Annotation of src/usr.bin/ssh/ssh.1, Revision 1.72
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: .\"
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.
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: .\"
1.72 ! markus 37: .\" $OpenBSD: ssh.1,v 1.71 2000/12/07 04:24:59 djm Exp $
1.2 deraadt 38: .Dd September 25, 1999
39: .Dt SSH 1
40: .Os
41: .Sh NAME
42: .Nm ssh
1.20 provos 43: .Nd OpenSSH secure shell client (remote login program)
1.2 deraadt 44: .Sh SYNOPSIS
45: .Nm ssh
46: .Op Fl l Ar login_name
1.5 deraadt 47: .Op Ar hostname | user@hostname
1.2 deraadt 48: .Op Ar command
49: .Pp
50: .Nm ssh
1.54 markus 51: .Op Fl afgknqtvxACNPTX246
1.51 markus 52: .Op Fl c Ar cipher_spec
1.2 deraadt 53: .Op Fl e Ar escape_char
54: .Op Fl i Ar identity_file
55: .Op Fl l Ar login_name
56: .Op Fl o Ar option
57: .Op Fl p Ar port
1.12 aaron 58: .Oo Fl L Xo
59: .Sm off
1.33 markus 60: .Ar port :
1.12 aaron 61: .Ar host :
62: .Ar hostport
63: .Sm on
64: .Xc
65: .Oc
66: .Oo Fl R Xo
67: .Sm off
1.33 markus 68: .Ar port :
1.12 aaron 69: .Ar host :
70: .Ar hostport
71: .Sm on
72: .Xc
73: .Oc
1.5 deraadt 74: .Op Ar hostname | user@hostname
1.2 deraadt 75: .Op Ar command
1.44 aaron 76: .Sh DESCRIPTION
1.2 deraadt 77: .Nm
1.5 deraadt 78: (Secure Shell) is a program for logging into a remote machine and for
1.40 aaron 79: executing commands on a remote machine.
80: It is intended to replace
1.1 deraadt 81: rlogin and rsh, and provide secure encrypted communications between
1.40 aaron 82: two untrusted hosts over an insecure network.
83: X11 connections and
1.1 deraadt 84: arbitrary TCP/IP ports can also be forwarded over the secure channel.
1.2 deraadt 85: .Pp
86: .Nm
1.44 aaron 87: connects and logs into the specified
1.2 deraadt 88: .Ar hostname .
1.1 deraadt 89: The user must prove
1.49 markus 90: his/her identity to the remote machine using one of several methods
91: depending on the protocol version used:
92: .Pp
93: .Ss SSH protocol version 1
1.2 deraadt 94: .Pp
1.1 deraadt 95: First, if the machine the user logs in from is listed in
1.2 deraadt 96: .Pa /etc/hosts.equiv
1.1 deraadt 97: or
1.2 deraadt 98: .Pa /etc/shosts.equiv
1.1 deraadt 99: on the remote machine, and the user names are
100: the same on both sides, the user is immediately permitted to log in.
1.44 aaron 101: Second, if
1.2 deraadt 102: .Pa \&.rhosts
1.1 deraadt 103: or
1.2 deraadt 104: .Pa \&.shosts
1.1 deraadt 105: exists in the user's home directory on the
106: remote machine and contains a line containing the name of the client
107: machine and the name of the user on that machine, the user is
1.40 aaron 108: permitted to log in.
109: This form of authentication alone is normally not
1.1 deraadt 110: allowed by the server because it is not secure.
1.2 deraadt 111: .Pp
1.1 deraadt 112: The second (and primary) authentication method is the
1.2 deraadt 113: .Pa rhosts
1.1 deraadt 114: or
1.2 deraadt 115: .Pa hosts.equiv
1.40 aaron 116: method combined with RSA-based host authentication.
117: It means that if the login would be permitted by
1.49 markus 118: .Pa $HOME/.rhosts ,
119: .Pa $HOME/.shosts ,
1.2 deraadt 120: .Pa /etc/hosts.equiv ,
1.1 deraadt 121: or
1.2 deraadt 122: .Pa /etc/shosts.equiv ,
1.11 deraadt 123: and if additionally the server can verify the client's
1.44 aaron 124: host key (see
1.2 deraadt 125: .Pa /etc/ssh_known_hosts
1.23 markus 126: and
127: .Pa $HOME/.ssh/known_hosts
1.1 deraadt 128: in the
1.2 deraadt 129: .Sx FILES
1.40 aaron 130: section), only then login is permitted.
131: This authentication method closes security holes due to IP
132: spoofing, DNS spoofing and routing spoofing.
133: [Note to the administrator:
1.2 deraadt 134: .Pa /etc/hosts.equiv ,
1.49 markus 135: .Pa $HOME/.rhosts ,
1.1 deraadt 136: and the rlogin/rsh protocol in general, are inherently insecure and should be
137: disabled if security is desired.]
1.2 deraadt 138: .Pp
1.44 aaron 139: As a third authentication method,
1.2 deraadt 140: .Nm
1.1 deraadt 141: supports RSA based authentication.
142: The scheme is based on public-key cryptography: there are cryptosystems
143: where encryption and decryption are done using separate keys, and it
144: is not possible to derive the decryption key from the encryption key.
1.40 aaron 145: RSA is one such system.
1.44 aaron 146: The idea is that each user creates a public/private
1.40 aaron 147: key pair for authentication purposes.
148: The server knows the public key, and only the user knows the private key.
1.44 aaron 149: The file
1.2 deraadt 150: .Pa $HOME/.ssh/authorized_keys
1.1 deraadt 151: lists the public keys that are permitted for logging
1.40 aaron 152: in.
153: When the user logs in, the
1.2 deraadt 154: .Nm
1.1 deraadt 155: program tells the server which key pair it would like to use for
1.40 aaron 156: authentication.
157: The server checks if this key is permitted, and if
1.1 deraadt 158: so, sends the user (actually the
1.2 deraadt 159: .Nm
1.1 deraadt 160: program running on behalf of the user) a challenge, a random number,
1.40 aaron 161: encrypted by the user's public key.
162: The challenge can only be
163: decrypted using the proper private key.
164: The user's client then decrypts the
1.1 deraadt 165: challenge using the private key, proving that he/she knows the private
166: key 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
1.49 markus 173: .Pa $HOME/.ssh/identity
1.1 deraadt 174: and the public key in
1.49 markus 175: .Pa $HOME/.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
1.49 markus 180: .Pa $HOME/.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
1.49 markus 184: .Pa $HOME/.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.
188: RSA authentication is much
1.1 deraadt 189: more secure than rhosts authentication.
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.
1.2 deraadt 203: .Pp
1.49 markus 204: .Ss SSH protocol version 2
205: .Pp
206: When a user connects using the protocol version 2
207: different authentication methods are available:
208: At first, the client attempts to authenticate using the public key method.
