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 1.231 2005/12/31 01:38:45 stevesk 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/IP 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/IP 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
481 .It RhostsRSAAuthentication
482 .It RSAAuthentication
484 .It ServerAliveInterval
485 .It ServerAliveCountMax
487 .It StrictHostKeyChecking
491 .It UsePrivilegedPort
493 .It UserKnownHostsFile
498 Port to connect to on the remote host.
499 This can be specified on a
500 per-host basis in the configuration file.
503 Causes all warning and diagnostic messages to be suppressed.
506 .Oo Ar bind_address : Oc
507 .Ar port : host : hostport
510 Specifies that the given port on the remote (server) host is to be
511 forwarded to the given host and port on the local side.
512 This works by allocating a socket to listen to
514 on the remote side, and whenever a connection is made to this port, the
515 connection is forwarded over the secure channel, and a connection is
520 from the local machine.
522 Port forwardings can also be specified in the configuration file.
523 Privileged ports can be forwarded only when
524 logging in as root on the remote machine.
525 IPv6 addresses can be specified by enclosing the address in square braces or
526 using an alternative syntax:
529 .Op Ar bind_address No /
530 .Ar host No / Ar port No /
535 By default, the listening socket on the server will be bound to the loopback
537 This may be overriden by specifying a
543 indicates that the remote socket should listen on all interfaces.
546 will only succeed if the server's
548 option is enabled (see
549 .Xr sshd_config 5 ) .
551 Specifies the location of a control socket for connection sharing.
552 Refer to the description of
560 May be used to request invocation of a subsystem on the remote system.
561 Subsystems are a feature of the SSH2 protocol which facilitate the use
562 of SSH as a secure transport for other applications (eg.\&
564 The subsystem is specified as the remote command.
566 Disable pseudo-tty allocation.
568 Force pseudo-tty allocation.
569 This can be used to execute arbitrary
570 screen-based programs on a remote machine, which can be very useful,
571 e.g., when implementing menu services.
574 options force tty allocation, even if
578 Display the version number and exit.
583 to print debugging messages about its progress.
585 debugging connection, authentication, and configuration problems.
588 options increase the verbosity.
590 .It Fl w Ar tunnel : Ns Ar tunnel
601 The devices may be specified by numerical ID or the keyword
603 which uses the next available tunnel device.
609 Enables X11 forwarding.
610 This can also be specified on a per-host basis in a configuration file.
612 X11 forwarding should be enabled with caution.
613 Users with the ability to bypass file permissions on the remote host
614 (for the user's X authorization database)
615 can access the local X11 display through the forwarded connection.
616 An attacker may then be able to perform activities such as keystroke monitoring.
618 For this reason, X11 forwarding is subjected to X11 SECURITY extension
619 restrictions by default.
624 .Cm ForwardX11Trusted
627 for more information.
629 Disables X11 forwarding.
631 Enables trusted X11 forwarding.
632 Trusted X11 forwardings are not subjected to the X11 SECURITY extension
637 may additionally obtain configuration data from
638 a per-user configuration file and a system-wide configuration file.
639 The file format and configuration options are described in
643 exits with the exit status of the remote command or with 255
644 if an error occurred.
646 The OpenSSH SSH client supports OpenSSH protocols 1 and 2.
647 Protocol 2 is the default, with
649 falling back to protocol 1 if it detects protocol 2 is unsupported.
650 These settings may be altered using the
654 or enforced using the
659 Both protocols support similar authentication methods,
660 but protocol 2 is preferred since
661 it provides additional mechanisms for confidentiality
662 (the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour)
663 and integrity (hmac-md5, hmac-sha1, hmac-ripemd160).
664 Protocol 1 lacks a strong mechanism for ensuring the
665 integrity of the connection.
667 The methods available for authentication are:
668 host-based authentication,
669 public key authentication,
670 challenge-response authentication,
671 and password authentication.
672 Authentication methods are tried in the order specified above,
673 though protocol 2 has a configuration option to change the default order:
674 .Cm PreferredAuthentications .
676 Host-based authentication works as follows:
677 If the machine the user logs in from is listed in
680 .Pa /etc/shosts.equiv
681 on the remote machine, and the user names are
682 the same on both sides, or if the files
686 exist in the user's home directory on the
687 remote machine and contain a line containing the name of the client
688 machine and the name of the user on that machine, the user is
689 considered for login.
690 Additionally, the server
692 be able to verify the client's
693 host key (see the description of
694 .Pa /etc/ssh/ssh_known_hosts
696 .Pa ~/.ssh/known_hosts ,
698 for login to be permitted.
699 This authentication method closes security holes due to IP
700 spoofing, DNS spoofing, and routing spoofing.
