Annotation of src/usr.bin/ssh/ssh.1, Revision 1.356
1.1 deraadt 1: .\"
2: .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
3: .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
4: .\" All rights reserved
5: .\"
1.59 deraadt 6: .\" As far as I am concerned, the code I have written for this software
7: .\" can be used freely for any purpose. Any derived versions of this
8: .\" software must be clearly marked as such, and if the derived work is
9: .\" incompatible with the protocol description in the RFC file, it must be
10: .\" called by a name other than "ssh" or "Secure Shell".
11: .\"
1.93 deraadt 12: .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
13: .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
14: .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
1.59 deraadt 15: .\"
16: .\" Redistribution and use in source and binary forms, with or without
17: .\" modification, are permitted provided that the following conditions
18: .\" are met:
19: .\" 1. Redistributions of source code must retain the above copyright
20: .\" notice, this list of conditions and the following disclaimer.
21: .\" 2. Redistributions in binary form must reproduce the above copyright
22: .\" notice, this list of conditions and the following disclaimer in the
23: .\" documentation and/or other materials provided with the distribution.
1.1 deraadt 24: .\"
1.59 deraadt 25: .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
26: .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
27: .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
28: .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
29: .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
30: .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
31: .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
32: .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
33: .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
34: .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
1.1 deraadt 35: .\"
1.356 ! djm 36: .\" $OpenBSD: ssh.1,v 1.355 2015/01/30 11:43:14 djm Exp $
! 37: .Dd $Mdocdate: January 30 2015 $
1.2 deraadt 38: .Dt SSH 1
39: .Os
40: .Sh NAME
41: .Nm ssh
1.96 deraadt 42: .Nd OpenSSH SSH client (remote login program)
1.2 deraadt 43: .Sh SYNOPSIS
44: .Nm ssh
1.306 jmc 45: .Bk -words
1.351 jmc 46: .Op Fl 1246AaCfGgKkMNnqsTtVvXxYy
1.108 markus 47: .Op Fl b Ar bind_address
1.51 markus 48: .Op Fl c Ar cipher_spec
1.306 jmc 49: .Op Fl D Oo Ar bind_address : Oc Ns Ar port
1.331 dtucker 50: .Op Fl E Ar log_file
1.2 deraadt 51: .Op Fl e Ar escape_char
1.176 jmc 52: .Op Fl F Ar configfile
1.292 jmc 53: .Op Fl I Ar pkcs11
1.2 deraadt 54: .Op Fl i Ar identity_file
1.306 jmc 55: .Op Fl L Oo Ar bind_address : Oc Ns Ar port : Ns Ar host : Ns Ar hostport
1.176 jmc 56: .Op Fl l Ar login_name
57: .Op Fl m Ar mac_spec
1.198 djm 58: .Op Fl O Ar ctl_cmd
1.176 jmc 59: .Op Fl o Ar option
60: .Op Fl p Ar port
1.356 ! djm 61: .Op Fl Q Cm cipher | cipher-auth | mac | kex | key | protocol-version
1.306 jmc 62: .Op Fl R Oo Ar bind_address : Oc Ns Ar port : Ns Ar host : Ns Ar hostport
1.198 djm 63: .Op Fl S Ar ctl_path
1.290 dtucker 64: .Op Fl W Ar host : Ns Ar port
1.306 jmc 65: .Op Fl w Ar local_tun Ns Op : Ns Ar remote_tun
1.176 jmc 66: .Oo Ar user Ns @ Oc Ns Ar hostname
1.2 deraadt 67: .Op Ar command
1.306 jmc 68: .Ek
1.44 aaron 69: .Sh DESCRIPTION
1.2 deraadt 70: .Nm
1.96 deraadt 71: (SSH client) is a program for logging into a remote machine and for
1.40 aaron 72: executing commands on a remote machine.
1.176 jmc 73: It is intended to replace rlogin and rsh,
74: and provide secure encrypted communications between
1.40 aaron 75: two untrusted hosts over an insecure network.
1.348 millert 76: X11 connections, arbitrary TCP ports and
77: .Ux Ns -domain
78: sockets can also be forwarded over the secure channel.
1.2 deraadt 79: .Pp
80: .Nm
1.44 aaron 81: connects and logs into the specified
1.176 jmc 82: .Ar hostname
83: (with optional
84: .Ar user
85: name).
1.1 deraadt 86: The user must prove
1.49 markus 87: his/her identity to the remote machine using one of several methods
1.221 jmc 88: depending on the protocol version used (see below).
1.49 markus 89: .Pp
1.176 jmc 90: If
91: .Ar command
92: is specified,
1.219 jmc 93: it is executed on the remote host instead of a login shell.
1.2 deraadt 94: .Pp
1.218 jmc 95: The options are as follows:
96: .Bl -tag -width Ds
97: .It Fl 1
98: Forces
1.2 deraadt 99: .Nm
1.218 jmc 100: to try protocol version 1 only.
101: .It Fl 2
102: Forces
1.2 deraadt 103: .Nm
1.218 jmc 104: to try protocol version 2 only.
105: .It Fl 4
106: Forces
1.2 deraadt 107: .Nm
1.218 jmc 108: to use IPv4 addresses only.
109: .It Fl 6
110: Forces
1.2 deraadt 111: .Nm
1.218 jmc 112: to use IPv6 addresses only.
113: .It Fl A
114: Enables forwarding of the authentication agent connection.
115: This can also be specified on a per-host basis in a configuration file.
1.2 deraadt 116: .Pp
1.218 jmc 117: Agent forwarding should be enabled with caution.
118: Users with the ability to bypass file permissions on the remote host
1.285 sobrado 119: (for the agent's
1.286 sobrado 120: .Ux Ns -domain
121: socket) can access the local agent through the forwarded connection.
1.218 jmc 122: An attacker cannot obtain key material from the agent,
123: however they can perform operations on the keys that enable them to
124: authenticate using the identities loaded into the agent.
125: .It Fl a
126: Disables forwarding of the authentication agent connection.
127: .It Fl b Ar bind_address
128: Use
129: .Ar bind_address
130: on the local machine as the source address
131: of the connection.
132: Only useful on systems with more than one address.
133: .It Fl C
134: Requests compression of all data (including stdin, stdout, stderr, and
1.348 millert 135: data for forwarded X11, TCP and
136: .Ux Ns -domain
137: connections).
1.218 jmc 138: The compression algorithm is the same used by
139: .Xr gzip 1 ,
140: and the
141: .Dq level
142: can be controlled by the
143: .Cm CompressionLevel
144: option for protocol version 1.
145: Compression is desirable on modem lines and other
146: slow connections, but will only slow down things on fast networks.
147: The default value can be set on a host-by-host basis in the
148: configuration files; see the
149: .Cm Compression
150: option.
151: .It Fl c Ar cipher_spec
152: Selects the cipher specification for encrypting the session.
1.2 deraadt 153: .Pp
1.218 jmc 154: Protocol version 1 allows specification of a single cipher.
155: The supported values are
156: .Dq 3des ,
1.220 jmc 157: .Dq blowfish ,
1.218 jmc 158: and
159: .Dq des .
1.230 jmc 160: For protocol version 2,
1.218 jmc 161: .Ar cipher_spec
162: is a comma-separated list of ciphers
163: listed in order of preference.
1.283 jmc 164: See the
165: .Cm Ciphers
1.307 dtucker 166: keyword in
167: .Xr ssh_config 5
168: for more information.
1.218 jmc 169: .It Fl D Xo
170: .Sm off
171: .Oo Ar bind_address : Oc
172: .Ar port
173: .Sm on
174: .Xc
175: Specifies a local
176: .Dq dynamic
177: application-level port forwarding.
178: This works by allocating a socket to listen to
179: .Ar port
180: on the local side, optionally bound to the specified
181: .Ar bind_address .
182: Whenever a connection is made to this port, the
183: connection is forwarded over the secure channel, and the application
184: protocol is then used to determine where to connect to from the
185: remote machine.
186: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.107 markus 187: .Nm
1.218 jmc 188: will act as a SOCKS server.
189: Only root can forward privileged ports.
190: Dynamic port forwardings can also be specified in the configuration file.
