Annotation of src/usr.bin/ssh/ssh.1, Revision 1.50
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: .\"
1.50 ! markus 12: .\" $Id: ssh.1,v 1.49 2000/05/03 22:01:09 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
1.12 aaron 28: .Op Fl c Ar blowfish | 3des
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
205: (the traffic is encrypted using 3DES, blowfish, cast128 or arcfour)
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
1.5 deraadt 345: cipher which is no longer supported in ssh.
346: .Ar blowfish
347: is a fast block cipher, it appears very secure and is much faster than
1.40 aaron 348: .Ar 3des .
1.2 deraadt 349: .It Fl e Ar ch|^ch|none
350: Sets the escape character for sessions with a pty (default:
351: .Ql ~ ) .
1.40 aaron 352: The escape character is only recognized at the beginning of a line.
353: The escape character followed by a dot
1.2 deraadt 354: .Pq Ql \&.
355: closes the connection, followed
1.1 deraadt 356: by control-Z suspends the connection, and followed by itself sends the
1.40 aaron 357: escape character once.
358: Setting the character to
1.2 deraadt 359: .Dq none
360: disables any escapes and makes the session fully transparent.
361: .It Fl f
362: Requests
363: .Nm
1.40 aaron 364: to go to background just before command execution.
365: This is useful if
1.2 deraadt 366: .Nm
367: is going to ask for passwords or passphrases, but the user
1.40 aaron 368: wants it in the background.
1.44 aaron 369: This implies
1.2 deraadt 370: .Fl n .
1.1 deraadt 371: The recommended way to start X11 programs at a remote site is with
1.2 deraadt 372: something like
373: .Ic ssh -f host xterm .
1.34 markus 374: .It Fl g
375: Allows remote hosts to connect to local forwarded ports.
1.2 deraadt 376: .It Fl i Ar identity_file
1.44 aaron 377: Selects the file from which the identity (private key) for
1.40 aaron 378: RSA authentication is read.
1.44 aaron 379: Default is
1.49 markus 380: .Pa $HOME/.ssh/identity
1.40 aaron 381: in the user's home directory.
382: Identity files may also be specified on
383: a per-host basis in the configuration file.
384: It is possible to have multiple
1.2 deraadt 385: .Fl i
386: options (and multiple identities specified in
1.1 deraadt 387: configuration files).
1.2 deraadt 388: .It Fl k
1.42 aaron 389: Disables forwarding of Kerberos tickets and AFS tokens.
390: This may also be specified on a per-host basis in the configuration file.
1.2 deraadt 391: .It Fl l Ar login_name
1.40 aaron 392: Specifies the user to log in as on the remote machine.
393: This also may be specified on a per-host basis in the configuration file.
1.2 deraadt 394: .It Fl n
395: Redirects stdin from
396: .Pa /dev/null
397: (actually, prevents reading from stdin).
1.1 deraadt 398: This must be used when
1.2 deraadt 399: .Nm
1.40 aaron 400: is run in the background.
401: A common trick is to use this to run X11 programs on a remote machine.
402: For example,
1.2 deraadt 403: .Ic ssh -n shadows.cs.hut.fi emacs &
404: will start an emacs on shadows.cs.hut.fi, and the X11
1.1 deraadt 405: connection will be automatically forwarded over an encrypted channel.
406: The
1.2 deraadt 407: .Nm
1.1 deraadt 408: program will be put in the background.
409: (This does not work if
1.2 deraadt 410: .Nm
411: needs to ask for a password or passphrase; see also the
412: .Fl f
413: option.)
414: .It Fl o Ar option
1.1 deraadt 415: Can be used to give options in the format used in the config file.
416: This is useful for specifying options for which there is no separate
1.40 aaron 417: command-line flag.
418: The option has the same format as a line in the configuration file.
1.2 deraadt 419: .It Fl p Ar port
1.40 aaron 420: Port to connect to on the remote host.
421: This can be specified on a
1.1 deraadt 422: per-host basis in the configuration file.
1.16 markus 423: .It Fl P
424: Use a non-privileged port for outgoing connections.
425: This can be used if your firewall does
426: not permit connections from privileged ports.
1.30 provos 427: Note that this option turns off
1.16 markus 428: .Cm RhostsAuthentication
429: and
430: .Cm RhostsRSAAuthentication .
1.2 deraadt 431: .It Fl q
1.40 aaron 432: Quiet mode.
433: Causes all warning and diagnostic messages to be suppressed.
434: Only fatal errors are displayed.
1.2 deraadt 435: .It Fl t
1.40 aaron 436: Force pseudo-tty allocation.
1.43 brad 437: This can be used to execute arbitrary
1.40 aaron 438: screen-based programs on a remote machine, which can be very useful,
439: e.g., when implementing menu services.
1.2 deraadt 440: .It Fl v
1.40 aaron 441: Verbose mode.
