1.218 jmc 216: will act as a SOCKS server.
217: Only root can forward privileged ports.
218: Dynamic port forwardings can also be specified in the configuration file.
1.49 markus 219: .Pp
1.218 jmc 220: IPv6 addresses can be specified with an alternative syntax:
221: .Sm off
222: .Xo
223: .Op Ar bind_address No /
224: .Ar port
225: .Xc
226: .Sm on
227: or by enclosing the address in square brackets.
228: Only the superuser can forward privileged ports.
229: By default, the local port is bound in accordance with the
230: .Cm GatewayPorts
231: setting.
232: However, an explicit
233: .Ar bind_address
234: may be used to bind the connection to a specific address.
235: The
236: .Ar bind_address
237: of
238: .Dq localhost
239: indicates that the listening port be bound for local use only, while an
240: empty address or
241: .Sq *
242: indicates that the port should be available from all interfaces.
1.229 jmc 243: .It Fl e Ar escape_char
1.218 jmc 244: Sets the escape character for sessions with a pty (default:
245: .Ql ~ ) .
246: The escape character is only recognized at the beginning of a line.
247: The escape character followed by a dot
248: .Pq Ql \&.
249: closes the connection;
250: followed by control-Z suspends the connection;
251: and followed by itself sends the escape character once.
252: Setting the character to
1.2 deraadt 253: .Dq none
1.218 jmc 254: disables any escapes and makes the session fully transparent.
255: .It Fl F Ar configfile
256: Specifies an alternative per-user configuration file.
257: If a configuration file is given on the command line,
258: the system-wide configuration file
259: .Pq Pa /etc/ssh/ssh_config
260: will be ignored.
261: The default for the per-user configuration file is
262: .Pa ~/.ssh/config .
263: .It Fl f
264: Requests
265: .Nm
266: to go to background just before command execution.
267: This is useful if
1.176 jmc 268: .Nm
1.218 jmc 269: is going to ask for passwords or passphrases, but the user
270: wants it in the background.
271: This implies
272: .Fl n .
273: The recommended way to start X11 programs at a remote site is with
274: something like
275: .Ic ssh -f host xterm .
1.277 djm 276: .Pp
277: If the
278: .Cm ExitOnForwardFailure
279: configuration option is set to
280: .Dq yes ,
281: then a client started with
282: .Fl f
283: will wait for all remote port forwards to be successfully established
284: before placing itself in the background.
1.218 jmc 285: .It Fl g
286: Allows remote hosts to connect to local forwarded ports.
287: .It Fl I Ar smartcard_device
1.229 jmc 288: Specify the device
1.176 jmc 289: .Nm
1.218 jmc 290: should use to communicate with a smartcard used for storing the user's
291: private RSA key.
1.229 jmc 292: This option is only available if support for smartcard devices
293: is compiled in (default is no support).
1.218 jmc 294: .It Fl i Ar identity_file
295: Selects a file from which the identity (private key) for
296: RSA or DSA authentication is read.
297: The default is
298: .Pa ~/.ssh/identity
299: for protocol version 1, and
300: .Pa ~/.ssh/id_rsa
1.149 jakob 301: and
1.218 jmc 302: .Pa ~/.ssh/id_dsa
303: for protocol version 2.
304: Identity files may also be specified on
305: a per-host basis in the configuration file.
306: It is possible to have multiple
307: .Fl i
308: options (and multiple identities specified in
309: configuration files).
1.269 djm 310: .It Fl K
311: Enables GSSAPI-based authentication and forwarding (delegation) of GSSAPI
312: credentials to the server.
1.218 jmc 313: .It Fl k
314: Disables forwarding (delegation) of GSSAPI credentials to the server.
315: .It Fl L Xo
316: .Sm off
317: .Oo Ar bind_address : Oc
318: .Ar port : host : hostport
319: .Sm on
320: .Xc
321: Specifies that the given port on the local (client) host is to be
322: forwarded to the given host and port on the remote side.
323: This works by allocating a socket to listen to
324: .Ar port
325: on the local side, optionally bound to the specified
326: .Ar bind_address .
327: Whenever a connection is made to this port, the
328: connection is forwarded over the secure channel, and a connection is
329: made to
330: .Ar host
331: port
332: .Ar hostport
333: from the remote machine.
334: Port forwardings can also be specified in the configuration file.
335: IPv6 addresses can be specified with an alternative syntax:
336: .Sm off
337: .Xo
338: .Op Ar bind_address No /
339: .Ar port No / Ar host No /
340: .Ar hostport
341: .Xc
342: .Sm on
343: or by enclosing the address in square brackets.
344: Only the superuser can forward privileged ports.
345: By default, the local port is bound in accordance with the
346: .Cm GatewayPorts
347: setting.
348: However, an explicit
349: .Ar bind_address
350: may be used to bind the connection to a specific address.
1.2 deraadt 351: The
1.218 jmc 352: .Ar bind_address
353: of
354: .Dq localhost
355: indicates that the listening port be bound for local use only, while an
356: empty address or
357: .Sq *
358: indicates that the port should be available from all interfaces.
359: .It Fl l Ar login_name
360: Specifies the user to log in as on the remote machine.
361: This also may be specified on a per-host basis in the configuration file.
362: .It Fl M
363: Places the
364: .Nm
365: client into
366: .Dq master
367: mode for connection sharing.
1.231 stevesk 368: Multiple
369: .Fl M
370: options places
371: .Nm
372: into
373: .Dq master
374: mode with confirmation required before slave connections are accepted.
1.218 jmc 375: Refer to the description of
376: .Cm ControlMaster
377: in
378: .Xr ssh_config 5
379: for details.
