Annotation of src/usr.bin/ssh/ssh.1, Revision 1.196.2.1
1.1 deraadt 1: .\" -*- nroff -*-
2: .\"
3: .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
4: .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5: .\" All rights reserved
6: .\"
1.59 deraadt 7: .\" As far as I am concerned, the code I have written for this software
8: .\" can be used freely for any purpose. Any derived versions of this
9: .\" software must be clearly marked as such, and if the derived work is
10: .\" incompatible with the protocol description in the RFC file, it must be
11: .\" called by a name other than "ssh" or "Secure Shell".
12: .\"
1.93 deraadt 13: .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
14: .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
15: .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
1.59 deraadt 16: .\"
17: .\" Redistribution and use in source and binary forms, with or without
18: .\" modification, are permitted provided that the following conditions
19: .\" are met:
20: .\" 1. Redistributions of source code must retain the above copyright
21: .\" notice, this list of conditions and the following disclaimer.
22: .\" 2. Redistributions in binary form must reproduce the above copyright
23: .\" notice, this list of conditions and the following disclaimer in the
24: .\" documentation and/or other materials provided with the distribution.
1.1 deraadt 25: .\"
1.59 deraadt 26: .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
27: .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
28: .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
29: .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
30: .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
31: .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
32: .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
33: .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
34: .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
35: .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
1.1 deraadt 36: .\"
1.196.2.1! brad 37: .\" $OpenBSD: ssh.1,v 1.205 2005/03/07 23:41:54 jmc Exp $
1.2 deraadt 38: .Dd September 25, 1999
39: .Dt SSH 1
40: .Os
41: .Sh NAME
42: .Nm ssh
1.96 deraadt 43: .Nd OpenSSH SSH client (remote login program)
1.2 deraadt 44: .Sh SYNOPSIS
45: .Nm ssh
1.196.2.1! brad 46: .Bk -words
1.191 djm 47: .Op Fl 1246AaCfgkMNnqsTtVvXxY
1.108 markus 48: .Op Fl b Ar bind_address
1.51 markus 49: .Op Fl c Ar cipher_spec
1.176 jmc 50: .Op Fl D Ar port
1.2 deraadt 51: .Op Fl e Ar escape_char
1.176 jmc 52: .Op Fl F Ar configfile
1.2 deraadt 53: .Op Fl i Ar identity_file
1.196.2.1! brad 54: .Oo Fl L\ \&
1.12 aaron 55: .Sm off
1.196.2.1! brad 56: .Oo Ar bind_address : Oc
! 57: .Ar port : host : hostport
1.12 aaron 58: .Sm on
59: .Oc
1.176 jmc 60: .Op Fl l Ar login_name
61: .Op Fl m Ar mac_spec
1.196.2.1! brad 62: .Op Fl O Ar ctl_cmd
1.176 jmc 63: .Op Fl o Ar option
64: .Op Fl p Ar port
1.196.2.1! brad 65: .Oo Fl R\ \&
1.12 aaron 66: .Sm off
1.196.2.1! brad 67: .Oo Ar bind_address : Oc
! 68: .Ar port : host : hostport
1.12 aaron 69: .Sm on
70: .Oc
1.196.2.1! brad 71: .Op Fl S Ar ctl_path
1.176 jmc 72: .Oo Ar user Ns @ Oc Ns Ar hostname
1.2 deraadt 73: .Op Ar command
1.196.2.1! brad 74: .Ek
1.44 aaron 75: .Sh DESCRIPTION
1.2 deraadt 76: .Nm
1.96 deraadt 77: (SSH client) is a program for logging into a remote machine and for
1.40 aaron 78: executing commands on a remote machine.
1.176 jmc 79: It is intended to replace rlogin and rsh,
80: and provide secure encrypted communications between
1.40 aaron 81: two untrusted hosts over an insecure network.
1.176 jmc 82: X11 connections and arbitrary TCP/IP ports
83: can also be forwarded over the secure channel.
1.2 deraadt 84: .Pp
85: .Nm
1.44 aaron 86: connects and logs into the specified
1.176 jmc 87: .Ar hostname
88: (with optional
89: .Ar user
90: name).
1.1 deraadt 91: The user must prove
1.49 markus 92: his/her identity to the remote machine using one of several methods
1.176 jmc 93: depending on the protocol version used.
1.49 markus 94: .Pp
1.176 jmc 95: If
96: .Ar command
97: is specified,
98: .Ar command
99: is executed on the remote host instead of a login shell.
1.49 markus 100: .Ss SSH protocol version 1
1.195 markus 101: The first authentication method is the
102: .Em rhosts
103: or
104: .Em hosts.equiv
105: method combined with RSA-based host authentication.
106: If the machine the user logs in from is listed in
1.2 deraadt 107: .Pa /etc/hosts.equiv
1.1 deraadt 108: or
1.2 deraadt 109: .Pa /etc/shosts.equiv
1.1 deraadt 110: on the remote machine, and the user names are
1.195 markus 111: the same on both sides, or if the files
112: .Pa $HOME/.rhosts
1.1 deraadt 113: or
1.195 markus 114: .Pa $HOME/.shosts
115: exist in the user's home directory on the
116: remote machine and contain a line containing the name of the client
1.1 deraadt 117: machine and the name of the user on that machine, the user is
1.195 markus 118: considered for log in.
119: Additionally, if the server can verify the client's
1.44 aaron 120: host key (see
1.147 deraadt 121: .Pa /etc/ssh/ssh_known_hosts
1.23 markus 122: and
123: .Pa $HOME/.ssh/known_hosts
1.1 deraadt 124: in the
1.2 deraadt 125: .Sx FILES
1.176 jmc 126: section), only then is login permitted.
1.40 aaron 127: This authentication method closes security holes due to IP
128: spoofing, DNS spoofing and routing spoofing.
129: [Note to the administrator:
1.2 deraadt 130: .Pa /etc/hosts.equiv ,
1.49 markus 131: .Pa $HOME/.rhosts ,
1.1 deraadt 132: and the rlogin/rsh protocol in general, are inherently insecure and should be
133: disabled if security is desired.]
1.2 deraadt 134: .Pp
1.195 markus 135: As a second authentication method,
1.2 deraadt 136: .Nm
1.1 deraadt 137: supports RSA based authentication.
138: The scheme is based on public-key cryptography: there are cryptosystems
139: where encryption and decryption are done using separate keys, and it
140: is not possible to derive the decryption key from the encryption key.
1.40 aaron 141: RSA is one such system.
1.44 aaron 142: The idea is that each user creates a public/private
1.40 aaron 143: key pair for authentication purposes.
