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For troubleshooting purposes, sometimes it is required to boot into a non-default target.

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So how does that work?

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Well, first you need a target that is isolatable.

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A systemd target that is not isolatable is just a group of unit files.

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So if you have the isolate is yes option in the systemd target unit file,

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you can boot into that target.

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And four common targets are used.

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But there is nothing preventing you from creating your own targets if you want.

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The commonly used targets are emergency target, rescue target, multi-user target and graphical target.

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And you can enter the group to boot menu by pressing E.

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And then you add systemd.unit is whatever.target to boot into a non-default target.

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Alternatively, use systemctl set default to set your default.

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Let me show you.

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So let me use systemctl cat printer.target.

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Because in the end, a target is just a group of unit files.

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And here we can see it is quite minimal configuration.

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Now what happens if we do rescue.target, for instance?

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There we can see the last option in the configuration.

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And that's the option that matters.

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Allow isolate is yes.

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If a target has allow isolate is yes, then you can boot into it.

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And I'm going to show you how to do that from the group bootloader menu.

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So first we need to reboot.

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And press escape at the right moment.

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If you see the firmware, and we just did,

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it's right after the loading of the firmware where you press escape.

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And then you get the group boot menu, as you can see right here.

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So from here I'm going to use E for edit.

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I'm going to the end of the line that loads Linux.

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And I'm using systemd.unit is rescue.target.

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And then control X to boot with normal options.

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So rescue target, as well as emergency target,

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are going to prompt for a root password.

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It's a little bit hard to see,

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because after the prompt,

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which is about 12 lines from the bottom of the screen,

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some more messages were printed,

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but it is really prompting give root password for maintenance.

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If you don't have a root password,

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you cannot use these options for troubleshooting.

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But I did set a root password on this one.

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So here I am in my root shell.

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Now I'm going to use systemctl start graphical.target.

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From a minimal target,

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just use systemctl start to go to a target

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that is offering more.

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So here I am back in my graphical target

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where I can log in again.