Boot Management (boom)

Skill Level: Advanced

1. Overview

Boom is a boot manager for Linux systems that support the 'BootLoader Specification' (BLS).

In short, boom:

simplifies creation of new or modified boot entries
includes a set of Python libraries and a command line tool
does not modify the existing boot loader configuration
only inserts additional entries

The objectives of this exercise are quite simple:

familiarize yourself with the basics of creating and mangaging boot entries
create a customized alternative boot entry to load a detectable kernel parameter

2. Getting Started

For these exercises, you will be using the host node3 as user root. However, due to the unique circumstances of this exercise, we need to ensure the host is running on its latest kernel with all updates applied and system reboot. Thus we being by rebooting node3.

ssh node3 sudo reboot

Now, give the host a few seconds to reboot and then let’s ssh to node3 from host bastion.

ssh node3

Use sudo to elevate your privileges.

[[ "$UID" == 0 ]] || 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. Core Concepts

The Boom system uses a concept of "profiles" and "entries" to allow templated configurations to be cloned and modified. This minimizes the need for the user to input complex boot parameters manually for each iteration of the configuration. These configurations are known as Boot Loader Specification (BLS) files.

To confirm that grub is configured with BLS enabled, run the following.

grep BLSCFG /etc/default/grub

GRUB_ENABLE_BLSCFG=true

So now we begin with the management of boom (BLS) profiles.

3.1. Profile

3.1.1. List / Show

Just for reference, let’s take a look at this system’s existing profiles. There could be many, or in some cases none.

boom profile list

OsID    Name                            OsVersion

For a more detailed view, you can use the profile show sub-command.

boom profile show

3.1.2. Create

Creating a profile is handled by a simple command. However, determining all of the various parameters can be challeging and is outside the scope of this lab. Thus we have prepared a simple script to do the hard work.

workshop-boom-mkprofile.sh

Creating adjusted BOOM profile (prefixing /boot to bootpath)...

Created profile with os_id 2947e1a:
  OS ID: "2947e1a899af7d2129944dce8d3c98031fa3a6da",
  Name: "Red Hat Enterprise Linux", Short name: "rhel",
  Version: "10.0 (Coughlan)", Version ID: "10.0",
  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} console=tty0 console=ttyS0,115200n8 no_timer_check crashkernel=2G-64G:256M,64G-:512M",
  Title: "%{os_name} %{os_version_id} (%{version})",
  Optional keys: "grub_users grub_arg grub_class id", UTS release pattern: "el10"

3.1.3. Inspect

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

boom profile list --osversion "10.0 (Coughlan)"

OsID    Name                     OsVersion
2947e1a Red Hat Enterprise Linux 10.0 (Coughlan)

And for a more detailed view:

boom profile show --osversion "10.0 (Coughlan)"

OS Profile (os_id=2947e1a)
  OS ID: "2947e1a899af7d2129944dce8d3c98031fa3a6da",
  Name: "Red Hat Enterprise Linux", Short name: "rhel",
  Version: "10.0 (Coughlan)", Version ID: "10.0",
  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} console=tty0 console=ttyS0,115200n8 no_timer_check crashkernel=2G-64G:256M,64G-:512M",
  Title: "%{os_name} %{os_version_id} (%{version})",
  Optional keys: "grub_users grub_arg grub_class id", UTS release pattern: "el10"

3.2. Boot Entry

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

3.2.1. List / Show

Before we do any work, let’s take a quick look at what exists already.

boom entry list

BootID  Version                      Name                     RootDevice
feb94ba 6.12.0-55.9.1.el10_0.x86_64  Red Hat Enterprise Linux UUID=15507695-22bb-4c65-94e6-a438e095983f
07574e0 6.12.0-55.11.1.el10_0.x86_64 Red Hat Enterprise Linux UUID=15507695-22bb-4c65-94e6-a438e095983f

And for a more detailed view

boom entry show

Boot Entry (boot_id=feb94ba)
  title Red Hat Enterprise Linux (6.12.0-55.9.1.el10_0.x86_64) 10.0 (Coughlan)
  version 6.12.0-55.9.1.el10_0.x86_64
  linux /boot/vmlinuz-6.12.0-55.9.1.el10_0.x86_64
  initrd /boot/initramfs-6.12.0-55.9.1.el10_0.x86_64.img $tuned_initrd
  options root=UUID=15507695-22bb-4c65-94e6-a438e095983f console=tty0 console=ttyS0,115200n8 no_timer_check crashkernel=2G-64G:256M,64G-:512M $tuned_params
  grub_users $grub_users
  grub_arg --unrestricted
  grub_class rhel

