Annotation of src/usr.bin/ssh/ssh.1, Revision 1.54
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: .\"
1.54 ! markus 12: .\" $Id: ssh.1,v 1.53 2000/05/15 06:54:03 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
1.54 ! markus 27: .Op Fl afgknqtvxACNPTX246
1.51 markus 28: .Op Fl c Ar cipher_spec
1.2 deraadt 29: .Op Fl e Ar escape_char
30: .Op Fl i Ar identity_file
31: .Op Fl l Ar login_name
32: .Op Fl o Ar option
33: .Op Fl p Ar port
1.12 aaron 34: .Oo Fl L Xo
35: .Sm off
1.33 markus 36: .Ar port :
1.12 aaron 37: .Ar host :
38: .Ar hostport
39: .Sm on
40: .Xc
41: .Oc
42: .Oo Fl R Xo
43: .Sm off
1.33 markus 44: .Ar port :
1.12 aaron 45: .Ar host :
46: .Ar hostport
47: .Sm on
48: .Xc
49: .Oc
1.5 deraadt 50: .Op Ar hostname | user@hostname
1.2 deraadt 51: .Op Ar command
1.44 aaron 52: .Sh DESCRIPTION
1.2 deraadt 53: .Nm
1.5 deraadt 54: (Secure Shell) is a program for logging into a remote machine and for
1.40 aaron 55: executing commands on a remote machine.
56: It is intended to replace
1.1 deraadt 57: rlogin and rsh, and provide secure encrypted communications between
1.40 aaron 58: two untrusted hosts over an insecure network.
59: X11 connections and
1.1 deraadt 60: arbitrary TCP/IP ports can also be forwarded over the secure channel.
1.2 deraadt 61: .Pp
62: .Nm
1.44 aaron 63: connects and logs into the specified
1.2 deraadt 64: .Ar hostname .
1.1 deraadt 65: The user must prove
1.49 markus 66: his/her identity to the remote machine using one of several methods
67: depending on the protocol version used:
68: .Pp
69: .Ss SSH protocol version 1
1.2 deraadt 70: .Pp
1.1 deraadt 71: First, if the machine the user logs in from is listed in
1.2 deraadt 72: .Pa /etc/hosts.equiv
1.1 deraadt 73: or
1.2 deraadt 74: .Pa /etc/shosts.equiv
1.1 deraadt 75: on the remote machine, and the user names are
76: the same on both sides, the user is immediately permitted to log in.
1.44 aaron 77: Second, if
1.2 deraadt 78: .Pa \&.rhosts
1.1 deraadt 79: or
1.2 deraadt 80: .Pa \&.shosts
1.1 deraadt 81: exists in the user's home directory on the
82: remote machine and contains a line containing the name of the client
83: machine and the name of the user on that machine, the user is
1.40 aaron 84: permitted to log in.
85: This form of authentication alone is normally not
1.1 deraadt 86: allowed by the server because it is not secure.
1.2 deraadt 87: .Pp
1.1 deraadt 88: The second (and primary) authentication method is the
1.2 deraadt 89: .Pa rhosts
1.1 deraadt 90: or
1.2 deraadt 91: .Pa hosts.equiv
1.40 aaron 92: method combined with RSA-based host authentication.
93: It means that if the login would be permitted by
1.49 markus 94: .Pa $HOME/.rhosts ,
95: .Pa $HOME/.shosts ,
1.2 deraadt 96: .Pa /etc/hosts.equiv ,
1.1 deraadt 97: or
1.2 deraadt 98: .Pa /etc/shosts.equiv ,
1.11 deraadt 99: and if additionally the server can verify the client's
1.44 aaron 100: host key (see
1.2 deraadt 101: .Pa /etc/ssh_known_hosts
1.23 markus 102: and
103: .Pa $HOME/.ssh/known_hosts
1.1 deraadt 104: in the
1.2 deraadt 105: .Sx FILES
1.40 aaron 106: section), only then login is permitted.
107: This authentication method closes security holes due to IP
108: spoofing, DNS spoofing and routing spoofing.
109: [Note to the administrator:
1.2 deraadt 110: .Pa /etc/hosts.equiv ,
1.49 markus 111: .Pa $HOME/.rhosts ,
1.1 deraadt 112: and the rlogin/rsh protocol in general, are inherently insecure and should be
113: disabled if security is desired.]
1.2 deraadt 114: .Pp
1.44 aaron 115: As a third authentication method,
1.2 deraadt 116: .Nm
1.1 deraadt 117: supports RSA based authentication.
118: The scheme is based on public-key cryptography: there are cryptosystems
119: where encryption and decryption are done using separate keys, and it
120: is not possible to derive the decryption key from the encryption key.
1.40 aaron 121: RSA is one such system.
1.44 aaron 122: The idea is that each user creates a public/private
1.40 aaron 123: key pair for authentication purposes.
124: The server knows the public key, and only the user knows the private key.
1.44 aaron 125: The file
1.2 deraadt 126: .Pa $HOME/.ssh/authorized_keys
1.1 deraadt 127: lists the public keys that are permitted for logging
1.40 aaron 128: in.
129: When the user logs in, the
1.2 deraadt 130: .Nm
1.1 deraadt 131: program tells the server which key pair it would like to use for
1.40 aaron 132: authentication.
133: The server checks if this key is permitted, and if
1.1 deraadt 134: so, sends the user (actually the
1.2 deraadt 135: .Nm
1.1 deraadt 136: program running on behalf of the user) a challenge, a random number,
1.40 aaron 137: encrypted by the user's public key.
138: The challenge can only be
139: decrypted using the proper private key.
140: The user's client then decrypts the
1.1 deraadt 141: challenge using the private key, proving that he/she knows the private
142: key but without disclosing it to the server.
1.2 deraadt 143: .Pp
144: .Nm
1.40 aaron 145: implements the RSA authentication protocol automatically.
146: The user creates his/her RSA key pair by running
1.2 deraadt 147: .Xr ssh-keygen 1 .
1.44 aaron 148: This stores the private key in
1.49 markus 149: .Pa $HOME/.ssh/identity
1.1 deraadt 150: and the public key in
1.49 markus 151: .Pa $HOME/.ssh/identity.pub
1.40 aaron 152: in the user's home directory.
153: The user should then copy the
1.2 deraadt 154: .Pa identity.pub
1.44 aaron 155: to
1.49 markus 156: .Pa $HOME/.ssh/authorized_keys
1.44 aaron 157: in his/her home directory on the remote machine (the
1.2 deraadt 158: .Pa authorized_keys
1.44 aaron 159: file corresponds to the conventional
1.49 markus 160: .Pa $HOME/.rhosts
1.1 deraadt 161: file, and has one key
1.40 aaron 162: per line, though the lines can be very long).
163: After this, the user can log in without giving the password.
