Annotation of src/usr.bin/ssh/ssh.1, Revision 1.210
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: .\"
1.210 ! djm 37: .\" $OpenBSD: ssh.1,v 1.209 2005/07/06 09:33:05 dtucker 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
1.202 jmc 46: .Bk -words
1.191 djm 47: .Op Fl 1246AaCfgkMNnqsTtVvXxY
1.108 markus 48: .Op Fl b Ar bind_address
1.51 markus 49: .Op Fl c Ar cipher_spec
1.210 ! djm 50: .Oo Fl D\ \&
! 51: .Sm off
! 52: .Oo Ar bind_address : Oc
! 53: .Ar port
! 54: .Sm on
! 55: .Oc
1.2 deraadt 56: .Op Fl e Ar escape_char
1.176 jmc 57: .Op Fl F Ar configfile
1.2 deraadt 58: .Op Fl i Ar identity_file
1.202 jmc 59: .Oo Fl L\ \&
1.12 aaron 60: .Sm off
1.200 djm 61: .Oo Ar bind_address : Oc
1.202 jmc 62: .Ar port : host : hostport
1.12 aaron 63: .Sm on
64: .Oc
1.176 jmc 65: .Op Fl l Ar login_name
66: .Op Fl m Ar mac_spec
1.198 djm 67: .Op Fl O Ar ctl_cmd
1.176 jmc 68: .Op Fl o Ar option
69: .Op Fl p Ar port
1.202 jmc 70: .Oo Fl R\ \&
1.12 aaron 71: .Sm off
1.200 djm 72: .Oo Ar bind_address : Oc
1.202 jmc 73: .Ar port : host : hostport
1.12 aaron 74: .Sm on
75: .Oc
1.198 djm 76: .Op Fl S Ar ctl_path
1.176 jmc 77: .Oo Ar user Ns @ Oc Ns Ar hostname
1.2 deraadt 78: .Op Ar command
1.202 jmc 79: .Ek
1.44 aaron 80: .Sh DESCRIPTION
1.2 deraadt 81: .Nm
1.96 deraadt 82: (SSH client) is a program for logging into a remote machine and for
1.40 aaron 83: executing commands on a remote machine.
1.176 jmc 84: It is intended to replace rlogin and rsh,
85: and provide secure encrypted communications between
1.40 aaron 86: two untrusted hosts over an insecure network.
1.176 jmc 87: X11 connections and arbitrary TCP/IP ports
88: can also be forwarded over the secure channel.
1.2 deraadt 89: .Pp
90: .Nm
1.44 aaron 91: connects and logs into the specified
1.176 jmc 92: .Ar hostname
93: (with optional
94: .Ar user
95: name).
1.1 deraadt 96: The user must prove
1.49 markus 97: his/her identity to the remote machine using one of several methods
1.176 jmc 98: depending on the protocol version used.
1.49 markus 99: .Pp
1.176 jmc 100: If
101: .Ar command
102: is specified,
103: .Ar command
104: is executed on the remote host instead of a login shell.
1.49 markus 105: .Ss SSH protocol version 1
1.195 markus 106: The first authentication method is the
107: .Em rhosts
108: or
109: .Em hosts.equiv
110: method combined with RSA-based host authentication.
111: If the machine the user logs in from is listed in
1.2 deraadt 112: .Pa /etc/hosts.equiv
1.1 deraadt 113: or
1.2 deraadt 114: .Pa /etc/shosts.equiv
1.1 deraadt 115: on the remote machine, and the user names are
1.195 markus 116: the same on both sides, or if the files
1.207 djm 117: .Pa ~/.rhosts
1.1 deraadt 118: or
1.207 djm 119: .Pa ~/.shosts
1.195 markus 120: exist in the user's home directory on the
121: remote machine and contain a line containing the name of the client
1.1 deraadt 122: machine and the name of the user on that machine, the user is
1.195 markus 123: considered for log in.
124: Additionally, if the server can verify the client's
1.44 aaron 125: host key (see
1.147 deraadt 126: .Pa /etc/ssh/ssh_known_hosts
1.23 markus 127: and
1.207 djm 128: .Pa ~/.ssh/known_hosts
1.1 deraadt 129: in the
1.2 deraadt 130: .Sx FILES
1.176 jmc 131: section), only then is login permitted.
1.40 aaron 132: This authentication method closes security holes due to IP
133: spoofing, DNS spoofing and routing spoofing.
134: [Note to the administrator:
1.2 deraadt 135: .Pa /etc/hosts.equiv ,
1.207 djm 136: .Pa ~/.rhosts ,
1.1 deraadt 137: and the rlogin/rsh protocol in general, are inherently insecure and should be
138: disabled if security is desired.]
1.2 deraadt 139: .Pp
1.195 markus 140: As a second authentication method,
1.2 deraadt 141: .Nm
1.1 deraadt 142: supports RSA based authentication.
143: The scheme is based on public-key cryptography: there are cryptosystems
144: where encryption and decryption are done using separate keys, and it
145: is not possible to derive the decryption key from the encryption key.
1.40 aaron 146: RSA is one such system.
1.44 aaron 147: The idea is that each user creates a public/private
1.40 aaron 148: key pair for authentication purposes.
149: The server knows the public key, and only the user knows the private key.
1.176 jmc 150: .Pp
1.44 aaron 151: The file
1.207 djm 152: .Pa ~/.ssh/authorized_keys
1.176 jmc 153: lists the public keys that are permitted for logging in.
1.40 aaron 154: When the user logs in, the
1.2 deraadt 155: .Nm
1.1 deraadt 156: program tells the server which key pair it would like to use for
1.40 aaron 157: authentication.
1.176 jmc 158: The server checks if this key is permitted, and if so,
159: sends the user (actually the
1.2 deraadt 160: .Nm
1.1 deraadt 161: program running on behalf of the user) a challenge, a random number,
1.40 aaron 162: encrypted by the user's public key.
1.176 jmc 163: The challenge can only be decrypted using the proper private key.
164: The user's client then decrypts the challenge using the private key,
165: proving that he/she knows the private key
166: but without disclosing it to the server.
1.2 deraadt 167: .Pp
168: .Nm
1.40 aaron 169: implements the RSA authentication protocol automatically.
170: The user creates his/her RSA key pair by running
1.2 deraadt 171: .Xr ssh-keygen 1 .
1.44 aaron 172: This stores the private key in
1.207 djm 173: .Pa ~/.ssh/identity
1.176 jmc 174: and stores the public key in
1.207 djm 175: .Pa ~/.ssh/identity.pub
1.40 aaron 176: in the user's home directory.
