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 1.253 2006/01/30 13:37:49 jmc Exp $
39 .Dd September 25, 1999
44 .Nd OpenSSH SSH client (remote login program)
47 .Op Fl 1246AaCfgkMNnqsTtVvXxY
48 .Op Fl b Ar bind_address
49 .Op Fl c Ar cipher_spec
52 .Oo Ar bind_address : Oc
56 .Op Fl e Ar escape_char
57 .Op Fl F Ar configfile
59 .Op Fl i Ar identity_file
63 .Oo Ar bind_address : Oc
64 .Ar port : host : hostport
68 .Op Fl l Ar login_name
76 .Oo Ar bind_address : Oc
77 .Ar port : host : hostport
82 .Op Fl w Ar tunnel : Ns Ar tunnel
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 Disables forwarding (delegation) of GSSAPI credentials to the server.
322 .Oo Ar bind_address : Oc
323 .Ar port : host : hostport
326 Specifies that the given port on the local (client) host is to be
327 forwarded to the given host and port on the remote side.
328 This works by allocating a socket to listen to
330 on the local side, optionally bound to the specified
332 Whenever a connection is made to this port, the
333 connection is forwarded over the secure channel, and a connection is
338 from the remote machine.
339 Port forwardings can also be specified in the configuration file.
340 IPv6 addresses can be specified with an alternative syntax:
343 .Op Ar bind_address No /
344 .Ar port No / Ar host No /
348 or by enclosing the address in square brackets.
349 Only the superuser can forward privileged ports.
350 By default, the local port is bound in accordance with the
355 may be used to bind the connection to a specific address.
360 indicates that the listening port be bound for local use only, while an
363 indicates that the port should be available from all interfaces.
364 .It Fl l Ar login_name
365 Specifies the user to log in as on the remote machine.
366 This also may be specified on a per-host basis in the configuration file.
372 mode for connection sharing.
379 mode with confirmation required before slave connections are accepted.
380 Refer to the description of
386 Additionally, for protocol version 2 a comma-separated list of MAC
387 (message authentication code) algorithms can
388 be specified in order of preference.
391 keyword for more information.
393 Do not execute a remote command.
394 This is useful for just forwarding ports
395 (protocol version 2 only).
399 (actually, prevents reading from stdin).
400 This must be used when
402 is run in the background.
403 A common trick is to use this to run X11 programs on a remote machine.
405 .Ic ssh -n shadows.cs.hut.fi emacs &
406 will start an emacs on shadows.cs.hut.fi, and the X11
407 connection will be automatically forwarded over an encrypted channel.
410 program will be put in the background.
411 (This does not work if
413 needs to ask for a password or passphrase; see also the
417 Control an active connection multiplexing master process.
420 option is specified, the
422 argument is interpreted and passed to the master process.
425 (check that the master process is running) and
427 (request the master to exit).
429 Can be used to give options in the format used in the configuration file.
430 This is useful for specifying options for which there is no separate
432 For full details of the options listed below, and their possible values, see
435 .Bl -tag -width Ds -offset indent -compact
439 .It ChallengeResponseAuthentication
443 .It ClearAllForwardings
446 .It ConnectionAttempts
454 .It ForwardX11Trusted
456 .It GlobalKnownHostsFile
457 .It GSSAPIAuthentication
458 .It GSSAPIDelegateCredentials
461 .It HostbasedAuthentication
462 .It HostKeyAlgorithms
467 .It KbdInteractiveDevices
472 .It NoHostAuthenticationForLocalhost
473 .It NumberOfPasswordPrompts
474 .It PasswordAuthentication
475 .It PermitLocalCommand
477 .It PreferredAuthentications
480 .It PubkeyAuthentication
483 .It RhostsRSAAuthentication
484 .It RSAAuthentication
486 .It ServerAliveInterval
487 .It ServerAliveCountMax
489 .It StrictHostKeyChecking
493 .It UsePrivilegedPort
495 .It UserKnownHostsFile
501 Port to connect to on the remote host.
502 This can be specified on a
503 per-host basis in the configuration file.
506 Causes all warning and diagnostic messages to be suppressed.
509 .Oo Ar bind_address : Oc
510 .Ar port : host : hostport
513 Specifies that the given port on the remote (server) host is to be
514 forwarded to the given host and port on the local side.
515 This works by allocating a socket to listen to
517 on the remote side, and whenever a connection is made to this port, the
518 connection is forwarded over the secure channel, and a connection is
523 from the local machine.
525 Port forwardings can also be specified in the configuration file.
526 Privileged ports can be forwarded only when
527 logging in as root on the remote machine.
528 IPv6 addresses can be specified by enclosing the address in square braces or
529 using an alternative syntax:
532 .Op Ar bind_address No /
533 .Ar host No / Ar port No /
538 By default, the listening socket on the server will be bound to the loopback
540 This may be overriden by specifying a
546 indicates that the remote socket should listen on all interfaces.
549 will only succeed if the server's
551 option is enabled (see
552 .Xr sshd_config 5 ) .
554 Specifies the location of a control socket for connection sharing.
555 Refer to the description of
563 May be used to request invocation of a subsystem on the remote system.
564 Subsystems are a feature of the SSH2 protocol which facilitate the use
565 of SSH as a secure transport for other applications (eg.\&
567 The subsystem is specified as the remote command.
569 Disable pseudo-tty allocation.
571 Force pseudo-tty allocation.
572 This can be used to execute arbitrary
573 screen-based programs on a remote machine, which can be very useful,
574 e.g., when implementing menu services.
577 options force tty allocation, even if
581 Display the version number and exit.
586 to print debugging messages about its progress.
588 debugging connection, authentication, and configuration problems.
591 options increase the verbosity.
593 .It Fl w Ar tunnel : Ns Ar tunnel
604 The devices may be specified by numerical ID or the keyword
606 which uses the next available tunnel device.
612 Enables X11 forwarding.
613 This can also be specified on a per-host basis in a configuration file.
615 X11 forwarding should be enabled with caution.
616 Users with the ability to bypass file permissions on the remote host
617 (for the user's X authorization database)
618 can access the local X11 display through the forwarded connection.
619 An attacker may then be able to perform activities such as keystroke monitoring.
621 For this reason, X11 forwarding is subjected to X11 SECURITY extension
622 restrictions by default.
627 .Cm ForwardX11Trusted
630 for more information.
632 Disables X11 forwarding.
634 Enables trusted X11 forwarding.
635 Trusted X11 forwardings are not subjected to the X11 SECURITY extension
640 may additionally obtain configuration data from
641 a per-user configuration file and a system-wide configuration file.
642 The file format and configuration options are described in
646 exits with the exit status of the remote command or with 255
647 if an error occurred.
649 The OpenSSH SSH client supports SSH protocols 1 and 2.
650 Protocol 2 is the default, with
652 falling back to protocol 1 if it detects protocol 2 is unsupported.
653 These settings may be altered using the
657 or enforced using the
662 Both protocols support similar authentication methods,
663 but protocol 2 is preferred since
664 it provides additional mechanisms for confidentiality
665 (the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour)
666 and integrity (hmac-md5, hmac-sha1, hmac-ripemd160).
667 Protocol 1 lacks a strong mechanism for ensuring the
668 integrity of the connection.
670 The methods available for authentication are:
671 host-based authentication,
672 public key authentication,
673 challenge-response authentication,
674 and password authentication.
675 Authentication methods are tried in the order specified above,
676 though protocol 2 has a configuration option to change the default order:
677 .Cm PreferredAuthentications .
679 Host-based authentication works as follows:
680 If the machine the user logs in from is listed in
683 .Pa /etc/shosts.equiv
684 on the remote machine, and the user names are
685 the same on both sides, or if the files
689 exist in the user's home directory on the
690 remote machine and contain a line containing the name of the client
691 machine and the name of the user on that machine, the user is
692 considered for login.
