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CHRONYC(1) User manual CHRONYC(1) NAME chronyc - command-line interface for chrony daemon SYNOPSIS chronyc [OPTION]... [COMMAND]... DESCRIPTION chronyc is a command-line interface program which can be used to monitor chronyd's performance and to change various operating parameters whilst it is running. If no commands are specified on the command line, chronyc will expect input from the user. The prompt chronyc> will be displayed when it is being run from a terminal. If chronyc's input or output are redirected from or to a file, the prompt 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 con- nect to the Unix domain socket. The compiled-in default path is /var/run/chrony/chronyd.sock. If that fails (e.g. because chronyc is run- ning under a non-root user), it will try to connect to 127.0.0.1 and then ::1. Only the following monitoring commands, which do not affect the behaviour of chronyd, are allowed from the network by default: activity, manual list, rtcdata, smoothing, sourcename, sources, sourcestats, tracking, waitsync. The set of hosts from which chronyd will accept these commands can be con- figured with the cmdallow directive in the chronyd's configuration file or the cmdallow command in chronyc. By default, the commands are accepted only from localhost (127.0.0.1 or ::1). Other monitoring commands can be enabled for network access by the opencom- mands directive. Monitoring commands with disabled network access and com- mands that affect the behaviour of chronyd are allowed only through the Unix domain socket. If they are sent over the network, chronyd will respond with a `Not authorised' error, even if it is from localhost. Having full access to chronyd via chronyc is more or less equivalent to be- ing able to modify the chronyd's configuration file and restart it. OPTIONS -4 With this option hostnames will be resolved only to IPv4 addresses. -6 With this option hostnames will be resolved only to IPv6 addresses. -n This option disables resolving of IP addresses to hostnames, e.g. to avoid slow DNS lookups. Long addresses will not be truncated to fit into the column. -N This option enables printing of original hostnames or IP addresses of NTP sources that were specified in the configuration file, or chronyc commands. Without the -n and -N option, the printed hostnames are ob- tained from reverse DNS lookups and can be different from the specified hostnames. -c This option enables printing of reports in a comma-separated values (CSV) format. Reverse DNS lookups will be disabled, time will be printed as number of seconds since the epoch, and values in seconds will not be converted to other units. -e With this option each chronyc response will end with a line containing a single dot. -d This option enables printing of debugging messages if chronyc was com- piled with debugging support. -m Normally, all arguments on the command line are interpreted as one com- mand. With this option multiple commands can be specified. Each argu- ment will be interpreted as a whole command. -h host This option specifies the host to be contacted by chronyc. It can be specified with a hostname, IP address, or path to the local Unix domain socket. Multiple values can be specified as a comma-separated list to provide a fallback. The default value is /var/run/chrony/chronyd.sock,127.0.0.1,::1, i.e. the host where chronyc is being run. First, it tries to connect to the Unix domain socket and if that fails (e.g. due to running under a non-root user), it will try to connect to 127.0.0.1 and then ::1. -p port This option allows the user to specify the UDP port number which the target chronyd is using for its monitoring connections. This defaults to 323; there would rarely be a need to change this. -u user This option sets the name of the user to which chronyc will switch when it is started under the root user in order to drop its privileges. chronyc will not try to change its identity if the option is set to root, or the effective user ID of the started process is not 0. The compiled-in default value is root. -f file This option is ignored and is provided only for compatibility. -a This option is ignored and is provided only for compatibility. -v, --version With this option chronyc displays its version number on the terminal and exits. --help With this option chronyc displays a help message on the terminal and exits. COMMANDS This section describes each of the commands available within the chronyc program. System clock tracking The tracking command displays parameters about the system's clock per- formance. An example of the output is shown below. Reference ID : CB00710F (ntp1.example.net) Stratum : 3 Ref time (UTC) : Fri Jan 27 09:49:17 2017 System time : 0.000006523 seconds slow of NTP time Last offset : -0.000006747 seconds RMS offset : 0.000035822 seconds Frequency : 3.225 ppm slow Residual freq : -0.000 ppm Skew : 0.129 ppm Root delay : 0.013639022 seconds Root dispersion : 0.001100737 seconds Update interval : 64.2 seconds Leap status : Normal The fields are explained as follows: Reference ID This is the reference ID and name (or IP address) of the server to which the computer is currently synchronised. For IPv4 addresses, the reference ID is equal to the address and for IPv6 addresses it is the first 32 bits of the MD5 sum of the address. If the reference ID is 7F7F0101 and there is no name or IP address, it means the computer is not synchronised to any external source and that you have the local mode operating (via the local command in chronyc, or the local directive in the configuration file). The reference ID is printed as a hexadecimal number. Note that in older versions it used to be printed in quad-dotted notation and could be confused with an IPv4 address. Stratum The stratum indicates how many hops away from a computer with an attached reference clock we are. Such a computer is a stratum-1 computer, so the computer in the example is two hops away (i.e. ntp1.example.net is a stratum-2 and