209: If this method fails password authentication is tried.
210: .Pp
211: The public key method is similar to RSA authentication described
1.68 markus 212: in the previous section except that the DSA or RSA algorithm is used
213: instead.
214: The client uses his private key
1.49 markus 215: .Pa $HOME/.ssh/id_dsa
216: to sign the session identifier and sends the result to the server.
217: The server checks whether the matching public key is listed in
218: .Pa $HOME/.ssh/authorized_keys2
219: and grants access if both the key is found and the signature is correct.
220: The session identifier is derived from a shared Diffie-Hellman value
221: and is only known to the client and the server.
222: .Pp
223: If public key authentication fails or is not available a password
224: can be sent encrypted to the remote host for proving the user's identity.
225: This protocol 2 implementation does not yet support Kerberos or
226: S/Key authentication.
227: .Pp
228: Protocol 2 provides additional mechanisms for confidentiality
1.51 markus 229: (the traffic is encrypted using 3DES, Blowfish, CAST128 or Arcfour)
1.49 markus 230: and integrity (hmac-sha1, hmac-md5).
231: Note that protocol 1 lacks a strong mechanism for ensuring the
232: integrity of the connection.
233: .Pp
234: .Ss Login session and remote execution
235: .Pp
1.1 deraadt 236: When the user's identity has been accepted by the server, the server
237: either executes the given command, or logs into the machine and gives
1.40 aaron 238: the user a normal shell on the remote machine.
239: All communication with
1.1 deraadt 240: the remote command or shell will be automatically encrypted.
1.2 deraadt 241: .Pp
1.1 deraadt 242: If a pseudo-terminal has been allocated (normal login session), the
1.2 deraadt 243: user can disconnect with
244: .Ic ~. ,
245: and suspend
246: .Nm
247: with
248: .Ic ~^Z .
249: All forwarded connections can be listed with
1.44 aaron 250: .Ic ~#
1.2 deraadt 251: and if
1.1 deraadt 252: the session blocks waiting for forwarded X11 or TCP/IP
1.2 deraadt 253: connections to terminate, it can be backgrounded with
254: .Ic ~&
255: (this should not be used while the user shell is active, as it can cause the
1.40 aaron 256: shell to hang).
257: All available escapes can be listed with
1.2 deraadt 258: .Ic ~? .
259: .Pp
260: A single tilde character can be sent as
261: .Ic ~~
262: (or by following the tilde by a character other than those described above).
1.1 deraadt 263: The escape character must always follow a newline to be interpreted as
1.40 aaron 264: special.
265: The escape character can be changed in configuration files
266: or on the command line.
1.2 deraadt 267: .Pp
1.1 deraadt 268: If no pseudo tty has been allocated, the
269: session is transparent and can be used to reliably transfer binary
1.40 aaron 270: data.
271: On most systems, setting the escape character to
1.2 deraadt 272: .Dq none
273: will also make the session transparent even if a tty is used.
274: .Pp
1.71 djm 275: The session terminates when the command or shell on the remote
1.1 deraadt 276: machine exists and all X11 and TCP/IP connections have been closed.
277: The exit status of the remote program is returned as the exit status
278: of
1.2 deraadt 279: .Nm ssh .
280: .Pp
1.49 markus 281: .Ss X11 and TCP forwarding
282: .Pp
1.1 deraadt 283: If the user is using X11 (the
1.2 deraadt 284: .Ev DISPLAY
1.1 deraadt 285: environment variable is set), the connection to the X11 display is
286: automatically forwarded to the remote side in such a way that any X11
287: programs started from the shell (or command) will go through the
288: encrypted channel, and the connection to the real X server will be made
1.40 aaron 289: from the local machine.
290: The user should not manually set
1.2 deraadt 291: .Ev DISPLAY .
1.1 deraadt 292: Forwarding of X11 connections can be
293: configured on the command line or in configuration files.
1.2 deraadt 294: .Pp
295: The
1.44 aaron 296: .Ev DISPLAY
1.2 deraadt 297: value set by
298: .Nm
1.1 deraadt 299: will point to the server machine, but with a display number greater
1.40 aaron 300: than zero.
301: This is normal, and happens because
1.2 deraadt 302: .Nm
303: creates a
304: .Dq proxy
305: X server on the server machine for forwarding the
1.1 deraadt 306: connections over the encrypted channel.
1.2 deraadt 307: .Pp
308: .Nm
1.1 deraadt 309: will also automatically set up Xauthority data on the server machine.
310: For this purpose, it will generate a random authorization cookie,
311: store it in Xauthority on the server, and verify that any forwarded
312: connections carry this cookie and replace it by the real cookie when
1.40 aaron 313: the connection is opened.
314: The real authentication cookie is never
1.1 deraadt 315: sent to the server machine (and no cookies are sent in the plain).
1.2 deraadt 316: .Pp
1.1 deraadt 317: If the user is using an authentication agent, the connection to the agent
318: is automatically forwarded to the remote side unless disabled on
319: command line or in a configuration file.
1.2 deraadt 320: .Pp
1.1 deraadt 321: Forwarding of arbitrary TCP/IP connections over the secure channel can
1.40 aaron 322: be specified either on command line or in a configuration file.
323: One possible application of TCP/IP forwarding is a secure connection to an
1.1 deraadt 324: electronic purse; another is going trough firewalls.
1.2 deraadt 325: .Pp
1.49 markus 326: .Ss Server authentication
327: .Pp
1.2 deraadt 328: .Nm
1.49 markus 329: automatically maintains and checks a database containing
1.40 aaron 330: identifications for all hosts it has ever been used with.
1.49 markus 331: RSA host keys are stored in
332: .Pa $HOME/.ssh/known_hosts
333: and
1.68 markus 334: host keys used in the protocol version 2 are stored in
1.49 markus 335: .Pa $HOME/.ssh/known_hosts2
1.40 aaron 336: in the user's home directory.
1.49 markus 337: Additionally, the files
1.2 deraadt 338: .Pa /etc/ssh_known_hosts
1.49 markus 339: and
340: .Pa /etc/ssh_known_hosts2
341: are automatically checked for known hosts.
1.40 aaron 342: Any new hosts are automatically added to the user's file.
343: If a host's identification
1.1 deraadt 344: ever changes,
1.2 deraadt 345: .Nm
1.1 deraadt 346: warns about this and disables password authentication to prevent a
1.40 aaron 347: trojan horse from getting the user's password.
348: Another purpose of
1.1 deraadt 349: this mechanism is to prevent man-in-the-middle attacks which could
1.40 aaron 350: otherwise be used to circumvent the encryption.
351: The
1.2 deraadt 352: .Cm StrictHostKeyChecking
1.1 deraadt 353: option (see below) can be used to prevent logins to machines whose
354: host key is not known or has changed.