164: RSA authentication is much
1.1 deraadt 165: more secure than rhosts authentication.
1.2 deraadt 166: .Pp
1.1 deraadt 167: The most convenient way to use RSA authentication may be with an
1.40 aaron 168: authentication agent.
169: See
1.2 deraadt 170: .Xr ssh-agent 1
1.1 deraadt 171: for more information.
1.2 deraadt 172: .Pp
1.44 aaron 173: If other authentication methods fail,
1.2 deraadt 174: .Nm
1.40 aaron 175: prompts the user for a password.
176: The password is sent to the remote
1.1 deraadt 177: host for checking; however, since all communications are encrypted,
178: the password cannot be seen by someone listening on the network.
1.2 deraadt 179: .Pp
1.49 markus 180: .Ss SSH protocol version 2
181: .Pp
182: When a user connects using the protocol version 2
183: different authentication methods are available:
184: At first, the client attempts to authenticate using the public key method.
185: If this method fails password authentication is tried.
186: .Pp
187: The public key method is similar to RSA authentication described
188: in the previous section except that the DSA algorithm is used
189: instead of the patented RSA algorithm.
190: The client uses his private DSA key
191: .Pa $HOME/.ssh/id_dsa
192: to sign the session identifier and sends the result to the server.
193: The server checks whether the matching public key is listed in
194: .Pa $HOME/.ssh/authorized_keys2
195: and grants access if both the key is found and the signature is correct.
196: The session identifier is derived from a shared Diffie-Hellman value
197: and is only known to the client and the server.
198: .Pp
199: If public key authentication fails or is not available a password
200: can be sent encrypted to the remote host for proving the user's identity.
201: This protocol 2 implementation does not yet support Kerberos or
202: S/Key authentication.
203: .Pp
204: Protocol 2 provides additional mechanisms for confidentiality
1.51 markus 205: (the traffic is encrypted using 3DES, Blowfish, CAST128 or Arcfour)
1.49 markus 206: and integrity (hmac-sha1, hmac-md5).
207: Note that protocol 1 lacks a strong mechanism for ensuring the
208: integrity of the connection.
209: .Pp
210: .Ss Login session and remote execution
211: .Pp
1.1 deraadt 212: When the user's identity has been accepted by the server, the server
213: either executes the given command, or logs into the machine and gives
1.40 aaron 214: the user a normal shell on the remote machine.
215: All communication with
1.1 deraadt 216: the remote command or shell will be automatically encrypted.
1.2 deraadt 217: .Pp
1.1 deraadt 218: If a pseudo-terminal has been allocated (normal login session), the
1.2 deraadt 219: user can disconnect with
220: .Ic ~. ,
221: and suspend
222: .Nm
223: with
224: .Ic ~^Z .
225: All forwarded connections can be listed with
1.44 aaron 226: .Ic ~#
1.2 deraadt 227: and if
1.1 deraadt 228: the session blocks waiting for forwarded X11 or TCP/IP
1.2 deraadt 229: connections to terminate, it can be backgrounded with
230: .Ic ~&
231: (this should not be used while the user shell is active, as it can cause the
1.40 aaron 232: shell to hang).
233: All available escapes can be listed with
1.2 deraadt 234: .Ic ~? .
235: .Pp
236: A single tilde character can be sent as
237: .Ic ~~
238: (or by following the tilde by a character other than those described above).
1.1 deraadt 239: The escape character must always follow a newline to be interpreted as
1.40 aaron 240: special.
241: The escape character can be changed in configuration files
242: or on the command line.
1.2 deraadt 243: .Pp
1.1 deraadt 244: If no pseudo tty has been allocated, the
245: session is transparent and can be used to reliably transfer binary
1.40 aaron 246: data.
247: On most systems, setting the escape character to
1.2 deraadt 248: .Dq none
249: will also make the session transparent even if a tty is used.
250: .Pp
1.1 deraadt 251: The session terminates when the command or shell in on the remote
252: machine exists and all X11 and TCP/IP connections have been closed.
253: The exit status of the remote program is returned as the exit status
254: of
1.2 deraadt 255: .Nm ssh .
256: .Pp
1.49 markus 257: .Ss X11 and TCP forwarding
258: .Pp
1.1 deraadt 259: If the user is using X11 (the
1.2 deraadt 260: .Ev DISPLAY
1.1 deraadt 261: environment variable is set), the connection to the X11 display is
262: automatically forwarded to the remote side in such a way that any X11
263: programs started from the shell (or command) will go through the
264: encrypted channel, and the connection to the real X server will be made
1.40 aaron 265: from the local machine.
266: The user should not manually set
1.2 deraadt 267: .Ev DISPLAY .
1.1 deraadt 268: Forwarding of X11 connections can be
269: configured on the command line or in configuration files.
1.2 deraadt 270: .Pp
271: The
1.44 aaron 272: .Ev DISPLAY
1.2 deraadt 273: value set by
274: .Nm
1.1 deraadt 275: will point to the server machine, but with a display number greater
1.40 aaron 276: than zero.
277: This is normal, and happens because
1.2 deraadt 278: .Nm
279: creates a
280: .Dq proxy
281: X server on the server machine for forwarding the
1.1 deraadt 282: connections over the encrypted channel.
1.2 deraadt 283: .Pp
284: .Nm
1.1 deraadt 285: will also automatically set up Xauthority data on the server machine.
286: For this purpose, it will generate a random authorization cookie,
287: store it in Xauthority on the server, and verify that any forwarded
288: connections carry this cookie and replace it by the real cookie when
1.40 aaron 289: the connection is opened.
290: The real authentication cookie is never
1.1 deraadt 291: sent to the server machine (and no cookies are sent in the plain).
1.2 deraadt 292: .Pp
1.1 deraadt 293: If the user is using an authentication agent, the connection to the agent
294: is automatically forwarded to the remote side unless disabled on
295: command line or in a configuration file.
1.2 deraadt 296: .Pp
1.1 deraadt 297: Forwarding of arbitrary TCP/IP connections over the secure channel can
1.40 aaron 298: be specified either on command line or in a configuration file.
299: One possible application of TCP/IP forwarding is a secure connection to an
1.1 deraadt 300: electronic purse; another is going trough firewalls.
1.2 deraadt 301: .Pp
1.49 markus 302: .Ss Server authentication
303: .Pp
1.2 deraadt 304: .Nm
1.49 markus 305: automatically maintains and checks a database containing
1.40 aaron 306: identifications for all hosts it has ever been used with.
1.49 markus 307: RSA host keys are stored in
308: .Pa $HOME/.ssh/known_hosts
309: and
310: DSA host keys are stored in
311: .Pa $HOME/.ssh/known_hosts2
1.40 aaron 312: in the user's home directory.
