CHRONYC(1) User manual CHRONYC(1)
NAME
chronyc - command-line interface for chrony daemon
SYNOPSIS
chronyc [OPTION]... [COMMAND]...
DESCRIPTION
chronyc is a command-line interface program which can be used to
monitor chronyd's performance and to change various operating
parameters whilst it is running.
If no commands are specified on the command line, chronyc will expect
input from the user. The prompt chronyc> will be displayed when it is
being run from a terminal. If chronyc's input or output are redirected
from or to a file, the prompt will not be shown.
There are two ways chronyc can access chronyd. One is the Internet
Protocol (IPv4 or IPv6) and the other is a Unix domain socket, which is
accessible locally by the root or chrony user. By default, chronyc
first tries to connect to the Unix domain socket. The compiled-in
default path is /run/chrony/chronyd.sock. If that fails (e.g. because
chronyc is running under a non-root user), it will try to connect to
127.0.0.1 and then ::1.
Only the following monitoring commands, which do not affect the
behaviour of chronyd, are allowed from the network: activity, manual
list, rtcdata, smoothing, sourcename, sources, sourcestats, tracking,
waitsync. The set of hosts from which chronyd will accept these
commands can be configured with the cmdallow directive in the chronyd's
configuration file or the cmdallow command in chronyc. By default, the
commands are accepted only from localhost (127.0.0.1 or ::1).
All other commands are allowed only through the Unix domain socket.
When sent over the network, chronyd will respond with a `Not
authorised' error, even if it is from localhost.
Having full access to chronyd via chronyc is more or less equivalent to
being able to modify the chronyd's configuration file and restart it.
OPTIONS
-4
With this option hostnames will be resolved only to IPv4 addresses.
-6
With this option hostnames will be resolved only to IPv6 addresses.
-n
This option disables resolving of IP addresses to hostnames, e.g.
to avoid slow DNS lookups. Long addresses will not be truncated to
fit into the column.
-N
This option enables printing of original hostnames or IP addresses
of NTP sources that were specified in the configuration file, or
chronyc commands. Without the -n and -N option, the printed
hostnames are obtained from reverse DNS lookups and can be
different from the specified hostnames.
-c
This option enables printing of reports in a comma-separated values
(CSV) format. Reverse DNS lookups will be disabled, time will be
printed as number of seconds since the epoch, and values in seconds
will not be converted to other units.
-e
With this option each chronyc response will end with a line
containing a single dot.
-d
This option enables printing of debugging messages if chronyc was
compiled with debugging support.
-m
Normally, all arguments on the command line are interpreted as one
command. With this option multiple commands can be specified. Each
argument will be interpreted as a whole command.
-h host
This option specifies the host to be contacted by chronyc. It can
be specified with a hostname, IP address, or path to the local Unix
domain socket. Multiple values can be specified as a
comma-separated list to provide a fallback.
The default value is /run/chrony/chronyd.sock,127.0.0.1,::1, i.e.
the host where chronyc is being run. First, it tries to connect to
the Unix domain socket and if that fails (e.g. due to running under
a non-root user), it will try to connect to 127.0.0.1 and then ::1.
-p port
This option allows the user to specify the UDP port number which
the target chronyd is using for its monitoring connections. This
defaults to 323; there would rarely be a need to change this.
-f file
This option is ignored and is provided only for compatibility.
-a
This option is ignored and is provided only for compatibility.
-v, --version
With this option chronyc displays its version number on the
terminal and exits.
--help
With this option chronyc displays a help message on the terminal
and exits.
COMMANDS
This section describes each of the commands available within the
chronyc program.
System clock
tracking
The tracking command displays parameters about the system's clock
performance. An example of the output is shown below.
Reference ID : CB00710F (ntp1.example.net)
Stratum : 3
Ref time (UTC) : Fri Jan 27 09:49:17 2017
System time : 0.000006523 seconds slow of NTP time
Last offset : -0.000006747 seconds
RMS offset : 0.000035822 seconds
Frequency : 3.225 ppm slow
Residual freq : -0.000 ppm
Skew : 0.129 ppm
Root delay : 0.013639022 seconds
Root dispersion : 0.001100737 seconds
Update interval : 64.2 seconds
Leap status : Normal
The fields are explained as follows:
Reference ID
This is the reference ID and name (or IP address) of the server
to which the computer is currently synchronised. For IPv4
addresses, the reference ID is equal to the address and for
IPv6 addresses it is the first 32 bits of the MD5 sum of the
address.
If the reference ID is 7F7F0101 and there is no name or IP
address, it means the computer is not synchronised to any
external source and that you have the local mode operating (via
the local command in chronyc, or the local directive in the
configuration file).
The reference ID is printed as a hexadecimal number. Note that
in older versions it used to be printed in quad-dotted notation
and could be confused with an IPv4 address.
Stratum
The stratum indicates how many hops away from a computer with
an attached reference clock we are. Such a computer is a
stratum-1 computer, so the computer in the example is two hops
away (i.e. ntp1.example.net is a stratum-2 and is synchronised
from a stratum-1).
Ref time
This is the time (UTC) at which the last measurement from the
reference source was processed.
System time
This is the current offset between the NTP clock and system
clock. The NTP clock is a software (virtual) clock maintained
by chronyd, which is synchronised to the configured time
sources and provides time to NTP clients. The system clock is
synchronised to the NTP clock. To avoid steps in the system
time, which might have adverse consequences for certain
applications, the system clock is normally corrected only by
speeding up or slowing down (up to the rate configured by the
maxslewrate directive). If the offset is too large, this
correction will take a very long time. A step can be forced by
the makestep command, or the makestep directive in the
configuration file.
Note that all other offsets reported by chronyc and most
offsets in the log files are relative to the NTP clock, not the
system clock.
Last offset
This is the estimated local offset on the last clock update. A
positive value indicates the local time (as previously
estimated true time) was ahead of the time sources.
RMS offset
This is a long-term average of the offset value.
