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In this video, you'll learn about managing the INIT-RAMFS, also known as the INIT-RD.

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So the main purpose of the INIT-RAMFS is to provide kernel modules, which are required

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to mount the root file system. INIT-RAMFS or INIT-RD is generated automatically when

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you install your system. The installer detects all the hardware that is present, and it generates

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the INIT-RAMFS for you. And the INIT-RAMFS consists of a set of directories that are

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required to create it, and it is bundled into a CPIO archive. CPIO is an ancient way of

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making backups. Every now and then you will encounter it, and every now and then it's

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still used as a format. This CPIO archive is extracted at boot time. And if all modules

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that are required to mount the root file system are compiled in the kernel, booting can happen

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without INIT-RAMFS. But that is never the case. INIT-RAMFS can also offer additional

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functionality, which allows the system to boot from non-default storage, like LVM, encrypted

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root file system, or a network-based root file system. If ever you want to reconfigure

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your system later on to do something like that, you need to know how to rebuild your

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INIT-RAMFS. So how does that work? Well, on Red Hat family distributions, the DRAKUT utility

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has become the standard tool for building an INIT-RAMFS. And it can be configured with

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settings in etcdrakut.conf. And when you are running DRAKUT without configuration arguments,

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it will build an INIT-RAMFS based on current settings. So after adding new hardware, of

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which you want to have the drivers in your INIT-RAMFS, first make sure that the hardware

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drivers are present, and then run DRAKUT. On Ubuntu, you can use mkinitrd. And mkinitrd

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is the Ubuntu alternative for generating the INIT-RAMFS. Now there's a funny thing that

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we can do on Red Hat. On Red Hat, you can use the rd.breakboot argument to boot straight

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into the INIT-RAMFS. And that can be useful for troubleshooting. Let me show you. So to

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use this boot argument, you need to go to the group boot menu. Press E to open the editor

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interface. And from there, at the end of the line that loads Linux, you type rd.break.

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And then you use Ctrl-X to continue booting. So what is this doing? Well, this is entering

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the emergency mode. And kind of fun, we do need to pass the root password. So I'm going

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to enter the root password. And then I'm in the shell. And what is the shell? Well, if

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you type mount, then you can see on the top line that I have a rootfs on slash type rootfs.

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And that is my INIT-RAMFS. So when I type ls slash, the directories that I see are in

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the INIT-RAMFS. And this environment can be handy for troubleshooting. Now, this is

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the RAM file system that is normally processed while booting. The root file system is already

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on the sysroot directory, which is in slash. And here, your booting will continue once

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you have passed your options in the INIT-RAMFS. You can see that in the last line of output

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of the mount command, you can also see that this slash sysroot is read-only. You see the

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letters ro indicating it's read-only. So if ever you want to do something from this point

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of view, then you need mount minus o remount comma rw on slash sysroot. And that is giving

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access to all files on your ordinary operating system. And that's how you can boot into the

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INIT-RAMFS using rd.break on Red Hat. It's a Red Hat-specific option, so it won't work

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on Ubuntu, for instance.