#gps ntp servers

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[khushicomms]

GPS splitters, also known as GNSS (Global Navigation Satellite System) splitters, allow multiple devices to share a single GPS signal from one antenna. Understand more explained by a supplier of NTP Timing Server.

[acluent]

Homelab Changes

Okay, so Portainer stacks are where its at. I now have fully redudent time servers.

Is it unecessary–yes, but redundent time servers in Docker is kinda neat.

At somepoint I will have to pickup some proper NTP hardware and run my own fully operated time server. The clocks and GPS stuff seems cool.

I just can't bring myself to spend that money right now. It is shockingly pricey and I don't know that it is that interesting yet. We will see what happens.

[kreuzaderny]

Microsecond accurate NTP with a Raspberry Pi and PPS GPS

Lots of acronyms in that title. If I expand them out, it says – “microsecond accurate network time protocol with a Raspberry Pi and pulse per second global positioning system [receiver]”. What it means is you can get super accurate timekeeping (1 microsecond = 0.000001 seconds) with a Raspberry Pi and a GPS receiver (the GT-U7 is less than $12) that spits out pulses every second. By following this guide, you will your very own Stratum 1 NTP server at home!

[ahiijny]

an interesting thing I learned today was that global warming might result in a negative leap second sometime in the future

(admittedly the earth's rotation is affected by lots of complicated factors so it might not be that clear-cut, but anyway)

so you may be thinking 'but leap seconds are like a single second? so short! who's going to notice?'

well tbf the impact from these leap seconds is going to be most strongly felt by high precision things like GPS or NTP servers whatever (and the poor devs who have to maintain the software lol) but leap seconds have historically caused unexpected problems in financial markets and all sorts of websites and servers as well, so...

in any case, I find all this really fascinating and pls bear with me while I nerd out a bit about this :P

so normally speaking, the Earth's rotation should be gradually slowing, because the pull of tides from the Moon and so on (though there are other influences too, like fluid flow in the outer core, the movement of Earth's crust, etc. so it's all very complicated)

until recently, the length of a day has been about on average 1-2 milliseconds longer than 24 hours (note that there are seasonal variations though).

1-2 milliseconds may not seem like much, but it adds up over time!

in fact, it's the job of the IERS to monitor the difference between UTC (universal coordinated time) and earth's rotation angle (UT1), and decide when to insert a leap second to prevent them from drifting too far apart

the current version of UTC (as defined by the ITU) requires the difference between UTC and UT1 to be no greater than 0.9 seconds. The IERS typically inserts a leap second when the difference grows to 0.6 seconds.

HERE'S A GRAPH

see, the difference between UTC and Earth's actual rotation angle keeps drifting. UT1 keeps falling behind UTC, so those vertical lines are every time the IERS inserted a leap second, to bring UTC and UT1 back closer together

since UTC is ticking faster than UT1 bc of Earth's rotation slowing, we typically need to insert positive leap seconds for when UTC gets too far ahead

positive leap seconds take the form of an extra time second 23:59:60, which happens at the same instant UTC everywhere around the world

historically, we've needed to insert a leap second every 1-2 years or so

it's not very regular tho, bc the Earth's rotation can vary in unpredictable ways. Even earthquakes and the filling of the three gorges dam had a detectable effect on the Earth's rotation.

but what's this? if you look back up at the graph above, you may notice that the graph seems to flatten out near the end there. Why's this happening?

here's ANOTHER GRAPH (with tiny text sorry)

the squiggly green line here shows the deviation in length of day relative to a SI day (i.e. 86400 SI seconds). Look for the ±0 ms baseline on the left vertical axis.

in the 1970s Earth's rotation was in the range of 1-2 ms longer than an SI day

but recently the length of a day has been shortening, and in 2020, there were a large number of days where the length of a day was actually slightly less than 86400 SI seconds! (mostly by less than a millisecond, but still)

