Annotation of src/usr.bin/ssh/ssh.1, Revision 1.209.2.1
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: .\"
1.209.2.1! brad 37: .\" $OpenBSD: ssh.1,v 1.253 2006/01/30 13:37:49 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
1.191 djm 46: .Op Fl 1246AaCfgkMNnqsTtVvXxY
1.108 markus 47: .Op Fl b Ar bind_address
1.51 markus 48: .Op Fl c Ar cipher_spec
1.209.2.1! brad 49: .Oo Fl D\ \&
! 50: .Sm off
! 51: .Oo Ar bind_address : Oc
! 52: .Ar port
! 53: .Sm on
! 54: .Oc
1.2 deraadt 55: .Op Fl e Ar escape_char
1.176 jmc 56: .Op Fl F Ar configfile
1.209.2.1! brad 57: .Bk -words
1.2 deraadt 58: .Op Fl i Ar identity_file
1.209.2.1! brad 59: .Ek
1.202 jmc 60: .Oo Fl L\ \&
1.12 aaron 61: .Sm off
1.200 djm 62: .Oo Ar bind_address : Oc
1.202 jmc 63: .Ar port : host : hostport
1.12 aaron 64: .Sm on
65: .Oc
1.209.2.1! brad 66: .Bk -words
1.176 jmc 67: .Op Fl l Ar login_name
1.209.2.1! brad 68: .Ek
1.176 jmc 69: .Op Fl m Ar mac_spec
1.198 djm 70: .Op Fl O Ar ctl_cmd
1.176 jmc 71: .Op Fl o Ar option
72: .Op Fl p Ar port
1.202 jmc 73: .Oo Fl R\ \&
1.12 aaron 74: .Sm off
1.200 djm 75: .Oo Ar bind_address : Oc
1.202 jmc 76: .Ar port : host : hostport
1.12 aaron 77: .Sm on
78: .Oc
1.198 djm 79: .Op Fl S Ar ctl_path
1.209.2.1! brad 80: .Bk -words
! 81: .Op Fl w Ar tunnel : Ns Ar tunnel
1.176 jmc 82: .Oo Ar user Ns @ Oc Ns Ar hostname
1.2 deraadt 83: .Op Ar command
1.202 jmc 84: .Ek
1.44 aaron 85: .Sh DESCRIPTION
1.2 deraadt 86: .Nm
1.96 deraadt 87: (SSH client) is a program for logging into a remote machine and for
1.40 aaron 88: executing commands on a remote machine.
1.176 jmc 89: It is intended to replace rlogin and rsh,
90: and provide secure encrypted communications between
1.40 aaron 91: two untrusted hosts over an insecure network.
1.209.2.1! brad 92: X11 connections and arbitrary TCP ports
1.176 jmc 93: can also be forwarded over the secure channel.
1.2 deraadt 94: .Pp
95: .Nm
1.44 aaron 96: connects and logs into the specified
1.176 jmc 97: .Ar hostname
98: (with optional
99: .Ar user
100: name).
1.1 deraadt 101: The user must prove
1.49 markus 102: his/her identity to the remote machine using one of several methods
1.209.2.1! brad 103: depending on the protocol version used (see below).
1.49 markus 104: .Pp
1.176 jmc 105: If
106: .Ar command
107: is specified,
1.209.2.1! brad 108: it is executed on the remote host instead of a login shell.
1.65 aaron 109: .Pp
110: The options are as follows:
1.2 deraadt 111: .Bl -tag -width Ds
1.176 jmc 112: .It Fl 1
113: Forces
114: .Nm
115: to try protocol version 1 only.
116: .It Fl 2
117: Forces
118: .Nm
119: to try protocol version 2 only.
120: .It Fl 4
121: Forces
122: .Nm
123: to use IPv4 addresses only.
124: .It Fl 6
125: Forces
126: .Nm
127: to use IPv6 addresses only.
1.54 markus 128: .It Fl A
129: Enables forwarding of the authentication agent connection.
130: This can also be specified on a per-host basis in a configuration file.
1.165 stevesk 131: .Pp
1.168 jmc 132: Agent forwarding should be enabled with caution.
133: Users with the ability to bypass file permissions on the remote host
134: (for the agent's Unix-domain socket)
135: can access the local agent through the forwarded connection.
136: An attacker cannot obtain key material from the agent,
1.165 stevesk 137: however they can perform operations on the keys that enable them to
138: authenticate using the identities loaded into the agent.
1.176 jmc 139: .It Fl a
140: Disables forwarding of the authentication agent connection.
1.108 markus 141: .It Fl b Ar bind_address
1.209 dtucker 142: Use
143: .Ar bind_address
144: on the local machine as the source address
145: of the connection.
146: Only useful on systems with more than one address.
1.176 jmc 147: .It Fl C
148: Requests compression of all data (including stdin, stdout, stderr, and
1.209.2.1! brad 149: data for forwarded X11 and TCP connections).
1.176 jmc 150: The compression algorithm is the same used by
151: .Xr gzip 1 ,
152: and the
153: .Dq level
154: can be controlled by the
155: .Cm CompressionLevel
156: option for protocol version 1.
157: Compression is desirable on modem lines and other
158: slow connections, but will only slow down things on fast networks.
159: The default value can be set on a host-by-host basis in the
160: configuration files; see the
161: .Cm Compression
162: option.
1.189 dtucker 163: .It Fl c Ar cipher_spec
164: Selects the cipher specification for encrypting the session.
165: .Pp
166: Protocol version 1 allows specification of a single cipher.
1.209.2.1! brad 167: The supported values are
1.189 dtucker 168: .Dq 3des ,
1.209.2.1! brad 169: .Dq blowfish ,
1.189 dtucker 170: and
171: .Dq des .
1.2 deraadt 172: .Ar 3des
1.189 dtucker 173: (triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
1.44 aaron 174: It is believed to be secure.
1.5 deraadt 175: .Ar blowfish
1.176 jmc 176: is a fast block cipher; it appears very secure and is much faster than
1.40 aaron 177: .Ar 3des .
1.131 stevesk 178: .Ar des
179: is only supported in the
180: .Nm
181: client for interoperability with legacy protocol 1 implementations
182: that do not support the
183: .Ar 3des
1.168 jmc 184: cipher.
185: Its use is strongly discouraged due to cryptographic weaknesses.
1.189 dtucker 186: The default is
187: .Dq 3des .
188: .Pp
1.209.2.1! brad 189: For protocol version 2,
1.189 dtucker 190: .Ar cipher_spec
191: is a comma-separated list of ciphers
192: listed in order of preference.
