2 .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
3 .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
4 .\" All rights reserved
6 .\" As far as I am concerned, the code I have written for this software
7 .\" can be used freely for any purpose. Any derived versions of this
8 .\" software must be clearly marked as such, and if the derived work is
9 .\" incompatible with the protocol description in the RFC file, it must be
10 .\" called by a name other than "ssh" or "Secure Shell".
12 .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
13 .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
14 .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
16 .\" Redistribution and use in source and binary forms, with or without
17 .\" modification, are permitted provided that the following conditions
19 .\" 1. Redistributions of source code must retain the above copyright
20 .\" notice, this list of conditions and the following disclaimer.
21 .\" 2. Redistributions in binary form must reproduce the above copyright
22 .\" notice, this list of conditions and the following disclaimer in the
23 .\" documentation and/or other materials provided with the distribution.
25 .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
26 .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
27 .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
28 .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
29 .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
30 .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
31 .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
32 .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
33 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
34 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
36 .\" $OpenBSD: sshd.8,v 1.273 2013/12/07 11:58:46 naddy Exp $
37 .Dd $Mdocdate: December 7 2013 $
42 .Nd OpenSSH SSH daemon
48 .Op Fl C Ar connection_spec
49 .Op Fl c Ar host_certificate_file
51 .Op Fl f Ar config_file
52 .Op Fl g Ar login_grace_time
53 .Op Fl h Ar host_key_file
54 .Op Fl k Ar key_gen_time
61 (OpenSSH Daemon) is the daemon program for
63 Together these programs replace
67 and provide secure encrypted communications between two untrusted hosts
68 over an insecure network.
71 listens for connections from clients.
72 It is normally started at boot from
75 daemon for each incoming connection.
76 The forked daemons handle
77 key exchange, encryption, authentication, command execution,
81 can be configured using command-line options or a configuration file
84 command-line options override values specified in the
87 rereads its configuration file when it receives a hangup signal,
89 by executing itself with the name and options it was started with, e.g.\&
92 The options are as follows:
97 to use IPv4 addresses only.
101 to use IPv6 addresses only.
103 Specifies the number of bits in the ephemeral protocol version 1
104 server key (default 1024).
105 .It Fl C Ar connection_spec
106 Specify the connection parameters to use for the
111 directives in the configuration file
112 that would apply to the specified user, host, and address will be set before
113 the configuration is written to standard output.
114 The connection parameters are supplied as keyword=value pairs.
122 All are required and may be supplied in any order, either with multiple
124 options or as a comma-separated list.
125 .It Fl c Ar host_certificate_file
126 Specifies a path to a certificate file to identify
129 The certificate file must match a host key file specified using the
133 configuration directive.
135 When this option is specified,
137 will not detach and does not become a daemon.
138 This allows easy monitoring of
142 The server sends verbose debug output to standard error,
143 and does not put itself in the background.
144 The server also will not fork and will only process one connection.
145 This option is only intended for debugging for the server.
148 options increase the debugging level.
153 instead of the system log.
155 Write debug logs to standard error instead of the system log.
156 .It Fl f Ar config_file
157 Specifies the name of the configuration file.
159 .Pa /etc/ssh/sshd_config .
161 refuses to start if there is no configuration file.
162 .It Fl g Ar login_grace_time
163 Gives the grace time for clients to authenticate themselves (default
165 If the client fails to authenticate the user within
166 this many seconds, the server disconnects and exits.
167 A value of zero indicates no limit.
168 .It Fl h Ar host_key_file
169 Specifies a file from which a host key is read.
170 This option must be given if
172 is not run as root (as the normal
173 host key files are normally not readable by anyone but root).
175 .Pa /etc/ssh/ssh_host_key
176 for protocol version 1, and
177 .Pa /etc/ssh/ssh_host_dsa_key ,
178 .Pa /etc/ssh/ssh_host_ecdsa_key .
179 .Pa /etc/ssh/ssh_host_ed25519_key
181 .Pa /etc/ssh/ssh_host_rsa_key
182 for protocol version 2.
183 It is possible to have multiple host key files for
184 the different protocol versions and host key algorithms.
