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 1.260 2010/10/28 18:33:28 jmc Exp $
43 .Nd OpenSSH SSH daemon
49 .Op Fl C Ar connection_spec
50 .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.
120 All are required and may be supplied in any order, either with multiple
122 options or as a comma-separated list.
123 .It Fl c Ar host_certificate_file
124 Specifies a path to a certificate file to identify
127 The certificate file must match a host key file specified using the
131 configuration directive.
133 When this option is specified,
135 will not detach and does not become a daemon.
136 This allows easy monitoring of
140 The server sends verbose debug output to standard error,
141 and does not put itself in the background.
142 The server also will not fork and will only process one connection.
143 This option is only intended for debugging for the server.
146 options increase the debugging level.
149 When this option is specified,
151 will send the output to the standard error instead of the system log.
152 .It Fl f Ar config_file
153 Specifies the name of the configuration file.
155 .Pa /etc/ssh/sshd_config .
157 refuses to start if there is no configuration file.
158 .It Fl g Ar login_grace_time
159 Gives the grace time for clients to authenticate themselves (default
161 If the client fails to authenticate the user within
162 this many seconds, the server disconnects and exits.
163 A value of zero indicates no limit.
164 .It Fl h Ar host_key_file
165 Specifies a file from which a host key is read.
166 This option must be given if
168 is not run as root (as the normal
169 host key files are normally not readable by anyone but root).
171 .Pa /etc/ssh/ssh_host_key
172 for protocol version 1, and
173 .Pa /etc/ssh/ssh_host_dsa_key ,
174 .Pa /etc/ssh/ssh_host_ecdsa_key
176 .Pa /etc/ssh/ssh_host_rsa_key
177 for protocol version 2.
178 It is possible to have multiple host key files for
179 the different protocol versions and host key algorithms.
187 from inetd because it needs to generate the server key before it can
188 respond to the client, and this may take tens of seconds.
189 Clients would have to wait too long if the key was regenerated every time.
190 However, with small key sizes (e.g. 512) using
194 .It Fl k Ar key_gen_time
195 Specifies how often the ephemeral protocol version 1 server key is
196 regenerated (default 3600 seconds, or one hour).
197 The motivation for regenerating the key fairly
198 often is that the key is not stored anywhere, and after about an hour
199 it becomes impossible to recover the key for decrypting intercepted
200 communications even if the machine is cracked into or physically
202 A value of zero indicates that the key will never be regenerated.
204 Can be used to give options in the format used in the configuration file.
205 This is useful for specifying options for which there is no separate
207 For full details of the options, and their values, see
210 Specifies the port on which the server listens for connections
212 Multiple port options are permitted.
213 Ports specified in the configuration file with the
215 option are ignored when a command-line port is specified.
216 Ports specified using the
218 option override command-line ports.
221 Nothing is sent to the system log.
222 Normally the beginning,
223 authentication, and termination of each connection is logged.
226 Check the validity of the configuration file, output the effective configuration
227 to stdout and then exit.
230 rules may be applied by specifying the connection parameters using one or more
235 Only check the validity of the configuration file and sanity of the keys.
236 This is useful for updating
238 reliably as configuration options may change.
240 This option is used to specify the size of the field
243 structure that holds the remote host name.
244 If the resolved host name is longer than
246 the dotted decimal value will be used instead.
247 This allows hosts with very long host names that
248 overflow this field to still be uniquely identified.
251 indicates that only dotted decimal addresses
252 should be put into the
256 may also be used to prevent
258 from making DNS requests unless the authentication
259 mechanism or configuration requires it.
260 Authentication mechanisms that may require DNS include
261 .Cm RhostsRSAAuthentication ,
262 .Cm HostbasedAuthentication ,
264 .Cm from="pattern-list"
265 option in a key file.
266 Configuration options that require DNS include using a
273 The OpenSSH SSH daemon supports SSH protocols 1 and 2.
274 The default is to use protocol 2 only,
275 though this can be changed via the
279 Protocol 2 supports DSA, ECDSA and RSA keys;
280 protocol 1 only supports RSA keys.
282 each host has a host-specific key,
284 used to identify the host.
286 Forward security for protocol 1 is provided through
287 an additional server key,
289 generated when the server starts.
290 This key is normally regenerated every hour if it has been used, and
291 is never stored on disk.
292 Whenever a client connects, the daemon responds with its public
293 host and server keys.