177: The user should then copy the
1.2 deraadt 178: .Pa identity.pub
1.44 aaron 179: to
1.207 djm 180: .Pa ~/.ssh/authorized_keys
1.44 aaron 181: in his/her home directory on the remote machine (the
1.2 deraadt 182: .Pa authorized_keys
1.44 aaron 183: file corresponds to the conventional
1.207 djm 184: .Pa ~/.rhosts
1.1 deraadt 185: file, and has one key
1.40 aaron 186: per line, though the lines can be very long).
187: After this, the user can log in without giving the password.
1.2 deraadt 188: .Pp
1.1 deraadt 189: The most convenient way to use RSA authentication may be with an
1.40 aaron 190: authentication agent.
191: See
1.2 deraadt 192: .Xr ssh-agent 1
1.1 deraadt 193: for more information.
1.2 deraadt 194: .Pp
1.44 aaron 195: If other authentication methods fail,
1.2 deraadt 196: .Nm
1.40 aaron 197: prompts the user for a password.
198: The password is sent to the remote
1.1 deraadt 199: host for checking; however, since all communications are encrypted,
200: the password cannot be seen by someone listening on the network.
1.49 markus 201: .Ss SSH protocol version 2
1.176 jmc 202: When a user connects using protocol version 2,
1.145 markus 203: similar authentication methods are available.
1.107 markus 204: Using the default values for
205: .Cm PreferredAuthentications ,
1.123 markus 206: the client will try to authenticate first using the hostbased method;
1.176 jmc 207: if this method fails, public key authentication is attempted,
208: and finally if this method fails, keyboard-interactive and
1.123 markus 209: password authentication are tried.
1.49 markus 210: .Pp
211: The public key method is similar to RSA authentication described
1.107 markus 212: in the previous section and allows the RSA or DSA algorithm to be used:
1.102 itojun 213: The client uses his private key,
1.207 djm 214: .Pa ~/.ssh/id_dsa
1.102 itojun 215: or
1.207 djm 216: .Pa ~/.ssh/id_rsa ,
1.49 markus 217: to sign the session identifier and sends the result to the server.
218: The server checks whether the matching public key is listed in
1.207 djm 219: .Pa ~/.ssh/authorized_keys
1.49 markus 220: and grants access if both the key is found and the signature is correct.
221: The session identifier is derived from a shared Diffie-Hellman value
222: and is only known to the client and the server.
223: .Pp
1.176 jmc 224: If public key authentication fails or is not available, a password
225: can be sent encrypted to the remote host to prove the user's identity.
1.107 markus 226: .Pp
227: Additionally,
228: .Nm
229: supports hostbased or challenge response authentication.
1.49 markus 230: .Pp
231: Protocol 2 provides additional mechanisms for confidentiality
1.189 dtucker 232: (the traffic is encrypted using AES, 3DES, Blowfish, CAST128 or Arcfour)
233: and integrity (hmac-md5, hmac-sha1, hmac-ripemd160).
1.49 markus 234: Note that protocol 1 lacks a strong mechanism for ensuring the
235: integrity of the connection.
236: .Ss Login session and remote execution
1.1 deraadt 237: When the user's identity has been accepted by the server, the server
238: either executes the given command, or logs into the machine and gives
1.40 aaron 239: the user a normal shell on the remote machine.
240: All communication with
1.1 deraadt 241: the remote command or shell will be automatically encrypted.
1.2 deraadt 242: .Pp
1.1 deraadt 243: If a pseudo-terminal has been allocated (normal login session), the
1.104 djm 244: user may use the escape characters noted below.
1.2 deraadt 245: .Pp
1.176 jmc 246: If no pseudo-tty has been allocated,
247: the session is transparent and can be used to reliably transfer binary data.
1.40 aaron 248: On most systems, setting the escape character to
1.2 deraadt 249: .Dq none
250: will also make the session transparent even if a tty is used.
251: .Pp
1.71 djm 252: The session terminates when the command or shell on the remote
1.92 markus 253: machine exits and all X11 and TCP/IP connections have been closed.
1.176 jmc 254: The exit status of the remote program is returned as the exit status of
1.2 deraadt 255: .Nm ssh .
1.104 djm 256: .Ss Escape Characters
1.176 jmc 257: When a pseudo-terminal has been requested,
258: .Nm
259: supports a number of functions through the use of an escape character.
1.104 djm 260: .Pp
261: A single tilde character can be sent as
262: .Ic ~~
1.119 stevesk 263: or by following the tilde by a character other than those described below.
1.104 djm 264: The escape character must always follow a newline to be interpreted as
265: special.
266: The escape character can be changed in configuration files using the
267: .Cm EscapeChar
1.117 itojun 268: configuration directive or on the command line by the
1.104 djm 269: .Fl e
270: option.
271: .Pp
272: The supported escapes (assuming the default
273: .Ql ~ )
274: are:
275: .Bl -tag -width Ds
276: .It Cm ~.
1.176 jmc 277: Disconnect.
1.104 djm 278: .It Cm ~^Z
1.176 jmc 279: Background
280: .Nm ssh .
1.104 djm 281: .It Cm ~#
1.176 jmc 282: List forwarded connections.
1.104 djm 283: .It Cm ~&
1.176 jmc 284: Background
285: .Nm
286: at logout when waiting for forwarded connection / X11 sessions to terminate.
1.104 djm 287: .It Cm ~?
1.176 jmc 288: Display a list of escape characters.
1.170 markus 289: .It Cm ~B
1.176 jmc 290: Send a BREAK to the remote system
291: (only useful for SSH protocol version 2 and if the peer supports it).
1.149 jakob 292: .It Cm ~C
1.186 djm 293: Open command line.
294: Currently this allows the addition of port forwardings using the
1.149 jakob 295: .Fl L
296: and
297: .Fl R
1.186 djm 298: options (see below).
1.188 jmc 299: It also allows the cancellation of existing remote port-forwardings
1.186 djm 300: using
301: .Fl KR Ar hostport .
1.187 djm 302: Basic help is available, using the
303: .Fl h
1.186 djm 304: option.
1.104 djm 305: .It Cm ~R
1.176 jmc 306: Request rekeying of the connection
307: (only useful for SSH protocol version 2 and if the peer supports it).