192 from inetd because it needs to generate the server key before it can
193 respond to the client, and this may take tens of seconds.
194 Clients would have to wait too long if the key was regenerated every time.
195 However, with small key sizes (e.g. 512) using
199 .It Fl k Ar key_gen_time
200 Specifies how often the ephemeral protocol version 1 server key is
201 regenerated (default 3600 seconds, or one hour).
202 The motivation for regenerating the key fairly
203 often is that the key is not stored anywhere, and after about an hour
204 it becomes impossible to recover the key for decrypting intercepted
205 communications even if the machine is cracked into or physically
207 A value of zero indicates that the key will never be regenerated.
209 Can be used to give options in the format used in the configuration file.
210 This is useful for specifying options for which there is no separate
212 For full details of the options, and their values, see
215 Specifies the port on which the server listens for connections
217 Multiple port options are permitted.
218 Ports specified in the configuration file with the
220 option are ignored when a command-line port is specified.
221 Ports specified using the
223 option override command-line ports.
226 Nothing is sent to the system log.
227 Normally the beginning,
228 authentication, and termination of each connection is logged.
231 Check the validity of the configuration file, output the effective configuration
232 to stdout and then exit.
235 rules may be applied by specifying the connection parameters using one or more
240 Only check the validity of the configuration file and sanity of the keys.
241 This is useful for updating
243 reliably as configuration options may change.
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 may also be used to prevent
263 from making DNS requests unless the authentication
264 mechanism or configuration requires it.
265 Authentication mechanisms that may require DNS include
266 .Cm RhostsRSAAuthentication ,
267 .Cm HostbasedAuthentication ,
269 .Cm from="pattern-list"
270 option in a key file.
271 Configuration options that require DNS include using a
278 The OpenSSH SSH daemon supports SSH protocols 1 and 2.
279 The default is to use protocol 2 only,
280 though this can be changed via the
284 Protocol 2 supports DSA, ECDSA, ED25519 and RSA keys;
285 protocol 1 only supports RSA keys.
287 each host has a host-specific key,
289 used to identify the host.
291 Forward security for protocol 1 is provided through
292 an additional server key,
294 generated when the server starts.
295 This key is normally regenerated every hour if it has been used, and
296 is never stored on disk.
297 Whenever a client connects, the daemon responds with its public
298 host and server keys.
299 The client compares the
300 RSA host key against its own database to verify that it has not changed.
301 The client then generates a 256-bit random number.
303 random number using both the host key and the server key, and sends
304 the encrypted number to the server.
305 Both sides then use this
306 random number as a session key which is used to encrypt all further
307 communications in the session.
308 The rest of the session is encrypted
309 using a conventional cipher, currently Blowfish or 3DES, with 3DES
310 being used by default.
311 The client selects the encryption algorithm
312 to use from those offered by the server.
315 forward security is provided through a Diffie-Hellman key agreement.
316 This key agreement results in a shared session key.
317 The rest of the session is encrypted using a symmetric cipher, currently
318 128-bit AES, Blowfish, 3DES, CAST128, Arcfour, 192-bit AES, or 256-bit AES.
319 The client selects the encryption algorithm
320 to use from those offered by the server.
321 Additionally, session integrity is provided
322 through a cryptographic message authentication code
323 (hmac-md5, hmac-sha1, umac-64, umac-128, hmac-ripemd160,
324 hmac-sha2-256 or hmac-sha2-512).
326 Finally, the server and the client enter an authentication dialog.
327 The client tries to authenticate itself using
328 host-based authentication,
329 public key authentication,
330 challenge-response authentication,
331 or password authentication.
333 Regardless of the authentication type, the account is checked to
334 ensure that it is accessible. An account is not accessible if it is
337 or its group is listed in
339 \&. The definition of a locked account is system dependant. Some platforms
340 have their own account database (eg AIX) and some modify the passwd field (
342 on Solaris and UnixWare,
349 on FreeBSD and a leading
352 If there is a requirement to disable password authentication
353 for the account while allowing still public-key, then the passwd field
354 should be set to something other than these values (eg
360 If the client successfully authenticates itself, a dialog for
361 preparing the session is entered.