701 [Note to the administrator:
702 .Pa /etc/hosts.equiv ,
704 and the rlogin/rsh protocol in general, are inherently insecure and should be
705 disabled if security is desired.]
707 Public key authentication works as follows:
708 The scheme is based on public-key cryptography,
710 where encryption and decryption are done using separate keys,
711 and it is unfeasible to derive the decryption key from the encryption key.
712 The idea is that each user creates a public/private
713 key pair for authentication purposes.
714 The server knows the public key, and only the user knows the private key.
716 implements public key authentication protocol automatically,
717 using either the RSA or DSA algorithms.
718 Protocol 1 is restricted to using only RSA keys,
719 but protocol 2 may use either.
724 contains a brief discussion of the two algorithms.
727 .Pa ~/.ssh/authorized_keys
728 lists the public keys that are permitted for logging in.
729 When the user logs in, the
731 program tells the server which key pair it would like to use for
733 The client proves that it has access to the private key
734 and the server checks that the corresponding public key
735 is authorized to accept the account.
737 The user creates his/her key pair by running
739 This stores the private key in
747 and stores the public key in
748 .Pa ~/.ssh/identity.pub
750 .Pa ~/.ssh/id_dsa.pub
753 .Pa ~/.ssh/id_rsa.pub
755 in the user's home directory.
756 The user should then copy the public key
758 .Pa ~/.ssh/authorized_keys
759 in his/her home directory on the remote machine.
762 file corresponds to the conventional
764 file, and has one key
765 per line, though the lines can be very long.
766 After this, the user can log in without giving the password.
768 The most convenient way to use public key authentication may be with an
769 authentication agent.
772 for more information.
774 Challenge-response authentication works as follows:
775 The server sends an arbitrary
777 text, and prompts for a response.
778 Protocol 2 allows multiple challenges and responses;
779 protocol 1 is restricted to just one challenge/response.
780 Examples of challenge-response authentication include
781 BSD Authentication (see
783 and PAM (some non-OpenBSD systems).
785 Finally, if other authentication methods fail,
787 prompts the user for a password.
788 The password is sent to the remote
789 host for checking; however, since all communications are encrypted,
790 the password cannot be seen by someone listening on the network.
791 .Sh LOGIN SESSION AND REMOTE EXECUTION
792 When the user's identity has been accepted by the server, the server
793 either executes the given command, or logs into the machine and gives
794 the user a normal shell on the remote machine.
795 All communication with
796 the remote command or shell will be automatically encrypted.
798 If a pseudo-terminal has been allocated (normal login session), the
799 user may use the escape characters noted below.
801 If no pseudo-tty has been allocated,
802 the session is transparent and can be used to reliably transfer binary data.
803 On most systems, setting the escape character to
805 will also make the session transparent even if a tty is used.
807 The session terminates when the command or shell on the remote
808 machine exits and all X11 and TCP/IP connections have been closed.
809 .Sh ESCAPE CHARACTERS
810 When a pseudo-terminal has been requested,
812 supports a number of functions through the use of an escape character.
814 A single tilde character can be sent as
816 or by following the tilde by a character other than those described below.
817 The escape character must always follow a newline to be interpreted as
819 The escape character can be changed in configuration files using the
821 configuration directive or on the command line by the
825 The supported escapes (assuming the default
835 List forwarded connections.
839 at logout when waiting for forwarded connection / X11 sessions to terminate.
841 Display a list of escape characters.
843 Send a BREAK to the remote system
844 (only useful for SSH protocol version 2 and if the peer supports it).
847 Currently this allows the addition of port forwardings using the
852 It also allows the cancellation of existing remote port-forwardings
855 .Ic !\& Ns Ar command
856 allows the user to execute a local command if the
857 .Ic PermitLocalCommand
860 Basic help is available, using the
864 Request rekeying of the connection
865 (only useful for SSH protocol version 2 and if the peer supports it).
867 .Sh X11 AND TCP FORWARDING
872 (or see the description of the
878 and the user is using X11 (the
880 environment variable is set), the connection to the X11 display is
881 automatically forwarded to the remote side in such a way that any X11
882 programs started from the shell (or command) will go through the
883 encrypted channel, and the connection to the real X server will be made
884 from the local machine.
885 The user should not manually set
887 Forwarding of X11 connections can be
888 configured on the command line or in configuration files.
894 will point to the server machine, but with a display number greater than zero.
895 This is normal, and happens because
899 X server on the server machine for forwarding the
900 connections over the encrypted channel.
903 will also automatically set up Xauthority data on the server machine.
904 For this purpose, it will generate a random authorization cookie,
905 store it in Xauthority on the server, and verify that any forwarded
906 connections carry this cookie and replace it by the real cookie when
907 the connection is opened.
908 The real authentication cookie is never
909 sent to the server machine (and no cookies are sent in the plain).
