Annotation of src/usr.bin/ssh/ssh.1, Revision 1.49
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: .\"
1.49 ! markus 12: .\" $Id: ssh.1,v 1.48 2000/05/03 18:04:39 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
505: to use 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.
1.2 deraadt 622: .It Cm EscapeChar
623: Sets the escape character (default:
624: .Ql ~ ) .
625: The escape character can also
1.40 aaron 626: be set on the command line.
627: The argument should be a single character,
1.2 deraadt 628: .Ql ^
629: followed by a letter, or
630: .Dq none
631: to disable the escape
1.1 deraadt 632: character entirely (making the connection transparent for binary
633: data).
1.44 aaron 634: .It Cm FallBackToRsh
1.1 deraadt 635: Specifies that if connecting via
1.2 deraadt 636: .Nm
1.1 deraadt 637: fails due to a connection refused error (there is no
1.2 deraadt 638: .Xr sshd 8
1.44 aaron 639: listening on the remote host),
1.2 deraadt 640: .Xr rsh 1
1.1 deraadt 641: should automatically be used instead (after a suitable warning about
1.40 aaron 642: the session being unencrypted).
643: The argument must be
1.2 deraadt 644: .Dq yes
645: or
646: .Dq no .
647: .It Cm ForwardAgent
1.1 deraadt 648: Specifies whether the connection to the authentication agent (if any)
1.40 aaron 649: will be forwarded to the remote machine.
650: The argument must be
1.2 deraadt 651: .Dq yes
652: or
653: .Dq no .
654: .It Cm ForwardX11
1.1 deraadt 655: Specifies whether X11 connections will be automatically redirected
1.44 aaron 656: over the secure channel and
1.2 deraadt 657: .Ev DISPLAY
1.40 aaron 658: set.
1.44 aaron 659: The argument must be
1.2 deraadt 660: .Dq yes
661: or
1.38 markus 662: .Dq no .
663: The default is
1.3 deraadt 664: .Dq no .
665: .It Cm GatewayPorts
666: Specifies whether remote hosts are allowed to connect to local
667: forwarded ports.
668: The argument must be
669: .Dq yes
670: or
671: .Dq no .
672: The default is
1.2 deraadt 673: .Dq no .
674: .It Cm GlobalKnownHostsFile
1.44 aaron 675: Specifies a file to use instead of
1.2 deraadt 676: .Pa /etc/ssh_known_hosts .
677: .It Cm HostName
1.40 aaron 678: Specifies the real host name to log into.
679: This can be used to specify nicknames or abbreviations for hosts.
680: Default is the name given on the command line.
681: Numeric IP addresses are also permitted (both on the command line and in
1.2 deraadt 682: .Cm HostName
1.1 deraadt 683: specifications).
1.2 deraadt 684: .It Cm IdentityFile
1.1 deraadt 685: Specifies the file from which the user's RSA authentication identity
1.2 deraadt 686: is read (default
1.49 ! markus 687: .Pa $HOME/.ssh/identity
1.2 deraadt 688: in the user's home directory).
1.1 deraadt 689: Additionally, any identities represented by the authentication agent
1.40 aaron 690: will be used for authentication.
691: The file name may use the tilde
692: syntax to refer to a user's home directory.
693: It is possible to have
1.1 deraadt 694: multiple identity files specified in configuration files; all these
695: identities will be tried in sequence.
1.48 markus 696: .It Cm IdentityFile2
697: Specifies the file from which the user's DSA authentication identity
698: is read (default
1.49 ! markus 699: .Pa $HOME/.ssh/id_dsa
1.48 markus 700: in the user's home directory).
701: The file name may use the tilde
702: syntax to refer to a user's home directory.
703: It is possible to have
704: multiple identity files specified in configuration files; all these
705: identities will be tried in sequence.
1.2 deraadt 706: .It Cm KeepAlive
1.1 deraadt 707: Specifies whether the system should send keepalive messages to the
1.40 aaron 708: other side.
709: If they are sent, death of the connection or crash of one
710: of the machines will be properly noticed.
711: However, this means that
1.1 deraadt 712: connections will die if the route is down temporarily, and some people
1.41 aaron 713: find it annoying.
1.2 deraadt 714: .Pp
715: The default is
716: .Dq yes
717: (to send keepalives), and the client will notice
1.40 aaron 718: if the network goes down or the remote host dies.
719: This is important in scripts, and many users want it too.