2020 had 28 of the shortest days on record since 1960, and days in 2021 are predicted to be even shorter (note that the difference is on the order of milliseconds... but stillllll)

this is actually why we haven't seen any leap seconds recently. The previous one was in 2016. In fact this is the first time since 2003 when we will have had a 256 week period without leap seconds

and this in fact might cause some GPS systems to bug out hehe. In the widely used gpsd package, there was a recently reported bug "GPSD time will jump back 1024 weeks at after week=2180 (23-October-2021)". This bug happened bc the code author wrongly assumed that leap seconds would be more frequent :3

and if the Earth continues to speed up like this, the IERS may need to insert a negative leap second at some point in the future, to bring UT1 and UTC back closer together

this would take the form of the UTC clock going from 23:59:57 to 23:59:58 and then skipping directly to 00:00:00.

in the history of UTC there has never been a negative leap second, so needless to say software ppl aren't too excited at the prospect of this happening :3

so what's causing the earth's spinning to unexpectedly speed up?

there's been some research that suggests changes in the density and circulation of ocean temperature rises might result in a net transfer of mass to higher latitudes. but the predicted time deviation doesn't fully explain the changes we currently see

there's also the idea that ice melt results in water running downhill, resulting in a redistribution of mass closer to its axis of rotation

but at the same time, a redistribution of ocean mass to the equatorial latitudes would result in mass going farther away from Earth's axis of rotation

or maybe it's just Earth's crust and magma and stuff doing weird things again, who knows!

the Earth's rotational axis isn't static either; it can shift, and that might also change the effective rotational inertia

it's probably a complicated combination of a whole bunch of factors

but anyway, why do we even have leap seconds?

well the main motivation for leap seconds was when we switched from solar time to atomic time around the 1950s-ish. So before our clocks became accurate enough to tell the difference, we just said "yo, a second is 1/86400 of the time it takes for the sun to go all the around the sky, by definition" and that's good enough! the length of a day can vary by a few milliseconds from year to year but we wouldn't have been able to tell the difference.

but gradually timekeeping precision requirements grew so eventually in 1967 a second was defined to be "9,192,631,770 periods of the something something something caesium atom" which was way more precise and good for atomic clocks but bad for keeping the clocks in sync with the sun

so the concern was without leap seconds our atomic-clock-based timescale would drift relative the sun and then eventually we'd have solar noon when our clocks said midnight and vice versa

I mean, sure, that probably wouldn't happen for thousands for years, but procrastination is bad, ok?

but still admittedly leap seconds are somewhat controversial and there's plenty of Discourse��� about this, esp. in academic circles and stuff, so if any of you into that kind of thing here's one possible starting point :3

anyway some ppl have made some code to make predictions based on IERS bulletin A, so based on the latest Earth rotation measurements as of 29 July 2021, and whole bunch of (and I quote) "very large, probably unjustified assumptions"...

expect a negative leap second in the ballpark of June 2029 :3

[atlanticcanada]

Why a faster spinning Earth is expected to make 2021 the shortest year on record

Scientists say 2021 is expected to be a shorter year than normal with the Earth spinning at a faster rate than it has in the last 50 years.

York University astronomy and physics professor Paul Delaney explained to CTV's Your Morning that as the Earth’s rotation speeds up, the shift means that time is slowing on the planet’s surface, making each day a "fraction of a second" shorter than 24 hours.

He said in an interview on Tuesday that this phenomenon is likely being caused by climate change.

"There is such [sic] a lot of ice that is becoming liquid and is flowing into the oceans, as a consequence of that you're changing the way the mass on the surface of the Earth is situated. Instead of a really heavy mass around the pole, you're melting it and [spreading] it all around the planet, and that is changing the way we are rotating on our axis," Delaney said.

"When you bring the amount of material, the amount of mass, closer to our rotation axis that actually spins up our rotation rate a little bit faster."

Sign up for The Climate Barometer, delivered to your inbox every week

Delaney compared this shift in the Earth’s mass to that of figure skaters pulling their arms in closer to their body in order to spin faster.

However, he says this change does not mean the timing of one's day-to-day activities will change.

"We're talking about a fraction of a second here. People shouldn't think they're about to get an hour's extra sleep as a result of this, but it really is associated with the melting of the polar ice caps," he said.

While the planet's rotational speed often drifts around slightly, Delaney said the melting of the ice caps with climate change can alter the global time frame as well as the marking of days.

