1ntp.conf(5)                      File Formats                      ntp.conf(5)
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NAME

6       ntp.conf - Network Time Protocol (NTP) daemon configuration file format
7

SYNOPSIS

9       ntp.conf [--option-name] [--option-name value]
10
11       All arguments must be options.
12
13

DESCRIPTION

15       The  ntp.conf  configuration  file  is  read  at initial startup by the
16       ntpd(8) daemon in order to specify the synchronization  sources,  modes
17       and  other  related  information.  Usually, it is installed in the /etc
18       directory, but could be installed elsewhere (see the daemon's  -c  com‐
19       mand line option).
20
21       The file format is similar to other UNIX configuration files.  Comments
22       begin with a ‘#’ character and extend to the end  of  the  line;  blank
23       lines  are  ignored.  Configuration commands consist of an initial key‐
24       word followed by a list of arguments, some of which  may  be  optional,
25       separated  by  whitespace.  Commands may not be continued over multiple
26       lines.  Arguments may be host names, host addresses written in numeric,
27       dotted-quad  form,  integers,  floating  point numbers (when specifying
28       times in seconds) and text strings.
29
30       The rest of this page describes the configuration and control  options.
31       The  "Notes  on  Configuring  NTP  and  Setting  up an NTP Subnet" page
32       (available  as   part   of   the   HTML   documentation   provided   in
33       /usr/share/doc/ntp)  contains  an extended discussion of these options.
34       In addition to the discussion of general Configuration  Options,  there
35       are  sections  describing the following supported functionality and the
36       options used to control it:
37
38       · Authentication Support
39
40       · Monitoring Support
41
42       · Access Control Support
43
44       · Automatic NTP Configuration Options
45
46       · Reference Clock Support
47
48       · Miscellaneous Options
49
50       Following these is a section describing Miscellaneous  Options.   While
51       there  is  a rich set of options available, the only required option is
52       one or more pool, server, peer, broadcast or manycastclient commands.
53

Configuration Support

55       Following is a description of  the  configuration  commands  in  NTPv4.
56       These  commands  have  the same basic functions as in NTPv3 and in some
57       cases new functions and new arguments.  There are two classes  of  com‐
58       mands,  configuration  commands that configure a persistent association
59       with a remote server or peer or reference clock, and auxiliary commands
60       that specify environmental variables that control various related oper‐
61       ations.
62
63   Configuration Commands
64       The various modes are determined by the command keyword and the type of
65       the required IP address.  Addresses are classed by type as (s) a remote
66       server or peer (IPv4 class A, B and C), (b) the broadcast address of  a
67       local  interface, (m) a multicast address (IPv4 class D), or (r) a ref‐
68       erence clock address  (127.127.x.x).   Note  that  only  those  options
69       applicable to each command are listed below.  Use of options not listed
70       may not be caught as an error, but may result in some  weird  and  even
71       destructive behavior.
72
73       If  the  Basic  Socket  Interface  Extensions  for  IPv6  (RFC-2553) is
74       detected, support for the IPv6 address family is generated in  addition
75       to  the  default  support  of the IPv4 address family.  In a few cases,
76       including the reslist billboard generated by ntpq(8) or ntpdc(8),  IPv6
77       addresses  are  automatically generated.  IPv6 addresses can be identi‐
78       fied by the presence of colons : in the address field.  IPv6  addresses
79       can  be  used  almost everywhere where IPv4 addresses can be used, with
80       the exception of reference clock addresses, which are always IPv4.
81
82       Note that in contexts where a host name is  expected,  a  -4  qualifier
83       preceding  the  host  name forces DNS resolution to the IPv4 namespace,
84       while a -6 qualifier forces DNS resolution to the IPv6 namespace.   See
85       IPv6 references for the equivalent classes for that address family.
86
87       pool  address [burst] [iburst] [version version] [prefer] [minpoll min‐
88       poll] [maxpoll maxpoll] [xmtnonce]
89
90       server address [key key | autokey] [burst] [iburst]  [version  version]
91       [prefer] [minpoll minpoll] [maxpoll maxpoll] [true] [xmtnonce]
92
93       peer  address  [key  key | autokey] [version version] [prefer] [minpoll
94       minpoll] [maxpoll maxpoll] [true] [xleave]
95
96       broadcast address [key key | autokey] [version version] [prefer]  [min‐
97       poll minpoll] [ttl ttl] [xleave]
98
99       manycastclient  address  [key key | autokey] [version version] [prefer]
100       [minpoll minpoll] [maxpoll maxpoll] [ttl ttl]
101
102       These five commands specify the time server name or address to be  used
103       and the mode in which to operate.  The address can be either a DNS name
104       or an IP address in dotted-quad notation.   Additional  information  on
105       association  behavior can be found in the "Association Management" page
106       (available  as   part   of   the   HTML   documentation   provided   in
107       /usr/share/doc/ntp).
108
109       pool   For type s addresses, this command mobilizes a persistent client
110              mode association with a number of remote servers.  In this  mode
111              the  local  clock can synchronized to the remote server, but the
112              remote server can never be synchronized to the local clock.
113
114       server For type s and r addresses, this command mobilizes a  persistent
115              client  mode  association  with  the  specified remote server or
116              local radio clock.  In this mode the local  clock  can  synchro‐
117              nized  to  the remote server, but the remote server can never be
118              synchronized to the local clock.  This  command  should  not  be
119              used for type b or m addresses.
120
121       peer   For type s addresses (only), this command mobilizes a persistent
122              symmetric-active mode  association  with  the  specified  remote
123              peer.   In  this mode the local clock can be synchronized to the
124              remote peer or the remote peer can be synchronized to the  local
125              clock.   This is useful in a network of servers where, depending
126              on various failure scenarios, either the local  or  remote  peer
127              may  be  the  better source of time.  This command should NOT be
128              used for type b, m or r addresses.
129
130       broadcast
131              For type b and m addresses (only), this command mobilizes a per‐
132              sistent  broadcast  mode  association.  Multiple commands can be
133              used to specify multiple local  broadcast  interfaces  (subnets)
134              and/or  multiple  multicast  groups.   Note that local broadcast
135              messages go only to the interface  associated  with  the  subnet
136              specified,  but  multicast  messages  go  to all interfaces.  In
137              broadcast mode the local server sends  periodic  broadcast  mes‐
138              sages  to a client population at the address specified, which is
139              usually the broadcast address on (one of) the  local  network(s)
140              or  a  multicast address assigned to NTP.  The IANA has assigned
141              the multicast group address IPv4 224.0.1.1  and  IPv6  ff05::101
142              (site  local)  exclusively  to  NTP,  but  other  nonconflicting
143              addresses can be used to contain the messages within administra‐
144              tive boundaries.  Ordinarily, this specification applies only to
145              the local server operating as  a  sender;  for  operation  as  a
146              broadcast  client,  see  the  broadcastclient or multicastclient
147              commands below.
148
149       manycastclient
150              For type m addresses (only), this command mobilizes  a  manycast
151              client mode association for the multicast address specified.  In
152              this case a specific address must be supplied which matches  the
153              address  used  on  the manycastserver command for the designated
154              manycast servers.  The NTP multicast address 224.0.1.1  assigned
155              by  the IANA should NOT be used, unless specific means are taken
156              to avoid spraying large areas of the Internet  with  these  mes‐
157              sages and causing a possibly massive implosion of replies at the
158              sender.  The manycastserver command  specifies  that  the  local
159              server is to operate in client mode with the remote servers that
160              are discovered as the result  of  broadcast/multicast  messages.
161              The  client  broadcasts  a  request message to the group address
162              associated with the specified address and  specifically  enabled
163              servers  respond  to  these  messages.   The  client selects the
164              servers providing the best time and continues as with the server
165              command.  The remaining servers are discarded as if never heard.
166
167       Options:
168
169       autokey
170              All  packets sent to and received from the server or peer are to
171              include authentication fields encrypted using the autokey scheme
172              described in Authentication Options.
173
174       burst  when  the  server  is  reachable,  send a burst of eight packets
175              instead of the usual one.  The packet spacing is normally  2  s;
176              however, the spacing between the first and second packets can be
177              changed with the calldelay command to allow additional time  for
178              a  modem  or ISDN call to complete.  This is designed to improve
179              timekeeping quality with the server command and s addresses.
180
181       iburst When the server is unreachable, send a burst  of  eight  packets
182              instead  of  the usual one.  The packet spacing is normally 2 s;
183              however, the spacing  between  the  first  two  packets  can  be
184              changed  with the calldelay command to allow additional time for
185              a modem or ISDN call to complete.  This is designed to speed the
186              initial  synchronization acquisition with the server command and
187              s addresses and when ntpd(8) is started with the -q option.
188
189       key key
190              All packets sent to and received from the server or peer are  to
191              include  authentication fields encrypted using the specified key
192              identifier with values from 1 to 65535, inclusive.  The  default
193              is to include no encryption field.
194
195       minpoll minpoll
196
197       maxpoll maxpoll
198              These options specify the minimum and maximum poll intervals for
199              NTP messages, as a power of 2 in seconds The maximum poll inter‐
200              val  defaults  to 10 (1,024 s), but can be increased by the max‐
201              poll option to an upper limit of 17 (36.4 h).  The minimum  poll
202              interval  defaults to 6 (64 s), but can be decreased by the min‐
203              poll option to a lower limit of 4 (16 s).
204
205       noselect
206              Marks the server as unused, except for  display  purposes.   The
207              server is discarded by the selection algroithm.
208
209       preempt
210              Says the association can be preempted.
211
212       prefer Marks  the  server  as preferred.  All other things being equal,
213              this host will be chosen for synchronization among a set of cor‐
214              rectly  operating hosts.  See the "Mitigation Rules and the pre‐
215              fer Keyword" page (available as part of the  HTML  documentation
216              provided in /usr/share/doc/ntp) for further information.
217
218       true   Marks  the  server  as  a truechimer, forcing the association to
219              always survive the selection and  clustering  algorithms.   This
220              option  should  almost  certainly  only be used while testing an
221              association.
222
223       ttl ttl
224              This option is used only  with  broadcast  server  and  manycast
225              client  modes.   It  specifies  the  time-to-live  ttl to use on
226              broadcast server and multicast server and the  maximum  ttl  for
227              the  expanding ring search with manycast client packets.  Selec‐
228              tion of the proper value, which defaults to 127, is something of
229              a  black art and should be coordinated with the network adminis‐
230              trator.
231
232       version version
233              Specifies the version number to be used for outgoing  NTP  pack‐
234              ets.  Versions 1-4 are the choices, with version 4 the default.
235
236       xleave Valid in peer and broadcast modes only, this flag enables inter‐
237              leave mode.
238
239       xmtnonce
240              Valid only for server and pool modes, this flag  puts  a  random
241              number in the packet's transmit timestamp.
242
243   Auxiliary Commands
244       broadcastclient
245              This  command  enables reception of broadcast server messages to
246              any local interface (type b) address.  Upon receiving a  message
247              for  the  first  time, the broadcast client measures the nominal
248              server propagation delay using a  brief  client/server  exchange
249              with the server, then enters the broadcast client mode, in which
250              it synchronizes to succeeding broadcast messages.  Note that, in
251              order  to avoid accidental or malicious disruption in this mode,
252              both the server and client should operate using symmetric-key or
253              public-key   authentication   as   described  in  Authentication
254              Options.
255
256       manycastserver address ...
257              This command enables reception of manycast  client  messages  to
258              the  multicast  group  address(es) (type m) specified.  At least
259              one address is required, but the NTP multicast address 224.0.1.1
260              assigned  by  the IANA should NOT be used, unless specific means
261              are taken to limit the span of the reply and  avoid  a  possibly
262              massive  implosion  at the original sender.  Note that, in order
263              to avoid accidental or malicious disruption in this  mode,  both
264              the server and client should operate using symmetric-key or pub‐
265              lic-key authentication as described in Authentication Options.
266
267       multicastclient address ...
268              This command enables reception of multicast server  messages  to
269              the  multicast  group  address(es)  (type  m)  specified.   Upon
270              receiving a message for the first  time,  the  multicast  client
271              measures  the  nominal  server  propagation  delay using a brief
272              client/server exchange with the server, then enters  the  broad‐
273              cast  client mode, in which it synchronizes to succeeding multi‐
274              cast messages.  Note that, in order to avoid accidental or mali‐
275              cious disruption in this mode, both the server and client should
276              operate using  symmetric-key  or  public-key  authentication  as
277              described in Authentication Options.
278
279       mdnstries number
280              If  we  are participating in mDNS, after we have synched for the
281              first time we attempt to register with the mDNS system.  If that
282              registration attempt fails, we try again at one minute intervals
283              for up to mdnstries times.  After  all,  ntpd  may  be  starting
284              before mDNS.  The default value for mdnstries is 5.
285

