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 1.213 2005/11/30 11:18:27 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 .Oo Ar bind_address : Oc
55 .Op Fl e Ar escape_char
56 .Op Fl F Ar configfile
58 .Op Fl i Ar identity_file
62 .Oo Ar bind_address : Oc
63 .Ar port : host : hostport
67 .Op Fl l Ar login_name
75 .Oo Ar bind_address : Oc
76 .Ar port : host : hostport
80 .Oo Ar user Ns @ Oc Ns Ar hostname
84 (SSH client) is a program for logging into a remote machine and for
85 executing commands on a remote machine.
86 It is intended to replace rlogin and rsh,
87 and provide secure encrypted communications between
88 two untrusted hosts over an insecure network.
89 X11 connections and arbitrary TCP/IP ports
90 can also be forwarded over the secure channel.
93 connects and logs into the specified
99 his/her identity to the remote machine using one of several methods
100 depending on the protocol version used.
106 is executed on the remote host instead of a login shell.
107 .Ss SSH protocol version 1
108 The first authentication method is the
112 method combined with RSA-based host authentication.
113 If the machine the user logs in from is listed in
116 .Pa /etc/shosts.equiv
117 on the remote machine, and the user names are
118 the same on both sides, or if the files
122 exist in the user's home directory on the
123 remote machine and contain a line containing the name of the client
124 machine and the name of the user on that machine, the user is
125 considered for log in.
126 Additionally, if the server can verify the client's
128 .Pa /etc/ssh/ssh_known_hosts
130 .Pa ~/.ssh/known_hosts
133 section), only then is login permitted.
134 This authentication method closes security holes due to IP
135 spoofing, DNS spoofing and routing spoofing.
136 [Note to the administrator:
137 .Pa /etc/hosts.equiv ,
139 and the rlogin/rsh protocol in general, are inherently insecure and should be
140 disabled if security is desired.]
142 As a second authentication method,
144 supports RSA based authentication.
145 The scheme is based on public-key cryptography: there are cryptosystems
146 where encryption and decryption are done using separate keys, and it
147 is not possible to derive the decryption key from the encryption key.
148 RSA is one such system.
149 The idea is that each user creates a public/private
150 key pair for authentication purposes.
151 The server knows the public key, and only the user knows the private key.
154 .Pa ~/.ssh/authorized_keys
155 lists the public keys that are permitted for logging in.
156 When the user logs in, the
158 program tells the server which key pair it would like to use for
160 The server checks if this key is permitted, and if so,
161 sends the user (actually the
163 program running on behalf of the user) a challenge, a random number,
164 encrypted by the user's public key.
165 The challenge can only be decrypted using the proper private key.
166 The user's client then decrypts the challenge using the private key,
167 proving that he/she knows the private key
168 but without disclosing it to the server.
171 implements the RSA authentication protocol automatically.
172 The user creates his/her RSA key pair by running
174 This stores the private key in
176 and stores the public key in
177 .Pa ~/.ssh/identity.pub
178 in the user's home directory.
179 The user should then copy the
182 .Pa ~/.ssh/authorized_keys
183 in his/her home directory on the remote machine (the
185 file corresponds to the conventional
187 file, and has one key
188 per line, though the lines can be very long).
189 After this, the user can log in without giving the password.
191 The most convenient way to use RSA authentication may be with an
192 authentication agent.
195 for more information.
197 If other authentication methods fail,
199 prompts the user for a password.
200 The password is sent to the remote
201 host for checking; however, since all communications are encrypted,
202 the password cannot be seen by someone listening on the network.
203 .Ss SSH protocol version 2
204 When a user connects using protocol version 2,
205 similar authentication methods are available.
206 Using the default values for
207 .Cm PreferredAuthentications ,
208 the client will try to authenticate first using the hostbased method;
209 if this method fails, public key authentication is attempted,
210 and finally if this method fails, keyboard-interactive and
211 password authentication are tried.
213 The public key method is similar to RSA authentication described
214 in the previous section and allows the RSA or DSA algorithm to be used:
215 The client uses his private key,
219 to sign the session identifier and sends the result to the server.
220 The server checks whether the matching public key is listed in
221 .Pa ~/.ssh/authorized_keys
222 and grants access if both the key is found and the signature is correct.
223 The session identifier is derived from a shared Diffie-Hellman value
224 and is only known to the client and the server.
226 If public key authentication fails or is not available, a password
227 can be sent encrypted to the remote host to prove the user's identity.