1.49 markus 191: .Pp
1.308 djm 192: IPv6 addresses can be specified by enclosing the address in square brackets.
1.218 jmc 193: Only the superuser can forward privileged ports.
194: By default, the local port is bound in accordance with the
195: .Cm GatewayPorts
196: setting.
197: However, an explicit
198: .Ar bind_address
199: may be used to bind the connection to a specific address.
200: The
201: .Ar bind_address
202: of
203: .Dq localhost
204: indicates that the listening port be bound for local use only, while an
205: empty address or
206: .Sq *
207: indicates that the port should be available from all interfaces.
1.331 dtucker 208: .It Fl E Ar log_file
209: Append debug logs to
210: .Ar log_file
211: instead of standard error.
1.229 jmc 212: .It Fl e Ar escape_char
1.218 jmc 213: Sets the escape character for sessions with a pty (default:
214: .Ql ~ ) .
215: The escape character is only recognized at the beginning of a line.
216: The escape character followed by a dot
217: .Pq Ql \&.
218: closes the connection;
219: followed by control-Z suspends the connection;
220: and followed by itself sends the escape character once.
221: Setting the character to
1.2 deraadt 222: .Dq none
1.218 jmc 223: disables any escapes and makes the session fully transparent.
224: .It Fl F Ar configfile
225: Specifies an alternative per-user configuration file.
226: If a configuration file is given on the command line,
227: the system-wide configuration file
228: .Pq Pa /etc/ssh/ssh_config
229: will be ignored.
230: The default for the per-user configuration file is
231: .Pa ~/.ssh/config .
232: .It Fl f
233: Requests
234: .Nm
235: to go to background just before command execution.
236: This is useful if
1.176 jmc 237: .Nm
1.218 jmc 238: is going to ask for passwords or passphrases, but the user
239: wants it in the background.
240: This implies
241: .Fl n .
242: The recommended way to start X11 programs at a remote site is with
243: something like
244: .Ic ssh -f host xterm .
1.277 djm 245: .Pp
246: If the
247: .Cm ExitOnForwardFailure
248: configuration option is set to
249: .Dq yes ,
250: then a client started with
251: .Fl f
252: will wait for all remote port forwards to be successfully established
253: before placing itself in the background.
1.350 djm 254: .It Fl G
255: Causes
256: .Nm
257: to print its configuration after evaluating
258: .Cm Host
259: and
260: .Cm Match
261: blocks and exit.
1.218 jmc 262: .It Fl g
263: Allows remote hosts to connect to local forwarded ports.
1.346 djm 264: If used on a multiplexed connection, then this option must be specified
265: on the master process.
1.291 markus 266: .It Fl I Ar pkcs11
1.294 jmc 267: Specify the PKCS#11 shared library
1.176 jmc 268: .Nm
1.293 markus 269: should use to communicate with a PKCS#11 token providing the user's
1.218 jmc 270: private RSA key.
271: .It Fl i Ar identity_file
272: Selects a file from which the identity (private key) for
1.310 djm 273: public key authentication is read.
1.218 jmc 274: The default is
275: .Pa ~/.ssh/identity
276: for protocol version 1, and
1.310 djm 277: .Pa ~/.ssh/id_dsa ,
1.343 naddy 278: .Pa ~/.ssh/id_ecdsa ,
279: .Pa ~/.ssh/id_ed25519
1.310 djm 280: and
1.218 jmc 281: .Pa ~/.ssh/id_rsa
282: for protocol version 2.
283: Identity files may also be specified on
284: a per-host basis in the configuration file.
285: It is possible to have multiple
286: .Fl i
287: options (and multiple identities specified in
288: configuration files).
1.302 djm 289: .Nm
290: will also try to load certificate information from the filename obtained
291: by appending
292: .Pa -cert.pub
293: to identity filenames.
1.269 djm 294: .It Fl K
295: Enables GSSAPI-based authentication and forwarding (delegation) of GSSAPI
296: credentials to the server.
1.218 jmc 297: .It Fl k
298: Disables forwarding (delegation) of GSSAPI credentials to the server.
299: .It Fl L Xo
300: .Sm off
301: .Oo Ar bind_address : Oc
302: .Ar port : host : hostport
303: .Sm on
304: .Xc
305: Specifies that the given port on the local (client) host is to be
306: forwarded to the given host and port on the remote side.
307: This works by allocating a socket to listen to
308: .Ar port
309: on the local side, optionally bound to the specified
310: .Ar bind_address .
311: Whenever a connection is made to this port, the
312: connection is forwarded over the secure channel, and a connection is
313: made to
314: .Ar host
315: port
316: .Ar hostport
317: from the remote machine.
318: Port forwardings can also be specified in the configuration file.
1.308 djm 319: IPv6 addresses can be specified by enclosing the address in square brackets.
1.218 jmc 320: Only the superuser can forward privileged ports.
321: By default, the local port is bound in accordance with the
322: .Cm GatewayPorts
323: setting.
324: However, an explicit
325: .Ar bind_address
326: may be used to bind the connection to a specific address.
1.2 deraadt 327: The
1.218 jmc 328: .Ar bind_address
329: of
330: .Dq localhost
331: indicates that the listening port be bound for local use only, while an
332: empty address or
333: .Sq *
334: indicates that the port should be available from all interfaces.
335: .It Fl l Ar login_name
336: Specifies the user to log in as on the remote machine.
337: This also may be specified on a per-host basis in the configuration file.
338: .It Fl M
339: Places the
340: .Nm
341: client into
342: .Dq master
343: mode for connection sharing.
1.231 stevesk 344: Multiple
345: .Fl M
346: options places
347: .Nm
348: into
349: .Dq master
350: mode with confirmation required before slave connections are accepted.
1.218 jmc 351: Refer to the description of
352: .Cm ControlMaster
353: in
354: .Xr ssh_config 5
355: for details.
356: .It Fl m Ar mac_spec
357: Additionally, for protocol version 2 a comma-separated list of MAC
358: (message authentication code) algorithms can
359: be specified in order of preference.
360: See the
361: .Cm MACs
362: keyword for more information.
363: .It Fl N
364: Do not execute a remote command.
365: This is useful for just forwarding ports
366: (protocol version 2 only).
367: .It Fl n
368: Redirects stdin from
369: .Pa /dev/null
370: (actually, prevents reading from stdin).
371: This must be used when
1.2 deraadt 372: .Nm
1.218 jmc 373: is run in the background.
374: A common trick is to use this to run X11 programs on a remote machine.
375: For example,
376: .Ic ssh -n shadows.cs.hut.fi emacs &
377: will start an emacs on shadows.cs.hut.fi, and the X11
378: connection will be automatically forwarded over an encrypted channel.
379: The
1.2 deraadt 380: .Nm
1.218 jmc 381: program will be put in the background.
382: (This does not work if
1.2 deraadt 383: .Nm
1.218 jmc 384: needs to ask for a password or passphrase; see also the
385: .Fl f
386: option.)
387: .It Fl O Ar ctl_cmd
388: Control an active connection multiplexing master process.
389: When the
390: .Fl O
391: option is specified, the
392: .Ar ctl_cmd
393: argument is interpreted and passed to the master process.
394: Valid commands are:
395: .Dq check
1.305 markus 396: (check that the master process is running),
397: .Dq forward
1.318 jmc 398: (request forwardings without command execution),
1.323 okan 399: .Dq cancel
400: (cancel forwardings),
1.218 jmc 401: .Dq exit
1.318 jmc 402: (request the master to exit), and
1.317 djm 403: .Dq stop
404: (request the master to stop accepting further multiplexing requests).
1.218 jmc 405: .It Fl o Ar option
406: Can be used to give options in the format used in the configuration file.
407: This is useful for specifying options for which there is no separate
408: command-line flag.
409: For full details of the options listed below, and their possible values, see
410: .Xr ssh_config 5 .