442: Causes
1.2 deraadt 443: .Nm
1.40 aaron 444: to print debugging messages about its progress.
445: This is helpful in
1.1 deraadt 446: debugging connection, authentication, and configuration problems.
1.22 provos 447: The verbose mode is also used to display
448: .Xr skey 1
449: challenges, if the user entered "s/key" as password.
1.2 deraadt 450: .It Fl x
1.40 aaron 451: Disables X11 forwarding.
452: This can also be specified on a per-host basis in a configuration file.
1.2 deraadt 453: .It Fl X
1.1 deraadt 454: Enables X11 forwarding.
1.2 deraadt 455: .It Fl C
1.1 deraadt 456: Requests compression of all data (including stdin, stdout, stderr, and
1.40 aaron 457: data for forwarded X11 and TCP/IP connections).
458: The compression algorithm is the same used by
1.34 markus 459: .Xr gzip 1 ,
460: and the
1.2 deraadt 461: .Dq level
462: can be controlled by the
463: .Cm CompressionLevel
1.40 aaron 464: option (see below).
465: Compression is desirable on modem lines and other
1.1 deraadt 466: slow connections, but will only slow down things on fast networks.
467: The default value can be set on a host-by-host basis in the
468: configuration files; see the
1.2 deraadt 469: .Cm Compress
1.1 deraadt 470: option below.
1.2 deraadt 471: .It Fl L Ar port:host:hostport
1.1 deraadt 472: Specifies that the given port on the local (client) host is to be
1.40 aaron 473: forwarded to the given host and port on the remote side.
474: This works by allocating a socket to listen to
1.2 deraadt 475: .Ar port
1.1 deraadt 476: on the local side, and whenever a connection is made to this port, the
477: connection is forwarded over the secure channel, and a connection is
478: made to
1.32 markus 479: .Ar host
480: port
481: .Ar hostport
1.40 aaron 482: from the remote machine.
483: Port forwardings can also be specified in the configuration file.
484: Only root can forward privileged ports.
1.32 markus 485: IPv6 addresses can be specified with an alternative syntax:
486: .Ar port/host/hostport
1.2 deraadt 487: .It Fl R Ar port:host:hostport
1.1 deraadt 488: Specifies that the given port on the remote (server) host is to be
1.40 aaron 489: forwarded to the given host and port on the local side.
490: This works by allocating a socket to listen to
1.2 deraadt 491: .Ar port
1.1 deraadt 492: on the remote side, and whenever a connection is made to this port, the
493: connection is forwarded over the secure channel, and a connection is
494: made to
1.32 markus 495: .Ar host
496: port
497: .Ar hostport
1.40 aaron 498: from the local machine.
499: Port forwardings can also be specified in the configuration file.
500: Privileged ports can be forwarded only when
1.1 deraadt 501: logging in as root on the remote machine.
1.46 markus 502: .It Fl 2
503: Forces
504: .Nm
1.50 ! markus 505: to try protocol version 2 only.
1.32 markus 506: .It Fl 4
507: Forces
508: .Nm
509: to use IPv4 addresses only.
510: .It Fl 6
511: Forces
512: .Nm
513: to use IPv6 addresses only.
1.2 deraadt 514: .El
515: .Sh CONFIGURATION FILES
516: .Nm
1.1 deraadt 517: obtains configuration data from the following sources (in this order):
518: command line options, user's configuration file
1.2 deraadt 519: .Pq Pa $HOME/.ssh/config ,
520: and system-wide configuration file
521: .Pq Pa /etc/ssh_config .
522: For each parameter, the first obtained value
1.40 aaron 523: will be used.
524: The configuration files contain sections bracketed by
525: .Dq Host
526: specifications, and that section is only applied for hosts that
527: match one of the patterns given in the specification.
528: The matched host name is the one given on the command line.
1.2 deraadt 529: .Pp
1.1 deraadt 530: Since the first obtained value for each parameter is used, more
531: host-specific declarations should be given near the beginning of the
532: file, and general defaults at the end.
1.2 deraadt 533: .Pp
1.1 deraadt 534: The configuration file has the following format:
1.2 deraadt 535: .Pp
536: Empty lines and lines starting with
537: .Ql #
538: are comments.
539: .Pp
540: Otherwise a line is of the format
541: .Dq keyword arguments .
542: The possible
1.1 deraadt 543: keywords and their meanings are as follows (note that the
544: configuration files are case-sensitive):
1.2 deraadt 545: .Bl -tag -width Ds
546: .It Cm Host
1.1 deraadt 547: Restricts the following declarations (up to the next
1.2 deraadt 548: .Cm Host
1.1 deraadt 549: keyword) to be only for those hosts that match one of the patterns
1.2 deraadt 550: given after the keyword.
551: .Ql \&*
552: and
553: .Ql ?
554: can be used as wildcards in the
1.40 aaron 555: patterns.
