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 1.190 2004/06/13 15:03:02 djm Exp $
38 .Dd September 25, 1999
43 .Nd OpenSSH SSH client (remote login program)
46 .Op Fl 1246AaCfgkMNnqSsTtVvXxY
47 .Op Fl b Ar bind_address
48 .Op Fl c Ar cipher_spec
50 .Op Fl e Ar escape_char
51 .Op Fl F Ar configfile
52 .Op Fl i Ar identity_file
63 .Op Fl l Ar login_name
77 .Oo Ar user Ns @ Oc Ns Ar hostname
81 (SSH client) is a program for logging into a remote machine and for
82 executing commands on a remote machine.
83 It is intended to replace rlogin and rsh,
84 and provide secure encrypted communications between
85 two untrusted hosts over an insecure network.
86 X11 connections and arbitrary TCP/IP ports
87 can also be forwarded over the secure channel.
90 connects and logs into the specified
96 his/her identity to the remote machine using one of several methods
97 depending on the protocol version used.
103 is executed on the remote host instead of a login shell.
104 .Ss SSH protocol version 1
105 First, if the machine the user logs in from is listed in
108 .Pa /etc/shosts.equiv
109 on the remote machine, and the user names are
110 the same on both sides, the user is immediately permitted to log in.
115 exists in the user's home directory on the
116 remote machine and contains a line containing the name of the client
117 machine and the name of the user on that machine, the user is
119 This form of authentication alone is normally not
120 allowed by the server because it is not secure.
122 The second authentication method is the
126 method combined with RSA-based host authentication.
127 It means that if the login would be permitted by
130 .Pa /etc/hosts.equiv ,
132 .Pa /etc/shosts.equiv ,
133 and if additionally the server can verify the client's
135 .Pa /etc/ssh/ssh_known_hosts
137 .Pa $HOME/.ssh/known_hosts
140 section), only then is login permitted.
141 This authentication method closes security holes due to IP
142 spoofing, DNS spoofing and routing spoofing.
143 [Note to the administrator:
144 .Pa /etc/hosts.equiv ,
146 and the rlogin/rsh protocol in general, are inherently insecure and should be
147 disabled if security is desired.]
149 As a third authentication method,
151 supports RSA based authentication.
152 The scheme is based on public-key cryptography: there are cryptosystems
153 where encryption and decryption are done using separate keys, and it
154 is not possible to derive the decryption key from the encryption key.
155 RSA is one such system.
156 The idea is that each user creates a public/private
157 key pair for authentication purposes.
158 The server knows the public key, and only the user knows the private key.
161 .Pa $HOME/.ssh/authorized_keys
162 lists the public keys that are permitted for logging in.
163 When the user logs in, the
165 program tells the server which key pair it would like to use for
167 The server checks if this key is permitted, and if so,
168 sends the user (actually the
170 program running on behalf of the user) a challenge, a random number,
171 encrypted by the user's public key.
172 The challenge can only be decrypted using the proper private key.
173 The user's client then decrypts the challenge using the private key,
174 proving that he/she knows the private key
175 but without disclosing it to the server.
178 implements the RSA authentication protocol automatically.
179 The user creates his/her RSA key pair by running
181 This stores the private key in
182 .Pa $HOME/.ssh/identity
183 and stores the public key in
184 .Pa $HOME/.ssh/identity.pub
185 in the user's home directory.
186 The user should then copy the
189 .Pa $HOME/.ssh/authorized_keys
190 in his/her home directory on the remote machine (the
192 file corresponds to the conventional
194 file, and has one key
195 per line, though the lines can be very long).
196 After this, the user can log in without giving the password.
197 RSA authentication is much more secure than
201 The most convenient way to use RSA authentication may be with an
202 authentication agent.
205 for more information.
207 If other authentication methods fail,
209 prompts the user for a password.
210 The password is sent to the remote
211 host for checking; however, since all communications are encrypted,
212 the password cannot be seen by someone listening on the network.