1.209.2.1! brad 193: The supported ciphers are:
! 194: 3des-cbc,
! 195: aes128-cbc,
! 196: aes192-cbc,
! 197: aes256-cbc,
! 198: aes128-ctr,
! 199: aes192-ctr,
! 200: aes256-ctr,
! 201: arcfour128,
! 202: arcfour256,
! 203: arcfour,
! 204: blowfish-cbc,
1.189 dtucker 205: and
1.209.2.1! brad 206: cast128-cbc.
! 207: The default is:
! 208: .Bd -literal -offset indent
! 209: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
! 210: arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
! 211: aes192-ctr,aes256-ctr
1.189 dtucker 212: .Ed
1.209.2.1! brad 213: .It Fl D Xo
! 214: .Sm off
! 215: .Oo Ar bind_address : Oc
! 216: .Ar port
! 217: .Sm on
! 218: .Xc
1.176 jmc 219: Specifies a local
220: .Dq dynamic
221: application-level port forwarding.
222: This works by allocating a socket to listen to
223: .Ar port
1.209.2.1! brad 224: on the local side, optionally bound to the specified
! 225: .Ar bind_address .
! 226: Whenever a connection is made to this port, the
1.176 jmc 227: connection is forwarded over the secure channel, and the application
228: protocol is then used to determine where to connect to from the
229: remote machine.
230: Currently the SOCKS4 and SOCKS5 protocols are supported, and
231: .Nm
232: will act as a SOCKS server.
233: Only root can forward privileged ports.
234: Dynamic port forwardings can also be specified in the configuration file.
1.209.2.1! brad 235: .Pp
! 236: IPv6 addresses can be specified with an alternative syntax:
! 237: .Sm off
! 238: .Xo
! 239: .Op Ar bind_address No /
! 240: .Ar port
! 241: .Xc
! 242: .Sm on
! 243: or by enclosing the address in square brackets.
! 244: Only the superuser can forward privileged ports.
! 245: By default, the local port is bound in accordance with the
! 246: .Cm GatewayPorts
! 247: setting.
! 248: However, an explicit
! 249: .Ar bind_address
! 250: may be used to bind the connection to a specific address.
! 251: The
! 252: .Ar bind_address
! 253: of
! 254: .Dq localhost
! 255: indicates that the listening port be bound for local use only, while an
! 256: empty address or
! 257: .Sq *
! 258: indicates that the port should be available from all interfaces.
! 259: .It Fl e Ar escape_char
1.2 deraadt 260: Sets the escape character for sessions with a pty (default:
261: .Ql ~ ) .
1.40 aaron 262: The escape character is only recognized at the beginning of a line.
263: The escape character followed by a dot
1.2 deraadt 264: .Pq Ql \&.
1.176 jmc 265: closes the connection;
266: followed by control-Z suspends the connection;
267: and followed by itself sends the escape character once.
1.40 aaron 268: Setting the character to
1.2 deraadt 269: .Dq none
270: disables any escapes and makes the session fully transparent.
1.176 jmc 271: .It Fl F Ar configfile
272: Specifies an alternative per-user configuration file.
273: If a configuration file is given on the command line,
274: the system-wide configuration file
275: .Pq Pa /etc/ssh/ssh_config
276: will be ignored.
277: The default for the per-user configuration file is
1.207 djm 278: .Pa ~/.ssh/config .
1.2 deraadt 279: .It Fl f
280: Requests
281: .Nm
1.40 aaron 282: to go to background just before command execution.
283: This is useful if
1.2 deraadt 284: .Nm
285: is going to ask for passwords or passphrases, but the user
1.40 aaron 286: wants it in the background.
1.44 aaron 287: This implies
1.2 deraadt 288: .Fl n .
1.1 deraadt 289: The recommended way to start X11 programs at a remote site is with
1.2 deraadt 290: something like
291: .Ic ssh -f host xterm .
1.34 markus 292: .It Fl g
293: Allows remote hosts to connect to local forwarded ports.
1.176 jmc 294: .It Fl I Ar smartcard_device
1.209.2.1! brad 295: Specify the device
1.176 jmc 296: .Nm
297: should use to communicate with a smartcard used for storing the user's
298: private RSA key.
1.209.2.1! brad 299: This option is only available if support for smartcard devices
! 300: is compiled in (default is no support).
1.2 deraadt 301: .It Fl i Ar identity_file
1.144 stevesk 302: Selects a file from which the identity (private key) for
1.68 markus 303: RSA or DSA authentication is read.
1.144 stevesk 304: The default is
1.207 djm 305: .Pa ~/.ssh/identity
1.144 stevesk 306: for protocol version 1, and
1.207 djm 307: .Pa ~/.ssh/id_rsa
1.144 stevesk 308: and
1.207 djm 309: .Pa ~/.ssh/id_dsa
1.144 stevesk 310: for protocol version 2.
1.40 aaron 311: Identity files may also be specified on
312: a per-host basis in the configuration file.
313: It is possible to have multiple
1.2 deraadt 314: .Fl i
315: options (and multiple identities specified in
1.1 deraadt 316: configuration files).
1.2 deraadt 317: .It Fl k
1.179 dtucker 318: Disables forwarding (delegation) of GSSAPI credentials to the server.
1.176 jmc 319: .It Fl L Xo
320: .Sm off
1.200 djm 321: .Oo Ar bind_address : Oc
1.176 jmc 322: .Ar port : host : hostport
323: .Sm on
324: .Xc
325: Specifies that the given port on the local (client) host is to be
326: forwarded to the given host and port on the remote side.
327: This works by allocating a socket to listen to
328: .Ar port
1.200 djm 329: on the local side, optionally bound to the specified
330: .Ar bind_address .
331: Whenever a connection is made to this port, the
1.176 jmc 332: connection is forwarded over the secure channel, and a connection is
333: made to
334: .Ar host
335: port
336: .Ar hostport
337: from the remote machine.
338: Port forwardings can also be specified in the configuration file.
339: IPv6 addresses can be specified with an alternative syntax:
340: .Sm off
341: .Xo
1.205 jmc 342: .Op Ar bind_address No /
1.176 jmc 343: .Ar port No / Ar host No /
1.200 djm 344: .Ar hostport
1.176 jmc 345: .Xc
346: .Sm on
1.200 djm 347: or by enclosing the address in square brackets.
348: Only the superuser can forward privileged ports.
349: By default, the local port is bound in accordance with the
350: .Cm GatewayPorts
351: setting.
352: However, an explicit
353: .Ar bind_address
354: may be used to bind the connection to a specific address.
355: The
356: .Ar bind_address
357: of
358: .Dq localhost
1.202 jmc 359: indicates that the listening port be bound for local use only, while an
360: empty address or
361: .Sq *
1.200 djm 362: indicates that the port should be available from all interfaces.
1.2 deraadt 363: .It Fl l Ar login_name
1.40 aaron 364: Specifies the user to log in as on the remote machine.
365: This also may be specified on a per-host basis in the configuration file.