1.49 markus 313: Additionally, the files
1.2 deraadt 314: .Pa /etc/ssh_known_hosts
1.49 markus 315: and
316: .Pa /etc/ssh_known_hosts2
317: are automatically checked for known hosts.
1.40 aaron 318: Any new hosts are automatically added to the user's file.
319: If a host's identification
1.1 deraadt 320: ever changes,
1.2 deraadt 321: .Nm
1.1 deraadt 322: warns about this and disables password authentication to prevent a
1.40 aaron 323: trojan horse from getting the user's password.
324: Another purpose of
1.1 deraadt 325: this mechanism is to prevent man-in-the-middle attacks which could
1.40 aaron 326: otherwise be used to circumvent the encryption.
327: The
1.2 deraadt 328: .Cm StrictHostKeyChecking
1.1 deraadt 329: option (see below) can be used to prevent logins to machines whose
330: host key is not known or has changed.
1.2 deraadt 331: .Sh OPTIONS
332: .Bl -tag -width Ds
1.4 dugsong 333: .It Fl a
1.42 aaron 334: Disables forwarding of the authentication agent connection.
1.54 ! markus 335: .It Fl A
! 336: Enables forwarding of the authentication agent connection.
! 337: This can also be specified on a per-host basis in a configuration file.
1.6 deraadt 338: .It Fl c Ar blowfish|3des
1.44 aaron 339: Selects the cipher to use for encrypting the session.
1.2 deraadt 340: .Ar 3des
1.40 aaron 341: is used by default.
1.44 aaron 342: It is believed to be secure.
1.5 deraadt 343: .Ar 3des
344: (triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
345: It is presumably more secure than the
1.2 deraadt 346: .Ar des
1.51 markus 347: cipher which is no longer supported in
348: .Nm ssh .
1.5 deraadt 349: .Ar blowfish
350: is a fast block cipher, it appears very secure and is much faster than
1.40 aaron 351: .Ar 3des .
1.51 markus 352: .It Fl c Ar "3des-cbc,blowfish-cbc,arcfour,cast128-cbc"
353: Additionally, for protocol version 2 a comma-separated list of ciphers can
354: be specified in order of preference. Protocol version 2 supports
355: 3DES, Blowfish and CAST128 in CBC mode and Arcfour.
1.2 deraadt 356: .It Fl e Ar ch|^ch|none
357: Sets the escape character for sessions with a pty (default:
358: .Ql ~ ) .
1.40 aaron 359: The escape character is only recognized at the beginning of a line.
360: The escape character followed by a dot
1.2 deraadt 361: .Pq Ql \&.
362: closes the connection, followed
1.1 deraadt 363: by control-Z suspends the connection, and followed by itself sends the
1.40 aaron 364: escape character once.
365: Setting the character to
1.2 deraadt 366: .Dq none
367: disables any escapes and makes the session fully transparent.
368: .It Fl f
369: Requests
370: .Nm
1.40 aaron 371: to go to background just before command execution.
372: This is useful if
1.2 deraadt 373: .Nm
374: is going to ask for passwords or passphrases, but the user
1.40 aaron 375: wants it in the background.
1.44 aaron 376: This implies
1.2 deraadt 377: .Fl n .
1.1 deraadt 378: The recommended way to start X11 programs at a remote site is with
1.2 deraadt 379: something like
380: .Ic ssh -f host xterm .
1.34 markus 381: .It Fl g
382: Allows remote hosts to connect to local forwarded ports.
1.2 deraadt 383: .It Fl i Ar identity_file
1.44 aaron 384: Selects the file from which the identity (private key) for
1.40 aaron 385: RSA authentication is read.
1.44 aaron 386: Default is
1.49 markus 387: .Pa $HOME/.ssh/identity
1.40 aaron 388: in the user's home directory.
389: Identity files may also be specified on
390: a per-host basis in the configuration file.
391: It is possible to have multiple
1.2 deraadt 392: .Fl i
393: options (and multiple identities specified in
1.1 deraadt 394: configuration files).
1.2 deraadt 395: .It Fl k
1.42 aaron 396: Disables forwarding of Kerberos tickets and AFS tokens.
397: This may also be specified on a per-host basis in the configuration file.
1.2 deraadt 398: .It Fl l Ar login_name
1.40 aaron 399: Specifies the user to log in as on the remote machine.
400: This also may be specified on a per-host basis in the configuration file.
1.2 deraadt 401: .It Fl n
402: Redirects stdin from
403: .Pa /dev/null
404: (actually, prevents reading from stdin).
1.1 deraadt 405: This must be used when
1.2 deraadt 406: .Nm
1.40 aaron 407: is run in the background.
408: A common trick is to use this to run X11 programs on a remote machine.
409: For example,
1.2 deraadt 410: .Ic ssh -n shadows.cs.hut.fi emacs &
411: will start an emacs on shadows.cs.hut.fi, and the X11
1.1 deraadt 412: connection will be automatically forwarded over an encrypted channel.
413: The
1.2 deraadt 414: .Nm
1.1 deraadt 415: program will be put in the background.
416: (This does not work if
1.2 deraadt 417: .Nm
418: needs to ask for a password or passphrase; see also the
419: .Fl f
420: option.)
1.53 markus 421: .It Fl N
422: Do not execute a remote command.
423: This is usefull if you just want to forward ports
424: (protocol version 2 only).
1.2 deraadt 425: .It Fl o Ar option
1.1 deraadt 426: Can be used to give options in the format used in the config file.
427: This is useful for specifying options for which there is no separate
1.40 aaron 428: command-line flag.
429: The option has the same format as a line in the configuration file.
1.2 deraadt 430: .It Fl p Ar port
1.40 aaron 431: Port to connect to on the remote host.
432: This can be specified on a
1.1 deraadt 433: per-host basis in the configuration file.
1.16 markus 434: .It Fl P
435: Use a non-privileged port for outgoing connections.
436: This can be used if your firewall does
437: not permit connections from privileged ports.
1.30 provos 438: Note that this option turns off
1.16 markus 439: .Cm RhostsAuthentication
440: and
441: .Cm RhostsRSAAuthentication .
1.2 deraadt 442: .It Fl q
1.40 aaron 443: Quiet mode.
444: Causes all warning and diagnostic messages to be suppressed.
445: Only fatal errors are displayed.
1.2 deraadt 446: .It Fl t
1.40 aaron 447: Force pseudo-tty allocation.
1.43 brad 448: This can be used to execute arbitrary
1.40 aaron 449: screen-based programs on a remote machine, which can be very useful,
450: e.g., when implementing menu services.
1.53 markus 451: .It Fl T
452: Disable pseudo-tty allocation (protocol version 2 only).
1.2 deraadt 453: .It Fl v
1.40 aaron 454: Verbose mode.
455: Causes
1.2 deraadt 456: .Nm
1.40 aaron 457: to print debugging messages about its progress.
