What causes "Failed to close ssh session" in apache/seatunnel?

Check logs for the original SSH failure that broke the session; this is often secondary

apache/seatunnel · error · ClickhouseConnectorException

Failed to close ssh session

Error message

Failed to close ssh session

What it means

ScpFileTransfer.close() wraps an IOException from clientSession.close() into SSH_OPERATION_FAILED with the message 'Failed to close ssh session'. Identical in shape to the rsync variant but on the SCP transfer path; it fires during sink shutdown.

Source

Thrown at seatunnel-connectors-v2/connector-clickhouse/src/main/java/org/apache/seatunnel/connectors/seatunnel/clickhouse/sink/file/ScpFileTransfer.java:141

        }
    }

    @Override
    public void transferAndChown(List<String> sourcePaths, String targetPath) {
        if (sourcePaths == null) {
            throw new ClickhouseConnectorException(
                    CommonErrorCodeDeprecated.ILLEGAL_ARGUMENT, "sourcePath is null");
        }
        sourcePaths.forEach(sourcePath -> transferAndChown(sourcePath, targetPath));
    }

    @Override
    public void close() {
        if (clientSession != null && clientSession.isOpen()) {
            try {
                clientSession.close();
            } catch (IOException e) {
                throw new ClickhouseConnectorException(
                        ClickhouseConnectorErrorCode.SSH_OPERATION_FAILED,
                        "Failed to close ssh session",
                        e);
            }
        }
        if (sshClient != null && sshClient.isOpen()) {
            sshClient.stop();
            try {
                sshClient.close();
            } catch (IOException e) {
                throw new ClickhouseConnectorException(
                        ClickhouseConnectorErrorCode.SSH_OPERATION_FAILED,
                        "Failed to close ssh client",
                        e);
            }
        }
    }
}

View on GitHub (pinned to cf67b549a7)

Solutions

Check logs for the original SSH failure that broke the session; this is often secondary
Verify network stability and SSH keepalive/idle timeouts between worker and host
Retry the job; intermittent failures indicate transient network problems
Confirm sshd is healthy and not rate-limiting or dropping connections

Defensive patterns

Strategy: try-catch

Validate before calling

// pre-job SSH reachability check
ssh -o ConnectTimeout=5 user@host true && echo OK

Try / catch

try {
    transfer.close();
} catch (ClickhouseConnectorException e) {
    log.warn("SCP session close failed; likely already broken connection", e);
}

Prevention

Enable SSH keepalives to keep sessions alive during long jobs
Investigate the first SSH error in logs, not just the close failure
Retry intermittent network failures

When it happens

Trigger: close() is invoked and the SCP clientSession.close() throws IOException — connection already dropped, server closed the session, or teardown raced with an in-flight transfer.

Common situations: Idle SCP session killed by firewall/NAT during a long job, remote host rebooted, or session already errored from a failed transfer leaving close to fail too.

Related errors

AI-assisted analysis of apache/seatunnel@cf67b549a7 (2026-09-10). Data as JSON: /api/errors/eea8f64e83ad8a2c. Report an issue: GitHub.