1.190 djm 366: .It Fl M
367: Places the
368: .Nm
369: client into
370: .Dq master
371: mode for connection sharing.
1.209.2.1! brad 372: Multiple
! 373: .Fl M
! 374: options places
! 375: .Nm
! 376: into
! 377: .Dq master
! 378: mode with confirmation required before slave connections are accepted.
! 379: Refer to the description of
1.190 djm 380: .Cm ControlMaster
381: in
382: .Xr ssh_config 5
383: for details.
1.193 jmc 384: .It Fl m Ar mac_spec
385: Additionally, for protocol version 2 a comma-separated list of MAC
386: (message authentication code) algorithms can
387: be specified in order of preference.
388: See the
389: .Cm MACs
390: keyword for more information.
1.176 jmc 391: .It Fl N
392: Do not execute a remote command.
393: This is useful for just forwarding ports
394: (protocol version 2 only).
1.2 deraadt 395: .It Fl n
396: Redirects stdin from
397: .Pa /dev/null
398: (actually, prevents reading from stdin).
1.1 deraadt 399: This must be used when
1.2 deraadt 400: .Nm
1.40 aaron 401: is run in the background.
402: A common trick is to use this to run X11 programs on a remote machine.
403: For example,
1.2 deraadt 404: .Ic ssh -n shadows.cs.hut.fi emacs &
405: will start an emacs on shadows.cs.hut.fi, and the X11
1.1 deraadt 406: connection will be automatically forwarded over an encrypted channel.
407: The
1.2 deraadt 408: .Nm
1.1 deraadt 409: program will be put in the background.
410: (This does not work if
1.2 deraadt 411: .Nm
412: needs to ask for a password or passphrase; see also the
413: .Fl f
414: option.)
1.199 jmc 415: .It Fl O Ar ctl_cmd
416: Control an active connection multiplexing master process.
417: When the
418: .Fl O
419: option is specified, the
420: .Ar ctl_cmd
421: argument is interpreted and passed to the master process.
422: Valid commands are:
423: .Dq check
424: (check that the master process is running) and
425: .Dq exit
426: (request the master to exit).
1.2 deraadt 427: .It Fl o Ar option
1.127 stevesk 428: Can be used to give options in the format used in the configuration file.
1.1 deraadt 429: This is useful for specifying options for which there is no separate
1.40 aaron 430: command-line flag.
1.176 jmc 431: For full details of the options listed below, and their possible values, see
432: .Xr ssh_config 5 .
433: .Pp
434: .Bl -tag -width Ds -offset indent -compact
435: .It AddressFamily
436: .It BatchMode
437: .It BindAddress
438: .It ChallengeResponseAuthentication
439: .It CheckHostIP
440: .It Cipher
441: .It Ciphers
442: .It ClearAllForwardings
443: .It Compression
444: .It CompressionLevel
445: .It ConnectionAttempts
1.185 dtucker 446: .It ConnectTimeout
1.190 djm 447: .It ControlMaster
448: .It ControlPath
1.176 jmc 449: .It DynamicForward
450: .It EscapeChar
451: .It ForwardAgent
452: .It ForwardX11
1.178 markus 453: .It ForwardX11Trusted
1.176 jmc 454: .It GatewayPorts
455: .It GlobalKnownHostsFile
456: .It GSSAPIAuthentication
457: .It GSSAPIDelegateCredentials
1.201 djm 458: .It HashKnownHosts
1.176 jmc 459: .It Host
460: .It HostbasedAuthentication
461: .It HostKeyAlgorithms
462: .It HostKeyAlias
463: .It HostName
464: .It IdentityFile
1.182 markus 465: .It IdentitiesOnly
1.197 djm 466: .It KbdInteractiveDevices
1.209.2.1! brad 467: .It LocalCommand
1.176 jmc 468: .It LocalForward
469: .It LogLevel
470: .It MACs
471: .It NoHostAuthenticationForLocalhost
472: .It NumberOfPasswordPrompts
473: .It PasswordAuthentication
1.209.2.1! brad 474: .It PermitLocalCommand
1.176 jmc 475: .It Port
476: .It PreferredAuthentications
477: .It Protocol
478: .It ProxyCommand
479: .It PubkeyAuthentication
1.209.2.1! brad 480: .It RekeyLimit
1.176 jmc 481: .It RemoteForward
482: .It RhostsRSAAuthentication
483: .It RSAAuthentication
1.184 jmc 484: .It SendEnv
1.181 markus 485: .It ServerAliveInterval
486: .It ServerAliveCountMax
1.176 jmc 487: .It SmartcardDevice
488: .It StrictHostKeyChecking
1.180 markus 489: .It TCPKeepAlive
1.209.2.1! brad 490: .It Tunnel
! 491: .It TunnelDevice
1.176 jmc 492: .It UsePrivilegedPort
493: .It User
494: .It UserKnownHostsFile
495: .It VerifyHostKeyDNS
496: .It XAuthLocation
497: .El
1.2 deraadt 498: .It Fl p Ar port
1.40 aaron 499: Port to connect to on the remote host.
500: This can be specified on a
1.1 deraadt 501: per-host basis in the configuration file.
1.2 deraadt 502: .It Fl q
1.40 aaron 503: Quiet mode.
504: Causes all warning and diagnostic messages to be suppressed.
1.176 jmc 505: .It Fl R Xo
506: .Sm off
1.200 djm 507: .Oo Ar bind_address : Oc
1.176 jmc 508: .Ar port : host : hostport
509: .Sm on
510: .Xc
511: Specifies that the given port on the remote (server) host is to be
512: forwarded to the given host and port on the local side.
513: This works by allocating a socket to listen to
514: .Ar port
515: on the remote side, and whenever a connection is made to this port, the
516: connection is forwarded over the secure channel, and a connection is
517: made to
518: .Ar host
519: port
520: .Ar hostport
521: from the local machine.
1.200 djm 522: .Pp
1.176 jmc 523: Port forwardings can also be specified in the configuration file.
524: Privileged ports can be forwarded only when
525: logging in as root on the remote machine.
1.200 djm 526: IPv6 addresses can be specified by enclosing the address in square braces or
527: using an alternative syntax:
1.202 jmc 528: .Sm off
1.200 djm 529: .Xo
1.205 jmc 530: .Op Ar bind_address No /
1.202 jmc 531: .Ar host No / Ar port No /
532: .Ar hostport
533: .Xc .
1.176 jmc 534: .Sm on
1.200 djm 535: .Pp
536: By default, the listening socket on the server will be bound to the loopback
537: interface only.
538: This may be overriden by specifying a
539: .Ar bind_address .
1.202 jmc 540: An empty
541: .Ar bind_address ,
1.200 djm 542: or the address
1.202 jmc 543: .Ql * ,
1.200 djm 544: indicates that the remote socket should listen on all interfaces.
545: Specifying a remote
546: .Ar bind_address
1.202 jmc 547: will only succeed if the server's
548: .Cm GatewayPorts
1.200 djm 549: option is enabled (see
1.202 jmc 550: .Xr sshd_config 5 ) .
1.198 djm 551: .It Fl S Ar ctl_path
1.193 jmc 552: Specifies the location of a control socket for connection sharing.
1.190 djm 553: Refer to the description of
1.191 djm 554: .Cm ControlPath
555: and
1.190 djm 556: .Cm ControlMaster
557: in
558: .Xr ssh_config 5
559: for details.
1.80 djm 560: .It Fl s
1.172 jmc 561: May be used to request invocation of a subsystem on the remote system.
562: Subsystems are a feature of the SSH2 protocol which facilitate the use
1.176 jmc 563: of SSH as a secure transport for other applications (eg.\&
564: .Xr sftp 1 ) .
1.172 jmc 565: The subsystem is specified as the remote command.
1.176 jmc 566: .It Fl T
567: Disable pseudo-tty allocation.
1.2 deraadt 568: .It Fl t
1.40 aaron 569: Force pseudo-tty allocation.
1.43 brad 570: This can be used to execute arbitrary
1.40 aaron 571: screen-based programs on a remote machine, which can be very useful,
572: e.g., when implementing menu services.
1.73 markus 573: Multiple
574: .Fl t
575: options force tty allocation, even if
576: .Nm
577: has no local tty.
1.176 jmc 578: .It Fl V
579: Display the version number and exit.
1.2 deraadt 580: .It Fl v
1.40 aaron 581: Verbose mode.
582: Causes
1.2 deraadt 583: .Nm
1.40 aaron 584: to print debugging messages about its progress.
585: This is helpful in
1.1 deraadt 586: debugging connection, authentication, and configuration problems.
1.73 markus 587: Multiple
588: .Fl v
1.169 naddy 589: options increase the verbosity.
590: The maximum is 3.
1.209.2.1! brad 591: .It Fl w Ar tunnel : Ns Ar tunnel
! 592: Requests a
! 593: .Xr tun 4
! 594: device on the client
! 595: (first
! 596: .Ar tunnel
! 597: arg)
! 598: and server
! 599: (second
! 600: .Ar tunnel
! 601: arg).
! 602: The devices may be specified by numerical ID or the keyword
! 603: .Dq any ,
! 604: which uses the next available tunnel device.
! 605: See also the
! 606: .Cm Tunnel
! 607: directive in
! 608: .Xr ssh_config 5 .
1.2 deraadt 609: .It Fl X
1.1 deraadt 610: Enables X11 forwarding.
1.54 markus 611: This can also be specified on a per-host basis in a configuration file.
1.165 stevesk 612: .Pp
1.168 jmc 613: X11 forwarding should be enabled with caution.
614: Users with the ability to bypass file permissions on the remote host
615: (for the user's X authorization database)
616: can access the local X11 display through the forwarded connection.
617: An attacker may then be able to perform activities such as keystroke monitoring.
1.203 djm 618: .Pp
1.204 jmc 619: For this reason, X11 forwarding is subjected to X11 SECURITY extension
1.203 djm 620: restrictions by default.
621: Please refer to the
622: .Nm
623: .Fl Y
624: option and the
625: .Cm ForwardX11Trusted
626: directive in
627: .Xr ssh_config 5
628: for more information.
1.176 jmc 629: .It Fl x
630: Disables X11 forwarding.
1.178 markus 631: .It Fl Y
632: Enables trusted X11 forwarding.
1.203 djm 633: Trusted X11 forwardings are not subjected to the X11 SECURITY extension
634: controls.
1.2 deraadt 635: .El
1.209.2.1! brad 636: .Pp
1.2 deraadt 637: .Nm
1.158 stevesk 638: may additionally obtain configuration data from
639: a per-user configuration file and a system-wide configuration file.
640: The file format and configuration options are described in
641: .Xr ssh_config 5 .
1.209.2.1! brad 642: .Pp
! 643: .Nm
! 644: exits with the exit status of the remote command or with 255
! 645: if an error occurred.
! 646: .Sh AUTHENTICATION
! 647: The OpenSSH SSH client supports SSH protocols 1 and 2.
! 648: Protocol 2 is the default, with
! 649: .Nm
! 650: falling back to protocol 1 if it detects protocol 2 is unsupported.
! 651: These settings may be altered using the
! 652: .Cm Protocol
! 653: option in
! 654: .Xr ssh_config 5 ,
! 655: or enforced using the
! 656: .Fl 1
! 657: and
! 658: .Fl 2
! 659: options (see above).
! 660: Both protocols support similar authentication methods,
! 661: but protocol 2 is preferred since
! 662: it provides additional mechanisms for confidentiality
! 663: (the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour)
! 664: and integrity (hmac-md5, hmac-sha1, hmac-ripemd160).
! 665: Protocol 1 lacks a strong mechanism for ensuring the
! 666: integrity of the connection.
! 667: .Pp
! 668: The methods available for authentication are:
! 669: host-based authentication,
! 670: public key authentication,
! 671: challenge-response authentication,
! 672: and password authentication.
! 673: Authentication methods are tried in the order specified above,
! 674: though protocol 2 has a configuration option to change the default order:
! 675: .Cm PreferredAuthentications .
! 676: .Pp
! 677: Host-based authentication works as follows:
! 678: If the machine the user logs in from is listed in
! 679: .Pa /etc/hosts.equiv
! 680: or
! 681: .Pa /etc/shosts.equiv
! 682: on the remote machine, and the user names are
! 683: the same on both sides, or if the files
! 684: .Pa ~/.rhosts
! 685: or
! 686: .Pa ~/.shosts
! 687: exist in the user's home directory on the
! 688: remote machine and contain a line containing the name of the client
! 689: machine and the name of the user on that machine, the user is
! 690: considered for login.
! 691: Additionally, the server
! 692: .Em must
! 693: be able to verify the client's
! 694: host key (see the description of
! 695: .Pa /etc/ssh/ssh_known_hosts
! 696: and
! 697: .Pa ~/.ssh/known_hosts ,
! 698: below)
! 699: for login to be permitted.
! 700: This authentication method closes security holes due to IP
! 701: spoofing, DNS spoofing, and routing spoofing.
! 702: [Note to the administrator:
! 703: .Pa /etc/hosts.equiv ,
! 704: .Pa ~/.rhosts ,
! 705: and the rlogin/rsh protocol in general, are inherently insecure and should be
! 706: disabled if security is desired.]
! 707: .Pp
! 708: Public key authentication works as follows:
! 709: The scheme is based on public-key cryptography,
! 710: using cryptosystems
! 711: where encryption and decryption are done using separate keys,
! 712: and it is unfeasible to derive the decryption key from the encryption key.
