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 config-
ure 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 command 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
exception of reference clock addresses, which are always IPv4. Note
that in contexts where a host name is expected, a -4 qualifier preced-
ing 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 nota-
tion. 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 mobi-
lizes a persistent client mode association with the
specified remote server or local reference 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 symmetric-active mode association with the
specified remote peer.
broadcast
For type b and m addressees (only), this command mobi-
lizes 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
interfaces.
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 com-
mand of one or more designated manycast servers.
pool For type s messages (only) this command mobilizes a
client mode association 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 quali-
fier designating the server geographic area such as us
or europe.
unpeer This command removes a previously configured associa-
tion. An address or association ID can be used to iden-
tify 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 recom-
mended 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 recom-
mended 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 algo-
rithm 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 manycastclient and pool
commands.
prefer Mark the server as preferred. All other things being equal,
this host will be chosen for synchronization among a set of
correctly operating hosts. See the Mitigation 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 pre-
cision pulse-per-second (PPS) signals. Caution: this option
defeats the algorithms 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 maximum ttl for the expanding ring search used
by the manycastclient command. Selection 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 pack-
ets. Versions 1-4 are the choices, with version 4 the default.
xleave Operate in interleaved mode (symmetric and broadcast modes
only). (see NTP Interleaved Modes)
AUXILLIARY COMMANDS
broadcastclient
Enable reception of broadcast server messages to any local
interface (type b address). Ordinarily, upon receiving a broad-
cast 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 exe-
cuted. Note: the novolley option has been deprecated for future
enhancements. Note that, in order to avoid accidental or mali-
cious disruption 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 authentica-
tion.
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 synchronizes to succeeding multicast messages. Note
that, in order to avoid accidental or malicious disruption in
this mode, both the server and client should operate using sym-
metric key or public key authentication as described in the
Authentication 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)
Linux-Distributionen
Huschi als Linux-Admin