~]${nbsp}chronyc sources
210 Number of sources = 3
MS Name/IP address Stratum Poll Reach LastRx Last sample
#* GPS0 0 4 377 11 -479ns[ -621ns] +/- 134ns
^? a.b.c 2 6 377 23 -923us[ -924us] +/- 43ms
^+ d.e.f 1 6 377 21 -2629us[-2619us] +/- 86ms
~]${nbsp}pass:attributes[{blank}][command]#chronyc -h _hostname_pass:attributes[{blank}]#
~]${nbsp}pass:attributes[{blank}][command]#chronyc -h _hostname_ -p _port_pass:attributes[{blank}]#
~]${nbsp}pass:attributes[{blank}][command]#chronyc sourcestats#
210 Number of sources = 1
Name/IP Address NP NR Span Frequency Freq Skew Offset Std Dev
abc.def.ghi 11 5 46m -0.001 0.045 1us 25us
~]${nbsp}pass:attributes[{blank}][command]#chronyc tracking#
Reference ID : (a.b.c)
Stratum : 3
Ref time (UTC) : Fri Feb 3 15:00:29 2012
System time : 0.000001501 seconds slow of NTP time
Last offset : -0.000001632 seconds
RMS offset : 0.000002360 seconds
Frequency : 331.898 ppm fast
Residual freq : 0.004 ppm
Skew : 0.154 ppm
Root delay : 0.373169 seconds
Root dispersion : 0.024780 seconds
Update interval : 64.2 seconds
Leap status : Normal
~]${nbsp}pass:attributes[{blank}][command]#systemctl status chronyd#
chronyd.service - NTP client/server
Loaded: loaded (/usr/lib/systemd/system/chronyd.service; enabled)
Active: active (running) since Wed 2013-06-12 22:23:16 CEST; 11h ago
1 SHA1 HEX:A6CFC50C9C93AB6E5A19754C246242FC5471BCDF
20 foobar
Accurate time keeping is important for a number of reasons in IT. In networking for example, accurate time stamps in packets and logs are required. In Linux systems, the `NTP` protocol is implemented by a daemon running in user space.
Additional Resources
After the first clock update, `chronyd` will check the offset on every clock update, it will ignore two adjustments larger than 1000 seconds and exit on another one.
A large value of 10 indicates that the clock is so many hops away from a reference clock that its time is unreliable. If the computer ever has access to another computer which is ultimately synchronized to a reference clock, it will almost certainly be at a stratum less than 10. Therefore, the choice of a high value like 10 for the [command]#local# command prevents the machine’s own time from ever being confused with real time, were it ever to leak out to clients that have visibility of real servers.
allow 2001:db8::/32
allow server1.example.com
A manual entry in the key file, used to authenticate packets from certain `NTP` servers or peers, can be as simple as the following:
An example of the command is:
An example of the format of the default entry in the key file, `/etc/chrony.keys`, for the command key is: