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 1.84 2001/01/28 10:24:04 markus 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 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).
211 It is possible to have multiple host key files for
212 the different protocol versions.
216 is being run from inetd.
219 from inetd because it needs to generate the server key before it can
220 respond to the client, and this may take tens of seconds.
221 Clients would have to wait too long if the key was regenerated every time.
222 However, with small key sizes (e.g., 512) using
226 .It Fl k Ar key_gen_time
227 Specifies how often the server key is regenerated (default 3600
228 seconds, or one hour).
229 The motivation for regenerating the key fairly
230 often is that the key is not stored anywhere, and after about an hour,
231 it becomes impossible to recover the key for decrypting intercepted
232 communications even if the machine is cracked into or physically
234 A value of zero indicates that the key will never be regenerated.
236 Specifies the port on which the server listens for connections
240 Nothing is sent to the system log.
241 Normally the beginning,
242 authentication, and termination of each connection is logged.
244 This option is used to specify the size of the field
247 structure that holds the remote host name.
248 If the resolved host name is longer than
250 the dotted decimal value will be used instead.
251 This allows hosts with very long host names that
252 overflow this field to still be uniquely identified.
255 indicates that only dotted decimal addresses
256 should be put into the
260 When this option is specified
262 will not detach and does not become a daemon.
263 This allows easy monitoring of
266 Do not print an error message if RSA support is missing.
267 .It Fl V Ar client_protocol_id
268 SSH-2 compatibility mode.
269 When this option is specified
271 assumes the client has sent the supplied version string
273 Protocol Version Identification Exchange.
274 This option is not intended to be called directly.
278 to use IPv4 addresses only.
282 to use IPv6 addresses only.
284 .Sh CONFIGURATION FILE
286 reads configuration data from
288 (or the file specified with
290 on the command line).
291 The file contains keyword-value pairs, one per line.
294 and empty lines are interpreted as comments.
296 The following keywords are possible.
298 .It Cm AFSTokenPassing
299 Specifies whether an AFS token may be forwarded to the server.
303 This keyword can be followed by a number of group names, separated
305 If specified, login is allowed only for users whose primary
306 group or supplementary group list matches one of the patterns.
311 wildcards in the patterns.
312 Only group names are valid; a numerical group ID isn't recognized.
313 By default login is allowed regardless of the group list.
315 .It Cm AllowTcpForwarding
316 Specifies whether TCP forwarding is permitted.
319 Note that disabling TCP forwarding does not improve security unless
320 users are also denied shell access, as they can always install their
324 This keyword can be followed by a number of user names, separated
326 If specified, login is allowed only for users names that
327 match one of the patterns.
332 wildcards in the patterns.
333 Only user names are valid; a numerical user ID isn't recognized.
334 By default login is allowed regardless of the user name.
337 In some jurisdictions, sending a warning message before authentication
338 may be relevant for getting legal protection.
339 The contents of the specified file are sent to the remote user before
340 authentication is allowed.
341 This option is only available for protocol version 2.
344 Specifies the ciphers allowed for protocol version 2.
345 Multiple ciphers must be comma-separated.
347 .Dq 3des-cbc,blowfish-cbc,cast128-cbc,arcfour,aes128-cbc .
351 should check for new mail for interactive logins.
355 This keyword can be followed by a number of group names, separated
357 Users whose primary group or supplementary group list matches
358 one of the patterns aren't allowed to log in.
363 wildcards in the patterns.
364 Only group names are valid; a numerical group ID isn't recognized.
365 By default login is allowed regardless of the group list.
368 This keyword can be followed by a number of user names, separated
370 Login is disallowed for user names that match one of the patterns.
374 can be used as wildcards in the patterns.
375 Only user names are valid; a numerical user ID isn't recognized.
376 By default login is allowed regardless of the user name.
377 .It Cm PubkeyAuthentication
378 Specifies whether public key authentication is allowed.
381 Note that this option applies to protocol version 2 only.
383 Specifies whether remote hosts are allowed to connect to ports
384 forwarded for the client.
392 Specifies the file containing the private host keys (default
393 .Pa /etc/ssh_host_key )
394 used by SSH protocol versions 1 and 2.
397 will refuse to use a file if it is group/world-accessible.