1.104 djm 308: .El
1.49 markus 309: .Ss X11 and TCP forwarding
1.110 deraadt 310: If the
311: .Cm ForwardX11
312: variable is set to
313: .Dq yes
1.176 jmc 314: (or see the description of the
1.110 deraadt 315: .Fl X
316: and
317: .Fl x
318: options described later)
319: and the user is using X11 (the
1.2 deraadt 320: .Ev DISPLAY
1.1 deraadt 321: environment variable is set), the connection to the X11 display is
322: automatically forwarded to the remote side in such a way that any X11
323: programs started from the shell (or command) will go through the
324: encrypted channel, and the connection to the real X server will be made
1.40 aaron 325: from the local machine.
326: The user should not manually set
1.2 deraadt 327: .Ev DISPLAY .
1.1 deraadt 328: Forwarding of X11 connections can be
329: configured on the command line or in configuration files.
1.2 deraadt 330: .Pp
331: The
1.44 aaron 332: .Ev DISPLAY
1.2 deraadt 333: value set by
334: .Nm
1.176 jmc 335: will point to the server machine, but with a display number greater than zero.
1.40 aaron 336: This is normal, and happens because
1.2 deraadt 337: .Nm
338: creates a
339: .Dq proxy
340: X server on the server machine for forwarding the
1.1 deraadt 341: connections over the encrypted channel.
1.2 deraadt 342: .Pp
343: .Nm
1.1 deraadt 344: will also automatically set up Xauthority data on the server machine.
345: For this purpose, it will generate a random authorization cookie,
346: store it in Xauthority on the server, and verify that any forwarded
347: connections carry this cookie and replace it by the real cookie when
1.40 aaron 348: the connection is opened.
349: The real authentication cookie is never
1.1 deraadt 350: sent to the server machine (and no cookies are sent in the plain).
1.2 deraadt 351: .Pp
1.163 stevesk 352: If the
353: .Cm ForwardAgent
354: variable is set to
355: .Dq yes
1.176 jmc 356: (or see the description of the
1.163 stevesk 357: .Fl A
358: and
359: .Fl a
1.168 jmc 360: options described later) and
1.163 stevesk 361: the user is using an authentication agent, the connection to the agent
362: is automatically forwarded to the remote side.
1.2 deraadt 363: .Pp
1.1 deraadt 364: Forwarding of arbitrary TCP/IP connections over the secure channel can
1.120 stevesk 365: be specified either on the command line or in a configuration file.
1.40 aaron 366: One possible application of TCP/IP forwarding is a secure connection to an
1.92 markus 367: electronic purse; another is going through firewalls.
1.49 markus 368: .Ss Server authentication
1.2 deraadt 369: .Nm
1.49 markus 370: automatically maintains and checks a database containing
1.40 aaron 371: identifications for all hosts it has ever been used with.
1.116 markus 372: Host keys are stored in
1.207 djm 373: .Pa ~/.ssh/known_hosts
1.40 aaron 374: in the user's home directory.
1.116 markus 375: Additionally, the file
1.147 deraadt 376: .Pa /etc/ssh/ssh_known_hosts
1.116 markus 377: is automatically checked for known hosts.
1.40 aaron 378: Any new hosts are automatically added to the user's file.
1.176 jmc 379: If a host's identification ever changes,
1.2 deraadt 380: .Nm
1.1 deraadt 381: warns about this and disables password authentication to prevent a
1.40 aaron 382: trojan horse from getting the user's password.
1.176 jmc 383: Another purpose of this mechanism is to prevent man-in-the-middle attacks
384: which could otherwise be used to circumvent the encryption.
1.40 aaron 385: The
1.2 deraadt 386: .Cm StrictHostKeyChecking
1.158 stevesk 387: option can be used to prevent logins to machines whose
1.1 deraadt 388: host key is not known or has changed.
1.194 jakob 389: .Pp
390: .Nm
391: can be configured to verify host identification using fingerprint resource
392: records (SSHFP) published in DNS.
393: The
394: .Cm VerifyHostKeyDNS
395: option can be used to control how DNS lookups are performed.
396: SSHFP resource records can be generated using
397: .Xr ssh-keygen 1 .
1.65 aaron 398: .Pp
399: The options are as follows:
1.2 deraadt 400: .Bl -tag -width Ds
1.176 jmc 401: .It Fl 1
402: Forces
403: .Nm
404: to try protocol version 1 only.
405: .It Fl 2
406: Forces
407: .Nm
408: to try protocol version 2 only.
409: .It Fl 4
410: Forces
411: .Nm
412: to use IPv4 addresses only.
413: .It Fl 6
414: Forces
415: .Nm
416: to use IPv6 addresses only.
1.54 markus 417: .It Fl A
418: Enables forwarding of the authentication agent connection.
419: This can also be specified on a per-host basis in a configuration file.
1.165 stevesk 420: .Pp
1.168 jmc 421: Agent forwarding should be enabled with caution.
422: Users with the ability to bypass file permissions on the remote host
423: (for the agent's Unix-domain socket)
424: can access the local agent through the forwarded connection.
425: An attacker cannot obtain key material from the agent,
1.165 stevesk 426: however they can perform operations on the keys that enable them to
427: authenticate using the identities loaded into the agent.
1.176 jmc 428: .It Fl a
429: Disables forwarding of the authentication agent connection.
1.108 markus 430: .It Fl b Ar bind_address
1.209 dtucker 431: Use
432: .Ar bind_address
433: on the local machine as the source address
434: of the connection.
435: Only useful on systems with more than one address.
1.176 jmc 436: .It Fl C
437: Requests compression of all data (including stdin, stdout, stderr, and
438: data for forwarded X11 and TCP/IP connections).
439: The compression algorithm is the same used by
440: .Xr gzip 1 ,
441: and the
442: .Dq level
443: can be controlled by the
444: .Cm CompressionLevel
445: option for protocol version 1.
446: Compression is desirable on modem lines and other
447: slow connections, but will only slow down things on fast networks.
448: The default value can be set on a host-by-host basis in the
449: configuration files; see the
450: .Cm Compression
451: option.
1.189 dtucker 452: .It Fl c Ar cipher_spec
453: Selects the cipher specification for encrypting the session.
454: .Pp
455: Protocol version 1 allows specification of a single cipher.
456: The suported values are
457: .Dq 3des ,
458: .Dq blowfish
459: and
460: .Dq des .
1.2 deraadt 461: .Ar 3des
1.189 dtucker 462: (triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
1.44 aaron 463: It is believed to be secure.
1.5 deraadt 464: .Ar blowfish
1.176 jmc 465: is a fast block cipher; it appears very secure and is much faster than
1.40 aaron 466: .Ar 3des .
1.131 stevesk 467: .Ar des
468: is only supported in the
469: .Nm
470: client for interoperability with legacy protocol 1 implementations
471: that do not support the
472: .Ar 3des
1.168 jmc 473: cipher.
