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 1.227 2005/12/21 12:53:31 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
618 may additionally obtain configuration data from
619 a per-user configuration file and a system-wide configuration file.
620 The file format and configuration options are described in
624 exits with the exit status of the remote command or with 255
625 if an error occurred.
627 The OpenSSH SSH client supports OpenSSH protocols 1 and 2.
628 Protocol 2 is the default, with
630 falling back to protocol 1 if it detects protocol 2 is unsupported.
631 These settings may be altered using the
635 or enforced using the
640 Both protocols support similar authentication methods,
641 but protocol 2 is preferred since
642 it provides additional mechanisms for confidentiality
643 (the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour)
644 and integrity (hmac-md5, hmac-sha1, hmac-ripemd160).
645 Protocol 1 lacks a strong mechanism for ensuring the
646 integrity of the connection.
648 The methods available for authentication are:
649 host-based authentication,
650 public key authentication,
651 challenge-response authentication,
652 and password authentication.
653 Authentication methods are tried in the order specified above,
654 though protocol 2 has a configuration option to change the default order:
655 .Cm PreferredAuthentications .
657 Host-based authentication works as follows:
658 If the machine the user logs in from is listed in
661 .Pa /etc/shosts.equiv
662 on the remote machine, and the user names are
663 the same on both sides, or if the files
667 exist in the user's home directory on the
668 remote machine and contain a line containing the name of the client
669 machine and the name of the user on that machine, the user is
670 considered for login.
671 Additionally, the server
673 be able to verify the client's
674 host key (see the description of
675 .Pa /etc/ssh/ssh_known_hosts
677 .Pa ~/.ssh/known_hosts ,
679 for login to be permitted.
680 This authentication method closes security holes due to IP
681 spoofing, DNS spoofing, and routing spoofing.
682 [Note to the administrator:
683 .Pa /etc/hosts.equiv ,
685 and the rlogin/rsh protocol in general, are inherently insecure and should be
686 disabled if security is desired.]
688 Public key authentication works as follows:
689 The scheme is based on public-key cryptography,
691 where encryption and decryption are done using separate keys,
692 and it is unfeasible to derive the decryption key from the encryption key.
693 The idea is that each user creates a public/private
694 key pair for authentication purposes.
695 The server knows the public key, and only the user knows the private key.
697 implements public key authentication protocol automatically,
698 using either the RSA or DSA algorithms.
699 Protocol 1 is restricted to using only RSA keys,
700 but protocol 2 may use either.
705 contains a brief discussion of the two algorithms.
708 .Pa ~/.ssh/authorized_keys
709 lists the public keys that are permitted for logging in.
710 When the user logs in, the
712 program tells the server which key pair it would like to use for
714 The client proves that it has access to the private key
715 and the server checks that the corresponding public key
716 is authorized to accept the account.
718 The user creates his/her key pair by running
720 This stores the private key in
728 and stores the public key in
729 .Pa ~/.ssh/identity.pub
731 .Pa ~/.ssh/id_dsa.pub
734 .Pa ~/.ssh/id_rsa.pub
736 in the user's home directory.
737 The user should then copy the public key
739 .Pa ~/.ssh/authorized_keys
740 in his/her home directory on the remote machine.
743 file corresponds to the conventional
745 file, and has one key
746 per line, though the lines can be very long.
747 After this, the user can log in without giving the password.
749 The most convenient way to use public key authentication may be with an
750 authentication agent.
753 for more information.
755 Challenge-response authentication works as follows:
756 The server sends an arbitrary
758 text, and prompts for a response.
759 Protocol 2 allows multiple challenges and responses;
760 protocol 1 is restricted to just one challenge/response.
761 Examples of challenge-response authentication include
762 BSD Authentication (see
764 and PAM (some non-OpenBSD systems).
766 Finally, if other authentication methods fail,
768 prompts the user for a password.
769 The password is sent to the remote
770 host for checking; however, since all communications are encrypted,
771 the password cannot be seen by someone listening on the network.