1.2 deraadt 411: .Pp
1.218 jmc 412: .Bl -tag -width Ds -offset indent -compact
413: .It AddressFamily
414: .It BatchMode
415: .It BindAddress
1.338 djm 416: .It CanonicalDomains
1.339 djm 417: .It CanonicalizeFallbackLocal
418: .It CanonicalizeHostname
419: .It CanonicalizeMaxDots
420: .It CanonicalizePermittedCNAMEs
1.218 jmc 421: .It ChallengeResponseAuthentication
422: .It CheckHostIP
423: .It Cipher
424: .It Ciphers
425: .It ClearAllForwardings
426: .It Compression
427: .It CompressionLevel
428: .It ConnectionAttempts
429: .It ConnectTimeout
430: .It ControlMaster
431: .It ControlPath
1.321 djm 432: .It ControlPersist
1.218 jmc 433: .It DynamicForward
434: .It EscapeChar
1.263 markus 435: .It ExitOnForwardFailure
1.353 jmc 436: .It FingerprintHash
1.218 jmc 437: .It ForwardAgent
438: .It ForwardX11
1.321 djm 439: .It ForwardX11Timeout
1.218 jmc 440: .It ForwardX11Trusted
441: .It GatewayPorts
442: .It GlobalKnownHostsFile
443: .It GSSAPIAuthentication
444: .It GSSAPIDelegateCredentials
445: .It HashKnownHosts
446: .It Host
447: .It HostbasedAuthentication
1.355 djm 448: .It HostbasedKeyTypes
1.218 jmc 449: .It HostKeyAlgorithms
450: .It HostKeyAlias
451: .It HostName
452: .It IdentityFile
453: .It IdentitiesOnly
1.316 jmc 454: .It IPQoS
1.321 djm 455: .It KbdInteractiveAuthentication
1.218 jmc 456: .It KbdInteractiveDevices
1.314 jmc 457: .It KexAlgorithms
1.218 jmc 458: .It LocalCommand
459: .It LocalForward
460: .It LogLevel
461: .It MACs
1.337 jmc 462: .It Match
1.218 jmc 463: .It NoHostAuthenticationForLocalhost
464: .It NumberOfPasswordPrompts
465: .It PasswordAuthentication
466: .It PermitLocalCommand
1.291 markus 467: .It PKCS11Provider
1.218 jmc 468: .It Port
469: .It PreferredAuthentications
470: .It Protocol
471: .It ProxyCommand
1.336 jmc 472: .It ProxyUseFdpass
1.218 jmc 473: .It PubkeyAuthentication
1.251 dtucker 474: .It RekeyLimit
1.218 jmc 475: .It RemoteForward
1.319 jmc 476: .It RequestTTY
1.218 jmc 477: .It RhostsRSAAuthentication
478: .It RSAAuthentication
479: .It SendEnv
480: .It ServerAliveInterval
481: .It ServerAliveCountMax
1.347 jmc 482: .It StreamLocalBindMask
483: .It StreamLocalBindUnlink
1.218 jmc 484: .It StrictHostKeyChecking
485: .It TCPKeepAlive
486: .It Tunnel
487: .It TunnelDevice
1.354 djm 488: .It UpdateHostKeys
1.218 jmc 489: .It UsePrivilegedPort
490: .It User
491: .It UserKnownHostsFile
492: .It VerifyHostKeyDNS
1.276 jmc 493: .It VisualHostKey
1.218 jmc 494: .It XAuthLocation
495: .El
496: .It Fl p Ar port
497: Port to connect to on the remote host.
498: This can be specified on a
499: per-host basis in the configuration file.
1.356 ! djm 500: .It Fl Q Cm cipher | cipher-auth | mac | kex | key | protocol-version
1.332 djm 501: Queries
502: .Nm
1.341 deraadt 503: for the algorithms supported for the specified version 2.
504: The available features are:
505: .Ar cipher
1.332 djm 506: (supported symmetric ciphers),
1.341 deraadt 507: .Ar cipher-auth
1.340 djm 508: (supported symmetric ciphers that support authenticated encryption),
1.341 deraadt 509: .Ar mac
1.332 djm 510: (supported message integrity codes),
1.341 deraadt 511: .Ar kex
1.332 djm 512: (key exchange algorithms),
1.341 deraadt 513: .Ar key
1.356 ! djm 514: (key types) and
! 515: .Ar protocol-version
! 516: (supported SSH protocol versions).
1.218 jmc 517: .It Fl q
518: Quiet mode.
1.271 djm 519: Causes most warning and diagnostic messages to be suppressed.
1.218 jmc 520: .It Fl R Xo
521: .Sm off
522: .Oo Ar bind_address : Oc
523: .Ar port : host : hostport
524: .Sm on
525: .Xc
526: Specifies that the given port on the remote (server) host is to be
527: forwarded to the given host and port on the local side.
528: This works by allocating a socket to listen to
529: .Ar port
530: on the remote side, and whenever a connection is made to this port, the
531: connection is forwarded over the secure channel, and a connection is
532: made to
533: .Ar host
534: port
535: .Ar hostport
536: from the local machine.
1.2 deraadt 537: .Pp
1.218 jmc 538: Port forwardings can also be specified in the configuration file.
539: Privileged ports can be forwarded only when
540: logging in as root on the remote machine.
1.324 jmc 541: IPv6 addresses can be specified by enclosing the address in square brackets.
1.194 jakob 542: .Pp
1.218 jmc 543: By default, the listening socket on the server will be bound to the loopback
544: interface only.
1.280 tobias 545: This may be overridden by specifying a
1.218 jmc 546: .Ar bind_address .
547: An empty
548: .Ar bind_address ,
549: or the address
550: .Ql * ,
551: indicates that the remote socket should listen on all interfaces.
552: Specifying a remote
553: .Ar bind_address
554: will only succeed if the server's
555: .Cm GatewayPorts
556: option is enabled (see
557: .Xr sshd_config 5 ) .
1.281 djm 558: .Pp
559: If the
560: .Ar port
561: argument is
1.282 djm 562: .Ql 0 ,
1.281 djm 563: the listen port will be dynamically allocated on the server and reported
564: to the client at run time.
1.305 markus 565: When used together with
566: .Ic -O forward
567: the allocated port will be printed to the standard output.
1.218 jmc 568: .It Fl S Ar ctl_path
1.304 jmc 569: Specifies the location of a control socket for connection sharing,
1.303 djm 570: or the string
571: .Dq none
572: to disable connection sharing.
1.218 jmc 573: Refer to the description of
574: .Cm ControlPath
575: and
576: .Cm ControlMaster
577: in
578: .Xr ssh_config 5
579: for details.
580: .It Fl s
581: May be used to request invocation of a subsystem on the remote system.
582: Subsystems are a feature of the SSH2 protocol which facilitate the use
583: of SSH as a secure transport for other applications (eg.\&
584: .Xr sftp 1 ) .
585: The subsystem is specified as the remote command.
586: .It Fl T
587: Disable pseudo-tty allocation.
588: .It Fl t
589: Force pseudo-tty allocation.
590: This can be used to execute arbitrary
591: screen-based programs on a remote machine, which can be very useful,
1.257 jmc 592: e.g. when implementing menu services.
1.218 jmc 593: Multiple
594: .Fl t
595: options force tty allocation, even if
1.194 jakob 596: .Nm
1.218 jmc 597: has no local tty.
598: .It Fl V
599: Display the version number and exit.
600: .It Fl v
601: Verbose mode.
602: Causes
1.176 jmc 603: .Nm
1.218 jmc 604: to print debugging messages about its progress.
605: This is helpful in
606: debugging connection, authentication, and configuration problems.
607: Multiple
608: .Fl v
609: options increase the verbosity.
610: The maximum is 3.
1.290 dtucker 611: .It Fl W Ar host : Ns Ar port
612: Requests that standard input and output on the client be forwarded to
613: .Ar host
614: on
615: .Ar port
616: over the secure channel.
617: Implies
618: .Fl N ,
619: .Fl T ,
620: .Cm ExitOnForwardFailure
621: and
1.326 dtucker 622: .Cm ClearAllForwardings .
623: Works with Protocol version 2 only.
1.261 stevesk 624: .It Fl w Xo
625: .Ar local_tun Ns Op : Ns Ar remote_tun
626: .Xc
627: Requests
628: tunnel
629: device forwarding with the specified
1.218 jmc 630: .Xr tun 4
1.261 stevesk 631: devices between the client
632: .Pq Ar local_tun
633: and the server
634: .Pq Ar remote_tun .
