Annotation of src/usr.bin/ssh/ssh.1, Revision 1.218
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: .\"
1.218 ! jmc 37: .\" $OpenBSD: ssh.1,v 1.217 2005/12/08 14:59:44 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
1.210 djm 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
1.211 jmc 57: .Bk -words
1.2 deraadt 58: .Op Fl i Ar identity_file
1.211 jmc 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
1.211 jmc 66: .Bk -words
1.176 jmc 67: .Op Fl l Ar login_name
1.211 jmc 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
1.216 jmc 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
1.216 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.
1.176 jmc 92: X11 connections and arbitrary TCP/IP ports
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
1.176 jmc 103: depending on the protocol version used.
1.49 markus 104: .Pp
1.176 jmc 105: If
106: .Ar command
107: is specified,
108: .Ar command
109: is executed on the remote host instead of a login shell.
1.2 deraadt 110: .Pp
1.218 ! jmc 111: The options are as follows:
! 112: .Bl -tag -width Ds
! 113: .It Fl 1
! 114: Forces
1.2 deraadt 115: .Nm
1.218 ! jmc 116: to try protocol version 1 only.
! 117: .It Fl 2
! 118: Forces
1.2 deraadt 119: .Nm
1.218 ! jmc 120: to try protocol version 2 only.
! 121: .It Fl 4
! 122: Forces
1.2 deraadt 123: .Nm
1.218 ! jmc 124: to use IPv4 addresses only.
! 125: .It Fl 6
! 126: Forces
1.2 deraadt 127: .Nm
1.218 ! jmc 128: to use IPv6 addresses only.
! 129: .It Fl A
! 130: Enables forwarding of the authentication agent connection.
! 131: This can also be specified on a per-host basis in a configuration file.
1.2 deraadt 132: .Pp
1.218 ! jmc 133: Agent forwarding should be enabled with caution.
! 134: Users with the ability to bypass file permissions on the remote host
! 135: (for the agent's Unix-domain socket)
! 136: can access the local agent through the forwarded connection.
! 137: An attacker cannot obtain key material from the agent,
! 138: however they can perform operations on the keys that enable them to
! 139: authenticate using the identities loaded into the agent.
! 140: .It Fl a
! 141: Disables forwarding of the authentication agent connection.
! 142: .It Fl b Ar bind_address
! 143: Use
! 144: .Ar bind_address
! 145: on the local machine as the source address
! 146: of the connection.
! 147: Only useful on systems with more than one address.
! 148: .It Fl C
! 149: Requests compression of all data (including stdin, stdout, stderr, and
! 150: data for forwarded X11 and TCP/IP connections).
! 151: The compression algorithm is the same used by
! 152: .Xr gzip 1 ,
! 153: and the
! 154: .Dq level
! 155: can be controlled by the
! 156: .Cm CompressionLevel
! 157: option for protocol version 1.
! 158: Compression is desirable on modem lines and other
! 159: slow connections, but will only slow down things on fast networks.
! 160: The default value can be set on a host-by-host basis in the
! 161: configuration files; see the
! 162: .Cm Compression
! 163: option.
! 164: .It Fl c Ar cipher_spec
! 165: Selects the cipher specification for encrypting the session.
1.2 deraadt 166: .Pp
1.218 ! jmc 167: Protocol version 1 allows specification of a single cipher.
! 168: The supported values are
! 169: .Dq 3des ,
! 170: .Dq blowfish
! 171: and
! 172: .Dq des .
! 173: .Ar 3des
! 174: (triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
! 175: It is believed to be secure.
! 176: .Ar blowfish
! 177: is a fast block cipher; it appears very secure and is much faster than
! 178: .Ar 3des .
! 179: .Ar des
! 180: is only supported in the
1.2 deraadt 181: .Nm
1.218 ! jmc 182: client for interoperability with legacy protocol 1 implementations
! 183: that do not support the
! 184: .Ar 3des
! 185: cipher.
! 186: Its use is strongly discouraged due to cryptographic weaknesses.
! 187: The default is
! 188: .Dq 3des .
1.49 markus 189: .Pp
1.218 ! jmc 190: For protocol version 2
! 191: .Ar cipher_spec
! 192: is a comma-separated list of ciphers
! 193: listed in order of preference.
! 194: The supported ciphers are
! 195: .Dq 3des-cbc ,
! 196: .Dq aes128-cbc ,
! 197: .Dq aes192-cbc ,
! 198: .Dq aes256-cbc ,
! 199: .Dq aes128-ctr ,
! 200: .Dq aes192-ctr ,
! 201: .Dq aes256-ctr ,
! 202: .Dq arcfour128 ,
! 203: .Dq arcfour256 ,
! 204: .Dq arcfour ,
! 205: .Dq blowfish-cbc ,
! 206: and
! 207: .Dq cast128-cbc .
! 208: The default is
! 209: .Bd -literal
! 210: ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
! 211: arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
! 212: aes192-ctr,aes256-ctr''
! 213: .Ed
! 214: .It Fl D Xo
! 215: .Sm off
! 216: .Oo Ar bind_address : Oc
! 217: .Ar port
! 218: .Sm on
! 219: .Xc
! 220: Specifies a local
! 221: .Dq dynamic
! 222: application-level port forwarding.
! 223: This works by allocating a socket to listen to
! 224: .Ar port
! 225: on the local side, optionally bound to the specified
! 226: .Ar bind_address .
! 227: Whenever a connection is made to this port, the
! 228: connection is forwarded over the secure channel, and the application
! 229: protocol is then used to determine where to connect to from the
! 230: remote machine.
! 231: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.107 markus 232: .Nm
1.218 ! jmc 233: will act as a SOCKS server.
! 234: Only root can forward privileged ports.
! 235: Dynamic port forwardings can also be specified in the configuration file.
1.49 markus 236: .Pp
1.218 ! jmc 237: IPv6 addresses can be specified with an alternative syntax:
! 238: .Sm off
! 239: .Xo
! 240: .Op Ar bind_address No /
! 241: .Ar port
! 242: .Xc
! 243: .Sm on
! 244: or by enclosing the address in square brackets.
