NTPDC(8) BSD System Manager's Manual NTPDC(8)
ntpdc -- special NTP query program
ntpdc [-ilnps] [-c command] [host ...]
The ntpdc utility is used to query the ntpd(8) daemon about its current
state and to request changes in that state. The program may be run
either in interactive 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 specified at startup using ntpd's configuration file may also be spec-
ified at run time using ntpdc.
The following options are available:
The following argument is interpreted as an interactive format
command and is added to the list of commands to be executed on
the specified host(s). Multiple -c options may be given.
-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'.
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. The ntpdc util-
ity will prompt for commands if the standard input is a terminal device.
The ntpdc utility uses NTP mode 7 packets to communicate with the NTP
server, and hence can be used to query any compatible server on the net-
work which permits it. Note that since NTP is a UDP protocol this commu-
nication will be somewhat unreliable, especially over large distances in
terms of network topology. The ntpdc utility 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(8) daemon and can be expected to work only with this and maybe
some previous versions of the daemon. Requests from a remote ntpdc util-
ity 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. Specifying a command line option other than -i
or -n will cause the specified query (queries) to be sent to the indi-
cated host(s) immediately. Otherwise, ntpdc will attempt to read inter-
active format commands from the standard input.
Interactive format commands consist of a keyword followed by zero to four
arguments. Only enough characters of the full keyword to uniquely iden-
tify 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
A number of interactive format commands are executed entirely within the
ntpdc utility itself and do not result in NTP mode 7 requests being sent
to a server. These are described following.
A ? will print a list of all the command keywords known to this
incarnation of ntpdc. A ? followed by a command keyword will
print function and usage information about the command. This
command is probably a better source of information about ntpq(8)
than this manual page.
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 unsynchronized. Actually
the server does not now require timestamps in authenticated
requests, so this command may be obsolete.
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 dis-
plays. If no is specified, numeric addresses are printed
instead. The default is yes, unless modified using the command
line -n switch.
This command allows the specification of a key number to be used
to authenticate configuration requests. This must correspond to
a key number the server has been configured to use for this pur-
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
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 configured peer
associations as well as those peers whose stratum is such that
they are considered by the server to be possible future syn-
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 seconds,
the reachability register, in octal, and the current estimated
delay, offset and dispersion of the peer, all in seconds.
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 cur-
rently synchronizing 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 displayed.
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.
showpeer 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 Ver-
sion 2 specification.
pstats peer_address ...
Show per-peer statistic counters associated with the specified
clockinfo clock_peer_address ...
Obtain and print information concerning a peer clock. The values
obtained provide information on the setting of fudge factors and
other clock performance information.
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
frequency 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
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(8) documentation for the mean-
ing 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 modifi-
cations 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 PPS signal.
The 'stability' is the residual frequency error remaining after
the 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 nominal
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
kern.clockrate.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.
Print statistics counters maintained in the input-output module.
Print statistics counters maintained in the timer/event queue
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.
Obtain and print traffic counts collected and maintained by the
monitor facility. The version number should not normally need to
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 disabled
by the server by not configuring a key). The key number and the corre-
sponding key must also be made known to ntpdc. 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 dif-
ficult. Second, it makes it more difficult to request configuration
changes to your server from topologically remote hosts. While the recon-
figuration 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 adequate level of secu-
The following commands all make authenticated requests.
addpeer peer_address [keyid] [version] [prefer]
Add a configured peer association at the given address and oper-
ating in symmetric active mode. Note that an existing associa-
tion with the same peer may be deleted when this command is exe-
cuted, or may simply be converted to conform to the new configu-
ration, as appropriate. If the optional keyid is a nonzero inte-
ger, all outgoing packets to the remote server will have an
authentication 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
indicates 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.
addserver peer_address [keyid] [version] [prefer]
Identical to the addpeer command, except that the operating mode
broadcast peer_address [keyid] [version] [prefer]
Identical to the addpeer command, except that the operating mode
is broadcast. 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.
unconfig peer_address ...
This command causes the configured bit to be removed from the
specified peer(s). In many cases this will cause the peer asso-
ciation to be deleted. When appropriate, however, the associa-
tion 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.
enable flag ...
disable flag ...
These commands operate in the same way as the enable and disable
configuration file commands of ntpd(8). Following is a descrip-
tion 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 read-only.
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.
Enables the server to listen for a message from a broad-
cast or multicast server, as in the multicastclient com-
mand with default address. The default for this flag is
Enables the monitoring facility. See the monlist command
for further information. The default for this flag is
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 syn-
chronization to other clients. In this case, the local
clock driver is used. See the "Reference Clock Drivers"
page (available as part of the HTML documentation pro-
vided in /usr/share/doc/ntp) page for further informa-
tion. The default for this flag is enable.
pps Enables the pulse-per-second (PPS) signal when frequency
and time is disciplined by the precision time kernel mod-
ifications. See the "A Kernel Model for Precision
Timekeeping" page for further information. The default
for this flag is disable.
stats Enables the statistics facility. See the Monitoring
Options section of the ntp.conf(5) page for further
information. The default for this flag is enable.
When the precision time kernel modifications are
installed, this indicates the kernel controls the clock
discipline; otherwise, the daemon controls the clock dis-
When the precision time kernel modifications are
installed and a pulse-per-second (PPS) signal is avail-
able, 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.
restrict address mask flag ...
This command operates in the same way as the restrict configura-
tion file commands of ntpd(8).
unrestrict address mask flag ...
Unrestrict the matching entry from the restrict list.
delrestrict address mask [ntpport]
Delete the matching entry from the restrict list.
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(8) configuration file). This
allows encryption keys to be changed without restarting the
trustedkey keyid ...
untrustedkey keyid ...
These commands operate in the same way as the trustedkey and
untrustedkey configuration file commands of ntpd(8).
Returns information concerning the authentication module, includ-
ing 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
addtrap address [port] [interface]
Set a trap for asynchronous messages. See the source listing for
clrtrap 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.
David L. Mills, Network Time Protocol (Version 3), RFC1305.
The ntpdc utility is a crude hack. Much of the information it shows is
deadly boring 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.
BSD January 7, 2000 BSD