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 1.195 2004/08/26 16:00:55 markus 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 .Op Fl e Ar escape_char
52 .Op Fl F Ar configfile
53 .Op Fl i Ar identity_file
63 .Op Fl l Ar login_name
78 .Oo Ar user Ns @ Oc Ns Ar hostname
82 (SSH client) is a program for logging into a remote machine and for
83 executing commands on a remote machine.
84 It is intended to replace rlogin and rsh,
85 and provide secure encrypted communications between
86 two untrusted hosts over an insecure network.
87 X11 connections and arbitrary TCP/IP ports
88 can also be forwarded over the secure channel.
91 connects and logs into the specified
97 his/her identity to the remote machine using one of several methods
98 depending on the protocol version used.
104 is executed on the remote host instead of a login shell.
105 .Ss SSH protocol version 1
106 The first authentication method is the
110 method combined with RSA-based host authentication.
111 If the machine the user logs in from is listed in
114 .Pa /etc/shosts.equiv
115 on the remote machine, and the user names are
116 the same on both sides, or if the files
120 exist in the user's home directory on the
121 remote machine and contain a line containing the name of the client
122 machine and the name of the user on that machine, the user is
123 considered for log in.
124 Additionally, if the server can verify the client's
126 .Pa /etc/ssh/ssh_known_hosts
128 .Pa $HOME/.ssh/known_hosts
131 section), only then is login permitted.
132 This authentication method closes security holes due to IP
133 spoofing, DNS spoofing and routing spoofing.
134 [Note to the administrator:
135 .Pa /etc/hosts.equiv ,
137 and the rlogin/rsh protocol in general, are inherently insecure and should be
138 disabled if security is desired.]
140 As a second authentication method,
142 supports RSA based authentication.
143 The scheme is based on public-key cryptography: there are cryptosystems
144 where encryption and decryption are done using separate keys, and it
145 is not possible to derive the decryption key from the encryption key.
146 RSA is one such system.
147 The idea is that each user creates a public/private
148 key pair for authentication purposes.
149 The server knows the public key, and only the user knows the private key.
152 .Pa $HOME/.ssh/authorized_keys
153 lists the public keys that are permitted for logging in.
154 When the user logs in, the
156 program tells the server which key pair it would like to use for
158 The server checks if this key is permitted, and if so,
159 sends the user (actually the
161 program running on behalf of the user) a challenge, a random number,
162 encrypted by the user's public key.
163 The challenge can only be decrypted using the proper private key.
164 The user's client then decrypts the challenge using the private key,
165 proving that he/she knows the private key
166 but without disclosing it to the server.
169 implements the RSA authentication protocol automatically.
170 The user creates his/her RSA key pair by running
172 This stores the private key in
173 .Pa $HOME/.ssh/identity
174 and stores the public key in
175 .Pa $HOME/.ssh/identity.pub
176 in the user's home directory.
177 The user should then copy the
180 .Pa $HOME/.ssh/authorized_keys
181 in his/her home directory on the remote machine (the
183 file corresponds to the conventional
185 file, and has one key
186 per line, though the lines can be very long).
187 After this, the user can log in without giving the password.
189 The most convenient way to use RSA authentication may be with an
190 authentication agent.
193 for more information.
195 If other authentication methods fail,
197 prompts the user for a password.
198 The password is sent to the remote
199 host for checking; however, since all communications are encrypted,
200 the password cannot be seen by someone listening on the network.
201 .Ss SSH protocol version 2
202 When a user connects using protocol version 2,
203 similar authentication methods are available.
204 Using the default values for
205 .Cm PreferredAuthentications ,
206 the client will try to authenticate first using the hostbased method;
207 if this method fails, public key authentication is attempted,
208 and finally if this method fails, keyboard-interactive and
209 password authentication are tried.
211 The public key method is similar to RSA authentication described
212 in the previous section and allows the RSA or DSA algorithm to be used:
213 The client uses his private key,
214 .Pa $HOME/.ssh/id_dsa
216 .Pa $HOME/.ssh/id_rsa ,
217 to sign the session identifier and sends the result to the server.
218 The server checks whether the matching public key is listed in
219 .Pa $HOME/.ssh/authorized_keys
220 and grants access if both the key is found and the signature is correct.
221 The session identifier is derived from a shared Diffie-Hellman value
222 and is only known to the client and the server.
224 If public key authentication fails or is not available, a password
225 can be sent encrypted to the remote host to prove the user's identity.
229 supports hostbased or challenge response authentication.
231 Protocol 2 provides additional mechanisms for confidentiality
232 (the traffic is encrypted using AES, 3DES, Blowfish, CAST128 or Arcfour)
233 and integrity (hmac-md5, hmac-sha1, hmac-ripemd160).
234 Note that protocol 1 lacks a strong mechanism for ensuring the
235 integrity of the connection.
236 .Ss Login session and remote execution
237 When the user's identity has been accepted by the server, the server
238 either executes the given command, or logs into the machine and gives
239 the user a normal shell on the remote machine.
240 All communication with
241 the remote command or shell will be automatically encrypted.
243 If a pseudo-terminal has been allocated (normal login session), the
244 user may use the escape characters noted below.
246 If no pseudo-tty has been allocated,
247 the session is transparent and can be used to reliably transfer binary data.
248 On most systems, setting the escape character to
250 will also make the session transparent even if a tty is used.
252 The session terminates when the command or shell on the remote
253 machine exits and all X11 and TCP/IP connections have been closed.
254 The exit status of the remote program is returned as the exit status of
256 .Ss Escape Characters
257 When a pseudo-terminal has been requested,
259 supports a number of functions through the use of an escape character.
261 A single tilde character can be sent as
263 or by following the tilde by a character other than those described below.
264 The escape character must always follow a newline to be interpreted as
266 The escape character can be changed in configuration files using the
268 configuration directive or on the command line by the
272 The supported escapes (assuming the default
282 List forwarded connections.
286 at logout when waiting for forwarded connection / X11 sessions to terminate.
288 Display a list of escape characters.
290 Send a BREAK to the remote system
291 (only useful for SSH protocol version 2 and if the peer supports it).
294 Currently this allows the addition of port forwardings using the
299 It also allows the cancellation of existing remote port-forwardings
302 Basic help is available, using the
306 Request rekeying of the connection
307 (only useful for SSH protocol version 2 and if the peer supports it).
309 .Ss X11 and TCP forwarding
314 (or see the description of the
318 options described later)
319 and the user is using X11 (the
321 environment variable is set), the connection to the X11 display is
322 automatically forwarded to the remote side in such a way that any X11
323 programs started from the shell (or command) will go through the
324 encrypted channel, and the connection to the real X server will be made
325 from the local machine.
326 The user should not manually set
328 Forwarding of X11 connections can be
329 configured on the command line or in configuration files.
335 will point to the server machine, but with a display number greater than zero.
336 This is normal, and happens because
340 X server on the server machine for forwarding the
341 connections over the encrypted channel.
344 will also automatically set up Xauthority data on the server machine.
345 For this purpose, it will generate a random authorization cookie,
346 store it in Xauthority on the server, and verify that any forwarded
347 connections carry this cookie and replace it by the real cookie when
348 the connection is opened.
349 The real authentication cookie is never
350 sent to the server machine (and no cookies are sent in the plain).
356 (or see the description of the
360 options described later) and
361 the user is using an authentication agent, the connection to the agent
362 is automatically forwarded to the remote side.
364 Forwarding of arbitrary TCP/IP connections over the secure channel can
365 be specified either on the command line or in a configuration file.
366 One possible application of TCP/IP forwarding is a secure connection to an
367 electronic purse; another is going through firewalls.
368 .Ss Server authentication
370 automatically maintains and checks a database containing
371 identifications for all hosts it has ever been used with.
372 Host keys are stored in
373 .Pa $HOME/.ssh/known_hosts
374 in the user's home directory.
375 Additionally, the file
376 .Pa /etc/ssh/ssh_known_hosts
377 is automatically checked for known hosts.
378 Any new hosts are automatically added to the user's file.
379 If a host's identification ever changes,
381 warns about this and disables password authentication to prevent a
382 trojan horse from getting the user's password.
383 Another purpose of this mechanism is to prevent man-in-the-middle attacks
384 which could otherwise be used to circumvent the encryption.
