Annotation of src/usr.bin/ssh/ssh.1, Revision 1.48
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: .\"
1.48 ! markus 12: .\" $Id: ssh.1,v 1.47 2000/05/02 22:01:55 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
66: his/her identity to the remote machine using one of several methods.
1.2 deraadt 67: .Pp
1.1 deraadt 68: First, if the machine the user logs in from is listed in
1.2 deraadt 69: .Pa /etc/hosts.equiv
1.1 deraadt 70: or
1.2 deraadt 71: .Pa /etc/shosts.equiv
1.1 deraadt 72: on the remote machine, and the user names are
73: the same on both sides, the user is immediately permitted to log in.
1.44 aaron 74: Second, if
1.2 deraadt 75: .Pa \&.rhosts
1.1 deraadt 76: or
1.2 deraadt 77: .Pa \&.shosts
1.1 deraadt 78: exists in the user's home directory on the
79: remote machine and contains a line containing the name of the client
80: machine and the name of the user on that machine, the user is
1.40 aaron 81: permitted to log in.
82: This form of authentication alone is normally not
1.1 deraadt 83: allowed by the server because it is not secure.
1.2 deraadt 84: .Pp
1.1 deraadt 85: The second (and primary) authentication method is the
1.2 deraadt 86: .Pa rhosts
1.1 deraadt 87: or
1.2 deraadt 88: .Pa hosts.equiv
1.40 aaron 89: method combined with RSA-based host authentication.
90: It means that if the login would be permitted by
1.2 deraadt 91: .Pa \&.rhosts ,
92: .Pa \&.shosts ,
93: .Pa /etc/hosts.equiv ,
1.1 deraadt 94: or
1.2 deraadt 95: .Pa /etc/shosts.equiv ,
1.11 deraadt 96: and if additionally the server can verify the client's
1.44 aaron 97: host key (see
1.2 deraadt 98: .Pa /etc/ssh_known_hosts
1.23 markus 99: and
100: .Pa $HOME/.ssh/known_hosts
1.1 deraadt 101: in the
1.2 deraadt 102: .Sx FILES
1.40 aaron 103: section), only then login is permitted.
104: This authentication method closes security holes due to IP
105: spoofing, DNS spoofing and routing spoofing.
106: [Note to the administrator:
1.2 deraadt 107: .Pa /etc/hosts.equiv ,
108: .Pa \&.rhosts ,
1.1 deraadt 109: and the rlogin/rsh protocol in general, are inherently insecure and should be
110: disabled if security is desired.]
1.2 deraadt 111: .Pp
1.44 aaron 112: As a third authentication method,
1.2 deraadt 113: .Nm
1.1 deraadt 114: supports RSA based authentication.
115: The scheme is based on public-key cryptography: there are cryptosystems
116: where encryption and decryption are done using separate keys, and it
117: is not possible to derive the decryption key from the encryption key.
1.40 aaron 118: RSA is one such system.
1.44 aaron 119: The idea is that each user creates a public/private
1.40 aaron 120: key pair for authentication purposes.
121: The server knows the public key, and only the user knows the private key.
1.44 aaron 122: The file
1.2 deraadt 123: .Pa $HOME/.ssh/authorized_keys
1.1 deraadt 124: lists the public keys that are permitted for logging
1.40 aaron 125: in.
126: When the user logs in, the
1.2 deraadt 127: .Nm
1.1 deraadt 128: program tells the server which key pair it would like to use for
1.40 aaron 129: authentication.
130: The server checks if this key is permitted, and if
1.1 deraadt 131: so, sends the user (actually the
1.2 deraadt 132: .Nm
1.1 deraadt 133: program running on behalf of the user) a challenge, a random number,
1.40 aaron 134: encrypted by the user's public key.
135: The challenge can only be
136: decrypted using the proper private key.
137: The user's client then decrypts the
1.1 deraadt 138: challenge using the private key, proving that he/she knows the private
139: key but without disclosing it to the server.
1.2 deraadt 140: .Pp
141: .Nm
1.40 aaron 142: implements the RSA authentication protocol automatically.
143: The user creates his/her RSA key pair by running
1.2 deraadt 144: .Xr ssh-keygen 1 .
1.44 aaron 145: This stores the private key in
1.2 deraadt 146: .Pa \&.ssh/identity
1.1 deraadt 147: and the public key in
1.2 deraadt 148: .Pa \&.ssh/identity.pub
1.40 aaron 149: in the user's home directory.
150: The user should then copy the
1.2 deraadt 151: .Pa identity.pub
1.44 aaron 152: to
1.2 deraadt 153: .Pa \&.ssh/authorized_keys
1.44 aaron 154: in his/her home directory on the remote machine (the
1.2 deraadt 155: .Pa authorized_keys
1.44 aaron 156: file corresponds to the conventional
1.2 deraadt 157: .Pa \&.rhosts
1.1 deraadt 158: file, and has one key
1.40 aaron 159: per line, though the lines can be very long).
160: After this, the user can log in without giving the password.
161: RSA authentication is much
1.1 deraadt 162: more secure than rhosts authentication.
1.2 deraadt 163: .Pp
1.1 deraadt 164: The most convenient way to use RSA authentication may be with an
1.40 aaron 165: authentication agent.
166: See
1.2 deraadt 167: .Xr ssh-agent 1
1.1 deraadt 168: for more information.
1.2 deraadt 169: .Pp
1.44 aaron 170: If other authentication methods fail,
1.2 deraadt 171: .Nm
1.40 aaron 172: prompts the user for a password.
173: The password is sent to the remote
1.1 deraadt 174: host for checking; however, since all communications are encrypted,
175: the password cannot be seen by someone listening on the network.
1.2 deraadt 176: .Pp
1.1 deraadt 177: When the user's identity has been accepted by the server, the server
178: either executes the given command, or logs into the machine and gives
1.40 aaron 179: the user a normal shell on the remote machine.
180: All communication with
1.1 deraadt 181: the remote command or shell will be automatically encrypted.
1.2 deraadt 182: .Pp
1.1 deraadt 183: If a pseudo-terminal has been allocated (normal login session), the
1.2 deraadt 184: user can disconnect with
185: .Ic ~. ,
186: and suspend
187: .Nm
188: with
189: .Ic ~^Z .