693 Additionally, the server
695 be able to verify the client's
696 host key (see the description of
697 .Pa /etc/ssh/ssh_known_hosts
699 .Pa ~/.ssh/known_hosts ,
701 for login to be permitted.
702 This authentication method closes security holes due to IP
703 spoofing, DNS spoofing, and routing spoofing.
704 [Note to the administrator:
705 .Pa /etc/hosts.equiv ,
707 and the rlogin/rsh protocol in general, are inherently insecure and should be
708 disabled if security is desired.]
710 Public key authentication works as follows:
711 The scheme is based on public-key cryptography,
713 where encryption and decryption are done using separate keys,
714 and it is unfeasible to derive the decryption key from the encryption key.
715 The idea is that each user creates a public/private
716 key pair for authentication purposes.
717 The server knows the public key, and only the user knows the private key.
719 implements public key authentication protocol automatically,
720 using either the RSA or DSA algorithms.
721 Protocol 1 is restricted to using only RSA keys,
722 but protocol 2 may use either.
727 contains a brief discussion of the two algorithms.
730 .Pa ~/.ssh/authorized_keys
731 lists the public keys that are permitted for logging in.
732 When the user logs in, the
734 program tells the server which key pair it would like to use for
736 The client proves that it has access to the private key
737 and the server checks that the corresponding public key
738 is authorized to accept the account.
740 The user creates his/her key pair by running
742 This stores the private key in
750 and stores the public key in
751 .Pa ~/.ssh/identity.pub
753 .Pa ~/.ssh/id_dsa.pub
756 .Pa ~/.ssh/id_rsa.pub
758 in the user's home directory.
759 The user should then copy the public key
761 .Pa ~/.ssh/authorized_keys
762 in his/her home directory on the remote machine.
765 file corresponds to the conventional
767 file, and has one key
768 per line, though the lines can be very long.
769 After this, the user can log in without giving the password.
771 The most convenient way to use public key authentication may be with an
772 authentication agent.
775 for more information.
777 Challenge-response authentication works as follows:
778 The server sends an arbitrary
780 text, and prompts for a response.
781 Protocol 2 allows multiple challenges and responses;
782 protocol 1 is restricted to just one challenge/response.
783 Examples of challenge-response authentication include
784 BSD Authentication (see
786 and PAM (some non-OpenBSD systems).
788 Finally, if other authentication methods fail,
790 prompts the user for a password.
791 The password is sent to the remote
792 host for checking; however, since all communications are encrypted,
793 the password cannot be seen by someone listening on the network.
796 automatically maintains and checks a database containing
797 identification for all hosts it has ever been used with.
798 Host keys are stored in
799 .Pa ~/.ssh/known_hosts
800 in the user's home directory.
801 Additionally, the file
802 .Pa /etc/ssh/ssh_known_hosts
803 is automatically checked for known hosts.
804 Any new hosts are automatically added to the user's file.
805 If a host's identification ever changes,
807 warns about this and disables password authentication to prevent
808 server spoofing or man-in-the-middle attacks,
809 which could otherwise be used to circumvent the encryption.
811 .Cm StrictHostKeyChecking
812 option can be used to control logins to machines whose
813 host key is not known or has changed.
815 When the user's identity has been accepted by the server, the server
816 either executes the given command, or logs into the machine and gives
817 the user a normal shell on the remote machine.
818 All communication with
819 the remote command or shell will be automatically encrypted.
821 If a pseudo-terminal has been allocated (normal login session), the
822 user may use the escape characters noted below.
824 If no pseudo-tty has been allocated,
825 the session is transparent and can be used to reliably transfer binary data.
826 On most systems, setting the escape character to
828 will also make the session transparent even if a tty is used.
830 The session terminates when the command or shell on the remote
831 machine exits and all X11 and TCP connections have been closed.
832 .Sh ESCAPE CHARACTERS
833 When a pseudo-terminal has been requested,
835 supports a number of functions through the use of an escape character.
