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 1.209 2005/07/06 09:33:05 dtucker Exp $
39 .Dd September 25, 1999
44 .Nd OpenSSH SSH client (remote login program)
47 .Op Fl 1246AaCfgkMNnqsTtVvXxY
48 .Op Fl b Ar bind_address
49 .Op Fl c Ar cipher_spec
52 .Op Fl e Ar escape_char
53 .Op Fl F Ar configfile
54 .Op Fl i Ar identity_file
64 .Op Fl l Ar login_name
79 .Oo Ar user Ns @ Oc Ns Ar hostname
83 (SSH client) is a program for logging into a remote machine and for
84 executing commands on a remote machine.
85 It is intended to replace rlogin and rsh,
86 and provide secure encrypted communications between
87 two untrusted hosts over an insecure network.
88 X11 connections and arbitrary TCP/IP ports
89 can also be forwarded over the secure channel.
92 connects and logs into the specified
98 his/her identity to the remote machine using one of several methods
99 depending on the protocol version used.
105 is executed on the remote host instead of a login shell.
106 .Ss SSH protocol version 1
107 First, if the machine the user logs in from is listed in
110 .Pa /etc/ssh/shosts.equiv
111 on the remote machine, and the user names are
112 the same on both sides, the user is immediately permitted to log in.
117 exists in the user's home directory on the
118 remote machine and contains a line containing the name of the client
119 machine and the name of the user on that machine, the user is
121 This form of authentication alone is normally not
122 allowed by the server because it is not secure.
124 The second authentication method is the
128 method combined with RSA-based host authentication.
129 If the machine the user logs in from is listed in
132 .Pa /etc/shosts.equiv
133 on the remote machine, and the user names are
134 the same on both sides, or if the files
138 exist in the user's home directory on the
139 remote machine and contain a line containing the name of the client
140 machine and the name of the user on that machine, the user is
141 considered for log in.
142 Additionally, if the server can verify the client's
144 .Pa /etc/ssh/ssh_known_hosts
146 .Pa ~/.ssh/known_hosts
149 section), only then is login permitted.
150 This authentication method closes security holes due to IP
151 spoofing, DNS spoofing and routing spoofing.
152 [Note to the administrator:
153 .Pa /etc/hosts.equiv ,
155 and the rlogin/rsh protocol in general, are inherently insecure and should be
156 disabled if security is desired.]
158 As a third authentication method,
160 supports RSA based authentication.
161 The scheme is based on public-key cryptography: there are cryptosystems
162 where encryption and decryption are done using separate keys, and it
163 is not possible to derive the decryption key from the encryption key.
164 RSA is one such system.
165 The idea is that each user creates a public/private
166 key pair for authentication purposes.
167 The server knows the public key, and only the user knows the private key.
170 .Pa ~/.ssh/authorized_keys
171 lists the public keys that are permitted for logging in.
172 When the user logs in, the
174 program tells the server which key pair it would like to use for
176 The server checks if this key is permitted, and if so,
177 sends the user (actually the
179 program running on behalf of the user) a challenge, a random number,
180 encrypted by the user's public key.
181 The challenge can only be decrypted using the proper private key.
182 The user's client then decrypts the challenge using the private key,
183 proving that he/she knows the private key
184 but without disclosing it to the server.
187 implements the RSA authentication protocol automatically.
188 The user creates his/her RSA key pair by running
190 This stores the private key in
192 and stores the public key in
193 .Pa ~/.ssh/identity.pub
194 in the user's home directory.
195 The user should then copy the
198 .Pa ~/.ssh/authorized_keys
199 in his/her home directory on the remote machine (the
201 file corresponds to the conventional
203 file, and has one key
204 per line, though the lines can be very long).
205 After this, the user can log in without giving the password.
206 RSA authentication is much more secure than
210 The most convenient way to use RSA authentication may be with an
211 authentication agent.
214 for more information.
216 If other authentication methods fail,
218 prompts the user for a password.
219 The password is sent to the remote
220 host for checking; however, since all communications are encrypted,
221 the password cannot be seen by someone listening on the network.
222 .Ss SSH protocol version 2
223 When a user connects using protocol version 2,
224 similar authentication methods are available.