380: .It Fl m Ar mac_spec
381: Additionally, for protocol version 2 a comma-separated list of MAC
382: (message authentication code) algorithms can
383: be specified in order of preference.
384: See the
385: .Cm MACs
386: keyword for more information.
387: .It Fl N
388: Do not execute a remote command.
389: This is useful for just forwarding ports
390: (protocol version 2 only).
391: .It Fl n
392: Redirects stdin from
393: .Pa /dev/null
394: (actually, prevents reading from stdin).
395: This must be used when
1.2 deraadt 396: .Nm
1.218 jmc 397: is run in the background.
398: A common trick is to use this to run X11 programs on a remote machine.
399: For example,
400: .Ic ssh -n shadows.cs.hut.fi emacs &
401: will start an emacs on shadows.cs.hut.fi, and the X11
402: connection will be automatically forwarded over an encrypted channel.
403: The
1.2 deraadt 404: .Nm
1.218 jmc 405: program will be put in the background.
406: (This does not work if
1.2 deraadt 407: .Nm
1.218 jmc 408: needs to ask for a password or passphrase; see also the
409: .Fl f
410: option.)
411: .It Fl O Ar ctl_cmd
412: Control an active connection multiplexing master process.
413: When the
414: .Fl O
415: option is specified, the
416: .Ar ctl_cmd
417: argument is interpreted and passed to the master process.
418: Valid commands are:
419: .Dq check
420: (check that the master process is running) and
421: .Dq exit
422: (request the master to exit).
423: .It Fl o Ar option
424: Can be used to give options in the format used in the configuration file.
425: This is useful for specifying options for which there is no separate
426: command-line flag.
427: For full details of the options listed below, and their possible values, see
428: .Xr ssh_config 5 .
1.2 deraadt 429: .Pp
1.218 jmc 430: .Bl -tag -width Ds -offset indent -compact
431: .It AddressFamily
432: .It BatchMode
433: .It BindAddress
434: .It ChallengeResponseAuthentication
435: .It CheckHostIP
436: .It Cipher
437: .It Ciphers
438: .It ClearAllForwardings
439: .It Compression
440: .It CompressionLevel
441: .It ConnectionAttempts
442: .It ConnectTimeout
443: .It ControlMaster
444: .It ControlPath
445: .It DynamicForward
446: .It EscapeChar
1.263 markus 447: .It ExitOnForwardFailure
1.218 jmc 448: .It ForwardAgent
449: .It ForwardX11
450: .It ForwardX11Trusted
451: .It GatewayPorts
452: .It GlobalKnownHostsFile
453: .It GSSAPIAuthentication
454: .It GSSAPIDelegateCredentials
455: .It HashKnownHosts
456: .It Host
457: .It HostbasedAuthentication
458: .It HostKeyAlgorithms
459: .It HostKeyAlias
460: .It HostName
461: .It IdentityFile
462: .It IdentitiesOnly
463: .It KbdInteractiveDevices
464: .It LocalCommand
465: .It LocalForward
466: .It LogLevel
467: .It MACs
468: .It NoHostAuthenticationForLocalhost
469: .It NumberOfPasswordPrompts
470: .It PasswordAuthentication
471: .It PermitLocalCommand
472: .It Port
473: .It PreferredAuthentications
474: .It Protocol
475: .It ProxyCommand
476: .It PubkeyAuthentication
1.251 dtucker 477: .It RekeyLimit
1.218 jmc 478: .It RemoteForward
479: .It RhostsRSAAuthentication
480: .It RSAAuthentication
481: .It SendEnv
482: .It ServerAliveInterval
483: .It ServerAliveCountMax
484: .It SmartcardDevice
485: .It StrictHostKeyChecking
486: .It TCPKeepAlive
487: .It Tunnel
488: .It TunnelDevice
489: .It UsePrivilegedPort
490: .It User
491: .It UserKnownHostsFile
492: .It VerifyHostKeyDNS
1.276 jmc 493: .It VisualHostKey
1.218 jmc 494: .It XAuthLocation
495: .El
496: .It Fl p Ar port
497: Port to connect to on the remote host.
498: This can be specified on a
499: per-host basis in the configuration file.
500: .It Fl q
501: Quiet mode.
1.271 djm 502: Causes most warning and diagnostic messages to be suppressed.
1.218 jmc 503: .It Fl R Xo
504: .Sm off
505: .Oo Ar bind_address : Oc
506: .Ar port : host : hostport
507: .Sm on
508: .Xc
509: Specifies that the given port on the remote (server) host is to be
510: forwarded to the given host and port on the local side.
511: This works by allocating a socket to listen to
512: .Ar port
513: on the remote side, and whenever a connection is made to this port, the
514: connection is forwarded over the secure channel, and a connection is
515: made to
516: .Ar host
517: port
518: .Ar hostport
519: from the local machine.
1.2 deraadt 520: .Pp
1.218 jmc 521: Port forwardings can also be specified in the configuration file.
522: Privileged ports can be forwarded only when
523: logging in as root on the remote machine.
524: IPv6 addresses can be specified by enclosing the address in square braces or
525: using an alternative syntax:
526: .Sm off
527: .Xo
528: .Op Ar bind_address No /
529: .Ar host No / Ar port No /
530: .Ar hostport
531: .Xc .
532: .Sm on
1.194 jakob 533: .Pp
1.218 jmc 534: By default, the listening socket on the server will be bound to the loopback
535: interface only.
1.280 tobias 536: This may be overridden by specifying a
1.218 jmc 537: .Ar bind_address .
538: An empty
539: .Ar bind_address ,
540: or the address
541: .Ql * ,
542: indicates that the remote socket should listen on all interfaces.
