Annotation of src/usr.bin/ssh/ssh.1, Revision 1.214
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: .\"
1.214 ! jmc 37: .\" $OpenBSD: ssh.1,v 1.213 2005/11/30 11:18:27 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
1.176 jmc 80: .Oo Ar user Ns @ Oc Ns Ar hostname
1.2 deraadt 81: .Op Ar command
1.44 aaron 82: .Sh DESCRIPTION
1.2 deraadt 83: .Nm
1.96 deraadt 84: (SSH client) is a program for logging into a remote machine and for
1.40 aaron 85: executing commands on a remote machine.
1.176 jmc 86: It is intended to replace rlogin and rsh,
87: and provide secure encrypted communications between
1.40 aaron 88: two untrusted hosts over an insecure network.
1.176 jmc 89: X11 connections and arbitrary TCP/IP ports
90: can also be forwarded over the secure channel.
1.2 deraadt 91: .Pp
92: .Nm
1.44 aaron 93: connects and logs into the specified
1.176 jmc 94: .Ar hostname
95: (with optional
96: .Ar user
97: name).
1.1 deraadt 98: The user must prove
1.49 markus 99: his/her identity to the remote machine using one of several methods
1.176 jmc 100: depending on the protocol version used.
1.49 markus 101: .Pp
1.176 jmc 102: If
103: .Ar command
104: is specified,
105: .Ar command
106: is executed on the remote host instead of a login shell.
1.49 markus 107: .Ss SSH protocol version 1
1.195 markus 108: The first authentication method is the
109: .Em rhosts
110: or
111: .Em hosts.equiv
112: method combined with RSA-based host authentication.
113: If the machine the user logs in from is listed in
1.2 deraadt 114: .Pa /etc/hosts.equiv
1.1 deraadt 115: or
1.2 deraadt 116: .Pa /etc/shosts.equiv
1.1 deraadt 117: on the remote machine, and the user names are
1.195 markus 118: the same on both sides, or if the files
1.207 djm 119: .Pa ~/.rhosts
1.1 deraadt 120: or
1.207 djm 121: .Pa ~/.shosts
1.195 markus 122: exist in the user's home directory on the
123: remote machine and contain a line containing the name of the client
1.1 deraadt 124: machine and the name of the user on that machine, the user is
1.195 markus 125: considered for log in.
126: Additionally, if the server can verify the client's
1.44 aaron 127: host key (see
1.147 deraadt 128: .Pa /etc/ssh/ssh_known_hosts
1.23 markus 129: and
1.207 djm 130: .Pa ~/.ssh/known_hosts
1.1 deraadt 131: in the
1.2 deraadt 132: .Sx FILES
1.176 jmc 133: section), only then is login permitted.
1.40 aaron 134: This authentication method closes security holes due to IP
135: spoofing, DNS spoofing and routing spoofing.
136: [Note to the administrator:
1.2 deraadt 137: .Pa /etc/hosts.equiv ,
1.207 djm 138: .Pa ~/.rhosts ,
1.1 deraadt 139: and the rlogin/rsh protocol in general, are inherently insecure and should be
140: disabled if security is desired.]
1.2 deraadt 141: .Pp
1.195 markus 142: As a second authentication method,
1.2 deraadt 143: .Nm
1.1 deraadt 144: supports RSA based authentication.
145: The scheme is based on public-key cryptography: there are cryptosystems
146: where encryption and decryption are done using separate keys, and it
147: is not possible to derive the decryption key from the encryption key.
1.40 aaron 148: RSA is one such system.
1.44 aaron 149: The idea is that each user creates a public/private
1.40 aaron 150: key pair for authentication purposes.
151: The server knows the public key, and only the user knows the private key.
1.176 jmc 152: .Pp
1.44 aaron 153: The file
1.207 djm 154: .Pa ~/.ssh/authorized_keys
1.176 jmc 155: lists the public keys that are permitted for logging in.
1.40 aaron 156: When the user logs in, the
1.2 deraadt 157: .Nm
1.1 deraadt 158: program tells the server which key pair it would like to use for
1.40 aaron 159: authentication.
1.176 jmc 160: The server checks if this key is permitted, and if so,
161: sends the user (actually the
1.2 deraadt 162: .Nm
1.1 deraadt 163: program running on behalf of the user) a challenge, a random number,
1.40 aaron 164: encrypted by the user's public key.
1.176 jmc 165: The challenge can only be decrypted using the proper private key.
166: The user's client then decrypts the challenge using the private key,
167: proving that he/she knows the private key
168: but without disclosing it to the server.
1.2 deraadt 169: .Pp
170: .Nm
1.40 aaron 171: implements the RSA authentication protocol automatically.
172: The user creates his/her RSA key pair by running
1.2 deraadt 173: .Xr ssh-keygen 1 .
1.44 aaron 174: This stores the private key in
1.207 djm 175: .Pa ~/.ssh/identity
1.176 jmc 176: and stores the public key in
1.207 djm 177: .Pa ~/.ssh/identity.pub
1.40 aaron 178: in the user's home directory.
179: The user should then copy the
1.2 deraadt 180: .Pa identity.pub
1.44 aaron 181: to
1.207 djm 182: .Pa ~/.ssh/authorized_keys
1.44 aaron 183: in his/her home directory on the remote machine (the
1.2 deraadt 184: .Pa authorized_keys
1.44 aaron 185: file corresponds to the conventional
1.207 djm 186: .Pa ~/.rhosts
1.1 deraadt 187: file, and has one key
1.40 aaron 188: per line, though the lines can be very long).
189: After this, the user can log in without giving the password.
1.2 deraadt 190: .Pp
1.1 deraadt 191: The most convenient way to use RSA authentication may be with an
1.40 aaron 192: authentication agent.
193: See
1.2 deraadt 194: .Xr ssh-agent 1
1.1 deraadt 195: for more information.
1.2 deraadt 196: .Pp
1.44 aaron 197: If other authentication methods fail,
1.2 deraadt 198: .Nm
1.40 aaron 199: prompts the user for a password.
200: The password is sent to the remote
1.1 deraadt 201: host for checking; however, since all communications are encrypted,
202: the password cannot be seen by someone listening on the network.
1.49 markus 203: .Ss SSH protocol version 2
1.176 jmc 204: When a user connects using protocol version 2,
1.145 markus 205: similar authentication methods are available.