Due to this increase in rotation speed, scientists report that the average day in 2021 is expected to be 0.05 milliseconds shorter than the 86,400 seconds that normally make up the 24-hour period.

Delaney says adding an extra second to clocks in what is called a leap second can help with this.

"The fraction of a second per day is not going to make much of a difference to you and me, but things like leap seconds have been introduced over the last sort of 40 to 50 years to compensate for this change in the Earth's rotation rate compared to what we call our fixed frame," Delaney said.

Delaney explained that leap seconds are irregular, with one second added to the last minute of a given calendar year. Since 1972, scientists have added leap seconds about every year-and-a-half, on average, according to the National Institute of Standards and Technology (NIST).

But with the Earth rotating faster over recent years, the International Earth Rotation and Reference Systems Service (IERS) says no leap seconds have been necessary since 2016.

IERS announced in July that no leap second would be added to the world’s official timekeeping in December 2020. However, a second may actually have to be subtracted in the future in what is known as a negative leap second, which would be a first for the IERS.

While the change in time may not affect every day activities, Delaney says atomic clocks used in GPS satellites do not consider the planet's evolving motion, which can cause potentially confusing implications for smartphones, computers, and communications systems that synchronize with Network Time Protocol (NTP) servers.

"Most computer systems are expecting 60 seconds in a minute and when you get 61 seconds in a minute, then you can cause computer crashes, so it's a little bit like having Y2K thrown around in a way that you just don't expect," Delaney said.

Because leap seconds are irregular, he says there may be only a "few weeks or a few months notice" that time will be added or subtracted. This can lead to computer glitches and crashes, which Delaney said is a "big problem in our very computerized society."

Delaney added that this can also be a problem for stock markets. For example, he noted that the New York Stock Exchange went down for over an hour on June 30, 2015 because of a leap second.

"If you're the person who is on the selling floor trying to transact millions if not billions of dollars, and the stock market disappears on you, you're not going to be a very happy camper. So there is financial issues that are driving this whole question of leap seconds, and that brings into sharper focus the changing of the day," Delaney said.

So, what can be done to help adjust the Earth’s rotation? Delaney said there isn't much people can do.

"The Earth is doing what it wants to do. As we move around the sun, as we rotate on our axis, the rate at which we are rotating is completely independent of what you and I are wanting to do," he said.

With ice caps melting as a result of climate change, Delaney said the "easy answer" would be to stop the global warming of the planet.

"Let's keep the ice where it should be so that the rate of rotation is retained in the way that we're expecting it to be," he said.

from CTV News - Atlantic https://ift.tt/35UpWG6

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[khushicomms]

How does a NTP server ease computers stay synchronized?

A NTP (Network Time Protocol) server helps computers stay synchronized by providing them with the correct time. Here’s how it works:

Computers need accurate time to perform tasks like logging events, scheduling tasks, and coordinating activities with other computers. However, each computer may have its own internal clock that can drift or lose accuracy over time.

To keep all computers on the same time, they connect to a NTP server over the internet or a local network. The NTP server itself gets its time from highly accurate sources, such as atomic clocks or GPS satellites. When a computer asks the NTP server for the time, the server sends back the current time.

The computer adjusts its internal clock based on this time information from the NTP server. This process ensures that all computers connected to the NTP server stay synchronized to within a few milliseconds of each other.

For more, contact the best NTP Timing Server suppliers in India.

[matty]

CDMA to last for several more years

My last post reminded me about something I haven’t thought about in years: CDMA-based time servers. One of the better ways to get a precise time reference for an NTP server is a GPS signal, but GPS tends to have poor indoor coverage, and data centers tend to be concrete bunkers.

CDMA requires an extremely precise time reference, and that time reference is slaved to GPS time and broadcast from CDMA base stations. Cell signals generally do penetrate into data centers. A few companies make CDMA NTP servers. The obvious question is: how long will CMDA be around?

The answer appears to be: years. Surely, you can’t turn up a new CDMA phone, but Sprint and Verizon (at least) both still operate the networks. Verizon had pledged to shut down their CDMA network at the end of 2019, but is leaving it running longer for machine-to-machine customers. Sprint apparently has several years left as well. For something that’s just watching the base station’s timing reference, rather than requiring an actual reference, that’s all you need.