543: Specifying a remote
544: .Ar bind_address
545: will only succeed if the server's
546: .Cm GatewayPorts
547: option is enabled (see
548: .Xr sshd_config 5 ) .
1.281 djm 549: .Pp
550: If the
551: .Ar port
552: argument is
1.282 djm 553: .Ql 0 ,
1.281 djm 554: the listen port will be dynamically allocated on the server and reported
555: to the client at run time.
1.218 jmc 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.
1.278 djm 651: .It Fl y
652: Send log information using the
653: .Xr syslog 3
654: system module.
655: By default this information is sent to stderr.
1.218 jmc 656: .El
1.224 jmc 657: .Pp
658: .Nm
659: may additionally obtain configuration data from
660: a per-user configuration file and a system-wide configuration file.
661: The file format and configuration options are described in
662: .Xr ssh_config 5 .
663: .Pp
664: .Nm
665: exits with the exit status of the remote command or with 255
666: if an error occurred.
1.222 jmc 667: .Sh AUTHENTICATION
1.249 jmc 668: The OpenSSH SSH client supports SSH protocols 1 and 2.
1.222 jmc 669: Protocol 2 is the default, with
670: .Nm
671: falling back to protocol 1 if it detects protocol 2 is unsupported.
672: These settings may be altered using the
673: .Cm Protocol
674: option in
675: .Xr ssh_config 5 ,
676: or enforced using the
677: .Fl 1
678: and
679: .Fl 2
680: options (see above).
681: Both protocols support similar authentication methods,
682: but protocol 2 is preferred since
683: it provides additional mechanisms for confidentiality
684: (the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour)
1.268 pvalchev 685: and integrity (hmac-md5, hmac-sha1, umac-64, hmac-ripemd160).
1.222 jmc 686: Protocol 1 lacks a strong mechanism for ensuring the
687: integrity of the connection.
688: .Pp
689: The methods available for authentication are:
1.260 jmc 690: GSSAPI-based authentication,
1.222 jmc 691: host-based authentication,
692: public key authentication,
693: challenge-response authentication,
694: and password authentication.
695: Authentication methods are tried in the order specified above,
696: though protocol 2 has a configuration option to change the default order:
697: .Cm PreferredAuthentications .
698: .Pp
699: Host-based authentication works as follows:
1.218 jmc 700: If the machine the user logs in from is listed in
701: .Pa /etc/hosts.equiv
702: or
703: .Pa /etc/shosts.equiv
704: on the remote machine, and the user names are
705: the same on both sides, or if the files
706: .Pa ~/.rhosts
707: or
708: .Pa ~/.shosts
709: exist in the user's home directory on the
710: remote machine and contain a line containing the name of the client
711: machine and the name of the user on that machine, the user is
1.222 jmc 712: considered for login.
713: Additionally, the server
714: .Em must
715: be able to verify the client's
716: host key (see the description of
1.218 jmc 717: .Pa /etc/ssh/ssh_known_hosts
1.189 dtucker 718: and
1.222 jmc 719: .Pa ~/.ssh/known_hosts ,
720: below)
721: for login to be permitted.
1.218 jmc 722: This authentication method closes security holes due to IP
1.222 jmc 723: spoofing, DNS spoofing, and routing spoofing.
1.218 jmc 724: [Note to the administrator:
725: .Pa /etc/hosts.equiv ,
726: .Pa ~/.rhosts ,
727: and the rlogin/rsh protocol in general, are inherently insecure and should be
728: disabled if security is desired.]
1.189 dtucker 729: .Pp
1.222 jmc 730: Public key authentication works as follows:
731: The scheme is based on public-key cryptography,
732: using cryptosystems
733: where encryption and decryption are done using separate keys,
734: and it is unfeasible to derive the decryption key from the encryption key.
1.218 jmc 735: The idea is that each user creates a public/private
736: key pair for authentication purposes.
737: The server knows the public key, and only the user knows the private key.
1.222 jmc 738: .Nm
739: implements public key authentication protocol automatically,
740: using either the RSA or DSA algorithms.
741: Protocol 1 is restricted to using only RSA keys,
742: but protocol 2 may use either.
743: The
744: .Sx HISTORY
745: section of
746: .Xr ssl 8
747: contains a brief discussion of the two algorithms.
1.210 djm 748: .Pp
1.218 jmc 749: The file
750: .Pa ~/.ssh/authorized_keys
751: lists the public keys that are permitted for logging in.
752: When the user logs in, the
1.2 deraadt 753: .Nm
1.218 jmc 754: program tells the server which key pair it would like to use for
755: authentication.
1.222 jmc 756: The client proves that it has access to the private key
757: and the server checks that the corresponding public key
758: is authorized to accept the account.
1.218 jmc 759: .Pp
1.222 jmc 760: The user creates his/her key pair by running
1.218 jmc 761: .Xr ssh-keygen 1 .
762: This stores the private key in
1.207 djm 763: .Pa ~/.ssh/identity
1.222 jmc 764: (protocol 1),
765: .Pa ~/.ssh/id_dsa
766: (protocol 2 DSA),
767: or
768: .Pa ~/.ssh/id_rsa
769: (protocol 2 RSA)
1.218 jmc 770: and stores the public key in
771: .Pa ~/.ssh/identity.pub
1.222 jmc 772: (protocol 1),
773: .Pa ~/.ssh/id_dsa.pub
774: (protocol 2 DSA),
775: or
776: .Pa ~/.ssh/id_rsa.pub
777: (protocol 2 RSA)
1.218 jmc 778: in the user's home directory.
