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 1.219 2005/12/16 18:08:53 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.
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
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
616 .Ss SSH protocol version 1
617 The first authentication method is the
621 method combined with RSA-based host authentication.
622 If the machine the user logs in from is listed in
625 .Pa /etc/shosts.equiv
626 on the remote machine, and the user names are
627 the same on both sides, or if the files
631 exist in the user's home directory on the
632 remote machine and contain a line containing the name of the client
633 machine and the name of the user on that machine, the user is
634 considered for log in.
635 Additionally, if the server can verify the client's
637 .Pa /etc/ssh/ssh_known_hosts
639 .Pa ~/.ssh/known_hosts
642 section), only then is login permitted.
643 This authentication method closes security holes due to IP
644 spoofing, DNS spoofing and routing spoofing.
645 [Note to the administrator:
646 .Pa /etc/hosts.equiv ,
648 and the rlogin/rsh protocol in general, are inherently insecure and should be
649 disabled if security is desired.]
651 As a second authentication method,
653 supports RSA based authentication.
654 The scheme is based on public-key cryptography: there are cryptosystems
655 where encryption and decryption are done using separate keys, and it
656 is not possible to derive the decryption key from the encryption key.
657 RSA is one such system.
658 The idea is that each user creates a public/private
659 key pair for authentication purposes.
660 The server knows the public key, and only the user knows the private key.
663 .Pa ~/.ssh/authorized_keys
664 lists the public keys that are permitted for logging in.
665 When the user logs in, the
667 program tells the server which key pair it would like to use for
669 The server checks if this key is permitted, and if so,
670 sends the user (actually the
672 program running on behalf of the user) a challenge, a random number,
673 encrypted by the user's public key.
674 The challenge can only be decrypted using the proper private key.
675 The user's client then decrypts the challenge using the private key,
676 proving that he/she knows the private key
677 but without disclosing it to the server.
680 implements the RSA authentication protocol automatically.
681 The user creates his/her RSA key pair by running
683 This stores the private key in
685 and stores the public key in
686 .Pa ~/.ssh/identity.pub
687 in the user's home directory.
688 The user should then copy the
691 .Pa ~/.ssh/authorized_keys
692 in his/her home directory on the remote machine (the
694 file corresponds to the conventional
696 file, and has one key
697 per line, though the lines can be very long).
698 After this, the user can log in without giving the password.
700 The most convenient way to use RSA authentication may be with an
701 authentication agent.
704 for more information.
706 If other authentication methods fail,
708 prompts the user for a password.
709 The password is sent to the remote
710 host for checking; however, since all communications are encrypted,
711 the password cannot be seen by someone listening on the network.
712 .Ss SSH protocol version 2
713 When a user connects using protocol version 2,
714 similar authentication methods are available.
715 Using the default values for
716 .Cm PreferredAuthentications ,
717 the client will try to authenticate first using the hostbased method;
718 if this method fails, public key authentication is attempted,
719 and finally if this method fails, keyboard-interactive and
720 password authentication are tried.
722 The public key method is similar to RSA authentication described
723 in the previous section and allows the RSA or DSA algorithm to be used:
724 The client uses his private key,
728 to sign the session identifier and sends the result to the server.
729 The server checks whether the matching public key is listed in
730 .Pa ~/.ssh/authorized_keys
731 and grants access if both the key is found and the signature is correct.
732 The session identifier is derived from a shared Diffie-Hellman value
733 and is only known to the client and the server.
735 If public key authentication fails or is not available, a password
736 can be sent encrypted to the remote host to prove the user's identity.
740 supports hostbased or challenge response authentication.
742 Protocol 2 provides additional mechanisms for confidentiality
743 (the traffic is encrypted using AES, 3DES, Blowfish, CAST128 or Arcfour)
744 and integrity (hmac-md5, hmac-sha1, hmac-ripemd160).
745 Note that protocol 1 lacks a strong mechanism for ensuring the
746 integrity of the connection.
747 .Ss Login session and remote execution
748 When the user's identity has been accepted by the server, the server
749 either executes the given command, or logs into the machine and gives
750 the user a normal shell on the remote machine.