144: The server knows the public key, and only the user knows the private key.
1.176 jmc 145: .Pp
1.44 aaron 146: The file
1.2 deraadt 147: .Pa $HOME/.ssh/authorized_keys
1.176 jmc 148: lists the public keys that are permitted for logging in.
1.40 aaron 149: When the user logs in, the
1.2 deraadt 150: .Nm
1.1 deraadt 151: program tells the server which key pair it would like to use for
1.40 aaron 152: authentication.
1.176 jmc 153: The server checks if this key is permitted, and if so,
154: sends the user (actually the
1.2 deraadt 155: .Nm
1.1 deraadt 156: program running on behalf of the user) a challenge, a random number,
1.40 aaron 157: encrypted by the user's public key.
1.176 jmc 158: The challenge can only be decrypted using the proper private key.
159: The user's client then decrypts the challenge using the private key,
160: proving that he/she knows the private key
161: but without disclosing it to the server.
1.2 deraadt 162: .Pp
163: .Nm
1.40 aaron 164: implements the RSA authentication protocol automatically.
165: The user creates his/her RSA key pair by running
1.2 deraadt 166: .Xr ssh-keygen 1 .
1.44 aaron 167: This stores the private key in
1.49 markus 168: .Pa $HOME/.ssh/identity
1.176 jmc 169: and stores the public key in
1.49 markus 170: .Pa $HOME/.ssh/identity.pub
1.40 aaron 171: in the user's home directory.
172: The user should then copy the
1.2 deraadt 173: .Pa identity.pub
1.44 aaron 174: to
1.49 markus 175: .Pa $HOME/.ssh/authorized_keys
1.44 aaron 176: in his/her home directory on the remote machine (the
1.2 deraadt 177: .Pa authorized_keys
1.44 aaron 178: file corresponds to the conventional
1.49 markus 179: .Pa $HOME/.rhosts
1.1 deraadt 180: file, and has one key
1.40 aaron 181: per line, though the lines can be very long).
182: After this, the user can log in without giving the password.
1.2 deraadt 183: .Pp
1.1 deraadt 184: The most convenient way to use RSA authentication may be with an
1.40 aaron 185: authentication agent.
186: See
1.2 deraadt 187: .Xr ssh-agent 1
1.1 deraadt 188: for more information.
1.2 deraadt 189: .Pp
1.44 aaron 190: If other authentication methods fail,
1.2 deraadt 191: .Nm
1.40 aaron 192: prompts the user for a password.
193: The password is sent to the remote
1.1 deraadt 194: host for checking; however, since all communications are encrypted,
195: the password cannot be seen by someone listening on the network.
1.49 markus 196: .Ss SSH protocol version 2
1.176 jmc 197: When a user connects using protocol version 2,
1.145 markus 198: similar authentication methods are available.
1.107 markus 199: Using the default values for
200: .Cm PreferredAuthentications ,
1.123 markus 201: the client will try to authenticate first using the hostbased method;
1.176 jmc 202: if this method fails, public key authentication is attempted,
203: and finally if this method fails, keyboard-interactive and
1.123 markus 204: password authentication are tried.
1.49 markus 205: .Pp
206: The public key method is similar to RSA authentication described
1.107 markus 207: in the previous section and allows the RSA or DSA algorithm to be used:
1.102 itojun 208: The client uses his private key,
1.49 markus 209: .Pa $HOME/.ssh/id_dsa
1.102 itojun 210: or
211: .Pa $HOME/.ssh/id_rsa ,
1.49 markus 212: to sign the session identifier and sends the result to the server.
213: The server checks whether the matching public key is listed in
1.115 markus 214: .Pa $HOME/.ssh/authorized_keys
1.49 markus 215: and grants access if both the key is found and the signature is correct.
216: The session identifier is derived from a shared Diffie-Hellman value
217: and is only known to the client and the server.
218: .Pp
1.176 jmc 219: If public key authentication fails or is not available, a password
220: can be sent encrypted to the remote host to prove the user's identity.
1.107 markus 221: .Pp
222: Additionally,
223: .Nm
224: supports hostbased or challenge response authentication.
1.49 markus 225: .Pp
226: Protocol 2 provides additional mechanisms for confidentiality
1.189 dtucker 227: (the traffic is encrypted using AES, 3DES, Blowfish, CAST128 or Arcfour)
228: and integrity (hmac-md5, hmac-sha1, hmac-ripemd160).
1.49 markus 229: Note that protocol 1 lacks a strong mechanism for ensuring the
230: integrity of the connection.
231: .Ss Login session and remote execution
1.1 deraadt 232: When the user's identity has been accepted by the server, the server
233: either executes the given command, or logs into the machine and gives
1.40 aaron 234: the user a normal shell on the remote machine.
235: All communication with
1.1 deraadt 236: the remote command or shell will be automatically encrypted.
1.2 deraadt 237: .Pp
1.1 deraadt 238: If a pseudo-terminal has been allocated (normal login session), the
1.104 djm 239: user may use the escape characters noted below.
1.2 deraadt 240: .Pp
1.176 jmc 241: If no pseudo-tty has been allocated,
242: the session is transparent and can be used to reliably transfer binary data.
1.40 aaron 243: On most systems, setting the escape character to
1.2 deraadt 244: .Dq none
245: will also make the session transparent even if a tty is used.
246: .Pp
1.71 djm 247: The session terminates when the command or shell on the remote
1.92 markus 248: machine exits and all X11 and TCP/IP connections have been closed.
1.176 jmc 249: The exit status of the remote program is returned as the exit status of
1.2 deraadt 250: .Nm ssh .
1.104 djm 251: .Ss Escape Characters
1.176 jmc 252: When a pseudo-terminal has been requested,
253: .Nm
254: supports a number of functions through the use of an escape character.
1.104 djm 255: .Pp
256: A single tilde character can be sent as
257: .Ic ~~
1.119 stevesk 258: or by following the tilde by a character other than those described below.
1.104 djm 259: The escape character must always follow a newline to be interpreted as
260: special.
261: The escape character can be changed in configuration files using the
262: .Cm EscapeChar
1.117 itojun 263: configuration directive or on the command line by the
1.104 djm 264: .Fl e
265: option.
266: .Pp
267: The supported escapes (assuming the default
268: .Ql ~ )
269: are:
270: .Bl -tag -width Ds
271: .It Cm ~.
1.176 jmc 272: Disconnect.
1.104 djm 273: .It Cm ~^Z
1.176 jmc 274: Background
275: .Nm ssh .