is synchronised from a stra- tum-1). Ref time This is the time (UTC) at which the last measurement from the ref- erence source was processed. System time This is the current offset between the NTP clock and system clock. The NTP clock is a software (virtual) clock maintained by chronyd, which is synchronised to the configured time sources and provides time to NTP clients. The system clock is synchronised to the NTP clock. To avoid steps in the system time, which might have adverse consequences for certain applications, the system clock is normally corrected only by speeding up or slowing down (up to the rate con- figured by the maxslewrate directive). If the offset is too large, this correction will take a very long time. A step can be forced by the makestep command, or the makestep directive in the configura- tion file. Note that all other offsets reported by chronyc and most offsets in the log files are relative to the NTP clock, not the system clock. Last offset This is the estimated local offset on the last clock update. A pos- itive 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 ac- tually advanced by 1.000001 seconds relative to true time. Residual freq This shows the `residual frequency' for the currently selected ref- erence source. This reflects any difference between what the mea- surements 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 refer- ence 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 refer- ence 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 com- puter 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 ulti- mately 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 cer- tain 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 sys- tem 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 sec- onds) 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 nor- mally.) 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 maxi- mum 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 cor- rection of the system clock and the maximum allowed skew (in ppm) as reported by the tracking command in the System time and Skew fields. If not specified or zero, the value will not be checked. The fourth argument is the interval specified in seconds in which the check is repeated. The interval is 10 seconds by default. An example is: waitsync 60 0.01 which will wait up to about 10 minutes (60 times 10 seconds) for chronyd to synchronise to a source and the remaining correction to be less than 10 milliseconds. Time sources sources [-a] [-v] This command displays information about the current time sources that chronyd is accessing. If the -a option is specified, all sources are displayed, including those that do not have a known address yet. Such sources have an iden- tifier in the format ID#XXXXXXXXXX, which can be used in other commands expecting a source address. The -v option enables a verbose output. In this case, extra caption lines are shown as a reminder of the meanings of the columns. MS Name/IP address Stratum Poll Reach LastRx Last sample =============================================================================== #* GPS0 0 4 377 11 -479ns[ -621ns] +/- 134ns ^? ntp1.example.net 2 6 377 23 -923us[ -924us] +/- 43ms ^+ ntp2.example.net 1 6 377 21 -2629us[-2619us] +/- 86ms The columns are as follows: M This indicates the mode of the source. ^ means a server, = means a peer and # indicates a locally connected reference clock. S This column indicates the selection state of the source. * * indicates the best source which is currently selected for synchronisation. * + indicates other sources selected for synchronisation, which are combined with the best source. * - indicates a source which is considered to be selectable for synchronisation, but not currently selected. * x indicates a source which chronyd thinks is a falseticker (i.e. its time is inconsistent with a majority of other sources, or sources specified with the trust option). * ~ indicates a source whose time appears to have too much vari- ability. * ? indicates a source which is not considered to be selectable for synchronisation for other reasons (e.g. unreachable, not synchronised, or does not have enough measurements). The selectdata command can be used to get more details about the selection state. Name/IP address This shows the name or the IP address of the source, or reference ID for reference clocks. Stratum This shows the stratum of the source, as reported in its most re- cently received sample. Stratum 1 indicates a computer with a lo- cally attached reference clock. A computer that is synchronised to a stratum 1 computer is at stratum 2. A computer that is synchro- nised 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 pre- vailing conditions. Reach This shows the source's reachability register printed as an octal number. The register has 8 bits. It is shifted to left by one bit with each poll and it is updated by 1 when a valid NTP response, or just a sample in case of a reference clock, is received from the source. A value of 377 indicates that a valid response or sample was received for all of the last 8 polls. Note that samples can be dropped if they are not considered good enough for synchronisation, but the reachability register will still have 1s for their polls. LastRx This column shows how long ago the last good sample (which is shown in the next column) was received from the source. Measurements that failed some tests are ignored. This is normally in seconds. The letters m, h, d or y indicate minutes, hours, days, or years. Last sample This column shows the offset between the local clock and the source at the last measurement. The number in the square brackets shows the actual measured offset. This can be suffixed by ns (indicating nanoseconds), us (indicating microseconds), ms (indicating mil- liseconds), or s (indicating seconds). The number to the left of the square brackets shows the original measurement, adjusted to al- low for any slews applied to the local clock since. Positive off- sets indicate that