751 All communication with
752 the remote command or shell will be automatically encrypted.
754 If a pseudo-terminal has been allocated (normal login session), the
755 user may use the escape characters noted below.
757 If no pseudo-tty has been allocated,
758 the session is transparent and can be used to reliably transfer binary data.
759 On most systems, setting the escape character to
761 will also make the session transparent even if a tty is used.
763 The session terminates when the command or shell on the remote
764 machine exits and all X11 and TCP/IP connections have been closed.
765 The exit status of the remote program is returned as the exit status of
769 may additionally obtain configuration data from
770 a per-user configuration file and a system-wide configuration file.
771 The file format and configuration options are described in
773 .Ss Escape Characters
774 When a pseudo-terminal has been requested,
776 supports a number of functions through the use of an escape character.
778 A single tilde character can be sent as
780 or by following the tilde by a character other than those described below.
781 The escape character must always follow a newline to be interpreted as
783 The escape character can be changed in configuration files using the
785 configuration directive or on the command line by the
789 The supported escapes (assuming the default
799 List forwarded connections.
803 at logout when waiting for forwarded connection / X11 sessions to terminate.
805 Display a list of escape characters.
807 Send a BREAK to the remote system
808 (only useful for SSH protocol version 2 and if the peer supports it).
811 Currently this allows the addition of port forwardings using the
816 It also allows the cancellation of existing remote port-forwardings
819 .Ic !\& Ns Ar command
820 allows the user to execute a local command if the
821 .Ic PermitLocalCommand
824 Basic help is available, using the
828 Request rekeying of the connection
829 (only useful for SSH protocol version 2 and if the peer supports it).
831 .Ss X11 and TCP forwarding
836 (or see the description of the
840 options described later)
841 and the user is using X11 (the
843 environment variable is set), the connection to the X11 display is
844 automatically forwarded to the remote side in such a way that any X11
845 programs started from the shell (or command) will go through the
846 encrypted channel, and the connection to the real X server will be made
847 from the local machine.
848 The user should not manually set
850 Forwarding of X11 connections can be
851 configured on the command line or in configuration files.
857 will point to the server machine, but with a display number greater than zero.
858 This is normal, and happens because
862 X server on the server machine for forwarding the
863 connections over the encrypted channel.
866 will also automatically set up Xauthority data on the server machine.
867 For this purpose, it will generate a random authorization cookie,
868 store it in Xauthority on the server, and verify that any forwarded
869 connections carry this cookie and replace it by the real cookie when
870 the connection is opened.
871 The real authentication cookie is never
872 sent to the server machine (and no cookies are sent in the plain).
878 (or see the description of the
882 options described later) and
883 the user is using an authentication agent, the connection to the agent
884 is automatically forwarded to the remote side.
886 Forwarding of arbitrary TCP/IP connections over the secure channel can
887 be specified either on the command line or in a configuration file.
888 One possible application of TCP/IP forwarding is a secure connection to an
889 electronic purse; another is going through firewalls.
890 .Ss Server authentication
892 automatically maintains and checks a database containing
893 identifications for all hosts it has ever been used with.
894 Host keys are stored in
895 .Pa ~/.ssh/known_hosts
896 in the user's home directory.
897 Additionally, the file
898 .Pa /etc/ssh/ssh_known_hosts
899 is automatically checked for known hosts.
900 Any new hosts are automatically added to the user's file.
901 If a host's identification ever changes,
903 warns about this and disables password authentication to prevent a
904 trojan horse from getting the user's password.
905 Another purpose of this mechanism is to prevent man-in-the-middle attacks
906 which could otherwise be used to circumvent the encryption.
908 .Cm StrictHostKeyChecking
909 option can be used to prevent logins to machines whose
910 host key is not known or has changed.
913 can be configured to verify host identification using fingerprint resource
914 records (SSHFP) published in DNS.
917 option can be used to control how DNS lookups are performed.
