Annotation of src/usr.bin/ssh/ssh.1, Revision 1.284
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: .\"
1.284 ! jmc 37: .\" $OpenBSD: ssh.1,v 1.283 2009/03/19 15:15:09 jmc Exp $
! 38: .Dd $Mdocdate: March 19 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.
1.284 ! jmc 669: The default is to use protocol 2 only,
! 670: though this can be changed via the
1.222 jmc 671: .Cm Protocol
672: option in
1.284 ! jmc 673: .Xr ssh_config 5
! 674: or the
1.222 jmc 675: .Fl 1
676: and
677: .Fl 2
678: options (see above).
679: Both protocols support similar authentication methods,
1.284 ! jmc 680: but protocol 2 is the default since
1.222 jmc 681: it provides additional mechanisms for confidentiality
682: (the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour)
1.268 pvalchev 683: and integrity (hmac-md5, hmac-sha1, umac-64, hmac-ripemd160).
1.222 jmc 684: Protocol 1 lacks a strong mechanism for ensuring the
685: integrity of the connection.
686: .Pp
687: The methods available for authentication are:
1.260 jmc 688: GSSAPI-based authentication,
1.222 jmc 689: host-based authentication,
690: public key authentication,
691: challenge-response authentication,
692: and password authentication.
693: Authentication methods are tried in the order specified above,
694: though protocol 2 has a configuration option to change the default order:
695: .Cm PreferredAuthentications .
696: .Pp
697: Host-based authentication works as follows:
1.218 jmc 698: If the machine the user logs in from is listed in
699: .Pa /etc/hosts.equiv
700: or
701: .Pa /etc/shosts.equiv
702: on the remote machine, and the user names are
703: the same on both sides, or if the files
704: .Pa ~/.rhosts
705: or
706: .Pa ~/.shosts
707: exist in the user's home directory on the
708: remote machine and contain a line containing the name of the client
709: machine and the name of the user on that machine, the user is
1.222 jmc 710: considered for login.
711: Additionally, the server
712: .Em must
713: be able to verify the client's
714: host key (see the description of
1.218 jmc 715: .Pa /etc/ssh/ssh_known_hosts
1.189 dtucker 716: and
1.222 jmc 717: .Pa ~/.ssh/known_hosts ,
718: below)
719: for login to be permitted.
1.218 jmc 720: This authentication method closes security holes due to IP
1.222 jmc 721: spoofing, DNS spoofing, and routing spoofing.
1.218 jmc 722: [Note to the administrator:
723: .Pa /etc/hosts.equiv ,
724: .Pa ~/.rhosts ,
725: and the rlogin/rsh protocol in general, are inherently insecure and should be
726: disabled if security is desired.]
1.189 dtucker 727: .Pp
1.222 jmc 728: Public key authentication works as follows:
729: The scheme is based on public-key cryptography,
730: using cryptosystems
731: where encryption and decryption are done using separate keys,
732: and it is unfeasible to derive the decryption key from the encryption key.
1.218 jmc 733: The idea is that each user creates a public/private
734: key pair for authentication purposes.
735: The server knows the public key, and only the user knows the private key.
1.222 jmc 736: .Nm
737: implements public key authentication protocol automatically,
738: using either the RSA or DSA algorithms.
739: Protocol 1 is restricted to using only RSA keys,
740: but protocol 2 may use either.
741: The
742: .Sx HISTORY
743: section of
744: .Xr ssl 8
745: contains a brief discussion of the two algorithms.
1.210 djm 746: .Pp
1.218 jmc 747: The file
748: .Pa ~/.ssh/authorized_keys
749: lists the public keys that are permitted for logging in.
750: When the user logs in, the
1.2 deraadt 751: .Nm
1.218 jmc 752: program tells the server which key pair it would like to use for
753: authentication.
1.222 jmc 754: The client proves that it has access to the private key
755: and the server checks that the corresponding public key
756: is authorized to accept the account.
1.218 jmc 757: .Pp
1.222 jmc 758: The user creates his/her key pair by running
1.218 jmc 759: .Xr ssh-keygen 1 .