1.222 jmc 779: The user should then copy the public key
1.218 jmc 780: to
781: .Pa ~/.ssh/authorized_keys
1.222 jmc 782: in his/her home directory on the remote machine.
783: The
1.218 jmc 784: .Pa authorized_keys
785: file corresponds to the conventional
786: .Pa ~/.rhosts
787: file, and has one key
1.222 jmc 788: per line, though the lines can be very long.
1.218 jmc 789: After this, the user can log in without giving the password.
790: .Pp
1.222 jmc 791: The most convenient way to use public key authentication may be with an
1.218 jmc 792: authentication agent.
793: See
794: .Xr ssh-agent 1
795: for more information.
796: .Pp
1.222 jmc 797: Challenge-response authentication works as follows:
798: The server sends an arbitrary
799: .Qq challenge
800: text, and prompts for a response.
801: Protocol 2 allows multiple challenges and responses;
802: protocol 1 is restricted to just one challenge/response.
803: Examples of challenge-response authentication include
804: BSD Authentication (see
805: .Xr login.conf 5 )
806: and PAM (some non-OpenBSD systems).
807: .Pp
808: Finally, if other authentication methods fail,
1.218 jmc 809: .Nm
810: prompts the user for a password.
811: The password is sent to the remote
812: host for checking; however, since all communications are encrypted,
813: the password cannot be seen by someone listening on the network.
1.232 jmc 814: .Pp
815: .Nm
816: automatically maintains and checks a database containing
817: identification for all hosts it has ever been used with.
818: Host keys are stored in
819: .Pa ~/.ssh/known_hosts
820: in the user's home directory.
821: Additionally, the file
822: .Pa /etc/ssh/ssh_known_hosts
823: is automatically checked for known hosts.
824: Any new hosts are automatically added to the user's file.
825: If a host's identification ever changes,
826: .Nm
827: warns about this and disables password authentication to prevent
828: server spoofing or man-in-the-middle attacks,
829: which could otherwise be used to circumvent the encryption.
830: The
831: .Cm StrictHostKeyChecking
832: option can be used to control logins to machines whose
833: host key is not known or has changed.
834: .Pp
1.218 jmc 835: When the user's identity has been accepted by the server, the server
836: either executes the given command, or logs into the machine and gives
837: the user a normal shell on the remote machine.
838: All communication with
839: the remote command or shell will be automatically encrypted.
840: .Pp
841: If a pseudo-terminal has been allocated (normal login session), the
842: user may use the escape characters noted below.
843: .Pp
844: If no pseudo-tty has been allocated,
845: the session is transparent and can be used to reliably transfer binary data.
846: On most systems, setting the escape character to
847: .Dq none
848: will also make the session transparent even if a tty is used.
849: .Pp
850: The session terminates when the command or shell on the remote
1.247 jmc 851: machine exits and all X11 and TCP connections have been closed.
1.223 jmc 852: .Sh ESCAPE CHARACTERS
1.218 jmc 853: When a pseudo-terminal has been requested,
1.2 deraadt 854: .Nm
1.218 jmc 855: supports a number of functions through the use of an escape character.
856: .Pp
857: A single tilde character can be sent as
858: .Ic ~~
859: or by following the tilde by a character other than those described below.
860: The escape character must always follow a newline to be interpreted as
861: special.
862: The escape character can be changed in configuration files using the
863: .Cm EscapeChar
864: configuration directive or on the command line by the
865: .Fl e
866: option.
867: .Pp
868: The supported escapes (assuming the default
869: .Ql ~ )
870: are:
871: .Bl -tag -width Ds
872: .It Cm ~.
873: Disconnect.
874: .It Cm ~^Z
875: Background
1.234 jmc 876: .Nm .
1.218 jmc 877: .It Cm ~#
878: List forwarded connections.
879: .It Cm ~&
880: Background
1.2 deraadt 881: .Nm
1.218 jmc 882: at logout when waiting for forwarded connection / X11 sessions to terminate.
883: .It Cm ~?
884: Display a list of escape characters.
885: .It Cm ~B
886: Send a BREAK to the remote system
887: (only useful for SSH protocol version 2 and if the peer supports it).
888: .It Cm ~C
889: Open command line.
890: Currently this allows the addition of port forwardings using the
1.279 stevesk 891: .Fl L ,
892: .Fl R
1.218 jmc 893: and
1.279 stevesk 894: .Fl D
1.225 jmc 895: options (see above).
1.218 jmc 896: It also allows the cancellation of existing remote port-forwardings
897: using
1.262 stevesk 898: .Sm off
899: .Fl KR Oo Ar bind_address : Oc Ar port .
900: .Sm on
1.218 jmc 901: .Ic !\& Ns Ar command
902: allows the user to execute a local command if the
903: .Ic PermitLocalCommand
904: option is enabled in
1.176 jmc 905: .Xr ssh_config 5 .
1.218 jmc 906: Basic help is available, using the
907: .Fl h
908: option.
909: .It Cm ~R
910: Request rekeying of the connection
911: (only useful for SSH protocol version 2 and if the peer supports it).
1.176 jmc 912: .El
1.246 jmc 913: .Sh TCP FORWARDING
914: Forwarding of arbitrary TCP connections over the secure channel can
915: be specified either on the command line or in a configuration file.
916: One possible application of TCP forwarding is a secure connection to a
917: mail server; another is going through firewalls.
918: .Pp
919: In the example below, we look at encrypting communication between
920: an IRC client and server, even though the IRC server does not directly
921: support encrypted communications.
922: This works as follows:
923: the user connects to the remote host using
924: .Nm ,
925: specifying a port to be used to forward connections
926: to the remote server.
