Annotation of src/usr.bin/ssh/ssh.1, Revision 1.107
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: .\"
1.107 ! markus 37: .\" $OpenBSD: ssh.1,v 1.106 2001/04/22 13:32:27 markus 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
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
1.86 jakob 51: .Op Fl afgknqstvxACNPTX1246
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
1.91 markus 56: .Op Fl m Ar mac_spec
1.2 deraadt 57: .Op Fl o Ar option
58: .Op Fl p Ar port
1.12 aaron 59: .Oo Fl L Xo
60: .Sm off
1.33 markus 61: .Ar port :
1.12 aaron 62: .Ar host :
63: .Ar hostport
64: .Sm on
65: .Xc
66: .Oc
67: .Oo Fl R Xo
68: .Sm off
1.33 markus 69: .Ar port :
1.12 aaron 70: .Ar host :
71: .Ar hostport
72: .Sm on
73: .Xc
74: .Oc
1.5 deraadt 75: .Op Ar hostname | user@hostname
1.2 deraadt 76: .Op Ar command
1.44 aaron 77: .Sh DESCRIPTION
1.2 deraadt 78: .Nm
1.96 deraadt 79: (SSH client) is a program for logging into a remote machine and for
1.40 aaron 80: executing commands on a remote machine.
81: It is intended to replace
1.1 deraadt 82: rlogin and rsh, and provide secure encrypted communications between
1.40 aaron 83: two untrusted hosts over an insecure network.
84: X11 connections and
1.1 deraadt 85: arbitrary TCP/IP ports can also be forwarded over the secure channel.
1.2 deraadt 86: .Pp
87: .Nm
1.44 aaron 88: connects and logs into the specified
1.2 deraadt 89: .Ar hostname .
1.1 deraadt 90: The user must prove
1.49 markus 91: his/her identity to the remote machine using one of several methods
92: depending on the protocol version used:
93: .Pp
94: .Ss SSH protocol version 1
1.2 deraadt 95: .Pp
1.1 deraadt 96: First, if the machine the user logs in from is listed in
1.2 deraadt 97: .Pa /etc/hosts.equiv
1.1 deraadt 98: or
1.2 deraadt 99: .Pa /etc/shosts.equiv
1.1 deraadt 100: on the remote machine, and the user names are
101: the same on both sides, the user is immediately permitted to log in.
1.44 aaron 102: Second, if
1.2 deraadt 103: .Pa \&.rhosts
1.1 deraadt 104: or
1.2 deraadt 105: .Pa \&.shosts
1.1 deraadt 106: exists in the user's home directory on the
107: remote machine and contains a line containing the name of the client
108: machine and the name of the user on that machine, the user is
1.40 aaron 109: permitted to log in.
110: This form of authentication alone is normally not
1.1 deraadt 111: allowed by the server because it is not secure.
1.2 deraadt 112: .Pp
1.107 ! markus 113: The second authentication method is the
1.2 deraadt 114: .Pa rhosts
1.1 deraadt 115: or
1.2 deraadt 116: .Pa hosts.equiv
1.40 aaron 117: method combined with RSA-based host authentication.
118: It means that if the login would be permitted by
1.49 markus 119: .Pa $HOME/.rhosts ,
120: .Pa $HOME/.shosts ,
1.2 deraadt 121: .Pa /etc/hosts.equiv ,
1.1 deraadt 122: or
1.2 deraadt 123: .Pa /etc/shosts.equiv ,
1.11 deraadt 124: and if additionally the server can verify the client's
1.44 aaron 125: host key (see
1.2 deraadt 126: .Pa /etc/ssh_known_hosts
1.23 markus 127: and
128: .Pa $HOME/.ssh/known_hosts
1.1 deraadt 129: in the
1.2 deraadt 130: .Sx FILES
1.40 aaron 131: section), only then login is permitted.
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 ,
1.49 markus 136: .Pa $HOME/.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
1.44 aaron 140: As a third 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.
1.44 aaron 150: The file
1.2 deraadt 151: .Pa $HOME/.ssh/authorized_keys
1.1 deraadt 152: lists the public keys that are permitted for logging
1.40 aaron 153: in.
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.
158: The server checks if this key is permitted, and if
1.1 deraadt 159: so, 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.
163: The challenge can only be
164: decrypted using the proper private key.
165: The user's client then decrypts the
1.1 deraadt 166: challenge using the private key, proving that he/she knows the private
167: key but without disclosing it to the server.
1.2 deraadt 168: .Pp
169: .Nm
1.40 aaron 170: implements the RSA authentication protocol automatically.
171: The user creates his/her RSA key pair by running
1.2 deraadt 172: .Xr ssh-keygen 1 .
1.44 aaron 173: This stores the private key in
1.49 markus 174: .Pa $HOME/.ssh/identity
1.1 deraadt 175: and the public key in
1.49 markus 176: .Pa $HOME/.ssh/identity.pub
1.40 aaron 177: in the user's home directory.
178: The user should then copy the
1.2 deraadt 179: .Pa identity.pub
1.44 aaron 180: to
1.49 markus 181: .Pa $HOME/.ssh/authorized_keys
1.44 aaron 182: in his/her home directory on the remote machine (the
1.2 deraadt 183: .Pa authorized_keys
1.44 aaron 184: file corresponds to the conventional
1.49 markus 185: .Pa $HOME/.rhosts
1.1 deraadt 186: file, and has one key
1.40 aaron 187: per line, though the lines can be very long).
188: After this, the user can log in without giving the password.
189: RSA authentication is much
1.1 deraadt 190: more secure than rhosts authentication.
1.2 deraadt 191: .Pp
1.1 deraadt 192: The most convenient way to use RSA authentication may be with an
1.40 aaron 193: authentication agent.
194: See
1.2 deraadt 195: .Xr ssh-agent 1
1.1 deraadt 196: for more information.
1.2 deraadt 197: .Pp
1.44 aaron 198: If other authentication methods fail,
1.2 deraadt 199: .Nm
1.40 aaron 200: prompts the user for a password.
201: The password is sent to the remote
1.1 deraadt 202: host for checking; however, since all communications are encrypted,
203: the password cannot be seen by someone listening on the network.
1.2 deraadt 204: .Pp
1.49 markus 205: .Ss SSH protocol version 2
206: .Pp
207: When a user connects using the protocol version 2
1.107 ! markus 208: different authentication methods are available.
! 209: Using the default values for
! 210: .Cm PreferredAuthentications ,
! 211: the client will try to authenticate first using the public key method;
! 212: if this method fails password authentication is attempted,
! 213: and finally if this method fails keyboard-interactive authentication
! 214: is attempted.
! 215: If this method fails password authentication is
! 216: tried.
1.49 markus 217: .Pp
218: The public key method is similar to RSA authentication described
1.107 ! markus 219: in the previous section and allows the RSA or DSA algorithm to be used:
1.102 itojun 220: The client uses his private key,
1.49 markus 221: .Pa $HOME/.ssh/id_dsa
1.102 itojun 222: or
223: .Pa $HOME/.ssh/id_rsa ,
1.49 markus 224: to sign the session identifier and sends the result to the server.
225: The server checks whether the matching public key is listed in
226: .Pa $HOME/.ssh/authorized_keys2
227: and grants access if both the key is found and the signature is correct.
228: The session identifier is derived from a shared Diffie-Hellman value
229: and is only known to the client and the server.
