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 1.217 2005/12/08 14:59:44 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
81 .Op Fl w Ar tunnel : Ns Ar tunnel
82 .Oo Ar user Ns @ Oc Ns Ar hostname
87 (SSH client) is a program for logging into a remote machine and for
88 executing commands on a remote machine.
89 It is intended to replace rlogin and rsh,
90 and provide secure encrypted communications between
91 two untrusted hosts over an insecure network.
92 X11 connections and arbitrary TCP/IP ports
93 can also be forwarded over the secure channel.
96 connects and logs into the specified
102 his/her identity to the remote machine using one of several methods
103 depending on the protocol version used.
109 is executed on the remote host instead of a login shell.
110 .Ss SSH protocol version 1
111 The first authentication method is the
115 method combined with RSA-based host authentication.
116 If the machine the user logs in from is listed in
119 .Pa /etc/shosts.equiv
120 on the remote machine, and the user names are
121 the same on both sides, or if the files
125 exist in the user's home directory on the
126 remote machine and contain a line containing the name of the client
127 machine and the name of the user on that machine, the user is
128 considered for log in.
129 Additionally, if the server can verify the client's
131 .Pa /etc/ssh/ssh_known_hosts
133 .Pa ~/.ssh/known_hosts
136 section), only then is login permitted.
137 This authentication method closes security holes due to IP
138 spoofing, DNS spoofing and routing spoofing.
139 [Note to the administrator:
140 .Pa /etc/hosts.equiv ,
142 and the rlogin/rsh protocol in general, are inherently insecure and should be
143 disabled if security is desired.]
145 As a second authentication method,
147 supports RSA based authentication.
148 The scheme is based on public-key cryptography: there are cryptosystems
149 where encryption and decryption are done using separate keys, and it
150 is not possible to derive the decryption key from the encryption key.
151 RSA is one such system.
152 The idea is that each user creates a public/private
153 key pair for authentication purposes.
154 The server knows the public key, and only the user knows the private key.
157 .Pa ~/.ssh/authorized_keys
158 lists the public keys that are permitted for logging in.
159 When the user logs in, the
161 program tells the server which key pair it would like to use for
163 The server checks if this key is permitted, and if so,
164 sends the user (actually the
166 program running on behalf of the user) a challenge, a random number,
167 encrypted by the user's public key.
168 The challenge can only be decrypted using the proper private key.
169 The user's client then decrypts the challenge using the private key,
170 proving that he/she knows the private key
171 but without disclosing it to the server.
174 implements the RSA authentication protocol automatically.
175 The user creates his/her RSA key pair by running
177 This stores the private key in
179 and stores the public key in
180 .Pa ~/.ssh/identity.pub
181 in the user's home directory.
182 The user should then copy the
185 .Pa ~/.ssh/authorized_keys
186 in his/her home directory on the remote machine (the
188 file corresponds to the conventional
190 file, and has one key
191 per line, though the lines can be very long).
192 After this, the user can log in without giving the password.
194 The most convenient way to use RSA authentication may be with an
195 authentication agent.
198 for more information.
200 If other authentication methods fail,
202 prompts the user for a password.
203 The password is sent to the remote
204 host for checking; however, since all communications are encrypted,
205 the password cannot be seen by someone listening on the network.
206 .Ss SSH protocol version 2
207 When a user connects using protocol version 2,
208 similar authentication methods are available.
209 Using the default values for
210 .Cm PreferredAuthentications ,
211 the client will try to authenticate first using the hostbased method;
212 if this method fails, public key authentication is attempted,
213 and finally if this method fails, keyboard-interactive and
214 password authentication are tried.
216 The public key method is similar to RSA authentication described
217 in the previous section and allows the RSA or DSA algorithm to be used:
218 The client uses his private key,
222 to sign the session identifier and sends the result to the server.
223 The server checks whether the matching public key is listed in
224 .Pa ~/.ssh/authorized_keys
225 and grants access if both the key is found and the signature is correct.
226 The session identifier is derived from a shared Diffie-Hellman value
227 and is only known to the client and the server.
229 If public key authentication fails or is not available, a password
230 can be sent encrypted to the remote host to prove the user's identity.
234 supports hostbased or challenge response authentication.
236 Protocol 2 provides additional mechanisms for confidentiality
237 (the traffic is encrypted using AES, 3DES, Blowfish, CAST128 or Arcfour)
238 and integrity (hmac-md5, hmac-sha1, hmac-ripemd160).
