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 1.101 2001/03/04 11:16:06 stevesk Exp $
38 .Dd September 25, 1999
43 .Nd OpenSSH 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,
178 by executing itself with the name it was started as, ie.
181 The options are as follows:
184 Specifies the number of bits in the server key (default 768).
188 The server sends verbose debug output to the system
189 log, and does not put itself in the background.
190 The server also will not fork and will only process one connection.
191 This option is only intended for debugging for the server.
192 Multiple -d options increases the debugging level.
194 .It Fl f Ar configuration_file
195 Specifies the name of the configuration file.
197 .Pa /etc/sshd_config .
199 refuses to start if there is no configuration file.
200 .It Fl g Ar login_grace_time
201 Gives the grace time for clients to authenticate themselves (default
203 If the client fails to authenticate the user within
204 this many seconds, the server disconnects and exits.
205 A value of zero indicates no limit.
206 .It Fl h Ar host_key_file
207 Specifies the file from which the host key is read (default
208 .Pa /etc/ssh_host_key ) .
209 This option must be given if
211 is not run as root (as the normal
212 host file is normally not readable by anyone but root).
213 It is possible to have multiple host key files for
214 the different protocol versions.
218 is being run from inetd.
221 from inetd because it needs to generate the server key before it can
222 respond to the client, and this may take tens of seconds.
223 Clients would have to wait too long if the key was regenerated every time.
224 However, with small key sizes (e.g., 512) using
228 .It Fl k Ar key_gen_time
229 Specifies how often the server key is regenerated (default 3600
230 seconds, or one hour).
231 The motivation for regenerating the key fairly
232 often is that the key is not stored anywhere, and after about an hour,
233 it becomes impossible to recover the key for decrypting intercepted
234 communications even if the machine is cracked into or physically
236 A value of zero indicates that the key will never be regenerated.
238 Specifies the port on which the server listens for connections
242 Nothing is sent to the system log.
243 Normally the beginning,
244 authentication, and termination of each connection is logged.
246 This option is used to specify the size of the field
249 structure that holds the remote host name.
250 If the resolved host name is longer than
252 the dotted decimal value will be used instead.
253 This allows hosts with very long host names that
254 overflow this field to still be uniquely identified.
257 indicates that only dotted decimal addresses
258 should be put into the
262 When this option is specified
264 will not detach and does not become a daemon.
265 This allows easy monitoring of
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 list 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 list 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 available MAC (message authentication code) algorithms.
508 The MAC algorithm is used in protocol version 2
509 for data integrity protection.
510 Multiple algorithms must be comma-separated.
514 ``hmac-sha1,hmac-md5,hmac-ripemd160,hmac-ripemd160@openssh.com,
515 hmac-sha1-96,hmac-md5-96''
518 Specifies the maximum number of concurrent unauthenticated connections to the
521 Additional connections will be dropped until authentication succeeds or the
523 expires for a connection.
526 Alternatively, random early drop can be enabled by specifying
527 the three colon separated values
531 will refuse connection attempts with a probability of
534 if there are currently
537 unauthenticated connections.
538 The probability increases linearly and all connection attempts
539 are refused if the number of unauthenticated connections reaches
542 .It Cm PasswordAuthentication
543 Specifies whether password authentication is allowed.
546 Note that this option applies to both protocol versions 1 and 2.
547 .It Cm PermitEmptyPasswords
548 When password authentication is allowed, it specifies whether the
549 server allows login to accounts with empty password strings.
552 .It Cm PermitRootLogin
553 Specifies whether root can login using
557 .Dq without-password ,
558 .Dq forced-commands-only
564 If this option is set to
566 password authentication is disabled for root.
568 If this option is set to
569 .Dq forced-commands-only
570 root login with public key authentication will be allowed,
573 option has been specified
574 (which may be useful for taking remote backups even if root login is
575 normally not allowed). All other authentication methods are disabled
578 If this option is set to
580 root is not allowed to login.
582 Specifies the file that contains the process identifier of the
586 .Pa /var/run/sshd.pid .
588 Specifies the port number that
592 Multiple options of this type are permitted.
598 when a user logs in interactively.
599 (On some systems it is also printed by the shell,
605 Specifies the protocol versions
608 The possible values are
612 Multiple versions must be comma-separated.
615 .It Cm ReverseMappingCheck
618 should try to verify the remote host name and check that
619 the resolved host name for the remote IP address maps back to the
620 very same IP address.
