1 00:00:00,000 --> 00:00:10,680 In this video, we'll talk about managing time services. 2 00:00:10,680 --> 00:00:16,240 On Linux, typically Network Time Protocol, or NTP, is used to pick up time from the internet 3 00:00:16,240 --> 00:00:19,280 and to synchronize the local machine. 4 00:00:19,280 --> 00:00:24,440 The different Linux distributors have different solutions to work with NTP. 5 00:00:24,440 --> 00:00:30,600 It can be the somewhat older NTPD, or SystemD TimeSyncD, which is integrated in SystemD. 6 00:00:30,600 --> 00:00:33,360 And on Red Hat and Family, there's CronyD. 7 00:00:33,360 --> 00:00:37,439 All of these are services that are used to synchronize with time services that have been 8 00:00:37,439 --> 00:00:39,759 defined. 9 00:00:39,759 --> 00:00:43,000 Commonly used time services are in pool.ntp.org. 10 00:00:43,000 --> 00:00:44,599 They are publicly available. 11 00:00:44,599 --> 00:00:49,240 They are very accurate as they are connected to an atomic clock, so many servers are using 12 00:00:49,240 --> 00:00:51,240 this to synchronize. 13 00:00:51,240 --> 00:00:56,680 The TimeDateCTL utility can be used to set time, to synchronize time, as well as to set 14 00:00:56,680 --> 00:00:57,680 time zones. 15 00:00:57,680 --> 00:01:02,840 It's a relatively new utility, and it's offering everything you need to have the accurate time 16 00:01:02,840 --> 00:01:04,440 on your system. 17 00:01:04,440 --> 00:01:07,320 HWClock is another utility. 18 00:01:07,320 --> 00:01:12,239 You use it to manage hardware time and synchronize system time with hardware time. 19 00:01:12,239 --> 00:01:17,800 And that is useful because your system time is always set based on hardware time. 20 00:01:17,800 --> 00:01:21,120 And next, your system time is synchronized with internet time, and if the difference 21 00:01:21,120 --> 00:01:24,959 is too big, then NTP refuses to synchronize. 22 00:01:24,959 --> 00:01:31,639 And that is why it might make sense to set your system time based on the hardware clock 23 00:01:31,639 --> 00:01:34,720 correctly using HWClock. 24 00:01:34,720 --> 00:01:40,320 The Date utility can be used to set local time, but as you can also do that with TimeDateCTL, 25 00:01:40,320 --> 00:01:43,919 date nowadays is considered a little bit legacy. 26 00:01:43,919 --> 00:01:47,360 But date is useful for all the different display formats. 27 00:01:47,360 --> 00:01:52,720 So you can easily use it to show the time in a way that makes sense in your geographical 28 00:01:52,720 --> 00:01:53,720 area. 29 00:01:53,720 --> 00:02:00,239 Another legacy utility is TZSelect, which you can use to select a current time zone. 30 00:02:00,239 --> 00:02:06,680 But nowadays, TimeDateCTL is a modern alternative, and I would recommend using that. 31 00:02:06,680 --> 00:02:09,520 Let's talk about SystemD TimeSyncD. 32 00:02:09,520 --> 00:02:17,759 SystemD TimeSyncD is a SystemD service that provides a simple NTP-based time synchronization. 33 00:02:17,759 --> 00:02:23,360 And if you are using a complex configuration, it is recommended not to use SystemD TimeSyncD. 34 00:02:23,360 --> 00:02:29,479 And that is exactly why on Reddit, you will find ChronyD instead of SystemD TimeSyncD. 35 00:02:29,479 --> 00:02:34,399 The TimeDateCTL is a common utility to work with SystemD TimeSyncD. 36 00:02:34,399 --> 00:02:41,720 And SystemD TimeDateD is a tiny daemon that can be used to control time in related settings. 37 00:02:41,720 --> 00:02:46,800 It can control the start and stop of the SystemD TimeSyncD service. 38 00:02:46,800 --> 00:02:50,520 On Reddit family, you should learn about ChronyD. 39 00:02:50,520 --> 00:02:57,119 ChronyD reads the etcchrony.conf configuration file for instructions on how to synchronize. 40 00:02:57,119 --> 00:03:01,880 And ChronyD is running on every server, because every server needs to be synchronized with 41 00:03:01,880 --> 00:03:03,779 the internet. 42 00:03:03,779 --> 00:03:08,860 If you want to check current synchronization status, you can use ChronyC Sources. 43 00:03:08,860 --> 00:03:09,860 Let me show you. 44 00:03:09,860 --> 00:03:17,339 So first, I want to show you date, which is showing that it's Wednesday, August 13, 850. 