213 .Ss SSH protocol version 2
214 When a user connects using protocol version 2,
215 similar authentication methods are available.
216 Using the default values for
217 .Cm PreferredAuthentications ,
218 the client will try to authenticate first using the hostbased method;
219 if this method fails, public key authentication is attempted,
220 and finally if this method fails, keyboard-interactive and
221 password authentication are tried.
223 The public key method is similar to RSA authentication described
224 in the previous section and allows the RSA or DSA algorithm to be used:
225 The client uses his private key,
226 .Pa $HOME/.ssh/id_dsa
228 .Pa $HOME/.ssh/id_rsa ,
229 to sign the session identifier and sends the result to the server.
230 The server checks whether the matching public key is listed in
231 .Pa $HOME/.ssh/authorized_keys
232 and grants access if both the key is found and the signature is correct.
233 The session identifier is derived from a shared Diffie-Hellman value
234 and is only known to the client and the server.
236 If public key authentication fails or is not available, a password
237 can be sent encrypted to the remote host to prove the user's identity.
241 supports hostbased or challenge response authentication.
243 Protocol 2 provides additional mechanisms for confidentiality
244 (the traffic is encrypted using AES, 3DES, Blowfish, CAST128 or Arcfour)
245 and integrity (hmac-md5, hmac-sha1, hmac-ripemd160).
246 Note that protocol 1 lacks a strong mechanism for ensuring the
247 integrity of the connection.
248 .Ss Login session and remote execution
249 When the user's identity has been accepted by the server, the server
250 either executes the given command, or logs into the machine and gives
251 the user a normal shell on the remote machine.
252 All communication with
253 the remote command or shell will be automatically encrypted.
255 If a pseudo-terminal has been allocated (normal login session), the
256 user may use the escape characters noted below.
258 If no pseudo-tty has been allocated,
259 the session is transparent and can be used to reliably transfer binary data.
260 On most systems, setting the escape character to
262 will also make the session transparent even if a tty is used.
264 The session terminates when the command or shell on the remote
265 machine exits and all X11 and TCP/IP connections have been closed.
266 The exit status of the remote program is returned as the exit status of
268 .Ss Escape Characters
269 When a pseudo-terminal has been requested,
271 supports a number of functions through the use of an escape character.
273 A single tilde character can be sent as
275 or by following the tilde by a character other than those described below.
276 The escape character must always follow a newline to be interpreted as
278 The escape character can be changed in configuration files using the
280 configuration directive or on the command line by the
284 The supported escapes (assuming the default
294 List forwarded connections.
298 at logout when waiting for forwarded connection / X11 sessions to terminate.
300 Display a list of escape characters.
302 Send a BREAK to the remote system
303 (only useful for SSH protocol version 2 and if the peer supports it).
306 Currently this allows the addition of port forwardings using the
311 It also allows the cancellation of existing remote port-forwardings
314 Basic help is available, using the
318 Request rekeying of the connection
319 (only useful for SSH protocol version 2 and if the peer supports it).
321 .Ss X11 and TCP forwarding
326 (or see the description of the
330 options described later)
331 and the user is using X11 (the
333 environment variable is set), the connection to the X11 display is
334 automatically forwarded to the remote side in such a way that any X11
335 programs started from the shell (or command) will go through the
336 encrypted channel, and the connection to the real X server will be made
337 from the local machine.
338 The user should not manually set
340 Forwarding of X11 connections can be
341 configured on the command line or in configuration files.
347 will point to the server machine, but with a display number greater than zero.
348 This is normal, and happens because
352 X server on the server machine for forwarding the
353 connections over the encrypted channel.
356 will also automatically set up Xauthority data on the server machine.
357 For this purpose, it will generate a random authorization cookie,
358 store it in Xauthority on the server, and verify that any forwarded
359 connections carry this cookie and replace it by the real cookie when
360 the connection is opened.
361 The real authentication cookie is never
362 sent to the server machine (and no cookies are sent in the plain).