362 At this time the client may request
363 things like allocating a pseudo-tty, forwarding X11 connections,
364 forwarding TCP connections, or forwarding the authentication agent
365 connection over the secure channel.
367 After this, the client either requests a shell or execution of a command.
368 The sides then enter session mode.
369 In this mode, either side may send
370 data at any time, and such data is forwarded to/from the shell or
371 command on the server side, and the user terminal in the client side.
373 When the user program terminates and all forwarded X11 and other
374 connections have been closed, the server sends command exit status to
375 the client, and both sides exit.
377 When a user successfully logs in,
380 .Bl -enum -offset indent
382 If the login is on a tty, and no command has been specified,
383 prints last login time and
385 (unless prevented in the configuration file or by
391 If the login is on a tty, records login time.
395 if it exists, prints contents and quits
398 Changes to run with normal user privileges.
400 Sets up basic environment.
403 .Pa ~/.ssh/environment ,
404 if it exists, and users are allowed to change their environment.
406 .Cm PermitUserEnvironment
410 Changes to user's home directory.
414 exists, runs it; else if
417 it; otherwise runs xauth.
420 files are given the X11
421 authentication protocol and cookie in standard input.
426 Runs user's shell or command.
433 runs it after reading the
434 environment files but before starting the user's shell or command.
435 It must not produce any output on stdout; stderr must be used
437 If X11 forwarding is in use, it will receive the "proto cookie" pair in
438 its standard input (and
445 will not run xauth automatically to add X11 cookies.
447 The primary purpose of this file is to run any initialization routines
448 which may be needed before the user's home directory becomes
449 accessible; AFS is a particular example of such an environment.
451 This file will probably contain some initialization code followed by
452 something similar to:
453 .Bd -literal -offset 3n
454 if read proto cookie && [ -n "$DISPLAY" ]; then
455 if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then
456 # X11UseLocalhost=yes
457 echo add unix:`echo $DISPLAY |
458 cut -c11-` $proto $cookie
461 echo add $DISPLAY $proto $cookie
466 If this file does not exist,
469 does not exist either, xauth is used to add the cookie.
470 .Sh AUTHORIZED_KEYS FILE FORMAT
471 .Cm AuthorizedKeysFile
472 specifies the files containing public keys for
473 public key authentication;
474 if none is specified, the default is
475 .Pa ~/.ssh/authorized_keys
477 .Pa ~/.ssh/authorized_keys2 .
478 Each line of the file contains one
479 key (empty lines and lines starting with a
483 Protocol 1 public keys consist of the following space-separated fields:
484 options, bits, exponent, modulus, comment.
485 Protocol 2 public key consist of:
486 options, keytype, base64-encoded key, comment.
487 The options field is optional;
488 its presence is determined by whether the line starts
489 with a number or not (the options field never starts with a number).
490 The bits, exponent, modulus, and comment fields give the RSA key for
491 protocol version 1; the
492 comment field is not used for anything (but may be convenient for the
493 user to identify the key).
494 For protocol version 2 the keytype is
495 .Dq ecdsa-sha2-nistp256 ,
496 .Dq ecdsa-sha2-nistp384 ,
497 .Dq ecdsa-sha2-nistp521 ,
503 Note that lines in this file are usually several hundred bytes long
504 (because of the size of the public key encoding) up to a limit of
505 8 kilobytes, which permits DSA keys up to 8 kilobits and RSA
506 keys up to 16 kilobits.
507 You don't want to type them in; instead, copy the
517 enforces a minimum RSA key modulus size for protocol 1
518 and protocol 2 keys of 768 bits.
520 The options (if present) consist of comma-separated option
522 No spaces are permitted, except within double quotes.
523 The following option specifications are supported (note
524 that option keywords are case-insensitive):
526 .It Cm cert-authority
527 Specifies that the listed key is a certification authority (CA) that is
528 trusted to validate signed certificates for user authentication.
530 Certificates may encode access restrictions similar to these key options.
531 If both certificate restrictions and key options are present, the most
532 restrictive union of the two is applied.
