Annotation of src/usr.bin/ssh/ssh.1, Revision 1.217
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: .\"
1.217 ! jmc 37: .\" $OpenBSD: ssh.1,v 1.216 2005/12/07 10:52:13 jmc Exp $
1.2 deraadt 38: .Dd September 25, 1999
39: .Dt SSH 1
40: .Os
41: .Sh NAME
42: .Nm ssh
1.96 deraadt 43: .Nd OpenSSH SSH client (remote login program)
1.2 deraadt 44: .Sh SYNOPSIS
45: .Nm ssh
1.191 djm 46: .Op Fl 1246AaCfgkMNnqsTtVvXxY
1.108 markus 47: .Op Fl b Ar bind_address
1.51 markus 48: .Op Fl c Ar cipher_spec
1.210 djm 49: .Oo Fl D\ \&
50: .Sm off
51: .Oo Ar bind_address : Oc
52: .Ar port
53: .Sm on
54: .Oc
1.2 deraadt 55: .Op Fl e Ar escape_char
1.176 jmc 56: .Op Fl F Ar configfile
1.211 jmc 57: .Bk -words
1.2 deraadt 58: .Op Fl i Ar identity_file
1.211 jmc 59: .Ek
1.202 jmc 60: .Oo Fl L\ \&
1.12 aaron 61: .Sm off
1.200 djm 62: .Oo Ar bind_address : Oc
1.202 jmc 63: .Ar port : host : hostport
1.12 aaron 64: .Sm on
65: .Oc
1.211 jmc 66: .Bk -words
1.176 jmc 67: .Op Fl l Ar login_name
1.211 jmc 68: .Ek
1.176 jmc 69: .Op Fl m Ar mac_spec
1.198 djm 70: .Op Fl O Ar ctl_cmd
1.176 jmc 71: .Op Fl o Ar option
72: .Op Fl p Ar port
1.202 jmc 73: .Oo Fl R\ \&
1.12 aaron 74: .Sm off
1.200 djm 75: .Oo Ar bind_address : Oc
1.202 jmc 76: .Ar port : host : hostport
1.12 aaron 77: .Sm on
78: .Oc
1.198 djm 79: .Op Fl S Ar ctl_path
1.216 jmc 80: .Bk -words
81: .Op Fl w Ar tunnel : Ns Ar tunnel
1.176 jmc 82: .Oo Ar user Ns @ Oc Ns Ar hostname
1.2 deraadt 83: .Op Ar command
1.216 jmc 84: .Ek
1.44 aaron 85: .Sh DESCRIPTION
1.2 deraadt 86: .Nm
1.96 deraadt 87: (SSH client) is a program for logging into a remote machine and for
1.40 aaron 88: executing commands on a remote machine.
1.176 jmc 89: It is intended to replace rlogin and rsh,
90: and provide secure encrypted communications between
1.40 aaron 91: two untrusted hosts over an insecure network.
1.176 jmc 92: X11 connections and arbitrary TCP/IP ports
93: can also be forwarded over the secure channel.
1.2 deraadt 94: .Pp
95: .Nm
1.44 aaron 96: connects and logs into the specified
1.176 jmc 97: .Ar hostname
98: (with optional
99: .Ar user
100: name).
1.1 deraadt 101: The user must prove
1.49 markus 102: his/her identity to the remote machine using one of several methods
1.176 jmc 103: depending on the protocol version used.
1.49 markus 104: .Pp
1.176 jmc 105: If
106: .Ar command
107: is specified,
108: .Ar command
109: is executed on the remote host instead of a login shell.
1.49 markus 110: .Ss SSH protocol version 1
1.195 markus 111: The first authentication method is the
112: .Em rhosts
113: or
114: .Em hosts.equiv
115: method combined with RSA-based host authentication.
116: If the machine the user logs in from is listed in
1.2 deraadt 117: .Pa /etc/hosts.equiv
1.1 deraadt 118: or
1.2 deraadt 119: .Pa /etc/shosts.equiv
1.1 deraadt 120: on the remote machine, and the user names are
1.195 markus 121: the same on both sides, or if the files
1.207 djm 122: .Pa ~/.rhosts
1.1 deraadt 123: or
1.207 djm 124: .Pa ~/.shosts
1.195 markus 125: exist in the user's home directory on the
126: remote machine and contain a line containing the name of the client
1.1 deraadt 127: machine and the name of the user on that machine, the user is
1.195 markus 128: considered for log in.
129: Additionally, if the server can verify the client's
1.44 aaron 130: host key (see
1.147 deraadt 131: .Pa /etc/ssh/ssh_known_hosts
1.23 markus 132: and
1.207 djm 133: .Pa ~/.ssh/known_hosts
1.1 deraadt 134: in the
1.2 deraadt 135: .Sx FILES
1.176 jmc 136: section), only then is login permitted.
1.40 aaron 137: This authentication method closes security holes due to IP
138: spoofing, DNS spoofing and routing spoofing.
139: [Note to the administrator:
1.2 deraadt 140: .Pa /etc/hosts.equiv ,
1.207 djm 141: .Pa ~/.rhosts ,
1.1 deraadt 142: and the rlogin/rsh protocol in general, are inherently insecure and should be
143: disabled if security is desired.]
1.2 deraadt 144: .Pp
1.195 markus 145: As a second authentication method,
1.2 deraadt 146: .Nm
1.1 deraadt 147: supports RSA based authentication.
148: The scheme is based on public-key cryptography: there are cryptosystems
149: where encryption and decryption are done using separate keys, and it
150: is not possible to derive the decryption key from the encryption key.
1.40 aaron 151: RSA is one such system.
1.44 aaron 152: The idea is that each user creates a public/private
1.40 aaron 153: key pair for authentication purposes.
154: The server knows the public key, and only the user knows the private key.
1.176 jmc 155: .Pp
1.44 aaron 156: The file
1.207 djm 157: .Pa ~/.ssh/authorized_keys
1.176 jmc 158: lists the public keys that are permitted for logging in.
1.40 aaron 159: When the user logs in, the
1.2 deraadt 160: .Nm
1.1 deraadt 161: program tells the server which key pair it would like to use for
1.40 aaron 162: authentication.
1.176 jmc 163: The server checks if this key is permitted, and if so,
164: sends the user (actually the
1.2 deraadt 165: .Nm
1.1 deraadt 166: program running on behalf of the user) a challenge, a random number,
1.40 aaron 167: encrypted by the user's public key.
1.176 jmc 168: The challenge can only be decrypted using the proper private key.
169: The user's client then decrypts the challenge using the private key,
170: proving that he/she knows the private key
171: but without disclosing it to the server.
1.2 deraadt 172: .Pp
173: .Nm
1.40 aaron 174: implements the RSA authentication protocol automatically.
