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 1.199 2004/11/07 17:42:36 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 .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
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 The first authentication method is the
111 method combined with RSA-based host authentication.
112 If the machine the user logs in from is listed in
115 .Pa /etc/shosts.equiv
116 on the remote machine, and the user names are
117 the same on both sides, or if the files
121 exist in the user's home directory on the
122 remote machine and contain a line containing the name of the client
123 machine and the name of the user on that machine, the user is
124 considered for log in.
125 Additionally, if the server can verify the client's
127 .Pa /etc/ssh/ssh_known_hosts
129 .Pa $HOME/.ssh/known_hosts
132 section), only then is login permitted.
133 This authentication method closes security holes due to IP
134 spoofing, DNS spoofing and routing spoofing.
135 [Note to the administrator:
136 .Pa /etc/hosts.equiv ,
138 and the rlogin/rsh protocol in general, are inherently insecure and should be
139 disabled if security is desired.]
141 As a second authentication method,
143 supports RSA based authentication.
144 The scheme is based on public-key cryptography: there are cryptosystems
145 where encryption and decryption are done using separate keys, and it
146 is not possible to derive the decryption key from the encryption key.
147 RSA is one such system.
148 The idea is that each user creates a public/private
149 key pair for authentication purposes.
150 The server knows the public key, and only the user knows the private key.
153 .Pa $HOME/.ssh/authorized_keys
154 lists the public keys that are permitted for logging in.
155 When the user logs in, the
157 program tells the server which key pair it would like to use for
159 The server checks if this key is permitted, and if so,
160 sends the user (actually the
162 program running on behalf of the user) a challenge, a random number,
163 encrypted by the user's public key.
164 The challenge can only be decrypted using the proper private key.
165 The user's client then decrypts the challenge using the private key,
166 proving that he/she knows the private key
167 but without disclosing it to the server.
170 implements the RSA authentication protocol automatically.
171 The user creates his/her RSA key pair by running
173 This stores the private key in
174 .Pa $HOME/.ssh/identity
175 and stores the public key in
176 .Pa $HOME/.ssh/identity.pub
177 in the user's home directory.
178 The user should then copy the
181 .Pa $HOME/.ssh/authorized_keys
182 in his/her home directory on the remote machine (the
184 file corresponds to the conventional
186 file, and has one key
187 per line, though the lines can be very long).
188 After this, the user can log in without giving the password.
190 The most convenient way to use RSA authentication may be with an
191 authentication agent.
194 for more information.
196 If other authentication methods fail,
198 prompts the user for a password.
199 The password is sent to the remote
200 host for checking; however, since all communications are encrypted,
201 the password cannot be seen by someone listening on the network.
202 .Ss SSH protocol version 2
203 When a user connects using protocol version 2,
204 similar authentication methods are available.
205 Using the default values for
206 .Cm PreferredAuthentications ,
207 the client will try to authenticate first using the hostbased method;
208 if this method fails, public key authentication is attempted,
209 and finally if this method fails, keyboard-interactive and
210 password authentication are tried.
212 The public key method is similar to RSA authentication described
213 in the previous section and allows the RSA or DSA algorithm to be used:
214 The client uses his private key,
215 .Pa $HOME/.ssh/id_dsa
217 .Pa $HOME/.ssh/id_rsa ,
218 to sign the session identifier and sends the result to the server.
219 The server checks whether the matching public key is listed in
220 .Pa $HOME/.ssh/authorized_keys
221 and grants access if both the key is found and the signature is correct.
222 The session identifier is derived from a shared Diffie-Hellman value
223 and is only known to the client and the server.
225 If public key authentication fails or is not available, a password
226 can be sent encrypted to the remote host to prove the user's identity.
230 supports hostbased or challenge response authentication.
232 Protocol 2 provides additional mechanisms for confidentiality
233 (the traffic is encrypted using AES, 3DES, Blowfish, CAST128 or Arcfour)
234 and integrity (hmac-md5, hmac-sha1, hmac-ripemd160).
235 Note that protocol 1 lacks a strong mechanism for ensuring the
236 integrity of the connection.
