kernel_remove: init script to remove a specified kernel

This script basically cleans up all the possible paths that might be
populated from a `make modules_install` and `make install`. Given that
the kernel is removed, the grub entry is also removed with the help of
`grubby`.

This is an ad-hoc script created to quickly remove a kernel without much
fuss about it.

Author: thefossguy-ciq

README.md

@@ -80,3 +80,34 @@ This is the full script that end with the engineer ready to reboot the VM into t
 
 ### kernel_recompile_kabi.sh
 Will only recompile the kernel and check the KABI.
+
+### kernel_remove.sh
+This script is intended to clean up "development" kernels. By
+"development" kernels, the author means such a kernel that was built
+locally for testing if patch(es) for a CVE or customer request apply
+correctly and test them. Mainly, it means kernels installed using
+`make`, instead of as an RPM package.
+
+The script accepts **only one** `kernel release` (`uname -r`) to
+remove. Like so:
+```bash
+$ ./kernel_remove.sh 4.18.0-ciqlts8_6-83208b00c+
++ requested_kernel_to_remove=4.18.0-ciqlts8_6-83208b00c+
+++ dnf repoquery --latest-limit=1 --queryformat '%{version}-%{release}' kernel-core
++ latest_rpm_kernel=4.18.0-372.32.1.el8_6.86ciq_lts.12.1
+++ uname -r
++ current_kernel=4.18.0-372.32.1.el8_6.86ciq_lts.12.1.x86_64
++ '[' -z 4.18.0-ciqlts8_6-83208b00c+ ']'
++ '[' 4.18.0-ciqlts8_6-83208b00c+ == 4.18.0-372.32.1.el8_6.86ciq_lts.12.1 ']'
+++ uname -m
++ '[' 4.18.0-ciqlts8_6-83208b00c+ == 4.18.0-372.32.1.el8_6.86ciq_lts.12.1.x86_64 ']'
++ '[' 4.18.0-ciqlts8_6-83208b00c+ == 4.18.0-372.32.1.el8_6.86ciq_lts.12.1.x86_64 ']'
++ '[' -d /lib/modules/4.18.0-ciqlts8_6-83208b00c+ ']'
++ sudo rm -fr /lib/modules/4.18.0-ciqlts8_6-83208b00c+
++ '[' -d /boot/dtb-4.18.0-ciqlts8_6-83208b00c+ ']'
++ '[' -f /boot/config-4.18.0-ciqlts8_6-83208b00c+ ']'
++ '[' -f /boot/System-4.18.0-ciqlts8_6-83208b00c+ ']'
++ '[' -f /boot/vmlinuz-4.18.0-ciqlts8_6-83208b00c+ ']'
++ sudo rm -f /boot/vmlinuz-4.18.0-ciqlts8_6-83208b00c+
++ sudo grubby --remove-kernel=/boot/vmlinuz-4.18.0-ciqlts8_6-83208b00c+
+```

kernel_remove.sh

@@ -0,0 +1,30 @@
+#!/usr/bin/env bash
+set -xeuf -o pipefail
+
+requested_kernel_to_remove="${1:-}"
+latest_rpm_kernel="$(dnf repoquery --latest-limit=1 --queryformat '%{version}-%{release}' kernel-core 2>/dev/null)"
+current_kernel="$(uname -r)"
+
+if [ -z "${requested_kernel_to_remove}" ]; then
+    echo 'Specify the kernel version'
+    echo 'Look under /lib/modules/ for "correct" versions'
+    exit 1
+fi
+
+if [ "${requested_kernel_to_remove}" == "${latest_rpm_kernel}" ] || [ "${requested_kernel_to_remove}" == "${latest_rpm_kernel}.$(uname -m)" ]; then
+    echo 'ERROR: Will not remove the *latest kernel* installed as an RPM package'
+    exit 1
+elif [ "${requested_kernel_to_remove}" == "${current_kernel}" ]; then
+    echo 'ERROR: Will not remove the current kernel'
+    exit 1
+else
+    # The checks exist to prevent "no such [file|directory] found" "errors" on console
+    # Also helps with error management
+    [ -d "/lib/modules/${requested_kernel_to_remove}" ] && sudo rm -fr "/lib/modules/${requested_kernel_to_remove}"
+    [ -d "/boot/dtb-${requested_kernel_to_remove}" ] && sudo rm -fr "/boot/dtb-${requested_kernel_to_remove}"
+    [ -f "/boot/config-${requested_kernel_to_remove}" ] && sudo rm -f "/boot/config-${requested_kernel_to_remove}"
+    [ -f "/boot/System-${requested_kernel_to_remove}" ] && sudo rm -f "/boot/System-${requested_kernel_to_remove}"
+    [ -f "/boot/vmlinuz-${requested_kernel_to_remove}" ] && sudo rm -f "/boot/vmlinuz-${requested_kernel_to_remove}"
+    # If $requested_kernel_to_remove is current default kernel, grubby will make the next-in-line kernel default
+    sudo grubby --remove-kernel="/boot/vmlinuz-${requested_kernel_to_remove}"
+fi