1.104 djm 276: .It Cm ~#
1.176 jmc 277: List forwarded connections.
1.104 djm 278: .It Cm ~&
1.176 jmc 279: Background
280: .Nm
281: at logout when waiting for forwarded connection / X11 sessions to terminate.
1.104 djm 282: .It Cm ~?
1.176 jmc 283: Display a list of escape characters.
1.170 markus 284: .It Cm ~B
1.176 jmc 285: Send a BREAK to the remote system
286: (only useful for SSH protocol version 2 and if the peer supports it).
1.149 jakob 287: .It Cm ~C
1.186 djm 288: Open command line.
289: Currently this allows the addition of port forwardings using the
1.149 jakob 290: .Fl L
291: and
292: .Fl R
1.186 djm 293: options (see below).
1.188 jmc 294: It also allows the cancellation of existing remote port-forwardings
1.186 djm 295: using
296: .Fl KR Ar hostport .
1.187 djm 297: Basic help is available, using the
298: .Fl h
1.186 djm 299: option.
1.104 djm 300: .It Cm ~R
1.176 jmc 301: Request rekeying of the connection
302: (only useful for SSH protocol version 2 and if the peer supports it).
1.104 djm 303: .El
1.49 markus 304: .Ss X11 and TCP forwarding
1.110 deraadt 305: If the
306: .Cm ForwardX11
307: variable is set to
308: .Dq yes
1.176 jmc 309: (or see the description of the
1.110 deraadt 310: .Fl X
311: and
312: .Fl x
313: options described later)
314: and the user is using X11 (the
1.2 deraadt 315: .Ev DISPLAY
1.1 deraadt 316: environment variable is set), the connection to the X11 display is
317: automatically forwarded to the remote side in such a way that any X11
318: programs started from the shell (or command) will go through the
319: encrypted channel, and the connection to the real X server will be made
1.40 aaron 320: from the local machine.
321: The user should not manually set
1.2 deraadt 322: .Ev DISPLAY .
1.1 deraadt 323: Forwarding of X11 connections can be
324: configured on the command line or in configuration files.
1.2 deraadt 325: .Pp
326: The
1.44 aaron 327: .Ev DISPLAY
1.2 deraadt 328: value set by
329: .Nm
1.176 jmc 330: will point to the server machine, but with a display number greater than zero.
1.40 aaron 331: This is normal, and happens because
1.2 deraadt 332: .Nm
333: creates a
334: .Dq proxy
335: X server on the server machine for forwarding the
1.1 deraadt 336: connections over the encrypted channel.
1.2 deraadt 337: .Pp
338: .Nm
1.1 deraadt 339: will also automatically set up Xauthority data on the server machine.
340: For this purpose, it will generate a random authorization cookie,
341: store it in Xauthority on the server, and verify that any forwarded
342: connections carry this cookie and replace it by the real cookie when
1.40 aaron 343: the connection is opened.
344: The real authentication cookie is never
1.1 deraadt 345: sent to the server machine (and no cookies are sent in the plain).
1.2 deraadt 346: .Pp
1.163 stevesk 347: If the
348: .Cm ForwardAgent
349: variable is set to
350: .Dq yes
1.176 jmc 351: (or see the description of the
1.163 stevesk 352: .Fl A
353: and
354: .Fl a
1.168 jmc 355: options described later) and
1.163 stevesk 356: the user is using an authentication agent, the connection to the agent
357: is automatically forwarded to the remote side.
1.2 deraadt 358: .Pp
1.1 deraadt 359: Forwarding of arbitrary TCP/IP connections over the secure channel can
1.120 stevesk 360: be specified either on the command line or in a configuration file.
1.40 aaron 361: One possible application of TCP/IP forwarding is a secure connection to an
1.92 markus 362: electronic purse; another is going through firewalls.
1.49 markus 363: .Ss Server authentication
1.2 deraadt 364: .Nm
1.49 markus 365: automatically maintains and checks a database containing
1.40 aaron 366: identifications for all hosts it has ever been used with.
1.116 markus 367: Host keys are stored in
1.49 markus 368: .Pa $HOME/.ssh/known_hosts
1.40 aaron 369: in the user's home directory.
1.116 markus 370: Additionally, the file
1.147 deraadt 371: .Pa /etc/ssh/ssh_known_hosts
1.116 markus 372: is automatically checked for known hosts.
1.40 aaron 373: Any new hosts are automatically added to the user's file.
1.176 jmc 374: If a host's identification ever changes,
1.2 deraadt 375: .Nm
1.1 deraadt 376: warns about this and disables password authentication to prevent a
1.40 aaron 377: trojan horse from getting the user's password.
1.176 jmc 378: Another purpose of this mechanism is to prevent man-in-the-middle attacks
379: which could otherwise be used to circumvent the encryption.
1.40 aaron 380: The
1.2 deraadt 381: .Cm StrictHostKeyChecking
1.158 stevesk 382: option can be used to prevent logins to machines whose
1.1 deraadt 383: host key is not known or has changed.
1.194 jakob 384: .Pp
385: .Nm
386: can be configured to verify host identification using fingerprint resource
387: records (SSHFP) published in DNS.
388: The
389: .Cm VerifyHostKeyDNS
390: option can be used to control how DNS lookups are performed.
391: SSHFP resource records can be generated using
392: .Xr ssh-keygen 1 .
1.65 aaron 393: .Pp
394: The options are as follows:
1.2 deraadt 395: .Bl -tag -width Ds
1.176 jmc 396: .It Fl 1
397: Forces
398: .Nm
399: to try protocol version 1 only.
400: .It Fl 2
401: Forces
402: .Nm
403: to try protocol version 2 only.
404: .It Fl 4
405: Forces
406: .Nm
407: to use IPv4 addresses only.
408: .It Fl 6
409: Forces
410: .Nm
411: to use IPv6 addresses only.
1.54 markus 412: .It Fl A
413: Enables forwarding of the authentication agent connection.
414: This can also be specified on a per-host basis in a configuration file.
1.165 stevesk 415: .Pp
1.168 jmc 416: Agent forwarding should be enabled with caution.
417: Users with the ability to bypass file permissions on the remote host
418: (for the agent's Unix-domain socket)
419: can access the local agent through the forwarded connection.
420: An attacker cannot obtain key material from the agent,
1.165 stevesk 421: however they can perform operations on the keys that enable them to
422: authenticate using the identities loaded into the agent.
1.176 jmc 423: .It Fl a
424: Disables forwarding of the authentication agent connection.
1.108 markus 425: .It Fl b Ar bind_address
426: Specify the interface to transmit from on machines with multiple
427: interfaces or aliased addresses.