225 Using the default values for
226 .Cm PreferredAuthentications ,
227 the client will try to authenticate first using the hostbased method;
228 if this method fails, public key authentication is attempted,
229 and finally if this method fails, keyboard-interactive and
230 password authentication are tried.
232 The public key method is similar to RSA authentication described
233 in the previous section and allows the RSA or DSA algorithm to be used:
234 The client uses his private key,
238 to sign the session identifier and sends the result to the server.
239 The server checks whether the matching public key is listed in
240 .Pa ~/.ssh/authorized_keys
241 and grants access if both the key is found and the signature is correct.
242 The session identifier is derived from a shared Diffie-Hellman value
243 and is only known to the client and the server.
245 If public key authentication fails or is not available, a password
246 can be sent encrypted to the remote host to prove the user's identity.
250 supports hostbased or challenge response authentication.
252 Protocol 2 provides additional mechanisms for confidentiality
253 (the traffic is encrypted using AES, 3DES, Blowfish, CAST128 or Arcfour)
254 and integrity (hmac-md5, hmac-sha1, hmac-ripemd160).
255 Note that protocol 1 lacks a strong mechanism for ensuring the
256 integrity of the connection.
257 .Ss Login session and remote execution
258 When the user's identity has been accepted by the server, the server
259 either executes the given command, or logs into the machine and gives
260 the user a normal shell on the remote machine.
261 All communication with
262 the remote command or shell will be automatically encrypted.
264 If a pseudo-terminal has been allocated (normal login session), the
265 user may use the escape characters noted below.
267 If no pseudo-tty has been allocated,
268 the session is transparent and can be used to reliably transfer binary data.
269 On most systems, setting the escape character to
271 will also make the session transparent even if a tty is used.
273 The session terminates when the command or shell on the remote
274 machine exits and all X11 and TCP/IP connections have been closed.
275 The exit status of the remote program is returned as the exit status of
277 .Ss Escape Characters
278 When a pseudo-terminal has been requested,
280 supports a number of functions through the use of an escape character.
282 A single tilde character can be sent as
284 or by following the tilde by a character other than those described below.
285 The escape character must always follow a newline to be interpreted as
287 The escape character can be changed in configuration files using the
289 configuration directive or on the command line by the
293 The supported escapes (assuming the default
303 List forwarded connections.
307 at logout when waiting for forwarded connection / X11 sessions to terminate.
309 Display a list of escape characters.
311 Send a BREAK to the remote system
312 (only useful for SSH protocol version 2 and if the peer supports it).
315 Currently this allows the addition of port forwardings using the
320 It also allows the cancellation of existing remote port-forwardings
323 Basic help is available, using the
327 Request rekeying of the connection
328 (only useful for SSH protocol version 2 and if the peer supports it).
330 .Ss X11 and TCP forwarding
335 (or see the description of the
339 options described later)
340 and the user is using X11 (the
342 environment variable is set), the connection to the X11 display is
343 automatically forwarded to the remote side in such a way that any X11
344 programs started from the shell (or command) will go through the
345 encrypted channel, and the connection to the real X server will be made
346 from the local machine.
347 The user should not manually set
349 Forwarding of X11 connections can be
350 configured on the command line or in configuration files.
356 will point to the server machine, but with a display number greater than zero.
357 This is normal, and happens because
361 X server on the server machine for forwarding the
362 connections over the encrypted channel.
365 will also automatically set up Xauthority data on the server machine.
366 For this purpose, it will generate a random authorization cookie,
367 store it in Xauthority on the server, and verify that any forwarded
368 connections carry this cookie and replace it by the real cookie when
369 the connection is opened.
370 The real authentication cookie is never
371 sent to the server machine (and no cookies are sent in the plain).
377 (or see the description of the
381 options described later) and
382 the user is using an authentication agent, the connection to the agent
383 is automatically forwarded to the remote side.
385 Forwarding of arbitrary TCP/IP connections over the secure channel can
386 be specified either on the command line or in a configuration file.
387 One possible application of TCP/IP forwarding is a secure connection to an
388 electronic purse; another is going through firewalls.
389 .Ss Server authentication
391 automatically maintains and checks a database containing
392 identifications for all hosts it has ever been used with.