230: .Pp
231: If public key authentication fails or is not available a password
232: can be sent encrypted to the remote host for proving the user's identity.
1.107 ! markus 233: .Pp
! 234: Additionally,
! 235: .Nm
! 236: supports hostbased or challenge response authentication.
1.49 markus 237: .Pp
238: Protocol 2 provides additional mechanisms for confidentiality
1.51 markus 239: (the traffic is encrypted using 3DES, Blowfish, CAST128 or Arcfour)
1.94 deraadt 240: and integrity (hmac-md5, hmac-sha1).
1.49 markus 241: Note that protocol 1 lacks a strong mechanism for ensuring the
242: integrity of the connection.
243: .Pp
244: .Ss Login session and remote execution
245: .Pp
1.1 deraadt 246: When the user's identity has been accepted by the server, the server
247: either executes the given command, or logs into the machine and gives
1.40 aaron 248: the user a normal shell on the remote machine.
249: All communication with
1.1 deraadt 250: the remote command or shell will be automatically encrypted.
1.2 deraadt 251: .Pp
1.1 deraadt 252: If a pseudo-terminal has been allocated (normal login session), the
1.104 djm 253: user may use the escape characters noted below.
1.2 deraadt 254: .Pp
1.1 deraadt 255: If no pseudo tty has been allocated, the
256: session is transparent and can be used to reliably transfer binary
1.40 aaron 257: data.
258: On most systems, setting the escape character to
1.2 deraadt 259: .Dq none
260: will also make the session transparent even if a tty is used.
261: .Pp
1.71 djm 262: The session terminates when the command or shell on the remote
1.92 markus 263: machine exits and all X11 and TCP/IP connections have been closed.
1.1 deraadt 264: The exit status of the remote program is returned as the exit status
265: of
1.2 deraadt 266: .Nm ssh .
1.104 djm 267: .Pp
268: .Ss Escape Characters
269: .Pp
270: When a pseudo terminal has been requested, ssh supports a number of functions
1.105 djm 271: through the use of an escape character.
1.104 djm 272: .Pp
273: A single tilde character can be sent as
274: .Ic ~~
275: (or by following the tilde by a character other than those described above).
276: The escape character must always follow a newline to be interpreted as
277: special.
278: The escape character can be changed in configuration files using the
279: .Cm EscapeChar
280: configuration directive or on the command line by the
281: .Fl e
282: option.
283: .Pp
284: The supported escapes (assuming the default
285: .Ql ~ )
286: are:
287: .Bl -tag -width Ds
288: .It Cm ~.
289: Disconnect
290: .It Cm ~^Z
291: Background ssh
292: .It Cm ~#
293: List forwarded connections
294: .It Cm ~&
295: Background ssh at logout when waiting for forwarded connection / X11 sessions
1.107 ! markus 296: to terminate (protocol version 1 only)
1.104 djm 297: .It Cm ~?
298: Display a list of escape characters
299: .It Cm ~R
1.105 djm 300: Request rekeying of the connection (only useful for SSH protocol version 2
301: and if the peer supports it)
1.104 djm 302: .El
1.2 deraadt 303: .Pp
1.49 markus 304: .Ss X11 and TCP forwarding
305: .Pp
1.1 deraadt 306: If the user is using X11 (the
1.2 deraadt 307: .Ev DISPLAY
1.1 deraadt 308: environment variable is set), the connection to the X11 display is
309: automatically forwarded to the remote side in such a way that any X11
310: programs started from the shell (or command) will go through the
311: encrypted channel, and the connection to the real X server will be made
1.40 aaron 312: from the local machine.
313: The user should not manually set
1.2 deraadt 314: .Ev DISPLAY .
1.1 deraadt 315: Forwarding of X11 connections can be
316: configured on the command line or in configuration files.
1.2 deraadt 317: .Pp
318: The
1.44 aaron 319: .Ev DISPLAY
1.2 deraadt 320: value set by
321: .Nm
1.1 deraadt 322: will point to the server machine, but with a display number greater
1.40 aaron 323: than zero.
324: This is normal, and happens because
1.2 deraadt 325: .Nm
326: creates a
327: .Dq proxy
328: X server on the server machine for forwarding the
1.1 deraadt 329: connections over the encrypted channel.
1.2 deraadt 330: .Pp
331: .Nm
1.1 deraadt 332: will also automatically set up Xauthority data on the server machine.
333: For this purpose, it will generate a random authorization cookie,
334: store it in Xauthority on the server, and verify that any forwarded
335: connections carry this cookie and replace it by the real cookie when
1.40 aaron 336: the connection is opened.
337: The real authentication cookie is never
1.1 deraadt 338: sent to the server machine (and no cookies are sent in the plain).
1.2 deraadt 339: .Pp
1.1 deraadt 340: If the user is using an authentication agent, the connection to the agent
341: is automatically forwarded to the remote side unless disabled on
342: command line or in a configuration file.
1.2 deraadt 343: .Pp
1.1 deraadt 344: Forwarding of arbitrary TCP/IP connections over the secure channel can
1.40 aaron 345: be specified either on command line or in a configuration file.
346: One possible application of TCP/IP forwarding is a secure connection to an
1.92 markus 347: electronic purse; another is going through firewalls.
1.2 deraadt 348: .Pp
1.49 markus 349: .Ss Server authentication
350: .Pp
1.2 deraadt 351: .Nm
1.49 markus 352: automatically maintains and checks a database containing
1.40 aaron 353: identifications for all hosts it has ever been used with.
1.49 markus 354: RSA host keys are stored in
355: .Pa $HOME/.ssh/known_hosts
356: and
1.68 markus 357: host keys used in the protocol version 2 are stored in
1.49 markus 358: .Pa $HOME/.ssh/known_hosts2
1.40 aaron 359: in the user's home directory.
1.49 markus 360: Additionally, the files
1.2 deraadt 361: .Pa /etc/ssh_known_hosts
1.49 markus 362: and
363: .Pa /etc/ssh_known_hosts2
364: are automatically checked for known hosts.
1.40 aaron 365: Any new hosts are automatically added to the user's file.
366: If a host's identification
1.1 deraadt 367: ever changes,
1.2 deraadt 368: .Nm
1.1 deraadt 369: warns about this and disables password authentication to prevent a
1.40 aaron 370: trojan horse from getting the user's password.
371: Another purpose of
1.1 deraadt 372: this mechanism is to prevent man-in-the-middle attacks which could
1.40 aaron 373: otherwise be used to circumvent the encryption.
374: The
1.2 deraadt 375: .Cm StrictHostKeyChecking
1.1 deraadt 376: option (see below) can be used to prevent logins to machines whose
377: host key is not known or has changed.
1.65 aaron 378: .Pp
379: The options are as follows:
1.2 deraadt 380: .Bl -tag -width Ds
1.4 dugsong 381: .It Fl a
1.42 aaron 382: Disables forwarding of the authentication agent connection.
1.54 markus 383: .It Fl A
384: Enables forwarding of the authentication agent connection.
385: This can also be specified on a per-host basis in a configuration file.
1.6 deraadt 386: .It Fl c Ar blowfish|3des
1.44 aaron 387: Selects the cipher to use for encrypting the session.
1.2 deraadt 388: .Ar 3des
1.40 aaron 389: is used by default.
1.44 aaron 390: It is believed to be secure.
