Annotation of src/usr.bin/ssh/ssh.1, Revision 1.51
1.1 deraadt 1: .\" -*- nroff -*-
2: .\"
3: .\" ssh.1.in
4: .\"
5: .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
6: .\"
7: .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
8: .\" All rights reserved
9: .\"
10: .\" Created: Sat Apr 22 21:55:14 1995 ylo
11: .\"
1.51 ! markus 12: .\" $Id: ssh.1,v 1.50 2000/05/06 17:45:37 markus Exp $
1.1 deraadt 13: .\"
1.2 deraadt 14: .Dd September 25, 1999
15: .Dt SSH 1
16: .Os
17: .Sh NAME
18: .Nm ssh
1.20 provos 19: .Nd OpenSSH secure shell client (remote login program)
1.2 deraadt 20: .Sh SYNOPSIS
21: .Nm ssh
22: .Op Fl l Ar login_name
1.5 deraadt 23: .Op Ar hostname | user@hostname
1.2 deraadt 24: .Op Ar command
25: .Pp
26: .Nm ssh
1.46 markus 27: .Op Fl afgknqtvxCPX246
1.51 ! markus 28: .Op Fl c Ar cipher_spec
1.2 deraadt 29: .Op Fl e Ar escape_char
30: .Op Fl i Ar identity_file
31: .Op Fl l Ar login_name
32: .Op Fl o Ar option
33: .Op Fl p Ar port
1.12 aaron 34: .Oo Fl L Xo
35: .Sm off
1.33 markus 36: .Ar port :
1.12 aaron 37: .Ar host :
38: .Ar hostport
39: .Sm on
40: .Xc
41: .Oc
42: .Oo Fl R Xo
43: .Sm off
1.33 markus 44: .Ar port :
1.12 aaron 45: .Ar host :
46: .Ar hostport
47: .Sm on
48: .Xc
49: .Oc
1.5 deraadt 50: .Op Ar hostname | user@hostname
1.2 deraadt 51: .Op Ar command
1.44 aaron 52: .Sh DESCRIPTION
1.2 deraadt 53: .Nm
1.5 deraadt 54: (Secure Shell) is a program for logging into a remote machine and for
1.40 aaron 55: executing commands on a remote machine.
56: It is intended to replace
1.1 deraadt 57: rlogin and rsh, and provide secure encrypted communications between
1.40 aaron 58: two untrusted hosts over an insecure network.
59: X11 connections and
1.1 deraadt 60: arbitrary TCP/IP ports can also be forwarded over the secure channel.
1.2 deraadt 61: .Pp
62: .Nm
1.44 aaron 63: connects and logs into the specified
1.2 deraadt 64: .Ar hostname .
1.1 deraadt 65: The user must prove
1.49 markus 66: his/her identity to the remote machine using one of several methods
67: depending on the protocol version used:
68: .Pp
69: .Ss SSH protocol version 1
1.2 deraadt 70: .Pp
1.1 deraadt 71: First, if the machine the user logs in from is listed in
1.2 deraadt 72: .Pa /etc/hosts.equiv
1.1 deraadt 73: or
1.2 deraadt 74: .Pa /etc/shosts.equiv
1.1 deraadt 75: on the remote machine, and the user names are
76: the same on both sides, the user is immediately permitted to log in.
1.44 aaron 77: Second, if
1.2 deraadt 78: .Pa \&.rhosts
1.1 deraadt 79: or
1.2 deraadt 80: .Pa \&.shosts
1.1 deraadt 81: exists in the user's home directory on the
82: remote machine and contains a line containing the name of the client
83: machine and the name of the user on that machine, the user is
1.40 aaron 84: permitted to log in.
85: This form of authentication alone is normally not
1.1 deraadt 86: allowed by the server because it is not secure.
1.2 deraadt 87: .Pp
1.1 deraadt 88: The second (and primary) authentication method is the
1.2 deraadt 89: .Pa rhosts
1.1 deraadt 90: or
1.2 deraadt 91: .Pa hosts.equiv
1.40 aaron 92: method combined with RSA-based host authentication.
93: It means that if the login would be permitted by
1.49 markus 94: .Pa $HOME/.rhosts ,
95: .Pa $HOME/.shosts ,
1.2 deraadt 96: .Pa /etc/hosts.equiv ,
1.1 deraadt 97: or
1.2 deraadt 98: .Pa /etc/shosts.equiv ,
1.11 deraadt 99: and if additionally the server can verify the client's
1.44 aaron 100: host key (see
1.2 deraadt 101: .Pa /etc/ssh_known_hosts
1.23 markus 102: and
103: .Pa $HOME/.ssh/known_hosts
1.1 deraadt 104: in the
1.2 deraadt 105: .Sx FILES
1.40 aaron 106: section), only then login is permitted.
107: This authentication method closes security holes due to IP
108: spoofing, DNS spoofing and routing spoofing.
109: [Note to the administrator:
1.2 deraadt 110: .Pa /etc/hosts.equiv ,
1.49 markus 111: .Pa $HOME/.rhosts ,
1.1 deraadt 112: and the rlogin/rsh protocol in general, are inherently insecure and should be
113: disabled if security is desired.]
1.2 deraadt 114: .Pp
1.44 aaron 115: As a third authentication method,
1.2 deraadt 116: .Nm
1.1 deraadt 117: supports RSA based authentication.
118: The scheme is based on public-key cryptography: there are cryptosystems
119: where encryption and decryption are done using separate keys, and it
120: is not possible to derive the decryption key from the encryption key.
1.40 aaron 121: RSA is one such system.
1.44 aaron 122: The idea is that each user creates a public/private
1.40 aaron 123: key pair for authentication purposes.
124: The server knows the public key, and only the user knows the private key.
1.44 aaron 125: The file
1.2 deraadt 126: .Pa $HOME/.ssh/authorized_keys
1.1 deraadt 127: lists the public keys that are permitted for logging
1.40 aaron 128: in.
129: When the user logs in, the
1.2 deraadt 130: .Nm
1.1 deraadt 131: program tells the server which key pair it would like to use for
1.40 aaron 132: authentication.
133: The server checks if this key is permitted, and if
1.1 deraadt 134: so, sends the user (actually the
1.2 deraadt 135: .Nm
1.1 deraadt 136: program running on behalf of the user) a challenge, a random number,
1.40 aaron 137: encrypted by the user's public key.
138: The challenge can only be
139: decrypted using the proper private key.
140: The user's client then decrypts the
1.1 deraadt 141: challenge using the private key, proving that he/she knows the private
142: key but without disclosing it to the server.
1.2 deraadt 143: .Pp
144: .Nm
1.40 aaron 145: implements the RSA authentication protocol automatically.
146: The user creates his/her RSA key pair by running
1.2 deraadt 147: .Xr ssh-keygen 1 .
