3 .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
4 .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5 .\" All rights reserved
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".
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.
17 .\" Redistribution and use in source and binary forms, with or without
18 .\" modification, are permitted provided that the following conditions
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.
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.
37 .\" $OpenBSD: ssh.1,v 1.270 2007/06/12 13:43:55 jmc Exp $
38 .Dd $Mdocdate: June 12 2007 $
43 .Nd OpenSSH SSH client (remote login program)
46 .Op Fl 1246AaCfgKkMNnqsTtVvXxY
47 .Op Fl b Ar bind_address
48 .Op Fl c Ar cipher_spec
51 .Oo Ar bind_address : Oc
55 .Op Fl e Ar escape_char
56 .Op Fl F Ar configfile
58 .Op Fl i Ar identity_file
62 .Oo Ar bind_address : Oc
63 .Ar port : host : hostport
67 .Op Fl l Ar login_name
75 .Oo Ar bind_address : Oc
76 .Ar port : host : hostport
81 .Oo Fl w Ar local_tun Ns
82 .Op : Ns Ar remote_tun Oc
83 .Oo Ar user Ns @ Oc Ns Ar hostname
88 (SSH client) is a program for logging into a remote machine and for
89 executing commands on a remote machine.
90 It is intended to replace rlogin and rsh,
91 and provide secure encrypted communications between
92 two untrusted hosts over an insecure network.
93 X11 connections and arbitrary TCP ports
94 can also be forwarded over the secure channel.
97 connects and logs into the specified
103 his/her identity to the remote machine using one of several methods
104 depending on the protocol version used (see below).
109 it is executed on the remote host instead of a login shell.
111 The options are as follows:
116 to try protocol version 1 only.
120 to try protocol version 2 only.
124 to use IPv4 addresses only.
128 to use IPv6 addresses only.
130 Enables forwarding of the authentication agent connection.
131 This can also be specified on a per-host basis in a configuration file.
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.
141 Disables forwarding of the authentication agent connection.
142 .It Fl b Ar bind_address
145 on the local machine as the source address
147 Only useful on systems with more than one address.
149 Requests compression of all data (including stdin, stdout, stderr, and
150 data for forwarded X11 and TCP connections).
151 The compression algorithm is the same used by
155 can be controlled by the
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
164 .It Fl c Ar cipher_spec
165 Selects the cipher specification for encrypting the session.
167 Protocol version 1 allows specification of a single cipher.
168 The supported values are
174 (triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
175 It is believed to be secure.
177 is a fast block cipher; it appears very secure and is much faster than
180 is only supported in the
182 client for interoperability with legacy protocol 1 implementations
183 that do not support the
186 Its use is strongly discouraged due to cryptographic weaknesses.
190 For protocol version 2,
192 is a comma-separated list of ciphers
193 listed in order of preference.
194 The supported ciphers are:
209 .Bd -literal -offset indent
210 aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
211 arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
212 aes192-ctr,aes256-ctr
216 .Oo Ar bind_address : Oc
222 application-level port forwarding.
223 This works by allocating a socket to listen to
225 on the local side, optionally bound to the specified
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
231 Currently the SOCKS4 and SOCKS5 protocols are supported, and
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.
237 IPv6 addresses can be specified with an alternative syntax:
240 .Op Ar bind_address No /
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
251 may be used to bind the connection to a specific address.
256 indicates that the listening port be bound for local use only, while an
259 indicates that the port should be available from all interfaces.
260 .It Fl e Ar escape_char
261 Sets the escape character for sessions with a pty (default:
263 The escape character is only recognized at the beginning of a line.
264 The escape character followed by a dot
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
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
278 The default for the per-user configuration file is
283 to go to background just before command execution.
286 is going to ask for passwords or passphrases, but the user
287 wants it in the background.
290 The recommended way to start X11 programs at a remote site is with
292 .Ic ssh -f host xterm .
294 Allows remote hosts to connect to local forwarded ports.
295 .It Fl I Ar smartcard_device
298 should use to communicate with a smartcard used for storing the user's
300 This option is only available if support for smartcard devices
301 is compiled in (default is no support).