398 It is possible to have multiple host key files.
400 keys are used for version 1 and
404 are used for version 2 of the SSH protocol.
410 files will not be used in authentication.
413 .Pa /etc/shosts.equiv
417 .It Cm IgnoreUserKnownHosts
420 should ignore the user's
421 .Pa $HOME/.ssh/known_hosts
423 .Cm RhostsRSAAuthentication .
427 Specifies whether the system should send keepalive messages to the
429 If they are sent, death of the connection or crash of one
430 of the machines will be properly noticed.
431 However, this means that
432 connections will die if the route is down temporarily, and some people
434 On the other hand, if keepalives are not sent,
435 sessions may hang indefinitely on the server, leaving
437 users and consuming server resources.
441 (to send keepalives), and the server will notice
442 if the network goes down or the client host reboots.
443 This avoids infinitely hanging sessions.
445 To disable keepalives, the value should be set to
447 in both the server and the client configuration files.
448 .It Cm KerberosAuthentication
449 Specifies whether Kerberos authentication is allowed.
450 This can be in the form of a Kerberos ticket, or if
451 .Cm PasswordAuthentication
452 is yes, the password provided by the user will be validated through
454 To use this option, the server needs a
455 Kerberos servtab which allows the verification of the KDC's identity.
458 .It Cm KerberosOrLocalPasswd
459 If set then if password authentication through Kerberos fails then
460 the password will be validated via any additional local mechanism
465 .It Cm KerberosTgtPassing
466 Specifies whether a Kerberos TGT may be forwarded to the server.
469 as this only works when the Kerberos KDC is actually an AFS kaserver.
470 .It Cm KerberosTicketCleanup
471 Specifies whether to automatically destroy the user's ticket cache
475 .It Cm KeyRegenerationInterval
476 The server key is automatically regenerated after this many seconds
477 (if it has been used).
478 The purpose of regeneration is to prevent
479 decrypting captured sessions by later breaking into the machine and
481 The key is never stored anywhere.
482 If the value is 0, the key is never regenerated.
483 The default is 3600 (seconds).
485 Specifies what local address
488 The default is to listen to all local addresses.
489 Multiple options of this type are permitted.
492 options must precede this option.
493 .It Cm LoginGraceTime
494 The server disconnects after this time if the user has not
495 successfully logged in.
496 If the value is 0, there is no time limit.
497 The default is 600 (seconds).
499 Gives the verbosity level that is used when logging messages from
501 The possible values are:
502 QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG.
504 Logging with level DEBUG violates the privacy of users
505 and is not recommended.
507 Specifies the maximum number of concurrent unauthenticated connections to the
510 Additional connections will be dropped until authentication succeeds or the
512 expires for a connection.
515 Alternatively, random early drop can be enabled by specifying
516 the three colon separated values
520 will refuse connection attempts with a probabillity of
523 if there are currently
526 unauthenticated connections.
527 The probabillity increases linearly and all connection attempts
528 are refused if the number of unauthenticated connections reaches
531 .It Cm PasswordAuthentication
532 Specifies whether password authentication is allowed.
535 Note that this option applies to both protocol versions 1 and 2.
536 .It Cm PermitEmptyPasswords
537 When password authentication is allowed, it specifies whether the
538 server allows login to accounts with empty password strings.
541 .It Cm PermitRootLogin
542 Specifies whether the root can log in using
551 If this options is set to
553 only password authentication is disabled for root.
555 Root login with RSA authentication when the
558 specified will be allowed regardless of the value of this setting
559 (which may be useful for taking remote backups even if root login is
560 normally not allowed).
562 Specifies the file that contains the process identifier of the
566 .Pa /var/run/sshd.pid .
568 Specifies the port number that
572 Multiple options of this type are permitted.
578 when a user logs in interactively.
579 (On some systems it is also printed by the shell,
585 Specifies the protocol versions
588 The possible values are
592 Multiple versions must be comma-separated.
597 Random number generation uses other techniques.
598 .It Cm RhostsAuthentication
599 Specifies whether authentication using rhosts or /etc/hosts.equiv
601 Normally, this method should not be permitted because it is insecure.
602 .Cm RhostsRSAAuthentication
604 instead, because it performs RSA-based host authentication in addition
605 to normal rhosts or /etc/hosts.equiv authentication.
608 .It Cm RhostsRSAAuthentication
609 Specifies whether rhosts or /etc/hosts.equiv authentication together
610 with successful RSA host authentication is allowed.
613 .It Cm RSAAuthentication
614 Specifies whether pure RSA authentication is allowed.
617 Note that this option applies to protocol version 1 only.
619 Defines the number of bits in the server key.
620 The minimum value is 512, and the default is 768.
621 .It Cm SkeyAuthentication
624 authentication is allowed.
627 Note that s/key authentication is enabled only if
628 .Cm PasswordAuthentication
633 should check file modes and ownership of the
634 user's files and home directory before accepting login.
635 This is normally desirable because novices sometimes accidentally leave their
636 directory or files world-writable.
640 Configures an external subsystem (e.g., file transfer daemon).
641 Arguments should be a subsystem name and a command to execute upon subsystem
647 file transfer subsystem.
648 By default no subsystems are defined.
649 Note that this option applies to protocol version 2 only.
650 .It Cm SyslogFacility
651 Gives the facility code that is used when logging messages from
653 The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
654 LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
659 is used for interactive login sessions.
662 is never used for remote command execution.
665 .It Cm X11DisplayOffset
666 Specifies the first display number available for
671 from interfering with real X11 servers.
674 Specifies whether X11 forwarding is permitted.
677 Note that disabling X11 forwarding does not improve security in any
678 way, as users can always install their own forwarders.
680 Specifies the location of the
684 .Pa /usr/X11R6/bin/xauth .
687 When a user successfully logs in,
690 .Bl -enum -offset indent
692 If the login is on a tty, and no command has been specified,
693 prints last login time and
695 (unless prevented in the configuration file or by
696 .Pa $HOME/.hushlogin ;
701 If the login is on a tty, records login time.
705 if it exists, prints contents and quits
708 Changes to run with normal user privileges.
710 Sets up basic environment.
713 .Pa $HOME/.ssh/environment
716 Changes to user's home directory.
720 exists, runs it; else if
723 it; otherwise runs xauth.
726 files are given the X11
727 authentication protocol and cookie in standard input.
729 Runs user's shell or command.
731 .Sh AUTHORIZED_KEYS FILE FORMAT
733 .Pa $HOME/.ssh/authorized_keys
734 file lists the RSA keys that are
735 permitted for RSA authentication in SSH protocols 1.3 and 1.5
737 .Pa $HOME/.ssh/authorized_keys2
738 file lists the DSA and RSA keys that are
739 permitted for public key authentication (PubkeyAuthentication)
742 Each line of the file contains one
743 key (empty lines and lines starting with a
747 Each RSA public key consists of the following fields, separated by
748 spaces: options, bits, exponent, modulus, comment.
749 Each protocol version 2 public key consists of:
750 options, keytype, base64 encoded key, comment.
752 are optional; its presence is determined by whether the line starts
753 with a number or not (the option field never starts with a number).
754 The bits, exponent, modulus and comment fields give the RSA key for
755 protocol version 1; the
756 comment field is not used for anything (but may be convenient for the
757 user to identify the key).
758 For protocol version 2 the keytype is
763 Note that lines in this file are usually several hundred bytes long
764 (because of the size of the RSA key modulus).
765 You don't want to type them in; instead, copy the
771 The options (if present) consist of comma-separated option
773 No spaces are permitted, except within double quotes.
774 The following option specifications are supported:
776 .It Cm from="pattern-list"
777 Specifies that in addition to RSA authentication, the canonical name
778 of the remote host must be present in the comma-separated list of
784 The list may also contain
785 patterns negated by prefixing them with
787 if the canonical host name matches a negated pattern, the key is not accepted.
789 of this option is to optionally increase security: RSA authentication
790 by itself does not trust the network or name servers or anything (but
791 the key); however, if somebody somehow steals the key, the key
792 permits an intruder to log in from anywhere in the world.
793 This additional option makes using a stolen key more difficult (name
794 servers and/or routers would have to be compromised in addition to
796 .It Cm command="command"
797 Specifies that the command is executed whenever this key is used for
799 The command supplied by the user (if any) is ignored.
800 The command is run on a pty if the connection requests a pty;
801 otherwise it is run without a tty.
