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- Alright, well sometimes you
cannot boot into grip anymore.

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Then what can you do?

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You can use a rescue disk,

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and I know I'm on a fully
installed system here,

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but that is because I want to show you

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how to connect to the rescue disk

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from the virtualization software.

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This is one of the few
cases where I do think

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it's useful to know about
a virtualization software

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because you need to insert a disk, right?

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How are you inserting a
disk in virtualization?

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Well, typically by going to your devices,

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and by connecting your CD, DVD

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which in VMWare Fusion is
this option right here.

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And you need to look for something similar

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if you're also in virtualization.

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Next, we need to get
access to a boot prompt,

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and that can be a little bit challenging

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because while you see the boot logo

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in my virtualization environment
that'll be the VMware logo

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I need to press a key,
probably the escape key

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with the exact key depends
on your boot software.

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Might be escape, might be F12,

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might be F10, might be something else.

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I'm going for escape and I'm
going to show you right now.

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Let's restart.

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All right, so here we have the boot menu.

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I finally got there by pressing
escape at the right moment,

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but my VMware BIOS is
giving me a second or less.

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So you really need to be fast,

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and I'm selecting CD ROM drive.

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And with the CD ROM drive
connected, this is what I get.

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So this time we are not going
to install CentOS Stream 9,

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no, I'm going to select troubleshooting.

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No matter which
distribution you are using,

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on the installation disk, you
will always have an option

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to start a live system, or
a troubleshooting system.

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And if you're using Ubuntu,

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and you want to start a
live system from the DVD,

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that's okay as well.

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From the live system, you are
going to access your disk,

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and you can do your troubleshooting.

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Now I am not going for install,

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I am going for a rescue
CentOS Stream system.

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So at this point it is really
booting from an initramfs

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that is installed on
the installation disk.

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It's basically the same program

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as what you use to install Linux.

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Now what do we see?

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We see that the rescue environment

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will now attempt to find
the Linux installation.

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I don't wanna do that.

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I want to make it a little
bit harder for myself.

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I'm going to use option
three to skip to the shell,

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and yet it's not mounting
the system, that is right.

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I wanna do it myself because
I want to show you something

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that works in all cases.

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So here's my cell, a root shell.

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I'm using lsblk for list block
devices and what do we see?

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Well, we see sda1 and sda2.

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sda2 is the partition that
has my lvm, oh boy lvm.

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So lvs is what I wanna
do, and fortunately;

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lvs is showing me the logical volumes.

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So I have my root logical
volume that is visible.

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So how am I going to access it?

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mount /dev/cs, that's the volume group

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as we can see in the vg
column in the output of lvs,

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/root /mnt I just need to mount
it on a temporary directory,

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and oh that's not going
smoothly, I'm getting a message.

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"Special device dev/cs/root
does not exist."

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So we need vgs to inspect
the volume groups.

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And that is interesting,

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I do see the volume
group with the name cs.

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I do see the lv with the name root,

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but I don't see it as a device.

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So we need to further investigate.

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lv display is what I'm
going to do this time

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because I want to check
that it is available.

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And what do we see in lv status

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for both of them we see not available.

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Well if that is what you get,
you need to activate them.

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And what is that?

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vgchange, vgchange --help.

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This is one of these commands

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that most people don't use too often,

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and oh boy, too much help output.

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I'm just looking for what
again whilst this syntax.

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So the command that you
need is vgchange -a y,

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that is going to activate it.

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And now if I use lvdisplay again

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now I can see that my
lvstatus is available.

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That means that I can now
repeat my mount command.

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And there we go, in the mnt directory,

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I now have access to my operating system.

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Now next step in troubleshooting
will be "chroot .",

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which will make the current directory

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your new root directory,

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and from here you can do
whatever you wanna do.

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Well if you needed a rescue disk,

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then most likely you
need to use grub2 install

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because if you needed to rescue this,

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then your grub configuration was damaged.

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But hey, in order to install
grub to the boot loader,

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we do also need access
to the boot partition,

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and ls /boot is giving me nothing.

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Now, fortunately there is mount -a,

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and now can we use grub
to install on /dev/sda

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to reinstall the grip boot loader,

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and oh boy, I am getting,

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"error: cannot find a
device for /boot/grub2".

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The thing is that I now have access

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to my root file system,
and the boot partition,

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but my proc directory is still empty,

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and my dev directory is
still empty, that's not good.

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The dev directory is the
first thing that I need,

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and I am going to use
exit to take care of it

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because in the rescue disk,
we do have a dev directory.

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This dev directory contains devices,

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and this directory is
dynamically generated

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while you are booting.

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And I'm going to use mount
-o bind /dev /mnt/dev,

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and that makes that within the /mnt/dev,

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I now have my devices, so where am I?

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I'm still in the mnt directory.

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That's good, so I can go get
back in my root environment.

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Next I need mount proc proc proc.

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Believe it or not, we want
to mount the proc file system

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on the proc directory with
the option -t proc and okay,

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I admit /proc makes it a little
bit easier to understand,

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but it's cool to type
mount proc proc proc,

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and actually it makes sense.

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Now we have proc, we have
dev, and that means that

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I should be able to run my
grub2 install at this point.

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Okay, there we go, grub2,
telling me no error report it.

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Please ignore the the
messages that you see.

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You should be good and you
should be able to reboot

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back into a normal
operating system right now.

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Oops, get out of the to root environment,

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then you can reboot
and you should be good.

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Oh no, we messed it up.

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Well that means that we need to

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try something else to
repair it, let's do it.

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I just restarted and I
see grub, great then,

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and I don't see anything else
anymore, that's not good.

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So what can we do from here?

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Well we do have a grub boot menu,

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and in the grub boot menu,
we can try to troubleshoot.

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Now this grub boot menu is
a very rich environment.

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The environment is so rich
that I don't like it very much.

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It's confusing and if I
get problems like this,

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then I am getting back
to my rescue system.

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So let's get back to the rescue system,

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and see if we can get it going again.

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So back to the CD-ROM Drive.

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And on this CentOS system,
there's another option

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that's hidden in troubleshooting,
boot from local drive.

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This boot from local drive is
making it a little bit easier,

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and oh, not bringing me anywhere.

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Okay then I need to go hardcore.

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And back to the CD-ROM Drive,

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and troubleshooting once more.

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So I definitely need my rescue
with CentOS Stream system

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because with this grub boot
prompt, we don't get very far.

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So this time, I am
going to use this option

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where the rescue system is
trying to load everything.

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So that is option number one.

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That's giving me access to a
completely functional system,

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and I like the idea of having

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a completely functional system.

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So it's telling me chroot
/mnt/sysroot, sounds good.

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So chroot /mnt/sysroot,

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and there we have all these directories.

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Now I need to do my checks, ls /boot.

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We do have a boot.

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ls /dev, we do have a dev,

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ls /proc, that's not ls.

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ls /proc, we do have a proc.

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And last, ls /sys, we also do
have a sys, that's all good.

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So now I'm going to try to run my grub

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to install on /dev/sda, again,

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because that definitely
filled in the first attempt.

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So here we go, I don't
have my errors anymore.

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So that is looking all good.

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Using exits to get out of the true deal

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using a reboot to reboot.

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And then what do I get?

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I get access to my CentOS Stream, again,

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and that means that this
problem has been fixed.