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ntp.conf(5) File Formats Manual ntp.conf(5)
NAME
ntp.conf - Server Options
Following is a description of the configuration commands in NTPv4. There are two classes
of commands, configuration commands that configure an association with a remote server,
peer or reference clock, and auxilliary commands that specify environmental variables that
control various related operations.
The various modes described on the Association Management page are determined by the com-
mand keyword and the DNS name or IP address. Addresses are classed by type as (s) a remote
server or peer (IPv4 class A, B and C), (b) the IP broadcast address of a local interface,
(m) a multicast address (IPv4 class D), or (r) a reference clock address (127.127.x.x).
For type m addresses the IANA has assigned the multicast group address IPv4 224.0.1.1 and
IPv6 ff05::101 (site local) exclusively to NTP, but other nonconflicting addresses can be
used.
If the Basic Socket Interface Extensions for IPv6 (RFC-2553) is detected, support for the
IPv6 address family is generated in addition to the default IPv4 address family. IPv6
addresses can be identified by the presence of colons ":" in the address field. IPv6
addresses can be used almost everywhere where IPv4 addresses can be used, with the excep-
tion of reference clock addresses, which are always IPv4. Note that in contexts where a
host name is expected, a -4 qualifier preceding the host name forces DNS resolution to the
IPv4 namespace, while a -6 qualifier forces DNS resolution to the IPv6 namespace.
CONFIGURATION COMMANDS
server address [options ...]
peer address [options ...]
broadcast address [options ...]
manycastclient address [options ...]
pool address [options ...]
unpeer [address | associd]
These commands specify the time server name or address to be used and the mode in
which to operate. The address can be either a DNS name or a IPv4 or IPv6 address
in standard notation. In general, multiple commands of each type can be used for
different server and peer addresses or multicast groups.
server For type s and r addresses (only), this command mobilizes a persistent
client mode association with the specified remote server or local refer-
ence clock. If the preempt flag is specified, a preemptable client mode
association is mobilized instead.
peer For type s addresses (only), this command mobilizes a persistent symmet-
ric-active mode association with the specified remote peer.
broadcast
For type b and m addressees (only), this command mobilizes a persistent
broadcast or multicast server mode association. Note that type b messages
go only to the interface specified, but type m messages go to all inter-
faces.
manycastclient
For type m addresses (only), this command mobilizes a manycast client mode
association for the multicast group address specified. In this mode the
address must match the address specified on the manycastserver command of
one or more designated manycast servers.
pool For type s messages (only) this command mobilizes a client mode associa-
tion for servers implementing the pool automatic server discovery scheme
described on the Association Management page. The address is a DNS name in
the form area.pool.ntp.org, where area is a qualifier designating the
server geographic area such as us or europe.
unpeer This command removes a previously configured association. An address or
association ID can be used to identify the association. Either an IP
address or DNS name can be used. This command is most useful when supplied
via ntpq runtime configuration commands :config and config-from-file.
COMMAND OPTIONS
autokey Send and receive packets authenticated by the Autokey scheme described in the
Authentication Options page. This option is mutually exclusive with the key
option.
burst When the server is reachable, send a burst of eight packets instead of the usual
one. The packet spacing is normally 2 s; however, the spacing between the first
and second packets can be changed with the calldelay command to allow additional
time for a modem or ISDN call to complete. This option is valid only with the
server command and type s addressesa. It is a recommended option when the maxpoll
option is greater than 10 (1024 s).
iburst When the server is unreachable, send a burst of eight packets instead of the usual
one. The packet spacing is normally 2 s; however, the spacing between the first
and second packets can be changed with the calldelay command to allow additional
time for a modem or ISDN call to complete. This option is valid only with the
server command and type s addresses. It is a recommended option with this command.
key key Send and receive packets authenticated by the symmetric key scheme described in
the Authentication Options page. The key specifies the key identifier with values
from 1 to 65534, inclusive. This option is mutually exclusive with the autokey
option.
