During upgrades from 7.x to 8.x if a node was holding a frozen cache file, the system considers that as an unknown file and prevents starting the node:
```
java.lang.IllegalStateException: unexpected file/folder encountered during data folder upgrade: /app/data/nodes/0/shared_snapshot_cache
	at org.elasticsearch.env.NodeEnvironment.upgradeLegacyNodeFolders(NodeEnvironment.java:443) ~[elasticsearch-8.0.1.jar:8.0.1]
	at org.elasticsearch.env.NodeEnvironment.<init>(NodeEnvironment.java:290) ~[elasticsearch-8.0.1.jar:8.0.1]
	at org.elasticsearch.node.Node.<init>(Node.java:388) ~[elasticsearch-8.0.1.jar:8.0.1]
	at org.elasticsearch.node.Node.<init>(Node.java:277) ~[elasticsearch-8.0.1.jar:8.0.1]
	at org.elasticsearch.bootstrap.Bootstrap$5.<init>(Bootstrap.java:234) ~[elasticsearch-8.0.1.jar:8.0.1]
	at org.elasticsearch.bootstrap.Bootstrap.setup(Bootstrap.java:234) ~[elasticsearch-8.0.1.jar:8.0.1]
	at org.elasticsearch.bootstrap.Bootstrap.init(Bootstrap.java:358) [elasticsearch-8.0.1.jar:8.0.1]
	at org.elasticsearch.bootstrap.Elasticsearch.init(Elasticsearch.java:166) [elasticsearch-8.0.1.jar:8.0.1]
	at org.elasticsearch.bootstrap.Elasticsearch.execute(Elasticsearch.java:157) [elasticsearch-8.0.1.jar:8.0.1]
	at org.elasticsearch.cli.EnvironmentAwareCommand.execute(EnvironmentAwareCommand.java:77) [elasticsearch-8.0.1.jar:8.0.1]
	at org.elasticsearch.cli.Command.mainWithoutErrorHandling(Command.java:112) [elasticsearch-cli-8.0.1.jar:8.0.1]
	at org.elasticsearch.cli.Command.main(Command.java:77) [elasticsearch-cli-8.0.1.jar:8.0.1]
	at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:122) [elasticsearch-8.0.1.jar:8.0.1]
	at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:80) [elasticsearch-8.0.1.jar:8.0.1]
```
These files are expected files and should be ignored/accepted during the data folder upgrade.
server/src/main/java/org/elasticsearch/env/NodeEnvironment.java
assert metadata.nodeVersion().equals(Version.CURRENT) : metadata.nodeVersion() + " != " + Version.CURRENT;
        return metadata;
    }
    public static String generateNodeId(Settings settings) {
        Random random = Randomness.get(settings, NODE_ID_SEED_SETTING);
        return UUIDs.randomBase64UUID(random);
    }
    @SuppressForbidden(reason = "System.out.*")
    static void applySegmentInfosTrace(Settings settings) {
        if (ENABLE_LUCENE_SEGMENT_INFOS_TRACE_SETTING.get(settings)) {
            SegmentInfos.setInfoStream(System.out);
        }
    }
    private static String toString(Collection<String> items) {
        StringBuilder b = new StringBuilder();
        for (String item : items) {
            if (b.length() > 0) {
                b.append(", ");
            }
            b.append(item);
        }
        return b.toString();
    }
    /**
     * Deletes a shard data directory iff the shards locks were successfully acquired.
     *
     * @param shardId the id of the shard to delete to delete
     * @throws IOException if an IOException occurs
     */
    public void deleteShardDirectorySafe(ShardId shardId, IndexSettings indexSettings, Consumer<Path[]> listener) throws IOException,