1.107 markus 206: Using the default values for
207: .Cm PreferredAuthentications ,
1.123 markus 208: the client will try to authenticate first using the hostbased method;
1.176 jmc 209: if this method fails, public key authentication is attempted,
210: and finally if this method fails, keyboard-interactive and
1.123 markus 211: password authentication are tried.
1.49 markus 212: .Pp
213: The public key method is similar to RSA authentication described
1.107 markus 214: in the previous section and allows the RSA or DSA algorithm to be used:
1.102 itojun 215: The client uses his private key,
1.207 djm 216: .Pa ~/.ssh/id_dsa
1.102 itojun 217: or
1.207 djm 218: .Pa ~/.ssh/id_rsa ,
1.49 markus 219: to sign the session identifier and sends the result to the server.
220: The server checks whether the matching public key is listed in
1.207 djm 221: .Pa ~/.ssh/authorized_keys
1.49 markus 222: and grants access if both the key is found and the signature is correct.
223: The session identifier is derived from a shared Diffie-Hellman value
224: and is only known to the client and the server.
225: .Pp
1.176 jmc 226: If public key authentication fails or is not available, a password
227: can be sent encrypted to the remote host to prove the user's identity.
1.107 markus 228: .Pp
229: Additionally,
230: .Nm
231: supports hostbased or challenge response authentication.
1.49 markus 232: .Pp
233: Protocol 2 provides additional mechanisms for confidentiality
1.189 dtucker 234: (the traffic is encrypted using AES, 3DES, Blowfish, CAST128 or Arcfour)
235: and integrity (hmac-md5, hmac-sha1, hmac-ripemd160).
1.49 markus 236: Note that protocol 1 lacks a strong mechanism for ensuring the
237: integrity of the connection.
238: .Ss Login session and remote execution
1.1 deraadt 239: When the user's identity has been accepted by the server, the server
240: either executes the given command, or logs into the machine and gives
1.40 aaron 241: the user a normal shell on the remote machine.
242: All communication with
1.1 deraadt 243: the remote command or shell will be automatically encrypted.
1.2 deraadt 244: .Pp
1.1 deraadt 245: If a pseudo-terminal has been allocated (normal login session), the
1.104 djm 246: user may use the escape characters noted below.
1.2 deraadt 247: .Pp
1.176 jmc 248: If no pseudo-tty has been allocated,
249: the session is transparent and can be used to reliably transfer binary data.
1.40 aaron 250: On most systems, setting the escape character to
1.2 deraadt 251: .Dq none
252: will also make the session transparent even if a tty is used.
253: .Pp
1.71 djm 254: The session terminates when the command or shell on the remote
1.92 markus 255: machine exits and all X11 and TCP/IP connections have been closed.
1.176 jmc 256: The exit status of the remote program is returned as the exit status of
1.2 deraadt 257: .Nm ssh .
1.104 djm 258: .Ss Escape Characters
1.176 jmc 259: When a pseudo-terminal has been requested,
260: .Nm
261: supports a number of functions through the use of an escape character.
1.104 djm 262: .Pp
263: A single tilde character can be sent as
264: .Ic ~~
1.119 stevesk 265: or by following the tilde by a character other than those described below.
1.104 djm 266: The escape character must always follow a newline to be interpreted as
267: special.
268: The escape character can be changed in configuration files using the
269: .Cm EscapeChar
1.117 itojun 270: configuration directive or on the command line by the
1.104 djm 271: .Fl e
272: option.
273: .Pp
274: The supported escapes (assuming the default
275: .Ql ~ )
276: are:
277: .Bl -tag -width Ds
278: .It Cm ~.
1.176 jmc 279: Disconnect.
1.104 djm 280: .It Cm ~^Z
1.176 jmc 281: Background
282: .Nm ssh .
1.104 djm 283: .It Cm ~#
1.176 jmc 284: List forwarded connections.
1.104 djm 285: .It Cm ~&
1.176 jmc 286: Background
287: .Nm
288: at logout when waiting for forwarded connection / X11 sessions to terminate.
1.104 djm 289: .It Cm ~?
1.176 jmc 290: Display a list of escape characters.
1.170 markus 291: .It Cm ~B
1.176 jmc 292: Send a BREAK to the remote system
293: (only useful for SSH protocol version 2 and if the peer supports it).
1.149 jakob 294: .It Cm ~C
1.186 djm 295: Open command line.
296: Currently this allows the addition of port forwardings using the
1.149 jakob 297: .Fl L
298: and
299: .Fl R
1.186 djm 300: options (see below).
1.188 jmc 301: It also allows the cancellation of existing remote port-forwardings
1.186 djm 302: using
303: .Fl KR Ar hostport .
1.187 djm 304: Basic help is available, using the
305: .Fl h
1.186 djm 306: option.
1.104 djm 307: .It Cm ~R
1.176 jmc 308: Request rekeying of the connection
309: (only useful for SSH protocol version 2 and if the peer supports it).
1.104 djm 310: .El
1.49 markus 311: .Ss X11 and TCP forwarding
1.110 deraadt 312: If the
313: .Cm ForwardX11
314: variable is set to
315: .Dq yes
1.176 jmc 316: (or see the description of the
1.110 deraadt 317: .Fl X
318: and
319: .Fl x
320: options described later)
321: and the user is using X11 (the
1.2 deraadt 322: .Ev DISPLAY
1.1 deraadt 323: environment variable is set), the connection to the X11 display is
324: automatically forwarded to the remote side in such a way that any X11
325: programs started from the shell (or command) will go through the
326: encrypted channel, and the connection to the real X server will be made
1.40 aaron 327: from the local machine.
328: The user should not manually set
1.2 deraadt 329: .Ev DISPLAY .
1.1 deraadt 330: Forwarding of X11 connections can be
331: configured on the command line or in configuration files.
1.2 deraadt 332: .Pp
333: The
1.44 aaron 334: .Ev DISPLAY
1.2 deraadt 335: value set by
336: .Nm
1.176 jmc 337: will point to the server machine, but with a display number greater than zero.
1.40 aaron 338: This is normal, and happens because
1.2 deraadt 339: .Nm
340: creates a
341: .Dq proxy
342: X server on the server machine for forwarding the
1.1 deraadt 343: connections over the encrypted channel.
1.2 deraadt 344: .Pp
345: .Nm
1.1 deraadt 346: will also automatically set up Xauthority data on the server machine.