635: .Pp
1.228 jmc 636: The devices may be specified by numerical ID or the keyword
637: .Dq any ,
638: which uses the next available tunnel device.
1.261 stevesk 639: If
640: .Ar remote_tun
641: is not specified, it defaults to
642: .Dq any .
1.228 jmc 643: See also the
1.218 jmc 644: .Cm Tunnel
1.261 stevesk 645: and
646: .Cm TunnelDevice
647: directives in
1.218 jmc 648: .Xr ssh_config 5 .
1.261 stevesk 649: If the
650: .Cm Tunnel
651: directive is unset, it is set to the default tunnel mode, which is
652: .Dq point-to-point .
1.218 jmc 653: .It Fl X
654: Enables X11 forwarding.
1.54 markus 655: This can also be specified on a per-host basis in a configuration file.
1.165 stevesk 656: .Pp
1.218 jmc 657: X11 forwarding should be enabled with caution.
1.168 jmc 658: Users with the ability to bypass file permissions on the remote host
1.218 jmc 659: (for the user's X authorization database)
660: can access the local X11 display through the forwarded connection.
661: An attacker may then be able to perform activities such as keystroke monitoring.
662: .Pp
663: For this reason, X11 forwarding is subjected to X11 SECURITY extension
664: restrictions by default.
665: Please refer to the
666: .Nm
667: .Fl Y
668: option and the
669: .Cm ForwardX11Trusted
670: directive in
671: .Xr ssh_config 5
672: for more information.
673: .It Fl x
674: Disables X11 forwarding.
675: .It Fl Y
676: Enables trusted X11 forwarding.
677: Trusted X11 forwardings are not subjected to the X11 SECURITY extension
678: controls.
1.278 djm 679: .It Fl y
680: Send log information using the
681: .Xr syslog 3
682: system module.
683: By default this information is sent to stderr.
1.218 jmc 684: .El
1.224 jmc 685: .Pp
686: .Nm
687: may additionally obtain configuration data from
688: a per-user configuration file and a system-wide configuration file.
689: The file format and configuration options are described in
690: .Xr ssh_config 5 .
1.222 jmc 691: .Sh AUTHENTICATION
1.249 jmc 692: The OpenSSH SSH client supports SSH protocols 1 and 2.
1.284 jmc 693: The default is to use protocol 2 only,
694: though this can be changed via the
1.222 jmc 695: .Cm Protocol
696: option in
1.284 jmc 697: .Xr ssh_config 5
698: or the
1.222 jmc 699: .Fl 1
700: and
701: .Fl 2
702: options (see above).
703: Both protocols support similar authentication methods,
1.284 jmc 704: but protocol 2 is the default since
1.222 jmc 705: it provides additional mechanisms for confidentiality
706: (the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour)
1.320 djm 707: and integrity (hmac-md5, hmac-sha1,
708: hmac-sha2-256, hmac-sha2-512,
1.330 markus 709: umac-64, umac-128, hmac-ripemd160).
1.222 jmc 710: Protocol 1 lacks a strong mechanism for ensuring the
711: integrity of the connection.
712: .Pp
713: The methods available for authentication are:
1.260 jmc 714: GSSAPI-based authentication,
1.222 jmc 715: host-based authentication,
716: public key authentication,
717: challenge-response authentication,
718: and password authentication.
719: Authentication methods are tried in the order specified above,
720: though protocol 2 has a configuration option to change the default order:
721: .Cm PreferredAuthentications .
722: .Pp
723: Host-based authentication works as follows:
1.218 jmc 724: If the machine the user logs in from is listed in
725: .Pa /etc/hosts.equiv
726: or
727: .Pa /etc/shosts.equiv
728: on the remote machine, and the user names are
729: the same on both sides, or if the files
730: .Pa ~/.rhosts
731: or
732: .Pa ~/.shosts
733: exist in the user's home directory on the
734: remote machine and contain a line containing the name of the client
735: machine and the name of the user on that machine, the user is
1.222 jmc 736: considered for login.
737: Additionally, the server
738: .Em must
739: be able to verify the client's
740: host key (see the description of
1.218 jmc 741: .Pa /etc/ssh/ssh_known_hosts
1.189 dtucker 742: and
1.222 jmc 743: .Pa ~/.ssh/known_hosts ,
744: below)
745: for login to be permitted.
1.218 jmc 746: This authentication method closes security holes due to IP
1.222 jmc 747: spoofing, DNS spoofing, and routing spoofing.
1.218 jmc 748: [Note to the administrator:
749: .Pa /etc/hosts.equiv ,
750: .Pa ~/.rhosts ,
751: and the rlogin/rsh protocol in general, are inherently insecure and should be
752: disabled if security is desired.]
1.189 dtucker 753: .Pp
1.222 jmc 754: Public key authentication works as follows:
755: The scheme is based on public-key cryptography,
756: using cryptosystems
757: where encryption and decryption are done using separate keys,
758: and it is unfeasible to derive the decryption key from the encryption key.
1.218 jmc 759: The idea is that each user creates a public/private
760: key pair for authentication purposes.
761: The server knows the public key, and only the user knows the private key.
1.222 jmc 762: .Nm
763: implements public key authentication protocol automatically,
1.349 sobrado 764: using one of the DSA, ECDSA, Ed25519 or RSA algorithms.
1.222 jmc 765: Protocol 1 is restricted to using only RSA keys,
1.310 djm 766: but protocol 2 may use any.
1.333 jmc 767: The HISTORY section of
1.222 jmc 768: .Xr ssl 8
1.311 jmc 769: contains a brief discussion of the DSA and RSA algorithms.
1.210 djm 770: .Pp
1.218 jmc 771: The file
772: .Pa ~/.ssh/authorized_keys
773: lists the public keys that are permitted for logging in.
774: When the user logs in, the
1.2 deraadt 775: .Nm
1.218 jmc 776: program tells the server which key pair it would like to use for
777: authentication.
1.222 jmc 778: The client proves that it has access to the private key
779: and the server checks that the corresponding public key
780: is authorized to accept the account.
1.218 jmc 781: .Pp
1.222 jmc 782: The user creates his/her key pair by running
1.218 jmc 783: .Xr ssh-keygen 1 .
784: This stores the private key in
1.207 djm 785: .Pa ~/.ssh/identity
1.222 jmc 786: (protocol 1),
787: .Pa ~/.ssh/id_dsa
788: (protocol 2 DSA),
1.310 djm 789: .Pa ~/.ssh/id_ecdsa
790: (protocol 2 ECDSA),
1.343 naddy 791: .Pa ~/.ssh/id_ed25519
1.349 sobrado 792: (protocol 2 Ed25519),
1.222 jmc 793: or
794: .Pa ~/.ssh/id_rsa
795: (protocol 2 RSA)
1.218 jmc 796: and stores the public key in
797: .Pa ~/.ssh/identity.pub
1.222 jmc 798: (protocol 1),
799: .Pa ~/.ssh/id_dsa.pub
800: (protocol 2 DSA),
1.310 djm 801: .Pa ~/.ssh/id_ecdsa.pub
802: (protocol 2 ECDSA),
1.343 naddy 803: .Pa ~/.ssh/id_ed25519.pub
1.349 sobrado 804: (protocol 2 Ed25519),
1.222 jmc 805: or
806: .Pa ~/.ssh/id_rsa.pub
807: (protocol 2 RSA)
1.218 jmc 808: in the user's home directory.
1.222 jmc 809: The user should then copy the public key
1.218 jmc 810: to
811: .Pa ~/.ssh/authorized_keys
1.222 jmc 812: in his/her home directory on the remote machine.
813: The
1.218 jmc 814: .Pa authorized_keys
815: file corresponds to the conventional
816: .Pa ~/.rhosts
817: file, and has one key
1.222 jmc 818: per line, though the lines can be very long.
1.218 jmc 819: After this, the user can log in without giving the password.
820: .Pp
1.301 jmc 821: A variation on public key authentication
822: is available in the form of certificate authentication:
823: instead of a set of public/private keys,
824: signed certificates are used.
825: This has the advantage that a single trusted certification authority
826: can be used in place of many public/private keys.
