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 1.223 2005/12/20 22:02:50 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/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 ch | ^ch | none
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
295 Specifies which smartcard device to use.
296 The argument is the device
298 should use to communicate with a smartcard used for storing the user's
300 .It Fl i Ar identity_file
301 Selects a file from which the identity (private key) for
302 RSA or DSA authentication is read.
305 for protocol version 1, and
309 for protocol version 2.
310 Identity files may also be specified on
311 a per-host basis in the configuration file.
312 It is possible to have multiple
314 options (and multiple identities specified in
315 configuration files).
317 Disables forwarding (delegation) of GSSAPI credentials to the server.
320 .Oo Ar bind_address : Oc
321 .Ar port : host : hostport
324 Specifies that the given port on the local (client) host is to be
325 forwarded to the given host and port on the remote side.
326 This works by allocating a socket to listen to
328 on the local side, optionally bound to the specified
330 Whenever a connection is made to this port, the
331 connection is forwarded over the secure channel, and a connection is
336 from the remote machine.
337 Port forwardings can also be specified in the configuration file.
338 IPv6 addresses can be specified with an alternative syntax:
341 .Op Ar bind_address No /
342 .Ar port No / Ar host No /
346 or by enclosing the address in square brackets.
347 Only the superuser can forward privileged ports.
348 By default, the local port is bound in accordance with the
353 may be used to bind the connection to a specific address.
358 indicates that the listening port be bound for local use only, while an
361 indicates that the port should be available from all interfaces.
362 .It Fl l Ar login_name
363 Specifies the user to log in as on the remote machine.
364 This also may be specified on a per-host basis in the configuration file.
370 mode for connection sharing.
371 Refer to the description of
377 Additionally, for protocol version 2 a comma-separated list of MAC
378 (message authentication code) algorithms can
379 be specified in order of preference.
382 keyword for more information.
384 Do not execute a remote command.
385 This is useful for just forwarding ports
386 (protocol version 2 only).
390 (actually, prevents reading from stdin).
391 This must be used when
393 is run in the background.
394 A common trick is to use this to run X11 programs on a remote machine.
396 .Ic ssh -n shadows.cs.hut.fi emacs &
397 will start an emacs on shadows.cs.hut.fi, and the X11
398 connection will be automatically forwarded over an encrypted channel.
401 program will be put in the background.
402 (This does not work if
404 needs to ask for a password or passphrase; see also the
408 Control an active connection multiplexing master process.
411 option is specified, the
413 argument is interpreted and passed to the master process.
416 (check that the master process is running) and
418 (request the master to exit).
420 Can be used to give options in the format used in the configuration file.
421 This is useful for specifying options for which there is no separate
423 For full details of the options listed below, and their possible values, see
426 .Bl -tag -width Ds -offset indent -compact
430 .It ChallengeResponseAuthentication
434 .It ClearAllForwardings
437 .It ConnectionAttempts
445 .It ForwardX11Trusted
447 .It GlobalKnownHostsFile
448 .It GSSAPIAuthentication
449 .It GSSAPIDelegateCredentials
452 .It HostbasedAuthentication
453 .It HostKeyAlgorithms
458 .It KbdInteractiveDevices
463 .It NoHostAuthenticationForLocalhost
464 .It NumberOfPasswordPrompts
465 .It PasswordAuthentication
466 .It PermitLocalCommand
468 .It PreferredAuthentications
471 .It PubkeyAuthentication
473 .It RhostsRSAAuthentication
474 .It RSAAuthentication
476 .It ServerAliveInterval
477 .It ServerAliveCountMax
479 .It StrictHostKeyChecking
483 .It UsePrivilegedPort
485 .It UserKnownHostsFile
490 Port to connect to on the remote host.
491 This can be specified on a
492 per-host basis in the configuration file.
495 Causes all warning and diagnostic messages to be suppressed.
498 .Oo Ar bind_address : Oc
499 .Ar port : host : hostport
502 Specifies that the given port on the remote (server) host is to be
503 forwarded to the given host and port on the local side.
504 This works by allocating a socket to listen to
506 on the remote side, and whenever a connection is made to this port, the
507 connection is forwarded over the secure channel, and a connection is
512 from the local machine.
514 Port forwardings can also be specified in the configuration file.
515 Privileged ports can be forwarded only when
516 logging in as root on the remote machine.