623 .It Cm RhostsAuthentication
624 Specifies whether authentication using rhosts or /etc/hosts.equiv
626 Normally, this method should not be permitted because it is insecure.
627 .Cm RhostsRSAAuthentication
629 instead, because it performs RSA-based host authentication in addition
630 to normal rhosts or /etc/hosts.equiv authentication.
633 .It Cm RhostsRSAAuthentication
634 Specifies whether rhosts or /etc/hosts.equiv authentication together
635 with successful RSA host authentication is allowed.
638 .It Cm RSAAuthentication
639 Specifies whether pure RSA authentication is allowed.
642 Note that this option applies to protocol version 1 only.
644 Defines the number of bits in the server key.
645 The minimum value is 512, and the default is 768.
646 .It Cm ChallengeResponseAuthentication
649 authentication is allowed.
650 Currently there is support for
652 and PAM authentication.
655 Note that enabling ChallengeResponseAuthentication for PAM bypasses
656 OpenSSH's password checking code, thus rendering options such as
657 .Cm PasswordAuthentication
659 .Cm PermitEmptyPasswords
664 should check file modes and ownership of the
665 user's files and home directory before accepting login.
666 This is normally desirable because novices sometimes accidentally leave their
667 directory or files world-writable.
671 Configures an external subsystem (e.g., file transfer daemon).
672 Arguments should be a subsystem name and a command to execute upon subsystem
678 file transfer subsystem.
679 By default no subsystems are defined.
680 Note that this option applies to protocol version 2 only.
681 .It Cm SyslogFacility
682 Gives the facility code that is used when logging messages from
684 The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
685 LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
690 is used for interactive login sessions.
693 is never used for remote command execution.
696 .It Cm X11DisplayOffset
697 Specifies the first display number available for
702 from interfering with real X11 servers.
705 Specifies whether X11 forwarding is permitted.
708 Note that disabling X11 forwarding does not improve security in any
709 way, as users can always install their own forwarders.
711 Specifies the location of the
715 .Pa /usr/X11R6/bin/xauth .
718 When a user successfully logs in,
721 .Bl -enum -offset indent
723 If the login is on a tty, and no command has been specified,
724 prints last login time and
726 (unless prevented in the configuration file or by
727 .Pa $HOME/.hushlogin ;
732 If the login is on a tty, records login time.
736 if it exists, prints contents and quits
739 Changes to run with normal user privileges.
741 Sets up basic environment.
744 .Pa $HOME/.ssh/environment
747 Changes to user's home directory.
751 exists, runs it; else if
754 it; otherwise runs xauth.
757 files are given the X11
758 authentication protocol and cookie in standard input.
760 Runs user's shell or command.
762 .Sh AUTHORIZED_KEYS FILE FORMAT
764 .Pa $HOME/.ssh/authorized_keys
765 file lists the RSA keys that are
766 permitted for RSA authentication in SSH protocols 1.3 and 1.5
768 .Pa $HOME/.ssh/authorized_keys2
769 file lists the DSA and RSA keys that are
770 permitted for public key authentication (PubkeyAuthentication)
773 Each line of the file contains one
774 key (empty lines and lines starting with a
778 Each RSA public key consists of the following fields, separated by
779 spaces: options, bits, exponent, modulus, comment.
780 Each protocol version 2 public key consists of:
781 options, keytype, base64 encoded key, comment.
783 are optional; its presence is determined by whether the line starts
784 with a number or not (the option field never starts with a number).
785 The bits, exponent, modulus and comment fields give the RSA key for
786 protocol version 1; the
787 comment field is not used for anything (but may be convenient for the
788 user to identify the key).
789 For protocol version 2 the keytype is
794 Note that lines in this file are usually several hundred bytes long
795 (because of the size of the RSA key modulus).
796 You don't want to type them in; instead, copy the
802 The options (if present) consist of comma-separated option
804 No spaces are permitted, except within double quotes.
805 The following option specifications are supported:
807 .It Cm from="pattern-list"
808 Specifies that in addition to RSA authentication, the canonical name
809 of the remote host must be present in the comma-separated list of
815 The list may also contain
816 patterns negated by prefixing them with
818 if the canonical host name matches a negated pattern, the key is not accepted.
820 of this option is to optionally increase security: RSA authentication
821 by itself does not trust the network or name servers or anything (but
822 the key); however, if somebody somehow steals the key, the key
823 permits an intruder to log in from anywhere in the world.
824 This additional option makes using a stolen key more difficult (name
825 servers and/or routers would have to be compromised in addition to
827 .It Cm command="command"
828 Specifies that the command is executed whenever this key is used for
830 The command supplied by the user (if any) is ignored.
831 The command is run on a pty if the connection requests a pty;
832 otherwise it is run without a tty.