231 supports hostbased or challenge response authentication.
233 Protocol 2 provides additional mechanisms for confidentiality
234 (the traffic is encrypted using AES, 3DES, Blowfish, CAST128 or Arcfour)
235 and integrity (hmac-md5, hmac-sha1, hmac-ripemd160).
236 Note that protocol 1 lacks a strong mechanism for ensuring the
237 integrity of the connection.
238 .Ss Login session and remote execution
239 When the user's identity has been accepted by the server, the server
240 either executes the given command, or logs into the machine and gives
241 the user a normal shell on the remote machine.
242 All communication with
243 the remote command or shell will be automatically encrypted.
245 If a pseudo-terminal has been allocated (normal login session), the
246 user may use the escape characters noted below.
248 If no pseudo-tty has been allocated,
249 the session is transparent and can be used to reliably transfer binary data.
250 On most systems, setting the escape character to
252 will also make the session transparent even if a tty is used.
254 The session terminates when the command or shell on the remote
255 machine exits and all X11 and TCP/IP connections have been closed.
256 The exit status of the remote program is returned as the exit status of
258 .Ss Escape Characters
259 When a pseudo-terminal has been requested,
261 supports a number of functions through the use of an escape character.
263 A single tilde character can be sent as
265 or by following the tilde by a character other than those described below.
266 The escape character must always follow a newline to be interpreted as
268 The escape character can be changed in configuration files using the
270 configuration directive or on the command line by the
274 The supported escapes (assuming the default
284 List forwarded connections.
288 at logout when waiting for forwarded connection / X11 sessions to terminate.
290 Display a list of escape characters.
292 Send a BREAK to the remote system
293 (only useful for SSH protocol version 2 and if the peer supports it).
296 Currently this allows the addition of port forwardings using the
301 It also allows the cancellation of existing remote port-forwardings
304 Basic help is available, using the
308 Request rekeying of the connection
309 (only useful for SSH protocol version 2 and if the peer supports it).
311 .Ss X11 and TCP forwarding
316 (or see the description of the
320 options described later)
321 and the user is using X11 (the
323 environment variable is set), the connection to the X11 display is
324 automatically forwarded to the remote side in such a way that any X11
325 programs started from the shell (or command) will go through the
326 encrypted channel, and the connection to the real X server will be made
327 from the local machine.
328 The user should not manually set
330 Forwarding of X11 connections can be
331 configured on the command line or in configuration files.
337 will point to the server machine, but with a display number greater than zero.
338 This is normal, and happens because
342 X server on the server machine for forwarding the
343 connections over the encrypted channel.
346 will also automatically set up Xauthority data on the server machine.
347 For this purpose, it will generate a random authorization cookie,
348 store it in Xauthority on the server, and verify that any forwarded
349 connections carry this cookie and replace it by the real cookie when
350 the connection is opened.
351 The real authentication cookie is never
352 sent to the server machine (and no cookies are sent in the plain).
358 (or see the description of the
362 options described later) and
363 the user is using an authentication agent, the connection to the agent
364 is automatically forwarded to the remote side.
366 Forwarding of arbitrary TCP/IP connections over the secure channel can
367 be specified either on the command line or in a configuration file.
368 One possible application of TCP/IP forwarding is a secure connection to an
369 electronic purse; another is going through firewalls.
370 .Ss Server authentication
372 automatically maintains and checks a database containing
373 identifications for all hosts it has ever been used with.
374 Host keys are stored in
375 .Pa ~/.ssh/known_hosts
376 in the user's home directory.
377 Additionally, the file
378 .Pa /etc/ssh/ssh_known_hosts
379 is automatically checked for known hosts.
380 Any new hosts are automatically added to the user's file.
381 If a host's identification ever changes,
383 warns about this and disables password authentication to prevent a
384 trojan horse from getting the user's password.
385 Another purpose of this mechanism is to prevent man-in-the-middle attacks
386 which could otherwise be used to circumvent the encryption.
388 .Cm StrictHostKeyChecking
389 option can be used to prevent logins to machines whose
390 host key is not known or has changed.
393 can be configured to verify host identification using fingerprint resource
394 records (SSHFP) published in DNS.
397 option can be used to control how DNS lookups are performed.
398 SSHFP resource records can be generated using
401 The options are as follows:
406 to try protocol version 1 only.
410 to try protocol version 2 only.
414 to use IPv4 addresses only.
418 to use IPv6 addresses only.