1.333 jmc 827: See the CERTIFICATES section of
1.301 jmc 828: .Xr ssh-keygen 1
829: for more information.
830: .Pp
831: The most convenient way to use public key or certificate authentication
832: may be with an authentication agent.
1.218 jmc 833: See
834: .Xr ssh-agent 1
835: for more information.
836: .Pp
1.222 jmc 837: Challenge-response authentication works as follows:
838: The server sends an arbitrary
839: .Qq challenge
840: text, and prompts for a response.
841: Protocol 2 allows multiple challenges and responses;
842: protocol 1 is restricted to just one challenge/response.
843: Examples of challenge-response authentication include
1.335 jmc 844: .Bx
845: Authentication (see
1.222 jmc 846: .Xr login.conf 5 )
1.335 jmc 847: and PAM (some
848: .Pf non- Ox
849: systems).
1.222 jmc 850: .Pp
851: Finally, if other authentication methods fail,
1.218 jmc 852: .Nm
853: prompts the user for a password.
854: The password is sent to the remote
855: host for checking; however, since all communications are encrypted,
856: the password cannot be seen by someone listening on the network.
1.232 jmc 857: .Pp
858: .Nm
859: automatically maintains and checks a database containing
860: identification for all hosts it has ever been used with.
861: Host keys are stored in
862: .Pa ~/.ssh/known_hosts
863: in the user's home directory.
864: Additionally, the file
865: .Pa /etc/ssh/ssh_known_hosts
866: is automatically checked for known hosts.
867: Any new hosts are automatically added to the user's file.
868: If a host's identification ever changes,
869: .Nm
870: warns about this and disables password authentication to prevent
871: server spoofing or man-in-the-middle attacks,
872: which could otherwise be used to circumvent the encryption.
873: The
874: .Cm StrictHostKeyChecking
875: option can be used to control logins to machines whose
876: host key is not known or has changed.
877: .Pp
1.218 jmc 878: When the user's identity has been accepted by the server, the server
879: either executes the given command, or logs into the machine and gives
880: the user a normal shell on the remote machine.
881: All communication with
882: the remote command or shell will be automatically encrypted.
883: .Pp
884: If a pseudo-terminal has been allocated (normal login session), the
885: user may use the escape characters noted below.
886: .Pp
887: If no pseudo-tty has been allocated,
888: the session is transparent and can be used to reliably transfer binary data.
889: On most systems, setting the escape character to
890: .Dq none
891: will also make the session transparent even if a tty is used.
892: .Pp
893: The session terminates when the command or shell on the remote
1.247 jmc 894: machine exits and all X11 and TCP connections have been closed.
1.223 jmc 895: .Sh ESCAPE CHARACTERS
1.218 jmc 896: When a pseudo-terminal has been requested,
1.2 deraadt 897: .Nm
1.218 jmc 898: supports a number of functions through the use of an escape character.
899: .Pp
900: A single tilde character can be sent as
901: .Ic ~~
902: or by following the tilde by a character other than those described below.
903: The escape character must always follow a newline to be interpreted as
904: special.
905: The escape character can be changed in configuration files using the
906: .Cm EscapeChar
907: configuration directive or on the command line by the
908: .Fl e
909: option.
910: .Pp
911: The supported escapes (assuming the default
912: .Ql ~ )
913: are:
914: .Bl -tag -width Ds
915: .It Cm ~.
916: Disconnect.
917: .It Cm ~^Z
918: Background
1.234 jmc 919: .Nm .
1.218 jmc 920: .It Cm ~#
921: List forwarded connections.
922: .It Cm ~&
923: Background
1.2 deraadt 924: .Nm
1.218 jmc 925: at logout when waiting for forwarded connection / X11 sessions to terminate.
926: .It Cm ~?
927: Display a list of escape characters.
928: .It Cm ~B
929: Send a BREAK to the remote system
930: (only useful for SSH protocol version 2 and if the peer supports it).
931: .It Cm ~C
932: Open command line.
933: Currently this allows the addition of port forwardings using the
1.279 stevesk 934: .Fl L ,
935: .Fl R
1.218 jmc 936: and
1.279 stevesk 937: .Fl D
1.225 jmc 938: options (see above).
1.322 markus 939: It also allows the cancellation of existing port-forwardings
940: with
1.262 stevesk 941: .Sm off
1.322 markus 942: .Fl KL Oo Ar bind_address : Oc Ar port
1.262 stevesk 943: .Sm on
1.322 markus 944: for local,
945: .Sm off
946: .Fl KR Oo Ar bind_address : Oc Ar port
947: .Sm on
948: for remote and
949: .Sm off
950: .Fl KD Oo Ar bind_address : Oc Ar port
951: .Sm on
952: for dynamic port-forwardings.
1.218 jmc 953: .Ic !\& Ns Ar command
954: allows the user to execute a local command if the
955: .Ic PermitLocalCommand
956: option is enabled in
1.176 jmc 957: .Xr ssh_config 5 .
1.218 jmc 958: Basic help is available, using the
959: .Fl h
960: option.
961: .It Cm ~R
962: Request rekeying of the connection
963: (only useful for SSH protocol version 2 and if the peer supports it).
1.327 dtucker 964: .It Cm ~V
965: Decrease the verbosity
966: .Pq Ic LogLevel
967: when errors are being written to stderr.
968: .It Cm ~v
1.328 jmc 969: Increase the verbosity
1.327 dtucker 970: .Pq Ic LogLevel
971: when errors are being written to stderr.
1.176 jmc 972: .El
1.246 jmc 973: .Sh TCP FORWARDING
974: Forwarding of arbitrary TCP connections over the secure channel can
975: be specified either on the command line or in a configuration file.
976: One possible application of TCP forwarding is a secure connection to a
977: mail server; another is going through firewalls.
978: .Pp
979: In the example below, we look at encrypting communication between
980: an IRC client and server, even though the IRC server does not directly
981: support encrypted communications.
982: This works as follows:
983: the user connects to the remote host using
984: .Nm ,
985: specifying a port to be used to forward connections
986: to the remote server.
987: After that it is possible to start the service which is to be encrypted
988: on the client machine,
989: connecting to the same local port,
990: and
991: .Nm
992: will encrypt and forward the connection.
993: .Pp
994: The following example tunnels an IRC session from client machine
995: .Dq 127.0.0.1
996: (localhost)
997: to remote server
998: .Dq server.example.com :
999: .Bd -literal -offset 4n
1000: $ ssh -f -L 1234:localhost:6667 server.example.com sleep 10
1001: $ irc -c '#users' -p 1234 pinky 127.0.0.1
1002: .Ed
1003: .Pp
1004: This tunnels a connection to IRC server
1005: .Dq server.example.com ,
1006: joining channel
1007: .Dq #users ,
1008: nickname
1009: .Dq pinky ,
1010: using port 1234.
1011: It doesn't matter which port is used,
1012: as long as it's greater than 1023
1013: (remember, only root can open sockets on privileged ports)
1014: and doesn't conflict with any ports already in use.
1015: The connection is forwarded to port 6667 on the remote server,
1016: since that's the standard port for IRC services.
1017: .Pp
1018: The
1019: .Fl f
1020: option backgrounds
1021: .Nm
1022: and the remote command
1023: .Dq sleep 10
1024: is specified to allow an amount of time
1025: (10 seconds, in the example)
1026: to start the service which is to be tunnelled.
1027: If no connections are made within the time specified,
1028: .Nm
1029: will exit.
1030: .Sh X11 FORWARDING
1.218 jmc 1031: If the
1032: .Cm ForwardX11
1033: variable is set to
1034: .Dq yes
1035: (or see the description of the
1.227 jmc 1036: .Fl X ,
1037: .Fl x ,
1.218 jmc 1038: and
1.227 jmc 1039: .Fl Y
1.226 jmc 1040: options above)
1.218 jmc 1041: and the user is using X11 (the
1042: .Ev DISPLAY
1043: environment variable is set), the connection to the X11 display is
1044: automatically forwarded to the remote side in such a way that any X11
1045: programs started from the shell (or command) will go through the
1046: encrypted channel, and the connection to the real X server will be made
1.176 jmc 1047: from the local machine.