1.65 aaron 355: .Pp
356: The options are as follows:
1.2 deraadt 357: .Bl -tag -width Ds
1.4 dugsong 358: .It Fl a
1.42 aaron 359: Disables forwarding of the authentication agent connection.
1.54 markus 360: .It Fl A
361: Enables forwarding of the authentication agent connection.
362: This can also be specified on a per-host basis in a configuration file.
1.6 deraadt 363: .It Fl c Ar blowfish|3des
1.44 aaron 364: Selects the cipher to use for encrypting the session.
1.2 deraadt 365: .Ar 3des
1.40 aaron 366: is used by default.
1.44 aaron 367: It is believed to be secure.
1.5 deraadt 368: .Ar 3des
369: (triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
370: It is presumably more secure than the
1.2 deraadt 371: .Ar des
1.64 markus 372: cipher which is no longer fully supported in
1.51 markus 373: .Nm ssh .
1.5 deraadt 374: .Ar blowfish
375: is a fast block cipher, it appears very secure and is much faster than
1.40 aaron 376: .Ar 3des .
1.51 markus 377: .It Fl c Ar "3des-cbc,blowfish-cbc,arcfour,cast128-cbc"
378: Additionally, for protocol version 2 a comma-separated list of ciphers can
1.61 aaron 379: be specified in order of preference.
380: Protocol version 2 supports 3DES, Blowfish, and CAST128 in CBC mode
381: and Arcfour.
1.2 deraadt 382: .It Fl e Ar ch|^ch|none
383: Sets the escape character for sessions with a pty (default:
384: .Ql ~ ) .
1.40 aaron 385: The escape character is only recognized at the beginning of a line.
386: The escape character followed by a dot
1.2 deraadt 387: .Pq Ql \&.
388: closes the connection, followed
1.1 deraadt 389: by control-Z suspends the connection, and followed by itself sends the
1.40 aaron 390: escape character once.
391: Setting the character to
1.2 deraadt 392: .Dq none
393: disables any escapes and makes the session fully transparent.
394: .It Fl f
395: Requests
396: .Nm
1.40 aaron 397: to go to background just before command execution.
398: This is useful if
1.2 deraadt 399: .Nm
400: is going to ask for passwords or passphrases, but the user
1.40 aaron 401: wants it in the background.
1.44 aaron 402: This implies
1.2 deraadt 403: .Fl n .
1.1 deraadt 404: The recommended way to start X11 programs at a remote site is with
1.2 deraadt 405: something like
406: .Ic ssh -f host xterm .
1.34 markus 407: .It Fl g
408: Allows remote hosts to connect to local forwarded ports.
1.2 deraadt 409: .It Fl i Ar identity_file
1.44 aaron 410: Selects the file from which the identity (private key) for
1.68 markus 411: RSA or DSA authentication is read.
1.44 aaron 412: Default is
1.49 markus 413: .Pa $HOME/.ssh/identity
1.40 aaron 414: in the user's home directory.
415: Identity files may also be specified on
416: a per-host basis in the configuration file.
417: It is possible to have multiple
1.2 deraadt 418: .Fl i
419: options (and multiple identities specified in
1.1 deraadt 420: configuration files).
1.2 deraadt 421: .It Fl k
1.42 aaron 422: Disables forwarding of Kerberos tickets and AFS tokens.
423: This may also be specified on a per-host basis in the configuration file.
1.2 deraadt 424: .It Fl l Ar login_name
1.40 aaron 425: Specifies the user to log in as on the remote machine.
426: This also may be specified on a per-host basis in the configuration file.
1.2 deraadt 427: .It Fl n
428: Redirects stdin from
429: .Pa /dev/null
430: (actually, prevents reading from stdin).
1.1 deraadt 431: This must be used when
1.2 deraadt 432: .Nm
1.40 aaron 433: is run in the background.
434: A common trick is to use this to run X11 programs on a remote machine.
435: For example,
1.2 deraadt 436: .Ic ssh -n shadows.cs.hut.fi emacs &
437: will start an emacs on shadows.cs.hut.fi, and the X11
1.1 deraadt 438: connection will be automatically forwarded over an encrypted channel.
439: The
1.2 deraadt 440: .Nm
1.1 deraadt 441: program will be put in the background.
442: (This does not work if
1.2 deraadt 443: .Nm
444: needs to ask for a password or passphrase; see also the
445: .Fl f
446: option.)
1.53 markus 447: .It Fl N
448: Do not execute a remote command.
1.70 markus 449: This is useful if you just want to forward ports
1.53 markus 450: (protocol version 2 only).
1.2 deraadt 451: .It Fl o Ar option
1.1 deraadt 452: Can be used to give options in the format used in the config file.
453: This is useful for specifying options for which there is no separate
1.40 aaron 454: command-line flag.
455: The option has the same format as a line in the configuration file.
1.2 deraadt 456: .It Fl p Ar port
1.40 aaron 457: Port to connect to on the remote host.
458: This can be specified on a
1.1 deraadt 459: per-host basis in the configuration file.
1.16 markus 460: .It Fl P
461: Use a non-privileged port for outgoing connections.
462: This can be used if your firewall does
463: not permit connections from privileged ports.
1.30 provos 464: Note that this option turns off
1.16 markus 465: .Cm RhostsAuthentication
466: and
1.72 ! markus 467: .Cm RhostsRSAAuthentication
! 468: for older servers.
1.2 deraadt 469: .It Fl q
1.40 aaron 470: Quiet mode.
471: Causes all warning and diagnostic messages to be suppressed.
472: Only fatal errors are displayed.
1.2 deraadt 473: .It Fl t
1.40 aaron 474: Force pseudo-tty allocation.
1.43 brad 475: This can be used to execute arbitrary
1.40 aaron 476: screen-based programs on a remote machine, which can be very useful,
477: e.g., when implementing menu services.
1.53 markus 478: .It Fl T
1.69 markus 479: Disable pseudo-tty allocation.
1.2 deraadt 480: .It Fl v
1.40 aaron 481: Verbose mode.
482: Causes
1.2 deraadt 483: .Nm
1.40 aaron 484: to print debugging messages about its progress.
485: This is helpful in
1.1 deraadt 486: debugging connection, authentication, and configuration problems.
1.22 provos 487: The verbose mode is also used to display
488: .Xr skey 1
489: challenges, if the user entered "s/key" as password.
1.61 aaron 490: Multiple -v options increases the verbosity.
491: Maximum is 3.
1.2 deraadt 492: .It Fl x
1.40 aaron 493: Disables X11 forwarding.
1.2 deraadt 494: .It Fl X
1.1 deraadt 495: Enables X11 forwarding.
1.54 markus 496: This can also be specified on a per-host basis in a configuration file.
1.2 deraadt 497: .It Fl C
1.1 deraadt 498: Requests compression of all data (including stdin, stdout, stderr, and
1.40 aaron 499: data for forwarded X11 and TCP/IP connections).