837 A single tilde character can be sent as
839 or by following the tilde by a character other than those described below.
840 The escape character must always follow a newline to be interpreted as
842 The escape character can be changed in configuration files using the
844 configuration directive or on the command line by the
848 The supported escapes (assuming the default
858 List forwarded connections.
862 at logout when waiting for forwarded connection / X11 sessions to terminate.
864 Display a list of escape characters.
866 Send a BREAK to the remote system
867 (only useful for SSH protocol version 2 and if the peer supports it).
870 Currently this allows the addition of port forwardings using the
875 It also allows the cancellation of existing remote port-forwardings
878 .Ic !\& Ns Ar command
879 allows the user to execute a local command if the
880 .Ic PermitLocalCommand
883 Basic help is available, using the
887 Request rekeying of the connection
888 (only useful for SSH protocol version 2 and if the peer supports it).
891 Forwarding of arbitrary TCP connections over the secure channel can
892 be specified either on the command line or in a configuration file.
893 One possible application of TCP forwarding is a secure connection to a
894 mail server; another is going through firewalls.
896 In the example below, we look at encrypting communication between
897 an IRC client and server, even though the IRC server does not directly
898 support encrypted communications.
899 This works as follows:
900 the user connects to the remote host using
902 specifying a port to be used to forward connections
903 to the remote server.
904 After that it is possible to start the service which is to be encrypted
905 on the client machine,
906 connecting to the same local port,
909 will encrypt and forward the connection.
911 The following example tunnels an IRC session from client machine
915 .Dq server.example.com :
916 .Bd -literal -offset 4n
917 $ ssh -f -L 1234:localhost:6667 server.example.com sleep 10
918 $ irc -c '#users' -p 1234 pinky 127.0.0.1
921 This tunnels a connection to IRC server
922 .Dq server.example.com ,
928 It doesn't matter which port is used,
929 as long as it's greater than 1023
930 (remember, only root can open sockets on privileged ports)
931 and doesn't conflict with any ports already in use.
932 The connection is forwarded to port 6667 on the remote server,
933 since that's the standard port for IRC services.
939 and the remote command
941 is specified to allow an amount of time
942 (10 seconds, in the example)
943 to start the service which is to be tunnelled.
944 If no connections are made within the time specified,
952 (or see the description of the
958 and the user is using X11 (the
960 environment variable is set), the connection to the X11 display is
961 automatically forwarded to the remote side in such a way that any X11
962 programs started from the shell (or command) will go through the
963 encrypted channel, and the connection to the real X server will be made
964 from the local machine.
965 The user should not manually set
967 Forwarding of X11 connections can be
968 configured on the command line or in configuration files.
974 will point to the server machine, but with a display number greater than zero.
975 This is normal, and happens because
979 X server on the server machine for forwarding the
980 connections over the encrypted channel.
983 will also automatically set up Xauthority data on the server machine.
984 For this purpose, it will generate a random authorization cookie,
985 store it in Xauthority on the server, and verify that any forwarded
986 connections carry this cookie and replace it by the real cookie when
987 the connection is opened.
988 The real authentication cookie is never
989 sent to the server machine (and no cookies are sent in the plain).
995 (or see the description of the
1000 the user is using an authentication agent, the connection to the agent
1001 is automatically forwarded to the remote side.
1002 .Sh VERIFYING HOST KEYS
1003 When connecting to a server for the first time,
1004 a fingerprint of the server's public key is presented to the user
1006 .Cm StrictHostKeyChecking
1008 Fingerprints can be determined using
1011 .Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key
1013 If the fingerprint is already known,
1014 it can be matched and verified,
1015 and the key can be accepted.
1016 If the fingerprint is unknown,
1017 an alternative method of verification is available:
1018 SSH fingerprints verified by DNS.
1019 An additional resource record (RR),
1021 is added to a zonefile
1022 and the connecting client is able to match the fingerprint
1023 with that of the key presented.