556: A single
1.2 deraadt 557: .Ql \&*
558: as a pattern can be used to provide global
1.40 aaron 559: defaults for all hosts.
560: The host is the
1.2 deraadt 561: .Ar hostname
1.1 deraadt 562: argument given on the command line (i.e., the name is not converted to
563: a canonicalized host name before matching).
1.2 deraadt 564: .It Cm AFSTokenPassing
1.42 aaron 565: Specifies whether to pass AFS tokens to remote host.
566: The argument to this keyword must be
1.2 deraadt 567: .Dq yes
568: or
569: .Dq no .
570: .It Cm BatchMode
571: If set to
572: .Dq yes ,
1.40 aaron 573: passphrase/password querying will be disabled.
574: This option is useful in scripts and other batch jobs where you have no
575: user to supply the password.
576: The argument must be
1.2 deraadt 577: .Dq yes
578: or
579: .Dq no .
1.34 markus 580: .It Cm CheckHostIP
581: If this flag is set to
582: .Dq yes ,
583: ssh will additionally check the host ip address in the
584: .Pa known_hosts
1.42 aaron 585: file.
586: This allows ssh to detect if a host key changed due to DNS spoofing.
1.34 markus 587: If the option is set to
588: .Dq no ,
589: the check will not be executed.
1.2 deraadt 590: .It Cm Cipher
1.40 aaron 591: Specifies the cipher to use for encrypting the session.
592: Currently,
1.2 deraadt 593: .Dq blowfish ,
1.1 deraadt 594: and
1.10 provos 595: .Dq 3des
1.40 aaron 596: are supported.
597: The default is
1.2 deraadt 598: .Dq 3des .
1.45 markus 599: .It Cm Ciphers
600: Specifies the ciphers allowed for protocol version 2
601: in order of preference.
602: Multiple ciphers must be comma-separated.
603: The default is
604: .Dq blowfish-cbc,3des-cbc,arcfour,cast128-cbc .
1.2 deraadt 605: .It Cm Compression
1.40 aaron 606: Specifies whether to use compression.
607: The argument must be
1.2 deraadt 608: .Dq yes
609: or
610: .Dq no .
611: .It Cm CompressionLevel
1.40 aaron 612: Specifies the compression level to use if compression is enable.
613: The argument must be an integer from 1 (fast) to 9 (slow, best).
614: The default level is 6, which is good for most applications.
615: The meaning of the values is the same as in
1.34 markus 616: .Xr gzip 1 .
1.2 deraadt 617: .It Cm ConnectionAttempts
1.1 deraadt 618: Specifies the number of tries (one per second) to make before falling
1.40 aaron 619: back to rsh or exiting.
620: The argument must be an integer.
621: This may be useful in scripts if the connection sometimes fails.
1.50 ! markus 622: .It Cm DSAAuthentication
! 623: Specifies whether to try DSA authentication.
! 624: The argument to this keyword must be
! 625: .Dq yes
! 626: or
! 627: .Dq no .
! 628: DSA authentication will only be
! 629: attempted if a DSA identity file exists.
! 630: Note that this option applies to protocol version 2 only.
1.2 deraadt 631: .It Cm EscapeChar
632: Sets the escape character (default:
633: .Ql ~ ) .
634: The escape character can also
1.40 aaron 635: be set on the command line.
636: The argument should be a single character,
1.2 deraadt 637: .Ql ^
638: followed by a letter, or
639: .Dq none
640: to disable the escape
1.1 deraadt 641: character entirely (making the connection transparent for binary
642: data).
1.44 aaron 643: .It Cm FallBackToRsh
1.1 deraadt 644: Specifies that if connecting via
1.2 deraadt 645: .Nm
1.1 deraadt 646: fails due to a connection refused error (there is no
1.2 deraadt 647: .Xr sshd 8
1.44 aaron 648: listening on the remote host),
1.2 deraadt 649: .Xr rsh 1
1.1 deraadt 650: should automatically be used instead (after a suitable warning about
1.40 aaron 651: the session being unencrypted).
652: The argument must be
1.2 deraadt 653: .Dq yes
654: or
655: .Dq no .
656: .It Cm ForwardAgent
1.1 deraadt 657: Specifies whether the connection to the authentication agent (if any)
1.40 aaron 658: will be forwarded to the remote machine.
659: The argument must be
1.2 deraadt 660: .Dq yes
661: or
662: .Dq no .
663: .It Cm ForwardX11
1.1 deraadt 664: Specifies whether X11 connections will be automatically redirected
1.44 aaron 665: over the secure channel and
1.2 deraadt 666: .Ev DISPLAY
1.40 aaron 667: set.
1.44 aaron 668: The argument must be
1.2 deraadt 669: .Dq yes
670: or
1.38 markus 671: .Dq no .
672: The default is
1.3 deraadt 673: .Dq no .
674: .It Cm GatewayPorts
675: Specifies whether remote hosts are allowed to connect to local
676: forwarded ports.