347: For this purpose, it will generate a random authorization cookie,
348: store it in Xauthority on the server, and verify that any forwarded
349: connections carry this cookie and replace it by the real cookie when
1.40 aaron 350: the connection is opened.
351: The real authentication cookie is never
1.1 deraadt 352: sent to the server machine (and no cookies are sent in the plain).
1.2 deraadt 353: .Pp
1.163 stevesk 354: If the
355: .Cm ForwardAgent
356: variable is set to
357: .Dq yes
1.176 jmc 358: (or see the description of the
1.163 stevesk 359: .Fl A
360: and
361: .Fl a
1.168 jmc 362: options described later) and
1.163 stevesk 363: the user is using an authentication agent, the connection to the agent
364: is automatically forwarded to the remote side.
1.2 deraadt 365: .Pp
1.1 deraadt 366: Forwarding of arbitrary TCP/IP connections over the secure channel can
1.120 stevesk 367: be specified either on the command line or in a configuration file.
1.40 aaron 368: One possible application of TCP/IP forwarding is a secure connection to an
1.92 markus 369: electronic purse; another is going through firewalls.
1.49 markus 370: .Ss Server authentication
1.2 deraadt 371: .Nm
1.49 markus 372: automatically maintains and checks a database containing
1.40 aaron 373: identifications for all hosts it has ever been used with.
1.116 markus 374: Host keys are stored in
1.207 djm 375: .Pa ~/.ssh/known_hosts
1.40 aaron 376: in the user's home directory.
1.116 markus 377: Additionally, the file
1.147 deraadt 378: .Pa /etc/ssh/ssh_known_hosts
1.116 markus 379: is automatically checked for known hosts.
1.40 aaron 380: Any new hosts are automatically added to the user's file.
1.176 jmc 381: If a host's identification ever changes,
1.2 deraadt 382: .Nm
1.1 deraadt 383: warns about this and disables password authentication to prevent a
1.40 aaron 384: trojan horse from getting the user's password.
1.176 jmc 385: Another purpose of this mechanism is to prevent man-in-the-middle attacks
386: which could otherwise be used to circumvent the encryption.
1.40 aaron 387: The
1.2 deraadt 388: .Cm StrictHostKeyChecking
1.158 stevesk 389: option can be used to prevent logins to machines whose
1.1 deraadt 390: host key is not known or has changed.
1.194 jakob 391: .Pp
392: .Nm
393: can be configured to verify host identification using fingerprint resource
394: records (SSHFP) published in DNS.
395: The
396: .Cm VerifyHostKeyDNS
397: option can be used to control how DNS lookups are performed.
398: SSHFP resource records can be generated using
399: .Xr ssh-keygen 1 .
1.65 aaron 400: .Pp
401: The options are as follows:
1.2 deraadt 402: .Bl -tag -width Ds
1.176 jmc 403: .It Fl 1
404: Forces
405: .Nm
406: to try protocol version 1 only.
407: .It Fl 2
408: Forces
409: .Nm
410: to try protocol version 2 only.
411: .It Fl 4
412: Forces
413: .Nm
414: to use IPv4 addresses only.
415: .It Fl 6
416: Forces
417: .Nm
418: to use IPv6 addresses only.
1.54 markus 419: .It Fl A
420: Enables forwarding of the authentication agent connection.
421: This can also be specified on a per-host basis in a configuration file.
1.165 stevesk 422: .Pp
1.168 jmc 423: Agent forwarding should be enabled with caution.
424: Users with the ability to bypass file permissions on the remote host
425: (for the agent's Unix-domain socket)
426: can access the local agent through the forwarded connection.
427: An attacker cannot obtain key material from the agent,
1.165 stevesk 428: however they can perform operations on the keys that enable them to
429: authenticate using the identities loaded into the agent.
1.176 jmc 430: .It Fl a
431: Disables forwarding of the authentication agent connection.
1.108 markus 432: .It Fl b Ar bind_address
1.209 dtucker 433: Use
434: .Ar bind_address
435: on the local machine as the source address
436: of the connection.
437: Only useful on systems with more than one address.
1.176 jmc 438: .It Fl C
439: Requests compression of all data (including stdin, stdout, stderr, and
440: data for forwarded X11 and TCP/IP connections).
441: The compression algorithm is the same used by
442: .Xr gzip 1 ,
443: and the
444: .Dq level
445: can be controlled by the
446: .Cm CompressionLevel
447: option for protocol version 1.
448: Compression is desirable on modem lines and other
449: slow connections, but will only slow down things on fast networks.
450: The default value can be set on a host-by-host basis in the
451: configuration files; see the
452: .Cm Compression
453: option.
1.189 dtucker 454: .It Fl c Ar cipher_spec
455: Selects the cipher specification for encrypting the session.
456: .Pp
457: Protocol version 1 allows specification of a single cipher.
1.212 djm 458: The supported values are
1.189 dtucker 459: .Dq 3des ,
460: .Dq blowfish
461: and
462: .Dq des .
1.2 deraadt 463: .Ar 3des
1.189 dtucker 464: (triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
1.44 aaron 465: It is believed to be secure.
1.5 deraadt 466: .Ar blowfish
1.176 jmc 467: is a fast block cipher; it appears very secure and is much faster than
1.40 aaron 468: .Ar 3des .
1.131 stevesk 469: .Ar des
470: is only supported in the
471: .Nm
472: client for interoperability with legacy protocol 1 implementations
473: that do not support the
474: .Ar 3des
1.168 jmc 475: cipher.
476: Its use is strongly discouraged due to cryptographic weaknesses.
1.189 dtucker 477: The default is
478: .Dq 3des .
479: .Pp
480: For protocol version 2
481: .Ar cipher_spec
482: is a comma-separated list of ciphers
483: listed in order of preference.
484: The supported ciphers are
485: .Dq 3des-cbc ,
486: .Dq aes128-cbc ,
487: .Dq aes192-cbc ,
488: .Dq aes256-cbc ,
489: .Dq aes128-ctr ,
490: .Dq aes192-ctr ,
491: .Dq aes256-ctr ,
1.208 djm 492: .Dq arcfour128 ,
493: .Dq arcfour256 ,
1.189 dtucker 494: .Dq arcfour ,
495: .Dq blowfish-cbc ,
496: and
497: .Dq cast128-cbc .