239 Note that protocol 1 lacks a strong mechanism for ensuring the
240 integrity of the connection.
241 .Ss Login session and remote execution
242 When the user's identity has been accepted by the server, the server
243 either executes the given command, or logs into the machine and gives
244 the user a normal shell on the remote machine.
245 All communication with
246 the remote command or shell will be automatically encrypted.
248 If a pseudo-terminal has been allocated (normal login session), the
249 user may use the escape characters noted below.
251 If no pseudo-tty has been allocated,
252 the session is transparent and can be used to reliably transfer binary data.
253 On most systems, setting the escape character to
255 will also make the session transparent even if a tty is used.
257 The session terminates when the command or shell on the remote
258 machine exits and all X11 and TCP/IP connections have been closed.
259 The exit status of the remote program is returned as the exit status of
261 .Ss Escape Characters
262 When a pseudo-terminal has been requested,
264 supports a number of functions through the use of an escape character.
266 A single tilde character can be sent as
268 or by following the tilde by a character other than those described below.
269 The escape character must always follow a newline to be interpreted as
271 The escape character can be changed in configuration files using the
273 configuration directive or on the command line by the
277 The supported escapes (assuming the default
287 List forwarded connections.
291 at logout when waiting for forwarded connection / X11 sessions to terminate.
293 Display a list of escape characters.
295 Send a BREAK to the remote system
296 (only useful for SSH protocol version 2 and if the peer supports it).
299 Currently this allows the addition of port forwardings using the
304 It also allows the cancellation of existing remote port-forwardings
307 .Ic !\& Ns Ar command
308 allows the user to execute a local command if the
309 .Ic PermitLocalCommand
312 Basic help is available, using the
316 Request rekeying of the connection
317 (only useful for SSH protocol version 2 and if the peer supports it).
319 .Ss X11 and TCP forwarding
324 (or see the description of the
328 options described later)
329 and the user is using X11 (the
331 environment variable is set), the connection to the X11 display is
332 automatically forwarded to the remote side in such a way that any X11
333 programs started from the shell (or command) will go through the
334 encrypted channel, and the connection to the real X server will be made
335 from the local machine.
336 The user should not manually set
338 Forwarding of X11 connections can be
339 configured on the command line or in configuration files.
345 will point to the server machine, but with a display number greater than zero.
346 This is normal, and happens because
350 X server on the server machine for forwarding the
351 connections over the encrypted channel.
354 will also automatically set up Xauthority data on the server machine.
355 For this purpose, it will generate a random authorization cookie,
356 store it in Xauthority on the server, and verify that any forwarded
357 connections carry this cookie and replace it by the real cookie when
358 the connection is opened.
359 The real authentication cookie is never
360 sent to the server machine (and no cookies are sent in the plain).
366 (or see the description of the
370 options described later) and
371 the user is using an authentication agent, the connection to the agent
372 is automatically forwarded to the remote side.
374 Forwarding of arbitrary TCP/IP connections over the secure channel can
375 be specified either on the command line or in a configuration file.
376 One possible application of TCP/IP forwarding is a secure connection to an
377 electronic purse; another is going through firewalls.
378 .Ss Server authentication
380 automatically maintains and checks a database containing
381 identifications for all hosts it has ever been used with.
382 Host keys are stored in
383 .Pa ~/.ssh/known_hosts
384 in the user's home directory.
385 Additionally, the file
386 .Pa /etc/ssh/ssh_known_hosts
387 is automatically checked for known hosts.
388 Any new hosts are automatically added to the user's file.
389 If a host's identification ever changes,
391 warns about this and disables password authentication to prevent a
392 trojan horse from getting the user's password.
393 Another purpose of this mechanism is to prevent man-in-the-middle attacks
394 which could otherwise be used to circumvent the encryption.
396 .Cm StrictHostKeyChecking
397 option can be used to prevent logins to machines whose
398 host key is not known or has changed.
401 can be configured to verify host identification using fingerprint resource
402 records (SSHFP) published in DNS.
405 option can be used to control how DNS lookups are performed.
406 SSHFP resource records can be generated using
409 The options are as follows:
414 to try protocol version 1 only.
418 to try protocol version 2 only.
422 to use IPv4 addresses only.
426 to use IPv6 addresses only.