760: This stores the private key in
1.207 djm 761: .Pa ~/.ssh/identity
1.222 jmc 762: (protocol 1),
763: .Pa ~/.ssh/id_dsa
764: (protocol 2 DSA),
765: or
766: .Pa ~/.ssh/id_rsa
767: (protocol 2 RSA)
1.218 jmc 768: and stores the public key in
769: .Pa ~/.ssh/identity.pub
1.222 jmc 770: (protocol 1),
771: .Pa ~/.ssh/id_dsa.pub
772: (protocol 2 DSA),
773: or
774: .Pa ~/.ssh/id_rsa.pub
775: (protocol 2 RSA)
1.218 jmc 776: in the user's home directory.
1.222 jmc 777: The user should then copy the public key
1.218 jmc 778: to
779: .Pa ~/.ssh/authorized_keys
1.222 jmc 780: in his/her home directory on the remote machine.
781: The
1.218 jmc 782: .Pa authorized_keys
783: file corresponds to the conventional
784: .Pa ~/.rhosts
785: file, and has one key
1.222 jmc 786: per line, though the lines can be very long.
1.218 jmc 787: After this, the user can log in without giving the password.
788: .Pp
1.222 jmc 789: The most convenient way to use public key authentication may be with an
1.218 jmc 790: authentication agent.
791: See
792: .Xr ssh-agent 1
793: for more information.
794: .Pp
1.222 jmc 795: Challenge-response authentication works as follows:
796: The server sends an arbitrary
797: .Qq challenge
798: text, and prompts for a response.
799: Protocol 2 allows multiple challenges and responses;
800: protocol 1 is restricted to just one challenge/response.
801: Examples of challenge-response authentication include
802: BSD Authentication (see
803: .Xr login.conf 5 )
804: and PAM (some non-OpenBSD systems).
805: .Pp
806: Finally, if other authentication methods fail,
1.218 jmc 807: .Nm
808: prompts the user for a password.
809: The password is sent to the remote
810: host for checking; however, since all communications are encrypted,
811: the password cannot be seen by someone listening on the network.
1.232 jmc 812: .Pp
813: .Nm
814: automatically maintains and checks a database containing
815: identification for all hosts it has ever been used with.
816: Host keys are stored in
817: .Pa ~/.ssh/known_hosts
818: in the user's home directory.
819: Additionally, the file
820: .Pa /etc/ssh/ssh_known_hosts
821: is automatically checked for known hosts.
822: Any new hosts are automatically added to the user's file.
823: If a host's identification ever changes,
824: .Nm
825: warns about this and disables password authentication to prevent
826: server spoofing or man-in-the-middle attacks,
827: which could otherwise be used to circumvent the encryption.
828: The
829: .Cm StrictHostKeyChecking
830: option can be used to control logins to machines whose
831: host key is not known or has changed.
832: .Pp
1.218 jmc 833: When the user's identity has been accepted by the server, the server
834: either executes the given command, or logs into the machine and gives
835: the user a normal shell on the remote machine.
836: All communication with
837: the remote command or shell will be automatically encrypted.
838: .Pp
839: If a pseudo-terminal has been allocated (normal login session), the
840: user may use the escape characters noted below.
841: .Pp
842: If no pseudo-tty has been allocated,
843: the session is transparent and can be used to reliably transfer binary data.
844: On most systems, setting the escape character to
845: .Dq none
846: will also make the session transparent even if a tty is used.
847: .Pp
848: The session terminates when the command or shell on the remote
1.247 jmc 849: machine exits and all X11 and TCP connections have been closed.
1.223 jmc 850: .Sh ESCAPE CHARACTERS
1.218 jmc 851: When a pseudo-terminal has been requested,
1.2 deraadt 852: .Nm
1.218 jmc 853: supports a number of functions through the use of an escape character.
854: .Pp
855: A single tilde character can be sent as
856: .Ic ~~
857: or by following the tilde by a character other than those described below.
858: The escape character must always follow a newline to be interpreted as
859: special.
860: The escape character can be changed in configuration files using the
861: .Cm EscapeChar
862: configuration directive or on the command line by the
863: .Fl e
864: option.
865: .Pp
866: The supported escapes (assuming the default
867: .Ql ~ )
868: are:
869: .Bl -tag -width Ds
870: .It Cm ~.