498: The default is
499: .Bd -literal
1.208 djm 500: ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
501: arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
502: aes192-ctr,aes256-ctr''
1.189 dtucker 503: .Ed
1.210 djm 504: .It Fl D Xo
505: .Sm off
506: .Oo Ar bind_address : Oc
507: .Ar port
508: .Sm on
509: .Xc
1.176 jmc 510: Specifies a local
511: .Dq dynamic
512: application-level port forwarding.
513: This works by allocating a socket to listen to
514: .Ar port
1.210 djm 515: on the local side, optionally bound to the specified
516: .Ar bind_address .
517: Whenever a connection is made to this port, the
1.176 jmc 518: connection is forwarded over the secure channel, and the application
519: protocol is then used to determine where to connect to from the
520: remote machine.
521: Currently the SOCKS4 and SOCKS5 protocols are supported, and
522: .Nm
523: will act as a SOCKS server.
524: Only root can forward privileged ports.
525: Dynamic port forwardings can also be specified in the configuration file.
1.210 djm 526: .Pp
527: IPv6 addresses can be specified with an alternative syntax:
528: .Sm off
529: .Xo
530: .Op Ar bind_address No /
531: .Ar port
532: .Xc
533: .Sm on
534: or by enclosing the address in square brackets.
535: Only the superuser can forward privileged ports.
536: By default, the local port is bound in accordance with the
537: .Cm GatewayPorts
538: setting.
539: However, an explicit
540: .Ar bind_address
541: may be used to bind the connection to a specific address.
542: The
543: .Ar bind_address
544: of
545: .Dq localhost
546: indicates that the listening port be bound for local use only, while an
547: empty address or
548: .Sq *
549: indicates that the port should be available from all interfaces.
1.176 jmc 550: .It Fl e Ar ch | ^ch | none
1.2 deraadt 551: Sets the escape character for sessions with a pty (default:
552: .Ql ~ ) .
1.40 aaron 553: The escape character is only recognized at the beginning of a line.
554: The escape character followed by a dot
1.2 deraadt 555: .Pq Ql \&.
1.176 jmc 556: closes the connection;
557: followed by control-Z suspends the connection;
558: and followed by itself sends the escape character once.
1.40 aaron 559: Setting the character to
1.2 deraadt 560: .Dq none
561: disables any escapes and makes the session fully transparent.
1.176 jmc 562: .It Fl F Ar configfile
563: Specifies an alternative per-user configuration file.
564: If a configuration file is given on the command line,
565: the system-wide configuration file
566: .Pq Pa /etc/ssh/ssh_config
567: will be ignored.
568: The default for the per-user configuration file is
1.207 djm 569: .Pa ~/.ssh/config .
1.2 deraadt 570: .It Fl f
571: Requests
572: .Nm
1.40 aaron 573: to go to background just before command execution.
574: This is useful if
1.2 deraadt 575: .Nm
576: is going to ask for passwords or passphrases, but the user
1.40 aaron 577: wants it in the background.
1.44 aaron 578: This implies
1.2 deraadt 579: .Fl n .
1.1 deraadt 580: The recommended way to start X11 programs at a remote site is with
1.2 deraadt 581: something like
582: .Ic ssh -f host xterm .
1.34 markus 583: .It Fl g
584: Allows remote hosts to connect to local forwarded ports.
1.176 jmc 585: .It Fl I Ar smartcard_device
586: Specifies which smartcard device to use.
587: The argument is the device
588: .Nm
589: should use to communicate with a smartcard used for storing the user's
590: private RSA key.
1.2 deraadt 591: .It Fl i Ar identity_file
1.144 stevesk 592: Selects a file from which the identity (private key) for
1.68 markus 593: RSA or DSA authentication is read.
1.144 stevesk 594: The default is
1.207 djm 595: .Pa ~/.ssh/identity
1.144 stevesk 596: for protocol version 1, and
1.207 djm 597: .Pa ~/.ssh/id_rsa
1.144 stevesk 598: and
1.207 djm 599: .Pa ~/.ssh/id_dsa
1.144 stevesk 600: for protocol version 2.
1.40 aaron 601: Identity files may also be specified on
602: a per-host basis in the configuration file.
603: It is possible to have multiple
1.2 deraadt 604: .Fl i
605: options (and multiple identities specified in
1.1 deraadt 606: configuration files).
1.2 deraadt 607: .It Fl k
1.179 dtucker 608: Disables forwarding (delegation) of GSSAPI credentials to the server.
1.176 jmc 609: .It Fl L Xo
610: .Sm off
1.200 djm 611: .Oo Ar bind_address : Oc
1.176 jmc 612: .Ar port : host : hostport
613: .Sm on
614: .Xc
615: Specifies that the given port on the local (client) host is to be
616: forwarded to the given host and port on the remote side.
617: This works by allocating a socket to listen to
618: .Ar port
1.200 djm 619: on the local side, optionally bound to the specified
620: .Ar bind_address .
621: Whenever a connection is made to this port, the
1.176 jmc 622: connection is forwarded over the secure channel, and a connection is
623: made to
624: .Ar host
625: port
626: .Ar hostport
627: from the remote machine.
628: Port forwardings can also be specified in the configuration file.
629: IPv6 addresses can be specified with an alternative syntax:
630: .Sm off
631: .Xo
1.205 jmc 632: .Op Ar bind_address No /
1.176 jmc 633: .Ar port No / Ar host No /
1.200 djm 634: .Ar hostport
1.176 jmc 635: .Xc
636: .Sm on
1.200 djm 637: or by enclosing the address in square brackets.
638: Only the superuser can forward privileged ports.
639: By default, the local port is bound in accordance with the
640: .Cm GatewayPorts
641: setting.
642: However, an explicit
643: .Ar bind_address
644: may be used to bind the connection to a specific address.
645: The
646: .Ar bind_address
647: of
648: .Dq localhost
1.202 jmc 649: indicates that the listening port be bound for local use only, while an
650: empty address or
651: .Sq *
1.200 djm 652: indicates that the port should be available from all interfaces.
1.2 deraadt 653: .It Fl l Ar login_name
1.40 aaron 654: Specifies the user to log in as on the remote machine.
655: This also may be specified on a per-host basis in the configuration file.
1.190 djm 656: .It Fl M
657: Places the
658: .Nm
659: client into
660: .Dq master
661: mode for connection sharing.
662: Refer to the description of
663: .Cm ControlMaster
664: in
665: .Xr ssh_config 5
666: for details.