! 713: The idea is that each user creates a public/private
! 714: key pair for authentication purposes.
! 715: The server knows the public key, and only the user knows the private key.
! 716: .Nm
! 717: implements public key authentication protocol automatically,
! 718: using either the RSA or DSA algorithms.
! 719: Protocol 1 is restricted to using only RSA keys,
! 720: but protocol 2 may use either.
! 721: The
! 722: .Sx HISTORY
! 723: section of
! 724: .Xr ssl 8
! 725: contains a brief discussion of the two algorithms.
! 726: .Pp
! 727: The file
! 728: .Pa ~/.ssh/authorized_keys
! 729: lists the public keys that are permitted for logging in.
! 730: When the user logs in, the
! 731: .Nm
! 732: program tells the server which key pair it would like to use for
! 733: authentication.
! 734: The client proves that it has access to the private key
! 735: and the server checks that the corresponding public key
! 736: is authorized to accept the account.
! 737: .Pp
! 738: The user creates his/her key pair by running
! 739: .Xr ssh-keygen 1 .
! 740: This stores the private key in
! 741: .Pa ~/.ssh/identity
! 742: (protocol 1),
! 743: .Pa ~/.ssh/id_dsa
! 744: (protocol 2 DSA),
! 745: or
! 746: .Pa ~/.ssh/id_rsa
! 747: (protocol 2 RSA)
! 748: and stores the public key in
! 749: .Pa ~/.ssh/identity.pub
! 750: (protocol 1),
! 751: .Pa ~/.ssh/id_dsa.pub
! 752: (protocol 2 DSA),
! 753: or
! 754: .Pa ~/.ssh/id_rsa.pub
! 755: (protocol 2 RSA)
! 756: in the user's home directory.
! 757: The user should then copy the public key
! 758: to
! 759: .Pa ~/.ssh/authorized_keys
! 760: in his/her home directory on the remote machine.
! 761: The
! 762: .Pa authorized_keys
! 763: file corresponds to the conventional
! 764: .Pa ~/.rhosts
! 765: file, and has one key
! 766: per line, though the lines can be very long.
! 767: After this, the user can log in without giving the password.
! 768: .Pp
! 769: The most convenient way to use public key authentication may be with an
! 770: authentication agent.
! 771: See
! 772: .Xr ssh-agent 1
! 773: for more information.
! 774: .Pp
! 775: Challenge-response authentication works as follows:
! 776: The server sends an arbitrary
! 777: .Qq challenge
! 778: text, and prompts for a response.
! 779: Protocol 2 allows multiple challenges and responses;
! 780: protocol 1 is restricted to just one challenge/response.
! 781: Examples of challenge-response authentication include
! 782: BSD Authentication (see
! 783: .Xr login.conf 5 )
! 784: and PAM (some non-OpenBSD systems).
! 785: .Pp
! 786: Finally, if other authentication methods fail,
! 787: .Nm
! 788: prompts the user for a password.
! 789: The password is sent to the remote
! 790: host for checking; however, since all communications are encrypted,
! 791: the password cannot be seen by someone listening on the network.
! 792: .Pp
! 793: .Nm
! 794: automatically maintains and checks a database containing
! 795: identification for all hosts it has ever been used with.
! 796: Host keys are stored in
! 797: .Pa ~/.ssh/known_hosts
! 798: in the user's home directory.
! 799: Additionally, the file
! 800: .Pa /etc/ssh/ssh_known_hosts
! 801: is automatically checked for known hosts.
! 802: Any new hosts are automatically added to the user's file.
! 803: If a host's identification ever changes,
! 804: .Nm
! 805: warns about this and disables password authentication to prevent
! 806: server spoofing or man-in-the-middle attacks,
! 807: which could otherwise be used to circumvent the encryption.
! 808: The
! 809: .Cm StrictHostKeyChecking
! 810: option can be used to control logins to machines whose
! 811: host key is not known or has changed.
! 812: .Pp
! 813: When the user's identity has been accepted by the server, the server
! 814: either executes the given command, or logs into the machine and gives
! 815: the user a normal shell on the remote machine.
! 816: All communication with
! 817: the remote command or shell will be automatically encrypted.
! 818: .Pp
! 819: If a pseudo-terminal has been allocated (normal login session), the
! 820: user may use the escape characters noted below.
! 821: .Pp
! 822: If no pseudo-tty has been allocated,
! 823: the session is transparent and can be used to reliably transfer binary data.
! 824: On most systems, setting the escape character to
! 825: .Dq none
! 826: will also make the session transparent even if a tty is used.
! 827: .Pp
! 828: The session terminates when the command or shell on the remote
! 829: machine exits and all X11 and TCP connections have been closed.
! 830: .Sh ESCAPE CHARACTERS
! 831: When a pseudo-terminal has been requested,
! 832: .Nm
! 833: supports a number of functions through the use of an escape character.
! 834: .Pp
! 835: A single tilde character can be sent as
! 836: .Ic ~~
! 837: or by following the tilde by a character other than those described below.
! 838: The escape character must always follow a newline to be interpreted as
! 839: special.
! 840: The escape character can be changed in configuration files using the
! 841: .Cm EscapeChar
! 842: configuration directive or on the command line by the
! 843: .Fl e
! 844: option.
! 845: .Pp
! 846: The supported escapes (assuming the default
! 847: .Ql ~ )
! 848: are:
! 849: .Bl -tag -width Ds
! 850: .It Cm ~.
! 851: Disconnect.
! 852: .It Cm ~^Z
! 853: Background
! 854: .Nm .
! 855: .It Cm ~#
! 856: List forwarded connections.
! 857: .It Cm ~&
! 858: Background
! 859: .Nm
! 860: at logout when waiting for forwarded connection / X11 sessions to terminate.
! 861: .It Cm ~?
! 862: Display a list of escape characters.
! 863: .It Cm ~B
! 864: Send a BREAK to the remote system
! 865: (only useful for SSH protocol version 2 and if the peer supports it).
! 866: .It Cm ~C
! 867: Open command line.
! 868: Currently this allows the addition of port forwardings using the
! 869: .Fl L
! 870: and
! 871: .Fl R
! 872: options (see above).
! 873: It also allows the cancellation of existing remote port-forwardings
! 874: using
! 875: .Fl KR Ar hostport .
! 876: .Ic !\& Ns Ar command
! 877: allows the user to execute a local command if the
! 878: .Ic PermitLocalCommand
! 879: option is enabled in
! 880: .Xr ssh_config 5 .
! 881: Basic help is available, using the
! 882: .Fl h
! 883: option.
! 884: .It Cm ~R
! 885: Request rekeying of the connection
! 886: (only useful for SSH protocol version 2 and if the peer supports it).
! 887: .El
! 888: .Sh TCP FORWARDING
! 889: Forwarding of arbitrary TCP connections over the secure channel can
! 890: be specified either on the command line or in a configuration file.