517 IPv6 addresses can be specified by enclosing the address in square braces or
518 using an alternative syntax:
521 .Op Ar bind_address No /
522 .Ar host No / Ar port No /
527 By default, the listening socket on the server will be bound to the loopback
529 This may be overriden by specifying a
535 indicates that the remote socket should listen on all interfaces.
538 will only succeed if the server's
540 option is enabled (see
541 .Xr sshd_config 5 ) .
543 Specifies the location of a control socket for connection sharing.
544 Refer to the description of
552 May be used to request invocation of a subsystem on the remote system.
553 Subsystems are a feature of the SSH2 protocol which facilitate the use
554 of SSH as a secure transport for other applications (eg.\&
556 The subsystem is specified as the remote command.
558 Disable pseudo-tty allocation.
560 Force pseudo-tty allocation.
561 This can be used to execute arbitrary
562 screen-based programs on a remote machine, which can be very useful,
563 e.g., when implementing menu services.
566 options force tty allocation, even if
570 Display the version number and exit.
575 to print debugging messages about its progress.
577 debugging connection, authentication, and configuration problems.
580 options increase the verbosity.
582 .It Fl w Ar tunnel : Ns Ar tunnel
585 device on the client and server like the
590 Enables X11 forwarding.
591 This can also be specified on a per-host basis in a configuration file.
593 X11 forwarding should be enabled with caution.
594 Users with the ability to bypass file permissions on the remote host
595 (for the user's X authorization database)
596 can access the local X11 display through the forwarded connection.
597 An attacker may then be able to perform activities such as keystroke monitoring.
599 For this reason, X11 forwarding is subjected to X11 SECURITY extension
600 restrictions by default.
605 .Cm ForwardX11Trusted
608 for more information.
610 Disables X11 forwarding.
612 Enables trusted X11 forwarding.
613 Trusted X11 forwardings are not subjected to the X11 SECURITY extension
617 The OpenSSH SSH client supports OpenSSH protocols 1 and 2.
618 Protocol 2 is the default, with
620 falling back to protocol 1 if it detects protocol 2 is unsupported.
621 These settings may be altered using the
625 or enforced using the
630 Both protocols support similar authentication methods,
631 but protocol 2 is preferred since
632 it provides additional mechanisms for confidentiality
633 (the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour)
634 and integrity (hmac-md5, hmac-sha1, hmac-ripemd160).
635 Protocol 1 lacks a strong mechanism for ensuring the
636 integrity of the connection.
638 The methods available for authentication are:
639 host-based authentication,
640 public key authentication,
641 challenge-response authentication,
642 and password authentication.
643 Authentication methods are tried in the order specified above,
644 though protocol 2 has a configuration option to change the default order:
645 .Cm PreferredAuthentications .
647 Host-based authentication works as follows:
648 If the machine the user logs in from is listed in
651 .Pa /etc/shosts.equiv
652 on the remote machine, and the user names are
653 the same on both sides, or if the files
657 exist in the user's home directory on the
658 remote machine and contain a line containing the name of the client
659 machine and the name of the user on that machine, the user is
660 considered for login.
661 Additionally, the server
663 be able to verify the client's
664 host key (see the description of
665 .Pa /etc/ssh/ssh_known_hosts
667 .Pa ~/.ssh/known_hosts ,
669 for login to be permitted.
670 This authentication method closes security holes due to IP
671 spoofing, DNS spoofing, and routing spoofing.
672 [Note to the administrator:
673 .Pa /etc/hosts.equiv ,
675 and the rlogin/rsh protocol in general, are inherently insecure and should be
676 disabled if security is desired.]
678 Public key authentication works as follows:
679 The scheme is based on public-key cryptography,
681 where encryption and decryption are done using separate keys,
682 and it is unfeasible to derive the decryption key from the encryption key.
683 The idea is that each user creates a public/private
684 key pair for authentication purposes.
685 The server knows the public key, and only the user knows the private key.
687 implements public key authentication protocol automatically,
688 using either the RSA or DSA algorithms.
689 Protocol 1 is restricted to using only RSA keys,
690 but protocol 2 may use either.
695 contains a brief discussion of the two algorithms.
698 .Pa ~/.ssh/authorized_keys
699 lists the public keys that are permitted for logging in.
700 When the user logs in, the
702 program tells the server which key pair it would like to use for
704 The client proves that it has access to the private key
705 and the server checks that the corresponding public key
706 is authorized to accept the account.