Frequency
The `frequency' is the rate by which the system's clock would
be wrong if chronyd was not correcting it. It is expressed in
ppm (parts per million). For example, a value of 1 ppm would
mean that when the system's clock thinks it has advanced 1
second, it has actually advanced by 1.000001 seconds relative
to true time.
Residual freq
This shows the `residual frequency' for the currently selected
reference source. This reflects any difference between what the
measurements from the reference source indicate the frequency
should be and the frequency currently being used.
The reason this is not always zero is that a smoothing
procedure is applied to the frequency. Each time a measurement
from the reference source is obtained and a new residual
frequency computed, the estimated accuracy of this residual is
compared with the estimated accuracy (see `skew' next) of the
existing frequency value. A weighted average is computed for
the new frequency, with weights depending on these accuracies.
If the measurements from the reference source follow a
consistent trend, the residual will be driven to zero over
time.
Skew
This is the estimated error bound on the frequency.
Root delay
This is the total of the network path delays to the stratum-1
computer from which the computer is ultimately synchronised.
Root dispersion
This is the total dispersion accumulated through all the
computers back to the stratum-1 computer from which the
computer is ultimately synchronised. Dispersion is due to
system clock resolution, statistical measurement variations,
etc.
An absolute bound on the computer's clock accuracy (assuming
the stratum-1 computer is correct) is given by:
clock_error <= |system_time_offset| + root_dispersion + (0.5 * root_delay)
Update interval
This is the interval between the last two clock updates.
Leap status
This is the leap status, which can be Normal, Insert second,
Delete second or Not synchronised.
makestep, makestep threshold limit
Normally chronyd will cause the system to gradually correct any
time offset, by slowing down or speeding up the clock as required.
In certain situations, the system clock might be so far adrift that
this slewing process would take a very long time to correct the
system clock.
The makestep command can be used in this situation. There are two
forms of the command. The first form has no parameters. It tells
chronyd to cancel any remaining correction that was being slewed
and jump the system clock by the equivalent amount, making it
correct immediately.
The second form configures the automatic stepping, similarly to the
makestep directive. It has two parameters, stepping threshold (in
seconds) and number of future clock updates for which the threshold
will be active. This can be used with the burst command to quickly
make a new measurement and correct the clock by stepping if needed,
without waiting for chronyd to complete the measurement and update
the clock.
makestep 0.1 1
burst 1/2
BE WARNED: Certain software will be seriously affected by such
jumps in the system time. (That is the reason why chronyd uses
slewing normally.)
maxupdateskew skew-in-ppm
This command has the same effect as the maxupdateskew directive in
the configuration file.
waitsync [max-tries [max-correction [max-skew [interval]]]]
The waitsync command waits for chronyd to synchronise.
Up to four optional arguments can be specified. The first is the
maximum number of tries before giving up and returning a non-zero
error code. When 0 is specified, or there are no arguments, the
number of tries will not be limited.
The second and third arguments are the maximum allowed remaining
correction of the system clock and the maximum allowed skew (in
ppm) as reported by the tracking command in the System time and
Skew fields. If not specified or zero, the value will not be
checked.
The fourth argument is the interval specified in seconds in which
the check is repeated. The interval is 10 seconds by default.
An example is:
waitsync 60 0.01
which will wait up to about 10 minutes (60 times 10 seconds) for
chronyd to synchronise to a source and the remaining correction to
be less than 10 milliseconds.
Time sources
sources [-a] [-v]
This command displays information about the current time sources
that chronyd is accessing.
If the -a option is specified, all sources are displayed, including
those that do not have a known address yet. Such sources have an
identifier in the format ID#XXXXXXXXXX, which can be used in other
commands expecting a source address.
The -v option enables a verbose output. In this case, extra caption
lines are shown as a reminder of the meanings of the columns.
MS Name/IP address Stratum Poll Reach LastRx Last sample
===============================================================================
#* GPS0 0 4 377 11 -479ns[ -621ns] +/- 134ns
^? ntp1.example.net 2 6 377 23 -923us[ -924us] +/- 43ms
^+ ntp2.example.net 1 6 377 21 -2629us[-2619us] +/- 86ms
The columns are as follows:
M
This indicates the mode of the source. ^ means a server, =
means a peer and # indicates a locally connected reference
clock.
S
This column indicates the selection state of the source.
o * indicates the best source which is currently selected for
synchronisation.
o + indicates other sources selected for synchronisation,
which are combined with the best source.
o - indicates a source which is considered to be selectable
for synchronisation, but not currently selected.
o x indicates a source which chronyd thinks is a falseticker
(i.e. its time is inconsistent with a majority of other
sources, or sources specified with the trust option).
o ~ indicates a source whose time appears to have too much
variability.
o ? indicates a source which is not considered to be
selectable for synchronisation for other reasons (e.g.
unreachable, not synchronised, or does not have enough
measurements).
The selectdata command can be used to get more details about
the selection state.
Name/IP address
This shows the name or the IP address of the source, or
reference ID for reference clocks.
Stratum
This shows the stratum of the source, as reported in its most
recently received sample. Stratum 1 indicates a computer with a
locally attached reference clock. A computer that is
synchronised to a stratum 1 computer is at stratum 2. A
computer that is synchronised to a stratum 2 computer is at
stratum 3, and so on.
Poll
This shows the rate at which the source is being polled, as a
base-2 logarithm of the interval in seconds. Thus, a value of 6
would indicate that a measurement is being made every 64
seconds. chronyd automatically varies the polling rate in
response to prevailing conditions.
Reach
This shows the source's reachability register printed as an
octal number. The register has 8 bits and is updated on every
received or missed packet from the source. A value of 377
indicates that a valid reply was received for all from the last
eight transmissions.
LastRx
This column shows how long ago the last good sample (which is
shown in the next column) was received from the source.
Measurements that failed some tests are ignored. This is
normally in seconds. The letters m, h, d or y indicate minutes,
hours, days, or years.
