Time keeping is an important part of keeping an efficient software. Any service using event based system where the time has to be traced, includes functionalities like authentication, or systems running on distributed platforms, all functionalities like these requires the main system to be upto date with the time stamp of every event that occurred, it works like a time logger.
\nThe service used for this is the Network Time Protocol (NTP), to use the system clock to our advantage with the outside workings of a system. Now this system clock can be an atomic clock, a GPS clock, or any other trusted clock that can work with NTP.
\nThe practical implementation of NTP is NTP Pool Project. The pool consists of time servers that provides access to \u201ctheir time\u201d for a huge number of clients around the globe. NTP time is the default of many Linux based Operatiing Systems and many of its Applications.
\nIn this article you will learn how to setup NTP on your own server and how to configure it to your use, so the users connected to your server will have the accurate time with them. It is needed because it can help you use the complete bandwidth by knowing about the spare CPU cycles.
\nBefore joining the NTP Pool Project you must fulfil the basic three requirement, and they are:
\n\u2981 Static IP:
\nYour server must have a static IP address.
\n\u2981 Stable Internet Connection:
\nYour server must have a permanent and stable internet connection.
\n\u2981 Consistent IP address:
\nYour IP address most not change, or only changes infrequently (once a year or less).
\nStep 1 \u2014 Installing NTP
\nJust like always lets just firstly, update your packages:
\n\u2981 sudo yum update
\n\u2981
\nThen install NTP:
\n\u2981 sudo yum install ntp
\n\u2981
\nOnce the installation completes, start the service and configure it so it starts automatically each time the server boots:
\n\u2981 sudo systemctl start ntpd
\n\u2981
\n\u2981 sudo systemctl enable ntpd
\n\u2981
\nIf you’ve configured the firewall as specified in the prerequisites, you must allow UDP traffic for the NTP service in order to communicate with the NTP pool:
\n\u2981 sudo firewall-cmd –permanent –add-service=ntp
\n\u2981
\n\u2981 sudo firewall-cmd –reload
\n\u2981
\nFor more on FirewallD, refer to\u00a0How To Set Up a Firewall Using FirewallD on CentOS 7.
\nNTP is now installed, but it’s configured to use the default NTP pool time servers. Lets pick some specific time servers instead.
\nStep 2 \u2014 Choosing an Upstream Server
\nBasically NTP Pool Project has a list of time servers they are Stratum 1 and Stratum 2. Down is the list of servers available for public access under stated restrictions:<\/p>\n
\u2981 OpenAccess: This time server is open to any client complying with the NTP Pool\u00a0\u2981 usage recommendations.
\n\u2981 RestrictedAccess: This time server has some access restrictions in addition to the NTP Pool usage recommendations.
\n\u2981 ClosedAccess: This time server is closed or requires prior arrangement.
\nVisit the\u00a0Stratum 1 Time Servers list. You’ll see a list like the following:<\/p>\n
The list above should be sorted by ISO code and find one or two servers that are close to you geographically. When the server’s\u00a0Access Policy\u00a0column states\u00a0OpenAccess, you can use it without issue. If it says “RestrictedAccess”, click to open the entry and read the instructions noted in the\u00a0AccessDetails\u00a0field. Often, you’ll find that\u00a0NotificationMessage\u00a0is set to\u00a0Yes, which means you have to craft an informal email directed to the address provided in\u00a0ServerContact, informing the server operator about your desire to use this time server as a time source for your NTP Pool Project member.
\nOnce you’ve identified the servers you’d like to use, click the link for each server in the\u00a0ISO\u00a0column and copy its host name or IP address. You’ll use these addresses in Step 3.
\nNext, select three or four servers from the\u00a0Stratum 2\u00a0list, following the same process.
\nOnce you have selected your time servers, it’s time to configure your NTP client to use them.
