diff --git a/internal/os/mock_os/os.go b/internal/os/mock_os/os.go
index 1e149bf9..d6f2eaf2 100644
--- a/internal/os/mock_os/os.go
+++ b/internal/os/mock_os/os.go
@@ -105,17 +105,3 @@ func (mr *MockOSMockRecorder) Stat(arg0 interface{}) *gomock.Call {
 	mr.mock.ctrl.T.Helper()
 	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Stat", reflect.TypeOf((*MockOS)(nil).Stat), arg0)
 }
-
-// Unsetenv mocks base method
-func (m *MockOS) Unsetenv(arg0 string) error {
-	m.ctrl.T.Helper()
-	ret := m.ctrl.Call(m, "Unsetenv", arg0)
-	ret0, _ := ret[0].(error)
-	return ret0
-}
-
-// Unsetenv indicates an expected call of Unsetenv
-func (mr *MockOSMockRecorder) Unsetenv(arg0 interface{}) *gomock.Call {
-	mr.mock.ctrl.T.Helper()
-	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Unsetenv", reflect.TypeOf((*MockOS)(nil).Unsetenv), arg0)
-}
diff --git a/internal/os/os.go b/internal/os/os.go
index 8c686704..37e6069e 100644
--- a/internal/os/os.go
+++ b/internal/os/os.go
@@ -9,7 +9,6 @@ type OS interface {
 	MkdirAll(name string, perm FileMode) error
 	Remove(name string) error
 	Chown(name string, uid int, gid int) error
-	Unsetenv(key string) error
 	Stat(name string) (nativeos.FileInfo, error)
 }
 
@@ -31,9 +30,6 @@ func (o *os) Remove(name string) error {
 func (o *os) Chown(name string, uid, gid int) error {
 	return nativeos.Chown(name, uid, gid)
 }
-func (o *os) Unsetenv(key string) error {
-	return nativeos.Unsetenv(key)
-}
 func (o *os) Stat(name string) (nativeos.FileInfo, error) {
 	return nativeos.Stat(name)
 }
diff --git a/internal/params/openvpn.go b/internal/params/openvpn.go
index caa28c31..5c421437 100644
--- a/internal/params/openvpn.go
+++ b/internal/params/openvpn.go
@@ -10,24 +10,15 @@ import (
 
 // GetUser obtains the user to use to connect to the VPN servers.
 func (r *reader) GetUser() (s string, err error) {
-	defer func() {
-		unsetenvErr := r.os.Unsetenv("USER")
-		if err == nil {
-			err = unsetenvErr
-		}
-	}()
-	return r.envParams.GetEnv("USER", libparams.CaseSensitiveValue(), libparams.Compulsory())
+	return r.envParams.GetEnv("USER",
+		libparams.CaseSensitiveValue(),
+		libparams.Compulsory(),
+		libparams.Unset())
 }
 
 // GetPassword obtains the password to use to connect to the VPN servers.
 func (r *reader) GetPassword(required bool) (s string, err error) {
-	defer func() {
-		unsetenvErr := r.os.Unsetenv("PASSWORD")
-		if err == nil {
-			err = unsetenvErr
-		}
-	}()
-	options := []libparams.GetEnvSetter{libparams.CaseSensitiveValue()}
+	options := []libparams.GetEnvSetter{libparams.CaseSensitiveValue(), libparams.Unset()}
 	if required {
 		options = append(options, libparams.Compulsory())
 	}
diff --git a/internal/params/shadowsocks.go b/internal/params/shadowsocks.go
index b2703572..2f97d212 100644
--- a/internal/params/shadowsocks.go
+++ b/internal/params/shadowsocks.go
@@ -35,13 +35,7 @@ func (r *reader) GetShadowSocksPort() (port uint16, err error) {
 // GetShadowSocksPassword obtains the ShadowSocks server password from the environment variable
 // SHADOWSOCKS_PASSWORD.
 func (r *reader) GetShadowSocksPassword() (password string, err error) {
-	defer func() {
-		unsetErr := r.os.Unsetenv("SHADOWSOCKS_PASSWORD")
-		if err == nil {
-			err = unsetErr
-		}
-	}()
-	return r.envParams.GetEnv("SHADOWSOCKS_PASSWORD", libparams.CaseSensitiveValue())
+	return r.envParams.GetEnv("SHADOWSOCKS_PASSWORD", libparams.CaseSensitiveValue(), libparams.Unset())
 }
 
 // GetShadowSocksMethod obtains the ShadowSocks method to use from the environment variable