302 .It Fl i Ar identity_file
303 Selects a file from which the identity (private key) for
304 RSA or DSA authentication is read.
307 for protocol version 1, and
311 for protocol version 2.
312 Identity files may also be specified on
313 a per-host basis in the configuration file.
314 It is possible to have multiple
316 options (and multiple identities specified in
317 configuration files).
319 Enables GSSAPI-based authentication and forwarding (delegation) of GSSAPI
320 credentials to the server.
322 Disables forwarding (delegation) of GSSAPI credentials to the server.
325 .Oo Ar bind_address : Oc
326 .Ar port : host : hostport
329 Specifies that the given port on the local (client) host is to be
330 forwarded to the given host and port on the remote side.
331 This works by allocating a socket to listen to
333 on the local side, optionally bound to the specified
335 Whenever a connection is made to this port, the
336 connection is forwarded over the secure channel, and a connection is
341 from the remote machine.
342 Port forwardings can also be specified in the configuration file.
343 IPv6 addresses can be specified with an alternative syntax:
346 .Op Ar bind_address No /
347 .Ar port No / Ar host No /
351 or by enclosing the address in square brackets.
352 Only the superuser can forward privileged ports.
353 By default, the local port is bound in accordance with the
358 may be used to bind the connection to a specific address.
363 indicates that the listening port be bound for local use only, while an
366 indicates that the port should be available from all interfaces.
367 .It Fl l Ar login_name
368 Specifies the user to log in as on the remote machine.
369 This also may be specified on a per-host basis in the configuration file.
375 mode for connection sharing.
382 mode with confirmation required before slave connections are accepted.
383 Refer to the description of
389 Additionally, for protocol version 2 a comma-separated list of MAC
390 (message authentication code) algorithms can
391 be specified in order of preference.
394 keyword for more information.
396 Do not execute a remote command.
397 This is useful for just forwarding ports
398 (protocol version 2 only).
402 (actually, prevents reading from stdin).
403 This must be used when
405 is run in the background.
406 A common trick is to use this to run X11 programs on a remote machine.
408 .Ic ssh -n shadows.cs.hut.fi emacs &
409 will start an emacs on shadows.cs.hut.fi, and the X11
410 connection will be automatically forwarded over an encrypted channel.
413 program will be put in the background.
414 (This does not work if
416 needs to ask for a password or passphrase; see also the
420 Control an active connection multiplexing master process.
423 option is specified, the
425 argument is interpreted and passed to the master process.
428 (check that the master process is running) and
430 (request the master to exit).
432 Can be used to give options in the format used in the configuration file.
433 This is useful for specifying options for which there is no separate
435 For full details of the options listed below, and their possible values, see
438 .Bl -tag -width Ds -offset indent -compact
442 .It ChallengeResponseAuthentication
446 .It ClearAllForwardings
449 .It ConnectionAttempts
455 .It ExitOnForwardFailure
458 .It ForwardX11Trusted
460 .It GlobalKnownHostsFile
461 .It GSSAPIAuthentication
462 .It GSSAPIDelegateCredentials
465 .It HostbasedAuthentication
466 .It HostKeyAlgorithms
471 .It KbdInteractiveDevices
476 .It NoHostAuthenticationForLocalhost
477 .It NumberOfPasswordPrompts
478 .It PasswordAuthentication
479 .It PermitLocalCommand
481 .It PreferredAuthentications
484 .It PubkeyAuthentication
487 .It RhostsRSAAuthentication
488 .It RSAAuthentication
490 .It ServerAliveInterval
491 .It ServerAliveCountMax
493 .It StrictHostKeyChecking
497 .It UsePrivilegedPort
499 .It UserKnownHostsFile
504 Port to connect to on the remote host.
505 This can be specified on a
506 per-host basis in the configuration file.
509 Causes all warning and diagnostic messages to be suppressed.
512 .Oo Ar bind_address : Oc
513 .Ar port : host : hostport
516 Specifies that the given port on the remote (server) host is to be
517 forwarded to the given host and port on the local side.
518 This works by allocating a socket to listen to
520 on the remote side, and whenever a connection is made to this port, the
521 connection is forwarded over the secure channel, and a connection is
526 from the local machine.
528 Port forwardings can also be specified in the configuration file.
529 Privileged ports can be forwarded only when
530 logging in as root on the remote machine.
531 IPv6 addresses can be specified by enclosing the address in square braces or
532 using an alternative syntax:
535 .Op Ar bind_address No /
536 .Ar host No / Ar port No /
541 By default, the listening socket on the server will be bound to the loopback
543 This may be overriden by specifying a
549 indicates that the remote socket should listen on all interfaces.
552 will only succeed if the server's
554 option is enabled (see
555 .Xr sshd_config 5 ) .
557 Specifies the location of a control socket for connection sharing.
558 Refer to the description of
566 May be used to request invocation of a subsystem on the remote system.
567 Subsystems are a feature of the SSH2 protocol which facilitate the use
568 of SSH as a secure transport for other applications (eg.\&
570 The subsystem is specified as the remote command.
572 Disable pseudo-tty allocation.
574 Force pseudo-tty allocation.
575 This can be used to execute arbitrary
576 screen-based programs on a remote machine, which can be very useful,
577 e.g. when implementing menu services.
580 options force tty allocation, even if
584 Display the version number and exit.
589 to print debugging messages about its progress.
591 debugging connection, authentication, and configuration problems.
594 options increase the verbosity.
597 .Ar local_tun Ns Op : Ns Ar remote_tun
601 device forwarding with the specified
603 devices between the client
608 The devices may be specified by numerical ID or the keyword
610 which uses the next available tunnel device.
613 is not specified, it defaults to
623 directive is unset, it is set to the default tunnel mode, which is
626 Enables X11 forwarding.
627 This can also be specified on a per-host basis in a configuration file.
629 X11 forwarding should be enabled with caution.
630 Users with the ability to bypass file permissions on the remote host
631 (for the user's X authorization database)
632 can access the local X11 display through the forwarded connection.
633 An attacker may then be able to perform activities such as keystroke monitoring.
635 For this reason, X11 forwarding is subjected to X11 SECURITY extension
636 restrictions by default.
641 .Cm ForwardX11Trusted
644 for more information.
646 Disables X11 forwarding.
648 Enables trusted X11 forwarding.
649 Trusted X11 forwardings are not subjected to the X11 SECURITY extension
654 may additionally obtain configuration data from
655 a per-user configuration file and a system-wide configuration file.
656 The file format and configuration options are described in
660 exits with the exit status of the remote command or with 255
661 if an error occurred.
663 The OpenSSH SSH client supports SSH protocols 1 and 2.
664 Protocol 2 is the default, with
666 falling back to protocol 1 if it detects protocol 2 is unsupported.
667 These settings may be altered using the
671 or enforced using the
676 Both protocols support similar authentication methods,
677 but protocol 2 is preferred since
678 it provides additional mechanisms for confidentiality
679 (the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour)
680 and integrity (hmac-md5, hmac-sha1, umac-64, hmac-ripemd160).
681 Protocol 1 lacks a strong mechanism for ensuring the
682 integrity of the connection.
684 The methods available for authentication are:
685 GSSAPI-based authentication,
686 host-based authentication,
687 public key authentication,
688 challenge-response authentication,
689 and password authentication.
690 Authentication methods are tried in the order specified above,
691 though protocol 2 has a configuration option to change the default order:
692 .Cm PreferredAuthentications .
694 Host-based authentication works as follows:
695 If the machine the user logs in from is listed in
698 .Pa /etc/shosts.equiv
699 on the remote machine, and the user names are
700 the same on both sides, or if the files
704 exist in the user's home directory on the
705 remote machine and contain a line containing the name of the client
706 machine and the name of the user on that machine, the user is
707 considered for login.
708 Additionally, the server
710 be able to verify the client's
711 host key (see the description of
712 .Pa /etc/ssh/ssh_known_hosts
714 .Pa ~/.ssh/known_hosts ,
716 for login to be permitted.