393 Host keys are stored in
394 .Pa ~/.ssh/known_hosts
395 in the user's home directory.
396 Additionally, the file
397 .Pa /etc/ssh/ssh_known_hosts
398 is automatically checked for known hosts.
399 Any new hosts are automatically added to the user's file.
400 If a host's identification ever changes,
402 warns about this and disables password authentication to prevent a
403 trojan horse from getting the user's password.
404 Another purpose of this mechanism is to prevent man-in-the-middle attacks
405 which could otherwise be used to circumvent the encryption.
407 .Cm StrictHostKeyChecking
408 option can be used to prevent logins to machines whose
409 host key is not known or has changed.
412 can be configured to verify host identification using fingerprint resource
413 records (SSHFP) published in DNS.
416 option can be used to control how DNS lookups are performed.
417 SSHFP resource records can be generated using
420 The options are as follows:
425 to try protocol version 1 only.
429 to try protocol version 2 only.
433 to use IPv4 addresses only.
437 to use IPv6 addresses only.
439 Enables forwarding of the authentication agent connection.
440 This can also be specified on a per-host basis in a configuration file.
442 Agent forwarding should be enabled with caution.
443 Users with the ability to bypass file permissions on the remote host
444 (for the agent's Unix-domain socket)
445 can access the local agent through the forwarded connection.
446 An attacker cannot obtain key material from the agent,
447 however they can perform operations on the keys that enable them to
448 authenticate using the identities loaded into the agent.
450 Disables forwarding of the authentication agent connection.
451 .It Fl b Ar bind_address
454 on the local machine as the source address
456 Only useful on systems with more than one address.
458 Requests compression of all data (including stdin, stdout, stderr, and
459 data for forwarded X11 and TCP/IP connections).
460 The compression algorithm is the same used by
464 can be controlled by the
466 option for protocol version 1.
467 Compression is desirable on modem lines and other
468 slow connections, but will only slow down things on fast networks.
469 The default value can be set on a host-by-host basis in the
470 configuration files; see the
473 .It Fl c Ar cipher_spec
474 Selects the cipher specification for encrypting the session.
476 Protocol version 1 allows specification of a single cipher.
477 The suported values are
483 (triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
484 It is believed to be secure.
486 is a fast block cipher; it appears very secure and is much faster than
489 is only supported in the
491 client for interoperability with legacy protocol 1 implementations
492 that do not support the
495 Its use is strongly discouraged due to cryptographic weaknesses.
499 For protocol version 2
501 is a comma-separated list of ciphers
502 listed in order of preference.
503 The supported ciphers are
519 ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
520 arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
521 aes192-ctr,aes256-ctr''
526 application-level port forwarding.
527 This works by allocating a socket to listen to
529 on the local side, and whenever a connection is made to this port, the
530 connection is forwarded over the secure channel, and the application
531 protocol is then used to determine where to connect to from the
533 Currently the SOCKS4 and SOCKS5 protocols are supported, and
535 will act as a SOCKS server.
536 Only root can forward privileged ports.
537 Dynamic port forwardings can also be specified in the configuration file.
538 .It Fl e Ar ch | ^ch | none
539 Sets the escape character for sessions with a pty (default:
541 The escape character is only recognized at the beginning of a line.
542 The escape character followed by a dot
544 closes the connection;
545 followed by control-Z suspends the connection;
546 and followed by itself sends the escape character once.
547 Setting the character to
549 disables any escapes and makes the session fully transparent.
550 .It Fl F Ar configfile
551 Specifies an alternative per-user configuration file.
552 If a configuration file is given on the command line,
553 the system-wide configuration file
554 .Pq Pa /etc/ssh/ssh_config
556 The default for the per-user configuration file is
561 to go to background just before command execution.
564 is going to ask for passwords or passphrases, but the user
565 wants it in the background.
568 The recommended way to start X11 programs at a remote site is with
570 .Ic ssh -f host xterm .
572 Allows remote hosts to connect to local forwarded ports.
573 .It Fl I Ar smartcard_device
574 Specifies which smartcard device to use.
575 The argument is the device
577 should use to communicate with a smartcard used for storing the user's
579 .It Fl i Ar identity_file
580 Selects a file from which the identity (private key) for
581 RSA or DSA authentication is read.
584 for protocol version 1, and
588 for protocol version 2.