1.44 aaron 148: This stores the private key in
1.49 markus 149: .Pa $HOME/.ssh/identity
1.1 deraadt 150: and the public key in
1.49 markus 151: .Pa $HOME/.ssh/identity.pub
1.40 aaron 152: in the user's home directory.
153: The user should then copy the
1.2 deraadt 154: .Pa identity.pub
1.44 aaron 155: to
1.49 markus 156: .Pa $HOME/.ssh/authorized_keys
1.44 aaron 157: in his/her home directory on the remote machine (the
1.2 deraadt 158: .Pa authorized_keys
1.44 aaron 159: file corresponds to the conventional
1.49 markus 160: .Pa $HOME/.rhosts
1.1 deraadt 161: file, and has one key
1.40 aaron 162: per line, though the lines can be very long).
163: After this, the user can log in without giving the password.
164: RSA authentication is much
1.1 deraadt 165: more secure than rhosts authentication.
1.2 deraadt 166: .Pp
1.1 deraadt 167: The most convenient way to use RSA authentication may be with an
1.40 aaron 168: authentication agent.
169: See
1.2 deraadt 170: .Xr ssh-agent 1
1.1 deraadt 171: for more information.
1.2 deraadt 172: .Pp
1.44 aaron 173: If other authentication methods fail,
1.2 deraadt 174: .Nm
1.40 aaron 175: prompts the user for a password.
176: The password is sent to the remote
1.1 deraadt 177: host for checking; however, since all communications are encrypted,
178: the password cannot be seen by someone listening on the network.
1.2 deraadt 179: .Pp
1.49 markus 180: .Ss SSH protocol version 2
181: .Pp
182: When a user connects using the protocol version 2
183: different authentication methods are available:
184: At first, the client attempts to authenticate using the public key method.
185: If this method fails password authentication is tried.
186: .Pp
187: The public key method is similar to RSA authentication described
188: in the previous section except that the DSA algorithm is used
189: instead of the patented RSA algorithm.
190: The client uses his private DSA key
191: .Pa $HOME/.ssh/id_dsa
192: to sign the session identifier and sends the result to the server.
193: The server checks whether the matching public key is listed in
194: .Pa $HOME/.ssh/authorized_keys2
195: and grants access if both the key is found and the signature is correct.
196: The session identifier is derived from a shared Diffie-Hellman value
197: and is only known to the client and the server.
198: .Pp
199: If public key authentication fails or is not available a password
200: can be sent encrypted to the remote host for proving the user's identity.
201: This protocol 2 implementation does not yet support Kerberos or
202: S/Key authentication.
203: .Pp
204: Protocol 2 provides additional mechanisms for confidentiality
1.51 ! markus 205: (the traffic is encrypted using 3DES, Blowfish, CAST128 or Arcfour)
1.49 markus 206: and integrity (hmac-sha1, hmac-md5).
207: Note that protocol 1 lacks a strong mechanism for ensuring the
208: integrity of the connection.
209: .Pp
210: .Ss Login session and remote execution
211: .Pp
1.1 deraadt 212: When the user's identity has been accepted by the server, the server
213: either executes the given command, or logs into the machine and gives
1.40 aaron 214: the user a normal shell on the remote machine.
215: All communication with
1.1 deraadt 216: the remote command or shell will be automatically encrypted.
1.2 deraadt 217: .Pp
1.1 deraadt 218: If a pseudo-terminal has been allocated (normal login session), the
1.2 deraadt 219: user can disconnect with
220: .Ic ~. ,
221: and suspend
222: .Nm
223: with
224: .Ic ~^Z .
225: All forwarded connections can be listed with
1.44 aaron 226: .Ic ~#
1.2 deraadt 227: and if
1.1 deraadt 228: the session blocks waiting for forwarded X11 or TCP/IP
1.2 deraadt 229: connections to terminate, it can be backgrounded with
230: .Ic ~&
231: (this should not be used while the user shell is active, as it can cause the
1.40 aaron 232: shell to hang).
233: All available escapes can be listed with
1.2 deraadt 234: .Ic ~? .
235: .Pp
236: A single tilde character can be sent as
237: .Ic ~~
238: (or by following the tilde by a character other than those described above).
1.1 deraadt 239: The escape character must always follow a newline to be interpreted as
1.40 aaron 240: special.
241: The escape character can be changed in configuration files
242: or on the command line.
1.2 deraadt 243: .Pp
1.1 deraadt 244: If no pseudo tty has been allocated, the
245: session is transparent and can be used to reliably transfer binary
1.40 aaron 246: data.
247: On most systems, setting the escape character to
1.2 deraadt 248: .Dq none
249: will also make the session transparent even if a tty is used.
250: .Pp
1.1 deraadt 251: The session terminates when the command or shell in on the remote
252: machine exists and all X11 and TCP/IP connections have been closed.
253: The exit status of the remote program is returned as the exit status
254: of
1.2 deraadt 255: .Nm ssh .
256: .Pp
1.49 markus 257: .Ss X11 and TCP forwarding
258: .Pp
1.1 deraadt 259: If the user is using X11 (the
1.2 deraadt 260: .Ev DISPLAY
1.1 deraadt 261: environment variable is set), the connection to the X11 display is
262: automatically forwarded to the remote side in such a way that any X11
263: programs started from the shell (or command) will go through the
264: encrypted channel, and the connection to the real X server will be made
1.40 aaron 265: from the local machine.
266: The user should not manually set
1.2 deraadt 267: .Ev DISPLAY .
1.1 deraadt 268: Forwarding of X11 connections can be
269: configured on the command line or in configuration files.
1.2 deraadt 270: .Pp
271: The
1.44 aaron 272: .Ev DISPLAY
1.2 deraadt 273: value set by
274: .Nm
1.1 deraadt 275: will point to the server machine, but with a display number greater
1.40 aaron 276: than zero.
277: This is normal, and happens because
1.2 deraadt 278: .Nm
279: creates a
280: .Dq proxy
281: X server on the server machine for forwarding the
1.1 deraadt 282: connections over the encrypted channel.
1.2 deraadt 283: .Pp
284: .Nm
1.1 deraadt 285: will also automatically set up Xauthority data on the server machine.
286: For this purpose, it will generate a random authorization cookie,
287: store it in Xauthority on the server, and verify that any forwarded
288: connections carry this cookie and replace it by the real cookie when
1.40 aaron 289: the connection is opened.
290: The real authentication cookie is never
1.1 deraadt 291: sent to the server machine (and no cookies are sent in the plain).
1.2 deraadt 292: .Pp
1.1 deraadt 293: If the user is using an authentication agent, the connection to the agent
294: is automatically forwarded to the remote side unless disabled on
295: command line or in a configuration file.
1.2 deraadt 296: .Pp
1.1 deraadt 297: Forwarding of arbitrary TCP/IP connections over the secure channel can
1.40 aaron 298: be specified either on command line or in a configuration file.