Authentication Support

287       Authentication  support allows the NTP client to verify that the server
288       is in fact known and trusted and not an intruder intending accidentally
289       or  on  purpose  to masquerade as that server.  The NTPv3 specification
290       RFC-1305 defines a scheme which provides  cryptographic  authentication
291       of  received  NTP  packets.   Originally,  this was done using the Data
292       Encryption Standard (DES) algorithm operating in Cipher Block  Chaining
293       (CBC)  mode,  commonly called DES-CBC.  Subsequently, this was replaced
294       by the RSA Message Digest 5 (MD5) algorithm using a private  key,  com‐
295       monly called keyed-MD5.  Either algorithm computes a message digest, or
296       one-way hash, which can be used to verify the server  has  the  correct
297       private key and key identifier.
298
299       NTPv4  retains  the  NTPv3  scheme, properly described as symmetric key
300       cryptography and, in addition, provides a new Autokey scheme  based  on
301       public  key cryptography.  Public key cryptography is generally consid‐
302       ered more secure than symmetric key cryptography, since the security is
303       based  on  a  private value which is generated by each server and never
304       revealed.  With Autokey all key distribution and  management  functions
305       involve only public values, which considerably simplifies key distribu‐
306       tion and storage.  Public key management is  based  on  X.509  certifi‐
307       cates,  which  can  be  provided  by commercial services or produced by
308       utility programs in the OpenSSL software library or the NTPv4 distribu‐
309       tion.
310
311       While the algorithms for symmetric key cryptography are included in the
312       NTPv4 distribution, public key cryptography requires the OpenSSL  soft‐
313       ware  library  to  be  installed  before building the NTP distribution.
314       Directions for doing that are on the Building and Installing  the  Dis‐
315       tribution page.
316
317       Authentication  is configured separately for each association using the
318       key or autokey subcommand on the peer, server, broadcast and  manycast‐
319       client  configuration  commands  as  described in Configuration Options
320       page.  The authentication options described below specify the locations
321       of  the  key  files,  if  other  than default, which symmetric keys are
322       trusted and the interval between  various  operations,  if  other  than
323       default.
324
325       Authentication  is  always enabled, although ineffective if not config‐
326       ured as described below.  If a NTP packet arrives including  a  message
327       authentication code (MAC), it is accepted only if it passes all crypto‐
328       graphic checks.  The checks require correct key ID, key value and  mes‐
329       sage digest.  If the packet has been modified in any way or replayed by
330       an intruder, it will fail one or more of these checks and be discarded.
331       Furthermore,   the  Autokey  scheme  requires  a  preliminary  protocol
332       exchange to obtain the server certificate, verify its  credentials  and
333       initialize the protocol
334
335       The auth flag controls whether new associations or remote configuration
336       commands require cryptographic authentication.  This flag can be set or
337       reset  by the enable and disable commands and also by remote configura‐
338       tion commands sent by a ntpdc(8) program running  on  another  machine.
339       If  this  flag  is  enabled,  which  is the default case, new broadcast
340       client and symmetric passive associations and remote configuration com‐
341       mands  must  be  cryptographically authenticated using either symmetric
342       key or public key cryptography.  If this flag is disabled, these opera‐
343       tions are effective even if not cryptographic authenticated.  It should
344       be understood that operating with the auth flag disabled invites a sig‐
345       nificant vulnerability where a rogue hacker can masquerade as a falset‐
346       icker and seriously disrupt system timekeeping.   It  is  important  to
347       note  that  this  flag has no purpose other than to allow or disallow a
348       new association in response to new broadcast and symmetric active  mes‐
349       sages  and  remote  configuration commands and, in particular, the flag
350       has no effect on the authentication process itself.
351
352       An attractive alternative where multicast support is available is many‐
353       cast mode, in which clients periodically troll for servers as described
354       in the Automatic NTP Configuration Options page.  Either symmetric  key
355       or  public  key  cryptographic authentication can be used in this mode.
356       The principle advantage of manycast mode is that potential servers need
357       not  be configured in advance, since the client finds them during regu‐
358       lar operation, and the configuration files for all clients can be iden‐
359       tical.
360
361       The security model and protocol schemes for both symmetric key and pub‐
362       lic key cryptography are summarized below; further details are  in  the
363       briefings,  papers  and  reports  at  the  NTP project page linked from
364       http://www.ntp.org/.
365
366   Symmetric-Key Cryptography
367       The original RFC-1305 specification allows any one of  possibly  65,535
368       keys, each distinguished by a 32-bit key identifier, to authenticate an
369       association.  The servers and clients involved must agree  on  the  key
370       and  key  identifier  to  authenticate  NTP  packets.  Keys and related
371       information are specified in a key file, usually called ntp.keys, which
372       must  be  distributed and stored using secure means beyond the scope of
373       the NTP protocol itself.  Besides the keys used for ordinary NTP  asso‐
374       ciations,  additional keys can be used as passwords for the ntpq(8) and
375       ntpdc(8) utility programs.
376
377       When ntpd(8) is first started, it reads the key file specified  in  the
378       keys  configuration  command  and  installs  the keys in the key cache.
379       However, individual keys must be activated  with  the  trusted  command
380       before  use.   This  allows, for instance, the installation of possibly
381       several batches of keys and then activating or deactivating each  batch
382       remotely  using  ntpdc(8).   This also provides a revocation capability
383       that can be used if a key becomes compromised.  The requestkey  command
384       selects  the  key  used as the password for the ntpdc(8) utility, while
385       the controlkey command selects the key used as  the  password  for  the
386       ntpq(8) utility.
387
388   Public Key Cryptography
389       NTPv4  supports  the  original  NTPv3 symmetric key scheme described in
390       RFC-1305 and in addition the Autokey protocol, which is based on public
391       key  cryptography.   The  Autokey  Version  2 protocol described on the
392       Autokey Protocol page  verifies  packet  integrity  using  MD5  message
393       digests and verifies the source with digital signatures and any of sev‐
394       eral digest/signature schemes.  Optional identity schemes described  on
395       the Identity Schemes page and based on cryptographic challenge/response
396       algorithms are also available.  Using all  of  these  schemes  provides
397       strong  security against replay with or without modification, spoofing,
398       masquerade and most forms of clogging attacks.
399
400       The Autokey protocol has several modes of  operation  corresponding  to
401       the various NTP modes supported.  Most modes use a special cookie which
402       can be computed independently by the client and server,  but  encrypted
403       in  transmission.   All  modes  use  in addition a variant of the S-KEY
404       scheme, in which a pseudo-random key list  is  generated  and  used  in
405       reverse  order.   These  schemes  are described along with an executive
406       summary, current status, briefing slides and reading list on the Auton‐
407       omous Authentication page.
408
409       The  specific  cryptographic  environment  used  by Autokey servers and
410       clients is determined by a set of files and soft links generated by the
411       ntp-keygen(1ntpkeygenmdoc)  program.  This includes a required host key
412       file, required certificate file and optional sign key file,  leapsecond
413       file  and identity scheme files.  The digest/signature scheme is speci‐
414       fied in the X.509 certificate along with the matching sign key.   There
415       are  several  schemes  available  in the OpenSSL software library, each
416       identified by a specific string  such  as  md5WithRSAEncryption,  which
417       stands for the MD5 message digest with RSA encryption scheme.  The cur‐
418       rent NTP distribution supports all the schemes in the OpenSSL  library,
419       including those based on RSA and DSA digital signatures.
420
421       NTP  secure groups can be used to define cryptographic compartments and
422       security hierarchies.  It is important that every host in the group  be
423       able  to  construct a certificate trail to one or more trusted hosts in
424       the same group.  Each group host runs the Autokey  protocol  to  obtain
425       the  certificates  for all hosts along the trail to one or more trusted
426       hosts.  This requires the configuration file in all hosts to  be  engi‐
427       neered so that, even under anticipated failure conditions, the NTP sub‐
428       net will form such that every group host can find a trail to  at  least
429       one trusted host.
430
431   Naming and Addressing
432       It  is  important  to  note  that  Autokey  does not use DNS to resolve
433       addresses, since DNS can't be completely trusted until the name servers
434       have  synchronized  clocks.   The cryptographic name used by Autokey to
435       bind the host identity credentials and  cryptographic  values  must  be
436       independent of interface, network and any other naming convention.  The
437       name appears in the host certificate in either or both the subject  and
438       issuer fields, so protection against DNS compromise is essential.
439
440       By  convention, the name of an Autokey host is the name returned by the
441       Unix gethostname(2) system call or equivalent in other systems.  By the
442       system  design  model, there are no provisions to allow alternate names
443       or aliases.  However, this is not to say that  DNS  aliases,  different
444       names for each interface, etc., are constrained in any way.
445
446       It  is  also important to note that Autokey verifies authenticity using
447       the host name, network address and public keys, all of which are  bound
448       together  by  the  protocol specifically to deflect masquerade attacks.
449       For  this  reason  Autokey  includes  the  source  and  destination  IP
450       addresses in message digest computations and so the same addresses must
451       be available at both the server and client.  For this reason  operation
452       with  network  address  translation  schemes  is  not  possible.   This
453       reflects the intended robust security model where government and corpo‐
454       rate NTP servers are operated outside firewall perimeters.
455
456   Operation
457       A  specific  combination of authentication scheme (none, symmetric key,
458       public key) and identity scheme is called a  cryptotype,  although  not
459       all  combinations  are  compatible.  There may be management configura‐
460       tions where the clients, servers and peers may not all support the same
461       cryptotypes.   A  secure  NTPv4  subnet  can be configured in many ways
462       while keeping in mind the principles explained above and in  this  sec‐
463       tion.   Note however that some cryptotype combinations may successfully
464       interoperate with each other, but may not represent good security prac‐
465       tice.
466
467       The cryptotype of an association is determined at the time of mobiliza‐
468       tion, either at configuration time or some time later when a message of
469       appropriate  cryptotype  arrives.   When  mobilized by a server or peer
470       configuration command and no key or autokey  subcommands  are  present,
471       the association is not authenticated; if the key subcommand is present,
472       the association is authenticated using the symmetric key ID  specified;
473       if  the autokey subcommand is present, the association is authenticated
474       using Autokey.
475
476       When multiple identity schemes are supported in the  Autokey  protocol,
477       the  first  message  exchange determines which one is used.  The client
478       request message contains bits corresponding to  which  schemes  it  has
479       available.   The server response message contains bits corresponding to
480       which schemes it has available.   Both  server  and  client  match  the
481       received bits with their own and select a common scheme.
482
483       Following  the principle that time is a public value, a server responds
484       to any client packet that matches its cryptotype capabilities.  Thus, a
485       server  receiving  an unauthenticated packet will respond with an unau‐
486       thenticated packet, while the same server receiving a packet of a cryp‐
487       totype  it supports will respond with packets of that cryptotype.  How‐
488       ever, unconfigured broadcast or manycast client associations or symmet‐
489       ric  passive  associations will not be mobilized unless the server sup‐
490       ports a cryptotype compatible  with  the  first  packet  received.   By
491       default,  unauthenticated  associations  will  not  be mobilized unless
492       overridden in a decidedly dangerous way.
493
494       Some examples may help to reduce confusion.  Client Alice has  no  spe‐
495       cific  cryptotype  selected.   Server Bob has both a symmetric key file
496       and minimal Autokey files.  Alice's unauthenticated messages arrive  at
497       Bob,  who  replies  with unauthenticated messages.  Cathy has a copy of
498       Bob's symmetric key file and has selected key ID 4 in messages to  Bob.
499       Bob  verifies  the message with his key ID 4.  If it's the same key and
500       the message is verified, Bob sends Cathy  a  reply  authenticated  with
501       that  key.   If  verification  fails,  Bob sends Cathy a thing called a
502       crypto-NAK, which tells her something broke.  She can see the  evidence
503       using the ntpq(8) program.
504
505       Denise  has rolled her own host key and certificate.  She also uses one
506       of the identity schemes as Bob.  She sends the first Autokey message to
507       Bob and they both dance the protocol authentication and identity steps.
508       If all comes out okay, Denise and Bob continue as described above.
509
510       It should be clear from the above that Bob can support all the girls at
511       the same time, as long as he has compatible authentication and identity
512       credentials.  Now, Bob can act just like the girls in his own choice of
513       servers; he can run multiple configured associations with multiple dif‐
514       ferent servers (or the same server, although that might not be useful).
515       But,  wise security policy might preclude some cryptotype combinations;
516       for instance, running an identity scheme with one server and no authen‐
517       tication with another might not be wise.
518
519   Key Management
520       The  cryptographic values used by the Autokey protocol are incorporated
521       as a set of files generated by the  ntp-keygen(1ntpkeygenmdoc)  utility
522       program,  including  symmetric  key,  host  key  and public certificate
523       files, as well as sign key, identity parameters and leapseconds  files.
524       Alternatively,  host  and sign keys and certificate files can be gener‐
525       ated by the OpenSSL utilities and certificates  can  be  imported  from
526       public certificate authorities.  Note that symmetric keys are necessary
527       for the ntpq(8) and ntpdc(8) utility programs.  The remaining files are
528       necessary only for the Autokey protocol.
529
530       Certificates  imported  from  OpenSSL or public certificate authorities
531       have certian limitations.  The certificate should be in  ASN.1  syntax,
532       X.509  Version  3  format  and encoded in PEM, which is the same format
533       used by OpenSSL.  The overall length  of  the  certificate  encoded  in
534       ASN.1 must not exceed 1024 bytes.  The subject distinguished name field
535       (CN) is the fully qualified name of the host on which it is  used;  the
536       remaining subject fields are ignored.  The certificate extension fields
537       must not contain either a subject key identifier or a issuer key  iden‐
538       tifier  field;  however, an extended key usage field for a trusted host
539       must contain the value trustRoot;.  Other extension fields are ignored.
540
541   Authentication Commands
542       autokey [logsec]
543              Specifies the interval between regenerations of the session  key
544              list  used with the Autokey protocol.  Note that the size of the
545              key list for each association depends on this interval  and  the
546              current poll interval.  The default value is 12 (4096 s or about
547              1.1 hours).  For poll intervals above the specified interval,  a
548              session  key  list  with  a single entry will be regenerated for
549              every message sent.
550
551       controlkey key
552              Specifies the key identifier to use with  the  ntpq(8)  utility,
553              which  uses  the standard protocol defined in RFC-1305.  The key
554              argument is the key identifier for  a  trusted  key,  where  the
555              value can be in the range 1 to 65,535, inclusive.
556
557       crypto  [cert file] [leap file] [randfile file] [host file] [sign file]
558       [gq file] [gqpar file] [iffpar file] [mvpar file] [pw password]
559              This command requires the OpenSSL library.  It activates  public
560              key  cryptography,  selects  the  message  digest  and signature
561              encryption scheme and loads the required private and public val‐
562              ues described above.  If one or more files are left unspecified,
563              the default names are used as described above.  Unless the  com‐
564              plete path and name of the file are specified, the location of a
565              file is relative to the keys directory specified in the  keysdir
566              command  or  default  /usr/local/etc.  Following are the subcom‐
567              mands:
568
569              cert file
570                     Specifies the location of the required host  public  cer‐
571                     tificate file.  This overrides the link ntpkey_cert_host‐
572                     name in the keys directory.
573
574              gqpar file
575                     Specifies the location  of  the  optional  GQ  parameters
576                     file.   This overrides the link ntpkey_gq_hostname in the
577                     keys directory.
578
579              host file
580                     Specifies the location of the  required  host  key  file.
581                     This  overrides  the link ntpkey_key_hostname in the keys
582                     directory.
583
584              iffpar file
585                     Specifies the location of  the  optional  IFF  parameters
586                     file.  This overrides the link ntpkey_iff_hostname in the
587                     keys directory.
588
589              leap file
590                     Specifies the location of the optional  leapsecond  file.
591                     This  overrides  the  link ntpkey_leap in the keys direc‐
592                     tory.
593
594              mvpar file
595                     Specifies the location  of  the  optional  MV  parameters
596                     file.   This overrides the link ntpkey_mv_hostname in the
597                     keys directory.
598
599              pw password
600                     Specifies the password to decrypt files  containing  pri‐
601                     vate keys and identity parameters.  This is required only
602                     if these files have been encrypted.
603
604              randfile file
605                     Specifies the location of the random seed  file  used  by
606                     the  OpenSSL  library.  The defaults are described in the
607                     main text above.
608
609              sign file
610                     Specifies the location of the  optional  sign  key  file.
611                     This  overrides the link ntpkey_sign_hostname in the keys
612                     directory.  If this file is not found, the  host  key  is
613                     also the sign key.
614
615       keys keyfile
616              Specifies  the  complete  path  and location of the MD5 key file
617              containing the keys and key identifiers used by ntpd(8), ntpq(8)
618              and  ntpdc(8)  when  operating  with symmetric key cryptography.
619              This is the same operation as the -k command line option.
620
621       keysdir path
622              This command specifies the default directory  path  for  crypto‐
623              graphic  keys,  parameters  and  certificates.   The  default is
624              /usr/local/etc/.
625
626       requestkey key
627              Specifies the key identifier to use with  the  ntpdc(8)  utility
628              program,  which  uses  a  proprietary  protocol specific to this
629              implementation of ntpd(8).  The key argument is a key identifier
630              for  the  trusted  key, where the value can be in the range 1 to
631              65,535, inclusive.
632
633       revoke logsec
634              Specifies the interval between re-randomization of certain cryp‐
635              tographic  values used by the Autokey scheme, as a power of 2 in
636              seconds.  These values need to be updated frequently in order to
637              deflect  brute-force  attacks  on  the algorithms of the scheme;
638              however, updating some values is a relatively  expensive  opera‐
639              tion.   The default interval is 16 (65,536 s or about 18 hours).
640              For poll intervals above the specified interval, the values will
641              be updated for every message sent.
642
643       trustedkey key ...
644              Specifies the key identifiers which are trusted for the purposes
645              of authenticating peers with symmetric key cryptography, as well
646              as  keys used by the ntpq(8) and ntpdc(8) programs.  The authen‐
647              tication procedures require  that  both  the  local  and  remote
648              servers  share the same key and key identifier for this purpose,
649              although different keys can be used with different servers.  The
650              key arguments are 32-bit unsigned integers with values from 1 to
651              65,535.
652
653   Error Codes
654       The following error codes are reported via the NTP control and monitor‐
655       ing protocol trap mechanism.
656
657       101    (bad  field  format  or  length) The packet has invalid version,
658              length or format.
659
660       102    (bad timestamp) The packet timestamp is the same or  older  than
661              the  most  recent  received.  This could be due to a replay or a
662              server clock time step.
663
664       103    (bad filestamp) The packet filestamp is the same or  older  than
665              the  most  recent  received.  This could be due to a replay or a
666              key file generation error.
667
668       104    (bad or missing public key)  The  public  key  is  missing,  has
669              incorrect format or is an unsupported type.
670
671       105    (unsupported  digest  type)  The  server requires an unsupported
672              digest/signature scheme.
673
674       106    (mismatched digest types) Not used.
675
676       107    (bad signature length) The signature length does not  match  the
677              current public key.
678
679       108    (signature  not verified) The message fails the signature check.
680              It could be bogus or signed by a different private key.
681
682       109    (certificate not verified) The certificate is invalid or  signed
683              with the wrong key.
684
685       110    (certificate  not  verified) The certificate is not yet valid or
686              has expired or the signature could not be verified.
687
688       111    (bad or missing cookie) The  cookie  is  missing,  corrupted  or
689              bogus.
690
691       112    (bad  or  missing  leapseconds  table)  The leapseconds table is
692              missing, corrupted or bogus.
693
694       113    (bad or missing certificate) The certificate  is  missing,  cor‐
695              rupted or bogus.
696
697       114    (bad  or  missing identity) The identity key is missing, corrupt
698              or bogus.
699

Monitoring Support

701       ntpd(8) includes a comprehensive monitoring facility suitable for  con‐
702       tinuous,  long  term recording of server and client timekeeping perfor‐
703       mance.  See the statistics command below for a listing and  example  of
704       each  type of statistics currently supported.  Statistic files are man‐
705       aged using file generation sets and scripts in the ./scripts  directory
706       of  the  source  code  distribution.   Using  these facilities and UNIX
707       cron(8) jobs, the data can be automatically summarized and archived for
708       retrospective analysis.
709
710   Monitoring Commands
711       statistics name ...
712              Enables  writing  of statistics records.  Currently, eight kinds
713              of name statistics are supported.
714
715              clockstats
716                     Enables recording of clock driver statistics information.
717                     Each  update  received from a clock driver appends a line
718                     of the following form to the file  generation  set  named
719                     clockstats:
720                         49213 525.624 127.127.4.1 93 226 00:08:29.606 D
721
722                     The  first two fields show the date (Modified Julian Day)
723                     and time (seconds and fraction past UTC  midnight).   The
724                     next  field  shows the clock address in dotted-quad nota‐
725                     tion.  The final field shows the last  timecode  received
726                     from the clock in decoded ASCII format, where meaningful.
727                     In some clock drivers a good deal of additional  informa‐
728                     tion can be gathered and displayed as well.  See informa‐
729                     tion specific to each clock for further details.
730
731              cryptostats
732                     This option requires the OpenSSL  cryptographic  software
733                     library.   It  enables  recording of cryptographic public
734                     key protocol information.  Each message received  by  the
735                     protocol  module  appends a line of the following form to
736                     the file generation set named cryptostats:
737                         49213 525.624 127.127.4.1 message
738
739                     The first two fields show the date (Modified Julian  Day)
740                     and  time  (seconds and fraction past UTC midnight).  The
741                     next field shows the peer address  in  dotted-quad  nota‐
742                     tion,  The  final message field includes the message type
743                     and certain ancillary information.  See  the  Authentica‐
744                     tion Options section for further information.
745
746              loopstats
747                     Enables  recording of loop filter statistics information.
748                     Each update of the local clock outputs a line of the fol‐
749                     lowing form to the file generation set named loopstats:
750                         50935 75440.031 0.000006019 13.778190 0.000351733 0.0133806
751
752                     The  first two fields show the date (Modified Julian Day)
753                     and time (seconds and fraction past UTC  midnight).   The
754                     next  five  fields  show time offset (seconds), frequency
755                     offset (parts per million - PPM), RMS  jitter  (seconds),
756                     Allan deviation (PPM) and clock discipline time constant.
757
758              peerstats
759                     Enables  recording  of peer statistics information.  This
760                     includes statistics records of all peers of a NTP  server
761                     and  of  special  signals,  where present and configured.
762                     Each valid update appends a line of the following form to
763                     the  current element of a file generation set named peer‐
764                     stats:
765                         48773 10847.650 127.127.4.1 9714 -0.001605376 0.000000000 0.001424877 0.000958674
766
767                     The first two fields show the date (Modified Julian  Day)
768                     and  time  (seconds and fraction past UTC midnight).  The
769                     next two fields show  the  peer  address  in  dotted-quad
770                     notation  and  status, respectively.  The status field is
771                     encoded in hex in the format described in Appendix  A  of
772                     the  NTP  specification  RFC 1305.  The final four fields
773                     show the offset, delay, dispersion and RMS jitter, all in
774                     seconds.
775
776              rawstats
777                     Enables  recording  of  raw-timestamp statistics informa‐
778                     tion.  This includes statistics records of all peers of a
779                     NTP server and of special signals, where present and con‐
780                     figured.  Each NTP message received from a peer or  clock
781                     driver  appends  a line of the following form to the file
782                     generation set named rawstats:
783                         50928 2132.543 128.4.1.1 128.4.1.20 3102453281.584327000 3102453281.58622800031 02453332.540806000 3102453332.541458000
784
785                     The first two fields show the date (Modified Julian  Day)
786                     and  time  (seconds and fraction past UTC midnight).  The
787                     next two fields show the remote  peer  or  clock  address
788                     followed  by  the  local address in dotted-quad notation.
789                     The final four fields show the originate, receive, trans‐
790                     mit  and  final  NTP  timestamps in order.  The timestamp
791                     values are as received and before processing by the vari‐
792                     ous data smoothing and mitigation algorithms.
793
794              sysstats
795                     Enables  recording of ntpd statistics counters on a peri‐
796                     odic basis.  Each hour a line of the  following  form  is
797                     appended to the file generation set named sysstats:
798                         50928 2132.543 36000 81965 0 9546 56 71793 512 540 10 147
799
800                     The  first two fields show the date (Modified Julian Day)
801                     and time (seconds and fraction past UTC  midnight).   The
802                     remaining  ten  fields show the statistics counter values
803                     accumulated since the last generated line.
804
805                     Time since restart 36000
806                            Time in hours since the system was last rebooted.
807
808                     Packets received 81965
809                            Total number of packets received.
810
811                     Packets processed 0
812                            Number of packets received in response to previous
813                            packets sent
814
815                     Current version 9546
816                            Number  of  packets  matching the current NTP ver‐
817                            sion.
818
819                     Previous version 56
820                            Number of packets matching the previous  NTP  ver‐
821                            sion.
822
823                     Bad version 71793
824                            Number of packets matching neither NTP version.
825
826                     Access denied 512
827                            Number of packets denied access for any reason.
828
829                     Bad length or format 540
830                            Number  of  packets with invalid length, format or
831                            port number.
832
833                     Bad authentication 10
834                            Number of packets not verified as authentic.
835
836                     Rate exceeded 147
837                            Number of packets discarded due  to  rate  limita‐
838                            tion.
839
840              statsdir directory_path
841                     Indicates  the  full path of a directory where statistics
842                     files should be created (see below).  This keyword allows
843                     the  (otherwise  constant)  filegen filename prefix to be
844                     modified for file generation sets, which  is  useful  for
845                     handling statistics logs.
846
847              filegen  name  [file  filename]  [type typename] [link | nolink]
848              [enable | disable]
849                     Configures setting of generation file set name.   Genera‐
850                     tion  file  sets  provide a means for handling files that
851                     are continuously growing during the lifetime of a server.
852                     Server  statistics  are a typical example for such files.
853                     Generation file sets provide access to  a  set  of  files
854                     used  to  store the actual data.  At any time at most one
855                     element of the set is being written to.  The  type  given
856                     specifies  when  and  how  data will be directed to a new
857                     element of the set.  This way, information stored in ele‐
858                     ments  of a file set that are currently unused are avail‐
859                     able for administrational operations without the risk  of
860                     disturbing  the operation of ntpd.  (Most important: they
861                     can be removed to free space for new data produced.)
862
863                     Note that this command can be sent from the ntpdc(8) pro‐
864                     gram running at a remote location.
865
866                     name   This  is  the  type  of the statistics records, as
867                            shown in the statistics command.
868
869                     file filename
870                            This is the file name for the statistics  records.
871                            Filenames of set members are built from three con‐
872                            catenated elements prefix, filename and suffix:
873
874                            prefix This is a constant filename  path.   It  is
875                                   not  subject to modifications via the file‐
876                                   gen option.  It is defined by  the  server,
877                                   usually  specified  as  a compile-time con‐
878                                   stant.  It may,  however,  be  configurable
879                                   for  individual  file  generation  sets via
880                                   other commands.  For  example,  the  prefix
881                                   used  with  loopstats and peerstats genera‐
882                                   tion can be configured using  the  statsdir
883                                   option explained above.
884
885                            filename
886                                   This string is directly concatenated to the
887                                   prefix  mentioned  above  (no   intervening
888                                   ‘/’).   This can be modified using the file
889                                   argument to the filegen statement.   No  ..
890                                   elements  are  allowed in this component to
891                                   prevent filenames referring to  parts  out‐
892                                   side  the  filesystem  hierarchy denoted by
893                                   prefix.
894
895                            suffix This part is reflects  individual  elements
896                                   of  a  file set.  It is generated according
897                                   to the type of a file set.
898
899                     type typename
900                            A file generation  set  is  characterized  by  its
901                            type.  The following types are supported:
902
903                            none   The  file  set  is  actually a single plain
904                                   file.
905
906                            pid    One element of file set is used per  incar‐
907                                   nation  of  a  ntpd server.  This type does
908                                   not perform any changes to file set members
909                                   during runtime, however it provides an easy
910                                   way of separating files belonging  to  dif‐
911                                   ferent  ntpd(8)  server  incarnations.  The
912                                   set member filename is built by appending a
913                                   ‘.’   to  concatenated  prefix and filename
914                                   strings, and appending the  decimal  repre‐
915                                   sentation  of the process ID of the ntpd(8)
916                                   server process.
917
918                            day    One file generation set element is  created
919                                   per  day.   A  day is defined as the period
920                                   between 00:00 and 24:00 UTC.  The file  set
921                                   member  suffix consists of a ‘.’  and a day
922                                   specification in the form  YYYYMMdd.   YYYY
923                                   is  a 4-digit year number (e.g., 1992).  MM
924                                   is a two digit month number.  dd is  a  two
925                                   digit  day  number.   Thus, all information
926                                   written at 10 December 1992 would end up in
927                                   a file named prefix filename.19921210.
928
929                            week   Any  file  set member contains data related
930                                   to a certain week of a year.  The term week
931                                   is  defined by computing day-of-year modulo
932                                   7.  Elements of such a file generation  set
933                                   are  distinguished by appending the follow‐
934                                   ing suffix to the file set filename base: A
935                                   dot,  a  4-digit year number, the letter W,
936                                   and a 2-digit week  number.   For  example,
937                                   information  from  January, 10th 1992 would
938                                   end up in a file with suffix
939
940                            month  One generation file set element  is  gener‐
941                                   ated  per month.  The file name suffix con‐
942                                   sists of a dot, a 4-digit year number,  and
943                                   a 2-digit month.
944
945                            year   One  generation  file  element is generated
946                                   per year.  The filename suffix consists  of
947                                   a dot and a 4 digit year number.
948
949                            age    This  type  of file generation sets changes
950                                   to a new element of the file set  every  24
951                                   hours  of  server  operation.  The filename
952                                   suffix consists of a dot, the letter a, and
953                                   an 8-digit number.  This number is taken to
954                                   be the number of seconds the server is run‐
955                                   ning  at  the  start  of  the corresponding
956                                   24-hour period.  Information is only  writ‐
957                                   ten  to  a  file  generation  by specifying
958                                   enable; output is prevented  by  specifying
959                                   disable.
960
961                     link | nolink
962                            It  is convenient to be able to access the current
963                            element of a file generation set by a fixed  name.
964                            This  feature  is  enabled  by specifying link and
965                            disabled using nolink.  If link  is  specified,  a
966                            hard  link  from the current file set element to a
967                            file without suffix is  created.   When  there  is
968                            already  a  file  with this name and the number of
969                            links of this file is one, it is renamed appending
970                            a  dot,  the  letter C, and the pid of the ntpd(8)
971                            server process.   When  the  number  of  links  is
972                            greater  than  one,  the  file  is unlinked.  This
973                            allows the current file to be accessed by  a  con‐
974                            stant name.
975
976                     enable | disable
977                            Enables or disables the recording function.
978

Access Control Support

980       The  ntpd(8)  daemon  implements  a  general purpose address/mask based
981       restriction list.  The list contains address/match entries sorted first
982       by increasing address values and and then by increasing mask values.  A
983       match occurs when the bitwise AND of the mask  and  the  packet  source
984       address  is  equal  to  the  bitwise AND of the mask and address in the
985       list.  The list is searched in order with the last match found defining
986       the  restriction  flags associated with the entry.  Additional informa‐
987       tion and examples can be found in the "Notes  on  Configuring  NTP  and
988       Setting up a NTP Subnet" page (available as part of the HTML documenta‐
989       tion provided in /usr/share/doc/ntp).
990
991       The restriction facility was implemented in conformance with the access
992       policies  for  the  original  NSFnet  backbone time servers.  Later the
993       facility was expanded to deflect cryptographic  and  clogging  attacks.
994       While  this  facility  may  be useful for keeping unwanted or broken or
995       malicious clients from congesting innocent servers, it  should  not  be
996       considered an alternative to the NTP authentication facilities.  Source
997       address based restrictions are  easily  circumvented  by  a  determined
998       cracker.
999
1000       Clients  can  be denied service because they are explicitly included in
1001       the restrict list created by the restrict command or implicitly as  the
1002       result of cryptographic or rate limit violations.  Cryptographic viola‐
1003       tions include certificate or identity verification failure; rate  limit
1004       violations  generally  result  from  defective NTP implementations that
1005       send packets at abusive rates.  Some violations  cause  denied  service
1006       only  for the offending packet, others cause denied service for a timed
1007       period and others cause the denied service for  an  indefinite  period.
1008       When a client or network is denied access for an indefinite period, the
1009       only way at present to remove the restrictions  is  by  restarting  the
1010       server.
1011
1012   The Kiss-of-Death Packet
1013       Ordinarily,  packets  denied service are simply dropped with no further
1014       action except  incrementing  statistics  counters.   Sometimes  a  more
1015       proactive  response is needed, such as a server message that explicitly
1016       requests the client to stop sending and leave a message for the  system
1017       operator.   A  special  packet format has been created for this purpose
1018       called the "kiss-of-death" (KoD) packet.  KoD  packets  have  the  leap
1019       bits set unsynchronized and stratum set to zero and the reference iden‐
1020       tifier field set to a four-byte ASCII code.  If the noserve or  notrust
1021       flag of the matching restrict list entry is set, the code is "DENY"; if
1022       the limited flag is set and the rate limit is  exceeded,  the  code  is
1023       "RATE".   Finally,  if  a  cryptographic  violation occurs, the code is
1024       "CRYP".
1025
1026       A client receiving a KoD performs a set of sanity  checks  to  minimize
1027       security  exposure,  then  updates the stratum and reference identifier
1028       peer variables, sets the access denied (TEST4) bit in  the  peer  flash
1029       variable  and  sends a message to the log.  As long as the TEST4 bit is
1030       set, the client will send no further packets to the server.   The  only
1031       way  at present to recover from this condition is to restart the proto‐
1032       col at both the client and server.  This happens automatically  at  the
1033       client  when  the  association times out.  It will happen at the server
1034       only if the server operator cooperates.
1035
1036   Access Control Commands
1037       discard [average avg] [minimum min] [monitor prob]
1038              Set the parameters of the limited facility  which  protects  the
1039              server  from client abuse.  The average subcommand specifies the
1040              minimum average packet spacing,  while  the  minimum  subcommand
1041              specifies  the  minimum  packet  spacing.   Packets that violate
1042              these minima are discarded and a kiss-o'-death  packet  returned
1043              if  enabled.   The default minimum average and minimum are 5 and
1044              2, respectively.  The monitor subcommand specifies the probabil‐
1045              ity  of  discard for packets that overflow the rate-control win‐
1046              dow.
1047
1048       restrict address [mask mask] [ippeerlimit int] [flag ...]
1049              The address  argument  expressed  in  dotted-quad  form  is  the
1050              address  of a host or network.  Alternatively, the address argu‐
1051              ment can be a valid host DNS name.  The mask argument  expressed
1052              in  dotted-quad  form  defaults to 255.255.255.255, meaning that
1053              the address is treated as the address of an individual host.   A
1054              default entry (address 0.0.0.0, mask 0.0.0.0) is always included
1055              and is always the first entry  in  the  list.   Note  that  text
1056              string default, with no mask option, may be used to indicate the
1057              default entry.  The ippeerlimit directive limits the  number  of
1058              peer  requests  for  each  IP  to int, where a value of -1 means
1059              "unlimited", the current default.  A value of  0  means  "none".
1060              There  would usually be at most 1 peering request per IP, but if
1061              the remote peering requests are behind a proxy there could  well
1062              be  more  than  1  per  IP.  In the current implementation, flag
1063              always restricts access, i.e., an entry with no flags  indicates
1064              that  free  access  to the server is to be given.  The flags are
1065              not orthogonal, in that more restrictive flags will  often  make
1066              less  restrictive  ones  redundant.   The flags can generally be
1067              classed into two categories, those which restrict  time  service
1068              and  those  which restrict informational queries and attempts to
1069              do run-time reconfiguration of the server.  One or more  of  the
1070              following flags may be specified:
1071
1072              ignore Deny packets of all kinds, including ntpq(8) and ntpdc(8)
1073                     queries.
1074
1075              kod    If this flag is set when an access  violation  occurs,  a
1076                     kiss-o'-death (KoD) packet is sent.  KoD packets are rate
1077                     limited to no more than one per second.  If  another  KoD
1078                     packet  occurs  within one second after the last one, the
1079                     packet is dropped.
1080
1081              limited
1082                     Deny service if the packet  spacing  violates  the  lower
1083                     limits  specified  in  the discard command.  A history of
1084                     clients  is  kept  using  the  monitoring  capability  of
1085                     ntpd(8).   Thus,  monitoring  is always active as long as
1086                     there is a restriction entry with the limited flag.
1087
1088              lowpriotrap
1089                     Declare traps set by matching hosts to be  low  priority.
1090                     The number of traps a server can maintain is limited (the
1091                     current limit is 3).  Traps are  usually  assigned  on  a
1092                     first   come,   first   served  basis,  with  later  trap
1093                     requestors being denied service.  This flag modifies  the
1094                     assignment algorithm by allowing low priority traps to be
1095                     overridden by later requests for normal priority traps.
1096
1097              noepeer
1098                     Deny ephemeral peer requests, even if they come  from  an
1099                     authenticated  source.   Note  that  the ability to use a
1100                     symmetric key for authentication may be restricted to one
1101                     or  more  IPs  or  subnets  via  the  third  field of the
1102                     ntp.keys  file.   This  restriction  is  not  enabled  by
1103                     default,  to  maintain  backward  compatability.   Expect
1104                     noepeer to become the default in ntp-4.4.
1105
1106              nomodify
1107                     Deny ntpq(8) and ntpdc(8) queries which attempt to modify
1108                     the state of the server (i.e., run time reconfiguration).
1109                     Queries which return information are permitted.
1110
1111              noquery
1112                     Deny ntpq(8) and ntpdc(8) queries.  Time service  is  not
1113                     affected.
1114
1115              nopeer Deny  unauthenticated packets which would result in mobi‐
1116                     lizing a new association.  This  includes  broadcast  and
1117                     symmetric  active  packets  when a configured association
1118                     does not exist.  It also includes pool  associations,  so
1119                     if you want to use servers from a pool directive and also
1120                     want to use nopeer by default,  you'll  want  a  restrict
1121                     source ...  line as well that does not include the nopeer
1122                     directive.
1123
1124              noserve
1125                     Deny all packets except ntpq(8) and ntpdc(8) queries.
1126
1127              notrap Decline to provide mode 6 control message trap service to
1128                     matching  hosts.   The trap service is a subsystem of the
1129                     ntpq(8) control message protocol which  is  intended  for
1130                     use by remote event logging programs.
1131
1132              notrust
1133                     Deny  service  unless  the  packet  is  cryptographically
1134                     authenticated.
1135
1136              ntpport
1137                     This is actually a match algorithm modifier, rather  than
1138                     a  restriction flag.  Its presence causes the restriction
1139                     entry to be matched only if the source port in the packet
1140                     is  the  standard  NTP  UDP port (123).  Both ntpport and
1141                     non-ntpport may be specified.  The ntpport is  considered
1142                     more specific and is sorted later in the list.
1143
1144              serverresponse fuzz
1145                     When  reponding  to  server  requests, fuzz the low order
1146                     bits of the reftime.
1147
1148              version
1149                     Deny packets that do not match the current NTP version.
1150
1151       Default restriction list entries with the flags ignore, interface, ntp‐
1152       port,  for  each  of  the local host's interface addresses are inserted
1153       into the table at startup to prevent the server from attempting to syn‐
1154       chronize  to  its  own  time.   A default entry is also always present,
1155       though if it is otherwise unconfigured; no flags  are  associated  with
1156       the  default  entry  (i.e.,  everything  besides your own NTP server is
1157       unrestricted).
1158

