diff --git a/commands_test.go b/commands_test.go
index 841079a..acfdedd 100644
--- a/commands_test.go
+++ b/commands_test.go
@@ -9,6 +9,9 @@ import (
 	"context"
 	"errors"
 	"net"
+	"os"
+	"path/filepath"
+	"strconv"
 	"testing"
 	"time"
 
@@ -237,6 +240,29 @@ func TestFormatChainSyncDaemonStopping_Good(t *testing.T) {
 	assert.Equal(t, "Stopping background chain sync (PID 42).", formatChainSyncDaemonStopping(42))
 }
 
+func TestFormatChainSyncDaemonAlreadyRunning_Good(t *testing.T) {
+	assert.Equal(t, `background chain sync is already running for data dir "/tmp/chain" (PID 42). Stop it with core-chain chain sync --stop --data-dir "/tmp/chain".`, formatChainSyncDaemonAlreadyRunning("/tmp/chain", 42))
+}
+
+func TestFormatChainSyncDaemonNotRunning_Good(t *testing.T) {
+	assert.Equal(t, `No background chain sync is running for data dir "/tmp/chain".`, formatChainSyncDaemonNotRunning("/tmp/chain"))
+}
+
+func TestRunChainSyncDaemon_Bad_RejectsExistingDaemonForDataDir(t *testing.T) {
+	dataDir := t.TempDir()
+	pidFile := filepath.Join(dataDir, "sync.pid")
+	pid := os.Getpid()
+	require.NoError(t, os.WriteFile(pidFile, []byte(strconv.Itoa(pid)), 0o644))
+
+	err := runChainSyncDaemon(dataDir, "127.0.0.1:36942", false)
+	require.EqualError(t, err, `blockchain: background chain sync is already running for data dir "`+dataDir+`" (PID `+strconv.Itoa(pid)+`). Stop it with core-chain chain sync --stop --data-dir "`+dataDir+`".`)
+}
+
+func TestStopChainSyncDaemon_Good_NoRunningDaemonForDataDir(t *testing.T) {
+	err := stopChainSyncDaemon(t.TempDir())
+	require.NoError(t, err)
+}
+
 func TestRunChainSyncOnce_Bad_RespectsCancelledContext(t *testing.T) {
 	ctx, cancel := context.WithCancel(context.Background())
 	cancel()
diff --git a/sync_command.go b/sync_command.go
index be23f71..eb13bef 100644
--- a/sync_command.go
+++ b/sync_command.go
@@ -102,6 +102,9 @@ func runChainSyncDaemon(dataDir, seed string, testnet bool) error {
 	}
 
 	pidFile := filepath.Join(dataDir, "sync.pid")
+	if pid, running := process.ReadPID(pidFile); running {
+		return fmt.Errorf("blockchain: %s", formatChainSyncDaemonAlreadyRunning(dataDir, pid))
+	}
 
 	syncDaemon := process.NewDaemon(process.DaemonOptions{
 		PIDFile:  pidFile,
@@ -153,7 +156,8 @@ func stopChainSyncDaemon(dataDir string) error {
 	pidFile := filepath.Join(dataDir, "sync.pid")
 	pid, running := process.ReadPID(pidFile)
 	if pid == 0 || !running {
-		return coreerr.E("stopChainSyncDaemon", "no running background sync process found", nil)
+		log.Print(formatChainSyncDaemonNotRunning(dataDir))
+		return nil
 	}
 
 	processHandle, err := os.FindProcess(pid)
@@ -188,3 +192,11 @@ func formatChainSyncStopCommand(dataDir string) string {
 func formatChainSyncDaemonStopping(pid int) string {
 	return fmt.Sprintf("Stopping background chain sync (PID %d).", pid)
 }
+
+func formatChainSyncDaemonAlreadyRunning(dataDir string, pid int) string {
+	return fmt.Sprintf("background chain sync is already running for data dir %q (PID %d). Stop it with %s.", dataDir, pid, formatChainSyncStopCommand(dataDir))
+}
+
+func formatChainSyncDaemonNotRunning(dataDir string) string {
+	return fmt.Sprintf("No background chain sync is running for data dir %q.", dataDir)
+}