368 (or see the description of the
372 options described later) and
373 the user is using an authentication agent, the connection to the agent
374 is automatically forwarded to the remote side.
376 Forwarding of arbitrary TCP/IP connections over the secure channel can
377 be specified either on the command line or in a configuration file.
378 One possible application of TCP/IP forwarding is a secure connection to an
379 electronic purse; another is going through firewalls.
380 .Ss Server authentication
382 automatically maintains and checks a database containing
383 identifications for all hosts it has ever been used with.
384 Host keys are stored in
385 .Pa $HOME/.ssh/known_hosts
386 in the user's home directory.
387 Additionally, the file
388 .Pa /etc/ssh/ssh_known_hosts
389 is automatically checked for known hosts.
390 Any new hosts are automatically added to the user's file.
391 If a host's identification ever changes,
393 warns about this and disables password authentication to prevent a
394 trojan horse from getting the user's password.
395 Another purpose of this mechanism is to prevent man-in-the-middle attacks
396 which could otherwise be used to circumvent the encryption.
398 .Cm StrictHostKeyChecking
399 option can be used to prevent logins to machines whose
400 host key is not known or has changed.
402 The options are as follows:
407 to try protocol version 1 only.
411 to try protocol version 2 only.
415 to use IPv4 addresses only.
419 to use IPv6 addresses only.
421 Enables forwarding of the authentication agent connection.
422 This can also be specified on a per-host basis in a configuration file.
424 Agent forwarding should be enabled with caution.
425 Users with the ability to bypass file permissions on the remote host
426 (for the agent's Unix-domain socket)
427 can access the local agent through the forwarded connection.
428 An attacker cannot obtain key material from the agent,
429 however they can perform operations on the keys that enable them to
430 authenticate using the identities loaded into the agent.
432 Disables forwarding of the authentication agent connection.
433 .It Fl b Ar bind_address
434 Specify the interface to transmit from on machines with multiple
435 interfaces or aliased addresses.
437 Requests compression of all data (including stdin, stdout, stderr, and
438 data for forwarded X11 and TCP/IP connections).
439 The compression algorithm is the same used by
443 can be controlled by the
445 option for protocol version 1.
446 Compression is desirable on modem lines and other
447 slow connections, but will only slow down things on fast networks.
448 The default value can be set on a host-by-host basis in the
449 configuration files; see the
452 .It Fl c Ar cipher_spec
453 Selects the cipher specification for encrypting the session.
455 Protocol version 1 allows specification of a single cipher.
456 The suported values are
462 (triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
463 It is believed to be secure.
465 is a fast block cipher; it appears very secure and is much faster than
468 is only supported in the
470 client for interoperability with legacy protocol 1 implementations
471 that do not support the
474 Its use is strongly discouraged due to cryptographic weaknesses.
478 For protocol version 2
480 is a comma-separated list of ciphers
481 listed in order of preference.
482 The supported ciphers are
496 ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,
497 aes192-cbc,aes256-cbc''
502 application-level port forwarding.
503 This works by allocating a socket to listen to
505 on the local side, and whenever a connection is made to this port, the
506 connection is forwarded over the secure channel, and the application
507 protocol is then used to determine where to connect to from the
509 Currently the SOCKS4 and SOCKS5 protocols are supported, and
511 will act as a SOCKS server.
512 Only root can forward privileged ports.
513 Dynamic port forwardings can also be specified in the configuration file.
514 .It Fl e Ar ch | ^ch | none
515 Sets the escape character for sessions with a pty (default:
517 The escape character is only recognized at the beginning of a line.
518 The escape character followed by a dot
520 closes the connection;
521 followed by control-Z suspends the connection;
522 and followed by itself sends the escape character once.
523 Setting the character to
525 disables any escapes and makes the session fully transparent.
526 .It Fl F Ar configfile
527 Specifies an alternative per-user configuration file.
528 If a configuration file is given on the command line,
529 the system-wide configuration file
530 .Pq Pa /etc/ssh/ssh_config
532 The default for the per-user configuration file is
533 .Pa $HOME/.ssh/config .
