ntpdc - special NTP query program
ntpdc [ -ilnps ] [ -c command ] [ host ] [ ... ]
ntpdc is used to query the ntpd daemon about its current state and to
request changes in that state. The program may be run either in inter-
active mode or controlled using command line arguments. Extensive state
and statistics information is available through the ntpdc interface.
In addition, nearly all the configuration options which can be speci-
fied at startup using ntpd’s configuration file may also be specified
at run time using ntpdc .
If one or more request options are included on the command line when
ntpdc is executed, each of the requests will be sent to the NTP
servers running on each of the hosts given as command line arguments,
or on localhost by default. If no request options are given, ntpdc
will attempt to read commands from the standard input and execute these
on the NTP server running on the first host given on the command line,
again defaulting to localhost when no other host is specified. ntpdc
will prompt for commands if the standard input is a terminal device.
ntpdc uses NTP mode 7 packets to communicate with the NTP server, and
hence can be used to query any compatable server on the network which
permits it. Note that since NTP is a UDP protocol this communication
will be somewhat unreliable, especially over large distances in terms
of network topology. ntpdc makes no attempt to retransmit requests,
and will time requests out if the remote host is not heard from within
a suitable timeout time.
The operation of ntpdc are specific to the particular implementation
of the ntpd daemon and can be expected to work only with this and
maybe some previous versions of the daemon. Requests from a remote
ntpdc program which affect the state of the local server must be
authenticated, which requires both the remote program and local server
share a common key and key identifier.
COMMAND LINE OPTIONS
Specifying a command line option other than -i or -n will cause the
specified query (queries) to be sent to the indicated host(s) immedi-
ately. Otherwise, ntpdc will attempt to read interactive format com-
mands from the standard input.
-c command The following argument is interpreted as an interactive
format command and is added to the list of commands to be exe-
cuted on the specified host(s). Multiple -c options may be
-i Force ntpdc to operate in interactive mode. Prompts will be
written to the standard output and commands read from the stan-
-l Obtain a list of peers which are known to the server(s). This
switch is equivalent to -c listpeers .
-n Output all host addresses in dotted-quad numeric format rather
than converting to the canonical host names.
-p Print a list of the peers known to the server as well as a sum-
mary of their state. This is equivalent to -c peers .
-s Print a list of the peers known to the server as well as a sum-
mary of their state, but in a slightly different format than
the -p switch. This is equivalent to -c dmpeers .
Interactive format commands consist of a keyword followed by zero to
four arguments. Only enough characters of the full keyword to uniquely
identify the command need be typed. The output of a command is normally
sent to the standard output, but optionally the output of individual
commands may be sent to a file by appending a < , followed by a file
name, to the command line.
A number of interactive format commands are executed entirely within
the ntpdc program itself and do not result in NTP mode 7 requests
being sent to a server. These are described following.
? [ command_keyword ]
help [ command_keyword ] A ? by itself will print a list of
all the command keywords known to this incarnation of ntpq . A
? followed by a command keyword will print funcation and usage
information about the command. This command is probably a bet-
ter source of information about ntpq than this manual page.
delay milliseconds Specify a time interval to be added to timestamps
included in requests which require authentication. This is used
to enable (unreliable) server reconfiguration over long delay
network paths or between machines whose clocks are unsynchro-
nized. Actually the server does not now require timestamps in
authenticated requests, so this command may be obsolete.
host hostname Set the host to which future queries will be sent.
Hostname may be either a host name or a numeric address.
hostnames [ yes | no ]
If yes is specified, host names are printed in information
displays. If no is specified, numeric addresses are printed
instead. The default is yes , unless modified using the command
line -n switch.
keyid keyid This command allows the specification of a key number to
be used to authenticate configuration requests. This must cor-
respond to a key number the server has been configured to use
for this purpose.
quit Exit ntpdc .
passwd This command prompts you to type in a password (which will not
be echoed) which will be used to authenticate configuration
requests. The password must correspond to the key configured
for use by the NTP server for this purpose if such requests are
to be successful.
timeout millseconds Specify a timeout period for responses to server
queries. The default is about 8000 milliseconds. Note that
since ntpdc retries each query once after a timeout, the total
waiting time for a timeout will be twice the timeout value set.
CONTROL MESSAGE COMMANDS
Query commands result in NTP mode 7 packets containing requests for
information being sent to the server. These are read-only commands in
that they make no modification of the server configuration state.
Obtains and prints a brief list of the peers for which the
server is maintaining state. These should include all config-
ured peer associations as well as those peers whose stratum is
such that they are considered by the server to be possible
future synchonization candidates.
peers Obtains a list of peers for which the server is maintaining
state, along with a summary of that state. Summary information
includes the address of the remote peer, the local interface
address (0.0.0.0 if a local address has yet to be determined),
the stratum of the remote peer (a stratum of 16 indicates the
remote peer is unsynchronized), the polling interval, in sec-
onds, the reachability register, in octal, and the current
estimated delay, offset and dispersion of the peer, all in sec-
onds. The character in the left margin indicates the mode this
peer entry is operating in. A + denotes symmetric active, a -
indicates symmetric passive, a = means the remote server is
being polled in client mode, a ^ indicates that the server is
broadcasting to this address, a ~ denotes that the remote peer
is sending broadcasts and a * marks the peer the server is
currently synchonizing to.