Boot Entry (boot_id=07574e0)
  title Red Hat Enterprise Linux (6.12.0-55.11.1.el10_0.x86_64) 10.0 (Coughlan)
  version 6.12.0-55.11.1.el10_0.x86_64
  linux /boot/vmlinuz-6.12.0-55.11.1.el10_0.x86_64
  initrd /boot/initramfs-6.12.0-55.11.1.el10_0.x86_64.img $tuned_initrd
  options root=UUID=15507695-22bb-4c65-94e6-a438e095983f console=tty0 console=ttyS0,115200n8 no_timer_check crashkernel=2G-64G:256M,64G-:512M $tuned_params
  grub_users $grub_users
  grub_arg --unrestricted
  grub_class rhel

3.2.2. Create

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,gpt3)/boot/vmlinuz-6.12.0-55.9.1.el10_0.x86_64 root=UUID=15507695-22bb-4c65-94e6-a438e095983f console=tty0 console=ttyS0,115200n8 no_timer_check crashkernel=2G-64G:256M,64G-:512M

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

grep -o '\broot=[^ ]*' /proc/cmdline

root=UUID=15507695-22bb-4c65-94e6-a438e095983f

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 10 Workshop' --root-device /dev/vda3

Created entry with boot_id 4f9e987:
  title RHEL 10 Workshop
  machine-id e3be83f0851e5559a36599c4d6d4d6cf
  version 6.12.0-55.9.1.el10_0.x86_64
  linux /vmlinuz-6.12.0-55.9.1.el10_0.x86_64
  initrd /initramfs-6.12.0-55.9.1.el10_0.x86_64.img
  options root=/dev/vda3 ro console=tty0 console=ttyS0,115200n8 no_timer_check crashkernel=2G-64G:256M,64G-:512M
  grub_users $grub_users
  grub_arg --unrestricted
  grub_class kernel

3.2.3. Inspect

Take a look at currently configured boom-boot entries.

boom entry list

BootID  Version                      Name                     RootDevice
feb94ba 6.12.0-55.9.1.el10_0.x86_64  Red Hat Enterprise Linux UUID=15507695-22bb-4c65-94e6-a438e095983f
07574e0 6.12.0-55.11.1.el10_0.x86_64 Red Hat Enterprise Linux UUID=15507695-22bb-4c65-94e6-a438e095983f
5895dcc 6.12.0-55.11.1.el10_0.x86_64 Red Hat Enterprise Linux /dev/vda3

Show details about our boom-boot entry.

export BOOM_BOOTID=$(boom entry list --title "RHEL 10 Workshop" -o bootid,title | grep -m 1 Workshop | awk '{print $1}')
boom entry show $BOOM_BOOTID

boom entry show $BOOM_BOOTID
Boot Entry (boot_id=5895dcc)
  title RHEL 10 Workshop
  machine-id 844418c5c475527cb6a87daa00873089
  version 6.12.0-55.11.1.el10_0.x86_64
  linux /boot/vmlinuz-6.12.0-55.11.1.el10_0.x86_64
  initrd /boot/initramfs-6.12.0-55.11.1.el10_0.x86_64.img
  options root=/dev/vda3 ro console=tty0 console=ttyS0,115200n8 no_timer_check crashkernel=2G-64G:256M,64G-:512M
  grub_users $grub_users
  grub_arg --unrestricted
  grub_class kernel

3.2.4. Delete

In order to delete a boot entry, you need to identify the BOOTID and then use the 'delete' option.

export BOOM_BOOTID=$(boom entry list --title "RHEL 10 Workshop" -o bootid,title | grep -m 1 Workshop | awk '{print $1}')
boom entry delete $BOOM_BOOTID

Deleted 1 entry

4. Exercise: Custom Kernel Options

4.1. Profile

The profile we will use was created during the Core Concepts exercise above. Let’s take a look at the details to confirm everthing is in order.

boom profile show --osversion "10.0 (Coughlan)"