! 245: Only the superuser can forward privileged ports.
! 246: By default, the local port is bound in accordance with the
! 247: .Cm GatewayPorts
! 248: setting.
! 249: However, an explicit
! 250: .Ar bind_address
! 251: may be used to bind the connection to a specific address.
! 252: The
! 253: .Ar bind_address
! 254: of
! 255: .Dq localhost
! 256: indicates that the listening port be bound for local use only, while an
! 257: empty address or
! 258: .Sq *
! 259: indicates that the port should be available from all interfaces.
! 260: .It Fl e Ar ch | ^ch | none
! 261: Sets the escape character for sessions with a pty (default:
! 262: .Ql ~ ) .
! 263: The escape character is only recognized at the beginning of a line.
! 264: The escape character followed by a dot
! 265: .Pq Ql \&.
! 266: closes the connection;
! 267: followed by control-Z suspends the connection;
! 268: and followed by itself sends the escape character once.
! 269: Setting the character to
1.2 deraadt 270: .Dq none
1.218 ! jmc 271: disables any escapes and makes the session fully transparent.
! 272: .It Fl F Ar configfile
! 273: Specifies an alternative per-user configuration file.
! 274: If a configuration file is given on the command line,
! 275: the system-wide configuration file
! 276: .Pq Pa /etc/ssh/ssh_config
! 277: will be ignored.
! 278: The default for the per-user configuration file is
! 279: .Pa ~/.ssh/config .
! 280: .It Fl f
! 281: Requests
! 282: .Nm
! 283: to go to background just before command execution.
! 284: This is useful if
1.176 jmc 285: .Nm
1.218 ! jmc 286: is going to ask for passwords or passphrases, but the user
! 287: wants it in the background.
! 288: This implies
! 289: .Fl n .
! 290: The recommended way to start X11 programs at a remote site is with
! 291: something like
! 292: .Ic ssh -f host xterm .
! 293: .It Fl g
! 294: Allows remote hosts to connect to local forwarded ports.
! 295: .It Fl I Ar smartcard_device
! 296: Specifies which smartcard device to use.
! 297: The argument is the device
1.176 jmc 298: .Nm
1.218 ! jmc 299: should use to communicate with a smartcard used for storing the user's
! 300: private RSA key.
! 301: .It Fl i Ar identity_file
! 302: Selects a file from which the identity (private key) for
! 303: RSA or DSA authentication is read.
! 304: The default is
! 305: .Pa ~/.ssh/identity
! 306: for protocol version 1, and
! 307: .Pa ~/.ssh/id_rsa
1.149 jakob 308: and
1.218 ! jmc 309: .Pa ~/.ssh/id_dsa
! 310: for protocol version 2.
! 311: Identity files may also be specified on
! 312: a per-host basis in the configuration file.
! 313: It is possible to have multiple
! 314: .Fl i
! 315: options (and multiple identities specified in
! 316: configuration files).
! 317: .It Fl k
! 318: Disables forwarding (delegation) of GSSAPI credentials to the server.
! 319: .It Fl L Xo
! 320: .Sm off
! 321: .Oo Ar bind_address : Oc
! 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
! 329: on the local side, optionally bound to the specified
! 330: .Ar bind_address .
! 331: Whenever a connection is made to this port, the
! 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
! 342: .Op Ar bind_address No /
! 343: .Ar port No / Ar host No /
! 344: .Ar hostport
! 345: .Xc
! 346: .Sm on
! 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.
1.2 deraadt 355: The
1.218 ! jmc 356: .Ar bind_address
! 357: of
! 358: .Dq localhost
! 359: indicates that the listening port be bound for local use only, while an
! 360: empty address or
! 361: .Sq *
! 362: indicates that the port should be available from all interfaces.
! 363: .It Fl l Ar login_name
! 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.
! 366: .It Fl M
! 367: Places the
! 368: .Nm
! 369: client into
! 370: .Dq master
! 371: mode for connection sharing.
! 372: Refer to the description of
! 373: .Cm ControlMaster
! 374: in
! 375: .Xr ssh_config 5
! 376: for details.
! 377: .It Fl m Ar mac_spec
! 378: Additionally, for protocol version 2 a comma-separated list of MAC
! 379: (message authentication code) algorithms can
! 380: be specified in order of preference.
! 381: See the
! 382: .Cm MACs
! 383: keyword for more information.
! 384: .It Fl N
! 385: Do not execute a remote command.
! 386: This is useful for just forwarding ports
! 387: (protocol version 2 only).
! 388: .It Fl n
! 389: Redirects stdin from
! 390: .Pa /dev/null
! 391: (actually, prevents reading from stdin).
! 392: This must be used when
1.2 deraadt 393: .Nm
1.218 ! jmc 394: is run in the background.
! 395: A common trick is to use this to run X11 programs on a remote machine.
! 396: For example,
! 397: .Ic ssh -n shadows.cs.hut.fi emacs &
! 398: will start an emacs on shadows.cs.hut.fi, and the X11
! 399: connection will be automatically forwarded over an encrypted channel.
! 400: The
1.2 deraadt 401: .Nm
1.218 ! jmc 402: program will be put in the background.
! 403: (This does not work if
1.2 deraadt 404: .Nm
1.218 ! jmc 405: needs to ask for a password or passphrase; see also the
! 406: .Fl f
! 407: option.)
! 408: .It Fl O Ar ctl_cmd
! 409: Control an active connection multiplexing master process.
! 410: When the
! 411: .Fl O
! 412: option is specified, the
! 413: .Ar ctl_cmd
! 414: argument is interpreted and passed to the master process.
! 415: Valid commands are:
! 416: .Dq check
! 417: (check that the master process is running) and
! 418: .Dq exit
! 419: (request the master to exit).
! 420: .It Fl o Ar option
! 421: Can be used to give options in the format used in the configuration file.
! 422: This is useful for specifying options for which there is no separate
! 423: command-line flag.
! 424: For full details of the options listed below, and their possible values, see
! 425: .Xr ssh_config 5 .