190: All forwarded connections can be listed with
1.44 aaron 191: .Ic ~#
1.2 deraadt 192: and if
1.1 deraadt 193: the session blocks waiting for forwarded X11 or TCP/IP
1.2 deraadt 194: connections to terminate, it can be backgrounded with
195: .Ic ~&
196: (this should not be used while the user shell is active, as it can cause the
1.40 aaron 197: shell to hang).
198: All available escapes can be listed with
1.2 deraadt 199: .Ic ~? .
200: .Pp
201: A single tilde character can be sent as
202: .Ic ~~
203: (or by following the tilde by a character other than those described above).
1.1 deraadt 204: The escape character must always follow a newline to be interpreted as
1.40 aaron 205: special.
206: The escape character can be changed in configuration files
207: or on the command line.
1.2 deraadt 208: .Pp
1.1 deraadt 209: If no pseudo tty has been allocated, the
210: session is transparent and can be used to reliably transfer binary
1.40 aaron 211: data.
212: On most systems, setting the escape character to
1.2 deraadt 213: .Dq none
214: will also make the session transparent even if a tty is used.
215: .Pp
1.1 deraadt 216: The session terminates when the command or shell in on the remote
217: machine exists and all X11 and TCP/IP connections have been closed.
218: The exit status of the remote program is returned as the exit status
219: of
1.2 deraadt 220: .Nm ssh .
221: .Pp
1.1 deraadt 222: If the user is using X11 (the
1.2 deraadt 223: .Ev DISPLAY
1.1 deraadt 224: environment variable is set), the connection to the X11 display is
225: automatically forwarded to the remote side in such a way that any X11
226: programs started from the shell (or command) will go through the
227: encrypted channel, and the connection to the real X server will be made
1.40 aaron 228: from the local machine.
229: The user should not manually set
1.2 deraadt 230: .Ev DISPLAY .
1.1 deraadt 231: Forwarding of X11 connections can be
232: configured on the command line or in configuration files.
1.2 deraadt 233: .Pp
234: The
1.44 aaron 235: .Ev DISPLAY
1.2 deraadt 236: value set by
237: .Nm
1.1 deraadt 238: will point to the server machine, but with a display number greater
1.40 aaron 239: than zero.
240: This is normal, and happens because
1.2 deraadt 241: .Nm
242: creates a
243: .Dq proxy
244: X server on the server machine for forwarding the
1.1 deraadt 245: connections over the encrypted channel.
1.2 deraadt 246: .Pp
247: .Nm
1.1 deraadt 248: will also automatically set up Xauthority data on the server machine.
249: For this purpose, it will generate a random authorization cookie,
250: store it in Xauthority on the server, and verify that any forwarded
251: connections carry this cookie and replace it by the real cookie when
1.40 aaron 252: the connection is opened.
253: The real authentication cookie is never
1.1 deraadt 254: sent to the server machine (and no cookies are sent in the plain).
1.2 deraadt 255: .Pp
1.1 deraadt 256: If the user is using an authentication agent, the connection to the agent
257: is automatically forwarded to the remote side unless disabled on
258: command line or in a configuration file.
1.2 deraadt 259: .Pp
1.1 deraadt 260: Forwarding of arbitrary TCP/IP connections over the secure channel can
1.40 aaron 261: be specified either on command line or in a configuration file.
262: One possible application of TCP/IP forwarding is a secure connection to an
1.1 deraadt 263: electronic purse; another is going trough firewalls.
1.2 deraadt 264: .Pp
265: .Nm
1.1 deraadt 266: automatically maintains and checks a database containing RSA-based
1.40 aaron 267: identifications for all hosts it has ever been used with.
1.44 aaron 268: The database is stored in
1.2 deraadt 269: .Pa \&.ssh/known_hosts
1.40 aaron 270: in the user's home directory.
1.44 aaron 271: Additionally, the file
1.2 deraadt 272: .Pa /etc/ssh_known_hosts
1.40 aaron 273: is automatically checked for known hosts.
274: Any new hosts are automatically added to the user's file.
275: If a host's identification
1.1 deraadt 276: ever changes,
1.2 deraadt 277: .Nm
1.1 deraadt 278: warns about this and disables password authentication to prevent a
1.40 aaron 279: trojan horse from getting the user's password.
280: Another purpose of
1.1 deraadt 281: this mechanism is to prevent man-in-the-middle attacks which could
1.40 aaron 282: otherwise be used to circumvent the encryption.
283: The
1.2 deraadt 284: .Cm StrictHostKeyChecking
1.1 deraadt 285: option (see below) can be used to prevent logins to machines whose
286: host key is not known or has changed.
1.2 deraadt 287: .Sh OPTIONS
288: .Bl -tag -width Ds
1.4 dugsong 289: .It Fl a
1.42 aaron 290: Disables forwarding of the authentication agent connection.
291: This may also be specified on a per-host basis in the configuration file.
1.6 deraadt 292: .It Fl c Ar blowfish|3des
1.44 aaron 293: Selects the cipher to use for encrypting the session.
1.2 deraadt 294: .Ar 3des
1.40 aaron 295: is used by default.
1.44 aaron 296: It is believed to be secure.
1.5 deraadt 297: .Ar 3des
298: (triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
299: It is presumably more secure than the
1.2 deraadt 300: .Ar des
1.5 deraadt 301: cipher which is no longer supported in ssh.
302: .Ar blowfish
303: is a fast block cipher, it appears very secure and is much faster than
1.40 aaron 304: .Ar 3des .
1.2 deraadt 305: .It Fl e Ar ch|^ch|none
306: Sets the escape character for sessions with a pty (default:
307: .Ql ~ ) .
1.40 aaron 308: The escape character is only recognized at the beginning of a line.
309: The escape character followed by a dot
1.2 deraadt 310: .Pq Ql \&.
311: closes the connection, followed
1.1 deraadt 312: by control-Z suspends the connection, and followed by itself sends the
1.40 aaron 313: escape character once.
314: Setting the character to
1.2 deraadt 315: .Dq none
316: disables any escapes and makes the session fully transparent.