299: One possible application of TCP/IP forwarding is a secure connection to an
1.1 deraadt 300: electronic purse; another is going trough firewalls.
1.2 deraadt 301: .Pp
1.49 markus 302: .Ss Server authentication
303: .Pp
1.2 deraadt 304: .Nm
1.49 markus 305: automatically maintains and checks a database containing
1.40 aaron 306: identifications for all hosts it has ever been used with.
1.49 markus 307: RSA host keys are stored in
308: .Pa $HOME/.ssh/known_hosts
309: and
310: DSA host keys are stored in
311: .Pa $HOME/.ssh/known_hosts2
1.40 aaron 312: in the user's home directory.
1.49 markus 313: Additionally, the files
1.2 deraadt 314: .Pa /etc/ssh_known_hosts
1.49 markus 315: and
316: .Pa /etc/ssh_known_hosts2
317: are automatically checked for known hosts.
1.40 aaron 318: Any new hosts are automatically added to the user's file.
319: If a host's identification
1.1 deraadt 320: ever changes,
1.2 deraadt 321: .Nm
1.1 deraadt 322: warns about this and disables password authentication to prevent a
1.40 aaron 323: trojan horse from getting the user's password.
324: Another purpose of
1.1 deraadt 325: this mechanism is to prevent man-in-the-middle attacks which could
1.40 aaron 326: otherwise be used to circumvent the encryption.
327: The
1.2 deraadt 328: .Cm StrictHostKeyChecking
1.1 deraadt 329: option (see below) can be used to prevent logins to machines whose
330: host key is not known or has changed.
1.2 deraadt 331: .Sh OPTIONS
332: .Bl -tag -width Ds
1.4 dugsong 333: .It Fl a
1.42 aaron 334: Disables forwarding of the authentication agent connection.
335: This may also be specified on a per-host basis in the configuration file.
1.6 deraadt 336: .It Fl c Ar blowfish|3des
1.44 aaron 337: Selects the cipher to use for encrypting the session.
1.2 deraadt 338: .Ar 3des
1.40 aaron 339: is used by default.
1.44 aaron 340: It is believed to be secure.
1.5 deraadt 341: .Ar 3des
342: (triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
343: It is presumably more secure than the
1.2 deraadt 344: .Ar des
1.51 ! markus 345: cipher which is no longer supported in
! 346: .Nm ssh .
1.5 deraadt 347: .Ar blowfish
348: is a fast block cipher, it appears very secure and is much faster than
1.40 aaron 349: .Ar 3des .
1.51 ! markus 350: .It Fl c Ar "3des-cbc,blowfish-cbc,arcfour,cast128-cbc"
! 351: Additionally, for protocol version 2 a comma-separated list of ciphers can
! 352: be specified in order of preference. Protocol version 2 supports
! 353: 3DES, Blowfish and CAST128 in CBC mode and Arcfour.
1.2 deraadt 354: .It Fl e Ar ch|^ch|none
355: Sets the escape character for sessions with a pty (default:
356: .Ql ~ ) .
1.40 aaron 357: The escape character is only recognized at the beginning of a line.
358: The escape character followed by a dot
1.2 deraadt 359: .Pq Ql \&.
360: closes the connection, followed
1.1 deraadt 361: by control-Z suspends the connection, and followed by itself sends the
1.40 aaron 362: escape character once.
363: Setting the character to
1.2 deraadt 364: .Dq none
365: disables any escapes and makes the session fully transparent.
366: .It Fl f
367: Requests
368: .Nm
1.40 aaron 369: to go to background just before command execution.
370: This is useful if
1.2 deraadt 371: .Nm
372: is going to ask for passwords or passphrases, but the user
1.40 aaron 373: wants it in the background.
1.44 aaron 374: This implies
1.2 deraadt 375: .Fl n .
1.1 deraadt 376: The recommended way to start X11 programs at a remote site is with
1.2 deraadt 377: something like
378: .Ic ssh -f host xterm .
1.34 markus 379: .It Fl g
380: Allows remote hosts to connect to local forwarded ports.
1.2 deraadt 381: .It Fl i Ar identity_file
1.44 aaron 382: Selects the file from which the identity (private key) for
1.40 aaron 383: RSA authentication is read.
1.44 aaron 384: Default is
1.49 markus 385: .Pa $HOME/.ssh/identity
1.40 aaron 386: in the user's home directory.
387: Identity files may also be specified on
388: a per-host basis in the configuration file.
389: It is possible to have multiple
1.2 deraadt 390: .Fl i
391: options (and multiple identities specified in
1.1 deraadt 392: configuration files).
1.2 deraadt 393: .It Fl k
1.42 aaron 394: Disables forwarding of Kerberos tickets and AFS tokens.
395: This may also be specified on a per-host basis in the configuration file.
1.2 deraadt 396: .It Fl l Ar login_name
1.40 aaron 397: Specifies the user to log in as on the remote machine.
398: This also may be specified on a per-host basis in the configuration file.
1.2 deraadt 399: .It Fl n
400: Redirects stdin from
401: .Pa /dev/null
402: (actually, prevents reading from stdin).
1.1 deraadt 403: This must be used when
1.2 deraadt 404: .Nm
1.40 aaron 405: is run in the background.
406: A common trick is to use this to run X11 programs on a remote machine.
407: For example,
1.2 deraadt 408: .Ic ssh -n shadows.cs.hut.fi emacs &
409: will start an emacs on shadows.cs.hut.fi, and the X11
1.1 deraadt 410: connection will be automatically forwarded over an encrypted channel.
411: The
1.2 deraadt 412: .Nm
1.1 deraadt 413: program will be put in the background.
414: (This does not work if
1.2 deraadt 415: .Nm
416: needs to ask for a password or passphrase; see also the
417: .Fl f
418: option.)
419: .It Fl o Ar option
1.1 deraadt 420: Can be used to give options in the format used in the config file.
421: This is useful for specifying options for which there is no separate
1.40 aaron 422: command-line flag.
423: The option has the same format as a line in the configuration file.
1.2 deraadt 424: .It Fl p Ar port
1.40 aaron 425: Port to connect to on the remote host.
426: This can be specified on a
1.1 deraadt 427: per-host basis in the configuration file.
1.16 markus 428: .It Fl P
429: Use a non-privileged port for outgoing connections.
430: This can be used if your firewall does
431: not permit connections from privileged ports.
1.30 provos 432: Note that this option turns off
1.16 markus 433: .Cm RhostsAuthentication
434: and
435: .Cm RhostsRSAAuthentication .
1.2 deraadt 436: .It Fl q
1.40 aaron 437: Quiet mode.
438: Causes all warning and diagnostic messages to be suppressed.
439: Only fatal errors are displayed.
1.2 deraadt 440: .It Fl t
1.40 aaron 441: Force pseudo-tty allocation.
