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 $
38 .Dd September 25, 1999
43 .Nd OpenSSH SSH client (remote login program)
46 .Op Fl 1246AaCfgkMNnqsTtVvXxY
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 .Op Fl w Ar tunnel : Ns Ar tunnel
82 .Oo Ar user Ns @ Oc Ns Ar hostname
87 (SSH client) is a program for logging into a remote machine and for
88 executing commands on a remote machine.
89 It is intended to replace rlogin and rsh,
90 and provide secure encrypted communications between
91 two untrusted hosts over an insecure network.
92 X11 connections and arbitrary TCP ports
93 can also be forwarded over the secure channel.
96 connects and logs into the specified
102 his/her identity to the remote machine using one of several methods
103 depending on the protocol version used (see below).
108 it is executed on the remote host instead of a login shell.
110 The options are as follows:
115 to try protocol version 1 only.
119 to try protocol version 2 only.
123 to use IPv4 addresses only.
127 to use IPv6 addresses only.
129 Enables forwarding of the authentication agent connection.
130 This can also be specified on a per-host basis in a configuration file.
132 Agent forwarding should be enabled with caution.
133 Users with the ability to bypass file permissions on the remote host
134 (for the agent's Unix-domain socket)
135 can access the local agent through the forwarded connection.
136 An attacker cannot obtain key material from the agent,
137 however they can perform operations on the keys that enable them to
138 authenticate using the identities loaded into the agent.
140 Disables forwarding of the authentication agent connection.
141 .It Fl b Ar bind_address
144 on the local machine as the source address
146 Only useful on systems with more than one address.
148 Requests compression of all data (including stdin, stdout, stderr, and
149 data for forwarded X11 and TCP connections).
150 The compression algorithm is the same used by
154 can be controlled by the
156 option for protocol version 1.
157 Compression is desirable on modem lines and other
158 slow connections, but will only slow down things on fast networks.
159 The default value can be set on a host-by-host basis in the
160 configuration files; see the
163 .It Fl c Ar cipher_spec
164 Selects the cipher specification for encrypting the session.
166 Protocol version 1 allows specification of a single cipher.
167 The supported values are
173 (triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
174 It is believed to be secure.
176 is a fast block cipher; it appears very secure and is much faster than
179 is only supported in the
181 client for interoperability with legacy protocol 1 implementations
182 that do not support the
185 Its use is strongly discouraged due to cryptographic weaknesses.
189 For protocol version 2,
191 is a comma-separated list of ciphers
192 listed in order of preference.
193 The supported ciphers are:
208 .Bd -literal -offset indent
209 aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
210 arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
211 aes192-ctr,aes256-ctr
215 .Oo Ar bind_address : Oc
221 application-level port forwarding.
222 This works by allocating a socket to listen to
224 on the local side, optionally bound to the specified
226 Whenever a connection is made to this port, the
227 connection is forwarded over the secure channel, and the application
228 protocol is then used to determine where to connect to from the
230 Currently the SOCKS4 and SOCKS5 protocols are supported, and
232 will act as a SOCKS server.
233 Only root can forward privileged ports.
234 Dynamic port forwardings can also be specified in the configuration file.
236 IPv6 addresses can be specified with an alternative syntax:
239 .Op Ar bind_address No /
243 or by enclosing the address in square brackets.
244 Only the superuser can forward privileged ports.
245 By default, the local port is bound in accordance with the
250 may be used to bind the connection to a specific address.
255 indicates that the listening port be bound for local use only, while an
258 indicates that the port should be available from all interfaces.
259 .It Fl e Ar escape_char
260 Sets the escape character for sessions with a pty (default:
262 The escape character is only recognized at the beginning of a line.
263 The escape character followed by a dot
265 closes the connection;
266 followed by control-Z suspends the connection;
267 and followed by itself sends the escape character once.
268 Setting the character to
270 disables any escapes and makes the session fully transparent.