1.193 jmc 667: .It Fl m Ar mac_spec
668: Additionally, for protocol version 2 a comma-separated list of MAC
669: (message authentication code) algorithms can
670: be specified in order of preference.
671: See the
672: .Cm MACs
673: keyword for more information.
1.176 jmc 674: .It Fl N
675: Do not execute a remote command.
676: This is useful for just forwarding ports
677: (protocol version 2 only).
1.2 deraadt 678: .It Fl n
679: Redirects stdin from
680: .Pa /dev/null
681: (actually, prevents reading from stdin).
1.1 deraadt 682: This must be used when
1.2 deraadt 683: .Nm
1.40 aaron 684: is run in the background.
685: A common trick is to use this to run X11 programs on a remote machine.
686: For example,
1.2 deraadt 687: .Ic ssh -n shadows.cs.hut.fi emacs &
688: will start an emacs on shadows.cs.hut.fi, and the X11
1.1 deraadt 689: connection will be automatically forwarded over an encrypted channel.
690: The
1.2 deraadt 691: .Nm
1.1 deraadt 692: program will be put in the background.
693: (This does not work if
1.2 deraadt 694: .Nm
695: needs to ask for a password or passphrase; see also the
696: .Fl f
697: option.)
1.199 jmc 698: .It Fl O Ar ctl_cmd
699: Control an active connection multiplexing master process.
700: When the
701: .Fl O
702: option is specified, the
703: .Ar ctl_cmd
704: argument is interpreted and passed to the master process.
705: Valid commands are:
706: .Dq check
707: (check that the master process is running) and
708: .Dq exit
709: (request the master to exit).
1.2 deraadt 710: .It Fl o Ar option
1.127 stevesk 711: Can be used to give options in the format used in the configuration file.
1.1 deraadt 712: This is useful for specifying options for which there is no separate
1.40 aaron 713: command-line flag.
1.176 jmc 714: For full details of the options listed below, and their possible values, see
715: .Xr ssh_config 5 .
716: .Pp
717: .Bl -tag -width Ds -offset indent -compact
718: .It AddressFamily
719: .It BatchMode
720: .It BindAddress
721: .It ChallengeResponseAuthentication
722: .It CheckHostIP
723: .It Cipher
724: .It Ciphers
725: .It ClearAllForwardings
726: .It Compression
727: .It CompressionLevel
728: .It ConnectionAttempts
1.185 dtucker 729: .It ConnectTimeout
1.190 djm 730: .It ControlMaster
731: .It ControlPath
1.176 jmc 732: .It DynamicForward
733: .It EscapeChar
734: .It ForwardAgent
735: .It ForwardX11
1.178 markus 736: .It ForwardX11Trusted
1.176 jmc 737: .It GatewayPorts
738: .It GlobalKnownHostsFile
739: .It GSSAPIAuthentication
740: .It GSSAPIDelegateCredentials
1.201 djm 741: .It HashKnownHosts
1.176 jmc 742: .It Host
743: .It HostbasedAuthentication
744: .It HostKeyAlgorithms
745: .It HostKeyAlias
746: .It HostName
747: .It IdentityFile
1.182 markus 748: .It IdentitiesOnly
1.197 djm 749: .It KbdInteractiveDevices
1.176 jmc 750: .It LocalForward
751: .It LogLevel
752: .It MACs
753: .It NoHostAuthenticationForLocalhost
754: .It NumberOfPasswordPrompts
755: .It PasswordAuthentication
756: .It Port
757: .It PreferredAuthentications
758: .It Protocol
759: .It ProxyCommand
760: .It PubkeyAuthentication
761: .It RemoteForward
762: .It RhostsRSAAuthentication
763: .It RSAAuthentication
1.184 jmc 764: .It SendEnv
1.181 markus 765: .It ServerAliveInterval
766: .It ServerAliveCountMax
1.176 jmc 767: .It SmartcardDevice
768: .It StrictHostKeyChecking
1.180 markus 769: .It TCPKeepAlive
1.176 jmc 770: .It UsePrivilegedPort
771: .It User
772: .It UserKnownHostsFile
773: .It VerifyHostKeyDNS
774: .It XAuthLocation
775: .El
1.2 deraadt 776: .It Fl p Ar port
1.40 aaron 777: Port to connect to on the remote host.
778: This can be specified on a
1.1 deraadt 779: per-host basis in the configuration file.
1.2 deraadt 780: .It Fl q
1.40 aaron 781: Quiet mode.
782: Causes all warning and diagnostic messages to be suppressed.
1.176 jmc 783: .It Fl R Xo
784: .Sm off
1.200 djm 785: .Oo Ar bind_address : Oc
1.176 jmc 786: .Ar port : host : hostport
787: .Sm on
788: .Xc
789: Specifies that the given port on the remote (server) host is to be
790: forwarded to the given host and port on the local side.
791: This works by allocating a socket to listen to
792: .Ar port
793: on the remote side, and whenever a connection is made to this port, the
794: connection is forwarded over the secure channel, and a connection is
795: made to
796: .Ar host
797: port
798: .Ar hostport
799: from the local machine.
1.200 djm 800: .Pp
1.176 jmc 801: Port forwardings can also be specified in the configuration file.
802: Privileged ports can be forwarded only when
803: logging in as root on the remote machine.
1.200 djm 804: IPv6 addresses can be specified by enclosing the address in square braces or
805: using an alternative syntax:
1.202 jmc 806: .Sm off
1.200 djm 807: .Xo
1.205 jmc 808: .Op Ar bind_address No /
1.202 jmc 809: .Ar host No / Ar port No /
810: .Ar hostport
811: .Xc .
1.176 jmc 812: .Sm on
1.200 djm 813: .Pp
814: By default, the listening socket on the server will be bound to the loopback
815: interface only.
816: This may be overriden by specifying a
817: .Ar bind_address .
1.202 jmc 818: An empty
819: .Ar bind_address ,
1.200 djm 820: or the address
1.202 jmc 821: .Ql * ,
1.200 djm 822: indicates that the remote socket should listen on all interfaces.
823: Specifying a remote
824: .Ar bind_address
1.202 jmc 825: will only succeed if the server's
826: .Cm GatewayPorts
1.200 djm 827: option is enabled (see
1.202 jmc 828: .Xr sshd_config 5 ) .