717 This authentication method closes security holes due to IP
718 spoofing, DNS spoofing, and routing spoofing.
719 [Note to the administrator:
720 .Pa /etc/hosts.equiv ,
722 and the rlogin/rsh protocol in general, are inherently insecure and should be
723 disabled if security is desired.]
725 Public key authentication works as follows:
726 The scheme is based on public-key cryptography,
728 where encryption and decryption are done using separate keys,
729 and it is unfeasible to derive the decryption key from the encryption key.
730 The idea is that each user creates a public/private
731 key pair for authentication purposes.
732 The server knows the public key, and only the user knows the private key.
734 implements public key authentication protocol automatically,
735 using either the RSA or DSA algorithms.
736 Protocol 1 is restricted to using only RSA keys,
737 but protocol 2 may use either.
742 contains a brief discussion of the two algorithms.
745 .Pa ~/.ssh/authorized_keys
746 lists the public keys that are permitted for logging in.
747 When the user logs in, the
749 program tells the server which key pair it would like to use for
751 The client proves that it has access to the private key
752 and the server checks that the corresponding public key
753 is authorized to accept the account.
755 The user creates his/her key pair by running
757 This stores the private key in
765 and stores the public key in
766 .Pa ~/.ssh/identity.pub
768 .Pa ~/.ssh/id_dsa.pub
771 .Pa ~/.ssh/id_rsa.pub
773 in the user's home directory.
774 The user should then copy the public key
776 .Pa ~/.ssh/authorized_keys
777 in his/her home directory on the remote machine.
780 file corresponds to the conventional
782 file, and has one key
783 per line, though the lines can be very long.
784 After this, the user can log in without giving the password.
786 The most convenient way to use public key authentication may be with an
787 authentication agent.
790 for more information.
792 Challenge-response authentication works as follows:
793 The server sends an arbitrary
795 text, and prompts for a response.
796 Protocol 2 allows multiple challenges and responses;
797 protocol 1 is restricted to just one challenge/response.
798 Examples of challenge-response authentication include
799 BSD Authentication (see
801 and PAM (some non-OpenBSD systems).
803 Finally, if other authentication methods fail,
805 prompts the user for a password.
806 The password is sent to the remote
807 host for checking; however, since all communications are encrypted,
808 the password cannot be seen by someone listening on the network.
811 automatically maintains and checks a database containing
812 identification for all hosts it has ever been used with.
813 Host keys are stored in
814 .Pa ~/.ssh/known_hosts
815 in the user's home directory.
816 Additionally, the file
817 .Pa /etc/ssh/ssh_known_hosts
818 is automatically checked for known hosts.
819 Any new hosts are automatically added to the user's file.
820 If a host's identification ever changes,
822 warns about this and disables password authentication to prevent
823 server spoofing or man-in-the-middle attacks,
824 which could otherwise be used to circumvent the encryption.
826 .Cm StrictHostKeyChecking
827 option can be used to control logins to machines whose
828 host key is not known or has changed.
830 When the user's identity has been accepted by the server, the server
831 either executes the given command, or logs into the machine and gives
832 the user a normal shell on the remote machine.
833 All communication with
834 the remote command or shell will be automatically encrypted.
836 If a pseudo-terminal has been allocated (normal login session), the
837 user may use the escape characters noted below.
839 If no pseudo-tty has been allocated,
840 the session is transparent and can be used to reliably transfer binary data.
841 On most systems, setting the escape character to
843 will also make the session transparent even if a tty is used.
845 The session terminates when the command or shell on the remote
846 machine exits and all X11 and TCP connections have been closed.
847 .Sh ESCAPE CHARACTERS
848 When a pseudo-terminal has been requested,
850 supports a number of functions through the use of an escape character.
852 A single tilde character can be sent as
854 or by following the tilde by a character other than those described below.
855 The escape character must always follow a newline to be interpreted as
857 The escape character can be changed in configuration files using the
859 configuration directive or on the command line by the
863 The supported escapes (assuming the default
873 List forwarded connections.
877 at logout when waiting for forwarded connection / X11 sessions to terminate.
