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: sshd.8,v 1.73 2000/11/22 15:38:30 provos Exp $
38 .Dd September 25, 1999
43 .Nd secure shell daemon
48 .Op Fl f Ar config_file
49 .Op Fl g Ar login_grace_time
50 .Op Fl h Ar host_key_file
51 .Op Fl k Ar key_gen_time
54 .Op Fl V Ar client_protocol_id
57 (Secure Shell Daemon) is the daemon program for
59 Together these programs replace rlogin and rsh, and
60 provide secure encrypted communications between two untrusted hosts
61 over an insecure network.
62 The programs are intended to be as easy to
63 install and use as possible.
66 is the daemon that listens for connections from clients.
67 It is normally started at boot from
70 daemon for each incoming connection.
71 The forked daemons handle
72 key exchange, encryption, authentication, command execution,
74 This implementation of
76 supports both SSH protocol version 1 and 2 simultaneously.
80 .Ss SSH protocol version 1
82 Each host has a host-specific RSA key
83 (normally 1024 bits) used to identify the host.
85 the daemon starts, it generates a server RSA key (normally 768 bits).
86 This key is normally regenerated every hour if it has been used, and
87 is never stored on disk.
89 Whenever a client connects the daemon responds with its public
91 The client compares the
92 RSA host key against its own database to verify that it has not changed.
93 The client then generates a 256 bit random number.
95 random number using both the host key and the server key, and sends
96 the encrypted number to the server.
97 Both sides then use this
98 random number as a session key which is used to encrypt all further
99 communications in the session.
100 The rest of the session is encrypted
101 using a conventional cipher, currently Blowfish or 3DES, with 3DES
102 being used by default.
103 The client selects the encryption algorithm
104 to use from those offered by the server.
106 Next, the server and the client enter an authentication dialog.
107 The client tries to authenticate itself using
111 authentication combined with RSA host
112 authentication, RSA challenge-response authentication, or password
113 based authentication.
115 Rhosts authentication is normally disabled
116 because it is fundamentally insecure, but can be enabled in the server
117 configuration file if desired.
118 System security is not improved unless
124 are disabled (thus completely disabling
130 .Ss SSH protocol version 2
132 Version 2 works similarly:
133 Each host has a host-specific DSA key used to identify the host.
134 However, when the daemon starts, it does not generate a server key.
135 Forward security is provided through a Diffie-Hellman key agreement.
136 This key agreement results in a shared session key.
137 The rest of the session is encrypted
138 using a symmetric cipher, currently
139 Blowfish, 3DES or CAST128 in CBC mode or Arcfour.
140 The client selects the encryption algorithm
141 to use from those offered by the server.
142 Additionally, session integrity is provided
143 through a cryptographic message authentication code
144 (hmac-sha1 or hmac-md5).
146 Protocol version 2 provides a public key based
147 user authentication method (PubkeyAuthentication)
148 and conventional password authentication.
150 .Ss Command execution and data forwarding
152 If the client successfully authenticates itself, a dialog for
153 preparing the session is entered.
154 At this time the client may request
155 things like allocating a pseudo-tty, forwarding X11 connections,
156 forwarding TCP/IP connections, or forwarding the authentication agent
157 connection over the secure channel.
159 Finally, the client either requests a shell or execution of a command.
160 The sides then enter session mode.
161 In this mode, either side may send
162 data at any time, and such data is forwarded to/from the shell or
163 command on the server side, and the user terminal in the client side.
165 When the user program terminates and all forwarded X11 and other
166 connections have been closed, the server sends command exit status to
167 the client, and both sides exit.
170 can be configured using command-line options or a configuration
172 Command-line options override values specified in the
176 rereads its configuration file when it receives a hangup signal,
179 The options are as follows:
182 Specifies the number of bits in the server key (default 768).
186 The server sends verbose debug output to the system
187 log, and does not put itself in the background.
188 The server also will not fork and will only process one connection.
189 This option is only intended for debugging for the server.
190 Multiple -d options increases the debugging level.
192 .It Fl f Ar configuration_file
193 Specifies the name of the configuration file.
195 .Pa /etc/sshd_config .
197 refuses to start if there is no configuration file.
198 .It Fl g Ar login_grace_time
199 Gives the grace time for clients to authenticate themselves (default
201 If the client fails to authenticate the user within
202 this many seconds, the server disconnects and exits.