1.43 brad 442: This can be used to execute arbitrary
1.40 aaron 443: screen-based programs on a remote machine, which can be very useful,
444: e.g., when implementing menu services.
1.2 deraadt 445: .It Fl v
1.40 aaron 446: Verbose mode.
447: Causes
1.2 deraadt 448: .Nm
1.40 aaron 449: to print debugging messages about its progress.
450: This is helpful in
1.1 deraadt 451: debugging connection, authentication, and configuration problems.
1.22 provos 452: The verbose mode is also used to display
453: .Xr skey 1
454: challenges, if the user entered "s/key" as password.
1.2 deraadt 455: .It Fl x
1.40 aaron 456: Disables X11 forwarding.
457: This can also be specified on a per-host basis in a configuration file.
1.2 deraadt 458: .It Fl X
1.1 deraadt 459: Enables X11 forwarding.
1.2 deraadt 460: .It Fl C
1.1 deraadt 461: Requests compression of all data (including stdin, stdout, stderr, and
1.40 aaron 462: data for forwarded X11 and TCP/IP connections).
463: The compression algorithm is the same used by
1.34 markus 464: .Xr gzip 1 ,
465: and the
1.2 deraadt 466: .Dq level
467: can be controlled by the
468: .Cm CompressionLevel
1.40 aaron 469: option (see below).
470: Compression is desirable on modem lines and other
1.1 deraadt 471: slow connections, but will only slow down things on fast networks.
472: The default value can be set on a host-by-host basis in the
473: configuration files; see the
1.2 deraadt 474: .Cm Compress
1.1 deraadt 475: option below.
1.2 deraadt 476: .It Fl L Ar port:host:hostport
1.1 deraadt 477: Specifies that the given port on the local (client) host is to be
1.40 aaron 478: forwarded to the given host and port on the remote side.
479: This works by allocating a socket to listen to
1.2 deraadt 480: .Ar port
1.1 deraadt 481: on the local side, and whenever a connection is made to this port, the
482: connection is forwarded over the secure channel, and a connection is
483: made to
1.32 markus 484: .Ar host
485: port
486: .Ar hostport
1.40 aaron 487: from the remote machine.
488: Port forwardings can also be specified in the configuration file.
489: Only root can forward privileged ports.
1.32 markus 490: IPv6 addresses can be specified with an alternative syntax:
491: .Ar port/host/hostport
1.2 deraadt 492: .It Fl R Ar port:host:hostport
1.1 deraadt 493: Specifies that the given port on the remote (server) host is to be
1.40 aaron 494: forwarded to the given host and port on the local side.
495: This works by allocating a socket to listen to
1.2 deraadt 496: .Ar port
1.1 deraadt 497: on the remote side, and whenever a connection is made to this port, the
498: connection is forwarded over the secure channel, and a connection is
499: made to
1.32 markus 500: .Ar host
501: port
502: .Ar hostport
1.40 aaron 503: from the local machine.
504: Port forwardings can also be specified in the configuration file.
505: Privileged ports can be forwarded only when
1.1 deraadt 506: logging in as root on the remote machine.
1.46 markus 507: .It Fl 2
508: Forces
509: .Nm
1.50 markus 510: to try protocol version 2 only.
1.32 markus 511: .It Fl 4
512: Forces
513: .Nm
514: to use IPv4 addresses only.
515: .It Fl 6
516: Forces
517: .Nm
518: to use IPv6 addresses only.
1.2 deraadt 519: .El
520: .Sh CONFIGURATION FILES
521: .Nm
1.1 deraadt 522: obtains configuration data from the following sources (in this order):
523: command line options, user's configuration file
1.2 deraadt 524: .Pq Pa $HOME/.ssh/config ,
525: and system-wide configuration file
526: .Pq Pa /etc/ssh_config .
527: For each parameter, the first obtained value
1.40 aaron 528: will be used.
529: The configuration files contain sections bracketed by
530: .Dq Host
531: specifications, and that section is only applied for hosts that
532: match one of the patterns given in the specification.
533: The matched host name is the one given on the command line.
1.2 deraadt 534: .Pp
1.1 deraadt 535: Since the first obtained value for each parameter is used, more
536: host-specific declarations should be given near the beginning of the
537: file, and general defaults at the end.
1.2 deraadt 538: .Pp
1.1 deraadt 539: The configuration file has the following format:
1.2 deraadt 540: .Pp
541: Empty lines and lines starting with
542: .Ql #
543: are comments.
544: .Pp
545: Otherwise a line is of the format
546: .Dq keyword arguments .
547: The possible
1.1 deraadt 548: keywords and their meanings are as follows (note that the
549: configuration files are case-sensitive):
1.2 deraadt 550: .Bl -tag -width Ds
551: .It Cm Host
1.1 deraadt 552: Restricts the following declarations (up to the next
1.2 deraadt 553: .Cm Host
1.1 deraadt 554: keyword) to be only for those hosts that match one of the patterns
1.2 deraadt 555: given after the keyword.
556: .Ql \&*
557: and
558: .Ql ?
559: can be used as wildcards in the
1.40 aaron 560: patterns.
561: A single
1.2 deraadt 562: .Ql \&*
563: as a pattern can be used to provide global
1.40 aaron 564: defaults for all hosts.
565: The host is the
1.2 deraadt 566: .Ar hostname
1.1 deraadt 567: argument given on the command line (i.e., the name is not converted to
568: a canonicalized host name before matching).
1.2 deraadt 569: .It Cm AFSTokenPassing
1.42 aaron 570: Specifies whether to pass AFS tokens to remote host.
571: The argument to this keyword must be
1.2 deraadt 572: .Dq yes
573: or
574: .Dq no .
575: .It Cm BatchMode
576: If set to
577: .Dq yes ,
1.40 aaron 578: passphrase/password querying will be disabled.
579: This option is useful in scripts and other batch jobs where you have no
580: user to supply the password.
581: The argument must be
1.2 deraadt 582: .Dq yes
583: or
584: .Dq no .
1.34 markus 585: .It Cm CheckHostIP
586: If this flag is set to
587: .Dq yes ,
588: ssh will additionally check the host ip address in the
589: .Pa known_hosts
1.42 aaron 590: file.
591: This allows ssh to detect if a host key changed due to DNS spoofing.
1.34 markus 592: If the option is set to
593: .Dq no ,
594: the check will not be executed.
1.2 deraadt 595: .It Cm Cipher
1.40 aaron 596: Specifies the cipher to use for encrypting the session.
597: Currently,
1.2 deraadt 598: .Dq blowfish ,
1.1 deraadt 599: and
1.10 provos 600: .Dq 3des
1.40 aaron 601: are supported.
602: The default is
1.2 deraadt 603: .Dq 3des .
1.45 markus 604: .It Cm Ciphers
605: Specifies the ciphers allowed for protocol version 2
606: in order of preference.
