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boom-kernel-parms.adoc

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Boom (with kernel parameters)

Table of Contents

1. Overview

BOOM is a boot manager for Linux systems that support the 'BootLoader Specification' for boot entry configuration (ie: RHEL8 with GRUB2). It simplifies the creation of new or modified boot entries: for example, to boot snapshot images of the system created using LVM.

BOOM does not modify the existing boot loader configuration, and only inserts additional entries. The existing configuration is maintained, and any distribution integration, such as kernel installation and update scripts, continue to function as before.

BOOM also has a simple command-line interface (CLI) and API.

The object of this exercise is quite simple. We care going to create an alternative boot entry which will load the same kernel with a few additional detectable parameters.

2. Getting Started

For these exercises, you will be using the host node3 as user root.

From host bastion, ssh to node3.

ssh node3

Use sudo to elevate your priviledges.

sudo -i

Verify that you are on the right host for these exercises.

workshop-boom-checkhost.sh

You are now ready to proceed with these exercises.

3. Installation

The following set of instructions will install Boom.

yum install -y boom-boot

That was easy!

4. Create Profile

Creating a new boot entry begins with a boom profile.

workshop-boom-mkprofile.sh
Determining root device...
Creating BOOM profile with tweaks (UUID disk)...

Created profile with os_id f44fb52:
  OS ID: "f44fb528ff8360ad67e2fe0274750b838da0bd6a",
  Name: "Red Hat Enterprise Linux", Short name: "rhel",
  Version: "8.1 (Ootpa)", Version ID: "8.1",
  UTS release pattern: "el8",
  Kernel pattern: "/boot/vmlinuz-%{version}", Initramfs pattern: "/boot/initramfs-%{version}.img",
  Root options (LVM2): "rd.lvm.lv=%{lvm_root_lv}",
  Root options (BTRFS): "rootflags=%{btrfs_subvolume}",
  Options: "root=%{root_device} ro %{root_opts}",
  Title: "%{os_name} %{os_version_id} (%{version})"
ℹ️
 In this example, the root disk is identified by a UUID. As a result, boom will incorrectly identify the paths to the kernel and initiramfs when creating the grub entry. To avoid this current problem (bug?), we tweak the boom profile to add /boot to the paths.
ℹ️

Native command(s) to make boom profile

boom profile create --from-host --uname-pattern el8 --kernel-pattern="/boot/vmlinuz-%{version}" --initramfs-pattern="/boot/initramfs-%{version}.img"

Verify that the boom profile was created by the previous command.

boom profile list
OsID    Name                     OsVersion
f44fb52 Red Hat Enterprise Linux 8.1 (Ootpa)

5. Create GRUB Entry

Now to create a boot entry for grub which utilizes the same boot environment as the current system, but with a few added kernel parameters.

5.1. Determine Root Device

First we need to determine the root device. We can do this by inspecting the current kernel’s boot commandline.

cat /proc/cmdline
BOOT_IMAGE=(hd0,msdos1)/boot/vmlinuz-4.18.0-147.el8.x86_64 *root=UUID=f7614c41-2835-4125-bb13-50772dc2f30c* ro console=ttyS0 cons
ole=ttyS0,115200n8 no_timer_check net.ifnames=0 crashkernel=auto

We can futher isolate the undesired parameters with a simple grep.

grep -o '\broot=[^ ]*' /proc/cmdline
root=UUID=f7614c41-2835-4125-bb13-50772dc2f30c
ℹ️
 In this scenario, the boot device is listed by a UUID. Depending on the lab environment, you could see a logical volume name or a physcial device path.

Now we need to get to the actual device (or lvm) path. Although this logic is not complicated, it’s not really the focus of this exercise, so you’ve been provided another workshop-script.

workshop-boom-mkentry.sh
Determining root device...
UUID reduction if necessary...
Creating GRUB2 entry...

