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Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+// This file is part of chrony
+//
+// Copyright (C) Richard P. Curnow  1997-2003
+// Copyright (C) Stephen Wadeley  2016
+// Copyright (C) Miroslav Lichvar  2009-2017, 2019-2020
+//
+// This program is free software; you can redistribute it and/or modify
+// it under the terms of version 2 of the GNU General Public License as
+// published by the Free Software Foundation.
+//
+// This program is distributed in the hope that it will be useful, but
+// WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+// General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with this program; if not, write to the Free Software Foundation, Inc.,
+// 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+
+= chronyc(1)
+:doctype: manpage
+:man manual: User manual
+:man source: chrony @CHRONY_VERSION@
+
+== 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
+_@CHRONYRUNDIR@/chronyd.sock_. If that fails (e.g. because *chronyc* is
+running under a non-root user), it will try to connect to 127.0.0.1 and then
+::1.
+
+Only the following monitoring commands, which do not affect the behaviour of
+*chronyd*, are allowed from the network: *activity*, *manual list*,
+*rtcdata*, *smoothing*, *sourcename*, *sources*, *sourcestats*, *tracking*,
+*waitsync*. The
+set of hosts from which *chronyd* will accept these commands can be configured
+with the <<chrony.conf.adoc#cmdallow,*cmdallow*>> directive in the *chronyd*'s
+configuration file or the <<cmdallow,*cmdallow*>> command in *chronyc*. By
+default, the commands are accepted only from localhost (127.0.0.1 or ::1).
+
+All other commands are allowed only through the Unix domain socket. When sent
+over the network, *chronyd* will respond with a '`Not authorised`' error, even
+if it is from localhost.
+
+Having full access to *chronyd* via *chronyc* is more or less equivalent to
+being able to modify the *chronyd*'s configuration file and restart it.
+
+== OPTIONS
+
+*-4*::
+With this option hostnames will be resolved only to IPv4 addresses.
+
+*-6*::
+With this option hostnames will be resolved only to IPv6 addresses.
+
+*-n*::
+This option disables resolving of IP addresses to hostnames, e.g. to avoid slow
+DNS lookups. Long addresses will not be truncated to fit into the column.
+
+*-N*::
+This option enables printing of the original names of NTP sources that were
+specified in the configuration file, or *chronyc* commands, and are internally
+used by *chronyd*. Without the *-n* and *-N* option, the names of NTP sources
+are obtained from reverse DNS lookups and can be different from the original
+names.
+
+*-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.
+
+*-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*, *--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]]*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,*local*>> command in *chronyc*, or the
+<<chrony.conf.adoc#local,*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 as a server). 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. 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*::
+*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
+<<chrony.conf.adoc#makestep,*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,*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]]*maxupdateskew* _skew-in-ppm_::
+This command has the same effect as the
+<<chrony.conf.adoc#maxupdateskew,*maxupdateskew*>> directive in the
+configuration file.
+
+[[waitsync]]*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,*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]]*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
+^? 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 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).
+{blank}:::
+The <<selectdata,*selectdata*>> command can be used to get more details about
+the selection state.
+*Name/IP address*:::
+This shows the name or the IP address of the source, or reference ID for reference
+clocks.
+*Stratum*:::
+This shows the stratum of the source, as reported in its most recently
+received sample. Stratum 1 indicates a computer with a locally attached
+reference clock. A computer that is synchronised to a stratum 1 computer is
+at stratum 2. A computer that is synchronised to a stratum 2 computer is at
+stratum 3, and so on.
+*Poll*:::
+This shows the rate at which the source is being polled, as a base-2
+logarithm of the interval in seconds. Thus, a value of 6 would indicate that
+a measurement is being made every 64 seconds. *chronyd* automatically varies
+the polling rate in response to prevailing conditions.
+*Reach*:::
+This shows the source's reachability register printed as an octal number. The
+register has 8 bits and is updated on every received or missed packet from
+the source. A value of 377 indicates that a valid reply was received for all
+from the last eight transmissions.