175: The user creates his/her RSA key pair by running
1.2 deraadt 176: .Xr ssh-keygen 1 .
1.44 aaron 177: This stores the private key in
1.207 djm 178: .Pa ~/.ssh/identity
1.176 jmc 179: and stores the public key in
1.207 djm 180: .Pa ~/.ssh/identity.pub
1.40 aaron 181: in the user's home directory.
182: The user should then copy the
1.2 deraadt 183: .Pa identity.pub
1.44 aaron 184: to
1.207 djm 185: .Pa ~/.ssh/authorized_keys
1.44 aaron 186: in his/her home directory on the remote machine (the
1.2 deraadt 187: .Pa authorized_keys
1.44 aaron 188: file corresponds to the conventional
1.207 djm 189: .Pa ~/.rhosts
1.1 deraadt 190: file, and has one key
1.40 aaron 191: per line, though the lines can be very long).
192: After this, the user can log in without giving the password.
1.2 deraadt 193: .Pp
1.1 deraadt 194: The most convenient way to use RSA authentication may be with an
1.40 aaron 195: authentication agent.
196: See
1.2 deraadt 197: .Xr ssh-agent 1
1.1 deraadt 198: for more information.
1.2 deraadt 199: .Pp
1.44 aaron 200: If other authentication methods fail,
1.2 deraadt 201: .Nm
1.40 aaron 202: prompts the user for a password.
203: The password is sent to the remote
1.1 deraadt 204: host for checking; however, since all communications are encrypted,
205: the password cannot be seen by someone listening on the network.
1.49 markus 206: .Ss SSH protocol version 2
1.176 jmc 207: When a user connects using protocol version 2,
1.145 markus 208: similar authentication methods are available.
1.107 markus 209: Using the default values for
210: .Cm PreferredAuthentications ,
1.123 markus 211: the client will try to authenticate first using the hostbased method;
1.176 jmc 212: if this method fails, public key authentication is attempted,
213: and finally if this method fails, keyboard-interactive and
1.123 markus 214: password authentication are tried.
1.49 markus 215: .Pp
216: The public key method is similar to RSA authentication described
1.107 markus 217: in the previous section and allows the RSA or DSA algorithm to be used:
1.102 itojun 218: The client uses his private key,
1.207 djm 219: .Pa ~/.ssh/id_dsa
1.102 itojun 220: or
1.207 djm 221: .Pa ~/.ssh/id_rsa ,
1.49 markus 222: to sign the session identifier and sends the result to the server.
223: The server checks whether the matching public key is listed in
1.207 djm 224: .Pa ~/.ssh/authorized_keys
1.49 markus 225: and grants access if both the key is found and the signature is correct.
226: The session identifier is derived from a shared Diffie-Hellman value
227: and is only known to the client and the server.
228: .Pp
1.176 jmc 229: If public key authentication fails or is not available, a password
230: can be sent encrypted to the remote host to prove the user's identity.
1.107 markus 231: .Pp
232: Additionally,
233: .Nm
234: supports hostbased or challenge response authentication.
1.49 markus 235: .Pp
236: Protocol 2 provides additional mechanisms for confidentiality
1.189 dtucker 237: (the traffic is encrypted using AES, 3DES, Blowfish, CAST128 or Arcfour)
238: and integrity (hmac-md5, hmac-sha1, hmac-ripemd160).
1.49 markus 239: Note that protocol 1 lacks a strong mechanism for ensuring the
240: integrity of the connection.
241: .Ss Login session and remote execution
1.1 deraadt 242: When the user's identity has been accepted by the server, the server
243: either executes the given command, or logs into the machine and gives
1.40 aaron 244: the user a normal shell on the remote machine.
245: All communication with
1.1 deraadt 246: the remote command or shell will be automatically encrypted.
1.2 deraadt 247: .Pp
1.1 deraadt 248: If a pseudo-terminal has been allocated (normal login session), the
1.104 djm 249: user may use the escape characters noted below.
1.2 deraadt 250: .Pp
1.176 jmc 251: If no pseudo-tty has been allocated,
252: the session is transparent and can be used to reliably transfer binary data.
1.40 aaron 253: On most systems, setting the escape character to
1.2 deraadt 254: .Dq none
255: will also make the session transparent even if a tty is used.
256: .Pp
1.71 djm 257: The session terminates when the command or shell on the remote
1.92 markus 258: machine exits and all X11 and TCP/IP connections have been closed.
1.176 jmc 259: The exit status of the remote program is returned as the exit status of
1.2 deraadt 260: .Nm ssh .
1.104 djm 261: .Ss Escape Characters
1.176 jmc 262: When a pseudo-terminal has been requested,
263: .Nm
264: supports a number of functions through the use of an escape character.
1.104 djm 265: .Pp
266: A single tilde character can be sent as
267: .Ic ~~
1.119 stevesk 268: or by following the tilde by a character other than those described below.
1.104 djm 269: The escape character must always follow a newline to be interpreted as
270: special.
271: The escape character can be changed in configuration files using the
272: .Cm EscapeChar
1.117 itojun 273: configuration directive or on the command line by the
1.104 djm 274: .Fl e
275: option.
276: .Pp
277: The supported escapes (assuming the default
278: .Ql ~ )
279: are:
280: .Bl -tag -width Ds
281: .It Cm ~.
1.176 jmc 282: Disconnect.
1.104 djm 283: .It Cm ~^Z
1.176 jmc 284: Background
285: .Nm ssh .
1.104 djm 286: .It Cm ~#
1.176 jmc 287: List forwarded connections.
1.104 djm 288: .It Cm ~&
1.176 jmc 289: Background
290: .Nm
291: at logout when waiting for forwarded connection / X11 sessions to terminate.
1.104 djm 292: .It Cm ~?
1.176 jmc 293: Display a list of escape characters.
1.170 markus 294: .It Cm ~B
1.176 jmc 295: Send a BREAK to the remote system
296: (only useful for SSH protocol version 2 and if the peer supports it).
1.149 jakob 297: .It Cm ~C
1.186 djm 298: Open command line.
299: Currently this allows the addition of port forwardings using the
1.149 jakob 300: .Fl L
301: and
302: .Fl R
1.186 djm 303: options (see below).
1.188 jmc 304: It also allows the cancellation of existing remote port-forwardings
1.186 djm 305: using
306: .Fl KR Ar hostport .
1.217 ! jmc 307: .Ic !\& Ns Ar command
1.215 reyk 308: allows the user to execute a local command if the
309: .Ic PermitLocalCommand
310: option is enabled in
311: .Xr ssh_config 5 .
1.187 djm 312: Basic help is available, using the
313: .Fl h
1.186 djm 314: option.
