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 1.266 2012/06/18 12:07:07 dtucker Exp $
37 .Dd $Mdocdate: June 18 2012 $
42 .Nd OpenSSH SSH daemon
48 .Op Fl C Ar connection_spec
49 .Op Fl c Ar host_certificate_file
50 .Op Fl f Ar config_file
51 .Op Fl g Ar login_grace_time
52 .Op Fl h Ar host_key_file
53 .Op Fl k Ar key_gen_time
60 (OpenSSH Daemon) is the daemon program for
62 Together these programs replace
66 and provide secure encrypted communications between two untrusted hosts
67 over an insecure network.
70 listens for connections from clients.
71 It is normally started at boot from
74 daemon for each incoming connection.
75 The forked daemons handle
76 key exchange, encryption, authentication, command execution,
80 can be configured using command-line options or a configuration file
83 command-line options override values specified in the
86 rereads its configuration file when it receives a hangup signal,
88 by executing itself with the name and options it was started with, e.g.\&
91 The options are as follows:
96 to use IPv4 addresses only.
100 to use IPv6 addresses only.
102 Specifies the number of bits in the ephemeral protocol version 1
103 server key (default 1024).
104 .It Fl C Ar connection_spec
105 Specify the connection parameters to use for the
110 directives in the configuration file
111 that would apply to the specified user, host, and address will be set before
112 the configuration is written to standard output.
113 The connection parameters are supplied as keyword=value pairs.
121 All are required and may be supplied in any order, either with multiple
123 options or as a comma-separated list.
124 .It Fl c Ar host_certificate_file
125 Specifies a path to a certificate file to identify
128 The certificate file must match a host key file specified using the
132 configuration directive.
134 When this option is specified,
136 will not detach and does not become a daemon.
137 This allows easy monitoring of
141 The server sends verbose debug output to standard error,
142 and does not put itself in the background.
143 The server also will not fork and will only process one connection.
144 This option is only intended for debugging for the server.
147 options increase the debugging level.
150 When this option is specified,
152 will send the output to the standard error instead of the system log.
153 .It Fl f Ar config_file
154 Specifies the name of the configuration file.
156 .Pa /etc/ssh/sshd_config .
158 refuses to start if there is no configuration file.
159 .It Fl g Ar login_grace_time
160 Gives the grace time for clients to authenticate themselves (default
162 If the client fails to authenticate the user within
163 this many seconds, the server disconnects and exits.
164 A value of zero indicates no limit.
165 .It Fl h Ar host_key_file
166 Specifies a file from which a host key is read.
167 This option must be given if
169 is not run as root (as the normal
170 host key files are normally not readable by anyone but root).
172 .Pa /etc/ssh/ssh_host_key
173 for protocol version 1, and
174 .Pa /etc/ssh/ssh_host_dsa_key ,
175 .Pa /etc/ssh/ssh_host_ecdsa_key
177 .Pa /etc/ssh/ssh_host_rsa_key
178 for protocol version 2.
179 It is possible to have multiple host key files for
180 the different protocol versions and host key algorithms.
188 from inetd because it needs to generate the server key before it can
189 respond to the client, and this may take tens of seconds.
190 Clients would have to wait too long if the key was regenerated every time.
191 However, with small key sizes (e.g. 512) using
195 .It Fl k Ar key_gen_time
196 Specifies how often the ephemeral protocol version 1 server key is
197 regenerated (default 3600 seconds, or one hour).
198 The motivation for regenerating the key fairly
199 often is that the key is not stored anywhere, and after about an hour
200 it becomes impossible to recover the key for decrypting intercepted
201 communications even if the machine is cracked into or physically
203 A value of zero indicates that the key will never be regenerated.
205 Can be used to give options in the format used in the configuration file.
206 This is useful for specifying options for which there is no separate
208 For full details of the options, and their values, see
211 Specifies the port on which the server listens for connections
213 Multiple port options are permitted.
214 Ports specified in the configuration file with the
216 option are ignored when a command-line port is specified.
217 Ports specified using the
219 option override command-line ports.
222 Nothing is sent to the system log.
223 Normally the beginning,
224 authentication, and termination of each connection is logged.
227 Check the validity of the configuration file, output the effective configuration
228 to stdout and then exit.
231 rules may be applied by specifying the connection parameters using one or more
236 Only check the validity of the configuration file and sanity of the keys.
237 This is useful for updating
239 reliably as configuration options may change.
241 This option is used to specify the size of the field
244 structure that holds the remote host name.
245 If the resolved host name is longer than
247 the dotted decimal value will be used instead.
