In this video, you'll learn how to use GRUB2 Runtime Parameters.
These GRUB2 Runtime Parameters allow you to specify options while you are booting.
You want to do so?
From the GRUB2 boot menu, press E to edit Runtime Boot Options to the end of the line
that starts with Linux.
That influences how your kernel is starting.
Now there is one challenge, and the challenge is that you don't see the GRUB2 boot menu
by default.
There are two options to see it.
Either you press Escape at the appropriate moment at the start of your boot procedure.
That's not always easy.
And that is why you might like the second option.
If you reset your machine while it is booting, that will be detected.
And the next time you boot, the GRUB2 boot menu shows automatically.
That might be easier.
And next, you can pass options like systemd.unit is emergency.target or systemd.unit is rescue.target.
I will tell you more about these options and what you can do with these options in lesson
22, which is about troubleshooting.
You can press C to enter the GRUB2 command mode.
The GRUB2 command mode is an alternative to pressing E. Pressing E is easy.
I would advise you only use E, and don't go into GRUB2 command mode.
In the GRUB2 command mode, you can type help for an overview of available options, but
it really requires some expertise and some practice before you are getting used to it.
Most people are getting completely lost in the GRUB2 command mode.
So if you ever go there, remember to command exit to get out and get back into the boot
menu option.
Let me show you what it looks like.
So here I'm in my running machine, and I'm going to use a reboot.
And let's try and see if I can press escape at the right moment.
And oh, I was too late.
So what am I going to do?
Well, I'm just going to restart my virtual machine while it is booting.
And here we have the result.
This is the GRUB2 boot menu.
So in the GRUB2 boot menu, you see three options.
It's only the first option that you really should be interested in.
That's a default kernel that you are starting.
The second option is a rescue kernel.
That's a kernel with minimal options.
And in case you are having driver issues, this might be convenient.
For RHCSA, it's unlikely that you are going to need it.
The UEFI firmware settings is bringing you to the UEFI firmware.
That's like your BIOS menu where you can change system properties.
Very interesting, but not for RHCSA.
Now let me first show you where you don't want to go to.
That's here.
GRUB2 command mode.
Press escape to get out of there.
If you get there by accident, you want to use E for edit.
And there we have the line that starts with Linux.
And this line that starts with Linux is loading your Linux kernel.
Look, it is looking at $root.
$root is where it finds your boot file system.
And then we have vmlinux and vmlinux.
That's your kernel.
The kernel specifies the root file system.
That's interesting.
So the root file system is already initiated from GRUB.
And that is obvious, because how would you
find the root file system if you need
a file on the root file system, like etcfstab, to find it?
Then you can see that it is mounted initially
as RO, read only.
It's doing something for the crash kernel.
That's interesting, but not for RHCSA.
And then we have RHDB and QUIET.
RHDB and QUIET, that is Red Hat Graphical Boot and QUIET.
By default, all messages will be hidden.
I don't want these messages to be hidden,
so I'm going to remove these options.
Of course, systemdunit is emergency target.
It's an interesting one as well, but it's
problematic if your root user doesn't have a password.
So we will talk about that in lesson 22.
For now, I'm going to change the way
my system is booting by removing these two options.
The last line in what we see here is running the initrd.
initrd is the initial RAM drive.
That's a RAM file system that contains
drivers that are needed for booting your system.
Normally, you don't change anything here.
So once you are happy with it, you
use Control-X or F10 to boot.
So let me use Control-X, and then we
can see that nothing is hidden anymore,
and we see nice boot messages.
So in the end, the GDM is loaded,
and we can log in again and access the shell.
That's it.