Downgrade all packages to the latest available version with yum

downgrade-to-latest.sh

#!/usr/bin/env bash

set -euo pipefail
IFS=$'\n\t'

export LANC=C LC_ALL=C
readonly RE_EVRA="^([[:digit:]]+):(.+)-([^-]+)\.([^.-]+)$"
readonly RE_UNSUPPORTED='\(systemd\|yum\|selinux-policy\|dbus\|kernel\)'
readonly USAGE="$(basename "${BASH_SOURCE[0]}") [-hynk] [-f FILE]

Be warned! This script is dangerous and shouldn't be used on a production system.
Make sure to have a system backup at hand.

Tested on RHEL 7 only!!

Downgrade all installed packages to the latest available version.
The purpose of this script is to enable for normal package installations after
a switch to different RPM repositories with older packages available.

To actually perform the downgrade, -y option must be given.

Options:
  -h       Print this message and exit.
  -n       Dry run. Only print packages to downgrade.
  -y       Assume yes. Do the downgrade without any confirmation.
  -k       Keep the temporary directory with the list of packages
           to downgrade that can be used next time.
  -s       Safe. Skip critical packages. Critical packages are those
           that yum refuses to downgrade by default since their
           downgrade is not supported (yum, kernel, dbus, etc.).
  -f FILE  Path to the file with the list of packages to downgrade
           produced by this script. Can be used for subsequent
           runs once the list of packages is generated and kept
           with -k.
"

dry_run=0
assume_yes=0
keep_files=0
to_downgrade=""
safe=0

while getopts 'hnykf:s' opt; do
    case "${opt}" in
        h) echo "${USAGE}"; exit 0; ;;
        y) assume_yes=1; ;;
        n) dry_run=1; ;;
        k) keep_files=1; ;;
        f) to_downgrade="${OPTARG}"; ;;
        s) safe=1; ;;
        *)
            echo "Unknown option '$opt'! See help!" >&2
            exit 1
            ;;
    esac
done

shift $(($OPTIND - 1))

tmp="$(mktemp -d)"

function cleanup() {
    if [[ "${keep_files}" == 0 ]]; then
        rm -rf "${tmp}" ||:
    elif [[ -n "${to_downgrade:-}" ]]; then
        rm -vf "${tmp}/*.rpm" ||:
        printf '\nThe list of packages to downgrade is available at "%s".\n' \
            "${to_downgrade}"
    fi
}
trap cleanup EXIT

if ! rpm -q rpmdevtools >/dev/null; then
    if ! sudo yum  install  -y rpmdevtools; then
        # try to install without dependency check
        pushd "${tmp}"
            yumdownloader rpmdevtools
            find -maxdepth 1 -name 'rpmdevtools*.rpm' | \
                sort -V | tail -n 1 | xargs sudo rpm --nodeps -Uvh
        popd
    fi
fi

downgrade_args=( --tolerant --skip-broken )
out="/dev/null"
[[ "$assume_yes" == 1 ]] && downgrade_args+=( '-y' ) || pkg_handler+=( '--assumeno' )
[[ "$dry_run"    == 1 ]] && out="/dev/fd/1"

function mkpkglist() {
    rpm -qa --qf='%{NAME}\n' | xargs sudo repoquery -q --qf='%{NAME}#%{EVRA}' | while IFS=  read -r line; do
        pkgname="${line%%#*}"
        aevra="${line##*#}"
        if [[ "${aevra}" =~ $RE_EVRA ]]; then
            aepoch="${BASH_REMATCH[1]}"
            aversion="${BASH_REMATCH[2]}"
            arelease="${BASH_REMATCH[3]}"
            aarch="${BASH_REMATCH[4]}"
        else
            echo "failed to parse evra '${aevra}' of available package! skipping..." >&2
            continue
        fi
        ievra="$(rpm -q "${pkgname}" --qf='%{EPOCH}:%{VERSION}-%{RELEASE}.%{ARCH}\n' | \
                 sed 's/^(none):/0:/' | rpmdev-sort | tail -n 1)"
        if echo "${ievra}" | grep -q 'not installed'; then
            echo "package '$pkgname' is not installed -> skipping line '$line'" >&2
            continue
        fi
        if [[ "${ievra}" =~ $RE_EVRA ]]; then
            iepoch="${BASH_REMATCH[1]}"
            iversion="${BASH_REMATCH[2]}"
            irelease="${BASH_REMATCH[3]}"
            iarch="${BASH_REMATCH[4]}"
        else
            echo "failed to parse evra '${ievra}' of installed package! skipping..." >&2
            continue
        fi
        
        if [[ "${iarch}" != "${aarch}" ]]; then
            continue
        fi
        rpmdev-vercmp \
            "${iepoch}" "${iversion}" "${irelease}" \
            "${aepoch}" "${aversion}" "${arelease}" >/dev/null && rc=$? || rc=$?
        if [[ "$rc" == 11 ]]; then
            # installed package is newer -> downgrade
            echo "${aepoch}:${pkgname}-${aversion}-${arelease}.${aarch}"
        fi
    done
}

function get_critical() {
    grep ":${RE_UNSUPPORTED}" "${to_downgrade}"
}

function get_noncritical() {
    grep -v ":${RE_UNSUPPORTED}" "${to_downgrade}"
}

function downgrade_critical() {
    # Warning: Dangerous - upgrades of these packages are unsupported!
    local answer
    [[ "${safe}" == 1 || -z "$(get_critical)" ]] && return 0

    if [[ "$assume_yes" == 0 ]]; then
        echo "Do you want to downgrade to the following critical packages?"
        get_critical | sed 's/^/  /'
        while IFS= read -p "[yes/no]: " -r answer; do
            echo "${answer}" | grep -iq '^\s*no\?\s*$'      && return 0
            echo "${answer}" | grep -iq '^\s*y\(es\)\?\s*$' && break
        done
    fi

    pushd "${tmp}"
        get_critical | xargs -r yumdownloader 
        find -name '*.rpm' | grep "${RE_UNSUPPORTED}" | xargs sudo rpm -Uvh --force --nodeps
    popd
}

if [[ -z "${to_downgrade:-}" ]]; then
    to_downgrade="${tmp}/to_downgrade"
    mkpkglist | tee "${to_downgrade}" >"${out}"
fi

[[ "$dry_run" == 1 ]] && exit 0

downgrade_critical

get_noncritical | xargs -r sudo yum downgrade "${downgrade_args[@]}"

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