802 A quote may be included in the command by quoting it with a backslash.
803 This option might be useful
804 to restrict certain RSA keys to perform just a specific operation.
805 An example might be a key that permits remote backups but nothing else.
806 Note that the client may specify TCP/IP and/or X11
807 forwarding unless they are explicitly prohibited.
808 .It Cm environment="NAME=value"
809 Specifies that the string is to be added to the environment when
810 logging in using this key.
811 Environment variables set this way
812 override other default environment values.
813 Multiple options of this type are permitted.
814 .It Cm no-port-forwarding
815 Forbids TCP/IP forwarding when this key is used for authentication.
816 Any port forward requests by the client will return an error.
817 This might be used, e.g., in connection with the
820 .It Cm no-X11-forwarding
821 Forbids X11 forwarding when this key is used for authentication.
822 Any X11 forward requests by the client will return an error.
823 .It Cm no-agent-forwarding
824 Forbids authentication agent forwarding when this key is used for
827 Prevents tty allocation (a request to allocate a pty will fail).
830 1024 33 12121.\|.\|.\|312314325 ylo@foo.bar
832 from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula
834 command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi
835 .Sh SSH_KNOWN_HOSTS FILE FORMAT
837 .Pa /etc/ssh_known_hosts ,
838 .Pa /etc/ssh_known_hosts2 ,
839 .Pa $HOME/.ssh/known_hosts ,
841 .Pa $HOME/.ssh/known_hosts2
842 files contain host public keys for all known hosts.
843 The global file should
844 be prepared by the administrator (optional), and the per-user file is
845 maintained automatically: whenever the user connects from an unknown host
846 its key is added to the per-user file.
848 Each line in these files contains the following fields: hostnames,
849 bits, exponent, modulus, comment.
850 The fields are separated by spaces.
852 Hostnames is a comma-separated list of patterns ('*' and '?' act as
853 wildcards); each pattern in turn is matched against the canonical host
854 name (when authenticating a client) or against the user-supplied
855 name (when authenticating a server).
856 A pattern may also be preceded by
858 to indicate negation: if the host name matches a negated
859 pattern, it is not accepted (by that line) even if it matched another
862 Bits, exponent, and modulus are taken directly from the RSA host key; they
863 can be obtained, e.g., from
864 .Pa /etc/ssh_host_key.pub .
865 The optional comment field continues to the end of the line, and is not used.
869 and empty lines are ignored as comments.
871 When performing host authentication, authentication is accepted if any
872 matching line has the proper key.
873 It is thus permissible (but not
874 recommended) to have several lines or different host keys for the same
876 This will inevitably happen when short forms of host names
877 from different domains are put in the file.
879 that the files contain conflicting information; authentication is
880 accepted if valid information can be found from either file.
882 Note that the lines in these files are typically hundreds of characters
883 long, and you definitely don't want to type in the host keys by hand.
884 Rather, generate them by a script
886 .Pa /etc/ssh_host_key.pub
887 and adding the host names at the front.
889 closenet,closenet.hut.fi,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi
892 .It Pa /etc/sshd_config
893 Contains configuration data for
895 This file should be writable by root only, but it is recommended
896 (though not necessary) that it be world-readable.
897 .It Pa /etc/ssh_host_key
898 Contains the private part of the host key.
899 This file should only be owned by root, readable only by root, and not
900 accessible to others.
903 does not start if this file is group/world-accessible.
904 .It Pa /etc/ssh_host_key.pub
905 Contains the public part of the host key.
906 This file should be world-readable but writable only by
908 Its contents should match the private part.
910 really used for anything; it is only provided for the convenience of
911 the user so its contents can be copied to known hosts files.
912 These two files are created using
915 Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange".
916 .It Pa /var/run/sshd.pid
917 Contains the process ID of the
919 listening for connections (if there are several daemons running
920 concurrently for different ports, this contains the pid of the one
922 The content of this file is not sensitive; it can be world-readable.
923 .It Pa $HOME/.ssh/authorized_keys
924 Lists the RSA keys that can be used to log into the user's account.
925 This file must be readable by root (which may on some machines imply
926 it being world-readable if the user's home directory resides on an NFS
928 It is recommended that it not be accessible by others.
929 The format of this file is described above.
930 Users will place the contents of their
932 files into this file, as described in
934 .It Pa $HOME/.ssh/authorized_keys2
935 Lists the DSA keys that can be used to log into the user's account.
936 This file must be readable by root (which may on some machines imply
937 it being world-readable if the user's home directory resides on an NFS
939 It is recommended that it not be accessible by others.
940 The format of this file is described above.
941 Users will place the contents of their
943 files into this file, as described in
945 .It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts"
946 These files are consulted when using rhosts with RSA host
947 authentication to check the public key of the host.