871: Disconnect.
872: .It Cm ~^Z
873: Background
1.234 jmc 874: .Nm .
1.218 jmc 875: .It Cm ~#
876: List forwarded connections.
877: .It Cm ~&
878: Background
1.2 deraadt 879: .Nm
1.218 jmc 880: at logout when waiting for forwarded connection / X11 sessions to terminate.
881: .It Cm ~?
882: Display a list of escape characters.
883: .It Cm ~B
884: Send a BREAK to the remote system
885: (only useful for SSH protocol version 2 and if the peer supports it).
886: .It Cm ~C
887: Open command line.
888: Currently this allows the addition of port forwardings using the
1.279 stevesk 889: .Fl L ,
890: .Fl R
1.218 jmc 891: and
1.279 stevesk 892: .Fl D
1.225 jmc 893: options (see above).
1.218 jmc 894: It also allows the cancellation of existing remote port-forwardings
895: using
1.262 stevesk 896: .Sm off
897: .Fl KR Oo Ar bind_address : Oc Ar port .
898: .Sm on
1.218 jmc 899: .Ic !\& Ns Ar command
900: allows the user to execute a local command if the
901: .Ic PermitLocalCommand
902: option is enabled in
1.176 jmc 903: .Xr ssh_config 5 .
1.218 jmc 904: Basic help is available, using the
905: .Fl h
906: option.
907: .It Cm ~R
908: Request rekeying of the connection
909: (only useful for SSH protocol version 2 and if the peer supports it).
1.176 jmc 910: .El
1.246 jmc 911: .Sh TCP FORWARDING
912: Forwarding of arbitrary TCP connections over the secure channel can
913: be specified either on the command line or in a configuration file.
914: One possible application of TCP forwarding is a secure connection to a
915: mail server; another is going through firewalls.
916: .Pp
917: In the example below, we look at encrypting communication between
918: an IRC client and server, even though the IRC server does not directly
919: support encrypted communications.
920: This works as follows:
921: the user connects to the remote host using
922: .Nm ,
923: specifying a port to be used to forward connections
924: to the remote server.
925: After that it is possible to start the service which is to be encrypted
926: on the client machine,
927: connecting to the same local port,
928: and
929: .Nm
930: will encrypt and forward the connection.
931: .Pp
932: The following example tunnels an IRC session from client machine
933: .Dq 127.0.0.1
934: (localhost)
935: to remote server
936: .Dq server.example.com :
937: .Bd -literal -offset 4n
938: $ ssh -f -L 1234:localhost:6667 server.example.com sleep 10
939: $ irc -c '#users' -p 1234 pinky 127.0.0.1
940: .Ed
941: .Pp
942: This tunnels a connection to IRC server
943: .Dq server.example.com ,
944: joining channel
945: .Dq #users ,
946: nickname
947: .Dq pinky ,
948: using port 1234.
949: It doesn't matter which port is used,
950: as long as it's greater than 1023
951: (remember, only root can open sockets on privileged ports)
952: and doesn't conflict with any ports already in use.
953: The connection is forwarded to port 6667 on the remote server,
954: since that's the standard port for IRC services.
955: .Pp
956: The
957: .Fl f
958: option backgrounds
959: .Nm
960: and the remote command
961: .Dq sleep 10
962: is specified to allow an amount of time
963: (10 seconds, in the example)
964: to start the service which is to be tunnelled.
965: If no connections are made within the time specified,
966: .Nm
967: will exit.
968: .Sh X11 FORWARDING
1.218 jmc 969: If the
970: .Cm ForwardX11
971: variable is set to
972: .Dq yes
973: (or see the description of the
1.227 jmc 974: .Fl X ,
975: .Fl x ,
1.218 jmc 976: and
1.227 jmc 977: .Fl Y
1.226 jmc 978: options above)
1.218 jmc 979: and the user is using X11 (the
980: .Ev DISPLAY
981: environment variable is set), the connection to the X11 display is
982: automatically forwarded to the remote side in such a way that any X11
983: programs started from the shell (or command) will go through the
984: encrypted channel, and the connection to the real X server will be made
1.176 jmc 985: from the local machine.