708 The user creates his/her key pair by running
710 This stores the private key in
718 and stores the public key in
719 .Pa ~/.ssh/identity.pub
721 .Pa ~/.ssh/id_dsa.pub
724 .Pa ~/.ssh/id_rsa.pub
726 in the user's home directory.
727 The user should then copy the public key
729 .Pa ~/.ssh/authorized_keys
730 in his/her home directory on the remote machine.
733 file corresponds to the conventional
735 file, and has one key
736 per line, though the lines can be very long.
737 After this, the user can log in without giving the password.
739 The most convenient way to use public key authentication may be with an
740 authentication agent.
743 for more information.
745 Challenge-response authentication works as follows:
746 The server sends an arbitrary
748 text, and prompts for a response.
749 Protocol 2 allows multiple challenges and responses;
750 protocol 1 is restricted to just one challenge/response.
751 Examples of challenge-response authentication include
752 BSD Authentication (see
754 and PAM (some non-OpenBSD systems).
756 Finally, if other authentication methods fail,
758 prompts the user for a password.
759 The password is sent to the remote
760 host for checking; however, since all communications are encrypted,
761 the password cannot be seen by someone listening on the network.
762 .Sh LOGIN SESSION AND REMOTE EXECUTION
763 When the user's identity has been accepted by the server, the server
764 either executes the given command, or logs into the machine and gives
765 the user a normal shell on the remote machine.
766 All communication with
767 the remote command or shell will be automatically encrypted.
769 If a pseudo-terminal has been allocated (normal login session), the
770 user may use the escape characters noted below.
772 If no pseudo-tty has been allocated,
773 the session is transparent and can be used to reliably transfer binary data.
774 On most systems, setting the escape character to
776 will also make the session transparent even if a tty is used.
778 The session terminates when the command or shell on the remote
779 machine exits and all X11 and TCP/IP connections have been closed.
780 The exit status of the remote program is returned as the exit status of
784 may additionally obtain configuration data from
785 a per-user configuration file and a system-wide configuration file.
786 The file format and configuration options are described in
788 .Sh ESCAPE CHARACTERS
789 When a pseudo-terminal has been requested,
791 supports a number of functions through the use of an escape character.
793 A single tilde character can be sent as
795 or by following the tilde by a character other than those described below.
796 The escape character must always follow a newline to be interpreted as
798 The escape character can be changed in configuration files using the
800 configuration directive or on the command line by the
804 The supported escapes (assuming the default
814 List forwarded connections.
818 at logout when waiting for forwarded connection / X11 sessions to terminate.
820 Display a list of escape characters.
822 Send a BREAK to the remote system
823 (only useful for SSH protocol version 2 and if the peer supports it).
826 Currently this allows the addition of port forwardings using the
831 It also allows the cancellation of existing remote port-forwardings
834 .Ic !\& Ns Ar command
835 allows the user to execute a local command if the
836 .Ic PermitLocalCommand
839 Basic help is available, using the
843 Request rekeying of the connection
844 (only useful for SSH protocol version 2 and if the peer supports it).
846 .Sh X11 AND TCP FORWARDING
851 (or see the description of the
855 options described later)
856 and the user is using X11 (the
858 environment variable is set), the connection to the X11 display is
859 automatically forwarded to the remote side in such a way that any X11
860 programs started from the shell (or command) will go through the
861 encrypted channel, and the connection to the real X server will be made
862 from the local machine.
863 The user should not manually set
865 Forwarding of X11 connections can be
866 configured on the command line or in configuration files.
872 will point to the server machine, but with a display number greater than zero.
873 This is normal, and happens because
877 X server on the server machine for forwarding the
878 connections over the encrypted channel.
881 will also automatically set up Xauthority data on the server machine.
882 For this purpose, it will generate a random authorization cookie,
883 store it in Xauthority on the server, and verify that any forwarded
884 connections carry this cookie and replace it by the real cookie when
885 the connection is opened.
886 The real authentication cookie is never
887 sent to the server machine (and no cookies are sent in the plain).
893 (or see the description of the
897 options described later) and
898 the user is using an authentication agent, the connection to the agent
899 is automatically forwarded to the remote side.
901 Forwarding of arbitrary TCP/IP connections over the secure channel can
902 be specified either on the command line or in a configuration file.
903 One possible application of TCP/IP forwarding is a secure connection to an
904 electronic purse; another is going through firewalls.
905 .Sh SERVER AUTHENTICATION
907 automatically maintains and checks a database containing
908 identifications for all hosts it has ever been used with.
909 Host keys are stored in
910 .Pa ~/.ssh/known_hosts
911 in the user's home directory.