1.2 deraadt 720: .Pp
721: To disable keepalives, the value should be set to
722: .Dq no
723: in both the server and the client configuration files.
724: .It Cm KerberosAuthentication
1.42 aaron 725: Specifies whether Kerberos authentication will be used.
726: The argument to this keyword must be
1.4 dugsong 727: .Dq yes
728: or
729: .Dq no .
1.2 deraadt 730: .It Cm KerberosTgtPassing
1.42 aaron 731: Specifies whether a Kerberos TGT will be forwarded to the server.
732: This will only work if the Kerberos server is actually an AFS kaserver.
733: The argument to this keyword must be
1.4 dugsong 734: .Dq yes
735: or
736: .Dq no .
1.2 deraadt 737: .It Cm LocalForward
1.1 deraadt 738: Specifies that a TCP/IP port on the local machine be forwarded over
1.40 aaron 739: the secure channel to given host:port from the remote machine.
740: The first argument must be a port number, and the second must be
741: host:port.
742: Multiple forwardings may be specified, and additional
743: forwardings can be given on the command line.
744: Only the superuser can forward privileged ports.
1.24 markus 745: .It Cm LogLevel
746: Gives the verbosity level that is used when logging messages from
747: .Nm ssh .
748: The possible values are:
1.39 djm 749: QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG.
1.24 markus 750: The default is INFO.
1.14 dugsong 751: .It Cm NumberOfPasswordPrompts
1.42 aaron 752: Specifies the number of password prompts before giving up.
753: The argument to this keyword must be an integer.
754: Default is 3.
1.34 markus 755: .It Cm PasswordAuthentication
1.40 aaron 756: Specifies whether to use password authentication.
757: The argument to this keyword must be
1.34 markus 758: .Dq yes
759: or
760: .Dq no .
1.2 deraadt 761: .It Cm Port
1.40 aaron 762: Specifies the port number to connect on the remote host.
763: Default is 22.
1.45 markus 764: .It Cm Protocol
765: Specifies the protocol versions
766: .Nm
767: should support in order of preference.
768: The possible values are
769: .Dq 1
770: and
771: .Dq 2 .
772: Multiple versions must be comma-separated.
773: The default is
1.49 ! markus 774: .Dq 1,2 .
! 775: This means that
! 776: .Nm
! 777: tries version 1 and falls back to version 2
! 778: if version 1 is no available.
1.2 deraadt 779: .It Cm ProxyCommand
1.40 aaron 780: Specifies the command to use to connect to the server.
781: The command
782: string extends to the end of the line, and is executed with
783: .Pa /bin/sh .
784: In the command string,
785: .Ql %h
786: will be substituted by the host name to
787: connect and
788: .Ql %p
789: by the port.
790: The command can be basically anything,
791: and should read from its standard input and write to its standard output.
792: It should eventually connect an
1.2 deraadt 793: .Xr sshd 8
1.1 deraadt 794: server running on some machine, or execute
1.2 deraadt 795: .Ic sshd -i
1.40 aaron 796: somewhere.
797: Host key management will be done using the
1.1 deraadt 798: HostName of the host being connected (defaulting to the name typed by
799: the user).
1.29 markus 800: Note that
801: .Cm CheckHostIP
802: is not available for connects with a proxy command.
1.2 deraadt 803: .Pp
804: .It Cm RemoteForward
1.1 deraadt 805: Specifies that a TCP/IP port on the remote machine be forwarded over
1.40 aaron 806: the secure channel to given host:port from the local machine.
807: The first argument must be a port number, and the second must be
808: host:port.
809: Multiple forwardings may be specified, and additional
810: forwardings can be given on the command line.
811: Only the superuser can forward privileged ports.
1.2 deraadt 812: .It Cm RhostsAuthentication
1.40 aaron 813: Specifies whether to try rhosts based authentication.
814: Note that this
1.1 deraadt 815: declaration only affects the client side and has no effect whatsoever
1.40 aaron 816: on security.
817: Disabling rhosts authentication may reduce
1.1 deraadt 818: authentication time on slow connections when rhosts authentication is
1.40 aaron 819: not used.
820: Most servers do not permit RhostsAuthentication because it
821: is not secure (see RhostsRSAAuthentication).
822: The argument to this keyword must be
1.2 deraadt 823: .Dq yes
824: or
825: .Dq no .