1.104 djm 315: .It Cm ~R
1.176 jmc 316: Request rekeying of the connection
317: (only useful for SSH protocol version 2 and if the peer supports it).
1.104 djm 318: .El
1.49 markus 319: .Ss X11 and TCP forwarding
1.110 deraadt 320: If the
321: .Cm ForwardX11
322: variable is set to
323: .Dq yes
1.176 jmc 324: (or see the description of the
1.110 deraadt 325: .Fl X
326: and
327: .Fl x
328: options described later)
329: and the user is using X11 (the
1.2 deraadt 330: .Ev DISPLAY
1.1 deraadt 331: environment variable is set), the connection to the X11 display is
332: automatically forwarded to the remote side in such a way that any X11
333: programs started from the shell (or command) will go through the
334: encrypted channel, and the connection to the real X server will be made
1.40 aaron 335: from the local machine.
336: The user should not manually set
1.2 deraadt 337: .Ev DISPLAY .
1.1 deraadt 338: Forwarding of X11 connections can be
339: configured on the command line or in configuration files.
1.2 deraadt 340: .Pp
341: The
1.44 aaron 342: .Ev DISPLAY
1.2 deraadt 343: value set by
344: .Nm
1.176 jmc 345: will point to the server machine, but with a display number greater than zero.
1.40 aaron 346: This is normal, and happens because
1.2 deraadt 347: .Nm
348: creates a
349: .Dq proxy
350: X server on the server machine for forwarding the
1.1 deraadt 351: connections over the encrypted channel.
1.2 deraadt 352: .Pp
353: .Nm
1.1 deraadt 354: will also automatically set up Xauthority data on the server machine.
355: For this purpose, it will generate a random authorization cookie,
356: store it in Xauthority on the server, and verify that any forwarded
357: connections carry this cookie and replace it by the real cookie when
1.40 aaron 358: the connection is opened.
359: The real authentication cookie is never
1.1 deraadt 360: sent to the server machine (and no cookies are sent in the plain).
1.2 deraadt 361: .Pp
1.163 stevesk 362: If the
363: .Cm ForwardAgent
364: variable is set to
365: .Dq yes
1.176 jmc 366: (or see the description of the
1.163 stevesk 367: .Fl A
368: and
369: .Fl a
1.168 jmc 370: options described later) and
1.163 stevesk 371: the user is using an authentication agent, the connection to the agent
372: is automatically forwarded to the remote side.
1.2 deraadt 373: .Pp
1.1 deraadt 374: Forwarding of arbitrary TCP/IP connections over the secure channel can
1.120 stevesk 375: be specified either on the command line or in a configuration file.
1.40 aaron 376: One possible application of TCP/IP forwarding is a secure connection to an
1.92 markus 377: electronic purse; another is going through firewalls.
1.49 markus 378: .Ss Server authentication
1.2 deraadt 379: .Nm
1.49 markus 380: automatically maintains and checks a database containing
1.40 aaron 381: identifications for all hosts it has ever been used with.
1.116 markus 382: Host keys are stored in
1.207 djm 383: .Pa ~/.ssh/known_hosts
1.40 aaron 384: in the user's home directory.
1.116 markus 385: Additionally, the file
1.147 deraadt 386: .Pa /etc/ssh/ssh_known_hosts
1.116 markus 387: is automatically checked for known hosts.
1.40 aaron 388: Any new hosts are automatically added to the user's file.
1.176 jmc 389: If a host's identification ever changes,
1.2 deraadt 390: .Nm
1.1 deraadt 391: warns about this and disables password authentication to prevent a
1.40 aaron 392: trojan horse from getting the user's password.
1.176 jmc 393: Another purpose of this mechanism is to prevent man-in-the-middle attacks
394: which could otherwise be used to circumvent the encryption.
1.40 aaron 395: The
1.2 deraadt 396: .Cm StrictHostKeyChecking
1.158 stevesk 397: option can be used to prevent logins to machines whose
1.1 deraadt 398: host key is not known or has changed.
1.194 jakob 399: .Pp
400: .Nm
401: can be configured to verify host identification using fingerprint resource
402: records (SSHFP) published in DNS.
403: The
404: .Cm VerifyHostKeyDNS
405: option can be used to control how DNS lookups are performed.
406: SSHFP resource records can be generated using
407: .Xr ssh-keygen 1 .
1.65 aaron 408: .Pp
409: The options are as follows:
1.2 deraadt 410: .Bl -tag -width Ds
1.176 jmc 411: .It Fl 1
412: Forces
413: .Nm
414: to try protocol version 1 only.
415: .It Fl 2
416: Forces
417: .Nm
418: to try protocol version 2 only.
419: .It Fl 4
420: Forces
421: .Nm
422: to use IPv4 addresses only.
423: .It Fl 6
424: Forces
425: .Nm
426: to use IPv6 addresses only.
1.54 markus 427: .It Fl A
428: Enables forwarding of the authentication agent connection.
429: This can also be specified on a per-host basis in a configuration file.
1.165 stevesk 430: .Pp
1.168 jmc 431: Agent forwarding should be enabled with caution.
432: Users with the ability to bypass file permissions on the remote host
433: (for the agent's Unix-domain socket)
434: can access the local agent through the forwarded connection.
435: An attacker cannot obtain key material from the agent,
1.165 stevesk 436: however they can perform operations on the keys that enable them to
437: authenticate using the identities loaded into the agent.
1.176 jmc 438: .It Fl a
439: Disables forwarding of the authentication agent connection.
1.108 markus 440: .It Fl b Ar bind_address
1.209 dtucker 441: Use
442: .Ar bind_address
443: on the local machine as the source address
444: of the connection.
445: Only useful on systems with more than one address.
1.176 jmc 446: .It Fl C
447: Requests compression of all data (including stdin, stdout, stderr, and
448: data for forwarded X11 and TCP/IP connections).
449: The compression algorithm is the same used by
450: .Xr gzip 1 ,
451: and the
452: .Dq level
453: can be controlled by the
454: .Cm CompressionLevel
455: option for protocol version 1.
456: Compression is desirable on modem lines and other
457: slow connections, but will only slow down things on fast networks.
458: The default value can be set on a host-by-host basis in the
459: configuration files; see the
460: .Cm Compression
461: option.
1.189 dtucker 462: .It Fl c Ar cipher_spec
463: Selects the cipher specification for encrypting the session.
464: .Pp
465: Protocol version 1 allows specification of a single cipher.
1.212 djm 466: The supported values are
1.189 dtucker 467: .Dq 3des ,
468: .Dq blowfish
469: and
470: .Dq des .
1.2 deraadt 471: .Ar 3des
1.189 dtucker 472: (triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
1.44 aaron 473: It is believed to be secure.