912 Additionally, the file
913 .Pa /etc/ssh/ssh_known_hosts
914 is automatically checked for known hosts.
915 Any new hosts are automatically added to the user's file.
916 If a host's identification ever changes,
918 warns about this and disables password authentication to prevent a
919 trojan horse from getting the user's password.
920 Another purpose of this mechanism is to prevent man-in-the-middle attacks
921 which could otherwise be used to circumvent the encryption.
923 .Cm StrictHostKeyChecking
924 option can be used to prevent logins to machines whose
925 host key is not known or has changed.
928 can be configured to verify host identification using fingerprint resource
929 records (SSHFP) published in DNS.
932 option can be used to control how DNS lookups are performed.
933 SSHFP resource records can be generated using
937 will normally set the following environment variables:
938 .Bl -tag -width LOGNAME
942 variable indicates the location of the X11 server.
943 It is automatically set by
945 to point to a value of the form
947 where hostname indicates
948 the host where the shell runs, and n is an integer \*(Ge 1.
950 uses this special value to forward X11 connections over the secure
952 The user should normally not set
955 will render the X11 connection insecure (and will require the user to
956 manually copy any required authorization cookies).
958 Set to the path of the user's home directory.
962 set for compatibility with systems that use this variable.
964 Set to the path of the user's mailbox.
968 as specified when compiling
973 needs a passphrase, it will read the passphrase from the current
974 terminal if it was run from a terminal.
977 does not have a terminal associated with it but
981 are set, it will execute the program specified by
983 and open an X11 window to read the passphrase.
984 This is particularly useful when calling
989 (Note that on some machines it
990 may be necessary to redirect the input from
994 Identifies the path of a unix-domain socket used to communicate with the
996 .It Ev SSH_CONNECTION
997 Identifies the client and server ends of the connection.
998 The variable contains
999 four space-separated values: client ip-address, client port number,
1000 server ip-address and server port number.
1001 .It Ev SSH_ORIGINAL_COMMAND
1002 The variable contains the original command line if a forced command
1004 It can be used to extract the original arguments.
1006 This is set to the name of the tty (path to the device) associated
1007 with the current shell or command.
1008 If the current session has no tty,
1009 this variable is not set.
1011 This variable is set to indicate the present time zone if it
1012 was set when the daemon was started (i.e., the daemon passes the value
1013 on to new connections).
1015 Set to the name of the user logging in.
1021 .Pa ~/.ssh/environment ,
1022 and adds lines of the format
1024 to the environment if the file exists and if users are allowed to
1025 change their environment.
1026 For more information, see the
1027 .Cm PermitUserEnvironment
1032 .It Pa ~/.ssh/known_hosts
1033 Records host keys for all hosts the user has logged into that are not
1035 .Pa /etc/ssh/ssh_known_hosts .
1038 .It Pa ~/.ssh/identity, ~/.ssh/id_dsa, ~/.ssh/id_rsa
1039 Contains the authentication identity of the user.
1040 They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively.
1042 contain sensitive data and should be readable by the user but not
1043 accessible by others (read/write/execute).
1046 ignores a private key file if it is accessible by others.
1047 It is possible to specify a passphrase when
1048 generating the key; the passphrase will be used to encrypt the
1049 sensitive part of this file using 3DES.
1050 .It Pa ~/.ssh/identity.pub, ~/.ssh/id_dsa.pub, ~/.ssh/id_rsa.pub
1051 Contains the public key for authentication (public part of the
1052 identity file in human-readable form).
1054 .Pa ~/.ssh/identity.pub
1055 file should be added to the file
1056 .Pa ~/.ssh/authorized_keys
1058 where the user wishes to log in using protocol version 1 RSA authentication.
1060 .Pa ~/.ssh/id_dsa.pub
1062 .Pa ~/.ssh/id_rsa.pub
1063 file should be added to
1064 .Pa ~/.ssh/authorized_keys
1066 where the user wishes to log in using protocol version 2 DSA/RSA authentication.
1068 sensitive and can (but need not) be readable by anyone.
1070 never used automatically and are not necessary; they are only provided for
1071 the convenience of the user.
1072 .It Pa ~/.ssh/config
1073 This is the per-user configuration file.
1074 The file format and configuration options are described in
1076 Because of the potential for abuse, this file must have strict permissions:
1077 read/write for the user, and not accessible by others.