294 The client compares the
295 RSA host key against its own database to verify that it has not changed.
296 The client then generates a 256-bit random number.
298 random number using both the host key and the server key, and sends
299 the encrypted number to the server.
300 Both sides then use this
301 random number as a session key which is used to encrypt all further
302 communications in the session.
303 The rest of the session is encrypted
304 using a conventional cipher, currently Blowfish or 3DES, with 3DES
305 being used by default.
306 The client selects the encryption algorithm
307 to use from those offered by the server.
310 forward security is provided through a Diffie-Hellman key agreement.
311 This key agreement results in a shared session key.
312 The rest of the session is encrypted using a symmetric cipher, currently
313 128-bit AES, Blowfish, 3DES, CAST128, Arcfour, 192-bit AES, or 256-bit AES.
314 The client selects the encryption algorithm
315 to use from those offered by the server.
316 Additionally, session integrity is provided
317 through a cryptographic message authentication code
318 (hmac-md5, hmac-sha1, umac-64 or hmac-ripemd160).
320 Finally, the server and the client enter an authentication dialog.
321 The client tries to authenticate itself using
322 host-based authentication,
323 public key authentication,
324 challenge-response authentication,
325 or password authentication.
327 Regardless of the authentication type, the account is checked to
328 ensure that it is accessible. An account is not accessible if it is
331 or its group is listed in
333 \&. The definition of a locked account is system dependant. Some platforms
334 have their own account database (eg AIX) and some modify the passwd field (
336 on Solaris and UnixWare,
343 on FreeBSD and a leading
346 If there is a requirement to disable password authentication
347 for the account while allowing still public-key, then the passwd field
348 should be set to something other than these values (eg
354 If the client successfully authenticates itself, a dialog for
355 preparing the session is entered.
356 At this time the client may request
357 things like allocating a pseudo-tty, forwarding X11 connections,
358 forwarding TCP connections, or forwarding the authentication agent
359 connection over the secure channel.
361 After this, the client either requests a shell or execution of a command.
362 The sides then enter session mode.
363 In this mode, either side may send
364 data at any time, and such data is forwarded to/from the shell or
365 command on the server side, and the user terminal in the client side.
367 When the user program terminates and all forwarded X11 and other
368 connections have been closed, the server sends command exit status to
369 the client, and both sides exit.
371 When a user successfully logs in,
374 .Bl -enum -offset indent
376 If the login is on a tty, and no command has been specified,
377 prints last login time and
379 (unless prevented in the configuration file or by
385 If the login is on a tty, records login time.
389 .Pa /var/run/nologin ;
390 if one exists, it prints the contents and quits
393 Changes to run with normal user privileges.
395 Sets up basic environment.
398 .Pa ~/.ssh/environment ,
399 if it exists, and users are allowed to change their environment.
401 .Cm PermitUserEnvironment
405 Changes to user's home directory.
409 exists, runs it; else if
416 files are given the X11
417 authentication protocol and cookie in standard input.
422 Runs user's shell or command.
429 runs it after reading the
430 environment files but before starting the user's shell or command.
431 It must not produce any output on stdout; stderr must be used
433 If X11 forwarding is in use, it will receive the "proto cookie" pair in
434 its standard input (and
441 will not run xauth automatically to add X11 cookies.
443 The primary purpose of this file is to run any initialization routines
444 which may be needed before the user's home directory becomes
445 accessible; AFS is a particular example of such an environment.
447 This file will probably contain some initialization code followed by
448 something similar to:
449 .Bd -literal -offset 3n
450 if read proto cookie && [ -n "$DISPLAY" ]; then
451 if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then
452 # X11UseLocalhost=yes
453 echo add unix:`echo $DISPLAY |
454 cut -c11-` $proto $cookie
457 echo add $DISPLAY $proto $cookie
462 If this file does not exist,
465 does not exist either, xauth is used to add the cookie.
466 .Sh AUTHORIZED_KEYS FILE FORMAT
467 .Cm AuthorizedKeysFile
468 specifies the file containing public keys for
469 public key authentication;
470 if none is specified, the default is
471 .Pa ~/.ssh/authorized_keys .
472 Each line of the file contains one
473 key (empty lines and lines starting with a
477 Protocol 1 public keys consist of the following space-separated fields:
478 options, bits, exponent, modulus, comment.
479 Protocol 2 public key consist of:
480 options, keytype, base64-encoded key, comment.
481 The options field is optional;
482 its presence is determined by whether the line starts
483 with a number or not (the options field never starts with a number).