The contents of the host field may be one of four forms. It may
be a host name, an IP address, a reference clock implementation
name with its parameter or REFCLK( implementation number ,
parameter ) . On hostnames no only IP-addresses will be dis-
dmpeers A slightly different peer summary list. Identical to the output
of the peers command, except for the character in the leftmost
column. Characters only appear beside peers which were included
in the final stage of the clock selection algorithm. A . indi-
cates that this peer was cast off in the falseticker detection,
while a + indicates that the peer made it through. A *
denotes the peer the server is currently synchronizing with.
peer_address [...] Shows a detailed display of the current
peer variables for one or more peers. Most of these values are
described in the NTP Version 2 specification.
pstats peer_address [...] Show per-peer statistic counters associ-
ated with the specified peer(s).
clock_peer_address [...] Obtain and print information con-
cerning a peer clock. The values obtained provide information
on the setting of fudge factors and other clock performance
Obtain and print kernel phase-lock loop operating parameters.
This information is available only if the kernel has been spe-
cially modified for a precision timekeeping function.
loopinfo [ oneline | multiline ]
Print the values of selected loop filter variables. The loop
filter is the part of NTP which deals with adjusting the local
system clock. The offset is the last offset given to the loop
filter by the packet processing code. The frequency is the fre-
quency error of the local clock in parts-per-million (ppm). The
time_const controls the stiffness of the phase-lock loop and
thus the speed at which it can adapt to oscillator drift. The
watchdog timer value is the number of seconds which have
elapsed since the last sample offset was given to the loop fil-
ter. The oneline and multiline options specify the format in
which this information is to be printed, with multiline as the
sysinfo Print a variety of system state variables, i.e., state related
to the local server. All except the last four lines are
described in the NTP Version 3 specification, RFC-1305. The
system flags show various system flags, some of which can be
set and cleared by the enable and disable configuration com-
mands, respectively. These are the auth , bclient , monitor ,
pll , pps and stats flags. See the ntpd documentation for the
meaning of these flags. There are two additional flags which
are read only, the kernel_pll and kernel_pps . These flags
indicate the synchronization status when the precision time
kernel modifications are in use. The kernel_pll indicates that
the local clock is being disciplined by the kernel, while the
kernel_pps indicates the kernel discipline is provided by the
The stability is the residual frequency error remaining
afterthe system frequency correction is applied and is intended
for maintenance and debugging. In most architectures, this
value will initially decrease from as high as 500 ppm to a nom-
inal value in the range .01 to 0.1 ppm. If it remains high for
some time after starting the daemon, something may be wrong
with the local clock, or the value of the kernel variable tick
may be incorrect.
The broadcastdelay shows the default broadcast delay, as set
by the broadcastdelay configuration command.
The authdelay shows the default authentication delay, as set
by the authdelay configuration command.
Print statistics counters maintained in the protocol module.
Print statistics counters related to memory allocation code.
iostats Print statistics counters maintained in the input-output mod-
Print statistics counters maintained in the timer/event queue
reslist Obtain and print the server’s restriction list. This list is
(usually) printed in sorted order and may help to understand
how the restrictions are applied.
version ] Obtain and print traffic counts collected and main-
tained by the monitor facility. The version number should not
normally need to be specified.
clkbug clock_peer_address [...] Obtain debugging information for a
reference clock driver. This information is provided only by
some clock drivers and is mostly undecodable without a copy of
the driver source in hand.
RUNTIME CONFIGURATION REQUESTS
All requests which cause state changes in the server are authenticated
by the server using a configured NTP key (the facility can also be dis-
abled by the server by not configuring a key). The key number and the
corresponding key must also be made known to xtnpdc. This can be done
using the keyid and passwd commands, the latter of which will prompt at
the terminal for a password to use as the encryption key. You will also
be prompted automatically for both the key number and password the
first time a command which would result in an authenticated request to
the server is given. Authentication not only provides verification that
the requester has permission to make such changes, but also gives an
extra degree of protection again transmission errors.
Authenticated requests always include a timestamp in the packet data,
which is included in the computation of the authentication code. This
timestamp is compared by the server to its receive time stamp. If they
differ by more than a small amount the request is rejected. This is
done for two reasons. First, it makes simple replay attacks on the
server, by someone who might be able to overhear traffic on your LAN,
much more difficult. Second, it makes it more difficult to request con-
figuration changes to your server from topologically remote hosts.