533 .It Cm command="command"
534 Specifies that the command is executed whenever this key is used for
536 The command supplied by the user (if any) is ignored.
537 The command is run on a pty if the client requests a pty;
538 otherwise it is run without a tty.
539 If an 8-bit clean channel is required,
540 one must not request a pty or should specify
542 A quote may be included in the command by quoting it with a backslash.
543 This option might be useful
544 to restrict certain public keys to perform just a specific operation.
545 An example might be a key that permits remote backups but nothing else.
546 Note that the client may specify TCP and/or X11
547 forwarding unless they are explicitly prohibited.
548 The command originally supplied by the client is available in the
549 .Ev SSH_ORIGINAL_COMMAND
550 environment variable.
551 Note that this option applies to shell, command or subsystem execution.
552 Also note that this command may be superseded by either a
555 directive or a command embedded in a certificate.
556 .It Cm environment="NAME=value"
557 Specifies that the string is to be added to the environment when
558 logging in using this key.
559 Environment variables set this way
560 override other default environment values.
561 Multiple options of this type are permitted.
562 Environment processing is disabled by default and is
564 .Cm PermitUserEnvironment
566 This option is automatically disabled if
569 .It Cm from="pattern-list"
570 Specifies that in addition to public key authentication, either the canonical
571 name of the remote host or its IP address must be present in the
572 comma-separated list of patterns.
575 for more information on patterns.
577 In addition to the wildcard matching that may be applied to hostnames or
580 stanza may match IP addresses using CIDR address/masklen notation.
582 The purpose of this option is to optionally increase security: public key
583 authentication by itself does not trust the network or name servers or
584 anything (but the key); however, if somebody somehow steals the key, the key
585 permits an intruder to log in from anywhere in the world.
586 This additional option makes using a stolen key more difficult (name
587 servers and/or routers would have to be compromised in addition to
589 .It Cm no-agent-forwarding
590 Forbids authentication agent forwarding when this key is used for
592 .It Cm no-port-forwarding
593 Forbids TCP forwarding when this key is used for authentication.
594 Any port forward requests by the client will return an error.
595 This might be used, e.g. in connection with the
599 Prevents tty allocation (a request to allocate a pty will fail).
601 Disables execution of
603 .It Cm no-X11-forwarding
604 Forbids X11 forwarding when this key is used for authentication.
605 Any X11 forward requests by the client will return an error.
606 .It Cm permitopen="host:port"
609 port forwarding such that it may only connect to the specified host and
611 IPv6 addresses can be specified by enclosing the address in square brackets.
614 options may be applied separated by commas.
615 No pattern matching is performed on the specified hostnames,
616 they must be literal domains or addresses.
617 A port specification of
620 .It Cm principals="principals"
623 line, specifies allowed principals for certificate authentication as a
624 comma-separated list.
625 At least one name from the list must appear in the certificate's
626 list of principals for the certificate to be accepted.
627 This option is ignored for keys that are not marked as trusted certificate
634 device on the server.
635 Without this option, the next available device will be used if
636 the client requests a tunnel.
639 An example authorized_keys file:
640 .Bd -literal -offset 3n
641 # Comments allowed at start of line
642 ssh-rsa AAAAB3Nza...LiPk== user@example.net
643 from="*.sales.example.net,!pc.sales.example.net" ssh-rsa
644 AAAAB2...19Q== john@example.net
645 command="dump /home",no-pty,no-port-forwarding ssh-dss
646 AAAAC3...51R== example.net
647 permitopen="192.0.2.1:80",permitopen="192.0.2.2:25" ssh-dss
649 tunnel="0",command="sh /etc/netstart tun0" ssh-rsa AAAA...==
652 .Sh SSH_KNOWN_HOSTS FILE FORMAT
654 .Pa /etc/ssh/ssh_known_hosts
656 .Pa ~/.ssh/known_hosts
657 files contain host public keys for all known hosts.
658 The global file should
659 be prepared by the administrator (optional), and the per-user file is
660 maintained automatically: whenever the user connects from an unknown host,
661 its key is added to the per-user file.
663 Each line in these files contains the following fields: markers (optional),
664 hostnames, bits, exponent, modulus, comment.