1.5 deraadt 474: .Ar blowfish
1.176 jmc 475: is a fast block cipher; it appears very secure and is much faster than
1.40 aaron 476: .Ar 3des .
1.131 stevesk 477: .Ar des
478: is only supported in the
479: .Nm
480: client for interoperability with legacy protocol 1 implementations
481: that do not support the
482: .Ar 3des
1.168 jmc 483: cipher.
484: Its use is strongly discouraged due to cryptographic weaknesses.
1.189 dtucker 485: The default is
486: .Dq 3des .
487: .Pp
488: For protocol version 2
489: .Ar cipher_spec
490: is a comma-separated list of ciphers
491: listed in order of preference.
492: The supported ciphers are
493: .Dq 3des-cbc ,
494: .Dq aes128-cbc ,
495: .Dq aes192-cbc ,
496: .Dq aes256-cbc ,
497: .Dq aes128-ctr ,
498: .Dq aes192-ctr ,
499: .Dq aes256-ctr ,
1.208 djm 500: .Dq arcfour128 ,
501: .Dq arcfour256 ,
1.189 dtucker 502: .Dq arcfour ,
503: .Dq blowfish-cbc ,
504: and
505: .Dq cast128-cbc .
506: The default is
507: .Bd -literal
1.208 djm 508: ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
509: arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
510: aes192-ctr,aes256-ctr''
1.189 dtucker 511: .Ed
1.210 djm 512: .It Fl D Xo
513: .Sm off
514: .Oo Ar bind_address : Oc
515: .Ar port
516: .Sm on
517: .Xc
1.176 jmc 518: Specifies a local
519: .Dq dynamic
520: application-level port forwarding.
521: This works by allocating a socket to listen to
522: .Ar port
1.210 djm 523: on the local side, optionally bound to the specified
524: .Ar bind_address .
525: Whenever a connection is made to this port, the
1.176 jmc 526: connection is forwarded over the secure channel, and the application
527: protocol is then used to determine where to connect to from the
528: remote machine.
529: Currently the SOCKS4 and SOCKS5 protocols are supported, and
530: .Nm
531: will act as a SOCKS server.
532: Only root can forward privileged ports.
533: Dynamic port forwardings can also be specified in the configuration file.
1.210 djm 534: .Pp
535: IPv6 addresses can be specified with an alternative syntax:
536: .Sm off
537: .Xo
538: .Op Ar bind_address No /
539: .Ar port
540: .Xc
541: .Sm on
542: or by enclosing the address in square brackets.
543: Only the superuser can forward privileged ports.
544: By default, the local port is bound in accordance with the
545: .Cm GatewayPorts
546: setting.
547: However, an explicit
548: .Ar bind_address
549: may be used to bind the connection to a specific address.
550: The
551: .Ar bind_address
552: of
553: .Dq localhost
554: indicates that the listening port be bound for local use only, while an
555: empty address or
556: .Sq *
557: indicates that the port should be available from all interfaces.
1.176 jmc 558: .It Fl e Ar ch | ^ch | none
1.2 deraadt 559: Sets the escape character for sessions with a pty (default:
560: .Ql ~ ) .
1.40 aaron 561: The escape character is only recognized at the beginning of a line.
562: The escape character followed by a dot
1.2 deraadt 563: .Pq Ql \&.
1.176 jmc 564: closes the connection;
565: followed by control-Z suspends the connection;
566: and followed by itself sends the escape character once.
1.40 aaron 567: Setting the character to
1.2 deraadt 568: .Dq none
569: disables any escapes and makes the session fully transparent.
1.176 jmc 570: .It Fl F Ar configfile
571: Specifies an alternative per-user configuration file.
572: If a configuration file is given on the command line,
573: the system-wide configuration file
574: .Pq Pa /etc/ssh/ssh_config
575: will be ignored.
576: The default for the per-user configuration file is
1.207 djm 577: .Pa ~/.ssh/config .
1.2 deraadt 578: .It Fl f
579: Requests
580: .Nm
1.40 aaron 581: to go to background just before command execution.
582: This is useful if
1.2 deraadt 583: .Nm
584: is going to ask for passwords or passphrases, but the user
1.40 aaron 585: wants it in the background.
1.44 aaron 586: This implies
1.2 deraadt 587: .Fl n .
1.1 deraadt 588: The recommended way to start X11 programs at a remote site is with
1.2 deraadt 589: something like
590: .Ic ssh -f host xterm .
1.34 markus 591: .It Fl g
592: Allows remote hosts to connect to local forwarded ports.
1.176 jmc 593: .It Fl I Ar smartcard_device
594: Specifies which smartcard device to use.
595: The argument is the device
596: .Nm
597: should use to communicate with a smartcard used for storing the user's
598: private RSA key.
1.2 deraadt 599: .It Fl i Ar identity_file
1.144 stevesk 600: Selects a file from which the identity (private key) for
1.68 markus 601: RSA or DSA authentication is read.
1.144 stevesk 602: The default is
1.207 djm 603: .Pa ~/.ssh/identity
1.144 stevesk 604: for protocol version 1, and
1.207 djm 605: .Pa ~/.ssh/id_rsa
1.144 stevesk 606: and
1.207 djm 607: .Pa ~/.ssh/id_dsa
1.144 stevesk 608: for protocol version 2.
1.40 aaron 609: Identity files may also be specified on
610: a per-host basis in the configuration file.
611: It is possible to have multiple
1.2 deraadt 612: .Fl i
613: options (and multiple identities specified in
1.1 deraadt 614: configuration files).
1.2 deraadt 615: .It Fl k
1.179 dtucker 616: Disables forwarding (delegation) of GSSAPI credentials to the server.
1.176 jmc 617: .It Fl L Xo
618: .Sm off
1.200 djm 619: .Oo Ar bind_address : Oc
1.176 jmc 620: .Ar port : host : hostport
621: .Sm on
622: .Xc
623: Specifies that the given port on the local (client) host is to be
624: forwarded to the given host and port on the remote side.
625: This works by allocating a socket to listen to
626: .Ar port
1.200 djm 627: on the local side, optionally bound to the specified
628: .Ar bind_address .
629: Whenever a connection is made to this port, the
1.176 jmc 630: connection is forwarded over the secure channel, and a connection is
631: made to
632: .Ar host
633: port
634: .Ar hostport
635: from the remote machine.
636: Port forwardings can also be specified in the configuration file.
637: IPv6 addresses can be specified with an alternative syntax:
638: .Sm off
639: .Xo
1.205 jmc 640: .Op Ar bind_address No /
1.176 jmc 641: .Ar port No / Ar host No /
1.200 djm 642: .Ar hostport
1.176 jmc 643: .Xc
644: .Sm on
1.200 djm 645: or by enclosing the address in square brackets.