1.5 deraadt 391: .Ar 3des
392: (triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
393: It is presumably more secure than the
1.2 deraadt 394: .Ar des
1.64 markus 395: cipher which is no longer fully supported in
1.51 markus 396: .Nm ssh .
1.5 deraadt 397: .Ar blowfish
398: is a fast block cipher, it appears very secure and is much faster than
1.40 aaron 399: .Ar 3des .
1.90 markus 400: .It Fl c Ar cipher_spec
1.51 markus 401: Additionally, for protocol version 2 a comma-separated list of ciphers can
1.61 aaron 402: be specified in order of preference.
1.90 markus 403: See
404: .Cm Ciphers
405: for more information.
1.2 deraadt 406: .It Fl e Ar ch|^ch|none
407: Sets the escape character for sessions with a pty (default:
408: .Ql ~ ) .
1.40 aaron 409: The escape character is only recognized at the beginning of a line.
410: The escape character followed by a dot
1.2 deraadt 411: .Pq Ql \&.
412: closes the connection, followed
1.1 deraadt 413: by control-Z suspends the connection, and followed by itself sends the
1.40 aaron 414: escape character once.
415: Setting the character to
1.2 deraadt 416: .Dq none
417: disables any escapes and makes the session fully transparent.
418: .It Fl f
419: Requests
420: .Nm
1.40 aaron 421: to go to background just before command execution.
422: This is useful if
1.2 deraadt 423: .Nm
424: is going to ask for passwords or passphrases, but the user
1.40 aaron 425: wants it in the background.
1.44 aaron 426: This implies
1.2 deraadt 427: .Fl n .
1.1 deraadt 428: The recommended way to start X11 programs at a remote site is with
1.2 deraadt 429: something like
430: .Ic ssh -f host xterm .
1.34 markus 431: .It Fl g
432: Allows remote hosts to connect to local forwarded ports.
1.2 deraadt 433: .It Fl i Ar identity_file
1.44 aaron 434: Selects the file from which the identity (private key) for
1.68 markus 435: RSA or DSA authentication is read.
1.44 aaron 436: Default is
1.49 markus 437: .Pa $HOME/.ssh/identity
1.40 aaron 438: in the user's home directory.
439: Identity files may also be specified on
440: a per-host basis in the configuration file.
441: It is possible to have multiple
1.2 deraadt 442: .Fl i
443: options (and multiple identities specified in
1.1 deraadt 444: configuration files).
1.2 deraadt 445: .It Fl k
1.42 aaron 446: Disables forwarding of Kerberos tickets and AFS tokens.
447: This may also be specified on a per-host basis in the configuration file.
1.2 deraadt 448: .It Fl l Ar login_name
1.40 aaron 449: Specifies the user to log in as on the remote machine.
450: This also may be specified on a per-host basis in the configuration file.
1.91 markus 451: .It Fl m Ar mac_spec
452: Additionally, for protocol version 2 a comma-separated list of MAC
453: (message authentication code) algorithms can
454: be specified in order of preference.
455: See the
456: .Cm MACs
457: keyword for more information.
1.2 deraadt 458: .It Fl n
459: Redirects stdin from
460: .Pa /dev/null
461: (actually, prevents reading from stdin).
1.1 deraadt 462: This must be used when
1.2 deraadt 463: .Nm
1.40 aaron 464: is run in the background.
465: A common trick is to use this to run X11 programs on a remote machine.
466: For example,
1.2 deraadt 467: .Ic ssh -n shadows.cs.hut.fi emacs &
468: will start an emacs on shadows.cs.hut.fi, and the X11
1.1 deraadt 469: connection will be automatically forwarded over an encrypted channel.
470: The
1.2 deraadt 471: .Nm
1.1 deraadt 472: program will be put in the background.
473: (This does not work if
1.2 deraadt 474: .Nm
475: needs to ask for a password or passphrase; see also the
476: .Fl f
477: option.)
1.53 markus 478: .It Fl N
479: Do not execute a remote command.
1.70 markus 480: This is useful if you just want to forward ports
1.53 markus 481: (protocol version 2 only).
1.2 deraadt 482: .It Fl o Ar option
1.1 deraadt 483: Can be used to give options in the format used in the config file.
484: This is useful for specifying options for which there is no separate
1.40 aaron 485: command-line flag.
486: The option has the same format as a line in the configuration file.
1.2 deraadt 487: .It Fl p Ar port
1.40 aaron 488: Port to connect to on the remote host.
489: This can be specified on a
1.1 deraadt 490: per-host basis in the configuration file.
1.16 markus 491: .It Fl P
492: Use a non-privileged port for outgoing connections.
493: This can be used if your firewall does
494: not permit connections from privileged ports.
1.30 provos 495: Note that this option turns off
1.16 markus 496: .Cm RhostsAuthentication
497: and
1.72 markus 498: .Cm RhostsRSAAuthentication
499: for older servers.
1.2 deraadt 500: .It Fl q
1.40 aaron 501: Quiet mode.
502: Causes all warning and diagnostic messages to be suppressed.
503: Only fatal errors are displayed.
1.80 djm 504: .It Fl s
505: May be used to request invocation of a subsystem on the remote system. Subsystems are a feature of the SSH2 protocol which facilitate the use
506: of SSH as a secure transport for other application (eg. sftp). The
507: subsystem is specified as the remote command.
1.2 deraadt 508: .It Fl t
1.40 aaron 509: Force pseudo-tty allocation.
1.43 brad 510: This can be used to execute arbitrary
1.40 aaron 511: screen-based programs on a remote machine, which can be very useful,
512: e.g., when implementing menu services.
1.73 markus 513: Multiple
514: .Fl t
515: options force tty allocation, even if
516: .Nm
517: has no local tty.
1.53 markus 518: .It Fl T
1.69 markus 519: Disable pseudo-tty allocation.
1.2 deraadt 520: .It Fl v
1.40 aaron 521: Verbose mode.
522: Causes
1.2 deraadt 523: .Nm
1.40 aaron 524: to print debugging messages about its progress.
525: This is helpful in
1.1 deraadt 526: debugging connection, authentication, and configuration problems.
1.73 markus 527: Multiple
528: .Fl v
529: options increases the verbosity.
1.61 aaron 530: Maximum is 3.
1.2 deraadt 531: .It Fl x
1.40 aaron 532: Disables X11 forwarding.
1.2 deraadt 533: .It Fl X
1.1 deraadt 534: Enables X11 forwarding.
1.54 markus 535: This can also be specified on a per-host basis in a configuration file.
1.2 deraadt 536: .It Fl C
1.1 deraadt 537: Requests compression of all data (including stdin, stdout, stderr, and
1.40 aaron 538: data for forwarded X11 and TCP/IP connections).
539: The compression algorithm is the same used by
1.34 markus 540: .Xr gzip 1 ,
541: and the
1.2 deraadt 542: .Dq level
543: can be controlled by the
544: .Cm CompressionLevel
1.40 aaron 545: option (see below).
546: Compression is desirable on modem lines and other
1.1 deraadt 547: slow connections, but will only slow down things on fast networks.
548: The default value can be set on a host-by-host basis in the
549: configuration files; see the
1.2 deraadt 550: .Cm Compress
1.1 deraadt 551: option below.
1.2 deraadt 552: .It Fl L Ar port:host:hostport
1.1 deraadt 553: Specifies that the given port on the local (client) host is to be
1.40 aaron 554: forwarded to the given host and port on the remote side.