\nStep 3 \u2014 Configuring NTP to Join the Pool
\nTo use your server with the NTP pool, and configure your new time servers, you’ll need to make some modifications to your NTP daemon’s configuration. To do so, edit the\u00a0\/etc\/ntp.conf\u00a0file:
\n\u2981 sudo vi \/etc\/ntp.conf
\n\u2981
\nFirst, make sure a\u00a0driftfile\u00a0is configured. A driftfile stores the frequency offset between the system clock running at its nominal frequency, and the frequency required to remain in synchronization with correct time. It helps to achieve a stable and accurate time. You should find this at the top of your configuration file on a default installation:
\n\/etc\/ntp.conf
\n# For more information about this file, see the man pages
\n# ntp.conf(5), ntp_acc(5), ntp_auth(5), ntp_clock(5), ntp_misc(5), ntp_mon(5).<\/p>\n
driftfile \/var\/lib\/ntp\/drift<\/p>\n
…
\nNext, remove the default time source entries from the configuration. You’re looking for all lines which are of the pattern\u00a0server 0.centos.pool.ntp.org iburst. If you’re using a default configuration, remove the highlighted lines as shown in the following example:
\n\/etc\/ntp.conf
\n…
\n# Use public servers from the pool.ntp.org project.
\n# Please consider joining the pool (http:\/\/www.pool.ntp.org\/join.html).
\nserver 0.centos.pool.ntp.org iburst
\nserver 1.centos.pool.ntp.org iburst
\nserver 2.centos.pool.ntp.org iburst
\nserver 3.centos.pool.ntp.org iburst
\nReplace the lines you removed with the hand-picked servers you selected in the previous step.
\n\/etc\/ntp.conf
\n…
\nserver ntp_server_hostname_1 iburst
\nserver ntp_server_hostname_2 iburst
\nserver ntp_server_hostname_3 iburst
\nserver ntp_server_hostname_4 iburst
\nserver ntp_server_hostname_5 iburst
\n…
\nWe use the\u00a0iburst\u00a0option for each servers, per the NTP Pool recommendations. That way, if the server is unreachable, this will send a burst of eight packets instead of the usual one packet. Using the\u00a0burstoption in the NTP Pool Project is considered abuse as it will send those eight packets every poll interval, whereas\u00a0iburst\u00a0sends the eight packets only the first time.
\nNext, make sure the default configuration does not allow management queries. If you don’t, your server could be used in NTP reflection attacks, or could be vulnerable to\u00a0ntpq\u00a0and\u00a0ntpdc\u00a0queries that attempt to modify the state of the server. Check that the\u00a0noquery\u00a0option is added to the default\u00a0restrict\u00a0lines. Also make sure you add the options\u00a0kod\u00a0and\u00a0limited\u00a0as they restrict too eagerly asking clients and enforce rate limiting.
\n\/etc\/ntp.conf
\n…
\n# Permit time synchronization with our time source, but do not
\n# permit the source to query or modify the service on this system.
\nrestrict default nomodify notrap nopeer noquery kod limited<\/p>\n
# Permit all access over the loopback interface. This could
\n# be tightened as well, but to do so would effect some of
\n# the administrative functions.
\nrestrict 127.0.0.1
\nrestrict ::1
\nYou can find more information about the other options in the\u00a0official documentation.
\nYour NTP daemon configuration file now should look like the following, although your file may have additional comments, which you can safely disregard:
\n\/etc\/ntp.conf<\/p>\n
driftfile \/var\/lib\/ntp\/ntp.drift<\/p>\n
restrict default nomodify notrap nopeer noquery kod limited<\/p>\n
restrict 127.0.0.1
\nrestrict ::1<\/p>\n
server ntp_server_hostname_1 iburst
\nserver ntp_server_hostname_2 iburst
\nserver ntp_server_hostname_3 iburst
\nserver ntp_server_hostname_4 iburst
\nserver ntp_server_hostname_5 iburst
\nSave the file and exit the editor.
\nNow restart the NTP service and let your time server synchronize its clock to the upstream servers.
