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 1.208 2005/05/23 23:32:46 djm Exp $
38 .Dd September 25, 1999
43 .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
51 .Op Fl e Ar escape_char
52 .Op Fl F Ar configfile
53 .Op Fl i Ar identity_file
56 .Oo Ar bind_address : Oc
57 .Ar port : host : hostport
60 .Op Fl l Ar login_name
67 .Oo Ar bind_address : Oc
68 .Ar port : host : hostport
72 .Oo Ar user Ns @ Oc Ns Ar hostname
77 (SSH client) is a program for logging into a remote machine and for
78 executing commands on a remote machine.
79 It is intended to replace rlogin and rsh,
80 and provide secure encrypted communications between
81 two untrusted hosts over an insecure network.
82 X11 connections and arbitrary TCP/IP ports
83 can also be forwarded over the secure channel.
86 connects and logs into the specified
92 his/her identity to the remote machine using one of several methods
93 depending on the protocol version used.
99 is executed on the remote host instead of a login shell.
100 .Ss SSH protocol version 1
101 The first authentication method is the
105 method combined with RSA-based host authentication.
106 If the machine the user logs in from is listed in
109 .Pa /etc/shosts.equiv
110 on the remote machine, and the user names are
111 the same on both sides, or if the files
115 exist in the user's home directory on the
116 remote machine and contain a line containing the name of the client
117 machine and the name of the user on that machine, the user is
118 considered for log in.
119 Additionally, if the server can verify the client's
121 .Pa /etc/ssh/ssh_known_hosts
123 .Pa ~/.ssh/known_hosts
126 section), only then is login permitted.
127 This authentication method closes security holes due to IP
128 spoofing, DNS spoofing and routing spoofing.
129 [Note to the administrator:
130 .Pa /etc/hosts.equiv ,
132 and the rlogin/rsh protocol in general, are inherently insecure and should be
133 disabled if security is desired.]
135 As a second authentication method,
137 supports RSA based authentication.
138 The scheme is based on public-key cryptography: there are cryptosystems
139 where encryption and decryption are done using separate keys, and it
140 is not possible to derive the decryption key from the encryption key.
141 RSA is one such system.
142 The idea is that each user creates a public/private
143 key pair for authentication purposes.
144 The server knows the public key, and only the user knows the private key.
147 .Pa ~/.ssh/authorized_keys
148 lists the public keys that are permitted for logging in.
149 When the user logs in, the
151 program tells the server which key pair it would like to use for
153 The server checks if this key is permitted, and if so,
154 sends the user (actually the
156 program running on behalf of the user) a challenge, a random number,
157 encrypted by the user's public key.
158 The challenge can only be decrypted using the proper private key.
159 The user's client then decrypts the challenge using the private key,
160 proving that he/she knows the private key
161 but without disclosing it to the server.
164 implements the RSA authentication protocol automatically.
165 The user creates his/her RSA key pair by running
167 This stores the private key in
169 and stores the public key in
170 .Pa ~/.ssh/identity.pub
171 in the user's home directory.
172 The user should then copy the
175 .Pa ~/.ssh/authorized_keys
176 in his/her home directory on the remote machine (the
178 file corresponds to the conventional
180 file, and has one key
181 per line, though the lines can be very long).
182 After this, the user can log in without giving the password.
184 The most convenient way to use RSA authentication may be with an
185 authentication agent.
188 for more information.
190 If other authentication methods fail,
192 prompts the user for a password.
193 The password is sent to the remote
194 host for checking; however, since all communications are encrypted,
195 the password cannot be seen by someone listening on the network.
196 .Ss SSH protocol version 2
197 When a user connects using protocol version 2,
198 similar authentication methods are available.
199 Using the default values for
200 .Cm PreferredAuthentications ,
201 the client will try to authenticate first using the hostbased method;
202 if this method fails, public key authentication is attempted,
203 and finally if this method fails, keyboard-interactive and
204 password authentication are tried.
206 The public key method is similar to RSA authentication described
207 in the previous section and allows the RSA or DSA algorithm to be used:
208 The client uses his private key,
212 to sign the session identifier and sends the result to the server.
213 The server checks whether the matching public key is listed in
214 .Pa ~/.ssh/authorized_keys
215 and grants access if both the key is found and the signature is correct.