555: This works by allocating a socket to listen to
1.2 deraadt 556: .Ar port
1.1 deraadt 557: on the local side, and whenever a connection is made to this port, the
558: connection is forwarded over the secure channel, and a connection is
559: made to
1.32 markus 560: .Ar host
561: port
562: .Ar hostport
1.40 aaron 563: from the remote machine.
564: Port forwardings can also be specified in the configuration file.
565: Only root can forward privileged ports.
1.32 markus 566: IPv6 addresses can be specified with an alternative syntax:
567: .Ar port/host/hostport
1.2 deraadt 568: .It Fl R Ar port:host:hostport
1.1 deraadt 569: Specifies that the given port on the remote (server) host is to be
1.40 aaron 570: forwarded to the given host and port on the local side.
571: This works by allocating a socket to listen to
1.2 deraadt 572: .Ar port
1.1 deraadt 573: on the remote side, and whenever a connection is made to this port, the
574: connection is forwarded over the secure channel, and a connection is
575: made to
1.32 markus 576: .Ar host
577: port
578: .Ar hostport
1.40 aaron 579: from the local machine.
580: Port forwardings can also be specified in the configuration file.
581: Privileged ports can be forwarded only when
1.1 deraadt 582: logging in as root on the remote machine.
1.107 ! markus 583: IPv6 addresses can be specified with an alternative syntax:
! 584: .Ar port/host/hostport
1.85 jakob 585: .It Fl 1
586: Forces
587: .Nm
588: to try protocol version 1 only.
1.46 markus 589: .It Fl 2
590: Forces
591: .Nm
1.50 markus 592: to try protocol version 2 only.
1.32 markus 593: .It Fl 4
594: Forces
595: .Nm
596: to use IPv4 addresses only.
597: .It Fl 6
598: Forces
599: .Nm
600: to use IPv6 addresses only.
1.2 deraadt 601: .El
602: .Sh CONFIGURATION FILES
603: .Nm
1.1 deraadt 604: obtains configuration data from the following sources (in this order):
605: command line options, user's configuration file
1.2 deraadt 606: .Pq Pa $HOME/.ssh/config ,
607: and system-wide configuration file
608: .Pq Pa /etc/ssh_config .
609: For each parameter, the first obtained value
1.40 aaron 610: will be used.
611: The configuration files contain sections bracketed by
612: .Dq Host
613: specifications, and that section is only applied for hosts that
614: match one of the patterns given in the specification.
615: The matched host name is the one given on the command line.
1.2 deraadt 616: .Pp
1.1 deraadt 617: Since the first obtained value for each parameter is used, more
618: host-specific declarations should be given near the beginning of the
619: file, and general defaults at the end.
1.2 deraadt 620: .Pp
1.1 deraadt 621: The configuration file has the following format:
1.2 deraadt 622: .Pp
623: Empty lines and lines starting with
624: .Ql #
625: are comments.
626: .Pp
627: Otherwise a line is of the format
628: .Dq keyword arguments .
629: The possible
1.1 deraadt 630: keywords and their meanings are as follows (note that the
631: configuration files are case-sensitive):
1.2 deraadt 632: .Bl -tag -width Ds
633: .It Cm Host
1.1 deraadt 634: Restricts the following declarations (up to the next
1.2 deraadt 635: .Cm Host
1.1 deraadt 636: keyword) to be only for those hosts that match one of the patterns
1.2 deraadt 637: given after the keyword.
638: .Ql \&*
639: and
640: .Ql ?
641: can be used as wildcards in the
1.40 aaron 642: patterns.
643: A single
1.2 deraadt 644: .Ql \&*
645: as a pattern can be used to provide global
1.40 aaron 646: defaults for all hosts.
647: The host is the
1.2 deraadt 648: .Ar hostname
1.1 deraadt 649: argument given on the command line (i.e., the name is not converted to
650: a canonicalized host name before matching).
1.2 deraadt 651: .It Cm AFSTokenPassing
1.42 aaron 652: Specifies whether to pass AFS tokens to remote host.
653: The argument to this keyword must be
1.2 deraadt 654: .Dq yes
655: or
656: .Dq no .
1.107 ! markus 657: This option applies to protocol version 1 only.
1.2 deraadt 658: .It Cm BatchMode
659: If set to
660: .Dq yes ,
1.40 aaron 661: passphrase/password querying will be disabled.
662: This option is useful in scripts and other batch jobs where you have no
663: user to supply the password.
664: The argument must be
1.2 deraadt 665: .Dq yes
666: or
667: .Dq no .
1.100 stevesk 668: The default is
669: .Dq no .
1.34 markus 670: .It Cm CheckHostIP
671: If this flag is set to
672: .Dq yes ,
1.100 stevesk 673: ssh will additionally check the host IP address in the
1.34 markus 674: .Pa known_hosts
1.42 aaron 675: file.
676: This allows ssh to detect if a host key changed due to DNS spoofing.
1.34 markus 677: If the option is set to
678: .Dq no ,
679: the check will not be executed.
1.100 stevesk 680: The default is
681: .Dq yes .
1.2 deraadt 682: .It Cm Cipher
1.62 markus 683: Specifies the cipher to use for encrypting the session
1.64 markus 684: in protocol version 1.
1.40 aaron 685: Currently,
1.64 markus 686: .Dq blowfish
1.1 deraadt 687: and
1.10 provos 688: .Dq 3des
1.40 aaron 689: are supported.
690: The default is
1.2 deraadt 691: .Dq 3des .
1.45 markus 692: .It Cm Ciphers
693: Specifies the ciphers allowed for protocol version 2
694: in order of preference.
695: Multiple ciphers must be comma-separated.
696: The default is
1.88 provos 697: .Pp
698: .Bd -literal
1.94 deraadt 699: ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,
1.107 ! markus 700: aes192-cbc,aes256-cbc''
1.88 provos 701: .Ed
1.2 deraadt 702: .It Cm Compression
1.40 aaron 703: Specifies whether to use compression.
704: The argument must be
1.2 deraadt 705: .Dq yes
706: or
707: .Dq no .
1.100 stevesk 708: The default is
709: .Dq no .
1.2 deraadt 710: .It Cm CompressionLevel
1.100 stevesk 711: Specifies the compression level to use if compression is enabled.
1.40 aaron 712: The argument must be an integer from 1 (fast) to 9 (slow, best).
713: The default level is 6, which is good for most applications.
714: The meaning of the values is the same as in
1.34 markus 715: .Xr gzip 1 .
1.107 ! markus 716: Note that this option applies to protocol version 1 only.
1.2 deraadt 717: .It Cm ConnectionAttempts
1.1 deraadt 718: Specifies the number of tries (one per second) to make before falling
1.40 aaron 719: back to rsh or exiting.
720: The argument must be an integer.
721: This may be useful in scripts if the connection sometimes fails.
1.100 stevesk 722: The default is 4.
1.2 deraadt 723: .It Cm EscapeChar
724: Sets the escape character (default:
725: .Ql ~ ) .
726: The escape character can also
1.40 aaron 727: be set on the command line.
728: The argument should be a single character,
1.2 deraadt 729: .Ql ^
730: followed by a letter, or
731: .Dq none
732: to disable the escape
1.1 deraadt 733: character entirely (making the connection transparent for binary
734: data).