237 .Ss Login session and remote execution
238 When the user's identity has been accepted by the server, the server
239 either executes the given command, or logs into the machine and gives
240 the user a normal shell on the remote machine.
241 All communication with
242 the remote command or shell will be automatically encrypted.
244 If a pseudo-terminal has been allocated (normal login session), the
245 user may use the escape characters noted below.
247 If no pseudo-tty has been allocated,
248 the session is transparent and can be used to reliably transfer binary data.
249 On most systems, setting the escape character to
251 will also make the session transparent even if a tty is used.
253 The session terminates when the command or shell on the remote
254 machine exits and all X11 and TCP/IP connections have been closed.
255 The exit status of the remote program is returned as the exit status of
257 .Ss Escape Characters
258 When a pseudo-terminal has been requested,
260 supports a number of functions through the use of an escape character.
262 A single tilde character can be sent as
264 or by following the tilde by a character other than those described below.
265 The escape character must always follow a newline to be interpreted as
267 The escape character can be changed in configuration files using the
269 configuration directive or on the command line by the
273 The supported escapes (assuming the default
283 List forwarded connections.
287 at logout when waiting for forwarded connection / X11 sessions to terminate.
289 Display a list of escape characters.
291 Send a BREAK to the remote system
292 (only useful for SSH protocol version 2 and if the peer supports it).
295 Currently this allows the addition of port forwardings using the
300 It also allows the cancellation of existing remote port-forwardings
303 Basic help is available, using the
307 Request rekeying of the connection
308 (only useful for SSH protocol version 2 and if the peer supports it).
310 .Ss X11 and TCP forwarding
315 (or see the description of the
319 options described later)
320 and the user is using X11 (the
322 environment variable is set), the connection to the X11 display is
323 automatically forwarded to the remote side in such a way that any X11
324 programs started from the shell (or command) will go through the
325 encrypted channel, and the connection to the real X server will be made
326 from the local machine.
327 The user should not manually set
329 Forwarding of X11 connections can be
330 configured on the command line or in configuration files.
336 will point to the server machine, but with a display number greater than zero.
337 This is normal, and happens because
341 X server on the server machine for forwarding the
342 connections over the encrypted channel.
345 will also automatically set up Xauthority data on the server machine.
346 For this purpose, it will generate a random authorization cookie,
347 store it in Xauthority on the server, and verify that any forwarded
348 connections carry this cookie and replace it by the real cookie when
349 the connection is opened.
350 The real authentication cookie is never
351 sent to the server machine (and no cookies are sent in the plain).
357 (or see the description of the
361 options described later) and
362 the user is using an authentication agent, the connection to the agent
363 is automatically forwarded to the remote side.
365 Forwarding of arbitrary TCP/IP connections over the secure channel can
366 be specified either on the command line or in a configuration file.
367 One possible application of TCP/IP forwarding is a secure connection to an
368 electronic purse; another is going through firewalls.
369 .Ss Server authentication
371 automatically maintains and checks a database containing
372 identifications for all hosts it has ever been used with.
373 Host keys are stored in
374 .Pa $HOME/.ssh/known_hosts
375 in the user's home directory.
376 Additionally, the file
377 .Pa /etc/ssh/ssh_known_hosts
378 is automatically checked for known hosts.
379 Any new hosts are automatically added to the user's file.
380 If a host's identification ever changes,
382 warns about this and disables password authentication to prevent a
383 trojan horse from getting the user's password.
384 Another purpose of this mechanism is to prevent man-in-the-middle attacks
385 which could otherwise be used to circumvent the encryption.
387 .Cm StrictHostKeyChecking
388 option can be used to prevent logins to machines whose
389 host key is not known or has changed.
392 can be configured to verify host identification using fingerprint resource
393 records (SSHFP) published in DNS.
396 option can be used to control how DNS lookups are performed.
397 SSHFP resource records can be generated using
400 The options are as follows:
405 to try protocol version 1 only.
409 to try protocol version 2 only.
413 to use IPv4 addresses only.
417 to use IPv6 addresses only.