1.2 deraadt 426: .Pp
1.218 ! jmc 427: .Bl -tag -width Ds -offset indent -compact
! 428: .It AddressFamily
! 429: .It BatchMode
! 430: .It BindAddress
! 431: .It ChallengeResponseAuthentication
! 432: .It CheckHostIP
! 433: .It Cipher
! 434: .It Ciphers
! 435: .It ClearAllForwardings
! 436: .It Compression
! 437: .It CompressionLevel
! 438: .It ConnectionAttempts
! 439: .It ConnectTimeout
! 440: .It ControlMaster
! 441: .It ControlPath
! 442: .It DynamicForward
! 443: .It EscapeChar
! 444: .It ForwardAgent
! 445: .It ForwardX11
! 446: .It ForwardX11Trusted
! 447: .It GatewayPorts
! 448: .It GlobalKnownHostsFile
! 449: .It GSSAPIAuthentication
! 450: .It GSSAPIDelegateCredentials
! 451: .It HashKnownHosts
! 452: .It Host
! 453: .It HostbasedAuthentication
! 454: .It HostKeyAlgorithms
! 455: .It HostKeyAlias
! 456: .It HostName
! 457: .It IdentityFile
! 458: .It IdentitiesOnly
! 459: .It KbdInteractiveDevices
! 460: .It LocalCommand
! 461: .It LocalForward
! 462: .It LogLevel
! 463: .It MACs
! 464: .It NoHostAuthenticationForLocalhost
! 465: .It NumberOfPasswordPrompts
! 466: .It PasswordAuthentication
! 467: .It PermitLocalCommand
! 468: .It Port
! 469: .It PreferredAuthentications
! 470: .It Protocol
! 471: .It ProxyCommand
! 472: .It PubkeyAuthentication
! 473: .It RemoteForward
! 474: .It RhostsRSAAuthentication
! 475: .It RSAAuthentication
! 476: .It SendEnv
! 477: .It ServerAliveInterval
! 478: .It ServerAliveCountMax
! 479: .It SmartcardDevice
! 480: .It StrictHostKeyChecking
! 481: .It TCPKeepAlive
! 482: .It Tunnel
! 483: .It TunnelDevice
! 484: .It UsePrivilegedPort
! 485: .It User
! 486: .It UserKnownHostsFile
! 487: .It VerifyHostKeyDNS
! 488: .It XAuthLocation
! 489: .El
! 490: .It Fl p Ar port
! 491: Port to connect to on the remote host.
! 492: This can be specified on a
! 493: per-host basis in the configuration file.
! 494: .It Fl q
! 495: Quiet mode.
! 496: Causes all warning and diagnostic messages to be suppressed.
! 497: .It Fl R Xo
! 498: .Sm off
! 499: .Oo Ar bind_address : Oc
! 500: .Ar port : host : hostport
! 501: .Sm on
! 502: .Xc
! 503: Specifies that the given port on the remote (server) host is to be
! 504: forwarded to the given host and port on the local side.
! 505: This works by allocating a socket to listen to
! 506: .Ar port
! 507: on the remote side, and whenever a connection is made to this port, the
! 508: connection is forwarded over the secure channel, and a connection is
! 509: made to
! 510: .Ar host
! 511: port
! 512: .Ar hostport
! 513: from the local machine.
1.2 deraadt 514: .Pp
1.218 ! jmc 515: Port forwardings can also be specified in the configuration file.
! 516: Privileged ports can be forwarded only when
! 517: logging in as root on the remote machine.
! 518: IPv6 addresses can be specified by enclosing the address in square braces or
! 519: using an alternative syntax:
! 520: .Sm off
! 521: .Xo
! 522: .Op Ar bind_address No /
! 523: .Ar host No / Ar port No /
! 524: .Ar hostport
! 525: .Xc .
! 526: .Sm on
1.194 jakob 527: .Pp
1.218 ! jmc 528: By default, the listening socket on the server will be bound to the loopback
! 529: interface only.
! 530: This may be overriden by specifying a
! 531: .Ar bind_address .
! 532: An empty
! 533: .Ar bind_address ,
! 534: or the address
! 535: .Ql * ,
! 536: indicates that the remote socket should listen on all interfaces.
! 537: Specifying a remote
! 538: .Ar bind_address
! 539: will only succeed if the server's
! 540: .Cm GatewayPorts
! 541: option is enabled (see
! 542: .Xr sshd_config 5 ) .
! 543: .It Fl S Ar ctl_path
! 544: Specifies the location of a control socket for connection sharing.
! 545: Refer to the description of
! 546: .Cm ControlPath
! 547: and
! 548: .Cm ControlMaster
! 549: in
! 550: .Xr ssh_config 5
! 551: for details.
! 552: .It Fl s
! 553: May be used to request invocation of a subsystem on the remote system.
! 554: Subsystems are a feature of the SSH2 protocol which facilitate the use
! 555: of SSH as a secure transport for other applications (eg.\&
! 556: .Xr sftp 1 ) .
! 557: The subsystem is specified as the remote command.
! 558: .It Fl T
! 559: Disable pseudo-tty allocation.
! 560: .It Fl t
! 561: Force pseudo-tty allocation.
! 562: This can be used to execute arbitrary
! 563: screen-based programs on a remote machine, which can be very useful,
! 564: e.g., when implementing menu services.
! 565: Multiple
! 566: .Fl t
! 567: options force tty allocation, even if
1.194 jakob 568: .Nm
1.218 ! jmc 569: has no local tty.
! 570: .It Fl V
! 571: Display the version number and exit.
! 572: .It Fl v
! 573: Verbose mode.
! 574: Causes
1.176 jmc 575: .Nm
1.218 ! jmc 576: to print debugging messages about its progress.
! 577: This is helpful in
! 578: debugging connection, authentication, and configuration problems.
! 579: Multiple
! 580: .Fl v
! 581: options increase the verbosity.
! 582: The maximum is 3.
! 583: .It Fl w Ar tunnel : Ns Ar tunnel
! 584: Requests a
! 585: .Xr tun 4
! 586: device on the client and server like the
! 587: .Cm Tunnel
! 588: directive in
! 589: .Xr ssh_config 5 .