474: Its use is strongly discouraged due to cryptographic weaknesses.
1.189 dtucker 475: The default is
476: .Dq 3des .
477: .Pp
478: For protocol version 2
479: .Ar cipher_spec
480: is a comma-separated list of ciphers
481: listed in order of preference.
482: The supported ciphers are
483: .Dq 3des-cbc ,
484: .Dq aes128-cbc ,
485: .Dq aes192-cbc ,
486: .Dq aes256-cbc ,
487: .Dq aes128-ctr ,
488: .Dq aes192-ctr ,
489: .Dq aes256-ctr ,
1.208 djm 490: .Dq arcfour128 ,
491: .Dq arcfour256 ,
1.189 dtucker 492: .Dq arcfour ,
493: .Dq blowfish-cbc ,
494: and
495: .Dq cast128-cbc .
496: The default is
497: .Bd -literal
1.208 djm 498: ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
499: arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
500: aes192-ctr,aes256-ctr''
1.189 dtucker 501: .Ed
1.210 ! djm 502: .It Fl D Xo
! 503: .Sm off
! 504: .Oo Ar bind_address : Oc
! 505: .Ar port
! 506: .Sm on
! 507: .Xc
1.176 jmc 508: Specifies a local
509: .Dq dynamic
510: application-level port forwarding.
511: This works by allocating a socket to listen to
512: .Ar port
1.210 ! djm 513: on the local side, optionally bound to the specified
! 514: .Ar bind_address .
! 515: Whenever a connection is made to this port, the
1.176 jmc 516: connection is forwarded over the secure channel, and the application
517: protocol is then used to determine where to connect to from the
518: remote machine.
519: Currently the SOCKS4 and SOCKS5 protocols are supported, and
520: .Nm
521: will act as a SOCKS server.
522: Only root can forward privileged ports.
523: Dynamic port forwardings can also be specified in the configuration file.
1.210 ! djm 524: .Pp
! 525: IPv6 addresses can be specified with an alternative syntax:
! 526: .Sm off
! 527: .Xo
! 528: .Op Ar bind_address No /
! 529: .Ar port
! 530: .Xc
! 531: .Sm on
! 532: or by enclosing the address in square brackets.
! 533: Only the superuser can forward privileged ports.
! 534: By default, the local port is bound in accordance with the
! 535: .Cm GatewayPorts
! 536: setting.
! 537: However, an explicit
! 538: .Ar bind_address
! 539: may be used to bind the connection to a specific address.
! 540: The
! 541: .Ar bind_address
! 542: of
! 543: .Dq localhost
! 544: indicates that the listening port be bound for local use only, while an
! 545: empty address or
! 546: .Sq *
! 547: indicates that the port should be available from all interfaces.
1.176 jmc 548: .It Fl e Ar ch | ^ch | none
1.2 deraadt 549: Sets the escape character for sessions with a pty (default:
550: .Ql ~ ) .
1.40 aaron 551: The escape character is only recognized at the beginning of a line.
552: The escape character followed by a dot
1.2 deraadt 553: .Pq Ql \&.
1.176 jmc 554: closes the connection;
555: followed by control-Z suspends the connection;
556: and followed by itself sends the escape character once.
1.40 aaron 557: Setting the character to
1.2 deraadt 558: .Dq none
559: disables any escapes and makes the session fully transparent.
1.176 jmc 560: .It Fl F Ar configfile
561: Specifies an alternative per-user configuration file.
562: If a configuration file is given on the command line,
563: the system-wide configuration file
564: .Pq Pa /etc/ssh/ssh_config
565: will be ignored.
566: The default for the per-user configuration file is
1.207 djm 567: .Pa ~/.ssh/config .
1.2 deraadt 568: .It Fl f
569: Requests
570: .Nm
1.40 aaron 571: to go to background just before command execution.
572: This is useful if
1.2 deraadt 573: .Nm
574: is going to ask for passwords or passphrases, but the user
1.40 aaron 575: wants it in the background.
1.44 aaron 576: This implies
1.2 deraadt 577: .Fl n .
1.1 deraadt 578: The recommended way to start X11 programs at a remote site is with
1.2 deraadt 579: something like
580: .Ic ssh -f host xterm .
1.34 markus 581: .It Fl g
582: Allows remote hosts to connect to local forwarded ports.
1.176 jmc 583: .It Fl I Ar smartcard_device
584: Specifies which smartcard device to use.
585: The argument is the device
586: .Nm
587: should use to communicate with a smartcard used for storing the user's
588: private RSA key.
1.2 deraadt 589: .It Fl i Ar identity_file
1.144 stevesk 590: Selects a file from which the identity (private key) for
1.68 markus 591: RSA or DSA authentication is read.
1.144 stevesk 592: The default is
1.207 djm 593: .Pa ~/.ssh/identity
1.144 stevesk 594: for protocol version 1, and
1.207 djm 595: .Pa ~/.ssh/id_rsa
1.144 stevesk 596: and
1.207 djm 597: .Pa ~/.ssh/id_dsa
1.144 stevesk 598: for protocol version 2.
1.40 aaron 599: Identity files may also be specified on
600: a per-host basis in the configuration file.
601: It is possible to have multiple
1.2 deraadt 602: .Fl i
603: options (and multiple identities specified in
1.1 deraadt 604: configuration files).
1.2 deraadt 605: .It Fl k
1.179 dtucker 606: Disables forwarding (delegation) of GSSAPI credentials to the server.
1.176 jmc 607: .It Fl L Xo
608: .Sm off
1.200 djm 609: .Oo Ar bind_address : Oc
1.176 jmc 610: .Ar port : host : hostport
611: .Sm on
612: .Xc
613: Specifies that the given port on the local (client) host is to be
614: forwarded to the given host and port on the remote side.
615: This works by allocating a socket to listen to
616: .Ar port
1.200 djm 617: on the local side, optionally bound to the specified
618: .Ar bind_address .
619: Whenever a connection is made to this port, the
1.176 jmc 620: connection is forwarded over the secure channel, and a connection is
621: made to
622: .Ar host
623: port
624: .Ar hostport
625: from the remote machine.
626: Port forwardings can also be specified in the configuration file.
627: IPv6 addresses can be specified with an alternative syntax:
628: .Sm off
629: .Xo
1.205 jmc 630: .Op Ar bind_address No /
1.176 jmc 631: .Ar port No / Ar host No /
1.200 djm 632: .Ar hostport
1.176 jmc 633: .Xc
634: .Sm on
1.200 djm 635: or by enclosing the address in square brackets.
636: Only the superuser can forward privileged ports.