248 This allows hosts with very long host names that
249 overflow this field to still be uniquely identified.
252 indicates that only dotted decimal addresses
253 should be put into the
257 may also be used to prevent
259 from making DNS requests unless the authentication
260 mechanism or configuration requires it.
261 Authentication mechanisms that may require DNS include
262 .Cm RhostsRSAAuthentication ,
263 .Cm HostbasedAuthentication ,
265 .Cm from="pattern-list"
266 option in a key file.
267 Configuration options that require DNS include using a
274 The OpenSSH SSH daemon supports SSH protocols 1 and 2.
275 The default is to use protocol 2 only,
276 though this can be changed via the
280 Protocol 2 supports DSA, ECDSA and RSA keys;
281 protocol 1 only supports RSA keys.
283 each host has a host-specific key,
285 used to identify the host.
287 Forward security for protocol 1 is provided through
288 an additional server key,
290 generated when the server starts.
291 This key is normally regenerated every hour if it has been used, and
292 is never stored on disk.
293 Whenever a client connects, the daemon responds with its public
294 host and server keys.
295 The client compares the
296 RSA host key against its own database to verify that it has not changed.
297 The client then generates a 256-bit random number.
299 random number using both the host key and the server key, and sends
300 the encrypted number to the server.
301 Both sides then use this
302 random number as a session key which is used to encrypt all further
303 communications in the session.
304 The rest of the session is encrypted
305 using a conventional cipher, currently Blowfish or 3DES, with 3DES
306 being used by default.
307 The client selects the encryption algorithm
308 to use from those offered by the server.
311 forward security is provided through a Diffie-Hellman key agreement.
312 This key agreement results in a shared session key.
313 The rest of the session is encrypted using a symmetric cipher, currently
314 128-bit AES, Blowfish, 3DES, CAST128, Arcfour, 192-bit AES, or 256-bit AES.
315 The client selects the encryption algorithm
316 to use from those offered by the server.
317 Additionally, session integrity is provided
318 through a cryptographic message authentication code
319 (hmac-md5, hmac-sha1, umac-64, hmac-ripemd160,
320 hmac-sha2-256 or hmac-sha2-512).
322 Finally, the server and the client enter an authentication dialog.
323 The client tries to authenticate itself using
324 host-based authentication,
325 public key authentication,
326 challenge-response authentication,
327 or password authentication.
329 Regardless of the authentication type, the account is checked to
330 ensure that it is accessible. An account is not accessible if it is
333 or its group is listed in
335 \&. The definition of a locked account is system dependant. Some platforms
336 have their own account database (eg AIX) and some modify the passwd field (
338 on Solaris and UnixWare,
345 on FreeBSD and a leading
348 If there is a requirement to disable password authentication
349 for the account while allowing still public-key, then the passwd field
350 should be set to something other than these values (eg
356 If the client successfully authenticates itself, a dialog for
357 preparing the session is entered.
358 At this time the client may request
359 things like allocating a pseudo-tty, forwarding X11 connections,
360 forwarding TCP connections, or forwarding the authentication agent
361 connection over the secure channel.
363 After this, the client either requests a shell or execution of a command.
364 The sides then enter session mode.
365 In this mode, either side may send
366 data at any time, and such data is forwarded to/from the shell or
367 command on the server side, and the user terminal in the client side.
369 When the user program terminates and all forwarded X11 and other
370 connections have been closed, the server sends command exit status to
371 the client, and both sides exit.
373 When a user successfully logs in,
376 .Bl -enum -offset indent
378 If the login is on a tty, and no command has been specified,
379 prints last login time and
381 (unless prevented in the configuration file or by
387 If the login is on a tty, records login time.
391 if it exists, prints contents and quits
394 Changes to run with normal user privileges.
396 Sets up basic environment.
399 .Pa ~/.ssh/environment ,
400 if it exists, and users are allowed to change their environment.
402 .Cm PermitUserEnvironment
406 Changes to user's home directory.
410 exists, runs it; else if
413 it; otherwise runs xauth.
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 files containing public keys for
469 public key authentication;
470 if none is specified, the default is
471 .Pa ~/.ssh/authorized_keys
473 .Pa ~/.ssh/authorized_keys2 .
474 Each line of the file contains one
475 key (empty lines and lines starting with a
479 Protocol 1 public keys consist of the following space-separated fields:
480 options, bits, exponent, modulus, comment.
481 Protocol 2 public key consist of:
482 options, keytype, base64-encoded key, comment.