677: The argument must be
678: .Dq yes
679: or
680: .Dq no .
681: The default is
1.2 deraadt 682: .Dq no .
683: .It Cm GlobalKnownHostsFile
1.44 aaron 684: Specifies a file to use instead of
1.2 deraadt 685: .Pa /etc/ssh_known_hosts .
686: .It Cm HostName
1.40 aaron 687: Specifies the real host name to log into.
688: This can be used to specify nicknames or abbreviations for hosts.
689: Default is the name given on the command line.
690: Numeric IP addresses are also permitted (both on the command line and in
1.2 deraadt 691: .Cm HostName
1.1 deraadt 692: specifications).
1.2 deraadt 693: .It Cm IdentityFile
1.1 deraadt 694: Specifies the file from which the user's RSA authentication identity
1.2 deraadt 695: is read (default
1.49 markus 696: .Pa $HOME/.ssh/identity
1.2 deraadt 697: in the user's home directory).
1.1 deraadt 698: Additionally, any identities represented by the authentication agent
1.40 aaron 699: will be used for authentication.
700: The file name may use the tilde
701: syntax to refer to a user's home directory.
702: It is possible to have
1.1 deraadt 703: multiple identity files specified in configuration files; all these
704: identities will be tried in sequence.
1.48 markus 705: .It Cm IdentityFile2
706: Specifies the file from which the user's DSA authentication identity
707: is read (default
1.49 markus 708: .Pa $HOME/.ssh/id_dsa
1.48 markus 709: in the user's home directory).
710: The file name may use the tilde
711: syntax to refer to a user's home directory.
712: It is possible to have
713: multiple identity files specified in configuration files; all these
714: identities will be tried in sequence.
1.2 deraadt 715: .It Cm KeepAlive
1.1 deraadt 716: Specifies whether the system should send keepalive messages to the
1.40 aaron 717: other side.
718: If they are sent, death of the connection or crash of one
719: of the machines will be properly noticed.
720: However, this means that
1.1 deraadt 721: connections will die if the route is down temporarily, and some people
1.41 aaron 722: find it annoying.
1.2 deraadt 723: .Pp
724: The default is
725: .Dq yes
726: (to send keepalives), and the client will notice
1.40 aaron 727: if the network goes down or the remote host dies.
728: This is important in scripts, and many users want it too.
1.2 deraadt 729: .Pp
730: To disable keepalives, the value should be set to
731: .Dq no
732: in both the server and the client configuration files.
733: .It Cm KerberosAuthentication
1.42 aaron 734: Specifies whether Kerberos authentication will be used.
735: The argument to this keyword must be
1.4 dugsong 736: .Dq yes
737: or
738: .Dq no .
1.2 deraadt 739: .It Cm KerberosTgtPassing
1.42 aaron 740: Specifies whether a Kerberos TGT will be forwarded to the server.
741: This will only work if the Kerberos server is actually an AFS kaserver.
742: The argument to this keyword must be
1.4 dugsong 743: .Dq yes
744: or
745: .Dq no .
1.2 deraadt 746: .It Cm LocalForward
1.1 deraadt 747: Specifies that a TCP/IP port on the local machine be forwarded over
1.40 aaron 748: the secure channel to given host:port from the remote machine.
749: The first argument must be a port number, and the second must be
750: host:port.
751: Multiple forwardings may be specified, and additional
752: forwardings can be given on the command line.
753: Only the superuser can forward privileged ports.
1.24 markus 754: .It Cm LogLevel
755: Gives the verbosity level that is used when logging messages from
756: .Nm ssh .
757: The possible values are:
1.39 djm 758: QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG.
1.24 markus 759: The default is INFO.
1.14 dugsong 760: .It Cm NumberOfPasswordPrompts
1.42 aaron 761: Specifies the number of password prompts before giving up.
762: The argument to this keyword must be an integer.
763: Default is 3.
1.34 markus 764: .It Cm PasswordAuthentication
1.40 aaron 765: Specifies whether to use password authentication.
766: The argument to this keyword must be
1.34 markus 767: .Dq yes
768: or
769: .Dq no .
1.50 ! markus 770: Note that this option applies to both protocol version 1 and 2.
1.2 deraadt 771: .It Cm Port
1.40 aaron 772: Specifies the port number to connect on the remote host.
773: Default is 22.
1.45 markus 774: .It Cm Protocol
775: Specifies the protocol versions
776: .Nm
777: should support in order of preference.
778: The possible values are
779: .Dq 1
780: and
781: .Dq 2 .
782: Multiple versions must be comma-separated.
783: The default is
1.49 markus 784: .Dq 1,2 .
785: This means that
786: .Nm
787: tries version 1 and falls back to version 2
788: if version 1 is no available.
1.2 deraadt 789: .It Cm ProxyCommand
1.40 aaron 790: Specifies the command to use to connect to the server.
