Make everything old and install more oldest-possible-packages and start all services.

yum-make-everything-old.sh

#!/bin/bash

install_version() {
	# This would be: NetworkManager.x86_64         1:1.14.0-14.el8            rhel-8-baseos-rhui-rpms
	local -r version_entry="$1"
	# What yum operation do you want?
	local -r operation="$2" 

	echo "    Attempting to install version entry: $version_entry"

	# This would be: NetworkManager.x86_64
	local -r package_arch="$(echo $version_entry | awk -F" " '{print $1}')"
	# This would be: NetworkManager (we remove the .x86_64 or any architecture)
	local -r package="$(echo "$package_arch" | rev | cut -d'.' -f2- | rev)"

	# This would be: 1:1.14.0-14.el8
	local -r version_with_redhat_embellishment="$(echo $version_entry | awk -F" " '{print $2}')"
	# This would be: 1.14.0-14.el8
	local -r version=$(echo "$version_with_redhat_embellishment" | cut -d':' -f2-)

	# This should be: NetworkManager-1.14.0-14.el8
	local -r package_version="$package-$version"

	echo "      Normalized install package name: $package_version"
	yum $operation -y $package_version 1>/dev/null 2>/dev/null
	[ $? -ne 0 ] && echo "      FAIL!" && return 1

	echo "      SUCCESS!"
}

install_oldest_version() {
	local -r package="$1"
	# What operation is this? Install or downgrage?
	local -r operation="$2"

	echo "  ${operation}ing oldest version of package $package..."

	local -r output=$(yum --showduplicates list available $package 2>/dev/null)

	#Set the field separator to new line
	IFS=$'\n'

	local found_available_packages=""
	local oldest_package_line=""

	local line
	for line in $output; do
		if [ "$found_available_packages" == "true" ]; then
			install_version "$line" "$operation"
			[ $? -eq 0 ] && return 0
		elif [[ "$line" == *"Available Packages"* ]]; then
			found_available_packages="true"
		fi
	done

	# Nothing installed
	return 1
}

skip_package() {
	local -r package="$1"
	
	# skip authselect since it can prevent any logins, especially on EC2.
	if [[ "$package" == *"authselect"* ]]; then
		return 1
	elif [[ "$package" == *"pam"* ]]; then
		return 1
	fi
}

yum_downgrade_all() {
	echo "Downgrading all packages to oldest possible versions."
	echo "  Finding installed packages..."
	local -r installed=$(yum list installed | awk -F" " '{print $1}')

	echo "    Found $(echo $installed | wc -w) packages installed."

	echo ""
	echo "    For each package, attempting to downgrade to oldest possible version..."
	local something_changed=""
	local package
	for package in $installed; do
		# should this package be skipped for whatever reason?
		skip_package "$package"
		[ $? -ne 0 ] && echo "    Skipping package $package" && continue


		install_oldest_version "$package" "downgrade"
		[ $? -eq 0 ] && something_changed="true"

		# test ssh works
		ssh -i PolyverseDevelopmentKey.pem ec2-user@localhost "exit"
		[ $? -ne 0 ] && echo "SSH failed!!!" && exit 1 
	done

	if [[ "$something_changed" == "true" ]]; then
		return 0
	else
		return 1
	fi
}

yum_install_all() {
        echo "Installing all available packages to oldest possible versions."
        echo "  Finding available packages..."
        local -r available=$(yum list available | awk -F" " '{print $1}')

        echo "    Found $(echo $installed | wc -w) packages available."

	echo "    For each package, attempting to install oldest possible version..."
	local something_changed=""
	local package
        for package in $available; do
                # should this package be skipped for whatever reason?
                skip_package "$package"
                [ $? -ne 0 ] && echo "    Skipping package $package" && continue

                install_oldest_version "$package" "install"
		[ $? -eq 0 ] && something_changed="true"

		# test ssh works
		ssh -i PolyverseDevelopmentKey.pem ec2-user@localhost "exit"
		[ $? -ne 0 ] && echo "SSH failed!!!" && exit 1 
        done

	if [[ "$something_changed" == "true" ]]; then
		return 0
	else
		return 1
	fi
}


systemctl_start_all() {
	echo "Starting all possible services..."
	
    systemctl list-unit-files --type=service \
        | grep disabled \
        | awk -F" " '{print $1}' \
        | grep -v "initial-setup" \
        | grep -v "redboot-auto-reboot" \
        | grep -v "redboot-task-runner" \
        | grep -v "iptables" \
        | grep -v "ip6tables" \
        | grep -v "arptables" \
	| grep -v "inkscape" \
        | xargs -I % sh -c 'echo "Starting Service %" && systemctl start % && sleep 1'
}

echo "Making this system the oldest possible set of packages and maximum services."

yum_downgrade_all
[ $? -eq 0 ] && something_changed="true"

yum_install_all
[ $? -eq 0 ] && something_changed="true"

systemctl_start_all
[ $? -eq 0 ] && something_changed="true"