483 The options field is optional;
484 its presence is determined by whether the line starts
485 with a number or not (the options field never starts with a number).
486 The bits, exponent, modulus, and comment fields give the RSA key for
487 protocol version 1; the
488 comment field is not used for anything (but may be convenient for the
489 user to identify the key).
490 For protocol version 2 the keytype is
491 .Dq ecdsa-sha2-nistp256 ,
492 .Dq ecdsa-sha2-nistp384 ,
493 .Dq ecdsa-sha2-nistp521 ,
498 Note that lines in this file are usually several hundred bytes long
499 (because of the size of the public key encoding) up to a limit of
500 8 kilobytes, which permits DSA keys up to 8 kilobits and RSA
501 keys up to 16 kilobits.
502 You don't want to type them in; instead, copy the
511 enforces a minimum RSA key modulus size for protocol 1
512 and protocol 2 keys of 768 bits.
514 The options (if present) consist of comma-separated option
516 No spaces are permitted, except within double quotes.
517 The following option specifications are supported (note
518 that option keywords are case-insensitive):
520 .It Cm cert-authority
521 Specifies that the listed key is a certification authority (CA) that is
522 trusted to validate signed certificates for user authentication.
524 Certificates may encode access restrictions similar to these key options.
525 If both certificate restrictions and key options are present, the most
526 restrictive union of the two is applied.
527 .It Cm command="command"
528 Specifies that the command is executed whenever this key is used for
530 The command supplied by the user (if any) is ignored.
531 The command is run on a pty if the client requests a pty;
532 otherwise it is run without a tty.
533 If an 8-bit clean channel is required,
534 one must not request a pty or should specify
536 A quote may be included in the command by quoting it with a backslash.
537 This option might be useful
538 to restrict certain public keys to perform just a specific operation.
539 An example might be a key that permits remote backups but nothing else.
540 Note that the client may specify TCP and/or X11
541 forwarding unless they are explicitly prohibited.
542 The command originally supplied by the client is available in the
543 .Ev SSH_ORIGINAL_COMMAND
544 environment variable.
545 Note that this option applies to shell, command or subsystem execution.
546 Also note that this command may be superseded by either a
549 directive or a command embedded in a certificate.
550 .It Cm environment="NAME=value"
551 Specifies that the string is to be added to the environment when
552 logging in using this key.
553 Environment variables set this way
554 override other default environment values.
555 Multiple options of this type are permitted.
556 Environment processing is disabled by default and is
558 .Cm PermitUserEnvironment
560 This option is automatically disabled if
563 .It Cm from="pattern-list"
564 Specifies that in addition to public key authentication, either the canonical
565 name of the remote host or its IP address must be present in the
566 comma-separated list of patterns.
571 for more information on patterns.
573 In addition to the wildcard matching that may be applied to hostnames or
576 stanza may match IP addresses using CIDR address/masklen notation.
578 The purpose of this option is to optionally increase security: public key
579 authentication by itself does not trust the network or name servers or
580 anything (but the key); however, if somebody somehow steals the key, the key
581 permits an intruder to log in from anywhere in the world.
582 This additional option makes using a stolen key more difficult (name
583 servers and/or routers would have to be compromised in addition to
585 .It Cm no-agent-forwarding
586 Forbids authentication agent forwarding when this key is used for
588 .It Cm no-port-forwarding
589 Forbids TCP forwarding when this key is used for authentication.
590 Any port forward requests by the client will return an error.
591 This might be used, e.g. in connection with the
595 Prevents tty allocation (a request to allocate a pty will fail).
597 Disables execution of
599 .It Cm no-X11-forwarding
600 Forbids X11 forwarding when this key is used for authentication.
601 Any X11 forward requests by the client will return an error.
602 .It Cm permitopen="host:port"
605 port forwarding such that it may only connect to the specified host and
607 IPv6 addresses can be specified by enclosing the address in square brackets.
610 options may be applied separated by commas.
611 No pattern matching is performed on the specified hostnames,
612 they must be literal domains or addresses.
613 A port specification of
616 .It Cm principals="principals"
619 line, specifies allowed principals for certificate authentication as a
620 comma-separated list.
621 At least one name from the list must appear in the certificate's
622 list of principals for the certificate to be accepted.
623 This option is ignored for keys that are not marked as trusted certificate
630 device on the server.
631 Without this option, the next available device will be used if
632 the client requests a tunnel.