420 Enables forwarding of the authentication agent connection.
421 This can also be specified on a per-host basis in a configuration file.
423 Agent forwarding should be enabled with caution.
424 Users with the ability to bypass file permissions on the remote host
425 (for the agent's Unix-domain socket)
426 can access the local agent through the forwarded connection.
427 An attacker cannot obtain key material from the agent,
428 however they can perform operations on the keys that enable them to
429 authenticate using the identities loaded into the agent.
431 Disables forwarding of the authentication agent connection.
432 .It Fl b Ar bind_address
435 on the local machine as the source address
437 Only useful on systems with more than one address.
439 Requests compression of all data (including stdin, stdout, stderr, and
440 data for forwarded X11 and TCP/IP connections).
441 The compression algorithm is the same used by
445 can be controlled by the
447 option for protocol version 1.
448 Compression is desirable on modem lines and other
449 slow connections, but will only slow down things on fast networks.
450 The default value can be set on a host-by-host basis in the
451 configuration files; see the
454 .It Fl c Ar cipher_spec
455 Selects the cipher specification for encrypting the session.
457 Protocol version 1 allows specification of a single cipher.
458 The supported values are
464 (triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
465 It is believed to be secure.
467 is a fast block cipher; it appears very secure and is much faster than
470 is only supported in the
472 client for interoperability with legacy protocol 1 implementations
473 that do not support the
476 Its use is strongly discouraged due to cryptographic weaknesses.
480 For protocol version 2
482 is a comma-separated list of ciphers
483 listed in order of preference.
484 The supported ciphers are
500 ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
501 arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
502 aes192-ctr,aes256-ctr''
506 .Oo Ar bind_address : Oc
512 application-level port forwarding.
513 This works by allocating a socket to listen to
515 on the local side, optionally bound to the specified
517 Whenever a connection is made to this port, the
518 connection is forwarded over the secure channel, and the application
519 protocol is then used to determine where to connect to from the
521 Currently the SOCKS4 and SOCKS5 protocols are supported, and
523 will act as a SOCKS server.
524 Only root can forward privileged ports.
525 Dynamic port forwardings can also be specified in the configuration file.
527 IPv6 addresses can be specified with an alternative syntax:
530 .Op Ar bind_address No /
534 or by enclosing the address in square brackets.
535 Only the superuser can forward privileged ports.
536 By default, the local port is bound in accordance with the
541 may be used to bind the connection to a specific address.
546 indicates that the listening port be bound for local use only, while an
549 indicates that the port should be available from all interfaces.
550 .It Fl e Ar ch | ^ch | none
551 Sets the escape character for sessions with a pty (default:
553 The escape character is only recognized at the beginning of a line.
554 The escape character followed by a dot
556 closes the connection;
557 followed by control-Z suspends the connection;
558 and followed by itself sends the escape character once.
559 Setting the character to
561 disables any escapes and makes the session fully transparent.
562 .It Fl F Ar configfile
563 Specifies an alternative per-user configuration file.
564 If a configuration file is given on the command line,
565 the system-wide configuration file
566 .Pq Pa /etc/ssh/ssh_config
568 The default for the per-user configuration file is
573 to go to background just before command execution.
576 is going to ask for passwords or passphrases, but the user
577 wants it in the background.
580 The recommended way to start X11 programs at a remote site is with
582 .Ic ssh -f host xterm .
584 Allows remote hosts to connect to local forwarded ports.
585 .It Fl I Ar smartcard_device
586 Specifies which smartcard device to use.
587 The argument is the device
589 should use to communicate with a smartcard used for storing the user's
591 .It Fl i Ar identity_file
592 Selects a file from which the identity (private key) for
593 RSA or DSA authentication is read.
596 for protocol version 1, and
600 for protocol version 2.
601 Identity files may also be specified on
602 a per-host basis in the configuration file.
603 It is possible to have multiple
605 options (and multiple identities specified in
606 configuration files).
608 Disables forwarding (delegation) of GSSAPI credentials to the server.
611 .Oo Ar bind_address : Oc
612 .Ar port : host : hostport
615 Specifies that the given port on the local (client) host is to be
616 forwarded to the given host and port on the remote side.
617 This works by allocating a socket to listen to
619 on the local side, optionally bound to the specified
621 Whenever a connection is made to this port, the
622 connection is forwarded over the secure channel, and a connection is
627 from the remote machine.