879 Display a list of escape characters.
881 Send a BREAK to the remote system
882 (only useful for SSH protocol version 2 and if the peer supports it).
885 Currently this allows the addition of port forwardings using the
890 It also allows the cancellation of existing remote port-forwardings
893 .Fl KR Oo Ar bind_address : Oc Ar port .
895 .Ic !\& Ns Ar command
896 allows the user to execute a local command if the
897 .Ic PermitLocalCommand
900 Basic help is available, using the
904 Request rekeying of the connection
905 (only useful for SSH protocol version 2 and if the peer supports it).
908 Forwarding of arbitrary TCP connections over the secure channel can
909 be specified either on the command line or in a configuration file.
910 One possible application of TCP forwarding is a secure connection to a
911 mail server; another is going through firewalls.
913 In the example below, we look at encrypting communication between
914 an IRC client and server, even though the IRC server does not directly
915 support encrypted communications.
916 This works as follows:
917 the user connects to the remote host using
919 specifying a port to be used to forward connections
920 to the remote server.
921 After that it is possible to start the service which is to be encrypted
922 on the client machine,
923 connecting to the same local port,
926 will encrypt and forward the connection.
928 The following example tunnels an IRC session from client machine
932 .Dq server.example.com :
933 .Bd -literal -offset 4n
934 $ ssh -f -L 1234:localhost:6667 server.example.com sleep 10
935 $ irc -c '#users' -p 1234 pinky 127.0.0.1
938 This tunnels a connection to IRC server
939 .Dq server.example.com ,
945 It doesn't matter which port is used,
946 as long as it's greater than 1023
947 (remember, only root can open sockets on privileged ports)
948 and doesn't conflict with any ports already in use.
949 The connection is forwarded to port 6667 on the remote server,
950 since that's the standard port for IRC services.
956 and the remote command
958 is specified to allow an amount of time
959 (10 seconds, in the example)
960 to start the service which is to be tunnelled.
961 If no connections are made within the time specified,
969 (or see the description of the
975 and the user is using X11 (the
977 environment variable is set), the connection to the X11 display is
978 automatically forwarded to the remote side in such a way that any X11
979 programs started from the shell (or command) will go through the
980 encrypted channel, and the connection to the real X server will be made
981 from the local machine.
982 The user should not manually set
984 Forwarding of X11 connections can be
985 configured on the command line or in configuration files.
991 will point to the server machine, but with a display number greater than zero.
992 This is normal, and happens because
996 X server on the server machine for forwarding the
997 connections over the encrypted channel.
1000 will also automatically set up Xauthority data on the server machine.
1001 For this purpose, it will generate a random authorization cookie,
1002 store it in Xauthority on the server, and verify that any forwarded
1003 connections carry this cookie and replace it by the real cookie when
1004 the connection is opened.
1005 The real authentication cookie is never
1006 sent to the server machine (and no cookies are sent in the plain).
1012 (or see the description of the
1017 the user is using an authentication agent, the connection to the agent
1018 is automatically forwarded to the remote side.
1019 .Sh VERIFYING HOST KEYS
1020 When connecting to a server for the first time,
1021 a fingerprint of the server's public key is presented to the user
1023 .Cm StrictHostKeyChecking
1025 Fingerprints can be determined using
1028 .Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key
1030 If the fingerprint is already known,
1031 it can be matched and verified,
1032 and the key can be accepted.
1033 If the fingerprint is unknown,
1034 an alternative method of verification is available:
1035 SSH fingerprints verified by DNS.
1036 An additional resource record (RR),
1038 is added to a zonefile
1039 and the connecting client is able to match the fingerprint
1040 with that of the key presented.
1042 In this example, we are connecting a client to a server,
1043 .Dq host.example.com .
1044 The SSHFP resource records should first be added to the zonefile for
1046 .Bd -literal -offset indent
1047 $ ssh-keygen -r host.example.com.