DEBUG: boom create --title 'RHEL 8 Workshop' --root-device /dev/vda1

WARNING - Boom grub2 integration is disabled in '/boot/../etc/default/boom'
Created entry with boot_id : 40d2351
  title RHEL 8 Workshop
  machine-id 4739d97a827c41e2a71d911afb7941af
  version 4.18.0-147.el8.x86_64
  linux /vmlinuz-4.18.0-147.el8.x86_64
  initrd /initramfs-4.18.0-147.el8.x86_64.img
  options root=/dev/vda1 ro
ℹ️

Native command(s) to make grub entry

# For LVM base root
boom create --title "RHEL 8 Workshop" --rootlv <VG>/<LV>

# For block device base root
boom create --title "RHEL 8 Workshop" --root-device <ROOT-DEVICE>

Take a look at currently configured boom-boot entries.

boom entry list
BootID  Version                  Name                     RootDevice
40d2351 4.18.0-147.el8.x86_64    Red Hat Enterprise Linux /dev/vda1

Show details about our boom-boot entry.

boom entry show 40d2351
Boot Entry (boot_id=40d2351)
  title Alt Kernel Parms
  machine-id 298b11e40a1e46a5a1ce834b845cc51b
  version 4.18.0-147.el8.x86_64
  linux /vmlinuz-4.18.0-147.el8.x86_64
  initrd /initramfs-4.18.0-147.el8.x86_64.img
  options root=/dev/vda1 ro

6. Delete Grub Entry

boom entry delete 40d2351

7. Create Grub Entry with Custom Options

workshop-boom-mkentry-custom.sh
Determining root device...
UUID reduction if necessary...
Creating GRUB2 entry...

DEBUG: boom create --title 'RHEL 8 Workshop' --root-device /dev/vda1 -a custom_value=true

WARNING - Boom grub2 integration is disabled in '/boot/../etc/default/boom'
Created entry with boot_id a07736e:
  title RHEL 8 Workshop
  machine-id 4739d97a827c41e2a71d911afb7941af
  version 4.18.0-147.el8.x86_64
  linux /vmlinuz-4.18.0-147.el8.x86_64
  initrd /initramfs-4.18.0-147.el8.x86_64.img
  options root=/dev/vda1 ro custom_value=true

8. Reboot to Alternate Entry

⚠️
 If possible, bring up the virtual machine console for node3 before proceeding.

Before reboot, there are 2 options to invoke the right loader at restart: . enter the GRUB menu and select at boot time . use grub-set-default to pre-select which one to load by default

We are going to opt for pre-select since it’s easier to script. Use the following workshop to inspect the currently configured GRUB menu options.

workshop-boom-grublist.sh
     0  title="Red Hat Enterprise Linux (4.18.0-147.el8.x86_64) 8.1 (Ootpa)"
     1  title="RHEL 8 Workshop"

Let us now inspect the GRUB configuration for RHEL 8 Workshop, which in this example is entry #1.

grubby --info=1
index=2
kernel="/boot/vmlinuz-4.18.0-147.el8.x86_64"
args="ro custom_value=true"
root="/dev/vda1"
initrd="/boot/initramfs-4.18.0-147.el8.x86_64.img"
title="RHEL 8 Workshop"
id="44d81e936d7e445797933e8cbc199cea-b8f0549-4.18.0-147.el8.x86_64"
⚠️
 DO NOT PROCEED TO REBOOT unless both kernel= and initrd= include the path /boot/<filename>.

We want to reboot to our "RHEL 8 Workshop", so again in this example the entry is #1.

grub2-set-default 1

Verify that the parameters stuck. Notice that "saved_entry=1", that’s what we want.

grub2-editenv list
saved_entry=1
kernelopts=root=/dev/mapper/rhel-root_snapshot ro crashkernel=auto resume=/dev/mapper/rhel-swap rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap rhgb quiet
boot_success=0

We will now reset our host and boot with the alternate kernel arguments.

reboot

8.1. Confirm Previous State of Host

Once the host is back online, ssh to back to node3 and verify that the alternate kernel parameters are active.

cat /proc/cmdline
BOOT_IMAGE=(hd0,msdos1)/vmlinuz-4.18.0-147.el8.x86_64 root=/dev/vg_rhel/root ro rd.lvm.lv=vg_rhel/root *custom_value=true*

Confirm that the custom key-value is now part of the kernel boot options.

Wahoo! You are done. If you have any questions, please ask.