628 Port forwardings can also be specified in the configuration file.
629 IPv6 addresses can be specified with an alternative syntax:
632 .Op Ar bind_address No /
633 .Ar port No / Ar host No /
637 or by enclosing the address in square brackets.
638 Only the superuser can forward privileged ports.
639 By default, the local port is bound in accordance with the
644 may be used to bind the connection to a specific address.
649 indicates that the listening port be bound for local use only, while an
652 indicates that the port should be available from all interfaces.
653 .It Fl l Ar login_name
654 Specifies the user to log in as on the remote machine.
655 This also may be specified on a per-host basis in the configuration file.
661 mode for connection sharing.
662 Refer to the description of
668 Additionally, for protocol version 2 a comma-separated list of MAC
669 (message authentication code) algorithms can
670 be specified in order of preference.
673 keyword for more information.
675 Do not execute a remote command.
676 This is useful for just forwarding ports
677 (protocol version 2 only).
681 (actually, prevents reading from stdin).
682 This must be used when
684 is run in the background.
685 A common trick is to use this to run X11 programs on a remote machine.
687 .Ic ssh -n shadows.cs.hut.fi emacs &
688 will start an emacs on shadows.cs.hut.fi, and the X11
689 connection will be automatically forwarded over an encrypted channel.
692 program will be put in the background.
693 (This does not work if
695 needs to ask for a password or passphrase; see also the
699 Control an active connection multiplexing master process.
702 option is specified, the
704 argument is interpreted and passed to the master process.
707 (check that the master process is running) and
709 (request the master to exit).
711 Can be used to give options in the format used in the configuration file.
712 This is useful for specifying options for which there is no separate
714 For full details of the options listed below, and their possible values, see
717 .Bl -tag -width Ds -offset indent -compact
721 .It ChallengeResponseAuthentication
725 .It ClearAllForwardings
728 .It ConnectionAttempts
736 .It ForwardX11Trusted
738 .It GlobalKnownHostsFile
739 .It GSSAPIAuthentication
740 .It GSSAPIDelegateCredentials
743 .It HostbasedAuthentication
744 .It HostKeyAlgorithms
749 .It KbdInteractiveDevices
753 .It NoHostAuthenticationForLocalhost
754 .It NumberOfPasswordPrompts
755 .It PasswordAuthentication
757 .It PreferredAuthentications
760 .It PubkeyAuthentication
762 .It RhostsRSAAuthentication
763 .It RSAAuthentication
765 .It ServerAliveInterval
766 .It ServerAliveCountMax
768 .It StrictHostKeyChecking
770 .It UsePrivilegedPort
772 .It UserKnownHostsFile
777 Port to connect to on the remote host.
778 This can be specified on a
779 per-host basis in the configuration file.
782 Causes all warning and diagnostic messages to be suppressed.
785 .Oo Ar bind_address : Oc
786 .Ar port : host : hostport
789 Specifies that the given port on the remote (server) host is to be
790 forwarded to the given host and port on the local side.
791 This works by allocating a socket to listen to
793 on the remote side, and whenever a connection is made to this port, the
794 connection is forwarded over the secure channel, and a connection is
799 from the local machine.
801 Port forwardings can also be specified in the configuration file.
802 Privileged ports can be forwarded only when
803 logging in as root on the remote machine.
804 IPv6 addresses can be specified by enclosing the address in square braces or
805 using an alternative syntax:
808 .Op Ar bind_address No /
809 .Ar host No / Ar port No /
814 By default, the listening socket on the server will be bound to the loopback
816 This may be overriden by specifying a
822 indicates that the remote socket should listen on all interfaces.
825 will only succeed if the server's
827 option is enabled (see
828 .Xr sshd_config 5 ) .
830 Specifies the location of a control socket for connection sharing.
831 Refer to the description of
839 May be used to request invocation of a subsystem on the remote system.
840 Subsystems are a feature of the SSH2 protocol which facilitate the use
841 of SSH as a secure transport for other applications (eg.\&
843 The subsystem is specified as the remote command.
845 Disable pseudo-tty allocation.
847 Force pseudo-tty allocation.
848 This can be used to execute arbitrary
849 screen-based programs on a remote machine, which can be very useful,
850 e.g., when implementing menu services.
853 options force tty allocation, even if
857 Display the version number and exit.
862 to print debugging messages about its progress.
864 debugging connection, authentication, and configuration problems.
867 options increase the verbosity.
