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Manual: chronyc

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 by default: 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).

Other monitoring commands can be enabled for network access by the opencommands directive. Monitoring
commands with disabled network access and commands that affect the behaviour of chronyd are allowed
only through the Unix domain socket. If they are 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.

-u user
This option sets the name of the user to which chronyc will switch when it is started under the
root user in order to drop its privileges. chronyc will not try to change its identity if the
option is set to root, or the effective user ID of the started process is not 0. The compiled-in
default value is _chrony.

-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.

• * indicates the best source which is currently selected for synchronisation.

• + indicates other sources selected for synchronisation, which are combined with the best
source.

• - indicates a source which is considered to be selectable for synchronisation, but not
currently selected.

• 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).

• ~ indicates a source whose time appears to have too much variability.

• ? 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. It is shifted to left by one bit with each poll and it is updated by 1 when a valid NTP
response, or just a sample in case of a reference clock, is received from the source. A value
of 377 indicates that a valid response or sample was received for all of the last 8 polls.
Note that samples can be dropped if they are not considered good enough for synchronisation,
but the reachability register will still have 1s for their polls.

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.

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:

• N - has the noselect option.

• M - does not have enough measurements.

• s - is not synchronised.

• d - has a root distance larger than the maximum distance (configured by the maxdistance
directive).

• ~ - has a jitter larger than the maximum jitter (configured by the maxjitter directive).

• w - waits for other sources to get out of the M state.

• S - has only measurements older than reachable sources, or is unreachable for too many
polls (configured by the maxunreach option).

• O - has a stratum equal or larger than the orphan stratum (configured by the local
directive).

• T - does not fully agree with sources that have the trust option.

• 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:

• W - waits for other sources to be selectable (required by the minsources directive, or
the require option of another source).

• P - another selectable source is preferred due to the prefer option.

• U - waits for a new measurement (after selecting a different best source).

• 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:

• + - combined with the best source.

• * - 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 indicates 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.

• N indicates the noselect option.

• P indicates the prefer option.

• T indicates the trust option.

• 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.

• N indicates the normal status (no leap second).

• + indicates that a leap second will be inserted at the end of the month.

• - indicates that a leap second will be deleted at the end of the month.

• ? 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.

offset address|refid offset
The offset command modifies the offset correction 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. It is equivalent to the offset option in the server or refclock
directive respectively.

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:

• 1: MD5

• 2: SHA1

• 3: SHA256

• 4: SHA384

• 5: SHA512

• 6: SHA3-224

• 7: SHA3-256

• 8: SHA3-384

• 9: SHA3-512

• 10: TIGER

• 11: WHIRLPOOL

• 13: AES128

• 14: AES256

• 15: AEAD-AES-SIV-CMAC-256

• 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
Total kernel TX : 24
Total kernel RX : 24
Total HW TX : 0
Total HW RX : 0

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.

Total kernel TX
The number of packets sent to the source for which a timestamp was captured by the kernel.

Total kernel RX
The number of packets received from the source for which a timestamp was captured by the
kernel.

Total HW TX
The number of packets sent to the source for which a timestamp was captured by the NIC.

Total HW RX
The number of packets received from the source for which a timestamp was captured by the NIC.

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

Note that log files enabled by the log directive are opened when the first entry is made. The
message log file specified by the chronyd's -l option is opened early on start and closed on the
cyclelogs command only if opening of the new file succeeds to avoid losing messages. If chronyd
is configured to drop root privileges and the directory containing the log file is not writable
for the specified user, chronyd will not be able to open the file again.

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.

Manual: chronyc

Related Commands: