5 .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
7 .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
8 .\" All rights reserved
10 .\" Created: Sat Apr 22 21:55:14 1995 ylo
14 .Dd September 25, 1999
19 .Nd OpenSSH secure shell client (remote login program)
22 .Op Fl l Ar login_name
23 .Op Ar hostname | user@hostname
27 .Op Fl afgknqtvxCPX246
28 .Op Fl c Ar cipher_spec
29 .Op Fl e Ar escape_char
30 .Op Fl i Ar identity_file
31 .Op Fl l Ar login_name
50 .Op Ar hostname | user@hostname
54 (Secure Shell) is a program for logging into a remote machine and for
55 executing commands on a remote machine.
56 It is intended to replace
57 rlogin and rsh, and provide secure encrypted communications between
58 two untrusted hosts over an insecure network.
60 arbitrary TCP/IP ports can also be forwarded over the secure channel.
63 connects and logs into the specified
66 his/her identity to the remote machine using one of several methods
67 depending on the protocol version used:
69 .Ss SSH protocol version 1
71 First, if the machine the user logs in from is listed in
75 on the remote machine, and the user names are
76 the same on both sides, the user is immediately permitted to log in.
81 exists in the user's home directory on the
82 remote machine and contains a line containing the name of the client
83 machine and the name of the user on that machine, the user is
85 This form of authentication alone is normally not
86 allowed by the server because it is not secure.
88 The second (and primary) authentication method is the
92 method combined with RSA-based host authentication.
93 It means that if the login would be permitted by
96 .Pa /etc/hosts.equiv ,
98 .Pa /etc/shosts.equiv ,
99 and if additionally the server can verify the client's
101 .Pa /etc/ssh_known_hosts
103 .Pa $HOME/.ssh/known_hosts
106 section), only then login is permitted.
107 This authentication method closes security holes due to IP
108 spoofing, DNS spoofing and routing spoofing.
109 [Note to the administrator:
110 .Pa /etc/hosts.equiv ,
112 and the rlogin/rsh protocol in general, are inherently insecure and should be
113 disabled if security is desired.]
115 As a third authentication method,
117 supports RSA based authentication.
118 The scheme is based on public-key cryptography: there are cryptosystems
119 where encryption and decryption are done using separate keys, and it
120 is not possible to derive the decryption key from the encryption key.
121 RSA is one such system.
122 The idea is that each user creates a public/private
123 key pair for authentication purposes.
124 The server knows the public key, and only the user knows the private key.
126 .Pa $HOME/.ssh/authorized_keys
127 lists the public keys that are permitted for logging
129 When the user logs in, the
131 program tells the server which key pair it would like to use for
133 The server checks if this key is permitted, and if
134 so, sends the user (actually the
136 program running on behalf of the user) a challenge, a random number,
137 encrypted by the user's public key.
138 The challenge can only be
139 decrypted using the proper private key.
140 The user's client then decrypts the
141 challenge using the private key, proving that he/she knows the private
142 key but without disclosing it to the server.
145 implements the RSA authentication protocol automatically.
146 The user creates his/her RSA key pair by running
148 This stores the private key in
149 .Pa $HOME/.ssh/identity
150 and the public key in
151 .Pa $HOME/.ssh/identity.pub
152 in the user's home directory.
153 The user should then copy the
156 .Pa $HOME/.ssh/authorized_keys
157 in his/her home directory on the remote machine (the
159 file corresponds to the conventional
161 file, and has one key
162 per line, though the lines can be very long).
163 After this, the user can log in without giving the password.
164 RSA authentication is much
165 more secure than rhosts authentication.
167 The most convenient way to use RSA authentication may be with an
168 authentication agent.
171 for more information.
173 If other authentication methods fail,
175 prompts the user for a password.
176 The password is sent to the remote
177 host for checking; however, since all communications are encrypted,
178 the password cannot be seen by someone listening on the network.
180 .Ss SSH protocol version 2
182 When a user connects using the protocol version 2
183 different authentication methods are available:
184 At first, the client attempts to authenticate using the public key method.
185 If this method fails password authentication is tried.
187 The public key method is similar to RSA authentication described
188 in the previous section except that the DSA algorithm is used
189 instead of the patented RSA algorithm.