791: The command
792: string extends to the end of the line, and is executed with
793: .Pa /bin/sh .
794: In the command string,
795: .Ql %h
796: will be substituted by the host name to
797: connect and
798: .Ql %p
799: by the port.
800: The command can be basically anything,
801: and should read from its standard input and write to its standard output.
802: It should eventually connect an
1.2 deraadt 803: .Xr sshd 8
1.1 deraadt 804: server running on some machine, or execute
1.2 deraadt 805: .Ic sshd -i
1.40 aaron 806: somewhere.
807: Host key management will be done using the
1.1 deraadt 808: HostName of the host being connected (defaulting to the name typed by
809: the user).
1.29 markus 810: Note that
811: .Cm CheckHostIP
812: is not available for connects with a proxy command.
1.2 deraadt 813: .Pp
814: .It Cm RemoteForward
1.1 deraadt 815: Specifies that a TCP/IP port on the remote machine be forwarded over
1.40 aaron 816: the secure channel to given host:port from the local machine.
817: The first argument must be a port number, and the second must be
818: host:port.
819: Multiple forwardings may be specified, and additional
820: forwardings can be given on the command line.
821: Only the superuser can forward privileged ports.
1.2 deraadt 822: .It Cm RhostsAuthentication
1.40 aaron 823: Specifies whether to try rhosts based authentication.
824: Note that this
1.1 deraadt 825: declaration only affects the client side and has no effect whatsoever
1.40 aaron 826: on security.
827: Disabling rhosts authentication may reduce
1.1 deraadt 828: authentication time on slow connections when rhosts authentication is
1.40 aaron 829: not used.
830: Most servers do not permit RhostsAuthentication because it
831: is not secure (see RhostsRSAAuthentication).
832: The argument to this keyword must be
1.2 deraadt 833: .Dq yes
834: or
835: .Dq no .
836: .It Cm RhostsRSAAuthentication
1.1 deraadt 837: Specifies whether to try rhosts based authentication with RSA host
1.40 aaron 838: authentication.
839: This is the primary authentication method for most sites.
840: The argument must be
1.2 deraadt 841: .Dq yes
842: or
843: .Dq no .
844: .It Cm RSAAuthentication
1.40 aaron 845: Specifies whether to try RSA authentication.
846: The argument to this keyword must be
1.2 deraadt 847: .Dq yes
848: or
849: .Dq no .
1.1 deraadt 850: RSA authentication will only be
851: attempted if the identity file exists, or an authentication agent is
852: running.
1.50 ! markus 853: Note that this option applies to protocol version 1 only.
1.27 markus 854: .It Cm SkeyAuthentication
855: Specifies whether to use
856: .Xr skey 1
1.40 aaron 857: authentication.
858: The argument to this keyword must be
1.27 markus 859: .Dq yes
860: or
861: .Dq no .
862: The default is
863: .Dq no .
1.2 deraadt 864: .It Cm StrictHostKeyChecking
865: If this flag is set to
1.44 aaron 866: .Dq yes ,
1.2 deraadt 867: .Nm
1.1 deraadt 868: ssh will never automatically add host keys to the
1.2 deraadt 869: .Pa $HOME/.ssh/known_hosts
1.48 markus 870: and
871: .Pa $HOME/.ssh/known_hosts2
872: files, and refuses to connect hosts whose host key has changed.
1.40 aaron 873: This provides maximum protection against trojan horse attacks.
874: However, it can be somewhat annoying if you don't have good
1.2 deraadt 875: .Pa /etc/ssh_known_hosts
1.48 markus 876: and
877: .Pa /etc/ssh_known_hosts2
1.1 deraadt 878: files installed and frequently
1.40 aaron 879: connect new hosts.
880: Basically this option forces the user to manually
881: add any new hosts.
882: Normally this option is disabled, and new hosts
883: will automatically be added to the known host files.
884: The host keys of
885: known hosts will be verified automatically in either case.
886: The argument must be
1.2 deraadt 887: .Dq yes
888: or
889: .Dq no .
1.16 markus 890: .It Cm UsePrivilegedPort
891: Specifies whether to use a privileged port for outgoing connections.
892: The argument must be
893: .Dq yes
894: or
895: .Dq no .
896: The default is
897: .Dq yes .
898: Note that setting this option to
899: .Dq no
1.30 provos 900: turns off
1.16 markus 901: .Cm RhostsAuthentication
902: and
903: .Cm RhostsRSAAuthentication .
1.34 markus 904: .It Cm User
1.40 aaron 905: Specifies the user to log in as.
906: This can be useful if you have a different user name on different machines.
907: This saves the trouble of
1.34 markus 908: having to remember to give the user name on the command line.
909: .It Cm UserKnownHostsFile
910: Specifies a file to use instead of
911: .Pa $HOME/.ssh/known_hosts .
1.2 deraadt 912: .It Cm UseRsh
1.40 aaron 913: Specifies that rlogin/rsh should be used for this host.