! 590: .It Fl X
! 591: Enables X11 forwarding.
1.54 markus 592: This can also be specified on a per-host basis in a configuration file.
1.165 stevesk 593: .Pp
1.218 ! jmc 594: X11 forwarding should be enabled with caution.
1.168 jmc 595: Users with the ability to bypass file permissions on the remote host
1.218 ! jmc 596: (for the user's X authorization database)
! 597: can access the local X11 display through the forwarded connection.
! 598: An attacker may then be able to perform activities such as keystroke monitoring.
! 599: .Pp
! 600: For this reason, X11 forwarding is subjected to X11 SECURITY extension
! 601: restrictions by default.
! 602: Please refer to the
! 603: .Nm
! 604: .Fl Y
! 605: option and the
! 606: .Cm ForwardX11Trusted
! 607: directive in
! 608: .Xr ssh_config 5
! 609: for more information.
! 610: .It Fl x
! 611: Disables X11 forwarding.
! 612: .It Fl Y
! 613: Enables trusted X11 forwarding.
! 614: Trusted X11 forwardings are not subjected to the X11 SECURITY extension
! 615: controls.
! 616: .El
! 617: .Ss SSH protocol version 1
! 618: The first authentication method is the
! 619: .Em rhosts
! 620: or
! 621: .Em hosts.equiv
! 622: method combined with RSA-based host authentication.
! 623: If the machine the user logs in from is listed in
! 624: .Pa /etc/hosts.equiv
! 625: or
! 626: .Pa /etc/shosts.equiv
! 627: on the remote machine, and the user names are
! 628: the same on both sides, or if the files
! 629: .Pa ~/.rhosts
! 630: or
! 631: .Pa ~/.shosts
! 632: exist in the user's home directory on the
! 633: remote machine and contain a line containing the name of the client
! 634: machine and the name of the user on that machine, the user is
! 635: considered for log in.
! 636: Additionally, if the server can verify the client's
! 637: host key (see
! 638: .Pa /etc/ssh/ssh_known_hosts
1.189 dtucker 639: and
1.218 ! jmc 640: .Pa ~/.ssh/known_hosts
! 641: in the
! 642: .Sx FILES
! 643: section), only then is login permitted.
! 644: This authentication method closes security holes due to IP
! 645: spoofing, DNS spoofing and routing spoofing.
! 646: [Note to the administrator:
! 647: .Pa /etc/hosts.equiv ,
! 648: .Pa ~/.rhosts ,
! 649: and the rlogin/rsh protocol in general, are inherently insecure and should be
! 650: disabled if security is desired.]
1.189 dtucker 651: .Pp
1.218 ! jmc 652: As a second authentication method,
1.176 jmc 653: .Nm
1.218 ! jmc 654: supports RSA based authentication.
! 655: The scheme is based on public-key cryptography: there are cryptosystems
! 656: where encryption and decryption are done using separate keys, and it
! 657: is not possible to derive the decryption key from the encryption key.
! 658: RSA is one such system.
! 659: The idea is that each user creates a public/private
! 660: key pair for authentication purposes.
! 661: The server knows the public key, and only the user knows the private key.
1.210 djm 662: .Pp
1.218 ! jmc 663: The file
! 664: .Pa ~/.ssh/authorized_keys
! 665: lists the public keys that are permitted for logging in.
! 666: When the user logs in, the
1.2 deraadt 667: .Nm
1.218 ! jmc 668: program tells the server which key pair it would like to use for
! 669: authentication.
! 670: The server checks if this key is permitted, and if so,
! 671: sends the user (actually the
1.2 deraadt 672: .Nm
1.218 ! jmc 673: program running on behalf of the user) a challenge, a random number,
! 674: encrypted by the user's public key.
! 675: The challenge can only be decrypted using the proper private key.
! 676: The user's client then decrypts the challenge using the private key,
! 677: proving that he/she knows the private key
! 678: but without disclosing it to the server.
! 679: .Pp
1.176 jmc 680: .Nm
1.218 ! jmc 681: implements the RSA authentication protocol automatically.
! 682: The user creates his/her RSA key pair by running
! 683: .Xr ssh-keygen 1 .
! 684: This stores the private key in
1.207 djm 685: .Pa ~/.ssh/identity
1.218 ! jmc 686: and stores the public key in
! 687: .Pa ~/.ssh/identity.pub
! 688: in the user's home directory.
! 689: The user should then copy the
! 690: .Pa identity.pub
! 691: to
! 692: .Pa ~/.ssh/authorized_keys
! 693: in his/her home directory on the remote machine (the
! 694: .Pa authorized_keys
! 695: file corresponds to the conventional
! 696: .Pa ~/.rhosts
! 697: file, and has one key
! 698: per line, though the lines can be very long).
! 699: After this, the user can log in without giving the password.
! 700: .Pp
! 701: The most convenient way to use RSA authentication may be with an
! 702: authentication agent.
! 703: See
! 704: .Xr ssh-agent 1
! 705: for more information.
! 706: .Pp
! 707: If other authentication methods fail,
! 708: .Nm
! 709: prompts the user for a password.
! 710: The password is sent to the remote
! 711: host for checking; however, since all communications are encrypted,
! 712: the password cannot be seen by someone listening on the network.
! 713: .Ss SSH protocol version 2
! 714: When a user connects using protocol version 2,
! 715: similar authentication methods are available.
! 716: Using the default values for
! 717: .Cm PreferredAuthentications ,
! 718: the client will try to authenticate first using the hostbased method;
! 719: if this method fails, public key authentication is attempted,
! 720: and finally if this method fails, keyboard-interactive and
! 721: password authentication are tried.
! 722: .Pp
! 723: The public key method is similar to RSA authentication described
! 724: in the previous section and allows the RSA or DSA algorithm to be used:
! 725: The client uses his private key,
1.207 djm 726: .Pa ~/.ssh/id_dsa
1.218 ! jmc 727: or
! 728: .Pa ~/.ssh/id_rsa ,
! 729: to sign the session identifier and sends the result to the server.