826: .It Cm RhostsRSAAuthentication
1.1 deraadt 827: Specifies whether to try rhosts based authentication with RSA host
1.40 aaron 828: authentication.
829: This is the primary authentication method for most sites.
830: The argument must be
1.2 deraadt 831: .Dq yes
832: or
833: .Dq no .
834: .It Cm RSAAuthentication
1.40 aaron 835: Specifies whether to try RSA authentication.
836: The argument to this keyword must be
1.2 deraadt 837: .Dq yes
838: or
839: .Dq no .
1.1 deraadt 840: RSA authentication will only be
841: attempted if the identity file exists, or an authentication agent is
842: running.
1.27 markus 843: .It Cm SkeyAuthentication
844: Specifies whether to use
845: .Xr skey 1
1.40 aaron 846: authentication.
847: The argument to this keyword must be
1.27 markus 848: .Dq yes
849: or
850: .Dq no .
851: The default is
852: .Dq no .
1.2 deraadt 853: .It Cm StrictHostKeyChecking
854: If this flag is set to
1.44 aaron 855: .Dq yes ,
1.2 deraadt 856: .Nm
1.1 deraadt 857: ssh will never automatically add host keys to the
1.2 deraadt 858: .Pa $HOME/.ssh/known_hosts
1.48 markus 859: and
860: .Pa $HOME/.ssh/known_hosts2
861: files, and refuses to connect hosts whose host key has changed.
1.40 aaron 862: This provides maximum protection against trojan horse attacks.
863: However, it can be somewhat annoying if you don't have good
1.2 deraadt 864: .Pa /etc/ssh_known_hosts
1.48 markus 865: and
866: .Pa /etc/ssh_known_hosts2
1.1 deraadt 867: files installed and frequently
1.40 aaron 868: connect new hosts.
869: Basically this option forces the user to manually
870: add any new hosts.
871: Normally this option is disabled, and new hosts
872: will automatically be added to the known host files.
873: The host keys of
874: known hosts will be verified automatically in either case.
875: The argument must be
1.2 deraadt 876: .Dq yes
877: or
878: .Dq no .
1.16 markus 879: .It Cm UsePrivilegedPort
880: Specifies whether to use a privileged port for outgoing connections.
881: The argument must be
882: .Dq yes
883: or
884: .Dq no .
885: The default is
886: .Dq yes .
887: Note that setting this option to
888: .Dq no
1.30 provos 889: turns off
1.16 markus 890: .Cm RhostsAuthentication
891: and
892: .Cm RhostsRSAAuthentication .
1.34 markus 893: .It Cm User
1.40 aaron 894: Specifies the user to log in as.
895: This can be useful if you have a different user name on different machines.
896: This saves the trouble of
1.34 markus 897: having to remember to give the user name on the command line.
898: .It Cm UserKnownHostsFile
899: Specifies a file to use instead of
900: .Pa $HOME/.ssh/known_hosts .
1.2 deraadt 901: .It Cm UseRsh
1.40 aaron 902: Specifies that rlogin/rsh should be used for this host.
903: It is possible that the host does not at all support the
1.2 deraadt 904: .Nm
1.40 aaron 905: protocol.
906: This causes
1.2 deraadt 907: .Nm
1.40 aaron 908: to immediately execute
1.2 deraadt 909: .Xr rsh 1 .
1.1 deraadt 910: All other options (except
1.2 deraadt 911: .Cm HostName )
1.40 aaron 912: are ignored if this has been specified.
913: The argument must be
1.2 deraadt 914: .Dq yes
915: or
916: .Dq no .
917: .Sh ENVIRONMENT
918: .Nm
1.1 deraadt 919: will normally set the following environment variables:
1.2 deraadt 920: .Bl -tag -width Ds
921: .It Ev DISPLAY
922: The
923: .Ev DISPLAY
1.40 aaron 924: variable indicates the location of the X11 server.
1.44 aaron 925: It is automatically set by
1.2 deraadt 926: .Nm
927: to point to a value of the form
928: .Dq hostname:n
929: where hostname indicates
1.40 aaron 930: the host where the shell runs, and n is an integer >= 1.
931: .Nm
932: uses this special value to forward X11 connections over the secure
933: channel.
934: The user should normally not set DISPLAY explicitly, as that
1.1 deraadt 935: will render the X11 connection insecure (and will require the user to
936: manually copy any required authorization cookies).
1.2 deraadt 937: .It Ev HOME
1.1 deraadt 938: Set to the path of the user's home directory.