646: Only the superuser can forward privileged ports.
647: By default, the local port is bound in accordance with the
648: .Cm GatewayPorts
649: setting.
650: However, an explicit
651: .Ar bind_address
652: may be used to bind the connection to a specific address.
653: The
654: .Ar bind_address
655: of
656: .Dq localhost
1.202 jmc 657: indicates that the listening port be bound for local use only, while an
658: empty address or
659: .Sq *
1.200 djm 660: indicates that the port should be available from all interfaces.
1.2 deraadt 661: .It Fl l Ar login_name
1.40 aaron 662: Specifies the user to log in as on the remote machine.
663: This also may be specified on a per-host basis in the configuration file.
1.190 djm 664: .It Fl M
665: Places the
666: .Nm
667: client into
668: .Dq master
669: mode for connection sharing.
670: Refer to the description of
671: .Cm ControlMaster
672: in
673: .Xr ssh_config 5
674: for details.
1.193 jmc 675: .It Fl m Ar mac_spec
676: Additionally, for protocol version 2 a comma-separated list of MAC
677: (message authentication code) algorithms can
678: be specified in order of preference.
679: See the
680: .Cm MACs
681: keyword for more information.
1.176 jmc 682: .It Fl N
683: Do not execute a remote command.
684: This is useful for just forwarding ports
685: (protocol version 2 only).
1.2 deraadt 686: .It Fl n
687: Redirects stdin from
688: .Pa /dev/null
689: (actually, prevents reading from stdin).
1.1 deraadt 690: This must be used when
1.2 deraadt 691: .Nm
1.40 aaron 692: is run in the background.
693: A common trick is to use this to run X11 programs on a remote machine.
694: For example,
1.2 deraadt 695: .Ic ssh -n shadows.cs.hut.fi emacs &
696: will start an emacs on shadows.cs.hut.fi, and the X11
1.1 deraadt 697: connection will be automatically forwarded over an encrypted channel.
698: The
1.2 deraadt 699: .Nm
1.1 deraadt 700: program will be put in the background.
701: (This does not work if
1.2 deraadt 702: .Nm
703: needs to ask for a password or passphrase; see also the
704: .Fl f
705: option.)
1.199 jmc 706: .It Fl O Ar ctl_cmd
707: Control an active connection multiplexing master process.
708: When the
709: .Fl O
710: option is specified, the
711: .Ar ctl_cmd
712: argument is interpreted and passed to the master process.
713: Valid commands are:
714: .Dq check
715: (check that the master process is running) and
716: .Dq exit
717: (request the master to exit).
1.2 deraadt 718: .It Fl o Ar option
1.127 stevesk 719: Can be used to give options in the format used in the configuration file.
1.1 deraadt 720: This is useful for specifying options for which there is no separate
1.40 aaron 721: command-line flag.
1.176 jmc 722: For full details of the options listed below, and their possible values, see
723: .Xr ssh_config 5 .
724: .Pp
725: .Bl -tag -width Ds -offset indent -compact
726: .It AddressFamily
727: .It BatchMode
728: .It BindAddress
729: .It ChallengeResponseAuthentication
730: .It CheckHostIP
731: .It Cipher
732: .It Ciphers
733: .It ClearAllForwardings
734: .It Compression
735: .It CompressionLevel
736: .It ConnectionAttempts
1.185 dtucker 737: .It ConnectTimeout
1.190 djm 738: .It ControlMaster
739: .It ControlPath
1.176 jmc 740: .It DynamicForward
741: .It EscapeChar
742: .It ForwardAgent
743: .It ForwardX11
1.178 markus 744: .It ForwardX11Trusted
1.176 jmc 745: .It GatewayPorts
746: .It GlobalKnownHostsFile
747: .It GSSAPIAuthentication
748: .It GSSAPIDelegateCredentials
1.201 djm 749: .It HashKnownHosts
1.176 jmc 750: .It Host
751: .It HostbasedAuthentication
752: .It HostKeyAlgorithms
753: .It HostKeyAlias
754: .It HostName
755: .It IdentityFile
1.182 markus 756: .It IdentitiesOnly
1.197 djm 757: .It KbdInteractiveDevices
1.215 reyk 758: .It LocalCommand
1.176 jmc 759: .It LocalForward
760: .It LogLevel
761: .It MACs
762: .It NoHostAuthenticationForLocalhost
763: .It NumberOfPasswordPrompts
764: .It PasswordAuthentication
1.215 reyk 765: .It PermitLocalCommand
1.176 jmc 766: .It Port
767: .It PreferredAuthentications
768: .It Protocol
769: .It ProxyCommand
770: .It PubkeyAuthentication
771: .It RemoteForward
772: .It RhostsRSAAuthentication
773: .It RSAAuthentication
1.184 jmc 774: .It SendEnv
1.181 markus 775: .It ServerAliveInterval
776: .It ServerAliveCountMax
1.176 jmc 777: .It SmartcardDevice
778: .It StrictHostKeyChecking
1.180 markus 779: .It TCPKeepAlive
1.215 reyk 780: .It Tunnel
781: .It TunnelDevice
1.176 jmc 782: .It UsePrivilegedPort
783: .It User
784: .It UserKnownHostsFile
785: .It VerifyHostKeyDNS
786: .It XAuthLocation
787: .El
1.2 deraadt 788: .It Fl p Ar port
1.40 aaron 789: Port to connect to on the remote host.
790: This can be specified on a
1.1 deraadt 791: per-host basis in the configuration file.
1.2 deraadt 792: .It Fl q
1.40 aaron 793: Quiet mode.
794: Causes all warning and diagnostic messages to be suppressed.
1.176 jmc 795: .It Fl R Xo
796: .Sm off
1.200 djm 797: .Oo Ar bind_address : Oc
1.176 jmc 798: .Ar port : host : hostport
799: .Sm on
800: .Xc
801: Specifies that the given port on the remote (server) host is to be
802: forwarded to the given host and port on the local side.
803: This works by allocating a socket to listen to
804: .Ar port
805: on the remote side, and whenever a connection is made to this port, the
806: connection is forwarded over the secure channel, and a connection is
807: made to
808: .Ar host
809: port
810: .Ar hostport
811: from the local machine.
1.200 djm 812: .Pp
1.176 jmc 813: Port forwardings can also be specified in the configuration file.
814: Privileged ports can be forwarded only when
815: logging in as root on the remote machine.
1.200 djm 816: IPv6 addresses can be specified by enclosing the address in square braces or
817: using an alternative syntax:
1.202 jmc 818: .Sm off
1.200 djm 819: .Xo
1.205 jmc 820: .Op Ar bind_address No /
1.202 jmc 821: .Ar host No / Ar port No /
822: .Ar hostport
823: .Xc .