537 to go to background just before command execution.
540 is going to ask for passwords or passphrases, but the user
541 wants it in the background.
544 The recommended way to start X11 programs at a remote site is with
546 .Ic ssh -f host xterm .
548 Allows remote hosts to connect to local forwarded ports.
549 .It Fl I Ar smartcard_device
550 Specifies which smartcard device to use.
551 The argument is the device
553 should use to communicate with a smartcard used for storing the user's
555 .It Fl i Ar identity_file
556 Selects a file from which the identity (private key) for
557 RSA or DSA authentication is read.
559 .Pa $HOME/.ssh/identity
560 for protocol version 1, and
561 .Pa $HOME/.ssh/id_rsa
563 .Pa $HOME/.ssh/id_dsa
564 for protocol version 2.
565 Identity files may also be specified on
566 a per-host basis in the configuration file.
567 It is possible to have multiple
569 options (and multiple identities specified in
570 configuration files).
572 Disables forwarding (delegation) of GSSAPI credentials to the server.
575 .Ar port : host : hostport
578 Specifies that the given port on the local (client) host is to be
579 forwarded to the given host and port on the remote side.
580 This works by allocating a socket to listen to
582 on the local side, and whenever a connection is made to this port, the
583 connection is forwarded over the secure channel, and a connection is
588 from the remote machine.
589 Port forwardings can also be specified in the configuration file.
590 Only root can forward privileged ports.
591 IPv6 addresses can be specified with an alternative syntax:
594 .Ar port No / Ar host No /
598 .It Fl l Ar login_name
599 Specifies the user to log in as on the remote machine.
600 This also may be specified on a per-host basis in the configuration file.
602 Additionally, for protocol version 2 a comma-separated list of MAC
603 (message authentication code) algorithms can
604 be specified in order of preference.
607 keyword for more information.
613 mode for connection sharing.
614 Refer to the description of
620 Do not execute a remote command.
621 This is useful for just forwarding ports
622 (protocol version 2 only).
626 (actually, prevents reading from stdin).
627 This must be used when
629 is run in the background.
630 A common trick is to use this to run X11 programs on a remote machine.
632 .Ic ssh -n shadows.cs.hut.fi emacs &
633 will start an emacs on shadows.cs.hut.fi, and the X11
634 connection will be automatically forwarded over an encrypted channel.
637 program will be put in the background.
638 (This does not work if
640 needs to ask for a password or passphrase; see also the
644 Can be used to give options in the format used in the configuration file.
645 This is useful for specifying options for which there is no separate
647 For full details of the options listed below, and their possible values, see
650 .Bl -tag -width Ds -offset indent -compact
654 .It ChallengeResponseAuthentication
658 .It ClearAllForwardings
661 .It ConnectionAttempts
669 .It ForwardX11Trusted
671 .It GlobalKnownHostsFile
672 .It GSSAPIAuthentication
673 .It GSSAPIDelegateCredentials
675 .It HostbasedAuthentication
676 .It HostKeyAlgorithms
684 .It NoHostAuthenticationForLocalhost
685 .It NumberOfPasswordPrompts
686 .It PasswordAuthentication
688 .It PreferredAuthentications
691 .It PubkeyAuthentication
693 .It RhostsRSAAuthentication
694 .It RSAAuthentication
696 .It ServerAliveInterval
697 .It ServerAliveCountMax
699 .It StrictHostKeyChecking
701 .It UsePrivilegedPort
703 .It UserKnownHostsFile
708 Port to connect to on the remote host.
709 This can be specified on a
710 per-host basis in the configuration file.
713 Causes all warning and diagnostic messages to be suppressed.
716 .Ar port : host : hostport
719 Specifies that the given port on the remote (server) host is to be
720 forwarded to the given host and port on the local side.
721 This works by allocating a socket to listen to
723 on the remote side, and whenever a connection is made to this port, the
724 connection is forwarded over the secure channel, and a connection is
729 from the local machine.