607: Multiple ciphers must be comma-separated.
608: The default is
1.51 ! markus 609: .Dq 3des-cbc,blowfish-cbc,arcfour,cast128-cbc .
1.2 deraadt 610: .It Cm Compression
1.40 aaron 611: Specifies whether to use compression.
612: The argument must be
1.2 deraadt 613: .Dq yes
614: or
615: .Dq no .
616: .It Cm CompressionLevel
1.40 aaron 617: Specifies the compression level to use if compression is enable.
618: The argument must be an integer from 1 (fast) to 9 (slow, best).
619: The default level is 6, which is good for most applications.
620: The meaning of the values is the same as in
1.34 markus 621: .Xr gzip 1 .
1.2 deraadt 622: .It Cm ConnectionAttempts
1.1 deraadt 623: Specifies the number of tries (one per second) to make before falling
1.40 aaron 624: back to rsh or exiting.
625: The argument must be an integer.
626: This may be useful in scripts if the connection sometimes fails.
1.50 markus 627: .It Cm DSAAuthentication
628: Specifies whether to try DSA authentication.
629: The argument to this keyword must be
630: .Dq yes
631: or
632: .Dq no .
633: DSA authentication will only be
634: attempted if a DSA identity file exists.
635: Note that this option applies to protocol version 2 only.
1.2 deraadt 636: .It Cm EscapeChar
637: Sets the escape character (default:
638: .Ql ~ ) .
639: The escape character can also
1.40 aaron 640: be set on the command line.
641: The argument should be a single character,
1.2 deraadt 642: .Ql ^
643: followed by a letter, or
644: .Dq none
645: to disable the escape
1.1 deraadt 646: character entirely (making the connection transparent for binary
647: data).
1.44 aaron 648: .It Cm FallBackToRsh
1.1 deraadt 649: Specifies that if connecting via
1.2 deraadt 650: .Nm
1.1 deraadt 651: fails due to a connection refused error (there is no
1.2 deraadt 652: .Xr sshd 8
1.44 aaron 653: listening on the remote host),
1.2 deraadt 654: .Xr rsh 1
1.1 deraadt 655: should automatically be used instead (after a suitable warning about
1.40 aaron 656: the session being unencrypted).
657: The argument must be
1.2 deraadt 658: .Dq yes
659: or
660: .Dq no .
661: .It Cm ForwardAgent
1.1 deraadt 662: Specifies whether the connection to the authentication agent (if any)
1.40 aaron 663: will be forwarded to the remote machine.
664: The argument must be
1.2 deraadt 665: .Dq yes
666: or
667: .Dq no .
668: .It Cm ForwardX11
1.1 deraadt 669: Specifies whether X11 connections will be automatically redirected
1.44 aaron 670: over the secure channel and
1.2 deraadt 671: .Ev DISPLAY
1.40 aaron 672: set.
1.44 aaron 673: The argument must be
1.2 deraadt 674: .Dq yes
675: or
1.38 markus 676: .Dq no .
677: The default is
1.3 deraadt 678: .Dq no .
679: .It Cm GatewayPorts
680: Specifies whether remote hosts are allowed to connect to local
681: forwarded ports.
682: The argument must be
683: .Dq yes
684: or
685: .Dq no .
686: The default is
1.2 deraadt 687: .Dq no .
688: .It Cm GlobalKnownHostsFile
1.44 aaron 689: Specifies a file to use instead of
1.2 deraadt 690: .Pa /etc/ssh_known_hosts .
691: .It Cm HostName
1.40 aaron 692: Specifies the real host name to log into.
693: This can be used to specify nicknames or abbreviations for hosts.
694: Default is the name given on the command line.
695: Numeric IP addresses are also permitted (both on the command line and in
1.2 deraadt 696: .Cm HostName
1.1 deraadt 697: specifications).
1.2 deraadt 698: .It Cm IdentityFile
1.1 deraadt 699: Specifies the file from which the user's RSA authentication identity
1.2 deraadt 700: is read (default
1.49 markus 701: .Pa $HOME/.ssh/identity
1.2 deraadt 702: in the user's home directory).
1.1 deraadt 703: Additionally, any identities represented by the authentication agent
1.40 aaron 704: will be used for authentication.
705: The file name may use the tilde
706: syntax to refer to a user's home directory.
707: It is possible to have
1.1 deraadt 708: multiple identity files specified in configuration files; all these
709: identities will be tried in sequence.
1.48 markus 710: .It Cm IdentityFile2
711: Specifies the file from which the user's DSA authentication identity
712: is read (default
1.49 markus 713: .Pa $HOME/.ssh/id_dsa
1.48 markus 714: in the user's home directory).
715: The file name may use the tilde
716: syntax to refer to a user's home directory.
717: It is possible to have
718: multiple identity files specified in configuration files; all these
719: identities will be tried in sequence.
1.2 deraadt 720: .It Cm KeepAlive
1.1 deraadt 721: Specifies whether the system should send keepalive messages to the
1.40 aaron 722: other side.
723: If they are sent, death of the connection or crash of one
724: of the machines will be properly noticed.
725: However, this means that
1.1 deraadt 726: connections will die if the route is down temporarily, and some people
1.41 aaron 727: find it annoying.
1.2 deraadt 728: .Pp
729: The default is
730: .Dq yes
731: (to send keepalives), and the client will notice
1.40 aaron 732: if the network goes down or the remote host dies.
733: This is important in scripts, and many users want it too.
1.2 deraadt 734: .Pp
735: To disable keepalives, the value should be set to
736: .Dq no
737: in both the server and the client configuration files.
738: .It Cm KerberosAuthentication
1.42 aaron 739: Specifies whether Kerberos authentication will be used.
740: The argument to this keyword must be
1.4 dugsong 741: .Dq yes
742: or
743: .Dq no .
1.2 deraadt 744: .It Cm KerberosTgtPassing
1.42 aaron 745: Specifies whether a Kerberos TGT will be forwarded to the server.
746: This will only work if the Kerberos server is actually an AFS kaserver.
747: The argument to this keyword must be
1.4 dugsong 748: .Dq yes
749: or
750: .Dq no .
1.2 deraadt 751: .It Cm LocalForward
1.1 deraadt 752: Specifies that a TCP/IP port on the local machine be forwarded over
1.40 aaron 753: the secure channel to given host:port from the remote machine.
754: The first argument must be a port number, and the second must be
755: host:port.
756: Multiple forwardings may be specified, and additional
757: forwardings can be given on the command line.
758: Only the superuser can forward privileged ports.
1.24 markus 759: .It Cm LogLevel
760: Gives the verbosity level that is used when logging messages from
761: .Nm ssh .
762: The possible values are:
1.39 djm 763: QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG.
1.24 markus 764: The default is INFO.
1.14 dugsong 765: .It Cm NumberOfPasswordPrompts
1.42 aaron 766: Specifies the number of password prompts before giving up.
