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On 29/08/2017 15:57, Rich Freeman wrote: |
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> On Tue, Aug 29, 2017 at 9:14 AM, Alan McKinnon <alan.mckinnon@×××××.com> wrote: |
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>> |
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>> ntp is designed for timeservers that by design do not make the clock |
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>> jump around. Every second on the wall clock actually happens, none are |
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>> missing. To do that, ntp adjusts the length of a second till the |
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>> machine's time creeps up towards the real time as defined by the U.S |
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>> Navy. Unless you are running software that is extremely time-critical |
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>> (eg centralized auth servers, science experiments, etc) or you operate a |
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>> proper time server, you absolutely do not need this behaviour ever.[1] |
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>> |
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> |
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> I'd argue the opposite. Assuming your system boots with approximately |
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> the correct time then slewing the clock is going to be the best way to |
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> maintain time. |
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Yeah but this is Stroller, and I gave an answer specific to him. |
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He doesn't run a fleet of business servers in containers like you do, or |
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maintain awful amounts of ISP infrastructure like I do. He's a regular |
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guy with regular machines. |
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We sysadmins can easily tend to get way too involved with the specifics |
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of how something works and how awesome it all is, and lose sight of what |
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people really need. |
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Another example is LVM. You or I might really need it (debatable now we |
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have ZFS) but the average user has no concept of what it might be, or |
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care. So why do Ubuntu installers shove it in your face as something |
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really cool that you should really really use? Because the author of the |
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installer thinks it's really cool, that's why. |
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ntpdate in a cron is a really easy way to keep time more or less |
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accurate. The average user and his software couldn't care less about |
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slew and couldn't care less if his computer time is 10 seconds off or |
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even a minute, same with his wristwatch. |
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But having said that, chrony just does it all without oversight and |
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without even needing to make a crontab, it's the perfect fire and forget |
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background daemon. I keep forgetting about chrony (have no real pressing |
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need to get it at install time) |
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> Now, if you're talking about a system that starts up with no concept |
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> of the real time then I'd say the best approach is to do a one-time |
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> sync to a time server, and then run ntpd from then on to maintain the |
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> time using slewing. Obviously you don't want to slew from the epoch |
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> to the current time. |
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> |
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> The one-time sync strikes me as the sort of thing that might ideally |
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> go into an initramfs. If you're obtaining your root filesystem over |
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> the network it might even be a dependency. Doing it that early |
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> eliminates most of the issues with logging and running services. |
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> |
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-- |
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Alan McKinnon |
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alan.mckinnon@×××××.com |