Last sample
This column shows the offset between the local clock and the
source at the last measurement. The number in the square
brackets shows the actual measured offset. This can be suffixed
by ns (indicating nanoseconds), us (indicating microseconds),
ms (indicating milliseconds), or s (indicating seconds). The
number to the left of the square brackets shows the original
measurement, adjusted to allow for any slews applied to the
local clock since. Positive offsets indicate that the local
clock is ahead of the source. The number following the +/-
indicator shows the margin of error in the measurement (NTP
root distance).
sourcestats [-a] [-v]
The sourcestats command displays information about the drift rate
and offset estimation process for each of the sources currently
being examined by chronyd.
If the -a option is specified, all sources are displayed, including
those that do not have a known address yet. Such sources have an
identifier in the format ID#XXXXXXXXXX, which can be used in other
commands expecting a source address.
The -v option enables a verbose output. In this case, extra caption
lines are shown as a reminder of the meanings of the columns.
An example report is:
Name/IP Address NP NR Span Frequency Freq Skew Offset Std Dev
===============================================================================
ntp1.example.net 11 5 46m -0.001 0.045 1us 25us
The columns are as follows:
Name/IP Address
This is the name or IP address of the NTP server (or peer) or
reference ID of the reference clock to which the rest of the
line relates.
NP
This is the number of sample points currently being retained
for the server. The drift rate and current offset are estimated
by performing a linear regression through these points.
NR
This is the number of runs of residuals having the same sign
following the last regression. If this number starts to become
too small relative to the number of samples, it indicates that
a straight line is no longer a good fit to the data. If the
number of runs is too low, chronyd discards older samples and
re-runs the regression until the number of runs becomes
acceptable.
Span
This is the interval between the oldest and newest samples. If
no unit is shown the value is in seconds. In the example, the
interval is 46 minutes.
Frequency
This is the estimated residual frequency for the server, in
parts per million. In this case, the computer's clock is
estimated to be running 1 part in 10^9 slow relative to the
server.
Freq Skew
This is the estimated error bounds on Freq (again in parts per
million).
Offset
This is the estimated offset of the source.
Std Dev
This is the estimated sample standard deviation.
selectdata [-a] [-v]
The selectdata command displays information specific to the
selection of time sources. If the -a option is specified, all
sources are displayed, including those that do not have a known
address yet. With the -v option, extra caption lines are shown as a
reminder of the meanings of the columns.
An example of the output is shown below.
S Name/IP Address Auth COpts EOpts Last Score Interval Leap
=======================================================================
D ntp1.example.net Y ----- --TR- 4 1.0 -61ms +62ms N
* ntp2.example.net N ----- ----- 0 1.0 -6846us +7305us N
+ ntp3.example.net N ----- ----- 10 1.0 -7381us +7355us N
The columns are as follows:
S
This column indicates the state of the source after the last
source selection. It is similar to the state reported by the
sources command, but more states are reported.
The following states indicate the source is not considered
selectable for synchronisation:
o N - has the noselect option.
o s - is not synchronised.
o M - does not have enough measurements.
o d - has a root distance larger than the maximum distance
(configured by the maxdistance directive).
o ~ - has a jitter larger than the maximum jitter (configured
by the maxjitter directive).
o w - waits for other sources to get out of the M state.
o S - has older measurements than other sources.
o O - has a stratum equal or larger than the orphan stratum
(configured by the local directive).
o T - does not fully agree with sources that have the trust
option.
o x - does not agree with other sources (falseticker).
The following states indicate the source is considered
selectable, but it is not currently used for synchronisation:
o W - waits for other sources to be selectable (required by
the minsources directive, or the require option of another
source).
o P - another selectable source is preferred due to the
prefer option.
o U - waits for a new measurement (after selecting a
different best source).
o D - has, or recently had, a root distance which is too
large to be combined with other sources (configured by the
combinelimit directive).
The following states indicate the source is used for
synchronisation of the local clock:
o + - combined with the best source.
o * - selected as the best source to update the reference
data (e.g. root delay, root dispersion).
Name/IP address
This column shows the name or IP address of the source if it is
an NTP server, or the reference ID if it is a reference clock.
Auth
This column indicites whether an authentication mechanism is
enabled for the source. Y means yes and N means no.
COpts
This column displays the configured selection options of the
source.
o N indicates the noselect option.
o P indicates the prefer option.
o T indicates the trust option.
o R indicates the require option.
EOpts
This column displays the current effective selection options of
the source, which can be different from the configured options
due to the authentication selection mode (configured by the
authselectmode directive). The symbols are the same as in the
COpts column.
Last
This column displays how long ago was the last measurement of
the source made when the selection was performed.
Score
This column displays the current score against the source in
the * state. The scoring system avoids frequent reselection
when multiple sources have a similar root distance. A value
larger than 1 indicates this source was better than the *
source in recent selections. If the score reaches 10, the best
source will be reselected and the scores will be reset to 1.
Interval
This column displays the lower and upper endpoint of the
interval which was expected to contain the true offset of the
local clock considering the root distance at the time of the
selection.
Leap
This column displays the current leap status of the source.
o N indicates the normal status (no leap second).
o + indicates that a leap second will be inserted at the end
of the month.
o - indicates that a leap second will be deleted at the end
of the month.
o ? indicates the unknown status (i.e. no valid measurement
was made).
selectopts address|refid [+|-option]...
The selectopts command modifies the configured selection options of
an NTP source specified by IP address (or the ID#XXXXXXXXXX
identifier used for unknown addresses), or a reference clock
specified by reference ID as a string.
The selection options can be added with the + symbol or removed
with the - symbol. The selectdata command can be used to verify the
configuration. The modified options will be applied in the next
source selection, e.g. when a new measurement is made, or the
reselect command is executed.
An example of using this command is shown below.
selectopts 1.2.3.4 -noselect +prefer
selectopts GPS +trust
reselect
To avoid excessive switching between sources, chronyd can stay
synchronised to a source even when it is not currently the best one
among the available sources.