the local clock is ahead of the source. The num- ber following the +/- indicator shows the margin of error in the measurement (NTP root distance). sourcestats [-a] [-v] The sourcestats command displays information about the drift rate and offset estimation process for each of the sources currently being exam- ined 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 iden- tifier in the format ID#XXXXXXXXXX, which can be used in other commands expecting a source address. The -v option enables a verbose output. In this case, extra caption lines are shown as a reminder of the meanings of the columns. An example report is: Name/IP Address NP NR Span Frequency Freq Skew Offset Std Dev =============================================================================== ntp1.example.net 11 5 46m -0.001 0.045 1us 25us The columns are as follows: Name/IP Address This is the name or IP address of the NTP server (or peer) or ref- erence ID of the reference clock to which the rest of the line re- lates. NP This is the number of sample points currently being retained for the server. The drift rate and current offset are estimated by per- forming a linear regression through these points. NR This is the number of runs of residuals having the same sign fol- lowing 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 re- gression 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 mil- lion). Offset This is the estimated offset of the source. Std Dev This is the estimated sample standard deviation. selectdata [-a] [-v] The selectdata command displays information specific to the selection of time sources. If the -a option is specified, all sources are dis- played, including those that do not have a known address yet. With the -v option, extra caption lines are shown as a reminder of the meanings of the columns. An example of the output is shown below. S Name/IP Address Auth COpts EOpts Last Score Interval Leap ======================================================================= D ntp1.example.net Y ----- --TR- 4 1.0 -61ms +62ms N * ntp2.example.net N ----- ----- 0 1.0 -6846us +7305us N + ntp3.example.net N ----- ----- 10 1.0 -7381us +7355us N The columns are as follows: S This column indicates the state of the source after the last source selection. It is similar to the state reported by the sources com- mand, but more states are reported. The following states indicate the source is not considered selec- table for synchronisation: * N - has the noselect option. * M - does not have enough measurements. * s - is not synchronised. * d - has a root distance larger than the maximum distance (con- figured by the maxdistance directive). * ~ - has a jitter larger than the maximum jitter (configured by the maxjitter directive). * w - waits for other sources to get out of the M state. * S - has only measurements older than reachable sources, or is unreachable for too many polls (configured by the maxunreach option). * O - has a stratum equal or larger than the orphan stratum (con- figured by the local directive). * T - does not fully agree with sources that have the trust op- tion. * x - does not agree with other sources (falseticker). The following states indicate the source is considered selectable, but it is not currently used for synchronisation: * W - waits for other sources to be selectable (required by the minsources directive, or the require option of another source). * P - another selectable source is preferred due to the prefer option. * U - waits for a new measurement (after selecting a different best source). * D - has, or recently had, a root distance which is too large to be combined with other sources (configured by the combinelimit directive). The following states indicate the source is used for synchronisa- tion of the local clock: * + - combined with the best source. * * - selected as the best source to update the reference data (e.g. root delay, root dispersion). Name/IP address This column shows the name or IP address of the source if it is an NTP server, or the reference ID if it is a reference clock. Auth This column indicates whether an authentication mechanism is en- abled for the source. Y means yes and N means no. COpts This column displays the configured selection options of the source. * N indicates the noselect option. * P indicates the prefer option. * T indicates the trust option. * R indicates the require option. EOpts This column displays the current effective selection options of the source, which can be different from the configured options due to the authentication selection mode (configured by the authselectmode directive). The symbols are the same as in the COpts column. Last This column displays how long ago was the last measurement of the source made when the selection was performed. Score This column displays the current score against the source in the * state. The scoring system avoids frequent reselection when multiple sources have a similar root distance. A value larger than 1 indi- cates this source was better than the * source in recent selec- tions. If the score reaches 10, the best source will be reselected and the scores will be reset to 1. Interval This column displays the lower and upper endpoint of the interval which was expected to contain the true offset of the local clock considering the root distance at the time of the selection. Leap This column displays the current leap status of the source. * N indicates the normal status (no leap second). * + indicates that a leap second will be inserted at the end of the month. * - indicates that a leap second will be deleted at the end of the month. * ? indicates the unknown status (i.e. no valid measurement was made). selectopts address|refid [+|-option]... The selectopts command modifies the configured selection options of an NTP source specified by IP address (or the ID#XXXXXXXXXX identifier used for unknown addresses), or a reference clock specified by refer- ence ID as a string. The selection options can be added with the + symbol or removed with the - symbol. The