589 Identity files may also be specified on
590 a per-host basis in the configuration file.
591 It is possible to have multiple
593 options (and multiple identities specified in
594 configuration files).
596 Disables forwarding (delegation) of GSSAPI credentials to the server.
599 .Ar port : host : hostport
602 Specifies that the given port on the local (client) host is to be
603 forwarded to the given host and port on the remote side.
604 This works by allocating a socket to listen to
606 on the local side, and whenever a connection is made to this port, the
607 connection is forwarded over the secure channel, and a connection is
612 from the remote machine.
613 Port forwardings can also be specified in the configuration file.
614 Only root can forward privileged ports.
615 IPv6 addresses can be specified with an alternative syntax:
618 .Ar port No / Ar host No /
622 .It Fl l Ar login_name
623 Specifies the user to log in as on the remote machine.
624 This also may be specified on a per-host basis in the configuration file.
630 mode for connection sharing.
631 Refer to the description of
637 Additionally, for protocol version 2 a comma-separated list of MAC
638 (message authentication code) algorithms can
639 be specified in order of preference.
642 keyword for more information.
644 Do not execute a remote command.
645 This is useful for just forwarding ports
646 (protocol version 2 only).
650 (actually, prevents reading from stdin).
651 This must be used when
653 is run in the background.
654 A common trick is to use this to run X11 programs on a remote machine.
656 .Ic ssh -n shadows.cs.hut.fi emacs &
657 will start an emacs on shadows.cs.hut.fi, and the X11
658 connection will be automatically forwarded over an encrypted channel.
661 program will be put in the background.
662 (This does not work if
664 needs to ask for a password or passphrase; see also the
668 Can be used to give options in the format used in the configuration file.
669 This is useful for specifying options for which there is no separate
671 For full details of the options listed below, and their possible values, see
674 .Bl -tag -width Ds -offset indent -compact
678 .It ChallengeResponseAuthentication
682 .It ClearAllForwardings
685 .It ConnectionAttempts
693 .It ForwardX11Trusted
695 .It GlobalKnownHostsFile
696 .It GSSAPIAuthentication
697 .It GSSAPIDelegateCredentials
699 .It HostbasedAuthentication
700 .It HostKeyAlgorithms
708 .It NoHostAuthenticationForLocalhost
709 .It NumberOfPasswordPrompts
710 .It PasswordAuthentication
712 .It PreferredAuthentications
715 .It PubkeyAuthentication
717 .It RhostsRSAAuthentication
718 .It RSAAuthentication
720 .It ServerAliveInterval
721 .It ServerAliveCountMax
723 .It StrictHostKeyChecking
725 .It UsePrivilegedPort
727 .It UserKnownHostsFile
732 Port to connect to on the remote host.
733 This can be specified on a
734 per-host basis in the configuration file.
737 Causes all warning and diagnostic messages to be suppressed.
740 .Ar port : host : hostport
743 Specifies that the given port on the remote (server) host is to be
744 forwarded to the given host and port on the local side.
745 This works by allocating a socket to listen to
747 on the remote side, and whenever a connection is made to this port, the
748 connection is forwarded over the secure channel, and a connection is
753 from the local machine.
754 Port forwardings can also be specified in the configuration file.
755 Privileged ports can be forwarded only when
756 logging in as root on the remote machine.
757 IPv6 addresses can be specified with an alternative syntax:
760 .Ar port No / Ar host No /
765 Specifies the location of a control socket for connection sharing.
766 Refer to the description of
774 May be used to request invocation of a subsystem on the remote system.
775 Subsystems are a feature of the SSH2 protocol which facilitate the use
776 of SSH as a secure transport for other applications (eg.\&
778 The subsystem is specified as the remote command.
780 Disable pseudo-tty allocation.
782 Force pseudo-tty allocation.
783 This can be used to execute arbitrary
784 screen-based programs on a remote machine, which can be very useful,
785 e.g., when implementing menu services.
788 options force tty allocation, even if
792 Display the version number and exit.
797 to print debugging messages about its progress.