The reselect command can be used to force chronyd to reselect the
best synchronisation source.
reselectdist distance
The reselectdist command sets the reselection distance. It is
equivalent to the reselectdist directive in the configuration file.
NTP sources
activity
This command reports the number of servers and peers that are
online and offline. If the auto_offline option is used in
specifying some of the servers or peers, the activity command can
be useful for detecting when all of them have entered the offline
state after the network link has been disconnected.
The report shows the number of servers and peers in 5 states:
online
the server or peer is currently online (i.e. assumed by chronyd
to be reachable)
offline
the server or peer is currently offline (i.e. assumed by
chronyd to be unreachable, and no measurements from it will be
attempted.)
burst_online
a burst command has been initiated for the server or peer and
is being performed; after the burst is complete, the server or
peer will be returned to the online state.
burst_offline
a burst command has been initiated for the server or peer and
is being performed; after the burst is complete, the server or
peer will be returned to the offline state.
unresolved
the name of the server or peer was not resolved to an address
yet; this source is not visible in the sources and sourcestats
reports.
authdata [-a]
The authdata command displays information specific to
authentication of NTP sources. If the -a option is specified, all
sources are displayed, including those that do not have a known
address yet. An example of the output is shown below.
Name/IP address Mode KeyID Type KLen Last Atmp NAK Cook CLen
=========================================================================
ntp1.example.net NTS 1 15 256 135m 0 0 8 100
ntp2.example.net SK 30 13 128 - 0 0 0 0
ntp3.example.net - 0 0 0 - 0 0 0 0
The columns are as follows:
Name/IP address
This column shows the name or the IP address of the source.
Mode
This column shows which mechanism authenticates NTP packets
received from the source. NTS means Network Time Security, SK
means a symmetric key, and - means authentication is disabled.
KeyID
This column shows an identifier of the key used for
authentication. With a symmetric key, it is the ID from the key
file. With NTS, it is a number starting at zero and incremented
by one with each successful key establishment using the NTS-KE
protocol, i.e. it shows how many times the key establishment
was performed with this source.
Type
This columns shows an identifier of the algorithm used for
authentication. With a symmetric key, it is the hash function
or cipher specified in the key file. With NTS, it is an
authenticated encryption with associated data (AEAD) algorithm,
which is negotiated in the NTS-KE protocol. The following
values can be reported:
o 1: MD5
o 2: SHA1
o 3: SHA256
o 4: SHA384
o 5: SHA512
o 6: SHA3-224
o 7: SHA3-256
o 8: SHA3-384
o 9: SHA3-512
o 10: TIGER
o 11: WHIRLPOOL
o 13: AES128
o 14: AES256
o 15: AEAD-AES-SIV-CMAC-256
o 30: AEAD-AES-128-GCM-SIV
KLen
This column shows the length of the key in bits.
Last
This column shows how long ago the last successful key
establishment was performed. It is in seconds, or letters m, h,
d or y indicate minutes, hours, days, or years.
Atmp
This column shows the number of attempts to perform the key
establishment since the last successful key establishment. A
number larger than 1 indicates a problem with the network or
server.
NAK
This column shows whether an NTS NAK was received since the
last request. A NAK indicates that authentication failed on the
server side due to chronyd using a cookie which is no longer
valid and that it needs to perform the key establishment again
in order to get new cookies.
Cook
This column shows the number of NTS cookies that chronyd
currently has. If the key establishment was successful, a
number smaller than 8 indicates a problem with the network or
server.
CLen
This column shows the length in bytes of the NTS cookie which
will be used in the next request.
ntpdata [address]
The ntpdata command displays the last valid measurement and other
NTP-specific information about the specified NTP source, or all NTP
sources (with a known address) if no address was specified. An
example of the output is shown below.
Remote address : 203.0.113.15 (CB00710F)
Remote port : 123
Local address : 203.0.113.74 (CB00714A)
Leap status : Normal
Version : 4
Mode : Server
Stratum : 1
Poll interval : 10 (1024 seconds)
Precision : -24 (0.000000060 seconds)
Root delay : 0.000015 seconds
Root dispersion : 0.000015 seconds
Reference ID : 47505300 (GPS)
Reference time : Fri Nov 25 15:22:12 2016
Offset : -0.000060878 seconds
Peer delay : 0.000175634 seconds
Peer dispersion : 0.000000681 seconds
Response time : 0.000053050 seconds
Jitter asymmetry: +0.00
NTP tests : 111 111 1111
Interleaved : No
Authenticated : No
TX timestamping : Kernel
RX timestamping : Kernel
Total TX : 24
Total RX : 24
Total valid RX : 24
Total good RX : 22
The fields are explained as follows:
Remote address
The IP address of the NTP server or peer, and the corresponding
reference ID.
Remote port
The UDP port number to which the request was sent. The standard
NTP port is 123.
Local address
The local IP address which received the response, and the
corresponding reference ID.
Leap status, Version, Mode, Stratum, Poll interval, Precision, Root
delay, Root dispersion, Reference ID, Reference time
The NTP values from the last valid response.
Offset, Peer delay, Peer dispersion
The measured values.
Response time
The time the server or peer spent in processing of the request
and waiting before sending the response.
Jitter asymmetry
The estimated asymmetry of network jitter on the path to the
source. The asymmetry can be between -0.5 and 0.5. A negative
value means the delay of packets sent to the source is more
variable than the delay of packets sent from the source back.
NTP tests
Results of RFC 5905 tests 1 through 3, 5 through 7, and tests
for maximum delay, delay ratio, delay dev ratio (or delay
quantile), and synchronisation loop.
Interleaved
This shows if the response was in the interleaved mode.
Authenticated
This shows if the response was authenticated.
TX timestamping
The source of the local transmit timestamp. Valid values are
Daemon, Kernel, and Hardware.
RX timestamping
The source of the local receive timestamp.
Total TX
The number of packets sent to the source.
Total RX
The number of all packets received from the source.