1.44 aaron 735: .It Cm FallBackToRsh
1.1 deraadt 736: Specifies that if connecting via
1.2 deraadt 737: .Nm
1.1 deraadt 738: fails due to a connection refused error (there is no
1.2 deraadt 739: .Xr sshd 8
1.44 aaron 740: listening on the remote host),
1.2 deraadt 741: .Xr rsh 1
1.1 deraadt 742: should automatically be used instead (after a suitable warning about
1.40 aaron 743: the session being unencrypted).
744: The argument must be
1.2 deraadt 745: .Dq yes
746: or
747: .Dq no .
1.100 stevesk 748: The default is
749: .Dq no .
1.2 deraadt 750: .It Cm ForwardAgent
1.1 deraadt 751: Specifies whether the connection to the authentication agent (if any)
1.40 aaron 752: will be forwarded to the remote machine.
753: The argument must be
1.2 deraadt 754: .Dq yes
755: or
1.54 markus 756: .Dq no .
757: The default is
1.2 deraadt 758: .Dq no .
759: .It Cm ForwardX11
1.1 deraadt 760: Specifies whether X11 connections will be automatically redirected
1.44 aaron 761: over the secure channel and
1.2 deraadt 762: .Ev DISPLAY
1.40 aaron 763: set.
1.44 aaron 764: The argument must be
1.2 deraadt 765: .Dq yes
766: or
1.38 markus 767: .Dq no .
768: The default is
1.3 deraadt 769: .Dq no .
770: .It Cm GatewayPorts
771: Specifies whether remote hosts are allowed to connect to local
772: forwarded ports.
773: The argument must be
774: .Dq yes
775: or
776: .Dq no .
777: The default is
1.2 deraadt 778: .Dq no .
779: .It Cm GlobalKnownHostsFile
1.95 stevesk 780: Specifies a file to use for the protocol version 1 global
781: host key database instead of
1.2 deraadt 782: .Pa /etc/ssh_known_hosts .
1.95 stevesk 783: .It Cm GlobalKnownHostsFile2
784: Specifies a file to use for the protocol version 2 global
785: host key database instead of
786: .Pa /etc/ssh_known_hosts2 .
1.107 ! markus 787: .It Cm HostbasedAuthentication
! 788: Specifies whether to try rhosts based authentication with public key
! 789: authentication.
! 790: The argument must be
! 791: .Dq yes
! 792: or
! 793: .Dq no .
! 794: The default is
! 795: .Dq yes .
! 796: This option applies to protocol version 2 only and
! 797: is similar to
! 798: .Cm RhostsRSAAuthentication .
! 799: .It Cm HostKeyAlgorithms
! 800: Specfies the protocol version 2 host key algorithms
! 801: that the client wants to use in order of preference.
! 802: The default for this option is:
! 803: .Dq ssh-rsa,ssh-dss
1.74 markus 804: .It Cm HostKeyAlias
805: Specifies an alias that should be used instead of the
806: real host name when looking up or saving the host key
1.107 ! markus 807: in the host key database files.
1.82 stevesk 808: This option is useful for tunneling ssh connections
1.74 markus 809: or if you have multiple servers running on a single host.
1.2 deraadt 810: .It Cm HostName
1.40 aaron 811: Specifies the real host name to log into.
812: This can be used to specify nicknames or abbreviations for hosts.
813: Default is the name given on the command line.
814: Numeric IP addresses are also permitted (both on the command line and in
1.2 deraadt 815: .Cm HostName
1.1 deraadt 816: specifications).
1.2 deraadt 817: .It Cm IdentityFile
1.107 ! markus 818: Specifies the file from which the user's RSA or DSA authentication identity
1.2 deraadt 819: is read (default
1.49 markus 820: .Pa $HOME/.ssh/identity
1.2 deraadt 821: in the user's home directory).
1.1 deraadt 822: Additionally, any identities represented by the authentication agent
1.40 aaron 823: will be used for authentication.
824: The file name may use the tilde
825: syntax to refer to a user's home directory.
826: It is possible to have
1.1 deraadt 827: multiple identity files specified in configuration files; all these
828: identities will be tried in sequence.
1.2 deraadt 829: .It Cm KeepAlive
1.1 deraadt 830: Specifies whether the system should send keepalive messages to the
1.40 aaron 831: other side.
832: If they are sent, death of the connection or crash of one
833: of the machines will be properly noticed.
834: However, this means that
1.1 deraadt 835: connections will die if the route is down temporarily, and some people
1.41 aaron 836: find it annoying.
1.2 deraadt 837: .Pp
838: The default is
839: .Dq yes
840: (to send keepalives), and the client will notice
1.40 aaron 841: if the network goes down or the remote host dies.
842: This is important in scripts, and many users want it too.
1.2 deraadt 843: .Pp
844: To disable keepalives, the value should be set to
845: .Dq no
846: in both the server and the client configuration files.
847: .It Cm KerberosAuthentication
1.42 aaron 848: Specifies whether Kerberos authentication will be used.
849: The argument to this keyword must be
1.4 dugsong 850: .Dq yes
851: or
852: .Dq no .
1.2 deraadt 853: .It Cm KerberosTgtPassing
1.42 aaron 854: Specifies whether a Kerberos TGT will be forwarded to the server.
855: This will only work if the Kerberos server is actually an AFS kaserver.
856: The argument to this keyword must be
1.4 dugsong 857: .Dq yes
858: or
859: .Dq no .
1.2 deraadt 860: .It Cm LocalForward
1.1 deraadt 861: Specifies that a TCP/IP port on the local machine be forwarded over
1.40 aaron 862: the secure channel to given host:port from the remote machine.
863: The first argument must be a port number, and the second must be
864: host:port.
865: Multiple forwardings may be specified, and additional
866: forwardings can be given on the command line.
867: Only the superuser can forward privileged ports.
1.24 markus 868: .It Cm LogLevel
869: Gives the verbosity level that is used when logging messages from
870: .Nm ssh .
871: The possible values are:
1.77 markus 872: QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG.
873: The default is INFO.
1.91 markus 874: .It Cm MACs
875: Specifies the MAC (message authentication code) algorithms
876: in order of preference.
877: The MAC algorithm is used in protocol version 2
878: for data integrity protection.
879: Multiple algorithms must be comma-separated.
880: The default is
881: .Pp
882: .Bd -literal
1.94 deraadt 883: ``hmac-md5,hmac-sha1,hmac-ripemd160,hmac-ripemd160@openssh.com,
1.91 markus 884: hmac-sha1-96,hmac-md5-96''
885: .Ed
1.14 dugsong 886: .It Cm NumberOfPasswordPrompts
1.42 aaron 887: Specifies the number of password prompts before giving up.
888: The argument to this keyword must be an integer.
889: Default is 3.
1.34 markus 890: .It Cm PasswordAuthentication
1.40 aaron 891: Specifies whether to use password authentication.
892: The argument to this keyword must be
1.34 markus 893: .Dq yes
894: or
895: .Dq no .
1.100 stevesk 896: The default is
897: .Dq yes .
1.2 deraadt 898: .It Cm Port
1.40 aaron 899: Specifies the port number to connect on the remote host.
900: Default is 22.
1.99 djm 901: .It Cm PreferredAuthentications
902: Specifies the order in which the client should try protocol 2
903: authentication methods. This allows a client to prefer one method (e.g.
904: .Cm keyboard-interactive )
905: over another method (e.g.
906: .Cm password )
907: The default for this option is:
908: .Dq publickey, password, keyboard-interactive
1.45 markus 909: .It Cm Protocol
910: Specifies the protocol versions
911: .Nm
912: should support in order of preference.