1.218 jmc 1048: The user should not manually set
1049: .Ev DISPLAY .
1050: Forwarding of X11 connections can be
1051: configured on the command line or in configuration files.
1052: .Pp
1053: The
1054: .Ev DISPLAY
1055: value set by
1056: .Nm
1057: will point to the server machine, but with a display number greater than zero.
1058: This is normal, and happens because
1059: .Nm
1060: creates a
1061: .Dq proxy
1062: X server on the server machine for forwarding the
1063: connections over the encrypted channel.
1.200 djm 1064: .Pp
1.218 jmc 1065: .Nm
1066: will also automatically set up Xauthority data on the server machine.
1067: For this purpose, it will generate a random authorization cookie,
1068: store it in Xauthority on the server, and verify that any forwarded
1069: connections carry this cookie and replace it by the real cookie when
1070: the connection is opened.
1071: The real authentication cookie is never
1072: sent to the server machine (and no cookies are sent in the plain).
1.200 djm 1073: .Pp
1.218 jmc 1074: If the
1075: .Cm ForwardAgent
1076: variable is set to
1077: .Dq yes
1078: (or see the description of the
1079: .Fl A
1.191 djm 1080: and
1.218 jmc 1081: .Fl a
1.226 jmc 1082: options above) and
1.218 jmc 1083: the user is using an authentication agent, the connection to the agent
1084: is automatically forwarded to the remote side.
1.252 jmc 1085: .Sh VERIFYING HOST KEYS
1086: When connecting to a server for the first time,
1087: a fingerprint of the server's public key is presented to the user
1088: (unless the option
1089: .Cm StrictHostKeyChecking
1090: has been disabled).
1091: Fingerprints can be determined using
1092: .Xr ssh-keygen 1 :
1093: .Pp
1094: .Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key
1095: .Pp
1.274 grunk 1096: If the fingerprint is already known, it can be matched
1097: and the key can be accepted or rejected.
1098: Because of the difficulty of comparing host keys
1.352 djm 1099: just by looking at fingerprint strings,
1.274 grunk 1100: there is also support to compare host keys visually,
1101: using
1102: .Em random art .
1103: By setting the
1.275 grunk 1104: .Cm VisualHostKey
1.274 grunk 1105: option to
1.275 grunk 1106: .Dq yes ,
1.274 grunk 1107: a small ASCII graphic gets displayed on every login to a server, no matter
1108: if the session itself is interactive or not.
1109: By learning the pattern a known server produces, a user can easily
1110: find out that the host key has changed when a completely different pattern
1111: is displayed.
1112: Because these patterns are not unambiguous however, a pattern that looks
1113: similar to the pattern remembered only gives a good probability that the
1114: host key is the same, not guaranteed proof.
1115: .Pp
1116: To get a listing of the fingerprints along with their random art for
1117: all known hosts, the following command line can be used:
1118: .Pp
1119: .Dl $ ssh-keygen -lv -f ~/.ssh/known_hosts
1120: .Pp
1.252 jmc 1121: If the fingerprint is unknown,
1122: an alternative method of verification is available:
1123: SSH fingerprints verified by DNS.
1124: An additional resource record (RR),
1125: SSHFP,
1126: is added to a zonefile
1127: and the connecting client is able to match the fingerprint
1128: with that of the key presented.
1129: .Pp
1130: In this example, we are connecting a client to a server,
1131: .Dq host.example.com .
1132: The SSHFP resource records should first be added to the zonefile for
1133: host.example.com:
1134: .Bd -literal -offset indent
1.259 jakob 1135: $ ssh-keygen -r host.example.com.
1.252 jmc 1136: .Ed
1137: .Pp
1138: The output lines will have to be added to the zonefile.
1139: To check that the zone is answering fingerprint queries:
1140: .Pp
1141: .Dl $ dig -t SSHFP host.example.com
1142: .Pp
1143: Finally the client connects:
1144: .Bd -literal -offset indent
1145: $ ssh -o "VerifyHostKeyDNS ask" host.example.com
1146: [...]
1147: Matching host key fingerprint found in DNS.
1148: Are you sure you want to continue connecting (yes/no)?
1149: .Ed
1150: .Pp
1151: See the
1152: .Cm VerifyHostKeyDNS
1153: option in
1154: .Xr ssh_config 5
1155: for more information.
1.250 jmc 1156: .Sh SSH-BASED VIRTUAL PRIVATE NETWORKS
1157: .Nm
1158: contains support for Virtual Private Network (VPN) tunnelling
1159: using the
1160: .Xr tun 4
1161: network pseudo-device,
1162: allowing two networks to be joined securely.
1163: The
1164: .Xr sshd_config 5
1165: configuration option
1166: .Cm PermitTunnel
1167: controls whether the server supports this,
1168: and at what level (layer 2 or 3 traffic).
1169: .Pp
1170: The following example would connect client network 10.0.50.0/24
1.265 otto 1171: with remote network 10.0.99.0/24 using a point-to-point connection
1172: from 10.1.1.1 to 10.1.1.2,
1173: provided that the SSH server running on the gateway to the remote network,
1174: at 192.168.1.15, allows it.
1175: .Pp
1176: On the client:
1.250 jmc 1177: .Bd -literal -offset indent
1178: # ssh -f -w 0:1 192.168.1.15 true
1.265 otto 1179: # ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252
1180: # route add 10.0.99.0/24 10.1.1.2
1181: .Ed
1182: .Pp
1183: On the server:
1184: .Bd -literal -offset indent
1185: # ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252
1186: # route add 10.0.50.0/24 10.1.1.1
1.250 jmc 1187: .Ed
1188: .Pp
1189: Client access may be more finely tuned via the
1190: .Pa /root/.ssh/authorized_keys
1191: file (see below) and the
1192: .Cm PermitRootLogin
1193: server option.
1.255 jmc 1194: The following entry would permit connections on
1.250 jmc 1195: .Xr tun 4
1.255 jmc 1196: device 1 from user
1.250 jmc 1197: .Dq jane
1.255 jmc 1198: and on tun device 2 from user
1.250 jmc 1199: .Dq john ,
1200: if
1201: .Cm PermitRootLogin
1202: is set to
1203: .Dq forced-commands-only :
1204: .Bd -literal -offset 2n
1205: tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane
1.254 msf 1206: tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john
1.250 jmc 1207: .Ed
1208: .Pp
1.264 ray 1209: Since an SSH-based setup entails a fair amount of overhead,
1.250 jmc 1210: it may be more suited to temporary setups,
1211: such as for wireless VPNs.
1212: More permanent VPNs are better provided by tools such as
1213: .Xr ipsecctl 8
1214: and
1215: .Xr isakmpd 8 .
1.2 deraadt 1216: .Sh ENVIRONMENT
1217: .Nm
1.1 deraadt 1218: will normally set the following environment variables:
1.237 jmc 1219: .Bl -tag -width "SSH_ORIGINAL_COMMAND"
1.2 deraadt 1220: .It Ev DISPLAY
1221: The
1222: .Ev DISPLAY
1.40 aaron 1223: variable indicates the location of the X11 server.
1.44 aaron 1224: It is automatically set by
1.2 deraadt 1225: .Nm
1226: to point to a value of the form
1.233 jmc 1227: .Dq hostname:n ,
1228: where
1229: .Dq hostname
1230: indicates the host where the shell runs, and
1231: .Sq n
1232: is an integer \*(Ge 1.
1.40 aaron 1233: .Nm
1234: uses this special value to forward X11 connections over the secure
1235: channel.
1.107 markus 1236: The user should normally not set
1237: .Ev DISPLAY
1238: explicitly, as that
1.1 deraadt 1239: will render the X11 connection insecure (and will require the user to
1240: manually copy any required authorization cookies).
1.2 deraadt 1241: .It Ev HOME
1.1 deraadt 1242: Set to the path of the user's home directory.
1.2 deraadt 1243: .It Ev LOGNAME
1244: Synonym for
1.12 aaron 1245: .Ev USER ;
1246: set for compatibility with systems that use this variable.
1.2 deraadt 1247: .It Ev MAIL
1.129 stevesk 1248: Set to the path of the user's mailbox.