Total valid RX
The number of packets which passed the first two groups of NTP
tests.
Total good RX
The number of packets which passed all three groups of NTP
tests, i.e. the NTP measurement was accepted.
add peer name [option]...
The add peer command allows a new NTP peer to be added whilst
chronyd is running.
Following the words add peer, the syntax of the following
parameters and options is identical to that for the peer directive
in the configuration file.
An example of using this command is shown below.
add peer ntp1.example.net minpoll 6 maxpoll 10 key 25
add pool name [option]...
The add pool command allows a pool of NTP servers to be added
whilst chronyd is running.
Following the words add pool, the syntax of the following
parameters and options is identical to that for the pool directive
in the configuration file.
An example of using this command is shown below:
add pool ntp1.example.net maxsources 3 iburst
add server name [option]...
The add server command allows a new NTP server to be added whilst
chronyd is running.
Following the words add server, the syntax of the following
parameters and options is identical to that for the server
directive in the configuration file.
An example of using this command is shown below:
add server ntp1.example.net minpoll 6 maxpoll 10 key 25
delete address
The delete command allows an NTP server or peer to be removed from
the current set of sources.
burst good/max [mask/masked-address], burst good/max
[masked-address/masked-bits], burst good/max [address]
The burst command tells chronyd to make a set of measurements to
each of its NTP sources over a short duration (rather than the
usual periodic measurements that it makes). After such a burst,
chronyd will revert to the previous state for each source. This
might be either online, if the source was being periodically
measured in the normal way, or offline, if the source had been
indicated as being offline. (A source can be switched between the
online and offline states with the online and offline commands.)
The mask and masked-address arguments are optional, in which case
chronyd will initiate a burst for all of its currently defined
sources.
The arguments have the following meaning and format:
good
This defines the number of good measurements that chronyd will
want to obtain from each source. A measurement is good if it
passes certain tests, for example, the round trip time to the
source must be acceptable. (This allows chronyd to reject
measurements that are likely to be bogus.)
max
This defines the maximum number of measurements that chronyd
will attempt to make, even if the required number of good
measurements has not been obtained.
mask
This is an IP address with which the IP address of each of
chronyd's sources is to be masked.
masked-address
This is an IP address. If the masked IP address of a source
matches this value then the burst command is applied to that
source.
masked-bits
This can be used with masked-address for CIDR notation, which
is a shorter alternative to the form with mask.
address
This is an IP address or a hostname. The burst command is
applied only to that source.
If no mask or masked-address arguments are provided, every source
will be matched.
An example of the two-argument form of the command is:
burst 2/10
This will cause chronyd to attempt to get two good measurements
from each source, stopping after two have been obtained, but in no
event will it try more than ten probes to the source.
Examples of the four-argument form of the command are:
burst 2/10 255.255.0.0/1.2.0.0
burst 2/10 2001:db8:789a::/48
In the first case, the two out of ten sampling will only be applied
to sources whose IPv4 addresses are of the form 1.2.x.y, where x
and y are arbitrary. In the second case, the sampling will be
applied to sources whose IPv6 addresses have first 48 bits equal to
2001:db8:789a.
Example of the three-argument form of the command is:
burst 2/10 ntp1.example.net
maxdelay address delay
This allows the maxdelay option for one of the sources to be
modified, in the same way as specifying the maxdelay option for the
server directive in the configuration file.
maxdelaydevratio address ratio
This allows the maxdelaydevratio option for one of the sources to
be modified, in the same way as specifying the maxdelaydevratio
option for the server directive in the configuration file.
maxdelayratio address ratio
This allows the maxdelayratio option for one of the sources to be
modified, in the same way as specifying the maxdelayratio option
for the server directive in the configuration file.
maxpoll address maxpoll
The maxpoll command is used to modify the maximum polling interval
for one of the current set of sources. It is equivalent to the
maxpoll option in the server directive in the configuration file.
Note that the new maximum polling interval only takes effect after
the next measurement has been made.
minpoll address minpoll
The minpoll command is used to modify the minimum polling interval
for one of the current set of sources. It is equivalent to the
minpoll option in the server directive in the configuration file.
Note that the new minimum polling interval only takes effect after
the next measurement has been made.
minstratum address minstratum
The minstratum command is used to modify the minimum stratum for
one of the current set of sources. It is equivalent to the
minstratum option in the server directive in the configuration
file.
offline [address], offline [masked-address/masked-bits], offline
[mask/masked-address]
The offline command is used to warn chronyd that the network
connection to a particular host or hosts is about to be lost, e.g.
on computers with intermittent connection to their time sources.
Another case where offline could be used is where a computer serves
time to a local group of computers, and has a permanent connection
to true time servers outside the organisation. However, the
external connection is heavily loaded at certain times of the day
and the measurements obtained are less reliable at those times. In
this case, it is probably most useful to determine the gain or loss
rate during the quiet periods and let the whole network coast
through the loaded periods. The offline and online commands can be
used to achieve this.
There are four forms of the offline command. The first form is a
wildcard, meaning all sources (including sources that do not have a
known address yet). The second form allows an IP address mask and a
masked address to be specified. The third form uses CIDR notation.
The fourth form uses an IP address or a hostname. These forms are
illustrated below.
offline
offline 255.255.255.0/1.2.3.0
offline 2001:db8:789a::/48
offline ntp1.example.net
The second form means that the offline command is to be applied to
any source whose IPv4 address is in the 1.2.3 subnet. (The host's
address is logically and-ed with the mask, and if the result
matches the masked-address the host is processed.) The third form
means that the command is to be applied to all sources whose IPv6
addresses have their first 48 bits equal to 2001:db8:789a. The
fourth form means that the command is to be applied only to that
one source.
The wildcard form of the address is equivalent to:
offline 0.0.0.0/0.0.0.0
offline ::/0
online [address], online [masked-address/masked-bits], online
[mask/masked-address]
The online command is opposite in function to the offline command.
