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- Alright. In this video, I want to

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show you systemd timers.

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Let me do a sudo systemctl

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list units minus t timer.

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That's how we can see
all the systemd timers.

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There's only four of
them currently active.

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That's not very much, so

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let's change that command
into list unit files.

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Sudo systemctl list unit
files minus t timer.

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And there we can see a
couple more systemd timers.

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So here we see fstrim.timer fringes.

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It's disabled... disabled.
That doesn't matter.

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We are going to investigate how it works.

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I am going to use

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systemctl

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list unit files

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Fstrim *.

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And there we can see that we have

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an fstrim timer and we
have an fstrim service.

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Now this is the first thing that you

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need to know about systemd timers.

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You have something dot timer,
and something dot timer

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needs something dot service,
because the timer is

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the modifier to the service.

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The service is what you
normally do... use to start

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your service, and the timer is

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how you can apply a timer to it.

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Now if you sudo

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systemctl

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cat

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on fstrim.timer,

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now we can see what it is doing.

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So we have the unit section,
and most importantly

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we have the timer section.

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And in the timer section,
we have this OnCalender,

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it's weekly,

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and AccuracySec and the position is true

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and the RandomizedDelay is 6000.

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Now the only thing that really matters is

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the OnCalender is weekly.
That means that systemd

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is going to make sure
that this timer is going

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to run weekly.

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But what exactly is it going to run?

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Well, the corresponding service.

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That is how timers are using.

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Whatever dot timer is looking
for, whatever dot service.

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And when the moment has
come that this timer

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is going to be activated,
it will run fstrim.service.

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And that's all that you need
to know about timers for now.

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Once you get deeper in the
Linux operating system,

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you will learn how to
create your own timers

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and what exactly to do in there.

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But for now, understanding them is enough.