665 The fields are separated by spaces.
667 The marker is optional, but if it is present then it must be one of
668 .Dq @cert-authority ,
669 to indicate that the line contains a certification authority (CA) key,
672 to indicate that the key contained on the line is revoked and must not ever
674 Only one marker should be used on a key line.
676 Hostnames is a comma-separated list of patterns
681 wildcards); each pattern in turn is matched against the canonical host
682 name (when authenticating a client) or against the user-supplied
683 name (when authenticating a server).
684 A pattern may also be preceded by
686 to indicate negation: if the host name matches a negated
687 pattern, it is not accepted (by that line) even if it matched another
689 A hostname or address may optionally be enclosed within
693 brackets then followed by
695 and a non-standard port number.
697 Alternately, hostnames may be stored in a hashed form which hides host names
698 and addresses should the file's contents be disclosed.
699 Hashed hostnames start with a
702 Only one hashed hostname may appear on a single line and none of the above
703 negation or wildcard operators may be applied.
705 Bits, exponent, and modulus are taken directly from the RSA host key; they
706 can be obtained, for example, from
707 .Pa /etc/ssh/ssh_host_key.pub .
708 The optional comment field continues to the end of the line, and is not used.
712 and empty lines are ignored as comments.
714 When performing host authentication, authentication is accepted if any
715 matching line has the proper key; either one that matches exactly or,
716 if the server has presented a certificate for authentication, the key
717 of the certification authority that signed the certificate.
718 For a key to be trusted as a certification authority, it must use the
720 marker described above.
722 The known hosts file also provides a facility to mark keys as revoked,
723 for example when it is known that the associated private key has been
725 Revoked keys are specified by including the
727 marker at the beginning of the key line, and are never accepted for
728 authentication or as certification authorities, but instead will
729 produce a warning from
731 when they are encountered.
733 It is permissible (but not
734 recommended) to have several lines or different host keys for the same
736 This will inevitably happen when short forms of host names
737 from different domains are put in the file.
739 that the files contain conflicting information; authentication is
740 accepted if valid information can be found from either file.
742 Note that the lines in these files are typically hundreds of characters
743 long, and you definitely don't want to type in the host keys by hand.
744 Rather, generate them by a script,
747 .Pa /etc/ssh/ssh_host_key.pub
748 and adding the host names at the front.
750 also offers some basic automated editing for
751 .Pa ~/.ssh/known_hosts
752 including removing hosts matching a host name and converting all host
753 names to their hashed representations.
755 An example ssh_known_hosts file:
756 .Bd -literal -offset 3n
757 # Comments allowed at start of line
758 closenet,...,192.0.2.53 1024 37 159...93 closenet.example.net
759 cvs.example.net,192.0.2.10 ssh-rsa AAAA1234.....=
761 |1|JfKTdBh7rNbXkVAQCRp4OQoPfmI=|USECr3SWf1JUPsms5AqfD5QfxkM= ssh-rsa
764 @revoked * ssh-rsa AAAAB5W...
765 # A CA key, accepted for any host in *.mydomain.com or *.mydomain.org
766 @cert-authority *.mydomain.org,*.mydomain.com ssh-rsa AAAAB5W...
769 .Bl -tag -width Ds -compact
771 This file is used to suppress printing the last login time and
779 It does not suppress printing of the banner specified by
783 This file is used for host-based authentication (see
785 for more information).
786 On some machines this file may need to be
787 world-readable if the user's home directory is on an NFS partition,
791 Additionally, this file must be owned by the user,
792 and must not have write permissions for anyone else.
794 permission for most machines is read/write for the user, and not
795 accessible by others.
798 This file is used in exactly the same way as
800 but allows host-based authentication without permitting login with
804 This directory is the default location for all user-specific configuration
805 and authentication information.
806 There is no general requirement to keep the entire contents of this directory
807 secret, but the recommended permissions are read/write/execute for the user,
808 and not accessible by others.
810 .It Pa ~/.ssh/authorized_keys
811 Lists the public keys (DSA, ECDSA, ED25519, RSA)
812 that can be used for logging in as this user.