1.176 jmc 428: .It Fl C
429: Requests compression of all data (including stdin, stdout, stderr, and
430: data for forwarded X11 and TCP/IP connections).
431: The compression algorithm is the same used by
432: .Xr gzip 1 ,
433: and the
434: .Dq level
435: can be controlled by the
436: .Cm CompressionLevel
437: option for protocol version 1.
438: Compression is desirable on modem lines and other
439: slow connections, but will only slow down things on fast networks.
440: The default value can be set on a host-by-host basis in the
441: configuration files; see the
442: .Cm Compression
443: option.
1.189 dtucker 444: .It Fl c Ar cipher_spec
445: Selects the cipher specification for encrypting the session.
446: .Pp
447: Protocol version 1 allows specification of a single cipher.
448: The suported values are
449: .Dq 3des ,
450: .Dq blowfish
451: and
452: .Dq des .
1.2 deraadt 453: .Ar 3des
1.189 dtucker 454: (triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
1.44 aaron 455: It is believed to be secure.
1.5 deraadt 456: .Ar blowfish
1.176 jmc 457: is a fast block cipher; it appears very secure and is much faster than
1.40 aaron 458: .Ar 3des .
1.131 stevesk 459: .Ar des
460: is only supported in the
461: .Nm
462: client for interoperability with legacy protocol 1 implementations
463: that do not support the
464: .Ar 3des
1.168 jmc 465: cipher.
466: Its use is strongly discouraged due to cryptographic weaknesses.
1.189 dtucker 467: The default is
468: .Dq 3des .
469: .Pp
470: For protocol version 2
471: .Ar cipher_spec
472: is a comma-separated list of ciphers
473: listed in order of preference.
474: The supported ciphers are
475: .Dq 3des-cbc ,
476: .Dq aes128-cbc ,
477: .Dq aes192-cbc ,
478: .Dq aes256-cbc ,
479: .Dq aes128-ctr ,
480: .Dq aes192-ctr ,
481: .Dq aes256-ctr ,
482: .Dq arcfour ,
483: .Dq blowfish-cbc ,
484: and
485: .Dq cast128-cbc .
486: The default is
487: .Bd -literal
488: ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,
489: aes192-cbc,aes256-cbc''
490: .Ed
1.176 jmc 491: .It Fl D Ar port
492: Specifies a local
493: .Dq dynamic
494: application-level port forwarding.
495: This works by allocating a socket to listen to
496: .Ar port
497: on the local side, and whenever a connection is made to this port, the
498: connection is forwarded over the secure channel, and the application
499: protocol is then used to determine where to connect to from the
500: remote machine.
501: Currently the SOCKS4 and SOCKS5 protocols are supported, and
502: .Nm
503: will act as a SOCKS server.
504: Only root can forward privileged ports.
505: Dynamic port forwardings can also be specified in the configuration file.
506: .It Fl e Ar ch | ^ch | none
1.2 deraadt 507: Sets the escape character for sessions with a pty (default:
508: .Ql ~ ) .
1.40 aaron 509: The escape character is only recognized at the beginning of a line.
510: The escape character followed by a dot
1.2 deraadt 511: .Pq Ql \&.
1.176 jmc 512: closes the connection;
513: followed by control-Z suspends the connection;
514: and followed by itself sends the escape character once.
1.40 aaron 515: Setting the character to
1.2 deraadt 516: .Dq none
517: disables any escapes and makes the session fully transparent.
1.176 jmc 518: .It Fl F Ar configfile
519: Specifies an alternative per-user configuration file.
520: If a configuration file is given on the command line,
521: the system-wide configuration file
522: .Pq Pa /etc/ssh/ssh_config
523: will be ignored.
524: The default for the per-user configuration file is
525: .Pa $HOME/.ssh/config .
1.2 deraadt 526: .It Fl f
527: Requests
528: .Nm
1.40 aaron 529: to go to background just before command execution.
530: This is useful if
1.2 deraadt 531: .Nm
532: is going to ask for passwords or passphrases, but the user
1.40 aaron 533: wants it in the background.
1.44 aaron 534: This implies
1.2 deraadt 535: .Fl n .
1.1 deraadt 536: The recommended way to start X11 programs at a remote site is with
1.2 deraadt 537: something like
538: .Ic ssh -f host xterm .
1.34 markus 539: .It Fl g
540: Allows remote hosts to connect to local forwarded ports.
1.176 jmc 541: .It Fl I Ar smartcard_device
542: Specifies which smartcard device to use.
543: The argument is the device
544: .Nm
545: should use to communicate with a smartcard used for storing the user's
546: private RSA key.
1.2 deraadt 547: .It Fl i Ar identity_file
1.144 stevesk 548: Selects a file from which the identity (private key) for
1.68 markus 549: RSA or DSA authentication is read.
1.144 stevesk 550: The default is
1.49 markus 551: .Pa $HOME/.ssh/identity
1.144 stevesk 552: for protocol version 1, and
553: .Pa $HOME/.ssh/id_rsa
554: and
555: .Pa $HOME/.ssh/id_dsa
556: for protocol version 2.
1.40 aaron 557: Identity files may also be specified on
558: a per-host basis in the configuration file.
559: It is possible to have multiple
1.2 deraadt 560: .Fl i
561: options (and multiple identities specified in
1.1 deraadt 562: configuration files).
1.2 deraadt 563: .It Fl k
1.179 dtucker 564: Disables forwarding (delegation) of GSSAPI credentials to the server.
1.176 jmc 565: .It Fl L Xo
566: .Sm off
1.196.2.1! brad 567: .Oo Ar bind_address : Oc
1.176 jmc 568: .Ar port : host : hostport
569: .Sm on
570: .Xc
571: Specifies that the given port on the local (client) host is to be
572: forwarded to the given host and port on the remote side.
573: This works by allocating a socket to listen to
574: .Ar port
1.196.2.1! brad 575: on the local side, optionally bound to the specified
! 576: .Ar bind_address .
! 577: Whenever a connection is made to this port, the
1.176 jmc 578: connection is forwarded over the secure channel, and a connection is
579: made to
580: .Ar host
581: port
582: .Ar hostport
583: from the remote machine.
584: Port forwardings can also be specified in the configuration file.
585: IPv6 addresses can be specified with an alternative syntax:
586: .Sm off
587: .Xo
1.196.2.1! brad 588: .Op Ar bind_address No /
1.176 jmc 589: .Ar port No / Ar host No /
1.196.2.1! brad 590: .Ar hostport
1.176 jmc 591: .Xc
592: .Sm on
1.196.2.1! brad 593: or by enclosing the address in square brackets.