458: This is helpful in
1.1 deraadt 459: debugging connection, authentication, and configuration problems.
1.22 provos 460: The verbose mode is also used to display
461: .Xr skey 1
462: challenges, if the user entered "s/key" as password.
1.2 deraadt 463: .It Fl x
1.40 aaron 464: Disables X11 forwarding.
1.2 deraadt 465: .It Fl X
1.1 deraadt 466: Enables X11 forwarding.
1.54 ! markus 467: This can also be specified on a per-host basis in a configuration file.
1.2 deraadt 468: .It Fl C
1.1 deraadt 469: Requests compression of all data (including stdin, stdout, stderr, and
1.40 aaron 470: data for forwarded X11 and TCP/IP connections).
471: The compression algorithm is the same used by
1.34 markus 472: .Xr gzip 1 ,
473: and the
1.2 deraadt 474: .Dq level
475: can be controlled by the
476: .Cm CompressionLevel
1.40 aaron 477: option (see below).
478: Compression is desirable on modem lines and other
1.1 deraadt 479: slow connections, but will only slow down things on fast networks.
480: The default value can be set on a host-by-host basis in the
481: configuration files; see the
1.2 deraadt 482: .Cm Compress
1.1 deraadt 483: option below.
1.2 deraadt 484: .It Fl L Ar port:host:hostport
1.1 deraadt 485: Specifies that the given port on the local (client) host is to be
1.40 aaron 486: forwarded to the given host and port on the remote side.
487: This works by allocating a socket to listen to
1.2 deraadt 488: .Ar port
1.1 deraadt 489: on the local side, and whenever a connection is made to this port, the
490: connection is forwarded over the secure channel, and a connection is
491: made to
1.32 markus 492: .Ar host
493: port
494: .Ar hostport
1.40 aaron 495: from the remote machine.
496: Port forwardings can also be specified in the configuration file.
497: Only root can forward privileged ports.
1.32 markus 498: IPv6 addresses can be specified with an alternative syntax:
499: .Ar port/host/hostport
1.2 deraadt 500: .It Fl R Ar port:host:hostport
1.1 deraadt 501: Specifies that the given port on the remote (server) host is to be
1.40 aaron 502: forwarded to the given host and port on the local side.
503: This works by allocating a socket to listen to
1.2 deraadt 504: .Ar port
1.1 deraadt 505: on the remote side, and whenever a connection is made to this port, the
506: connection is forwarded over the secure channel, and a connection is
507: made to
1.32 markus 508: .Ar host
509: port
510: .Ar hostport
1.40 aaron 511: from the local machine.
512: Port forwardings can also be specified in the configuration file.
513: Privileged ports can be forwarded only when
1.1 deraadt 514: logging in as root on the remote machine.
1.46 markus 515: .It Fl 2
516: Forces
517: .Nm
1.50 markus 518: to try protocol version 2 only.
1.32 markus 519: .It Fl 4
520: Forces
521: .Nm
522: to use IPv4 addresses only.
523: .It Fl 6
524: Forces
525: .Nm
526: to use IPv6 addresses only.
1.2 deraadt 527: .El
528: .Sh CONFIGURATION FILES
529: .Nm
1.1 deraadt 530: obtains configuration data from the following sources (in this order):
531: command line options, user's configuration file
1.2 deraadt 532: .Pq Pa $HOME/.ssh/config ,
533: and system-wide configuration file
534: .Pq Pa /etc/ssh_config .
535: For each parameter, the first obtained value
1.40 aaron 536: will be used.
537: The configuration files contain sections bracketed by
538: .Dq Host
539: specifications, and that section is only applied for hosts that
540: match one of the patterns given in the specification.
541: The matched host name is the one given on the command line.
1.2 deraadt 542: .Pp
1.1 deraadt 543: Since the first obtained value for each parameter is used, more
544: host-specific declarations should be given near the beginning of the
545: file, and general defaults at the end.
1.2 deraadt 546: .Pp
1.1 deraadt 547: The configuration file has the following format:
1.2 deraadt 548: .Pp
549: Empty lines and lines starting with
550: .Ql #
551: are comments.
552: .Pp
553: Otherwise a line is of the format
554: .Dq keyword arguments .
555: The possible
1.1 deraadt 556: keywords and their meanings are as follows (note that the
557: configuration files are case-sensitive):
1.2 deraadt 558: .Bl -tag -width Ds
559: .It Cm Host
1.1 deraadt 560: Restricts the following declarations (up to the next
1.2 deraadt 561: .Cm Host
1.1 deraadt 562: keyword) to be only for those hosts that match one of the patterns
1.2 deraadt 563: given after the keyword.
564: .Ql \&*
565: and
566: .Ql ?
567: can be used as wildcards in the
1.40 aaron 568: patterns.
569: A single
1.2 deraadt 570: .Ql \&*
571: as a pattern can be used to provide global
1.40 aaron 572: defaults for all hosts.
573: The host is the
1.2 deraadt 574: .Ar hostname
1.1 deraadt 575: argument given on the command line (i.e., the name is not converted to
576: a canonicalized host name before matching).
1.2 deraadt 577: .It Cm AFSTokenPassing
1.42 aaron 578: Specifies whether to pass AFS tokens to remote host.
579: The argument to this keyword must be
1.2 deraadt 580: .Dq yes
581: or
582: .Dq no .
583: .It Cm BatchMode
584: If set to
585: .Dq yes ,
1.40 aaron 586: passphrase/password querying will be disabled.
587: This option is useful in scripts and other batch jobs where you have no
588: user to supply the password.
589: The argument must be
1.2 deraadt 590: .Dq yes
591: or
592: .Dq no .
1.34 markus 593: .It Cm CheckHostIP
594: If this flag is set to
595: .Dq yes ,
596: ssh will additionally check the host ip address in the
597: .Pa known_hosts
1.42 aaron 598: file.
599: This allows ssh to detect if a host key changed due to DNS spoofing.
1.34 markus 600: If the option is set to
601: .Dq no ,
602: the check will not be executed.
1.2 deraadt 603: .It Cm Cipher
1.40 aaron 604: Specifies the cipher to use for encrypting the session.
605: Currently,
1.2 deraadt 606: .Dq blowfish ,
1.1 deraadt 607: and
1.10 provos 608: .Dq 3des
1.40 aaron 609: are supported.
610: The default is
1.2 deraadt 611: .Dq 3des .
1.45 markus 612: .It Cm Ciphers
613: Specifies the ciphers allowed for protocol version 2
614: in order of preference.
615: Multiple ciphers must be comma-separated.
616: The default is
1.51 markus 617: .Dq 3des-cbc,blowfish-cbc,arcfour,cast128-cbc .
1.2 deraadt 618: .It Cm Compression
1.40 aaron 619: Specifies whether to use compression.