! 891: One possible application of TCP forwarding is a secure connection to a
! 892: mail server; another is going through firewalls.
! 893: .Pp
! 894: In the example below, we look at encrypting communication between
! 895: an IRC client and server, even though the IRC server does not directly
! 896: support encrypted communications.
! 897: This works as follows:
! 898: the user connects to the remote host using
! 899: .Nm ,
! 900: specifying a port to be used to forward connections
! 901: to the remote server.
! 902: After that it is possible to start the service which is to be encrypted
! 903: on the client machine,
! 904: connecting to the same local port,
! 905: and
! 906: .Nm
! 907: will encrypt and forward the connection.
! 908: .Pp
! 909: The following example tunnels an IRC session from client machine
! 910: .Dq 127.0.0.1
! 911: (localhost)
! 912: to remote server
! 913: .Dq server.example.com :
! 914: .Bd -literal -offset 4n
! 915: $ ssh -f -L 1234:localhost:6667 server.example.com sleep 10
! 916: $ irc -c '#users' -p 1234 pinky 127.0.0.1
! 917: .Ed
! 918: .Pp
! 919: This tunnels a connection to IRC server
! 920: .Dq server.example.com ,
! 921: joining channel
! 922: .Dq #users ,
! 923: nickname
! 924: .Dq pinky ,
! 925: using port 1234.
! 926: It doesn't matter which port is used,
! 927: as long as it's greater than 1023
! 928: (remember, only root can open sockets on privileged ports)
! 929: and doesn't conflict with any ports already in use.
! 930: The connection is forwarded to port 6667 on the remote server,
! 931: since that's the standard port for IRC services.
! 932: .Pp
! 933: The
! 934: .Fl f
! 935: option backgrounds
! 936: .Nm
! 937: and the remote command
! 938: .Dq sleep 10
! 939: is specified to allow an amount of time
! 940: (10 seconds, in the example)
! 941: to start the service which is to be tunnelled.
! 942: If no connections are made within the time specified,
! 943: .Nm
! 944: will exit.
! 945: .Sh X11 FORWARDING
! 946: If the
! 947: .Cm ForwardX11
! 948: variable is set to
! 949: .Dq yes
! 950: (or see the description of the
! 951: .Fl X ,
! 952: .Fl x ,
! 953: and
! 954: .Fl Y
! 955: options above)
! 956: and the user is using X11 (the
! 957: .Ev DISPLAY
! 958: environment variable is set), the connection to the X11 display is
! 959: automatically forwarded to the remote side in such a way that any X11
! 960: programs started from the shell (or command) will go through the
! 961: encrypted channel, and the connection to the real X server will be made
! 962: from the local machine.
! 963: The user should not manually set
! 964: .Ev DISPLAY .
! 965: Forwarding of X11 connections can be
! 966: configured on the command line or in configuration files.
! 967: .Pp
! 968: The
! 969: .Ev DISPLAY
! 970: value set by
! 971: .Nm
! 972: will point to the server machine, but with a display number greater than zero.
! 973: This is normal, and happens because
! 974: .Nm
! 975: creates a
! 976: .Dq proxy
! 977: X server on the server machine for forwarding the
! 978: connections over the encrypted channel.
! 979: .Pp
! 980: .Nm
! 981: will also automatically set up Xauthority data on the server machine.
! 982: For this purpose, it will generate a random authorization cookie,
! 983: store it in Xauthority on the server, and verify that any forwarded
! 984: connections carry this cookie and replace it by the real cookie when
! 985: the connection is opened.
! 986: The real authentication cookie is never
! 987: sent to the server machine (and no cookies are sent in the plain).
! 988: .Pp
! 989: If the
! 990: .Cm ForwardAgent
! 991: variable is set to
! 992: .Dq yes
! 993: (or see the description of the
! 994: .Fl A
! 995: and
! 996: .Fl a
! 997: options above) and
! 998: the user is using an authentication agent, the connection to the agent
! 999: is automatically forwarded to the remote side.
! 1000: .Sh VERIFYING HOST KEYS
! 1001: When connecting to a server for the first time,
! 1002: a fingerprint of the server's public key is presented to the user
! 1003: (unless the option
! 1004: .Cm StrictHostKeyChecking
! 1005: has been disabled).
! 1006: Fingerprints can be determined using
! 1007: .Xr ssh-keygen 1 :
! 1008: .Pp
! 1009: .Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key
! 1010: .Pp
! 1011: If the fingerprint is already known,
! 1012: it can be matched and verified,
! 1013: and the key can be accepted.
! 1014: If the fingerprint is unknown,
! 1015: an alternative method of verification is available:
! 1016: SSH fingerprints verified by DNS.
! 1017: An additional resource record (RR),
! 1018: SSHFP,
! 1019: is added to a zonefile
! 1020: and the connecting client is able to match the fingerprint
! 1021: with that of the key presented.
! 1022: .Pp
! 1023: In this example, we are connecting a client to a server,
! 1024: .Dq host.example.com .
! 1025: The SSHFP resource records should first be added to the zonefile for
! 1026: host.example.com:
! 1027: .Bd -literal -offset indent
! 1028: $ ssh-keygen -f /etc/ssh/ssh_host_rsa_key.pub -r host.example.com.
! 1029: $ ssh-keygen -f /etc/ssh/ssh_host_dsa_key.pub -r host.example.com.
! 1030: .Ed
! 1031: .Pp
! 1032: The output lines will have to be added to the zonefile.
! 1033: To check that the zone is answering fingerprint queries:
! 1034: .Pp
! 1035: .Dl $ dig -t SSHFP host.example.com
! 1036: .Pp
! 1037: Finally the client connects:
! 1038: .Bd -literal -offset indent
! 1039: $ ssh -o "VerifyHostKeyDNS ask" host.example.com
! 1040: [...]
! 1041: Matching host key fingerprint found in DNS.
! 1042: Are you sure you want to continue connecting (yes/no)?
! 1043: .Ed
! 1044: .Pp
! 1045: See the
! 1046: .Cm VerifyHostKeyDNS
! 1047: option in
! 1048: .Xr ssh_config 5
! 1049: for more information.
! 1050: .Sh SSH-BASED VIRTUAL PRIVATE NETWORKS
! 1051: .Nm
! 1052: contains support for Virtual Private Network (VPN) tunnelling
! 1053: using the
! 1054: .Xr tun 4
! 1055: network pseudo-device,
! 1056: allowing two networks to be joined securely.
! 1057: The
! 1058: .Xr sshd_config 5
! 1059: configuration option
! 1060: .Cm PermitTunnel
! 1061: controls whether the server supports this,
! 1062: and at what level (layer 2 or 3 traffic).