386 .Cm StrictHostKeyChecking
387 option can be used to prevent logins to machines whose
388 host key is not known or has changed.
391 can be configured to verify host identification using fingerprint resource
392 records (SSHFP) published in DNS.
395 option can be used to control how DNS lookups are performed.
396 SSHFP resource records can be generated using
399 The options are as follows:
404 to try protocol version 1 only.
408 to try protocol version 2 only.
412 to use IPv4 addresses only.
416 to use IPv6 addresses only.
418 Enables forwarding of the authentication agent connection.
419 This can also be specified on a per-host basis in a configuration file.
421 Agent forwarding should be enabled with caution.
422 Users with the ability to bypass file permissions on the remote host
423 (for the agent's Unix-domain socket)
424 can access the local agent through the forwarded connection.
425 An attacker cannot obtain key material from the agent,
426 however they can perform operations on the keys that enable them to
427 authenticate using the identities loaded into the agent.
429 Disables forwarding of the authentication agent connection.
430 .It Fl b Ar bind_address
431 Specify the interface to transmit from on machines with multiple
432 interfaces or aliased addresses.
434 Requests compression of all data (including stdin, stdout, stderr, and
435 data for forwarded X11 and TCP/IP connections).
436 The compression algorithm is the same used by
440 can be controlled by the
442 option for protocol version 1.
443 Compression is desirable on modem lines and other
444 slow connections, but will only slow down things on fast networks.
445 The default value can be set on a host-by-host basis in the
446 configuration files; see the
449 .It Fl c Ar cipher_spec
450 Selects the cipher specification for encrypting the session.
452 Protocol version 1 allows specification of a single cipher.
453 The suported values are
459 (triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
460 It is believed to be secure.
462 is a fast block cipher; it appears very secure and is much faster than
465 is only supported in the
467 client for interoperability with legacy protocol 1 implementations
468 that do not support the
471 Its use is strongly discouraged due to cryptographic weaknesses.
475 For protocol version 2
477 is a comma-separated list of ciphers
478 listed in order of preference.
479 The supported ciphers are
493 ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,
494 aes192-cbc,aes256-cbc''
499 application-level port forwarding.
500 This works by allocating a socket to listen to
502 on the local side, and whenever a connection is made to this port, the
503 connection is forwarded over the secure channel, and the application
504 protocol is then used to determine where to connect to from the
506 Currently the SOCKS4 and SOCKS5 protocols are supported, and
508 will act as a SOCKS server.
509 Only root can forward privileged ports.
510 Dynamic port forwardings can also be specified in the configuration file.
511 .It Fl e Ar ch | ^ch | none
512 Sets the escape character for sessions with a pty (default:
514 The escape character is only recognized at the beginning of a line.
515 The escape character followed by a dot
517 closes the connection;
518 followed by control-Z suspends the connection;
519 and followed by itself sends the escape character once.
520 Setting the character to
522 disables any escapes and makes the session fully transparent.
523 .It Fl F Ar configfile
524 Specifies an alternative per-user configuration file.
525 If a configuration file is given on the command line,
526 the system-wide configuration file
527 .Pq Pa /etc/ssh/ssh_config
529 The default for the per-user configuration file is
530 .Pa $HOME/.ssh/config .
534 to go to background just before command execution.
537 is going to ask for passwords or passphrases, but the user
538 wants it in the background.
541 The recommended way to start X11 programs at a remote site is with
543 .Ic ssh -f host xterm .
545 Allows remote hosts to connect to local forwarded ports.
546 .It Fl I Ar smartcard_device
547 Specifies which smartcard device to use.
548 The argument is the device
550 should use to communicate with a smartcard used for storing the user's
552 .It Fl i Ar identity_file
553 Selects a file from which the identity (private key) for
554 RSA or DSA authentication is read.
556 .Pa $HOME/.ssh/identity
557 for protocol version 1, and
558 .Pa $HOME/.ssh/id_rsa
560 .Pa $HOME/.ssh/id_dsa
561 for protocol version 2.
562 Identity files may also be specified on
563 a per-host basis in the configuration file.
564 It is possible to have multiple
566 options (and multiple identities specified in
567 configuration files).