620: The argument must be
1.2 deraadt 621: .Dq yes
622: or
623: .Dq no .
624: .It Cm CompressionLevel
1.40 aaron 625: Specifies the compression level to use if compression is enable.
626: The argument must be an integer from 1 (fast) to 9 (slow, best).
627: The default level is 6, which is good for most applications.
628: The meaning of the values is the same as in
1.34 markus 629: .Xr gzip 1 .
1.2 deraadt 630: .It Cm ConnectionAttempts
1.1 deraadt 631: Specifies the number of tries (one per second) to make before falling
1.40 aaron 632: back to rsh or exiting.
633: The argument must be an integer.
634: This may be useful in scripts if the connection sometimes fails.
1.50 markus 635: .It Cm DSAAuthentication
636: Specifies whether to try DSA authentication.
637: The argument to this keyword must be
638: .Dq yes
639: or
640: .Dq no .
641: DSA authentication will only be
642: attempted if a DSA identity file exists.
643: Note that this option applies to protocol version 2 only.
1.2 deraadt 644: .It Cm EscapeChar
645: Sets the escape character (default:
646: .Ql ~ ) .
647: The escape character can also
1.40 aaron 648: be set on the command line.
649: The argument should be a single character,
1.2 deraadt 650: .Ql ^
651: followed by a letter, or
652: .Dq none
653: to disable the escape
1.1 deraadt 654: character entirely (making the connection transparent for binary
655: data).
1.44 aaron 656: .It Cm FallBackToRsh
1.1 deraadt 657: Specifies that if connecting via
1.2 deraadt 658: .Nm
1.1 deraadt 659: fails due to a connection refused error (there is no
1.2 deraadt 660: .Xr sshd 8
1.44 aaron 661: listening on the remote host),
1.2 deraadt 662: .Xr rsh 1
1.1 deraadt 663: should automatically be used instead (after a suitable warning about
1.40 aaron 664: the session being unencrypted).
665: The argument must be
1.2 deraadt 666: .Dq yes
667: or
668: .Dq no .
669: .It Cm ForwardAgent
1.1 deraadt 670: Specifies whether the connection to the authentication agent (if any)
1.40 aaron 671: will be forwarded to the remote machine.
672: The argument must be
1.2 deraadt 673: .Dq yes
674: or
1.54 ! markus 675: .Dq no .
! 676: The default is
1.2 deraadt 677: .Dq no .
678: .It Cm ForwardX11
1.1 deraadt 679: Specifies whether X11 connections will be automatically redirected
1.44 aaron 680: over the secure channel and
1.2 deraadt 681: .Ev DISPLAY
1.40 aaron 682: set.
1.44 aaron 683: The argument must be
1.2 deraadt 684: .Dq yes
685: or
1.38 markus 686: .Dq no .
687: The default is
1.3 deraadt 688: .Dq no .
689: .It Cm GatewayPorts
690: Specifies whether remote hosts are allowed to connect to local
691: forwarded ports.
692: The argument must be
693: .Dq yes
694: or
695: .Dq no .
696: The default is
1.2 deraadt 697: .Dq no .
698: .It Cm GlobalKnownHostsFile
1.44 aaron 699: Specifies a file to use instead of
1.2 deraadt 700: .Pa /etc/ssh_known_hosts .
701: .It Cm HostName
1.40 aaron 702: Specifies the real host name to log into.
703: This can be used to specify nicknames or abbreviations for hosts.
704: Default is the name given on the command line.
705: Numeric IP addresses are also permitted (both on the command line and in
1.2 deraadt 706: .Cm HostName
1.1 deraadt 707: specifications).
1.2 deraadt 708: .It Cm IdentityFile
1.1 deraadt 709: Specifies the file from which the user's RSA authentication identity
1.2 deraadt 710: is read (default
1.49 markus 711: .Pa $HOME/.ssh/identity
1.2 deraadt 712: in the user's home directory).
1.1 deraadt 713: Additionally, any identities represented by the authentication agent
1.40 aaron 714: will be used for authentication.
715: The file name may use the tilde
716: syntax to refer to a user's home directory.
717: It is possible to have
1.1 deraadt 718: multiple identity files specified in configuration files; all these
719: identities will be tried in sequence.
1.48 markus 720: .It Cm IdentityFile2
721: Specifies the file from which the user's DSA authentication identity
722: is read (default
1.49 markus 723: .Pa $HOME/.ssh/id_dsa
1.48 markus 724: in the user's home directory).
725: The file name may use the tilde
726: syntax to refer to a user's home directory.
727: It is possible to have
728: multiple identity files specified in configuration files; all these
729: identities will be tried in sequence.
1.2 deraadt 730: .It Cm KeepAlive
1.1 deraadt 731: Specifies whether the system should send keepalive messages to the
1.40 aaron 732: other side.
733: If they are sent, death of the connection or crash of one
734: of the machines will be properly noticed.
735: However, this means that
1.1 deraadt 736: connections will die if the route is down temporarily, and some people
1.41 aaron 737: find it annoying.
1.2 deraadt 738: .Pp
739: The default is
740: .Dq yes
741: (to send keepalives), and the client will notice
1.40 aaron 742: if the network goes down or the remote host dies.
743: This is important in scripts, and many users want it too.
1.2 deraadt 744: .Pp
745: To disable keepalives, the value should be set to
746: .Dq no
747: in both the server and the client configuration files.
748: .It Cm KerberosAuthentication
1.42 aaron 749: Specifies whether Kerberos authentication will be used.
750: The argument to this keyword must be
1.4 dugsong 751: .Dq yes
752: or
753: .Dq no .
1.2 deraadt 754: .It Cm KerberosTgtPassing
1.42 aaron 755: Specifies whether a Kerberos TGT will be forwarded to the server.
756: This will only work if the Kerberos server is actually an AFS kaserver.
757: The argument to this keyword must be
1.4 dugsong 758: .Dq yes
759: or
760: .Dq no .
1.2 deraadt 761: .It Cm LocalForward
1.1 deraadt 762: Specifies that a TCP/IP port on the local machine be forwarded over
1.40 aaron 763: the secure channel to given host:port from the remote machine.
764: The first argument must be a port number, and the second must be
765: host:port.
766: Multiple forwardings may be specified, and additional
767: forwardings can be given on the command line.
768: Only the superuser can forward privileged ports.
1.24 markus 769: .It Cm LogLevel
770: Gives the verbosity level that is used when logging messages from
771: .Nm ssh .
772: The possible values are:
1.39 djm 773: QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG.
1.24 markus 774: The default is INFO.
1.14 dugsong 775: .It Cm NumberOfPasswordPrompts
1.42 aaron 776: Specifies the number of password prompts before giving up.
777: The argument to this keyword must be an integer.
778: Default is 3.
1.34 markus 779: .It Cm PasswordAuthentication
1.40 aaron 780: Specifies whether to use password authentication.