428 Enables forwarding of the authentication agent connection.
429 This can also be specified on a per-host basis in a configuration file.
431 Agent forwarding should be enabled with caution.
432 Users with the ability to bypass file permissions on the remote host
433 (for the agent's Unix-domain socket)
434 can access the local agent through the forwarded connection.
435 An attacker cannot obtain key material from the agent,
436 however they can perform operations on the keys that enable them to
437 authenticate using the identities loaded into the agent.
439 Disables forwarding of the authentication agent connection.
440 .It Fl b Ar bind_address
443 on the local machine as the source address
445 Only useful on systems with more than one address.
447 Requests compression of all data (including stdin, stdout, stderr, and
448 data for forwarded X11 and TCP/IP connections).
449 The compression algorithm is the same used by
453 can be controlled by the
455 option for protocol version 1.
456 Compression is desirable on modem lines and other
457 slow connections, but will only slow down things on fast networks.
458 The default value can be set on a host-by-host basis in the
459 configuration files; see the
462 .It Fl c Ar cipher_spec
463 Selects the cipher specification for encrypting the session.
465 Protocol version 1 allows specification of a single cipher.
466 The supported values are
472 (triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
473 It is believed to be secure.
475 is a fast block cipher; it appears very secure and is much faster than
478 is only supported in the
480 client for interoperability with legacy protocol 1 implementations
481 that do not support the
484 Its use is strongly discouraged due to cryptographic weaknesses.
488 For protocol version 2
490 is a comma-separated list of ciphers
491 listed in order of preference.
492 The supported ciphers are
508 ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
509 arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
510 aes192-ctr,aes256-ctr''
514 .Oo Ar bind_address : Oc
520 application-level port forwarding.
521 This works by allocating a socket to listen to
523 on the local side, optionally bound to the specified
525 Whenever a connection is made to this port, the
526 connection is forwarded over the secure channel, and the application
527 protocol is then used to determine where to connect to from the
529 Currently the SOCKS4 and SOCKS5 protocols are supported, and
531 will act as a SOCKS server.
532 Only root can forward privileged ports.
533 Dynamic port forwardings can also be specified in the configuration file.
535 IPv6 addresses can be specified with an alternative syntax:
538 .Op Ar bind_address No /
542 or by enclosing the address in square brackets.
543 Only the superuser can forward privileged ports.
544 By default, the local port is bound in accordance with the
549 may be used to bind the connection to a specific address.
554 indicates that the listening port be bound for local use only, while an
557 indicates that the port should be available from all interfaces.
558 .It Fl e Ar ch | ^ch | none
559 Sets the escape character for sessions with a pty (default:
561 The escape character is only recognized at the beginning of a line.
562 The escape character followed by a dot
564 closes the connection;
565 followed by control-Z suspends the connection;
566 and followed by itself sends the escape character once.
567 Setting the character to
569 disables any escapes and makes the session fully transparent.
570 .It Fl F Ar configfile
571 Specifies an alternative per-user configuration file.
572 If a configuration file is given on the command line,
573 the system-wide configuration file
574 .Pq Pa /etc/ssh/ssh_config
576 The default for the per-user configuration file is
581 to go to background just before command execution.
584 is going to ask for passwords or passphrases, but the user
585 wants it in the background.
588 The recommended way to start X11 programs at a remote site is with
590 .Ic ssh -f host xterm .
592 Allows remote hosts to connect to local forwarded ports.
593 .It Fl I Ar smartcard_device
594 Specifies which smartcard device to use.
595 The argument is the device
597 should use to communicate with a smartcard used for storing the user's
599 .It Fl i Ar identity_file
600 Selects a file from which the identity (private key) for
601 RSA or DSA authentication is read.
604 for protocol version 1, and
608 for protocol version 2.
609 Identity files may also be specified on
610 a per-host basis in the configuration file.
611 It is possible to have multiple
613 options (and multiple identities specified in
614 configuration files).
616 Disables forwarding (delegation) of GSSAPI credentials to the server.
619 .Oo Ar bind_address : Oc
620 .Ar port : host : hostport
623 Specifies that the given port on the local (client) host is to be
624 forwarded to the given host and port on the remote side.
625 This works by allocating a socket to listen to
627 on the local side, optionally bound to the specified
629 Whenever a connection is made to this port, the
630 connection is forwarded over the secure channel, and a connection is
635 from the remote machine.
636 Port forwardings can also be specified in the configuration file.
637 IPv6 addresses can be specified with an alternative syntax:
640 .Op Ar bind_address No /
641 .Ar port No / Ar host No /
645 or by enclosing the address in square brackets.