271 .It Fl F Ar configfile
272 Specifies an alternative per-user configuration file.
273 If a configuration file is given on the command line,
274 the system-wide configuration file
275 .Pq Pa /etc/ssh/ssh_config
277 The default for the per-user configuration file is
282 to go to background just before command execution.
285 is going to ask for passwords or passphrases, but the user
286 wants it in the background.
289 The recommended way to start X11 programs at a remote site is with
291 .Ic ssh -f host xterm .
293 Allows remote hosts to connect to local forwarded ports.
294 .It Fl I Ar smartcard_device
297 should use to communicate with a smartcard used for storing the user's
299 This option is only available if support for smartcard devices
300 is compiled in (default is no support).
301 .It Fl i Ar identity_file
302 Selects a file from which the identity (private key) for
303 RSA or DSA authentication is read.
306 for protocol version 1, and
310 for protocol version 2.
311 Identity files may also be specified on
312 a per-host basis in the configuration file.
313 It is possible to have multiple
315 options (and multiple identities specified in
316 configuration files).
318 Disables forwarding (delegation) of GSSAPI credentials to the server.
321 .Oo Ar bind_address : Oc
322 .Ar port : host : hostport
325 Specifies that the given port on the local (client) host is to be
326 forwarded to the given host and port on the remote side.
327 This works by allocating a socket to listen to
329 on the local side, optionally bound to the specified
331 Whenever a connection is made to this port, the
332 connection is forwarded over the secure channel, and a connection is
337 from the remote machine.
338 Port forwardings can also be specified in the configuration file.
339 IPv6 addresses can be specified with an alternative syntax:
342 .Op Ar bind_address No /
343 .Ar port No / Ar host No /
347 or by enclosing the address in square brackets.
348 Only the superuser can forward privileged ports.
349 By default, the local port is bound in accordance with the
354 may be used to bind the connection to a specific address.
359 indicates that the listening port be bound for local use only, while an
362 indicates that the port should be available from all interfaces.
363 .It Fl l Ar login_name
364 Specifies the user to log in as on the remote machine.
365 This also may be specified on a per-host basis in the configuration file.
371 mode for connection sharing.
378 mode with confirmation required before slave connections are accepted.
379 Refer to the description of
385 Additionally, for protocol version 2 a comma-separated list of MAC
386 (message authentication code) algorithms can
387 be specified in order of preference.
390 keyword for more information.
392 Do not execute a remote command.
393 This is useful for just forwarding ports
394 (protocol version 2 only).
398 (actually, prevents reading from stdin).
399 This must be used when
401 is run in the background.
402 A common trick is to use this to run X11 programs on a remote machine.
404 .Ic ssh -n shadows.cs.hut.fi emacs &
405 will start an emacs on shadows.cs.hut.fi, and the X11
406 connection will be automatically forwarded over an encrypted channel.
409 program will be put in the background.
410 (This does not work if
412 needs to ask for a password or passphrase; see also the
416 Control an active connection multiplexing master process.
419 option is specified, the
421 argument is interpreted and passed to the master process.
424 (check that the master process is running) and
426 (request the master to exit).
428 Can be used to give options in the format used in the configuration file.
429 This is useful for specifying options for which there is no separate
431 For full details of the options listed below, and their possible values, see
434 .Bl -tag -width Ds -offset indent -compact
438 .It ChallengeResponseAuthentication
442 .It ClearAllForwardings
445 .It ConnectionAttempts
453 .It ForwardX11Trusted
455 .It GlobalKnownHostsFile
456 .It GSSAPIAuthentication
457 .It GSSAPIDelegateCredentials
460 .It HostbasedAuthentication
461 .It HostKeyAlgorithms
466 .It KbdInteractiveDevices
471 .It NoHostAuthenticationForLocalhost
472 .It NumberOfPasswordPrompts
473 .It PasswordAuthentication
474 .It PermitLocalCommand
476 .It PreferredAuthentications
479 .It PubkeyAuthentication
482 .It RhostsRSAAuthentication
483 .It RSAAuthentication
485 .It ServerAliveInterval
486 .It ServerAliveCountMax
488 .It StrictHostKeyChecking
492 .It UsePrivilegedPort
494 .It UserKnownHostsFile
499 Port to connect to on the remote host.
500 This can be specified on a
501 per-host basis in the configuration file.