730 Port forwardings can also be specified in the configuration file.
731 Privileged ports can be forwarded only when
732 logging in as root on the remote machine.
733 IPv6 addresses can be specified with an alternative syntax:
736 .Ar port No / Ar host No /
743 client into slave mode for connection sharing.
744 Refer to the description of
750 May be used to request invocation of a subsystem on the remote system.
751 Subsystems are a feature of the SSH2 protocol which facilitate the use
752 of SSH as a secure transport for other applications (eg.\&
754 The subsystem is specified as the remote command.
756 Disable pseudo-tty allocation.
758 Force pseudo-tty allocation.
759 This can be used to execute arbitrary
760 screen-based programs on a remote machine, which can be very useful,
761 e.g., when implementing menu services.
764 options force tty allocation, even if
768 Display the version number and exit.
773 to print debugging messages about its progress.
775 debugging connection, authentication, and configuration problems.
778 options increase the verbosity.
781 Enables X11 forwarding.
782 This can also be specified on a per-host basis in a configuration file.
784 X11 forwarding should be enabled with caution.
785 Users with the ability to bypass file permissions on the remote host
786 (for the user's X authorization database)
787 can access the local X11 display through the forwarded connection.
788 An attacker may then be able to perform activities such as keystroke monitoring.
790 Disables X11 forwarding.
792 Enables trusted X11 forwarding.
794 .Sh CONFIGURATION FILES
796 may additionally obtain configuration data from
797 a per-user configuration file and a system-wide configuration file.
798 The file format and configuration options are described in
802 will normally set the following environment variables:
803 .Bl -tag -width LOGNAME
807 variable indicates the location of the X11 server.
808 It is automatically set by
810 to point to a value of the form
812 where hostname indicates
813 the host where the shell runs, and n is an integer \*(Ge 1.
815 uses this special value to forward X11 connections over the secure
817 The user should normally not set
820 will render the X11 connection insecure (and will require the user to
821 manually copy any required authorization cookies).
823 Set to the path of the user's home directory.
827 set for compatibility with systems that use this variable.
829 Set to the path of the user's mailbox.
833 as specified when compiling
838 needs a passphrase, it will read the passphrase from the current
839 terminal if it was run from a terminal.
842 does not have a terminal associated with it but
846 are set, it will execute the program specified by
848 and open an X11 window to read the passphrase.
849 This is particularly useful when calling
854 (Note that on some machines it
855 may be necessary to redirect the input from
859 Identifies the path of a unix-domain socket used to communicate with the
861 .It Ev SSH_CONNECTION
862 Identifies the client and server ends of the connection.
863 The variable contains
864 four space-separated values: client ip-address, client port number,
865 server ip-address and server port number.
866 .It Ev SSH_ORIGINAL_COMMAND
867 The variable contains the original command line if a forced command
869 It can be used to extract the original arguments.
871 This is set to the name of the tty (path to the device) associated
872 with the current shell or command.
873 If the current session has no tty,
874 this variable is not set.
876 The timezone variable is set to indicate the present timezone if it
877 was set when the daemon was started (i.e., the daemon passes the value
878 on to new connections).
880 Set to the name of the user logging in.
886 .Pa $HOME/.ssh/environment ,
887 and adds lines of the format
889 to the environment if the file exists and if users are allowed to
890 change their environment.
891 For more information, see the
892 .Cm PermitUserEnvironment
897 .It Pa $HOME/.ssh/known_hosts
898 Records host keys for all hosts the user has logged into that are not
900 .Pa /etc/ssh/ssh_known_hosts .
903 .It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa, $HOME/.ssh/id_rsa
904 Contains the authentication identity of the user.
905 They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively.
907 contain sensitive data and should be readable by the user but not
908 accessible by others (read/write/execute).
911 ignores a private key file if it is accessible by others.
912 It is possible to specify a passphrase when
913 generating the key; the passphrase will be used to encrypt the
914 sensitive part of this file using 3DES.