915 (or see the description of the
920 the user is using an authentication agent, the connection to the agent
921 is automatically forwarded to the remote side.
923 Forwarding of arbitrary TCP/IP connections over the secure channel can
924 be specified either on the command line or in a configuration file.
925 One possible application of TCP/IP forwarding is a secure connection to an
926 electronic purse; another is going through firewalls.
927 .Sh SERVER AUTHENTICATION
929 automatically maintains and checks a database containing
930 identifications for all hosts it has ever been used with.
931 Host keys are stored in
932 .Pa ~/.ssh/known_hosts
933 in the user's home directory.
934 Additionally, the file
935 .Pa /etc/ssh/ssh_known_hosts
936 is automatically checked for known hosts.
937 Any new hosts are automatically added to the user's file.
938 If a host's identification ever changes,
940 warns about this and disables password authentication to prevent a
941 trojan horse from getting the user's password.
942 Another purpose of this mechanism is to prevent man-in-the-middle attacks
943 which could otherwise be used to circumvent the encryption.
945 .Cm StrictHostKeyChecking
946 option can be used to prevent logins to machines whose
947 host key is not known or has changed.
950 can be configured to verify host identification using fingerprint resource
951 records (SSHFP) published in DNS.
954 option can be used to control how DNS lookups are performed.
955 SSHFP resource records can be generated using
959 will normally set the following environment variables:
960 .Bl -tag -width LOGNAME
964 variable indicates the location of the X11 server.
965 It is automatically set by
967 to point to a value of the form
969 where hostname indicates
970 the host where the shell runs, and n is an integer \*(Ge 1.
972 uses this special value to forward X11 connections over the secure
974 The user should normally not set
977 will render the X11 connection insecure (and will require the user to
978 manually copy any required authorization cookies).
980 Set to the path of the user's home directory.
984 set for compatibility with systems that use this variable.
986 Set to the path of the user's mailbox.
990 as specified when compiling
995 needs a passphrase, it will read the passphrase from the current
996 terminal if it was run from a terminal.
999 does not have a terminal associated with it but
1003 are set, it will execute the program specified by
1005 and open an X11 window to read the passphrase.
1006 This is particularly useful when calling
1011 (Note that on some machines it
1012 may be necessary to redirect the input from
1015 .It Ev SSH_AUTH_SOCK
1016 Identifies the path of a unix-domain socket used to communicate with the
1018 .It Ev SSH_CONNECTION
1019 Identifies the client and server ends of the connection.
1020 The variable contains
1021 four space-separated values: client ip-address, client port number,
1022 server ip-address and server port number.
1023 .It Ev SSH_ORIGINAL_COMMAND
1024 The variable contains the original command line if a forced command
1026 It can be used to extract the original arguments.
1028 This is set to the name of the tty (path to the device) associated
1029 with the current shell or command.
1030 If the current session has no tty,
1031 this variable is not set.
1033 This variable is set to indicate the present time zone if it
1034 was set when the daemon was started (i.e., the daemon passes the value
1035 on to new connections).
1037 Set to the name of the user logging in.
1043 .Pa ~/.ssh/environment ,
1044 and adds lines of the format
1046 to the environment if the file exists and if users are allowed to
1047 change their environment.
1048 For more information, see the
1049 .Cm PermitUserEnvironment
1054 .It Pa ~/.ssh/known_hosts
1055 Records host keys for all hosts the user has logged into that are not
1057 .Pa /etc/ssh/ssh_known_hosts .
1060 .It Pa ~/.ssh/identity, ~/.ssh/id_dsa, ~/.ssh/id_rsa
1061 Contains the authentication identity of the user.
1062 They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively.
1064 contain sensitive data and should be readable by the user but not
1065 accessible by others (read/write/execute).
1068 ignores a private key file if it is accessible by others.
1069 It is possible to specify a passphrase when
1070 generating the key; the passphrase will be used to encrypt the
1071 sensitive part of this file using 3DES.
1072 .It Pa ~/.ssh/identity.pub, ~/.ssh/id_dsa.pub, ~/.ssh/id_rsa.pub
1073 Contains the public key for authentication (public part of the
1074 identity file in human-readable form).
1076 .Pa ~/.ssh/identity.pub
1077 file should be added to the file
1078 .Pa ~/.ssh/authorized_keys
1080 where the user wishes to log in using protocol version 1 RSA authentication.
1082 .Pa ~/.ssh/id_dsa.pub
1084 .Pa ~/.ssh/id_rsa.pub
1085 file should be added to
1086 .Pa ~/.ssh/authorized_keys
1088 where the user wishes to log in using protocol version 2 DSA/RSA authentication.
1090 sensitive and can (but need not) be readable by anyone.