772 .Sh LOGIN SESSION AND REMOTE EXECUTION
773 When the user's identity has been accepted by the server, the server
774 either executes the given command, or logs into the machine and gives
775 the user a normal shell on the remote machine.
776 All communication with
777 the remote command or shell will be automatically encrypted.
779 If a pseudo-terminal has been allocated (normal login session), the
780 user may use the escape characters noted below.
782 If no pseudo-tty has been allocated,
783 the session is transparent and can be used to reliably transfer binary data.
784 On most systems, setting the escape character to
786 will also make the session transparent even if a tty is used.
788 The session terminates when the command or shell on the remote
789 machine exits and all X11 and TCP/IP connections have been closed.
790 .Sh ESCAPE CHARACTERS
791 When a pseudo-terminal has been requested,
793 supports a number of functions through the use of an escape character.
795 A single tilde character can be sent as
797 or by following the tilde by a character other than those described below.
798 The escape character must always follow a newline to be interpreted as
800 The escape character can be changed in configuration files using the
802 configuration directive or on the command line by the
806 The supported escapes (assuming the default
816 List forwarded connections.
820 at logout when waiting for forwarded connection / X11 sessions to terminate.
822 Display a list of escape characters.
824 Send a BREAK to the remote system
825 (only useful for SSH protocol version 2 and if the peer supports it).
828 Currently this allows the addition of port forwardings using the
833 It also allows the cancellation of existing remote port-forwardings
836 .Ic !\& Ns Ar command
837 allows the user to execute a local command if the
838 .Ic PermitLocalCommand
841 Basic help is available, using the
845 Request rekeying of the connection
846 (only useful for SSH protocol version 2 and if the peer supports it).
848 .Sh X11 AND TCP FORWARDING
853 (or see the description of the
859 and the user is using X11 (the
861 environment variable is set), the connection to the X11 display is
862 automatically forwarded to the remote side in such a way that any X11
863 programs started from the shell (or command) will go through the
864 encrypted channel, and the connection to the real X server will be made
865 from the local machine.
866 The user should not manually set
868 Forwarding of X11 connections can be
869 configured on the command line or in configuration files.
875 will point to the server machine, but with a display number greater than zero.
876 This is normal, and happens because
880 X server on the server machine for forwarding the
881 connections over the encrypted channel.
884 will also automatically set up Xauthority data on the server machine.
885 For this purpose, it will generate a random authorization cookie,
886 store it in Xauthority on the server, and verify that any forwarded
887 connections carry this cookie and replace it by the real cookie when
888 the connection is opened.
889 The real authentication cookie is never
890 sent to the server machine (and no cookies are sent in the plain).
896 (or see the description of the
901 the user is using an authentication agent, the connection to the agent
902 is automatically forwarded to the remote side.
904 Forwarding of arbitrary TCP/IP connections over the secure channel can
905 be specified either on the command line or in a configuration file.
906 One possible application of TCP/IP forwarding is a secure connection to an
907 electronic purse; another is going through firewalls.
908 .Sh SERVER AUTHENTICATION
910 automatically maintains and checks a database containing
911 identifications for all hosts it has ever been used with.
912 Host keys are stored in
913 .Pa ~/.ssh/known_hosts
914 in the user's home directory.
915 Additionally, the file
916 .Pa /etc/ssh/ssh_known_hosts
917 is automatically checked for known hosts.
918 Any new hosts are automatically added to the user's file.
919 If a host's identification ever changes,
921 warns about this and disables password authentication to prevent a
922 trojan horse from getting the user's password.
923 Another purpose of this mechanism is to prevent man-in-the-middle attacks
924 which could otherwise be used to circumvent the encryption.
926 .Cm StrictHostKeyChecking
927 option can be used to prevent logins to machines whose
928 host key is not known or has changed.
931 can be configured to verify host identification using fingerprint resource
932 records (SSHFP) published in DNS.
935 option can be used to control how DNS lookups are performed.
936 SSHFP resource records can be generated using
940 will normally set the following environment variables:
941 .Bl -tag -width LOGNAME
945 variable indicates the location of the X11 server.