1.218 jmc 986: The user should not manually set
987: .Ev DISPLAY .
988: Forwarding of X11 connections can be
989: configured on the command line or in configuration files.
990: .Pp
991: The
992: .Ev DISPLAY
993: value set by
994: .Nm
995: will point to the server machine, but with a display number greater than zero.
996: This is normal, and happens because
997: .Nm
998: creates a
999: .Dq proxy
1000: X server on the server machine for forwarding the
1001: connections over the encrypted channel.
1.200 djm 1002: .Pp
1.218 jmc 1003: .Nm
1004: will also automatically set up Xauthority data on the server machine.
1005: For this purpose, it will generate a random authorization cookie,
1006: store it in Xauthority on the server, and verify that any forwarded
1007: connections carry this cookie and replace it by the real cookie when
1008: the connection is opened.
1009: The real authentication cookie is never
1010: sent to the server machine (and no cookies are sent in the plain).
1.200 djm 1011: .Pp
1.218 jmc 1012: If the
1013: .Cm ForwardAgent
1014: variable is set to
1015: .Dq yes
1016: (or see the description of the
1017: .Fl A
1.191 djm 1018: and
1.218 jmc 1019: .Fl a
1.226 jmc 1020: options above) and
1.218 jmc 1021: the user is using an authentication agent, the connection to the agent
1022: is automatically forwarded to the remote side.
1.252 jmc 1023: .Sh VERIFYING HOST KEYS
1024: When connecting to a server for the first time,
1025: a fingerprint of the server's public key is presented to the user
1026: (unless the option
1027: .Cm StrictHostKeyChecking
1028: has been disabled).
1029: Fingerprints can be determined using
1030: .Xr ssh-keygen 1 :
1031: .Pp
1032: .Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key
1033: .Pp
1.274 grunk 1034: If the fingerprint is already known, it can be matched
1035: and the key can be accepted or rejected.
1036: Because of the difficulty of comparing host keys
1037: just by looking at hex strings,
1038: there is also support to compare host keys visually,
1039: using
1040: .Em random art .
1041: By setting the
1.275 grunk 1042: .Cm VisualHostKey
1.274 grunk 1043: option to
1.275 grunk 1044: .Dq yes ,
1.274 grunk 1045: a small ASCII graphic gets displayed on every login to a server, no matter
1046: if the session itself is interactive or not.
1047: By learning the pattern a known server produces, a user can easily
1048: find out that the host key has changed when a completely different pattern
1049: is displayed.
1050: Because these patterns are not unambiguous however, a pattern that looks
1051: similar to the pattern remembered only gives a good probability that the
1052: host key is the same, not guaranteed proof.
1053: .Pp
1054: To get a listing of the fingerprints along with their random art for
1055: all known hosts, the following command line can be used:
1056: .Pp
1057: .Dl $ ssh-keygen -lv -f ~/.ssh/known_hosts
1058: .Pp
1.252 jmc 1059: If the fingerprint is unknown,
1060: an alternative method of verification is available:
1061: SSH fingerprints verified by DNS.
1062: An additional resource record (RR),
1063: SSHFP,
1064: is added to a zonefile
1065: and the connecting client is able to match the fingerprint
1066: with that of the key presented.
1067: .Pp
1068: In this example, we are connecting a client to a server,
1069: .Dq host.example.com .
1070: The SSHFP resource records should first be added to the zonefile for
1071: host.example.com:
1072: .Bd -literal -offset indent
1.259 jakob 1073: $ ssh-keygen -r host.example.com.
1.252 jmc 1074: .Ed
1075: .Pp
1076: The output lines will have to be added to the zonefile.
1077: To check that the zone is answering fingerprint queries:
1078: .Pp
1079: .Dl $ dig -t SSHFP host.example.com
1080: .Pp
1081: Finally the client connects:
1082: .Bd -literal -offset indent
1083: $ ssh -o "VerifyHostKeyDNS ask" host.example.com
1084: [...]
1085: Matching host key fingerprint found in DNS.
1086: Are you sure you want to continue connecting (yes/no)?