! 1063: .Pp
! 1064: The following example would connect client network 10.0.50.0/24
! 1065: with remote network 10.0.99.0/24, provided that the SSH server
! 1066: running on the gateway to the remote network,
! 1067: at 192.168.1.15, allows it:
! 1068: .Bd -literal -offset indent
! 1069: # ssh -f -w 0:1 192.168.1.15 true
! 1070: # ifconfig tun0 10.0.50.1 10.0.99.1 netmask 255.255.255.252
! 1071: .Ed
! 1072: .Pp
! 1073: Client access may be more finely tuned via the
! 1074: .Pa /root/.ssh/authorized_keys
! 1075: file (see below) and the
! 1076: .Cm PermitRootLogin
! 1077: server option.
! 1078: The following entry would permit connections on the first
! 1079: .Xr tun 4
! 1080: device from user
! 1081: .Dq jane
! 1082: and on the second device from user
! 1083: .Dq john ,
! 1084: if
! 1085: .Cm PermitRootLogin
! 1086: is set to
! 1087: .Dq forced-commands-only :
! 1088: .Bd -literal -offset 2n
! 1089: tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane
! 1090: tunnel="2",command="sh /etc/netstart tun1" ssh-rsa ... john
! 1091: .Ed
! 1092: .Pp
! 1093: Since a SSH-based setup entails a fair amount of overhead,
! 1094: it may be more suited to temporary setups,
! 1095: such as for wireless VPNs.
! 1096: More permanent VPNs are better provided by tools such as
! 1097: .Xr ipsecctl 8
! 1098: and
! 1099: .Xr isakmpd 8 .
1.2 deraadt 1100: .Sh ENVIRONMENT
1101: .Nm
1.1 deraadt 1102: will normally set the following environment variables:
1.209.2.1! brad 1103: .Bl -tag -width "SSH_ORIGINAL_COMMAND"
1.2 deraadt 1104: .It Ev DISPLAY
1105: The
1106: .Ev DISPLAY
1.40 aaron 1107: variable indicates the location of the X11 server.
1.44 aaron 1108: It is automatically set by
1.2 deraadt 1109: .Nm
1110: to point to a value of the form
1.209.2.1! brad 1111: .Dq hostname:n ,
! 1112: where
! 1113: .Dq hostname
! 1114: indicates the host where the shell runs, and
! 1115: .Sq n
! 1116: is an integer \*(Ge 1.
1.40 aaron 1117: .Nm
1118: uses this special value to forward X11 connections over the secure
1119: channel.
1.107 markus 1120: The user should normally not set
1121: .Ev DISPLAY
1122: explicitly, as that
1.1 deraadt 1123: will render the X11 connection insecure (and will require the user to
1124: manually copy any required authorization cookies).
1.2 deraadt 1125: .It Ev HOME
1.1 deraadt 1126: Set to the path of the user's home directory.
1.2 deraadt 1127: .It Ev LOGNAME
1128: Synonym for
1.12 aaron 1129: .Ev USER ;
1130: set for compatibility with systems that use this variable.
1.2 deraadt 1131: .It Ev MAIL
1.129 stevesk 1132: Set to the path of the user's mailbox.
1.40 aaron 1133: .It Ev PATH
1.2 deraadt 1134: Set to the default
1135: .Ev PATH ,
1136: as specified when compiling
1.209.2.1! brad 1137: .Nm .
1.118 markus 1138: .It Ev SSH_ASKPASS
1139: If
1140: .Nm
1141: needs a passphrase, it will read the passphrase from the current
1142: terminal if it was run from a terminal.
1143: If
1144: .Nm
1145: does not have a terminal associated with it but
1146: .Ev DISPLAY
1147: and
1148: .Ev SSH_ASKPASS
1149: are set, it will execute the program specified by
1150: .Ev SSH_ASKPASS
1151: and open an X11 window to read the passphrase.
1152: This is particularly useful when calling
1153: .Nm
1154: from a
1.196 jmc 1155: .Pa .xsession
1.118 markus 1156: or related script.
1157: (Note that on some machines it
1158: may be necessary to redirect the input from
1159: .Pa /dev/null
1160: to make this work.)
1.18 markus 1161: .It Ev SSH_AUTH_SOCK
1.209.2.1! brad 1162: Identifies the path of a
! 1163: .Ux Ns -domain
! 1164: socket used to communicate with the agent.
1.166 stevesk 1165: .It Ev SSH_CONNECTION
1166: Identifies the client and server ends of the connection.
1.40 aaron 1167: The variable contains
1.209.2.1! brad 1168: four space-separated values: client IP address, client port number,
! 1169: server IP address, and server port number.
1.73 markus 1170: .It Ev SSH_ORIGINAL_COMMAND
1.209.2.1! brad 1171: This variable contains the original command line if a forced command
1.73 markus 1172: is executed.
1173: It can be used to extract the original arguments.
1.2 deraadt 1174: .It Ev SSH_TTY
1.1 deraadt 1175: This is set to the name of the tty (path to the device) associated
1.40 aaron 1176: with the current shell or command.
1177: If the current session has no tty,
1.1 deraadt 1178: this variable is not set.
1.2 deraadt 1179: .It Ev TZ
1.209.2.1! brad 1180: This variable is set to indicate the present time zone if it
1.56 deraadt 1181: was set when the daemon was started (i.e., the daemon passes the value
1.1 deraadt 1182: on to new connections).
1.2 deraadt 1183: .It Ev USER
1.1 deraadt 1184: Set to the name of the user logging in.
1.2 deraadt 1185: .El
1186: .Pp
1.44 aaron 1187: Additionally,
1.2 deraadt 1188: .Nm
1.44 aaron 1189: reads
1.207 djm 1190: .Pa ~/.ssh/environment ,
1.2 deraadt 1191: and adds lines of the format
1192: .Dq VARNAME=value
1.209.2.1! brad 1193: to the environment if the file exists and users are allowed to
1.161 marc 1194: change their environment.
1.176 jmc 1195: For more information, see the
1.161 marc 1196: .Cm PermitUserEnvironment
1.162 stevesk 1197: option in
1.161 marc 1198: .Xr sshd_config 5 .
1.2 deraadt 1199: .Sh FILES
1.209.2.1! brad 1200: .Bl -tag -width Ds -compact
! 1201: .It ~/.rhosts
! 1202: This file is used for host-based authentication (see above).
! 1203: On some machines this file may need to be
! 1204: world-readable if the user's home directory is on an NFS partition,
! 1205: because
! 1206: .Xr sshd 8
! 1207: reads it as root.
! 1208: Additionally, this file must be owned by the user,
! 1209: and must not have write permissions for anyone else.
! 1210: The recommended
! 1211: permission for most machines is read/write for the user, and not
! 1212: accessible by others.
! 1213: .Pp
! 1214: .It ~/.shosts
! 1215: This file is used in exactly the same way as
! 1216: .Pa .rhosts ,
! 1217: but allows host-based authentication without permitting login with
! 1218: rlogin/rsh.