781: The argument to this keyword must be
1.34 markus 782: .Dq yes
783: or
784: .Dq no .
1.50 markus 785: Note that this option applies to both protocol version 1 and 2.
1.2 deraadt 786: .It Cm Port
1.40 aaron 787: Specifies the port number to connect on the remote host.
788: Default is 22.
1.45 markus 789: .It Cm Protocol
790: Specifies the protocol versions
791: .Nm
792: should support in order of preference.
793: The possible values are
794: .Dq 1
795: and
796: .Dq 2 .
797: Multiple versions must be comma-separated.
798: The default is
1.49 markus 799: .Dq 1,2 .
800: This means that
801: .Nm
802: tries version 1 and falls back to version 2
1.52 hugh 803: if version 1 is not available.
1.2 deraadt 804: .It Cm ProxyCommand
1.40 aaron 805: Specifies the command to use to connect to the server.
806: The command
807: string extends to the end of the line, and is executed with
808: .Pa /bin/sh .
809: In the command string,
810: .Ql %h
811: will be substituted by the host name to
812: connect and
813: .Ql %p
814: by the port.
815: The command can be basically anything,
816: and should read from its standard input and write to its standard output.
817: It should eventually connect an
1.2 deraadt 818: .Xr sshd 8
1.1 deraadt 819: server running on some machine, or execute
1.2 deraadt 820: .Ic sshd -i
1.40 aaron 821: somewhere.
822: Host key management will be done using the
1.1 deraadt 823: HostName of the host being connected (defaulting to the name typed by
824: the user).
1.29 markus 825: Note that
826: .Cm CheckHostIP
827: is not available for connects with a proxy command.
1.2 deraadt 828: .Pp
829: .It Cm RemoteForward
1.1 deraadt 830: Specifies that a TCP/IP port on the remote machine be forwarded over
1.40 aaron 831: the secure channel to given host:port from the local machine.
832: The first argument must be a port number, and the second must be
833: host:port.
834: Multiple forwardings may be specified, and additional
835: forwardings can be given on the command line.
836: Only the superuser can forward privileged ports.
1.2 deraadt 837: .It Cm RhostsAuthentication
1.40 aaron 838: Specifies whether to try rhosts based authentication.
839: Note that this
1.1 deraadt 840: declaration only affects the client side and has no effect whatsoever
1.40 aaron 841: on security.
842: Disabling rhosts authentication may reduce
1.1 deraadt 843: authentication time on slow connections when rhosts authentication is
1.40 aaron 844: not used.
845: Most servers do not permit RhostsAuthentication because it
846: is not secure (see RhostsRSAAuthentication).
847: The argument to this keyword must be
1.2 deraadt 848: .Dq yes
849: or
850: .Dq no .
851: .It Cm RhostsRSAAuthentication
1.1 deraadt 852: Specifies whether to try rhosts based authentication with RSA host
1.40 aaron 853: authentication.
854: This is the primary authentication method for most sites.
855: The argument must be
1.2 deraadt 856: .Dq yes
857: or
858: .Dq no .
859: .It Cm RSAAuthentication
1.40 aaron 860: Specifies whether to try RSA authentication.
861: The argument to this keyword must be
1.2 deraadt 862: .Dq yes
863: or
864: .Dq no .
1.1 deraadt 865: RSA authentication will only be
866: attempted if the identity file exists, or an authentication agent is
867: running.
1.50 markus 868: Note that this option applies to protocol version 1 only.
1.27 markus 869: .It Cm SkeyAuthentication
870: Specifies whether to use
871: .Xr skey 1
1.40 aaron 872: authentication.
873: The argument to this keyword must be
1.27 markus 874: .Dq yes
875: or
876: .Dq no .
877: The default is
878: .Dq no .
1.2 deraadt 879: .It Cm StrictHostKeyChecking
880: If this flag is set to
1.44 aaron 881: .Dq yes ,
1.2 deraadt 882: .Nm
1.1 deraadt 883: ssh will never automatically add host keys to the
1.2 deraadt 884: .Pa $HOME/.ssh/known_hosts
1.48 markus 885: and
886: .Pa $HOME/.ssh/known_hosts2
887: files, and refuses to connect hosts whose host key has changed.
1.40 aaron 888: This provides maximum protection against trojan horse attacks.
889: However, it can be somewhat annoying if you don't have good
1.2 deraadt 890: .Pa /etc/ssh_known_hosts
1.48 markus 891: and
892: .Pa /etc/ssh_known_hosts2
1.1 deraadt 893: files installed and frequently
1.40 aaron 894: connect new hosts.
895: Basically this option forces the user to manually
896: add any new hosts.
897: Normally this option is disabled, and new hosts
898: will automatically be added to the known host files.
899: The host keys of
900: known hosts will be verified automatically in either case.
901: The argument must be
1.2 deraadt 902: .Dq yes
903: or
904: .Dq no .
1.16 markus 905: .It Cm UsePrivilegedPort
906: Specifies whether to use a privileged port for outgoing connections.
907: The argument must be
908: .Dq yes
909: or
910: .Dq no .
911: The default is
912: .Dq yes .
913: Note that setting this option to
914: .Dq no
1.30 provos 915: turns off
1.16 markus 916: .Cm RhostsAuthentication
917: and
918: .Cm RhostsRSAAuthentication .
1.34 markus 919: .It Cm User
1.40 aaron 920: Specifies the user to log in as.
921: This can be useful if you have a different user name on different machines.
922: This saves the trouble of
1.34 markus 923: having to remember to give the user name on the command line.
924: .It Cm UserKnownHostsFile
925: Specifies a file to use instead of
926: .Pa $HOME/.ssh/known_hosts .
1.2 deraadt 927: .It Cm UseRsh
1.40 aaron 928: Specifies that rlogin/rsh should be used for this host.
929: It is possible that the host does not at all support the
1.2 deraadt 930: .Nm
1.40 aaron 931: protocol.
932: This causes
1.2 deraadt 933: .Nm
1.40 aaron 934: to immediately execute
1.2 deraadt 935: .Xr rsh 1 .
1.1 deraadt 936: All other options (except
1.2 deraadt 937: .Cm HostName )
1.40 aaron 938: are ignored if this has been specified.
939: The argument must be
1.2 deraadt 940: .Dq yes
941: or
942: .Dq no .
943: .Sh ENVIRONMENT
944: .Nm
1.1 deraadt 945: will normally set the following environment variables:
1.2 deraadt 946: .Bl -tag -width Ds
947: .It Ev DISPLAY
948: The
949: .Ev DISPLAY
1.40 aaron 950: variable indicates the location of the X11 server.
1.44 aaron 951: It is automatically set by
1.2 deraadt 952: .Nm
953: to point to a value of the form
954: .Dq hostname:n
955: where hostname indicates
1.40 aaron 956: the host where the shell runs, and n is an integer >= 1.