1087: .Ed
1088: .Pp
1089: See the
1090: .Cm VerifyHostKeyDNS
1091: option in
1092: .Xr ssh_config 5
1093: for more information.
1.250 jmc 1094: .Sh SSH-BASED VIRTUAL PRIVATE NETWORKS
1095: .Nm
1096: contains support for Virtual Private Network (VPN) tunnelling
1097: using the
1098: .Xr tun 4
1099: network pseudo-device,
1100: allowing two networks to be joined securely.
1101: The
1102: .Xr sshd_config 5
1103: configuration option
1104: .Cm PermitTunnel
1105: controls whether the server supports this,
1106: and at what level (layer 2 or 3 traffic).
1107: .Pp
1108: The following example would connect client network 10.0.50.0/24
1.265 otto 1109: with remote network 10.0.99.0/24 using a point-to-point connection
1110: from 10.1.1.1 to 10.1.1.2,
1111: provided that the SSH server running on the gateway to the remote network,
1112: at 192.168.1.15, allows it.
1113: .Pp
1114: On the client:
1.250 jmc 1115: .Bd -literal -offset indent
1116: # ssh -f -w 0:1 192.168.1.15 true
1.265 otto 1117: # ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252
1118: # route add 10.0.99.0/24 10.1.1.2
1119: .Ed
1120: .Pp
1121: On the server:
1122: .Bd -literal -offset indent
1123: # ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252
1124: # route add 10.0.50.0/24 10.1.1.1
1.250 jmc 1125: .Ed
1126: .Pp
1127: Client access may be more finely tuned via the
1128: .Pa /root/.ssh/authorized_keys
1129: file (see below) and the
1130: .Cm PermitRootLogin
1131: server option.
1.255 jmc 1132: The following entry would permit connections on
1.250 jmc 1133: .Xr tun 4
1.255 jmc 1134: device 1 from user
1.250 jmc 1135: .Dq jane
1.255 jmc 1136: and on tun device 2 from user
1.250 jmc 1137: .Dq john ,
1138: if
1139: .Cm PermitRootLogin
1140: is set to
1141: .Dq forced-commands-only :
1142: .Bd -literal -offset 2n
1143: tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane
1.254 msf 1144: tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john
1.250 jmc 1145: .Ed
1146: .Pp
1.264 ray 1147: Since an SSH-based setup entails a fair amount of overhead,
1.250 jmc 1148: it may be more suited to temporary setups,
1149: such as for wireless VPNs.
1150: More permanent VPNs are better provided by tools such as
1151: .Xr ipsecctl 8
1152: and
1153: .Xr isakmpd 8 .
1.2 deraadt 1154: .Sh ENVIRONMENT
1155: .Nm
1.1 deraadt 1156: will normally set the following environment variables:
1.237 jmc 1157: .Bl -tag -width "SSH_ORIGINAL_COMMAND"
1.2 deraadt 1158: .It Ev DISPLAY
1159: The
1160: .Ev DISPLAY
1.40 aaron 1161: variable indicates the location of the X11 server.
1.44 aaron 1162: It is automatically set by
1.2 deraadt 1163: .Nm
1164: to point to a value of the form
1.233 jmc 1165: .Dq hostname:n ,
1166: where
1167: .Dq hostname
1168: indicates the host where the shell runs, and
1169: .Sq n
1170: is an integer \*(Ge 1.
1.40 aaron 1171: .Nm
1172: uses this special value to forward X11 connections over the secure
1173: channel.
1.107 markus 1174: The user should normally not set
1175: .Ev DISPLAY
1176: explicitly, as that
1.1 deraadt 1177: will render the X11 connection insecure (and will require the user to
1178: manually copy any required authorization cookies).
1.2 deraadt 1179: .It Ev HOME
1.1 deraadt 1180: Set to the path of the user's home directory.
1.2 deraadt 1181: .It Ev LOGNAME
1182: Synonym for
1.12 aaron 1183: .Ev USER ;
1184: set for compatibility with systems that use this variable.
1.2 deraadt 1185: .It Ev MAIL
1.129 stevesk 1186: Set to the path of the user's mailbox.