OS Profile (os_id=2947e1a)
  OS ID: "2947e1a899af7d2129944dce8d3c98031fa3a6da",
  Name: "Red Hat Enterprise Linux", Short name: "rhel",
  Version: "10.0 (Coughlan)", Version ID: "10.0",
  Kernel pattern: "/vmlinuz-%{version}", Initramfs pattern: "/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} console=tty0 console=ttyS0,115200n8 no_timer_check crashkernel=2G-64G:256M,64G-:512M",
  Title: "%{os_name} %{os_version_id} (%{version})",
  Optional keys: "grub_users grub_arg grub_class id", UTS release pattern: "el10"

4.2. Boot Entry

Again, to avoid some of the complexities considered outside the scope of this lab we will run a prepared script to configure the boot entry.

workshop-boom-mkentry-custom.sh

Determining root device...
UUID reduction if necessary...
Creating GRUB2 entry...

DEBUG: boom create --title 'RHEL 10 Workshop' --root-device /dev/vda3 -a custom_value=true

Created entry with boot_id 742eafd:
  title RHEL 10 Workshop
  machine-id e3be83f0851e5559a36599c4d6d4d6cf
  version 6.12.0-55.9.1.el10_0.x86_64
  linux /vmlinuz-6.12.0-55.9.1.el10_0.x86_64
  initrd /initramfs-6.12.0-55.9.1.el10_0.x86_64.img
  options root=/dev/vda3 ro console=tty0 console=ttyS0,115200n8 no_timer_check crashkernel=2G-64G:256M,64G-:512M custom_value=true
  grub_users $grub_users
  grub_arg --unrestricted
  grub_class kernel

Notice in the script output that we appended a key-value parameter custom_value=true to the options line.

4.3. GRUB: Set Default 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 at startup and select at boot time
use grubby --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 script to inspect the currently-configured GRUB menu options.

workshop-boom-grublist.sh

     0  title="Red Hat Enterprise Linux (6.12.0-55.9.1.el10_0.x86_64) 10.0 (Coughlan)"
     1  title="Red Hat Enterprise Linux (6.12.0-55.11.1.el10_0.x86_64) 10.0 (Coughlan)"
     2  title="RHEL 10 Workshop"

Let us now inspect the GRUB configuration for RHEL 10 Workshop. The following complicated command figures out the index on your system.

grubby --info=$(workshop-boom-grublist.sh | grep -m1 "Workshop" | awk '{print $1}')

index=2
kernel="/boot/vmlinuz-6.12.0-55.11.1.el10_0.x86_64"
args="ro console=tty0 console=ttyS0,115200n8 no_timer_check crashkernel=2G-64G:256M,64G-:512M custom_value=true"
root="/dev/vda3"
initrd="/boot/initramfs-6.12.0-55.11.1.el10_0.x86_64.img"
title="RHEL 10 Workshop"
id="844418c5c475527cb6a87daa00873089-4cb687d-6.12.0-55.11.1.el10_0.x86_64"

DO NOT PROCEED unless both kernel= and initrd= include the path /boot/<filename>. This is neccessary if /boot is not on a dedicated partition/mount. In the majority of our workshop deployments, /boot is part of the root '/' filesystem. If you have questions, ask your instructor.

We want to reboot to our "RHEL 10 Workshop", so we need to isolate and use the grub boot "index" from above output.

eval $(grubby --info=$(workshop-boom-grublist.sh | grep -m1 "Workshop" | awk '{print $1}')| grep index)
grubby --set-default=$index

4.4. Inspect

Verify that the parameters stuck.

grub2-editenv list

saved_entry=<id-from-above-output>
boot_success=1
boot_indeterminate=0

And you can further verify the default boot option as follows.

grubby --default-title

RHEL 10 Workshop

4.5. Reboot

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

reboot

4.6. Validate

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

ssh node3

cat /proc/cmdline

BOOT_IMAGE=(hd0,gpt3)/boot/vmlinuz-6.12.0-55.25.1.el10_0.x86_64 root=/dev/vda3 ro console=tty0 console=ttyS0,115200n8 no_timer_check crashkernel=2G-64G:256M,64G-:512M custom_value=true

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

5. Conclusion

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

Time to finish this unit and return the shell to its home position.

workshop-finish-exercise.sh