diff --git a/weed/filer2/cassandra/cassandra_store.go b/weed/filer2/cassandra/cassandra_store.go
index 8214935f9..40f371e2f 100644
--- a/weed/filer2/cassandra/cassandra_store.go
+++ b/weed/filer2/cassandra/cassandra_store.go
@@ -2,7 +2,6 @@ package cassandra
 
 import (
 	"context"
-	"errors"
 	"fmt"
 	"github.com/gocql/gocql"
 
@@ -127,7 +126,7 @@ func (store *CassandraStore) DeleteFolderChildren(ctx context.Context, fullpath
 }
 
 func (store *CassandraStore) ListDirectoryPrefixedEntries(ctx context.Context, fullpath util.FullPath, startFileName string, inclusive bool, limit int, prefix string) (entries []*filer2.Entry, err error) {
-	return nil, errors.New(filer2.UnsupportedListDirectoryPrefixedErr)
+	return nil, filer2.UnsupportedListDirectoryPrefixedErr
 }
 
 func (store *CassandraStore) ListDirectoryEntries(ctx context.Context, fullpath util.FullPath, startFileName string, inclusive bool,
diff --git a/weed/filer2/etcd/etcd_store.go b/weed/filer2/etcd/etcd_store.go
index 93f3f3781..d0b1ff202 100644
--- a/weed/filer2/etcd/etcd_store.go
+++ b/weed/filer2/etcd/etcd_store.go
@@ -2,7 +2,6 @@ package etcd
 
 import (
 	"context"
-	"errors"
 	"fmt"
 	"strings"
 	"time"
@@ -137,7 +136,7 @@ func (store *EtcdStore) DeleteFolderChildren(ctx context.Context, fullpath weed_
 }
 
 func (store *EtcdStore) ListDirectoryPrefixedEntries(ctx context.Context, fullpath weed_util.FullPath, startFileName string, inclusive bool, limit int, prefix string) (entries []*filer2.Entry, err error) {
-	return nil, errors.New(filer2.UnsupportedListDirectoryPrefixedErr)
+	return nil, filer2.UnsupportedListDirectoryPrefixedErr
 }
 
 func (store *EtcdStore) ListDirectoryEntries(ctx context.Context, fullpath weed_util.FullPath, startFileName string, inclusive bool, limit int) (entries []*filer2.Entry, err error) {
diff --git a/weed/filer2/filer.go b/weed/filer2/filer.go
index ef81cae2b..a94052996 100644
--- a/weed/filer2/filer.go
+++ b/weed/filer2/filer.go
@@ -2,6 +2,7 @@ package filer2
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"os"
 	"strings"
@@ -19,13 +20,13 @@ import (
 )
 
 const (
-	PaginationSize                      = 1024 * 256
-	UnsupportedListDirectoryPrefixedErr = "UNSUPPORTED"
+	PaginationSize = 1024 * 256
 )
 
 var (
-	OS_UID = uint32(os.Getuid())
-	OS_GID = uint32(os.Getgid())
+	OS_UID                              = uint32(os.Getuid())
+	OS_GID                              = uint32(os.Getgid())
+	UnsupportedListDirectoryPrefixedErr = errors.New("UNSUPPORTED")
 )
 
 type Filer struct {
diff --git a/weed/filer2/filerstore.go b/weed/filer2/filerstore.go
index 3c1e555b1..642ebb3c8 100644
--- a/weed/filer2/filerstore.go
+++ b/weed/filer2/filerstore.go
@@ -138,7 +138,7 @@ func (fsw *FilerStoreWrapper) ListDirectoryPrefixedEntries(ctx context.Context,
 		stats.FilerStoreHistogram.WithLabelValues(fsw.ActualStore.GetName(), "list").Observe(time.Since(start).Seconds())
 	}()
 	entries, err := fsw.ActualStore.ListDirectoryPrefixedEntries(ctx, dirPath, startFileName, includeStartFile, limit, prefix)
-	if err.Error() == UnsupportedListDirectoryPrefixedErr {
+	if err.Error() == UnsupportedListDirectoryPrefixedErr.Error() {
 		count := 0
 		notPrefixed, err := fsw.ActualStore.ListDirectoryEntries(ctx, dirPath, startFileName, includeStartFile, limit)
 		if err != nil {
diff --git a/weed/filer2/leveldb/leveldb_store.go b/weed/filer2/leveldb/leveldb_store.go
index 787671c55..2ea88635b 100644
--- a/weed/filer2/leveldb/leveldb_store.go
+++ b/weed/filer2/leveldb/leveldb_store.go
@@ -3,7 +3,6 @@ package leveldb
 import (
 	"bytes"
 	"context"
-	"errors"
 	"fmt"
 	"github.com/syndtr/goleveldb/leveldb"
 	leveldb_errors "github.com/syndtr/goleveldb/leveldb/errors"
@@ -160,7 +159,7 @@ func (store *LevelDBStore) DeleteFolderChildren(ctx context.Context, fullpath we
 }
 
 func (store *LevelDBStore) ListDirectoryPrefixedEntries(ctx context.Context, fullpath weed_util.FullPath, startFileName string, inclusive bool, limit int, prefix string) (entries []*filer2.Entry, err error) {
-	return nil, errors.New(filer2.UnsupportedListDirectoryPrefixedErr)
+	return nil, filer2.UnsupportedListDirectoryPrefixedErr
 }
 