317: .It Fl f
318: Requests
319: .Nm
1.40 aaron 320: to go to background just before command execution.
321: This is useful if
1.2 deraadt 322: .Nm
323: is going to ask for passwords or passphrases, but the user
1.40 aaron 324: wants it in the background.
1.44 aaron 325: This implies
1.2 deraadt 326: .Fl n .
1.1 deraadt 327: The recommended way to start X11 programs at a remote site is with
1.2 deraadt 328: something like
329: .Ic ssh -f host xterm .
1.34 markus 330: .It Fl g
331: Allows remote hosts to connect to local forwarded ports.
1.2 deraadt 332: .It Fl i Ar identity_file
1.44 aaron 333: Selects the file from which the identity (private key) for
1.40 aaron 334: RSA authentication is read.
1.44 aaron 335: Default is
1.2 deraadt 336: .Pa \&.ssh/identity
1.40 aaron 337: in the user's home directory.
338: Identity files may also be specified on
339: a per-host basis in the configuration file.
340: It is possible to have multiple
1.2 deraadt 341: .Fl i
342: options (and multiple identities specified in
1.1 deraadt 343: configuration files).
1.2 deraadt 344: .It Fl k
1.42 aaron 345: Disables forwarding of Kerberos tickets and AFS tokens.
346: This may also be specified on a per-host basis in the configuration file.
1.2 deraadt 347: .It Fl l Ar login_name
1.40 aaron 348: Specifies the user to log in as on the remote machine.
349: This also may be specified on a per-host basis in the configuration file.
1.2 deraadt 350: .It Fl n
351: Redirects stdin from
352: .Pa /dev/null
353: (actually, prevents reading from stdin).
1.1 deraadt 354: This must be used when
1.2 deraadt 355: .Nm
1.40 aaron 356: is run in the background.
357: A common trick is to use this to run X11 programs on a remote machine.
358: For example,
1.2 deraadt 359: .Ic ssh -n shadows.cs.hut.fi emacs &
360: will start an emacs on shadows.cs.hut.fi, and the X11
1.1 deraadt 361: connection will be automatically forwarded over an encrypted channel.
362: The
1.2 deraadt 363: .Nm
1.1 deraadt 364: program will be put in the background.
365: (This does not work if
1.2 deraadt 366: .Nm
367: needs to ask for a password or passphrase; see also the
368: .Fl f
369: option.)
370: .It Fl o Ar option
1.1 deraadt 371: Can be used to give options in the format used in the config file.
372: This is useful for specifying options for which there is no separate
1.40 aaron 373: command-line flag.
374: The option has the same format as a line in the configuration file.
1.2 deraadt 375: .It Fl p Ar port
1.40 aaron 376: Port to connect to on the remote host.
377: This can be specified on a
1.1 deraadt 378: per-host basis in the configuration file.
1.16 markus 379: .It Fl P
380: Use a non-privileged port for outgoing connections.
381: This can be used if your firewall does
382: not permit connections from privileged ports.
1.30 provos 383: Note that this option turns off
1.16 markus 384: .Cm RhostsAuthentication
385: and
386: .Cm RhostsRSAAuthentication .
1.2 deraadt 387: .It Fl q
1.40 aaron 388: Quiet mode.
389: Causes all warning and diagnostic messages to be suppressed.
390: Only fatal errors are displayed.
1.2 deraadt 391: .It Fl t
1.40 aaron 392: Force pseudo-tty allocation.
1.43 brad 393: This can be used to execute arbitrary
1.40 aaron 394: screen-based programs on a remote machine, which can be very useful,
395: e.g., when implementing menu services.
1.2 deraadt 396: .It Fl v
1.40 aaron 397: Verbose mode.
398: Causes
1.2 deraadt 399: .Nm
1.40 aaron 400: to print debugging messages about its progress.
401: This is helpful in
1.1 deraadt 402: debugging connection, authentication, and configuration problems.
1.22 provos 403: The verbose mode is also used to display
404: .Xr skey 1
405: challenges, if the user entered "s/key" as password.
1.2 deraadt 406: .It Fl x
1.40 aaron 407: Disables X11 forwarding.
408: This can also be specified on a per-host basis in a configuration file.
1.2 deraadt 409: .It Fl X
1.1 deraadt 410: Enables X11 forwarding.
1.2 deraadt 411: .It Fl C
1.1 deraadt 412: Requests compression of all data (including stdin, stdout, stderr, and
1.40 aaron 413: data for forwarded X11 and TCP/IP connections).
414: The compression algorithm is the same used by
1.34 markus 415: .Xr gzip 1 ,
416: and the
1.2 deraadt 417: .Dq level
418: can be controlled by the
419: .Cm CompressionLevel
1.40 aaron 420: option (see below).
421: Compression is desirable on modem lines and other
1.1 deraadt 422: slow connections, but will only slow down things on fast networks.
423: The default value can be set on a host-by-host basis in the
424: configuration files; see the
1.2 deraadt 425: .Cm Compress
1.1 deraadt 426: option below.
1.2 deraadt 427: .It Fl L Ar port:host:hostport
1.1 deraadt 428: Specifies that the given port on the local (client) host is to be
1.40 aaron 429: forwarded to the given host and port on the remote side.
430: This works by allocating a socket to listen to
1.2 deraadt 431: .Ar port
1.1 deraadt 432: on the local side, and whenever a connection is made to this port, the
433: connection is forwarded over the secure channel, and a connection is
434: made to
1.32 markus 435: .Ar host
436: port
437: .Ar hostport
1.40 aaron 438: from the remote machine.
439: Port forwardings can also be specified in the configuration file.
440: Only root can forward privileged ports.
1.32 markus 441: IPv6 addresses can be specified with an alternative syntax:
442: .Ar port/host/hostport
1.2 deraadt 443: .It Fl R Ar port:host:hostport
1.1 deraadt 444: Specifies that the given port on the remote (server) host is to be
1.40 aaron 445: forwarded to the given host and port on the local side.
446: This works by allocating a socket to listen to
1.2 deraadt 447: .Ar port
1.1 deraadt 448: on the remote side, and whenever a connection is made to this port, the
449: connection is forwarded over the secure channel, and a connection is
450: made to
1.32 markus 451: .Ar host
452: port
453: .Ar hostport
1.40 aaron 454: from the local machine.