Automatic NTP Configuration Options

1160   Manycasting
1161       Manycasting is a automatic discovery and configuration paradigm new  to
1162       NTPv4.   It  is intended as a means for a multicast client to troll the
1163       nearby network neighborhood to find cooperating manycast servers, vali‐
1164       date them using cryptographic means and evaluate their time values with
1165       respect to other servers that might be lurking in  the  vicinity.   The
1166       intended  result is that each manycast client mobilizes client associa‐
1167       tions with some number of the "best" of the  nearby  manycast  servers,
1168       yet automatically reconfigures to sustain this number of servers should
1169       one or another fail.
1170
1171       Note that the manycasting paradigm does not coincide with  the  anycast
1172       paradigm  described  in  RFC-1546,  which  is designed to find a single
1173       server from a clique of servers providing the same service.  The  many‐
1174       cast paradigm is designed to find a plurality of redundant servers sat‐
1175       isfying defined optimality criteria.
1176
1177       Manycasting can be used with either symmetric key or public  key  cryp‐
1178       tography.   The public key infrastructure (PKI) offers the best protec‐
1179       tion against compromised keys and is generally considered stronger,  at
1180       least  with  relatively  large  key sizes.  It is implemented using the
1181       Autokey protocol and the OpenSSL cryptographic library  available  from
1182       http://www.openssl.org/.  The library can also be used with other NTPv4
1183       modes as well and  is  highly  recommended,  especially  for  broadcast
1184       modes.
1185
1186       A  persistent manycast client association is configured using the many‐
1187       castclient command, which is similar to the server command but  with  a
1188       multicast (IPv4 class D or IPv6 prefix FF) group address.  The IANA has
1189       designated IPv4 address 224.1.1.1  and  IPv6  address  FF05::101  (site
1190       local)  for  NTP.  When more servers are needed, it broadcasts manycast
1191       client messages to this address at the minimum feasible rate and  mini‐
1192       mum  feasible  time-to-live  (TTL)  hops, depending on how many servers
1193       have already been found.  There can be as many manycast client associa‐
1194       tions  as different group address, each one serving as a template for a
1195       future ephemeral unicast client/server association.
1196
1197       Manycast servers configured with the manycastserver command  listen  on
1198       the  specified  group  address  for manycast client messages.  Note the
1199       distinction between manycast client,  which  actively  broadcasts  mes‐
1200       sages,  and  manycast  server,  which passively responds to them.  If a
1201       manycast server is in scope of the current TTL and is  itself  synchro‐
1202       nized  to  a  valid source and operating at a stratum level equal to or
1203       lower than the manycast client, it replies to the manycast client  mes‐
1204       sage with an ordinary unicast server message.
1205
1206       The  manycast  client  receiving  this  message  mobilizes an ephemeral
1207       client/server association according to  the  matching  manycast  client
1208       template,  but  only  if cryptographically authenticated and the server
1209       stratum is less than or equal to the client stratum.  Authentication is
1210       explicitly  required  and  either symmetric key or public key (Autokey)
1211       can be used.  Then, the client polls the server at its unicast  address
1212       in  burst mode in order to reliably set the host clock and validate the
1213       source.  This normally results in a volley of  eight  client/server  at
1214       2-s  intervals  during which both the synchronization and cryptographic
1215       protocols run concurrently.  Following the volley, the client runs  the
1216       NTP  intersection  and  clustering algorithms, which act to discard all
1217       but the "best" associations according to  stratum  and  synchronization
1218       distance.    The  surviving  associations  then  continue  in  ordinary
1219       client/server mode.
1220
1221       The manycast client polling strategy is designed to reduce as  much  as
1222       possible  the  volume  of  manycast  client messages and the effects of
1223       implosion due to near-simultaneous arrival of manycast server messages.
1224       The  strategy is determined by the manycastclient, tos and ttl configu‐
1225       ration commands.  The manycast poll interval is  normally  eight  times
1226       the  system poll interval, which starts out at the minpoll value speci‐
1227       fied in the manycastclient, command and,  under  normal  circumstances,
1228       increments to the maxpolll value specified in this command.  Initially,
1229       the TTL is set at the minimum hops specified by the  ttl  command.   At
1230       each  retransmission  the  TTL  is increased until reaching the maximum
1231       hops specified by this command or a sufficient number  client  associa‐
1232       tions have been found.  Further retransmissions use the same TTL.
1233
1234       The  quality and reliability of the suite of associations discovered by
1235       the manycast client is determined by the NTP mitigation algorithms  and
1236       the minclock and minsane values specified in the tos configuration com‐
1237       mand.  At least minsane candidate servers must  be  available  and  the
1238       mitigation  algorithms  produce at least minclock survivors in order to
1239       synchronize the clock.  Byzantine agreement principles require at least
1240       four  candidates  in  order  to correctly discard a single falseticker.
1241       For legacy purposes, minsane defaults to 1 and minclock defaults to  3.
1242       For manycast service minsane should be explicitly set to 4, assuming at
1243       least that number of servers are available.
1244
1245       If at least minclock servers are found, the manycast poll  interval  is
1246       immediately  set to eight times maxpoll.  If less than minclock servers
1247       are found when the TTL has reached the maximum hops, the manycast  poll
1248       interval is doubled.  For each transmission after that, the poll inter‐
1249       val is doubled again until reaching the maximum of eight times maxpoll.
1250       Further  transmissions use the same poll interval and TTL values.  Note
1251       that while all this is going on, each client/server  association  found
1252       is operating normally it the system poll interval.
1253
1254       Administratively  scoped multicast boundaries are normally specified by
1255       the network  router  configuration  and,  in  the  case  of  IPv6,  the
1256       link/site  scope  prefix.  By default, the increment for TTL hops is 32
1257       starting from 31; however, the ttl configuration command can be used to
1258       modify the values to match the scope rules.
1259
1260       It  is often useful to narrow the range of acceptable servers which can
1261       be found by manycast client  associations.   Because  manycast  servers
1262       respond  only  when  the client stratum is equal to or greater than the
1263       server stratum, primary (stratum 1)  servers  fill  find  only  primary
1264       servers  in  TTL  range,  which  is probably the most common objective.
1265       However, unless configured otherwise, all manycast clients in TTL range
1266       will  eventually find all primary servers in TTL range, which is proba‐
1267       bly not the most common objective in large networks.  The  tos  command
1268       can  be used to modify this behavior.  Servers with stratum below floor
1269       or above ceiling specified in the tos command are strongly  discouraged
1270       during  the selection process; however, these servers may be temporally
1271       accepted if the number of servers within TTL range is  less  than  min‐
1272       clock.
1273
1274       The above actions occur for each manycast client message, which repeats
1275       at the designated poll interval.  However, once  the  ephemeral  client
1276       association  is  mobilized, subsequent manycast server replies are dis‐
1277       carded, since that would result in a duplicate association.  If  during
1278       a poll interval the number of client associations falls below minclock,
1279       all manycast client prototype associations are  reset  to  the  initial
1280       poll  interval  and  TTL hops and operation resumes from the beginning.
1281       It is important to avoid frequent manycast client messages, since  each
1282       one  requires all manycast servers in TTL range to respond.  The result
1283       could well be an implosion, either minor or  major,  depending  on  the
1284       number  of  servers  in range.  The recommended value for maxpoll is 12
1285       (4,096 s).
1286
1287       It is possible and frequently useful to configure a host as both  many‐
1288       cast client and manycast server.  A number of hosts configured this way
1289       and sharing a common group address will  automatically  organize  them‐
1290       selves in an optimum configuration based on stratum and synchronization
1291       distance.  For example, consider an NTP subnet of two  primary  servers
1292       and  a  hundred  or  more  dependent clients.  With two exceptions, all
1293       servers and clients have identical configuration files  including  both
1294       multicastclient  and multicastserver commands using, for instance, mul‐
1295       ticast group address 239.1.1.1.  The only exception is that  each  pri‐
1296       mary  server  configuration  file must include commands for the primary
1297       reference source such as a GPS receiver.
1298
1299       The remaining configuration files for all secondary servers and clients
1300       have  the  same contents, except for the tos command, which is specific
1301       for each stratum level.  For stratum 1 and stratum 2 servers, that com‐
1302       mand is not necessary.  For stratum 3 and above servers the floor value
1303       is set to the intended stratum number.  Thus, all stratum 3  configura‐
1304       tion  files  are  identical,  all  stratum 4 files are identical and so
1305       forth.
1306
1307       Once operations have stabilized in this scenario, the  primary  servers
1308       will  find the primary reference source and each other, since they both
1309       operate at the same stratum (1), but not with any secondary  server  or
1310       client, since these operate at a higher stratum.  The secondary servers
1311       will find the servers at the same stratum level.  If one of the primary
1312       servers loses its GPS receiver, it will continue to operate as a client
1313       and other clients will time out the corresponding association  and  re-
1314       associate accordingly.
1315
1316       Some  administrators  prefer  to avoid running ntpd(8) continuously and
1317       run either sntp(8) or ntpd(8) -q as a cron job.   In  either  case  the
1318       servers must be configured in advance and the program fails if none are
1319       available when the cron job runs.  A really slick application of  many‐
1320       cast  is  with ntpd(8) -q.  The program wakes up, scans the local land‐
1321       scape looking for the usual suspects, selects the best from  among  the
1322       rascals,  sets  the  clock and then departs.  Servers do not have to be
1323       configured in advance and all clients throughout the network  can  have
1324       the same configuration file.
1325
1326   Manycast Interactions with Autokey
1327       Each  time  a manycast client sends a client mode packet to a multicast
1328       group address, all manycast servers in scope generate a reply including
1329       the  host  name  and  status  word.   The manycast clients then run the
1330       Autokey  protocol,  which  collects  and  verifies   all   certificates
1331       involved.   Following  the  burst  interval all but three survivors are
1332       cast off, but the certificates remain in the  local  cache.   It  often
1333       happens  that  several  complete  signing trails from the client to the
1334       primary servers are collected in this way.
1335
1336       About once an hour or less often if the poll interval exceeds this, the
1337       client  regenerates the Autokey key list.  This is in general transpar‐
1338       ent in client/server mode.  However, about once per day the server pri‐
1339       vate  value  used to generate cookies is refreshed along with all many‐
1340       cast client  associations.   In  this  case  all  cryptographic  values
1341       including  certificates  is  refreshed.   If a new certificate has been
1342       generated since the last refresh epoch, it  will  automatically  revoke
1343       all  prior certificates that happen to be in the certificate cache.  At
1344       the same time, the manycast scheme starts all over from  the  beginning
1345       and the expanding ring shrinks to the minimum and increments from there
1346       while collecting all servers in scope.
1347
1348   Broadcast Options
1349       tos [bcpollbstep gate]
1350              This command provides a way to delay, by the specified number of
1351              broadcast  poll  intervals, believing backward time steps from a
1352              broadcast server.  Broadcast time networks are  expected  to  be
1353              trusted.   In  the  event  a  broadcast server's time is stepped
1354              backwards, there is clear benefit to having the  clients  notice
1355              this change as soon as possible.  Attacks such as replay attacks
1356              can happen, however, and even though there are a number of  pro‐
1357              tections  built  in  to  broadcast  mode,  attempts to perform a
1358              replay attack are possible.  This value defaults to 0,  but  can
1359              be changed to any number of poll intervals between 0 and 4.
1360
1361   Manycast Options
1362       tos  [ceiling  ceiling | cohort { 0 | 1 } | floor floor | minclock min‐
1363       clock | minsane minsane]
1364              This command affects the clock selection  and  clustering  algo‐
1365              rithms.   It  can  be used to select the quality and quantity of
1366              peers used to synchronize the system clock and is most useful in
1367              manycast mode.  The variables operate as follows:
1368
1369              ceiling ceiling
1370                     Peers  with  strata  above  ceiling  will be discarded if
1371                     there are at least minclock peers remaining.  This  value
1372                     defaults  to  15, but can be changed to any number from 1
1373                     to 15.
1374
1375              cohort {0 | 1 }
1376                     This is a binary flag which enables (0) or  disables  (1)
1377                     manycast server replies to manycast clients with the same
1378                     stratum level.  This is useful to reduce implosions where
1379                     large  numbers of clients with the same stratum level are
1380                     present.  The default is to enable these replies.
1381
1382              floor floor
1383                     Peers with strata below floor will be discarded if  there
1384                     are  at  least  minclock  peers  remaining.   This  value
1385                     defaults to 1, but can be changed to any number from 1 to
1386                     15.
1387
1388              minclock minclock
1389                     The  clustering  algorithm  repeatedly  casts out outlier
1390                     associations until no  more  than  minclock  associations
1391                     remain.   This value defaults to 3, but can be changed to
1392                     any number from 1 to the number of configured sources.
1393
1394              minsane minsane
1395                     This is the minimum number of candidates available to the
1396                     clock selection algorithm in order to produce one or more
1397                     truechimers for the clustering algorithm.  If fewer  than
1398                     this number are available, the clock is undisciplined and
1399                     allowed to run free.  The default is 1  for  legacy  pur‐
1400                     poses.   However,  according  to  principles of Byzantine
1401                     agreement, minsane should be  at  least  4  in  order  to
1402                     detect and discard a single falseticker.
1403
1404       ttl hop ...
1405              This command specifies a list of TTL values in increasing order,
1406              up to 8 values can be specified.  In manycast mode these  values
1407              are  used  in  turn in an expanding-ring search.  The default is
1408              eight multiples of 32 starting at 31.
1409