1.198 djm 829: .It Fl S Ar ctl_path
1.193 jmc 830: Specifies the location of a control socket for connection sharing.
1.190 djm 831: Refer to the description of
1.191 djm 832: .Cm ControlPath
833: and
1.190 djm 834: .Cm ControlMaster
835: in
836: .Xr ssh_config 5
837: for details.
1.80 djm 838: .It Fl s
1.172 jmc 839: May be used to request invocation of a subsystem on the remote system.
840: Subsystems are a feature of the SSH2 protocol which facilitate the use
1.176 jmc 841: of SSH as a secure transport for other applications (eg.\&
842: .Xr sftp 1 ) .
1.172 jmc 843: The subsystem is specified as the remote command.
1.176 jmc 844: .It Fl T
845: Disable pseudo-tty allocation.
1.2 deraadt 846: .It Fl t
1.40 aaron 847: Force pseudo-tty allocation.
1.43 brad 848: This can be used to execute arbitrary
1.40 aaron 849: screen-based programs on a remote machine, which can be very useful,
850: e.g., when implementing menu services.
1.73 markus 851: Multiple
852: .Fl t
853: options force tty allocation, even if
854: .Nm
855: has no local tty.
1.176 jmc 856: .It Fl V
857: Display the version number and exit.
1.2 deraadt 858: .It Fl v
1.40 aaron 859: Verbose mode.
860: Causes
1.2 deraadt 861: .Nm
1.40 aaron 862: to print debugging messages about its progress.
863: This is helpful in
1.1 deraadt 864: debugging connection, authentication, and configuration problems.
1.73 markus 865: Multiple
866: .Fl v
1.169 naddy 867: options increase the verbosity.
868: The maximum is 3.
1.2 deraadt 869: .It Fl X
1.1 deraadt 870: Enables X11 forwarding.
1.54 markus 871: This can also be specified on a per-host basis in a configuration file.
1.165 stevesk 872: .Pp
1.168 jmc 873: X11 forwarding should be enabled with caution.
874: Users with the ability to bypass file permissions on the remote host
875: (for the user's X authorization database)
876: can access the local X11 display through the forwarded connection.
877: An attacker may then be able to perform activities such as keystroke monitoring.
1.203 djm 878: .Pp
1.204 jmc 879: For this reason, X11 forwarding is subjected to X11 SECURITY extension
1.203 djm 880: restrictions by default.
881: Please refer to the
882: .Nm
883: .Fl Y
884: option and the
885: .Cm ForwardX11Trusted
886: directive in
887: .Xr ssh_config 5
888: for more information.
1.176 jmc 889: .It Fl x
890: Disables X11 forwarding.
1.178 markus 891: .It Fl Y
892: Enables trusted X11 forwarding.
1.203 djm 893: Trusted X11 forwardings are not subjected to the X11 SECURITY extension
894: controls.
1.2 deraadt 895: .El
896: .Sh CONFIGURATION FILES
897: .Nm
1.158 stevesk 898: may additionally obtain configuration data from
899: a per-user configuration file and a system-wide configuration file.
900: The file format and configuration options are described in
901: .Xr ssh_config 5 .
1.2 deraadt 902: .Sh ENVIRONMENT
903: .Nm
1.1 deraadt 904: will normally set the following environment variables:
1.176 jmc 905: .Bl -tag -width LOGNAME
1.2 deraadt 906: .It Ev DISPLAY
907: The
908: .Ev DISPLAY
1.40 aaron 909: variable indicates the location of the X11 server.
1.44 aaron 910: It is automatically set by
1.2 deraadt 911: .Nm
912: to point to a value of the form
913: .Dq hostname:n
914: where hostname indicates
1.176 jmc 915: the host where the shell runs, and n is an integer \*(Ge 1.
1.40 aaron 916: .Nm
917: uses this special value to forward X11 connections over the secure
918: channel.
1.107 markus 919: The user should normally not set
920: .Ev DISPLAY
921: explicitly, as that
1.1 deraadt 922: will render the X11 connection insecure (and will require the user to
923: manually copy any required authorization cookies).
1.2 deraadt 924: .It Ev HOME
1.1 deraadt 925: Set to the path of the user's home directory.
1.2 deraadt 926: .It Ev LOGNAME
927: Synonym for
1.12 aaron 928: .Ev USER ;
929: set for compatibility with systems that use this variable.
1.2 deraadt 930: .It Ev MAIL
1.129 stevesk 931: Set to the path of the user's mailbox.
1.40 aaron 932: .It Ev PATH
1.2 deraadt 933: Set to the default
934: .Ev PATH ,
935: as specified when compiling
1.12 aaron 936: .Nm ssh .
1.118 markus 937: .It Ev SSH_ASKPASS
938: If
939: .Nm
940: needs a passphrase, it will read the passphrase from the current
941: terminal if it was run from a terminal.
942: If
943: .Nm
944: does not have a terminal associated with it but
945: .Ev DISPLAY
946: and
947: .Ev SSH_ASKPASS
948: are set, it will execute the program specified by
949: .Ev SSH_ASKPASS
950: and open an X11 window to read the passphrase.
951: This is particularly useful when calling
952: .Nm
953: from a
1.196 jmc 954: .Pa .xsession
1.118 markus 955: or related script.
956: (Note that on some machines it
957: may be necessary to redirect the input from
958: .Pa /dev/null
959: to make this work.)
1.18 markus 960: .It Ev SSH_AUTH_SOCK
1.129 stevesk 961: Identifies the path of a unix-domain socket used to communicate with the
1.17 markus 962: agent.
1.166 stevesk 963: .It Ev SSH_CONNECTION
964: Identifies the client and server ends of the connection.
1.40 aaron 965: The variable contains
1.166 stevesk 966: four space-separated values: client ip-address, client port number,
967: server ip-address and server port number.
1.73 markus 968: .It Ev SSH_ORIGINAL_COMMAND
969: The variable contains the original command line if a forced command
970: is executed.
971: It can be used to extract the original arguments.
1.2 deraadt 972: .It Ev SSH_TTY
1.1 deraadt 973: This is set to the name of the tty (path to the device) associated
1.40 aaron 974: with the current shell or command.
975: If the current session has no tty,
1.1 deraadt 976: this variable is not set.
1.2 deraadt 977: .It Ev TZ
1.214 ! jmc 978: This variable is set to indicate the present time zone if it
1.56 deraadt 979: was set when the daemon was started (i.e., the daemon passes the value
1.1 deraadt 980: on to new connections).