1025 In this example, we are connecting a client to a server,
1026 .Dq host.example.com .
1027 The SSHFP resource records should first be added to the zonefile for
1029 .Bd -literal -offset indent
1030 $ ssh-keygen -f /etc/ssh/ssh_host_rsa_key.pub -r host.example.com.
1031 $ ssh-keygen -f /etc/ssh/ssh_host_dsa_key.pub -r host.example.com.
1034 The output lines will have to be added to the zonefile.
1035 To check that the zone is answering fingerprint queries:
1037 .Dl $ dig -t SSHFP host.example.com
1039 Finally the client connects:
1040 .Bd -literal -offset indent
1041 $ ssh -o "VerifyHostKeyDNS ask" host.example.com
1043 Matching host key fingerprint found in DNS.
1044 Are you sure you want to continue connecting (yes/no)?
1048 .Cm VerifyHostKeyDNS
1051 for more information.
1052 .Sh SSH-BASED VIRTUAL PRIVATE NETWORKS
1054 contains support for Virtual Private Network (VPN) tunnelling
1057 network pseudo-device,
1058 allowing two networks to be joined securely.
1061 configuration option
1063 controls whether the server supports this,
1064 and at what level (layer 2 or 3 traffic).
1066 The following example would connect client network 10.0.50.0/24
1067 with remote network 10.0.99.0/24, provided that the SSH server
1068 running on the gateway to the remote network,
1069 at 192.168.1.15, allows it:
1070 .Bd -literal -offset indent
1071 # ssh -f -w 0:1 192.168.1.15 true
1072 # ifconfig tun0 10.0.50.1 10.0.99.1 netmask 255.255.255.252
1075 Client access may be more finely tuned via the
1076 .Pa /root/.ssh/authorized_keys
1077 file (see below) and the
1080 The following entry would permit connections on the first
1084 and on the second device from user
1089 .Dq forced-commands-only :
1090 .Bd -literal -offset 2n
1091 tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane
1092 tunnel="2",command="sh /etc/netstart tun1" ssh-rsa ... john
1095 Since a SSH-based setup entails a fair amount of overhead,
1096 it may be more suited to temporary setups,
1097 such as for wireless VPNs.
1098 More permanent VPNs are better provided by tools such as
1104 will normally set the following environment variables:
1105 .Bl -tag -width "SSH_ORIGINAL_COMMAND"
1109 variable indicates the location of the X11 server.
1110 It is automatically set by
1112 to point to a value of the form
1116 indicates the host where the shell runs, and
1118 is an integer \*(Ge 1.
1120 uses this special value to forward X11 connections over the secure
1122 The user should normally not set
1125 will render the X11 connection insecure (and will require the user to
1126 manually copy any required authorization cookies).
1128 Set to the path of the user's home directory.
1132 set for compatibility with systems that use this variable.
1134 Set to the path of the user's mailbox.
1138 as specified when compiling
1143 needs a passphrase, it will read the passphrase from the current
1144 terminal if it was run from a terminal.
1147 does not have a terminal associated with it but
1151 are set, it will execute the program specified by
1153 and open an X11 window to read the passphrase.
1154 This is particularly useful when calling
1159 (Note that on some machines it
1160 may be necessary to redirect the input from
1163 .It Ev SSH_AUTH_SOCK
1164 Identifies the path of a
1166 socket used to communicate with the agent.
1167 .It Ev SSH_CONNECTION
1168 Identifies the client and server ends of the connection.
1169 The variable contains
1170 four space-separated values: client IP address, client port number,
1171 server IP address, and server port number.
1172 .It Ev SSH_ORIGINAL_COMMAND
1173 This variable contains the original command line if a forced command
1175 It can be used to extract the original arguments.
1177 This is set to the name of the tty (path to the device) associated
1178 with the current shell or command.
1179 If the current session has no tty,
1180 this variable is not set.
1182 This variable is set to indicate the present time zone if it
1183 was set when the daemon was started (i.e., the daemon passes the value
1184 on to new connections).