484 The bits, exponent, modulus, and comment fields give the RSA key for
485 protocol version 1; the
486 comment field is not used for anything (but may be convenient for the
487 user to identify the key).
488 For protocol version 2 the keytype is
489 .Dq ecdsa-sha2-nistp256 ,
490 .Dq ecdsa-sha2-nistp384 ,
491 .Dq ecdsa-sha2-nistp521 ,
496 Note that lines in this file are usually several hundred bytes long
497 (because of the size of the public key encoding) up to a limit of
498 8 kilobytes, which permits DSA keys up to 8 kilobits and RSA
499 keys up to 16 kilobits.
500 You don't want to type them in; instead, copy the
509 enforces a minimum RSA key modulus size for protocol 1
510 and protocol 2 keys of 768 bits.
512 The options (if present) consist of comma-separated option
514 No spaces are permitted, except within double quotes.
515 The following option specifications are supported (note
516 that option keywords are case-insensitive):
518 .It Cm cert-authority
519 Specifies that the listed key is a certification authority (CA) that is
520 trusted to validate signed certificates for user authentication.
522 Certificates may encode access restrictions similar to these key options.
523 If both certificate restrictions and key options are present, the most
524 restrictive union of the two is applied.
525 .It Cm command="command"
526 Specifies that the command is executed whenever this key is used for
528 The command supplied by the user (if any) is ignored.
529 The command is run on a pty if the client requests a pty;
530 otherwise it is run without a tty.
531 If an 8-bit clean channel is required,
532 one must not request a pty or should specify
534 A quote may be included in the command by quoting it with a backslash.
535 This option might be useful
536 to restrict certain public keys to perform just a specific operation.
537 An example might be a key that permits remote backups but nothing else.
538 Note that the client may specify TCP and/or X11
539 forwarding unless they are explicitly prohibited.
540 The command originally supplied by the client is available in the
541 .Ev SSH_ORIGINAL_COMMAND
542 environment variable.
543 Note that this option applies to shell, command or subsystem execution.
544 Also note that this command may be superseded by either a
547 directive or a command embedded in a certificate.
548 .It Cm environment="NAME=value"
549 Specifies that the string is to be added to the environment when
550 logging in using this key.
551 Environment variables set this way
552 override other default environment values.
553 Multiple options of this type are permitted.
554 Environment processing is disabled by default and is
556 .Cm PermitUserEnvironment
558 This option is automatically disabled if
561 .It Cm from="pattern-list"
562 Specifies that in addition to public key authentication, either the canonical
563 name of the remote host or its IP address must be present in the
564 comma-separated list of patterns.
569 for more information on patterns.
571 In addition to the wildcard matching that may be applied to hostnames or
574 stanza may match IP addresses using CIDR address/masklen notation.
576 The purpose of this option is to optionally increase security: public key
577 authentication by itself does not trust the network or name servers or
578 anything (but the key); however, if somebody somehow steals the key, the key
579 permits an intruder to log in from anywhere in the world.
580 This additional option makes using a stolen key more difficult (name
581 servers and/or routers would have to be compromised in addition to
583 .It Cm no-agent-forwarding
584 Forbids authentication agent forwarding when this key is used for
586 .It Cm no-port-forwarding
587 Forbids TCP forwarding when this key is used for authentication.
588 Any port forward requests by the client will return an error.
589 This might be used, e.g. in connection with the
593 Prevents tty allocation (a request to allocate a pty will fail).
595 Disables execution of
597 .It Cm no-X11-forwarding
598 Forbids X11 forwarding when this key is used for authentication.
599 Any X11 forward requests by the client will return an error.
600 .It Cm permitopen="host:port"
603 port forwarding such that it may only connect to the specified host and
605 IPv6 addresses can be specified by enclosing the address in square brackets.
608 options may be applied separated by commas.
609 No pattern matching is performed on the specified hostnames,
610 they must be literal domains or addresses.
611 .It Cm principals="principals"
614 line, specifies allowed principals for certificate authentication as a
615 comma-separated list.
616 At least one name from the list must appear in the certificate's
617 list of principals for the certificate to be accepted.
618 This option is ignored for keys that are not marked as trusted certificate
625 device on the server.
626 Without this option, the next available device will be used if
627 the client requests a tunnel.