1.2 deraadt 981: .It Ev USER
1.1 deraadt 982: Set to the name of the user logging in.
1.2 deraadt 983: .El
984: .Pp
1.44 aaron 985: Additionally,
1.2 deraadt 986: .Nm
1.44 aaron 987: reads
1.207 djm 988: .Pa ~/.ssh/environment ,
1.2 deraadt 989: and adds lines of the format
990: .Dq VARNAME=value
1.161 marc 991: to the environment if the file exists and if users are allowed to
992: change their environment.
1.176 jmc 993: For more information, see the
1.161 marc 994: .Cm PermitUserEnvironment
1.162 stevesk 995: option in
1.161 marc 996: .Xr sshd_config 5 .
1.2 deraadt 997: .Sh FILES
1.36 markus 998: .Bl -tag -width Ds
1.207 djm 999: .It Pa ~/.ssh/known_hosts
1.129 stevesk 1000: Records host keys for all hosts the user has logged into that are not
1.2 deraadt 1001: in
1.147 deraadt 1002: .Pa /etc/ssh/ssh_known_hosts .
1.2 deraadt 1003: See
1004: .Xr sshd 8 .
1.207 djm 1005: .It Pa ~/.ssh/identity, ~/.ssh/id_dsa, ~/.ssh/id_rsa
1.102 itojun 1006: Contains the authentication identity of the user.
1007: They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively.
1.48 markus 1008: These files
1009: contain sensitive data and should be readable by the user but not
1.15 markus 1010: accessible by others (read/write/execute).
1011: Note that
1012: .Nm
1.48 markus 1013: ignores a private key file if it is accessible by others.
1.15 markus 1014: It is possible to specify a passphrase when
1.1 deraadt 1015: generating the key; the passphrase will be used to encrypt the
1.8 deraadt 1016: sensitive part of this file using 3DES.
1.207 djm 1017: .It Pa ~/.ssh/identity.pub, ~/.ssh/id_dsa.pub, ~/.ssh/id_rsa.pub
1.1 deraadt 1018: Contains the public key for authentication (public part of the
1.40 aaron 1019: identity file in human-readable form).
1.48 markus 1020: The contents of the
1.207 djm 1021: .Pa ~/.ssh/identity.pub
1.176 jmc 1022: file should be added to the file
1.207 djm 1023: .Pa ~/.ssh/authorized_keys
1.2 deraadt 1024: on all machines
1.137 deraadt 1025: where the user wishes to log in using protocol version 1 RSA authentication.
1.48 markus 1026: The contents of the
1.207 djm 1027: .Pa ~/.ssh/id_dsa.pub
1.102 itojun 1028: and
1.207 djm 1029: .Pa ~/.ssh/id_rsa.pub
1.48 markus 1030: file should be added to
1.207 djm 1031: .Pa ~/.ssh/authorized_keys
1.48 markus 1032: on all machines
1.137 deraadt 1033: where the user wishes to log in using protocol version 2 DSA/RSA authentication.
1.48 markus 1034: These files are not
1.40 aaron 1035: sensitive and can (but need not) be readable by anyone.
1.48 markus 1036: These files are
1.84 markus 1037: never used automatically and are not necessary; they are only provided for
1.1 deraadt 1038: the convenience of the user.
1.207 djm 1039: .It Pa ~/.ssh/config
1.40 aaron 1040: This is the per-user configuration file.
1.158 stevesk 1041: The file format and configuration options are described in
1042: .Xr ssh_config 5 .
1.183 djm 1043: Because of the potential for abuse, this file must have strict permissions:
1044: read/write for the user, and not accessible by others.
1.207 djm 1045: .It Pa ~/.ssh/authorized_keys
1.115 markus 1046: Lists the public keys (RSA/DSA) that can be used for logging in as this user.
1.40 aaron 1047: The format of this file is described in the
1.2 deraadt 1048: .Xr sshd 8
1.40 aaron 1049: manual page.
1.176 jmc 1050: In the simplest form the format is the same as the
1051: .Pa .pub
1.116 markus 1052: identity files.
1.48 markus 1053: This file is not highly sensitive, but the recommended
1054: permissions are read/write for the user, and not accessible by others.
1.147 deraadt 1055: .It Pa /etc/ssh/ssh_known_hosts
1.40 aaron 1056: Systemwide list of known host keys.
1.116 markus 1057: This file should be prepared by the
1.1 deraadt 1058: system administrator to contain the public host keys of all machines in the
1.40 aaron 1059: organization.
1060: This file should be world-readable.
1061: This file contains
1.1 deraadt 1062: public keys, one per line, in the following format (fields separated
1.116 markus 1063: by spaces): system name, public key and optional comment field.
1.40 aaron 1064: When different names are used
1.1 deraadt 1065: for the same machine, all such names should be listed, separated by
1.40 aaron 1066: commas.
1.176 jmc 1067: The format is described in the
1.2 deraadt 1068: .Xr sshd 8
1.1 deraadt 1069: manual page.
1.2 deraadt 1070: .Pp
1.1 deraadt 1071: The canonical system name (as returned by name servers) is used by
1.2 deraadt 1072: .Xr sshd 8
1.1 deraadt 1073: to verify the client host when logging in; other names are needed because
1.2 deraadt 1074: .Nm
1.1 deraadt 1075: does not convert the user-supplied name to a canonical name before
1076: checking the key, because someone with access to the name servers
1077: would then be able to fool host authentication.
1.147 deraadt 1078: .It Pa /etc/ssh/ssh_config
1.40 aaron 1079: Systemwide configuration file.
1.158 stevesk 1080: The file format and configuration options are described in
1081: .Xr ssh_config 5 .
1.147 deraadt 1082: .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key
1.141 markus 1083: These three files contain the private parts of the host keys
1084: and are used for
1085: .Cm RhostsRSAAuthentication
1086: and
1087: .Cm HostbasedAuthentication .
1.155 stevesk 1088: If the protocol version 1
1089: .Cm RhostsRSAAuthentication
1.157 deraadt 1090: method is used,
1.155 stevesk 1091: .Nm
1092: must be setuid root, since the host key is readable only by root.
1093: For protocol version 2,
1094: .Nm
1095: uses
1096: .Xr ssh-keysign 8
1097: to access the host keys for
1098: .Cm HostbasedAuthentication .