500: The compression algorithm is the same used by
1.34 markus 501: .Xr gzip 1 ,
502: and the
1.2 deraadt 503: .Dq level
504: can be controlled by the
505: .Cm CompressionLevel
1.40 aaron 506: option (see below).
507: Compression is desirable on modem lines and other
1.1 deraadt 508: slow connections, but will only slow down things on fast networks.
509: The default value can be set on a host-by-host basis in the
510: configuration files; see the
1.2 deraadt 511: .Cm Compress
1.1 deraadt 512: option below.
1.2 deraadt 513: .It Fl L Ar port:host:hostport
1.1 deraadt 514: Specifies that the given port on the local (client) host is to be
1.40 aaron 515: forwarded to the given host and port on the remote side.
516: This works by allocating a socket to listen to
1.2 deraadt 517: .Ar port
1.1 deraadt 518: on the local side, and whenever a connection is made to this port, the
519: connection is forwarded over the secure channel, and a connection is
520: made to
1.32 markus 521: .Ar host
522: port
523: .Ar hostport
1.40 aaron 524: from the remote machine.
525: Port forwardings can also be specified in the configuration file.
526: Only root can forward privileged ports.
1.32 markus 527: IPv6 addresses can be specified with an alternative syntax:
528: .Ar port/host/hostport
1.2 deraadt 529: .It Fl R Ar port:host:hostport
1.1 deraadt 530: Specifies that the given port on the remote (server) host is to be
1.40 aaron 531: forwarded to the given host and port on the local side.
532: This works by allocating a socket to listen to
1.2 deraadt 533: .Ar port
1.1 deraadt 534: on the remote side, and whenever a connection is made to this port, the
535: connection is forwarded over the secure channel, and a connection is
536: made to
1.32 markus 537: .Ar host
538: port
539: .Ar hostport
1.40 aaron 540: from the local machine.
541: Port forwardings can also be specified in the configuration file.
542: Privileged ports can be forwarded only when
1.1 deraadt 543: logging in as root on the remote machine.
1.46 markus 544: .It Fl 2
545: Forces
546: .Nm
1.50 markus 547: to try protocol version 2 only.
1.32 markus 548: .It Fl 4
549: Forces
550: .Nm
551: to use IPv4 addresses only.
552: .It Fl 6
553: Forces
554: .Nm
555: to use IPv6 addresses only.
1.2 deraadt 556: .El
1.66 aaron 557: .Pp
558: If
559: .Nm
560: is not invoked with one of the standard program names
561: .Pf ( Dq ssh ,
562: .Dq slogin ,
563: .Dq rsh ,
564: .Dq rlogin ,
565: or
566: .Dq remsh ) ,
567: it uses this name as its
568: .Ar hostname
569: argument.
570: This is consistent with traditional
571: .Xr rsh 1
572: behavior.
1.2 deraadt 573: .Sh CONFIGURATION FILES
574: .Nm
1.1 deraadt 575: obtains configuration data from the following sources (in this order):
576: command line options, user's configuration file
1.2 deraadt 577: .Pq Pa $HOME/.ssh/config ,
578: and system-wide configuration file
579: .Pq Pa /etc/ssh_config .
580: For each parameter, the first obtained value
1.40 aaron 581: will be used.
582: The configuration files contain sections bracketed by
583: .Dq Host
584: specifications, and that section is only applied for hosts that
585: match one of the patterns given in the specification.
586: The matched host name is the one given on the command line.
1.2 deraadt 587: .Pp
1.1 deraadt 588: Since the first obtained value for each parameter is used, more
589: host-specific declarations should be given near the beginning of the
590: file, and general defaults at the end.
1.2 deraadt 591: .Pp
1.1 deraadt 592: The configuration file has the following format:
1.2 deraadt 593: .Pp
594: Empty lines and lines starting with
595: .Ql #
596: are comments.
597: .Pp
598: Otherwise a line is of the format
599: .Dq keyword arguments .
600: The possible
1.1 deraadt 601: keywords and their meanings are as follows (note that the
602: configuration files are case-sensitive):
1.2 deraadt 603: .Bl -tag -width Ds
604: .It Cm Host
1.1 deraadt 605: Restricts the following declarations (up to the next
1.2 deraadt 606: .Cm Host
1.1 deraadt 607: keyword) to be only for those hosts that match one of the patterns
1.2 deraadt 608: given after the keyword.
609: .Ql \&*
610: and
611: .Ql ?
612: can be used as wildcards in the
1.40 aaron 613: patterns.
614: A single
1.2 deraadt 615: .Ql \&*
616: as a pattern can be used to provide global
1.40 aaron 617: defaults for all hosts.
618: The host is the
1.2 deraadt 619: .Ar hostname
1.1 deraadt 620: argument given on the command line (i.e., the name is not converted to
621: a canonicalized host name before matching).
1.2 deraadt 622: .It Cm AFSTokenPassing
1.42 aaron 623: Specifies whether to pass AFS tokens to remote host.
624: The argument to this keyword must be
1.2 deraadt 625: .Dq yes
626: or
627: .Dq no .
628: .It Cm BatchMode
629: If set to
630: .Dq yes ,
1.40 aaron 631: passphrase/password querying will be disabled.
632: This option is useful in scripts and other batch jobs where you have no
633: user to supply the password.
634: The argument must be
1.2 deraadt 635: .Dq yes
636: or
637: .Dq no .
1.34 markus 638: .It Cm CheckHostIP
639: If this flag is set to
640: .Dq yes ,
641: ssh will additionally check the host ip address in the
642: .Pa known_hosts
1.42 aaron 643: file.
644: This allows ssh to detect if a host key changed due to DNS spoofing.
1.34 markus 645: If the option is set to
646: .Dq no ,
647: the check will not be executed.
1.2 deraadt 648: .It Cm Cipher
1.62 markus 649: Specifies the cipher to use for encrypting the session
1.64 markus 650: in protocol version 1.
1.40 aaron 651: Currently,
1.64 markus 652: .Dq blowfish
1.1 deraadt 653: and
1.10 provos 654: .Dq 3des
1.40 aaron 655: are supported.
656: The default is
1.2 deraadt 657: .Dq 3des .
1.45 markus 658: .It Cm Ciphers
659: Specifies the ciphers allowed for protocol version 2
660: in order of preference.
661: Multiple ciphers must be comma-separated.
662: The default is
1.62 markus 663: .Dq 3des-cbc,blowfish-cbc,cast128-cbc,arcfour .
1.2 deraadt 664: .It Cm Compression
1.40 aaron 665: Specifies whether to use compression.
666: The argument must be
1.2 deraadt 667: .Dq yes
668: or
669: .Dq no .
670: .It Cm CompressionLevel
1.40 aaron 671: Specifies the compression level to use if compression is enable.