1.2 deraadt 939: .It Ev LOGNAME
940: Synonym for
1.12 aaron 941: .Ev USER ;
942: set for compatibility with systems that use this variable.
1.2 deraadt 943: .It Ev MAIL
1.1 deraadt 944: Set to point the user's mailbox.
1.40 aaron 945: .It Ev PATH
1.2 deraadt 946: Set to the default
947: .Ev PATH ,
948: as specified when compiling
1.12 aaron 949: .Nm ssh .
1.18 markus 950: .It Ev SSH_AUTH_SOCK
1.17 markus 951: indicates the path of a unix-domain socket used to communicate with the
952: agent.
1.2 deraadt 953: .It Ev SSH_CLIENT
1.40 aaron 954: Identifies the client end of the connection.
955: The variable contains
1.1 deraadt 956: three space-separated values: client ip-address, client port number,
957: and server port number.
1.2 deraadt 958: .It Ev SSH_TTY
1.1 deraadt 959: This is set to the name of the tty (path to the device) associated
1.40 aaron 960: with the current shell or command.
961: If the current session has no tty,
1.1 deraadt 962: this variable is not set.
1.2 deraadt 963: .It Ev TZ
1.1 deraadt 964: The timezone variable is set to indicate the present timezone if it
965: was set when the daemon was started (e.i., the daemon passes the value
966: on to new connections).
1.2 deraadt 967: .It Ev USER
1.1 deraadt 968: Set to the name of the user logging in.
1.2 deraadt 969: .El
970: .Pp
1.44 aaron 971: Additionally,
1.2 deraadt 972: .Nm
1.44 aaron 973: reads
974: .Pa $HOME/.ssh/environment ,
1.2 deraadt 975: and adds lines of the format
976: .Dq VARNAME=value
1.12 aaron 977: to the environment.
1.2 deraadt 978: .Sh FILES
1.36 markus 979: .Bl -tag -width Ds
1.2 deraadt 980: .It Pa $HOME/.ssh/known_hosts
1.1 deraadt 981: Records host keys for all hosts the user has logged into (that are not
1.2 deraadt 982: in
983: .Pa /etc/ssh_known_hosts ) .
984: See
985: .Xr sshd 8 .
1.48 markus 986: .It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa
987: Contains the RSA and the DSA authentication identity of the user.
988: These files
989: contain sensitive data and should be readable by the user but not
1.15 markus 990: accessible by others (read/write/execute).
991: Note that
992: .Nm
1.48 markus 993: ignores a private key file if it is accessible by others.
1.15 markus 994: It is possible to specify a passphrase when
1.1 deraadt 995: generating the key; the passphrase will be used to encrypt the
1.8 deraadt 996: sensitive part of this file using 3DES.
1.48 markus 997: .It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub
1.1 deraadt 998: Contains the public key for authentication (public part of the
1.40 aaron 999: identity file in human-readable form).
1.48 markus 1000: The contents of the
1001: .Pa $HOME/.ssh/identity.pub
1002: file should be added to
1.2 deraadt 1003: .Pa $HOME/.ssh/authorized_keys
1004: on all machines
1.40 aaron 1005: where you wish to log in using RSA authentication.
1.48 markus 1006: The contents of the
1007: .Pa $HOME/.ssh/id_dsa.pub
1008: file should be added to
1009: .Pa $HOME/.ssh/authorized_keys2
1010: on all machines
1011: where you wish to log in using DSA authentication.
1012: These files are not
1.40 aaron 1013: sensitive and can (but need not) be readable by anyone.
1.48 markus 1014: These files are
1015: never used automatically and are not necessary; they is only provided for
1.1 deraadt 1016: the convenience of the user.
1.2 deraadt 1017: .It Pa $HOME/.ssh/config
1.40 aaron 1018: This is the per-user configuration file.
1019: The format of this file is described above.
1020: This file is used by the
1.2 deraadt 1021: .Nm
1.40 aaron 1022: client.
1023: This file does not usually contain any sensitive information,
1.1 deraadt 1024: but the recommended permissions are read/write for the user, and not
1025: accessible by others.
1.2 deraadt 1026: .It Pa $HOME/.ssh/authorized_keys
1.40 aaron 1027: Lists the RSA keys that can be used for logging in as this user.
1028: The format of this file is described in the
1.2 deraadt 1029: .Xr sshd 8
1.40 aaron 1030: manual page.