569 Disables forwarding (delegation) of GSSAPI credentials to the server.
572 .Ar port : host : hostport
575 Specifies that the given port on the local (client) host is to be
576 forwarded to the given host and port on the remote side.
577 This works by allocating a socket to listen to
579 on the local side, and whenever a connection is made to this port, the
580 connection is forwarded over the secure channel, and a connection is
585 from the remote machine.
586 Port forwardings can also be specified in the configuration file.
587 Only root can forward privileged ports.
588 IPv6 addresses can be specified with an alternative syntax:
591 .Ar port No / Ar host No /
595 .It Fl l Ar login_name
596 Specifies the user to log in as on the remote machine.
597 This also may be specified on a per-host basis in the configuration file.
603 mode for connection sharing.
604 Refer to the description of
610 Additionally, for protocol version 2 a comma-separated list of MAC
611 (message authentication code) algorithms can
612 be specified in order of preference.
615 keyword for more information.
617 Do not execute a remote command.
618 This is useful for just forwarding ports
619 (protocol version 2 only).
623 (actually, prevents reading from stdin).
624 This must be used when
626 is run in the background.
627 A common trick is to use this to run X11 programs on a remote machine.
629 .Ic ssh -n shadows.cs.hut.fi emacs &
630 will start an emacs on shadows.cs.hut.fi, and the X11
631 connection will be automatically forwarded over an encrypted channel.
634 program will be put in the background.
635 (This does not work if
637 needs to ask for a password or passphrase; see also the
641 Can be used to give options in the format used in the configuration file.
642 This is useful for specifying options for which there is no separate
644 For full details of the options listed below, and their possible values, see
647 .Bl -tag -width Ds -offset indent -compact
651 .It ChallengeResponseAuthentication
655 .It ClearAllForwardings
658 .It ConnectionAttempts
666 .It ForwardX11Trusted
668 .It GlobalKnownHostsFile
669 .It GSSAPIAuthentication
670 .It GSSAPIDelegateCredentials
672 .It HostbasedAuthentication
673 .It HostKeyAlgorithms
681 .It NoHostAuthenticationForLocalhost
682 .It NumberOfPasswordPrompts
683 .It PasswordAuthentication
685 .It PreferredAuthentications
688 .It PubkeyAuthentication
690 .It RhostsRSAAuthentication
691 .It RSAAuthentication
693 .It ServerAliveInterval
694 .It ServerAliveCountMax
696 .It StrictHostKeyChecking
698 .It UsePrivilegedPort
700 .It UserKnownHostsFile
705 Port to connect to on the remote host.
706 This can be specified on a
707 per-host basis in the configuration file.
710 Causes all warning and diagnostic messages to be suppressed.
713 .Ar port : host : hostport
716 Specifies that the given port on the remote (server) host is to be
717 forwarded to the given host and port on the local side.
718 This works by allocating a socket to listen to
720 on the remote side, and whenever a connection is made to this port, the
721 connection is forwarded over the secure channel, and a connection is
726 from the local machine.
727 Port forwardings can also be specified in the configuration file.
728 Privileged ports can be forwarded only when
729 logging in as root on the remote machine.
730 IPv6 addresses can be specified with an alternative syntax:
733 .Ar port No / Ar host No /
738 Specifies the location of a control socket for connection sharing.
739 Refer to the description of
747 May be used to request invocation of a subsystem on the remote system.
748 Subsystems are a feature of the SSH2 protocol which facilitate the use
749 of SSH as a secure transport for other applications (eg.\&
751 The subsystem is specified as the remote command.
753 Disable pseudo-tty allocation.
755 Force pseudo-tty allocation.
756 This can be used to execute arbitrary
757 screen-based programs on a remote machine, which can be very useful,
758 e.g., when implementing menu services.
761 options force tty allocation, even if
765 Display the version number and exit.
770 to print debugging messages about its progress.
772 debugging connection, authentication, and configuration problems.
775 options increase the verbosity.
778 Enables X11 forwarding.
779 This can also be specified on a per-host basis in a configuration file.
781 X11 forwarding should be enabled with caution.
782 Users with the ability to bypass file permissions on the remote host
783 (for the user's X authorization database)
784 can access the local X11 display through the forwarded connection.