913: The possible values are
914: .Dq 1
915: and
916: .Dq 2 .
917: Multiple versions must be comma-separated.
918: The default is
1.101 markus 919: .Dq 2,1 .
1.49 markus 920: This means that
921: .Nm
1.101 markus 922: tries version 2 and falls back to version 1
923: if version 2 is not available.
1.2 deraadt 924: .It Cm ProxyCommand
1.40 aaron 925: Specifies the command to use to connect to the server.
926: The command
927: string extends to the end of the line, and is executed with
928: .Pa /bin/sh .
929: In the command string,
930: .Ql %h
931: will be substituted by the host name to
932: connect and
933: .Ql %p
934: by the port.
935: The command can be basically anything,
936: and should read from its standard input and write to its standard output.
937: It should eventually connect an
1.2 deraadt 938: .Xr sshd 8
1.1 deraadt 939: server running on some machine, or execute
1.2 deraadt 940: .Ic sshd -i
1.40 aaron 941: somewhere.
942: Host key management will be done using the
1.1 deraadt 943: HostName of the host being connected (defaulting to the name typed by
944: the user).
1.29 markus 945: Note that
946: .Cm CheckHostIP
947: is not available for connects with a proxy command.
1.2 deraadt 948: .Pp
1.107 ! markus 949: .It Cm PubkeyAuthentication
! 950: Specifies whether to try public key authentication.
! 951: The argument to this keyword must be
! 952: .Dq yes
! 953: or
! 954: .Dq no .
! 955: The default is
! 956: .Dq yes .
! 957: This option applies to protocol version 2 only.
1.2 deraadt 958: .It Cm RemoteForward
1.1 deraadt 959: Specifies that a TCP/IP port on the remote machine be forwarded over
1.40 aaron 960: the secure channel to given host:port from the local machine.
961: The first argument must be a port number, and the second must be
962: host:port.
963: Multiple forwardings may be specified, and additional
964: forwardings can be given on the command line.
965: Only the superuser can forward privileged ports.
1.2 deraadt 966: .It Cm RhostsAuthentication
1.40 aaron 967: Specifies whether to try rhosts based authentication.
968: Note that this
1.1 deraadt 969: declaration only affects the client side and has no effect whatsoever
1.40 aaron 970: on security.
971: Disabling rhosts authentication may reduce
1.1 deraadt 972: authentication time on slow connections when rhosts authentication is
1.40 aaron 973: not used.
974: Most servers do not permit RhostsAuthentication because it
1.107 ! markus 975: is not secure (see
! 976: .Cm RhostsRSAAuthentication ).
1.40 aaron 977: The argument to this keyword must be
1.2 deraadt 978: .Dq yes
979: or
980: .Dq no .
1.100 stevesk 981: The default is
982: .Dq yes .
1.107 ! markus 983: This option applies to protocol version 1 only.
1.2 deraadt 984: .It Cm RhostsRSAAuthentication
1.1 deraadt 985: Specifies whether to try rhosts based authentication with RSA host
1.40 aaron 986: authentication.
987: The argument must be
1.2 deraadt 988: .Dq yes
989: or
990: .Dq no .
1.100 stevesk 991: The default is
992: .Dq yes .
1.107 ! markus 993: This option applies to protocol version 1 only.
1.2 deraadt 994: .It Cm RSAAuthentication
1.40 aaron 995: Specifies whether to try RSA authentication.
996: The argument to this keyword must be
1.2 deraadt 997: .Dq yes
998: or
999: .Dq no .
1.1 deraadt 1000: RSA authentication will only be
1001: attempted if the identity file exists, or an authentication agent is
1002: running.
1.100 stevesk 1003: The default is
1004: .Dq yes .
1.50 markus 1005: Note that this option applies to protocol version 1 only.
1.81 markus 1006: .It Cm ChallengeResponseAuthentication
1007: Specifies whether to use challenge response authentication.
1008: Currently there is only support for
1.27 markus 1009: .Xr skey 1
1.40 aaron 1010: authentication.
1011: The argument to this keyword must be
1.27 markus 1012: .Dq yes
1013: or
1014: .Dq no .
1015: The default is
1016: .Dq no .
1.2 deraadt 1017: .It Cm StrictHostKeyChecking
1018: If this flag is set to
1.44 aaron 1019: .Dq yes ,
1.2 deraadt 1020: .Nm
1.79 stevesk 1021: will never automatically add host keys to the
1.2 deraadt 1022: .Pa $HOME/.ssh/known_hosts
1.48 markus 1023: and
1024: .Pa $HOME/.ssh/known_hosts2
1.79 stevesk 1025: files, and refuses to connect to hosts whose host key has changed.
1.40 aaron 1026: This provides maximum protection against trojan horse attacks.
1027: However, it can be somewhat annoying if you don't have good
1.2 deraadt 1028: .Pa /etc/ssh_known_hosts
1.48 markus 1029: and
1030: .Pa /etc/ssh_known_hosts2
1.1 deraadt 1031: files installed and frequently
1.79 stevesk 1032: connect to new hosts.
1033: This option forces the user to manually
1034: add all new hosts.
1035: If this flag is set to
1036: .Dq no ,
1037: .Nm
1038: will automatically add new host keys to the
1039: user known hosts files.
1040: If this flag is set to
1041: .Dq ask ,
1042: new host keys
1043: will be added to the user known host files only after the user
1044: has confirmed that is what they really want to do, and
1045: .Nm
1046: will refuse to connect to hosts whose host key has changed.
1.40 aaron 1047: The host keys of
1.79 stevesk 1048: known hosts will be verified automatically in all cases.
1.40 aaron 1049: The argument must be
1.79 stevesk 1050: .Dq yes ,
1051: .Dq no
1.2 deraadt 1052: or
1.79 stevesk 1053: .Dq ask .
1054: The default is
1055: .Dq ask .
1.16 markus 1056: .It Cm UsePrivilegedPort
1057: Specifies whether to use a privileged port for outgoing connections.
1058: The argument must be
1059: .Dq yes
1060: or
1061: .Dq no .
1062: The default is
1.98 markus 1063: .Dq no .
1.107 ! markus 1064: Note that you need to set this option to
! 1065: .Dq yes
! 1066: if you want to use
1.16 markus 1067: .Cm RhostsAuthentication
1068: and
1.72 markus 1069: .Cm RhostsRSAAuthentication
1.107 ! markus 1070: with older servers.
1.34 markus 1071: .It Cm User
1.40 aaron 1072: Specifies the user to log in as.
1073: This can be useful if you have a different user name on different machines.
1074: This saves the trouble of
1.34 markus 1075: having to remember to give the user name on the command line.
1076: .It Cm UserKnownHostsFile
1.95 stevesk 1077: Specifies a file to use for the protocol version 1 user
1078: host key database instead of
1.34 markus 1079: .Pa $HOME/.ssh/known_hosts .
1.95 stevesk 1080: .It Cm UserKnownHostsFile2
1081: Specifies a file to use for the protocol version 2 user
1082: host key database instead of
1083: .Pa $HOME/.ssh/known_hosts2 .
1.2 deraadt 1084: .It Cm UseRsh
1.40 aaron 1085: Specifies that rlogin/rsh should be used for this host.
1086: It is possible that the host does not at all support the
1.2 deraadt 1087: .Nm
1.40 aaron 1088: protocol.