419 Enables forwarding of the authentication agent connection.
420 This can also be specified on a per-host basis in a configuration file.
422 Agent forwarding should be enabled with caution.
423 Users with the ability to bypass file permissions on the remote host
424 (for the agent's Unix-domain socket)
425 can access the local agent through the forwarded connection.
426 An attacker cannot obtain key material from the agent,
427 however they can perform operations on the keys that enable them to
428 authenticate using the identities loaded into the agent.
430 Disables forwarding of the authentication agent connection.
431 .It Fl b Ar bind_address
432 Specify the interface to transmit from on machines with multiple
433 interfaces or aliased addresses.
435 Requests compression of all data (including stdin, stdout, stderr, and
436 data for forwarded X11 and TCP/IP connections).
437 The compression algorithm is the same used by
441 can be controlled by the
443 option for protocol version 1.
444 Compression is desirable on modem lines and other
445 slow connections, but will only slow down things on fast networks.
446 The default value can be set on a host-by-host basis in the
447 configuration files; see the
450 .It Fl c Ar cipher_spec
451 Selects the cipher specification for encrypting the session.
453 Protocol version 1 allows specification of a single cipher.
454 The suported values are
460 (triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
461 It is believed to be secure.
463 is a fast block cipher; it appears very secure and is much faster than
466 is only supported in the
468 client for interoperability with legacy protocol 1 implementations
469 that do not support the
472 Its use is strongly discouraged due to cryptographic weaknesses.
476 For protocol version 2
478 is a comma-separated list of ciphers
479 listed in order of preference.
480 The supported ciphers are
494 ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,
495 aes192-cbc,aes256-cbc''
500 application-level port forwarding.
501 This works by allocating a socket to listen to
503 on the local side, and whenever a connection is made to this port, the
504 connection is forwarded over the secure channel, and the application
505 protocol is then used to determine where to connect to from the
507 Currently the SOCKS4 and SOCKS5 protocols are supported, and
509 will act as a SOCKS server.
510 Only root can forward privileged ports.
511 Dynamic port forwardings can also be specified in the configuration file.
512 .It Fl e Ar ch | ^ch | none
513 Sets the escape character for sessions with a pty (default:
515 The escape character is only recognized at the beginning of a line.
516 The escape character followed by a dot
518 closes the connection;
519 followed by control-Z suspends the connection;
520 and followed by itself sends the escape character once.
521 Setting the character to
523 disables any escapes and makes the session fully transparent.
524 .It Fl F Ar configfile
525 Specifies an alternative per-user configuration file.
526 If a configuration file is given on the command line,
527 the system-wide configuration file
528 .Pq Pa /etc/ssh/ssh_config
530 The default for the per-user configuration file is
531 .Pa $HOME/.ssh/config .
535 to go to background just before command execution.
538 is going to ask for passwords or passphrases, but the user
539 wants it in the background.
542 The recommended way to start X11 programs at a remote site is with
544 .Ic ssh -f host xterm .
546 Allows remote hosts to connect to local forwarded ports.
547 .It Fl I Ar smartcard_device
548 Specifies which smartcard device to use.
549 The argument is the device
551 should use to communicate with a smartcard used for storing the user's
553 .It Fl i Ar identity_file
554 Selects a file from which the identity (private key) for
555 RSA or DSA authentication is read.
557 .Pa $HOME/.ssh/identity
558 for protocol version 1, and
559 .Pa $HOME/.ssh/id_rsa
561 .Pa $HOME/.ssh/id_dsa
562 for protocol version 2.
563 Identity files may also be specified on
564 a per-host basis in the configuration file.
565 It is possible to have multiple
567 options (and multiple identities specified in
568 configuration files).
570 Disables forwarding (delegation) of GSSAPI credentials to the server.
573 .Ar port : host : hostport
576 Specifies that the given port on the local (client) host is to be
577 forwarded to the given host and port on the remote side.
578 This works by allocating a socket to listen to
580 on the local side, and whenever a connection is made to this port, the
581 connection is forwarded over the secure channel, and a connection is
586 from the remote machine.
