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- In this video, we'll
talk about systemd targets.

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So a systemd target is group of units.

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And if the target has
the isolate property set,

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then it can define the state
that the system starts in.

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When we are talking about targets

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that are used for system starts,

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there are four that matter.

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Emergency target is a target
for minimal troubleshooting.

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You use it if you want a minimal amount

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of units to be started.

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Rescue target is used for troubleshooting

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in a more complete system.

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And there's multi-user target,

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which starts a complete
non-graphical system.

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And graphical.target starts

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a complete graphical environment.

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You need to know how to
manage the default target,

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and you can do so using
systemctl get or set-default.

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Get will show you.

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Set will set it.

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And if you want to change your target,

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well, you can pass a desired target

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as a kernel argument

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in the Grub boot menu for troubleshooting.

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I'll show you that in the next video.

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For now, I would like to
show you what's going on

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in these targets.

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So let me start using
systemctl list unit files

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minus t target, so that
you get a complete overview

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of all the targets that are available.

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As you can see,

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multiple targets are available,

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and these include targets that you use

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to define your current system state,

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but they also include targets

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that are really just a group of units

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like sound.target for instance.

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Let's investigate two of these targets

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using systemctl cat
sound.target to start it.

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So what is that?

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Well, it just has a unit section,

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and for the rest of it, it has nothing.

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Why does it have nothing?

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Well, that is because
the target doesn't know

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about the units that belong to the target.

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The units know which
target they belong to.

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That's what we can see.

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If you use systemctl cat on any unit,

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sshd.service, for instance,

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there you can see the install section

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where we have wanted
by is multi-use.target.

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So that's how the unit knows
which target it belongs to.

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Now as I mentioned,

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targets that have a state of isolatable,

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these are the targets that you can use

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to start your system in a specific state.

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So if you use systemctl cat
on the emergency.target,

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we get an example,

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and there we can see allow isolate is yes,

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and this allow isolate is yes.

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That makes that you can start your system

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in emergency mode.

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Now the last thing I need to show you

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is systemctl get-default,

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which is showing the default target.

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And if you want a
different default target,

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that's fine, use systemctl
set-default multi-user.target.

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And that has created a symbolic link

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to etc systemd system default.target,

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which is pointing to multi-user target.

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So what's happening if
you reboot right now?

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Well, we will be starting
in multi-user target.

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You will see that in a few seconds.

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So here is the login prompt.

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It's a multi-user target login prompt.

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So it's non-graphical,

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and, well, I just need to
provide my credentials,

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and then I can use sudo
systemctl start graphical.target

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if I want to get back
to the graphical target.

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And there we go.

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Here we have the graphical target again.

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Now there is one thing that
I still need to show you,

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and that is how we can
switch between targets.

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You have just seen that I
used sudo systemctl start.

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Now I'm going to use
sudo systemctl isolate

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multi-user.target.

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Now what is the difference
between start and isolate?

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Well, isolate allows you to get back,

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back to a target that has
a fewer amount of services,

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and start only allows you to get forward.

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Graphical target builds on
top of multi-user targets.

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So you can easily start
that from multi-user target.

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If you are in graphical and
you want to go to multi-user,

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now you don't start, you
are going to isolate.

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You're going to isolate
only these services

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that are required in multi-user
and not in graphical.

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And there we go.

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We should see the multi-use
login prompt in a few seconds.

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There it is.

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So let me restore the original
situation, then we are done.

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So sudo systemctl
set-default graphical.target.

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And now sudo reboot.

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And it's rebooting.

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And after the reboot, we are
back in the graphical mode.

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That's it.