767: The argument to this keyword must be an integer.
768: Default is 3.
1.34 markus 769: .It Cm PasswordAuthentication
1.40 aaron 770: Specifies whether to use password authentication.
771: The argument to this keyword must be
1.34 markus 772: .Dq yes
773: or
774: .Dq no .
1.50 markus 775: Note that this option applies to both protocol version 1 and 2.
1.2 deraadt 776: .It Cm Port
1.40 aaron 777: Specifies the port number to connect on the remote host.
778: Default is 22.
1.45 markus 779: .It Cm Protocol
780: Specifies the protocol versions
781: .Nm
782: should support in order of preference.
783: The possible values are
784: .Dq 1
785: and
786: .Dq 2 .
787: Multiple versions must be comma-separated.
788: The default is
1.49 markus 789: .Dq 1,2 .
790: This means that
791: .Nm
792: tries version 1 and falls back to version 2
793: if version 1 is no available.
1.2 deraadt 794: .It Cm ProxyCommand
1.40 aaron 795: Specifies the command to use to connect to the server.
796: The command
797: string extends to the end of the line, and is executed with
798: .Pa /bin/sh .
799: In the command string,
800: .Ql %h
801: will be substituted by the host name to
802: connect and
803: .Ql %p
804: by the port.
805: The command can be basically anything,
806: and should read from its standard input and write to its standard output.
807: It should eventually connect an
1.2 deraadt 808: .Xr sshd 8
1.1 deraadt 809: server running on some machine, or execute
1.2 deraadt 810: .Ic sshd -i
1.40 aaron 811: somewhere.
812: Host key management will be done using the
1.1 deraadt 813: HostName of the host being connected (defaulting to the name typed by
814: the user).
1.29 markus 815: Note that
816: .Cm CheckHostIP
817: is not available for connects with a proxy command.
1.2 deraadt 818: .Pp
819: .It Cm RemoteForward
1.1 deraadt 820: Specifies that a TCP/IP port on the remote machine be forwarded over
1.40 aaron 821: the secure channel to given host:port from the local machine.
822: The first argument must be a port number, and the second must be
823: host:port.
824: Multiple forwardings may be specified, and additional
825: forwardings can be given on the command line.
826: Only the superuser can forward privileged ports.
1.2 deraadt 827: .It Cm RhostsAuthentication
1.40 aaron 828: Specifies whether to try rhosts based authentication.
829: Note that this
1.1 deraadt 830: declaration only affects the client side and has no effect whatsoever
1.40 aaron 831: on security.
832: Disabling rhosts authentication may reduce
1.1 deraadt 833: authentication time on slow connections when rhosts authentication is
1.40 aaron 834: not used.
835: Most servers do not permit RhostsAuthentication because it
836: is not secure (see RhostsRSAAuthentication).
837: The argument to this keyword must be
1.2 deraadt 838: .Dq yes
839: or
840: .Dq no .
841: .It Cm RhostsRSAAuthentication
1.1 deraadt 842: Specifies whether to try rhosts based authentication with RSA host
1.40 aaron 843: authentication.
844: This is the primary authentication method for most sites.
845: The argument must be
1.2 deraadt 846: .Dq yes
847: or
848: .Dq no .
849: .It Cm RSAAuthentication
1.40 aaron 850: Specifies whether to try RSA authentication.
851: The argument to this keyword must be
1.2 deraadt 852: .Dq yes
853: or
854: .Dq no .
1.1 deraadt 855: RSA authentication will only be
856: attempted if the identity file exists, or an authentication agent is
857: running.
1.50 markus 858: Note that this option applies to protocol version 1 only.
1.27 markus 859: .It Cm SkeyAuthentication
860: Specifies whether to use
861: .Xr skey 1
1.40 aaron 862: authentication.
863: The argument to this keyword must be
1.27 markus 864: .Dq yes
865: or
866: .Dq no .
867: The default is
868: .Dq no .
1.2 deraadt 869: .It Cm StrictHostKeyChecking
870: If this flag is set to
1.44 aaron 871: .Dq yes ,
1.2 deraadt 872: .Nm
1.1 deraadt 873: ssh will never automatically add host keys to the
1.2 deraadt 874: .Pa $HOME/.ssh/known_hosts
1.48 markus 875: and
876: .Pa $HOME/.ssh/known_hosts2
877: files, and refuses to connect hosts whose host key has changed.
1.40 aaron 878: This provides maximum protection against trojan horse attacks.
879: However, it can be somewhat annoying if you don't have good
1.2 deraadt 880: .Pa /etc/ssh_known_hosts
1.48 markus 881: and
882: .Pa /etc/ssh_known_hosts2
1.1 deraadt 883: files installed and frequently
1.40 aaron 884: connect new hosts.
885: Basically this option forces the user to manually
886: add any new hosts.
887: Normally this option is disabled, and new hosts
888: will automatically be added to the known host files.
889: The host keys of
890: known hosts will be verified automatically in either case.
891: The argument must be
1.2 deraadt 892: .Dq yes
893: or
894: .Dq no .
1.16 markus 895: .It Cm UsePrivilegedPort
896: Specifies whether to use a privileged port for outgoing connections.
897: The argument must be
898: .Dq yes
899: or
900: .Dq no .
901: The default is
902: .Dq yes .
903: Note that setting this option to
904: .Dq no
1.30 provos 905: turns off
1.16 markus 906: .Cm RhostsAuthentication
907: and
908: .Cm RhostsRSAAuthentication .
1.34 markus 909: .It Cm User
1.40 aaron 910: Specifies the user to log in as.
911: This can be useful if you have a different user name on different machines.
912: This saves the trouble of
1.34 markus 913: having to remember to give the user name on the command line.
914: .It Cm UserKnownHostsFile
915: Specifies a file to use instead of
916: .Pa $HOME/.ssh/known_hosts .
1.2 deraadt 917: .It Cm UseRsh
1.40 aaron 918: Specifies that rlogin/rsh should be used for this host.
919: It is possible that the host does not at all support the
1.2 deraadt 920: .Nm
1.40 aaron 921: protocol.
922: This causes
1.2 deraadt 923: .Nm
1.40 aaron 924: to immediately execute
1.2 deraadt 925: .Xr rsh 1 .
1.1 deraadt 926: All other options (except
1.2 deraadt 927: .Cm HostName )
1.40 aaron 928: are ignored if this has been specified.
929: The argument must be
1.2 deraadt 930: .Dq yes
931: or
932: .Dq no .
933: .Sh ENVIRONMENT
934: .Nm
1.1 deraadt 935: will normally set the following environment variables:
1.2 deraadt 936: .Bl -tag -width Ds
937: .It Ev DISPLAY
938: The
939: .Ev DISPLAY
1.40 aaron 940: variable indicates the location of the X11 server.