1.176 jmc 824: .Sm on
1.200 djm 825: .Pp
826: By default, the listening socket on the server will be bound to the loopback
827: interface only.
828: This may be overriden by specifying a
829: .Ar bind_address .
1.202 jmc 830: An empty
831: .Ar bind_address ,
1.200 djm 832: or the address
1.202 jmc 833: .Ql * ,
1.200 djm 834: indicates that the remote socket should listen on all interfaces.
835: Specifying a remote
836: .Ar bind_address
1.202 jmc 837: will only succeed if the server's
838: .Cm GatewayPorts
1.200 djm 839: option is enabled (see
1.202 jmc 840: .Xr sshd_config 5 ) .
1.198 djm 841: .It Fl S Ar ctl_path
1.193 jmc 842: Specifies the location of a control socket for connection sharing.
1.190 djm 843: Refer to the description of
1.191 djm 844: .Cm ControlPath
845: and
1.190 djm 846: .Cm ControlMaster
847: in
848: .Xr ssh_config 5
849: for details.
1.80 djm 850: .It Fl s
1.172 jmc 851: May be used to request invocation of a subsystem on the remote system.
852: Subsystems are a feature of the SSH2 protocol which facilitate the use
1.176 jmc 853: of SSH as a secure transport for other applications (eg.\&
854: .Xr sftp 1 ) .
1.172 jmc 855: The subsystem is specified as the remote command.
1.176 jmc 856: .It Fl T
857: Disable pseudo-tty allocation.
1.2 deraadt 858: .It Fl t
1.40 aaron 859: Force pseudo-tty allocation.
1.43 brad 860: This can be used to execute arbitrary
1.40 aaron 861: screen-based programs on a remote machine, which can be very useful,
862: e.g., when implementing menu services.
1.73 markus 863: Multiple
864: .Fl t
865: options force tty allocation, even if
866: .Nm
867: has no local tty.
1.176 jmc 868: .It Fl V
869: Display the version number and exit.
1.2 deraadt 870: .It Fl v
1.40 aaron 871: Verbose mode.
872: Causes
1.2 deraadt 873: .Nm
1.40 aaron 874: to print debugging messages about its progress.
875: This is helpful in
1.1 deraadt 876: debugging connection, authentication, and configuration problems.
1.73 markus 877: Multiple
878: .Fl v
1.169 naddy 879: options increase the verbosity.
880: The maximum is 3.
1.216 jmc 881: .It Fl w Ar tunnel : Ns Ar tunnel
1.215 reyk 882: Requests a
883: .Xr tun 4
884: device on the client and server like the
885: .Cm Tunnel
886: directive in
887: .Xr ssh_config 5 .
1.2 deraadt 888: .It Fl X
1.1 deraadt 889: Enables X11 forwarding.
1.54 markus 890: This can also be specified on a per-host basis in a configuration file.
1.165 stevesk 891: .Pp
1.168 jmc 892: X11 forwarding should be enabled with caution.
893: Users with the ability to bypass file permissions on the remote host
894: (for the user's X authorization database)
895: can access the local X11 display through the forwarded connection.
896: An attacker may then be able to perform activities such as keystroke monitoring.
1.203 djm 897: .Pp
1.204 jmc 898: For this reason, X11 forwarding is subjected to X11 SECURITY extension
1.203 djm 899: restrictions by default.
900: Please refer to the
901: .Nm
902: .Fl Y
903: option and the
904: .Cm ForwardX11Trusted
905: directive in
906: .Xr ssh_config 5
907: for more information.
1.176 jmc 908: .It Fl x
909: Disables X11 forwarding.
1.178 markus 910: .It Fl Y
911: Enables trusted X11 forwarding.
1.203 djm 912: Trusted X11 forwardings are not subjected to the X11 SECURITY extension
913: controls.
1.2 deraadt 914: .El
915: .Sh CONFIGURATION FILES
916: .Nm
1.158 stevesk 917: may additionally obtain configuration data from
918: a per-user configuration file and a system-wide configuration file.
919: The file format and configuration options are described in
920: .Xr ssh_config 5 .
1.2 deraadt 921: .Sh ENVIRONMENT
922: .Nm
1.1 deraadt 923: will normally set the following environment variables:
1.176 jmc 924: .Bl -tag -width LOGNAME
1.2 deraadt 925: .It Ev DISPLAY
926: The
927: .Ev DISPLAY
1.40 aaron 928: variable indicates the location of the X11 server.
1.44 aaron 929: It is automatically set by
1.2 deraadt 930: .Nm
931: to point to a value of the form
932: .Dq hostname:n
933: where hostname indicates
1.176 jmc 934: the host where the shell runs, and n is an integer \*(Ge 1.
1.40 aaron 935: .Nm
936: uses this special value to forward X11 connections over the secure
937: channel.
1.107 markus 938: The user should normally not set
939: .Ev DISPLAY
940: explicitly, as that
1.1 deraadt 941: will render the X11 connection insecure (and will require the user to
942: manually copy any required authorization cookies).
1.2 deraadt 943: .It Ev HOME
1.1 deraadt 944: Set to the path of the user's home directory.
1.2 deraadt 945: .It Ev LOGNAME
946: Synonym for
1.12 aaron 947: .Ev USER ;
948: set for compatibility with systems that use this variable.
1.2 deraadt 949: .It Ev MAIL
1.129 stevesk 950: Set to the path of the user's mailbox.
1.40 aaron 951: .It Ev PATH
1.2 deraadt 952: Set to the default
953: .Ev PATH ,
954: as specified when compiling
1.12 aaron 955: .Nm ssh .
1.118 markus 956: .It Ev SSH_ASKPASS
957: If
958: .Nm
959: needs a passphrase, it will read the passphrase from the current
960: terminal if it was run from a terminal.
961: If
962: .Nm
963: does not have a terminal associated with it but
964: .Ev DISPLAY
965: and
966: .Ev SSH_ASKPASS
967: are set, it will execute the program specified by
968: .Ev SSH_ASKPASS
969: and open an X11 window to read the passphrase.
970: This is particularly useful when calling
971: .Nm
972: from a
1.196 jmc 973: .Pa .xsession
1.118 markus 974: or related script.
975: (Note that on some machines it
976: may be necessary to redirect the input from
977: .Pa /dev/null
978: to make this work.)
1.18 markus 979: .It Ev SSH_AUTH_SOCK
1.129 stevesk 980: Identifies the path of a unix-domain socket used to communicate with the
1.17 markus 981: agent.
1.166 stevesk 982: .It Ev SSH_CONNECTION
983: Identifies the client and server ends of the connection.
1.40 aaron 984: The variable contains
1.166 stevesk 985: four space-separated values: client ip-address, client port number,
986: server ip-address and server port number.