1.40 aaron 1249: .It Ev PATH
1.2 deraadt 1250: Set to the default
1251: .Ev PATH ,
1252: as specified when compiling
1.234 jmc 1253: .Nm .
1.118 markus 1254: .It Ev SSH_ASKPASS
1255: If
1256: .Nm
1257: needs a passphrase, it will read the passphrase from the current
1258: terminal if it was run from a terminal.
1259: If
1260: .Nm
1261: does not have a terminal associated with it but
1262: .Ev DISPLAY
1263: and
1264: .Ev SSH_ASKPASS
1265: are set, it will execute the program specified by
1266: .Ev SSH_ASKPASS
1267: and open an X11 window to read the passphrase.
1268: This is particularly useful when calling
1269: .Nm
1270: from a
1.196 jmc 1271: .Pa .xsession
1.118 markus 1272: or related script.
1273: (Note that on some machines it
1274: may be necessary to redirect the input from
1275: .Pa /dev/null
1276: to make this work.)
1.18 markus 1277: .It Ev SSH_AUTH_SOCK
1.233 jmc 1278: Identifies the path of a
1279: .Ux Ns -domain
1280: socket used to communicate with the agent.
1.166 stevesk 1281: .It Ev SSH_CONNECTION
1282: Identifies the client and server ends of the connection.
1.40 aaron 1283: The variable contains
1.233 jmc 1284: four space-separated values: client IP address, client port number,
1285: server IP address, and server port number.
1.73 markus 1286: .It Ev SSH_ORIGINAL_COMMAND
1.233 jmc 1287: This variable contains the original command line if a forced command
1.73 markus 1288: is executed.
1289: It can be used to extract the original arguments.
1.2 deraadt 1290: .It Ev SSH_TTY
1.1 deraadt 1291: This is set to the name of the tty (path to the device) associated
1.40 aaron 1292: with the current shell or command.
1293: If the current session has no tty,
1.1 deraadt 1294: this variable is not set.
1.2 deraadt 1295: .It Ev TZ
1.214 jmc 1296: This variable is set to indicate the present time zone if it
1.257 jmc 1297: was set when the daemon was started (i.e. the daemon passes the value
1.1 deraadt 1298: on to new connections).
1.2 deraadt 1299: .It Ev USER
1.1 deraadt 1300: Set to the name of the user logging in.
1.2 deraadt 1301: .El
1302: .Pp
1.44 aaron 1303: Additionally,
1.2 deraadt 1304: .Nm
1.44 aaron 1305: reads
1.207 djm 1306: .Pa ~/.ssh/environment ,
1.2 deraadt 1307: and adds lines of the format
1308: .Dq VARNAME=value
1.233 jmc 1309: to the environment if the file exists and users are allowed to
1.161 marc 1310: change their environment.
1.176 jmc 1311: For more information, see the
1.161 marc 1312: .Cm PermitUserEnvironment
1.162 stevesk 1313: option in
1.161 marc 1314: .Xr sshd_config 5 .
1.2 deraadt 1315: .Sh FILES
1.236 jmc 1316: .Bl -tag -width Ds -compact
1.309 jmc 1317: .It Pa ~/.rhosts
1.240 jmc 1318: This file is used for host-based authentication (see above).
1.92 markus 1319: On some machines this file may need to be
1.240 jmc 1320: world-readable if the user's home directory is on an NFS partition,
1.1 deraadt 1321: because
1.2 deraadt 1322: .Xr sshd 8
1.40 aaron 1323: reads it as root.
1324: Additionally, this file must be owned by the user,
1325: and must not have write permissions for anyone else.
1326: The recommended
1.1 deraadt 1327: permission for most machines is read/write for the user, and not
1328: accessible by others.
1.2 deraadt 1329: .Pp
1.309 jmc 1330: .It Pa ~/.shosts
1.240 jmc 1331: This file is used in exactly the same way as
1332: .Pa .rhosts ,
1333: but allows host-based authentication without permitting login with
1334: rlogin/rsh.
1.272 mcbride 1335: .Pp
1.309 jmc 1336: .It Pa ~/.ssh/
1.272 mcbride 1337: This directory is the default location for all user-specific configuration
1338: and authentication information.
1339: There is no general requirement to keep the entire contents of this directory
1340: secret, but the recommended permissions are read/write/execute for the user,
1341: and not accessible by others.
1.236 jmc 1342: .Pp
1.309 jmc 1343: .It Pa ~/.ssh/authorized_keys
1.349 sobrado 1344: Lists the public keys (DSA, ECDSA, Ed25519, RSA)
1.343 naddy 1345: that can be used for logging in as this user.
1.238 jmc 1346: The format of this file is described in the
1347: .Xr sshd 8
1348: manual page.
1349: This file is not highly sensitive, but the recommended
1350: permissions are read/write for the user, and not accessible by others.
1351: .Pp
1.309 jmc 1352: .It Pa ~/.ssh/config
1.238 jmc 1353: This is the per-user configuration file.
1354: The file format and configuration options are described in
1355: .Xr ssh_config 5 .
1356: Because of the potential for abuse, this file must have strict permissions:
1.334 djm 1357: read/write for the user, and not writable by others.
1.238 jmc 1358: .Pp
1.309 jmc 1359: .It Pa ~/.ssh/environment
1.239 jmc 1360: Contains additional definitions for environment variables; see
1361: .Sx ENVIRONMENT ,
1.238 jmc 1362: above.
1363: .Pp
1.309 jmc 1364: .It Pa ~/.ssh/identity
1365: .It Pa ~/.ssh/id_dsa
1.310 djm 1366: .It Pa ~/.ssh/id_ecdsa
1.343 naddy 1367: .It Pa ~/.ssh/id_ed25519
1.309 jmc 1368: .It Pa ~/.ssh/id_rsa
1.238 jmc 1369: Contains the private key for authentication.
1370: These files
1371: contain sensitive data and should be readable by the user but not
1372: accessible by others (read/write/execute).
1373: .Nm
1374: will simply ignore a private key file if it is accessible by others.
1375: It is possible to specify a passphrase when
1376: generating the key which will be used to encrypt the
1377: sensitive part of this file using 3DES.
1378: .Pp
1.309 jmc 1379: .It Pa ~/.ssh/identity.pub
1380: .It Pa ~/.ssh/id_dsa.pub
1.310 djm 1381: .It Pa ~/.ssh/id_ecdsa.pub
1.343 naddy 1382: .It Pa ~/.ssh/id_ed25519.pub
1.309 jmc 1383: .It Pa ~/.ssh/id_rsa.pub
1.238 jmc 1384: Contains the public key for authentication.
1385: These files are not
1386: sensitive and can (but need not) be readable by anyone.
1387: .Pp
1.309 jmc 1388: .It Pa ~/.ssh/known_hosts
1.244 jmc 1389: Contains a list of host keys for all hosts the user has logged into
1390: that are not already in the systemwide list of known host keys.
1.238 jmc 1391: See
1.244 jmc 1392: .Xr sshd 8
1393: for further details of the format of this file.
1.238 jmc 1394: .Pp
1.309 jmc 1395: .It Pa ~/.ssh/rc
1.238 jmc 1396: Commands in this file are executed by
1397: .Nm
1.245 jmc 1398: when the user logs in, just before the user's shell (or command) is
1.238 jmc 1399: started.
1400: See the
1401: .Xr sshd 8
1402: manual page for more information.
1403: .Pp
1.309 jmc 1404: .It Pa /etc/hosts.equiv
1.240 jmc 1405: This file is for host-based authentication (see above).
1406: It should only be writable by root.
1.236 jmc 1407: .Pp
1.309 jmc 1408: .It Pa /etc/shosts.equiv
1.240 jmc 1409: This file is used in exactly the same way as
1410: .Pa hosts.equiv ,
1411: but allows host-based authentication without permitting login with
1412: rlogin/rsh.
1.236 jmc 1413: .Pp
1.238 jmc 1414: .It Pa /etc/ssh/ssh_config
1415: Systemwide configuration file.
1416: The file format and configuration options are described in
1417: .Xr ssh_config 5 .