948 The key must be listed in one of these files to be accepted.
949 The client uses the same files
950 to verify that the remote host is the one it intended to connect.
951 These files should be writable only by root/the owner.
952 .Pa /etc/ssh_known_hosts
953 should be world-readable, and
954 .Pa $HOME/.ssh/known_hosts
955 can but need not be world-readable.
959 refuses to let anyone except root log in.
960 The contents of the file
961 are displayed to anyone trying to log in, and non-root connections are
963 The file should be world-readable.
964 .It Pa /etc/hosts.allow, /etc/hosts.deny
967 support, tcp-wrappers access controls may be defined here as described in
970 This file contains host-username pairs, separated by a space, one per
972 The given user on the corresponding host is permitted to log in
974 The same file is used by rlogind and rshd.
976 be writable only by the user; it is recommended that it not be
977 accessible by others.
979 If is also possible to use netgroups in the file.
981 name may be of the form +@groupname to specify all hosts or all users
985 this file is exactly the same as for
987 However, this file is
988 not used by rlogin and rshd, so using this permits access using SSH only.
989 .It Pa /etc/hosts.equiv
990 This file is used during
993 In the simplest form, this file contains host names, one per line.
995 those hosts are permitted to log in without a password, provided they
996 have the same user name on both machines.
997 The host name may also be
998 followed by a user name; such users are permitted to log in as
1000 user on this machine (except root).
1001 Additionally, the syntax
1003 can be used to specify netgroups.
1004 Negated entries start with
1007 If the client host/user is successfully matched in this file, login is
1008 automatically permitted provided the client and server user names are the
1010 Additionally, successful RSA host authentication is normally required.
1011 This file must be writable only by root; it is recommended
1012 that it be world-readable.
1014 .Sy "Warning: It is almost never a good idea to use user names in"
1016 Beware that it really means that the named user(s) can log in as
1018 which includes bin, daemon, adm, and other accounts that own critical
1019 binaries and directories.
1020 Using a user name practically grants the user root access.
1021 The only valid use for user names that I can think
1022 of is in negative entries.
1024 Note that this warning also applies to rsh/rlogin.
1025 .It Pa /etc/shosts.equiv
1026 This is processed exactly as
1027 .Pa /etc/hosts.equiv .
1028 However, this file may be useful in environments that want to run both
1030 .It Pa $HOME/.ssh/environment
1031 This file is read into the environment at login (if it exists).
1032 It can only contain empty lines, comment lines (that start with
1034 and assignment lines of the form name=value.
1035 The file should be writable
1036 only by the user; it need not be readable by anyone else.
1037 .It Pa $HOME/.ssh/rc
1038 If this file exists, it is run with /bin/sh after reading the
1039 environment files but before starting the user's shell or command.
1040 If X11 spoofing is in use, this will receive the "proto cookie" pair in
1048 The primary purpose of this file is to run any initialization routines
1049 which may be needed before the user's home directory becomes
1050 accessible; AFS is a particular example of such an environment.
1052 This file will probably contain some initialization code followed by
1053 something similar to: "if read proto cookie; then echo add $DISPLAY
1054 $proto $cookie | xauth -q -; fi".
1056 If this file does not exist,
1059 does not exist either, xauth is used to store the cookie.
1061 This file should be writable only by the user, and need not be
1062 readable by anyone else.
1066 This can be used to specify
1067 machine-specific login-time initializations globally.
1068 This file should be writable only by root, and should be world-readable.
1071 OpenSSH is a derivative of the original and free
1072 ssh 1.2.12 release by Tatu Ylonen.
1073 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1074 Theo de Raadt and Dug Song
1075 removed many bugs, re-added newer features and
1077 Markus Friedl contributed the support for SSH
1078 protocol versions 1.5 and 2.0.
andersk / openssh.git / blob