914: It is possible that the host does not at all support the
1.2 deraadt 915: .Nm
1.40 aaron 916: protocol.
917: This causes
1.2 deraadt 918: .Nm
1.40 aaron 919: to immediately execute
1.2 deraadt 920: .Xr rsh 1 .
1.1 deraadt 921: All other options (except
1.2 deraadt 922: .Cm HostName )
1.40 aaron 923: are ignored if this has been specified.
924: The argument must be
1.2 deraadt 925: .Dq yes
926: or
927: .Dq no .
928: .Sh ENVIRONMENT
929: .Nm
1.1 deraadt 930: will normally set the following environment variables:
1.2 deraadt 931: .Bl -tag -width Ds
932: .It Ev DISPLAY
933: The
934: .Ev DISPLAY
1.40 aaron 935: variable indicates the location of the X11 server.
1.44 aaron 936: It is automatically set by
1.2 deraadt 937: .Nm
938: to point to a value of the form
939: .Dq hostname:n
940: where hostname indicates
1.40 aaron 941: the host where the shell runs, and n is an integer >= 1.
942: .Nm
943: uses this special value to forward X11 connections over the secure
944: channel.
945: The user should normally not set DISPLAY explicitly, as that
1.1 deraadt 946: will render the X11 connection insecure (and will require the user to
947: manually copy any required authorization cookies).
1.2 deraadt 948: .It Ev HOME
1.1 deraadt 949: Set to the path of the user's home directory.
1.2 deraadt 950: .It Ev LOGNAME
951: Synonym for
1.12 aaron 952: .Ev USER ;
953: set for compatibility with systems that use this variable.
1.2 deraadt 954: .It Ev MAIL
1.1 deraadt 955: Set to point the user's mailbox.
1.40 aaron 956: .It Ev PATH
1.2 deraadt 957: Set to the default
958: .Ev PATH ,
959: as specified when compiling
1.12 aaron 960: .Nm ssh .
1.18 markus 961: .It Ev SSH_AUTH_SOCK
1.17 markus 962: indicates the path of a unix-domain socket used to communicate with the
963: agent.
1.2 deraadt 964: .It Ev SSH_CLIENT
1.40 aaron 965: Identifies the client end of the connection.
966: The variable contains
1.1 deraadt 967: three space-separated values: client ip-address, client port number,
968: and server port number.
1.2 deraadt 969: .It Ev SSH_TTY
1.1 deraadt 970: This is set to the name of the tty (path to the device) associated
1.40 aaron 971: with the current shell or command.
972: If the current session has no tty,
1.1 deraadt 973: this variable is not set.
1.2 deraadt 974: .It Ev TZ
1.1 deraadt 975: The timezone variable is set to indicate the present timezone if it
976: was set when the daemon was started (e.i., the daemon passes the value
977: on to new connections).
1.2 deraadt 978: .It Ev USER
1.1 deraadt 979: Set to the name of the user logging in.
1.2 deraadt 980: .El
981: .Pp
1.44 aaron 982: Additionally,
1.2 deraadt 983: .Nm
1.44 aaron 984: reads
985: .Pa $HOME/.ssh/environment ,
1.2 deraadt 986: and adds lines of the format
987: .Dq VARNAME=value
1.12 aaron 988: to the environment.
1.2 deraadt 989: .Sh FILES
1.36 markus 990: .Bl -tag -width Ds
1.2 deraadt 991: .It Pa $HOME/.ssh/known_hosts
1.1 deraadt 992: Records host keys for all hosts the user has logged into (that are not
1.2 deraadt 993: in
994: .Pa /etc/ssh_known_hosts ) .
995: See
996: .Xr sshd 8 .
1.48 markus 997: .It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa
998: Contains the RSA and the DSA authentication identity of the user.
999: These files
1000: contain sensitive data and should be readable by the user but not
1.15 markus 1001: accessible by others (read/write/execute).
1002: Note that
1003: .Nm
1.48 markus 1004: ignores a private key file if it is accessible by others.
1.15 markus 1005: It is possible to specify a passphrase when
1.1 deraadt 1006: generating the key; the passphrase will be used to encrypt the
1.8 deraadt 1007: sensitive part of this file using 3DES.
1.48 markus 1008: .It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub
1.1 deraadt 1009: Contains the public key for authentication (public part of the
1.40 aaron 1010: identity file in human-readable form).
1.48 markus 1011: The contents of the
1012: .Pa $HOME/.ssh/identity.pub
1013: file should be added to
1.2 deraadt 1014: .Pa $HOME/.ssh/authorized_keys
1015: on all machines
1.40 aaron 1016: where you wish to log in using RSA authentication.
1.48 markus 1017: The contents of the
1018: .Pa $HOME/.ssh/id_dsa.pub
1019: file should be added to
1020: .Pa $HOME/.ssh/authorized_keys2
1021: on all machines
1022: where you wish to log in using DSA authentication.
