diff --git a/log/levels.go b/log/levels.go
index c1bf9ee..edd288d 100644
--- a/log/levels.go
+++ b/log/levels.go
@@ -13,15 +13,13 @@ const (
 	NOTSET   = 8
 )
 
-var (
-	idx = map[int]string{
-		CRITICAL: "critical",
-		ERROR:    "error",
-		WARNING:  "warning",
-		INFO:     "info",
-		DEBUG:    "debug",
-	}
-)
+var idx = map[int]string{
+	CRITICAL: "critical",
+	ERROR:    "error",
+	WARNING:  "warning",
+	INFO:     "info",
+	DEBUG:    "debug",
+}
 
 func GetLevelName(lev int) string {
 	if name, found := idx[lev]; found {
diff --git a/nfs/implv3/access.go b/nfs/implv3/access.go
index ab6d2b0..c3f6b3d 100644
--- a/nfs/implv3/access.go
+++ b/nfs/implv3/access.go
@@ -85,7 +85,7 @@ func Access(h *nfs.RPCMsgCall, ctx nfs.RPCContext) (int, error) {
 			AttributesFollow: true,
 			Attributes: &nfs.FileAttrs{
 				Type:  nfs.FTYPE_NF3DIR,
-				Mode:  uint32(0777),
+				Mode:  uint32(0o777),
 				Size:  0,
 				Used:  0,
 				ATime: nfs.MakeNfsTime(now),
diff --git a/nfs/implv3/fsinfo.go b/nfs/implv3/fsinfo.go
index 0c4b4f4..9cb367b 100644
--- a/nfs/implv3/fsinfo.go
+++ b/nfs/implv3/fsinfo.go
@@ -78,7 +78,7 @@ func FsInfo(h *nfs.RPCMsgCall, ctx nfs.RPCContext) (int, error) {
 			AttributesFollow: true,
 			Attributes: &nfs.FileAttrs{
 				Type:  nfs.FTYPE_NF3DIR,
-				Mode:  uint32(0755),
+				Mode:  uint32(0o755),
 				Size:  1 << 63,
 				Used:  0,
 				ATime: nfs.MakeNfsTime(now),
diff --git a/nfs/implv3/fsstat.go b/nfs/implv3/fsstat.go
index c3a2ae4..a779947 100644
--- a/nfs/implv3/fsstat.go
+++ b/nfs/implv3/fsstat.go
@@ -79,7 +79,7 @@ func FsStat(h *nfs.RPCMsgCall, ctx nfs.RPCContext) (int, error) {
 			AttributesFollow: true,
 			Attributes: &nfs.FileAttrs{
 				Type:  nfs.FTYPE_NF3DIR,
-				Mode:  uint32(0755),
+				Mode:  uint32(0o755),
 				Size:  capacity,
 				Used:  0,
 				ATime: nfs.MakeNfsTime(now),
diff --git a/nfs/implv3/getattr.go b/nfs/implv3/getattr.go
index bfbb51b..1b92a38 100644
--- a/nfs/implv3/getattr.go
+++ b/nfs/implv3/getattr.go
@@ -108,7 +108,7 @@ func GetAttr(h *nfs.RPCMsgCall, ctx nfs.RPCContext) (int, error) {
 
 			attr := nfs.FileAttrs{
 				Type:   ftype,
-				Mode:   uint32(0755),
+				Mode:   uint32(0o755),
 				Size:   uint64(fi.Size()),
 				Used:   uint64(fi.Size()),
 				Rdev:   nfs.SpecData{},
diff --git a/nfs/implv3/pathconf.go b/nfs/implv3/pathconf.go
index f96b77f..b685d89 100644
--- a/nfs/implv3/pathconf.go
+++ b/nfs/implv3/pathconf.go
@@ -76,7 +76,7 @@ func PathConf(h *nfs.RPCMsgCall, ctx nfs.RPCContext) (int, error) {
 			AttributesFollow: true,
 			Attributes: &nfs.FileAttrs{
 				Type:  nfs.FTYPE_NF3DIR,
-				Mode:  uint32(0755),
+				Mode:  uint32(0o755),
 				Size:  1 << 63,
 				Used:  0,
 				ATime: nfs.MakeNfsTime(now),
diff --git a/nfs/implv3/utils.go b/nfs/implv3/utils.go
index 0d2969c..56280ff 100644
--- a/nfs/implv3/utils.go
+++ b/nfs/implv3/utils.go
@@ -3,10 +3,11 @@ package implv3
 import (
 	"crypto/md5"
 	"encoding/binary"
-	"github.com/smallfz/libnfs-go/nfs"
 	"os"
 	"path"
 	"time"
+
+	"github.com/smallfz/libnfs-go/nfs"
 )
 
 func getFileId(name string) uint64 {
diff --git a/nfs/implv4/attrs_test.go b/nfs/implv4/attrs_test.go
index a4ed79d..7b95def 100644
--- a/nfs/implv4/attrs_test.go
+++ b/nfs/implv4/attrs_test.go
@@ -2,8 +2,9 @@ package implv4
 
 import (
 	"encoding/json"
-	"github.com/smallfz/libnfs-go/log"
 	"testing"
+
+	"github.com/smallfz/libnfs-go/log"
 )
 
 func TestFAttr4Decoding(t *testing.T) {
diff --git a/nfs/implv4/commit.go b/nfs/implv4/commit.go
index 82651a2..260c463 100644
--- a/nfs/implv4/commit.go
+++ b/nfs/implv4/commit.go
@@ -6,7 +6,6 @@ import (
 )
 
 func commit(x nfs.RPCContext, args *nfs.COMMIT4args) (*nfs.COMMIT4res, error) {
-
 	vfs := x.GetFS()
 	fh := x.Stat().CurrentHandle()
 	pathName, err := vfs.ResolveHandle(fh)
diff --git a/nfs/implv4/remove.go b/nfs/implv4/remove.go
index 328a970..ecefcc0 100644
--- a/nfs/implv4/remove.go
+++ b/nfs/implv4/remove.go
@@ -25,6 +25,7 @@ func remove(x nfs.RPCContext, args *nfs.REMOVE4args) (*nfs.REMOVE4res, error) {
 	fi, err := vfs.Stat(pathName)
 	if err != nil {
 		log.Warnf("  remove: vfs.Stat(%s): %v", pathName, err)
+		return &nfs.REMOVE4res{Status: nfs.NFS4ERR_PERM}, nil
 	}
 
 	if fi.IsDir() && fi.NumLinks() > 2 {
diff --git a/server/mux_v3.go b/server/mux_v3.go
index 896bd23..dedf1b6 100644
--- a/server/mux_v3.go
+++ b/server/mux_v3.go
@@ -17,6 +17,8 @@ type Mux struct {
 	stat   nfs.StatService
 }
 
+var _ nfs.RPCContext = (*Mux)(nil)
+
 func (x *Mux) Reader() *xdr.Reader {
 	return x.reader
 }
diff --git a/server/mux_v4.go b/server/mux_v4.go
index d874331..2978dc9 100644
--- a/server/mux_v4.go
+++ b/server/mux_v4.go
@@ -17,6 +17,8 @@ type Muxv4 struct {
 	stat   nfs.StatService
 }
 
+var _ nfs.RPCContext = (*Muxv4)(nil)
+
 func (x *Muxv4) Reader() *xdr.Reader {
 	return x.reader
 }