! 594: Only the superuser can forward privileged ports.
! 595: By default, the local port is bound in accordance with the
! 596: .Cm GatewayPorts
! 597: setting.
! 598: However, an explicit
! 599: .Ar bind_address
! 600: may be used to bind the connection to a specific address.
! 601: The
! 602: .Ar bind_address
! 603: of
! 604: .Dq localhost
! 605: indicates that the listening port be bound for local use only, while an
! 606: empty address or
! 607: .Sq *
! 608: indicates that the port should be available from all interfaces.
1.2 deraadt 609: .It Fl l Ar login_name
1.40 aaron 610: Specifies the user to log in as on the remote machine.
611: This also may be specified on a per-host basis in the configuration file.
1.190 djm 612: .It Fl M
613: Places the
614: .Nm
615: client into
616: .Dq master
617: mode for connection sharing.
618: Refer to the description of
619: .Cm ControlMaster
620: in
621: .Xr ssh_config 5
622: for details.
1.193 jmc 623: .It Fl m Ar mac_spec
624: Additionally, for protocol version 2 a comma-separated list of MAC
625: (message authentication code) algorithms can
626: be specified in order of preference.
627: See the
628: .Cm MACs
629: keyword for more information.
1.176 jmc 630: .It Fl N
631: Do not execute a remote command.
632: This is useful for just forwarding ports
633: (protocol version 2 only).
1.2 deraadt 634: .It Fl n
635: Redirects stdin from
636: .Pa /dev/null
637: (actually, prevents reading from stdin).
1.1 deraadt 638: This must be used when
1.2 deraadt 639: .Nm
1.40 aaron 640: is run in the background.
641: A common trick is to use this to run X11 programs on a remote machine.
642: For example,
1.2 deraadt 643: .Ic ssh -n shadows.cs.hut.fi emacs &
644: will start an emacs on shadows.cs.hut.fi, and the X11
1.1 deraadt 645: connection will be automatically forwarded over an encrypted channel.
646: The
1.2 deraadt 647: .Nm
1.1 deraadt 648: program will be put in the background.
649: (This does not work if
1.2 deraadt 650: .Nm
651: needs to ask for a password or passphrase; see also the
652: .Fl f
653: option.)
1.196.2.1! brad 654: .It Fl O Ar ctl_cmd
! 655: Control an active connection multiplexing master process.
! 656: When the
! 657: .Fl O
! 658: option is specified, the
! 659: .Ar ctl_cmd
! 660: argument is interpreted and passed to the master process.
! 661: Valid commands are:
! 662: .Dq check
! 663: (check that the master process is running) and
! 664: .Dq exit
! 665: (request the master to exit).
1.2 deraadt 666: .It Fl o Ar option
1.127 stevesk 667: Can be used to give options in the format used in the configuration file.
1.1 deraadt 668: This is useful for specifying options for which there is no separate
1.40 aaron 669: command-line flag.
1.176 jmc 670: For full details of the options listed below, and their possible values, see
671: .Xr ssh_config 5 .
672: .Pp
673: .Bl -tag -width Ds -offset indent -compact
674: .It AddressFamily
675: .It BatchMode
676: .It BindAddress
677: .It ChallengeResponseAuthentication
678: .It CheckHostIP
679: .It Cipher
680: .It Ciphers
681: .It ClearAllForwardings
682: .It Compression
683: .It CompressionLevel
684: .It ConnectionAttempts
1.185 dtucker 685: .It ConnectTimeout
1.190 djm 686: .It ControlMaster
687: .It ControlPath
1.176 jmc 688: .It DynamicForward
689: .It EscapeChar
690: .It ForwardAgent
691: .It ForwardX11
1.178 markus 692: .It ForwardX11Trusted
1.176 jmc 693: .It GatewayPorts
694: .It GlobalKnownHostsFile
695: .It GSSAPIAuthentication
696: .It GSSAPIDelegateCredentials
1.196.2.1! brad 697: .It HashKnownHosts
1.176 jmc 698: .It Host
699: .It HostbasedAuthentication
700: .It HostKeyAlgorithms
701: .It HostKeyAlias
702: .It HostName
703: .It IdentityFile
1.182 markus 704: .It IdentitiesOnly
1.196.2.1! brad 705: .It KbdInteractiveDevices
1.176 jmc 706: .It LocalForward
707: .It LogLevel
708: .It MACs
709: .It NoHostAuthenticationForLocalhost
710: .It NumberOfPasswordPrompts
711: .It PasswordAuthentication
712: .It Port
713: .It PreferredAuthentications
714: .It Protocol
715: .It ProxyCommand
716: .It PubkeyAuthentication
717: .It RemoteForward
718: .It RhostsRSAAuthentication
719: .It RSAAuthentication
1.184 jmc 720: .It SendEnv
1.181 markus 721: .It ServerAliveInterval
722: .It ServerAliveCountMax
1.176 jmc 723: .It SmartcardDevice
724: .It StrictHostKeyChecking
1.180 markus 725: .It TCPKeepAlive
1.176 jmc 726: .It UsePrivilegedPort
727: .It User
728: .It UserKnownHostsFile
729: .It VerifyHostKeyDNS
730: .It XAuthLocation
731: .El
1.2 deraadt 732: .It Fl p Ar port
1.40 aaron 733: Port to connect to on the remote host.
734: This can be specified on a
1.1 deraadt 735: per-host basis in the configuration file.
1.2 deraadt 736: .It Fl q
1.40 aaron 737: Quiet mode.
738: Causes all warning and diagnostic messages to be suppressed.
1.176 jmc 739: .It Fl R Xo
740: .Sm off
1.196.2.1! brad 741: .Oo Ar bind_address : Oc
1.176 jmc 742: .Ar port : host : hostport
743: .Sm on
744: .Xc
745: Specifies that the given port on the remote (server) host is to be
746: forwarded to the given host and port on the local side.
747: This works by allocating a socket to listen to
748: .Ar port
749: on the remote side, and whenever a connection is made to this port, the
750: connection is forwarded over the secure channel, and a connection is
751: made to
752: .Ar host
753: port
754: .Ar hostport
755: from the local machine.
1.196.2.1! brad 756: .Pp
1.176 jmc 757: Port forwardings can also be specified in the configuration file.
758: Privileged ports can be forwarded only when
759: logging in as root on the remote machine.