799 debugging connection, authentication, and configuration problems.
802 options increase the verbosity.
805 Enables X11 forwarding.
806 This can also be specified on a per-host basis in a configuration file.
808 X11 forwarding should be enabled with caution.
809 Users with the ability to bypass file permissions on the remote host
810 (for the user's X authorization database)
811 can access the local X11 display through the forwarded connection.
812 An attacker may then be able to perform activities such as keystroke monitoring.
814 Disables X11 forwarding.
816 Enables trusted X11 forwarding.
818 .Sh CONFIGURATION FILES
820 may additionally obtain configuration data from
821 a per-user configuration file and a system-wide configuration file.
822 The file format and configuration options are described in
826 will normally set the following environment variables:
827 .Bl -tag -width LOGNAME
831 variable indicates the location of the X11 server.
832 It is automatically set by
834 to point to a value of the form
836 where hostname indicates
837 the host where the shell runs, and n is an integer \*(Ge 1.
839 uses this special value to forward X11 connections over the secure
841 The user should normally not set
844 will render the X11 connection insecure (and will require the user to
845 manually copy any required authorization cookies).
847 Set to the path of the user's home directory.
851 set for compatibility with systems that use this variable.
853 Set to the path of the user's mailbox.
857 as specified when compiling
862 needs a passphrase, it will read the passphrase from the current
863 terminal if it was run from a terminal.
866 does not have a terminal associated with it but
870 are set, it will execute the program specified by
872 and open an X11 window to read the passphrase.
873 This is particularly useful when calling
878 (Note that on some machines it
879 may be necessary to redirect the input from
883 Identifies the path of a unix-domain socket used to communicate with the
885 .It Ev SSH_CONNECTION
886 Identifies the client and server ends of the connection.
887 The variable contains
888 four space-separated values: client ip-address, client port number,
889 server ip-address and server port number.
890 .It Ev SSH_ORIGINAL_COMMAND
891 The variable contains the original command line if a forced command
893 It can be used to extract the original arguments.
895 This is set to the name of the tty (path to the device) associated
896 with the current shell or command.
897 If the current session has no tty,
898 this variable is not set.
900 The timezone variable is set to indicate the present timezone if it
901 was set when the daemon was started (i.e., the daemon passes the value
902 on to new connections).
904 Set to the name of the user logging in.
910 .Pa ~/.ssh/environment ,
911 and adds lines of the format
913 to the environment if the file exists and if users are allowed to
914 change their environment.
915 For more information, see the
916 .Cm PermitUserEnvironment
921 .It Pa ~/.ssh/known_hosts
922 Records host keys for all hosts the user has logged into that are not
924 .Pa /etc/ssh/ssh_known_hosts .
927 .It Pa ~/.ssh/identity, ~/.ssh/id_dsa, ~/.ssh/id_rsa
928 Contains the authentication identity of the user.
929 They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively.
931 contain sensitive data and should be readable by the user but not
932 accessible by others (read/write/execute).
935 ignores a private key file if it is accessible by others.
936 It is possible to specify a passphrase when
937 generating the key; the passphrase will be used to encrypt the
938 sensitive part of this file using 3DES.
939 .It Pa ~/.ssh/identity.pub, ~/.ssh/id_dsa.pub, ~/.ssh/id_rsa.pub
940 Contains the public key for authentication (public part of the
941 identity file in human-readable form).
943 .Pa ~/.ssh/identity.pub
944 file should be added to the file
945 .Pa ~/.ssh/authorized_keys
947 where the user wishes to log in using protocol version 1 RSA authentication.
949 .Pa ~/.ssh/id_dsa.pub
951 .Pa ~/.ssh/id_rsa.pub
952 file should be added to
953 .Pa ~/.ssh/authorized_keys
955 where the user wishes to log in using protocol version 2 DSA/RSA authentication.
957 sensitive and can (but need not) be readable by anyone.
959 never used automatically and are not necessary; they are only provided for
960 the convenience of the user.
962 This is the per-user configuration file.
963 The file format and configuration options are described in
965 Because of the potential for abuse, this file must have strict permissions:
966 read/write for the user, and not accessible by others.