While the reconfiguration facility will work well with a server on the
local host, and may work adequately between time-synchronized hosts on
the same LAN, it will work very poorly for more distant hosts. As such,
if reasonable passwords are chosen, care is taken in the distribution
and protection of keys and appropriate source address restrictions are
applied, the run time reconfiguration facility should provide an ade-
quate level of security.
The following commands all make authenticated requests.
addpeer peer_address [ keyid ] [ version ] [ prefer ] Add a config-
ured peer association at the given address and operating in
symmetric active mode. Note that an existing association with
the same peer may be deleted when this command is executed, or
may simply be converted to conform to the new configuration, as
appropriate. If the optional keyid is a nonzero integer, all
outgoing packets to the remote server will have an authentica-
tion field attached encrypted with this key. If the value is 0
(or not given) no authentication will be done. The version#
can be 1, 2 or 3 and defaults to 3. The prefer keyword indi-
cates a preferred peer (and thus will be used primarily for
clock synchronisation if possible). The preferred peer also
determines the validity of the PPS signal - if the preferred
peer is suitable for synchronisation so is the PPS signal.
peer_address [ keyid ] [ version ] [ prefer ] Identical to
the addpeer command, except that the operating mode is client.
peer_address [ keyid ] [ version ] [ prefer ] Identical to
the addpeer command, except that the operating mode is broad-
cast. In this case a valid key identifier and key are required.
The peer_address parameter can be the broadcast address of the
local network or a multicast group address assigned to NTP. If
a multicast address, a multicast-capable kernel is required.
peer_address [...] This command causes the configured bit to
be removed from the specified peer(s). In many cases this will
cause the peer association to be deleted. When appropriate,
however, the association may persist in an unconfigured mode if
the remote peer is willing to continue on in this fashion.
fudge peer_address [ time1 ] [ time2 ] [ stratum ] [ refid ]
This command provides a way to set certain data for a reference
clock. See the source listing for further information.
flag ] [ ... ]
disable [ flag ] [ ... ] These commands operate in the same
way as the enable and disable configuration file commands of
ntpd . Following is a description of the flags. Note that only
the auth , bclient , monitor , pll , pps and stats flags can
be set by ntpdc ; the pll_kernel and pps_kernel flags are
auth Enables the server to synchronize with unconfigured peers only
if the peer has been correctly authenticated using a trusted
key and key identifier. The default for this flag is enable.
bclient Enables the server to listen for a message from a broadcast or
multicast server, as in the multicastclient command with
default address. The default for this flag is disable.
monitor Enables the monitoring facility. See the ntpdc program and the
monlist command or further information. The default for this
flag is enable.
pll Enables the server to adjust its local clock by means of NTP.
If disabled, the local clock free-runs at its intrinsic time
and frequency offset. This flag is useful in case the local
clock is controlled by some other device or protocol and NTP is
used only to provide synchronization to other clients. In this
case, the local clock driver is used. See the Reference Clock
Drivers page for further information. The default for this flag
pps Enables the pulse-per-second (PPS) signal when frequency and
time is disciplined by the precision time kernel modifications.
See the A Kernel Model for Precision Timekeepingpage for fur-
ther information. The default for this flag is disable.
stats Enables the statistics facility. See the Monitoring Options
page for further information. The default for this flag is
When the precision time kernel modifications are installed,
this indicates the kernel controls the clock discipline; other-
wise, the daemon controls the clock discipline.
When the precision time kernel modifications are installed and
a pulse-per-second (PPS) signal is available, this indicates
the PPS signal controls the clock discipline; otherwise, the
daemon or kernel controls the clock discipline, as indicated by
the pll_kernel flag.
address mask flag [ flag ] This command operates in the same
way as the restrict configuration file commands of ntpd .
address mask flag [ flag ] Unrestrict the matching entry from
the restrict list.
address mask [ ntpport ] Delete the matching entry from the
Causes the current set of authentication keys to be purged and
a new set to be obtained by rereading the keys file (which must
have been specified in the ntpd configuration file). This
allows encryption keys to be changed without restarting the
keyid [...] These commands operate in the same way as the
trustedkey and untrustedkey configuration file commands of
Returns information concerning the authentication module,
including known keys and counts of encryptions and decryptions
which have been done.
traps Display the traps set in the server. See the source listing for
address [ port ] [ interface ] Set a trap for asynchronous
messages. See the source listing for further information.
address [ port ] [ interface ] Clear a trap for asynchronous
messages. See the source listing for further information.
reset Clear the statistics counters in various modules of the server.
See the source listing for further information.
ntpdc is a crude hack. Much of the information it shows is deadly bor-
ing and could only be loved by its implementer. The program was
designed so that new (and temporary) features were easy to hack in, at
great expense to the program’s ease of use. Despite this, the program
is occasionally useful.
Primary source of documentation: /usr/share/doc/ntp-*/ntpdc.html
David L. Mills <firstname.lastname@example.org>
ntp 4.1.1b-r5 ntpdc(1)
Man(1) output converted with