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The version of Linux that we use

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manage the system by using the system D utility.

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Now in particular,

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it's going to use the system control command,

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and that's going to allow us

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to start, stop, restart, view all the different services

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that are running on the system.

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Now, older systems use SysVinit.

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That's been largely replaced by system D.

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So we're going to go through the process and just go

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over a few commands, few processes, how to manage them,

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what type of configuration files that are required

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for these services to start,

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from initial boots and how to switch in,

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and out different configuration settings.

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So let's go get started here.

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First thing we want to do,

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we want to use the process command.

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Now, we want to see everything that's running.

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So we're going to use process dash E.

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You can go pipe it in the search for the init command.

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Now, we're looking for the init command only by itself,

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'cause that will indicate

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that we're using the system Vinit,

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and that's the older version.

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But what we're going to do is look for the system MD now.

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And that should be number one.

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Okay?

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So since that's process number one,

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we realize that, that's the service

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that's going to start all other services.

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And again, that initializes our services.

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Start, stops and pulls different resources

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in order to fulfill the requirements

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of the services beneath them.

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Okay?

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Now, let's go ahead and check the configuration files.

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Now, and specifically we're going to view the target files

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that specify the services that will start

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when the system starts.

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Okay?

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So first thing we want to look at is the multi-user target.

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And now this one's mostly going to focus

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on the command line only interface for the system.

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So let's look that up real quick.

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Now, if you look, this is a file that gives us

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general information about this target.

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What we're going to key in on is the unit section,

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the description but we're going to focus

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on the requires field.

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And you see it requires the basic.target process

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to be running before it can start.

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Now, the basic.target process starts a lot

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of different services that are required,

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and it pulls together those different resources

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that gets the system established and up and running.

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Okay, let's just use the same thing,

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but now let's look at the graphical user interface one.

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Okay, and we'll focus on the requires,

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and we say we use them,

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we need the multi-user target first,

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up and running before we can process the graphical target.

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And you see the wants display,

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again, that's saying, "In order for this process to run,

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we're going to require the display manager."

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And again, this is a graphical user interface target.

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So that means we're going to have to initialize all

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of the devices and resources that are required

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to get the display up and running.

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This shows how these processes build upon one another.

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One requires another,

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so that's why the system D starts first,

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and it bootstraps everything else.

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So now we're going to use the system control,

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which is used to manage the system D utility.

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And we're going to get a view of all the services

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that are currently running in the system.

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Type, it's going to equal service.

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Okay, now this a list of every service

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that's currently running in the Linux system.

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Okay, now, if you look at the bottom,

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just indicates what those fields mean.

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So the low reflects

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whether the unit definition's proper loaded,

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active SUB, just further clarifying the status

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of each one of those services in this particular view.

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Now, we're going to go ahead and switch

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to the multi-user target really quick,

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and then we're going to switch to the graphical target,

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'cause remember,

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in order to even get to the graphical target,

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we have to go to the multi-user target first.

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Okay, so let's switch to the multi-user target,

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and see how the environment looks.

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System control

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isolate.

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All right, and again, this looks very familiar,

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but initially we defaulted into a graphical user interface,

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and then switched to a terminal.

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With this particular type of target,

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we go straight into command line and that is it.

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So let me log in.

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All right.

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Again, now, this is going to be a light version of the system,

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pretty much where we're not using it

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in the graphical user interface.

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So the system should run more efficiently,

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since all these services aren't being needed.

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Okay, now, let's switch to the system control isolate,

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and we're going to use the go back to the graphical target.

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Okay.

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And we see we're back to a more familiar setting.

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Okay?

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I'm going to here.

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Next, we're going to go ahead and go just change

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the default to this target,

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even though it's already set this way.

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Just going to demonstrate how to do that.

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Okay, let's do sudo, system control.

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Okay, now let's end this.

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Whenever we first log into the system,

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we're going to go into this target that we're currently in.

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Just want to check out some

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of the system control sub commands.

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And again, we can use that double tab,

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and it's gon' let us know everything we can do,

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all these sub commands that are available

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when you're using the system D,

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or AKA system control command.

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So in particular, we're going to note the start,

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stop and restart sub commands,

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'cause we're going to use those very frequently

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as Vinit system administrators.

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So let's go ahead and practice on a particular service.

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And one thing that we're going to look

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at is the SSH Daemon service.

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Okay, so we're going to do sudo.

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The status of

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the SSH Daemon service.

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All right.

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So we'll see that's up and running for us.

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This is a quick way again,

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to get the status of a service,

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and we can use any service in the scenario.

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So we can go through and actually stop this service.

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And we're going to bring that status up again,

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see what that looks like.

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Okay, now, we see the active status

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just went to inactive or dead.

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Okay, I'll re-enable that.

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Check the status, back to green.

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Easy enough.

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Again, I'm going to try one last one.

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It's going to be the firewall for low practice.

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Okay, we see it's actually inactive.

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So we'll go ahead and start the service up.

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Okay.

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See it's up and running.

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So we're going to explore the enable and disable command.

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And those reference the status of this service

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when the system reboots.

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If we look at again, really quick,

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we see it's active.

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Now, we're going to change this.

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We're going to disable this service.

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And so when it first starts up, it should be disabled.

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So it's going to reboot.

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Okay, let's check out the system control status.

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Okay, so we see it's now no longer running.

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But again, that's a key service that we need,

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so let's make sure we enable this,

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as well as starting this service.

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Okay.

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Looks like we're all good to go there.

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Well, that sums this lesson up.

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We went through how to use the system control,

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which is a utility of system D

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to monitor start, stop and change statuses

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of different processes and services

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that are running on a Linux system.

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And I'll see you in the next lesson.