Reference Clock Support

1411       The NTP Version 4 daemon supports some  three  dozen  different  radio,
1412       satellite  and  modem reference clocks plus a special pseudo-clock used
1413       for backup or when  no  other  clock  source  is  available.   Detailed
1414       descriptions  of  individual device drivers and options can be found in
1415       the "Reference Clock Drivers" page (available as part of the HTML docu‐
1416       mentation  provided in /usr/share/doc/ntp).  Additional information can
1417       be found in the pages linked there, including the "Debugging Hints  for
1418       Reference  Clock  Drivers"  and "How To Write a Reference Clock Driver"
1419       pages  (available  as  part  of  the  HTML  documentation  provided  in
1420       /usr/share/doc/ntp).   In  addition, support for a PPS signal is avail‐
1421       able as described in the "Pulse-per-second  (PPS)  Signal  Interfacing"
1422       page   (available  as  part  of  the  HTML  documentation  provided  in
1423       /usr/share/doc/ntp).   Many  drivers  support   special   line   disci‐
1424       pline/streams  modules  which  can  significantly  improve the accuracy
1425       using the driver.  These are described in  the  "Line  Disciplines  and
1426       Streams Drivers" page (available as part of the HTML documentation pro‐
1427       vided in /usr/share/doc/ntp).
1428
1429       A reference clock will generally (though not always) be a  radio  time‐
1430       code  receiver  which is synchronized to a source of standard time such
1431       as the services offered by the NRC in Canada and NIST and USNO  in  the
1432       US.   The  interface  between the computer and the timecode receiver is
1433       device dependent, but is usually a serial port.  A device  driver  spe‐
1434       cific to each reference clock must be selected and compiled in the dis‐
1435       tribution; however, most common radio, satellite and modem  clocks  are
1436       included  by  default.   Note  that an attempt to configure a reference
1437       clock when the driver has not been compiled or the  hardware  port  has
1438       not  been  appropriately configured results in a scalding remark to the
1439       system log file, but is otherwise non hazardous.
1440
1441       For the purposes of configuration, ntpd(8) treats reference clocks in a
1442       manner  analogous  to  normal NTP peers as much as possible.  Reference
1443       clocks are  identified  by  a  syntactically  correct  but  invalid  IP
1444       address, in order to distinguish them from normal NTP peers.  Reference
1445       clock addresses are of the form 127.127.t.u,  where  t  is  an  integer
1446       denoting  the  clock  type and u indicates the unit number in the range
1447       0-3.  While it may seem overkill, it is in  fact  sometimes  useful  to
1448       configure multiple reference clocks of the same type, in which case the
1449       unit numbers must be unique.
1450
1451       The server command is used to configure a reference  clock,  where  the
1452       address  argument  in that command is the clock address.  The key, ver‐
1453       sion and ttl options are not used for  reference  clock  support.   The
1454       mode  option  is added for reference clock support, as described below.
1455       The prefer option can be useful to persuade the  server  to  cherish  a
1456       reference  clock  with  somewhat  more  enthusiasm than other reference
1457       clocks or peers.  Further information on this option can  be  found  in
1458       the "Mitigation Rules and the prefer Keyword" (available as part of the
1459       HTML documentation provided in /usr/share/doc/ntp) page.   The  minpoll
1460       and  maxpoll options have meaning only for selected clock drivers.  See
1461       the individual clock driver document pages for additional information.
1462
1463       The fudge command is used to provide additional information  for  indi‐
1464       vidual  clock drivers and normally follows immediately after the server
1465       command.  The address argument specifies the clock address.  The  refid
1466       and  stratum  options  can  be  used  to  override the defaults for the
1467       device.  There are two optional device-dependent time offsets and  four
1468       flags that can be included in the fudge command as well.
1469
1470       The  stratum number of a reference clock is by default zero.  Since the
1471       ntpd(8) daemon adds one to the stratum of each peer, a  primary  server
1472       ordinarily  displays  an  external stratum of one.  In order to provide
1473       engineered backups, it is often useful to specify the  reference  clock
1474       stratum as greater than zero.  The stratum option is used for this pur‐
1475       pose.  Also, in cases involving both a reference clock and a pulse-per-
1476       second  (PPS)  discipline signal, it is useful to specify the reference
1477       clock identifier as other than the default, depending  on  the  driver.
1478       The  refid  option is used for this purpose.  Except where noted, these
1479       options apply to all clock drivers.
1480
1481   Reference Clock Commands
1482       server 127.127.t.u [prefer] [mode int] [minpoll int] [maxpoll int]
1483              This command can be used to configure reference clocks  in  spe‐
1484              cial ways.  The options are interpreted as follows:
1485
1486              prefer Marks the reference clock as preferred.  All other things
1487                     being equal, this host will be chosen for synchronization
1488                     among a set of correctly operating hosts.  See the "Miti‐
1489                     gation Rules and the prefer Keyword" page  (available  as
1490                     part    of    the    HTML   documentation   provided   in
1491                     /usr/share/doc/ntp) for further information.
1492
1493              mode int
1494                     Specifies a mode number which is interpreted in a device-
1495                     specific  fashion.   For  instance,  it selects a dialing
1496                     protocol in the ACTS driver and a device subtype  in  the
1497                     parse drivers.
1498
1499              minpoll int
1500
1501              maxpoll int
1502                     These  options  specify  the  minimum and maximum polling
1503                     interval for reference clock messages, as a power of 2 in
1504                     seconds  For  most  directly  connected reference clocks,
1505                     both minpoll and maxpoll default to 6 (64 s).  For  modem
1506                     reference  clocks,  minpoll  defaults  to 10 (17.1 m) and
1507                     maxpoll defaults to 14 (4.5 h).  The allowable range is 4
1508                     (16 s) to 17 (36.4 h) inclusive.
1509
1510       fudge  127.127.t.u [time1 sec] [time2 sec] [stratum int] [refid string]
1511       [mode int] [flag1 0 | 1] [flag2 0 | 1] [flag3 0 | 1] [flag4 0 | 1]
1512              This command can be used to configure reference clocks  in  spe‐
1513              cial  ways.  It must immediately follow the server command which
1514              configures the driver.  Note that the same capability is  possi‐
1515              ble  at  run  time  using the ntpdc(8) program.  The options are
1516              interpreted as follows:
1517
1518              time1 sec
1519                     Specifies a constant to be added to the time offset  pro‐
1520                     duced by the driver, a fixed-point decimal number in sec‐
1521                     onds.  This is used as a calibration constant  to  adjust
1522                     the  nominal  time  offset of a particular clock to agree
1523                     with an external standard, such as a precision  PPS  sig‐
1524                     nal.   It  also  provides  a  way to correct a systematic
1525                     error or bias due to  serial  port  or  operating  system
1526                     latencies,  different  cable lengths or receiver internal
1527                     delay.  The specified offset is in addition to the propa‐
1528                     gation  delay  provided  by other means, such as internal
1529                     DIPswitches.  Where a calibration for an individual  sys‐
1530                     tem and driver is available, an approximate correction is
1531                     noted in the driver documentation pages.  Note: in  order
1532                     to  facilitate calibration when more than one radio clock
1533                     or PPS signal is supported, a special calibration feature
1534                     is  available.   It  takes the form of an argument to the
1535                     enable command described in  Miscellaneous  Options  page
1536                     and  operates  as described in the "Reference Clock Driv‐
1537                     ers" page (available as part of  the  HTML  documentation
1538                     provided in /usr/share/doc/ntp).
1539
1540              time2 secs
1541                     Specifies  a fixed-point decimal number in seconds, which
1542                     is  interpreted  in  a  driver-dependent  way.   See  the
1543                     descriptions  of specific drivers in the "Reference Clock
1544                     Drivers" page (available as part of the  HTML  documenta‐
1545                     tion provided in /usr/share/doc/ntp ).
1546
1547              stratum int
1548                     Specifies  the  stratum number assigned to the driver, an
1549                     integer between 0 and  15.   This  number  overrides  the
1550                     default  stratum number ordinarily assigned by the driver
1551                     itself, usually zero.
1552
1553              refid string
1554                     Specifies an ASCII string of from one to four  characters
1555                     which  defines  the  reference  identifier  used  by  the
1556                     driver.  This string  overrides  the  default  identifier
1557                     ordinarily assigned by the driver itself.
1558
1559              mode int
1560                     Specifies a mode number which is interpreted in a device-
1561                     specific fashion.  For instance,  it  selects  a  dialing
1562                     protocol  in  the ACTS driver and a device subtype in the
1563                     parse drivers.
1564
1565              flag1 0 | 1
1566
1567              flag2 0 | 1
1568
1569              flag3 0 | 1
1570
1571              flag4 0 | 1
1572                     These four flags  are  used  for  customizing  the  clock
1573                     driver.   The interpretation of these values, and whether
1574                     they are used at all, is a  function  of  the  particular
1575                     clock  driver.   However,  by convention flag4 is used to
1576                     enable recording monitoring data to the  clockstats  file
1577                     configured with the filegen command.  Further information
1578                     on  the  filegen  command  can  be  found  in  Monitoring
1579                     Options.
1580