+*LastRx*:::
+This column shows how long ago the last good sample (which is shown in the next
+column) was received from the source. Measurements that failed some tests are
+ignored. This is normally in seconds. The letters _m_, _h_, _d_ or _y_ indicate
+minutes, hours, days, or years.
+*Last sample*:::
+This column shows the offset between the local clock and the source at the
+last measurement. The number in the square brackets shows the actual measured
+offset. This can be suffixed by _ns_ (indicating nanoseconds), _us_
+(indicating microseconds), _ms_ (indicating milliseconds), or _s_ (indicating
+seconds). The number to the left of the square brackets shows the original
+measurement, adjusted to allow for any slews applied to the local clock
+since. 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]]*sourcestats* [*-a*] [*-v*]::
+The *sourcestats* command displays information about the drift rate and offset
+estimation process for each of the sources currently being examined by
+*chronyd*.
++
+If the *-a* option is specified, all sources are displayed, including those that
+do not have a known address yet. Such sources have an identifier in the format
+_ID#XXXXXXXXXX_, which can be used in other commands expecting a source address.
++
+The *-v* option enables a verbose output. In this case,
+extra caption lines are shown as a reminder of the meanings of the columns.
++
+An example report is:
++
+----
+Name/IP Address            NP  NR  Span  Frequency  Freq Skew  Offset  Std Dev
+===============================================================================
+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.
+
+[[selectdata]]*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 foo.example.net           Y ----- --TR-    4   1.0   -61ms   +62ms  N
+* bar.example.net           N ----- -----    0   1.0 -6846us +7305us  N
++ baz.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.
+{blank}:::
+The following states indicate the source is not considered selectable for
+synchronisation:
+* _N_ - has the *noselect* option.
+* _M_ - does not have enough measurements.
+* _d_ - has a root distance larger than the maximum distance (configured by the
+        <<chrony.conf.adoc#maxdistance,*maxdistance*>> directive).
+* _~_ - has a jitter larger than the maximum jitter (configured by the
+        <<chrony.conf.adoc#maxjitter,*maxjitter*>> directive).
+* _w_ - waits for other sources to get out of the _M_ state.
+* _S_ - has older measurements than other sources.
+* _O_ - has a stratum equal or larger than the orphan stratum (configured by
+        the <<chrony.conf.adoc#local,*local*>> directive).
+* _T_ - does not fully agree with sources that have the *trust* option.
+* _x_ - does not agree with other sources (falseticker).
+{blank}:::
+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
+        <<chrony.conf.adoc#minsources,*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
+        <<chrony.conf.adoc#combinelimit,*combinelimit*>> directive).
+{blank}:::
+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 indicites whether an authentication mechanism is enabled for the
+source. _Y_ means yes and _N_ means no.
+*COpts*:::
+This column displays the configured selection options of the source.
+* _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
+<<chrony.conf.adoc#authselmode,*authselmode*>> 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).
+
+[[reselect]]*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]]*reselectdist* _distance_::
+The *reselectdist* command sets the reselection distance. It is equivalent to
+the <<chrony.conf.adoc#reselectdist,*reselectdist*>> directive in the
+configuration file.
+
+=== NTP sources
+
+[[activity]]*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]]*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
+=========================================================================
+foo.example.net              NTS     1   15  256 135m    0    0    8  100
+bar.example.net               SK    30   13  128    -    0    0    0    0
+baz.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 <<chrony.conf.adoc#keyfile,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
+*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]]*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
+----
++
+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]]*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
+<<chrony.conf.adoc#peer,*peer*>> directive in the configuration file.
++
+An example of using this command is shown below.
++
+----
+add peer foo.example.net minpoll 6 maxpoll 10 key 25
+----
+
+[[add_pool]]*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 <<chrony.conf.adoc#pool,*pool*>>
+directive in the configuration file.
++
+An example of using this command is shown below:
++
+----
+add pool foo.example.net maxsources 3 iburst
+----
+
+[[add_server]]*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 <<chrony.conf.adoc#server,*server*>>
+directive in the configuration file.