630 An example authorized_keys file:
631 .Bd -literal -offset 3n
632 # Comments allowed at start of line
633 ssh-rsa AAAAB3Nza...LiPk== user@example.net
634 from="*.sales.example.net,!pc.sales.example.net" ssh-rsa
635 AAAAB2...19Q== john@example.net
636 command="dump /home",no-pty,no-port-forwarding ssh-dss
637 AAAAC3...51R== example.net
638 permitopen="192.0.2.1:80",permitopen="192.0.2.2:25" ssh-dss
640 tunnel="0",command="sh /etc/netstart tun0" ssh-rsa AAAA...==
643 .Sh SSH_KNOWN_HOSTS FILE FORMAT
645 .Pa /etc/ssh/ssh_known_hosts
647 .Pa ~/.ssh/known_hosts
648 files contain host public keys for all known hosts.
649 The global file should
650 be prepared by the administrator (optional), and the per-user file is
651 maintained automatically: whenever the user connects from an unknown host,
652 its key is added to the per-user file.
654 Each line in these files contains the following fields: markers (optional),
655 hostnames, bits, exponent, modulus, comment.
656 The fields are separated by spaces.
658 The marker is optional, but if it is present then it must be one of
659 .Dq @cert-authority ,
660 to indicate that the line contains a certification authority (CA) key,
663 to indicate that the key contained on the line is revoked and must not ever
665 Only one marker should be used on a key line.
667 Hostnames is a comma-separated list of patterns
672 wildcards); each pattern in turn is matched against the canonical host
673 name (when authenticating a client) or against the user-supplied
674 name (when authenticating a server).
675 A pattern may also be preceded by
677 to indicate negation: if the host name matches a negated
678 pattern, it is not accepted (by that line) even if it matched another
680 A hostname or address may optionally be enclosed within
684 brackets then followed by
686 and a non-standard port number.
688 Alternately, hostnames may be stored in a hashed form which hides host names
689 and addresses should the file's contents be disclosed.
690 Hashed hostnames start with a
693 Only one hashed hostname may appear on a single line and none of the above
694 negation or wildcard operators may be applied.
696 Bits, exponent, and modulus are taken directly from the RSA host key; they
697 can be obtained, for example, from
698 .Pa /etc/ssh/ssh_host_key.pub .
699 The optional comment field continues to the end of the line, and is not used.
703 and empty lines are ignored as comments.
705 When performing host authentication, authentication is accepted if any
706 matching line has the proper key; either one that matches exactly or,
707 if the server has presented a certificate for authentication, the key
708 of the certification authority that signed the certificate.
709 For a key to be trusted as a certification authority, it must use the
711 marker described above.
713 The known hosts file also provides a facility to mark keys as revoked,
714 for example when it is known that the associated private key has been
716 Revoked keys are specified by including the
718 marker at the beginning of the key line, and are never accepted for
719 authentication or as certification authorities, but instead will
720 produce a warning from
722 when they are encountered.
724 It is permissible (but not
725 recommended) to have several lines or different host keys for the same
727 This will inevitably happen when short forms of host names
728 from different domains are put in the file.
730 that the files contain conflicting information; authentication is
731 accepted if valid information can be found from either file.
733 Note that the lines in these files are typically hundreds of characters
734 long, and you definitely don't want to type in the host keys by hand.
735 Rather, generate them by a script,
738 .Pa /etc/ssh/ssh_host_key.pub
739 and adding the host names at the front.
741 also offers some basic automated editing for
742 .Pa ~/.ssh/known_hosts
743 including removing hosts matching a host name and converting all host
744 names to their hashed representations.
746 An example ssh_known_hosts file:
747 .Bd -literal -offset 3n
748 # Comments allowed at start of line
749 closenet,...,192.0.2.53 1024 37 159...93 closenet.example.net
750 cvs.example.net,192.0.2.10 ssh-rsa AAAA1234.....=
752 |1|JfKTdBh7rNbXkVAQCRp4OQoPfmI=|USECr3SWf1JUPsms5AqfD5QfxkM= ssh-rsa
755 @revoked * ssh-rsa AAAAB5W...
756 # A CA key, accepted for any host in *.mydomain.com or *.mydomain.org
757 @cert-authority *.mydomain.org,*.mydomain.com ssh-rsa AAAAB5W...
760 .Bl -tag -width Ds -compact
762 This file is used to suppress printing the last login time and
770 It does not suppress printing of the banner specified by
774 This file is used for host-based authentication (see
776 for more information).
777 On some machines this file may need to be
778 world-readable if the user's home directory is on an NFS partition,
782 Additionally, this file must be owned by the user,
783 and must not have write permissions for anyone else.
785 permission for most machines is read/write for the user, and not
786 accessible by others.
