If you run nodetool netstats, you would be able to see the status of the node where it would either be "building" or "normal" if it completed. While it's building, it will also show you the active streams that are in progress.
Typically, most admins nohup it or at least redirect the output to a log file so you still have visibility when you lost your [SSH] session. That's also another thing to consider. Cheers! GOT QUESTIONS? Apache Cassandra experts from the community and DataStax have answers! Share your expertise on https://community.datastax.com/.