selectdata command can be used to verify the configu- ration. The modified options will be applied in the next source selec- tion, e.g. when a new measurement is made, or the reselect command is executed. An example of using this command is shown below. selectopts 1.2.3.4 -noselect +prefer selectopts GPS +trust reselect To avoid excessive switching between sources, chronyd can stay synchro- nised 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 equiva- lent to the reselectdist directive in the configuration file. offset address|refid offset The offset command modifies the offset correction of an NTP source specified by IP address (or the ID#XXXXXXXXXX identifier used for un- known addresses), or a reference clock specified by reference ID as a string. It is equivalent to the offset option in the server or refclock directive respectively. NTP sources activity This command reports the number of servers and peers that are online and offline. If the auto_offline option is used in specifying some of the servers or peers, the activity command can be useful for detecting when all of them have entered the offline state after the network link has been disconnected. The report shows the number of servers and peers in 5 states: online the server or peer is currently online (i.e. assumed by chronyd to be reachable) offline the server or peer is currently offline (i.e. assumed by chronyd to be unreachable, and no measurements from it will be attempted.) burst_online a burst command has been initiated for the server or peer and is being performed; after the burst is complete, the server or peer will be returned to the online state. burst_offline a burst command has been initiated for the server or peer and is being performed; after the burst is complete, the server or peer will be returned to the offline state. unresolved the name of the server or peer was not resolved to an address yet; this source is not visible in the sources and sourcestats reports. authdata [-a] The authdata command displays information specific to authentication of NTP sources. If the -a option is specified, all sources are displayed, including those that do not have a known address yet. An example of the output is shown below. Name/IP address Mode KeyID Type KLen Last Atmp NAK Cook CLen ========================================================================= ntp1.example.net NTS 1 15 256 135m 0 0 8 100 ntp2.example.net SK 30 13 128 - 0 0 0 0 ntp3.example.net - 0 0 0 - 0 0 0 0 The columns are as follows: Name/IP address This column shows the name or the IP address of the source. Mode This column shows which mechanism authenticates NTP packets re- ceived from the source. NTS means Network Time Security, SK means a symmetric key, and - means authentication is disabled. KeyID This column shows an identifier of the key used for authentication. With a symmetric key, it is the ID from the key file. With NTS, it is a number starting at zero and incremented by one with each suc- cessful 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 authen- tication. With a symmetric key, it is the hash function or cipher specified in the key file. With NTS, it is an authenticated encryp- tion with associated data (AEAD) algorithm, which is negotiated in the NTS-KE protocol. The following values can be reported: * 1: MD5 * 2: SHA1 * 3: SHA256 * 4: SHA384 * 5: SHA512 * 6: SHA3-224 * 7: SHA3-256 * 8: SHA3-384 * 9: SHA3-512 * 10: TIGER * 11: WHIRLPOOL * 13: AES128 * 14: AES256 * 15: AEAD-AES-SIV-CMAC-256 * 30: AEAD-AES-128-GCM-SIV KLen This column shows the length of the key in bits. Last This column shows how long ago the last successful key establish- ment was performed. It is in seconds, or letters m, h, d or y indi- cate minutes, hours, days, or years. Atmp This column shows the number of attempts to perform the key estab- lishment since the last successful key establishment. A number larger than 1 indicates a problem with the network or server. NAK This column shows whether an NTS NAK was received since the last request. A NAK indicates that authentication failed on the server side due to chronyd using a cookie which is no longer valid and that it needs to perform the key establishment again in order to get new cookies. Cook This column shows the number of NTS cookies that chronyd currently has. If the key establishment was successful, a number smaller than 8 indicates a problem with the network or server. CLen This column shows the length in bytes of the NTS cookie which will be used in the next request. ntpdata [address] The ntpdata command displays the last valid measurement and other NTP-specific information about the specified NTP source, or all NTP sources (with a known address) if no address was specified. An example of the output is shown below. Remote address : 203.0.113.15 (CB00710F) Remote port : 123 Local address : 203.0.113.74 (CB00714A) Leap status : Normal Version : 4 Mode : Server Stratum : 1 Poll interval : 10 (1024 seconds) Precision : -24 (0.000000060 seconds) Root delay : 0.000015 seconds Root dispersion : 0.000015 seconds Reference ID : 47505300 (GPS) Reference time : Fri Nov 25 15:22:12 2016 Offset : -0.000060878 seconds Peer delay : 0.000175634 seconds Peer dispersion : 0.000000681 seconds Response time : 0.000053050 seconds Jitter asymmetry: +0.00 NTP tests : 111 111 1111 Interleaved : No Authenticated : No TX timestamping : Kernel RX timestamping : Kernel Total TX : 24 Total RX : 24 Total valid RX : 24 Total good RX : 22 Total kernel TX : 24 Total kernel RX : 24 Total HW TX : 0 Total HW RX : 0 The fields are explained as follows: Remote address The IP address of the NTP server or peer, and the corresponding reference ID. Remote port The UDP port number to which the request was sent. The standard NTP port is 123. Local address The local IP address which received the response, and the corre- sponding reference ID. Leap status, Version, Mode, Stratum, Poll interval, Precision, Root de- lay, Root dispersion, Reference ID, Reference time The NTP values from the last valid