1.44 aaron 941: It is automatically set by
1.2 deraadt 942: .Nm
943: to point to a value of the form
944: .Dq hostname:n
945: where hostname indicates
1.40 aaron 946: the host where the shell runs, and n is an integer >= 1.
947: .Nm
948: uses this special value to forward X11 connections over the secure
949: channel.
950: The user should normally not set DISPLAY explicitly, as that
1.1 deraadt 951: will render the X11 connection insecure (and will require the user to
952: manually copy any required authorization cookies).
1.2 deraadt 953: .It Ev HOME
1.1 deraadt 954: Set to the path of the user's home directory.
1.2 deraadt 955: .It Ev LOGNAME
956: Synonym for
1.12 aaron 957: .Ev USER ;
958: set for compatibility with systems that use this variable.
1.2 deraadt 959: .It Ev MAIL
1.1 deraadt 960: Set to point the user's mailbox.
1.40 aaron 961: .It Ev PATH
1.2 deraadt 962: Set to the default
963: .Ev PATH ,
964: as specified when compiling
1.12 aaron 965: .Nm ssh .
1.18 markus 966: .It Ev SSH_AUTH_SOCK
1.17 markus 967: indicates the path of a unix-domain socket used to communicate with the
968: agent.
1.2 deraadt 969: .It Ev SSH_CLIENT
1.40 aaron 970: Identifies the client end of the connection.
971: The variable contains
1.1 deraadt 972: three space-separated values: client ip-address, client port number,
973: and server port number.
1.2 deraadt 974: .It Ev SSH_TTY
1.1 deraadt 975: This is set to the name of the tty (path to the device) associated
1.40 aaron 976: with the current shell or command.
977: If the current session has no tty,
1.1 deraadt 978: this variable is not set.
1.2 deraadt 979: .It Ev TZ
1.1 deraadt 980: The timezone variable is set to indicate the present timezone if it
981: was set when the daemon was started (e.i., the daemon passes the value
982: on to new connections).
1.2 deraadt 983: .It Ev USER
1.1 deraadt 984: Set to the name of the user logging in.
1.2 deraadt 985: .El
986: .Pp
1.44 aaron 987: Additionally,
1.2 deraadt 988: .Nm
1.44 aaron 989: reads
990: .Pa $HOME/.ssh/environment ,
1.2 deraadt 991: and adds lines of the format
992: .Dq VARNAME=value
1.12 aaron 993: to the environment.
1.2 deraadt 994: .Sh FILES
1.36 markus 995: .Bl -tag -width Ds
1.2 deraadt 996: .It Pa $HOME/.ssh/known_hosts
1.1 deraadt 997: Records host keys for all hosts the user has logged into (that are not
1.2 deraadt 998: in
999: .Pa /etc/ssh_known_hosts ) .
1000: See
1001: .Xr sshd 8 .
1.48 markus 1002: .It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa
1003: Contains the RSA and the DSA authentication identity of the user.
1004: These files
1005: contain sensitive data and should be readable by the user but not
1.15 markus 1006: accessible by others (read/write/execute).
1007: Note that
1008: .Nm
1.48 markus 1009: ignores a private key file if it is accessible by others.
1.15 markus 1010: It is possible to specify a passphrase when
1.1 deraadt 1011: generating the key; the passphrase will be used to encrypt the
1.8 deraadt 1012: sensitive part of this file using 3DES.
1.48 markus 1013: .It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub
1.1 deraadt 1014: Contains the public key for authentication (public part of the
1.40 aaron 1015: identity file in human-readable form).
1.48 markus 1016: The contents of the
1017: .Pa $HOME/.ssh/identity.pub
1018: file should be added to
1.2 deraadt 1019: .Pa $HOME/.ssh/authorized_keys
1020: on all machines
1.40 aaron 1021: where you wish to log in using RSA authentication.
1.48 markus 1022: The contents of the
1023: .Pa $HOME/.ssh/id_dsa.pub
1024: file should be added to
1025: .Pa $HOME/.ssh/authorized_keys2
1026: on all machines
1027: where you wish to log in using DSA authentication.
1028: These files are not
1.40 aaron 1029: sensitive and can (but need not) be readable by anyone.
1.48 markus 1030: These files are
1031: never used automatically and are not necessary; they is only provided for
1.1 deraadt 1032: the convenience of the user.
1.2 deraadt 1033: .It Pa $HOME/.ssh/config
1.40 aaron 1034: This is the per-user configuration file.
1035: The format of this file is described above.
1036: This file is used by the
1.2 deraadt 1037: .Nm
1.40 aaron 1038: client.
1039: This file does not usually contain any sensitive information,
1.1 deraadt 1040: but the recommended permissions are read/write for the user, and not
1041: accessible by others.
1.2 deraadt 1042: .It Pa $HOME/.ssh/authorized_keys
1.40 aaron 1043: Lists the RSA keys that can be used for logging in as this user.
1044: The format of this file is described in the
1.2 deraadt 1045: .Xr sshd 8
1.40 aaron 1046: manual page.
1047: In the simplest form the format is the same as the .pub
1.1 deraadt 1048: identity files (that is, each line contains the number of bits in
1049: modulus, public exponent, modulus, and comment fields, separated by
1.40 aaron 1050: spaces).
1051: This file is not highly sensitive, but the recommended
1.1 deraadt 1052: permissions are read/write for the user, and not accessible by others.
1.48 markus 1053: .It Pa $HOME/.ssh/authorized_keys2
1054: Lists the DSA keys that can be used for logging in as this user.
1055: This file is not highly sensitive, but the recommended
1056: permissions are read/write for the user, and not accessible by others.
1057: .It Pa /etc/ssh_known_hosts, /etc/ssh_known_hosts2
1.40 aaron 1058: Systemwide list of known host keys.
1.48 markus 1059: .Pa /etc/ssh_known_hosts
1060: contains RSA and
1061: .Pa /etc/ssh_known_hosts2
1062: contains DSA keys.
1063: These files should be prepared by the
1.1 deraadt 1064: system administrator to contain the public host keys of all machines in the
1.40 aaron 1065: organization.
1066: This file should be world-readable.
1067: This file contains
1.1 deraadt 1068: public keys, one per line, in the following format (fields separated
1069: by spaces): system name, number of bits in modulus, public exponent,
1.40 aaron 1070: modulus, and optional comment field.
1071: When different names are used
1.1 deraadt 1072: for the same machine, all such names should be listed, separated by
1.40 aaron 1073: commas.
1074: The format is described on the
1.2 deraadt 1075: .Xr sshd 8
1.1 deraadt 1076: manual page.
1.2 deraadt 1077: .Pp
1.1 deraadt 1078: The canonical system name (as returned by name servers) is used by
1.2 deraadt 1079: .Xr sshd 8
1.1 deraadt 1080: to verify the client host when logging in; other names are needed because
1.2 deraadt 1081: .Nm
1.1 deraadt 1082: does not convert the user-supplied name to a canonical name before
1083: checking the key, because someone with access to the name servers
1084: would then be able to fool host authentication.