504 Causes all warning and diagnostic messages to be suppressed.
507 .Oo Ar bind_address : Oc
508 .Ar port : host : hostport
511 Specifies that the given port on the remote (server) host is to be
512 forwarded to the given host and port on the local side.
513 This works by allocating a socket to listen to
515 on the remote side, and whenever a connection is made to this port, the
516 connection is forwarded over the secure channel, and a connection is
521 from the local machine.
523 Port forwardings can also be specified in the configuration file.
524 Privileged ports can be forwarded only when
525 logging in as root on the remote machine.
526 IPv6 addresses can be specified by enclosing the address in square braces or
527 using an alternative syntax:
530 .Op Ar bind_address No /
531 .Ar host No / Ar port No /
536 By default, the listening socket on the server will be bound to the loopback
538 This may be overriden by specifying a
544 indicates that the remote socket should listen on all interfaces.
547 will only succeed if the server's
549 option is enabled (see
550 .Xr sshd_config 5 ) .
552 Specifies the location of a control socket for connection sharing.
553 Refer to the description of
561 May be used to request invocation of a subsystem on the remote system.
562 Subsystems are a feature of the SSH2 protocol which facilitate the use
563 of SSH as a secure transport for other applications (eg.\&
565 The subsystem is specified as the remote command.
567 Disable pseudo-tty allocation.
569 Force pseudo-tty allocation.
570 This can be used to execute arbitrary
571 screen-based programs on a remote machine, which can be very useful,
572 e.g., when implementing menu services.
575 options force tty allocation, even if
579 Display the version number and exit.
584 to print debugging messages about its progress.
586 debugging connection, authentication, and configuration problems.
589 options increase the verbosity.
591 .It Fl w Ar tunnel : Ns Ar tunnel
602 The devices may be specified by numerical ID or the keyword
604 which uses the next available tunnel device.
610 Enables X11 forwarding.
611 This can also be specified on a per-host basis in a configuration file.
613 X11 forwarding should be enabled with caution.
614 Users with the ability to bypass file permissions on the remote host
615 (for the user's X authorization database)
616 can access the local X11 display through the forwarded connection.
617 An attacker may then be able to perform activities such as keystroke monitoring.
619 For this reason, X11 forwarding is subjected to X11 SECURITY extension
620 restrictions by default.
625 .Cm ForwardX11Trusted
628 for more information.
630 Disables X11 forwarding.
632 Enables trusted X11 forwarding.
633 Trusted X11 forwardings are not subjected to the X11 SECURITY extension
638 may additionally obtain configuration data from
639 a per-user configuration file and a system-wide configuration file.
640 The file format and configuration options are described in
644 exits with the exit status of the remote command or with 255
645 if an error occurred.
647 The OpenSSH SSH client supports SSH protocols 1 and 2.
648 Protocol 2 is the default, with
650 falling back to protocol 1 if it detects protocol 2 is unsupported.
651 These settings may be altered using the
655 or enforced using the
660 Both protocols support similar authentication methods,
661 but protocol 2 is preferred since
662 it provides additional mechanisms for confidentiality
663 (the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour)
664 and integrity (hmac-md5, hmac-sha1, hmac-ripemd160).
665 Protocol 1 lacks a strong mechanism for ensuring the
666 integrity of the connection.
668 The methods available for authentication are:
669 host-based authentication,
670 public key authentication,
671 challenge-response authentication,
672 and password authentication.
673 Authentication methods are tried in the order specified above,
674 though protocol 2 has a configuration option to change the default order:
675 .Cm PreferredAuthentications .
677 Host-based authentication works as follows:
678 If the machine the user logs in from is listed in
681 .Pa /etc/shosts.equiv
682 on the remote machine, and the user names are
683 the same on both sides, or if the files
687 exist in the user's home directory on the
688 remote machine and contain a line containing the name of the client
689 machine and the name of the user on that machine, the user is
690 considered for login.