813 The format of this file is described above.
814 The content of the file is not highly sensitive, but the recommended
815 permissions are read/write for the user, and not accessible by others.
819 directory, or the user's home directory are writable
820 by other users, then the file could be modified or replaced by unauthorized
824 will not allow it to be used unless the
826 option has been set to
829 .It Pa ~/.ssh/environment
830 This file is read into the environment at login (if it exists).
831 It can only contain empty lines, comment lines (that start with
833 and assignment lines of the form name=value.
834 The file should be writable
835 only by the user; it need not be readable by anyone else.
836 Environment processing is disabled by default and is
838 .Cm PermitUserEnvironment
841 .It Pa ~/.ssh/known_hosts
842 Contains a list of host keys for all hosts the user has logged into
843 that are not already in the systemwide list of known host keys.
844 The format of this file is described above.
845 This file should be writable only by root/the owner and
846 can, but need not be, world-readable.
849 Contains initialization routines to be run before
850 the user's home directory becomes accessible.
851 This file should be writable only by the user, and need not be
852 readable by anyone else.
854 .It Pa /etc/hosts.allow
855 .It Pa /etc/hosts.deny
856 Access controls that should be enforced by tcp-wrappers are defined here.
857 Further details are described in
860 .It Pa /etc/hosts.equiv
861 This file is for host-based authentication (see
863 It should only be writable by root.
866 Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange".
867 The file format is described in
877 refuses to let anyone except root log in.
878 The contents of the file
879 are displayed to anyone trying to log in, and non-root connections are
881 The file should be world-readable.
883 .It Pa /etc/ssh/shosts.equiv
884 This file is used in exactly the same way as
886 but allows host-based authentication without permitting login with
889 .It Pa /etc/ssh/ssh_host_key
890 .It Pa /etc/ssh/ssh_host_dsa_key
891 .It Pa /etc/ssh/ssh_host_ecdsa_key
892 .It Pa /etc/ssh/ssh_host_ed25519_key
893 .It Pa /etc/ssh/ssh_host_rsa_key
894 These files contain the private parts of the host keys.
895 These files should only be owned by root, readable only by root, and not
896 accessible to others.
899 does not start if these files are group/world-accessible.
901 .It Pa /etc/ssh/ssh_host_key.pub
902 .It Pa /etc/ssh/ssh_host_dsa_key.pub
903 .It Pa /etc/ssh/ssh_host_ecdsa_key.pub
904 .It Pa /etc/ssh/ssh_host_ed25519_key.pub
905 .It Pa /etc/ssh/ssh_host_rsa_key.pub
906 These files contain the public parts of the host keys.
907 These files should be world-readable but writable only by
909 Their contents should match the respective private parts.
911 really used for anything; they are provided for the convenience of
912 the user so their contents can be copied to known hosts files.
913 These files are created using
916 .It Pa /etc/ssh/ssh_known_hosts
917 Systemwide list of known host keys.
918 This file should be prepared by the
919 system administrator to contain the public host keys of all machines in the
921 The format of this file is described above.
922 This file should be writable only by root/the owner and
923 should be world-readable.
925 .It Pa /etc/ssh/sshd_config
926 Contains configuration data for
928 The file format and configuration options are described in
931 .It Pa /etc/ssh/sshrc
934 it can be used to specify
935 machine-specific login-time initializations globally.
936 This file should be writable only by root, and should be world-readable.
942 during privilege separation in the pre-authentication phase.
943 The directory should not contain any files and must be owned by root
944 and not group or world-writable.
946 .It Pa /var/run/sshd.pid
947 Contains the process ID of the
949 listening for connections (if there are several daemons running
950 concurrently for different ports, this contains the process ID of the one
952 The content of this file is not sensitive; it can be world-readable.
969 OpenSSH is a derivative of the original and free
970 ssh 1.2.12 release by Tatu Ylonen.
971 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
972 Theo de Raadt and Dug Song
973 removed many bugs, re-added newer features and
975 Markus Friedl contributed the support for SSH
976 protocol versions 1.5 and 2.0.
977 Niels Provos and Markus Friedl contributed support
978 for privilege separation.
980 System security is not improved unless
985 are disabled (thus completely disabling