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 1.118 2001/04/15 21:41:29 deraadt Exp $
38 .Dd September 25, 1999
43 .Nd OpenSSH ssh 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 (SSH 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 using a symmetric cipher, currently
138 Blowfish, 3DES, CAST128, Arcfour, 128 bit AES, or 256 bit AES.
139 The client selects the encryption algorithm
140 to use from those offered by the server.
141 Additionally, session integrity is provided
142 through a cryptographic message authentication code
143 (hmac-sha1 or hmac-md5).
145 Protocol version 2 provides a public key based
146 user authentication method (PubkeyAuthentication)
147 and conventional password authentication.
149 .Ss Command execution and data forwarding
151 If the client successfully authenticates itself, a dialog for
152 preparing the session is entered.
153 At this time the client may request
154 things like allocating a pseudo-tty, forwarding X11 connections,
155 forwarding TCP/IP connections, or forwarding the authentication agent
156 connection over the secure channel.
158 Finally, the client either requests a shell or execution of a command.
159 The sides then enter session mode.
160 In this mode, either side may send
161 data at any time, and such data is forwarded to/from the shell or
162 command on the server side, and the user terminal in the client side.
164 When the user program terminates and all forwarded X11 and other
165 connections have been closed, the server sends command exit status to
166 the client, and both sides exit.
169 can be configured using command-line options or a configuration
171 Command-line options override values specified in the
175 rereads its configuration file when it receives a hangup signal,
177 by executing itself with the name it was started as, ie.
180 The options are as follows:
183 Specifies the number of bits in the server key (default 768).
187 The server sends verbose debug output to the system
188 log, and does not put itself in the background.
189 The server also will not fork and will only process one connection.
190 This option is only intended for debugging for the server.
191 Multiple -d options increases the debugging level.
193 .It Fl f Ar configuration_file
194 Specifies the name of the configuration file.
196 .Pa /etc/sshd_config .
198 refuses to start if there is no configuration file.
199 .It Fl g Ar login_grace_time
200 Gives the grace time for clients to authenticate themselves (default
202 If the client fails to authenticate the user within
203 this many seconds, the server disconnects and exits.
204 A value of zero indicates no limit.
205 .It Fl h Ar host_key_file
206 Specifies the file from which the host key is read (default
207 .Pa /etc/ssh_host_key ) .
208 This option must be given if
210 is not run as root (as the normal
211 host file is normally not readable by anyone but root).
212 It is possible to have multiple host key files for
213 the different protocol versions.
217 is being run from inetd.
220 from inetd because it needs to generate the server key before it can
221 respond to the client, and this may take tens of seconds.
222 Clients would have to wait too long if the key was regenerated every time.
223 However, with small key sizes (e.g., 512) using
227 .It Fl k Ar key_gen_time
228 Specifies how often the server key is regenerated (default 3600
229 seconds, or one hour).
230 The motivation for regenerating the key fairly
231 often is that the key is not stored anywhere, and after about an hour,
232 it becomes impossible to recover the key for decrypting intercepted
233 communications even if the machine is cracked into or physically
235 A value of zero indicates that the key will never be regenerated.
237 Specifies the port on which the server listens for connections
241 Nothing is sent to the system log.
242 Normally the beginning,
243 authentication, and termination of each connection is logged.
245 This option is used to specify the size of the field
248 structure that holds the remote host name.
249 If the resolved host name is longer than
251 the dotted decimal value will be used instead.
252 This allows hosts with very long host names that
253 overflow this field to still be uniquely identified.
256 indicates that only dotted decimal addresses
257 should be put into the
261 When this option is specified
263 will not detach and does not become a daemon.
264 This allows easy monitoring of
267 When this option is specified,
269 will send the output to the standard error instead of the system log.
270 .It Fl V Ar client_protocol_id
271 SSH-2 compatibility mode.
272 When this option is specified
274 assumes the client has sent the supplied version string
276 Protocol Version Identification Exchange.
277 This option is not intended to be called directly.
281 to use IPv4 addresses only.
285 to use IPv6 addresses only.
287 .Sh CONFIGURATION FILE
289 reads configuration data from
291 (or the file specified with
293 on the command line).
294 The file contains keyword-value pairs, one per line.
297 and empty lines are interpreted as comments.
299 The following keywords are possible.
301 .It Cm AFSTokenPassing
302 Specifies whether an AFS token may be forwarded to the server.
306 This keyword can be followed by a list of group names, separated
308 If specified, login is allowed only for users whose primary
309 group or supplementary group list matches one of the patterns.