216 The session identifier is derived from a shared Diffie-Hellman value
217 and is only known to the client and the server.
219 If public key authentication fails or is not available, a password
220 can be sent encrypted to the remote host to prove the user's identity.
224 supports hostbased or challenge response authentication.
226 Protocol 2 provides additional mechanisms for confidentiality
227 (the traffic is encrypted using AES, 3DES, Blowfish, CAST128 or Arcfour)
228 and integrity (hmac-md5, hmac-sha1, hmac-ripemd160).
229 Note that protocol 1 lacks a strong mechanism for ensuring the
230 integrity of the connection.
231 .Ss Login session and remote execution
232 When the user's identity has been accepted by the server, the server
233 either executes the given command, or logs into the machine and gives
234 the user a normal shell on the remote machine.
235 All communication with
236 the remote command or shell will be automatically encrypted.
238 If a pseudo-terminal has been allocated (normal login session), the
239 user may use the escape characters noted below.
241 If no pseudo-tty has been allocated,
242 the session is transparent and can be used to reliably transfer binary data.
243 On most systems, setting the escape character to
245 will also make the session transparent even if a tty is used.
247 The session terminates when the command or shell on the remote
248 machine exits and all X11 and TCP/IP connections have been closed.
249 The exit status of the remote program is returned as the exit status of
251 .Ss Escape Characters
252 When a pseudo-terminal has been requested,
254 supports a number of functions through the use of an escape character.
256 A single tilde character can be sent as
258 or by following the tilde by a character other than those described below.
259 The escape character must always follow a newline to be interpreted as
261 The escape character can be changed in configuration files using the
263 configuration directive or on the command line by the
267 The supported escapes (assuming the default
277 List forwarded connections.
281 at logout when waiting for forwarded connection / X11 sessions to terminate.
283 Display a list of escape characters.
285 Send a BREAK to the remote system
286 (only useful for SSH protocol version 2 and if the peer supports it).
289 Currently this allows the addition of port forwardings using the
294 It also allows the cancellation of existing remote port-forwardings
297 Basic help is available, using the
301 Request rekeying of the connection
302 (only useful for SSH protocol version 2 and if the peer supports it).
304 .Ss X11 and TCP forwarding
309 (or see the description of the
313 options described later)
314 and the user is using X11 (the
316 environment variable is set), the connection to the X11 display is
317 automatically forwarded to the remote side in such a way that any X11
318 programs started from the shell (or command) will go through the
319 encrypted channel, and the connection to the real X server will be made
320 from the local machine.
321 The user should not manually set
323 Forwarding of X11 connections can be
324 configured on the command line or in configuration files.
330 will point to the server machine, but with a display number greater than zero.
331 This is normal, and happens because
335 X server on the server machine for forwarding the
336 connections over the encrypted channel.
339 will also automatically set up Xauthority data on the server machine.
340 For this purpose, it will generate a random authorization cookie,
341 store it in Xauthority on the server, and verify that any forwarded
342 connections carry this cookie and replace it by the real cookie when
343 the connection is opened.
344 The real authentication cookie is never
345 sent to the server machine (and no cookies are sent in the plain).
351 (or see the description of the
355 options described later) and
356 the user is using an authentication agent, the connection to the agent
357 is automatically forwarded to the remote side.
359 Forwarding of arbitrary TCP/IP connections over the secure channel can
360 be specified either on the command line or in a configuration file.
361 One possible application of TCP/IP forwarding is a secure connection to an
362 electronic purse; another is going through firewalls.
363 .Ss Server authentication
365 automatically maintains and checks a database containing
366 identifications for all hosts it has ever been used with.
367 Host keys are stored in
368 .Pa ~/.ssh/known_hosts
369 in the user's home directory.
370 Additionally, the file
371 .Pa /etc/ssh/ssh_known_hosts
372 is automatically checked for known hosts.
373 Any new hosts are automatically added to the user's file.
374 If a host's identification ever changes,
376 warns about this and disables password authentication to prevent a
377 trojan horse from getting the user's password.
378 Another purpose of this mechanism is to prevent man-in-the-middle attacks
379 which could otherwise be used to circumvent the encryption.
381 .Cm StrictHostKeyChecking
382 option can be used to prevent logins to machines whose
383 host key is not known or has changed.
386 can be configured to verify host identification using fingerprint resource
387 records (SSHFP) published in DNS.