! 730: The server checks whether the matching public key is listed in
! 731: .Pa ~/.ssh/authorized_keys
! 732: and grants access if both the key is found and the signature is correct.
! 733: The session identifier is derived from a shared Diffie-Hellman value
! 734: and is only known to the client and the server.
! 735: .Pp
! 736: If public key authentication fails or is not available, a password
! 737: can be sent encrypted to the remote host to prove the user's identity.
! 738: .Pp
! 739: Additionally,
1.190 djm 740: .Nm
1.218 ! jmc 741: supports hostbased or challenge response authentication.
! 742: .Pp
! 743: Protocol 2 provides additional mechanisms for confidentiality
! 744: (the traffic is encrypted using AES, 3DES, Blowfish, CAST128 or Arcfour)
! 745: and integrity (hmac-md5, hmac-sha1, hmac-ripemd160).
! 746: Note that protocol 1 lacks a strong mechanism for ensuring the
! 747: integrity of the connection.
! 748: .Ss Login session and remote execution
! 749: When the user's identity has been accepted by the server, the server
! 750: either executes the given command, or logs into the machine and gives
! 751: the user a normal shell on the remote machine.
! 752: All communication with
! 753: the remote command or shell will be automatically encrypted.
! 754: .Pp
! 755: If a pseudo-terminal has been allocated (normal login session), the
! 756: user may use the escape characters noted below.
! 757: .Pp
! 758: If no pseudo-tty has been allocated,
! 759: the session is transparent and can be used to reliably transfer binary data.
! 760: On most systems, setting the escape character to
! 761: .Dq none
! 762: will also make the session transparent even if a tty is used.
! 763: .Pp
! 764: The session terminates when the command or shell on the remote
! 765: machine exits and all X11 and TCP/IP connections have been closed.
! 766: The exit status of the remote program is returned as the exit status of
! 767: .Nm ssh .
! 768: .Pp
1.2 deraadt 769: .Nm
1.218 ! jmc 770: may additionally obtain configuration data from
! 771: a per-user configuration file and a system-wide configuration file.
! 772: The file format and configuration options are described in
! 773: .Xr ssh_config 5 .
! 774: .Ss Escape Characters
! 775: When a pseudo-terminal has been requested,
1.2 deraadt 776: .Nm
1.218 ! jmc 777: supports a number of functions through the use of an escape character.
! 778: .Pp
! 779: A single tilde character can be sent as
! 780: .Ic ~~
! 781: or by following the tilde by a character other than those described below.
! 782: The escape character must always follow a newline to be interpreted as
! 783: special.
! 784: The escape character can be changed in configuration files using the
! 785: .Cm EscapeChar
! 786: configuration directive or on the command line by the
! 787: .Fl e
! 788: option.
! 789: .Pp
! 790: The supported escapes (assuming the default
! 791: .Ql ~ )
! 792: are:
! 793: .Bl -tag -width Ds
! 794: .It Cm ~.
! 795: Disconnect.
! 796: .It Cm ~^Z
! 797: Background
! 798: .Nm ssh .
! 799: .It Cm ~#
! 800: List forwarded connections.
! 801: .It Cm ~&
! 802: Background
1.2 deraadt 803: .Nm
1.218 ! jmc 804: at logout when waiting for forwarded connection / X11 sessions to terminate.
! 805: .It Cm ~?
! 806: Display a list of escape characters.
! 807: .It Cm ~B
! 808: Send a BREAK to the remote system
! 809: (only useful for SSH protocol version 2 and if the peer supports it).
! 810: .It Cm ~C
! 811: Open command line.
! 812: Currently this allows the addition of port forwardings using the
! 813: .Fl L
! 814: and
! 815: .Fl R
! 816: options (see below).
! 817: It also allows the cancellation of existing remote port-forwardings
! 818: using
! 819: .Fl KR Ar hostport .
! 820: .Ic !\& Ns Ar command
! 821: allows the user to execute a local command if the
! 822: .Ic PermitLocalCommand
! 823: option is enabled in
1.176 jmc 824: .Xr ssh_config 5 .
1.218 ! jmc 825: Basic help is available, using the
! 826: .Fl h
! 827: option.
! 828: .It Cm ~R
! 829: Request rekeying of the connection
! 830: (only useful for SSH protocol version 2 and if the peer supports it).
1.176 jmc 831: .El
1.218 ! jmc 832: .Ss X11 and TCP forwarding
! 833: If the
! 834: .Cm ForwardX11
! 835: variable is set to
! 836: .Dq yes
! 837: (or see the description of the
! 838: .Fl X
! 839: and
! 840: .Fl x
! 841: options described later)
! 842: and the user is using X11 (the
! 843: .Ev DISPLAY
! 844: environment variable is set), the connection to the X11 display is
! 845: automatically forwarded to the remote side in such a way that any X11
! 846: programs started from the shell (or command) will go through the
! 847: encrypted channel, and the connection to the real X server will be made
1.176 jmc 848: from the local machine.
1.218 ! jmc 849: The user should not manually set
! 850: .Ev DISPLAY .
! 851: Forwarding of X11 connections can be
! 852: configured on the command line or in configuration files.
! 853: .Pp
! 854: The
! 855: .Ev DISPLAY
! 856: value set by
! 857: .Nm
! 858: will point to the server machine, but with a display number greater than zero.
! 859: This is normal, and happens because
! 860: .Nm
! 861: creates a
! 862: .Dq proxy
! 863: X server on the server machine for forwarding the
! 864: connections over the encrypted channel.
1.200 djm 865: .Pp
1.218 ! jmc 866: .Nm
! 867: will also automatically set up Xauthority data on the server machine.
! 868: For this purpose, it will generate a random authorization cookie,
! 869: store it in Xauthority on the server, and verify that any forwarded
! 870: connections carry this cookie and replace it by the real cookie when
! 871: the connection is opened.
! 872: The real authentication cookie is never
! 873: sent to the server machine (and no cookies are sent in the plain).