927: After that it is possible to start the service which is to be encrypted
928: on the client machine,
929: connecting to the same local port,
930: and
931: .Nm
932: will encrypt and forward the connection.
933: .Pp
934: The following example tunnels an IRC session from client machine
935: .Dq 127.0.0.1
936: (localhost)
937: to remote server
938: .Dq server.example.com :
939: .Bd -literal -offset 4n
940: $ ssh -f -L 1234:localhost:6667 server.example.com sleep 10
941: $ irc -c '#users' -p 1234 pinky 127.0.0.1
942: .Ed
943: .Pp
944: This tunnels a connection to IRC server
945: .Dq server.example.com ,
946: joining channel
947: .Dq #users ,
948: nickname
949: .Dq pinky ,
950: using port 1234.
951: It doesn't matter which port is used,
952: as long as it's greater than 1023
953: (remember, only root can open sockets on privileged ports)
954: and doesn't conflict with any ports already in use.
955: The connection is forwarded to port 6667 on the remote server,
956: since that's the standard port for IRC services.
957: .Pp
958: The
959: .Fl f
960: option backgrounds
961: .Nm
962: and the remote command
963: .Dq sleep 10
964: is specified to allow an amount of time
965: (10 seconds, in the example)
966: to start the service which is to be tunnelled.
967: If no connections are made within the time specified,
968: .Nm
969: will exit.
970: .Sh X11 FORWARDING
1.218 jmc 971: If the
972: .Cm ForwardX11
973: variable is set to
974: .Dq yes
975: (or see the description of the
1.227 jmc 976: .Fl X ,
977: .Fl x ,
1.218 jmc 978: and
1.227 jmc 979: .Fl Y
1.226 jmc 980: options above)
1.218 jmc 981: and the user is using X11 (the
982: .Ev DISPLAY
983: environment variable is set), the connection to the X11 display is
984: automatically forwarded to the remote side in such a way that any X11
985: programs started from the shell (or command) will go through the
986: encrypted channel, and the connection to the real X server will be made
1.176 jmc 987: from the local machine.
1.218 jmc 988: The user should not manually set
989: .Ev DISPLAY .
990: Forwarding of X11 connections can be
991: configured on the command line or in configuration files.
992: .Pp
993: The
994: .Ev DISPLAY
995: value set by
996: .Nm
997: will point to the server machine, but with a display number greater than zero.
998: This is normal, and happens because
999: .Nm
1000: creates a
1001: .Dq proxy
1002: X server on the server machine for forwarding the
1003: connections over the encrypted channel.
1.200 djm 1004: .Pp
1.218 jmc 1005: .Nm
1006: will also automatically set up Xauthority data on the server machine.
1007: For this purpose, it will generate a random authorization cookie,
1008: store it in Xauthority on the server, and verify that any forwarded
1009: connections carry this cookie and replace it by the real cookie when
1010: the connection is opened.
1011: The real authentication cookie is never
1012: sent to the server machine (and no cookies are sent in the plain).
1.200 djm 1013: .Pp
1.218 jmc 1014: If the
1015: .Cm ForwardAgent
1016: variable is set to
1017: .Dq yes
1018: (or see the description of the
1019: .Fl A
1.191 djm 1020: and
1.218 jmc 1021: .Fl a
1.226 jmc 1022: options above) and
1.218 jmc 1023: the user is using an authentication agent, the connection to the agent
1024: is automatically forwarded to the remote side.
1.252 jmc 1025: .Sh VERIFYING HOST KEYS
1026: When connecting to a server for the first time,
1027: a fingerprint of the server's public key is presented to the user
1028: (unless the option
1029: .Cm StrictHostKeyChecking
1030: has been disabled).
1031: Fingerprints can be determined using
1032: .Xr ssh-keygen 1 :
1033: .Pp
1034: .Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key
1035: .Pp
1.274 grunk 1036: If the fingerprint is already known, it can be matched
1037: and the key can be accepted or rejected.
1038: Because of the difficulty of comparing host keys
1039: just by looking at hex strings,
1040: there is also support to compare host keys visually,
1041: using
1042: .Em random art .
1043: By setting the
1.275 grunk 1044: .Cm VisualHostKey
1.274 grunk 1045: option to
1.275 grunk 1046: .Dq yes ,
1.274 grunk 1047: a small ASCII graphic gets displayed on every login to a server, no matter
1048: if the session itself is interactive or not.
1049: By learning the pattern a known server produces, a user can easily
1050: find out that the host key has changed when a completely different pattern
1051: is displayed.
1052: Because these patterns are not unambiguous however, a pattern that looks
1053: similar to the pattern remembered only gives a good probability that the
1054: host key is the same, not guaranteed proof.
1055: .Pp
1056: To get a listing of the fingerprints along with their random art for
1057: all known hosts, the following command line can be used:
1058: .Pp
1059: .Dl $ ssh-keygen -lv -f ~/.ssh/known_hosts
1060: .Pp
1.252 jmc 1061: If the fingerprint is unknown,
1062: an alternative method of verification is available:
1063: SSH fingerprints verified by DNS.
1064: An additional resource record (RR),
1065: SSHFP,
1066: is added to a zonefile
1067: and the connecting client is able to match the fingerprint
1068: with that of the key presented.
1069: .Pp
1070: In this example, we are connecting a client to a server,
1071: .Dq host.example.com .
1072: The SSHFP resource records should first be added to the zonefile for
1073: host.example.com:
1074: .Bd -literal -offset indent
1.259 jakob 1075: $ ssh-keygen -r host.example.com.
1.252 jmc 1076: .Ed
1077: .Pp
1078: The output lines will have to be added to the zonefile.