203 A value of zero indicates no limit.
204 .It Fl h Ar host_key_file
205 Specifies the file from which the RSA host key is read (default
206 .Pa /etc/ssh_host_key ) .
207 This option must be given if
209 is not run as root (as the normal
210 host file is normally not readable by anyone but root).
214 is being run from inetd.
217 from inetd because it needs to generate the server key before it can
218 respond to the client, and this may take tens of seconds.
219 Clients would have to wait too long if the key was regenerated every time.
220 However, with small key sizes (e.g., 512) using
224 .It Fl k Ar key_gen_time
225 Specifies how often the server key is regenerated (default 3600
226 seconds, or one hour).
227 The motivation for regenerating the key fairly
228 often is that the key is not stored anywhere, and after about an hour,
229 it becomes impossible to recover the key for decrypting intercepted
230 communications even if the machine is cracked into or physically
232 A value of zero indicates that the key will never be regenerated.
234 Specifies the port on which the server listens for connections
238 Nothing is sent to the system log.
239 Normally the beginning,
240 authentication, and termination of each connection is logged.
242 This option is used to specify the size of the field
245 structure that holds the remote host name.
246 If the resolved host name is longer than
248 the dotted decimal value will be used instead.
249 This allows hosts with very long host names that
250 overflow this field to still be uniquely identified.
253 indicates that only dotted decimal addresses
254 should be put into the
258 Do not print an error message if RSA support is missing.
259 .It Fl V Ar client_protocol_id
260 SSH-2 compatibility mode.
261 When this option is specified
263 assumes the client has sent the supplied version string
265 Protocol Version Identification Exchange.
266 This option is not intended to be called directly.
270 to use IPv4 addresses only.
274 to use IPv6 addresses only.
276 .Sh CONFIGURATION FILE
278 reads configuration data from
280 (or the file specified with
282 on the command line).
283 The file contains keyword-value pairs, one per line.
286 and empty lines are interpreted as comments.
288 The following keywords are possible.
290 .It Cm AFSTokenPassing
291 Specifies whether an AFS token may be forwarded to the server.
295 This keyword can be followed by a number of group names, separated
297 If specified, login is allowed only for users whose primary
298 group matches one of the patterns.
303 wildcards in the patterns.
304 Only group names are valid; a numerical group ID isn't recognized.
305 By default login is allowed regardless of the primary group.
307 .It Cm AllowTcpForwarding
308 Specifies whether TCP forwarding is permitted.
311 Note that disabling TCP forwarding does not improve security unless
312 users are also denied shell access, as they can always install their
316 This keyword can be followed by a number of user names, separated
318 If specified, login is allowed only for users names that
319 match one of the patterns.
324 wildcards in the patterns.
325 Only user names are valid; a numerical user ID isn't recognized.
326 By default login is allowed regardless of the user name.
329 Specifies the ciphers allowed for protocol version 2.
330 Multiple ciphers must be comma-separated.
332 .Dq 3des-cbc,blowfish-cbc,arcfour,cast128-cbc .
336 should check for new mail for interactive logins.
340 This keyword can be followed by a number of group names, separated
342 Users whose primary group matches one of the patterns
343 aren't allowed to log in.
348 wildcards in the patterns.
349 Only group names are valid; a numerical group ID isn't recognized.
350 By default login is allowed regardless of the primary group.
353 This keyword can be followed by a number of user names, separated
355 Login is disallowed for user names that match one of the patterns.
359 can be used as wildcards in the patterns.
360 Only user names are valid; a numerical user ID isn't recognized.
361 By default login is allowed regardless of the user name.
362 .It Cm PubkeyAuthentication
363 Specifies whether public key authentication is allowed.
366 Note that this option applies to protocol version 2 only.
368 Specifies whether remote hosts are allowed to connect to ports
369 forwarded for the client.
377 Specifies the file containing the private host keys (default
378 .Pa /etc/ssh_host_key )
379 used by SSH protocol versions 1 and 2.
382 if this file is group/world-accessible.
383 It is possible to have multiple host key files.
385 keys are used for version 1 and
389 are used for version 2 of the SSH protocol.
395 files will not be used in authentication.