1050 The output lines will have to be added to the zonefile.
1051 To check that the zone is answering fingerprint queries:
1053 .Dl $ dig -t SSHFP host.example.com
1055 Finally the client connects:
1056 .Bd -literal -offset indent
1057 $ ssh -o "VerifyHostKeyDNS ask" host.example.com
1059 Matching host key fingerprint found in DNS.
1060 Are you sure you want to continue connecting (yes/no)?
1064 .Cm VerifyHostKeyDNS
1067 for more information.
1068 .Sh SSH-BASED VIRTUAL PRIVATE NETWORKS
1070 contains support for Virtual Private Network (VPN) tunnelling
1073 network pseudo-device,
1074 allowing two networks to be joined securely.
1077 configuration option
1079 controls whether the server supports this,
1080 and at what level (layer 2 or 3 traffic).
1082 The following example would connect client network 10.0.50.0/24
1083 with remote network 10.0.99.0/24 using a point-to-point connection
1084 from 10.1.1.1 to 10.1.1.2,
1085 provided that the SSH server running on the gateway to the remote network,
1086 at 192.168.1.15, allows it.
1089 .Bd -literal -offset indent
1090 # ssh -f -w 0:1 192.168.1.15 true
1091 # ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252
1092 # route add 10.0.99.0/24 10.1.1.2
1096 .Bd -literal -offset indent
1097 # ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252
1098 # route add 10.0.50.0/24 10.1.1.1
1101 Client access may be more finely tuned via the
1102 .Pa /root/.ssh/authorized_keys
1103 file (see below) and the
1106 The following entry would permit connections on
1110 and on tun device 2 from user
1115 .Dq forced-commands-only :
1116 .Bd -literal -offset 2n
1117 tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane
1118 tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john
1121 Since an SSH-based setup entails a fair amount of overhead,
1122 it may be more suited to temporary setups,
1123 such as for wireless VPNs.
1124 More permanent VPNs are better provided by tools such as
1130 will normally set the following environment variables:
1131 .Bl -tag -width "SSH_ORIGINAL_COMMAND"
1135 variable indicates the location of the X11 server.
1136 It is automatically set by
1138 to point to a value of the form
1142 indicates the host where the shell runs, and
1144 is an integer \*(Ge 1.
1146 uses this special value to forward X11 connections over the secure
1148 The user should normally not set
1151 will render the X11 connection insecure (and will require the user to
1152 manually copy any required authorization cookies).
1154 Set to the path of the user's home directory.
1158 set for compatibility with systems that use this variable.
1160 Set to the path of the user's mailbox.
1164 as specified when compiling
1169 needs a passphrase, it will read the passphrase from the current
1170 terminal if it was run from a terminal.
1173 does not have a terminal associated with it but
1177 are set, it will execute the program specified by
1179 and open an X11 window to read the passphrase.
1180 This is particularly useful when calling
1185 (Note that on some machines it
1186 may be necessary to redirect the input from
1189 .It Ev SSH_AUTH_SOCK
1190 Identifies the path of a
1192 socket used to communicate with the agent.
1193 .It Ev SSH_CONNECTION
1194 Identifies the client and server ends of the connection.
1195 The variable contains
1196 four space-separated values: client IP address, client port number,
1197 server IP address, and server port number.
1198 .It Ev SSH_ORIGINAL_COMMAND
1199 This variable contains the original command line if a forced command
1201 It can be used to extract the original arguments.
1203 This is set to the name of the tty (path to the device) associated
1204 with the current shell or command.
1205 If the current session has no tty,
1206 this variable is not set.
1208 This variable is set to indicate the present time zone if it
1209 was set when the daemon was started (i.e. the daemon passes the value
1210 on to new connections).
1212 Set to the name of the user logging in.
1218 .Pa ~/.ssh/environment ,
1219 and adds lines of the format
1221 to the environment if the file exists and users are allowed to
1222 change their environment.
1223 For more information, see the
1224 .Cm PermitUserEnvironment
1228 .Bl -tag -width Ds -compact
1230 This file is used for host-based authentication (see above).
1231 On some machines this file may need to be
1232 world-readable if the user's home directory is on an NFS partition,
1236 Additionally, this file must be owned by the user,
1237 and must not have write permissions for anyone else.
