Solving ClickHouse Server Connection Problem

1- Ensure that the clickhouse-server is running

systemctl status clickhouse-server

You can check that by looking for the Ready for connections line in /var/log/clickhouse-server/clickhouse-server.log ( Information log-level needed)

2- Ensure you use the proper port IP / Interface.

sudo lsof -i -P -n | grep LISTEN

echo listen_host
sudo clickhouse-extract-from-config --config=/etc/clickhouse-server/config.xml --key=listen_host
echo tcp_port
sudo clickhouse-extract-from-config --config=/etc/clickhouse-server/config.xml --key=tcp_port
echo tcp_port_secure
sudo clickhouse-extract-from-config --config=/etc/clickhouse-server/config.xml --key=tcp_port_secure
echo http_port
sudo clickhouse-extract-from-config --config=/etc/clickhouse-server/config.xml --key=http_port
echo https_port
sudo clickhouse-extract-from-config --config=/etc/clickhouse-server/config.xml --key=https_port

3. Check for errors in /var/log/clickhouse-server/clickhouse-server.err.log

4. Is ClickHouse able to serve some trivial TCP / HTTP requests from localhost?

curl 127.0.0.1:9200
curl 127.0.0.1:8123

5. Check the number of sockets opened by ClickHouse

sudo lsof -i -a -p $(pidof clickhouse-server)

# or (adjust 9000 / 8123 ports if needed)
netstat -tn 2>/dev/null | tail -n +3 | awk '{ printf("%s\t%s\t%s\t%s\t%s\t%s\n", $1, $2, $3, $4, $5, $6) }' | clickhouse-local -S "Proto String, RecvQ Int64, SendQ Int64, LocalAddress String, ForeignAddress String, State LowCardinality(String)" --query="SELECT * FROM table WHERE LocalAddress like '%:9000' FORMAT PrettyCompact"

netstat -tn 2>/dev/null | tail -n +3 | awk '{ printf("%s\t%s\t%s\t%s\t%s\t%s\n", $1, $2, $3, $4, $5, $6) }' | clickhouse-local -S "Proto String, RecvQ Int64, SendQ Int64, LocalAddress String, ForeignAddress String, State LowCardinality(String)" --query="SELECT * FROM table WHERE LocalAddress like '%:8123' FORMAT PrettyCompact"

6. Check firewall and SELinux rules (if used)