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- Let's talk about persistent naming.

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Now, block device names
are subject to change.

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I'll show you in a bit.

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And because block devices
are subject to change,

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using a solution for persistent
naming is recommended.

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Because you know what's
happening if your sdb7

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is suddenly sdb6.

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Well if you reboot,
you'll get emergency mode.

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The solution, most common
solution, is the UUID,

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the Universal Unique ID.

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This is assigned to all block devices

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that have some type of file system on it.

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As an alternative,
administrators can manually

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assign labels for persistent naming.

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You can use the blkid
utility to get an overview

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of currently assigned UUIDs or labels.

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If you want to manually set the label,

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you can use tune2fs minus L

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for ext4,

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or xfs admin

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minus L for xfs.

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Let's go check it out.

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Alright, so I need to
prepare my demo a little bit.

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Mkdir slash xfs

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slash ext4

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minus minus mode

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700.

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You can note that this option even exists.

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Look, ls minus ld on xfs

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and ext4 has created a directly

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in a set of permission mode as all.

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Not that it's needed for
this demo, but I thought,

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let me show you something cool.

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Next I'm going to use mkfs dot ext4

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on dev sdb5

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and I'm going to use mkfs dot xfs on dev

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sdb6.

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Obviously we need to
put it in etc fstab to

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automatically mount it.

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So vim on etc fstab

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where dev sdb5 is mounted on slash ext4.

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File system type is ext4.

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And we use defaults,

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zero zero.

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And dev sdb6 is mounted on slash xfs.

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File system type is xfs
and defaults and zero zero.

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I choose mount minus a
and everything is mounted.

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Lsblk is still the easiest way to verify,

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and there you can see
that these partitions

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are mounted correctly.

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So let me also create a
file on both directories.

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So on ext4,

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I'm creating extfile

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and on xfs, I'm creating xfsfile.

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That makes it easier to
identify the mount points

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once I'm done with this
demo, because here it comes.

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Now, what is going to happen?

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Well I decided that I want to remove sdb5.

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Let me do that clearly,

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you mount dev sdb5 to disconnect it.

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Then back to etcfstab.

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In an fstab,

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I'm going to comment out this line, sdb5.

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Can always remove it later, right?

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And then, I'm going to fdisk dev sdb,

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because that's what I want.

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I want to delete the partition.

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Ignore the warning.

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This warning is for people

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that don't know what they're doing.

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We know what we are doing, don't we?

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So I'm using D for delete.

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5 for Partition number five.

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W for write, and uh oh,

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it's telling me kernel
still uses all partitions.

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New table will be used at next reboot.

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So I'm going to reboot.

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So here we have the boot
procedure and you can already see

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that it's getting stuck
on mounting something.

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It is mounted slash boot.

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It is mounted slash my data.

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And I don't see anything else anymore.

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What is going on?

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Well, I can tell you what is going on.

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We used sdb5 and sdb6.

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These are logical partitions.

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Logical partitions get
a device, device fail.

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But these device fails

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are generated at the moment of booting.

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And the first logical
partition will get sdb5,

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the second logical partition
will get sdb6, and so on.

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Now what is happening, if you delete sdb5

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like we've just done, and you reboot

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well then the partition previously known

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as sdb6 will now have become sdb5.

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And that is why we see this error message.

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Start job is running for dev sdb6.

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That's not going to work.

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The point I'm making here is that due

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to external circumstances,
you may find that device names

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on Linux are changing.

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And that is why you want to use

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either UUID

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or a label

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and that's what I'm going to show you

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once we are in the emergency mode.

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So the password for the
emergency mode, here we go.

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And I'm using blkid, block id,

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which allows you to see the labels,

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and let me filter it out.

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You can already see sdb5. We
don't have an sdb6 anymore.

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It's the sdb5 that we need.

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So I'm going to use blkid pipe grep sdb5.

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Let me put it on top of the
screen and there we can see

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in the second column we
have this, this UUID.

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I'm going to mount it by UUID.

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So let me do an

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awk print

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dollar two,

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which is the UUID.

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And now let me use a double grade then

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to append to etc fstab

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I mean, I'm in command line
mode, I can't copy paste here.

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So I need a smart
solution to get this UUID,

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which is pretty difficult
to handle, in etc fstab.

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Do mind. The double grade
then, you know that's append.

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If you use a single
grade, then you don't have

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an etc fstab anymore, and
that's pretty critical.

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Now I can go to my etc fstab.

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And in my etc fstab, I
can comment out Dev sdb6

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and replace dev sdb6 with the string

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that is now on the last line.

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So we are going to mount on slash xfs.

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The file system type is xfs.

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Then we get our defaults
and our zero and zero

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And that should be doing it.

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So mount minus a if you want,

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just to verify

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and control + D to quit
the troubleshooting shell.

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And that's how we have used the UUID.

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So let me log in, so that
I can also show you labels.

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(computer keys clicking)

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So once again blkid is showing sdb5.

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There we go. Oops, this is the one.

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That's what we are using right now.

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Lsblk, lsblk is showing
that sdb5 is mounted on xfs.

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Lsblk does not include
the blkid information.

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Now instead of using UUID,
you can also use labels.

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That's pretty easy.

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Xfs underscore admin

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minus uppercase L myfs.

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Oops. Am I missing something?

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Yes, I absolutely am missing something.

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I need to specify the device name as well.

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So xfs admin minus L myfs on dev sdb5.

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And there we go, xfs admin is telling me

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dude, you can't change it
on the mounted file system.

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So I need to umount my dev sdb5.

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And now I can set it.

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And then as an alternative,
I can edit etc fstab.

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And in etc fstab instead
of using this UUID,

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I can use the label.

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So label is myfs.

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We mount it on slash xfs.

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File system type is xfs.

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Defaults and zero zero.

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As I just unmounted it.

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I can now use mount minus a.

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Mount minus a is not
giving any complaints,

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so it should be happy.

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The quick fix, well ls on xfs,

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you can see the xfs file
that I created before.

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So all of this is working as expected.