672: The argument must be an integer from 1 (fast) to 9 (slow, best).
673: The default level is 6, which is good for most applications.
674: The meaning of the values is the same as in
1.34 markus 675: .Xr gzip 1 .
1.2 deraadt 676: .It Cm ConnectionAttempts
1.1 deraadt 677: Specifies the number of tries (one per second) to make before falling
1.40 aaron 678: back to rsh or exiting.
679: The argument must be an integer.
680: This may be useful in scripts if the connection sometimes fails.
1.68 markus 681: .It Cm PubkeyAuthentication
682: Specifies whether to try public key authentication.
1.50 markus 683: The argument to this keyword must be
684: .Dq yes
685: or
686: .Dq no .
687: Note that this option applies to protocol version 2 only.
1.2 deraadt 688: .It Cm EscapeChar
689: Sets the escape character (default:
690: .Ql ~ ) .
691: The escape character can also
1.40 aaron 692: be set on the command line.
693: The argument should be a single character,
1.2 deraadt 694: .Ql ^
695: followed by a letter, or
696: .Dq none
697: to disable the escape
1.1 deraadt 698: character entirely (making the connection transparent for binary
699: data).
1.44 aaron 700: .It Cm FallBackToRsh
1.1 deraadt 701: Specifies that if connecting via
1.2 deraadt 702: .Nm
1.1 deraadt 703: fails due to a connection refused error (there is no
1.2 deraadt 704: .Xr sshd 8
1.44 aaron 705: listening on the remote host),
1.2 deraadt 706: .Xr rsh 1
1.1 deraadt 707: should automatically be used instead (after a suitable warning about
1.40 aaron 708: the session being unencrypted).
709: The argument must be
1.2 deraadt 710: .Dq yes
711: or
712: .Dq no .
713: .It Cm ForwardAgent
1.1 deraadt 714: Specifies whether the connection to the authentication agent (if any)
1.40 aaron 715: will be forwarded to the remote machine.
716: The argument must be
1.2 deraadt 717: .Dq yes
718: or
1.54 markus 719: .Dq no .
720: The default is
1.2 deraadt 721: .Dq no .
722: .It Cm ForwardX11
1.1 deraadt 723: Specifies whether X11 connections will be automatically redirected
1.44 aaron 724: over the secure channel and
1.2 deraadt 725: .Ev DISPLAY
1.40 aaron 726: set.
1.44 aaron 727: The argument must be
1.2 deraadt 728: .Dq yes
729: or
1.38 markus 730: .Dq no .
731: The default is
1.3 deraadt 732: .Dq no .
733: .It Cm GatewayPorts
734: Specifies whether remote hosts are allowed to connect to local
735: forwarded ports.
736: The argument must be
737: .Dq yes
738: or
739: .Dq no .
740: The default is
1.2 deraadt 741: .Dq no .
742: .It Cm GlobalKnownHostsFile
1.44 aaron 743: Specifies a file to use instead of
1.2 deraadt 744: .Pa /etc/ssh_known_hosts .
745: .It Cm HostName
1.40 aaron 746: Specifies the real host name to log into.
747: This can be used to specify nicknames or abbreviations for hosts.
748: Default is the name given on the command line.
749: Numeric IP addresses are also permitted (both on the command line and in
1.2 deraadt 750: .Cm HostName
1.1 deraadt 751: specifications).
1.2 deraadt 752: .It Cm IdentityFile
1.1 deraadt 753: Specifies the file from which the user's RSA authentication identity
1.2 deraadt 754: is read (default
1.49 markus 755: .Pa $HOME/.ssh/identity
1.2 deraadt 756: in the user's home directory).
1.1 deraadt 757: Additionally, any identities represented by the authentication agent
1.40 aaron 758: will be used for authentication.
759: The file name may use the tilde
760: syntax to refer to a user's home directory.
761: It is possible to have
1.1 deraadt 762: multiple identity files specified in configuration files; all these
763: identities will be tried in sequence.
1.2 deraadt 764: .It Cm KeepAlive
1.1 deraadt 765: Specifies whether the system should send keepalive messages to the
1.40 aaron 766: other side.
767: If they are sent, death of the connection or crash of one
768: of the machines will be properly noticed.
769: However, this means that
1.1 deraadt 770: connections will die if the route is down temporarily, and some people
1.41 aaron 771: find it annoying.
1.2 deraadt 772: .Pp
773: The default is
774: .Dq yes
775: (to send keepalives), and the client will notice
1.40 aaron 776: if the network goes down or the remote host dies.
777: This is important in scripts, and many users want it too.
1.2 deraadt 778: .Pp
779: To disable keepalives, the value should be set to
780: .Dq no
781: in both the server and the client configuration files.
782: .It Cm KerberosAuthentication
1.42 aaron 783: Specifies whether Kerberos authentication will be used.
784: The argument to this keyword must be
1.4 dugsong 785: .Dq yes
786: or
787: .Dq no .
1.2 deraadt 788: .It Cm KerberosTgtPassing
1.42 aaron 789: Specifies whether a Kerberos TGT will be forwarded to the server.
790: This will only work if the Kerberos server is actually an AFS kaserver.
791: The argument to this keyword must be
1.4 dugsong 792: .Dq yes
793: or
794: .Dq no .
1.2 deraadt 795: .It Cm LocalForward
1.1 deraadt 796: Specifies that a TCP/IP port on the local machine be forwarded over
1.40 aaron 797: the secure channel to given host:port from the remote machine.
798: The first argument must be a port number, and the second must be
799: host:port.
800: Multiple forwardings may be specified, and additional
801: forwardings can be given on the command line.
802: Only the superuser can forward privileged ports.
1.24 markus 803: .It Cm LogLevel
804: Gives the verbosity level that is used when logging messages from
805: .Nm ssh .
806: The possible values are:
1.39 djm 807: QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG.
1.24 markus 808: The default is INFO.
1.14 dugsong 809: .It Cm NumberOfPasswordPrompts
1.42 aaron 810: Specifies the number of password prompts before giving up.
811: The argument to this keyword must be an integer.
812: Default is 3.
1.34 markus 813: .It Cm PasswordAuthentication
1.40 aaron 814: Specifies whether to use password authentication.
815: The argument to this keyword must be
1.34 markus 816: .Dq yes
817: or
818: .Dq no .
1.50 markus 819: Note that this option applies to both protocol version 1 and 2.
1.2 deraadt 820: .It Cm Port
1.40 aaron 821: Specifies the port number to connect on the remote host.
822: Default is 22.
1.45 markus 823: .It Cm Protocol
824: Specifies the protocol versions
825: .Nm
826: should support in order of preference.
827: The possible values are
828: .Dq 1
829: and
830: .Dq 2 .
831: Multiple versions must be comma-separated.
832: The default is
1.49 markus 833: .Dq 1,2 .