455: Port forwardings can also be specified in the configuration file.
456: Privileged ports can be forwarded only when
1.1 deraadt 457: logging in as root on the remote machine.
1.46 markus 458: .It Fl 2
459: Forces
460: .Nm
461: to use protocol version 2 only.
1.32 markus 462: .It Fl 4
463: Forces
464: .Nm
465: to use IPv4 addresses only.
466: .It Fl 6
467: Forces
468: .Nm
469: to use IPv6 addresses only.
1.2 deraadt 470: .El
471: .Sh CONFIGURATION FILES
472: .Nm
1.1 deraadt 473: obtains configuration data from the following sources (in this order):
474: command line options, user's configuration file
1.2 deraadt 475: .Pq Pa $HOME/.ssh/config ,
476: and system-wide configuration file
477: .Pq Pa /etc/ssh_config .
478: For each parameter, the first obtained value
1.40 aaron 479: will be used.
480: The configuration files contain sections bracketed by
481: .Dq Host
482: specifications, and that section is only applied for hosts that
483: match one of the patterns given in the specification.
484: The matched host name is the one given on the command line.
1.2 deraadt 485: .Pp
1.1 deraadt 486: Since the first obtained value for each parameter is used, more
487: host-specific declarations should be given near the beginning of the
488: file, and general defaults at the end.
1.2 deraadt 489: .Pp
1.1 deraadt 490: The configuration file has the following format:
1.2 deraadt 491: .Pp
492: Empty lines and lines starting with
493: .Ql #
494: are comments.
495: .Pp
496: Otherwise a line is of the format
497: .Dq keyword arguments .
498: The possible
1.1 deraadt 499: keywords and their meanings are as follows (note that the
500: configuration files are case-sensitive):
1.2 deraadt 501: .Bl -tag -width Ds
502: .It Cm Host
1.1 deraadt 503: Restricts the following declarations (up to the next
1.2 deraadt 504: .Cm Host
1.1 deraadt 505: keyword) to be only for those hosts that match one of the patterns
1.2 deraadt 506: given after the keyword.
507: .Ql \&*
508: and
509: .Ql ?
510: can be used as wildcards in the
1.40 aaron 511: patterns.
512: A single
1.2 deraadt 513: .Ql \&*
514: as a pattern can be used to provide global
1.40 aaron 515: defaults for all hosts.
516: The host is the
1.2 deraadt 517: .Ar hostname
1.1 deraadt 518: argument given on the command line (i.e., the name is not converted to
519: a canonicalized host name before matching).
1.2 deraadt 520: .It Cm AFSTokenPassing
1.42 aaron 521: Specifies whether to pass AFS tokens to remote host.
522: The argument to this keyword must be
1.2 deraadt 523: .Dq yes
524: or
525: .Dq no .
526: .It Cm BatchMode
527: If set to
528: .Dq yes ,
1.40 aaron 529: passphrase/password querying will be disabled.
530: This option is useful in scripts and other batch jobs where you have no
531: user to supply the password.
532: The argument must be
1.2 deraadt 533: .Dq yes
534: or
535: .Dq no .
1.34 markus 536: .It Cm CheckHostIP
537: If this flag is set to
538: .Dq yes ,
539: ssh will additionally check the host ip address in the
540: .Pa known_hosts
1.42 aaron 541: file.
542: This allows ssh to detect if a host key changed due to DNS spoofing.
1.34 markus 543: If the option is set to
544: .Dq no ,
545: the check will not be executed.
1.2 deraadt 546: .It Cm Cipher
1.40 aaron 547: Specifies the cipher to use for encrypting the session.
548: Currently,
1.2 deraadt 549: .Dq blowfish ,
1.1 deraadt 550: and
1.10 provos 551: .Dq 3des
1.40 aaron 552: are supported.
553: The default is
1.2 deraadt 554: .Dq 3des .
1.45 markus 555: .It Cm Ciphers
556: Specifies the ciphers allowed for protocol version 2
557: in order of preference.
558: Multiple ciphers must be comma-separated.
559: The default is
560: .Dq blowfish-cbc,3des-cbc,arcfour,cast128-cbc .
1.2 deraadt 561: .It Cm Compression
1.40 aaron 562: Specifies whether to use compression.
563: The argument must be
1.2 deraadt 564: .Dq yes
565: or
566: .Dq no .
567: .It Cm CompressionLevel
1.40 aaron 568: Specifies the compression level to use if compression is enable.
569: The argument must be an integer from 1 (fast) to 9 (slow, best).
570: The default level is 6, which is good for most applications.
571: The meaning of the values is the same as in
1.34 markus 572: .Xr gzip 1 .
1.2 deraadt 573: .It Cm ConnectionAttempts
1.1 deraadt 574: Specifies the number of tries (one per second) to make before falling
1.40 aaron 575: back to rsh or exiting.
576: The argument must be an integer.
577: This may be useful in scripts if the connection sometimes fails.
1.2 deraadt 578: .It Cm EscapeChar
579: Sets the escape character (default:
580: .Ql ~ ) .
581: The escape character can also
1.40 aaron 582: be set on the command line.
583: The argument should be a single character,
1.2 deraadt 584: .Ql ^
585: followed by a letter, or
586: .Dq none
587: to disable the escape
1.1 deraadt 588: character entirely (making the connection transparent for binary
589: data).
1.44 aaron 590: .It Cm FallBackToRsh
1.1 deraadt 591: Specifies that if connecting via
1.2 deraadt 592: .Nm
1.1 deraadt 593: fails due to a connection refused error (there is no
1.2 deraadt 594: .Xr sshd 8
1.44 aaron 595: listening on the remote host),
1.2 deraadt 596: .Xr rsh 1
1.1 deraadt 597: should automatically be used instead (after a suitable warning about
1.40 aaron 598: the session being unencrypted).
599: The argument must be
1.2 deraadt 600: .Dq yes
601: or
602: .Dq no .
603: .It Cm ForwardAgent
1.1 deraadt 604: Specifies whether the connection to the authentication agent (if any)
1.40 aaron 605: will be forwarded to the remote machine.