That might explain why they’re still pretty pricey on eBay.

[elinstechnologyshenzhen]

Why we choose H685fq 5G router?

The E-Lins H685fq is a compact, Gigabit Ethernet, ruggedized 3G/4G/LTE/5G cellular networking solution designed for mission-critical connectivity in the most challenging environments. It is qualified for M2M (Machine to Machine), IoT (Internet of Things) and In-Vehicle applications. Super mini size suitable for embedding applications. 

What fields or applications H685fq work in?

H685fq is widely used in more than twenty industrial fields, such as CCTV security surveillance, AMR, vehicle, retails, vending machines, power control, water schedule, traffic, oil field, weather forecast, environmental protection, street lamp control, post, bank and many other fields.

What key features of H685fq owns?

 Multi-carrier 2G/3G/4G LTE/5G support with SIM card slot

LAN/WAN Gigabit Ethernets * 2

Cellular/WAN RJ45/WiFi client failover and Load Balance (Bandwidth link bonding)

Supports LTE Advanced with SIM-based auto-carrier selection

Cloud-managed (with NMS network management system), TR-069, Web management, SMS, SSH/Telnet/Command, SNMP

WiFi (802.11 a/b/g/n, 2.4Ghz)

Certified 3G/4G/LTE enterprise/industrial grade internal modems

Built-in transient and reverse polarity voltage protection, over-current and over-voltage protection;

5-40V DC voltage input range (5-60V DC option), Dual Power Inputs / Power Failover;

GPS / GNSS support

Serial Port

DI/DO port * 4

Supports Ethernet (T1, DSL, Cable, MetroE), WiFi as WAN, and Metro WiFi

Ruggedized to ensure always-on connectivity

Create real-time alerts to monitor uptime

Offer secure, guest WiFi to passengers

Advanced security, VPN, and stateful firewall to protect sensitive data

Robust Metal Case is ruggedized for vibration, shock

Desktop, Wall-mount and Din-rail mount of installation

External antenna connectors for high gain antennas replacement

MIMO supported

Main Feature

Cellular 2G/3G/4G LTE/5G (FDD/TDD)(SA/NSA)

WiFi as WAN

Failover/Failback and Load Balance (Bandwidth  bonding)

Advanced Modem Failure Check

IP Passthrough

WAN  ports support Cell/Static IP/DHCP/PPPoE (on demand, keep alive, schedule,  manual, standby) 

DHCP  Server, Client, Relay

DNS  and DNS Proxy

DDNS

UPnP

DMZ

Multicast/Multicast  Proxy

QoS  (DSCP and Priority Queuing)

MAC  Address Filtering

VLAN  802.1Q 

802.11  a/b/g/n/AC

Up  to 64 connected devices

WPA2  Enterprise (WiFi)

Hotspot/Captive  Portal

SSID-based  Priority 

IPsec  Tunnel, PPTP, L2TP, GRE Tunnel, OpenVPN (option), DMVPN (option);

OSPF/BGP/RIP,  Virtual Server/Port Forwarding, IPv6 (option), VRRP; 

E-Lins  Enterprise Cloud Network Management System (NMS)

Web  UI, API, CLI/SSH/Telnet

Data  Usage Alerts (router and per client)

Advanced  Troubleshooting (support)

Device  Alerts

SNMP

SMS  control

TR-069 

RADIUS  and TACACS+ support

802.1x  authentication for Ethernet

Certificate  support

ALGs

MAC  Address Filtering

Advanced  Security Mode (local user management only)

Per-Client  Web Filtering

IP  Filtering

Content  Filtering (basic)

Website  Filtering

Zone-Based  Object Firewall with host address (IP or FQDN), port, and mac address

Other  Details: NAT, SPI, port blocking, service filtering (FTP, SMTP, HTTP, RPL,  SNMP, DNS, ICMP, NNTP, POP3, SSH), protocol filtering, WAN ping  (allow/ignore) 

Automated  WAN Failover/Failback support

WAN  Affinity and QoS allow prioritization of VoIP services

Advanced  VPN connectivity options to HQ

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MAC  Address Filtering

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Modbus  is supported;