It is used to advise chronyd that network connectivity to a
particular source or sources has been restored.
The syntax is identical to that of the offline command.
onoffline
The onoffline command tells chronyd to switch all sources that have
a known address to the online or offline status according to the
current network configuration. A source is considered online if it
is possible to send requests to it, i.e. a network route to the
source is present.
polltarget address polltarget
The polltarget command is used to modify the poll target for one of
the current set of sources. It is equivalent to the polltarget
option in the server directive in the configuration file.
refresh
The refresh command can be used to force chronyd to resolve the
names of configured NTP sources to IP addresses again and replace
any addresses missing in the list of resolved addresses.
Sources that stop responding are replaced with newly resolved
addresses automatically after 8 polling intervals. This command can
be used to replace them immediately, e.g. after suspending and
resuming the machine in a different network.
Note that with pools which have more than 16 addresses, or not all
IPv4 or IPv6 addresses are included in a single DNS response (e.g.
pool.ntp.org), this command might replace the addresses even if
they are still in the pool.
reload sources
The reload sources command causes chronyd to re-read all *.sources
files from the directories specified by the sourcedir directive.
Note that modified sources (e.g. specified with a new option) are
not modified in memory. They are removed and added again, which
causes them to lose old measurements and reset the selection state.
sourcename address
The sourcename command prints the original hostname or address that
was specified for an NTP source in the configuration file, or the
add command. This command is an alternative to the -N option, which
can be useful in scripts.
Note that different NTP sources can share the same name, e.g.
servers from a pool.
Manual time input
manual on, manual off, manual delete index, manual list, manual reset
The manual command enables and disables use of the settime command,
and is used to modify the behaviour of the manual clock driver.
The on form of the command enables use of the settime command.
The off form of the command disables use of the settime command.
The list form of the command lists all the samples currently stored
in chronyd. The output is illustrated below.
210 n_samples = 1
# Date Time(UTC) Slewed Original Residual
====================================================
0 27Jan99 22:09:20 0.00 0.97 0.00
The columns are as as follows:
1. The sample index (used for the manual delete command).
2. The date and time of the sample.
3. The system clock error when the timestamp was entered, adjusted
to allow for changes made to the system clock since.
4. The system clock error when the timestamp was entered, as it
originally was (without allowing for changes to the system
clock since).
5. The regression residual at this point, in seconds. This allows
`outliers' to be easily spotted, so that they can be deleted
using the manual delete command.
The delete form of the command deletes a single sample. The
parameter is the index of the sample, as shown in the first column
of the output from manual list. Following deletion of the data
point, the current error and drift rate are re-estimated from the
remaining data points and the system clock trimmed if necessary.
This option is intended to allow `outliers' to be discarded, i.e.
samples where the administrator realises they have entered a very
poor timestamp.
The reset form of the command deletes all samples at once. The
system clock is left running as it was before the command was
entered.
settime time
The settime command allows the current time to be entered manually,
if this option has been configured into chronyd. (It can be
configured either with the manual directive in the configuration
file, or with the manual command of chronyc.)
It should be noted that the computer's sense of time will only be
as accurate as the reference you use for providing this input (e.g.
your watch), as well as how well you can time the press of the
return key.
Providing your computer's time zone is set up properly, you will be
able to enter a local time (rather than UTC).
The response to a successful settime command indicates the amount
that the computer's clock was wrong. It should be apparent from
this if you have entered the time wrongly, e.g. with the wrong time
zone.
The rate of drift of the system clock is estimated by a regression
process using the entered measurement and all previous measurements
entered during the present run of chronyd. However, the entered
measurement is used for adjusting the current clock offset (rather
than the estimated intercept from the regression, which is
ignored). Contrast what happens with the manual delete command,
where the intercept is used to set the current offset (since there
is no measurement that has just been entered in that case).
The time is parsed by the public domain getdate algorithm.
Consequently, you can only specify time to the nearest second.
Examples of inputs that are valid are shown below:
settime 16:30
settime 16:30:05
settime Nov 21, 2015 16:30:05
For a full description of getdate, see the getdate documentation
(bundled, for example, with the source for GNU tar).
NTP access
accheck address
This command allows you to check whether client NTP access is
allowed from a particular host.
Examples of use, showing a named host and a numeric IP address, are
as follows:
accheck ntp1.example.net
accheck 1.2.3.4
accheck 2001:db8::1
This command can be used to examine the effect of a series of
allow, allow all, deny, and deny all commands specified either via
chronyc, or in chronyd's configuration file.
clients [-p packets] [-k] [-r]
This command shows a list of clients that have accessed the server,
through the NTP, command, or NTS-KE port. It does not include
accesses over the Unix domain command socket.
The -p option specifies the minimum number of received NTP or
command packets, or accepted NTS-KE connections, needed to include
a client in the list. The default value is 0, i.e. all clients are
reported. With the -k option the last four columns will show the
NTS-KE accesses instead of command accesses. If the -r option is
specified, chronyd will reset the counters of received and dropped
packets or connections after reporting the current values.
An example of the output is:
Hostname NTP Drop Int IntL Last Cmd Drop Int Last
===============================================================================
localhost 2 0 2 - 133 15 0 -1 7
ntp1.example.net 12 0 6 - 23 0 0 - -
Each row shows the data for a single host. Only hosts that have
passed the host access checks (set with the allow, deny, cmdallow
and cmddeny commands or configuration file directives) are logged.
The intervals are displayed as a power of 2 in seconds.
The columns are as follows:
1. The hostname of the client.
2. The number of NTP packets received from the client.
3. The number of NTP packets dropped to limit the response rate.
4. The average interval between NTP packets.
5. The average interval between NTP packets after limiting the
response rate.
6. Time since the last NTP packet was received
7. The number of command packets or NTS-KE connections
received/accepted from the client.
8. The number of command packets or NTS-KE connections dropped to
limit the response rate.
9. The average interval between command packets or NTS-KE
connections.