606: The argument must be
1.2 deraadt 607: .Dq yes
608: or
609: .Dq no .
610: .It Cm ForwardX11
1.1 deraadt 611: Specifies whether X11 connections will be automatically redirected
1.44 aaron 612: over the secure channel and
1.2 deraadt 613: .Ev DISPLAY
1.40 aaron 614: set.
1.44 aaron 615: The argument must be
1.2 deraadt 616: .Dq yes
617: or
1.38 markus 618: .Dq no .
619: The default is
1.3 deraadt 620: .Dq no .
621: .It Cm GatewayPorts
622: Specifies whether remote hosts are allowed to connect to local
623: forwarded ports.
624: The argument must be
625: .Dq yes
626: or
627: .Dq no .
628: The default is
1.2 deraadt 629: .Dq no .
630: .It Cm GlobalKnownHostsFile
1.44 aaron 631: Specifies a file to use instead of
1.2 deraadt 632: .Pa /etc/ssh_known_hosts .
633: .It Cm HostName
1.40 aaron 634: Specifies the real host name to log into.
635: This can be used to specify nicknames or abbreviations for hosts.
636: Default is the name given on the command line.
637: Numeric IP addresses are also permitted (both on the command line and in
1.2 deraadt 638: .Cm HostName
1.1 deraadt 639: specifications).
1.2 deraadt 640: .It Cm IdentityFile
1.1 deraadt 641: Specifies the file from which the user's RSA authentication identity
1.2 deraadt 642: is read (default
643: .Pa .ssh/identity
644: in the user's home directory).
1.1 deraadt 645: Additionally, any identities represented by the authentication agent
1.40 aaron 646: will be used for authentication.
647: The file name may use the tilde
648: syntax to refer to a user's home directory.
649: It is possible to have
1.1 deraadt 650: multiple identity files specified in configuration files; all these
651: identities will be tried in sequence.
1.48 ! markus 652: .It Cm IdentityFile2
! 653: Specifies the file from which the user's DSA authentication identity
! 654: is read (default
! 655: .Pa .ssh/id_dsa
! 656: in the user's home directory).
! 657: The file name may use the tilde
! 658: syntax to refer to a user's home directory.
! 659: It is possible to have
! 660: multiple identity files specified in configuration files; all these
! 661: identities will be tried in sequence.
1.2 deraadt 662: .It Cm KeepAlive
1.1 deraadt 663: Specifies whether the system should send keepalive messages to the
1.40 aaron 664: other side.
665: If they are sent, death of the connection or crash of one
666: of the machines will be properly noticed.
667: However, this means that
1.1 deraadt 668: connections will die if the route is down temporarily, and some people
1.41 aaron 669: find it annoying.
1.2 deraadt 670: .Pp
671: The default is
672: .Dq yes
673: (to send keepalives), and the client will notice
1.40 aaron 674: if the network goes down or the remote host dies.
675: This is important in scripts, and many users want it too.
1.2 deraadt 676: .Pp
677: To disable keepalives, the value should be set to
678: .Dq no
679: in both the server and the client configuration files.
680: .It Cm KerberosAuthentication
1.42 aaron 681: Specifies whether Kerberos authentication will be used.
682: The argument to this keyword must be
1.4 dugsong 683: .Dq yes
684: or
685: .Dq no .
1.2 deraadt 686: .It Cm KerberosTgtPassing
1.42 aaron 687: Specifies whether a Kerberos TGT will be forwarded to the server.
688: This will only work if the Kerberos server is actually an AFS kaserver.
689: The argument to this keyword must be
1.4 dugsong 690: .Dq yes
691: or
692: .Dq no .
1.2 deraadt 693: .It Cm LocalForward
1.1 deraadt 694: Specifies that a TCP/IP port on the local machine be forwarded over
1.40 aaron 695: the secure channel to given host:port from the remote machine.
696: The first argument must be a port number, and the second must be
697: host:port.
698: Multiple forwardings may be specified, and additional
699: forwardings can be given on the command line.
700: Only the superuser can forward privileged ports.
1.24 markus 701: .It Cm LogLevel
702: Gives the verbosity level that is used when logging messages from
703: .Nm ssh .
704: The possible values are:
1.39 djm 705: QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG.
1.24 markus 706: The default is INFO.
1.14 dugsong 707: .It Cm NumberOfPasswordPrompts
1.42 aaron 708: Specifies the number of password prompts before giving up.
709: The argument to this keyword must be an integer.
710: Default is 3.
1.34 markus 711: .It Cm PasswordAuthentication
1.40 aaron 712: Specifies whether to use password authentication.
713: The argument to this keyword must be
1.34 markus 714: .Dq yes
715: or
716: .Dq no .
1.2 deraadt 717: .It Cm Port
1.40 aaron 718: Specifies the port number to connect on the remote host.
719: Default is 22.
1.45 markus 720: .It Cm Protocol
721: Specifies the protocol versions
722: .Nm
723: should support in order of preference.
724: The possible values are
725: .Dq 1
726: and
727: .Dq 2 .
728: Multiple versions must be comma-separated.
729: The default is
730: .Dq 1 .
1.2 deraadt 731: .It Cm ProxyCommand
1.40 aaron 732: Specifies the command to use to connect to the server.
733: The command
734: string extends to the end of the line, and is executed with
735: .Pa /bin/sh .
736: In the command string,
737: .Ql %h
738: will be substituted by the host name to
739: connect and
740: .Ql %p
741: by the port.
742: The command can be basically anything,
743: and should read from its standard input and write to its standard output.
744: It should eventually connect an
1.2 deraadt 745: .Xr sshd 8
1.1 deraadt 746: server running on some machine, or execute
1.2 deraadt 747: .Ic sshd -i
1.40 aaron 748: somewhere.
749: Host key management will be done using the
1.1 deraadt 750: HostName of the host being connected (defaulting to the name typed by
751: the user).
1.29 markus 752: Note that
753: .Cm CheckHostIP
754: is not available for connects with a proxy command.
1.2 deraadt 755: .Pp
756: .It Cm RemoteForward
1.1 deraadt 757: Specifies that a TCP/IP port on the remote machine be forwarded over
1.40 aaron 758: the secure channel to given host:port from the local machine.