1031: In the simplest form the format is the same as the .pub
1.1 deraadt 1032: identity files (that is, each line contains the number of bits in
1033: modulus, public exponent, modulus, and comment fields, separated by
1.40 aaron 1034: spaces).
1035: This file is not highly sensitive, but the recommended
1.1 deraadt 1036: permissions are read/write for the user, and not accessible by others.
1.48 markus 1037: .It Pa $HOME/.ssh/authorized_keys2
1038: Lists the DSA keys that can be used for logging in as this user.
1039: This file is not highly sensitive, but the recommended
1040: permissions are read/write for the user, and not accessible by others.
1041: .It Pa /etc/ssh_known_hosts, /etc/ssh_known_hosts2
1.40 aaron 1042: Systemwide list of known host keys.
1.48 markus 1043: .Pa /etc/ssh_known_hosts
1044: contains RSA and
1045: .Pa /etc/ssh_known_hosts2
1046: contains DSA keys.
1047: These files should be prepared by the
1.1 deraadt 1048: system administrator to contain the public host keys of all machines in the
1.40 aaron 1049: organization.
1050: This file should be world-readable.
1051: This file contains
1.1 deraadt 1052: public keys, one per line, in the following format (fields separated
1053: by spaces): system name, number of bits in modulus, public exponent,
1.40 aaron 1054: modulus, and optional comment field.
1055: When different names are used
1.1 deraadt 1056: for the same machine, all such names should be listed, separated by
1.40 aaron 1057: commas.
1058: The format is described on the
1.2 deraadt 1059: .Xr sshd 8
1.1 deraadt 1060: manual page.
1.2 deraadt 1061: .Pp
1.1 deraadt 1062: The canonical system name (as returned by name servers) is used by
1.2 deraadt 1063: .Xr sshd 8
1.1 deraadt 1064: to verify the client host when logging in; other names are needed because
1.2 deraadt 1065: .Nm
1.1 deraadt 1066: does not convert the user-supplied name to a canonical name before
1067: checking the key, because someone with access to the name servers
1068: would then be able to fool host authentication.
1.2 deraadt 1069: .It Pa /etc/ssh_config
1.40 aaron 1070: Systemwide configuration file.
1071: This file provides defaults for those
1.1 deraadt 1072: values that are not specified in the user's configuration file, and
1.40 aaron 1073: for those users who do not have a configuration file.
1074: This file must be world-readable.
1.2 deraadt 1075: .It Pa $HOME/.rhosts
1076: This file is used in
1077: .Pa \&.rhosts
1078: authentication to list the
1.40 aaron 1079: host/user pairs that are permitted to log in.
1080: (Note that this file is
1.1 deraadt 1081: also used by rlogin and rsh, which makes using this file insecure.)
1082: Each line of the file contains a host name (in the canonical form
1083: returned by name servers), and then a user name on that host,
1.40 aaron 1084: separated by a space.
1085: One some machines this file may need to be
1.1 deraadt 1086: world-readable if the user's home directory is on a NFS partition,
1087: because
1.2 deraadt 1088: .Xr sshd 8
1.40 aaron 1089: reads it as root.
1090: Additionally, this file must be owned by the user,
1091: and must not have write permissions for anyone else.
1092: The recommended
1.1 deraadt 1093: permission for most machines is read/write for the user, and not
1094: accessible by others.
1.2 deraadt 1095: .Pp
1.1 deraadt 1096: Note that by default
1.2 deraadt 1097: .Xr sshd 8
1.1 deraadt 1098: will be installed so that it requires successful RSA host
1.40 aaron 1099: authentication before permitting \s+2.\s0rhosts authentication.
1100: If your server machine does not have the client's host key in
1.2 deraadt 1101: .Pa /etc/ssh_known_hosts ,
1102: you can store it in
1103: .Pa $HOME/.ssh/known_hosts .
1104: The easiest way to do this is to
1.1 deraadt 1105: connect back to the client from the server machine using ssh; this
1.48 markus 1106: will automatically add the host key to
1.2 deraadt 1107: .Pa $HOME/.ssh/known_hosts .
1108: .It Pa $HOME/.shosts
1109: This file is used exactly the same way as
1110: .Pa \&.rhosts .
1111: The purpose for
1.1 deraadt 1112: having this file is to be able to use rhosts authentication with
1.2 deraadt 1113: .Nm
1114: without permitting login with
1115: .Xr rlogin 1
1116: or
1117: .Xr rsh 1 .