390 option can be used to control how DNS lookups are performed.
391 SSHFP resource records can be generated using
394 The options are as follows:
399 to try protocol version 1 only.
403 to try protocol version 2 only.
407 to use IPv4 addresses only.
411 to use IPv6 addresses only.
413 Enables forwarding of the authentication agent connection.
414 This can also be specified on a per-host basis in a configuration file.
416 Agent forwarding should be enabled with caution.
417 Users with the ability to bypass file permissions on the remote host
418 (for the agent's Unix-domain socket)
419 can access the local agent through the forwarded connection.
420 An attacker cannot obtain key material from the agent,
421 however they can perform operations on the keys that enable them to
422 authenticate using the identities loaded into the agent.
424 Disables forwarding of the authentication agent connection.
425 .It Fl b Ar bind_address
426 Specify the interface address to transmit from on machines with multiple
427 interfaces or aliased addresses.
429 Requests compression of all data (including stdin, stdout, stderr, and
430 data for forwarded X11 and TCP/IP connections).
431 The compression algorithm is the same used by
435 can be controlled by the
437 option for protocol version 1.
438 Compression is desirable on modem lines and other
439 slow connections, but will only slow down things on fast networks.
440 The default value can be set on a host-by-host basis in the
441 configuration files; see the
444 .It Fl c Ar cipher_spec
445 Selects the cipher specification for encrypting the session.
447 Protocol version 1 allows specification of a single cipher.
448 The suported values are
454 (triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
455 It is believed to be secure.
457 is a fast block cipher; it appears very secure and is much faster than
460 is only supported in the
462 client for interoperability with legacy protocol 1 implementations
463 that do not support the
466 Its use is strongly discouraged due to cryptographic weaknesses.
470 For protocol version 2
472 is a comma-separated list of ciphers
473 listed in order of preference.
474 The supported ciphers are
490 ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
491 arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
492 aes192-ctr,aes256-ctr''
497 application-level port forwarding.
498 This works by allocating a socket to listen to
500 on the local side, and whenever a connection is made to this port, the
501 connection is forwarded over the secure channel, and the application
502 protocol is then used to determine where to connect to from the
504 Currently the SOCKS4 and SOCKS5 protocols are supported, and
506 will act as a SOCKS server.
507 Only root can forward privileged ports.
508 Dynamic port forwardings can also be specified in the configuration file.
509 .It Fl e Ar ch | ^ch | none
510 Sets the escape character for sessions with a pty (default:
512 The escape character is only recognized at the beginning of a line.
513 The escape character followed by a dot
515 closes the connection;
516 followed by control-Z suspends the connection;
517 and followed by itself sends the escape character once.
518 Setting the character to
520 disables any escapes and makes the session fully transparent.
521 .It Fl F Ar configfile
522 Specifies an alternative per-user configuration file.
523 If a configuration file is given on the command line,
524 the system-wide configuration file
525 .Pq Pa /etc/ssh/ssh_config
527 The default for the per-user configuration file is
532 to go to background just before command execution.
535 is going to ask for passwords or passphrases, but the user
536 wants it in the background.
539 The recommended way to start X11 programs at a remote site is with
541 .Ic ssh -f host xterm .
543 Allows remote hosts to connect to local forwarded ports.
544 .It Fl I Ar smartcard_device
545 Specifies which smartcard device to use.
546 The argument is the device
548 should use to communicate with a smartcard used for storing the user's
550 .It Fl i Ar identity_file
551 Selects a file from which the identity (private key) for
552 RSA or DSA authentication is read.
555 for protocol version 1, and
559 for protocol version 2.
560 Identity files may also be specified on
561 a per-host basis in the configuration file.
562 It is possible to have multiple
564 options (and multiple identities specified in
565 configuration files).
567 Disables forwarding (delegation) of GSSAPI credentials to the server.
570 .Oo Ar bind_address : Oc
571 .Ar port : host : hostport
574 Specifies that the given port on the local (client) host is to be
575 forwarded to the given host and port on the remote side.
576 This works by allocating a socket to listen to
578 on the local side, optionally bound to the specified
580 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 IPv6 addresses can be specified with an alternative syntax:
591 .Op Ar bind_address No /
592 .Ar port No / Ar host No /
596 or by enclosing the address in square brackets.