1.196.2.1! brad 760: IPv6 addresses can be specified by enclosing the address in square braces or
! 761: using an alternative syntax:
1.176 jmc 762: .Sm off
763: .Xo
1.196.2.1! brad 764: .Op Ar bind_address No /
! 765: .Ar host No / Ar port No /
! 766: .Ar hostport
! 767: .Xc .
1.176 jmc 768: .Sm on
1.196.2.1! brad 769: .Pp
! 770: By default, the listening socket on the server will be bound to the loopback
! 771: interface only.
! 772: This may be overriden by specifying a
! 773: .Ar bind_address .
! 774: An empty
! 775: .Ar bind_address ,
! 776: or the address
! 777: .Ql * ,
! 778: indicates that the remote socket should listen on all interfaces.
! 779: Specifying a remote
! 780: .Ar bind_address
! 781: will only succeed if the server's
! 782: .Cm GatewayPorts
! 783: option is enabled (see
! 784: .Xr sshd_config 5 ) .
! 785: .It Fl S Ar ctl_path
1.193 jmc 786: Specifies the location of a control socket for connection sharing.
1.190 djm 787: Refer to the description of
1.191 djm 788: .Cm ControlPath
789: and
1.190 djm 790: .Cm ControlMaster
791: in
792: .Xr ssh_config 5
793: for details.
1.80 djm 794: .It Fl s
1.172 jmc 795: May be used to request invocation of a subsystem on the remote system.
796: Subsystems are a feature of the SSH2 protocol which facilitate the use
1.176 jmc 797: of SSH as a secure transport for other applications (eg.\&
798: .Xr sftp 1 ) .
1.172 jmc 799: The subsystem is specified as the remote command.
1.176 jmc 800: .It Fl T
801: Disable pseudo-tty allocation.
1.2 deraadt 802: .It Fl t
1.40 aaron 803: Force pseudo-tty allocation.
1.43 brad 804: This can be used to execute arbitrary
1.40 aaron 805: screen-based programs on a remote machine, which can be very useful,
806: e.g., when implementing menu services.
1.73 markus 807: Multiple
808: .Fl t
809: options force tty allocation, even if
810: .Nm
811: has no local tty.
1.176 jmc 812: .It Fl V
813: Display the version number and exit.
1.2 deraadt 814: .It Fl v
1.40 aaron 815: Verbose mode.
816: Causes
1.2 deraadt 817: .Nm
1.40 aaron 818: to print debugging messages about its progress.
819: This is helpful in
1.1 deraadt 820: debugging connection, authentication, and configuration problems.
1.73 markus 821: Multiple
822: .Fl v
1.169 naddy 823: options increase the verbosity.
824: The maximum is 3.
1.2 deraadt 825: .It Fl X
1.1 deraadt 826: Enables X11 forwarding.
1.54 markus 827: This can also be specified on a per-host basis in a configuration file.
1.165 stevesk 828: .Pp
1.168 jmc 829: X11 forwarding should be enabled with caution.
830: Users with the ability to bypass file permissions on the remote host
831: (for the user's X authorization database)
832: can access the local X11 display through the forwarded connection.
833: An attacker may then be able to perform activities such as keystroke monitoring.
1.196.2.1! brad 834: .Pp
! 835: For this reason, X11 forwarding is subjected to X11 SECURITY extension
! 836: restrictions by default.
! 837: Please refer to the
! 838: .Nm
! 839: .Fl Y
! 840: option and the
! 841: .Cm ForwardX11Trusted
! 842: directive in
! 843: .Xr ssh_config 5
! 844: for more information.
1.176 jmc 845: .It Fl x
846: Disables X11 forwarding.
1.178 markus 847: .It Fl Y
848: Enables trusted X11 forwarding.
1.196.2.1! brad 849: Trusted X11 forwardings are not subjected to the X11 SECURITY extension
! 850: controls.
1.2 deraadt 851: .El
852: .Sh CONFIGURATION FILES
853: .Nm
1.158 stevesk 854: may additionally obtain configuration data from
855: a per-user configuration file and a system-wide configuration file.
856: The file format and configuration options are described in
857: .Xr ssh_config 5 .
1.2 deraadt 858: .Sh ENVIRONMENT
859: .Nm
1.1 deraadt 860: will normally set the following environment variables:
1.176 jmc 861: .Bl -tag -width LOGNAME
1.2 deraadt 862: .It Ev DISPLAY
863: The
864: .Ev DISPLAY
1.40 aaron 865: variable indicates the location of the X11 server.
1.44 aaron 866: It is automatically set by
1.2 deraadt 867: .Nm
868: to point to a value of the form
869: .Dq hostname:n
870: where hostname indicates
1.176 jmc 871: the host where the shell runs, and n is an integer \*(Ge 1.
1.40 aaron 872: .Nm
873: uses this special value to forward X11 connections over the secure
874: channel.
1.107 markus 875: The user should normally not set
876: .Ev DISPLAY
877: explicitly, as that
1.1 deraadt 878: will render the X11 connection insecure (and will require the user to
879: manually copy any required authorization cookies).
1.2 deraadt 880: .It Ev HOME
1.1 deraadt 881: Set to the path of the user's home directory.
1.2 deraadt 882: .It Ev LOGNAME
883: Synonym for
1.12 aaron 884: .Ev USER ;
885: set for compatibility with systems that use this variable.
1.2 deraadt 886: .It Ev MAIL
1.129 stevesk 887: Set to the path of the user's mailbox.
1.40 aaron 888: .It Ev PATH
1.2 deraadt 889: Set to the default
890: .Ev PATH ,
891: as specified when compiling
1.12 aaron 892: .Nm ssh .
1.118 markus 893: .It Ev SSH_ASKPASS
894: If
895: .Nm
896: needs a passphrase, it will read the passphrase from the current
897: terminal if it was run from a terminal.
898: If
899: .Nm
900: does not have a terminal associated with it but
901: .Ev DISPLAY
902: and
903: .Ev SSH_ASKPASS
904: are set, it will execute the program specified by
905: .Ev SSH_ASKPASS
906: and open an X11 window to read the passphrase.
907: This is particularly useful when calling
908: .Nm
909: from a
1.196 jmc 910: .Pa .xsession
1.118 markus 911: or related script.
912: (Note that on some machines it
913: may be necessary to redirect the input from
914: .Pa /dev/null
915: to make this work.)
1.18 markus 916: .It Ev SSH_AUTH_SOCK
1.129 stevesk 917: Identifies the path of a unix-domain socket used to communicate with the
1.17 markus 918: agent.
1.166 stevesk 919: .It Ev SSH_CONNECTION
920: Identifies the client and server ends of the connection.