response. Offset, Peer delay, Peer dispersion The measured values. Response time The time the server or peer spent in processing of the request and waiting before sending the response. Jitter asymmetry The estimated asymmetry of network jitter on the path to the source. The asymmetry can be between -0.5 and 0.5. A negative value means the delay of packets sent to the source is more variable than the delay of packets sent from the source back. NTP tests Results of RFC 5905 tests 1 through 3, 5 through 7, and tests for maximum delay, delay ratio, delay dev ratio (or delay quantile), and synchronisation loop. Interleaved This shows if the response was in the interleaved mode. Authenticated This shows if the response was authenticated. TX timestamping The source of the local transmit timestamp. Valid values are Dae- mon, Kernel, and Hardware. RX timestamping The source of the local receive timestamp. Total TX The number of packets sent to the source. Total RX The number of all packets received from the source. Total valid RX The number of packets which passed the first two groups of NTP tests. Total good RX The number of packets which passed all three groups of NTP tests, i.e. the NTP measurement was accepted. Total kernel TX The number of packets sent to the source for which a timestamp was captured by the kernel. Total kernel RX The number of packets received from the source for which a time- stamp was captured by the kernel. Total HW TX The number of packets sent to the source for which a timestamp was captured by the NIC. Total HW RX The number of packets received from the source for which a time- stamp was captured by the NIC. add peer name [option]... The add peer command allows a new NTP peer to be added whilst chronyd is running. Following the words add peer, the syntax of the following parameters and options is identical to that for the peer directive in the configu- ration file. An example of using this command is shown below. add peer ntp1.example.net minpoll 6 maxpoll 10 key 25 add pool name [option]... The add pool command allows a pool of NTP servers to be added whilst chronyd is running. Following the words add pool, the syntax of the following parameters and options is identical to that for the pool directive in the configu- ration file. An example of using this command is shown below: add pool ntp1.example.net maxsources 3 iburst add server name [option]... The add server command allows a new NTP server to be added whilst chronyd is running. Following the words add server, the syntax of the following parameters and options is identical to that for the server directive in the con- figuration file. An example of using this command is shown below: add server ntp1.example.net minpoll 6 maxpoll 10 key 25 delete address The delete command allows an NTP server or peer to be removed from the current set of sources. burst good/max [mask/masked-address], burst good/max [masked-ad- dress/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 peri- odic measurements that it makes). After such a burst, chronyd will re- vert to the previous state for each source. This might be either on- line, 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 cer- tain tests, for example, the round trip time to the source must be acceptable. (This allows chronyd to reject measurements that are likely to be bogus.) max This defines the maximum number of measurements that chronyd will attempt to make, even if the required number of good measurements has not been obtained. mask This is an IP address with which the IP address of each of chronyd's sources is to be masked. masked-address This is an IP address. If the masked IP address of a source matches this value then the burst command is applied to that source. masked-bits This can be used with masked-address for CIDR notation, which is a shorter alternative to the form with mask. address This is an IP address or a hostname. The burst command is applied only to that source. If no mask or masked-address arguments are provided, every source will be matched. An example of the two-argument form of the command is: burst 2/10 This will cause chronyd to attempt to get two good measurements from each source, stopping after two have been obtained, but in no event will it try more than ten probes to the source. Examples of the four-argument form of the command are: burst 2/10 255.255.0.0/1.2.0.0 burst 2/10 2001:db8:789a::/48 In the first case, the two out of ten sampling will only be applied to sources whose IPv4 addresses are of the form 1.2.x.y, where x and y are arbitrary. In the second case, the sampling will be applied to sources whose IPv6 addresses have first 48 bits equal to 2001:db8:789a. Example of the three-argument form of the command is: burst 2/10 ntp1.example.net maxdelay address delay This allows the maxdelay option for one of the sources to be modified, in the same way as specifying the maxdelay option for the server direc- tive 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 modi- fied, 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 op- tion 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 op- tion 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 con- nection is heavily loaded at certain times of the day and the measure- ments 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 peri- ods. The offline and online commands can be used to achieve this. There are four forms of the offline command. The first form is a wild- card, 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 be- low. offline offline 255.255.255.0/1.2.3.0 offline 2001:db8:789a::/48 offline ntp1.example.net The second form means that the offline command is to be applied to any source whose IPv4 address is in the 1.2.3 subnet. (The host's address is logically and-ed with the mask, and if the result matches the masked-address the host is processed.) The third form means that the command is to be applied to all sources whose IPv6 addresses have their first 48 bits equal to 2001:db8:789a. The fourth form