 func (store *LevelDBStore) ListDirectoryEntries(ctx context.Context, fullpath weed_util.FullPath, startFileName string, inclusive bool,
diff --git a/weed/filer2/leveldb2/leveldb2_store.go b/weed/filer2/leveldb2/leveldb2_store.go
index 4fc110d69..2a9c2fe3f 100644
--- a/weed/filer2/leveldb2/leveldb2_store.go
+++ b/weed/filer2/leveldb2/leveldb2_store.go
@@ -4,7 +4,6 @@ import (
 	"bytes"
 	"context"
 	"crypto/md5"
-	"errors"
 	"fmt"
 	"github.com/syndtr/goleveldb/leveldb"
 	leveldb_errors "github.com/syndtr/goleveldb/leveldb/errors"
@@ -169,7 +168,7 @@ func (store *LevelDB2Store) DeleteFolderChildren(ctx context.Context, fullpath w
 }
 
 func (store *LevelDB2Store) ListDirectoryPrefixedEntries(ctx context.Context, fullpath weed_util.FullPath, startFileName string, inclusive bool, limit int, prefix string) (entries []*filer2.Entry, err error) {
-	return nil, errors.New(filer2.UnsupportedListDirectoryPrefixedErr)
+	return nil, filer2.UnsupportedListDirectoryPrefixedErr
 }
 
 func (store *LevelDB2Store) ListDirectoryEntries(ctx context.Context, fullpath weed_util.FullPath, startFileName string, inclusive bool,
diff --git a/weed/filer2/mongodb/mongodb_store.go b/weed/filer2/mongodb/mongodb_store.go
index 314f36ce2..080d6248f 100644
--- a/weed/filer2/mongodb/mongodb_store.go
+++ b/weed/filer2/mongodb/mongodb_store.go
@@ -2,7 +2,6 @@ package mongodb
 
 import (
 	"context"
-	"errors"
 	"fmt"
 	"github.com/chrislusf/seaweedfs/weed/filer2"
 	"github.com/chrislusf/seaweedfs/weed/glog"
@@ -169,7 +168,7 @@ func (store *MongodbStore) DeleteFolderChildren(ctx context.Context, fullpath ut
 }
 
 func (store *MongodbStore) ListDirectoryPrefixedEntries(ctx context.Context, fullpath util.FullPath, startFileName string, inclusive bool, limit int, prefix string) (entries []*filer2.Entry, err error) {
-	return nil, errors.New(filer2.UnsupportedListDirectoryPrefixedErr)
+	return nil, filer2.UnsupportedListDirectoryPrefixedErr
 }
 
 func (store *MongodbStore) ListDirectoryEntries(ctx context.Context, fullpath util.FullPath, startFileName string, inclusive bool, limit int) (entries []*filer2.Entry, err error) {
diff --git a/weed/filer2/redis/universal_redis_store.go b/weed/filer2/redis/universal_redis_store.go
index 66450b5a7..8cc70c72b 100644
--- a/weed/filer2/redis/universal_redis_store.go
+++ b/weed/filer2/redis/universal_redis_store.go
@@ -2,7 +2,6 @@ package redis
 
 import (
 	"context"
-	"errors"
 	"fmt"
 	"sort"
 	"strings"
@@ -123,7 +122,7 @@ func (store *UniversalRedisStore) DeleteFolderChildren(ctx context.Context, full
 }
 
 func (store *UniversalRedisStore) ListDirectoryPrefixedEntries(ctx context.Context, fullpath util.FullPath, startFileName string, inclusive bool, limit int, prefix string) (entries []*filer2.Entry, err error) {
-	return nil, errors.New(filer2.UnsupportedListDirectoryPrefixedErr)
+	return nil, filer2.UnsupportedListDirectoryPrefixedErr
 }
 
 func (store *UniversalRedisStore) ListDirectoryEntries(ctx context.Context, fullpath util.FullPath, startFileName string, inclusive bool,
diff --git a/weed/filer2/redis2/universal_redis_store.go b/weed/filer2/redis2/universal_redis_store.go
index 9878799cf..2ce7ebec7 100644
--- a/weed/filer2/redis2/universal_redis_store.go
+++ b/weed/filer2/redis2/universal_redis_store.go
@@ -2,7 +2,6 @@ package redis2
 
 import (
 	"context"
-	"errors"
 	"fmt"
 	"time"
 
@@ -118,7 +117,7 @@ func (store *UniversalRedis2Store) DeleteFolderChildren(ctx context.Context, ful
 }
 
 func (store *UniversalRedis2Store) ListDirectoryPrefixedEntries(ctx context.Context, fullpath util.FullPath, startFileName string, inclusive bool, limit int, prefix string) (entries []*filer2.Entry, err error) {
-	return nil, errors.New(filer2.UnsupportedListDirectoryPrefixedErr)
+	return nil, filer2.UnsupportedListDirectoryPrefixedErr
 }
 
 func (store *UniversalRedis2Store) ListDirectoryEntries(ctx context.Context, fullpath util.FullPath, startFileName string, inclusive bool,