789 This file is used in exactly the same way as
791 but allows host-based authentication without permitting login with
795 This directory is the default location for all user-specific configuration
796 and authentication information.
797 There is no general requirement to keep the entire contents of this directory
798 secret, but the recommended permissions are read/write/execute for the user,
799 and not accessible by others.
801 .It Pa ~/.ssh/authorized_keys
802 Lists the public keys (DSA/ECDSA/RSA) that can be used for logging in
804 The format of this file is described above.
805 The content of the file is not highly sensitive, but the recommended
806 permissions are read/write for the user, and not accessible by others.
810 directory, or the user's home directory are writable
811 by other users, then the file could be modified or replaced by unauthorized
815 will not allow it to be used unless the
817 option has been set to
820 .It Pa ~/.ssh/environment
821 This file is read into the environment at login (if it exists).
822 It can only contain empty lines, comment lines (that start with
824 and assignment lines of the form name=value.
825 The file should be writable
826 only by the user; it need not be readable by anyone else.
827 Environment processing is disabled by default and is
829 .Cm PermitUserEnvironment
832 .It Pa ~/.ssh/known_hosts
833 Contains a list of host keys for all hosts the user has logged into
834 that are not already in the systemwide list of known host keys.
835 The format of this file is described above.
836 This file should be writable only by root/the owner and
837 can, but need not be, world-readable.
840 Contains initialization routines to be run before
841 the user's home directory becomes accessible.
842 This file should be writable only by the user, and need not be
843 readable by anyone else.
845 .It Pa /etc/hosts.allow
846 .It Pa /etc/hosts.deny
847 Access controls that should be enforced by tcp-wrappers are defined here.
848 Further details are described in
851 .It Pa /etc/hosts.equiv
852 This file is for host-based authentication (see
854 It should only be writable by root.
857 Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange".
858 The file format is described in
868 refuses to let anyone except root log in.
869 The contents of the file
870 are displayed to anyone trying to log in, and non-root connections are
872 The file should be world-readable.
874 .It Pa /etc/shosts.equiv
875 This file is used in exactly the same way as
877 but allows host-based authentication without permitting login with
880 .It Pa /etc/ssh/ssh_host_key
881 .It Pa /etc/ssh/ssh_host_dsa_key
882 .It Pa /etc/ssh/ssh_host_ecdsa_key
883 .It Pa /etc/ssh/ssh_host_rsa_key
884 These three files contain the private parts of the host keys.
885 These files should only be owned by root, readable only by root, and not
886 accessible to others.
889 does not start if these files are group/world-accessible.
891 .It Pa /etc/ssh/ssh_host_key.pub
892 .It Pa /etc/ssh/ssh_host_dsa_key.pub
893 .It Pa /etc/ssh/ssh_host_ecdsa_key.pub
894 .It Pa /etc/ssh/ssh_host_rsa_key.pub
895 These three files contain the public parts of the host keys.
896 These files should be world-readable but writable only by
898 Their contents should match the respective private parts.
900 really used for anything; they are provided for the convenience of
901 the user so their contents can be copied to known hosts files.
902 These files are created using
905 .It Pa /etc/ssh/ssh_known_hosts
906 Systemwide list of known host keys.
907 This file should be prepared by the
908 system administrator to contain the public host keys of all machines in the
910 The format of this file is described above.
911 This file should be writable only by root/the owner and
912 should be world-readable.
914 .It Pa /etc/ssh/sshd_config
915 Contains configuration data for
917 The file format and configuration options are described in
920 .It Pa /etc/ssh/sshrc
923 it can be used to specify
924 machine-specific login-time initializations globally.
925 This file should be writable only by root, and should be world-readable.
931 during privilege separation in the pre-authentication phase.
932 The directory should not contain any files and must be owned by root
933 and not group or world-writable.
935 .It Pa /var/run/sshd.pid
936 Contains the process ID of the
938 listening for connections (if there are several daemons running
939 concurrently for different ports, this contains the process ID of the one
941 The content of this file is not sensitive; it can be world-readable.
959 OpenSSH is a derivative of the original and free
960 ssh 1.2.12 release by Tatu Ylonen.
961 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
962 Theo de Raadt and Dug Song
963 removed many bugs, re-added newer features and
965 Markus Friedl contributed the support for SSH
966 protocol versions 1.5 and 2.0.
967 Niels Provos and Markus Friedl contributed support
968 for privilege separation.
970 System security is not improved unless
975 are disabled (thus completely disabling