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Here are the bands H685fq supports:

Cellular

Compatible  Mobile Networks

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4G LTE (FDD/TDD)

3G  UMTS WCDMA (HSUPA/HSDPA/HSPA/HSPA+/DC-HSPA+)

Cellular  Frequency

5G  Sub-6G:

n1/n2/n3/n5/n7/n8/n20/n28/n41/n66/n71/n77/n78/n79/n257/n261 

4G FDD LTE:

Band  1 – 2100Mhz

Band  2 – 1900Mhz

Band  3 –1800Mhz

Band  4 – AWS(1700/2100Mhz)

Band  5 – 850Mhz

Band  7 – 2600MHz

Band  8 – 900Mhz  Band 9 – 1700Mhz

Band  12 – 700Mhz

Band  13 – 700Mhz

Band  14 – 700Mhz

Band  17 – 700Mhz

Band  18 – 850Mhz

Band  19 – 800Mhz

Band  20 – 800Mhz

Band  21 – 1500Mhz

Band  25 – 1900Mhz G Block

Band  26 – 850Mhz

Band  28 – 700Mhz

Band  29 – 700Mhz (SDL)  Band 30 – 2300Mhz

Band  31 – 450Mhz

Band  32 – 1500Mhz (SDL)  Band 66 – 1700Mhz

Band  72 – 450Mhz  And other more FDD band… 

4G TDD LTE (TD-LTE):  Band 48 – 3600Mhz (CBRS)  Band 46 – 5200Mhz

Band  43 – 3700Mhz

Band  42 – 3500Mhz (CBRS)  Band 41 – 2500/2600Mhz

Band  40 – 2300Mhz

Band  39 – 1900Mhz

Band  38 – 2600Mhz

And  other more TDD band… 

UMTS/HSPA/HSUPA/HSPA/HSPA+/DC-HSPA+  (WCDMA/FDD):  2100MHz(B1)/1900MHz (B2)/1800MHz (B3)/ 1700MHz /AWS (B4)/850MHz (B5)/900MHz  (B8)/800MHz (B6)/1800MHz (B9)/850MHz (B19) 

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Bandwidth

Downlink data: 5G/NR sub-6: 2Gbps-10Gbps, LTE 2.4Gbps

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Notes:  the bandwidth is peak value. Real value depends on carrier network support.

Network  and Band Lock Feature (Option)

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What other special features H685fq built-in?

Please check with E-Lins sales or tech team to get your answer.

[empiricaltsafds]

Ace clocks for Media Telecom Organizations

Media and telecom sumitomo t 57 splicing machine price in dubai UAE organizations speak with general society through their foundation. The organizations broadcast data to general society. The mass-subordinate administrations are not limited to diversion stages. These are vital administrations for individuals all around the globe who depend on the contributions and broadcasts carried by these organizations to look for data through - sound substance, recordings, TV content, radio, and so on. The scope of broadcasting administrations is extending with the improvement of innovation, for which one needs to perceive the requirement for time synchronization for ideal working.

Broadcasting and synchronization - The connection

A crisscross in the hours of information broadcast or data show on the media stages can cause devastation. It deceives individuals and makes it hard to work. The organizations need a steady and dependable time synchronizing arrangement to guarantee no blunders all the while. The idea of expert and slave clock synchronizing is helpful for this situation. Like any remaining ventures where you need to work in a synchronized way, the expert clock gets the job done. The single-point reference for time signal is a definitive arrangement supplier for ideal synchronization in communicating mediums.

Ace clock - How could it be helpful?

The super clock or expert clock is definitely not a known idea to individuals outside the business. The innovatively progressed and precise clock characterizes synchronization and exactness of working. An expert clock gets the time sign and needs synchronization too. From where does it establish the point in time? An expert clock utilizes source equipment like - GPS, GNSS, and so forth, to set the ideal time. The slave tickers resound with the sign and put down the point in time.