637: By default, the local port is bound in accordance with the
638: .Cm GatewayPorts
639: setting.
640: However, an explicit
641: .Ar bind_address
642: may be used to bind the connection to a specific address.
643: The
644: .Ar bind_address
645: of
646: .Dq localhost
1.202 jmc 647: indicates that the listening port be bound for local use only, while an
648: empty address or
649: .Sq *
1.200 djm 650: indicates that the port should be available from all interfaces.
1.2 deraadt 651: .It Fl l Ar login_name
1.40 aaron 652: Specifies the user to log in as on the remote machine.
653: This also may be specified on a per-host basis in the configuration file.
1.190 djm 654: .It Fl M
655: Places the
656: .Nm
657: client into
658: .Dq master
659: mode for connection sharing.
660: Refer to the description of
661: .Cm ControlMaster
662: in
663: .Xr ssh_config 5
664: for details.
1.193 jmc 665: .It Fl m Ar mac_spec
666: Additionally, for protocol version 2 a comma-separated list of MAC
667: (message authentication code) algorithms can
668: be specified in order of preference.
669: See the
670: .Cm MACs
671: keyword for more information.
1.176 jmc 672: .It Fl N
673: Do not execute a remote command.
674: This is useful for just forwarding ports
675: (protocol version 2 only).
1.2 deraadt 676: .It Fl n
677: Redirects stdin from
678: .Pa /dev/null
679: (actually, prevents reading from stdin).
1.1 deraadt 680: This must be used when
1.2 deraadt 681: .Nm
1.40 aaron 682: is run in the background.
683: A common trick is to use this to run X11 programs on a remote machine.
684: For example,
1.2 deraadt 685: .Ic ssh -n shadows.cs.hut.fi emacs &
686: will start an emacs on shadows.cs.hut.fi, and the X11
1.1 deraadt 687: connection will be automatically forwarded over an encrypted channel.
688: The
1.2 deraadt 689: .Nm
1.1 deraadt 690: program will be put in the background.
691: (This does not work if
1.2 deraadt 692: .Nm
693: needs to ask for a password or passphrase; see also the
694: .Fl f
695: option.)
1.199 jmc 696: .It Fl O Ar ctl_cmd
697: Control an active connection multiplexing master process.
698: When the
699: .Fl O
700: option is specified, the
701: .Ar ctl_cmd
702: argument is interpreted and passed to the master process.
703: Valid commands are:
704: .Dq check
705: (check that the master process is running) and
706: .Dq exit
707: (request the master to exit).
1.2 deraadt 708: .It Fl o Ar option
1.127 stevesk 709: Can be used to give options in the format used in the configuration file.
1.1 deraadt 710: This is useful for specifying options for which there is no separate
1.40 aaron 711: command-line flag.
1.176 jmc 712: For full details of the options listed below, and their possible values, see
713: .Xr ssh_config 5 .
714: .Pp
715: .Bl -tag -width Ds -offset indent -compact
716: .It AddressFamily
717: .It BatchMode
718: .It BindAddress
719: .It ChallengeResponseAuthentication
720: .It CheckHostIP
721: .It Cipher
722: .It Ciphers
723: .It ClearAllForwardings
724: .It Compression
725: .It CompressionLevel
726: .It ConnectionAttempts
1.185 dtucker 727: .It ConnectTimeout
1.190 djm 728: .It ControlMaster
729: .It ControlPath
1.176 jmc 730: .It DynamicForward
731: .It EscapeChar
732: .It ForwardAgent
733: .It ForwardX11
1.178 markus 734: .It ForwardX11Trusted
1.176 jmc 735: .It GatewayPorts
736: .It GlobalKnownHostsFile
737: .It GSSAPIAuthentication
738: .It GSSAPIDelegateCredentials
1.201 djm 739: .It HashKnownHosts
1.176 jmc 740: .It Host
741: .It HostbasedAuthentication
742: .It HostKeyAlgorithms
743: .It HostKeyAlias
744: .It HostName
745: .It IdentityFile
1.182 markus 746: .It IdentitiesOnly
1.197 djm 747: .It KbdInteractiveDevices
1.176 jmc 748: .It LocalForward
749: .It LogLevel
750: .It MACs
751: .It NoHostAuthenticationForLocalhost
752: .It NumberOfPasswordPrompts
753: .It PasswordAuthentication
754: .It Port
755: .It PreferredAuthentications
756: .It Protocol
757: .It ProxyCommand
758: .It PubkeyAuthentication
759: .It RemoteForward
760: .It RhostsRSAAuthentication
761: .It RSAAuthentication
1.184 jmc 762: .It SendEnv
1.181 markus 763: .It ServerAliveInterval
764: .It ServerAliveCountMax
1.176 jmc 765: .It SmartcardDevice
766: .It StrictHostKeyChecking
1.180 markus 767: .It TCPKeepAlive
1.176 jmc 768: .It UsePrivilegedPort
769: .It User
770: .It UserKnownHostsFile
771: .It VerifyHostKeyDNS
772: .It XAuthLocation
773: .El
1.2 deraadt 774: .It Fl p Ar port
1.40 aaron 775: Port to connect to on the remote host.
776: This can be specified on a
1.1 deraadt 777: per-host basis in the configuration file.
1.2 deraadt 778: .It Fl q
1.40 aaron 779: Quiet mode.
780: Causes all warning and diagnostic messages to be suppressed.
1.176 jmc 781: .It Fl R Xo
782: .Sm off
1.200 djm 783: .Oo Ar bind_address : Oc
1.176 jmc 784: .Ar port : host : hostport
785: .Sm on
786: .Xc
787: Specifies that the given port on the remote (server) host is to be
788: forwarded to the given host and port on the local side.
789: This works by allocating a socket to listen to
790: .Ar port
791: on the remote side, and whenever a connection is made to this port, the
792: connection is forwarded over the secure channel, and a connection is
793: made to
794: .Ar host
795: port
796: .Ar hostport
797: from the local machine.
1.200 djm 798: .Pp
1.176 jmc 799: Port forwardings can also be specified in the configuration file.
800: Privileged ports can be forwarded only when
801: logging in as root on the remote machine.
1.200 djm 802: IPv6 addresses can be specified by enclosing the address in square braces or
803: using an alternative syntax:
1.202 jmc 804: .Sm off
1.200 djm 805: .Xo
1.205 jmc 806: .Op Ar bind_address No /
1.202 jmc 807: .Ar host No / Ar port No /
808: .Ar hostport
809: .Xc .
1.176 jmc 810: .Sm on
1.200 djm 811: .Pp
812: By default, the listening socket on the server will be bound to the loopback
813: interface only.
