Handle Red Hat-family hosts without /etc/redhat-release

install_script.sh.template

@@ -347,6 +347,33 @@ function remove_rpm_gpg_keys() {
     done
 }
 
+function get_redhat_release_version() {
+    local release_file
+    local version=""
+
+    for release_file in "${1:-/etc/redhat-release}" "${2:-/etc/system-release}"; do
+        if [ -r "$release_file" ]; then
+            version=$(grep -oE '[0-9]+' <"$release_file" | head -1)
+            if [ -n "$version" ]; then
+                printf '%s' "$version"
+                return 0
+            fi
+        fi
+    done
+
+    for release_file in "${3:-/etc/os-release}" "${4:-/usr/lib/os-release}"; do
+        if [ -r "$release_file" ]; then
+            version=$(grep -E '^VERSION_ID=' <"$release_file" | head -1 | cut -d = -f 2 | grep -oE '[0-9]+' | head -1)
+            if [ -n "$version" ]; then
+                printf '%s' "$version"
+                return 0
+            fi
+        fi
+    done
+
+    printf '7'
+}
+
 # Emulate hashmap with simple switch case
 function getMapData() {
 
@@ -1397,10 +1424,7 @@ if [ "$OS" == "Red Hat" ]; then
     fi
     # NOTE: CentOS/RHEL 6 don't have /etc/os-release. /etc/centos-release and /etc/redhat-release
     # aren't necessarily on the system, so this is not 100 % reliable, but best we can do
-    release_version=$(grep -oE '[0-9]+' </etc/redhat-release 2>/dev/null | head -1)
-    if [ -z "$release_version" ]; then
-        release_version=7
-    fi
+    release_version=$(get_redhat_release_version /etc/redhat-release /etc/system-release /etc/os-release /usr/lib/os-release)
     if { [ "$DISTRIBUTION" == "Red Hat" ] || [ "$DISTRIBUTION" == "CentOS" ]; } && [ "$release_version" -lt 7 ]; then
         if [ -n "$agent_minor_version_without_patch" ]; then
             if [ "$agent_minor_version_without_patch" -ge "52" ]; then

unit_tests/test_install_script.sh

@@ -418,6 +418,59 @@ testParEnabledWithoutApiKeyOnlyEnrollment() {
   assertEquals "$(sudo yq eval '.private_action_runner.api_key_only_enrollment' $config_file)" "null"
 }
 
+### get_redhat_release_version
+setUpReleaseFiles() {
+  release_dir=$(mktemp -d)
+  missing="$release_dir/missing"
+  redhat_release="$release_dir/redhat-release"
+  system_release="$release_dir/system-release"
+  os_release="$release_dir/os-release"
+  usr_lib_os_release="$release_dir/usr-lib-os-release"
+}
+testRedhatReleasePreferred() {
+  setUpReleaseFiles
+  echo "CentOS Linux release 7.9.2009 (Core)" > "$redhat_release"
+  echo "Amazon Linux release 2 (Karoo)" > "$system_release"
+  echo 'VERSION_ID="9.4"' > "$os_release"
+  assertEquals "7" "$(get_redhat_release_version "$redhat_release" "$system_release" "$os_release" "$usr_lib_os_release")"
+}
+testSystemReleaseUsedWhenRedhatReleaseMissing() {
+  setUpReleaseFiles
+  echo "Amazon Linux release 2 (Karoo)" > "$system_release"
+  echo 'VERSION_ID="9.4"' > "$os_release"
+  assertEquals "2" "$(get_redhat_release_version "$missing" "$system_release" "$os_release" "$usr_lib_os_release")"
+}
+testOsReleaseUsedWhenReleaseFilesMissing() {
+  setUpReleaseFiles
+  echo 'VERSION_ID="9.4"' > "$os_release"
+  assertEquals "9" "$(get_redhat_release_version "$missing" "$missing" "$os_release" "$usr_lib_os_release")"
+}
+testUsrLibOsReleaseUsedAsLastSource() {
+  setUpReleaseFiles
+  echo 'VERSION_ID=8' > "$usr_lib_os_release"
+  assertEquals "8" "$(get_redhat_release_version "$missing" "$missing" "$missing" "$usr_lib_os_release")"
+}
+testFallsBackToSevenWhenNothingAvailable() {
+  setUpReleaseFiles
+  assertEquals "7" "$(get_redhat_release_version "$missing" "$missing" "$missing" "$missing")"
+}
+testEmptyFilesFallThroughToNextSource() {
+  setUpReleaseFiles
+  : > "$redhat_release"
+  : > "$system_release"
+  echo 'VERSION_ID="9.4"' > "$os_release"
+  assertEquals "9" "$(get_redhat_release_version "$redhat_release" "$system_release" "$os_release" "$usr_lib_os_release")"
+}
+testNonNumericOsReleaseFallsBack() {
+  setUpReleaseFiles
+  echo 'VERSION_ID=rawhide' > "$os_release"
+  assertEquals "7" "$(get_redhat_release_version "$missing" "$missing" "$os_release" "$missing")"
+}
+testMissingRedhatReleaseIsSilent() {
+  setUpReleaseFiles
+  assertEquals "" "$(get_redhat_release_version "$missing" "$missing" "$missing" "$missing" 2>&1 >/dev/null)"
+}
+
 ### install_apm_ssi
 getApmSsiInstallerURL() {
   (