1099: This eliminates the requirement that
1100: .Nm
1101: be setuid root when that authentication method is used.
1102: By default
1.141 markus 1103: .Nm
1.155 stevesk 1104: is not setuid root.
1.207 djm 1105: .It Pa ~/.rhosts
1.2 deraadt 1106: This file is used in
1.195 markus 1107: .Cm RhostsRSAAuthentication
1108: and
1109: .Cm HostbasedAuthentication
1.2 deraadt 1110: authentication to list the
1.40 aaron 1111: host/user pairs that are permitted to log in.
1112: (Note that this file is
1.1 deraadt 1113: also used by rlogin and rsh, which makes using this file insecure.)
1114: Each line of the file contains a host name (in the canonical form
1115: returned by name servers), and then a user name on that host,
1.40 aaron 1116: separated by a space.
1.92 markus 1117: On some machines this file may need to be
1.1 deraadt 1118: world-readable if the user's home directory is on a NFS partition,
1119: because
1.2 deraadt 1120: .Xr sshd 8
1.40 aaron 1121: reads it as root.
1122: Additionally, this file must be owned by the user,
1123: and must not have write permissions for anyone else.
1124: The recommended
1.1 deraadt 1125: permission for most machines is read/write for the user, and not
1126: accessible by others.
1.2 deraadt 1127: .Pp
1.195 markus 1128: Note that
1.2 deraadt 1129: .Xr sshd 8
1.195 markus 1130: allows authentication only in combination with client host key
1131: authentication before permitting log in.
1.137 deraadt 1132: If the server machine does not have the client's host key in
1.147 deraadt 1133: .Pa /etc/ssh/ssh_known_hosts ,
1.137 deraadt 1134: it can be stored in
1.207 djm 1135: .Pa ~/.ssh/known_hosts .
1.2 deraadt 1136: The easiest way to do this is to
1.1 deraadt 1137: connect back to the client from the server machine using ssh; this
1.48 markus 1138: will automatically add the host key to
1.207 djm 1139: .Pa ~/.ssh/known_hosts .
1140: .It Pa ~/.shosts
1.2 deraadt 1141: This file is used exactly the same way as
1.176 jmc 1142: .Pa .rhosts .
1.2 deraadt 1143: The purpose for
1.195 markus 1144: having this file is to be able to use
1145: .Cm RhostsRSAAuthentication
1146: and
1147: .Cm HostbasedAuthentication
1148: authentication without permitting login with
1.176 jmc 1149: .Xr rlogin
1.2 deraadt 1150: or
1151: .Xr rsh 1 .
1152: .It Pa /etc/hosts.equiv
1153: This file is used during
1.195 markus 1154: .Cm RhostsRSAAuthentication
1155: and
1156: .Cm HostbasedAuthentication
1.173 jmc 1157: authentication.
1.40 aaron 1158: It contains
1.176 jmc 1159: canonical hosts names, one per line (the full format is described in the
1.2 deraadt 1160: .Xr sshd 8
1.40 aaron 1161: manual page).
1162: If the client host is found in this file, login is
1.1 deraadt 1163: automatically permitted provided client and server user names are the
1.40 aaron 1164: same.
1.195 markus 1165: Additionally, successful client host key authentication is required.
1.40 aaron 1166: This file should only be writable by root.
1.2 deraadt 1167: .It Pa /etc/shosts.equiv
1.44 aaron 1168: This file is processed exactly as
1.2 deraadt 1169: .Pa /etc/hosts.equiv .
1.1 deraadt 1170: This file may be useful to permit logins using
1.2 deraadt 1171: .Nm
1.1 deraadt 1172: but not using rsh/rlogin.
1.147 deraadt 1173: .It Pa /etc/ssh/sshrc
1.1 deraadt 1174: Commands in this file are executed by
1.2 deraadt 1175: .Nm
1.1 deraadt 1176: when the user logs in just before the user's shell (or command) is started.
1177: See the
1.2 deraadt 1178: .Xr sshd 8
1.1 deraadt 1179: manual page for more information.
1.207 djm 1180: .It Pa ~/.ssh/rc
1.1 deraadt 1181: Commands in this file are executed by
1.2 deraadt 1182: .Nm
1.1 deraadt 1183: when the user logs in just before the user's shell (or command) is
1184: started.
1.44 aaron 1185: See the
1.2 deraadt 1186: .Xr sshd 8
1.1 deraadt 1187: manual page for more information.
1.207 djm 1188: .It Pa ~/.ssh/environment
1.31 markus 1189: Contains additional definitions for environment variables, see section
1190: .Sx ENVIRONMENT
1191: above.
1.58 itojun 1192: .El
1.145 markus 1193: .Sh DIAGNOSTICS
1194: .Nm
1195: exits with the exit status of the remote command or with 255
1196: if an error occurred.
1.2 deraadt 1197: .Sh SEE ALSO
1.176 jmc 1198: .Xr gzip 1 ,
1.2 deraadt 1199: .Xr rsh 1 ,
1200: .Xr scp 1 ,
1.83 djm 1201: .Xr sftp 1 ,
1.2 deraadt 1202: .Xr ssh-add 1 ,
1203: .Xr ssh-agent 1 ,
1204: .Xr ssh-keygen 1 ,
1205: .Xr telnet 1 ,
1.176 jmc 1206: .Xr hosts.equiv 5 ,
1.159 stevesk 1207: .Xr ssh_config 5 ,
1.160 naddy 1208: .Xr ssh-keysign 8 ,
1.87 itojun 1209: .Xr sshd 8
1.106 markus 1210: .Rs
1211: .%A T. Ylonen
1212: .%A T. Kivinen
1213: .%A M. Saarinen
1214: .%A T. Rinne
1215: .%A S. Lehtinen
1216: .%T "SSH Protocol Architecture"
1.150 markus 1217: .%N draft-ietf-secsh-architecture-12.txt
1218: .%D January 2002
1.106 markus 1219: .%O work in progress material
1220: .Re
1.173 jmc 1221: .Sh AUTHORS
1222: OpenSSH is a derivative of the original and free
1223: ssh 1.2.12 release by Tatu Ylonen.
1224: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1225: Theo de Raadt and Dug Song
1226: removed many bugs, re-added newer features and
1227: created OpenSSH.
1228: Markus Friedl contributed the support for SSH
1229: protocol versions 1.5 and 2.0.
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