957: .Nm
958: uses this special value to forward X11 connections over the secure
959: channel.
960: The user should normally not set DISPLAY explicitly, as that
1.1 deraadt 961: will render the X11 connection insecure (and will require the user to
962: manually copy any required authorization cookies).
1.2 deraadt 963: .It Ev HOME
1.1 deraadt 964: Set to the path of the user's home directory.
1.2 deraadt 965: .It Ev LOGNAME
966: Synonym for
1.12 aaron 967: .Ev USER ;
968: set for compatibility with systems that use this variable.
1.2 deraadt 969: .It Ev MAIL
1.1 deraadt 970: Set to point the user's mailbox.
1.40 aaron 971: .It Ev PATH
1.2 deraadt 972: Set to the default
973: .Ev PATH ,
974: as specified when compiling
1.12 aaron 975: .Nm ssh .
1.18 markus 976: .It Ev SSH_AUTH_SOCK
1.17 markus 977: indicates the path of a unix-domain socket used to communicate with the
978: agent.
1.2 deraadt 979: .It Ev SSH_CLIENT
1.40 aaron 980: Identifies the client end of the connection.
981: The variable contains
1.1 deraadt 982: three space-separated values: client ip-address, client port number,
983: and server port number.
1.2 deraadt 984: .It Ev SSH_TTY
1.1 deraadt 985: This is set to the name of the tty (path to the device) associated
1.40 aaron 986: with the current shell or command.
987: If the current session has no tty,
1.1 deraadt 988: this variable is not set.
1.2 deraadt 989: .It Ev TZ
1.1 deraadt 990: The timezone variable is set to indicate the present timezone if it
991: was set when the daemon was started (e.i., the daemon passes the value
992: on to new connections).
1.2 deraadt 993: .It Ev USER
1.1 deraadt 994: Set to the name of the user logging in.
1.2 deraadt 995: .El
996: .Pp
1.44 aaron 997: Additionally,
1.2 deraadt 998: .Nm
1.44 aaron 999: reads
1000: .Pa $HOME/.ssh/environment ,
1.2 deraadt 1001: and adds lines of the format
1002: .Dq VARNAME=value
1.12 aaron 1003: to the environment.
1.2 deraadt 1004: .Sh FILES
1.36 markus 1005: .Bl -tag -width Ds
1.2 deraadt 1006: .It Pa $HOME/.ssh/known_hosts
1.1 deraadt 1007: Records host keys for all hosts the user has logged into (that are not
1.2 deraadt 1008: in
1009: .Pa /etc/ssh_known_hosts ) .
1010: See
1011: .Xr sshd 8 .
1.48 markus 1012: .It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa
1013: Contains the RSA and the DSA authentication identity of the user.
1014: These files
1015: contain sensitive data and should be readable by the user but not
1.15 markus 1016: accessible by others (read/write/execute).
1017: Note that
1018: .Nm
1.48 markus 1019: ignores a private key file if it is accessible by others.
1.15 markus 1020: It is possible to specify a passphrase when
1.1 deraadt 1021: generating the key; the passphrase will be used to encrypt the
1.8 deraadt 1022: sensitive part of this file using 3DES.
1.48 markus 1023: .It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub
1.1 deraadt 1024: Contains the public key for authentication (public part of the
1.40 aaron 1025: identity file in human-readable form).
1.48 markus 1026: The contents of the
1027: .Pa $HOME/.ssh/identity.pub
1028: file should be added to
1.2 deraadt 1029: .Pa $HOME/.ssh/authorized_keys
1030: on all machines
1.40 aaron 1031: where you wish to log in using RSA authentication.
1.48 markus 1032: The contents of the
1033: .Pa $HOME/.ssh/id_dsa.pub
1034: file should be added to
1035: .Pa $HOME/.ssh/authorized_keys2
1036: on all machines
1037: where you wish to log in using DSA authentication.
1038: These files are not
1.40 aaron 1039: sensitive and can (but need not) be readable by anyone.
1.48 markus 1040: These files are
1041: never used automatically and are not necessary; they is only provided for
1.1 deraadt 1042: the convenience of the user.
1.2 deraadt 1043: .It Pa $HOME/.ssh/config
1.40 aaron 1044: This is the per-user configuration file.
1045: The format of this file is described above.
1046: This file is used by the
1.2 deraadt 1047: .Nm
1.40 aaron 1048: client.
1049: This file does not usually contain any sensitive information,
1.1 deraadt 1050: but the recommended permissions are read/write for the user, and not
1051: accessible by others.
1.2 deraadt 1052: .It Pa $HOME/.ssh/authorized_keys
1.40 aaron 1053: Lists the RSA keys that can be used for logging in as this user.
1054: The format of this file is described in the
1.2 deraadt 1055: .Xr sshd 8
1.40 aaron 1056: manual page.
1057: In the simplest form the format is the same as the .pub
1.1 deraadt 1058: identity files (that is, each line contains the number of bits in
1059: modulus, public exponent, modulus, and comment fields, separated by
1.40 aaron 1060: spaces).
1061: This file is not highly sensitive, but the recommended
1.1 deraadt 1062: permissions are read/write for the user, and not accessible by others.
1.48 markus 1063: .It Pa $HOME/.ssh/authorized_keys2
1064: Lists the DSA keys that can be used for logging in as this user.
1065: This file is not highly sensitive, but the recommended
1066: permissions are read/write for the user, and not accessible by others.
1067: .It Pa /etc/ssh_known_hosts, /etc/ssh_known_hosts2
1.40 aaron 1068: Systemwide list of known host keys.
1.48 markus 1069: .Pa /etc/ssh_known_hosts
1070: contains RSA and
1071: .Pa /etc/ssh_known_hosts2
1072: contains DSA keys.
1073: These files should be prepared by the
1.1 deraadt 1074: system administrator to contain the public host keys of all machines in the
1.40 aaron 1075: organization.
1076: This file should be world-readable.
1077: This file contains
1.1 deraadt 1078: public keys, one per line, in the following format (fields separated
1079: by spaces): system name, number of bits in modulus, public exponent,
1.40 aaron 1080: modulus, and optional comment field.
1081: When different names are used
1.1 deraadt 1082: for the same machine, all such names should be listed, separated by
1.40 aaron 1083: commas.
1084: The format is described on the
1.2 deraadt 1085: .Xr sshd 8
1.1 deraadt 1086: manual page.
1.2 deraadt 1087: .Pp
1.1 deraadt 1088: The canonical system name (as returned by name servers) is used by
1.2 deraadt 1089: .Xr sshd 8
1.1 deraadt 1090: to verify the client host when logging in; other names are needed because
1.2 deraadt 1091: .Nm
1.1 deraadt 1092: does not convert the user-supplied name to a canonical name before
1093: checking the key, because someone with access to the name servers
1094: would then be able to fool host authentication.