++
+An example of using this command is shown below:
++
+----
+add server foo.example.net minpoll 6 maxpoll 10 key 25
+----
+
+[[delete]]*delete* _address_::
+The *delete* command allows an NTP server or peer to be removed
+from the current set of sources.
+
+[[burst]]
+*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,*online*>> and <<offline,*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.
+{blank}::
++
+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]]*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
+<<chrony.conf.adoc#server,*server*>> directive in the configuration file.
+
+[[maxdelaydevratio]]*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
+<<chrony.conf.adoc#server,*server*>> directive in the configuration file.
+
+[[maxdelayratio]]*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
+<<chrony.conf.adoc#server,*server*>> directive in the configuration file.
+
+[[maxpoll]]*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
+<<chrony.conf.adoc#server,*server*>> directive in the configuration file.
++
+Note that the new maximum polling interval only takes effect after the next
+measurement has been made.
+
+[[minpoll]]*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
+<<chrony.conf.adoc#server,*server*>> directive in the configuration file.
++
+Note that the new minimum polling interval only takes effect after the next
+measurement has been made.
+
+[[minstratum]]*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
+<<chrony.conf.adoc#server,*server*>> directive in the configuration file.
+
+[[offline]]
+*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 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]]
+*online* [_address_]::
+*online* [_masked-address_/_masked-bits_]::
+*online* [_mask_/_masked-address_]::
+The *online* command is opposite in function to the <<offline,*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,*offline*>> command.
+
+[[onoffline]]
+*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]]*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
+<<chrony.conf.adoc#server,*server*>> directive in the configuration file.
+
+[[refresh]]*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.
+
+[[reload]]*reload* *sources*::
+The *reload sources* command causes *chronyd* to re-read all _*.sources_ files
+from the directories specified by the
+<<chrony.conf.adoc#sourcedir,*sourcedir*>> directive.
+
+[[sourcename]]*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]]
+*manual* *on*::
+*manual* *off*::
+*manual* *delete* _index_::
+*manual* *list*::
+*manual* *reset*::
+The manual command enables and disables use of the <<settime,*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:
++
+. The sample index (used for the *manual delete* command).
+. The date and time of the sample.
+. The system clock error when the timestamp was entered, adjusted to allow
+  for changes made to the system clock since.
+. The system clock error when the timestamp was entered, as it originally was
+  (without allowing for changes to the system clock since).
+. 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.
+{blank}::
++
+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]]*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 <<chrony.conf.adoc#manual,*manual*>> directive in the configuration file,
+or with the <<manual,*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,*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]]*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]]*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
+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,*allow*>>, <<deny,*deny*>>,
+<<cmdallow,*cmdallow*>> and <<cmddeny,*cmddeny*>> commands or configuration
+file directives) are logged. The intervals are displayed as a power of 2 in
+seconds.
++
+The columns are as follows:
++
+. The hostname of the client.
+. The number of NTP packets received from the client.
+. The number of NTP packets dropped to limit the response rate.
+. The average interval between NTP packets.
+. The average interval between NTP packets after limiting the response rate.
+. Time since the last NTP packet was received
+. The number of command packets or NTS-KE connections received/accepted from
+  the client.
+. The number of command packets or NTS-KE connections dropped to limit the
+  response rate.
+. The average interval between command packets or NTS-KE connections.
+. Time since the last command packet or NTS-KE connection was
+  received/accepted.
+
+[[serverstats]]*serverstats*::
+The *serverstats* command displays how many valid NTP and command requests, and
+NTS-KE connections, *chronyd* operating as a server received from clients, and
+how many of them were dropped due to rate limiting. It also displays how many
+client log records were dropped due to the memory limit configured by the
+<<chrony.conf.adoc#clientloglimit,*clientloglimit*>> directive and how many of
+the NTP requests (from those which were not dropped) were authenticated. 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
+----
+
+[[allow]]*allow* [*all*] [_subnet_]::
+The effect of the allow command is identical to the
+<<chrony.conf.adoc#allow,*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]]*deny* [*all*] [_subnet_]::
+The effect of the allow command is identical to the
+<<chrony.conf.adoc#deny,*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]]
+*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 <<chrony.conf.adoc#local,*local*>> directive in the
+configuration file.