1.40 aaron 921: The variable contains
1.166 stevesk 922: four space-separated values: client ip-address, client port number,
923: server ip-address and server port number.
1.73 markus 924: .It Ev SSH_ORIGINAL_COMMAND
925: The variable contains the original command line if a forced command
926: is executed.
927: It can be used to extract the original arguments.
1.2 deraadt 928: .It Ev SSH_TTY
1.1 deraadt 929: This is set to the name of the tty (path to the device) associated
1.40 aaron 930: with the current shell or command.
931: If the current session has no tty,
1.1 deraadt 932: this variable is not set.
1.2 deraadt 933: .It Ev TZ
1.1 deraadt 934: The timezone variable is set to indicate the present timezone if it
1.56 deraadt 935: was set when the daemon was started (i.e., the daemon passes the value
1.1 deraadt 936: on to new connections).
1.2 deraadt 937: .It Ev USER
1.1 deraadt 938: Set to the name of the user logging in.
1.2 deraadt 939: .El
940: .Pp
1.44 aaron 941: Additionally,
1.2 deraadt 942: .Nm
1.44 aaron 943: reads
944: .Pa $HOME/.ssh/environment ,
1.2 deraadt 945: and adds lines of the format
946: .Dq VARNAME=value
1.161 marc 947: to the environment if the file exists and if users are allowed to
948: change their environment.
1.176 jmc 949: For more information, see the
1.161 marc 950: .Cm PermitUserEnvironment
1.162 stevesk 951: option in
1.161 marc 952: .Xr sshd_config 5 .
1.2 deraadt 953: .Sh FILES
1.36 markus 954: .Bl -tag -width Ds
1.116 markus 955: .It Pa $HOME/.ssh/known_hosts
1.129 stevesk 956: Records host keys for all hosts the user has logged into that are not
1.2 deraadt 957: in
1.147 deraadt 958: .Pa /etc/ssh/ssh_known_hosts .
1.2 deraadt 959: See
960: .Xr sshd 8 .
1.102 itojun 961: .It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa, $HOME/.ssh/id_rsa
962: Contains the authentication identity of the user.
963: They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively.
1.48 markus 964: These files
965: contain sensitive data and should be readable by the user but not
1.15 markus 966: accessible by others (read/write/execute).
967: Note that
968: .Nm
1.48 markus 969: ignores a private key file if it is accessible by others.
1.15 markus 970: It is possible to specify a passphrase when
1.1 deraadt 971: generating the key; the passphrase will be used to encrypt the
1.8 deraadt 972: sensitive part of this file using 3DES.
1.102 itojun 973: .It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub, $HOME/.ssh/id_rsa.pub
1.1 deraadt 974: Contains the public key for authentication (public part of the
1.40 aaron 975: identity file in human-readable form).
1.48 markus 976: The contents of the
977: .Pa $HOME/.ssh/identity.pub
1.176 jmc 978: file should be added to the file
1.2 deraadt 979: .Pa $HOME/.ssh/authorized_keys
980: on all machines
1.137 deraadt 981: where the user wishes to log in using protocol version 1 RSA authentication.
1.48 markus 982: The contents of the
983: .Pa $HOME/.ssh/id_dsa.pub
1.102 itojun 984: and
985: .Pa $HOME/.ssh/id_rsa.pub
1.48 markus 986: file should be added to
1.115 markus 987: .Pa $HOME/.ssh/authorized_keys
1.48 markus 988: on all machines
1.137 deraadt 989: where the user wishes to log in using protocol version 2 DSA/RSA authentication.
1.48 markus 990: These files are not
1.40 aaron 991: sensitive and can (but need not) be readable by anyone.
1.48 markus 992: These files are
1.84 markus 993: never used automatically and are not necessary; they are only provided for
1.1 deraadt 994: the convenience of the user.
1.2 deraadt 995: .It Pa $HOME/.ssh/config
1.40 aaron 996: This is the per-user configuration file.
1.158 stevesk 997: The file format and configuration options are described in
998: .Xr ssh_config 5 .
1.183 djm 999: Because of the potential for abuse, this file must have strict permissions:
1000: read/write for the user, and not accessible by others.
1.2 deraadt 1001: .It Pa $HOME/.ssh/authorized_keys
1.115 markus 1002: Lists the public keys (RSA/DSA) that can be used for logging in as this user.
1.40 aaron 1003: The format of this file is described in the
1.2 deraadt 1004: .Xr sshd 8
1.40 aaron 1005: manual page.
1.176 jmc 1006: In the simplest form the format is the same as the
1007: .Pa .pub
1.116 markus 1008: identity files.
1.48 markus 1009: This file is not highly sensitive, but the recommended
1010: permissions are read/write for the user, and not accessible by others.
1.147 deraadt 1011: .It Pa /etc/ssh/ssh_known_hosts
1.40 aaron 1012: Systemwide list of known host keys.
1.116 markus 1013: This file should be prepared by the
1.1 deraadt 1014: system administrator to contain the public host keys of all machines in the
1.40 aaron 1015: organization.
1016: This file should be world-readable.
1017: This file contains
1.1 deraadt 1018: public keys, one per line, in the following format (fields separated
1.116 markus 1019: by spaces): system name, public key and optional comment field.
1.40 aaron 1020: When different names are used
1.1 deraadt 1021: for the same machine, all such names should be listed, separated by
1.40 aaron 1022: commas.
1.176 jmc 1023: The format is described in the
1.2 deraadt 1024: .Xr sshd 8
1.1 deraadt 1025: manual page.
1.2 deraadt 1026: .Pp
1.1 deraadt 1027: The canonical system name (as returned by name servers) is used by
1.2 deraadt 1028: .Xr sshd 8
1.1 deraadt 1029: to verify the client host when logging in; other names are needed because
1.2 deraadt 1030: .Nm
1.1 deraadt 1031: does not convert the user-supplied name to a canonical name before
1032: checking the key, because someone with access to the name servers
1033: would then be able to fool host authentication.
1.147 deraadt 1034: .It Pa /etc/ssh/ssh_config
1.40 aaron 1035: Systemwide configuration file.
1.158 stevesk 1036: The file format and configuration options are described in
1037: .Xr ssh_config 5 .
1.147 deraadt 1038: .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key
1.141 markus 1039: These three files contain the private parts of the host keys
1040: and are used for
1041: .Cm RhostsRSAAuthentication
1042: and
1043: .Cm HostbasedAuthentication .
1.155 stevesk 1044: If the protocol version 1
1045: .Cm RhostsRSAAuthentication
1.157 deraadt 1046: method is used,
1.155 stevesk 1047: .Nm
1048: must be setuid root, since the host key is readable only by root.