785 An attacker may then be able to perform activities such as keystroke monitoring.
787 Disables X11 forwarding.
789 Enables trusted X11 forwarding.
791 .Sh CONFIGURATION FILES
793 may additionally obtain configuration data from
794 a per-user configuration file and a system-wide configuration file.
795 The file format and configuration options are described in
799 will normally set the following environment variables:
800 .Bl -tag -width LOGNAME
804 variable indicates the location of the X11 server.
805 It is automatically set by
807 to point to a value of the form
809 where hostname indicates
810 the host where the shell runs, and n is an integer \*(Ge 1.
812 uses this special value to forward X11 connections over the secure
814 The user should normally not set
817 will render the X11 connection insecure (and will require the user to
818 manually copy any required authorization cookies).
820 Set to the path of the user's home directory.
824 set for compatibility with systems that use this variable.
826 Set to the path of the user's mailbox.
830 as specified when compiling
835 needs a passphrase, it will read the passphrase from the current
836 terminal if it was run from a terminal.
839 does not have a terminal associated with it but
843 are set, it will execute the program specified by
845 and open an X11 window to read the passphrase.
846 This is particularly useful when calling
851 (Note that on some machines it
852 may be necessary to redirect the input from
856 Identifies the path of a unix-domain socket used to communicate with the
858 .It Ev SSH_CONNECTION
859 Identifies the client and server ends of the connection.
860 The variable contains
861 four space-separated values: client ip-address, client port number,
862 server ip-address and server port number.
863 .It Ev SSH_ORIGINAL_COMMAND
864 The variable contains the original command line if a forced command
866 It can be used to extract the original arguments.
868 This is set to the name of the tty (path to the device) associated
869 with the current shell or command.
870 If the current session has no tty,
871 this variable is not set.
873 The timezone variable is set to indicate the present timezone if it
874 was set when the daemon was started (i.e., the daemon passes the value
875 on to new connections).
877 Set to the name of the user logging in.
883 .Pa $HOME/.ssh/environment ,
884 and adds lines of the format
886 to the environment if the file exists and if users are allowed to
887 change their environment.
888 For more information, see the
889 .Cm PermitUserEnvironment
894 .It Pa $HOME/.ssh/known_hosts
895 Records host keys for all hosts the user has logged into that are not
897 .Pa /etc/ssh/ssh_known_hosts .
900 .It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa, $HOME/.ssh/id_rsa
901 Contains the authentication identity of the user.
902 They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively.
904 contain sensitive data and should be readable by the user but not
905 accessible by others (read/write/execute).
908 ignores a private key file if it is accessible by others.
909 It is possible to specify a passphrase when
910 generating the key; the passphrase will be used to encrypt the
911 sensitive part of this file using 3DES.
912 .It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub, $HOME/.ssh/id_rsa.pub
913 Contains the public key for authentication (public part of the
914 identity file in human-readable form).
916 .Pa $HOME/.ssh/identity.pub
917 file should be added to the file
918 .Pa $HOME/.ssh/authorized_keys
920 where the user wishes to log in using protocol version 1 RSA authentication.
922 .Pa $HOME/.ssh/id_dsa.pub
924 .Pa $HOME/.ssh/id_rsa.pub
925 file should be added to
926 .Pa $HOME/.ssh/authorized_keys
928 where the user wishes to log in using protocol version 2 DSA/RSA authentication.
930 sensitive and can (but need not) be readable by anyone.
932 never used automatically and are not necessary; they are only provided for
933 the convenience of the user.
934 .It Pa $HOME/.ssh/config
935 This is the per-user configuration file.
936 The file format and configuration options are described in
938 Because of the potential for abuse, this file must have strict permissions:
939 read/write for the user, and not accessible by others.
940 .It Pa $HOME/.ssh/authorized_keys
941 Lists the public keys (RSA/DSA) that can be used for logging in as this user.
942 The format of this file is described in the
945 In the simplest form the format is the same as the
948 This file is not highly sensitive, but the recommended
949 permissions are read/write for the user, and not accessible by others.