Miscellaneous Options

1582       broadcastdelay seconds
1583              The  broadcast and multicast modes require a special calibration
1584              to determine the network delay  between  the  local  and  remote
1585              servers.   Ordinarily, this is done automatically by the initial
1586              protocol exchanges between  the  client  and  server.   In  some
1587              cases,  the  calibration  procedure  may  fail due to network or
1588              server access controls, for example.  This command specifies the
1589              default  delay  to be used under these circumstances.  Typically
1590              (for Ethernet), a number between  0.003  and  0.007  seconds  is
1591              appropriate.  The default when this command is not used is 0.004
1592              seconds.
1593
1594       calldelay delay
1595              This option controls the delay in seconds between the first  and
1596              second  packets sent in burst or iburst mode to allow additional
1597              time for a modem or ISDN call to complete.
1598
1599       driftfile driftfile
1600              This command specifies the complete path and name  of  the  file
1601              used  to  record  the  frequency  of the local clock oscillator.
1602              This is the same operation as the -f command  line  option.   If
1603              the  file exists, it is read at startup in order to set the ini‐
1604              tial frequency and then updated once per hour with  the  current
1605              frequency  computed  by  the daemon.  If the file name is speci‐
1606              fied, but the file itself does not exist,  the  starts  with  an
1607              initial  frequency  of zero and creates the file when writing it
1608              for the first time.  If this command is not  given,  the  daemon
1609              will always start with an initial frequency of zero.
1610
1611              The  file  format  consists of a single line containing a single
1612              floating point number, which records the frequency  offset  mea‐
1613              sured  in parts-per-million (PPM).  The file is updated by first
1614              writing the current drift value into a temporary file  and  then
1615              renaming  this  file  to  replace the old version.  This implies
1616              that ntpd(8) must have write permission for  the  directory  the
1617              drift  file  is located in, and that file system links, symbolic
1618              or otherwise, should be avoided.
1619
1620       dscp value
1621              This option specifies the Differentiated Services Control  Point
1622              (DSCP) value, a 6-bit code.  The default value is 46, signifying
1623              Expedited Forwarding.
1624
1625       enable [auth | bclient | calibrate | kernel | mode7 | monitor |  ntp  |
1626       stats     |    peer_clear_digest_early    |    unpeer_crypto_early    |
1627       unpeer_crypto_nak_early | unpeer_digest_early]
1628
1629       disable [auth | bclient | calibrate | kernel | mode7 | monitor | ntp  |
1630       stats     |    peer_clear_digest_early    |    unpeer_crypto_early    |
1631       unpeer_crypto_nak_early | unpeer_digest_early]
1632              Provides a way to enable  or  disable  various  server  options.
1633              Flags  not  mentioned  are  unaffected.   Note that all of these
1634              flags can be controlled remotely using the ntpdc(8) utility pro‐
1635              gram.
1636
1637              auth   Enables the server to synchronize with unconfigured peers
1638                     only if the peer has been correctly  authenticated  using
1639                     either  public  key  or  private  key  cryptography.  The
1640                     default for this flag is enable.
1641
1642              bclient
1643                     Enables the server to listen for a message from a  broad‐
1644                     cast  or multicast server, as in the multicastclient com‐
1645                     mand with default address.  The default for this flag  is
1646                     disable.
1647
1648              calibrate
1649                     Enables  the calibrate feature for reference clocks.  The
1650                     default for this flag is disable.
1651
1652              kernel Enables the kernel time discipline,  if  available.   The
1653                     default  for this flag is enable if support is available,
1654                     otherwise disable.
1655
1656              mode7  Enables processing of NTP mode 7  implementation-specific
1657                     requests  which  are used by the deprecated ntpdc(8) pro‐
1658                     gram.  The default for this flag is disable.   This  flag
1659                     is  excluded  from  runtime  configuration using ntpq(8).
1660                     The ntpq(8) program provides  the  same  capabilities  as
1661                     ntpdc(8) using standard mode 6 requests.
1662
1663              monitor
1664                     Enables  the  monitoring facility.  See the ntpdc(8) pro‐
1665                     gram and the monlist command or further information.  The
1666                     default for this flag is enable.
1667
1668              ntp    Enables  time  and frequency discipline.  In effect, this
1669                     switch opens and closes the feedback loop, which is  use‐
1670                     ful for testing.  The default for this flag is enable.
1671
1672              peer_clear_digest_early
1673                     By default, if ntpd(8) is using autokey and it receives a
1674                     crypto-NAK packet that passes the  duplicate  packet  and
1675                     origin  timestamp  checks  the peer variables are immedi‐
1676                     ately cleared.  While this is generally a feature  as  it
1677                     allows  for quick recovery if a server key has changed, a
1678                     properly forged and  appropriately  delivered  crypto-NAK
1679                     packet  can  be used in a DoS attack.  If you have active
1680                     noticable problems with this type of DoS attack then  you
1681                     should  consider  disabling  this  option.  You can check
1682                     your peerstats file for evidence of any of these attacks.
1683                     The default for this flag is enable.
1684
1685              stats  Enables  the  statistics  facility.   See  the Monitoring
1686                     Options section for further information.  The default for
1687                     this flag is disable.
1688
1689              unpeer_crypto_early
1690                     By  default,  if  ntpd(8) receives an autokey packet that
1691                     fails TEST9, a crypto failure, the association is immedi‐
1692                     ately  cleared.   This is almost certainly a feature, but
1693                     if, in spite of the current recommendation of  not  using
1694                     autokey,  you  are still using autokey and you are seeing
1695                     this sort of DoS attack disabling this  flag  will  delay
1696                     tearing  down  the  association  until  the  reachability
1697                     counter becomes zero.  You can check your peerstats  file
1698                     for  evidence  of  any of these attacks.  The default for
1699                     this flag is enable.
1700
1701              unpeer_crypto_nak_early
1702                     By default, if ntpd(8) receives a crypto-NAK packet  that
1703                     passes  the  duplicate packet and origin timestamp checks
1704                     the association is immediately cleared.   While  this  is
1705                     generally  a feature as it allows for quick recovery if a
1706                     server key has changed, a properly forged  and  appropri‐
1707                     ately  delivered  crypto-NAK  packet can be used in a DoS
1708                     attack.  If you have active noticable problems with  this
1709                     type  of  DoS  attack  then you should consider disabling
1710                     this option.  You can check your peerstats file for  evi‐
1711                     dence of any of these attacks.  The default for this flag
1712                     is enable.
1713
1714              unpeer_digest_early
1715                     By default, if ntpd(8) receives what should be an authen‐
1716                     ticated packet that passes other packet sanity checks but
1717                     contains an invalid digest the association is immediately
1718                     cleared.   While this is generally a feature as it allows
1719                     for quick recovery, if this type of packet  is  carefully
1720                     forged  and  sent  during an appropriate window it can be
1721                     used for a DoS attack.   If  you  have  active  noticable
1722                     problems  with  this  type  of DoS attack then you should
1723                     consider disabling this option.  You can check your peer‐
1724                     stats  file  for  evidence  of any of these attacks.  The
1725                     default for this flag is enable.
1726
1727       includefile includefile
1728              This command allows  additional  configuration  commands  to  be
1729              included from a separate file.  Include files may be nested to a
1730              depth of five; upon reaching the end of any include  file,  com‐
1731              mand  processing  resumes  in  the  previous configuration file.
1732              This option is useful for sites that  run  ntpd(8)  on  multiple
1733              hosts, with (mostly) common options (e.g., a restriction list).
1734
1735       interface [listen | ignore | drop] [all | ipv4 | ipv6 | wildcard name |
1736       address [/ prefixlen]]
1737              The interface directive controls which network addresses ntpd(8)
1738              opens,  and  whether  input  is dropped without processing.  The
1739              first parameter determines the action for addresses which  match
1740              the second parameter.  The second parameter specifies a class of
1741              addresses, or a specific interface name, or an address.  In  the
1742              address  case, prefixlen determines how many bits must match for
1743              this rule to apply.  ignore prevents opening matching addresses,
1744              drop  causes  ntpd(8)  to open the address and drop all received
1745              packets without examination.  Multiple interface directives  can
1746              be  used.   The  last  rule  which  matches a particular address
1747              determines the action for it.  interface directives are disabled
1748              if  any  -I,  --interface,  -L,  or  --novirtualips command-line
1749              options are specified in the configuration file,  all  available
1750              network addresses are opened.  The nic directive is an alias for
1751              interface.
1752
1753       leapfile leapfile
1754              This command loads the IERS leapseconds file and initializes the
1755              leapsecond  values for the next leapsecond event, leapfile expi‐
1756              ration time, and TAI offset.  The file can be obtained  directly
1757              from the IERS at https://hpiers.obspm.fr/iers/bul/bulc/ntp/leap-
1758              seconds.list  or   ftp://hpiers.obspm.fr/iers/bul/bulc/ntp/leap-
1759              seconds.list.   The  leapfile  is scanned when ntpd(8) processes
1760              the leapfile directive or when ntpd detects  that  the  leapfile
1761              has  changed.  ntpd checks once a day to see if the leapfile has
1762              changed.  The update-leap(1update_leapmdoc) script can be run to
1763              see if the leapfile should be updated.
1764
1765       leapsmearinterval seconds
1766              This  EXPERIMENTAL option is only available if ntpd(8) was built
1767              with the --enable-leap-smear option to the configure script.  It
1768              specifies  the interval over which a leap second correction will
1769              be applied.  Recommended values for this option are between 7200
1770              (2  hours)  and  86400 (24 hours).  See http://bugs.ntp.org/2855
1771              for more information.
1772
1773       logconfig configkeyword
1774              This command controls the amount and type of output  written  to
1775              the system syslog(3) facility or the alternate logfile log file.
1776              By default, all output is turned on.  All configkeyword keywords
1777              can  be  prefixed with ‘=’, ‘+’ and ‘-’, where ‘=’ sets the sys‐
1778              log(3) priority mask, ‘+’ adds and ‘-’ removes  messages.   sys‐
1779              log(3)  messages can be controlled in four classes (clock, peer,
1780              sys and sync).  Within these classes four types of messages  can
1781              be  controlled:  informational  messages  (info), event messages
1782              (events), statistics messages (statistics) and  status  messages
1783              (status).
1784
1785              Configuration  keywords  are formed by concatenating the message
1786              class with the event class.  The all prefix can be used  instead
1787              of a message class.  A message class may also be followed by the
1788              all keyword to enable/disable all  messages  of  the  respective
1789              message  class.   Thus,  a  minimal log configuration could look
1790              like this:
1791                  logconfig =syncstatus +sysevents
1792
1793              This would just list the synchronizations state of  ntpd(8)  and
1794              the  major  system  events.   For a simple reference server, the
1795              following minimum message configuration could be useful:
1796                  logconfig =syncall +clockall
1797
1798              This configuration will list all clock information and  synchro‐
1799              nization  information.   All  other  events  and  messages about
1800              peers, system events and so on is suppressed.
1801
1802       logfile logfile
1803              This command specifies the location of an alternate log file  to
1804              be  used instead of the default system syslog(3) facility.  This
1805              is the same operation as the -l command line option.
1806
1807       mru [maxdepth count | maxmem kilobytes | mindepth count |  maxage  sec‐
1808       onds  |  initialloc count | initmem kilobytes | incalloc count | incmem