\n\u2981 sudo systemctl restart ntpd
\n\u2981
\nAfter a few minutes, check the health of your time server with the\u00a0ntpq\u00a0command:
\n\u2981 ntpq -p
\n\u2981
\nThe output should look similar to this:
\nOutput
\nremote refid st t when poll reach delay offset jitter
\n==============================================================================
\nmizbeaver.udel. .INIT. 16 u – 64 0 0.000 0.000 0.000
\nmontpelier.ilan .GPS. 1 u 25 64 7 55.190 2.121 130.492
\n+nist1-lnk.binar .ACTS. 1 u 28 64 7 52.728 23.860 3.247
\n*ntp.okstate.edu .GPS. 1 u 31 64 7 19.708 -8.344 6.853
\n+ntp.colby.edu .GPS. 1 u 34 64 7 51.518 -5.914 6.669
\nThe\u00a0remote\u00a0column tells you the hostname of the servers the NTP daemon is using, and the\u00a0refid\u00a0column tells you the source the servers are using. So for Stratum 1 servers, the\u00a0refid\u00a0field should show\u00a0GPS,\u00a0PPS,\u00a0ACTS, or\u00a0PTB, and Stratum 2 and higher servers will show the IP address of the upstream server. The\u00a0st\u00a0column shows the stratum, and\u00a0delay,\u00a0offset\u00a0and\u00a0jitter\u00a0tell you about the quality of the time source. Lower values are better for these three fields.
\nYour time server is now able to serve time to the public. You can verify this by calling\u00a0ntpdate\u00a0from another host:
\n\u2981 ntpdate -q your_server_ip
\n\u2981
\nThe output should look similar to this and it tells you it adjusted the time server and the offset:
\nOutput
\nserver your_server_ip, stratum 2, offset 0.001172, delay 0.16428
\n2 Mar 23:06:44 ntpdate[18427]: adjust time server your_server_ip offset 0.001172 sec
\nStep 4 \u2014 Adding the Server to the NTP Pool
\nTo add your server so others can use it, visit\u00a0manage.ntppool.org\u00a0and sign up for an account. You will receive an email from\u00a0NTP Pool\u00a0help@ntppool.org\u00a0requesting that you verify your account. Confirm your account by following the instructions in the email, and then log in to\u00a0manage.ntppool.org.
\nOnce logged in, you’ll see the simple interface for adding servers:<\/p>\n
Enter your server’s IP address and click\u00a0Submit.
\nThe next screen asks you to verify that it identified the region of your server. If it shows your server in a different region than you expect, use the\u00a0Comment\u00a0box to let them know.<\/p>\n
If you are happy, confirm the entry by clicking\u00a0Yes, this is my server, add it!
\nYour server is now part of the NTP Pool Project. Visit\u00a0http:\/\/www.pool.ntp.org\/scores\/your_server_ip\u00a0to see information the NTP Pool’s monitoring system has collected about your server. It checks your server a few times per hour and displays offset data, alog with the\u00a0score\u00a0of your system. As long as your server is keeping good time and is reachable, the score will rise untill it reaches 20 points. Only servers with a score higher than 10 are used in the pool.<\/p>\n","protected":false},"excerpt":{"rendered":"
Time keeping is an important part of keeping an efficient software. Any service using event based system where the time has to be traced, includes functionalities like authentication, or systems running on distributed platforms, all functionalities like these requires the main system to be upto date with the time stamp<\/p>\n","protected":false},"author":3,"featured_media":974,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[1],"tags":[],"class_list":["post-950","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-news-announcements"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"https:\/\/i0.wp.com\/www.virtono.com\/community\/wp-content\/uploads\/2017\/06\/centos-sam-galope-network-time-protocol-clocks.png?fit=1152%2C772&ssl=1","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p7ISfL-fk","jetpack_likes_enabled":true,"jetpack-related-posts":[{"id":2150,"url":"https:\/\/www.virtono.com\/community\/knowledgebase\/get-kernel-statistics-and-hardware-information\/","url_meta":{"origin":950,"position":0},"title":"Get kernel statistics and hardware information","author":"Shreyash Sharma","date":"December 17, 2020","format":false,"excerpt":"When administering Linux systems, quick information about the installed kernel and the existing hardware is often helpful.\u00a0The \/ proc filesystem provides extensive information on the console. 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In this tutorial, we will guide you through the installation process on popular Linux distributions such as CentOS, Ubuntu, AlmaLinux, and Rocky Linux. 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MicroK8s, a lightweight Kubernetes distribution, offers a convenient way to deploy Kubernetes clusters for development and testing purposes. 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