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 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 start up using ntpd's configuration file may also be specified
at run time using ntpdc.
If one or more request options is 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
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)
immediately. Otherwise, ntpdc will attempt to read interactive
format commands from the standard input.
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.
Force ntpdc to operate in interactive mode. Prompts will be written
to the standard output and commands read from the standard input.
Obtain a list of peers which are known to the server(s). This switch is
equivalent to -c listpeers.
Output all host addresses in dotted-quad numeric format rather than converting
to the canonical host names.
Print a list of the peers known to the server as well as a summary of their
state. This is equivalent to -c peers.
Print a list of the peers known to the server as well as a summary 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 ]
helpl [ 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 better source of information about ntpq
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 displays.
If no is specified, numeric addresses are printed instead. The
default is yes, unless modified using the command line -n
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 purpose.
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.
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 synchonization candidates.
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. In addition,
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 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 . indicates 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 Version 2 specification.
pstats peer_address [...]
Show per-peer statistic counters associated with the specified peer(s).
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
Obtain and print kernel phase-lock loop operating parameters. This information
is available only if the kernel has been specially modified for a precision
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 filter. The oneline and multiline options specify
the format in which this information is to be printed, with multiline
as the default.
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
commands, 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 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 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 support code.
Obtain and print the server's restriction list. This list is (usually)
printed in sorted order and may help to understand how the restrictions
monlist [ version ]
Obtain and print traffic counts collected and maintained 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 disabled
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
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 configuration 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 adequate level of security.
The following commands all make authenticated requests.
Add a configured 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 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
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 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.
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. 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 read-only.
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 broadcast or multicast
server, as in the multicastclient command with default address.
The default for this flag is disable.
Enables the monitoring facility. See the ntpdc program and the
monlist command or further information. The default for this flag
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
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 Timekeeping page for further information.
The default for this flag is disable.
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; otherwise, 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.
restrict address mask flag [ flag ]
This command operates in the same way as the restrict configuration
file commands of ntpd.
unrestrict address mask flag [ 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 configuration file). This allows encryption keys to
be changed without restarting the server.
trustkey keyid [...]
untrustkey keyid [...]
These commands operate in the same way as the trustedkey and untrustkey
configuration file commands of ntpd.
Returns information concerning the authentication module, including known
keys and counts of encryptions and decryptions which have been done.
Display the traps set in the server. See the source listing for further
addtrap [ address [ port ] [ interface ]
Set a trap for asynchronous messages. See the source listing for further
clrtrap [ address [ port ] [ interface]
Clear a trap for asynchronous messages. See the source listing for further
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
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
David L. Mills (email@example.com)