1809       kilobytes]
1810              Controls size limite of the monitoring facility's Most  Recently
1811              Used  (MRU)  list of client addresses, which is also used by the
1812              rate control facility.
1813
1814              maxdepth count
1815
1816              maxmem kilobytes
1817                     Equivalent upper limits on the size of the MRU  list,  in
1818                     terms  of entries or kilobytes.  The acutal limit will be
1819                     up to incalloc entries or incmem  kilobytes  larger.   As
1820                     with  all  of the mru options offered in units of entries
1821                     or kilobytes, if both maxdepth and maxmem are  used,  the
1822                     last one used controls.  The default is 1024 kilobytes.
1823
1824              mindepth count
1825                     Lower  limit on the MRU list size.  When the MRU list has
1826                     fewer than mindepth entries, existing entries  are  never
1827                     removed  to make room for newer ones, regardless of their
1828                     age.  The default is 600 entries.
1829
1830              maxage seconds
1831                     Once the MRU list has mindepth entries and an  additional
1832                     client  is  to  ba added to the list, if the oldest entry
1833                     was updated more than maxage seconds ago, that  entry  is
1834                     removed  and  its storage is reused.  If the oldest entry
1835                     was updated more recently the MRU list is grown,  subject
1836                     to maxdepth / moxmem.  The default is 64 seconds.
1837
1838              initalloc count
1839
1840              initmem kilobytes
1841                     Initial  memory  allocation at the time the monitoringfa‐
1842                     cility is first  enabled,  in  terms  of  the  number  of
1843                     entries or kilobytes.  The default is 4 kilobytes.
1844
1845              incalloc count
1846
1847              incmem kilobytes
1848                     Size  of  additional  memory allocations when growing the
1849                     MRU list, in entries or  kilobytes.   The  default  is  4
1850                     kilobytes.
1851
1852       nonvolatile threshold
1853              Specify  the  threshold delta in seconds before an hourly change
1854              to the driftfile  (frequency  file)  will  be  written,  with  a
1855              default  value  of  1e-7  (0.1  PPM).   The  frequency  file  is
1856              inspected each hour.  If the difference between the current fre‐
1857              quency  and  the  last  value written exceeds the threshold, the
1858              file is written and the  threshold  becomes  the  new  threshold
1859              value.   If  the  threshold  is  not exceeeded, it is reduced by
1860              half.  This is intended to reduce the number of file writes  for
1861              embedded systems with nonvolatile memory.
1862
1863       phone dial ...
1864              This  command  is used in conjunction with the ACTS modem driver
1865              (type 18) or the JJY driver (type 40, mode 100 - 180).  For  the
1866              ACTS  modem driver (type 18), the arguments consist of a maximum
1867              of 10 telephone numbers used to dial  USNO,  NIST,  or  European
1868              time  service.  For the JJY driver (type 40 mode 100 - 180), the
1869              argument is one telephone number used to dial the telephone  JJY
1870              service.   The  Hayes  command ATDT is normally prepended to the
1871              number.  The number can contain other  modem  control  codes  as
1872              well.
1873
1874       pollskewlist [poll value | value] ... [default value | value]
1875              Enable  skewing  of our poll requests to our servers.  poll is a
1876              number between 3 and 17 inclusive, identifying a  specific  poll
1877              interval.  A poll interval is 2^n seconds in duration, so a poll
1878              value of 3 corresponds to 8 seconds and a poll  interval  of  17
1879              corresponds  to 131,072 seconds, or about a day and a half.  The
1880              next two numbers must be between 0  and  one-half  of  the  poll
1881              interval,  inclusive.   The first number specifies how early the
1882              poll may start, while the second number specifies how  late  the
1883              poll  may  be  delayed.  With no arguments, internally specified
1884              default values are chosen.
1885
1886       reset [allpeers] [auth] [ctl] [io] [mem] [sys] [timer]
1887              Reset one or more groups of  counters  maintained  by  ntpd  and
1888              exposed by ntpq and ntpdc.
1889
1890       rlimit  [memlock  Nmegabytes | stacksize N4kPages filenum Nfiledescrip‐
1891       tors]
1892
1893              memlock Nmegabytes
1894                     Specify the number of megabytes of memory that should  be
1895                     allocated  and  locked.   Probably  only  available under
1896                     Linux, this option may be useful when dropping root  (the
1897                     -i  option).   The  default  is 32 megabytes on non-Linux
1898                     machines, and -1 under Linux.  -1 means "do not lock  the
1899                     process  into memory".  0 means "lock whatever memory the
1900                     process wants into memory".
1901
1902              stacksize N4kPages
1903                     Specifies the maximum size of the process stack  on  sys‐
1904                     tems  with  the  mlockall()  function.  Defaults to 50 4k
1905                     pages (200 4k pages in OpenBSD).
1906
1907              filenum Nfiledescriptors
1908                     Specifies the maximum number of file descriptors ntpd may
1909                     have open at once.  Defaults to the system default.
1910
1911       saveconfigdir directory_path
1912              Specify  the directory in which to write configuration snapshots
1913              requested with saveconfig command.  If  saveconfigdir  does  not
1914              appear  in  the  configuration  file,  saveconfig  requests  are
1915              rejected by ntpd.
1916
1917       saveconfig filename
1918              Write the current configuration, including any runtime modifica‐
1919              tions  given with :config or config-from-file to the ntpd host's
1920              filename in the saveconfigdir.  This command  will  be  rejected
1921              unless  the  saveconfigdir  directive  appears  in configuration
1922              file.  filename can use strftime(3) format directives to substi‐
1923              tute   the   current   date  and  time,  for  example,  savecon‐
1924              fig ntp-%Y%m%d-%H%M%S.conf.  The filename used is stored in  the
1925              system variable savedconfig.  Authentication is required.
1926
1927       setvar variable [default]
1928              This  command  adds  an additional system variable.  These vari‐
1929              ables can be used to distribute additional information  such  as
1930              the  access  policy.   If the variable of the form name=value is
1931              followed by the default keyword, the variable will be listed  as
1932              part  of  the  default  system  variables (ntpq(8) rv command)).
1933              These additional variables serve  informational  purposes  only.
1934              They  are  not  related  to  the protocol other that they can be
1935              listed.  The known protocol variables will always  override  any
1936              variables  defined  via  the  setvar mechanism.  There are three
1937              special variables that contain the names of all variable of  the
1938              same  group.   The  sys_var_list  holds  the names of all system
1939              variables.  The peer_var_list holds the names of all peer  vari‐
1940              ables  and  the  clock_var_list holds the names of the reference
1941              clock variables.
1942
1943       sysinfo
1944              Display operational summary.
1945
1946       sysstats
1947              Show statistics counters maintained in the protocol module.
1948
1949       tinker [allan allan | dispersion dispersion  |  freq  freq  |  huffpuff
1950       huffpuff  |  panic  panic  |  step  step  | stepback stepback | stepfwd
1951       stepfwd | stepout stepout]
1952              This command can be used to alter several  system  variables  in
1953              very exceptional circumstances.  It should occur in the configu‐
1954              ration file before any other configuration options.  The default
1955              values  of  these  variables have been carefully optimized for a
1956              wide range of network speeds and reliability  expectations.   In
1957              general,  they  interact in intricate ways that are hard to pre‐
1958              dict and some combinations can result in some very nasty  behav‐
1959              ior.   Very rarely is it necessary to change the default values;
1960              but, some folks cannot resist twisting the knobs anyway and this
1961              command  is for them.  Emphasis added: twisters are on their own
1962              and can expect no help from the support group.
1963
1964              The variables operate as follows:
1965
1966              allan allan
1967                     The argument becomes the new value for the minimum  Allan
1968                     intercept, which is a parameter of the PLL/FLL clock dis‐
1969                     cipline algorithm.  The value in log2 seconds defaults to
1970                     7 (1024 s), which is also the lower limit.
1971
1972              dispersion dispersion
1973                     The  argument  becomes  the  new value for the dispersion
1974                     increase rate, normally .000015 s/s.
1975
1976              freq freq
1977                     The argument becomes the initial value of  the  frequency
1978                     offset in parts-per-million.  This overrides the value in
1979                     the frequency file, if present, and  avoids  the  initial
1980                     training state if it is not.
1981
1982              huffpuff huffpuff
1983                     The  argument  becomes the new value for the experimental
1984                     huff-n'-puff  filter  span,  which  determines  the  most
1985                     recent  interval  the algorithm will search for a minimum
1986                     delay.  The lower limit is 900 s (15 m), but a more  rea‐
1987                     sonable  value  is  7200 (2 hours).  There is no default,
1988                     since the filter is not enabled unless  this  command  is
1989                     given.
1990
1991              panic panic
1992                     The argument is the panic threshold, normally 1000 s.  If
1993                     set to zero, the panic sanity check  is  disabled  and  a
1994                     clock offset of any value will be accepted.
1995
1996              step step
1997                     The  argument  is the step threshold, which by default is
1998                     0.128 s.  It can be set to any positive  number  in  sec‐
1999                     onds.  If set to zero, step adjustments will never occur.
2000                     Note: The kernel time discipline is disabled if the  step
2001                     threshold is set to zero or greater than the default.
2002
2003              stepback stepback
2004                     The  argument  is  the  step  threshold  for the backward
2005                     direction, which by default is 0.128 s.  It can be set to
2006                     any  positive number in seconds.  If both the forward and
2007                     backward step thresholds are set to  zero,  step  adjust‐
2008                     ments will never occur.  Note: The kernel time discipline
2009                     is disabled if  each  direction  of  step  threshold  are
2010                     either set to zero or greater than .5 second.
2011
2012              stepfwd stepfwd
2013                     As for stepback, but for the forward direction.
2014
2015              stepout stepout
2016                     The  argument is the stepout timeout, which by default is
2017                     900 s.  It can be set to any positive number in  seconds.
2018                     If  set  to  zero,  the  stepout  pulses will not be sup‐
2019                     pressed.
2020
2021       writevar assocID name = value [,...]
2022              Write (create or update) the specified variables.  If the  asso‐
2023              cID  is  zero,  the  variablea re from the system variables name
2024              space, otherwise they are from the peer  variables  name  space.
2025              The assocID is required, as the same name can occur in both name
2026              spaces.
2027
2028       trap host_address [port port_number] [interface interface_address]
2029              This command configures  a  trap  receiver  at  the  given  host
2030              address  and port number for sending messages with the specified
2031              local interface address.  If the port number is  unspecified,  a
2032              value  of 18447 is used.  If the interface address is not speci‐
2033              fied, the message is sent with a source  address  of  the  local
2034              interface  the  message  is sent through.  Note that on a multi‐
2035              homed host the interface used may vary from time  to  time  with
2036              routing changes.
2037
2038       ttl hop ...
2039              This command specifies a list of TTL values in increasing order.
2040              Up to 8 values can be specified.  In manycast mode these  values
2041              are  used  in-turn  in an expanding-ring search.  The default is
2042              eight multiples of 32 starting at 31.
2043
2044              The trap receiver will generally log event  messages  and  other
2045              information  from  the server in a log file.  While such monitor
2046              programs may also request their own trap dynamically,  configur‐
2047              ing  a  trap receiver will ensure that no messages are lost when
2048              the server is started.
2049
2050       hop ...
2051              This command specifies a list of TTL values in increasing order,
2052              up  to 8 values can be specified.  In manycast mode these values
2053              are used in turn in an expanding-ring search.   The  default  is
2054              eight multiples of 32 starting at 31.
2055