1089: This causes
1.2 deraadt 1090: .Nm
1.40 aaron 1091: to immediately execute
1.2 deraadt 1092: .Xr rsh 1 .
1.1 deraadt 1093: All other options (except
1.2 deraadt 1094: .Cm HostName )
1.40 aaron 1095: are ignored if this has been specified.
1096: The argument must be
1.2 deraadt 1097: .Dq yes
1098: or
1099: .Dq no .
1.55 markus 1100: .It Cm XAuthLocation
1101: Specifies the location of the
1102: .Xr xauth 1
1103: program.
1104: The default is
1105: .Pa /usr/X11R6/bin/xauth .
1.58 itojun 1106: .El
1.2 deraadt 1107: .Sh ENVIRONMENT
1108: .Nm
1.1 deraadt 1109: will normally set the following environment variables:
1.2 deraadt 1110: .Bl -tag -width Ds
1111: .It Ev DISPLAY
1112: The
1113: .Ev DISPLAY
1.40 aaron 1114: variable indicates the location of the X11 server.
1.44 aaron 1115: It is automatically set by
1.2 deraadt 1116: .Nm
1117: to point to a value of the form
1118: .Dq hostname:n
1119: where hostname indicates
1.40 aaron 1120: the host where the shell runs, and n is an integer >= 1.
1121: .Nm
1122: uses this special value to forward X11 connections over the secure
1123: channel.
1.107 ! markus 1124: The user should normally not set
! 1125: .Ev DISPLAY
! 1126: explicitly, as that
1.1 deraadt 1127: will render the X11 connection insecure (and will require the user to
1128: manually copy any required authorization cookies).
1.2 deraadt 1129: .It Ev HOME
1.1 deraadt 1130: Set to the path of the user's home directory.
1.2 deraadt 1131: .It Ev LOGNAME
1132: Synonym for
1.12 aaron 1133: .Ev USER ;
1134: set for compatibility with systems that use this variable.
1.2 deraadt 1135: .It Ev MAIL
1.1 deraadt 1136: Set to point the user's mailbox.
1.40 aaron 1137: .It Ev PATH
1.2 deraadt 1138: Set to the default
1139: .Ev PATH ,
1140: as specified when compiling
1.12 aaron 1141: .Nm ssh .
1.18 markus 1142: .It Ev SSH_AUTH_SOCK
1.17 markus 1143: indicates the path of a unix-domain socket used to communicate with the
1144: agent.
1.2 deraadt 1145: .It Ev SSH_CLIENT
1.40 aaron 1146: Identifies the client end of the connection.
1147: The variable contains
1.1 deraadt 1148: three space-separated values: client ip-address, client port number,
1149: and server port number.
1.73 markus 1150: .It Ev SSH_ORIGINAL_COMMAND
1151: The variable contains the original command line if a forced command
1152: is executed.
1153: It can be used to extract the original arguments.
1.2 deraadt 1154: .It Ev SSH_TTY
1.1 deraadt 1155: This is set to the name of the tty (path to the device) associated
1.40 aaron 1156: with the current shell or command.
1157: If the current session has no tty,
1.1 deraadt 1158: this variable is not set.
1.2 deraadt 1159: .It Ev TZ
1.1 deraadt 1160: The timezone variable is set to indicate the present timezone if it
1.56 deraadt 1161: was set when the daemon was started (i.e., the daemon passes the value
1.1 deraadt 1162: on to new connections).
1.2 deraadt 1163: .It Ev USER
1.1 deraadt 1164: Set to the name of the user logging in.
1.2 deraadt 1165: .El
1166: .Pp
1.44 aaron 1167: Additionally,
1.2 deraadt 1168: .Nm
1.44 aaron 1169: reads
1170: .Pa $HOME/.ssh/environment ,
1.2 deraadt 1171: and adds lines of the format
1172: .Dq VARNAME=value
1.12 aaron 1173: to the environment.
1.2 deraadt 1174: .Sh FILES
1.36 markus 1175: .Bl -tag -width Ds
1.95 stevesk 1176: .It Pa $HOME/.ssh/known_hosts, $HOME/.ssh/known_hosts2
1.1 deraadt 1177: Records host keys for all hosts the user has logged into (that are not
1.2 deraadt 1178: in
1.95 stevesk 1179: .Pa /etc/ssh_known_hosts
1180: for protocol version 1 or
1181: .Pa /etc/ssh_known_hosts2
1182: for protocol version 2).
1.2 deraadt 1183: See
1184: .Xr sshd 8 .
1.102 itojun 1185: .It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa, $HOME/.ssh/id_rsa
1186: Contains the authentication identity of the user.
1187: They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively.
1.48 markus 1188: These files
1189: contain sensitive data and should be readable by the user but not
1.15 markus 1190: accessible by others (read/write/execute).
1191: Note that
1192: .Nm
1.48 markus 1193: ignores a private key file if it is accessible by others.
1.15 markus 1194: It is possible to specify a passphrase when
1.1 deraadt 1195: generating the key; the passphrase will be used to encrypt the
1.8 deraadt 1196: sensitive part of this file using 3DES.
1.102 itojun 1197: .It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub, $HOME/.ssh/id_rsa.pub
1.1 deraadt 1198: Contains the public key for authentication (public part of the
1.40 aaron 1199: identity file in human-readable form).
1.48 markus 1200: The contents of the
1201: .Pa $HOME/.ssh/identity.pub
1202: file should be added to
1.2 deraadt 1203: .Pa $HOME/.ssh/authorized_keys
1204: on all machines
1.102 itojun 1205: where you wish to log in using protocol version 1 RSA authentication.
1.48 markus 1206: The contents of the
1207: .Pa $HOME/.ssh/id_dsa.pub
1.102 itojun 1208: and
1209: .Pa $HOME/.ssh/id_rsa.pub
1.48 markus 1210: file should be added to
1211: .Pa $HOME/.ssh/authorized_keys2
1212: on all machines
1.102 itojun 1213: where you wish to log in using protocol version 2 DSA/RSA authentication.
1.48 markus 1214: These files are not
1.40 aaron 1215: sensitive and can (but need not) be readable by anyone.
1.48 markus 1216: These files are
1.84 markus 1217: never used automatically and are not necessary; they are only provided for
1.1 deraadt 1218: the convenience of the user.
1.2 deraadt 1219: .It Pa $HOME/.ssh/config
1.40 aaron 1220: This is the per-user configuration file.
1221: The format of this file is described above.
1222: This file is used by the
1.2 deraadt 1223: .Nm
1.40 aaron 1224: client.
1225: This file does not usually contain any sensitive information,
1.1 deraadt 1226: but the recommended permissions are read/write for the user, and not
1227: accessible by others.
1.2 deraadt 1228: .It Pa $HOME/.ssh/authorized_keys
1.40 aaron 1229: Lists the RSA keys that can be used for logging in as this user.
1230: The format of this file is described in the
1.2 deraadt 1231: .Xr sshd 8
1.40 aaron 1232: manual page.
1233: In the simplest form the format is the same as the .pub
1.1 deraadt 1234: identity files (that is, each line contains the number of bits in
1235: modulus, public exponent, modulus, and comment fields, separated by
1.40 aaron 1236: spaces).
1237: This file is not highly sensitive, but the recommended
1.1 deraadt 1238: permissions are read/write for the user, and not accessible by others.