1.40 aaron 1187: .It Ev PATH
1.2 deraadt 1188: Set to the default
1189: .Ev PATH ,
1190: as specified when compiling
1.234 jmc 1191: .Nm .
1.118 markus 1192: .It Ev SSH_ASKPASS
1193: If
1194: .Nm
1195: needs a passphrase, it will read the passphrase from the current
1196: terminal if it was run from a terminal.
1197: If
1198: .Nm
1199: does not have a terminal associated with it but
1200: .Ev DISPLAY
1201: and
1202: .Ev SSH_ASKPASS
1203: are set, it will execute the program specified by
1204: .Ev SSH_ASKPASS
1205: and open an X11 window to read the passphrase.
1206: This is particularly useful when calling
1207: .Nm
1208: from a
1.196 jmc 1209: .Pa .xsession
1.118 markus 1210: or related script.
1211: (Note that on some machines it
1212: may be necessary to redirect the input from
1213: .Pa /dev/null
1214: to make this work.)
1.18 markus 1215: .It Ev SSH_AUTH_SOCK
1.233 jmc 1216: Identifies the path of a
1217: .Ux Ns -domain
1218: socket used to communicate with the agent.
1.166 stevesk 1219: .It Ev SSH_CONNECTION
1220: Identifies the client and server ends of the connection.
1.40 aaron 1221: The variable contains
1.233 jmc 1222: four space-separated values: client IP address, client port number,
1223: server IP address, and server port number.
1.73 markus 1224: .It Ev SSH_ORIGINAL_COMMAND
1.233 jmc 1225: This variable contains the original command line if a forced command
1.73 markus 1226: is executed.
1227: It can be used to extract the original arguments.
1.2 deraadt 1228: .It Ev SSH_TTY
1.1 deraadt 1229: This is set to the name of the tty (path to the device) associated
1.40 aaron 1230: with the current shell or command.
1231: If the current session has no tty,
1.1 deraadt 1232: this variable is not set.
1.2 deraadt 1233: .It Ev TZ
1.214 jmc 1234: This variable is set to indicate the present time zone if it
1.257 jmc 1235: was set when the daemon was started (i.e. the daemon passes the value
1.1 deraadt 1236: on to new connections).
1.2 deraadt 1237: .It Ev USER
1.1 deraadt 1238: Set to the name of the user logging in.
1.2 deraadt 1239: .El
1240: .Pp
1.44 aaron 1241: Additionally,
1.2 deraadt 1242: .Nm
1.44 aaron 1243: reads
1.207 djm 1244: .Pa ~/.ssh/environment ,
1.2 deraadt 1245: and adds lines of the format
1246: .Dq VARNAME=value
1.233 jmc 1247: to the environment if the file exists and users are allowed to
1.161 marc 1248: change their environment.
1.176 jmc 1249: For more information, see the
1.161 marc 1250: .Cm PermitUserEnvironment
1.162 stevesk 1251: option in
1.161 marc 1252: .Xr sshd_config 5 .
1.2 deraadt 1253: .Sh FILES
1.236 jmc 1254: .Bl -tag -width Ds -compact
1255: .It ~/.rhosts
1.240 jmc 1256: This file is used for host-based authentication (see above).
1.92 markus 1257: On some machines this file may need to be
1.240 jmc 1258: world-readable if the user's home directory is on an NFS partition,
1.1 deraadt 1259: because
1.2 deraadt 1260: .Xr sshd 8
1.40 aaron 1261: reads it as root.
1262: Additionally, this file must be owned by the user,
1263: and must not have write permissions for anyone else.
1264: The recommended
1.1 deraadt 1265: permission for most machines is read/write for the user, and not
1266: accessible by others.
1.2 deraadt 1267: .Pp
1.236 jmc 1268: .It ~/.shosts
1.240 jmc 1269: This file is used in exactly the same way as
1270: .Pa .rhosts ,
1271: but allows host-based authentication without permitting login with
1272: rlogin/rsh.
1.272 mcbride 1273: .Pp
1274: .It ~/.ssh/
1275: This directory is the default location for all user-specific configuration
1276: and authentication information.
1277: There is no general requirement to keep the entire contents of this directory
1278: secret, but the recommended permissions are read/write/execute for the user,
1279: and not accessible by others.