646 Only the superuser can forward privileged ports.
647 By default, the local port is bound in accordance with the
652 may be used to bind the connection to a specific address.
657 indicates that the listening port be bound for local use only, while an
660 indicates that the port should be available from all interfaces.
661 .It Fl l Ar login_name
662 Specifies the user to log in as on the remote machine.
663 This also may be specified on a per-host basis in the configuration file.
669 mode for connection sharing.
670 Refer to the description of
676 Additionally, for protocol version 2 a comma-separated list of MAC
677 (message authentication code) algorithms can
678 be specified in order of preference.
681 keyword for more information.
683 Do not execute a remote command.
684 This is useful for just forwarding ports
685 (protocol version 2 only).
689 (actually, prevents reading from stdin).
690 This must be used when
692 is run in the background.
693 A common trick is to use this to run X11 programs on a remote machine.
695 .Ic ssh -n shadows.cs.hut.fi emacs &
696 will start an emacs on shadows.cs.hut.fi, and the X11
697 connection will be automatically forwarded over an encrypted channel.
700 program will be put in the background.
701 (This does not work if
703 needs to ask for a password or passphrase; see also the
707 Control an active connection multiplexing master process.
710 option is specified, the
712 argument is interpreted and passed to the master process.
715 (check that the master process is running) and
717 (request the master to exit).
719 Can be used to give options in the format used in the configuration file.
720 This is useful for specifying options for which there is no separate
722 For full details of the options listed below, and their possible values, see
725 .Bl -tag -width Ds -offset indent -compact
729 .It ChallengeResponseAuthentication
733 .It ClearAllForwardings
736 .It ConnectionAttempts
744 .It ForwardX11Trusted
746 .It GlobalKnownHostsFile
747 .It GSSAPIAuthentication
748 .It GSSAPIDelegateCredentials
751 .It HostbasedAuthentication
752 .It HostKeyAlgorithms
757 .It KbdInteractiveDevices
762 .It NoHostAuthenticationForLocalhost
763 .It NumberOfPasswordPrompts
764 .It PasswordAuthentication
765 .It PermitLocalCommand
767 .It PreferredAuthentications
770 .It PubkeyAuthentication
772 .It RhostsRSAAuthentication
773 .It RSAAuthentication
775 .It ServerAliveInterval
776 .It ServerAliveCountMax
778 .It StrictHostKeyChecking
782 .It UsePrivilegedPort
784 .It UserKnownHostsFile
789 Port to connect to on the remote host.
790 This can be specified on a
791 per-host basis in the configuration file.
794 Causes all warning and diagnostic messages to be suppressed.
797 .Oo Ar bind_address : Oc
798 .Ar port : host : hostport
801 Specifies that the given port on the remote (server) host is to be
802 forwarded to the given host and port on the local side.
803 This works by allocating a socket to listen to
805 on the remote side, and whenever a connection is made to this port, the
806 connection is forwarded over the secure channel, and a connection is
811 from the local machine.
813 Port forwardings can also be specified in the configuration file.
814 Privileged ports can be forwarded only when
815 logging in as root on the remote machine.
816 IPv6 addresses can be specified by enclosing the address in square braces or
817 using an alternative syntax:
820 .Op Ar bind_address No /
821 .Ar host No / Ar port No /
826 By default, the listening socket on the server will be bound to the loopback
828 This may be overriden by specifying a
834 indicates that the remote socket should listen on all interfaces.
837 will only succeed if the server's
839 option is enabled (see
840 .Xr sshd_config 5 ) .
842 Specifies the location of a control socket for connection sharing.
843 Refer to the description of
851 May be used to request invocation of a subsystem on the remote system.
852 Subsystems are a feature of the SSH2 protocol which facilitate the use
853 of SSH as a secure transport for other applications (eg.\&
855 The subsystem is specified as the remote command.
857 Disable pseudo-tty allocation.
859 Force pseudo-tty allocation.
860 This can be used to execute arbitrary
861 screen-based programs on a remote machine, which can be very useful,
862 e.g., when implementing menu services.
865 options force tty allocation, even if
869 Display the version number and exit.
874 to print debugging messages about its progress.
876 debugging connection, authentication, and configuration problems.
879 options increase the verbosity.