means that the command is to be applied only to that one source. The wildcard form of the address is equivalent to: offline 0.0.0.0/0.0.0.0 offline ::/0 online [address], online [masked-address/masked-bits], online [mask/masked-address] The online command is opposite in function to the offline command. It is used to advise chronyd that network connectivity to a particular source or sources has been restored. The syntax is identical to that of the offline command. onoffline The onoffline command tells chronyd to switch all sources that have a known address to the online or offline status according to the current network configuration. A source is considered online if it is possible to send requests to it, i.e. a network route to the source is present. polltarget address polltarget The polltarget command is used to modify the poll target for one of the current set of sources. It is equivalent to the polltarget option in the server directive in the configuration file. refresh The refresh command can be used to force chronyd to resolve the names of configured NTP sources to IP addresses again and replace any ad- dresses missing in the list of resolved addresses. Sources that stop responding are replaced with newly resolved addresses automatically after 8 polling intervals. This command can be used to replace them immediately, e.g. after suspending and resuming the ma- chine in a different network. Note that with pools which have more than 16 addresses, or not all IPv4 or IPv6 addresses are included in a single DNS response (e.g. pool.ntp.org), this command might replace the addresses even if they are still in the pool. reload sources The reload sources command causes chronyd to re-read all *.sources files from the directories specified by the sourcedir directive. Note that modified sources (e.g. specified with a new option) are not modified in memory. They are removed and added again, which causes them to lose old measurements and reset the selection state. sourcename address The sourcename command prints the original hostname or address that was specified for an NTP source in the configuration file, or the add com- mand. This command is an alternative to the -N option, which can be useful in scripts. Note that different NTP sources can share the same name, e.g. servers from a pool. Manual time input manual on, manual off, manual delete index, manual list, manual reset The manual command enables and disables use of the settime command, and is used to modify the behaviour of the manual clock driver. The on form of the command enables use of the settime command. The off form of the command disables use of the settime command. The list form of the command lists all the samples currently stored in chronyd. The output is illustrated below. 210 n_samples = 1 # Date Time(UTC) Slewed Original Residual ==================================================== 0 27Jan99 22:09:20 0.00 0.97 0.00 The columns are as as follows: 1. The sample index (used for the manual delete command). 2. The date and time of the sample. 3. The system clock error when the timestamp was entered, adjusted to allow for changes made to the system clock since. 4. The system clock error when the timestamp was entered, as it origi- nally 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 er- ror 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 re- alises 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 ei- ther 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 en- tered during the present run of chronyd. However, the entered measure- ment 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. Conse- quently, 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 (bun- dled, for example, with the source for GNU tar). NTP access accheck address This command allows you to check whether client NTP access is allowed from a particular host. Examples of use, showing a named host and a numeric IP address, are as follows: accheck ntp1.example.net accheck 1.2.3.4 accheck 2001:db8::1 This command can be used to examine the effect of a series of allow, allow all, deny, and deny all commands specified either via chronyc, or in chronyd's configuration file. clients [-p packets] [-k] [-r] This command shows a list of clients that have accessed the server, through the NTP, command, or NTS-KE port. It does not include accesses over the Unix domain command socket. The -p option specifies the minimum number of received NTP or command packets, or accepted NTS-KE connections, needed to include a client in the list. The default value is 0, i.e. all clients are reported. With the -k option the last four columns will show the NTS-KE accesses in- stead of command accesses. If the -r option is specified, chronyd will reset the counters of received and dropped packets or connections after reporting the current values. An example of the output is: Hostname NTP Drop Int IntL Last Cmd Drop Int Last =============================================================================== localhost 2 0 2 - 133 15 0 -1 7 ntp1.example.net 12 0 6 - 23 0 0 - - Each row shows the data for a single host. Only hosts that have passed the host access checks (set with the allow, deny, cmdallow and cmddeny commands or configuration file directives) are logged. The intervals are displayed as a power of 2 in seconds. The columns are as follows: 1. The hostname of the client. 2. The number of NTP packets received from the client. 3. The number of NTP packets dropped to limit the response rate. 4. The average interval between NTP packets. 5. The average interval between NTP packets after limiting the re- sponse rate. 6. Time since the last NTP packet was received 7. The number of command packets or NTS-KE connections received/ac- cepted from the client. 8. The number of command packets or NTS-KE connections dropped to limit the response rate. 9. The average interval between command packets or NTS-KE connections. 