190 The client uses his private DSA key
191 .Pa $HOME/.ssh/id_dsa
192 to sign the session identifier and sends the result to the server.
193 The server checks whether the matching public key is listed in
194 .Pa $HOME/.ssh/authorized_keys2
195 and grants access if both the key is found and the signature is correct.
196 The session identifier is derived from a shared Diffie-Hellman value
197 and is only known to the client and the server.
199 If public key authentication fails or is not available a password
200 can be sent encrypted to the remote host for proving the user's identity.
201 This protocol 2 implementation does not yet support Kerberos or
202 S/Key authentication.
204 Protocol 2 provides additional mechanisms for confidentiality
205 (the traffic is encrypted using 3DES, Blowfish, CAST128 or Arcfour)
206 and integrity (hmac-sha1, hmac-md5).
207 Note that protocol 1 lacks a strong mechanism for ensuring the
208 integrity of the connection.
210 .Ss Login session and remote execution
212 When the user's identity has been accepted by the server, the server
213 either executes the given command, or logs into the machine and gives
214 the user a normal shell on the remote machine.
215 All communication with
216 the remote command or shell will be automatically encrypted.
218 If a pseudo-terminal has been allocated (normal login session), the
219 user can disconnect with
225 All forwarded connections can be listed with
228 the session blocks waiting for forwarded X11 or TCP/IP
229 connections to terminate, it can be backgrounded with
231 (this should not be used while the user shell is active, as it can cause the
233 All available escapes can be listed with
236 A single tilde character can be sent as
238 (or by following the tilde by a character other than those described above).
239 The escape character must always follow a newline to be interpreted as
241 The escape character can be changed in configuration files
242 or on the command line.
244 If no pseudo tty has been allocated, the
245 session is transparent and can be used to reliably transfer binary
247 On most systems, setting the escape character to
249 will also make the session transparent even if a tty is used.
251 The session terminates when the command or shell in on the remote
252 machine exists and all X11 and TCP/IP connections have been closed.
253 The exit status of the remote program is returned as the exit status
257 .Ss X11 and TCP forwarding
259 If the user is using X11 (the
261 environment variable is set), the connection to the X11 display is
262 automatically forwarded to the remote side in such a way that any X11
263 programs started from the shell (or command) will go through the
264 encrypted channel, and the connection to the real X server will be made
265 from the local machine.
266 The user should not manually set
268 Forwarding of X11 connections can be
269 configured on the command line or in configuration files.
275 will point to the server machine, but with a display number greater
277 This is normal, and happens because
281 X server on the server machine for forwarding the
282 connections over the encrypted channel.
285 will also automatically set up Xauthority data on the server machine.
286 For this purpose, it will generate a random authorization cookie,
287 store it in Xauthority on the server, and verify that any forwarded
288 connections carry this cookie and replace it by the real cookie when
289 the connection is opened.
290 The real authentication cookie is never
291 sent to the server machine (and no cookies are sent in the plain).
293 If the user is using an authentication agent, the connection to the agent
294 is automatically forwarded to the remote side unless disabled on
295 command line or in a configuration file.
297 Forwarding of arbitrary TCP/IP connections over the secure channel can
298 be specified either on command line or in a configuration file.
299 One possible application of TCP/IP forwarding is a secure connection to an
300 electronic purse; another is going trough firewalls.
302 .Ss Server authentication
305 automatically maintains and checks a database containing
306 identifications for all hosts it has ever been used with.
307 RSA host keys are stored in
308 .Pa $HOME/.ssh/known_hosts
310 DSA host keys are stored in
311 .Pa $HOME/.ssh/known_hosts2
312 in the user's home directory.
313 Additionally, the files
314 .Pa /etc/ssh_known_hosts
316 .Pa /etc/ssh_known_hosts2
317 are automatically checked for known hosts.
318 Any new hosts are automatically added to the user's file.
319 If a host's identification
322 warns about this and disables password authentication to prevent a
323 trojan horse from getting the user's password.
325 this mechanism is to prevent man-in-the-middle attacks which could
326 otherwise be used to circumvent the encryption.
328 .Cm StrictHostKeyChecking
329 option (see below) can be used to prevent logins to machines whose
330 host key is not known or has changed.
334 Disables forwarding of the authentication agent connection.
335 This may also be specified on a per-host basis in the configuration file.
336 .It Fl c Ar blowfish|3des
337 Selects the cipher to use for encrypting the session.
340 It is believed to be secure.
342 (triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
343 It is presumably more secure than the
345 cipher which is no longer supported in
348 is a fast block cipher, it appears very secure and is much faster than
350 .It Fl c Ar "3des-cbc,blowfish-cbc,arcfour,cast128-cbc"
351 Additionally, for protocol version 2 a comma-separated list of ciphers can
352 be specified in order of preference. Protocol version 2 supports
353 3DES, Blowfish and CAST128 in CBC mode and Arcfour.
354 .It Fl e Ar ch|^ch|none
355 Sets the escape character for sessions with a pty (default:
357 The escape character is only recognized at the beginning of a line.
358 The escape character followed by a dot
360 closes the connection, followed
361 by control-Z suspends the connection, and followed by itself sends the
362 escape character once.
363 Setting the character to
365 disables any escapes and makes the session fully transparent.
369 to go to background just before command execution.
372 is going to ask for passwords or passphrases, but the user
373 wants it in the background.
376 The recommended way to start X11 programs at a remote site is with
378 .Ic ssh -f host xterm .
380 Allows remote hosts to connect to local forwarded ports.
381 .It Fl i Ar identity_file
382 Selects the file from which the identity (private key) for
383 RSA authentication is read.
385 .Pa $HOME/.ssh/identity
386 in the user's home directory.
387 Identity files may also be specified on
388 a per-host basis in the configuration file.
389 It is possible to have multiple
391 options (and multiple identities specified in
392 configuration files).
394 Disables forwarding of Kerberos tickets and AFS tokens.
395 This may also be specified on a per-host basis in the configuration file.
396 .It Fl l Ar login_name
397 Specifies the user to log in as on the remote machine.
398 This also may be specified on a per-host basis in the configuration file.
402 (actually, prevents reading from stdin).
403 This must be used when
405 is run in the background.
406 A common trick is to use this to run X11 programs on a remote machine.
408 .Ic ssh -n shadows.cs.hut.fi emacs &
409 will start an emacs on shadows.cs.hut.fi, and the X11
410 connection will be automatically forwarded over an encrypted channel.
413 program will be put in the background.
414 (This does not work if
416 needs to ask for a password or passphrase; see also the
420 Can be used to give options in the format used in the config file.
421 This is useful for specifying options for which there is no separate
423 The option has the same format as a line in the configuration file.
425 Port to connect to on the remote host.
426 This can be specified on a
427 per-host basis in the configuration file.
429 Use a non-privileged port for outgoing connections.
430 This can be used if your firewall does
431 not permit connections from privileged ports.
432 Note that this option turns off
433 .Cm RhostsAuthentication
435 .Cm RhostsRSAAuthentication .
438 Causes all warning and diagnostic messages to be suppressed.
439 Only fatal errors are displayed.
441 Force pseudo-tty allocation.
442 This can be used to execute arbitrary
443 screen-based programs on a remote machine, which can be very useful,
444 e.g., when implementing menu services.
449 to print debugging messages about its progress.
451 debugging connection, authentication, and configuration problems.
452 The verbose mode is also used to display
454 challenges, if the user entered "s/key" as password.
456 Disables X11 forwarding.
457 This can also be specified on a per-host basis in a configuration file.
459 Enables X11 forwarding.
461 Requests compression of all data (including stdin, stdout, stderr, and
462 data for forwarded X11 and TCP/IP connections).
463 The compression algorithm is the same used by
467 can be controlled by the
470 Compression is desirable on modem lines and other
471 slow connections, but will only slow down things on fast networks.
472 The default value can be set on a host-by-host basis in the
473 configuration files; see the
476 .It Fl L Ar port:host:hostport
477 Specifies that the given port on the local (client) host is to be
478 forwarded to the given host and port on the remote side.
479 This works by allocating a socket to listen to
481 on the local side, and whenever a connection is made to this port, the
482 connection is forwarded over the secure channel, and a connection is
487 from the remote machine.
488 Port forwardings can also be specified in the configuration file.
489 Only root can forward privileged ports.
490 IPv6 addresses can be specified with an alternative syntax:
491 .Ar port/host/hostport
492 .It Fl R Ar port:host:hostport
493 Specifies that the given port on the remote (server) host is to be
494 forwarded to the given host and port on the local side.
495 This works by allocating a socket to listen to
497 on the remote side, and whenever a connection is made to this port, the
498 connection is forwarded over the secure channel, and a connection is
503 from the local machine.
504 Port forwardings can also be specified in the configuration file.
505 Privileged ports can be forwarded only when
506 logging in as root on the remote machine.
510 to try protocol version 2 only.
514 to use IPv4 addresses only.
518 to use IPv6 addresses only.
520 .Sh CONFIGURATION FILES
522 obtains configuration data from the following sources (in this order):
523 command line options, user's configuration file
524 .Pq Pa $HOME/.ssh/config ,
525 and system-wide configuration file
526 .Pq Pa /etc/ssh_config .
527 For each parameter, the first obtained value
529 The configuration files contain sections bracketed by
531 specifications, and that section is only applied for hosts that
532 match one of the patterns given in the specification.
533 The matched host name is the one given on the command line.
535 Since the first obtained value for each parameter is used, more
536 host-specific declarations should be given near the beginning of the
537 file, and general defaults at the end.
539 The configuration file has the following format:
541 Empty lines and lines starting with
545 Otherwise a line is of the format
546 .Dq keyword arguments .
548 keywords and their meanings are as follows (note that the
549 configuration files are case-sensitive):
552 Restricts the following declarations (up to the next
554 keyword) to be only for those hosts that match one of the patterns
555 given after the keyword.
559 can be used as wildcards in the
563 as a pattern can be used to provide global
564 defaults for all hosts.
567 argument given on the command line (i.e., the name is not converted to
568 a canonicalized host name before matching).
569 .It Cm AFSTokenPassing
570 Specifies whether to pass AFS tokens to remote host.
571 The argument to this keyword must be
578 passphrase/password querying will be disabled.
579 This option is useful in scripts and other batch jobs where you have no
580 user to supply the password.
586 If this flag is set to
588 ssh will additionally check the host ip address in the
591 This allows ssh to detect if a host key changed due to DNS spoofing.
592 If the option is set to
594 the check will not be executed.
596 Specifies the cipher to use for encrypting the session.
605 Specifies the ciphers allowed for protocol version 2
606 in order of preference.
607 Multiple ciphers must be comma-separated.
609 .Dq 3des-cbc,blowfish-cbc,arcfour,cast128-cbc .
611 Specifies whether to use compression.
616 .It Cm CompressionLevel
617 Specifies the compression level to use if compression is enable.
618 The argument must be an integer from 1 (fast) to 9 (slow, best).
619 The default level is 6, which is good for most applications.
620 The meaning of the values is the same as in
622 .It Cm ConnectionAttempts
623 Specifies the number of tries (one per second) to make before falling
624 back to rsh or exiting.
625 The argument must be an integer.
626 This may be useful in scripts if the connection sometimes fails.
627 .It Cm DSAAuthentication
628 Specifies whether to try DSA authentication.
629 The argument to this keyword must be
633 DSA authentication will only be
634 attempted if a DSA identity file exists.
635 Note that this option applies to protocol version 2 only.
637 Sets the escape character (default:
639 The escape character can also
640 be set on the command line.
641 The argument should be a single character,
643 followed by a letter, or
645 to disable the escape
646 character entirely (making the connection transparent for binary
649 Specifies that if connecting via
651 fails due to a connection refused error (there is no
653 listening on the remote host),
655 should automatically be used instead (after a suitable warning about
656 the session being unencrypted).
662 Specifies whether the connection to the authentication agent (if any)
663 will be forwarded to the remote machine.
669 Specifies whether X11 connections will be automatically redirected
670 over the secure channel and
680 Specifies whether remote hosts are allowed to connect to local
688 .It Cm GlobalKnownHostsFile
689 Specifies a file to use instead of
690 .Pa /etc/ssh_known_hosts .
692 Specifies the real host name to log into.
693 This can be used to specify nicknames or abbreviations for hosts.
694 Default is the name given on the command line.
695 Numeric IP addresses are also permitted (both on the command line and in
699 Specifies the file from which the user's RSA authentication identity
701 .Pa $HOME/.ssh/identity
702 in the user's home directory).
703 Additionally, any identities represented by the authentication agent
704 will be used for authentication.