881 .It Fl w Ar tunnel : Ns Ar tunnel
884 device on the client and server like the
889 Enables X11 forwarding.
890 This can also be specified on a per-host basis in a configuration file.
892 X11 forwarding should be enabled with caution.
893 Users with the ability to bypass file permissions on the remote host
894 (for the user's X authorization database)
895 can access the local X11 display through the forwarded connection.
896 An attacker may then be able to perform activities such as keystroke monitoring.
898 For this reason, X11 forwarding is subjected to X11 SECURITY extension
899 restrictions by default.
904 .Cm ForwardX11Trusted
907 for more information.
909 Disables X11 forwarding.
911 Enables trusted X11 forwarding.
912 Trusted X11 forwardings are not subjected to the X11 SECURITY extension
915 .Sh CONFIGURATION FILES
917 may additionally obtain configuration data from
918 a per-user configuration file and a system-wide configuration file.
919 The file format and configuration options are described in
923 will normally set the following environment variables:
924 .Bl -tag -width LOGNAME
928 variable indicates the location of the X11 server.
929 It is automatically set by
931 to point to a value of the form
933 where hostname indicates
934 the host where the shell runs, and n is an integer \*(Ge 1.
936 uses this special value to forward X11 connections over the secure
938 The user should normally not set
941 will render the X11 connection insecure (and will require the user to
942 manually copy any required authorization cookies).
944 Set to the path of the user's home directory.
948 set for compatibility with systems that use this variable.
950 Set to the path of the user's mailbox.
954 as specified when compiling
959 needs a passphrase, it will read the passphrase from the current
960 terminal if it was run from a terminal.
963 does not have a terminal associated with it but
967 are set, it will execute the program specified by
969 and open an X11 window to read the passphrase.
970 This is particularly useful when calling
975 (Note that on some machines it
976 may be necessary to redirect the input from
980 Identifies the path of a unix-domain socket used to communicate with the
982 .It Ev SSH_CONNECTION
983 Identifies the client and server ends of the connection.
984 The variable contains
985 four space-separated values: client ip-address, client port number,
986 server ip-address and server port number.
987 .It Ev SSH_ORIGINAL_COMMAND
988 The variable contains the original command line if a forced command
990 It can be used to extract the original arguments.
992 This is set to the name of the tty (path to the device) associated
993 with the current shell or command.
994 If the current session has no tty,
995 this variable is not set.
997 This variable is set to indicate the present time zone if it
998 was set when the daemon was started (i.e., the daemon passes the value
999 on to new connections).
1001 Set to the name of the user logging in.
1007 .Pa ~/.ssh/environment ,
1008 and adds lines of the format
1010 to the environment if the file exists and if users are allowed to
1011 change their environment.
1012 For more information, see the
1013 .Cm PermitUserEnvironment
1018 .It Pa ~/.ssh/known_hosts
1019 Records host keys for all hosts the user has logged into that are not
1021 .Pa /etc/ssh/ssh_known_hosts .
1024 .It Pa ~/.ssh/identity, ~/.ssh/id_dsa, ~/.ssh/id_rsa
1025 Contains the authentication identity of the user.
1026 They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively.
1028 contain sensitive data and should be readable by the user but not
1029 accessible by others (read/write/execute).
1032 ignores a private key file if it is accessible by others.
1033 It is possible to specify a passphrase when
1034 generating the key; the passphrase will be used to encrypt the
1035 sensitive part of this file using 3DES.
1036 .It Pa ~/.ssh/identity.pub, ~/.ssh/id_dsa.pub, ~/.ssh/id_rsa.pub
1037 Contains the public key for authentication (public part of the
1038 identity file in human-readable form).
1040 .Pa ~/.ssh/identity.pub
1041 file should be added to the file
1042 .Pa ~/.ssh/authorized_keys
1044 where the user wishes to log in using protocol version 1 RSA authentication.
1046 .Pa ~/.ssh/id_dsa.pub
1048 .Pa ~/.ssh/id_rsa.pub
1049 file should be added to
1050 .Pa ~/.ssh/authorized_keys
1052 where the user wishes to log in using protocol version 2 DSA/RSA authentication.
1054 sensitive and can (but need not) be readable by anyone.
1056 never used automatically and are not necessary; they are only provided for
1057 the convenience of the user.
1058 .It Pa ~/.ssh/config
1059 This is the per-user configuration file.
1060 The file format and configuration options are described in
1062 Because of the potential for abuse, this file must have strict permissions:
1063 read/write for the user, and not accessible by others.