946 It is automatically set by
948 to point to a value of the form
950 where hostname indicates
951 the host where the shell runs, and n is an integer \*(Ge 1.
953 uses this special value to forward X11 connections over the secure
955 The user should normally not set
958 will render the X11 connection insecure (and will require the user to
959 manually copy any required authorization cookies).
961 Set to the path of the user's home directory.
965 set for compatibility with systems that use this variable.
967 Set to the path of the user's mailbox.
971 as specified when compiling
976 needs a passphrase, it will read the passphrase from the current
977 terminal if it was run from a terminal.
980 does not have a terminal associated with it but
984 are set, it will execute the program specified by
986 and open an X11 window to read the passphrase.
987 This is particularly useful when calling
992 (Note that on some machines it
993 may be necessary to redirect the input from
997 Identifies the path of a unix-domain socket used to communicate with the
999 .It Ev SSH_CONNECTION
1000 Identifies the client and server ends of the connection.
1001 The variable contains
1002 four space-separated values: client ip-address, client port number,
1003 server ip-address and server port number.
1004 .It Ev SSH_ORIGINAL_COMMAND
1005 The variable contains the original command line if a forced command
1007 It can be used to extract the original arguments.
1009 This is set to the name of the tty (path to the device) associated
1010 with the current shell or command.
1011 If the current session has no tty,
1012 this variable is not set.
1014 This variable is set to indicate the present time zone if it
1015 was set when the daemon was started (i.e., the daemon passes the value
1016 on to new connections).
1018 Set to the name of the user logging in.
1024 .Pa ~/.ssh/environment ,
1025 and adds lines of the format
1027 to the environment if the file exists and if users are allowed to
1028 change their environment.
1029 For more information, see the
1030 .Cm PermitUserEnvironment
1035 .It Pa ~/.ssh/known_hosts
1036 Records host keys for all hosts the user has logged into that are not
1038 .Pa /etc/ssh/ssh_known_hosts .
1041 .It Pa ~/.ssh/identity, ~/.ssh/id_dsa, ~/.ssh/id_rsa
1042 Contains the authentication identity of the user.
1043 They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively.
1045 contain sensitive data and should be readable by the user but not
1046 accessible by others (read/write/execute).
1049 ignores a private key file if it is accessible by others.
1050 It is possible to specify a passphrase when
1051 generating the key; the passphrase will be used to encrypt the
1052 sensitive part of this file using 3DES.
1053 .It Pa ~/.ssh/identity.pub, ~/.ssh/id_dsa.pub, ~/.ssh/id_rsa.pub
1054 Contains the public key for authentication (public part of the
1055 identity file in human-readable form).
1057 .Pa ~/.ssh/identity.pub
1058 file should be added to the file
1059 .Pa ~/.ssh/authorized_keys
1061 where the user wishes to log in using protocol version 1 RSA authentication.
1063 .Pa ~/.ssh/id_dsa.pub
1065 .Pa ~/.ssh/id_rsa.pub
1066 file should be added to
1067 .Pa ~/.ssh/authorized_keys
1069 where the user wishes to log in using protocol version 2 DSA/RSA authentication.
1071 sensitive and can (but need not) be readable by anyone.
1073 never used automatically and are not necessary; they are only provided for
1074 the convenience of the user.
1075 .It Pa ~/.ssh/config
1076 This is the per-user configuration file.
1077 The file format and configuration options are described in
1079 Because of the potential for abuse, this file must have strict permissions:
1080 read/write for the user, and not accessible by others.
1081 .It Pa ~/.ssh/authorized_keys
1082 Lists the public keys (RSA/DSA) that can be used for logging in as this user.
1083 The format of this file is described in the
1086 In the simplest form the format is the same as the
1089 This file is not highly sensitive, but the recommended
1090 permissions are read/write for the user, and not accessible by others.