398 .Pa /etc/shosts.equiv
402 .It Cm IgnoreUserKnownHosts
405 should ignore the user's
406 .Pa $HOME/.ssh/known_hosts
408 .Cm RhostsRSAAuthentication .
412 Specifies whether the system should send keepalive messages to the
414 If they are sent, death of the connection or crash of one
415 of the machines will be properly noticed.
416 However, this means that
417 connections will die if the route is down temporarily, and some people
419 On the other hand, if keepalives are not sent,
420 sessions may hang indefinitely on the server, leaving
422 users and consuming server resources.
426 (to send keepalives), and the server will notice
427 if the network goes down or the client host reboots.
428 This avoids infinitely hanging sessions.
430 To disable keepalives, the value should be set to
432 in both the server and the client configuration files.
433 .It Cm KerberosAuthentication
434 Specifies whether Kerberos authentication is allowed.
435 This can be in the form of a Kerberos ticket, or if
436 .Cm PasswordAuthentication
437 is yes, the password provided by the user will be validated through
439 To use this option, the server needs a
440 Kerberos servtab which allows the verification of the KDC's identity.
443 .It Cm KerberosOrLocalPasswd
444 If set then if password authentication through Kerberos fails then
445 the password will be validated via any additional local mechanism
450 .It Cm KerberosTgtPassing
451 Specifies whether a Kerberos TGT may be forwarded to the server.
454 as this only works when the Kerberos KDC is actually an AFS kaserver.
455 .It Cm KerberosTicketCleanup
456 Specifies whether to automatically destroy the user's ticket cache
460 .It Cm KeyRegenerationInterval
461 The server key is automatically regenerated after this many seconds
462 (if it has been used).
463 The purpose of regeneration is to prevent
464 decrypting captured sessions by later breaking into the machine and
466 The key is never stored anywhere.
467 If the value is 0, the key is never regenerated.
468 The default is 3600 (seconds).
470 Specifies what local address
473 The default is to listen to all local addresses.
474 Multiple options of this type are permitted.
477 options must precede this option.
478 .It Cm LoginGraceTime
479 The server disconnects after this time if the user has not
480 successfully logged in.
481 If the value is 0, there is no time limit.
482 The default is 600 (seconds).
484 Gives the verbosity level that is used when logging messages from
486 The possible values are:
487 QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG.
489 Logging with level DEBUG violates the privacy of users
490 and is not recommended.
492 Specifies the maximum number of concurrent unauthenticated connections to the
495 Additional connections will be dropped until authentication succeeds or the
497 expires for a connection.
500 Alternatively, random early drop can be enabled by specifying
501 the three colon separated values
505 will refuse connection attempts with a probabillity of
508 if there are currently
511 unauthenticated connections.
512 The probabillity increases linearly and all connection attempts
513 are refused if the number of unauthenticated connections reaches
516 .It Cm PasswordAuthentication
517 Specifies whether password authentication is allowed.
520 Note that this option applies to both protocol versions 1 and 2.
521 .It Cm PermitEmptyPasswords
522 When password authentication is allowed, it specifies whether the
523 server allows login to accounts with empty password strings.
526 .It Cm PermitRootLogin
527 Specifies whether the root can log in using
536 If this options is set to
538 only password authentication is disabled for root.
540 Root login with RSA authentication when the
543 specified will be allowed regardless of the value of this setting
544 (which may be useful for taking remote backups even if root login is
545 normally not allowed).
547 Specifies the file that contains the process identifier of the
551 .Pa /var/run/sshd.pid .
553 Specifies the port number that
557 Multiple options of this type are permitted.
563 when a user logs in interactively.
564 (On some systems it is also printed by the shell,
570 Specifies the protocol versions
573 The possible values are
577 Multiple versions must be comma-separated.
582 Random number generation uses other techniques.
583 .It Cm RhostsAuthentication
584 Specifies whether authentication using rhosts or /etc/hosts.equiv
586 Normally, this method should not be permitted because it is insecure.
587 .Cm RhostsRSAAuthentication
589 instead, because it performs RSA-based host authentication in addition
590 to normal rhosts or /etc/hosts.equiv authentication.
593 .It Cm RhostsRSAAuthentication
594 Specifies whether rhosts or /etc/hosts.equiv authentication together
595 with successful RSA host authentication is allowed.