635 An example authorized_keys file:
636 .Bd -literal -offset 3n
637 # Comments allowed at start of line
638 ssh-rsa AAAAB3Nza...LiPk== user@example.net
639 from="*.sales.example.net,!pc.sales.example.net" ssh-rsa
640 AAAAB2...19Q== john@example.net
641 command="dump /home",no-pty,no-port-forwarding ssh-dss
642 AAAAC3...51R== example.net
643 permitopen="192.0.2.1:80",permitopen="192.0.2.2:25" ssh-dss
645 tunnel="0",command="sh /etc/netstart tun0" ssh-rsa AAAA...==
648 .Sh SSH_KNOWN_HOSTS FILE FORMAT
650 .Pa /etc/ssh/ssh_known_hosts
652 .Pa ~/.ssh/known_hosts
653 files contain host public keys for all known hosts.
654 The global file should
655 be prepared by the administrator (optional), and the per-user file is
656 maintained automatically: whenever the user connects from an unknown host,
657 its key is added to the per-user file.
659 Each line in these files contains the following fields: markers (optional),
660 hostnames, bits, exponent, modulus, comment.
661 The fields are separated by spaces.
663 The marker is optional, but if it is present then it must be one of
664 .Dq @cert-authority ,
665 to indicate that the line contains a certification authority (CA) key,
668 to indicate that the key contained on the line is revoked and must not ever
670 Only one marker should be used on a key line.
672 Hostnames is a comma-separated list of patterns
677 wildcards); each pattern in turn is matched against the canonical host
678 name (when authenticating a client) or against the user-supplied
679 name (when authenticating a server).
680 A pattern may also be preceded by
682 to indicate negation: if the host name matches a negated
683 pattern, it is not accepted (by that line) even if it matched another
685 A hostname or address may optionally be enclosed within
689 brackets then followed by
691 and a non-standard port number.
693 Alternately, hostnames may be stored in a hashed form which hides host names
694 and addresses should the file's contents be disclosed.
695 Hashed hostnames start with a
698 Only one hashed hostname may appear on a single line and none of the above
699 negation or wildcard operators may be applied.
701 Bits, exponent, and modulus are taken directly from the RSA host key; they
702 can be obtained, for example, from
703 .Pa /etc/ssh/ssh_host_key.pub .
704 The optional comment field continues to the end of the line, and is not used.
708 and empty lines are ignored as comments.
710 When performing host authentication, authentication is accepted if any
711 matching line has the proper key; either one that matches exactly or,
712 if the server has presented a certificate for authentication, the key
713 of the certification authority that signed the certificate.
714 For a key to be trusted as a certification authority, it must use the
716 marker described above.
718 The known hosts file also provides a facility to mark keys as revoked,
719 for example when it is known that the associated private key has been
721 Revoked keys are specified by including the
723 marker at the beginning of the key line, and are never accepted for
724 authentication or as certification authorities, but instead will
725 produce a warning from
727 when they are encountered.
729 It is permissible (but not
730 recommended) to have several lines or different host keys for the same
732 This will inevitably happen when short forms of host names
733 from different domains are put in the file.
735 that the files contain conflicting information; authentication is
736 accepted if valid information can be found from either file.
738 Note that the lines in these files are typically hundreds of characters
739 long, and you definitely don't want to type in the host keys by hand.
740 Rather, generate them by a script,
743 .Pa /etc/ssh/ssh_host_key.pub
744 and adding the host names at the front.
746 also offers some basic automated editing for
747 .Pa ~/.ssh/known_hosts
748 including removing hosts matching a host name and converting all host
749 names to their hashed representations.
751 An example ssh_known_hosts file:
752 .Bd -literal -offset 3n
753 # Comments allowed at start of line
754 closenet,...,192.0.2.53 1024 37 159...93 closenet.example.net
755 cvs.example.net,192.0.2.10 ssh-rsa AAAA1234.....=
757 |1|JfKTdBh7rNbXkVAQCRp4OQoPfmI=|USECr3SWf1JUPsms5AqfD5QfxkM= ssh-rsa
760 @revoked * ssh-rsa AAAAB5W...
761 # A CA key, accepted for any host in *.mydomain.com or *.mydomain.org
762 @cert-authority *.mydomain.org,*.mydomain.com ssh-rsa AAAAB5W...
765 .Bl -tag -width Ds -compact
767 This file is used to suppress printing the last login time and
775 It does not suppress printing of the banner specified by
779 This file is used for host-based authentication (see
781 for more information).
782 On some machines this file may need to be
783 world-readable if the user's home directory is on an NFS partition,
787 Additionally, this file must be owned by the user,
788 and must not have write permissions for anyone else.