1091 .It Pa /etc/ssh/ssh_known_hosts
1092 Systemwide list of known host keys.
1093 This file should be prepared by the
1094 system administrator to contain the public host keys of all machines in the
1096 This file should be world-readable.
1098 public keys, one per line, in the following format (fields separated
1099 by spaces): system name, public key and optional comment field.
1100 When different names are used
1101 for the same machine, all such names should be listed, separated by
1103 The format is described in the
1107 The canonical system name (as returned by name servers) is used by
1109 to verify the client host when logging in; other names are needed because
1111 does not convert the user-supplied name to a canonical name before
1112 checking the key, because someone with access to the name servers
1113 would then be able to fool host authentication.
1114 .It Pa /etc/ssh/ssh_config
1115 Systemwide configuration file.
1116 The file format and configuration options are described in
1118 .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key
1119 These three files contain the private parts of the host keys
1121 .Cm RhostsRSAAuthentication
1123 .Cm HostbasedAuthentication .
1124 If the protocol version 1
1125 .Cm RhostsRSAAuthentication
1128 must be setuid root, since the host key is readable only by root.
1129 For protocol version 2,
1133 to access the host keys for
1134 .Cm HostbasedAuthentication .
1135 This eliminates the requirement that
1137 be setuid root when that authentication method is used.
1142 This file is used in
1143 .Cm RhostsRSAAuthentication
1145 .Cm HostbasedAuthentication
1146 authentication to list the
1147 host/user pairs that are permitted to log in.
1148 (Note that this file is
1149 also used by rlogin and rsh, which makes using this file insecure.)
1150 Each line of the file contains a host name (in the canonical form
1151 returned by name servers), and then a user name on that host,
1152 separated by a space.
1153 On some machines this file may need to be
1154 world-readable if the user's home directory is on a NFS partition,
1158 Additionally, this file must be owned by the user,
1159 and must not have write permissions for anyone else.
1161 permission for most machines is read/write for the user, and not
1162 accessible by others.
1166 allows authentication only in combination with client host key
1167 authentication before permitting log in.
1168 If the server machine does not have the client's host key in
1169 .Pa /etc/ssh/ssh_known_hosts ,
1171 .Pa ~/.ssh/known_hosts .
1172 The easiest way to do this is to
1173 connect back to the client from the server machine using ssh; this
1174 will automatically add the host key to
1175 .Pa ~/.ssh/known_hosts .
1177 This file is used exactly the same way as
1180 having this file is to be able to use
1181 .Cm RhostsRSAAuthentication
1183 .Cm HostbasedAuthentication
1184 authentication without permitting login with
1188 .It Pa /etc/hosts.equiv
1189 This file is used during
1190 .Cm RhostsRSAAuthentication
1192 .Cm HostbasedAuthentication
1195 canonical hosts names, one per line (the full format is described in the
1198 If the client host is found in this file, login is
1199 automatically permitted provided client and server user names are the
1201 Additionally, successful client host key authentication is required.
1202 This file should only be writable by root.
1203 .It Pa /etc/shosts.equiv
1204 This file is processed exactly as
1205 .Pa /etc/hosts.equiv .
1206 This file may be useful to permit logins using
1208 but not using rsh/rlogin.
1209 .It Pa /etc/ssh/sshrc
1210 Commands in this file are executed by
1212 when the user logs in just before the user's shell (or command) is started.
1215 manual page for more information.
1217 Commands in this file are executed by
1219 when the user logs in just before the user's shell (or command) is
1223 manual page for more information.
1224 .It Pa ~/.ssh/environment
1225 Contains additional definitions for environment variables, see section
1248 .%T "SSH Protocol Architecture"
1249 .%N draft-ietf-secsh-architecture-12.txt
1251 .%O work in progress material
1254 OpenSSH is a derivative of the original and free
1255 ssh 1.2.12 release by Tatu Ylonen.
1256 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1257 Theo de Raadt and Dug Song
1258 removed many bugs, re-added newer features and
1260 Markus Friedl contributed the support for SSH
1261 protocol versions 1.5 and 2.0.
andersk / openssh.git / blob