759: The first argument must be a port number, and the second must be
760: host:port.
761: Multiple forwardings may be specified, and additional
762: forwardings can be given on the command line.
763: Only the superuser can forward privileged ports.
1.2 deraadt 764: .It Cm RhostsAuthentication
1.40 aaron 765: Specifies whether to try rhosts based authentication.
766: Note that this
1.1 deraadt 767: declaration only affects the client side and has no effect whatsoever
1.40 aaron 768: on security.
769: Disabling rhosts authentication may reduce
1.1 deraadt 770: authentication time on slow connections when rhosts authentication is
1.40 aaron 771: not used.
772: Most servers do not permit RhostsAuthentication because it
773: is not secure (see RhostsRSAAuthentication).
774: The argument to this keyword must be
1.2 deraadt 775: .Dq yes
776: or
777: .Dq no .
778: .It Cm RhostsRSAAuthentication
1.1 deraadt 779: Specifies whether to try rhosts based authentication with RSA host
1.40 aaron 780: authentication.
781: This is the primary authentication method for most sites.
782: The argument must be
1.2 deraadt 783: .Dq yes
784: or
785: .Dq no .
786: .It Cm RSAAuthentication
1.40 aaron 787: Specifies whether to try RSA authentication.
788: The argument to this keyword must be
1.2 deraadt 789: .Dq yes
790: or
791: .Dq no .
1.1 deraadt 792: RSA authentication will only be
793: attempted if the identity file exists, or an authentication agent is
794: running.
1.27 markus 795: .It Cm SkeyAuthentication
796: Specifies whether to use
797: .Xr skey 1
1.40 aaron 798: authentication.
799: The argument to this keyword must be
1.27 markus 800: .Dq yes
801: or
802: .Dq no .
803: The default is
804: .Dq no .
1.2 deraadt 805: .It Cm StrictHostKeyChecking
806: If this flag is set to
1.44 aaron 807: .Dq yes ,
1.2 deraadt 808: .Nm
1.1 deraadt 809: ssh will never automatically add host keys to the
1.2 deraadt 810: .Pa $HOME/.ssh/known_hosts
1.48 ! markus 811: and
! 812: .Pa $HOME/.ssh/known_hosts2
! 813: files, and refuses to connect hosts whose host key has changed.
1.40 aaron 814: This provides maximum protection against trojan horse attacks.
815: However, it can be somewhat annoying if you don't have good
1.2 deraadt 816: .Pa /etc/ssh_known_hosts
1.48 ! markus 817: and
! 818: .Pa /etc/ssh_known_hosts2
1.1 deraadt 819: files installed and frequently
1.40 aaron 820: connect new hosts.
821: Basically this option forces the user to manually
822: add any new hosts.
823: Normally this option is disabled, and new hosts
824: will automatically be added to the known host files.
825: The host keys of
826: known hosts will be verified automatically in either case.
827: The argument must be
1.2 deraadt 828: .Dq yes
829: or
830: .Dq no .
1.16 markus 831: .It Cm UsePrivilegedPort
832: Specifies whether to use a privileged port for outgoing connections.
833: The argument must be
834: .Dq yes
835: or
836: .Dq no .
837: The default is
838: .Dq yes .
839: Note that setting this option to
840: .Dq no
1.30 provos 841: turns off
1.16 markus 842: .Cm RhostsAuthentication
843: and
844: .Cm RhostsRSAAuthentication .
1.34 markus 845: .It Cm User
1.40 aaron 846: Specifies the user to log in as.
847: This can be useful if you have a different user name on different machines.
848: This saves the trouble of
1.34 markus 849: having to remember to give the user name on the command line.
850: .It Cm UserKnownHostsFile
851: Specifies a file to use instead of
852: .Pa $HOME/.ssh/known_hosts .
1.2 deraadt 853: .It Cm UseRsh
1.40 aaron 854: Specifies that rlogin/rsh should be used for this host.
855: It is possible that the host does not at all support the
1.2 deraadt 856: .Nm
1.40 aaron 857: protocol.
858: This causes
1.2 deraadt 859: .Nm
1.40 aaron 860: to immediately execute
1.2 deraadt 861: .Xr rsh 1 .
1.1 deraadt 862: All other options (except
1.2 deraadt 863: .Cm HostName )
1.40 aaron 864: are ignored if this has been specified.
865: The argument must be
1.2 deraadt 866: .Dq yes
867: or
868: .Dq no .
869: .Sh ENVIRONMENT
870: .Nm
1.1 deraadt 871: will normally set the following environment variables:
1.2 deraadt 872: .Bl -tag -width Ds
873: .It Ev DISPLAY
874: The
875: .Ev DISPLAY
1.40 aaron 876: variable indicates the location of the X11 server.
1.44 aaron 877: It is automatically set by
1.2 deraadt 878: .Nm
879: to point to a value of the form
880: .Dq hostname:n
881: where hostname indicates
1.40 aaron 882: the host where the shell runs, and n is an integer >= 1.
883: .Nm
884: uses this special value to forward X11 connections over the secure
885: channel.
886: The user should normally not set DISPLAY explicitly, as that
1.1 deraadt 887: will render the X11 connection insecure (and will require the user to
888: manually copy any required authorization cookies).
1.2 deraadt 889: .It Ev HOME
1.1 deraadt 890: Set to the path of the user's home directory.
1.2 deraadt 891: .It Ev LOGNAME
892: Synonym for
1.12 aaron 893: .Ev USER ;
894: set for compatibility with systems that use this variable.
1.2 deraadt 895: .It Ev MAIL
1.1 deraadt 896: Set to point the user's mailbox.
1.40 aaron 897: .It Ev PATH
1.2 deraadt 898: Set to the default
899: .Ev PATH ,
900: as specified when compiling
1.12 aaron 901: .Nm ssh .
1.18 markus 902: .It Ev SSH_AUTH_SOCK
1.17 markus 903: indicates the path of a unix-domain socket used to communicate with the
904: agent.
1.2 deraadt 905: .It Ev SSH_CLIENT
1.40 aaron 906: Identifies the client end of the connection.