915 .It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub, $HOME/.ssh/id_rsa.pub
916 Contains the public key for authentication (public part of the
917 identity file in human-readable form).
919 .Pa $HOME/.ssh/identity.pub
920 file should be added to the file
921 .Pa $HOME/.ssh/authorized_keys
923 where the user wishes to log in using protocol version 1 RSA authentication.
925 .Pa $HOME/.ssh/id_dsa.pub
927 .Pa $HOME/.ssh/id_rsa.pub
928 file should be added to
929 .Pa $HOME/.ssh/authorized_keys
931 where the user wishes to log in using protocol version 2 DSA/RSA authentication.
933 sensitive and can (but need not) be readable by anyone.
935 never used automatically and are not necessary; they are only provided for
936 the convenience of the user.
937 .It Pa $HOME/.ssh/config
938 This is the per-user configuration file.
939 The file format and configuration options are described in
941 Because of the potential for abuse, this file must have strict permissions:
942 read/write for the user, and not accessible by others.
943 .It Pa $HOME/.ssh/authorized_keys
944 Lists the public keys (RSA/DSA) that can be used for logging in as this user.
945 The format of this file is described in the
948 In the simplest form the format is the same as the
951 This file is not highly sensitive, but the recommended
952 permissions are read/write for the user, and not accessible by others.
953 .It Pa /etc/ssh/ssh_known_hosts
954 Systemwide list of known host keys.
955 This file should be prepared by the
956 system administrator to contain the public host keys of all machines in the
958 This file should be world-readable.
960 public keys, one per line, in the following format (fields separated
961 by spaces): system name, public key and optional comment field.
962 When different names are used
963 for the same machine, all such names should be listed, separated by
965 The format is described in the
969 The canonical system name (as returned by name servers) is used by
971 to verify the client host when logging in; other names are needed because
973 does not convert the user-supplied name to a canonical name before
974 checking the key, because someone with access to the name servers
975 would then be able to fool host authentication.
976 .It Pa /etc/ssh/ssh_config
977 Systemwide configuration file.
978 The file format and configuration options are described in
980 .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key
981 These three files contain the private parts of the host keys
983 .Cm RhostsRSAAuthentication
985 .Cm HostbasedAuthentication .
986 If the protocol version 1
987 .Cm RhostsRSAAuthentication
990 must be setuid root, since the host key is readable only by root.
991 For protocol version 2,
995 to access the host keys for
996 .Cm HostbasedAuthentication .
997 This eliminates the requirement that
999 be setuid root when that authentication method is used.
1003 .It Pa $HOME/.rhosts
1004 This file is used in
1006 authentication to list the
1007 host/user pairs that are permitted to log in.
1008 (Note that this file is
1009 also used by rlogin and rsh, which makes using this file insecure.)
1010 Each line of the file contains a host name (in the canonical form
1011 returned by name servers), and then a user name on that host,
1012 separated by a space.
1013 On some machines this file may need to be
1014 world-readable if the user's home directory is on a NFS partition,
1018 Additionally, this file must be owned by the user,
1019 and must not have write permissions for anyone else.
1021 permission for most machines is read/write for the user, and not
1022 accessible by others.
1024 Note that by default
1026 will be installed so that it requires successful RSA host
1027 authentication before permitting
1030 If the server machine does not have the client's host key in
1031 .Pa /etc/ssh/ssh_known_hosts ,
1033 .Pa $HOME/.ssh/known_hosts .
1034 The easiest way to do this is to
1035 connect back to the client from the server machine using ssh; this
1036 will automatically add the host key to
1037 .Pa $HOME/.ssh/known_hosts .
1038 .It Pa $HOME/.shosts
1039 This file is used exactly the same way as
1042 having this file is to be able to use rhosts authentication with
1044 without permitting login with
1048 .It Pa /etc/hosts.equiv
1049 This file is used during
1053 canonical hosts names, one per line (the full format is described in the
1056 If the client host is found in this file, login is
1057 automatically permitted provided client and server user names are the
1059 Additionally, successful RSA host authentication is normally
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