1.2 deraadt 1095: .It Pa /etc/ssh_config
1.40 aaron 1096: Systemwide configuration file.
1097: This file provides defaults for those
1.1 deraadt 1098: values that are not specified in the user's configuration file, and
1.40 aaron 1099: for those users who do not have a configuration file.
1100: This file must be world-readable.
1.2 deraadt 1101: .It Pa $HOME/.rhosts
1102: This file is used in
1103: .Pa \&.rhosts
1104: authentication to list the
1.40 aaron 1105: host/user pairs that are permitted to log in.
1106: (Note that this file is
1.1 deraadt 1107: also used by rlogin and rsh, which makes using this file insecure.)
1108: Each line of the file contains a host name (in the canonical form
1109: returned by name servers), and then a user name on that host,
1.40 aaron 1110: separated by a space.
1111: One some machines this file may need to be
1.1 deraadt 1112: world-readable if the user's home directory is on a NFS partition,
1113: because
1.2 deraadt 1114: .Xr sshd 8
1.40 aaron 1115: reads it as root.
1116: Additionally, this file must be owned by the user,
1117: and must not have write permissions for anyone else.
1118: The recommended
1.1 deraadt 1119: permission for most machines is read/write for the user, and not
1120: accessible by others.
1.2 deraadt 1121: .Pp
1.1 deraadt 1122: Note that by default
1.2 deraadt 1123: .Xr sshd 8
1.1 deraadt 1124: will be installed so that it requires successful RSA host
1.40 aaron 1125: authentication before permitting \s+2.\s0rhosts authentication.
1126: If your server machine does not have the client's host key in
1.2 deraadt 1127: .Pa /etc/ssh_known_hosts ,
1128: you can store it in
1129: .Pa $HOME/.ssh/known_hosts .
1130: The easiest way to do this is to
1.1 deraadt 1131: connect back to the client from the server machine using ssh; this
1.48 markus 1132: will automatically add the host key to
1.2 deraadt 1133: .Pa $HOME/.ssh/known_hosts .
1134: .It Pa $HOME/.shosts
1135: This file is used exactly the same way as
1136: .Pa \&.rhosts .
1137: The purpose for
1.1 deraadt 1138: having this file is to be able to use rhosts authentication with
1.2 deraadt 1139: .Nm
1140: without permitting login with
1141: .Xr rlogin 1
1142: or
1143: .Xr rsh 1 .
1144: .It Pa /etc/hosts.equiv
1145: This file is used during
1.40 aaron 1146: .Pa \&.rhosts authentication.
1147: It contains
1.1 deraadt 1148: canonical hosts names, one per line (the full format is described on
1149: the
1.2 deraadt 1150: .Xr sshd 8
1.40 aaron 1151: manual page).
1152: If the client host is found in this file, login is
1.1 deraadt 1153: automatically permitted provided client and server user names are the
1.40 aaron 1154: same.
1155: Additionally, successful RSA host authentication is normally
1156: required.
1157: This file should only be writable by root.
1.2 deraadt 1158: .It Pa /etc/shosts.equiv
1.44 aaron 1159: This file is processed exactly as
1.2 deraadt 1160: .Pa /etc/hosts.equiv .
1.1 deraadt 1161: This file may be useful to permit logins using
1.2 deraadt 1162: .Nm
1.1 deraadt 1163: but not using rsh/rlogin.
1.2 deraadt 1164: .It Pa /etc/sshrc
1.1 deraadt 1165: Commands in this file are executed by
1.2 deraadt 1166: .Nm
1.1 deraadt 1167: when the user logs in just before the user's shell (or command) is started.
1168: See the
1.2 deraadt 1169: .Xr sshd 8
1.1 deraadt 1170: manual page for more information.
1.2 deraadt 1171: .It Pa $HOME/.ssh/rc
1.1 deraadt 1172: Commands in this file are executed by
1.2 deraadt 1173: .Nm
1.1 deraadt 1174: when the user logs in just before the user's shell (or command) is
1175: started.
1.44 aaron 1176: See the
1.2 deraadt 1177: .Xr sshd 8
1.1 deraadt 1178: manual page for more information.
1.31 markus 1179: .It Pa $HOME/.ssh/environment
1180: Contains additional definitions for environment variables, see section
1181: .Sx ENVIRONMENT
1182: above.
1.5 deraadt 1183: .It Pa libcrypto.so.X.1
1184: A version of this library which includes support for the RSA algorithm
1185: is required for proper operation.
1.2 deraadt 1186: .Sh AUTHOR
1.20 provos 1187: OpenSSH
1.37 deraadt 1188: is a derivative of the original (free) ssh 1.2.12 release by Tatu Ylonen,
1.40 aaron 1189: but with bugs removed and newer features re-added.
1190: Rapidly after the
1.37 deraadt 1191: 1.2.12 release, newer versions of the original ssh bore successively
1192: more restrictive licenses, and thus demand for a free version was born.
1.47 markus 1193: .Pp
1.37 deraadt 1194: This version of OpenSSH
1.20 provos 1195: .Bl -bullet
1196: .It
1.35 aaron 1197: has all components of a restrictive nature (i.e., patents, see
1.21 deraadt 1198: .Xr ssl 8 )
1199: directly removed from the source code; any licensed or patented components
1200: are chosen from
1201: external libraries.
1.20 provos 1202: .It
1.47 markus 1203: has been updated to support SSH protocol 1.5 and 2, making it compatible with
1204: all other SSH clients and servers.
1.20 provos 1205: .It
1.44 aaron 1206: contains added support for
1.20 provos 1207: .Xr kerberos 8
1208: authentication and ticket passing.
1209: .It
1.21 deraadt 1210: supports one-time password authentication with
1.20 provos 1211: .Xr skey 1 .
1212: .El
1213: .Pp
1214: The libraries described in
1.5 deraadt 1215: .Xr ssl 8
1216: are required for proper operation.
1.25 provos 1217: .Pp
1.26 aaron 1218: OpenSSH has been created by Aaron Campbell, Bob Beck, Markus Friedl,
1.25 provos 1219: Niels Provos, Theo de Raadt, and Dug Song.
1.47 markus 1220: .Pp
1221: The support for SSH protocol 2 was written by Markus Friedl.
1.2 deraadt 1222: .Sh SEE ALSO
1223: .Xr rlogin 1 ,
1224: .Xr rsh 1 ,
1225: .Xr scp 1 ,
1226: .Xr ssh-add 1 ,
1227: .Xr ssh-agent 1 ,
1228: .Xr ssh-keygen 1 ,
1229: .Xr telnet 1 ,
1.5 deraadt 1230: .Xr sshd 8 ,
1231: .Xr ssl 8
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