juicedata/juicefs · error

Can't connect to cluster %s: %s

Error message

Can't connect to cluster %s: %s

What it means

newCeph calls conn.Connect() to establish the actual network connection to the Ceph cluster after reading the config. If the connection attempt fails (monitors unreachable, authentication keyring missing/invalid), construction aborts with this message.

Source

Thrown at pkg/object/ceph.go:363

			opt = "$run_dir/jfs-$cluster-$name-$pid.asok"
		}
		if err = conn.SetConfigOption("admin_socket", opt); err != nil {
			logger.Warnf("Failed to set admin_socket to %s: %s", opt, err)
		}
	}
	if opt := os.Getenv("CEPH_LOG_FILE"); opt != "none" {
		if opt == "" {
			opt = "/var/log/ceph/jfs-$cluster-$name.log"
		}
		if err = conn.SetConfigOption("log_file", opt); err != nil {
			logger.Warnf("Failed to set log_file to %s: %s", opt, err)
		}
	}
	if err := conn.ReadDefaultConfigFile(); err != nil {
		return nil, fmt.Errorf("Can't read default config file: %s", err)
	}
	if err := conn.Connect(); err != nil {
		return nil, fmt.Errorf("Can't connect to cluster %s: %s", cluster, err)
	}
	return &ceph{
		name: name,
		conn: conn,
		free: make(chan *rados.IOContext, 50),
	}, nil
}

func init() {
	Register("ceph", newCeph)
}

View on GitHub (pinned to c9a67b23e8)

Solutions

1. Verify monitor addresses in ceph.conf are reachable (ping/telnet mon host ports)
2. Ensure the client keyring for the configured user exists and is readable (e.g. /etc/ceph/ceph.client.admin.keyring)
3. Update mon_host in ceph.conf to the current monitor list
4. Check `ceph -s --name <user> --keyring <path>` works before mounting

Example fix

// before
mon_host = 10.0.0.1  # stale monitor
// after
mon_host = 10.0.0.10 10.0.0.11 10.0.0.12
keyring = /etc/ceph/ceph.client.admin.keyring

// Shell: preflight connectivity and auth
ceph -s --name client.admin --keyring /etc/ceph/ceph.client.admin.keyring || {
  echo "cluster unreachable or auth failed"; exit 1;
}

// Go
obj, err := object.NewCeph(endpoint, cluster, user, "")
if err != nil && strings.Contains(err.Error(), "Can't connect to cluster") {
    // check monitors reachable and keyring present; do not hot-retry blindly
}

When it happens

Trigger: conn.Connect() errors: monitor addresses unreachable from this host, client keyring missing for the configured user, or authentication rejected by the cluster.

Common situations: Network/firewall blocking monitor ports (6789/3300); missing or misplaced /etc/ceph/ceph.client.admin.keyring; monitor list in ceph.conf stale after cluster re-IP; clock skew or auth cap changes.

Understand the failure class

Background: ECONNREFUSED and "connection refused" / "could not connect to server" errors: what they mean and how to fix them — this error's family across 44 libraries.

Related errors

• Can't create connection to cluster %s for user %s: %s
• Can't read default config file: %s
• ceph: can't put empty file
• Failed to create bucket %s: %s, previous error: %s
• (max tries) upload block %s: %s (after %d tries)

AI-assisted analysis of juicedata/juicefs@c9a67b23e8 (2026-09-06). Data as JSON: /api/errors/250f3a9ad5b0aa78. Report an issue: GitHub.