1078 .It Pa ~/.ssh/authorized_keys
1079 Lists the public keys (RSA/DSA) that can be used for logging in as this user.
1080 The format of this file is described in the
1083 In the simplest form the format is the same as the
1086 This file is not highly sensitive, but the recommended
1087 permissions are read/write for the user, and not accessible by others.
1088 .It Pa /etc/ssh/ssh_known_hosts
1089 Systemwide list of known host keys.
1090 This file should be prepared by the
1091 system administrator to contain the public host keys of all machines in the
1093 This file should be world-readable.
1095 public keys, one per line, in the following format (fields separated
1096 by spaces): system name, public key and optional comment field.
1097 When different names are used
1098 for the same machine, all such names should be listed, separated by
1100 The format is described in the
1104 The canonical system name (as returned by name servers) is used by
1106 to verify the client host when logging in; other names are needed because
1108 does not convert the user-supplied name to a canonical name before
1109 checking the key, because someone with access to the name servers
1110 would then be able to fool host authentication.
1111 .It Pa /etc/ssh/ssh_config
1112 Systemwide configuration file.
1113 The file format and configuration options are described in
1115 .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key
1116 These three files contain the private parts of the host keys
1118 .Cm RhostsRSAAuthentication
1120 .Cm HostbasedAuthentication .
1121 If the protocol version 1
1122 .Cm RhostsRSAAuthentication
1125 must be setuid root, since the host key is readable only by root.
1126 For protocol version 2,
1130 to access the host keys for
1131 .Cm HostbasedAuthentication .
1132 This eliminates the requirement that
1134 be setuid root when that authentication method is used.
1139 This file is used in
1140 .Cm RhostsRSAAuthentication
1142 .Cm HostbasedAuthentication
1143 authentication to list the
1144 host/user pairs that are permitted to log in.
1145 (Note that this file is
1146 also used by rlogin and rsh, which makes using this file insecure.)
1147 Each line of the file contains a host name (in the canonical form
1148 returned by name servers), and then a user name on that host,
1149 separated by a space.
1150 On some machines this file may need to be
1151 world-readable if the user's home directory is on a NFS partition,
1155 Additionally, this file must be owned by the user,
1156 and must not have write permissions for anyone else.
1158 permission for most machines is read/write for the user, and not
1159 accessible by others.
1163 allows authentication only in combination with client host key
1164 authentication before permitting log in.
1165 If the server machine does not have the client's host key in
1166 .Pa /etc/ssh/ssh_known_hosts ,
1168 .Pa ~/.ssh/known_hosts .
1169 The easiest way to do this is to
1170 connect back to the client from the server machine using ssh; this
1171 will automatically add the host key to
1172 .Pa ~/.ssh/known_hosts .
1174 This file is used exactly the same way as
1177 having this file is to be able to use
1178 .Cm RhostsRSAAuthentication
1180 .Cm HostbasedAuthentication
1181 authentication without permitting login with
1185 .It Pa /etc/hosts.equiv
1186 This file is used during
1187 .Cm RhostsRSAAuthentication
1189 .Cm HostbasedAuthentication
1192 canonical hosts names, one per line (the full format is described in the
1195 If the client host is found in this file, login is
1196 automatically permitted provided client and server user names are the
1198 Additionally, successful client host key authentication is required.
1199 This file should only be writable by root.
1200 .It Pa /etc/shosts.equiv
1201 This file is processed exactly as
1202 .Pa /etc/hosts.equiv .
1203 This file may be useful to permit logins using
1205 but not using rsh/rlogin.
1206 .It Pa /etc/ssh/sshrc
1207 Commands in this file are executed by
1209 when the user logs in just before the user's shell (or command) is started.
1212 manual page for more information.
1214 Commands in this file are executed by
1216 when the user logs in just before the user's shell (or command) is
1220 manual page for more information.
1221 .It Pa ~/.ssh/environment
1222 Contains additional definitions for environment variables, see section
1228 exits with the exit status of the remote command or with 255
1229 if an error occurred.
1249 .%T "SSH Protocol Architecture"
1250 .%N draft-ietf-secsh-architecture-12.txt
1252 .%O work in progress material
1255 OpenSSH is a derivative of the original and free
1256 ssh 1.2.12 release by Tatu Ylonen.
1257 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1258 Theo de Raadt and Dug Song
1259 removed many bugs, re-added newer features and
1261 Markus Friedl contributed the support for SSH
1262 protocol versions 1.5 and 2.0.
andersk / openssh.git / blob