597 Only the superuser can forward privileged ports.
598 By default, the local port is bound in accordance with the
603 may be used to bind the connection to a specific address.
608 indicates that the listening port be bound for local use only, while an
611 indicates that the port should be available from all interfaces.
612 .It Fl l Ar login_name
613 Specifies the user to log in as on the remote machine.
614 This also may be specified on a per-host basis in the configuration file.
620 mode for connection sharing.
621 Refer to the description of
627 Additionally, for protocol version 2 a comma-separated list of MAC
628 (message authentication code) algorithms can
629 be specified in order of preference.
632 keyword for more information.
634 Do not execute a remote command.
635 This is useful for just forwarding ports
636 (protocol version 2 only).
640 (actually, prevents reading from stdin).
641 This must be used when
643 is run in the background.
644 A common trick is to use this to run X11 programs on a remote machine.
646 .Ic ssh -n shadows.cs.hut.fi emacs &
647 will start an emacs on shadows.cs.hut.fi, and the X11
648 connection will be automatically forwarded over an encrypted channel.
651 program will be put in the background.
652 (This does not work if
654 needs to ask for a password or passphrase; see also the
658 Control an active connection multiplexing master process.
661 option is specified, the
663 argument is interpreted and passed to the master process.
666 (check that the master process is running) and
668 (request the master to exit).
670 Can be used to give options in the format used in the configuration file.
671 This is useful for specifying options for which there is no separate
673 For full details of the options listed below, and their possible values, see
676 .Bl -tag -width Ds -offset indent -compact
680 .It ChallengeResponseAuthentication
684 .It ClearAllForwardings
687 .It ConnectionAttempts
695 .It ForwardX11Trusted
697 .It GlobalKnownHostsFile
698 .It GSSAPIAuthentication
699 .It GSSAPIDelegateCredentials
702 .It HostbasedAuthentication
703 .It HostKeyAlgorithms
708 .It KbdInteractiveDevices
712 .It NoHostAuthenticationForLocalhost
713 .It NumberOfPasswordPrompts
714 .It PasswordAuthentication
716 .It PreferredAuthentications
719 .It PubkeyAuthentication
721 .It RhostsRSAAuthentication
722 .It RSAAuthentication
724 .It ServerAliveInterval
725 .It ServerAliveCountMax
727 .It StrictHostKeyChecking
729 .It UsePrivilegedPort
731 .It UserKnownHostsFile
736 Port to connect to on the remote host.
737 This can be specified on a
738 per-host basis in the configuration file.
741 Causes all warning and diagnostic messages to be suppressed.
744 .Oo Ar bind_address : Oc
745 .Ar port : host : hostport
748 Specifies that the given port on the remote (server) host is to be
749 forwarded to the given host and port on the local side.
750 This works by allocating a socket to listen to
752 on the remote side, and whenever a connection is made to this port, the
753 connection is forwarded over the secure channel, and a connection is
758 from the local machine.
760 Port forwardings can also be specified in the configuration file.
761 Privileged ports can be forwarded only when
762 logging in as root on the remote machine.
763 IPv6 addresses can be specified by enclosing the address in square braces or
764 using an alternative syntax:
767 .Op Ar bind_address No /
768 .Ar host No / Ar port No /
773 By default, the listening socket on the server will be bound to the loopback
775 This may be overriden by specifying a
781 indicates that the remote socket should listen on all interfaces.
784 will only succeed if the server's
786 option is enabled (see
787 .Xr sshd_config 5 ) .
789 Specifies the location of a control socket for connection sharing.
790 Refer to the description of
798 May be used to request invocation of a subsystem on the remote system.
799 Subsystems are a feature of the SSH2 protocol which facilitate the use
800 of SSH as a secure transport for other applications (eg.\&
802 The subsystem is specified as the remote command.
804 Disable pseudo-tty allocation.
806 Force pseudo-tty allocation.
807 This can be used to execute arbitrary
808 screen-based programs on a remote machine, which can be very useful,
809 e.g., when implementing menu services.
812 options force tty allocation, even if
816 Display the version number and exit.
821 to print debugging messages about its progress.
823 debugging connection, authentication, and configuration problems.
826 options increase the verbosity.
829 Enables X11 forwarding.
830 This can also be specified on a per-host basis in a configuration file.
832 X11 forwarding should be enabled with caution.
833 Users with the ability to bypass file permissions on the remote host
834 (for the user's X authorization database)
835 can access the local X11 display through the forwarded connection.