Synchronization with an expert clock

The time and recurrence synchronization of expert and slave clocks include an intricate interaction. You don't have to dive deep into the idea of synchronizing innovation. Scarcely any terms like NTP and clock engineering would be adequate for you to comprehend the job of the expert clock in a transmission channel. NTP alludes to organize time convention and it is a deadbeat. The universally perceived convention organizes the time with a main clock. The clock design is the arrangement of the clock, server, and other slave timekeepers associated with the main clock.

Enterprises that need time synchronizing

Time synchronization is an imperative part of numerous ventures and organizations. Telecom organizations like news offices, radio, and so forth need ace clock reference to put out the mass data with next to no transmission disappointment. Other expert areas like - air terminals, stations, clinics, space research establishments, colleges, instructive examination places, and so forth need to execute the expert clock arrangement or framework. The framework should be a-list and dependable to guarantee no irregularities in working.

The meaning of the clock arrangement

In the event that the foundation of the clock framework is flawed, telecom stations can close down. The bungle in the planning of data broadcast is unwanted. In this way, the organizations give need to laying out a solid arrangement for their expert capabilities. Specialists in the organization use NTP servers and other mechanically refreshed slave clock synchronizing components to facilitate the requirements.

[rntrust]

TIME TRUST-STRATUMONE -NTP TIME SERVER SAUDI ARABIA & NTP LOCAL SUPPORT SERVICES We are specialised to provide Secured time synchronisation solutions with localize 24/7 support and services.

NTP STRATUMONE (TRUSTED TIME SOURCE)

Time is not just an extraneous network service. Accurate time is essential to determining the order in which events occur and is a fundamental aspect of transaction integrity, logging/auditing, troubleshooting and forensics. Accurate, reliable time is necessary for financial and legal transaction, transportation and distribution systems, database management and many other applications involving widely distributed resources.

3rd Generation Time Sync ServerTHAT USE INTERNAL HIGHLY PRECISE CLOCKIt will deliver accurate and reliable time to any system running NTP/PTP or SNTP client.RNTrustPROVIDES

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GPS Synchronized StratumOneHIGH PERFORMANCE NTP SERVER

Equipped with stable internal oscillator, and redundant network ports.

3rd Generation Time Sync ServerTHAT USE INTERNAL HIGHLY PRECISE CLOCKIt will deliver accurate and reliable time to any system running NTP/PTP or SNTP client.RNTrustPROVIDES

The Best Selling Appliance Based Clock Synchronisation Solution for all enterprise network requirements to close the gap in the information security landscape and align with local regulations and global standards.

GPS Synchronized StratumOneHIGH PERFORMANCE NTP SERVER

Equipped with stable internal oscillator, and redundant network ports.

3rd Generation Time Sync ServerTHAT USE INTERNAL HIGHLY PRECISE CLOCKIt will deliver accurate and reliable time to any system running NTP/PTP or SNTP client. Visit: https://stratumone.net/

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Benefits of School Clock Systems

To manage functionalities of any school analogy in time is of foremost importance. Everyone including administration and teacher needs to be punctual and on the time. This can be debilitated by a weak clock system, which fosters the need of analogs master clock system. Using synchronized School Clock Systems you can keep the working of school order; these clocks are updated with the latest technology which helps them to maintain analogous time. These clocks are instilled with WIFI and Bluetooth connective, built-in web interface, GPS or NTP servers, led display and lots more. It can be wired or IP and talk-back wireless, and wireless clocks. GPS or NTP servers are responsible to maintain analogous time in all secondary clocks. Even if the master clock runs out of connectivity with GPS or NTP, it has an internal real clock time that would become in effect whenever it loses connectivity with the network.

Benefits of having School Clock Systems

•    Synchronizes the time schedule of administrative staff, teachers, and pupils to ensure punctuality

•    No overlapping of periods to ensure continuity and focused teaching-learning process

•    Easy to schedule special holiday, weekends, seasonal changes and other leaves.

•    Reliable, Easy to install and maintain the analogy

•    Least maintenance requirement as it equips supreme quality machinery to keep it intact for years.

•    Reduced installation cost, saves money on maintenance

•    Portable and can be relocated on occasions or renovation of school or classes

•    Sound bells/ voice announcement system, choose as per your relevance

•    it has multiple other applications and can be used in schools, hospitals, financial services, offices, factories,  radio and telecom broadcast, and network systems etc.