598 .It Cm RSAAuthentication
599 Specifies whether pure RSA authentication is allowed.
602 Note that this option applies to protocol version 1 only.
604 Defines the number of bits in the server key.
605 The minimum value is 512, and the default is 768.
606 .It Cm SkeyAuthentication
609 authentication is allowed.
612 Note that s/key authentication is enabled only if
613 .Cm PasswordAuthentication
618 should check file modes and ownership of the
619 user's files and home directory before accepting login.
620 This is normally desirable because novices sometimes accidentally leave their
621 directory or files world-writable.
625 Configures an external subsystem (e.g., file transfer daemon).
626 Arguments should be a subsystem name and a command to execute upon subsystem
632 file transfer subsystem.
633 By default no subsystems are defined.
634 Note that this option applies to protocol version 2 only.
635 .It Cm SyslogFacility
636 Gives the facility code that is used when logging messages from
638 The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
639 LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
644 is used for interactive login sessions.
647 is never used for remote command execution.
650 .It Cm X11DisplayOffset
651 Specifies the first display number available for
656 from interfering with real X11 servers.
659 Specifies whether X11 forwarding is permitted.
662 Note that disabling X11 forwarding does not improve security in any
663 way, as users can always install their own forwarders.
665 Specifies the location of the
669 .Pa /usr/X11R6/bin/xauth .
672 When a user successfully logs in,
675 .Bl -enum -offset indent
677 If the login is on a tty, and no command has been specified,
678 prints last login time and
680 (unless prevented in the configuration file or by
681 .Pa $HOME/.hushlogin ;
686 If the login is on a tty, records login time.
690 if it exists, prints contents and quits
693 Changes to run with normal user privileges.
695 Sets up basic environment.
698 .Pa $HOME/.ssh/environment
701 Changes to user's home directory.
705 exists, runs it; else if
708 it; otherwise runs xauth.
711 files are given the X11
712 authentication protocol and cookie in standard input.
714 Runs user's shell or command.
716 .Sh AUTHORIZED_KEYS FILE FORMAT
718 .Pa $HOME/.ssh/authorized_keys
719 file lists the RSA keys that are
720 permitted for RSA authentication in SSH protocols 1.3 and 1.5
722 .Pa $HOME/.ssh/authorized_keys2
723 file lists the DSA keys that are
724 permitted for DSA authentication in SSH protocol 2.0.
725 Each line of the file contains one
726 key (empty lines and lines starting with a
730 Each line consists of the following fields, separated by
731 spaces: options, bits, exponent, modulus, comment.
733 is optional; its presence is determined by whether the line starts
734 with a number or not (the option field never starts with a number).
735 The bits, exponent, modulus and comment fields give the RSA key; the
736 comment field is not used for anything (but may be convenient for the
737 user to identify the key).
739 Note that lines in this file are usually several hundred bytes long
740 (because of the size of the RSA key modulus).
741 You don't want to type them in; instead, copy the
745 The options (if present) consist of comma-separated option
747 No spaces are permitted, except within double quotes.
748 The following option specifications are supported:
750 .It Cm from="pattern-list"
751 Specifies that in addition to RSA authentication, the canonical name
752 of the remote host must be present in the comma-separated list of
758 The list may also contain
759 patterns negated by prefixing them with
761 if the canonical host name matches a negated pattern, the key is not accepted.
763 of this option is to optionally increase security: RSA authentication
764 by itself does not trust the network or name servers or anything (but
765 the key); however, if somebody somehow steals the key, the key
766 permits an intruder to log in from anywhere in the world.
767 This additional option makes using a stolen key more difficult (name
768 servers and/or routers would have to be compromised in addition to
770 .It Cm command="command"
771 Specifies that the command is executed whenever this key is used for
773 The command supplied by the user (if any) is ignored.
774 The command is run on a pty if the connection requests a pty;
775 otherwise it is run without a tty.
776 A quote may be included in the command by quoting it with a backslash.
777 This option might be useful
778 to restrict certain RSA keys to perform just a specific operation.
779 An example might be a key that permits remote backups but nothing else.
780 Note that the client may specify TCP/IP and/or X11
781 forwarding unless they are explicitly prohibited.
782 .It Cm environment="NAME=value"
783 Specifies that the string is to be added to the environment when
784 logging in using this key.
785 Environment variables set this way
786 override other default environment values.
