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- In this video,

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I want to talk about NTP.

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NTP is the network time protocol

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and NTP plays an important role in Linux.

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Because from NTP you will
typically manage your system time.

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That's a time that is maintained
by your operating system

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about which we have talked before.

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In order to synchronize your system time,

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Linux knows different NTP services.

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Chrony is one of the fundamental services.

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Apart from that,

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there is systemd-timesyncd.

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Both are fulfilling the same role,

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and they get their time from the internet.

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To determine the trustworthiness
of a NTP time server

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that they are going to synchronize with,

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NTP uses the notion of stratum.

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The stratum explains the
reliability of an NTP time server.

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And stratum goes from
1 all the way up to 16,

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where 16 means do not use

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and 1 means the most reliable time server.

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Now what is going to happen

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if your chrony is getting the time

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from a time server that has stratum 1?

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Well then chrony knows

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that it's the highest level of reliability

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and it will most likely choose

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to synchronize with that
specific time server.

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In a time server's configuration

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you typically will work
with different time sources.

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So you might find that chrony

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is getting the time from
three different time servers,

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one of them having stratum 1,

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the other ones having stratum 3.

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So chrony definitely

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is going to synchronize
with the stratum 1.

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And as a result,

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your NTP stack on your
system will get stratum 2.

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And that allows you to determine

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the trustworthiness of time
services and time sources

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in an internet environment.

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The chrony utilities even allows you

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to figure out which
stratum currently is used,

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and you'll learn about these next.