790 permission for most machines is read/write for the user, and not
791 accessible by others.
794 This file is used in exactly the same way as
796 but allows host-based authentication without permitting login with
800 This directory is the default location for all user-specific configuration
801 and authentication information.
802 There is no general requirement to keep the entire contents of this directory
803 secret, but the recommended permissions are read/write/execute for the user,
804 and not accessible by others.
806 .It Pa ~/.ssh/authorized_keys
807 Lists the public keys (DSA/ECDSA/RSA) that can be used for logging in
809 The format of this file is described above.
810 The content of the file is not highly sensitive, but the recommended
811 permissions are read/write for the user, and not accessible by others.
815 directory, or the user's home directory are writable
816 by other users, then the file could be modified or replaced by unauthorized
820 will not allow it to be used unless the
822 option has been set to
825 .It Pa ~/.ssh/environment
826 This file is read into the environment at login (if it exists).
827 It can only contain empty lines, comment lines (that start with
829 and assignment lines of the form name=value.
830 The file should be writable
831 only by the user; it need not be readable by anyone else.
832 Environment processing is disabled by default and is
834 .Cm PermitUserEnvironment
837 .It Pa ~/.ssh/known_hosts
838 Contains a list of host keys for all hosts the user has logged into
839 that are not already in the systemwide list of known host keys.
840 The format of this file is described above.
841 This file should be writable only by root/the owner and
842 can, but need not be, world-readable.
845 Contains initialization routines to be run before
846 the user's home directory becomes accessible.
847 This file should be writable only by the user, and need not be
848 readable by anyone else.
850 .It Pa /etc/hosts.allow
851 .It Pa /etc/hosts.deny
852 Access controls that should be enforced by tcp-wrappers are defined here.
853 Further details are described in
856 .It Pa /etc/hosts.equiv
857 This file is for host-based authentication (see
859 It should only be writable by root.
862 Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange".
863 The file format is described in
873 refuses to let anyone except root log in.
874 The contents of the file
875 are displayed to anyone trying to log in, and non-root connections are
877 The file should be world-readable.
879 .It Pa /etc/shosts.equiv
880 This file is used in exactly the same way as
882 but allows host-based authentication without permitting login with
885 .It Pa /etc/ssh/ssh_host_key
886 .It Pa /etc/ssh/ssh_host_dsa_key
887 .It Pa /etc/ssh/ssh_host_ecdsa_key
888 .It Pa /etc/ssh/ssh_host_rsa_key
889 These files contain the private parts of the host keys.
890 These files should only be owned by root, readable only by root, and not
891 accessible to others.
894 does not start if these files are group/world-accessible.
896 .It Pa /etc/ssh/ssh_host_key.pub
897 .It Pa /etc/ssh/ssh_host_dsa_key.pub
898 .It Pa /etc/ssh/ssh_host_ecdsa_key.pub
899 .It Pa /etc/ssh/ssh_host_rsa_key.pub
900 These files contain the public parts of the host keys.
901 These files should be world-readable but writable only by
903 Their contents should match the respective private parts.
905 really used for anything; they are provided for the convenience of
906 the user so their contents can be copied to known hosts files.
907 These files are created using
910 .It Pa /etc/ssh/ssh_known_hosts
911 Systemwide list of known host keys.
912 This file should be prepared by the
913 system administrator to contain the public host keys of all machines in the
915 The format of this file is described above.
916 This file should be writable only by root/the owner and
917 should be world-readable.
919 .It Pa /etc/ssh/sshd_config
920 Contains configuration data for
922 The file format and configuration options are described in
925 .It Pa /etc/ssh/sshrc
928 it can be used to specify
929 machine-specific login-time initializations globally.
930 This file should be writable only by root, and should be world-readable.
936 during privilege separation in the pre-authentication phase.
937 The directory should not contain any files and must be owned by root
938 and not group or world-writable.
940 .It Pa /var/run/sshd.pid
941 Contains the process ID of the
943 listening for connections (if there are several daemons running
944 concurrently for different ports, this contains the process ID of the one
946 The content of this file is not sensitive; it can be world-readable.
964 OpenSSH is a derivative of the original and free
965 ssh 1.2.12 release by Tatu Ylonen.
966 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
967 Theo de Raadt and Dug Song
968 removed many bugs, re-added newer features and
970 Markus Friedl contributed the support for SSH
971 protocol versions 1.5 and 2.0.
972 Niels Provos and Markus Friedl contributed support
973 for privilege separation.
975 System security is not improved unless
980 are disabled (thus completely disabling