314 wildcards in the patterns.
315 Only group names are valid; a numerical group ID isn't recognized.
316 By default login is allowed regardless of the group list.
318 .It Cm AllowTcpForwarding
319 Specifies whether TCP forwarding is permitted.
322 Note that disabling TCP forwarding does not improve security unless
323 users are also denied shell access, as they can always install their
327 This keyword can be followed by a list of user names, separated
329 If specified, login is allowed only for users names that
330 match one of the patterns.
335 wildcards in the patterns.
336 Only user names are valid; a numerical user ID isn't recognized.
337 By default login is allowed regardless of the user name.
340 In some jurisdictions, sending a warning message before authentication
341 may be relevant for getting legal protection.
342 The contents of the specified file are sent to the remote user before
343 authentication is allowed.
344 This option is only available for protocol version 2.
346 .It Cm ChallengeResponseAuthentication
349 authentication is allowed.
350 Currently there is only support for
356 Specifies the ciphers allowed for protocol version 2.
357 Multiple ciphers must be comma-separated.
359 .Dq aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour.
363 should check for new mail for interactive logins.
366 .It Cm ClientAliveInterval
367 Sets a timeout interval in seconds after which if no data has been received
370 will send a message through the encrypted
371 channel to request a response from the client.
373 is 0, indicating that these messages will not be sent to the client.
374 This option applies to protocol version 2 only.
375 .It Cm ClientAliveCountMax
376 Sets the number of client alive messages (see above) which may be
379 receiving any messages back from the client. If this threshold is
380 reached while client alive messages are being sent,
382 will disconnect the client, terminating the session. It is important
383 to note that the use of client alive messages is very different from
385 (below). The client alive messages are sent through the
386 encrypted channel and therefore will not be spoofable. The TCP keepalive
389 is spoofable. You want to use the client
390 alive mechanism when you are basing something important on
391 clients having an active connection to the server.
393 The default value is 3. If you set
394 .Cm ClientAliveInterval
395 (above) to 15, and leave this value at the default, unresponsive ssh clients
396 will be disconnected after approximately 45 seconds.
398 This keyword can be followed by a number of group names, separated
400 Users whose primary group or supplementary group list matches
401 one of the patterns aren't allowed to log in.
406 wildcards in the patterns.
407 Only group names are valid; a numerical group ID isn't recognized.
408 By default login is allowed regardless of the group list.
411 This keyword can be followed by a number of user names, separated
413 Login is disallowed for user names that match one of the patterns.
417 can be used as wildcards in the patterns.
418 Only user names are valid; a numerical user ID isn't recognized.
419 By default login is allowed regardless of the user name.
421 Specifies whether remote hosts are allowed to connect to ports
422 forwarded for the client.
430 Specifies the file containing the private host keys (default
431 .Pa /etc/ssh_host_key )
432 used by SSH protocol versions 1 and 2.
435 will refuse to use a file if it is group/world-accessible.
436 It is possible to have multiple host key files.
438 keys are used for version 1 and
442 are used for version 2 of the SSH protocol.
448 files will not be used in authentication.
451 .Pa /etc/shosts.equiv
455 .It Cm IgnoreUserKnownHosts
458 should ignore the user's
459 .Pa $HOME/.ssh/known_hosts
461 .Cm RhostsRSAAuthentication .
465 Specifies whether the system should send keepalive messages to the
467 If they are sent, death of the connection or crash of one
468 of the machines will be properly noticed.
469 However, this means that
470 connections will die if the route is down temporarily, and some people
472 On the other hand, if keepalives are not sent,
473 sessions may hang indefinitely on the server, leaving
475 users and consuming server resources.
479 (to send keepalives), and the server will notice
480 if the network goes down or the client host reboots.
481 This avoids infinitely hanging sessions.
483 To disable keepalives, the value should be set to
485 in both the server and the client configuration files.
486 .It Cm KerberosAuthentication
487 Specifies whether Kerberos authentication is allowed.
488 This can be in the form of a Kerberos ticket, or if
489 .Cm PasswordAuthentication
490 is yes, the password provided by the user will be validated through
492 To use this option, the server needs a
493 Kerberos servtab which allows the verification of the KDC's identity.
496 .It Cm KerberosOrLocalPasswd
497 If set then if password authentication through Kerberos fails then
498 the password will be validated via any additional local mechanism
503 .It Cm KerberosTgtPassing
504 Specifies whether a Kerberos TGT may be forwarded to the server.
507 as this only works when the Kerberos KDC is actually an AFS kaserver.
508 .It Cm KerberosTicketCleanup
509 Specifies whether to automatically destroy the user's ticket cache
513 .It Cm KeyRegenerationInterval
514 The server key is automatically regenerated after this many seconds
515 (if it has been used).
516 The purpose of regeneration is to prevent
517 decrypting captured sessions by later breaking into the machine and
519 The key is never stored anywhere.
520 If the value is 0, the key is never regenerated.
521 The default is 3600 (seconds).
523 Specifies the local addresses
526 The following forms may be used:
528 .Bl -item -offset indent -compact
532 .Ar host No | Ar IPv4_addr No | Ar IPv6_addr
537 .Ar host No | Ar IPv4_addr No : Ar port
543 .Ar host No | Ar IPv6_addr Oc : Ar port
551 will listen on the address and all prior
553 options specified. The default is to listen on all local
556 options are permitted. Additionally, any
558 options must precede this option for non port qualified addresses.
559 .It Cm LoginGraceTime
560 The server disconnects after this time if the user has not
561 successfully logged in.
562 If the value is 0, there is no time limit.
563 The default is 600 (seconds).
565 Gives the verbosity level that is used when logging messages from
567 The possible values are:
568 QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG.
570 Logging with level DEBUG violates the privacy of users
571 and is not recommended.
573 Specifies the available MAC (message authentication code) algorithms.
574 The MAC algorithm is used in protocol version 2
575 for data integrity protection.
576 Multiple algorithms must be comma-separated.
580 ``hmac-md5,hmac-sha1,hmac-ripemd160,hmac-ripemd160@openssh.com,
581 hmac-sha1-96,hmac-md5-96''
584 Specifies the maximum number of concurrent unauthenticated connections to the
587 Additional connections will be dropped until authentication succeeds or the
589 expires for a connection.
592 Alternatively, random early drop can be enabled by specifying
593 the three colon separated values
597 will refuse connection attempts with a probability of
600 if there are currently
603 unauthenticated connections.
604 The probability increases linearly and all connection attempts
605 are refused if the number of unauthenticated connections reaches
608 .It Cm PasswordAuthentication
609 Specifies whether password authentication is allowed.
612 Note that this option applies to both protocol versions 1 and 2.
613 .It Cm PermitEmptyPasswords
614 When password authentication is allowed, it specifies whether the
615 server allows login to accounts with empty password strings.
618 .It Cm PermitRootLogin
619 Specifies whether root can login using
623 .Dq without-password ,
624 .Dq forced-commands-only
630 If this option is set to
632 password authentication is disabled for root.
634 If this option is set to
635 .Dq forced-commands-only
636 root login with public key authentication will be allowed,
639 option has been specified
640 (which may be useful for taking remote backups even if root login is
641 normally not allowed). All other authentication methods are disabled
644 If this option is set to
646 root is not allowed to login.
648 Specifies the file that contains the process identifier of the
652 .Pa /var/run/sshd.pid .
654 Specifies the port number that
658 Multiple options of this type are permitted.
662 should print the date and time when the user last logged in.
670 when a user logs in interactively.
671 (On some systems it is also printed by the shell,
677 Specifies the protocol versions
680 The possible values are
684 Multiple versions must be comma-separated.
687 .It Cm PubkeyAuthentication
688 Specifies whether public key authentication is allowed.
691 Note that this option applies to protocol version 2 only.
692 .It Cm ReverseMappingCheck
695 should try to verify the remote host name and check that
696 the resolved host name for the remote IP address maps back to the
697 very same IP address.
700 .It Cm RhostsAuthentication
701 Specifies whether authentication using rhosts or /etc/hosts.equiv
703 Normally, this method should not be permitted because it is insecure.
704 .Cm RhostsRSAAuthentication
706 instead, because it performs RSA-based host authentication in addition
707 to normal rhosts or /etc/hosts.equiv authentication.
710 .It Cm RhostsRSAAuthentication
711 Specifies whether rhosts or /etc/hosts.equiv authentication together
712 with successful RSA host authentication is allowed.
715 .It Cm RSAAuthentication
716 Specifies whether pure RSA authentication is allowed.
719 Note that this option applies to protocol version 1 only.
721 Defines the number of bits in the server key.
722 The minimum value is 512, and the default is 768.
726 should check file modes and ownership of the
727 user's files and home directory before accepting login.
728 This is normally desirable because novices sometimes accidentally leave their
729 directory or files world-writable.
733 Configures an external subsystem (e.g., file transfer daemon).
734 Arguments should be a subsystem name and a command to execute upon subsystem
740 file transfer subsystem.
741 By default no subsystems are defined.
742 Note that this option applies to protocol version 2 only.
743 .It Cm SyslogFacility
744 Gives the facility code that is used when logging messages from
746 The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
747 LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
752 is used for interactive login sessions.
755 is never used for remote command execution.
758 .It Cm X11DisplayOffset
759 Specifies the first display number available for
764 from interfering with real X11 servers.
767 Specifies whether X11 forwarding is permitted.
770 Note that disabling X11 forwarding does not improve security in any
771 way, as users can always install their own forwarders.
773 Specifies the location of the
777 .Pa /usr/X11R6/bin/xauth .
780 When a user successfully logs in,
783 .Bl -enum -offset indent
785 If the login is on a tty, and no command has been specified,
786 prints last login time and
788 (unless prevented in the configuration file or by
789 .Pa $HOME/.hushlogin ;
794 If the login is on a tty, records login time.
798 if it exists, prints contents and quits
801 Changes to run with normal user privileges.
803 Sets up basic environment.
806 .Pa $HOME/.ssh/environment
809 Changes to user's home directory.
813 exists, runs it; else if
816 it; otherwise runs xauth.
819 files are given the X11
820 authentication protocol and cookie in standard input.
822 Runs user's shell or command.
824 .Sh AUTHORIZED_KEYS FILE FORMAT
826 .Pa $HOME/.ssh/authorized_keys
827 file lists the RSA keys that are
828 permitted for RSA authentication in SSH protocols 1.3 and 1.5
830 .Pa $HOME/.ssh/authorized_keys2
831 file lists the DSA and RSA keys that are
832 permitted for public key authentication (PubkeyAuthentication)
835 Each line of the file contains one
836 key (empty lines and lines starting with a
840 Each RSA public key consists of the following fields, separated by
841 spaces: options, bits, exponent, modulus, comment.
842 Each protocol version 2 public key consists of:
843 options, keytype, base64 encoded key, comment.
845 are optional; its presence is determined by whether the line starts
846 with a number or not (the option field never starts with a number).
847 The bits, exponent, modulus and comment fields give the RSA key for
848 protocol version 1; the
849 comment field is not used for anything (but may be convenient for the
850 user to identify the key).
851 For protocol version 2 the keytype is
856 Note that lines in this file are usually several hundred bytes long
857 (because of the size of the RSA key modulus).
858 You don't want to type them in; instead, copy the
865 The options (if present) consist of comma-separated option
867 No spaces are permitted, except within double quotes.
868 The following option specifications are supported:
870 .It Cm from="pattern-list"
871 Specifies that in addition to RSA authentication, the canonical name
872 of the remote host must be present in the comma-separated list of
878 The list may also contain
879 patterns negated by prefixing them with
881 if the canonical host name matches a negated pattern, the key is not accepted.
883 of this option is to optionally increase security: RSA authentication
884 by itself does not trust the network or name servers or anything (but
885 the key); however, if somebody somehow steals the key, the key
886 permits an intruder to log in from anywhere in the world.
887 This additional option makes using a stolen key more difficult (name
888 servers and/or routers would have to be compromised in addition to
890 .It Cm command="command"
891 Specifies that the command is executed whenever this key is used for
893 The command supplied by the user (if any) is ignored.
894 The command is run on a pty if the connection requests a pty;
895 otherwise it is run without a tty.
896 Note that if you want a 8-bit clean channel,
897 you must not request a pty or should specify
899 A quote may be included in the command by quoting it with a backslash.
900 This option might be useful
901 to restrict certain RSA keys to perform just a specific operation.
902 An example might be a key that permits remote backups but nothing else.
903 Note that the client may specify TCP/IP and/or X11
904 forwarding unless they are explicitly prohibited.
905 .It Cm environment="NAME=value"
906 Specifies that the string is to be added to the environment when
907 logging in using this key.
908 Environment variables set this way
909 override other default environment values.
910 Multiple options of this type are permitted.
911 .It Cm no-port-forwarding
912 Forbids TCP/IP forwarding when this key is used for authentication.
913 Any port forward requests by the client will return an error.
914 This might be used, e.g., in connection with the
917 .It Cm no-X11-forwarding
918 Forbids X11 forwarding when this key is used for authentication.
919 Any X11 forward requests by the client will return an error.
920 .It Cm no-agent-forwarding
921 Forbids authentication agent forwarding when this key is used for
924 Prevents tty allocation (a request to allocate a pty will fail).
925 .It Cm permitopen="host:port"
928 port forwarding such that it may only connect to the specified host and
931 options may be applied separated by commas. No pattern matching is
932 performed on the specified hostnames, they must be literal domains or
936 1024 33 12121.\|.\|.\|312314325 ylo@foo.bar
938 from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula
940 command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi
942 permitopen="10.2.1.55:80",permitopen="10.2.1.56:25" 1024 33 23.\|.\|.\|2323
943 .Sh SSH_KNOWN_HOSTS FILE FORMAT
945 .Pa /etc/ssh_known_hosts ,
946 .Pa /etc/ssh_known_hosts2 ,
947 .Pa $HOME/.ssh/known_hosts ,
949 .Pa $HOME/.ssh/known_hosts2
950 files contain host public keys for all known hosts.
951 The global file should
952 be prepared by the administrator (optional), and the per-user file is
953 maintained automatically: whenever the user connects from an unknown host
954 its key is added to the per-user file.
956 Each line in these files contains the following fields: hostnames,
957 bits, exponent, modulus, comment.
958 The fields are separated by spaces.
960 Hostnames is a comma-separated list of patterns ('*' and '?' act as
961 wildcards); each pattern in turn is matched against the canonical host
962 name (when authenticating a client) or against the user-supplied
963 name (when authenticating a server).
964 A pattern may also be preceded by
966 to indicate negation: if the host name matches a negated
967 pattern, it is not accepted (by that line) even if it matched another
970 Bits, exponent, and modulus are taken directly from the RSA host key; they
971 can be obtained, e.g., from
972 .Pa /etc/ssh_host_key.pub .
973 The optional comment field continues to the end of the line, and is not used.
977 and empty lines are ignored as comments.
979 When performing host authentication, authentication is accepted if any
980 matching line has the proper key.
981 It is thus permissible (but not
982 recommended) to have several lines or different host keys for the same
984 This will inevitably happen when short forms of host names
985 from different domains are put in the file.
987 that the files contain conflicting information; authentication is
988 accepted if valid information can be found from either file.
990 Note that the lines in these files are typically hundreds of characters
991 long, and you definitely don't want to type in the host keys by hand.
992 Rather, generate them by a script
994 .Pa /etc/ssh_host_key.pub
995 and adding the host names at the front.
997 closenet,closenet.hut.fi,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi
1000 .It Pa /etc/sshd_config
1001 Contains configuration data for
1003 This file should be writable by root only, but it is recommended
1004 (though not necessary) that it be world-readable.
1005 .It Pa /etc/ssh_host_key, /etc/ssh_host_dsa_key, /etc/ssh_host_rsa_key
1006 These three files contain the private parts of the
1007 (SSH1, SSH2 DSA, and SSH2 RSA) host keys.
1008 These files should only be owned by root, readable only by root, and not
1009 accessible to others.
1012 does not start if this file is group/world-accessible.
1013 .It Pa /etc/ssh_host_key.pub, /etc/ssh_host_dsa_key.pub, /etc/ssh_host_rsa_key.pub
1014 These three files contain the public parts of the
1015 (SSH1, SSH2 DSA, and SSH2 RSA) host keys.
1016 These files should be world-readable but writable only by
1018 Their contents should match the respective private parts.
1020 really used for anything; they are provided for the convenience of
1021 the user so their contents can be copied to known hosts files.
1022 These files are created using
1025 Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange".
1026 .It Pa /var/run/sshd.pid
1027 Contains the process ID of the
1029 listening for connections (if there are several daemons running
1030 concurrently for different ports, this contains the pid of the one
1032 The content of this file is not sensitive; it can be world-readable.
1033 .It Pa $HOME/.ssh/authorized_keys
1034 Lists the RSA keys that can be used to log into the user's account.
1035 This file must be readable by root (which may on some machines imply
1036 it being world-readable if the user's home directory resides on an NFS
1038 It is recommended that it not be accessible by others.
1039 The format of this file is described above.
1040 Users will place the contents of their
1042 files into this file, as described in
1044 .It Pa $HOME/.ssh/authorized_keys2
1045 Lists the DSA keys that can be used to log into the user's account.
1046 This file must be readable by root (which may on some machines imply
1047 it being world-readable if the user's home directory resides on an NFS
1049 It is recommended that it not be accessible by others.
1050 The format of this file is described above.
1051 Users will place the contents of their
1055 files into this file, as described in
1057 .It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts"
1058 These files are consulted when using rhosts with RSA host
1059 authentication to check the public key of the host.
1060 The key must be listed in one of these files to be accepted.
1061 The client uses the same files
1062 to verify that it is connecting to the correct remote host.
1063 These files should be writable only by root/the owner.
1064 .Pa /etc/ssh_known_hosts
1065 should be world-readable, and
1066 .Pa $HOME/.ssh/known_hosts
1067 can but need not be world-readable.
1069 If this file exists,
1071 refuses to let anyone except root log in.
1072 The contents of the file
1073 are displayed to anyone trying to log in, and non-root connections are
1075 The file should be world-readable.
1076 .It Pa /etc/hosts.allow, /etc/hosts.deny
1079 support, tcp-wrappers access controls may be defined here as described in
1080 .Xr hosts_access 5 .
1081 .It Pa $HOME/.rhosts
1082 This file contains host-username pairs, separated by a space, one per
1084 The given user on the corresponding host is permitted to log in
1086 The same file is used by rlogind and rshd.
1088 be writable only by the user; it is recommended that it not be
1089 accessible by others.
1091 If is also possible to use netgroups in the file.
1093 name may be of the form +@groupname to specify all hosts or all users
1095 .It Pa $HOME/.shosts
1097 this file is exactly the same as for
1099 However, this file is
1100 not used by rlogin and rshd, so using this permits access using SSH only.
1101 .It Pa /etc/hosts.equiv
1102 This file is used during
1105 In the simplest form, this file contains host names, one per line.
1107 those hosts are permitted to log in without a password, provided they
1108 have the same user name on both machines.
1109 The host name may also be
1110 followed by a user name; such users are permitted to log in as
1112 user on this machine (except root).
1113 Additionally, the syntax
1115 can be used to specify netgroups.
1116 Negated entries start with
1119 If the client host/user is successfully matched in this file, login is
1120 automatically permitted provided the client and server user names are the
1122 Additionally, successful RSA host authentication is normally required.
1123 This file must be writable only by root; it is recommended
1124 that it be world-readable.
1126 .Sy "Warning: It is almost never a good idea to use user names in"
1128 Beware that it really means that the named user(s) can log in as
1130 which includes bin, daemon, adm, and other accounts that own critical
1131 binaries and directories.
1132 Using a user name practically grants the user root access.
1133 The only valid use for user names that I can think
1134 of is in negative entries.
1136 Note that this warning also applies to rsh/rlogin.
1137 .It Pa /etc/shosts.equiv
1138 This is processed exactly as
1139 .Pa /etc/hosts.equiv .
1140 However, this file may be useful in environments that want to run both
1142 .It Pa $HOME/.ssh/environment
1143 This file is read into the environment at login (if it exists).
1144 It can only contain empty lines, comment lines (that start with
1146 and assignment lines of the form name=value.
1147 The file should be writable
1148 only by the user; it need not be readable by anyone else.
1149 .It Pa $HOME/.ssh/rc
1150 If this file exists, it is run with /bin/sh after reading the
1151 environment files but before starting the user's shell or command.
1152 If X11 spoofing is in use, this will receive the "proto cookie" pair in
1160 The primary purpose of this file is to run any initialization routines
1161 which may be needed before the user's home directory becomes
1162 accessible; AFS is a particular example of such an environment.
1164 This file will probably contain some initialization code followed by
1165 something similar to: "if read proto cookie; then echo add $DISPLAY
1166 $proto $cookie | xauth -q -; fi".
1168 If this file does not exist,
1171 does not exist either, xauth is used to store the cookie.
1173 This file should be writable only by the user, and need not be
1174 readable by anyone else.
1178 This can be used to specify
1179 machine-specific login-time initializations globally.
1180 This file should be writable only by root, and should be world-readable.
1183 OpenSSH is a derivative of the original and free
1184 ssh 1.2.12 release by Tatu Ylonen.
1185 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1186 Theo de Raadt and Dug Song
1187 removed many bugs, re-added newer features and
1189 Markus Friedl contributed the support for SSH
1190 protocol versions 1.5 and 2.0.
andersk / openssh.git / blob