705 The file name may use the tilde
706 syntax to refer to a user's home directory.
707 It is possible to have
708 multiple identity files specified in configuration files; all these
709 identities will be tried in sequence.
711 Specifies the file from which the user's DSA authentication identity
713 .Pa $HOME/.ssh/id_dsa
714 in the user's home directory).
715 The file name may use the tilde
716 syntax to refer to a user's home directory.
717 It is possible to have
718 multiple identity files specified in configuration files; all these
719 identities will be tried in sequence.
721 Specifies whether the system should send keepalive messages to the
723 If they are sent, death of the connection or crash of one
724 of the machines will be properly noticed.
725 However, this means that
726 connections will die if the route is down temporarily, and some people
731 (to send keepalives), and the client will notice
732 if the network goes down or the remote host dies.
733 This is important in scripts, and many users want it too.
735 To disable keepalives, the value should be set to
737 in both the server and the client configuration files.
738 .It Cm KerberosAuthentication
739 Specifies whether Kerberos authentication will be used.
740 The argument to this keyword must be
744 .It Cm KerberosTgtPassing
745 Specifies whether a Kerberos TGT will be forwarded to the server.
746 This will only work if the Kerberos server is actually an AFS kaserver.
747 The argument to this keyword must be
752 Specifies that a TCP/IP port on the local machine be forwarded over
753 the secure channel to given host:port from the remote machine.
754 The first argument must be a port number, and the second must be
756 Multiple forwardings may be specified, and additional
757 forwardings can be given on the command line.
758 Only the superuser can forward privileged ports.
760 Gives the verbosity level that is used when logging messages from
762 The possible values are:
763 QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG.
765 .It Cm NumberOfPasswordPrompts
766 Specifies the number of password prompts before giving up.
767 The argument to this keyword must be an integer.
769 .It Cm PasswordAuthentication
770 Specifies whether to use password authentication.
771 The argument to this keyword must be
775 Note that this option applies to both protocol version 1 and 2.
777 Specifies the port number to connect on the remote host.
780 Specifies the protocol versions
782 should support in order of preference.
783 The possible values are
787 Multiple versions must be comma-separated.
792 tries version 1 and falls back to version 2
793 if version 1 is not available.
795 Specifies the command to use to connect to the server.
797 string extends to the end of the line, and is executed with
799 In the command string,
801 will be substituted by the host name to
805 The command can be basically anything,
806 and should read from its standard input and write to its standard output.
807 It should eventually connect an
809 server running on some machine, or execute
812 Host key management will be done using the
813 HostName of the host being connected (defaulting to the name typed by
817 is not available for connects with a proxy command.
820 Specifies that a TCP/IP port on the remote machine be forwarded over
821 the secure channel to given host:port from the local machine.
822 The first argument must be a port number, and the second must be
824 Multiple forwardings may be specified, and additional
825 forwardings can be given on the command line.
826 Only the superuser can forward privileged ports.
827 .It Cm RhostsAuthentication
828 Specifies whether to try rhosts based authentication.
830 declaration only affects the client side and has no effect whatsoever
832 Disabling rhosts authentication may reduce
833 authentication time on slow connections when rhosts authentication is
835 Most servers do not permit RhostsAuthentication because it
836 is not secure (see RhostsRSAAuthentication).
837 The argument to this keyword must be
841 .It Cm RhostsRSAAuthentication
842 Specifies whether to try rhosts based authentication with RSA host
844 This is the primary authentication method for most sites.
849 .It Cm RSAAuthentication
850 Specifies whether to try RSA authentication.
851 The argument to this keyword must be
855 RSA authentication will only be
856 attempted if the identity file exists, or an authentication agent is
858 Note that this option applies to protocol version 1 only.
859 .It Cm SkeyAuthentication
860 Specifies whether to use
863 The argument to this keyword must be
869 .It Cm StrictHostKeyChecking
870 If this flag is set to
873 ssh will never automatically add host keys to the
874 .Pa $HOME/.ssh/known_hosts
876 .Pa $HOME/.ssh/known_hosts2
877 files, and refuses to connect hosts whose host key has changed.
878 This provides maximum protection against trojan horse attacks.
879 However, it can be somewhat annoying if you don't have good
880 .Pa /etc/ssh_known_hosts
882 .Pa /etc/ssh_known_hosts2
883 files installed and frequently
885 Basically this option forces the user to manually
887 Normally this option is disabled, and new hosts
888 will automatically be added to the known host files.