1.200 djm 874: .Pp
1.218 ! jmc 875: If the
! 876: .Cm ForwardAgent
! 877: variable is set to
! 878: .Dq yes
! 879: (or see the description of the
! 880: .Fl A
1.191 djm 881: and
1.218 ! jmc 882: .Fl a
! 883: options described later) and
! 884: the user is using an authentication agent, the connection to the agent
! 885: is automatically forwarded to the remote side.
! 886: .Pp
! 887: Forwarding of arbitrary TCP/IP connections over the secure channel can
! 888: be specified either on the command line or in a configuration file.
! 889: One possible application of TCP/IP forwarding is a secure connection to an
! 890: electronic purse; another is going through firewalls.
! 891: .Ss Server authentication
1.73 markus 892: .Nm
1.218 ! jmc 893: automatically maintains and checks a database containing
! 894: identifications for all hosts it has ever been used with.
! 895: Host keys are stored in
! 896: .Pa ~/.ssh/known_hosts
! 897: in the user's home directory.
! 898: Additionally, the file
! 899: .Pa /etc/ssh/ssh_known_hosts
! 900: is automatically checked for known hosts.
! 901: Any new hosts are automatically added to the user's file.
! 902: If a host's identification ever changes,
1.2 deraadt 903: .Nm
1.218 ! jmc 904: warns about this and disables password authentication to prevent a
! 905: trojan horse from getting the user's password.
! 906: Another purpose of this mechanism is to prevent man-in-the-middle attacks
! 907: which could otherwise be used to circumvent the encryption.
! 908: The
! 909: .Cm StrictHostKeyChecking
! 910: option can be used to prevent logins to machines whose
! 911: host key is not known or has changed.
1.203 djm 912: .Pp
913: .Nm
1.218 ! jmc 914: can be configured to verify host identification using fingerprint resource
! 915: records (SSHFP) published in DNS.
! 916: The
! 917: .Cm VerifyHostKeyDNS
! 918: option can be used to control how DNS lookups are performed.
! 919: SSHFP resource records can be generated using
! 920: .Xr ssh-keygen 1 .
1.2 deraadt 921: .Sh ENVIRONMENT
922: .Nm
1.1 deraadt 923: will normally set the following environment variables:
1.176 jmc 924: .Bl -tag -width LOGNAME
1.2 deraadt 925: .It Ev DISPLAY
926: The
927: .Ev DISPLAY
1.40 aaron 928: variable indicates the location of the X11 server.
1.44 aaron 929: It is automatically set by
1.2 deraadt 930: .Nm
931: to point to a value of the form
932: .Dq hostname:n
933: where hostname indicates
1.176 jmc 934: the host where the shell runs, and n is an integer \*(Ge 1.
1.40 aaron 935: .Nm
936: uses this special value to forward X11 connections over the secure
937: channel.
1.107 markus 938: The user should normally not set
939: .Ev DISPLAY
940: explicitly, as that
1.1 deraadt 941: will render the X11 connection insecure (and will require the user to
942: manually copy any required authorization cookies).
1.2 deraadt 943: .It Ev HOME
1.1 deraadt 944: Set to the path of the user's home directory.
1.2 deraadt 945: .It Ev LOGNAME
946: Synonym for
1.12 aaron 947: .Ev USER ;
948: set for compatibility with systems that use this variable.
1.2 deraadt 949: .It Ev MAIL
1.129 stevesk 950: Set to the path of the user's mailbox.
1.40 aaron 951: .It Ev PATH
1.2 deraadt 952: Set to the default
953: .Ev PATH ,
954: as specified when compiling
1.12 aaron 955: .Nm ssh .
1.118 markus 956: .It Ev SSH_ASKPASS
957: If
958: .Nm
959: needs a passphrase, it will read the passphrase from the current
960: terminal if it was run from a terminal.
961: If
962: .Nm
963: does not have a terminal associated with it but
964: .Ev DISPLAY
965: and
966: .Ev SSH_ASKPASS
967: are set, it will execute the program specified by
968: .Ev SSH_ASKPASS
969: and open an X11 window to read the passphrase.
970: This is particularly useful when calling
971: .Nm
972: from a
1.196 jmc 973: .Pa .xsession
1.118 markus 974: or related script.
975: (Note that on some machines it
976: may be necessary to redirect the input from
977: .Pa /dev/null
978: to make this work.)
1.18 markus 979: .It Ev SSH_AUTH_SOCK
1.129 stevesk 980: Identifies the path of a unix-domain socket used to communicate with the
1.17 markus 981: agent.
1.166 stevesk 982: .It Ev SSH_CONNECTION
983: Identifies the client and server ends of the connection.
1.40 aaron 984: The variable contains
1.166 stevesk 985: four space-separated values: client ip-address, client port number,
986: server ip-address and server port number.
1.73 markus 987: .It Ev SSH_ORIGINAL_COMMAND
988: The variable contains the original command line if a forced command
989: is executed.
990: It can be used to extract the original arguments.
1.2 deraadt 991: .It Ev SSH_TTY
1.1 deraadt 992: This is set to the name of the tty (path to the device) associated
1.40 aaron 993: with the current shell or command.
994: If the current session has no tty,
1.1 deraadt 995: this variable is not set.
1.2 deraadt 996: .It Ev TZ
1.214 jmc 997: This variable is set to indicate the present time zone if it
1.56 deraadt 998: was set when the daemon was started (i.e., the daemon passes the value
1.1 deraadt 999: on to new connections).
1.2 deraadt 1000: .It Ev USER
1.1 deraadt 1001: Set to the name of the user logging in.
1.2 deraadt 1002: .El
1003: .Pp
1.44 aaron 1004: Additionally,
1.2 deraadt 1005: .Nm
1.44 aaron 1006: reads
1.207 djm 1007: .Pa ~/.ssh/environment ,
1.2 deraadt 1008: and adds lines of the format
1009: .Dq VARNAME=value
1.161 marc 1010: to the environment if the file exists and if users are allowed to
1011: change their environment.