1.236 jmc 1280: .Pp
1.238 jmc 1281: .It ~/.ssh/authorized_keys
1282: Lists the public keys (RSA/DSA) that can be used for logging in as this user.
1283: The format of this file is described in the
1284: .Xr sshd 8
1285: manual page.
1286: This file is not highly sensitive, but the recommended
1287: permissions are read/write for the user, and not accessible by others.
1288: .Pp
1289: .It ~/.ssh/config
1290: This is the per-user configuration file.
1291: The file format and configuration options are described in
1292: .Xr ssh_config 5 .
1293: Because of the potential for abuse, this file must have strict permissions:
1294: read/write for the user, and not accessible by others.
1295: .Pp
1296: .It ~/.ssh/environment
1.239 jmc 1297: Contains additional definitions for environment variables; see
1298: .Sx ENVIRONMENT ,
1.238 jmc 1299: above.
1300: .Pp
1301: .It ~/.ssh/identity
1302: .It ~/.ssh/id_dsa
1303: .It ~/.ssh/id_rsa
1304: Contains the private key for authentication.
1305: These files
1306: contain sensitive data and should be readable by the user but not
1307: accessible by others (read/write/execute).
1308: .Nm
1309: will simply ignore a private key file if it is accessible by others.
1310: It is possible to specify a passphrase when
1311: generating the key which will be used to encrypt the
1312: sensitive part of this file using 3DES.
1313: .Pp
1314: .It ~/.ssh/identity.pub
1315: .It ~/.ssh/id_dsa.pub
1316: .It ~/.ssh/id_rsa.pub
1317: Contains the public key for authentication.
1318: These files are not
1319: sensitive and can (but need not) be readable by anyone.
1320: .Pp
1321: .It ~/.ssh/known_hosts
1.244 jmc 1322: Contains a list of host keys for all hosts the user has logged into
1323: that are not already in the systemwide list of known host keys.
1.238 jmc 1324: See
1.244 jmc 1325: .Xr sshd 8
1326: for further details of the format of this file.
1.238 jmc 1327: .Pp
1328: .It ~/.ssh/rc
1329: Commands in this file are executed by
1330: .Nm
1.245 jmc 1331: when the user logs in, just before the user's shell (or command) is
1.238 jmc 1332: started.
1333: See the
1334: .Xr sshd 8
1335: manual page for more information.
1336: .Pp
1.236 jmc 1337: .It /etc/hosts.equiv
1.240 jmc 1338: This file is for host-based authentication (see above).
1339: It should only be writable by root.
1.236 jmc 1340: .Pp
1341: .It /etc/shosts.equiv
1.240 jmc 1342: This file is used in exactly the same way as
1343: .Pa hosts.equiv ,
1344: but allows host-based authentication without permitting login with
1345: rlogin/rsh.
1.236 jmc 1346: .Pp
1.238 jmc 1347: .It Pa /etc/ssh/ssh_config
1348: Systemwide configuration file.
1349: The file format and configuration options are described in
1350: .Xr ssh_config 5 .
1351: .Pp
1352: .It /etc/ssh/ssh_host_key
1353: .It /etc/ssh/ssh_host_dsa_key
1354: .It /etc/ssh/ssh_host_rsa_key
1355: These three files contain the private parts of the host keys
1.245 jmc 1356: and are used for host-based authentication.
1357: If protocol version 1 is used,
1.238 jmc 1358: .Nm
1359: must be setuid root, since the host key is readable only by root.
1360: For protocol version 2,
1361: .Nm
1362: uses
1363: .Xr ssh-keysign 8
1.245 jmc 1364: to access the host keys,
1365: eliminating the requirement that
1.238 jmc 1366: .Nm
1.245 jmc 1367: be setuid root when host-based authentication is used.
1.238 jmc 1368: By default
1.2 deraadt 1369: .Nm
1.238 jmc 1370: is not setuid root.
1371: .Pp
1372: .It /etc/ssh/ssh_known_hosts
1373: Systemwide list of known host keys.
1374: This file should be prepared by the
1375: system administrator to contain the public host keys of all machines in the
1376: organization.