814: This may be overriden by specifying a
815: .Ar bind_address .
1.202 jmc 816: An empty
817: .Ar bind_address ,
1.200 djm 818: or the address
1.202 jmc 819: .Ql * ,
1.200 djm 820: indicates that the remote socket should listen on all interfaces.
821: Specifying a remote
822: .Ar bind_address
1.202 jmc 823: will only succeed if the server's
824: .Cm GatewayPorts
1.200 djm 825: option is enabled (see
1.202 jmc 826: .Xr sshd_config 5 ) .
1.198 djm 827: .It Fl S Ar ctl_path
1.193 jmc 828: Specifies the location of a control socket for connection sharing.
1.190 djm 829: Refer to the description of
1.191 djm 830: .Cm ControlPath
831: and
1.190 djm 832: .Cm ControlMaster
833: in
834: .Xr ssh_config 5
835: for details.
1.80 djm 836: .It Fl s
1.172 jmc 837: May be used to request invocation of a subsystem on the remote system.
838: Subsystems are a feature of the SSH2 protocol which facilitate the use
1.176 jmc 839: of SSH as a secure transport for other applications (eg.\&
840: .Xr sftp 1 ) .
1.172 jmc 841: The subsystem is specified as the remote command.
1.176 jmc 842: .It Fl T
843: Disable pseudo-tty allocation.
1.2 deraadt 844: .It Fl t
1.40 aaron 845: Force pseudo-tty allocation.
1.43 brad 846: This can be used to execute arbitrary
1.40 aaron 847: screen-based programs on a remote machine, which can be very useful,
848: e.g., when implementing menu services.
1.73 markus 849: Multiple
850: .Fl t
851: options force tty allocation, even if
852: .Nm
853: has no local tty.
1.176 jmc 854: .It Fl V
855: Display the version number and exit.
1.2 deraadt 856: .It Fl v
1.40 aaron 857: Verbose mode.
858: Causes
1.2 deraadt 859: .Nm
1.40 aaron 860: to print debugging messages about its progress.
861: This is helpful in
1.1 deraadt 862: debugging connection, authentication, and configuration problems.
1.73 markus 863: Multiple
864: .Fl v
1.169 naddy 865: options increase the verbosity.
866: The maximum is 3.
1.2 deraadt 867: .It Fl X
1.1 deraadt 868: Enables X11 forwarding.
1.54 markus 869: This can also be specified on a per-host basis in a configuration file.
1.165 stevesk 870: .Pp
1.168 jmc 871: X11 forwarding should be enabled with caution.
872: Users with the ability to bypass file permissions on the remote host
873: (for the user's X authorization database)
874: can access the local X11 display through the forwarded connection.
875: An attacker may then be able to perform activities such as keystroke monitoring.
1.203 djm 876: .Pp
1.204 jmc 877: For this reason, X11 forwarding is subjected to X11 SECURITY extension
1.203 djm 878: restrictions by default.
879: Please refer to the
880: .Nm
881: .Fl Y
882: option and the
883: .Cm ForwardX11Trusted
884: directive in
885: .Xr ssh_config 5
886: for more information.
1.176 jmc 887: .It Fl x
888: Disables X11 forwarding.
1.178 markus 889: .It Fl Y
890: Enables trusted X11 forwarding.
1.203 djm 891: Trusted X11 forwardings are not subjected to the X11 SECURITY extension
892: controls.
1.2 deraadt 893: .El
894: .Sh CONFIGURATION FILES
895: .Nm
1.158 stevesk 896: may additionally obtain configuration data from
897: a per-user configuration file and a system-wide configuration file.
898: The file format and configuration options are described in
899: .Xr ssh_config 5 .
1.2 deraadt 900: .Sh ENVIRONMENT
901: .Nm
1.1 deraadt 902: will normally set the following environment variables:
1.176 jmc 903: .Bl -tag -width LOGNAME
1.2 deraadt 904: .It Ev DISPLAY
905: The
906: .Ev DISPLAY
1.40 aaron 907: variable indicates the location of the X11 server.
1.44 aaron 908: It is automatically set by
1.2 deraadt 909: .Nm
910: to point to a value of the form
911: .Dq hostname:n
912: where hostname indicates
1.176 jmc 913: the host where the shell runs, and n is an integer \*(Ge 1.
1.40 aaron 914: .Nm
915: uses this special value to forward X11 connections over the secure
916: channel.
1.107 markus 917: The user should normally not set
918: .Ev DISPLAY
919: explicitly, as that
1.1 deraadt 920: will render the X11 connection insecure (and will require the user to
921: manually copy any required authorization cookies).
1.2 deraadt 922: .It Ev HOME
1.1 deraadt 923: Set to the path of the user's home directory.
1.2 deraadt 924: .It Ev LOGNAME
925: Synonym for
1.12 aaron 926: .Ev USER ;
927: set for compatibility with systems that use this variable.
1.2 deraadt 928: .It Ev MAIL
1.129 stevesk 929: Set to the path of the user's mailbox.
1.40 aaron 930: .It Ev PATH
1.2 deraadt 931: Set to the default
932: .Ev PATH ,
933: as specified when compiling
1.12 aaron 934: .Nm ssh .
1.118 markus 935: .It Ev SSH_ASKPASS
936: If
937: .Nm
938: needs a passphrase, it will read the passphrase from the current
939: terminal if it was run from a terminal.
940: If
941: .Nm
942: does not have a terminal associated with it but
943: .Ev DISPLAY
944: and
945: .Ev SSH_ASKPASS
946: are set, it will execute the program specified by
947: .Ev SSH_ASKPASS
948: and open an X11 window to read the passphrase.
949: This is particularly useful when calling
950: .Nm
951: from a
1.196 jmc 952: .Pa .xsession
1.118 markus 953: or related script.
954: (Note that on some machines it
955: may be necessary to redirect the input from
956: .Pa /dev/null
957: to make this work.)
1.18 markus 958: .It Ev SSH_AUTH_SOCK
1.129 stevesk 959: Identifies the path of a unix-domain socket used to communicate with the
1.17 markus 960: agent.
1.166 stevesk 961: .It Ev SSH_CONNECTION
962: Identifies the client and server ends of the connection.
1.40 aaron 963: The variable contains
1.166 stevesk 964: four space-separated values: client ip-address, client port number,
965: server ip-address and server port number.
1.73 markus 966: .It Ev SSH_ORIGINAL_COMMAND
967: The variable contains the original command line if a forced command
968: is executed.
969: It can be used to extract the original arguments.