1092 never used automatically and are not necessary; they are only provided for
1093 the convenience of the user.
1094 .It Pa ~/.ssh/config
1095 This is the per-user configuration file.
1096 The file format and configuration options are described in
1098 Because of the potential for abuse, this file must have strict permissions:
1099 read/write for the user, and not accessible by others.
1100 .It Pa ~/.ssh/authorized_keys
1101 Lists the public keys (RSA/DSA) that can be used for logging in as this user.
1102 The format of this file is described in the
1105 In the simplest form the format is the same as the
1108 This file is not highly sensitive, but the recommended
1109 permissions are read/write for the user, and not accessible by others.
1110 .It Pa /etc/ssh/ssh_known_hosts
1111 Systemwide list of known host keys.
1112 This file should be prepared by the
1113 system administrator to contain the public host keys of all machines in the
1115 This file should be world-readable.
1117 public keys, one per line, in the following format (fields separated
1118 by spaces): system name, public key and optional comment field.
1119 When different names are used
1120 for the same machine, all such names should be listed, separated by
1122 The format is described in the
1126 The canonical system name (as returned by name servers) is used by
1128 to verify the client host when logging in; other names are needed because
1130 does not convert the user-supplied name to a canonical name before
1131 checking the key, because someone with access to the name servers
1132 would then be able to fool host authentication.
1133 .It Pa /etc/ssh/ssh_config
1134 Systemwide configuration file.
1135 The file format and configuration options are described in
1137 .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key
1138 These three files contain the private parts of the host keys
1140 .Cm RhostsRSAAuthentication
1142 .Cm HostbasedAuthentication .
1143 If the protocol version 1
1144 .Cm RhostsRSAAuthentication
1147 must be setuid root, since the host key is readable only by root.
1148 For protocol version 2,
1152 to access the host keys for
1153 .Cm HostbasedAuthentication .
1154 This eliminates the requirement that
1156 be setuid root when that authentication method is used.
1161 This file is used in
1162 .Cm RhostsRSAAuthentication
1164 .Cm HostbasedAuthentication
1165 authentication to list the
1166 host/user pairs that are permitted to log in.
1167 (Note that this file is
1168 also used by rlogin and rsh, which makes using this file insecure.)
1169 Each line of the file contains a host name (in the canonical form
1170 returned by name servers), and then a user name on that host,
1171 separated by a space.
1172 On some machines this file may need to be
1173 world-readable if the user's home directory is on a NFS partition,
1177 Additionally, this file must be owned by the user,
1178 and must not have write permissions for anyone else.
1180 permission for most machines is read/write for the user, and not
1181 accessible by others.
1185 allows authentication only in combination with client host key
1186 authentication before permitting log in.
1187 If the server machine does not have the client's host key in
1188 .Pa /etc/ssh/ssh_known_hosts ,
1190 .Pa ~/.ssh/known_hosts .
1191 The easiest way to do this is to
1192 connect back to the client from the server machine using ssh; this
1193 will automatically add the host key to
1194 .Pa ~/.ssh/known_hosts .
1196 This file is used exactly the same way as
1199 having this file is to be able to use
1200 .Cm RhostsRSAAuthentication
1202 .Cm HostbasedAuthentication
1203 authentication without permitting login with
1207 .It Pa /etc/hosts.equiv
1208 This file is used during
1209 .Cm RhostsRSAAuthentication
1211 .Cm HostbasedAuthentication
1214 canonical hosts names, one per line (the full format is described in the
1217 If the client host is found in this file, login is
1218 automatically permitted provided client and server user names are the
1220 Additionally, successful client host key authentication is required.
1221 This file should only be writable by root.
1222 .It Pa /etc/shosts.equiv
1223 This file is processed exactly as
1224 .Pa /etc/hosts.equiv .
1225 This file may be useful to permit logins using
1227 but not using rsh/rlogin.
1228 .It Pa /etc/ssh/sshrc
1229 Commands in this file are executed by
1231 when the user logs in just before the user's shell (or command) is started.
1234 manual page for more information.
1236 Commands in this file are executed by
1238 when the user logs in just before the user's shell (or command) is
1242 manual page for more information.
1243 .It Pa ~/.ssh/environment
1244 Contains additional definitions for environment variables, see section
1267 .%T "SSH Protocol Architecture"
1268 .%N draft-ietf-secsh-architecture-12.txt
1270 .%O work in progress material
1273 OpenSSH is a derivative of the original and free
1274 ssh 1.2.12 release by Tatu Ylonen.
1275 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1276 Theo de Raadt and Dug Song
1277 removed many bugs, re-added newer features and
1279 Markus Friedl contributed the support for SSH
1280 protocol versions 1.5 and 2.0.
andersk / openssh.git / blob