833 Note that if you want a 8-bit clean channel,
834 you must not request a pty or should specify
836 A quote may be included in the command by quoting it with a backslash.
837 This option might be useful
838 to restrict certain RSA keys to perform just a specific operation.
839 An example might be a key that permits remote backups but nothing else.
840 Note that the client may specify TCP/IP and/or X11
841 forwarding unless they are explicitly prohibited.
842 .It Cm environment="NAME=value"
843 Specifies that the string is to be added to the environment when
844 logging in using this key.
845 Environment variables set this way
846 override other default environment values.
847 Multiple options of this type are permitted.
848 .It Cm no-port-forwarding
849 Forbids TCP/IP forwarding when this key is used for authentication.
850 Any port forward requests by the client will return an error.
851 This might be used, e.g., in connection with the
854 .It Cm no-X11-forwarding
855 Forbids X11 forwarding when this key is used for authentication.
856 Any X11 forward requests by the client will return an error.
857 .It Cm no-agent-forwarding
858 Forbids authentication agent forwarding when this key is used for
861 Prevents tty allocation (a request to allocate a pty will fail).
864 1024 33 12121.\|.\|.\|312314325 ylo@foo.bar
866 from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula
868 command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi
869 .Sh SSH_KNOWN_HOSTS FILE FORMAT
871 .Pa /etc/ssh_known_hosts ,
872 .Pa /etc/ssh_known_hosts2 ,
873 .Pa $HOME/.ssh/known_hosts ,
875 .Pa $HOME/.ssh/known_hosts2
876 files contain host public keys for all known hosts.
877 The global file should
878 be prepared by the administrator (optional), and the per-user file is
879 maintained automatically: whenever the user connects from an unknown host
880 its key is added to the per-user file.
882 Each line in these files contains the following fields: hostnames,
883 bits, exponent, modulus, comment.
884 The fields are separated by spaces.
886 Hostnames is a comma-separated list of patterns ('*' and '?' act as
887 wildcards); each pattern in turn is matched against the canonical host
888 name (when authenticating a client) or against the user-supplied
889 name (when authenticating a server).
890 A pattern may also be preceded by
892 to indicate negation: if the host name matches a negated
893 pattern, it is not accepted (by that line) even if it matched another
896 Bits, exponent, and modulus are taken directly from the RSA host key; they
897 can be obtained, e.g., from
898 .Pa /etc/ssh_host_key.pub .
899 The optional comment field continues to the end of the line, and is not used.
903 and empty lines are ignored as comments.
905 When performing host authentication, authentication is accepted if any
906 matching line has the proper key.
907 It is thus permissible (but not
908 recommended) to have several lines or different host keys for the same
910 This will inevitably happen when short forms of host names
911 from different domains are put in the file.
913 that the files contain conflicting information; authentication is
914 accepted if valid information can be found from either file.
916 Note that the lines in these files are typically hundreds of characters
917 long, and you definitely don't want to type in the host keys by hand.
918 Rather, generate them by a script
920 .Pa /etc/ssh_host_key.pub
921 and adding the host names at the front.
923 closenet,closenet.hut.fi,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi
926 .It Pa /etc/sshd_config
927 Contains configuration data for
929 This file should be writable by root only, but it is recommended
930 (though not necessary) that it be world-readable.
931 .It Pa /etc/ssh_host_key, /etc/ssh_host_dsa_key, /etc/ssh_host_rsa_key
932 These three files contain the private parts of the
933 (SSH1, SSH2 DSA, and SSH2 RSA) host keys.
934 These files should only be owned by root, readable only by root, and not
935 accessible to others.
938 does not start if this file is group/world-accessible.
939 .It Pa /etc/ssh_host_key.pub, /etc/ssh_host_dsa_key.pub, /etc/ssh_host_rsa_key.pub
940 There three files contain the public parts of the
941 (SSH1, SSH2 DSA, and SSH2 RSA) host keys.
942 These files should be world-readable but writable only by
944 Their contents should match the respective private parts.
946 really used for anything; they are provided for the convenience of
947 the user so their contents can be copied to known hosts files.
948 These files are created using
951 Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange".
952 .It Pa /var/run/sshd.pid
953 Contains the process ID of the
955 listening for connections (if there are several daemons running
956 concurrently for different ports, this contains the pid of the one
958 The content of this file is not sensitive; it can be world-readable.
959 .It Pa $HOME/.ssh/authorized_keys
960 Lists the RSA keys that can be used to log into the user's account.
961 This file must be readable by root (which may on some machines imply
962 it being world-readable if the user's home directory resides on an NFS
964 It is recommended that it not be accessible by others.
965 The format of this file is described above.
966 Users will place the contents of their
968 files into this file, as described in
970 .It Pa $HOME/.ssh/authorized_keys2
971 Lists the DSA keys that can be used to log into the user's account.
972 This file must be readable by root (which may on some machines imply
973 it being world-readable if the user's home directory resides on an NFS
975 It is recommended that it not be accessible by others.
976 The format of this file is described above.
977 Users will place the contents of their
979 files into this file, as described in
981 .It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts"
982 These files are consulted when using rhosts with RSA host
983 authentication to check the public key of the host.
984 The key must be listed in one of these files to be accepted.
985 The client uses the same files
986 to verify that it is connecting to the correct remote host.
987 These files should be writable only by root/the owner.
988 .Pa /etc/ssh_known_hosts
989 should be world-readable, and
990 .Pa $HOME/.ssh/known_hosts
991 can but need not be world-readable.
995 refuses to let anyone except root log in.
996 The contents of the file
997 are displayed to anyone trying to log in, and non-root connections are
999 The file should be world-readable.
1000 .It Pa /etc/hosts.allow, /etc/hosts.deny
1003 support, tcp-wrappers access controls may be defined here as described in
1004 .Xr hosts_access 5 .
1005 .It Pa $HOME/.rhosts
1006 This file contains host-username pairs, separated by a space, one per
1008 The given user on the corresponding host is permitted to log in
1010 The same file is used by rlogind and rshd.
1012 be writable only by the user; it is recommended that it not be
1013 accessible by others.
1015 If is also possible to use netgroups in the file.
1017 name may be of the form +@groupname to specify all hosts or all users
1019 .It Pa $HOME/.shosts
1021 this file is exactly the same as for
1023 However, this file is
1024 not used by rlogin and rshd, so using this permits access using SSH only.
1025 .It Pa /etc/hosts.equiv
1026 This file is used during
1029 In the simplest form, this file contains host names, one per line.
1031 those hosts are permitted to log in without a password, provided they
1032 have the same user name on both machines.
1033 The host name may also be
1034 followed by a user name; such users are permitted to log in as
1036 user on this machine (except root).
1037 Additionally, the syntax
1039 can be used to specify netgroups.
1040 Negated entries start with
1043 If the client host/user is successfully matched in this file, login is
1044 automatically permitted provided the client and server user names are the
1046 Additionally, successful RSA host authentication is normally required.
1047 This file must be writable only by root; it is recommended
1048 that it be world-readable.
1050 .Sy "Warning: It is almost never a good idea to use user names in"
1052 Beware that it really means that the named user(s) can log in as
1054 which includes bin, daemon, adm, and other accounts that own critical
1055 binaries and directories.
1056 Using a user name practically grants the user root access.
1057 The only valid use for user names that I can think
1058 of is in negative entries.
1060 Note that this warning also applies to rsh/rlogin.
1061 .It Pa /etc/shosts.equiv
1062 This is processed exactly as
1063 .Pa /etc/hosts.equiv .
1064 However, this file may be useful in environments that want to run both
1066 .It Pa $HOME/.ssh/environment
1067 This file is read into the environment at login (if it exists).
1068 It can only contain empty lines, comment lines (that start with
1070 and assignment lines of the form name=value.
1071 The file should be writable
1072 only by the user; it need not be readable by anyone else.
1073 .It Pa $HOME/.ssh/rc
1074 If this file exists, it is run with /bin/sh after reading the
1075 environment files but before starting the user's shell or command.
1076 If X11 spoofing is in use, this will receive the "proto cookie" pair in
1084 The primary purpose of this file is to run any initialization routines
1085 which may be needed before the user's home directory becomes
1086 accessible; AFS is a particular example of such an environment.
1088 This file will probably contain some initialization code followed by
1089 something similar to: "if read proto cookie; then echo add $DISPLAY
1090 $proto $cookie | xauth -q -; fi".
1092 If this file does not exist,
1095 does not exist either, xauth is used to store the cookie.
1097 This file should be writable only by the user, and need not be
1098 readable by anyone else.
1102 This can be used to specify
1103 machine-specific login-time initializations globally.
1104 This file should be writable only by root, and should be world-readable.
1107 OpenSSH is a derivative of the original and free
1108 ssh 1.2.12 release by Tatu Ylonen.
1109 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1110 Theo de Raadt and Dug Song
1111 removed many bugs, re-added newer features and
1113 Markus Friedl contributed the support for SSH
1114 protocol versions 1.5 and 2.0.
andersk / openssh.git / blob