1023: These files are not
1.40 aaron 1024: sensitive and can (but need not) be readable by anyone.
1.48 markus 1025: These files are
1026: never used automatically and are not necessary; they is only provided for
1.1 deraadt 1027: the convenience of the user.
1.2 deraadt 1028: .It Pa $HOME/.ssh/config
1.40 aaron 1029: This is the per-user configuration file.
1030: The format of this file is described above.
1031: This file is used by the
1.2 deraadt 1032: .Nm
1.40 aaron 1033: client.
1034: This file does not usually contain any sensitive information,
1.1 deraadt 1035: but the recommended permissions are read/write for the user, and not
1036: accessible by others.
1.2 deraadt 1037: .It Pa $HOME/.ssh/authorized_keys
1.40 aaron 1038: Lists the RSA keys that can be used for logging in as this user.
1039: The format of this file is described in the
1.2 deraadt 1040: .Xr sshd 8
1.40 aaron 1041: manual page.
1042: In the simplest form the format is the same as the .pub
1.1 deraadt 1043: identity files (that is, each line contains the number of bits in
1044: modulus, public exponent, modulus, and comment fields, separated by
1.40 aaron 1045: spaces).
1046: This file is not highly sensitive, but the recommended
1.1 deraadt 1047: permissions are read/write for the user, and not accessible by others.
1.48 markus 1048: .It Pa $HOME/.ssh/authorized_keys2
1049: Lists the DSA keys that can be used for logging in as this user.
1050: This file is not highly sensitive, but the recommended
1051: permissions are read/write for the user, and not accessible by others.
1052: .It Pa /etc/ssh_known_hosts, /etc/ssh_known_hosts2
1.40 aaron 1053: Systemwide list of known host keys.
1.48 markus 1054: .Pa /etc/ssh_known_hosts
1055: contains RSA and
1056: .Pa /etc/ssh_known_hosts2
1057: contains DSA keys.
1058: These files should be prepared by the
1.1 deraadt 1059: system administrator to contain the public host keys of all machines in the
1.40 aaron 1060: organization.
1061: This file should be world-readable.
1062: This file contains
1.1 deraadt 1063: public keys, one per line, in the following format (fields separated
1064: by spaces): system name, number of bits in modulus, public exponent,
1.40 aaron 1065: modulus, and optional comment field.
1066: When different names are used
1.1 deraadt 1067: for the same machine, all such names should be listed, separated by
1.40 aaron 1068: commas.
1069: The format is described on the
1.2 deraadt 1070: .Xr sshd 8
1.1 deraadt 1071: manual page.
1.2 deraadt 1072: .Pp
1.1 deraadt 1073: The canonical system name (as returned by name servers) is used by
1.2 deraadt 1074: .Xr sshd 8
1.1 deraadt 1075: to verify the client host when logging in; other names are needed because
1.2 deraadt 1076: .Nm
1.1 deraadt 1077: does not convert the user-supplied name to a canonical name before
1078: checking the key, because someone with access to the name servers
1079: would then be able to fool host authentication.
1.2 deraadt 1080: .It Pa /etc/ssh_config
1.40 aaron 1081: Systemwide configuration file.
1082: This file provides defaults for those
1.1 deraadt 1083: values that are not specified in the user's configuration file, and
1.40 aaron 1084: for those users who do not have a configuration file.
1085: This file must be world-readable.
1.2 deraadt 1086: .It Pa $HOME/.rhosts
1087: This file is used in
1088: .Pa \&.rhosts
1089: authentication to list the
1.40 aaron 1090: host/user pairs that are permitted to log in.
1091: (Note that this file is
1.1 deraadt 1092: also used by rlogin and rsh, which makes using this file insecure.)
1093: Each line of the file contains a host name (in the canonical form
1094: returned by name servers), and then a user name on that host,
1.40 aaron 1095: separated by a space.
1096: One some machines this file may need to be
1.1 deraadt 1097: world-readable if the user's home directory is on a NFS partition,
1098: because
1.2 deraadt 1099: .Xr sshd 8
1.40 aaron 1100: reads it as root.
1101: Additionally, this file must be owned by the user,
1102: and must not have write permissions for anyone else.
1103: The recommended
1.1 deraadt 1104: permission for most machines is read/write for the user, and not
1105: accessible by others.
1.2 deraadt 1106: .Pp
1.1 deraadt 1107: Note that by default
1.2 deraadt 1108: .Xr sshd 8
1.1 deraadt 1109: will be installed so that it requires successful RSA host
1.40 aaron 1110: authentication before permitting \s+2.\s0rhosts authentication.
1111: If your server machine does not have the client's host key in
1.2 deraadt 1112: .Pa /etc/ssh_known_hosts ,
1113: you can store it in
1114: .Pa $HOME/.ssh/known_hosts .
1115: The easiest way to do this is to
1.1 deraadt 1116: connect back to the client from the server machine using ssh; this
1.48 markus 1117: will automatically add the host key to
1.2 deraadt 1118: .Pa $HOME/.ssh/known_hosts .
1119: .It Pa $HOME/.shosts
1120: This file is used exactly the same way as
1121: .Pa \&.rhosts .
1122: The purpose for
1.1 deraadt 1123: having this file is to be able to use rhosts authentication with
1.2 deraadt 1124: .Nm
1125: without permitting login with
1126: .Xr rlogin 1
1127: or
1128: .Xr rsh 1 .
1129: .It Pa /etc/hosts.equiv
1130: This file is used during
1.40 aaron 1131: .Pa \&.rhosts authentication.
1132: It contains
1.1 deraadt 1133: canonical hosts names, one per line (the full format is described on
1134: the
1.2 deraadt 1135: .Xr sshd 8
1.40 aaron 1136: manual page).
1137: If the client host is found in this file, login is
1.1 deraadt 1138: automatically permitted provided client and server user names are the
1.40 aaron 1139: same.
1140: Additionally, successful RSA host authentication is normally
1141: required.
1142: This file should only be writable by root.
1.2 deraadt 1143: .It Pa /etc/shosts.equiv
1.44 aaron 1144: This file is processed exactly as
1.2 deraadt 1145: .Pa /etc/hosts.equiv .
1.1 deraadt 1146: This file may be useful to permit logins using
1.2 deraadt 1147: .Nm
1.1 deraadt 1148: but not using rsh/rlogin.
1.2 deraadt 1149: .It Pa /etc/sshrc
1.1 deraadt 1150: Commands in this file are executed by
1.2 deraadt 1151: .Nm
1.1 deraadt 1152: when the user logs in just before the user's shell (or command) is started.
1153: See the
1.2 deraadt 1154: .Xr sshd 8
1.1 deraadt 1155: manual page for more information.
1.2 deraadt 1156: .It Pa $HOME/.ssh/rc
1.1 deraadt 1157: Commands in this file are executed by
1.2 deraadt 1158: .Nm
1.1 deraadt 1159: when the user logs in just before the user's shell (or command) is
1160: started.
1.44 aaron 1161: See the
1.2 deraadt 1162: .Xr sshd 8
1.1 deraadt 1163: manual page for more information.
1.31 markus 1164: .It Pa $HOME/.ssh/environment
1165: Contains additional definitions for environment variables, see section
1166: .Sx ENVIRONMENT
1167: above.
1.5 deraadt 1168: .It Pa libcrypto.so.X.1
1169: A version of this library which includes support for the RSA algorithm
1170: is required for proper operation.
1.2 deraadt 1171: .Sh AUTHOR
1.20 provos 1172: OpenSSH
1.37 deraadt 1173: is a derivative of the original (free) ssh 1.2.12 release by Tatu Ylonen,
1.40 aaron 1174: but with bugs removed and newer features re-added.
1175: Rapidly after the
1.37 deraadt 1176: 1.2.12 release, newer versions of the original ssh bore successively
1177: more restrictive licenses, and thus demand for a free version was born.
1.47 markus 1178: .Pp
1.37 deraadt 1179: This version of OpenSSH
1.20 provos 1180: .Bl -bullet
1181: .It
1.35 aaron 1182: has all components of a restrictive nature (i.e., patents, see
1.21 deraadt 1183: .Xr ssl 8 )
1184: directly removed from the source code; any licensed or patented components
1185: are chosen from
1186: external libraries.
1.20 provos 1187: .It
1.47 markus 1188: has been updated to support SSH protocol 1.5 and 2, making it compatible with
1189: all other SSH clients and servers.
1.20 provos 1190: .It
1.44 aaron 1191: contains added support for
1.20 provos 1192: .Xr kerberos 8
1193: authentication and ticket passing.
1194: .It
1.21 deraadt 1195: supports one-time password authentication with
1.20 provos 1196: .Xr skey 1 .
1197: .El
1198: .Pp
1199: The libraries described in
1.5 deraadt 1200: .Xr ssl 8
1201: are required for proper operation.
1.25 provos 1202: .Pp
1.26 aaron 1203: OpenSSH has been created by Aaron Campbell, Bob Beck, Markus Friedl,
1.25 provos 1204: Niels Provos, Theo de Raadt, and Dug Song.
1.47 markus 1205: .Pp
1206: The support for SSH protocol 2 was written by Markus Friedl.
1.2 deraadt 1207: .Sh SEE ALSO
1208: .Xr rlogin 1 ,
1209: .Xr rsh 1 ,
1210: .Xr scp 1 ,
1211: .Xr ssh-add 1 ,
1212: .Xr ssh-agent 1 ,
1213: .Xr ssh-keygen 1 ,
1214: .Xr telnet 1 ,
1.5 deraadt 1215: .Xr sshd 8 ,
1216: .Xr ssl 8
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