45 00:03:17,339 --> 00:03:24,339 Then I'm using TimeDateCTL TabTab, where TabTab is showing all the different commands. 46 00:03:24,339 --> 00:03:29,820 So TimeDateCTL status is giving me current information, a lot more detailed. 47 00:03:29,820 --> 00:03:36,059 So it's giving me the time zone, it's giving information about the system clock, synchronization, 48 00:03:36,059 --> 00:03:39,979 the local time versus universal time. 49 00:03:39,979 --> 00:03:45,740 And it also has commands to set the time zone if you want to. 50 00:03:45,740 --> 00:03:49,419 Now HWclock is the third command that matters. 51 00:03:49,419 --> 00:03:52,339 And HWclock is giving the hardware clock. 52 00:03:52,339 --> 00:03:55,179 And this hardware clock should be pretty close to the system clock. 53 00:03:55,179 --> 00:04:01,259 And if that is not the case, you can use the different options that are available. 54 00:04:01,259 --> 00:04:03,100 As you can see, there's a lot. 55 00:04:03,100 --> 00:04:05,419 There are only two that really matter. 56 00:04:05,419 --> 00:04:13,220 And these are minus S for hardware clock to Sys, and minus W for Sys to HC. 57 00:04:13,220 --> 00:04:17,700 So either your hardware clock is correct and the system clock is not, then you go for minus 58 00:04:17,700 --> 00:04:23,220 S. But more common is that your hardware clock is off because of a battery problem on the 59 00:04:23,260 --> 00:04:24,700 hardware clock, for instance. 60 00:04:24,700 --> 00:04:29,260 Then you set the time on the system and you synchronize it to the hardware clock. 61 00:04:29,260 --> 00:04:33,179 And after that, you will be all right. 62 00:04:33,179 --> 00:04:43,459 Now SystemCTL status on cronyd.service is showing that the cronyd service is currently loaded. 63 00:04:43,459 --> 00:04:49,540 It's also giving nice information about the service that it uses to synchronize with. 64 00:04:49,579 --> 00:04:54,739 Alternatively, you can use cronyc sources, which is giving the main information, but 65 00:04:54,739 --> 00:04:56,820 it is not as readable. 66 00:04:56,820 --> 00:05:02,059 Now what you care about in time synchronization is that you are synchronizing with a server 67 00:05:02,059 --> 00:05:04,220 that has a reliable stratum. 68 00:05:04,220 --> 00:05:08,779 The stratum indicates how close you are to the ultimate source of time. 69 00:05:08,779 --> 00:05:11,940 Stratum 1 means that you're directly on internet time. 70 00:05:11,940 --> 00:05:15,299 Stratum 2 means that you are synchronizing with stratum 1. 71 00:05:15,339 --> 00:05:20,579 Stratum 3 means that you are synchronizing with a stratum 2 and so on. 72 00:05:20,579 --> 00:05:26,940 Typically, stratum 11 is never to be found in internet synchronization because there 73 00:05:26,940 --> 00:05:30,339 will be 10 servers between the stratum 11 and the internet. 74 00:05:30,339 --> 00:05:35,260 But stratum 11 is commonly used for on-site synchronization. 75 00:05:35,260 --> 00:05:40,700 So if you want to offer your own NTP server without being connected to the internet, 76 00:05:40,700 --> 00:05:42,660 stratum 11 should be used. 77 00:05:42,739 --> 00:05:47,420 So that if ever you connect to the internet, internet time, which is more reliable, will 78 00:05:47,420 --> 00:05:49,299 always win. 79 00:05:49,299 --> 00:05:54,579 If ever you see stratum 16, that means that the server in question could not be used. 80 00:05:54,579 --> 00:06:00,220 And a configuration behind crony is in etc.crony.conf. 81 00:06:00,220 --> 00:06:06,700 So there you can see the line pool2.centOS or pool.ntp.org, which is indicating that 82 00:06:06,700 --> 00:06:09,220 it's synchronizing time from there. 83 00:06:09,220 --> 00:06:14,220 And the alternative option is server, followed by an IP address or a server. 84 00:06:14,220 --> 00:06:18,820 And that will make that you synchronize your time with that specific server. 85 00:06:18,820 --> 00:06:23,700 After adding a server, don't forget to use systemctl status on cronyd. 86 00:06:23,700 --> 00:06:29,619 And also don't forget cronyc sources to figure out if synchronization is working all right.