587 Port forwardings can also be specified in the configuration file.
588 Only root can forward privileged ports.
589 IPv6 addresses can be specified with an alternative syntax:
592 .Ar port No / Ar host No /
596 .It Fl l Ar login_name
597 Specifies the user to log in as on the remote machine.
598 This also may be specified on a per-host basis in the configuration file.
604 mode for connection sharing.
605 Refer to the description of
611 Additionally, for protocol version 2 a comma-separated list of MAC
612 (message authentication code) algorithms can
613 be specified in order of preference.
616 keyword for more information.
618 Do not execute a remote command.
619 This is useful for just forwarding ports
620 (protocol version 2 only).
624 (actually, prevents reading from stdin).
625 This must be used when
627 is run in the background.
628 A common trick is to use this to run X11 programs on a remote machine.
630 .Ic ssh -n shadows.cs.hut.fi emacs &
631 will start an emacs on shadows.cs.hut.fi, and the X11
632 connection will be automatically forwarded over an encrypted channel.
635 program will be put in the background.
636 (This does not work if
638 needs to ask for a password or passphrase; see also the
642 Control an active connection multiplexing master process.
645 option is specified, the
647 argument is interpreted and passed to the master process.
650 (check that the master process is running) and
652 (request the master to exit).
654 Can be used to give options in the format used in the configuration file.
655 This is useful for specifying options for which there is no separate
657 For full details of the options listed below, and their possible values, see
660 .Bl -tag -width Ds -offset indent -compact
664 .It ChallengeResponseAuthentication
668 .It ClearAllForwardings
671 .It ConnectionAttempts
679 .It ForwardX11Trusted
681 .It GlobalKnownHostsFile
682 .It GSSAPIAuthentication
683 .It GSSAPIDelegateCredentials
685 .It HostbasedAuthentication
686 .It HostKeyAlgorithms
691 .It KbdInteractiveDevices
695 .It NoHostAuthenticationForLocalhost
696 .It NumberOfPasswordPrompts
697 .It PasswordAuthentication
699 .It PreferredAuthentications
702 .It PubkeyAuthentication
704 .It RhostsRSAAuthentication
705 .It RSAAuthentication
707 .It ServerAliveInterval
708 .It ServerAliveCountMax
710 .It StrictHostKeyChecking
712 .It UsePrivilegedPort
714 .It UserKnownHostsFile
719 Port to connect to on the remote host.
720 This can be specified on a
721 per-host basis in the configuration file.
724 Causes all warning and diagnostic messages to be suppressed.
727 .Ar port : host : hostport
730 Specifies that the given port on the remote (server) host is to be
731 forwarded to the given host and port on the local side.
732 This works by allocating a socket to listen to
734 on the remote side, and whenever a connection is made to this port, the
735 connection is forwarded over the secure channel, and a connection is
740 from the local machine.
741 Port forwardings can also be specified in the configuration file.
742 Privileged ports can be forwarded only when
743 logging in as root on the remote machine.
744 IPv6 addresses can be specified with an alternative syntax:
747 .Ar port No / Ar host No /
752 Specifies the location of a control socket for connection sharing.
753 Refer to the description of
761 May be used to request invocation of a subsystem on the remote system.
762 Subsystems are a feature of the SSH2 protocol which facilitate the use
763 of SSH as a secure transport for other applications (eg.\&
765 The subsystem is specified as the remote command.
767 Disable pseudo-tty allocation.
769 Force pseudo-tty allocation.
770 This can be used to execute arbitrary
771 screen-based programs on a remote machine, which can be very useful,
772 e.g., when implementing menu services.
775 options force tty allocation, even if
779 Display the version number and exit.
784 to print debugging messages about its progress.
786 debugging connection, authentication, and configuration problems.
789 options increase the verbosity.
792 Enables X11 forwarding.
793 This can also be specified on a per-host basis in a configuration file.
795 X11 forwarding should be enabled with caution.
796 Users with the ability to bypass file permissions on the remote host
797 (for the user's X authorization database)
798 can access the local X11 display through the forwarded connection.