890 known hosts will be verified automatically in either case.
895 .It Cm UsePrivilegedPort
896 Specifies whether to use a privileged port for outgoing connections.
903 Note that setting this option to
906 .Cm RhostsAuthentication
908 .Cm RhostsRSAAuthentication .
910 Specifies the user to log in as.
911 This can be useful if you have a different user name on different machines.
912 This saves the trouble of
913 having to remember to give the user name on the command line.
914 .It Cm UserKnownHostsFile
915 Specifies a file to use instead of
916 .Pa $HOME/.ssh/known_hosts .
918 Specifies that rlogin/rsh should be used for this host.
919 It is possible that the host does not at all support the
924 to immediately execute
926 All other options (except
928 are ignored if this has been specified.
935 will normally set the following environment variables:
940 variable indicates the location of the X11 server.
941 It is automatically set by
943 to point to a value of the form
945 where hostname indicates
946 the host where the shell runs, and n is an integer >= 1.
948 uses this special value to forward X11 connections over the secure
950 The user should normally not set DISPLAY explicitly, as that
951 will render the X11 connection insecure (and will require the user to
952 manually copy any required authorization cookies).
954 Set to the path of the user's home directory.
958 set for compatibility with systems that use this variable.
960 Set to point the user's mailbox.
964 as specified when compiling
967 indicates the path of a unix-domain socket used to communicate with the
970 Identifies the client end of the connection.
971 The variable contains
972 three space-separated values: client ip-address, client port number,
973 and server port number.
975 This is set to the name of the tty (path to the device) associated
976 with the current shell or command.
977 If the current session has no tty,
978 this variable is not set.
980 The timezone variable is set to indicate the present timezone if it
981 was set when the daemon was started (e.i., the daemon passes the value
982 on to new connections).
984 Set to the name of the user logging in.
990 .Pa $HOME/.ssh/environment ,
991 and adds lines of the format
996 .It Pa $HOME/.ssh/known_hosts
997 Records host keys for all hosts the user has logged into (that are not
999 .Pa /etc/ssh_known_hosts ) .
1002 .It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa
1003 Contains the RSA and the DSA authentication identity of the user.
1005 contain sensitive data and should be readable by the user but not
1006 accessible by others (read/write/execute).
1009 ignores a private key file if it is accessible by others.
1010 It is possible to specify a passphrase when
1011 generating the key; the passphrase will be used to encrypt the
1012 sensitive part of this file using 3DES.
1013 .It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub
1014 Contains the public key for authentication (public part of the
1015 identity file in human-readable form).
1017 .Pa $HOME/.ssh/identity.pub
1018 file should be added to
1019 .Pa $HOME/.ssh/authorized_keys
1021 where you wish to log in using RSA authentication.
1023 .Pa $HOME/.ssh/id_dsa.pub
1024 file should be added to
1025 .Pa $HOME/.ssh/authorized_keys2
1027 where you wish to log in using DSA authentication.
1029 sensitive and can (but need not) be readable by anyone.
1031 never used automatically and are not necessary; they is only provided for
1032 the convenience of the user.
1033 .It Pa $HOME/.ssh/config
1034 This is the per-user configuration file.
1035 The format of this file is described above.
1036 This file is used by the
1039 This file does not usually contain any sensitive information,
1040 but the recommended permissions are read/write for the user, and not
1041 accessible by others.
1042 .It Pa $HOME/.ssh/authorized_keys
1043 Lists the RSA keys that can be used for logging in as this user.
1044 The format of this file is described in the
1047 In the simplest form the format is the same as the .pub
1048 identity files (that is, each line contains the number of bits in
1049 modulus, public exponent, modulus, and comment fields, separated by
1051 This file is not highly sensitive, but the recommended
1052 permissions are read/write for the user, and not accessible by others.
1053 .It Pa $HOME/.ssh/authorized_keys2
1054 Lists the DSA keys that can be used for logging in as this user.
1055 This file is not highly sensitive, but the recommended
1056 permissions are read/write for the user, and not accessible by others.