1186 Set to the name of the user logging in.
1192 .Pa ~/.ssh/environment ,
1193 and adds lines of the format
1195 to the environment if the file exists and users are allowed to
1196 change their environment.
1197 For more information, see the
1198 .Cm PermitUserEnvironment
1202 .Bl -tag -width Ds -compact
1204 This file is used for host-based authentication (see above).
1205 On some machines this file may need to be
1206 world-readable if the user's home directory is on an NFS partition,
1210 Additionally, this file must be owned by the user,
1211 and must not have write permissions for anyone else.
1213 permission for most machines is read/write for the user, and not
1214 accessible by others.
1217 This file is used in exactly the same way as
1219 but allows host-based authentication without permitting login with
1222 .It ~/.ssh/authorized_keys
1223 Lists the public keys (RSA/DSA) that can be used for logging in as this user.
1224 The format of this file is described in the
1227 This file is not highly sensitive, but the recommended
1228 permissions are read/write for the user, and not accessible by others.
1231 This is the per-user configuration file.
1232 The file format and configuration options are described in
1234 Because of the potential for abuse, this file must have strict permissions:
1235 read/write for the user, and not accessible by others.
1237 .It ~/.ssh/environment
1238 Contains additional definitions for environment variables; see
1245 Contains the private key for authentication.
1247 contain sensitive data and should be readable by the user but not
1248 accessible by others (read/write/execute).
1250 will simply ignore a private key file if it is accessible by others.
1251 It is possible to specify a passphrase when
1252 generating the key which will be used to encrypt the
1253 sensitive part of this file using 3DES.
1255 .It ~/.ssh/identity.pub
1256 .It ~/.ssh/id_dsa.pub
1257 .It ~/.ssh/id_rsa.pub
1258 Contains the public key for authentication.
1260 sensitive and can (but need not) be readable by anyone.
1262 .It ~/.ssh/known_hosts
1263 Contains a list of host keys for all hosts the user has logged into
1264 that are not already in the systemwide list of known host keys.
1267 for further details of the format of this file.
1270 Commands in this file are executed by
1272 when the user logs in, just before the user's shell (or command) is
1276 manual page for more information.
1278 .It /etc/hosts.equiv
1279 This file is for host-based authentication (see above).
1280 It should only be writable by root.
1282 .It /etc/shosts.equiv
1283 This file is used in exactly the same way as
1285 but allows host-based authentication without permitting login with
1288 .It Pa /etc/ssh/ssh_config
1289 Systemwide configuration file.
1290 The file format and configuration options are described in
1293 .It /etc/ssh/ssh_host_key
1294 .It /etc/ssh/ssh_host_dsa_key
1295 .It /etc/ssh/ssh_host_rsa_key
1296 These three files contain the private parts of the host keys
1297 and are used for host-based authentication.
1298 If protocol version 1 is used,
1300 must be setuid root, since the host key is readable only by root.
1301 For protocol version 2,
1305 to access the host keys,
1306 eliminating the requirement that
1308 be setuid root when host-based authentication is used.
1313 .It /etc/ssh/ssh_known_hosts
1314 Systemwide list of known host keys.
1315 This file should be prepared by the
1316 system administrator to contain the public host keys of all machines in the
1318 It should be world-readable.
1321 for further details of the format of this file.
1324 Commands in this file are executed by
1326 when the user logs in, just before the user's shell (or command) is started.
1329 manual page for more information.
1349 .%T "SSH Protocol Architecture"
1350 .%N draft-ietf-secsh-architecture-12.txt
1352 .%O work in progress material
1355 OpenSSH is a derivative of the original and free
1356 ssh 1.2.12 release by Tatu Ylonen.
1357 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1358 Theo de Raadt and Dug Song
1359 removed many bugs, re-added newer features and
1361 Markus Friedl contributed the support for SSH
1362 protocol versions 1.5 and 2.0.
projects / FreeBSD / FreeBSD.git / blob