787 Multiple options of this type are permitted.
788 .It Cm no-port-forwarding
789 Forbids TCP/IP forwarding when this key is used for authentication.
790 Any port forward requests by the client will return an error.
791 This might be used, e.g., in connection with the
794 .It Cm no-X11-forwarding
795 Forbids X11 forwarding when this key is used for authentication.
796 Any X11 forward requests by the client will return an error.
797 .It Cm no-agent-forwarding
798 Forbids authentication agent forwarding when this key is used for
801 Prevents tty allocation (a request to allocate a pty will fail).
804 1024 33 12121.\|.\|.\|312314325 ylo@foo.bar
806 from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula
808 command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi
809 .Sh SSH_KNOWN_HOSTS FILE FORMAT
811 .Pa /etc/ssh_known_hosts ,
812 .Pa /etc/ssh_known_hosts2 ,
813 .Pa $HOME/.ssh/known_hosts ,
815 .Pa $HOME/.ssh/known_hosts2
816 files contain host public keys for all known hosts.
817 The global file should
818 be prepared by the administrator (optional), and the per-user file is
819 maintained automatically: whenever the user connects from an unknown host
820 its key is added to the per-user file.
822 Each line in these files contains the following fields: hostnames,
823 bits, exponent, modulus, comment.
824 The fields are separated by spaces.
826 Hostnames is a comma-separated list of patterns ('*' and '?' act as
827 wildcards); each pattern in turn is matched against the canonical host
828 name (when authenticating a client) or against the user-supplied
829 name (when authenticating a server).
830 A pattern may also be preceded by
832 to indicate negation: if the host name matches a negated
833 pattern, it is not accepted (by that line) even if it matched another
836 Bits, exponent, and modulus are taken directly from the RSA host key; they
837 can be obtained, e.g., from
838 .Pa /etc/ssh_host_key.pub .
839 The optional comment field continues to the end of the line, and is not used.
843 and empty lines are ignored as comments.
845 When performing host authentication, authentication is accepted if any
846 matching line has the proper key.
847 It is thus permissible (but not
848 recommended) to have several lines or different host keys for the same
850 This will inevitably happen when short forms of host names
851 from different domains are put in the file.
853 that the files contain conflicting information; authentication is
854 accepted if valid information can be found from either file.
856 Note that the lines in these files are typically hundreds of characters
857 long, and you definitely don't want to type in the host keys by hand.
858 Rather, generate them by a script
860 .Pa /etc/ssh_host_key.pub
861 and adding the host names at the front.
863 closenet,closenet.hut.fi,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi
866 .It Pa /etc/sshd_config
867 Contains configuration data for
869 This file should be writable by root only, but it is recommended
870 (though not necessary) that it be world-readable.
871 .It Pa /etc/ssh_host_key
872 Contains the private part of the host key.
873 This file should only be owned by root, readable only by root, and not
874 accessible to others.
877 does not start if this file is group/world-accessible.
878 .It Pa /etc/ssh_host_key.pub
879 Contains the public part of the host key.
880 This file should be world-readable but writable only by
882 Its contents should match the private part.
884 really used for anything; it is only provided for the convenience of
885 the user so its contents can be copied to known hosts files.
886 These two files are created using
889 Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange".
890 .It Pa /var/run/sshd.pid
891 Contains the process ID of the
893 listening for connections (if there are several daemons running
894 concurrently for different ports, this contains the pid of the one
896 The content of this file is not sensitive; it can be world-readable.
897 .It Pa $HOME/.ssh/authorized_keys
898 Lists the RSA keys that can be used to log into the user's account.
899 This file must be readable by root (which may on some machines imply
900 it being world-readable if the user's home directory resides on an NFS
902 It is recommended that it not be accessible by others.
903 The format of this file is described above.
904 Users will place the contents of their
906 files into this file, as described in
908 .It Pa $HOME/.ssh/authorized_keys2
909 Lists the DSA keys that can be used to log into the user's account.
910 This file must be readable by root (which may on some machines imply
911 it being world-readable if the user's home directory resides on an NFS
913 It is recommended that it not be accessible by others.
914 The format of this file is described above.
915 Users will place the contents of their
917 files into this file, as described in
919 .It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts"
920 These files are consulted when using rhosts with RSA host
921 authentication to check the public key of the host.