834: This means that
835: .Nm
836: tries version 1 and falls back to version 2
1.52 hugh 837: if version 1 is not available.
1.2 deraadt 838: .It Cm ProxyCommand
1.40 aaron 839: Specifies the command to use to connect to the server.
840: The command
841: string extends to the end of the line, and is executed with
842: .Pa /bin/sh .
843: In the command string,
844: .Ql %h
845: will be substituted by the host name to
846: connect and
847: .Ql %p
848: by the port.
849: The command can be basically anything,
850: and should read from its standard input and write to its standard output.
851: It should eventually connect an
1.2 deraadt 852: .Xr sshd 8
1.1 deraadt 853: server running on some machine, or execute
1.2 deraadt 854: .Ic sshd -i
1.40 aaron 855: somewhere.
856: Host key management will be done using the
1.1 deraadt 857: HostName of the host being connected (defaulting to the name typed by
858: the user).
1.29 markus 859: Note that
860: .Cm CheckHostIP
861: is not available for connects with a proxy command.
1.2 deraadt 862: .Pp
863: .It Cm RemoteForward
1.1 deraadt 864: Specifies that a TCP/IP port on the remote machine be forwarded over
1.40 aaron 865: the secure channel to given host:port from the local machine.
866: The first argument must be a port number, and the second must be
867: host:port.
868: Multiple forwardings may be specified, and additional
869: forwardings can be given on the command line.
870: Only the superuser can forward privileged ports.
1.2 deraadt 871: .It Cm RhostsAuthentication
1.40 aaron 872: Specifies whether to try rhosts based authentication.
873: Note that this
1.1 deraadt 874: declaration only affects the client side and has no effect whatsoever
1.40 aaron 875: on security.
876: Disabling rhosts authentication may reduce
1.1 deraadt 877: authentication time on slow connections when rhosts authentication is
1.40 aaron 878: not used.
879: Most servers do not permit RhostsAuthentication because it
880: is not secure (see RhostsRSAAuthentication).
881: The argument to this keyword must be
1.2 deraadt 882: .Dq yes
883: or
884: .Dq no .
885: .It Cm RhostsRSAAuthentication
1.1 deraadt 886: Specifies whether to try rhosts based authentication with RSA host
1.40 aaron 887: authentication.
888: This is the primary authentication method for most sites.
889: The argument must be
1.2 deraadt 890: .Dq yes
891: or
892: .Dq no .
893: .It Cm RSAAuthentication
1.40 aaron 894: Specifies whether to try RSA authentication.
895: The argument to this keyword must be
1.2 deraadt 896: .Dq yes
897: or
898: .Dq no .
1.1 deraadt 899: RSA authentication will only be
900: attempted if the identity file exists, or an authentication agent is
901: running.
1.50 markus 902: Note that this option applies to protocol version 1 only.
1.27 markus 903: .It Cm SkeyAuthentication
904: Specifies whether to use
905: .Xr skey 1
1.40 aaron 906: authentication.
907: The argument to this keyword must be
1.27 markus 908: .Dq yes
909: or
910: .Dq no .
911: The default is
912: .Dq no .
1.2 deraadt 913: .It Cm StrictHostKeyChecking
914: If this flag is set to
1.44 aaron 915: .Dq yes ,
1.2 deraadt 916: .Nm
1.1 deraadt 917: ssh will never automatically add host keys to the
1.2 deraadt 918: .Pa $HOME/.ssh/known_hosts
1.48 markus 919: and
920: .Pa $HOME/.ssh/known_hosts2
921: files, and refuses to connect hosts whose host key has changed.
1.40 aaron 922: This provides maximum protection against trojan horse attacks.
923: However, it can be somewhat annoying if you don't have good
1.2 deraadt 924: .Pa /etc/ssh_known_hosts
1.48 markus 925: and
926: .Pa /etc/ssh_known_hosts2
1.1 deraadt 927: files installed and frequently
1.40 aaron 928: connect new hosts.
929: Basically this option forces the user to manually
930: add any new hosts.
931: Normally this option is disabled, and new hosts
932: will automatically be added to the known host files.
933: The host keys of
934: known hosts will be verified automatically in either case.
935: The argument must be
1.2 deraadt 936: .Dq yes
937: or
938: .Dq no .
1.16 markus 939: .It Cm UsePrivilegedPort
940: Specifies whether to use a privileged port for outgoing connections.
941: The argument must be
942: .Dq yes
943: or
944: .Dq no .
945: The default is
946: .Dq yes .
947: Note that setting this option to
948: .Dq no
1.30 provos 949: turns off
1.16 markus 950: .Cm RhostsAuthentication
951: and
1.72 ! markus 952: .Cm RhostsRSAAuthentication
! 953: for older servers.
1.34 markus 954: .It Cm User
1.40 aaron 955: Specifies the user to log in as.
956: This can be useful if you have a different user name on different machines.
957: This saves the trouble of
1.34 markus 958: having to remember to give the user name on the command line.
959: .It Cm UserKnownHostsFile
960: Specifies a file to use instead of
961: .Pa $HOME/.ssh/known_hosts .
1.2 deraadt 962: .It Cm UseRsh
1.40 aaron 963: Specifies that rlogin/rsh should be used for this host.
964: It is possible that the host does not at all support the
1.2 deraadt 965: .Nm
1.40 aaron 966: protocol.
967: This causes
1.2 deraadt 968: .Nm
1.40 aaron 969: to immediately execute
1.2 deraadt 970: .Xr rsh 1 .
1.1 deraadt 971: All other options (except
1.2 deraadt 972: .Cm HostName )
1.40 aaron 973: are ignored if this has been specified.
974: The argument must be
1.2 deraadt 975: .Dq yes
976: or
977: .Dq no .
1.55 markus 978: .It Cm XAuthLocation
979: Specifies the location of the
980: .Xr xauth 1
981: program.
982: The default is
983: .Pa /usr/X11R6/bin/xauth .
1.58 itojun 984: .El
1.2 deraadt 985: .Sh ENVIRONMENT
986: .Nm
1.1 deraadt 987: will normally set the following environment variables:
1.2 deraadt 988: .Bl -tag -width Ds
989: .It Ev DISPLAY
990: The
991: .Ev DISPLAY
1.40 aaron 992: variable indicates the location of the X11 server.
1.44 aaron 993: It is automatically set by
1.2 deraadt 994: .Nm
995: to point to a value of the form
996: .Dq hostname:n
997: where hostname indicates
1.40 aaron 998: the host where the shell runs, and n is an integer >= 1.
999: .Nm
1000: uses this special value to forward X11 connections over the secure
1001: channel.
1002: The user should normally not set DISPLAY explicitly, as that
1.1 deraadt 1003: will render the X11 connection insecure (and will require the user to
1004: manually copy any required authorization cookies).