10. Time since the last command packet or NTS-KE connection was
received/accepted.
serverstats
The serverstats command displays NTP and command server statistics.
An example of the output is shown below.
NTP packets received : 1598
NTP packets dropped : 8
Command packets received : 19
Command packets dropped : 0
Client log records dropped : 0
NTS-KE connections accepted: 3
NTS-KE connections dropped : 0
Authenticated NTP packets : 189
Interleaved NTP packets : 43
NTP timestamps held : 44
NTP timestamp span : 120
NTP daemon RX timestamps : 0
NTP daemon TX timestamps : 1537
NTP kernel RX timestamps : 1590
NTP kernel TX timestamps : 43
NTP hardware RX timestamps : 0
NTP hardware TX timestamps : 0
The fields have the following meaning:
NTP packets received
The number of valid NTP requests received by the server.
NTP packets dropped
The number of NTP requests dropped by the server due to rate
limiting (configured by the ratelimit directive).
Command packets received
The number of command requests received by the server.
Command packets dropped
The number of command requests dropped by the server due to
rate limiting (configured by the cmdratelimit directive).
Client log records dropped
The number of client log records dropped by the server to limit
the memory use (configured by the clientloglimit directive).
NTS-KE connections accepted
The number of NTS-KE connections accepted by the server.
NTS-KE connections dropped
The number of NTS-KE connections dropped by the server due to
rate limiting (configured by the ntsratelimit directive).
Authenticated NTP packets
The number of received NTP requests that were authenticated
(with a symmetric key or NTS).
Interleaved NTP packets
The number of received NTP requests that were detected to be in
the interleaved mode.
NTP timestamps held
The number of pairs of receive and transmit timestamps that the
server is currently holding in memory for clients using the
interleaved mode.
NTP timestamp span
The interval (in seconds) covered by the currently held NTP
timestamps.
NTP daemon RX timestamps
The number of NTP responses which included a receive timestamp
captured by the daemon.
NTP daemon TX timestamps
The number of NTP responses which included a transmit timestamp
captured by the daemon.
NTP kernel RX timestamps
The number of NTP responses which included a receive timestamp
captured by the kernel.
NTP kernel TX timestamps
The number of NTP responses (in the interleaved mode) which
included a transmit timestamp captured by the kernel.
NTP hardware RX timestamps
The number of NTP responses which included a receive timestamp
captured by the NIC.
NTP hardware TX timestamps
The number of NTP responses (in the interleaved mode) which
included a transmit timestamp captured by the NIC.
allow [all] [subnet]
The effect of the allow command is identical to the allow directive
in the configuration file.
The syntax is illustrated in the following examples:
allow 1.2.3.4
allow all 3.4.5.0/24
allow 2001:db8:789a::/48
allow 0/0
allow ::/0
allow
allow all
deny [all] [subnet]
The effect of the allow command is identical to the deny directive
in the configuration file.
The syntax is illustrated in the following examples:
deny 1.2.3.4
deny all 3.4.5.0/24
deny 2001:db8:789a::/48
deny 0/0
deny ::/0
deny
deny all
local [option]..., local off
The local command allows chronyd to be told that it is to appear as
a reference source, even if it is not itself properly synchronised
to an external source. This can be used on isolated networks, to
allow a computer to be the primary time server for other computers.
The first form enables the local reference mode on the host. The
syntax is identical to the local directive in the configuration
file.
The second form disables the local reference mode.
smoothing
The smoothing command displays the current state of the NTP server
time smoothing, which can be enabled with the smoothtime directive.
An example of the output is shown below.
Active : Yes
Offset : +1.000268817 seconds
Frequency : -0.142859 ppm
Wander : -0.010000 ppm per second
Last update : 17.8 seconds ago
Remaining time : 19988.4 seconds
The fields are explained as follows:
Active
This shows if the server time smoothing is currently active.
Possible values are Yes and No. If the leaponly option is
included in the smoothtime directive, (leap second only) will
be shown on the line.
Offset
This is the current offset applied to the time sent to NTP
clients. Positive value means the clients are getting time
that's ahead of true time.
Frequency
The current frequency offset of the served time. Negative value
means the time observed by clients is running slower than true
time.
Wander
The current frequency wander of the served time. Negative value
means the time observed by clients is slowing down.
Last update
This field shows how long ago the time smoothing process was
updated, e.g. chronyd accumulated a new measurement.
Remaining time
The time it would take for the smoothing process to get to zero
offset and frequency if there were no more updates.
smoothtime activate, smoothtime reset
The smoothtime command can be used to activate or reset the server
time smoothing process if it is configured with the smoothtime
directive.
Monitoring access
cmdaccheck address
This command is similar to the accheck command, except that it is
used to check whether monitoring access is permitted from a named
host.
Examples of use are as follows:
cmdaccheck ntp1.example.net
cmdaccheck 1.2.3.4
cmdaccheck 2001:db8::1
cmdallow [all] [subnet]
This is similar to the allow command, except that it is used to
allow particular hosts or subnets to use chronyc to monitor with
chronyd on the current host.
cmddeny [all] [subnet]
This is similar to the deny command, except that it is used to
allow particular hosts or subnets to use chronyc to monitor chronyd
on the current host.
Real-time clock (RTC)
rtcdata
The rtcdata command displays the current RTC parameters.
An example output is shown below.
RTC ref time (GMT) : Sat May 30 07:25:56 2015
Number of samples : 10
Number of runs : 5
Sample span period : 549
RTC is fast by : -1.632736 seconds
RTC gains time at : -107.623 ppm
The fields have the following meaning:
RTC ref time (GMT)
This is the RTC reading the last time its error was measured.
Number of samples
This is the number of previous measurements being used to
determine the RTC gain or loss rate.
Number of runs
This is the number of runs of residuals of the same sign
following the regression fit for (RTC error) versus (RTC time).
A value which is small indicates that the measurements are not
well approximated by a linear model, and that the algorithm
will tend to delete the older measurements to improve the fit.