691 Additionally, the server
693 be able to verify the client's
694 host key (see the description of
695 .Pa /etc/ssh/ssh_known_hosts
697 .Pa ~/.ssh/known_hosts ,
699 for login to be permitted.
700 This authentication method closes security holes due to IP
701 spoofing, DNS spoofing, and routing spoofing.
702 [Note to the administrator:
703 .Pa /etc/hosts.equiv ,
705 and the rlogin/rsh protocol in general, are inherently insecure and should be
706 disabled if security is desired.]
708 Public key authentication works as follows:
709 The scheme is based on public-key cryptography,
711 where encryption and decryption are done using separate keys,
712 and it is unfeasible to derive the decryption key from the encryption key.
713 The idea is that each user creates a public/private
714 key pair for authentication purposes.
715 The server knows the public key, and only the user knows the private key.
717 implements public key authentication protocol automatically,
718 using either the RSA or DSA algorithms.
719 Protocol 1 is restricted to using only RSA keys,
720 but protocol 2 may use either.
725 contains a brief discussion of the two algorithms.
728 .Pa ~/.ssh/authorized_keys
729 lists the public keys that are permitted for logging in.
730 When the user logs in, the
732 program tells the server which key pair it would like to use for
734 The client proves that it has access to the private key
735 and the server checks that the corresponding public key
736 is authorized to accept the account.
738 The user creates his/her key pair by running
740 This stores the private key in
748 and stores the public key in
749 .Pa ~/.ssh/identity.pub
751 .Pa ~/.ssh/id_dsa.pub
754 .Pa ~/.ssh/id_rsa.pub
756 in the user's home directory.
757 The user should then copy the public key
759 .Pa ~/.ssh/authorized_keys
760 in his/her home directory on the remote machine.
763 file corresponds to the conventional
765 file, and has one key
766 per line, though the lines can be very long.
767 After this, the user can log in without giving the password.
769 The most convenient way to use public key authentication may be with an
770 authentication agent.
773 for more information.
775 Challenge-response authentication works as follows:
776 The server sends an arbitrary
778 text, and prompts for a response.
779 Protocol 2 allows multiple challenges and responses;
780 protocol 1 is restricted to just one challenge/response.
781 Examples of challenge-response authentication include
782 BSD Authentication (see
784 and PAM (some non-OpenBSD systems).
786 Finally, if other authentication methods fail,
788 prompts the user for a password.
789 The password is sent to the remote
790 host for checking; however, since all communications are encrypted,
791 the password cannot be seen by someone listening on the network.
794 automatically maintains and checks a database containing
795 identification for all hosts it has ever been used with.
796 Host keys are stored in
797 .Pa ~/.ssh/known_hosts
798 in the user's home directory.
799 Additionally, the file
800 .Pa /etc/ssh/ssh_known_hosts
801 is automatically checked for known hosts.
802 Any new hosts are automatically added to the user's file.
803 If a host's identification ever changes,
805 warns about this and disables password authentication to prevent
806 server spoofing or man-in-the-middle attacks,
807 which could otherwise be used to circumvent the encryption.
809 .Cm StrictHostKeyChecking
810 option can be used to control logins to machines whose
811 host key is not known or has changed.
813 When the user's identity has been accepted by the server, the server
814 either executes the given command, or logs into the machine and gives
815 the user a normal shell on the remote machine.
816 All communication with
817 the remote command or shell will be automatically encrypted.
819 If a pseudo-terminal has been allocated (normal login session), the
820 user may use the escape characters noted below.
822 If no pseudo-tty has been allocated,
823 the session is transparent and can be used to reliably transfer binary data.
824 On most systems, setting the escape character to
826 will also make the session transparent even if a tty is used.
828 The session terminates when the command or shell on the remote
829 machine exits and all X11 and TCP connections have been closed.