++
+The second form disables the local reference mode.
+
+[[smoothing]]*smoothing*::
+The *smoothing* command displays the current state of the NTP server time
+smoothing, which can be enabled with the
+<<chrony.conf.adoc#smoothtime,*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]]
+*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
+<<chrony.conf.adoc#smoothtime,*smoothtime*>> directive.
+
+=== Monitoring access
+
+[[cmdaccheck]]*cmdaccheck* _address_::
+This command is similar to the <<accheck,*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]]*cmdallow* [*all*] [_subnet_]::
+This is similar to the <<allow,*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]]*cmddeny* [*all*] [_subnet_]::
+This is similar to the <<deny,*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]]*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,*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]]*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):
++
+. Remember the currently estimated gain or loss rate of the RTC and flush the
+  previous measurements.
+. Step the real-time clock to bring it within a second of the system clock.
+. 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).
+. Save the RTC parameters to the RTC file (specified with the
+  <<chrony.conf.adoc#rtcfile,*rtcfile*>> directive in the configuration file).
+{blank}::
++
+The last step is done as a precaution against the computer suffering a power
+failure before either the daemon exits or the <<writertc,*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
+<<chrony.conf.adoc#rtcautotrim,*rtcautotrim*>> directive in the configuration
+file.
+
+[[writertc]]*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
+<<chrony.conf.adoc#rtcfile,*rtcfile*>> directive). This information is also
+written automatically when *chronyd* is killed (by the SIGHUP, SIGINT, SIGQUIT
+or SIGTERM signals) or when the <<trimrtc,*trimrtc*>> command is issued.
+
+=== Other daemon commands
+
+[[cyclelogs]]*cyclelogs*::
+The *cyclelogs* command causes all of *chronyd*'s open log files to be closed
+and re-opened. This allows them to be renamed so that they can be periodically
+purged. An example of how to do this is shown below.
++
+----
+# mv /var/log/chrony/measurements.log /var/log/chrony/measurements1.log
+# chronyc cyclelogs
+# rm /var/log/chrony/measurements1.log
+----
+
+[[dump]]*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 <<chrony.conf.adoc#dumpdir,*dumpdir*>>
+directive and also write server NTS keys and client NTS cookies to the
+directory specified by the <<chrony.conf.adoc#ntsdumpdir1,*ntsdumpdir*>>
+directive. Note that *chronyd* does this automatically when it exits. This
+command is mainly useful for inspection whilst *chronyd* is running.
+
+[[rekey]]*rekey*::
+The *rekey* command causes *chronyd* to re-read the key file specified in the
+configuration file by the <<chrony.conf.adoc#keyfile,*keyfile*>> directive. It
+also re-reads the server NTS keys if
+<<chrony.conf.adoc#ntsdumpdir2,*ntsdumpdir*>> is specified and
+<<chrony.conf.adoc#ntsrotate,automatic rotation>> is disabled in the
+configuration file.
+
+[[reset]]*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]]*shutdown*::
+The *shutdown* command causes *chronyd* to exit. This is equivalent to sending
+the process the SIGTERM signal.
+
+=== Client commands
+
+[[dns]]*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,*sources*>>, <<sourcestats,*sourcestats*>>, <<tracking,*tracking*>>
+and <<clients,*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* _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,*retries*>> command.
++
+By default, the timeout is 1000 milliseconds.
+
+[[retries]]*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,*timeout*>> command.
++
+The default is 2.
+
+[[keygen]]*keygen* [_id_ [_type_ [_bits_]]]::
+The *keygen* command generates a key that can be added to the
+key file (specified with the <<chrony.conf.adoc#keyfile,*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]]*exit*::
+[[quit]]*quit*::
+The *exit* and *quit* commands exit from *chronyc* and return the user to the shell.
+
+[[help]]*help*::
+The *help* command displays a summary of the commands and their arguments.
+
+== SEE ALSO
+
+<<chrony.conf.adoc#,*chrony.conf(5)*>>, <<chronyd.adoc#,*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.