Sample span period
This is the period that the measurements span (from the oldest
to the newest). Without a unit the value is in seconds;
suffixes m for minutes, h for hours, d for days or y for years
can be used.
RTC is fast by
This is the estimate of how many seconds fast the RTC when it
thought the time was at the reference time (above). If this
value is large, you might (or might not) want to use the
trimrtc command to bring the RTC into line with the system
clock. (Note, a large error will not affect chronyd's
operation, unless it becomes so big as to start causing
rounding errors.)
RTC gains time at
This is the amount of time gained (positive) or lost (negative)
by the real time clock for each second that it ticks. It is
measured in parts per million. So if the value shown was +1,
suppose the RTC was exactly right when it crosses a particular
second boundary. Then it would be 1 microsecond fast when it
crosses its next second boundary.
trimrtc
The trimrtc command is used to correct the system's real-time clock
(RTC) to the main system clock. It has no effect if the error
between the two clocks is currently estimated at less than a
second.
The command takes no arguments. It performs the following steps (if
the RTC is more than 1 second away from the system clock):
1. Remember the currently estimated gain or loss rate of the RTC
and flush the previous measurements.
2. Step the real-time clock to bring it within a second of the
system clock.
3. Make several measurements to accurately determine the new
offset between the RTC and the system clock (i.e. the remaining
fraction of a second error).
4. Save the RTC parameters to the RTC file (specified with the
rtcfile directive in the configuration file).
The last step is done as a precaution against the computer
suffering a power failure before either the daemon exits or the
writertc command is issued.
chronyd will still work perfectly well both whilst operating and
across machine reboots even if the trimrtc command is never used
(and the RTC is allowed to drift away from true time). The trimrtc
command is provided as a method by which it can be corrected, in a
manner compatible with chronyd using it to maintain accurate time
across machine reboots.
The trimrtc command can be executed automatically by chronyd with
the rtcautotrim directive in the configuration file.
writertc
The writertc command writes the currently estimated error and gain
or loss rate parameters for the RTC to the RTC file (specified with
the rtcfile directive). This information is also written
automatically when chronyd is killed (by the SIGHUP, SIGINT,
SIGQUIT or SIGTERM signals) or when the trimrtc command is issued.
Other daemon commands
cyclelogs
The cyclelogs command causes all of chronyd's open log files to be
closed and re-opened. This allows them to be renamed so that they
can be periodically purged. An example of how to do this is shown
below.
# mv /var/log/chrony/measurements.log /var/log/chrony/measurements1.log
# chronyc cyclelogs
# rm /var/log/chrony/measurements1.log
dump
The dump command causes chronyd to write its current history of
measurements for each of its sources to dump files in the directory
specified in the configuration file by the dumpdir directive and
also write server NTS keys and client NTS cookies to the directory
specified by the ntsdumpdir directive. Note that chronyd does this
automatically when it exits. This command is mainly useful for
inspection whilst chronyd is running.
rekey
The rekey command causes chronyd to re-read the key file specified
in the configuration file by the keyfile directive. It also
re-reads the server NTS keys if ntsdumpdir is specified and
automatic rotation is disabled in the configuration file.
reset sources
The reset sources command causes chronyd to drop all measurements
and switch to the unsynchronised state. This command can help
chronyd with recovery when the measurements are known to be no
longer valid or accurate, e.g. due to moving the computer to a
different network, or resuming the computer from a low-power state
(which resets the system clock). chronyd will drop the measurements
automatically when it detects the clock has made an unexpected
jump, but the detection is not completely reliable.
shutdown
The shutdown command causes chronyd to exit. This is equivalent to
sending the process the SIGTERM signal.
Client commands
dns option
The dns command configures how hostnames and IP addresses are
resolved in chronyc. IP addresses can be resolved to hostnames when
printing results of sources, sourcestats, tracking and clients
commands. Hostnames are resolved in commands that take an address
as argument.
There are five options:
dns -n
Disables resolving IP addresses to hostnames. Raw IP addresses
will be displayed.
dns +n
Enables resolving IP addresses to hostnames. This is the
default unless chronyc was started with -n option.
dns -4
Resolves hostnames only to IPv4 addresses.
dns -6
Resolves hostnames only to IPv6 addresses.
dns -46
Resolves hostnames to both address families. This is the
default behaviour unless chronyc was started with the -4 or -6
option.
timeout timeout
The timeout command sets the initial timeout for chronyc requests
in milliseconds. If no response is received from chronyd, the
timeout is doubled and the request is resent. The maximum number of
retries is configured with the retries command.
By default, the timeout is 1000 milliseconds.
retries retries
The retries command sets the maximum number of retries for chronyc
requests before giving up. The response timeout is controlled by
the timeout command.
The default is 2.
keygen [id [type [bits]]]
The keygen command generates a key that can be added to the key
file (specified with the keyfile directive) to allow NTP
authentication between server and client, or peers. The key is
generated from the /dev/urandom device and it is printed to
standard output.
The command has three optional arguments. The first argument is the
key number (by default 1), which will be specified with the key
option of the server or peer directives in the configuration file.
The second argument is the name of the hash function or cipher (by
default SHA1, or MD5 if SHA1 is not available). The third argument
is the length of the key in bits if a hash function was selected,
between 80 and 4096 bits (by default 160 bits).
An example is:
keygen 73 SHA1 256
which generates a 256-bit SHA1 key with number 73. The printed line
should then be securely transferred and added to the key files on
both server and client, or peers. A different key should be
generated for each client or peer.
An example using the AES128 cipher is:
keygen 151 AES128
exit, quit
The exit and quit commands exit from chronyc and return the user to
the shell.
help
The help command displays a summary of the commands and their
arguments.
SEE ALSO
chrony.conf(5), chronyd(8)
BUGS
For instructions on how to report bugs, please visit
https://chrony-project.org/.
AUTHORS
chrony was written by Richard Curnow, Miroslav Lichvar, and others.
chrony 4.5 2023-12-05 CHRONYC(1)
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