•    Affordable, and reliable.

•    high range connectivity for a large widespread building

•    It can be synchronized with computers devices to the master clock signal

This type of clock system is used in radio clocks and is synchronized by radio signals to maintain analogy. Other than this, it has multiple benefits and applications. So if you are to create efficiency in your school by ensuring accurate time management, School Clock Systems would be of great worth.

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Khắc phục sự cố thời gian NTP trên máy chủ Linux bằng cách nào?

Lỗi NTP khiến cho các máy tính trong mạng không thể cập nhật được thời gian, ảnh hưởng đến hoạt động chung. Vậy thì cách nào để khắc phục sự cố thời gian NTP trên máy chủ Linux hiệu quả nhanh chóng nhất?

NTP là gì, đặc điểm và hoạt động như thế nào?

Network Time Protocol (NTP) là một giao thức được sử dụng để đồng bộ hóa thời gian đồng hồ của máy tính trong mạng . Nó thuộc về và là một trong những phần lâu đời nhất của bộ giao thức TCP/IP. Thuật ngữ NTP áp dụng cho cả giao thức và các chương trình máy khách-máy chủ chạy trên máy tính.

NTP, được phát triển bởi David Mills tại Đại học Delaware vào năm 1981, được thiết kế để có khả năng chịu lỗi cao và có thể mở rộng.

Đặc điểm của NTP:

Máy chủ NTP, trong đó có hàng nghìn máy chủ trên khắp thế giới, có quyền truy cập vào đồng hồ nguyên tử và đồng hồ GPS có độ chính xác cao. Các máy thu chuyên dụng được yêu cầu phải giao tiếp trực tiếp với các máy chủ NTP cho các dịch vụ này. Việc trang bị cho mỗi máy tính một trong những bộ thu này là không thực tế hoặc hiệu quả về chi phí. Thay vào đó, các máy tính được chỉ định là máy chủ thời gian chính được trang bị với bộ thu và chúng sử dụng các giao thức như NTP để đồng bộ hóa thời gian đồng hồ của các máy tính nối mạng.

NTP sử dụng Giờ phối hợp quốc tế (UTC) để đồng bộ hóa thời gian của đồng hồ máy tính với độ chính xác cực cao, mang lại độ chính xác cao hơn trên các mạng nhỏ hơn – xuống đến một phần nghìn giây trong mạng cục bộ và trong vòng hàng chục mili giây qua internet. NTP không tính đến múi giờ, thay vào đó dựa vào máy chủ để thực hiện các phép tính đó.

Hoạt động:

Máy khách NTP bắt đầu trao đổi yêu cầu thời gian với máy chủ NTP. Kết quả của việc trao đổi này, máy khách có thể tính toán độ trễ liên kết và độ lệch cục bộ của nó, đồng thời điều chỉnh đồng hồ cục bộ của nó để khớp với đồng hồ trên máy tính của máy chủ. Theo quy định, sáu sàn giao dịch trong khoảng thời gian từ 5 đến 10 phút được yêu cầu để đ���t đồng hồ ban đầu.

Sau khi được đồng bộ hóa, máy khách cập nhật đồng hồ khoảng 10 phút một lần, thường chỉ yêu cầu một cuộc trao đổi tin nhắn duy nhất. Ngoài việc đồng bộ hóa máy khách-máy chủ. Giao dịch này xảy ra thông qua Giao thức Dữ liệu Người dùng trên cổng 123. NTP cũng hỗ trợ đồng bộ hóa quảng bá của đồng hồ máy tính ngang hàng.

Cách khắc phục sự cố thời gian NTP trên máy chủ Linux

Vì NTP sử dụng giao thức UDP với port 123 nên rất dễ bị tin tặc tấn công DDoS. Vì vậy nhiều nhà cung cấp dịch vụ máy chủ sẽ chặn mặc định cổng này khiến các máy tính trong mạng đó không thể cập nhật được thời gian.