1.244 jmc 1377: It should be world-readable.
1378: See
1.238 jmc 1379: .Xr sshd 8
1.244 jmc 1380: for further details of the format of this file.
1.236 jmc 1381: .Pp
1.238 jmc 1382: .It /etc/ssh/sshrc
1.1 deraadt 1383: Commands in this file are executed by
1.2 deraadt 1384: .Nm
1.245 jmc 1385: when the user logs in, just before the user's shell (or command) is started.
1.44 aaron 1386: See the
1.2 deraadt 1387: .Xr sshd 8
1.1 deraadt 1388: manual page for more information.
1.58 itojun 1389: .El
1.2 deraadt 1390: .Sh SEE ALSO
1391: .Xr scp 1 ,
1.83 djm 1392: .Xr sftp 1 ,
1.2 deraadt 1393: .Xr ssh-add 1 ,
1394: .Xr ssh-agent 1 ,
1395: .Xr ssh-keygen 1 ,
1.242 jmc 1396: .Xr ssh-keyscan 1 ,
1.250 jmc 1397: .Xr tun 4 ,
1.176 jmc 1398: .Xr hosts.equiv 5 ,
1.159 stevesk 1399: .Xr ssh_config 5 ,
1.160 naddy 1400: .Xr ssh-keysign 8 ,
1.87 itojun 1401: .Xr sshd 8
1.106 markus 1402: .Rs
1.256 jmc 1403: .%R RFC 4250
1404: .%T "The Secure Shell (SSH) Protocol Assigned Numbers"
1405: .%D 2006
1406: .Re
1407: .Rs
1408: .%R RFC 4251
1409: .%T "The Secure Shell (SSH) Protocol Architecture"
1410: .%D 2006
1411: .Re
1412: .Rs
1413: .%R RFC 4252
1414: .%T "The Secure Shell (SSH) Authentication Protocol"
1415: .%D 2006
1416: .Re
1417: .Rs
1418: .%R RFC 4253
1419: .%T "The Secure Shell (SSH) Transport Layer Protocol"
1420: .%D 2006
1421: .Re
1422: .Rs
1423: .%R RFC 4254
1424: .%T "The Secure Shell (SSH) Connection Protocol"
1425: .%D 2006
1426: .Re
1427: .Rs
1428: .%R RFC 4255
1429: .%T "Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints"
1430: .%D 2006
1431: .Re
1432: .Rs
1433: .%R RFC 4256
1434: .%T "Generic Message Exchange Authentication for the Secure Shell Protocol (SSH)"
1435: .%D 2006
1436: .Re
1437: .Rs
1438: .%R RFC 4335
1439: .%T "The Secure Shell (SSH) Session Channel Break Extension"
1440: .%D 2006
1441: .Re
1442: .Rs
1443: .%R RFC 4344
1444: .%T "The Secure Shell (SSH) Transport Layer Encryption Modes"
1445: .%D 2006
1446: .Re
1447: .Rs
1448: .%R RFC 4345
1449: .%T "Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol"
1.258 djm 1450: .%D 2006
1451: .Re
1452: .Rs
1453: .%R RFC 4419
1454: .%T "Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol"
1.266 markus 1455: .%D 2006
1456: .Re
1457: .Rs
1458: .%R RFC 4716
1459: .%T "The Secure Shell (SSH) Public Key File Format"
1.256 jmc 1460: .%D 2006
1.274 grunk 1461: .Re
1462: .Rs
1463: .%T "Hash Visualization: a New Technique to improve Real-World Security"
1464: .%A A. Perrig
1465: .%A D. Song
1466: .%D 1999
1467: .%O "International Workshop on Cryptographic Techniques and E-Commerce (CrypTEC '99)"
1.106 markus 1468: .Re
1.173 jmc 1469: .Sh AUTHORS
1470: OpenSSH is a derivative of the original and free
1471: ssh 1.2.12 release by Tatu Ylonen.
1472: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1473: Theo de Raadt and Dug Song
1474: removed many bugs, re-added newer features and
1475: created OpenSSH.
1476: Markus Friedl contributed the support for SSH
1477: protocol versions 1.5 and 2.0.
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