1.73 markus 987: .It Ev SSH_ORIGINAL_COMMAND
988: The variable contains the original command line if a forced command
989: is executed.
990: It can be used to extract the original arguments.
1.2 deraadt 991: .It Ev SSH_TTY
1.1 deraadt 992: This is set to the name of the tty (path to the device) associated
1.40 aaron 993: with the current shell or command.
994: If the current session has no tty,
1.1 deraadt 995: this variable is not set.
1.2 deraadt 996: .It Ev TZ
1.214 jmc 997: This variable is set to indicate the present time zone if it
1.56 deraadt 998: was set when the daemon was started (i.e., the daemon passes the value
1.1 deraadt 999: on to new connections).
1.2 deraadt 1000: .It Ev USER
1.1 deraadt 1001: Set to the name of the user logging in.
1.2 deraadt 1002: .El
1003: .Pp
1.44 aaron 1004: Additionally,
1.2 deraadt 1005: .Nm
1.44 aaron 1006: reads
1.207 djm 1007: .Pa ~/.ssh/environment ,
1.2 deraadt 1008: and adds lines of the format
1009: .Dq VARNAME=value
1.161 marc 1010: to the environment if the file exists and if users are allowed to
1011: change their environment.
1.176 jmc 1012: For more information, see the
1.161 marc 1013: .Cm PermitUserEnvironment
1.162 stevesk 1014: option in
1.161 marc 1015: .Xr sshd_config 5 .
1.2 deraadt 1016: .Sh FILES
1.36 markus 1017: .Bl -tag -width Ds
1.207 djm 1018: .It Pa ~/.ssh/known_hosts
1.129 stevesk 1019: Records host keys for all hosts the user has logged into that are not
1.2 deraadt 1020: in
1.147 deraadt 1021: .Pa /etc/ssh/ssh_known_hosts .
1.2 deraadt 1022: See
1023: .Xr sshd 8 .
1.207 djm 1024: .It Pa ~/.ssh/identity, ~/.ssh/id_dsa, ~/.ssh/id_rsa
1.102 itojun 1025: Contains the authentication identity of the user.
1026: They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively.
1.48 markus 1027: These files
1028: contain sensitive data and should be readable by the user but not
1.15 markus 1029: accessible by others (read/write/execute).
1030: Note that
1031: .Nm
1.48 markus 1032: ignores a private key file if it is accessible by others.
1.15 markus 1033: It is possible to specify a passphrase when
1.1 deraadt 1034: generating the key; the passphrase will be used to encrypt the
1.8 deraadt 1035: sensitive part of this file using 3DES.
1.207 djm 1036: .It Pa ~/.ssh/identity.pub, ~/.ssh/id_dsa.pub, ~/.ssh/id_rsa.pub
1.1 deraadt 1037: Contains the public key for authentication (public part of the
1.40 aaron 1038: identity file in human-readable form).
1.48 markus 1039: The contents of the
1.207 djm 1040: .Pa ~/.ssh/identity.pub
1.176 jmc 1041: file should be added to the file
1.207 djm 1042: .Pa ~/.ssh/authorized_keys
1.2 deraadt 1043: on all machines
1.137 deraadt 1044: where the user wishes to log in using protocol version 1 RSA authentication.
1.48 markus 1045: The contents of the
1.207 djm 1046: .Pa ~/.ssh/id_dsa.pub
1.102 itojun 1047: and
1.207 djm 1048: .Pa ~/.ssh/id_rsa.pub
1.48 markus 1049: file should be added to
1.207 djm 1050: .Pa ~/.ssh/authorized_keys
1.48 markus 1051: on all machines
1.137 deraadt 1052: where the user wishes to log in using protocol version 2 DSA/RSA authentication.
1.48 markus 1053: These files are not
1.40 aaron 1054: sensitive and can (but need not) be readable by anyone.
1.48 markus 1055: These files are
1.84 markus 1056: never used automatically and are not necessary; they are only provided for
1.1 deraadt 1057: the convenience of the user.
1.207 djm 1058: .It Pa ~/.ssh/config
1.40 aaron 1059: This is the per-user configuration file.
1.158 stevesk 1060: The file format and configuration options are described in
1061: .Xr ssh_config 5 .
1.183 djm 1062: Because of the potential for abuse, this file must have strict permissions:
1063: read/write for the user, and not accessible by others.
1.207 djm 1064: .It Pa ~/.ssh/authorized_keys
1.115 markus 1065: Lists the public keys (RSA/DSA) that can be used for logging in as this user.
1.40 aaron 1066: The format of this file is described in the
1.2 deraadt 1067: .Xr sshd 8
1.40 aaron 1068: manual page.
1.176 jmc 1069: In the simplest form the format is the same as the
1070: .Pa .pub
1.116 markus 1071: identity files.
1.48 markus 1072: This file is not highly sensitive, but the recommended
1073: permissions are read/write for the user, and not accessible by others.
1.147 deraadt 1074: .It Pa /etc/ssh/ssh_known_hosts
1.40 aaron 1075: Systemwide list of known host keys.
1.116 markus 1076: This file should be prepared by the
1.1 deraadt 1077: system administrator to contain the public host keys of all machines in the
1.40 aaron 1078: organization.
1079: This file should be world-readable.
1080: This file contains
1.1 deraadt 1081: public keys, one per line, in the following format (fields separated
1.116 markus 1082: by spaces): system name, public key and optional comment field.
1.40 aaron 1083: When different names are used
1.1 deraadt 1084: for the same machine, all such names should be listed, separated by
1.40 aaron 1085: commas.
1.176 jmc 1086: The format is described in the
1.2 deraadt 1087: .Xr sshd 8
1.1 deraadt 1088: manual page.
1.2 deraadt 1089: .Pp
1.1 deraadt 1090: The canonical system name (as returned by name servers) is used by
1.2 deraadt 1091: .Xr sshd 8
1.1 deraadt 1092: to verify the client host when logging in; other names are needed because
1.2 deraadt 1093: .Nm
1.1 deraadt 1094: does not convert the user-supplied name to a canonical name before
1095: checking the key, because someone with access to the name servers
1096: would then be able to fool host authentication.
1.147 deraadt 1097: .It Pa /etc/ssh/ssh_config
1.40 aaron 1098: Systemwide configuration file.
1.158 stevesk 1099: The file format and configuration options are described in
1100: .Xr ssh_config 5 .
1.147 deraadt 1101: .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key
1.141 markus 1102: These three files contain the private parts of the host keys
1103: and are used for
1104: .Cm RhostsRSAAuthentication
1105: and
1106: .Cm HostbasedAuthentication .