1.2 deraadt 970: .It Ev SSH_TTY
1.1 deraadt 971: This is set to the name of the tty (path to the device) associated
1.40 aaron 972: with the current shell or command.
973: If the current session has no tty,
1.1 deraadt 974: this variable is not set.
1.2 deraadt 975: .It Ev TZ
1.1 deraadt 976: The timezone variable is set to indicate the present timezone if it
1.56 deraadt 977: was set when the daemon was started (i.e., the daemon passes the value
1.1 deraadt 978: on to new connections).
1.2 deraadt 979: .It Ev USER
1.1 deraadt 980: Set to the name of the user logging in.
1.2 deraadt 981: .El
982: .Pp
1.44 aaron 983: Additionally,
1.2 deraadt 984: .Nm
1.44 aaron 985: reads
1.207 djm 986: .Pa ~/.ssh/environment ,
1.2 deraadt 987: and adds lines of the format
988: .Dq VARNAME=value
1.161 marc 989: to the environment if the file exists and if users are allowed to
990: change their environment.
1.176 jmc 991: For more information, see the
1.161 marc 992: .Cm PermitUserEnvironment
1.162 stevesk 993: option in
1.161 marc 994: .Xr sshd_config 5 .
1.2 deraadt 995: .Sh FILES
1.36 markus 996: .Bl -tag -width Ds
1.207 djm 997: .It Pa ~/.ssh/known_hosts
1.129 stevesk 998: Records host keys for all hosts the user has logged into that are not
1.2 deraadt 999: in
1.147 deraadt 1000: .Pa /etc/ssh/ssh_known_hosts .
1.2 deraadt 1001: See
1002: .Xr sshd 8 .
1.207 djm 1003: .It Pa ~/.ssh/identity, ~/.ssh/id_dsa, ~/.ssh/id_rsa
1.102 itojun 1004: Contains the authentication identity of the user.
1005: They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively.
1.48 markus 1006: These files
1007: contain sensitive data and should be readable by the user but not
1.15 markus 1008: accessible by others (read/write/execute).
1009: Note that
1010: .Nm
1.48 markus 1011: ignores a private key file if it is accessible by others.
1.15 markus 1012: It is possible to specify a passphrase when
1.1 deraadt 1013: generating the key; the passphrase will be used to encrypt the
1.8 deraadt 1014: sensitive part of this file using 3DES.
1.207 djm 1015: .It Pa ~/.ssh/identity.pub, ~/.ssh/id_dsa.pub, ~/.ssh/id_rsa.pub
1.1 deraadt 1016: Contains the public key for authentication (public part of the
1.40 aaron 1017: identity file in human-readable form).
1.48 markus 1018: The contents of the
1.207 djm 1019: .Pa ~/.ssh/identity.pub
1.176 jmc 1020: file should be added to the file
1.207 djm 1021: .Pa ~/.ssh/authorized_keys
1.2 deraadt 1022: on all machines
1.137 deraadt 1023: where the user wishes to log in using protocol version 1 RSA authentication.
1.48 markus 1024: The contents of the
1.207 djm 1025: .Pa ~/.ssh/id_dsa.pub
1.102 itojun 1026: and
1.207 djm 1027: .Pa ~/.ssh/id_rsa.pub
1.48 markus 1028: file should be added to
1.207 djm 1029: .Pa ~/.ssh/authorized_keys
1.48 markus 1030: on all machines
1.137 deraadt 1031: where the user wishes to log in using protocol version 2 DSA/RSA authentication.
1.48 markus 1032: These files are not
1.40 aaron 1033: sensitive and can (but need not) be readable by anyone.
1.48 markus 1034: These files are
1.84 markus 1035: never used automatically and are not necessary; they are only provided for
1.1 deraadt 1036: the convenience of the user.
1.207 djm 1037: .It Pa ~/.ssh/config
1.40 aaron 1038: This is the per-user configuration file.
1.158 stevesk 1039: The file format and configuration options are described in
1040: .Xr ssh_config 5 .
1.183 djm 1041: Because of the potential for abuse, this file must have strict permissions:
1042: read/write for the user, and not accessible by others.
1.207 djm 1043: .It Pa ~/.ssh/authorized_keys
1.115 markus 1044: Lists the public keys (RSA/DSA) that can be used for logging in as this user.
1.40 aaron 1045: The format of this file is described in the
1.2 deraadt 1046: .Xr sshd 8
1.40 aaron 1047: manual page.
1.176 jmc 1048: In the simplest form the format is the same as the
1049: .Pa .pub
1.116 markus 1050: identity files.
1.48 markus 1051: This file is not highly sensitive, but the recommended
1052: permissions are read/write for the user, and not accessible by others.
1.147 deraadt 1053: .It Pa /etc/ssh/ssh_known_hosts
1.40 aaron 1054: Systemwide list of known host keys.
1.116 markus 1055: This file should be prepared by the
1.1 deraadt 1056: system administrator to contain the public host keys of all machines in the
1.40 aaron 1057: organization.
1058: This file should be world-readable.
1059: This file contains
1.1 deraadt 1060: public keys, one per line, in the following format (fields separated
1.116 markus 1061: by spaces): system name, public key and optional comment field.
1.40 aaron 1062: When different names are used
1.1 deraadt 1063: for the same machine, all such names should be listed, separated by
1.40 aaron 1064: commas.
1.176 jmc 1065: The format is described in the
1.2 deraadt 1066: .Xr sshd 8
1.1 deraadt 1067: manual page.
1.2 deraadt 1068: .Pp
1.1 deraadt 1069: The canonical system name (as returned by name servers) is used by
1.2 deraadt 1070: .Xr sshd 8
1.1 deraadt 1071: to verify the client host when logging in; other names are needed because
1.2 deraadt 1072: .Nm
1.1 deraadt 1073: does not convert the user-supplied name to a canonical name before
1074: checking the key, because someone with access to the name servers
1075: would then be able to fool host authentication.
1.147 deraadt 1076: .It Pa /etc/ssh/ssh_config
1.40 aaron 1077: Systemwide configuration file.
1.158 stevesk 1078: The file format and configuration options are described in
1079: .Xr ssh_config 5 .
1.147 deraadt 1080: .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key
1.141 markus 1081: These three files contain the private parts of the host keys
1082: and are used for
1083: .Cm RhostsRSAAuthentication
1084: and
1085: .Cm HostbasedAuthentication .
1.155 stevesk 1086: If the protocol version 1
1087: .Cm RhostsRSAAuthentication
1.157 deraadt 1088: method is used,
1.155 stevesk 1089: .Nm
1090: must be setuid root, since the host key is readable only by root.