1.2 deraadt 1085: .It Pa /etc/ssh_config
1.40 aaron 1086: Systemwide configuration file.
1087: This file provides defaults for those
1.1 deraadt 1088: values that are not specified in the user's configuration file, and
1.40 aaron 1089: for those users who do not have a configuration file.
1090: This file must be world-readable.
1.2 deraadt 1091: .It Pa $HOME/.rhosts
1092: This file is used in
1093: .Pa \&.rhosts
1094: authentication to list the
1.40 aaron 1095: host/user pairs that are permitted to log in.
1096: (Note that this file is
1.1 deraadt 1097: also used by rlogin and rsh, which makes using this file insecure.)
1098: Each line of the file contains a host name (in the canonical form
1099: returned by name servers), and then a user name on that host,
1.40 aaron 1100: separated by a space.
1101: One some machines this file may need to be
1.1 deraadt 1102: world-readable if the user's home directory is on a NFS partition,
1103: because
1.2 deraadt 1104: .Xr sshd 8
1.40 aaron 1105: reads it as root.
1106: Additionally, this file must be owned by the user,
1107: and must not have write permissions for anyone else.
1108: The recommended
1.1 deraadt 1109: permission for most machines is read/write for the user, and not
1110: accessible by others.
1.2 deraadt 1111: .Pp
1.1 deraadt 1112: Note that by default
1.2 deraadt 1113: .Xr sshd 8
1.1 deraadt 1114: will be installed so that it requires successful RSA host
1.40 aaron 1115: authentication before permitting \s+2.\s0rhosts authentication.
1116: If your server machine does not have the client's host key in
1.2 deraadt 1117: .Pa /etc/ssh_known_hosts ,
1118: you can store it in
1119: .Pa $HOME/.ssh/known_hosts .
1120: The easiest way to do this is to
1.1 deraadt 1121: connect back to the client from the server machine using ssh; this
1.48 markus 1122: will automatically add the host key to
1.2 deraadt 1123: .Pa $HOME/.ssh/known_hosts .
1124: .It Pa $HOME/.shosts
1125: This file is used exactly the same way as
1126: .Pa \&.rhosts .
1127: The purpose for
1.1 deraadt 1128: having this file is to be able to use rhosts authentication with
1.2 deraadt 1129: .Nm
1130: without permitting login with
1131: .Xr rlogin 1
1132: or
1133: .Xr rsh 1 .
1134: .It Pa /etc/hosts.equiv
1135: This file is used during
1.40 aaron 1136: .Pa \&.rhosts authentication.
1137: It contains
1.1 deraadt 1138: canonical hosts names, one per line (the full format is described on
1139: the
1.2 deraadt 1140: .Xr sshd 8
1.40 aaron 1141: manual page).
1142: If the client host is found in this file, login is
1.1 deraadt 1143: automatically permitted provided client and server user names are the
1.40 aaron 1144: same.
1145: Additionally, successful RSA host authentication is normally
1146: required.
1147: This file should only be writable by root.
1.2 deraadt 1148: .It Pa /etc/shosts.equiv
1.44 aaron 1149: This file is processed exactly as
1.2 deraadt 1150: .Pa /etc/hosts.equiv .
1.1 deraadt 1151: This file may be useful to permit logins using
1.2 deraadt 1152: .Nm
1.1 deraadt 1153: but not using rsh/rlogin.
1.2 deraadt 1154: .It Pa /etc/sshrc
1.1 deraadt 1155: Commands in this file are executed by
1.2 deraadt 1156: .Nm
1.1 deraadt 1157: when the user logs in just before the user's shell (or command) is started.
1158: See the
1.2 deraadt 1159: .Xr sshd 8
1.1 deraadt 1160: manual page for more information.
1.2 deraadt 1161: .It Pa $HOME/.ssh/rc
1.1 deraadt 1162: Commands in this file are executed by
1.2 deraadt 1163: .Nm
1.1 deraadt 1164: when the user logs in just before the user's shell (or command) is
1165: started.
1.44 aaron 1166: See the
1.2 deraadt 1167: .Xr sshd 8
1.1 deraadt 1168: manual page for more information.
1.31 markus 1169: .It Pa $HOME/.ssh/environment
1170: Contains additional definitions for environment variables, see section
1171: .Sx ENVIRONMENT
1172: above.
1.5 deraadt 1173: .It Pa libcrypto.so.X.1
1174: A version of this library which includes support for the RSA algorithm
1175: is required for proper operation.
1.2 deraadt 1176: .Sh AUTHOR
1.20 provos 1177: OpenSSH
1.37 deraadt 1178: is a derivative of the original (free) ssh 1.2.12 release by Tatu Ylonen,
1.40 aaron 1179: but with bugs removed and newer features re-added.
1180: Rapidly after the
1.37 deraadt 1181: 1.2.12 release, newer versions of the original ssh bore successively
1182: more restrictive licenses, and thus demand for a free version was born.
1.47 markus 1183: .Pp
1.37 deraadt 1184: This version of OpenSSH
1.20 provos 1185: .Bl -bullet
1186: .It
1.35 aaron 1187: has all components of a restrictive nature (i.e., patents, see
1.21 deraadt 1188: .Xr ssl 8 )
1189: directly removed from the source code; any licensed or patented components
1190: are chosen from
1191: external libraries.
1.20 provos 1192: .It
1.47 markus 1193: has been updated to support SSH protocol 1.5 and 2, making it compatible with
1194: all other SSH clients and servers.
1.20 provos 1195: .It
1.44 aaron 1196: contains added support for
1.20 provos 1197: .Xr kerberos 8
1198: authentication and ticket passing.
1199: .It
1.21 deraadt 1200: supports one-time password authentication with
1.20 provos 1201: .Xr skey 1 .
1202: .El
1203: .Pp
1204: The libraries described in
1.5 deraadt 1205: .Xr ssl 8
1206: are required for proper operation.
1.25 provos 1207: .Pp
1.26 aaron 1208: OpenSSH has been created by Aaron Campbell, Bob Beck, Markus Friedl,
1.25 provos 1209: Niels Provos, Theo de Raadt, and Dug Song.
1.47 markus 1210: .Pp
1211: The support for SSH protocol 2 was written by Markus Friedl.
1.2 deraadt 1212: .Sh SEE ALSO
1213: .Xr rlogin 1 ,
1214: .Xr rsh 1 ,
1215: .Xr scp 1 ,
1216: .Xr ssh-add 1 ,
1217: .Xr ssh-agent 1 ,
1218: .Xr ssh-keygen 1 ,
1219: .Xr telnet 1 ,
1.5 deraadt 1220: .Xr sshd 8 ,
1221: .Xr ssl 8
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