1.155 stevesk 1107: If the protocol version 1
1108: .Cm RhostsRSAAuthentication
1.157 deraadt 1109: method is used,
1.155 stevesk 1110: .Nm
1111: must be setuid root, since the host key is readable only by root.
1112: For protocol version 2,
1113: .Nm
1114: uses
1115: .Xr ssh-keysign 8
1116: to access the host keys for
1117: .Cm HostbasedAuthentication .
1118: This eliminates the requirement that
1119: .Nm
1120: be setuid root when that authentication method is used.
1121: By default
1.141 markus 1122: .Nm
1.155 stevesk 1123: is not setuid root.
1.207 djm 1124: .It Pa ~/.rhosts
1.2 deraadt 1125: This file is used in
1.195 markus 1126: .Cm RhostsRSAAuthentication
1127: and
1128: .Cm HostbasedAuthentication
1.2 deraadt 1129: authentication to list the
1.40 aaron 1130: host/user pairs that are permitted to log in.
1131: (Note that this file is
1.1 deraadt 1132: also used by rlogin and rsh, which makes using this file insecure.)
1133: Each line of the file contains a host name (in the canonical form
1134: returned by name servers), and then a user name on that host,
1.40 aaron 1135: separated by a space.
1.92 markus 1136: On some machines this file may need to be
1.1 deraadt 1137: world-readable if the user's home directory is on a NFS partition,
1138: because
1.2 deraadt 1139: .Xr sshd 8
1.40 aaron 1140: reads it as root.
1141: Additionally, this file must be owned by the user,
1142: and must not have write permissions for anyone else.
1143: The recommended
1.1 deraadt 1144: permission for most machines is read/write for the user, and not
1145: accessible by others.
1.2 deraadt 1146: .Pp
1.195 markus 1147: Note that
1.2 deraadt 1148: .Xr sshd 8
1.195 markus 1149: allows authentication only in combination with client host key
1150: authentication before permitting log in.
1.137 deraadt 1151: If the server machine does not have the client's host key in
1.147 deraadt 1152: .Pa /etc/ssh/ssh_known_hosts ,
1.137 deraadt 1153: it can be stored in
1.207 djm 1154: .Pa ~/.ssh/known_hosts .
1.2 deraadt 1155: The easiest way to do this is to
1.1 deraadt 1156: connect back to the client from the server machine using ssh; this
1.48 markus 1157: will automatically add the host key to
1.207 djm 1158: .Pa ~/.ssh/known_hosts .
1159: .It Pa ~/.shosts
1.2 deraadt 1160: This file is used exactly the same way as
1.176 jmc 1161: .Pa .rhosts .
1.2 deraadt 1162: The purpose for
1.195 markus 1163: having this file is to be able to use
1164: .Cm RhostsRSAAuthentication
1165: and
1166: .Cm HostbasedAuthentication
1167: authentication without permitting login with
1.176 jmc 1168: .Xr rlogin
1.2 deraadt 1169: or
1170: .Xr rsh 1 .
1171: .It Pa /etc/hosts.equiv
1172: This file is used during
1.195 markus 1173: .Cm RhostsRSAAuthentication
1174: and
1175: .Cm HostbasedAuthentication
1.173 jmc 1176: authentication.
1.40 aaron 1177: It contains
1.176 jmc 1178: canonical hosts names, one per line (the full format is described in the
1.2 deraadt 1179: .Xr sshd 8
1.40 aaron 1180: manual page).
1181: If the client host is found in this file, login is
1.1 deraadt 1182: automatically permitted provided client and server user names are the
1.40 aaron 1183: same.
1.195 markus 1184: Additionally, successful client host key authentication is required.
1.40 aaron 1185: This file should only be writable by root.
1.2 deraadt 1186: .It Pa /etc/shosts.equiv
1.44 aaron 1187: This file is processed exactly as
1.2 deraadt 1188: .Pa /etc/hosts.equiv .
1.1 deraadt 1189: This file may be useful to permit logins using
1.2 deraadt 1190: .Nm
1.1 deraadt 1191: but not using rsh/rlogin.
1.147 deraadt 1192: .It Pa /etc/ssh/sshrc
1.1 deraadt 1193: Commands in this file are executed by
1.2 deraadt 1194: .Nm
1.1 deraadt 1195: when the user logs in just before the user's shell (or command) is started.
1196: See the
1.2 deraadt 1197: .Xr sshd 8
1.1 deraadt 1198: manual page for more information.
1.207 djm 1199: .It Pa ~/.ssh/rc
1.1 deraadt 1200: Commands in this file are executed by
1.2 deraadt 1201: .Nm
1.1 deraadt 1202: when the user logs in just before the user's shell (or command) is
1203: started.
1.44 aaron 1204: See the
1.2 deraadt 1205: .Xr sshd 8
1.1 deraadt 1206: manual page for more information.
1.207 djm 1207: .It Pa ~/.ssh/environment
1.31 markus 1208: Contains additional definitions for environment variables, see section
1209: .Sx ENVIRONMENT
1210: above.
1.58 itojun 1211: .El
1.145 markus 1212: .Sh DIAGNOSTICS
1213: .Nm
1214: exits with the exit status of the remote command or with 255
1215: if an error occurred.
1.2 deraadt 1216: .Sh SEE ALSO
1.176 jmc 1217: .Xr gzip 1 ,
1.2 deraadt 1218: .Xr rsh 1 ,
1219: .Xr scp 1 ,
1.83 djm 1220: .Xr sftp 1 ,
1.2 deraadt 1221: .Xr ssh-add 1 ,
1222: .Xr ssh-agent 1 ,
1223: .Xr ssh-keygen 1 ,
1224: .Xr telnet 1 ,
1.176 jmc 1225: .Xr hosts.equiv 5 ,
1.159 stevesk 1226: .Xr ssh_config 5 ,
1.160 naddy 1227: .Xr ssh-keysign 8 ,
1.87 itojun 1228: .Xr sshd 8
1.106 markus 1229: .Rs
1230: .%A T. Ylonen
1231: .%A T. Kivinen
1232: .%A M. Saarinen
1233: .%A T. Rinne
1234: .%A S. Lehtinen
1235: .%T "SSH Protocol Architecture"
1.150 markus 1236: .%N draft-ietf-secsh-architecture-12.txt
1237: .%D January 2002
1.106 markus 1238: .%O work in progress material
1239: .Re
1.173 jmc 1240: .Sh AUTHORS
1241: OpenSSH is a derivative of the original and free
1242: ssh 1.2.12 release by Tatu Ylonen.
1243: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1244: Theo de Raadt and Dug Song
1245: removed many bugs, re-added newer features and
1246: created OpenSSH.
1247: Markus Friedl contributed the support for SSH
1248: protocol versions 1.5 and 2.0.
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