1049: For protocol version 2,
1050: .Nm
1051: uses
1052: .Xr ssh-keysign 8
1053: to access the host keys for
1054: .Cm HostbasedAuthentication .
1055: This eliminates the requirement that
1056: .Nm
1057: be setuid root when that authentication method is used.
1058: By default
1.141 markus 1059: .Nm
1.155 stevesk 1060: is not setuid root.
1.2 deraadt 1061: .It Pa $HOME/.rhosts
1062: This file is used in
1.195 markus 1063: .Cm RhostsRSAAuthentication
1064: and
1065: .Cm HostbasedAuthentication
1.2 deraadt 1066: authentication to list the
1.40 aaron 1067: host/user pairs that are permitted to log in.
1068: (Note that this file is
1.1 deraadt 1069: also used by rlogin and rsh, which makes using this file insecure.)
1070: Each line of the file contains a host name (in the canonical form
1071: returned by name servers), and then a user name on that host,
1.40 aaron 1072: separated by a space.
1.92 markus 1073: On some machines this file may need to be
1.1 deraadt 1074: world-readable if the user's home directory is on a NFS partition,
1075: because
1.2 deraadt 1076: .Xr sshd 8
1.40 aaron 1077: reads it as root.
1078: Additionally, this file must be owned by the user,
1079: and must not have write permissions for anyone else.
1080: The recommended
1.1 deraadt 1081: permission for most machines is read/write for the user, and not
1082: accessible by others.
1.2 deraadt 1083: .Pp
1.195 markus 1084: Note that
1.2 deraadt 1085: .Xr sshd 8
1.195 markus 1086: allows authentication only in combination with client host key
1087: authentication before permitting log in.
1.137 deraadt 1088: If the server machine does not have the client's host key in
1.147 deraadt 1089: .Pa /etc/ssh/ssh_known_hosts ,
1.137 deraadt 1090: it can be stored in
1.2 deraadt 1091: .Pa $HOME/.ssh/known_hosts .
1092: The easiest way to do this is to
1.1 deraadt 1093: connect back to the client from the server machine using ssh; this
1.48 markus 1094: will automatically add the host key to
1.2 deraadt 1095: .Pa $HOME/.ssh/known_hosts .
1096: .It Pa $HOME/.shosts
1097: This file is used exactly the same way as
1.176 jmc 1098: .Pa .rhosts .
1.2 deraadt 1099: The purpose for
1.195 markus 1100: having this file is to be able to use
1101: .Cm RhostsRSAAuthentication
1102: and
1103: .Cm HostbasedAuthentication
1104: authentication without permitting login with
1.176 jmc 1105: .Xr rlogin
1.2 deraadt 1106: or
1107: .Xr rsh 1 .
1108: .It Pa /etc/hosts.equiv
1109: This file is used during
1.195 markus 1110: .Cm RhostsRSAAuthentication
1111: and
1112: .Cm HostbasedAuthentication
1.173 jmc 1113: authentication.
1.40 aaron 1114: It contains
1.176 jmc 1115: canonical hosts names, one per line (the full format is described in the
1.2 deraadt 1116: .Xr sshd 8
1.40 aaron 1117: manual page).
1118: If the client host is found in this file, login is
1.1 deraadt 1119: automatically permitted provided client and server user names are the
1.40 aaron 1120: same.
1.195 markus 1121: Additionally, successful client host key authentication is required.
1.40 aaron 1122: This file should only be writable by root.
1.2 deraadt 1123: .It Pa /etc/shosts.equiv
1.44 aaron 1124: This file is processed exactly as
1.2 deraadt 1125: .Pa /etc/hosts.equiv .
1.1 deraadt 1126: This file may be useful to permit logins using
1.2 deraadt 1127: .Nm
1.1 deraadt 1128: but not using rsh/rlogin.
1.147 deraadt 1129: .It Pa /etc/ssh/sshrc
1.1 deraadt 1130: Commands in this file are executed by
1.2 deraadt 1131: .Nm
1.1 deraadt 1132: when the user logs in just before the user's shell (or command) is started.
1133: See the
1.2 deraadt 1134: .Xr sshd 8
1.1 deraadt 1135: manual page for more information.
1.2 deraadt 1136: .It Pa $HOME/.ssh/rc
1.1 deraadt 1137: Commands in this file are executed by
1.2 deraadt 1138: .Nm
1.1 deraadt 1139: when the user logs in just before the user's shell (or command) is
1140: started.
1.44 aaron 1141: See the
1.2 deraadt 1142: .Xr sshd 8
1.1 deraadt 1143: manual page for more information.
1.31 markus 1144: .It Pa $HOME/.ssh/environment
1145: Contains additional definitions for environment variables, see section
1146: .Sx ENVIRONMENT
1147: above.
1.58 itojun 1148: .El
1.145 markus 1149: .Sh DIAGNOSTICS
1150: .Nm
1151: exits with the exit status of the remote command or with 255
1152: if an error occurred.
1.2 deraadt 1153: .Sh SEE ALSO
1.176 jmc 1154: .Xr gzip 1 ,
1.2 deraadt 1155: .Xr rsh 1 ,
1156: .Xr scp 1 ,
1.83 djm 1157: .Xr sftp 1 ,
1.2 deraadt 1158: .Xr ssh-add 1 ,
1159: .Xr ssh-agent 1 ,
1160: .Xr ssh-keygen 1 ,
1161: .Xr telnet 1 ,
1.176 jmc 1162: .Xr hosts.equiv 5 ,
1.159 stevesk 1163: .Xr ssh_config 5 ,
1.160 naddy 1164: .Xr ssh-keysign 8 ,
1.87 itojun 1165: .Xr sshd 8
1.106 markus 1166: .Rs
1167: .%A T. Ylonen
1168: .%A T. Kivinen
1169: .%A M. Saarinen
1170: .%A T. Rinne
1171: .%A S. Lehtinen
1172: .%T "SSH Protocol Architecture"
1.150 markus 1173: .%N draft-ietf-secsh-architecture-12.txt
1174: .%D January 2002
1.106 markus 1175: .%O work in progress material
1176: .Re
1.173 jmc 1177: .Sh AUTHORS
1178: OpenSSH is a derivative of the original and free
1179: ssh 1.2.12 release by Tatu Ylonen.
1180: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1181: Theo de Raadt and Dug Song
1182: removed many bugs, re-added newer features and
1183: created OpenSSH.
1184: Markus Friedl contributed the support for SSH
1185: protocol versions 1.5 and 2.0.
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