1239 permission for most machines is read/write for the user, and not
1240 accessible by others.
1243 This file is used in exactly the same way as
1245 but allows host-based authentication without permitting login with
1248 .It ~/.ssh/authorized_keys
1249 Lists the public keys (RSA/DSA) that can be used for logging in as this user.
1250 The format of this file is described in the
1253 This file is not highly sensitive, but the recommended
1254 permissions are read/write for the user, and not accessible by others.
1257 This is the per-user configuration file.
1258 The file format and configuration options are described in
1260 Because of the potential for abuse, this file must have strict permissions:
1261 read/write for the user, and not accessible by others.
1263 .It ~/.ssh/environment
1264 Contains additional definitions for environment variables; see
1271 Contains the private key for authentication.
1273 contain sensitive data and should be readable by the user but not
1274 accessible by others (read/write/execute).
1276 will simply ignore a private key file if it is accessible by others.
1277 It is possible to specify a passphrase when
1278 generating the key which will be used to encrypt the
1279 sensitive part of this file using 3DES.
1281 .It ~/.ssh/identity.pub
1282 .It ~/.ssh/id_dsa.pub
1283 .It ~/.ssh/id_rsa.pub
1284 Contains the public key for authentication.
1286 sensitive and can (but need not) be readable by anyone.
1288 .It ~/.ssh/known_hosts
1289 Contains a list of host keys for all hosts the user has logged into
1290 that are not already in the systemwide list of known host keys.
1293 for further details of the format of this file.
1296 Commands in this file are executed by
1298 when the user logs in, just before the user's shell (or command) is
1302 manual page for more information.
1304 .It /etc/hosts.equiv
1305 This file is for host-based authentication (see above).
1306 It should only be writable by root.
1308 .It /etc/shosts.equiv
1309 This file is used in exactly the same way as
1311 but allows host-based authentication without permitting login with
1314 .It Pa /etc/ssh/ssh_config
1315 Systemwide configuration file.
1316 The file format and configuration options are described in
1319 .It /etc/ssh/ssh_host_key
1320 .It /etc/ssh/ssh_host_dsa_key
1321 .It /etc/ssh/ssh_host_rsa_key
1322 These three files contain the private parts of the host keys
1323 and are used for host-based authentication.
1324 If protocol version 1 is used,
1326 must be setuid root, since the host key is readable only by root.
1327 For protocol version 2,
1331 to access the host keys,
1332 eliminating the requirement that
1334 be setuid root when host-based authentication is used.
1339 .It /etc/ssh/ssh_known_hosts
1340 Systemwide list of known host keys.
1341 This file should be prepared by the
1342 system administrator to contain the public host keys of all machines in the
1344 It should be world-readable.
1347 for further details of the format of this file.
1350 Commands in this file are executed by
1352 when the user logs in, just before the user's shell (or command) is started.
1355 manual page for more information.
1371 .%T "The Secure Shell (SSH) Protocol Assigned Numbers"
1376 .%T "The Secure Shell (SSH) Protocol Architecture"
1381 .%T "The Secure Shell (SSH) Authentication Protocol"
1386 .%T "The Secure Shell (SSH) Transport Layer Protocol"
1391 .%T "The Secure Shell (SSH) Connection Protocol"
1396 .%T "Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints"
1401 .%T "Generic Message Exchange Authentication for the Secure Shell Protocol (SSH)"
1406 .%T "The Secure Shell (SSH) Session Channel Break Extension"
1411 .%T "The Secure Shell (SSH) Transport Layer Encryption Modes"
1416 .%T "Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol"
1421 .%T "Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol"
1426 .%T "The Secure Shell (SSH) Public Key File Format"
1430 OpenSSH is a derivative of the original and free
1431 ssh 1.2.12 release by Tatu Ylonen.
1432 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1433 Theo de Raadt and Dug Song
1434 removed many bugs, re-added newer features and
1436 Markus Friedl contributed the support for SSH
1437 protocol versions 1.5 and 2.0.
projects / dragonfly.git / blob