1091: For protocol version 2,
1092: .Nm
1093: uses
1094: .Xr ssh-keysign 8
1095: to access the host keys for
1096: .Cm HostbasedAuthentication .
1097: This eliminates the requirement that
1098: .Nm
1099: be setuid root when that authentication method is used.
1100: By default
1.141 markus 1101: .Nm
1.155 stevesk 1102: is not setuid root.
1.207 djm 1103: .It Pa ~/.rhosts
1.2 deraadt 1104: This file is used in
1.195 markus 1105: .Cm RhostsRSAAuthentication
1106: and
1107: .Cm HostbasedAuthentication
1.2 deraadt 1108: authentication to list the
1.40 aaron 1109: host/user pairs that are permitted to log in.
1110: (Note that this file is
1.1 deraadt 1111: also used by rlogin and rsh, which makes using this file insecure.)
1112: Each line of the file contains a host name (in the canonical form
1113: returned by name servers), and then a user name on that host,
1.40 aaron 1114: separated by a space.
1.92 markus 1115: On some machines this file may need to be
1.1 deraadt 1116: world-readable if the user's home directory is on a NFS partition,
1117: because
1.2 deraadt 1118: .Xr sshd 8
1.40 aaron 1119: reads it as root.
1120: Additionally, this file must be owned by the user,
1121: and must not have write permissions for anyone else.
1122: The recommended
1.1 deraadt 1123: permission for most machines is read/write for the user, and not
1124: accessible by others.
1.2 deraadt 1125: .Pp
1.195 markus 1126: Note that
1.2 deraadt 1127: .Xr sshd 8
1.195 markus 1128: allows authentication only in combination with client host key
1129: authentication before permitting log in.
1.137 deraadt 1130: If the server machine does not have the client's host key in
1.147 deraadt 1131: .Pa /etc/ssh/ssh_known_hosts ,
1.137 deraadt 1132: it can be stored in
1.207 djm 1133: .Pa ~/.ssh/known_hosts .
1.2 deraadt 1134: The easiest way to do this is to
1.1 deraadt 1135: connect back to the client from the server machine using ssh; this
1.48 markus 1136: will automatically add the host key to
1.207 djm 1137: .Pa ~/.ssh/known_hosts .
1138: .It Pa ~/.shosts
1.2 deraadt 1139: This file is used exactly the same way as
1.176 jmc 1140: .Pa .rhosts .
1.2 deraadt 1141: The purpose for
1.195 markus 1142: having this file is to be able to use
1143: .Cm RhostsRSAAuthentication
1144: and
1145: .Cm HostbasedAuthentication
1146: authentication without permitting login with
1.176 jmc 1147: .Xr rlogin
1.2 deraadt 1148: or
1149: .Xr rsh 1 .
1150: .It Pa /etc/hosts.equiv
1151: This file is used during
1.195 markus 1152: .Cm RhostsRSAAuthentication
1153: and
1154: .Cm HostbasedAuthentication
1.173 jmc 1155: authentication.
1.40 aaron 1156: It contains
1.176 jmc 1157: canonical hosts names, one per line (the full format is described in the
1.2 deraadt 1158: .Xr sshd 8
1.40 aaron 1159: manual page).
1160: If the client host is found in this file, login is
1.1 deraadt 1161: automatically permitted provided client and server user names are the
1.40 aaron 1162: same.
1.195 markus 1163: Additionally, successful client host key authentication is required.
1.40 aaron 1164: This file should only be writable by root.
1.2 deraadt 1165: .It Pa /etc/shosts.equiv
1.44 aaron 1166: This file is processed exactly as
1.2 deraadt 1167: .Pa /etc/hosts.equiv .
1.1 deraadt 1168: This file may be useful to permit logins using
1.2 deraadt 1169: .Nm
1.1 deraadt 1170: but not using rsh/rlogin.
1.147 deraadt 1171: .It Pa /etc/ssh/sshrc
1.1 deraadt 1172: Commands in this file are executed by
1.2 deraadt 1173: .Nm
1.1 deraadt 1174: when the user logs in just before the user's shell (or command) is started.
1175: See the
1.2 deraadt 1176: .Xr sshd 8
1.1 deraadt 1177: manual page for more information.
1.207 djm 1178: .It Pa ~/.ssh/rc
1.1 deraadt 1179: Commands in this file are executed by
1.2 deraadt 1180: .Nm
1.1 deraadt 1181: when the user logs in just before the user's shell (or command) is
1182: started.
1.44 aaron 1183: See the
1.2 deraadt 1184: .Xr sshd 8
1.1 deraadt 1185: manual page for more information.
1.207 djm 1186: .It Pa ~/.ssh/environment
1.31 markus 1187: Contains additional definitions for environment variables, see section
1188: .Sx ENVIRONMENT
1189: above.
1.58 itojun 1190: .El
1.145 markus 1191: .Sh DIAGNOSTICS
1192: .Nm
1193: exits with the exit status of the remote command or with 255
1194: if an error occurred.
1.2 deraadt 1195: .Sh SEE ALSO
1.176 jmc 1196: .Xr gzip 1 ,
1.2 deraadt 1197: .Xr rsh 1 ,
1198: .Xr scp 1 ,
1.83 djm 1199: .Xr sftp 1 ,
1.2 deraadt 1200: .Xr ssh-add 1 ,
1201: .Xr ssh-agent 1 ,
1202: .Xr ssh-keygen 1 ,
1203: .Xr telnet 1 ,
1.176 jmc 1204: .Xr hosts.equiv 5 ,
1.159 stevesk 1205: .Xr ssh_config 5 ,
1.160 naddy 1206: .Xr ssh-keysign 8 ,
1.87 itojun 1207: .Xr sshd 8
1.106 markus 1208: .Rs
1209: .%A T. Ylonen
1210: .%A T. Kivinen
1211: .%A M. Saarinen
1212: .%A T. Rinne
1213: .%A S. Lehtinen
1214: .%T "SSH Protocol Architecture"
1.150 markus 1215: .%N draft-ietf-secsh-architecture-12.txt
1216: .%D January 2002
1.106 markus 1217: .%O work in progress material
1218: .Re
1.173 jmc 1219: .Sh AUTHORS
1220: OpenSSH is a derivative of the original and free
1221: ssh 1.2.12 release by Tatu Ylonen.
1222: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1223: Theo de Raadt and Dug Song
1224: removed many bugs, re-added newer features and
1225: created OpenSSH.
1226: Markus Friedl contributed the support for SSH
1227: protocol versions 1.5 and 2.0.
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