1.48 markus 1239: .It Pa $HOME/.ssh/authorized_keys2
1.107 ! markus 1240: Lists the public keys (RSA/DSA) that can be used for logging in as this user.
1.48 markus 1241: This file is not highly sensitive, but the recommended
1242: permissions are read/write for the user, and not accessible by others.
1243: .It Pa /etc/ssh_known_hosts, /etc/ssh_known_hosts2
1.40 aaron 1244: Systemwide list of known host keys.
1.48 markus 1245: .Pa /etc/ssh_known_hosts
1246: contains RSA and
1247: .Pa /etc/ssh_known_hosts2
1.107 ! markus 1248: contains RSA or DSA keys for protocol version 2.
1.48 markus 1249: These files should be prepared by the
1.1 deraadt 1250: system administrator to contain the public host keys of all machines in the
1.40 aaron 1251: organization.
1252: This file should be world-readable.
1253: This file contains
1.1 deraadt 1254: public keys, one per line, in the following format (fields separated
1255: by spaces): system name, number of bits in modulus, public exponent,
1.40 aaron 1256: modulus, and optional comment field.
1257: When different names are used
1.1 deraadt 1258: for the same machine, all such names should be listed, separated by
1.40 aaron 1259: commas.
1260: The format is described on the
1.2 deraadt 1261: .Xr sshd 8
1.1 deraadt 1262: manual page.
1.2 deraadt 1263: .Pp
1.1 deraadt 1264: The canonical system name (as returned by name servers) is used by
1.2 deraadt 1265: .Xr sshd 8
1.1 deraadt 1266: to verify the client host when logging in; other names are needed because
1.2 deraadt 1267: .Nm
1.1 deraadt 1268: does not convert the user-supplied name to a canonical name before
1269: checking the key, because someone with access to the name servers
1270: would then be able to fool host authentication.
1.2 deraadt 1271: .It Pa /etc/ssh_config
1.40 aaron 1272: Systemwide configuration file.
1273: This file provides defaults for those
1.1 deraadt 1274: values that are not specified in the user's configuration file, and
1.40 aaron 1275: for those users who do not have a configuration file.
1276: This file must be world-readable.
1.2 deraadt 1277: .It Pa $HOME/.rhosts
1278: This file is used in
1279: .Pa \&.rhosts
1280: authentication to list the
1.40 aaron 1281: host/user pairs that are permitted to log in.
1282: (Note that this file is
1.1 deraadt 1283: also used by rlogin and rsh, which makes using this file insecure.)
1284: Each line of the file contains a host name (in the canonical form
1285: returned by name servers), and then a user name on that host,
1.40 aaron 1286: separated by a space.
1.92 markus 1287: On some machines this file may need to be
1.1 deraadt 1288: world-readable if the user's home directory is on a NFS partition,
1289: because
1.2 deraadt 1290: .Xr sshd 8
1.40 aaron 1291: reads it as root.
1292: Additionally, this file must be owned by the user,
1293: and must not have write permissions for anyone else.
1294: The recommended
1.1 deraadt 1295: permission for most machines is read/write for the user, and not
1296: accessible by others.
1.2 deraadt 1297: .Pp
1.1 deraadt 1298: Note that by default
1.2 deraadt 1299: .Xr sshd 8
1.1 deraadt 1300: will be installed so that it requires successful RSA host
1.40 aaron 1301: authentication before permitting \s+2.\s0rhosts authentication.
1302: If your server machine does not have the client's host key in
1.2 deraadt 1303: .Pa /etc/ssh_known_hosts ,
1304: you can store it in
1305: .Pa $HOME/.ssh/known_hosts .
1306: The easiest way to do this is to
1.1 deraadt 1307: connect back to the client from the server machine using ssh; this
1.48 markus 1308: will automatically add the host key to
1.2 deraadt 1309: .Pa $HOME/.ssh/known_hosts .
1310: .It Pa $HOME/.shosts
1311: This file is used exactly the same way as
1312: .Pa \&.rhosts .
1313: The purpose for
1.1 deraadt 1314: having this file is to be able to use rhosts authentication with
1.2 deraadt 1315: .Nm
1316: without permitting login with
1317: .Xr rlogin 1
1318: or
1319: .Xr rsh 1 .
1320: .It Pa /etc/hosts.equiv
1321: This file is used during
1.40 aaron 1322: .Pa \&.rhosts authentication.
1323: It contains
1.1 deraadt 1324: canonical hosts names, one per line (the full format is described on
1325: the
1.2 deraadt 1326: .Xr sshd 8
1.40 aaron 1327: manual page).
1328: If the client host is found in this file, login is
1.1 deraadt 1329: automatically permitted provided client and server user names are the
1.40 aaron 1330: same.
1331: Additionally, successful RSA host authentication is normally
1332: required.
1333: This file should only be writable by root.
1.2 deraadt 1334: .It Pa /etc/shosts.equiv
1.44 aaron 1335: This file is processed exactly as
1.2 deraadt 1336: .Pa /etc/hosts.equiv .
1.1 deraadt 1337: This file may be useful to permit logins using
1.2 deraadt 1338: .Nm
1.1 deraadt 1339: but not using rsh/rlogin.
1.2 deraadt 1340: .It Pa /etc/sshrc
1.1 deraadt 1341: Commands in this file are executed by
1.2 deraadt 1342: .Nm
1.1 deraadt 1343: when the user logs in just before the user's shell (or command) is started.
1344: See the
1.2 deraadt 1345: .Xr sshd 8
1.1 deraadt 1346: manual page for more information.
1.2 deraadt 1347: .It Pa $HOME/.ssh/rc
1.1 deraadt 1348: Commands in this file are executed by
1.2 deraadt 1349: .Nm
1.1 deraadt 1350: when the user logs in just before the user's shell (or command) is
1351: started.
1.44 aaron 1352: See the
1.2 deraadt 1353: .Xr sshd 8
1.1 deraadt 1354: manual page for more information.
1.31 markus 1355: .It Pa $HOME/.ssh/environment
1356: Contains additional definitions for environment variables, see section
1357: .Sx ENVIRONMENT
1358: above.
1.58 itojun 1359: .El
1.67 aaron 1360: .Sh AUTHORS
1.78 markus 1361: OpenSSH is a derivative of the original and free
1362: ssh 1.2.12 release by Tatu Ylonen.
1363: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1364: Theo de Raadt and Dug Song
1365: removed many bugs, re-added newer features and
1366: created OpenSSH.
1367: Markus Friedl contributed the support for SSH
1368: protocol versions 1.5 and 2.0.
1.2 deraadt 1369: .Sh SEE ALSO
1370: .Xr rlogin 1 ,
1371: .Xr rsh 1 ,
1372: .Xr scp 1 ,
1.83 djm 1373: .Xr sftp 1 ,
1.2 deraadt 1374: .Xr ssh-add 1 ,
1375: .Xr ssh-agent 1 ,
1376: .Xr ssh-keygen 1 ,
1377: .Xr telnet 1 ,
1.87 itojun 1378: .Xr sshd 8
1.106 markus 1379: .Rs
1380: .%A T. Ylonen
1381: .%A T. Kivinen
1382: .%A M. Saarinen
1383: .%A T. Rinne
1384: .%A S. Lehtinen
1385: .%T "SSH Protocol Architecture"
1386: .%N draft-ietf-secsh-architecture-07.txt
1387: .%D January 2001
1388: .%O work in progress material
1389: .Re
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