922 The key must be listed in one of these files to be accepted.
923 The client uses the same files
924 to verify that the remote host is the one it intended to connect.
925 These files should be writable only by root/the owner.
926 .Pa /etc/ssh_known_hosts
927 should be world-readable, and
928 .Pa $HOME/.ssh/known_hosts
929 can but need not be world-readable.
933 refuses to let anyone except root log in.
934 The contents of the file
935 are displayed to anyone trying to log in, and non-root connections are
937 The file should be world-readable.
938 .It Pa /etc/hosts.allow, /etc/hosts.deny
941 support, tcp-wrappers access controls may be defined here as described in
944 This file contains host-username pairs, separated by a space, one per
946 The given user on the corresponding host is permitted to log in
948 The same file is used by rlogind and rshd.
950 be writable only by the user; it is recommended that it not be
951 accessible by others.
953 If is also possible to use netgroups in the file.
955 name may be of the form +@groupname to specify all hosts or all users
959 this file is exactly the same as for
961 However, this file is
962 not used by rlogin and rshd, so using this permits access using SSH only.
963 .It Pa /etc/hosts.equiv
964 This file is used during
967 In the simplest form, this file contains host names, one per line.
969 those hosts are permitted to log in without a password, provided they
970 have the same user name on both machines.
971 The host name may also be
972 followed by a user name; such users are permitted to log in as
974 user on this machine (except root).
975 Additionally, the syntax
977 can be used to specify netgroups.
978 Negated entries start with
981 If the client host/user is successfully matched in this file, login is
982 automatically permitted provided the client and server user names are the
984 Additionally, successful RSA host authentication is normally required.
985 This file must be writable only by root; it is recommended
986 that it be world-readable.
988 .Sy "Warning: It is almost never a good idea to use user names in"
990 Beware that it really means that the named user(s) can log in as
992 which includes bin, daemon, adm, and other accounts that own critical
993 binaries and directories.
994 Using a user name practically grants the user root access.
995 The only valid use for user names that I can think
996 of is in negative entries.
998 Note that this warning also applies to rsh/rlogin.
999 .It Pa /etc/shosts.equiv
1000 This is processed exactly as
1001 .Pa /etc/hosts.equiv .
1002 However, this file may be useful in environments that want to run both
1004 .It Pa $HOME/.ssh/environment
1005 This file is read into the environment at login (if it exists).
1006 It can only contain empty lines, comment lines (that start with
1008 and assignment lines of the form name=value.
1009 The file should be writable
1010 only by the user; it need not be readable by anyone else.
1011 .It Pa $HOME/.ssh/rc
1012 If this file exists, it is run with /bin/sh after reading the
1013 environment files but before starting the user's shell or command.
1014 If X11 spoofing is in use, this will receive the "proto cookie" pair in
1022 The primary purpose of this file is to run any initialization routines
1023 which may be needed before the user's home directory becomes
1024 accessible; AFS is a particular example of such an environment.
1026 This file will probably contain some initialization code followed by
1027 something similar to: "if read proto cookie; then echo add $DISPLAY
1028 $proto $cookie | xauth -q -; fi".
1030 If this file does not exist,
1033 does not exist either, xauth is used to store the cookie.
1035 This file should be writable only by the user, and need not be
1036 readable by anyone else.
1040 This can be used to specify
1041 machine-specific login-time initializations globally.
1042 This file should be writable only by root, and should be world-readable.
1046 is a derivative of the original (free) ssh 1.2.12 release by Tatu Ylonen,
1047 but with bugs removed and newer features re-added.
1049 1.2.12 release, newer versions of the original ssh bore successively
1050 more restrictive licenses, and thus demand for a free version was born.
1052 This version of OpenSSH
1055 has all components of a restrictive nature (i.e., patents, see
1057 directly removed from the source code; any licensed or patented components
1061 has been updated to support SSH protocol 1.5 and 2, making it compatible with
1062 all other SSH clients and servers.
1064 contains added support for
1066 authentication and ticket passing.
1068 supports one-time password authentication with
1072 OpenSSH has been created by Aaron Campbell, Bob Beck, Markus Friedl,
1073 Niels Provos, Theo de Raadt, and Dug Song.
1075 The support for SSH protocol 2 was written by Markus Friedl.