1057 .It Pa /etc/ssh_known_hosts, /etc/ssh_known_hosts2
1058 Systemwide list of known host keys.
1059 .Pa /etc/ssh_known_hosts
1061 .Pa /etc/ssh_known_hosts2
1063 These files should be prepared by the
1064 system administrator to contain the public host keys of all machines in the
1066 This file should be world-readable.
1068 public keys, one per line, in the following format (fields separated
1069 by spaces): system name, number of bits in modulus, public exponent,
1070 modulus, and optional comment field.
1071 When different names are used
1072 for the same machine, all such names should be listed, separated by
1074 The format is described on the
1078 The canonical system name (as returned by name servers) is used by
1080 to verify the client host when logging in; other names are needed because
1082 does not convert the user-supplied name to a canonical name before
1083 checking the key, because someone with access to the name servers
1084 would then be able to fool host authentication.
1085 .It Pa /etc/ssh_config
1086 Systemwide configuration file.
1087 This file provides defaults for those
1088 values that are not specified in the user's configuration file, and
1089 for those users who do not have a configuration file.
1090 This file must be world-readable.
1091 .It Pa $HOME/.rhosts
1092 This file is used in
1094 authentication to list the
1095 host/user pairs that are permitted to log in.
1096 (Note that this file is
1097 also used by rlogin and rsh, which makes using this file insecure.)
1098 Each line of the file contains a host name (in the canonical form
1099 returned by name servers), and then a user name on that host,
1100 separated by a space.
1101 One some machines this file may need to be
1102 world-readable if the user's home directory is on a NFS partition,
1106 Additionally, this file must be owned by the user,
1107 and must not have write permissions for anyone else.
1109 permission for most machines is read/write for the user, and not
1110 accessible by others.
1112 Note that by default
1114 will be installed so that it requires successful RSA host
1115 authentication before permitting \s+2.\s0rhosts authentication.
1116 If your server machine does not have the client's host key in
1117 .Pa /etc/ssh_known_hosts ,
1119 .Pa $HOME/.ssh/known_hosts .
1120 The easiest way to do this is to
1121 connect back to the client from the server machine using ssh; this
1122 will automatically add the host key to
1123 .Pa $HOME/.ssh/known_hosts .
1124 .It Pa $HOME/.shosts
1125 This file is used exactly the same way as
1128 having this file is to be able to use rhosts authentication with
1130 without permitting login with
1134 .It Pa /etc/hosts.equiv
1135 This file is used during
1136 .Pa \&.rhosts authentication.
1138 canonical hosts names, one per line (the full format is described on
1142 If the client host is found in this file, login is
1143 automatically permitted provided client and server user names are the
1145 Additionally, successful RSA host authentication is normally
1147 This file should only be writable by root.
1148 .It Pa /etc/shosts.equiv
1149 This file is processed exactly as
1150 .Pa /etc/hosts.equiv .
1151 This file may be useful to permit logins using
1153 but not using rsh/rlogin.
1155 Commands in this file are executed by
1157 when the user logs in just before the user's shell (or command) is started.
1160 manual page for more information.
1161 .It Pa $HOME/.ssh/rc
1162 Commands in this file are executed by
1164 when the user logs in just before the user's shell (or command) is
1168 manual page for more information.
1169 .It Pa $HOME/.ssh/environment
1170 Contains additional definitions for environment variables, see section
1173 .It Pa libcrypto.so.X.1
1174 A version of this library which includes support for the RSA algorithm
1175 is required for proper operation.
1178 is a derivative of the original (free) ssh 1.2.12 release by Tatu Ylonen,
1179 but with bugs removed and newer features re-added.
1181 1.2.12 release, newer versions of the original ssh bore successively
1182 more restrictive licenses, and thus demand for a free version was born.
1184 This version of OpenSSH
1187 has all components of a restrictive nature (i.e., patents)
1188 directly removed from the source code; any licensed or patented components
1192 has been updated to support SSH protocol 1.5 and 2, making it compatible with
1193 all other SSH clients and servers.
1195 contains added support for
1197 authentication and ticket passing.
1199 supports one-time password authentication with
1203 OpenSSH has been created by Aaron Campbell, Bob Beck, Markus Friedl,
1204 Niels Provos, Theo de Raadt, and Dug Song.
1206 The support for SSH protocol 2 was written by Markus Friedl.
andersk / openssh.git / blob