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In this lesson, you will learn how to create custom service configuration.

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So in order to understand custom service configuration, you first need to understand unit file location

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and priority.

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Default units as provided from the packages are normally installed in userlib systemd

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system.

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There might be differences according to your distribution though.

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Custom units should be installed in etc systemd system.

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And there is a limited amount of auto-generated units which can be in the directory run systemd.

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Run systemd is the highest priority, then comes etc systemd system, and then comes the

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default unit.

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There can even be user-specific units, and if a user has a user-specific unit, it can

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be put in the .config/.systemd/.system directory in the user home directory.

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Now if you want to edit your units, systemd is providing the commands to do so.

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First you want to use systemctl cat to show current unit contents, and then you are going

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to use systemctl edit to edit the unit and create drop-in files in etc systemd system

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unit.d.

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There's also an old way that can be used to change unit configuration, and the old way

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is to copy the default unit file from userlib systemd system into etc systemd system, and

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you provide your edits in there.

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As etc systemd system has a higher priority, that one will win.

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And if during a packet update your unit file gets updated, it will be written to userlib

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systemd system, so your customizations will survive.

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But this is not recommended.

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It's the way how it was done in the beginning of systemd.

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The recommended way is to use systemctl edit.

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Let me show you what happens if you are using systemctl edit.

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So to start with, I'm going to use systemctl cat on sshd.service, because I happen to know

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that the sshd.service unit has an interesting option.

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And here we can see the unit file configuration in which the unit section is where you define

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your dependencies.

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Look, here we have an after, which is telling that this should happen after the network

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has been started.

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And we have some wants.

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The wants include information about other units that need to be started when this one

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is started.

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The most important one is service, where you have all the different unit properties.

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And I like this restart.

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Restart is on failure and restart sec is 42 seconds, is making sure that if anything bad

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is happening to this unit, it will be started again.

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So I'm going to copy that.

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Then we also have an install section.

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This install section is information that you need when you use systemctl enable.

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Because systemctl enable needs to create a link in the systemd target wants directory.

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And here you identify the systemd target wants directory.

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OK.

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I'm going to use systemctl edit httpd.service.

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And what do we get?

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Well, first, we are getting nano.

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It happens to be that I don't like nano.

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So I'm getting out of here and I want to fix it.

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Using export systemd editor is user bin vim.

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And now if I use my systemctl edit, the same thing is happening, but this time in vim editor.

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In the lower part of the screen, you can see that it is creating etc systemd system, httpd.service.d.

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And that is how it works.

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This is how it creates a drop-in file.

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This drop-in file will be a part of the configuration, and it will have the name override.conf.

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And anything that you put at the position where the cursor is right now will be included.

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Now you need to help systemd a little bit, and you need to identify the section.

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Well, I want my stuff to appear in the service section, and I copied it already.

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Restart is on failure and restart sec is 21 seconds.

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That sounds like an amazing feature.

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So I'm saving my changes.

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And as I'm happy with this, I'm also going to use echo, Ctrl-A to move my cursor to the

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start of the line, and then echo export.

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And I want to have that in d tilde slash dot bash rc.

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It will make it persistent.

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Good.

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Now I'm going to use systemctl cat, httpd.service.

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And in case you are wondering, don't we need to restart anything?

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Well, let's figure it out.

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Here systemctl cat is giving me the contents of userlib systemd system.

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Doesn't fit on one screen.

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If I use uppercase G to go all the way to the bottom, look at that.

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Here we have the drop-in file, etc systemd system, httpd.service.d.

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And if we use systemctl status on httpd, then what do we see?

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We see it considers this drop-in file as well.

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And that means that my httpd service is currently using the specific auto-restart option.

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So let's check it out.

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Let's use kill minus 9, 1, 4, 3, 3, 3, 5, to simulate a disaster that is happening on

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my process.

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Then let's use systemctl status.

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And systemctl status is giving me activating.

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So this is how you can add configuration to your units.

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And at the same time, this is how you can use this auto-restart feature, which is quite

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awesome.