1.2 deraadt 1005: .It Ev HOME
1.1 deraadt 1006: Set to the path of the user's home directory.
1.2 deraadt 1007: .It Ev LOGNAME
1008: Synonym for
1.12 aaron 1009: .Ev USER ;
1010: set for compatibility with systems that use this variable.
1.2 deraadt 1011: .It Ev MAIL
1.1 deraadt 1012: Set to point the user's mailbox.
1.40 aaron 1013: .It Ev PATH
1.2 deraadt 1014: Set to the default
1015: .Ev PATH ,
1016: as specified when compiling
1.12 aaron 1017: .Nm ssh .
1.18 markus 1018: .It Ev SSH_AUTH_SOCK
1.17 markus 1019: indicates the path of a unix-domain socket used to communicate with the
1020: agent.
1.2 deraadt 1021: .It Ev SSH_CLIENT
1.40 aaron 1022: Identifies the client end of the connection.
1023: The variable contains
1.1 deraadt 1024: three space-separated values: client ip-address, client port number,
1025: and server port number.
1.2 deraadt 1026: .It Ev SSH_TTY
1.1 deraadt 1027: This is set to the name of the tty (path to the device) associated
1.40 aaron 1028: with the current shell or command.
1029: If the current session has no tty,
1.1 deraadt 1030: this variable is not set.
1.2 deraadt 1031: .It Ev TZ
1.1 deraadt 1032: The timezone variable is set to indicate the present timezone if it
1.56 deraadt 1033: was set when the daemon was started (i.e., the daemon passes the value
1.1 deraadt 1034: on to new connections).
1.2 deraadt 1035: .It Ev USER
1.1 deraadt 1036: Set to the name of the user logging in.
1.2 deraadt 1037: .El
1038: .Pp
1.44 aaron 1039: Additionally,
1.2 deraadt 1040: .Nm
1.44 aaron 1041: reads
1042: .Pa $HOME/.ssh/environment ,
1.2 deraadt 1043: and adds lines of the format
1044: .Dq VARNAME=value
1.12 aaron 1045: to the environment.
1.2 deraadt 1046: .Sh FILES
1.36 markus 1047: .Bl -tag -width Ds
1.2 deraadt 1048: .It Pa $HOME/.ssh/known_hosts
1.1 deraadt 1049: Records host keys for all hosts the user has logged into (that are not
1.2 deraadt 1050: in
1051: .Pa /etc/ssh_known_hosts ) .
1052: See
1053: .Xr sshd 8 .
1.48 markus 1054: .It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa
1055: Contains the RSA and the DSA authentication identity of the user.
1056: These files
1057: contain sensitive data and should be readable by the user but not
1.15 markus 1058: accessible by others (read/write/execute).
1059: Note that
1060: .Nm
1.48 markus 1061: ignores a private key file if it is accessible by others.
1.15 markus 1062: It is possible to specify a passphrase when
1.1 deraadt 1063: generating the key; the passphrase will be used to encrypt the
1.8 deraadt 1064: sensitive part of this file using 3DES.
1.48 markus 1065: .It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub
1.1 deraadt 1066: Contains the public key for authentication (public part of the
1.40 aaron 1067: identity file in human-readable form).
1.48 markus 1068: The contents of the
1069: .Pa $HOME/.ssh/identity.pub
1070: file should be added to
1.2 deraadt 1071: .Pa $HOME/.ssh/authorized_keys
1072: on all machines
1.40 aaron 1073: where you wish to log in using RSA authentication.
1.48 markus 1074: The contents of the
1075: .Pa $HOME/.ssh/id_dsa.pub
1076: file should be added to
1077: .Pa $HOME/.ssh/authorized_keys2
1078: on all machines
1079: where you wish to log in using DSA authentication.
1080: These files are not
1.40 aaron 1081: sensitive and can (but need not) be readable by anyone.
1.48 markus 1082: These files are
1083: never used automatically and are not necessary; they is only provided for
1.1 deraadt 1084: the convenience of the user.
1.2 deraadt 1085: .It Pa $HOME/.ssh/config
1.40 aaron 1086: This is the per-user configuration file.
1087: The format of this file is described above.
1088: This file is used by the
1.2 deraadt 1089: .Nm
1.40 aaron 1090: client.
1091: This file does not usually contain any sensitive information,
1.1 deraadt 1092: but the recommended permissions are read/write for the user, and not
1093: accessible by others.
1.2 deraadt 1094: .It Pa $HOME/.ssh/authorized_keys
1.40 aaron 1095: Lists the RSA keys that can be used for logging in as this user.
1096: The format of this file is described in the
1.2 deraadt 1097: .Xr sshd 8
1.40 aaron 1098: manual page.
1099: In the simplest form the format is the same as the .pub
1.1 deraadt 1100: identity files (that is, each line contains the number of bits in
1101: modulus, public exponent, modulus, and comment fields, separated by
1.40 aaron 1102: spaces).
1103: This file is not highly sensitive, but the recommended
1.1 deraadt 1104: permissions are read/write for the user, and not accessible by others.
1.48 markus 1105: .It Pa $HOME/.ssh/authorized_keys2
1.68 markus 1106: Lists the public keys (DSA/RSA) that can be used for logging in as this user.
1.48 markus 1107: This file is not highly sensitive, but the recommended
1108: permissions are read/write for the user, and not accessible by others.
1109: .It Pa /etc/ssh_known_hosts, /etc/ssh_known_hosts2
1.40 aaron 1110: Systemwide list of known host keys.
1.48 markus 1111: .Pa /etc/ssh_known_hosts
1112: contains RSA and
1113: .Pa /etc/ssh_known_hosts2
1.68 markus 1114: contains DSA or RSA keys for protocol version 2.
1.48 markus 1115: These files should be prepared by the
1.1 deraadt 1116: system administrator to contain the public host keys of all machines in the
1.40 aaron 1117: organization.
1118: This file should be world-readable.
1119: This file contains
1.1 deraadt 1120: public keys, one per line, in the following format (fields separated
1121: by spaces): system name, number of bits in modulus, public exponent,
1.40 aaron 1122: modulus, and optional comment field.
1123: When different names are used
1.1 deraadt 1124: for the same machine, all such names should be listed, separated by
1.40 aaron 1125: commas.
1126: The format is described on the
1.2 deraadt 1127: .Xr sshd 8
1.1 deraadt 1128: manual page.
1.2 deraadt 1129: .Pp
1.1 deraadt 1130: The canonical system name (as returned by name servers) is used by
1.2 deraadt 1131: .Xr sshd 8
1.1 deraadt 1132: to verify the client host when logging in; other names are needed because
1.2 deraadt 1133: .Nm
1.1 deraadt 1134: does not convert the user-supplied name to a canonical name before
1135: checking the key, because someone with access to the name servers
1136: would then be able to fool host authentication.