minpoll minpoll
maxpoll maxpoll
These options specify the minimum and maximum poll intervals for NTP messages, in
seconds as a power of two. The maximum poll interval defaults to 10 (1024 s), but
can be increased by the maxpoll option to an upper limit of 17 (36 h). The minimum
poll interval defaults to 6 (64 s), but can be decreased by the minpoll option to
a lower limit of 3 (8 s).
mode option
Pass the option to a reference clock driver, where option is an integer in the
range from 0 to 255, inclusive. This option is valid only with type r addresses.
noselect
Marks the server or peer to be ignored by the selection algorithm but visible to
the monitoring program. This option is ignored with the broadcast command.
preempt Specifies the association as preemptable rather than the default persistent. This
option is ignored with the broadcast command and is most useful with the manycast-
client and pool commands.
prefer Mark the server as preferred. All other things being equal, this host will be cho-
sen for synchronization among a set of correctly operating hosts. See the Mitiga-
tion Rules and the prefer Keyword page for further information. This option is
valid only with the server and peer commands.
true Mark the association to assume truechimer status; that is, always survive the
selection and clustering algorithms. This option can be used with any association,
but is most useful for reference clocks with large jitter on the serial port and
precision pulse-per-second (PPS) signals. Caution: this option defeats the algo-
rithms designed to cast out falsetickers and can allow these sources to set the
system clock. This option is valid only with the server and peer commands.
ttl ttl This option specifies the time-to-live ttl for the broadcast command and the maxi-
mum ttl for the expanding ring search used by the manycastclient command. Selec-
tion of the proper value, which defaults to 127, is something of a black art and
should be coordinated with the network administrator. This option is invalid with
type r addresses.
version version
Specifies the version number to be used f or outgoing NTP packets. Versions 1-4
are the choices, with version 4 the default.
xleave Operate in interleaved mode (symmetric and broadcast modes only). (see NTP Inter-
leaved Modes)
AUXILLIARY COMMANDS
broadcastclient
Enable reception of broadcast server messages to any local interface (type b
address). Ordinarily, upon receiving a broadcast message for the first time, the
broadcast client measures the nominal server propagation delay using a brief
client/server exchange, after which it continues in listen-only mode. If a nonzero
value is specified in the broadcastdelay command, the value becomes the delay and
the volley is not executed. Note: the novolley option has been deprecated for
future enhancements. Note that, in order to avoid accidental or malicious disrup-
tion in this mode, both the server and client should operate using symmetric key
or public key authentication as described in the Authentication Options page. Note
that the novolley keyword is incompatible with public key authentication.
manycastserver address [...]
Enable reception of manycast client messages (type m)to the multicast group
address(es) (type m) specified. At least one address is required. Note that, in
order to avoid accidental or malicious disruption, both the server and client
should operate using symmetric key or public key authentication as described in
the Authentication Options page.
multicastclient address [...]
Enable reception of multicast server messages to the multicast group address(es)
(type m) specified. Upon receiving a message for the first time, the multicast
client measures the nominal server propagation delay using a brief client/server
exchange with the server, then enters the broadcast client mode, in which it syn-
chronizes to succeeding multicast messages. Note that, in order to avoid acciden-
tal or malicious disruption in this mode, both the server and client should oper-
ate using symmetric key or public key authentication as described in the Authenti-
cation Options page.
BUGS
The syntax checking is not picky; some combinations of ridiculous and even hilarious
options and modes may not be detected.
SEE ALSO
ntpd(8), ntp_auth(5), ntp_mon(5), ntp_acc(5), ntp_clock(5), ntp_misc(5)
The official HTML documentation.
This file was automatically generated from HTML source.
ntp.conf(5)
Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
On Apache
Under GNU General Public License
2024-04-25 12:53 @3.141.41.187 CrawledBy Mozilla/5.0 AppleWebKit/537.36 (KHTML, like Gecko; compatible; ClaudeBot/1.0; +claudebot@anthropic.com)