918 SSHFP resource records can be generated using
922 will normally set the following environment variables:
923 .Bl -tag -width LOGNAME
927 variable indicates the location of the X11 server.
928 It is automatically set by
930 to point to a value of the form
932 where hostname indicates
933 the host where the shell runs, and n is an integer \*(Ge 1.
935 uses this special value to forward X11 connections over the secure
937 The user should normally not set
940 will render the X11 connection insecure (and will require the user to
941 manually copy any required authorization cookies).
943 Set to the path of the user's home directory.
947 set for compatibility with systems that use this variable.
949 Set to the path of the user's mailbox.
953 as specified when compiling
958 needs a passphrase, it will read the passphrase from the current
959 terminal if it was run from a terminal.
962 does not have a terminal associated with it but
966 are set, it will execute the program specified by
968 and open an X11 window to read the passphrase.
969 This is particularly useful when calling
974 (Note that on some machines it
975 may be necessary to redirect the input from
979 Identifies the path of a unix-domain socket used to communicate with the
981 .It Ev SSH_CONNECTION
982 Identifies the client and server ends of the connection.
983 The variable contains
984 four space-separated values: client ip-address, client port number,
985 server ip-address and server port number.
986 .It Ev SSH_ORIGINAL_COMMAND
987 The variable contains the original command line if a forced command
989 It can be used to extract the original arguments.
991 This is set to the name of the tty (path to the device) associated
992 with the current shell or command.
993 If the current session has no tty,
994 this variable is not set.
996 This variable is set to indicate the present time zone if it
997 was set when the daemon was started (i.e., the daemon passes the value
998 on to new connections).
1000 Set to the name of the user logging in.
1006 .Pa ~/.ssh/environment ,
1007 and adds lines of the format
1009 to the environment if the file exists and if users are allowed to
1010 change their environment.
1011 For more information, see the
1012 .Cm PermitUserEnvironment
1017 .It Pa ~/.ssh/known_hosts
1018 Records host keys for all hosts the user has logged into that are not
1020 .Pa /etc/ssh/ssh_known_hosts .
1023 .It Pa ~/.ssh/identity, ~/.ssh/id_dsa, ~/.ssh/id_rsa
1024 Contains the authentication identity of the user.
1025 They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively.
1027 contain sensitive data and should be readable by the user but not
1028 accessible by others (read/write/execute).
1031 ignores a private key file if it is accessible by others.
1032 It is possible to specify a passphrase when
1033 generating the key; the passphrase will be used to encrypt the
1034 sensitive part of this file using 3DES.
1035 .It Pa ~/.ssh/identity.pub, ~/.ssh/id_dsa.pub, ~/.ssh/id_rsa.pub
1036 Contains the public key for authentication (public part of the
1037 identity file in human-readable form).
1039 .Pa ~/.ssh/identity.pub
1040 file should be added to the file
1041 .Pa ~/.ssh/authorized_keys
1043 where the user wishes to log in using protocol version 1 RSA authentication.
1045 .Pa ~/.ssh/id_dsa.pub
1047 .Pa ~/.ssh/id_rsa.pub
1048 file should be added to
1049 .Pa ~/.ssh/authorized_keys
1051 where the user wishes to log in using protocol version 2 DSA/RSA authentication.
1053 sensitive and can (but need not) be readable by anyone.
1055 never used automatically and are not necessary; they are only provided for
1056 the convenience of the user.
1057 .It Pa ~/.ssh/config
1058 This is the per-user configuration file.
1059 The file format and configuration options are described in
1061 Because of the potential for abuse, this file must have strict permissions:
1062 read/write for the user, and not accessible by others.
1063 .It Pa ~/.ssh/authorized_keys
1064 Lists the public keys (RSA/DSA) that can be used for logging in as this user.
1065 The format of this file is described in the
1068 In the simplest form the format is the same as the
1071 This file is not highly sensitive, but the recommended
1072 permissions are read/write for the user, and not accessible by others.