799 An attacker may then be able to perform activities such as keystroke monitoring.
801 Disables X11 forwarding.
803 Enables trusted X11 forwarding.
805 .Sh CONFIGURATION FILES
807 may additionally obtain configuration data from
808 a per-user configuration file and a system-wide configuration file.
809 The file format and configuration options are described in
813 will normally set the following environment variables:
814 .Bl -tag -width LOGNAME
818 variable indicates the location of the X11 server.
819 It is automatically set by
821 to point to a value of the form
823 where hostname indicates
824 the host where the shell runs, and n is an integer \*(Ge 1.
826 uses this special value to forward X11 connections over the secure
828 The user should normally not set
831 will render the X11 connection insecure (and will require the user to
832 manually copy any required authorization cookies).
834 Set to the path of the user's home directory.
838 set for compatibility with systems that use this variable.
840 Set to the path of the user's mailbox.
844 as specified when compiling
849 needs a passphrase, it will read the passphrase from the current
850 terminal if it was run from a terminal.
853 does not have a terminal associated with it but
857 are set, it will execute the program specified by
859 and open an X11 window to read the passphrase.
860 This is particularly useful when calling
865 (Note that on some machines it
866 may be necessary to redirect the input from
870 Identifies the path of a unix-domain socket used to communicate with the
872 .It Ev SSH_CONNECTION
873 Identifies the client and server ends of the connection.
874 The variable contains
875 four space-separated values: client ip-address, client port number,
876 server ip-address and server port number.
877 .It Ev SSH_ORIGINAL_COMMAND
878 The variable contains the original command line if a forced command
880 It can be used to extract the original arguments.
882 This is set to the name of the tty (path to the device) associated
883 with the current shell or command.
884 If the current session has no tty,
885 this variable is not set.
887 The timezone variable is set to indicate the present timezone if it
888 was set when the daemon was started (i.e., the daemon passes the value
889 on to new connections).
891 Set to the name of the user logging in.
897 .Pa $HOME/.ssh/environment ,
898 and adds lines of the format
900 to the environment if the file exists and if users are allowed to
901 change their environment.
902 For more information, see the
903 .Cm PermitUserEnvironment
908 .It Pa $HOME/.ssh/known_hosts
909 Records host keys for all hosts the user has logged into that are not
911 .Pa /etc/ssh/ssh_known_hosts .
914 .It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa, $HOME/.ssh/id_rsa
915 Contains the authentication identity of the user.
916 They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively.
918 contain sensitive data and should be readable by the user but not
919 accessible by others (read/write/execute).
922 ignores a private key file if it is accessible by others.
923 It is possible to specify a passphrase when
924 generating the key; the passphrase will be used to encrypt the
925 sensitive part of this file using 3DES.
926 .It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub, $HOME/.ssh/id_rsa.pub
927 Contains the public key for authentication (public part of the
928 identity file in human-readable form).
930 .Pa $HOME/.ssh/identity.pub
931 file should be added to the file
932 .Pa $HOME/.ssh/authorized_keys
934 where the user wishes to log in using protocol version 1 RSA authentication.
936 .Pa $HOME/.ssh/id_dsa.pub
938 .Pa $HOME/.ssh/id_rsa.pub
939 file should be added to
940 .Pa $HOME/.ssh/authorized_keys
942 where the user wishes to log in using protocol version 2 DSA/RSA authentication.
944 sensitive and can (but need not) be readable by anyone.
946 never used automatically and are not necessary; they are only provided for
947 the convenience of the user.
948 .It Pa $HOME/.ssh/config
949 This is the per-user configuration file.
950 The file format and configuration options are described in
952 Because of the potential for abuse, this file must have strict permissions:
953 read/write for the user, and not accessible by others.
954 .It Pa $HOME/.ssh/authorized_keys
955 Lists the public keys (RSA/DSA) that can be used for logging in as this user.
956 The format of this file is described in the
959 In the simplest form the format is the same as the
962 This file is not highly sensitive, but the recommended
963 permissions are read/write for the user, and not accessible by others.
964 .It Pa /etc/ssh/ssh_known_hosts
965 Systemwide list of known host keys.
966 This file should be prepared by the
967 system administrator to contain the public host keys of all machines in the
969 This file should be world-readable.
971 public keys, one per line, in the following format (fields separated
972 by spaces): system name, public key and optional comment field.
973 When different names are used
974 for the same machine, all such names should be listed, separated by
976 The format is described in the
980 The canonical system name (as returned by name servers) is used by
982 to verify the client host when logging in; other names are needed because
984 does not convert the user-supplied name to a canonical name before
985 checking the key, because someone with access to the name servers
986 would then be able to fool host authentication.
987 .It Pa /etc/ssh/ssh_config
988 Systemwide configuration file.
989 The file format and configuration options are described in
991 .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key
992 These three files contain the private parts of the host keys
994 .Cm RhostsRSAAuthentication
996 .Cm HostbasedAuthentication .
997 If the protocol version 1
998 .Cm RhostsRSAAuthentication
1001 must be setuid root, since the host key is readable only by root.
1002 For protocol version 2,
1006 to access the host keys for
1007 .Cm HostbasedAuthentication .
1008 This eliminates the requirement that
1010 be setuid root when that authentication method is used.
1014 .It Pa $HOME/.rhosts
1015 This file is used in
1016 .Cm RhostsRSAAuthentication
1018 .Cm HostbasedAuthentication
1019 authentication to list the
1020 host/user pairs that are permitted to log in.
1021 (Note that this file is
1022 also used by rlogin and rsh, which makes using this file insecure.)
1023 Each line of the file contains a host name (in the canonical form
1024 returned by name servers), and then a user name on that host,
1025 separated by a space.
1026 On some machines this file may need to be
1027 world-readable if the user's home directory is on a NFS partition,
1031 Additionally, this file must be owned by the user,
1032 and must not have write permissions for anyone else.
1034 permission for most machines is read/write for the user, and not
1035 accessible by others.
1039 allows authentication only in combination with client host key
1040 authentication before permitting log in.
1041 If the server machine does not have the client's host key in
1042 .Pa /etc/ssh/ssh_known_hosts ,
1044 .Pa $HOME/.ssh/known_hosts .
1045 The easiest way to do this is to
1046 connect back to the client from the server machine using ssh; this
1047 will automatically add the host key to
1048 .Pa $HOME/.ssh/known_hosts .
1049 .It Pa $HOME/.shosts
1050 This file is used exactly the same way as
1053 having this file is to be able to use
1054 .Cm RhostsRSAAuthentication
1056 .Cm HostbasedAuthentication
1057 authentication without permitting login with
1061 .It Pa /etc/hosts.equiv
1062 This file is used during
1063 .Cm RhostsRSAAuthentication
1065 .Cm HostbasedAuthentication
1068 canonical hosts names, one per line (the full format is described in the
1071 If the client host is found in this file, login is
1072 automatically permitted provided client and server user names are the
1074 Additionally, successful client host key authentication is required.
1075 This file should only be writable by root.
1076 .It Pa /etc/shosts.equiv
1077 This file is processed exactly as
1078 .Pa /etc/hosts.equiv .
1079 This file may be useful to permit logins using
1081 but not using rsh/rlogin.
1082 .It Pa /etc/ssh/sshrc
1083 Commands in this file are executed by
1085 when the user logs in just before the user's shell (or command) is started.
1088 manual page for more information.
1089 .It Pa $HOME/.ssh/rc
1090 Commands in this file are executed by
1092 when the user logs in just before the user's shell (or command) is
1096 manual page for more information.
1097 .It Pa $HOME/.ssh/environment
1098 Contains additional definitions for environment variables, see section
1104 exits with the exit status of the remote command or with 255
1105 if an error occurred.
1125 .%T "SSH Protocol Architecture"
1126 .%N draft-ietf-secsh-architecture-12.txt
1128 .%O work in progress material
1131 OpenSSH is a derivative of the original and free
1132 ssh 1.2.12 release by Tatu Ylonen.
1133 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1134 Theo de Raadt and Dug Song
1135 removed many bugs, re-added newer features and
1137 Markus Friedl contributed the support for SSH
1138 protocol versions 1.5 and 2.0.
andersk / openssh.git / blob