870 Enables X11 forwarding.
871 This can also be specified on a per-host basis in a configuration file.
873 X11 forwarding should be enabled with caution.
874 Users with the ability to bypass file permissions on the remote host
875 (for the user's X authorization database)
876 can access the local X11 display through the forwarded connection.
877 An attacker may then be able to perform activities such as keystroke monitoring.
879 For this reason, X11 forwarding is subjected to X11 SECURITY extension
880 restrictions by default.
885 .Cm ForwardX11Trusted
888 for more information.
890 Disables X11 forwarding.
892 Enables trusted X11 forwarding.
893 Trusted X11 forwardings are not subjected to the X11 SECURITY extension
896 .Sh CONFIGURATION FILES
898 may additionally obtain configuration data from
899 a per-user configuration file and a system-wide configuration file.
900 The file format and configuration options are described in
904 will normally set the following environment variables:
905 .Bl -tag -width LOGNAME
909 variable indicates the location of the X11 server.
910 It is automatically set by
912 to point to a value of the form
914 where hostname indicates
915 the host where the shell runs, and n is an integer \*(Ge 1.
917 uses this special value to forward X11 connections over the secure
919 The user should normally not set
922 will render the X11 connection insecure (and will require the user to
923 manually copy any required authorization cookies).
925 Set to the path of the user's home directory.
929 set for compatibility with systems that use this variable.
931 Set to the path of the user's mailbox.
935 as specified when compiling
940 needs a passphrase, it will read the passphrase from the current
941 terminal if it was run from a terminal.
944 does not have a terminal associated with it but
948 are set, it will execute the program specified by
950 and open an X11 window to read the passphrase.
951 This is particularly useful when calling
956 (Note that on some machines it
957 may be necessary to redirect the input from
961 Identifies the path of a unix-domain socket used to communicate with the
963 .It Ev SSH_CONNECTION
964 Identifies the client and server ends of the connection.
965 The variable contains
966 four space-separated values: client ip-address, client port number,
967 server ip-address and server port number.
968 .It Ev SSH_ORIGINAL_COMMAND
969 The variable contains the original command line if a forced command
971 It can be used to extract the original arguments.
973 This is set to the name of the tty (path to the device) associated
974 with the current shell or command.
975 If the current session has no tty,
976 this variable is not set.
978 The time zone variable is set to indicate the present time zone if it
979 was set when the daemon was started (i.e., the daemon passes the value
980 on to new connections).
982 Set to the name of the user logging in.
988 .Pa ~/.ssh/environment ,
989 and adds lines of the format
991 to the environment if the file exists and if users are allowed to
992 change their environment.
993 For more information, see the
994 .Cm PermitUserEnvironment
999 .It Pa ~/.ssh/known_hosts
1000 Records host keys for all hosts the user has logged into that are not
1002 .Pa /etc/ssh/ssh_known_hosts .
1005 .It Pa ~/.ssh/identity, ~/.ssh/id_dsa, ~/.ssh/id_rsa
1006 Contains the authentication identity of the user.
1007 They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively.
1009 contain sensitive data and should be readable by the user but not
1010 accessible by others (read/write/execute).
1013 ignores a private key file if it is accessible by others.
1014 It is possible to specify a passphrase when
1015 generating the key; the passphrase will be used to encrypt the
1016 sensitive part of this file using 3DES.
1017 .It Pa ~/.ssh/identity.pub, ~/.ssh/id_dsa.pub, ~/.ssh/id_rsa.pub
1018 Contains the public key for authentication (public part of the
1019 identity file in human-readable form).
1021 .Pa ~/.ssh/identity.pub
1022 file should be added to the file
1023 .Pa ~/.ssh/authorized_keys
1025 where the user wishes to log in using protocol version 1 RSA authentication.
1027 .Pa ~/.ssh/id_dsa.pub
1029 .Pa ~/.ssh/id_rsa.pub
1030 file should be added to
1031 .Pa ~/.ssh/authorized_keys
1033 where the user wishes to log in using protocol version 2 DSA/RSA authentication.
1035 sensitive and can (but need not) be readable by anyone.
1037 never used automatically and are not necessary; they are only provided for
1038 the convenience of the user.
1039 .It Pa ~/.ssh/config
1040 This is the per-user configuration file.
1041 The file format and configuration options are described in
1043 Because of the potential for abuse, this file must have strict permissions:
1044 read/write for the user, and not accessible by others.