967 .It Pa ~/.ssh/authorized_keys
968 Lists the public keys (RSA/DSA) that can be used for logging in as this user.
969 The format of this file is described in the
972 In the simplest form the format is the same as the
975 This file is not highly sensitive, but the recommended
976 permissions are read/write for the user, and not accessible by others.
977 .It Pa /etc/ssh/ssh_known_hosts
978 Systemwide list of known host keys.
979 This file should be prepared by the
980 system administrator to contain the public host keys of all machines in the
982 This file should be world-readable.
984 public keys, one per line, in the following format (fields separated
985 by spaces): system name, public key and optional comment field.
986 When different names are used
987 for the same machine, all such names should be listed, separated by
989 The format is described in the
993 The canonical system name (as returned by name servers) is used by
995 to verify the client host when logging in; other names are needed because
997 does not convert the user-supplied name to a canonical name before
998 checking the key, because someone with access to the name servers
999 would then be able to fool host authentication.
1000 .It Pa /etc/ssh/ssh_config
1001 Systemwide configuration file.
1002 The file format and configuration options are described in
1004 .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key
1005 These three files contain the private parts of the host keys
1007 .Cm RhostsRSAAuthentication
1009 .Cm HostbasedAuthentication .
1010 If the protocol version 1
1011 .Cm RhostsRSAAuthentication
1014 must be setuid root, since the host key is readable only by root.
1015 For protocol version 2,
1019 to access the host keys for
1020 .Cm HostbasedAuthentication .
1021 This eliminates the requirement that
1023 be setuid root when that authentication method is used.
1028 This file is used in
1030 authentication to list the
1031 host/user pairs that are permitted to log in.
1032 (Note that this file is
1033 also used by rlogin and rsh, which makes using this file insecure.)
1034 Each line of the file contains a host name (in the canonical form
1035 returned by name servers), and then a user name on that host,
1036 separated by a space.
1037 On some machines this file may need to be
1038 world-readable if the user's home directory is on a NFS partition,
1042 Additionally, this file must be owned by the user,
1043 and must not have write permissions for anyone else.
1045 permission for most machines is read/write for the user, and not
1046 accessible by others.
1048 Note that by default
1050 will be installed so that it requires successful RSA host
1051 authentication before permitting
1054 If the server machine does not have the client's host key in
1055 .Pa /etc/ssh/ssh_known_hosts ,
1057 .Pa ~/.ssh/known_hosts .
1058 The easiest way to do this is to
1059 connect back to the client from the server machine using ssh; this
1060 will automatically add the host key to
1061 .Pa ~/.ssh/known_hosts .
1063 This file is used exactly the same way as
1066 having this file is to be able to use rhosts authentication with
1068 without permitting login with
1072 .It Pa /etc/hosts.equiv
1073 This file is used during
1077 canonical hosts names, one per line (the full format is described in the
1080 If the client host is found in this file, login is
1081 automatically permitted provided client and server user names are the
1083 Additionally, successful RSA host authentication is normally
1085 This file should only be writable by root.
1086 .It Pa /etc/ssh/shosts.equiv
1087 This file is processed exactly as
1088 .Pa /etc/hosts.equiv .
1089 This file may be useful to permit logins using
1091 but not using rsh/rlogin.
1092 .It Pa /etc/ssh/sshrc
1093 Commands in this file are executed by
1095 when the user logs in just before the user's shell (or command) is started.
1098 manual page for more information.
1100 Commands in this file are executed by
1102 when the user logs in just before the user's shell (or command) is
1106 manual page for more information.
1107 .It Pa ~/.ssh/environment
1108 Contains additional definitions for environment variables, see section
1114 exits with the exit status of the remote command or with 255
1115 if an error occurred.
1135 .%T "SSH Protocol Architecture"
1136 .%N draft-ietf-secsh-architecture-12.txt
1138 .%O work in progress material
1141 OpenSSH is a derivative of the original and free
1142 ssh 1.2.12 release by Tatu Ylonen.
1143 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1144 Theo de Raadt and Dug Song
1145 removed many bugs, re-added newer features and
1147 Markus Friedl contributed the support for SSH
1148 protocol versions 1.5 and 2.0.
projects / FreeBSD / FreeBSD.git / blob