1418: .Pp
1.309 jmc 1419: .It Pa /etc/ssh/ssh_host_key
1420: .It Pa /etc/ssh/ssh_host_dsa_key
1.310 djm 1421: .It Pa /etc/ssh/ssh_host_ecdsa_key
1.343 naddy 1422: .It Pa /etc/ssh/ssh_host_ed25519_key
1.309 jmc 1423: .It Pa /etc/ssh/ssh_host_rsa_key
1.325 dtucker 1424: These files contain the private parts of the host keys
1.245 jmc 1425: and are used for host-based authentication.
1426: If protocol version 1 is used,
1.238 jmc 1427: .Nm
1428: must be setuid root, since the host key is readable only by root.
1429: For protocol version 2,
1430: .Nm
1431: uses
1432: .Xr ssh-keysign 8
1.245 jmc 1433: to access the host keys,
1434: eliminating the requirement that
1.238 jmc 1435: .Nm
1.245 jmc 1436: be setuid root when host-based authentication is used.
1.238 jmc 1437: By default
1.2 deraadt 1438: .Nm
1.238 jmc 1439: is not setuid root.
1440: .Pp
1.309 jmc 1441: .It Pa /etc/ssh/ssh_known_hosts
1.238 jmc 1442: Systemwide list of known host keys.
1443: This file should be prepared by the
1444: system administrator to contain the public host keys of all machines in the
1445: organization.
1.244 jmc 1446: It should be world-readable.
1447: See
1.238 jmc 1448: .Xr sshd 8
1.244 jmc 1449: for further details of the format of this file.
1.236 jmc 1450: .Pp
1.309 jmc 1451: .It Pa /etc/ssh/sshrc
1.1 deraadt 1452: Commands in this file are executed by
1.2 deraadt 1453: .Nm
1.245 jmc 1454: when the user logs in, just before the user's shell (or command) is started.
1.44 aaron 1455: See the
1.2 deraadt 1456: .Xr sshd 8
1.1 deraadt 1457: manual page for more information.
1.58 itojun 1458: .El
1.312 jmc 1459: .Sh EXIT STATUS
1460: .Nm
1461: exits with the exit status of the remote command or with 255
1462: if an error occurred.
1.2 deraadt 1463: .Sh SEE ALSO
1464: .Xr scp 1 ,
1.83 djm 1465: .Xr sftp 1 ,
1.2 deraadt 1466: .Xr ssh-add 1 ,
1467: .Xr ssh-agent 1 ,
1468: .Xr ssh-keygen 1 ,
1.242 jmc 1469: .Xr ssh-keyscan 1 ,
1.250 jmc 1470: .Xr tun 4 ,
1.159 stevesk 1471: .Xr ssh_config 5 ,
1.160 naddy 1472: .Xr ssh-keysign 8 ,
1.87 itojun 1473: .Xr sshd 8
1.329 jmc 1474: .Sh STANDARDS
1.106 markus 1475: .Rs
1.329 jmc 1476: .%A S. Lehtinen
1477: .%A C. Lonvick
1478: .%D January 2006
1.256 jmc 1479: .%R RFC 4250
1.329 jmc 1480: .%T The Secure Shell (SSH) Protocol Assigned Numbers
1.256 jmc 1481: .Re
1.329 jmc 1482: .Pp
1.256 jmc 1483: .Rs
1.329 jmc 1484: .%A T. Ylonen
1485: .%A C. Lonvick
1486: .%D January 2006
1.256 jmc 1487: .%R RFC 4251
1.329 jmc 1488: .%T The Secure Shell (SSH) Protocol Architecture
1.256 jmc 1489: .Re
1.329 jmc 1490: .Pp
1.256 jmc 1491: .Rs
1.329 jmc 1492: .%A T. Ylonen
1493: .%A C. Lonvick
1494: .%D January 2006
1.256 jmc 1495: .%R RFC 4252
1.329 jmc 1496: .%T The Secure Shell (SSH) Authentication Protocol
1.256 jmc 1497: .Re
1.329 jmc 1498: .Pp
1.256 jmc 1499: .Rs
1.329 jmc 1500: .%A T. Ylonen
1501: .%A C. Lonvick
1502: .%D January 2006
1.256 jmc 1503: .%R RFC 4253
1.329 jmc 1504: .%T The Secure Shell (SSH) Transport Layer Protocol
1.256 jmc 1505: .Re
1.329 jmc 1506: .Pp
1.256 jmc 1507: .Rs
1.329 jmc 1508: .%A T. Ylonen
1509: .%A C. Lonvick
1510: .%D January 2006
1.256 jmc 1511: .%R RFC 4254
1.329 jmc 1512: .%T The Secure Shell (SSH) Connection Protocol
1.256 jmc 1513: .Re
1.329 jmc 1514: .Pp
1.256 jmc 1515: .Rs
1.329 jmc 1516: .%A J. Schlyter
1517: .%A W. Griffin
1518: .%D January 2006
1.256 jmc 1519: .%R RFC 4255
1.329 jmc 1520: .%T Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints
1.256 jmc 1521: .Re
1.329 jmc 1522: .Pp
1.256 jmc 1523: .Rs
1.329 jmc 1524: .%A F. Cusack
1525: .%A M. Forssen
1526: .%D January 2006
1.256 jmc 1527: .%R RFC 4256
1.329 jmc 1528: .%T Generic Message Exchange Authentication for the Secure Shell Protocol (SSH)
1.256 jmc 1529: .Re
1.329 jmc 1530: .Pp
1.256 jmc 1531: .Rs
1.329 jmc 1532: .%A J. Galbraith
1533: .%A P. Remaker
1534: .%D January 2006
1.256 jmc 1535: .%R RFC 4335
1.329 jmc 1536: .%T The Secure Shell (SSH) Session Channel Break Extension
1.256 jmc 1537: .Re
1.329 jmc 1538: .Pp
1.256 jmc 1539: .Rs
1.329 jmc 1540: .%A M. Bellare
1541: .%A T. Kohno
1542: .%A C. Namprempre
1543: .%D January 2006
1.256 jmc 1544: .%R RFC 4344
1.329 jmc 1545: .%T The Secure Shell (SSH) Transport Layer Encryption Modes
1.256 jmc 1546: .Re
1.329 jmc 1547: .Pp
1.256 jmc 1548: .Rs
1.329 jmc 1549: .%A B. Harris
1550: .%D January 2006
1.256 jmc 1551: .%R RFC 4345
1.329 jmc 1552: .%T Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol
1.258 djm 1553: .Re
1.329 jmc 1554: .Pp
1.258 djm 1555: .Rs
1.329 jmc 1556: .%A M. Friedl
1557: .%A N. Provos
1558: .%A W. Simpson
1559: .%D March 2006
1.258 djm 1560: .%R RFC 4419
1.329 jmc 1561: .%T Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol
1.266 markus 1562: .Re
1.329 jmc 1563: .Pp
1.266 markus 1564: .Rs
1.329 jmc 1565: .%A J. Galbraith
1566: .%A R. Thayer
1567: .%D November 2006
1.266 markus 1568: .%R RFC 4716
1.329 jmc 1569: .%T The Secure Shell (SSH) Public Key File Format
1.313 djm 1570: .Re
1.329 jmc 1571: .Pp
1.313 djm 1572: .Rs
1.329 jmc 1573: .%A D. Stebila
1574: .%A J. Green
1575: .%D December 2009
1.313 djm 1576: .%R RFC 5656
1.329 jmc 1577: .%T Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer
1.274 grunk 1578: .Re
1.329 jmc 1579: .Pp
1.274 grunk 1580: .Rs
1581: .%A A. Perrig
1582: .%A D. Song
1583: .%D 1999
1.329 jmc 1584: .%O International Workshop on Cryptographic Techniques and E-Commerce (CrypTEC '99)
1585: .%T Hash Visualization: a New Technique to improve Real-World Security
1.106 markus 1586: .Re
1.173 jmc 1587: .Sh AUTHORS
1588: OpenSSH is a derivative of the original and free
1589: ssh 1.2.12 release by Tatu Ylonen.
1590: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1591: Theo de Raadt and Dug Song
1592: removed many bugs, re-added newer features and
1593: created OpenSSH.
1594: Markus Friedl contributed the support for SSH
1595: protocol versions 1.5 and 2.0.
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