1.176 jmc 1012: For more information, see the
1.161 marc 1013: .Cm PermitUserEnvironment
1.162 stevesk 1014: option in
1.161 marc 1015: .Xr sshd_config 5 .
1.2 deraadt 1016: .Sh FILES
1.36 markus 1017: .Bl -tag -width Ds
1.207 djm 1018: .It Pa ~/.ssh/known_hosts
1.129 stevesk 1019: Records host keys for all hosts the user has logged into that are not
1.2 deraadt 1020: in
1.147 deraadt 1021: .Pa /etc/ssh/ssh_known_hosts .
1.2 deraadt 1022: See
1023: .Xr sshd 8 .
1.207 djm 1024: .It Pa ~/.ssh/identity, ~/.ssh/id_dsa, ~/.ssh/id_rsa
1.102 itojun 1025: Contains the authentication identity of the user.
1026: They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively.
1.48 markus 1027: These files
1028: contain sensitive data and should be readable by the user but not
1.15 markus 1029: accessible by others (read/write/execute).
1030: Note that
1031: .Nm
1.48 markus 1032: ignores a private key file if it is accessible by others.
1.15 markus 1033: It is possible to specify a passphrase when
1.1 deraadt 1034: generating the key; the passphrase will be used to encrypt the
1.8 deraadt 1035: sensitive part of this file using 3DES.
1.207 djm 1036: .It Pa ~/.ssh/identity.pub, ~/.ssh/id_dsa.pub, ~/.ssh/id_rsa.pub
1.1 deraadt 1037: Contains the public key for authentication (public part of the
1.40 aaron 1038: identity file in human-readable form).
1.48 markus 1039: The contents of the
1.207 djm 1040: .Pa ~/.ssh/identity.pub
1.176 jmc 1041: file should be added to the file
1.207 djm 1042: .Pa ~/.ssh/authorized_keys
1.2 deraadt 1043: on all machines
1.137 deraadt 1044: where the user wishes to log in using protocol version 1 RSA authentication.
1.48 markus 1045: The contents of the
1.207 djm 1046: .Pa ~/.ssh/id_dsa.pub
1.102 itojun 1047: and
1.207 djm 1048: .Pa ~/.ssh/id_rsa.pub
1.48 markus 1049: file should be added to
1.207 djm 1050: .Pa ~/.ssh/authorized_keys
1.48 markus 1051: on all machines
1.137 deraadt 1052: where the user wishes to log in using protocol version 2 DSA/RSA authentication.
1.48 markus 1053: These files are not
1.40 aaron 1054: sensitive and can (but need not) be readable by anyone.
1.48 markus 1055: These files are
1.84 markus 1056: never used automatically and are not necessary; they are only provided for
1.1 deraadt 1057: the convenience of the user.
1.207 djm 1058: .It Pa ~/.ssh/config
1.40 aaron 1059: This is the per-user configuration file.
1.158 stevesk 1060: The file format and configuration options are described in
1061: .Xr ssh_config 5 .
1.183 djm 1062: Because of the potential for abuse, this file must have strict permissions:
1063: read/write for the user, and not accessible by others.
1.207 djm 1064: .It Pa ~/.ssh/authorized_keys
1.115 markus 1065: Lists the public keys (RSA/DSA) that can be used for logging in as this user.
1.40 aaron 1066: The format of this file is described in the
1.2 deraadt 1067: .Xr sshd 8
1.40 aaron 1068: manual page.
1.176 jmc 1069: In the simplest form the format is the same as the
1070: .Pa .pub
1.116 markus 1071: identity files.
1.48 markus 1072: This file is not highly sensitive, but the recommended
1073: permissions are read/write for the user, and not accessible by others.
1.147 deraadt 1074: .It Pa /etc/ssh/ssh_known_hosts
1.40 aaron 1075: Systemwide list of known host keys.
1.116 markus 1076: This file should be prepared by the
1.1 deraadt 1077: system administrator to contain the public host keys of all machines in the
1.40 aaron 1078: organization.
1079: This file should be world-readable.
1080: This file contains
1.1 deraadt 1081: public keys, one per line, in the following format (fields separated
1.116 markus 1082: by spaces): system name, public key and optional comment field.
1.40 aaron 1083: When different names are used
1.1 deraadt 1084: for the same machine, all such names should be listed, separated by
1.40 aaron 1085: commas.
1.176 jmc 1086: The format is described in the
1.2 deraadt 1087: .Xr sshd 8
1.1 deraadt 1088: manual page.
1.2 deraadt 1089: .Pp
1.1 deraadt 1090: The canonical system name (as returned by name servers) is used by
1.2 deraadt 1091: .Xr sshd 8
1.1 deraadt 1092: to verify the client host when logging in; other names are needed because
1.2 deraadt 1093: .Nm
1.1 deraadt 1094: does not convert the user-supplied name to a canonical name before
1095: checking the key, because someone with access to the name servers
1096: would then be able to fool host authentication.
1.147 deraadt 1097: .It Pa /etc/ssh/ssh_config
1.40 aaron 1098: Systemwide configuration file.
1.158 stevesk 1099: The file format and configuration options are described in
1100: .Xr ssh_config 5 .
1.147 deraadt 1101: .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key
1.141 markus 1102: These three files contain the private parts of the host keys
1103: and are used for
1104: .Cm RhostsRSAAuthentication
1105: and
1106: .Cm HostbasedAuthentication .
1.155 stevesk 1107: If the protocol version 1
1108: .Cm RhostsRSAAuthentication
1.157 deraadt 1109: method is used,
1.155 stevesk 1110: .Nm
1111: must be setuid root, since the host key is readable only by root.
1112: For protocol version 2,
1113: .Nm
1114: uses
1115: .Xr ssh-keysign 8
1116: to access the host keys for
1117: .Cm HostbasedAuthentication .
1118: This eliminates the requirement that
1119: .Nm
1120: be setuid root when that authentication method is used.
1121: By default
1.141 markus 1122: .Nm
1.155 stevesk 1123: is not setuid root.