1073 .It Pa /etc/ssh/ssh_known_hosts
1074 Systemwide list of known host keys.
1075 This file should be prepared by the
1076 system administrator to contain the public host keys of all machines in the
1078 This file should be world-readable.
1080 public keys, one per line, in the following format (fields separated
1081 by spaces): system name, public key and optional comment field.
1082 When different names are used
1083 for the same machine, all such names should be listed, separated by
1085 The format is described in the
1089 The canonical system name (as returned by name servers) is used by
1091 to verify the client host when logging in; other names are needed because
1093 does not convert the user-supplied name to a canonical name before
1094 checking the key, because someone with access to the name servers
1095 would then be able to fool host authentication.
1096 .It Pa /etc/ssh/ssh_config
1097 Systemwide configuration file.
1098 The file format and configuration options are described in
1100 .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key
1101 These three files contain the private parts of the host keys
1103 .Cm RhostsRSAAuthentication
1105 .Cm HostbasedAuthentication .
1106 If the protocol version 1
1107 .Cm RhostsRSAAuthentication
1110 must be setuid root, since the host key is readable only by root.
1111 For protocol version 2,
1115 to access the host keys for
1116 .Cm HostbasedAuthentication .
1117 This eliminates the requirement that
1119 be setuid root when that authentication method is used.
1124 This file is used in
1125 .Cm RhostsRSAAuthentication
1127 .Cm HostbasedAuthentication
1128 authentication to list the
1129 host/user pairs that are permitted to log in.
1130 (Note that this file is
1131 also used by rlogin and rsh, which makes using this file insecure.)
1132 Each line of the file contains a host name (in the canonical form
1133 returned by name servers), and then a user name on that host,
1134 separated by a space.
1135 On some machines this file may need to be
1136 world-readable if the user's home directory is on a NFS partition,
1140 Additionally, this file must be owned by the user,
1141 and must not have write permissions for anyone else.
1143 permission for most machines is read/write for the user, and not
1144 accessible by others.
1148 allows authentication only in combination with client host key
1149 authentication before permitting log in.
1150 If the server machine does not have the client's host key in
1151 .Pa /etc/ssh/ssh_known_hosts ,
1153 .Pa ~/.ssh/known_hosts .
1154 The easiest way to do this is to
1155 connect back to the client from the server machine using ssh; this
1156 will automatically add the host key to
1157 .Pa ~/.ssh/known_hosts .
1159 This file is used exactly the same way as
1162 having this file is to be able to use
1163 .Cm RhostsRSAAuthentication
1165 .Cm HostbasedAuthentication
1166 authentication without permitting login with
1170 .It Pa /etc/hosts.equiv
1171 This file is used during
1172 .Cm RhostsRSAAuthentication
1174 .Cm HostbasedAuthentication
1177 canonical hosts names, one per line (the full format is described in the
1180 If the client host is found in this file, login is
1181 automatically permitted provided client and server user names are the
1183 Additionally, successful client host key authentication is required.
1184 This file should only be writable by root.
1185 .It Pa /etc/shosts.equiv
1186 This file is processed exactly as
1187 .Pa /etc/hosts.equiv .
1188 This file may be useful to permit logins using
1190 but not using rsh/rlogin.
1191 .It Pa /etc/ssh/sshrc
1192 Commands in this file are executed by
1194 when the user logs in just before the user's shell (or command) is started.
1197 manual page for more information.
1199 Commands in this file are executed by
1201 when the user logs in just before the user's shell (or command) is
1205 manual page for more information.
1206 .It Pa ~/.ssh/environment
1207 Contains additional definitions for environment variables, see section
1213 exits with the exit status of the remote command or with 255
1214 if an error occurred.
1234 .%T "SSH Protocol Architecture"
1235 .%N draft-ietf-secsh-architecture-12.txt
1237 .%O work in progress material
1240 OpenSSH is a derivative of the original and free
1241 ssh 1.2.12 release by Tatu Ylonen.
1242 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1243 Theo de Raadt and Dug Song
1244 removed many bugs, re-added newer features and
1246 Markus Friedl contributed the support for SSH
1247 protocol versions 1.5 and 2.0.
andersk / openssh.git / blob