830 .Sh ESCAPE CHARACTERS
831 When a pseudo-terminal has been requested,
833 supports a number of functions through the use of an escape character.
835 A single tilde character can be sent as
837 or by following the tilde by a character other than those described below.
838 The escape character must always follow a newline to be interpreted as
840 The escape character can be changed in configuration files using the
842 configuration directive or on the command line by the
846 The supported escapes (assuming the default
856 List forwarded connections.
860 at logout when waiting for forwarded connection / X11 sessions to terminate.
862 Display a list of escape characters.
864 Send a BREAK to the remote system
865 (only useful for SSH protocol version 2 and if the peer supports it).
868 Currently this allows the addition of port forwardings using the
873 It also allows the cancellation of existing remote port-forwardings
876 .Ic !\& Ns Ar command
877 allows the user to execute a local command if the
878 .Ic PermitLocalCommand
881 Basic help is available, using the
885 Request rekeying of the connection
886 (only useful for SSH protocol version 2 and if the peer supports it).
889 Forwarding of arbitrary TCP connections over the secure channel can
890 be specified either on the command line or in a configuration file.
891 One possible application of TCP forwarding is a secure connection to a
892 mail server; another is going through firewalls.
894 In the example below, we look at encrypting communication between
895 an IRC client and server, even though the IRC server does not directly
896 support encrypted communications.
897 This works as follows:
898 the user connects to the remote host using
900 specifying a port to be used to forward connections
901 to the remote server.
902 After that it is possible to start the service which is to be encrypted
903 on the client machine,
904 connecting to the same local port,
907 will encrypt and forward the connection.
909 The following example tunnels an IRC session from client machine
913 .Dq server.example.com :
914 .Bd -literal -offset 4n
915 $ ssh -f -L 1234:localhost:6667 server.example.com sleep 10
916 $ irc -c '#users' -p 1234 pinky 127.0.0.1
919 This tunnels a connection to IRC server
920 .Dq server.example.com ,
926 It doesn't matter which port is used,
927 as long as it's greater than 1023
928 (remember, only root can open sockets on privileged ports)
929 and doesn't conflict with any ports already in use.
930 The connection is forwarded to port 6667 on the remote server,
931 since that's the standard port for IRC services.
937 and the remote command
939 is specified to allow an amount of time
940 (10 seconds, in the example)
941 to start the service which is to be tunnelled.
942 If no connections are made within the time specified,
950 (or see the description of the
956 and the user is using X11 (the
958 environment variable is set), the connection to the X11 display is
959 automatically forwarded to the remote side in such a way that any X11
960 programs started from the shell (or command) will go through the
961 encrypted channel, and the connection to the real X server will be made
962 from the local machine.
963 The user should not manually set
965 Forwarding of X11 connections can be
966 configured on the command line or in configuration files.
972 will point to the server machine, but with a display number greater than zero.
973 This is normal, and happens because
977 X server on the server machine for forwarding the
978 connections over the encrypted channel.
981 will also automatically set up Xauthority data on the server machine.
982 For this purpose, it will generate a random authorization cookie,
983 store it in Xauthority on the server, and verify that any forwarded
984 connections carry this cookie and replace it by the real cookie when
985 the connection is opened.
986 The real authentication cookie is never
987 sent to the server machine (and no cookies are sent in the plain).
993 (or see the description of the
998 the user is using an authentication agent, the connection to the agent
999 is automatically forwarded to the remote side.
1000 .Sh VERIFYING HOST KEYS
1001 When connecting to a server for the first time,
1002 a fingerprint of the server's public key is presented to the user
1004 .Cm StrictHostKeyChecking
1006 Fingerprints can be determined using
1009 .Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key
1011 If the fingerprint is already known,
1012 it can be matched and verified,
1013 and the key can be accepted.
1014 If the fingerprint is unknown,
1015 an alternative method of verification is available:
1016 SSH fingerprints verified by DNS.
1017 An additional resource record (RR),
1019 is added to a zonefile
1020 and the connecting client is able to match the fingerprint
1021 with that of the key presented.