1064 .It Pa ~/.ssh/authorized_keys
1065 Lists the public keys (RSA/DSA) that can be used for logging in as this user.
1066 The format of this file is described in the
1069 In the simplest form the format is the same as the
1072 This file is not highly sensitive, but the recommended
1073 permissions are read/write for the user, and not accessible by others.
1074 .It Pa /etc/ssh/ssh_known_hosts
1075 Systemwide list of known host keys.
1076 This file should be prepared by the
1077 system administrator to contain the public host keys of all machines in the
1079 This file should be world-readable.
1081 public keys, one per line, in the following format (fields separated
1082 by spaces): system name, public key and optional comment field.
1083 When different names are used
1084 for the same machine, all such names should be listed, separated by
1086 The format is described in the
1090 The canonical system name (as returned by name servers) is used by
1092 to verify the client host when logging in; other names are needed because
1094 does not convert the user-supplied name to a canonical name before
1095 checking the key, because someone with access to the name servers
1096 would then be able to fool host authentication.
1097 .It Pa /etc/ssh/ssh_config
1098 Systemwide configuration file.
1099 The file format and configuration options are described in
1101 .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key
1102 These three files contain the private parts of the host keys
1104 .Cm RhostsRSAAuthentication
1106 .Cm HostbasedAuthentication .
1107 If the protocol version 1
1108 .Cm RhostsRSAAuthentication
1111 must be setuid root, since the host key is readable only by root.
1112 For protocol version 2,
1116 to access the host keys for
1117 .Cm HostbasedAuthentication .
1118 This eliminates the requirement that
1120 be setuid root when that authentication method is used.
1125 This file is used in
1126 .Cm RhostsRSAAuthentication
1128 .Cm HostbasedAuthentication
1129 authentication to list the
1130 host/user pairs that are permitted to log in.
1131 (Note that this file is
1132 also used by rlogin and rsh, which makes using this file insecure.)
1133 Each line of the file contains a host name (in the canonical form
1134 returned by name servers), and then a user name on that host,
1135 separated by a space.
1136 On some machines this file may need to be
1137 world-readable if the user's home directory is on a NFS partition,
1141 Additionally, this file must be owned by the user,
1142 and must not have write permissions for anyone else.
1144 permission for most machines is read/write for the user, and not
1145 accessible by others.
1149 allows authentication only in combination with client host key
1150 authentication before permitting log in.
1151 If the server machine does not have the client's host key in
1152 .Pa /etc/ssh/ssh_known_hosts ,
1154 .Pa ~/.ssh/known_hosts .
1155 The easiest way to do this is to
1156 connect back to the client from the server machine using ssh; this
1157 will automatically add the host key to
1158 .Pa ~/.ssh/known_hosts .
1160 This file is used exactly the same way as
1163 having this file is to be able to use
1164 .Cm RhostsRSAAuthentication
1166 .Cm HostbasedAuthentication
1167 authentication without permitting login with
1171 .It Pa /etc/hosts.equiv
1172 This file is used during
1173 .Cm RhostsRSAAuthentication
1175 .Cm HostbasedAuthentication
1178 canonical hosts names, one per line (the full format is described in the
1181 If the client host is found in this file, login is
1182 automatically permitted provided client and server user names are the
1184 Additionally, successful client host key authentication is required.
1185 This file should only be writable by root.
1186 .It Pa /etc/shosts.equiv
1187 This file is processed exactly as
1188 .Pa /etc/hosts.equiv .
1189 This file may be useful to permit logins using
1191 but not using rsh/rlogin.
1192 .It Pa /etc/ssh/sshrc
1193 Commands in this file are executed by
1195 when the user logs in just before the user's shell (or command) is started.
1198 manual page for more information.
1200 Commands in this file are executed by
1202 when the user logs in just before the user's shell (or command) is
1206 manual page for more information.
1207 .It Pa ~/.ssh/environment
1208 Contains additional definitions for environment variables, see section
1214 exits with the exit status of the remote command or with 255
1215 if an error occurred.
1235 .%T "SSH Protocol Architecture"
1236 .%N draft-ietf-secsh-architecture-12.txt
1238 .%O work in progress material
1241 OpenSSH is a derivative of the original and free
1242 ssh 1.2.12 release by Tatu Ylonen.
1243 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1244 Theo de Raadt and Dug Song
1245 removed many bugs, re-added newer features and
1247 Markus Friedl contributed the support for SSH
1248 protocol versions 1.5 and 2.0.
andersk / openssh.git / blob