! 1219: .Pp
! 1220: .It ~/.ssh/authorized_keys
! 1221: Lists the public keys (RSA/DSA) that can be used for logging in as this user.
! 1222: The format of this file is described in the
! 1223: .Xr sshd 8
! 1224: manual page.
! 1225: This file is not highly sensitive, but the recommended
! 1226: permissions are read/write for the user, and not accessible by others.
! 1227: .Pp
! 1228: .It ~/.ssh/config
! 1229: This is the per-user configuration file.
! 1230: The file format and configuration options are described in
! 1231: .Xr ssh_config 5 .
! 1232: Because of the potential for abuse, this file must have strict permissions:
! 1233: read/write for the user, and not accessible by others.
! 1234: .Pp
! 1235: .It ~/.ssh/environment
! 1236: Contains additional definitions for environment variables; see
! 1237: .Sx ENVIRONMENT ,
! 1238: above.
! 1239: .Pp
! 1240: .It ~/.ssh/identity
! 1241: .It ~/.ssh/id_dsa
! 1242: .It ~/.ssh/id_rsa
! 1243: Contains the private key for authentication.
1.48 markus 1244: These files
1245: contain sensitive data and should be readable by the user but not
1.15 markus 1246: accessible by others (read/write/execute).
1247: .Nm
1.209.2.1! brad 1248: will simply ignore a private key file if it is accessible by others.
1.15 markus 1249: It is possible to specify a passphrase when
1.209.2.1! brad 1250: generating the key which will be used to encrypt the
1.8 deraadt 1251: sensitive part of this file using 3DES.
1.209.2.1! brad 1252: .Pp
! 1253: .It ~/.ssh/identity.pub
! 1254: .It ~/.ssh/id_dsa.pub
! 1255: .It ~/.ssh/id_rsa.pub
! 1256: Contains the public key for authentication.
1.48 markus 1257: These files are not
1.40 aaron 1258: sensitive and can (but need not) be readable by anyone.
1.2 deraadt 1259: .Pp
1.209.2.1! brad 1260: .It ~/.ssh/known_hosts
! 1261: Contains a list of host keys for all hosts the user has logged into
! 1262: that are not already in the systemwide list of known host keys.
! 1263: See
1.2 deraadt 1264: .Xr sshd 8
1.209.2.1! brad 1265: for further details of the format of this file.
! 1266: .Pp
! 1267: .It ~/.ssh/rc
! 1268: Commands in this file are executed by
1.2 deraadt 1269: .Nm
1.209.2.1! brad 1270: when the user logs in, just before the user's shell (or command) is
! 1271: started.
! 1272: See the
! 1273: .Xr sshd 8
! 1274: manual page for more information.
! 1275: .Pp
! 1276: .It /etc/hosts.equiv
! 1277: This file is for host-based authentication (see above).
! 1278: It should only be writable by root.
! 1279: .Pp
! 1280: .It /etc/shosts.equiv
! 1281: This file is used in exactly the same way as
! 1282: .Pa hosts.equiv ,
! 1283: but allows host-based authentication without permitting login with
! 1284: rlogin/rsh.
! 1285: .Pp
1.147 deraadt 1286: .It Pa /etc/ssh/ssh_config
1.40 aaron 1287: Systemwide configuration file.
1.158 stevesk 1288: The file format and configuration options are described in
1289: .Xr ssh_config 5 .
1.209.2.1! brad 1290: .Pp
! 1291: .It /etc/ssh/ssh_host_key
! 1292: .It /etc/ssh/ssh_host_dsa_key
! 1293: .It /etc/ssh/ssh_host_rsa_key
1.141 markus 1294: These three files contain the private parts of the host keys
1.209.2.1! brad 1295: and are used for host-based authentication.
! 1296: If protocol version 1 is used,
1.155 stevesk 1297: .Nm
1298: must be setuid root, since the host key is readable only by root.
1299: For protocol version 2,
1300: .Nm
1301: uses
1302: .Xr ssh-keysign 8
1.209.2.1! brad 1303: to access the host keys,
! 1304: eliminating the requirement that
1.155 stevesk 1305: .Nm
1.209.2.1! brad 1306: be setuid root when host-based authentication is used.
1.155 stevesk 1307: By default
1.141 markus 1308: .Nm
1.155 stevesk 1309: is not setuid root.
1.2 deraadt 1310: .Pp
1.209.2.1! brad 1311: .It /etc/ssh/ssh_known_hosts
! 1312: Systemwide list of known host keys.
! 1313: This file should be prepared by the
! 1314: system administrator to contain the public host keys of all machines in the
! 1315: organization.
! 1316: It should be world-readable.
! 1317: See
1.2 deraadt 1318: .Xr sshd 8
1.209.2.1! brad 1319: for further details of the format of this file.
! 1320: .Pp
! 1321: .It /etc/ssh/sshrc
1.1 deraadt 1322: Commands in this file are executed by
1.2 deraadt 1323: .Nm
1.209.2.1! brad 1324: when the user logs in, just before the user's shell (or command) is started.
1.44 aaron 1325: See the
1.2 deraadt 1326: .Xr sshd 8
1.1 deraadt 1327: manual page for more information.
1.58 itojun 1328: .El
1.2 deraadt 1329: .Sh SEE ALSO
1330: .Xr scp 1 ,
1.83 djm 1331: .Xr sftp 1 ,
1.2 deraadt 1332: .Xr ssh-add 1 ,
1333: .Xr ssh-agent 1 ,
1334: .Xr ssh-keygen 1 ,
1.209.2.1! brad 1335: .Xr ssh-keyscan 1 ,
! 1336: .Xr tun 4 ,
1.176 jmc 1337: .Xr hosts.equiv 5 ,
1.159 stevesk 1338: .Xr ssh_config 5 ,
1.160 naddy 1339: .Xr ssh-keysign 8 ,
1.87 itojun 1340: .Xr sshd 8
1.106 markus 1341: .Rs
1342: .%A T. Ylonen
1343: .%A T. Kivinen
1344: .%A M. Saarinen
1345: .%A T. Rinne
1346: .%A S. Lehtinen
1347: .%T "SSH Protocol Architecture"
1.150 markus 1348: .%N draft-ietf-secsh-architecture-12.txt
1349: .%D January 2002
1.106 markus 1350: .%O work in progress material
1351: .Re
1.173 jmc 1352: .Sh AUTHORS
1353: OpenSSH is a derivative of the original and free
1354: ssh 1.2.12 release by Tatu Ylonen.
1355: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1356: Theo de Raadt and Dug Song
1357: removed many bugs, re-added newer features and
1358: created OpenSSH.
1359: Markus Friedl contributed the support for SSH
1360: protocol versions 1.5 and 2.0.
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