OPTIONS

2057       --help Display usage information and exit.
2058
2059       --more-help
2060              Pass the extended usage information through a pager.
2061
2062       --version [{v|c|n}]
2063              Output  version of program and exit.  The default mode is `v', a
2064              simple version.  The `c' mode will print  copyright  information
2065              and `n' will print the full copyright notice.
2066

OPTION PRESETS

2068       Any option that is not marked as not presettable may be preset by load‐
2069       ing values from environment variables named:
2070         NTP_CONF_<option-name> or NTP_CONF
2071

ENVIRONMENT

2073       See OPTION PRESETS for configuration environment variables.
2074

FILES

2076       /etc/ntp.conf  the default name of the configuration file
2077       ntp.keys       private MD5 keys
2078       ntpkey         RSA private key
2079       ntpkey_host    RSA public key
2080       ntp_dh         Diffie-Hellman agreement parameters
2081

EXIT STATUS

2083       One of the following exit values will be returned:
2084
2085       0  (EXIT_SUCCESS)
2086              Successful program execution.
2087
2088       1  (EXIT_FAILURE)
2089              The operation failed or the command syntax was not valid.
2090
2091       70  (EX_SOFTWARE)
2092              libopts had an internal operational error.  Please report it  to
2093              autogen-users@lists.sourceforge.net.  Thank you.
2094

SEE ALSO

2096       ntpd(8), ntpdc(8), ntpq(8)
2097
2098       In  addition  to the manual pages provided, comprehensive documentation
2099       is available on the world wide web at http://www.ntp.org/.  A  snapshot
2100       of    this    documentation    is   available   in   HTML   format   in
2101       /usr/share/doc/ntp.  David L. Mills, Network Time Protocol (Version 4),
2102       RFC5905
2103

AUTHORS

2105       The University of Delaware and Network Time Foundation
2106
2108       Copyright  (C)  1992-2020  The  University of Delaware and Network Time
2109       Foundation all rights reserved.  This program  is  released  under  the
2110       terms of the NTP license, <http://ntp.org/license>.
2111

BUGS

2113       The  syntax  checking is not picky; some combinations of ridiculous and
2114       even hilarious options and modes may not be detected.
2115
2116       The ntpkey_host files are really digital certificates.  These should be
2117       obtained  via  secure  directory  services when they become universally
2118       available.
2119
2120       Please send bug reports to: http://bugs.ntp.org, bugs@ntp.org
2121

NOTES

2123       This document was derived from FreeBSD.
2124
2125       This manual page was AutoGen-erated from the  ntp.conf  option  defini‐
2126       tions.
2127
2128
2129
21304.2.8p15                          23 Jun 2020                      ntp.conf(5)
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