836 An attacker may then be able to perform activities such as keystroke monitoring.
838 For this reason, X11 forwarding is subjected to X11 SECURITY extension
839 restrictions by default.
844 .Cm ForwardX11Trusted
847 for more information.
849 Disables X11 forwarding.
851 Enables trusted X11 forwarding.
852 Trusted X11 forwardings are not subjected to the X11 SECURITY extension
855 .Sh CONFIGURATION FILES
857 may additionally obtain configuration data from
858 a per-user configuration file and a system-wide configuration file.
859 The file format and configuration options are described in
863 will normally set the following environment variables:
864 .Bl -tag -width LOGNAME
868 variable indicates the location of the X11 server.
869 It is automatically set by
871 to point to a value of the form
873 where hostname indicates
874 the host where the shell runs, and n is an integer \*(Ge 1.
876 uses this special value to forward X11 connections over the secure
878 The user should normally not set
881 will render the X11 connection insecure (and will require the user to
882 manually copy any required authorization cookies).
884 Set to the path of the user's home directory.
888 set for compatibility with systems that use this variable.
890 Set to the path of the user's mailbox.
894 as specified when compiling
899 needs a passphrase, it will read the passphrase from the current
900 terminal if it was run from a terminal.
903 does not have a terminal associated with it but
907 are set, it will execute the program specified by
909 and open an X11 window to read the passphrase.
910 This is particularly useful when calling
915 (Note that on some machines it
916 may be necessary to redirect the input from
920 Identifies the path of a unix-domain socket used to communicate with the
922 .It Ev SSH_CONNECTION
923 Identifies the client and server ends of the connection.
924 The variable contains
925 four space-separated values: client ip-address, client port number,
926 server ip-address and server port number.
927 .It Ev SSH_ORIGINAL_COMMAND
928 The variable contains the original command line if a forced command
930 It can be used to extract the original arguments.
932 This is set to the name of the tty (path to the device) associated
933 with the current shell or command.
934 If the current session has no tty,
935 this variable is not set.
937 The timezone variable is set to indicate the present timezone if it
938 was set when the daemon was started (i.e., the daemon passes the value
939 on to new connections).
941 Set to the name of the user logging in.
947 .Pa ~/.ssh/environment ,
948 and adds lines of the format
950 to the environment if the file exists and if users are allowed to
951 change their environment.
952 For more information, see the
953 .Cm PermitUserEnvironment
958 .It Pa ~/.ssh/known_hosts
959 Records host keys for all hosts the user has logged into that are not
961 .Pa /etc/ssh/ssh_known_hosts .
964 .It Pa ~/.ssh/identity, ~/.ssh/id_dsa, ~/.ssh/id_rsa
965 Contains the authentication identity of the user.
966 They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively.
968 contain sensitive data and should be readable by the user but not
969 accessible by others (read/write/execute).
972 ignores a private key file if it is accessible by others.
973 It is possible to specify a passphrase when
974 generating the key; the passphrase will be used to encrypt the
975 sensitive part of this file using 3DES.
976 .It Pa ~/.ssh/identity.pub, ~/.ssh/id_dsa.pub, ~/.ssh/id_rsa.pub
977 Contains the public key for authentication (public part of the
978 identity file in human-readable form).
980 .Pa ~/.ssh/identity.pub
981 file should be added to the file
982 .Pa ~/.ssh/authorized_keys
984 where the user wishes to log in using protocol version 1 RSA authentication.
986 .Pa ~/.ssh/id_dsa.pub
988 .Pa ~/.ssh/id_rsa.pub
989 file should be added to
990 .Pa ~/.ssh/authorized_keys
992 where the user wishes to log in using protocol version 2 DSA/RSA authentication.
994 sensitive and can (but need not) be readable by anyone.
996 never used automatically and are not necessary; they are only provided for
997 the convenience of the user.
999 This is the per-user configuration file.
1000 The file format and configuration options are described in
1002 Because of the potential for abuse, this file must have strict permissions:
1003 read/write for the user, and not accessible by others.
1004 .It Pa ~/.ssh/authorized_keys
1005 Lists the public keys (RSA/DSA) that can be used for logging in as this user.
1006 The format of this file is described in the
1009 In the simplest form the format is the same as the
1012 This file is not highly sensitive, but the recommended
1013 permissions are read/write for the user, and not accessible by others.