1023 In this example, we are connecting a client to a server,
1024 .Dq host.example.com .
1025 The SSHFP resource records should first be added to the zonefile for
1027 .Bd -literal -offset indent
1028 $ ssh-keygen -f /etc/ssh/ssh_host_rsa_key.pub -r host.example.com.
1029 $ ssh-keygen -f /etc/ssh/ssh_host_dsa_key.pub -r host.example.com.
1032 The output lines will have to be added to the zonefile.
1033 To check that the zone is answering fingerprint queries:
1035 .Dl $ dig -t SSHFP host.example.com
1037 Finally the client connects:
1038 .Bd -literal -offset indent
1039 $ ssh -o "VerifyHostKeyDNS ask" host.example.com
1041 Matching host key fingerprint found in DNS.
1042 Are you sure you want to continue connecting (yes/no)?
1046 .Cm VerifyHostKeyDNS
1049 for more information.
1050 .Sh SSH-BASED VIRTUAL PRIVATE NETWORKS
1052 contains support for Virtual Private Network (VPN) tunnelling
1055 network pseudo-device,
1056 allowing two networks to be joined securely.
1059 configuration option
1061 controls whether the server supports this,
1062 and at what level (layer 2 or 3 traffic).
1064 The following example would connect client network 10.0.50.0/24
1065 with remote network 10.0.99.0/24, provided that the SSH server
1066 running on the gateway to the remote network,
1067 at 192.168.1.15, allows it:
1068 .Bd -literal -offset indent
1069 # ssh -f -w 0:1 192.168.1.15 true
1070 # ifconfig tun0 10.0.50.1 10.0.99.1 netmask 255.255.255.252
1073 Client access may be more finely tuned via the
1074 .Pa /root/.ssh/authorized_keys
1075 file (see below) and the
1078 The following entry would permit connections on the first
1082 and on the second device from user
1087 .Dq forced-commands-only :
1088 .Bd -literal -offset 2n
1089 tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane
1090 tunnel="2",command="sh /etc/netstart tun1" ssh-rsa ... john
1093 Since a SSH-based setup entails a fair amount of overhead,
1094 it may be more suited to temporary setups,
1095 such as for wireless VPNs.
1096 More permanent VPNs are better provided by tools such as
1102 will normally set the following environment variables:
1103 .Bl -tag -width "SSH_ORIGINAL_COMMAND"
1107 variable indicates the location of the X11 server.
1108 It is automatically set by
1110 to point to a value of the form
1114 indicates the host where the shell runs, and
1116 is an integer \*(Ge 1.
1118 uses this special value to forward X11 connections over the secure
1120 The user should normally not set
1123 will render the X11 connection insecure (and will require the user to
1124 manually copy any required authorization cookies).
1126 Set to the path of the user's home directory.
1130 set for compatibility with systems that use this variable.
1132 Set to the path of the user's mailbox.
1136 as specified when compiling
1141 needs a passphrase, it will read the passphrase from the current
1142 terminal if it was run from a terminal.
1145 does not have a terminal associated with it but
1149 are set, it will execute the program specified by
1151 and open an X11 window to read the passphrase.
1152 This is particularly useful when calling
1157 (Note that on some machines it
1158 may be necessary to redirect the input from
1161 .It Ev SSH_AUTH_SOCK
1162 Identifies the path of a
1164 socket used to communicate with the agent.
1165 .It Ev SSH_CONNECTION
1166 Identifies the client and server ends of the connection.
1167 The variable contains
1168 four space-separated values: client IP address, client port number,
1169 server IP address, and server port number.
1170 .It Ev SSH_ORIGINAL_COMMAND
1171 This variable contains the original command line if a forced command
1173 It can be used to extract the original arguments.
1175 This is set to the name of the tty (path to the device) associated
1176 with the current shell or command.
1177 If the current session has no tty,
1178 this variable is not set.