1.207 djm 1124: .It Pa ~/.rhosts
1.2 deraadt 1125: This file is used in
1.195 markus 1126: .Cm RhostsRSAAuthentication
1127: and
1128: .Cm HostbasedAuthentication
1.2 deraadt 1129: authentication to list the
1.40 aaron 1130: host/user pairs that are permitted to log in.
1131: (Note that this file is
1.1 deraadt 1132: also used by rlogin and rsh, which makes using this file insecure.)
1133: Each line of the file contains a host name (in the canonical form
1134: returned by name servers), and then a user name on that host,
1.40 aaron 1135: separated by a space.
1.92 markus 1136: On some machines this file may need to be
1.1 deraadt 1137: world-readable if the user's home directory is on a NFS partition,
1138: because
1.2 deraadt 1139: .Xr sshd 8
1.40 aaron 1140: reads it as root.
1141: Additionally, this file must be owned by the user,
1142: and must not have write permissions for anyone else.
1143: The recommended
1.1 deraadt 1144: permission for most machines is read/write for the user, and not
1145: accessible by others.
1.2 deraadt 1146: .Pp
1.195 markus 1147: Note that
1.2 deraadt 1148: .Xr sshd 8
1.195 markus 1149: allows authentication only in combination with client host key
1150: authentication before permitting log in.
1.137 deraadt 1151: If the server machine does not have the client's host key in
1.147 deraadt 1152: .Pa /etc/ssh/ssh_known_hosts ,
1.137 deraadt 1153: it can be stored in
1.207 djm 1154: .Pa ~/.ssh/known_hosts .
1.2 deraadt 1155: The easiest way to do this is to
1.1 deraadt 1156: connect back to the client from the server machine using ssh; this
1.48 markus 1157: will automatically add the host key to
1.207 djm 1158: .Pa ~/.ssh/known_hosts .
1159: .It Pa ~/.shosts
1.2 deraadt 1160: This file is used exactly the same way as
1.176 jmc 1161: .Pa .rhosts .
1.2 deraadt 1162: The purpose for
1.195 markus 1163: having this file is to be able to use
1164: .Cm RhostsRSAAuthentication
1165: and
1166: .Cm HostbasedAuthentication
1167: authentication without permitting login with
1.176 jmc 1168: .Xr rlogin
1.2 deraadt 1169: or
1170: .Xr rsh 1 .
1171: .It Pa /etc/hosts.equiv
1172: This file is used during
1.195 markus 1173: .Cm RhostsRSAAuthentication
1174: and
1175: .Cm HostbasedAuthentication
1.173 jmc 1176: authentication.
1.40 aaron 1177: It contains
1.176 jmc 1178: canonical hosts names, one per line (the full format is described in the
1.2 deraadt 1179: .Xr sshd 8
1.40 aaron 1180: manual page).
1181: If the client host is found in this file, login is
1.1 deraadt 1182: automatically permitted provided client and server user names are the
1.40 aaron 1183: same.
1.195 markus 1184: Additionally, successful client host key authentication is required.
1.40 aaron 1185: This file should only be writable by root.
1.2 deraadt 1186: .It Pa /etc/shosts.equiv
1.44 aaron 1187: This file is processed exactly as
1.2 deraadt 1188: .Pa /etc/hosts.equiv .
1.1 deraadt 1189: This file may be useful to permit logins using
1.2 deraadt 1190: .Nm
1.1 deraadt 1191: but not using rsh/rlogin.
1.147 deraadt 1192: .It Pa /etc/ssh/sshrc
1.1 deraadt 1193: Commands in this file are executed by
1.2 deraadt 1194: .Nm
1.1 deraadt 1195: when the user logs in just before the user's shell (or command) is started.
1196: See the
1.2 deraadt 1197: .Xr sshd 8
1.1 deraadt 1198: manual page for more information.
1.207 djm 1199: .It Pa ~/.ssh/rc
1.1 deraadt 1200: Commands in this file are executed by
1.2 deraadt 1201: .Nm
1.1 deraadt 1202: when the user logs in just before the user's shell (or command) is
1203: started.
1.44 aaron 1204: See the
1.2 deraadt 1205: .Xr sshd 8
1.1 deraadt 1206: manual page for more information.
1.207 djm 1207: .It Pa ~/.ssh/environment
1.31 markus 1208: Contains additional definitions for environment variables, see section
1209: .Sx ENVIRONMENT
1210: above.
1.58 itojun 1211: .El
1.145 markus 1212: .Sh DIAGNOSTICS
1213: .Nm
1214: exits with the exit status of the remote command or with 255
1215: if an error occurred.
1.2 deraadt 1216: .Sh SEE ALSO
1.176 jmc 1217: .Xr gzip 1 ,
1.2 deraadt 1218: .Xr rsh 1 ,
1219: .Xr scp 1 ,
1.83 djm 1220: .Xr sftp 1 ,
1.2 deraadt 1221: .Xr ssh-add 1 ,
1222: .Xr ssh-agent 1 ,
1223: .Xr ssh-keygen 1 ,
1224: .Xr telnet 1 ,
1.176 jmc 1225: .Xr hosts.equiv 5 ,
1.159 stevesk 1226: .Xr ssh_config 5 ,
1.160 naddy 1227: .Xr ssh-keysign 8 ,
1.87 itojun 1228: .Xr sshd 8
1.106 markus 1229: .Rs
1230: .%A T. Ylonen
1231: .%A T. Kivinen
1232: .%A M. Saarinen
1233: .%A T. Rinne
1234: .%A S. Lehtinen
1235: .%T "SSH Protocol Architecture"
1.150 markus 1236: .%N draft-ietf-secsh-architecture-12.txt
1237: .%D January 2002
1.106 markus 1238: .%O work in progress material
1239: .Re
1.173 jmc 1240: .Sh AUTHORS
1241: OpenSSH is a derivative of the original and free
1242: ssh 1.2.12 release by Tatu Ylonen.
1243: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1244: Theo de Raadt and Dug Song
1245: removed many bugs, re-added newer features and
1246: created OpenSSH.
1247: Markus Friedl contributed the support for SSH
1248: protocol versions 1.5 and 2.0.
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