10. Time since the last command packet or NTS-KE connection was re- ceived/accepted. serverstats The serverstats command displays NTP and command server statistics. An example of the output is shown below. NTP packets received : 1598 NTP packets dropped : 8 Command packets received : 19 Command packets dropped : 0 Client log records dropped : 0 NTS-KE connections accepted: 3 NTS-KE connections dropped : 0 Authenticated NTP packets : 189 Interleaved NTP packets : 43 NTP timestamps held : 44 NTP timestamp span : 120 NTP daemon RX timestamps : 0 NTP daemon TX timestamps : 1537 NTP kernel RX timestamps : 1590 NTP kernel TX timestamps : 43 NTP hardware RX timestamps : 0 NTP hardware TX timestamps : 0 The fields have the following meaning: NTP packets received The number of valid NTP requests received by the server. NTP packets dropped The number of NTP requests dropped by the server due to rate limit- ing (configured by the ratelimit directive). Command packets received The number of command requests received by the server. Command packets dropped The number of command requests dropped by the server due to rate limiting (configured by the cmdratelimit directive). Client log records dropped The number of client log records dropped by the server to limit the memory use (configured by the clientloglimit directive). NTS-KE connections accepted The number of NTS-KE connections accepted by the server. NTS-KE connections dropped The number of NTS-KE connections dropped by the server due to rate limiting (configured by the ntsratelimit directive). Authenticated NTP packets The number of received NTP requests that were authenticated (with a symmetric key or NTS). Interleaved NTP packets The number of received NTP requests that were detected to be in the interleaved mode. NTP timestamps held The number of pairs of receive and transmit timestamps that the server is currently holding in memory for clients using the inter- leaved mode. NTP timestamp span The interval (in seconds) covered by the currently held NTP time- stamps. NTP daemon RX timestamps The number of NTP responses which included a receive timestamp cap- tured by the daemon. NTP daemon TX timestamps The number of NTP responses which included a transmit timestamp captured by the daemon. NTP kernel RX timestamps The number of NTP responses which included a receive timestamp cap- tured by the kernel. NTP kernel TX timestamps The number of NTP responses (in the interleaved mode) which in- cluded a transmit timestamp captured by the kernel. NTP hardware RX timestamps The number of NTP responses which included a receive timestamp cap- tured by the NIC. NTP hardware TX timestamps The number of NTP responses (in the interleaved mode) which in- cluded a transmit timestamp captured by the NIC. allow [all] [subnet] The effect of the allow command is identical to the allow directive in the configuration file. The syntax is illustrated in the following examples: allow 1.2.3.4 allow all 3.4.5.0/24 allow 2001:db8:789a::/48 allow 0/0 allow ::/0 allow allow all deny [all] [subnet] The effect of the allow command is identical to the deny directive in the configuration file. The syntax is illustrated in the following examples: deny 1.2.3.4 deny all 3.4.5.0/24 deny 2001:db8:789a::/48 deny 0/0 deny ::/0 deny deny all local [option]..., local off The local command allows chronyd to be told that it is to appear as a reference source, even if it is not itself properly synchronised to an external source. This can be used on isolated networks, to allow a com- puter to be the primary time server for other computers. The first form enables the local reference mode on the host. The syntax is identical to the local directive in the configuration file. The second form disables the local reference mode. smoothing The smoothing command displays the current state of the NTP server time smoothing, which can be enabled with the smoothtime directive. An exam- ple 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. Possi- ble 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 up- dated, e.g. chronyd accumulated a new measurement. Remaining time The time it would take for the smoothing process to get to zero offset and frequency if there were no more updates. smoothtime activate, smoothtime reset The smoothtime command can be used to activate or reset the server time smoothing process if it is configured with the smoothtime directive. Monitoring access cmdaccheck address This command is similar to the accheck command, except that it is used to check whether monitoring access is permitted from a named host. Examples of use are as follows: cmdaccheck ntp1.example.net cmdaccheck 1.2.3.4 cmdaccheck 2001:db8::1 cmdallow [all] [subnet] This is similar to the allow command, except that it is used to allow particular hosts or subnets to use chronyc to monitor with chronyd on the current host. cmddeny [all] [subnet] This is similar to the deny command, except that it is used to allow particular hosts or subnets to use chronyc to monitor chronyd on the current host. Real-time clock (RTC) rtcdata The rtcdata command displays the current RTC parameters. An example output is shown below. RTC ref time (GMT) : Sat May 30 07:25:56 2015 Number of samples : 10 Number of runs : 5 Sample span period : 549 RTC is fast by : -1.632736 seconds RTC gains time at : -107.623 ppm The fields have the following meaning: RTC ref time (GMT) This is the RTC reading the last time its error was measured. Number of samples This is the number of previous measurements being used to determine the RTC gain or loss rate. Number of runs This is the number of runs of residuals of the same sign following the regression fit for (RTC error) versus (RTC time). A value which is small indicates that the measurements are not well approximated by a linear model, and that the algorithm will tend to delete the older measurements to improve the fit. Sample span period This is the period that the measurements span (from the oldest to the newest). Without a unit the value is in seconds; suffixes m for minutes, h for hours, d for days or y for years can be used. RTC is fast by This is the estimate