1014 .It Pa /etc/ssh/ssh_known_hosts
1015 Systemwide list of known host keys.
1016 This file should be prepared by the
1017 system administrator to contain the public host keys of all machines in the
1019 This file should be world-readable.
1021 public keys, one per line, in the following format (fields separated
1022 by spaces): system name, public key and optional comment field.
1023 When different names are used
1024 for the same machine, all such names should be listed, separated by
1026 The format is described in the
1030 The canonical system name (as returned by name servers) is used by
1032 to verify the client host when logging in; other names are needed because
1034 does not convert the user-supplied name to a canonical name before
1035 checking the key, because someone with access to the name servers
1036 would then be able to fool host authentication.
1037 .It Pa /etc/ssh/ssh_config
1038 Systemwide configuration file.
1039 The file format and configuration options are described in
1041 .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key
1042 These three files contain the private parts of the host keys
1044 .Cm RhostsRSAAuthentication
1046 .Cm HostbasedAuthentication .
1047 If the protocol version 1
1048 .Cm RhostsRSAAuthentication
1051 must be setuid root, since the host key is readable only by root.
1052 For protocol version 2,
1056 to access the host keys for
1057 .Cm HostbasedAuthentication .
1058 This eliminates the requirement that
1060 be setuid root when that authentication method is used.
1065 This file is used in
1066 .Cm RhostsRSAAuthentication
1068 .Cm HostbasedAuthentication
1069 authentication to list the
1070 host/user pairs that are permitted to log in.
1071 (Note that this file is
1072 also used by rlogin and rsh, which makes using this file insecure.)
1073 Each line of the file contains a host name (in the canonical form
1074 returned by name servers), and then a user name on that host,
1075 separated by a space.
1076 On some machines this file may need to be
1077 world-readable if the user's home directory is on a NFS partition,
1081 Additionally, this file must be owned by the user,
1082 and must not have write permissions for anyone else.
1084 permission for most machines is read/write for the user, and not
1085 accessible by others.
1089 allows authentication only in combination with client host key
1090 authentication before permitting log in.
1091 If the server machine does not have the client's host key in
1092 .Pa /etc/ssh/ssh_known_hosts ,
1094 .Pa ~/.ssh/known_hosts .
1095 The easiest way to do this is to
1096 connect back to the client from the server machine using ssh; this
1097 will automatically add the host key to
1098 .Pa ~/.ssh/known_hosts .
1100 This file is used exactly the same way as
1103 having this file is to be able to use
1104 .Cm RhostsRSAAuthentication
1106 .Cm HostbasedAuthentication
1107 authentication without permitting login with
1111 .It Pa /etc/hosts.equiv
1112 This file is used during
1113 .Cm RhostsRSAAuthentication
1115 .Cm HostbasedAuthentication
1118 canonical hosts names, one per line (the full format is described in the
1121 If the client host is found in this file, login is
1122 automatically permitted provided client and server user names are the
1124 Additionally, successful client host key authentication is required.
1125 This file should only be writable by root.
1126 .It Pa /etc/shosts.equiv
1127 This file is processed exactly as
1128 .Pa /etc/hosts.equiv .
1129 This file may be useful to permit logins using
1131 but not using rsh/rlogin.
1132 .It Pa /etc/ssh/sshrc
1133 Commands in this file are executed by
1135 when the user logs in just before the user's shell (or command) is started.
1138 manual page for more information.
1140 Commands in this file are executed by
1142 when the user logs in just before the user's shell (or command) is
1146 manual page for more information.
1147 .It Pa ~/.ssh/environment
1148 Contains additional definitions for environment variables, see section
1154 exits with the exit status of the remote command or with 255
1155 if an error occurred.
1175 .%T "SSH Protocol Architecture"
1176 .%N draft-ietf-secsh-architecture-12.txt
1178 .%O work in progress material
1181 OpenSSH is a derivative of the original and free
1182 ssh 1.2.12 release by Tatu Ylonen.
1183 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1184 Theo de Raadt and Dug Song
1185 removed many bugs, re-added newer features and
1187 Markus Friedl contributed the support for SSH
1188 protocol versions 1.5 and 2.0.
andersk / openssh.git / blob