907: The variable contains
1.1 deraadt 908: three space-separated values: client ip-address, client port number,
909: and server port number.
1.2 deraadt 910: .It Ev SSH_TTY
1.1 deraadt 911: This is set to the name of the tty (path to the device) associated
1.40 aaron 912: with the current shell or command.
913: If the current session has no tty,
1.1 deraadt 914: this variable is not set.
1.2 deraadt 915: .It Ev TZ
1.1 deraadt 916: The timezone variable is set to indicate the present timezone if it
917: was set when the daemon was started (e.i., the daemon passes the value
918: on to new connections).
1.2 deraadt 919: .It Ev USER
1.1 deraadt 920: Set to the name of the user logging in.
1.2 deraadt 921: .El
922: .Pp
1.44 aaron 923: Additionally,
1.2 deraadt 924: .Nm
1.44 aaron 925: reads
926: .Pa $HOME/.ssh/environment ,
1.2 deraadt 927: and adds lines of the format
928: .Dq VARNAME=value
1.12 aaron 929: to the environment.
1.2 deraadt 930: .Sh FILES
1.36 markus 931: .Bl -tag -width Ds
1.2 deraadt 932: .It Pa $HOME/.ssh/known_hosts
1.1 deraadt 933: Records host keys for all hosts the user has logged into (that are not
1.2 deraadt 934: in
935: .Pa /etc/ssh_known_hosts ) .
936: See
937: .Xr sshd 8 .
1.48 ! markus 938: .It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa
! 939: Contains the RSA and the DSA authentication identity of the user.
! 940: These files
! 941: contain sensitive data and should be readable by the user but not
1.15 markus 942: accessible by others (read/write/execute).
943: Note that
944: .Nm
1.48 ! markus 945: ignores a private key file if it is accessible by others.
1.15 markus 946: It is possible to specify a passphrase when
1.1 deraadt 947: generating the key; the passphrase will be used to encrypt the
1.8 deraadt 948: sensitive part of this file using 3DES.
1.48 ! markus 949: .It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub
1.1 deraadt 950: Contains the public key for authentication (public part of the
1.40 aaron 951: identity file in human-readable form).
1.48 ! markus 952: The contents of the
! 953: .Pa $HOME/.ssh/identity.pub
! 954: file should be added to
1.2 deraadt 955: .Pa $HOME/.ssh/authorized_keys
956: on all machines
1.40 aaron 957: where you wish to log in using RSA authentication.
1.48 ! markus 958: The contents of the
! 959: .Pa $HOME/.ssh/id_dsa.pub
! 960: file should be added to
! 961: .Pa $HOME/.ssh/authorized_keys2
! 962: on all machines
! 963: where you wish to log in using DSA authentication.
! 964: These files are not
1.40 aaron 965: sensitive and can (but need not) be readable by anyone.
1.48 ! markus 966: These files are
! 967: never used automatically and are not necessary; they is only provided for
1.1 deraadt 968: the convenience of the user.
1.2 deraadt 969: .It Pa $HOME/.ssh/config
1.40 aaron 970: This is the per-user configuration file.
971: The format of this file is described above.
972: This file is used by the
1.2 deraadt 973: .Nm
1.40 aaron 974: client.
975: This file does not usually contain any sensitive information,
1.1 deraadt 976: but the recommended permissions are read/write for the user, and not
977: accessible by others.
1.2 deraadt 978: .It Pa $HOME/.ssh/authorized_keys
1.40 aaron 979: Lists the RSA keys that can be used for logging in as this user.
980: The format of this file is described in the
1.2 deraadt 981: .Xr sshd 8
1.40 aaron 982: manual page.
983: In the simplest form the format is the same as the .pub
1.1 deraadt 984: identity files (that is, each line contains the number of bits in
985: modulus, public exponent, modulus, and comment fields, separated by
1.40 aaron 986: spaces).
987: This file is not highly sensitive, but the recommended
1.1 deraadt 988: permissions are read/write for the user, and not accessible by others.
1.48 ! markus 989: .It Pa $HOME/.ssh/authorized_keys2
! 990: Lists the DSA keys that can be used for logging in as this user.
! 991: This file is not highly sensitive, but the recommended
! 992: permissions are read/write for the user, and not accessible by others.
! 993: .It Pa /etc/ssh_known_hosts, /etc/ssh_known_hosts2
1.40 aaron 994: Systemwide list of known host keys.
1.48 ! markus 995: .Pa /etc/ssh_known_hosts
! 996: contains RSA and
! 997: .Pa /etc/ssh_known_hosts2
! 998: contains DSA keys.
! 999: These files should be prepared by the
1.1 deraadt 1000: system administrator to contain the public host keys of all machines in the
1.40 aaron 1001: organization.
1002: This file should be world-readable.
1003: This file contains
1.1 deraadt 1004: public keys, one per line, in the following format (fields separated
1005: by spaces): system name, number of bits in modulus, public exponent,
1.40 aaron 1006: modulus, and optional comment field.
1007: When different names are used
1.1 deraadt 1008: for the same machine, all such names should be listed, separated by
1.40 aaron 1009: commas.
1010: The format is described on the
1.2 deraadt 1011: .Xr sshd 8
1.1 deraadt 1012: manual page.
1.2 deraadt 1013: .Pp
1.1 deraadt 1014: The canonical system name (as returned by name servers) is used by
1.2 deraadt 1015: .Xr sshd 8
1.1 deraadt 1016: to verify the client host when logging in; other names are needed because
1.2 deraadt 1017: .Nm
1.1 deraadt 1018: does not convert the user-supplied name to a canonical name before
1019: checking the key, because someone with access to the name servers
1020: would then be able to fool host authentication.
1.2 deraadt 1021: .It Pa /etc/ssh_config
1.40 aaron 1022: Systemwide configuration file.
1023: This file provides defaults for those
1.1 deraadt 1024: values that are not specified in the user's configuration file, and
1.40 aaron 1025: for those users who do not have a configuration file.
1026: This file must be world-readable.
1.2 deraadt 1027: .It Pa $HOME/.rhosts
1028: This file is used in
1029: .Pa \&.rhosts
1030: authentication to list the
1.40 aaron 1031: host/user pairs that are permitted to log in.