of how many seconds fast the RTC when it thought the time was at the reference time (above). If this value is large, you might (or might not) want to use the trimrtc command to bring the RTC into line with the system clock. (Note, a large error will not affect chronyd's operation, unless it becomes so big as to start causing rounding errors.) RTC gains time at This is the amount of time gained (positive) or lost (negative) by the real time clock for each second that it ticks. It is measured in parts per million. So if the value shown was +1, suppose the RTC was exactly right when it crosses a particular second boundary. Then it would be 1 microsecond fast when it crosses its next second boundary. trimrtc The trimrtc command is used to correct the system's real-time clock (RTC) to the main system clock. It has no effect if the error between the two clocks is currently estimated at less than a second. The command takes no arguments. It performs the following steps (if the RTC is more than 1 second away from the system clock): 1. Remember the currently estimated gain or loss rate of the RTC and flush the previous measurements. 2. Step the real-time clock to bring it within a second of the system clock. 3. Make several measurements to accurately determine the new offset between the RTC and the system clock (i.e. the remaining fraction of a second error). 4. Save the RTC parameters to the RTC file (specified with the rtcfile directive in the configuration file). The last step is done as a precaution against the computer suffering a power failure before either the daemon exits or the writertc command is issued. chronyd will still work perfectly well both whilst operating and across machine reboots even if the trimrtc command is never used (and the RTC is allowed to drift away from true time). The trimrtc command is pro- vided as a method by which it can be corrected, in a manner compatible with chronyd using it to maintain accurate time across machine reboots. The trimrtc command can be executed automatically by chronyd with the rtcautotrim directive in the configuration file. writertc The writertc command writes the currently estimated error and gain or loss rate parameters for the RTC to the RTC file (specified with the rtcfile directive). This information is also written automatically when chronyd is killed (by the SIGHUP, SIGINT, SIGQUIT or SIGTERM signals) or when the trimrtc command is issued. Other daemon commands cyclelogs The cyclelogs command causes all of chronyd's open log files to be closed and re-opened. This allows them to be renamed so that they can be periodically purged. An example of how to do this is shown below. # mv /var/log/chrony/measurements.log /var/log/chrony/measurements1.log # chronyc cyclelogs # rm /var/log/chrony/measurements1.log Note that log files enabled by the log directive are opened when the first entry is made. The message log file specified by the chronyd's -l option is opened early on start and closed on the cyclelogs command only if opening of the new file succeeds to avoid losing messages. If chronyd is configured to drop root privileges and the directory con- taining the log file is not writable for the specified user, chronyd will not be able to open the file again. dump The dump command causes chronyd to write its current history of mea- surements for each of its sources to dump files in the directory speci- fied in the configuration file by the dumpdir directive and also write server NTS keys and client NTS cookies to the directory specified by the ntsdumpdir directive. Note that chronyd does this automatically when it exits. This command is mainly useful for inspection whilst chronyd is running. rekey The rekey command causes chronyd to re-read the key file specified in the configuration file by the keyfile directive. It also re-reads the server NTS keys if ntsdumpdir is specified and automatic rotation is disabled in the configuration file. reset sources The reset sources command causes chronyd to drop all measurements and switch to the unsynchronised state. This command can help chronyd with recovery when the measurements are known to be no longer valid or accu- rate, e.g. due to moving the computer to a different network, or resum- ing the computer from a low-power state (which resets the system clock). chronyd will drop the measurements automatically when it de- tects the clock has made an unexpected jump, but the detection is not completely reliable. shutdown The shutdown command causes chronyd to exit. This is equivalent to sending the process the SIGTERM signal. Client commands dns option The dns command configures how hostnames and IP addresses are resolved in chronyc. IP addresses can be resolved to hostnames when printing re- sults 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 re- quests 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 be- tween 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 ar- gument is the name of the hash function or cipher (by default SHA1, or MD5 if SHA1 is not available). The third argument is the length of the key in bits if a hash function was selected, between 80 and 4096 bits (by default 160 bits). An example is: keygen 73 SHA1 256 which generates a 256-bit SHA1 key with number 73. The printed line should then be securely transferred and added to the key files on both server and client, or peers. A different key should be generated for each client or peer. An example using the AES128 cipher is: keygen 151 AES128 exit, quit The exit and quit commands exit from chronyc and return the user to the shell. help The help command displays a summary of the commands and their argu- ments. SEE ALSO chrony.conf(5), chronyd(8) BUGS For instructions on how to report bugs, please visit https://chrony-project.org/. AUTHORS chrony was written by Richard Curnow, Miroslav Lichvar, and others. chrony 4.8 2025-08-27 CHRONYC(1)
NAME | SYNOPSIS | DESCRIPTION | OPTIONS | COMMANDS | SEE ALSO | BUGS | AUTHORS
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