1079: To check that the zone is answering fingerprint queries:
1080: .Pp
1081: .Dl $ dig -t SSHFP host.example.com
1082: .Pp
1083: Finally the client connects:
1084: .Bd -literal -offset indent
1085: $ ssh -o "VerifyHostKeyDNS ask" host.example.com
1086: [...]
1087: Matching host key fingerprint found in DNS.
1088: Are you sure you want to continue connecting (yes/no)?
1089: .Ed
1090: .Pp
1091: See the
1092: .Cm VerifyHostKeyDNS
1093: option in
1094: .Xr ssh_config 5
1095: for more information.
1.250 jmc 1096: .Sh SSH-BASED VIRTUAL PRIVATE NETWORKS
1097: .Nm
1098: contains support for Virtual Private Network (VPN) tunnelling
1099: using the
1100: .Xr tun 4
1101: network pseudo-device,
1102: allowing two networks to be joined securely.
1103: The
1104: .Xr sshd_config 5
1105: configuration option
1106: .Cm PermitTunnel
1107: controls whether the server supports this,
1108: and at what level (layer 2 or 3 traffic).
1109: .Pp
1110: The following example would connect client network 10.0.50.0/24
1.265 otto 1111: with remote network 10.0.99.0/24 using a point-to-point connection
1112: from 10.1.1.1 to 10.1.1.2,
1113: provided that the SSH server running on the gateway to the remote network,
1114: at 192.168.1.15, allows it.
1115: .Pp
1116: On the client:
1.250 jmc 1117: .Bd -literal -offset indent
1118: # ssh -f -w 0:1 192.168.1.15 true
1.265 otto 1119: # ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252
1120: # route add 10.0.99.0/24 10.1.1.2
1121: .Ed
1122: .Pp
1123: On the server:
1124: .Bd -literal -offset indent
1125: # ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252
1126: # route add 10.0.50.0/24 10.1.1.1
1.250 jmc 1127: .Ed
1128: .Pp
1129: Client access may be more finely tuned via the
1130: .Pa /root/.ssh/authorized_keys
1131: file (see below) and the
1132: .Cm PermitRootLogin
1133: server option.
1.255 jmc 1134: The following entry would permit connections on
1.250 jmc 1135: .Xr tun 4
1.255 jmc 1136: device 1 from user
1.250 jmc 1137: .Dq jane
1.255 jmc 1138: and on tun device 2 from user
1.250 jmc 1139: .Dq john ,
1140: if
1141: .Cm PermitRootLogin
1142: is set to
1143: .Dq forced-commands-only :
1144: .Bd -literal -offset 2n
1145: tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane
1.254 msf 1146: tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john
1.250 jmc 1147: .Ed
1148: .Pp
1.264 ray 1149: Since an SSH-based setup entails a fair amount of overhead,
1.250 jmc 1150: it may be more suited to temporary setups,
1151: such as for wireless VPNs.
1152: More permanent VPNs are better provided by tools such as
1153: .Xr ipsecctl 8
1154: and
1155: .Xr isakmpd 8 .
1.2 deraadt 1156: .Sh ENVIRONMENT
1157: .Nm
1.1 deraadt 1158: will normally set the following environment variables:
1.237 jmc 1159: .Bl -tag -width "SSH_ORIGINAL_COMMAND"
1.2 deraadt 1160: .It Ev DISPLAY
1161: The
1162: .Ev DISPLAY
1.40 aaron 1163: variable indicates the location of the X11 server.
1.44 aaron 1164: It is automatically set by
1.2 deraadt 1165: .Nm
1166: to point to a value of the form
1.233 jmc 1167: .Dq hostname:n ,
1168: where
1169: .Dq hostname
1170: indicates the host where the shell runs, and
1171: .Sq n
1172: is an integer \*(Ge 1.
1.40 aaron 1173: .Nm
1174: uses this special value to forward X11 connections over the secure
1175: channel.
1.107 markus 1176: The user should normally not set
1177: .Ev DISPLAY
1178: explicitly, as that
1.1 deraadt 1179: will render the X11 connection insecure (and will require the user to
1180: manually copy any required authorization cookies).
1.2 deraadt 1181: .It Ev HOME
1.1 deraadt 1182: Set to the path of the user's home directory.
1.2 deraadt 1183: .It Ev LOGNAME
1184: Synonym for
1.12 aaron 1185: .Ev USER ;
1186: set for compatibility with systems that use this variable.
1.2 deraadt 1187: .It Ev MAIL
1.129 stevesk 1188: Set to the path of the user's mailbox.
1.40 aaron 1189: .It Ev PATH
1.2 deraadt 1190: Set to the default
1191: .Ev PATH ,
1192: as specified when compiling
1.234 jmc 1193: .Nm .
1.118 markus 1194: .It Ev SSH_ASKPASS
1195: If
1196: .Nm
1197: needs a passphrase, it will read the passphrase from the current
1198: terminal if it was run from a terminal.
1199: If
1200: .Nm
1201: does not have a terminal associated with it but
1202: .Ev DISPLAY
1203: and
1204: .Ev SSH_ASKPASS
1205: are set, it will execute the program specified by
1206: .Ev SSH_ASKPASS
1207: and open an X11 window to read the passphrase.
1208: This is particularly useful when calling
1209: .Nm
1210: from a
1.196 jmc 1211: .Pa .xsession
1.118 markus 1212: or related script.
1213: (Note that on some machines it
1214: may be necessary to redirect the input from
1215: .Pa /dev/null
1216: to make this work.)
1.18 markus 1217: .It Ev SSH_AUTH_SOCK
1.233 jmc 1218: Identifies the path of a
1219: .Ux Ns -domain
1220: socket used to communicate with the agent.