1032: (Note that this file is
1.1 deraadt 1033: also used by rlogin and rsh, which makes using this file insecure.)
1034: Each line of the file contains a host name (in the canonical form
1035: returned by name servers), and then a user name on that host,
1.40 aaron 1036: separated by a space.
1037: One some machines this file may need to be
1.1 deraadt 1038: world-readable if the user's home directory is on a NFS partition,
1039: because
1.2 deraadt 1040: .Xr sshd 8
1.40 aaron 1041: reads it as root.
1042: Additionally, this file must be owned by the user,
1043: and must not have write permissions for anyone else.
1044: The recommended
1.1 deraadt 1045: permission for most machines is read/write for the user, and not
1046: accessible by others.
1.2 deraadt 1047: .Pp
1.1 deraadt 1048: Note that by default
1.2 deraadt 1049: .Xr sshd 8
1.1 deraadt 1050: will be installed so that it requires successful RSA host
1.40 aaron 1051: authentication before permitting \s+2.\s0rhosts authentication.
1052: If your server machine does not have the client's host key in
1.2 deraadt 1053: .Pa /etc/ssh_known_hosts ,
1054: you can store it in
1055: .Pa $HOME/.ssh/known_hosts .
1056: The easiest way to do this is to
1.1 deraadt 1057: connect back to the client from the server machine using ssh; this
1.48 ! markus 1058: will automatically add the host key to
1.2 deraadt 1059: .Pa $HOME/.ssh/known_hosts .
1060: .It Pa $HOME/.shosts
1061: This file is used exactly the same way as
1062: .Pa \&.rhosts .
1063: The purpose for
1.1 deraadt 1064: having this file is to be able to use rhosts authentication with
1.2 deraadt 1065: .Nm
1066: without permitting login with
1067: .Xr rlogin 1
1068: or
1069: .Xr rsh 1 .
1070: .It Pa /etc/hosts.equiv
1071: This file is used during
1.40 aaron 1072: .Pa \&.rhosts authentication.
1073: It contains
1.1 deraadt 1074: canonical hosts names, one per line (the full format is described on
1075: the
1.2 deraadt 1076: .Xr sshd 8
1.40 aaron 1077: manual page).
1078: If the client host is found in this file, login is
1.1 deraadt 1079: automatically permitted provided client and server user names are the
1.40 aaron 1080: same.
1081: Additionally, successful RSA host authentication is normally
1082: required.
1083: This file should only be writable by root.
1.2 deraadt 1084: .It Pa /etc/shosts.equiv
1.44 aaron 1085: This file is processed exactly as
1.2 deraadt 1086: .Pa /etc/hosts.equiv .
1.1 deraadt 1087: This file may be useful to permit logins using
1.2 deraadt 1088: .Nm
1.1 deraadt 1089: but not using rsh/rlogin.
1.2 deraadt 1090: .It Pa /etc/sshrc
1.1 deraadt 1091: Commands in this file are executed by
1.2 deraadt 1092: .Nm
1.1 deraadt 1093: when the user logs in just before the user's shell (or command) is started.
1094: See the
1.2 deraadt 1095: .Xr sshd 8
1.1 deraadt 1096: manual page for more information.
1.2 deraadt 1097: .It Pa $HOME/.ssh/rc
1.1 deraadt 1098: Commands in this file are executed by
1.2 deraadt 1099: .Nm
1.1 deraadt 1100: when the user logs in just before the user's shell (or command) is
1101: started.
1.44 aaron 1102: See the
1.2 deraadt 1103: .Xr sshd 8
1.1 deraadt 1104: manual page for more information.
1.31 markus 1105: .It Pa $HOME/.ssh/environment
1106: Contains additional definitions for environment variables, see section
1107: .Sx ENVIRONMENT
1108: above.
1.5 deraadt 1109: .It Pa libcrypto.so.X.1
1110: A version of this library which includes support for the RSA algorithm
1111: is required for proper operation.
1.2 deraadt 1112: .Sh AUTHOR
1.20 provos 1113: OpenSSH
1.37 deraadt 1114: is a derivative of the original (free) ssh 1.2.12 release by Tatu Ylonen,
1.40 aaron 1115: but with bugs removed and newer features re-added.
1116: Rapidly after the
1.37 deraadt 1117: 1.2.12 release, newer versions of the original ssh bore successively
1118: more restrictive licenses, and thus demand for a free version was born.
1.47 markus 1119: .Pp
1.37 deraadt 1120: This version of OpenSSH
1.20 provos 1121: .Bl -bullet
1122: .It
1.35 aaron 1123: has all components of a restrictive nature (i.e., patents, see
1.21 deraadt 1124: .Xr ssl 8 )
1125: directly removed from the source code; any licensed or patented components
1126: are chosen from
1127: external libraries.
1.20 provos 1128: .It
1.47 markus 1129: has been updated to support SSH protocol 1.5 and 2, making it compatible with
1130: all other SSH clients and servers.
1.20 provos 1131: .It
1.44 aaron 1132: contains added support for
1.20 provos 1133: .Xr kerberos 8
1134: authentication and ticket passing.
1135: .It
1.21 deraadt 1136: supports one-time password authentication with
1.20 provos 1137: .Xr skey 1 .
1138: .El
1139: .Pp
1140: The libraries described in
1.5 deraadt 1141: .Xr ssl 8
1142: are required for proper operation.
1.25 provos 1143: .Pp
1.26 aaron 1144: OpenSSH has been created by Aaron Campbell, Bob Beck, Markus Friedl,
1.25 provos 1145: Niels Provos, Theo de Raadt, and Dug Song.
1.47 markus 1146: .Pp
1147: The support for SSH protocol 2 was written by Markus Friedl.
1.2 deraadt 1148: .Sh SEE ALSO
1149: .Xr rlogin 1 ,
1150: .Xr rsh 1 ,
1151: .Xr scp 1 ,
1152: .Xr ssh-add 1 ,
1153: .Xr ssh-agent 1 ,
1154: .Xr ssh-keygen 1 ,
1155: .Xr telnet 1 ,
1.5 deraadt 1156: .Xr sshd 8 ,
1157: .Xr ssl 8