Ntp Error Estimate

[ -c conffile ] [ -f driftfile ] [ -g ] [ -k keyfile ] [ -l logfile ] [ -N high ] [ -p pidfile ] [ -r broadcastdelay ] [ -s statsdir ] [ -t key ] [ -v variable ] [ -V

Ntp Commands Linux

variable ] [ -x ] Description The ntpd program is an operating system daemon which sets ntp jitter too high and maintains the system time of day in synchronism with Internet standard time servers. It is a complete implementation of the Network Time Protocol

Ntp Drift File

(NTP) version 4, but also retains compatibility with version 3, as defined by RFC-1305, and version 1 and 2, as defined by RFC-1059 and RFC-1119, respectively. ntpd does most computations in 64-bit floating point arithmetic and does relatively clumsy 64-bit http://www.ntp.org/ntpfaq/NTP-s-trouble.htm fixed point operations only when necessary to preserve the ultimate precision, about 232 picoseconds. While the ultimate precision, is not achievable with ordinary workstations and networks of today, it may be required with future gigahertz CPU clocks and gigabit LANs. How NTP Operates The ntpd program operates by exchanging messages with one or more configured servers at designated poll intervals. When started, whether for the first or subsequent times, the program requires several exahanges from the majority of these servers http://doc.ntp.org/4.1.0/ntpd.htm so the signal processing and mitigation algorithms can accumulate and groom the data and set the clock. In order to protect the network from bursts, the initial poll interval for each server is delayed an interval randomized over 0-16s. At the default initial poll interval of 64s, several minutes can elapse before the clock is set. The initial delay to set the clock can be reduced using the iburst keyword with the server configuration command, as described on the Configuration Options page. Most operating systems and hardware of today incorporate a time-of-year (TOY) chip to maintain the time during periods when the power is off. When the machine is booted, the chip is used to initialize the operating system time. After the machine has synchronized to a NTP server, the operating system corrects the chip from time to time. In case there is no TOY chip or for some reason its time is more than 1000s from the server time, ntpd assumes something must be terribly wrong and the only reliable action is for the operator to intervene and set the clock by hand. This causes ntpd to exit with a panic message to the system log. The -g option overrides this check and the clock will be set to the server time regardless of the chip time. However, and to protect against broken hardware, such as when the CMOS battery fails or the clock counter becomes defective,

here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss the workings and policies http://stackoverflow.com/questions/21732056/ntp-offset-error-from-real-time of this site About Us Learn more about Stack Overflow the company http://www.akadia.com/services/ntp_synchronize.html Business Learn more about hiring developers or posting ads with us Stack Overflow Questions Jobs Documentation Tags Users Badges Ask Question x Dismiss Join the Stack Overflow Community Stack Overflow is a community of 6.2 million programmers, just like you, helping each other. Join them; it only takes a ntp offset minute: Sign up NTP offset error from real time up vote 1 down vote favorite I'm working on a project where I need to find out the maximum offset an NTP synchronized clock can be from UTC. If I run ntpdc -c loopinfo it outputs an offset, is this the offset error from actual time? also if I run ntpq -p it ntp error estimate will show offset for each of the peers what is this offset? which of these can I use to find the maximum offset error from real time? Thank you. synchronization offset ntp share|improve this question asked Feb 12 '14 at 15:23 user3302253 62 add a comment| 2 Answers 2 active oldest votes up vote 1 down vote I think you are looking for the output of ntpq -c kerninfo or ntptime $ ntpq -c kerninfo associd=0 status=0615 leap_none, sync_ntp, 1 event, clock_sync, pll offset: 0.336481 pll frequency: -32.762 maximum error: 0.136773 estimated error: 0.000231 kernel status: pll nano pll time constant: 10 precision: 1e-06 frequency tolerance: 500 pps frequency: 0 pps stability: 0 pps jitter: 0.000 calibration interval 4 calibration cycles: 0 jitter exceeded: 0 stability exceeded: 0 calibration errors: 0 Or use ntptime: S ntptime ntp_gettime() returns code 0 (OK) time d6a66a56.372c300c Wed, Feb 12 2014 16:47:02.215, (.215518749), maximum error 141773 us, estimated error 231 us, TAI offset 35 ntp_adjtime() returns code 0 (OK) modes 0x0 (), offset 335.660 us, frequency -32.762 ppm, interval 4 s, maximum error 141773 us, estimated error 23

NTP is organised in a hierarchical client-server model. In the top of this hierarchy there are a small number of machines known as reference clocks. A reference clock is known as stratum 0 and is typically a cesium clock or a Global Positioning System (GPS) that receives time from satellites. Attached to these machines there are the so-called stratum 1 servers (that is, stratum 0 clients), which are the top level time servers available to the Internet, that is, they are the best NTP servers available. Note: in the NTP lingo measure for synchronization distance is termed as stratum: the number of steps that a system lies from a primary time source. Following this hierarchy, the next level in the structure are the stratum 2 servers which in turn are the clients for stratum 1 servers. The lowest level of the hierarchy is made up by stratum 16 servers. Generally speaking, every server syncronized with a stratum n server is termed as being at stratum n+1 level. So, there are a few stratum 1 servers which are referenced by stratum 2 servers, wich in turn are refenced by stratum 3 servers, which are referenced by stratum 4 and so on. NTP servers operating in the same stratum may be associated with others in a peer to peer basis, so they may decide who has the higher quality of time and then can synchronise to the most accurate. In addition to the client-server model and the peer to peer model, a server may broadcast time to a broadcast or multicast IP addresses and clients may be configured to synchronise to these broadcast time signals. So, at this point we know that NTP clients can operate with NTP servers in three ways: in a client-server basis in a peer to peer mode sending the time using broadcast/multicast How does it work Whenever ntpd starts it checks its configuration file (/etc/ntp.conf) to determine syncronization sources, authentication options, monitoring options, access control and other operating options. It also checks the frequency file (/etc/ntp/drift) that contains the latest estimate of clock frequency error. If specified, it will also look for a file containing the authentication keys (/etc/ntp/keys). Note that the path and/or name of these configuration fil