1.166 stevesk 1221: .It Ev SSH_CONNECTION
1222: Identifies the client and server ends of the connection.
1.40 aaron 1223: The variable contains
1.233 jmc 1224: four space-separated values: client IP address, client port number,
1225: server IP address, and server port number.
1.73 markus 1226: .It Ev SSH_ORIGINAL_COMMAND
1.233 jmc 1227: This variable contains the original command line if a forced command
1.73 markus 1228: is executed.
1229: It can be used to extract the original arguments.
1.2 deraadt 1230: .It Ev SSH_TTY
1.1 deraadt 1231: This is set to the name of the tty (path to the device) associated
1.40 aaron 1232: with the current shell or command.
1233: If the current session has no tty,
1.1 deraadt 1234: this variable is not set.
1.2 deraadt 1235: .It Ev TZ
1.214 jmc 1236: This variable is set to indicate the present time zone if it
1.257 jmc 1237: was set when the daemon was started (i.e. the daemon passes the value
1.1 deraadt 1238: on to new connections).
1.2 deraadt 1239: .It Ev USER
1.1 deraadt 1240: Set to the name of the user logging in.
1.2 deraadt 1241: .El
1242: .Pp
1.44 aaron 1243: Additionally,
1.2 deraadt 1244: .Nm
1.44 aaron 1245: reads
1.207 djm 1246: .Pa ~/.ssh/environment ,
1.2 deraadt 1247: and adds lines of the format
1248: .Dq VARNAME=value
1.233 jmc 1249: to the environment if the file exists and users are allowed to
1.161 marc 1250: change their environment.
1.176 jmc 1251: For more information, see the
1.161 marc 1252: .Cm PermitUserEnvironment
1.162 stevesk 1253: option in
1.161 marc 1254: .Xr sshd_config 5 .
1.2 deraadt 1255: .Sh FILES
1.236 jmc 1256: .Bl -tag -width Ds -compact
1257: .It ~/.rhosts
1.240 jmc 1258: This file is used for host-based authentication (see above).
1.92 markus 1259: On some machines this file may need to be
1.240 jmc 1260: world-readable if the user's home directory is on an NFS partition,
1.1 deraadt 1261: because
1.2 deraadt 1262: .Xr sshd 8
1.40 aaron 1263: reads it as root.
1264: Additionally, this file must be owned by the user,
1265: and must not have write permissions for anyone else.
1266: The recommended
1.1 deraadt 1267: permission for most machines is read/write for the user, and not
1268: accessible by others.
1.2 deraadt 1269: .Pp
1.236 jmc 1270: .It ~/.shosts
1.240 jmc 1271: This file is used in exactly the same way as
1272: .Pa .rhosts ,
1273: but allows host-based authentication without permitting login with
1274: rlogin/rsh.
1.272 mcbride 1275: .Pp
1276: .It ~/.ssh/
1277: This directory is the default location for all user-specific configuration
1278: and authentication information.
1279: There is no general requirement to keep the entire contents of this directory
1280: secret, but the recommended permissions are read/write/execute for the user,
1281: and not accessible by others.
1.236 jmc 1282: .Pp
1.238 jmc 1283: .It ~/.ssh/authorized_keys
1284: Lists the public keys (RSA/DSA) that can be used for logging in as this user.
1285: The format of this file is described in the
1286: .Xr sshd 8
1287: manual page.
1288: This file is not highly sensitive, but the recommended
1289: permissions are read/write for the user, and not accessible by others.
1290: .Pp
1291: .It ~/.ssh/config
1292: This is the per-user configuration file.
1293: The file format and configuration options are described in
1294: .Xr ssh_config 5 .
1295: Because of the potential for abuse, this file must have strict permissions:
1296: read/write for the user, and not accessible by others.
1297: .Pp
1298: .It ~/.ssh/environment
1.239 jmc 1299: Contains additional definitions for environment variables; see
1300: .Sx ENVIRONMENT ,
1.238 jmc 1301: above.
1302: .Pp
1303: .It ~/.ssh/identity
1304: .It ~/.ssh/id_dsa
1305: .It ~/.ssh/id_rsa
1306: Contains the private key for authentication.
1307: These files
1308: contain sensitive data and should be readable by the user but not
1309: accessible by others (read/write/execute).
1310: .Nm
1311: will simply ignore a private key file if it is accessible by others.
1312: It is possible to specify a passphrase when
1313: generating the key which will be used to encrypt the
1314: sensitive part of this file using 3DES.
1315: .Pp
1316: .It ~/.ssh/identity.pub
1317: .It ~/.ssh/id_dsa.pub
1318: .It ~/.ssh/id_rsa.pub
1319: Contains the public key for authentication.
1320: These files are not
1321: sensitive and can (but need not) be readable by anyone.
1322: .Pp
1323: .It ~/.ssh/known_hosts
1.244 jmc 1324: Contains a list of host keys for all hosts the user has logged into
1325: that are not already in the systemwide list of known host keys.
1.238 jmc 1326: See
1.244 jmc 1327: .Xr sshd 8
1328: for further details of the format of this file.
1.238 jmc 1329: .Pp
1330: .It ~/.ssh/rc
1331: Commands in this file are executed by
1332: .Nm
1.245 jmc 1333: when the user logs in, just before the user's shell (or command) is
1.238 jmc 1334: started.
1335: See the
1336: .Xr sshd 8
1337: manual page for more information.
1338: .Pp
1.236 jmc 1339: .It /etc/hosts.equiv
1.240 jmc 1340: This file is for host-based authentication (see above).
1341: It should only be writable by root.
1.236 jmc 1342: .Pp
1343: .It /etc/shosts.equiv
1.240 jmc 1344: This file is used in exactly the same way as
1345: .Pa hosts.equiv ,
1346: but allows host-based authentication without permitting login with
1347: rlogin/rsh.
1.236 jmc 1348: .Pp
1.238 jmc 1349: .It Pa /etc/ssh/ssh_config
1350: Systemwide configuration file.
1351: The file format and configuration options are described in
1352: .Xr ssh_config 5 .
1353: .Pp
1354: .It /etc/ssh/ssh_host_key
1355: .It /etc/ssh/ssh_host_dsa_key
1356: .It /etc/ssh/ssh_host_rsa_key
1357: These three files contain the private parts of the host keys
1.245 jmc 1358: and are used for host-based authentication.
1359: If protocol version 1 is used,
1.238 jmc 1360: .Nm
1361: must be setuid root, since the host key is readable only by root.
1362: For protocol version 2,
1363: .Nm
1364: uses
1365: .Xr ssh-keysign 8
1.245 jmc 1366: to access the host keys,
1367: eliminating the requirement that
1.238 jmc 1368: .Nm
1.245 jmc 1369: be setuid root when host-based authentication is used.
1.238 jmc 1370: By default
1.2 deraadt 1371: .Nm
1.238 jmc 1372: is not setuid root.
1373: .Pp
1374: .It /etc/ssh/ssh_known_hosts
1375: Systemwide list of known host keys.
1376: This file should be prepared by the
1377: system administrator to contain the public host keys of all machines in the
1378: organization.
1.244 jmc 1379: It should be world-readable.
1380: See
1.238 jmc 1381: .Xr sshd 8
1.244 jmc 1382: for further details of the format of this file.
1.236 jmc 1383: .Pp
1.238 jmc 1384: .It /etc/ssh/sshrc
1.1 deraadt 1385: Commands in this file are executed by
1.2 deraadt 1386: .Nm
1.245 jmc 1387: when the user logs in, just before the user's shell (or command) is started.
1.44 aaron 1388: See the
1.2 deraadt 1389: .Xr sshd 8
1.1 deraadt 1390: manual page for more information.
1.58 itojun 1391: .El
1.2 deraadt 1392: .Sh SEE ALSO
1393: .Xr scp 1 ,
1.83 djm 1394: .Xr sftp 1 ,
1.2 deraadt 1395: .Xr ssh-add 1 ,
1396: .Xr ssh-agent 1 ,
1397: .Xr ssh-keygen 1 ,
1.242 jmc 1398: .Xr ssh-keyscan 1 ,
1.250 jmc 1399: .Xr tun 4 ,
1.176 jmc 1400: .Xr hosts.equiv 5 ,
1.159 stevesk 1401: .Xr ssh_config 5 ,
1.160 naddy 1402: .Xr ssh-keysign 8 ,
1.87 itojun 1403: .Xr sshd 8
1.106 markus 1404: .Rs
1.256 jmc 1405: .%R RFC 4250
1406: .%T "The Secure Shell (SSH) Protocol Assigned Numbers"
1407: .%D 2006
1408: .Re
1409: .Rs
1410: .%R RFC 4251
1411: .%T "The Secure Shell (SSH) Protocol Architecture"
1412: .%D 2006
1413: .Re
1414: .Rs
1415: .%R RFC 4252
1416: .%T "The Secure Shell (SSH) Authentication Protocol"
1417: .%D 2006
1418: .Re
1419: .Rs
1420: .%R RFC 4253
1421: .%T "The Secure Shell (SSH) Transport Layer Protocol"
1422: .%D 2006
1423: .Re
1424: .Rs
1425: .%R RFC 4254
1426: .%T "The Secure Shell (SSH) Connection Protocol"
1427: .%D 2006
1428: .Re
1429: .Rs
1430: .%R RFC 4255
1431: .%T "Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints"
1432: .%D 2006
1433: .Re
1434: .Rs
1435: .%R RFC 4256
1436: .%T "Generic Message Exchange Authentication for the Secure Shell Protocol (SSH)"
1437: .%D 2006
1438: .Re
1439: .Rs
1440: .%R RFC 4335
1441: .%T "The Secure Shell (SSH) Session Channel Break Extension"
1442: .%D 2006
1443: .Re
1444: .Rs
1445: .%R RFC 4344
1446: .%T "The Secure Shell (SSH) Transport Layer Encryption Modes"
1447: .%D 2006
1448: .Re
1449: .Rs
1450: .%R RFC 4345
1451: .%T "Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol"
1.258 djm 1452: .%D 2006
1453: .Re
1454: .Rs
1455: .%R RFC 4419
1456: .%T "Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol"
1.266 markus 1457: .%D 2006
1458: .Re
1459: .Rs
1460: .%R RFC 4716
1461: .%T "The Secure Shell (SSH) Public Key File Format"
1.256 jmc 1462: .%D 2006
1.274 grunk 1463: .Re
1464: .Rs
1465: .%T "Hash Visualization: a New Technique to improve Real-World Security"
1466: .%A A. Perrig
1467: .%A D. Song
1468: .%D 1999
1469: .%O "International Workshop on Cryptographic Techniques and E-Commerce (CrypTEC '99)"
1.106 markus 1470: .Re
1.173 jmc 1471: .Sh AUTHORS
1472: OpenSSH is a derivative of the original and free
1473: ssh 1.2.12 release by Tatu Ylonen.
1474: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1475: Theo de Raadt and Dug Song
1476: removed many bugs, re-added newer features and
1477: created OpenSSH.
1478: Markus Friedl contributed the support for SSH
1479: protocol versions 1.5 and 2.0.