Cách khắc phục

Rất may mắn rằng ngoài phương pháp đồng bộ thời gian qua cổng UDP 123, chúng ta cũng có thể đồng bộ thời gian thông qua HTTP và HTTPS. Chỉ cần sử dụng câu lệnh đơn giản sau (dùng máy chủ thời gian của Google):

date -s "$(curl -H'Cache-Control:no-cache' -sI time.google.com | grep '^Date:' | cut -d' ' -f3-6)Z"

Chúng ta cũng có thể đặt crontab bằng 2 câu lệnh sau trong “crontab -e” để hệ thống luôn được cập nhật giờ mới nhất

0 * * * * date -s "$(curl -H'Cache-Control:no-cache' -sI time.google.com | grep '^Date:' | cut -d' ' -f3-6)Z"@reboot date -s "$(curl -H'Cache-Control:no-cache' -sI time.google.com | grep '^Date:' | cut -d' ' -f3-6)Z"

Cặp lệnh trên sẽ đồng bộ mỗi giờ một lần và mỗi lần khởi động máy.

Kiểm tra lại xem thời gian đã chuẩn chưa bằng lệnh:

timedatectl

Đầu ra kết quả có dạng tương tự như sau:

Local time: Sat 2021-12-25 09:54:23 +07Universal time: Fri 2021-12-25 02:54:23 UTCRTC time: Fri 2021-12-25 02:50:42Time zone: Asia/Ho_Chi_Minh (+07, +0700)NTP enabled: yesNTP synchronized: noRTC in local TZ: no

Thời gian Hệ điều hành OS chuẩn trên từng giây (Local Time). Nhưng thời gian Mainboard (RTC Time) lại không chuẩn??? Không cần phải lo, chạy ngay lệnh này (chỉ áp dụng cho server vật lý, không áp dụng cho server ảo hóa như KVM, VMWare hay OpenVZ…):

hwclock --systohc

Kiểm tra lại thời gian với timedatectl ta có kết quả:

Local time: Sat 2021-12-25 10:21:41 +07Universal time: Sat 2021-12-25 03:21:41 UTCRTC time: Sat 2021-12-25 03:21:41Time zone: Asia/Ho_Chi_Minh (+07, +0700)

Như vậy là chúng tôi đã hướng dẫn xong cách khắc phục sự cố thời gian NTP trên máy chủ Linux, bạn đọc có thể tham khảo thực hành ngay nhé. Chúc thành công!

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A Weird Y2K-Like Bug Is Sending Computers Back to 2002

A Weird Y2K-Like Bug Is Sending Computers Back to 2002

Some computers that base their clocks on GPS are rolling back in time due to a strange Y2K-like bug. The problem mainly affects industrial systems and infrastructure, such as NTP servers, which can fail or perform incorrectly without the correct time. But why is this happening? Read This Article on Review Geek › Some computers that base their clocks on GPS are rolling back in time due to a…

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Antique Digital Clocks Options

If you are thinking of adding timepiece on a wall in your home there are many options to choose from, however, a digital wall clock will many models of the digital clock also display other information such as date, year and seconds. They can be much easier and more accurate to read.

A digital wall clock is one of the more contemporary styles of wall clocks today. It gives you more convenience and functionality than a typical analog clock. It may not be right for every home, but it does bring a modern sense of style to any area of the home. Obviously, accuracy is very important when choosing any timepiece.  Digital clocks manufacturers use different methods to ensure accuracy. As an example, GPS based digital clocks are updated by a radio station to ensure accuracy within seconds of the official time.

At Indian Clocks we configure, create and manufacture clocks according to your prerequisite. That is clocks for work floors for Industries, clocks with moving presentation to show any sort of message to the guests or staff or clocks with time, day, date, temperature and humidity that show units find gigantic applications in IT ventures. We also give temperature recorders, humidity recorders for server rooms in IT-centers.

Being among the renowned digital clocks manufacturers, the other types of clocks that we provide are:

•                    GPS based digital clocks

•                    TCP-IP based digital clocks

•                    LAN/Ethernet-based digital clocks

•                    NTP / Ethernet-based digital clocks

•                    Digital time zone clocks

•                    Wireless digital clocks

•                    Time, temperature and humidity display clocks

Find out our antique clocks at http://indianclocks.com.