1118: .It Pa /etc/hosts.equiv
1119: This file is used during
1.40 aaron 1120: .Pa \&.rhosts authentication.
1121: It contains
1.1 deraadt 1122: canonical hosts names, one per line (the full format is described on
1123: the
1.2 deraadt 1124: .Xr sshd 8
1.40 aaron 1125: manual page).
1126: If the client host is found in this file, login is
1.1 deraadt 1127: automatically permitted provided client and server user names are the
1.40 aaron 1128: same.
1129: Additionally, successful RSA host authentication is normally
1130: required.
1131: This file should only be writable by root.
1.2 deraadt 1132: .It Pa /etc/shosts.equiv
1.44 aaron 1133: This file is processed exactly as
1.2 deraadt 1134: .Pa /etc/hosts.equiv .
1.1 deraadt 1135: This file may be useful to permit logins using
1.2 deraadt 1136: .Nm
1.1 deraadt 1137: but not using rsh/rlogin.
1.2 deraadt 1138: .It Pa /etc/sshrc
1.1 deraadt 1139: Commands in this file are executed by
1.2 deraadt 1140: .Nm
1.1 deraadt 1141: when the user logs in just before the user's shell (or command) is started.
1142: See the
1.2 deraadt 1143: .Xr sshd 8
1.1 deraadt 1144: manual page for more information.
1.2 deraadt 1145: .It Pa $HOME/.ssh/rc
1.1 deraadt 1146: Commands in this file are executed by
1.2 deraadt 1147: .Nm
1.1 deraadt 1148: when the user logs in just before the user's shell (or command) is
1149: started.
1.44 aaron 1150: See the
1.2 deraadt 1151: .Xr sshd 8
1.1 deraadt 1152: manual page for more information.
1.31 markus 1153: .It Pa $HOME/.ssh/environment
1154: Contains additional definitions for environment variables, see section
1155: .Sx ENVIRONMENT
1156: above.
1.5 deraadt 1157: .It Pa libcrypto.so.X.1
1158: A version of this library which includes support for the RSA algorithm
1159: is required for proper operation.
1.2 deraadt 1160: .Sh AUTHOR
1.20 provos 1161: OpenSSH
1.37 deraadt 1162: is a derivative of the original (free) ssh 1.2.12 release by Tatu Ylonen,
1.40 aaron 1163: but with bugs removed and newer features re-added.
1164: Rapidly after the
1.37 deraadt 1165: 1.2.12 release, newer versions of the original ssh bore successively
1166: more restrictive licenses, and thus demand for a free version was born.
1.47 markus 1167: .Pp
1.37 deraadt 1168: This version of OpenSSH
1.20 provos 1169: .Bl -bullet
1170: .It
1.35 aaron 1171: has all components of a restrictive nature (i.e., patents, see
1.21 deraadt 1172: .Xr ssl 8 )
1173: directly removed from the source code; any licensed or patented components
1174: are chosen from
1175: external libraries.
1.20 provos 1176: .It
1.47 markus 1177: has been updated to support SSH protocol 1.5 and 2, making it compatible with
1178: all other SSH clients and servers.
1.20 provos 1179: .It
1.44 aaron 1180: contains added support for
1.20 provos 1181: .Xr kerberos 8
1182: authentication and ticket passing.
1183: .It
1.21 deraadt 1184: supports one-time password authentication with
1.20 provos 1185: .Xr skey 1 .
1186: .El
1187: .Pp
1188: The libraries described in
1.5 deraadt 1189: .Xr ssl 8
1190: are required for proper operation.
1.25 provos 1191: .Pp
1.26 aaron 1192: OpenSSH has been created by Aaron Campbell, Bob Beck, Markus Friedl,
1.25 provos 1193: Niels Provos, Theo de Raadt, and Dug Song.
1.47 markus 1194: .Pp
1195: The support for SSH protocol 2 was written by Markus Friedl.
1.2 deraadt 1196: .Sh SEE ALSO
1197: .Xr rlogin 1 ,
1198: .Xr rsh 1 ,
1199: .Xr scp 1 ,
1200: .Xr ssh-add 1 ,
1201: .Xr ssh-agent 1 ,
1202: .Xr ssh-keygen 1 ,
1203: .Xr telnet 1 ,
1.5 deraadt 1204: .Xr sshd 8 ,
1205: .Xr ssl 8
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