1.2 deraadt 1137: .It Pa /etc/ssh_config
1.40 aaron 1138: Systemwide configuration file.
1139: This file provides defaults for those
1.1 deraadt 1140: values that are not specified in the user's configuration file, and
1.40 aaron 1141: for those users who do not have a configuration file.
1142: This file must be world-readable.
1.2 deraadt 1143: .It Pa $HOME/.rhosts
1144: This file is used in
1145: .Pa \&.rhosts
1146: authentication to list the
1.40 aaron 1147: host/user pairs that are permitted to log in.
1148: (Note that this file is
1.1 deraadt 1149: also used by rlogin and rsh, which makes using this file insecure.)
1150: Each line of the file contains a host name (in the canonical form
1151: returned by name servers), and then a user name on that host,
1.40 aaron 1152: separated by a space.
1153: One some machines this file may need to be
1.1 deraadt 1154: world-readable if the user's home directory is on a NFS partition,
1155: because
1.2 deraadt 1156: .Xr sshd 8
1.40 aaron 1157: reads it as root.
1158: Additionally, this file must be owned by the user,
1159: and must not have write permissions for anyone else.
1160: The recommended
1.1 deraadt 1161: permission for most machines is read/write for the user, and not
1162: accessible by others.
1.2 deraadt 1163: .Pp
1.1 deraadt 1164: Note that by default
1.2 deraadt 1165: .Xr sshd 8
1.1 deraadt 1166: will be installed so that it requires successful RSA host
1.40 aaron 1167: authentication before permitting \s+2.\s0rhosts authentication.
1168: If your server machine does not have the client's host key in
1.2 deraadt 1169: .Pa /etc/ssh_known_hosts ,
1170: you can store it in
1171: .Pa $HOME/.ssh/known_hosts .
1172: The easiest way to do this is to
1.1 deraadt 1173: connect back to the client from the server machine using ssh; this
1.48 markus 1174: will automatically add the host key to
1.2 deraadt 1175: .Pa $HOME/.ssh/known_hosts .
1176: .It Pa $HOME/.shosts
1177: This file is used exactly the same way as
1178: .Pa \&.rhosts .
1179: The purpose for
1.1 deraadt 1180: having this file is to be able to use rhosts authentication with
1.2 deraadt 1181: .Nm
1182: without permitting login with
1183: .Xr rlogin 1
1184: or
1185: .Xr rsh 1 .
1186: .It Pa /etc/hosts.equiv
1187: This file is used during
1.40 aaron 1188: .Pa \&.rhosts authentication.
1189: It contains
1.1 deraadt 1190: canonical hosts names, one per line (the full format is described on
1191: the
1.2 deraadt 1192: .Xr sshd 8
1.40 aaron 1193: manual page).
1194: If the client host is found in this file, login is
1.1 deraadt 1195: automatically permitted provided client and server user names are the
1.40 aaron 1196: same.
1197: Additionally, successful RSA host authentication is normally
1198: required.
1199: This file should only be writable by root.
1.2 deraadt 1200: .It Pa /etc/shosts.equiv
1.44 aaron 1201: This file is processed exactly as
1.2 deraadt 1202: .Pa /etc/hosts.equiv .
1.1 deraadt 1203: This file may be useful to permit logins using
1.2 deraadt 1204: .Nm
1.1 deraadt 1205: but not using rsh/rlogin.
1.2 deraadt 1206: .It Pa /etc/sshrc
1.1 deraadt 1207: Commands in this file are executed by
1.2 deraadt 1208: .Nm
1.1 deraadt 1209: when the user logs in just before the user's shell (or command) is started.
1210: See the
1.2 deraadt 1211: .Xr sshd 8
1.1 deraadt 1212: manual page for more information.
1.2 deraadt 1213: .It Pa $HOME/.ssh/rc
1.1 deraadt 1214: Commands in this file are executed by
1.2 deraadt 1215: .Nm
1.1 deraadt 1216: when the user logs in just before the user's shell (or command) is
1217: started.
1.44 aaron 1218: See the
1.2 deraadt 1219: .Xr sshd 8
1.1 deraadt 1220: manual page for more information.
1.31 markus 1221: .It Pa $HOME/.ssh/environment
1222: Contains additional definitions for environment variables, see section
1223: .Sx ENVIRONMENT
1224: above.
1.5 deraadt 1225: .It Pa libcrypto.so.X.1
1226: A version of this library which includes support for the RSA algorithm
1227: is required for proper operation.
1.58 itojun 1228: .El
1.67 aaron 1229: .Sh AUTHORS
1.20 provos 1230: OpenSSH
1.37 deraadt 1231: is a derivative of the original (free) ssh 1.2.12 release by Tatu Ylonen,
1.40 aaron 1232: but with bugs removed and newer features re-added.
1233: Rapidly after the
1.37 deraadt 1234: 1.2.12 release, newer versions of the original ssh bore successively
1235: more restrictive licenses, and thus demand for a free version was born.
1.47 markus 1236: .Pp
1.37 deraadt 1237: This version of OpenSSH
1.20 provos 1238: .Bl -bullet
1239: .It
1.35 aaron 1240: has all components of a restrictive nature (i.e., patents, see
1.21 deraadt 1241: .Xr ssl 8 )
1242: directly removed from the source code; any licensed or patented components
1243: are chosen from
1244: external libraries.
1.20 provos 1245: .It
1.47 markus 1246: has been updated to support SSH protocol 1.5 and 2, making it compatible with
1247: all other SSH clients and servers.
1.20 provos 1248: .It
1.44 aaron 1249: contains added support for
1.20 provos 1250: .Xr kerberos 8
1251: authentication and ticket passing.
1252: .It
1.21 deraadt 1253: supports one-time password authentication with
1.20 provos 1254: .Xr skey 1 .
1255: .El
1.25 provos 1256: .Pp
1.26 aaron 1257: OpenSSH has been created by Aaron Campbell, Bob Beck, Markus Friedl,
1.25 provos 1258: Niels Provos, Theo de Raadt, and Dug Song.
1.47 markus 1259: .Pp
1260: The support for SSH protocol 2 was written by Markus Friedl.
1.2 deraadt 1261: .Sh SEE ALSO
1262: .Xr rlogin 1 ,
1263: .Xr rsh 1 ,
1264: .Xr scp 1 ,
1265: .Xr ssh-add 1 ,
1266: .Xr ssh-agent 1 ,
1267: .Xr ssh-keygen 1 ,
1268: .Xr telnet 1 ,
1.5 deraadt 1269: .Xr sshd 8 ,
1270: .Xr ssl 8
![[BACK]](/icons/back.gif){kind=icon}
Return to ssh.1 CVS log ![[TXT]](/icons/text.gif){kind=icon}
![[DIR]](/icons/dir.gif){kind=icon}
Up to [local] / src / usr.bin / ssh