950 .It Pa /etc/ssh/ssh_known_hosts
951 Systemwide list of known host keys.
952 This file should be prepared by the
953 system administrator to contain the public host keys of all machines in the
955 This file should be world-readable.
957 public keys, one per line, in the following format (fields separated
958 by spaces): system name, public key and optional comment field.
959 When different names are used
960 for the same machine, all such names should be listed, separated by
962 The format is described in the
966 The canonical system name (as returned by name servers) is used by
968 to verify the client host when logging in; other names are needed because
970 does not convert the user-supplied name to a canonical name before
971 checking the key, because someone with access to the name servers
972 would then be able to fool host authentication.
973 .It Pa /etc/ssh/ssh_config
974 Systemwide configuration file.
975 The file format and configuration options are described in
977 .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key
978 These three files contain the private parts of the host keys
980 .Cm RhostsRSAAuthentication
982 .Cm HostbasedAuthentication .
983 If the protocol version 1
984 .Cm RhostsRSAAuthentication
987 must be setuid root, since the host key is readable only by root.
988 For protocol version 2,
992 to access the host keys for
993 .Cm HostbasedAuthentication .
994 This eliminates the requirement that
996 be setuid root when that authentication method is used.
1000 .It Pa $HOME/.rhosts
1001 This file is used in
1002 .Cm RhostsRSAAuthentication
1004 .Cm HostbasedAuthentication
1005 authentication to list the
1006 host/user pairs that are permitted to log in.
1007 (Note that this file is
1008 also used by rlogin and rsh, which makes using this file insecure.)
1009 Each line of the file contains a host name (in the canonical form
1010 returned by name servers), and then a user name on that host,
1011 separated by a space.
1012 On some machines this file may need to be
1013 world-readable if the user's home directory is on a NFS partition,
1017 Additionally, this file must be owned by the user,
1018 and must not have write permissions for anyone else.
1020 permission for most machines is read/write for the user, and not
1021 accessible by others.
1025 allows authentication only in combination with client host key
1026 authentication before permitting log in.
1027 If the server machine does not have the client's host key in
1028 .Pa /etc/ssh/ssh_known_hosts ,
1030 .Pa $HOME/.ssh/known_hosts .
1031 The easiest way to do this is to
1032 connect back to the client from the server machine using ssh; this
1033 will automatically add the host key to
1034 .Pa $HOME/.ssh/known_hosts .
1035 .It Pa $HOME/.shosts
1036 This file is used exactly the same way as
1039 having this file is to be able to use
1040 .Cm RhostsRSAAuthentication
1042 .Cm HostbasedAuthentication
1043 authentication without permitting login with
1047 .It Pa /etc/hosts.equiv
1048 This file is used during
1049 .Cm RhostsRSAAuthentication
1051 .Cm HostbasedAuthentication
1054 canonical hosts names, one per line (the full format is described in the
1057 If the client host is found in this file, login is
1058 automatically permitted provided client and server user names are the
1060 Additionally, successful client host key authentication is required.
1061 This file should only be writable by root.
1062 .It Pa /etc/shosts.equiv
1063 This file is processed exactly as
1064 .Pa /etc/hosts.equiv .
1065 This file may be useful to permit logins using
1067 but not using rsh/rlogin.
1068 .It Pa /etc/ssh/sshrc
1069 Commands in this file are executed by
1071 when the user logs in just before the user's shell (or command) is started.
1074 manual page for more information.
1075 .It Pa $HOME/.ssh/rc
1076 Commands in this file are executed by
1078 when the user logs in just before the user's shell (or command) is
1082 manual page for more information.
1083 .It Pa $HOME/.ssh/environment
1084 Contains additional definitions for environment variables, see section
1090 exits with the exit status of the remote command or with 255
1091 if an error occurred.
1111 .%T "SSH Protocol Architecture"
1112 .%N draft-ietf-secsh-architecture-12.txt
1114 .%O work in progress material
1117 OpenSSH is a derivative of the original and free
1118 ssh 1.2.12 release by Tatu Ylonen.
1119 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1120 Theo de Raadt and Dug Song
1121 removed many bugs, re-added newer features and
1123 Markus Friedl contributed the support for SSH
1124 protocol versions 1.5 and 2.0.
andersk / openssh.git / blob