1045 .It Pa ~/.ssh/authorized_keys
1046 Lists the public keys (RSA/DSA) that can be used for logging in as this user.
1047 The format of this file is described in the
1050 In the simplest form the format is the same as the
1053 This file is not highly sensitive, but the recommended
1054 permissions are read/write for the user, and not accessible by others.
1055 .It Pa /etc/ssh/ssh_known_hosts
1056 Systemwide list of known host keys.
1057 This file should be prepared by the
1058 system administrator to contain the public host keys of all machines in the
1060 This file should be world-readable.
1062 public keys, one per line, in the following format (fields separated
1063 by spaces): system name, public key and optional comment field.
1064 When different names are used
1065 for the same machine, all such names should be listed, separated by
1067 The format is described in the
1071 The canonical system name (as returned by name servers) is used by
1073 to verify the client host when logging in; other names are needed because
1075 does not convert the user-supplied name to a canonical name before
1076 checking the key, because someone with access to the name servers
1077 would then be able to fool host authentication.
1078 .It Pa /etc/ssh/ssh_config
1079 Systemwide configuration file.
1080 The file format and configuration options are described in
1082 .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key
1083 These three files contain the private parts of the host keys
1085 .Cm RhostsRSAAuthentication
1087 .Cm HostbasedAuthentication .
1088 If the protocol version 1
1089 .Cm RhostsRSAAuthentication
1092 must be setuid root, since the host key is readable only by root.
1093 For protocol version 2,
1097 to access the host keys for
1098 .Cm HostbasedAuthentication .
1099 This eliminates the requirement that
1101 be setuid root when that authentication method is used.
1106 This file is used in
1107 .Cm RhostsRSAAuthentication
1109 .Cm HostbasedAuthentication
1110 authentication to list the
1111 host/user pairs that are permitted to log in.
1112 (Note that this file is
1113 also used by rlogin and rsh, which makes using this file insecure.)
1114 Each line of the file contains a host name (in the canonical form
1115 returned by name servers), and then a user name on that host,
1116 separated by a space.
1117 On some machines this file may need to be
1118 world-readable if the user's home directory is on a NFS partition,
1122 Additionally, this file must be owned by the user,
1123 and must not have write permissions for anyone else.
1125 permission for most machines is read/write for the user, and not
1126 accessible by others.
1130 allows authentication only in combination with client host key
1131 authentication before permitting log in.
1132 If the server machine does not have the client's host key in
1133 .Pa /etc/ssh/ssh_known_hosts ,
1135 .Pa ~/.ssh/known_hosts .
1136 The easiest way to do this is to
1137 connect back to the client from the server machine using ssh; this
1138 will automatically add the host key to
1139 .Pa ~/.ssh/known_hosts .
1141 This file is used exactly the same way as
1144 having this file is to be able to use
1145 .Cm RhostsRSAAuthentication
1147 .Cm HostbasedAuthentication
1148 authentication without permitting login with
1152 .It Pa /etc/hosts.equiv
1153 This file is used during
1154 .Cm RhostsRSAAuthentication
1156 .Cm HostbasedAuthentication
1159 canonical hosts names, one per line (the full format is described in the
1162 If the client host is found in this file, login is
1163 automatically permitted provided client and server user names are the
1165 Additionally, successful client host key authentication is required.
1166 This file should only be writable by root.
1167 .It Pa /etc/shosts.equiv
1168 This file is processed exactly as
1169 .Pa /etc/hosts.equiv .
1170 This file may be useful to permit logins using
1172 but not using rsh/rlogin.
1173 .It Pa /etc/ssh/sshrc
1174 Commands in this file are executed by
1176 when the user logs in just before the user's shell (or command) is started.
1179 manual page for more information.
1181 Commands in this file are executed by
1183 when the user logs in just before the user's shell (or command) is
1187 manual page for more information.
1188 .It Pa ~/.ssh/environment
1189 Contains additional definitions for environment variables, see section
1195 exits with the exit status of the remote command or with 255
1196 if an error occurred.
1216 .%T "SSH Protocol Architecture"
1217 .%N draft-ietf-secsh-architecture-12.txt
1219 .%O work in progress material
1222 OpenSSH is a derivative of the original and free
1223 ssh 1.2.12 release by Tatu Ylonen.
1224 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1225 Theo de Raadt and Dug Song
1226 removed many bugs, re-added newer features and
1228 Markus Friedl contributed the support for SSH
1229 protocol versions 1.5 and 2.0.
andersk / openssh.git / blob