1180 This variable is set to indicate the present time zone if it
1181 was set when the daemon was started (i.e., the daemon passes the value
1182 on to new connections).
1184 Set to the name of the user logging in.
1190 .Pa ~/.ssh/environment ,
1191 and adds lines of the format
1193 to the environment if the file exists and users are allowed to
1194 change their environment.
1195 For more information, see the
1196 .Cm PermitUserEnvironment
1200 .Bl -tag -width Ds -compact
1202 This file is used for host-based authentication (see above).
1203 On some machines this file may need to be
1204 world-readable if the user's home directory is on an NFS partition,
1208 Additionally, this file must be owned by the user,
1209 and must not have write permissions for anyone else.
1211 permission for most machines is read/write for the user, and not
1212 accessible by others.
1215 This file is used in exactly the same way as
1217 but allows host-based authentication without permitting login with
1220 .It ~/.ssh/authorized_keys
1221 Lists the public keys (RSA/DSA) that can be used for logging in as this user.
1222 The format of this file is described in the
1225 This file is not highly sensitive, but the recommended
1226 permissions are read/write for the user, and not accessible by others.
1229 This is the per-user configuration file.
1230 The file format and configuration options are described in
1232 Because of the potential for abuse, this file must have strict permissions:
1233 read/write for the user, and not accessible by others.
1235 .It ~/.ssh/environment
1236 Contains additional definitions for environment variables; see
1243 Contains the private key for authentication.
1245 contain sensitive data and should be readable by the user but not
1246 accessible by others (read/write/execute).
1248 will simply ignore a private key file if it is accessible by others.
1249 It is possible to specify a passphrase when
1250 generating the key which will be used to encrypt the
1251 sensitive part of this file using 3DES.
1253 .It ~/.ssh/identity.pub
1254 .It ~/.ssh/id_dsa.pub
1255 .It ~/.ssh/id_rsa.pub
1256 Contains the public key for authentication.
1258 sensitive and can (but need not) be readable by anyone.
1260 .It ~/.ssh/known_hosts
1261 Contains a list of host keys for all hosts the user has logged into
1262 that are not already in the systemwide list of known host keys.
1265 for further details of the format of this file.
1268 Commands in this file are executed by
1270 when the user logs in, just before the user's shell (or command) is
1274 manual page for more information.
1276 .It /etc/hosts.equiv
1277 This file is for host-based authentication (see above).
1278 It should only be writable by root.
1280 .It /etc/shosts.equiv
1281 This file is used in exactly the same way as
1283 but allows host-based authentication without permitting login with
1286 .It Pa /etc/ssh/ssh_config
1287 Systemwide configuration file.
1288 The file format and configuration options are described in
1291 .It /etc/ssh/ssh_host_key
1292 .It /etc/ssh/ssh_host_dsa_key
1293 .It /etc/ssh/ssh_host_rsa_key
1294 These three files contain the private parts of the host keys
1295 and are used for host-based authentication.
1296 If protocol version 1 is used,
1298 must be setuid root, since the host key is readable only by root.
1299 For protocol version 2,
1303 to access the host keys,
1304 eliminating the requirement that
1306 be setuid root when host-based authentication is used.
1311 .It /etc/ssh/ssh_known_hosts
1312 Systemwide list of known host keys.
1313 This file should be prepared by the
1314 system administrator to contain the public host keys of all machines in the
1316 It should be world-readable.
1319 for further details of the format of this file.
1322 Commands in this file are executed by
1324 when the user logs in, just before the user's shell (or command) is started.
1327 manual page for more information.
1347 .%T "SSH Protocol Architecture"
1348 .%N draft-ietf-secsh-architecture-12.txt
1350 .%O work in progress material
1353 OpenSSH is a derivative of the original and free
1354 ssh 1.2.12 release by Tatu Ylonen.
1355 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1356 Theo de Raadt and Dug Song
1357 removed many bugs, re-added newer features and
1359 Markus Friedl contributed the support for SSH
1360 protocol versions 1.5 and 2.0.
projects / dragonfly.git / blob