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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 is not 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 /var/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, 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. In chrony versions
       before 2.2 they were allowed from the network if they were
       authenticated with a password, but that is no longer supported.
       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.
       -c
           This option enables printing of reports in a comma-separated values
           (CSV) format. IP addresses will not be resolved to hostnames, time
           will be printed as number of seconds since the epoch and values in
           seconds will not be converted to other units.
       -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 allows the user to specify which host (or
           comma-separated list of addresses) running the chronyd program is
           to be contacted. This allows for remote monitoring, without having
           to connect over SSH to the other host first.
           The default is to contact chronyd running on the same host where
           chronyc is being run.
       -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
           With this option chronyc displays its version number 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 (foo.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. foo.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
               In normal operation, chronyd by default never steps the system
               clock, because any jump in the time can have adverse
               consequences for certain application programs. Instead, any
               error in the system clock is corrected by slightly speeding up
               or slowing down the system clock until the error has been
               removed, and then returning to the system clock's normal speed.
               A consequence of this is that there will be a period when the
               system clock (as read by other programs) will be different from
               chronyd's estimate of the current true time (which it reports
               to NTP clients when it is operating in server mode). The value
               reported on this line is the difference due to this effect.
           Last offset
               This is the estimated local offset on the last clock update.
           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 [-v]
           This command displays information about the current time sources
           that chronyd is accessing.
           The optional argument -v can be specified, meaning verbose. In this
           case, extra caption lines are shown as a reminder of the meanings
           of the columns.
               210 Number of sources = 3
               MS Name/IP address         Stratum Poll Reach LastRx Last sample
               ===============================================================================
               #* GPS0                          0   4   377    11   -479ns[ -621ns] +/-  134ns
               ^? foo.example.net               2   6   377    23   -923us[ -924us] +/-   43ms
               ^+ bar.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 state of the source.
               o   * indicates the source to which chronyd is currently
                   synchronised.
               o   + indicates acceptable sources which are combined with the
                   selected source.
               o   - indicates acceptable sources which are excluded by the
                   combining algorithm.
               o   ? indicates sources to which connectivity has been lost or
                   whose packets do not pass all tests. It is also shown at
                   start-up, until at least 3 samples have been gathered from
                   it.
               o   x indicates a clock which chronyd thinks is a falseticker
                   (i.e. its time is inconsistent with a majority of other
                   sources).
               o   ~ indicates a source whose time appears to have too much
                   variability.
           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. The number following the +/- indicator shows
               the margin of error in the measurement. Positive offsets
               indicate that the local clock is ahead of the source.
       sourcestats [-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 optional argument -v can be specified, meaning verbose. In this
           case, extra caption lines are shown as a reminder of the meanings
           of the columns.
           An example report is:
               210 Number of sources = 1
               Name/IP Address            NP  NR  Span  Frequency  Freq Skew  Offset  Std Dev
               ===============================================================================
               foo.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.
       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.
       ntpdata [address]
           The ntpdata command displays the last valid measurement and other
           NTP-specific information about the specified NTP source, or all NTP
           sources 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
           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, 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 valid packets received from the source.
       add peer address [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 similar to that for the peer directive in
           the configuration file. The following peer options can be set in
           the command: port, minpoll, maxpoll, presend, maxdelayratio,
           maxdelay, key.
           An example of using this command is shown below.
               add peer foo.example.net minpoll 6 maxpoll 10 key 25
       add server address [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 similar to that for the server directive
           in the configuration file. The following server options can be set
           in the command: port, minpoll, maxpoll, presend, maxdelayratio,
           maxdelay, key.
           An example of using this command is shown below:
               add server foo.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 foo.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. 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 foo.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 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 route to the network 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 sources to IP addresses again, e.g. after
           suspending and resuming the machine in a different network.
           Sources that stop responding will be replaced with newly resolved
           addresses automatically after 8 polling intervals, but this command
           can still be useful to replace them immediately and not wait until
           they are marked as unreachable.
   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 foo.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
           This command shows a list of clients that have accessed the server,
           through either the NTP or command ports. It does not include
           accesses over the Unix domain command socket. There are no
           arguments.
           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
               foo.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 received from the client.
            8. The number of command packets dropped to limit the response
               rate.
            9. The average interval between command packets.
            10. Time since the last command packet was received.
       serverstats
           The serverstats command displays how many valid NTP and command
           requests chronyd as a server received from clients, how many of
           them were dropped to limit the response rate as configured by the
           ratelimit and cmdratelimit directives, and how many client log
           records were dropped due to the memory limit configured by the
           clientloglimit directive. 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
       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 foo.example.net
               allow all 1.2
               allow 3.4.5
               allow 6.7.8/22
               allow 6.7.8.9/22
               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 foo.example.net
               deny all 1.2
               deny 3.4.5
               deny 6.7.8/22
               deny 6.7.8.9/22
               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 one computer to be a master time server with the other
           computers slaving to it.)
           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 foo.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
               # ls -l /var/log/chrony
               -rw-r--r--   1 root     root            0 Jun  8 18:17 measurements.log
               -rw-r--r--   1 root     root        12345 Jun  8 18:17 measurements1.log
               # rm -f 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. Note
           that chronyd does this automatically when it exits. This command is
           mainly useful for inspection of the history 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.
       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 hash function (by default SHA1 or MD5 if
           SHA1 is not available) and the third argument is the number of bits
           the key should have, 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.
       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.tuxfamily.org/>.
AUTHORS
       chrony was written by Richard Curnow, Miroslav Lichvar, and others.

chrony 3.4                        2018-09-19                        CHRONYC(1)