chronyc(1) - command-line interface for chrony daemon



  • 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.
    
    	       ·   * indicates the source to which chronyd is currently
    		   synchronised.
    
    	       ·   + indicates acceptable sources which are combined with the
    		   selected source.
    
    	       ·   - indicates acceptable sources which are excluded by the
    		   combining algorithm.
    
    	       ·   ? 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.
    
    	       ·   x indicates a clock which chronyd thinks is a falseticker
    		   (i.e. its time is inconsistent with a majority of other
    		   sources).
    
    	       ·   ~ 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 sample was received
    	       from the source. 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.
    
           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.
    
       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 3.2			  2017-09-15			    CHRONYC(1)
    

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