diff --git a/cmd/vmr/cli/cli.go b/cmd/vmr/cli/cli.go
index 5029f14..fbddc4a 100644
--- a/cmd/vmr/cli/cli.go
+++ b/cmd/vmr/cli/cli.go
@@ -67,6 +67,7 @@ func (c *Cli) initiate() {
 	c.rootCmd.AddCommand(vcli.ShowInstalledSDKInfo)
 	c.rootCmd.AddCommand(vcli.UninstallVersionCmd)
 	c.rootCmd.AddCommand(vcli.SetupAutoCompletions)
+	c.rootCmd.AddCommand(vcli.ToggleAllowNestedSessions)
 }
 
 func (c *Cli) Run() {
diff --git a/cmd/vmr/cli/vcli/sessions.go b/cmd/vmr/cli/vcli/sessions.go
new file mode 100644
index 0000000..f722bb5
--- /dev/null
+++ b/cmd/vmr/cli/vcli/sessions.go
@@ -0,0 +1,28 @@
+package vcli
+
+import (
+	"fmt"
+
+	"github.com/gvcgo/goutils/pkgs/gtea/gprint"
+	"github.com/gvcgo/version-manager/internal/cnf"
+	"github.com/spf13/cobra"
+)
+
+/*
+Allow/Disallow nested sessions.
+*/
+
+var ToggleAllowNestedSessions = &cobra.Command{
+	Use:     "nested-sessions",
+	Aliases: []string{"ns"},
+	GroupID: GroupID,
+	Short:   "Toggle nested sessions.",
+	Long:    "Example: vmr ns.",
+	Run: func(cmd *cobra.Command, args []string) {
+		if ok := cnf.DefaultConfig.ToggleAllowNestedSessions(); ok {
+			fmt.Println(gprint.CyanStr("Nested sessions are now allowed."))
+		} else {
+			fmt.Println(gprint.YellowStr("Nested sessions are now disallowed."))
+		}
+	},
+}
diff --git a/internal/cnf/conf.go b/internal/cnf/conf.go
index 862fcf2..4340b99 100644
--- a/internal/cnf/conf.go
+++ b/internal/cnf/conf.go
@@ -28,12 +28,13 @@ const (
 Envs
 */
 const (
-	VMRSdkInstallationDirEnv string = "VMR_SDK_INSTALLATION_DIR"
-	VMRHostUrlEnv            string = "VMR_HOST"
-	VMRReverseProxyEnv       string = "VMR_REVERSE_PROXY"
-	VMRLocalProxyEnv         string = "VMR_LOCAL_PROXY"
-	VMRDonwloadThreadEnv     string = "VMR_DOWNLOAD_THREADS"
-	VMRUseCustomedMirrorEnv  string = "VMR_USE_CUSTOMED_MIRRORS"
+	VMRSdkInstallationDirEnv  string = "VMR_SDK_INSTALLATION_DIR"
+	VMRHostUrlEnv             string = "VMR_HOST"
+	VMRReverseProxyEnv        string = "VMR_REVERSE_PROXY"
+	VMRLocalProxyEnv          string = "VMR_LOCAL_PROXY"
+	VMRDonwloadThreadEnv      string = "VMR_DOWNLOAD_THREADS"
+	VMRUseCustomedMirrorEnv   string = "VMR_USE_CUSTOMED_MIRRORS"
+	VMRAllowNestedSessionsEnv string = "VMR_ALLOW_NESTED_SESSIONS"
 )
 
 /*
@@ -114,12 +115,13 @@ vmr config file.
 ==============================
 */
 type VMRConf struct {
-	ProxyUri           string `json,toml:"proxy_uri"`
-	ReverseProxy       string `json,toml:"reverse_proxy"`
-	SDKIntallationDir  string `json,toml:"sdk_installation_dir"`
-	VersionHostUrl     string `json,toml:"version_host_url"`
-	ThreadNum          int    `json,toml:"download_thread_num"`
-	UseCustomedMirrors bool   `json,toml:"use_customed_mirrors"`
+	ProxyUri            string `json,toml:"proxy_uri"`
+	ReverseProxy        string `json,toml:"reverse_proxy"`
+	SDKIntallationDir   string `json,toml:"sdk_installation_dir"`
+	VersionHostUrl      string `json,toml:"version_host_url"`
+	ThreadNum           int    `json,toml:"download_thread_num"`
+	UseCustomedMirrors  bool   `json,toml:"use_customed_mirrors"`
+	AllowNestedSessions bool   `json,toml:"allow_nested_sessions"`
 }
 
 func NewVMRConf() (v *VMRConf) {
@@ -145,6 +147,9 @@ func NewVMRConf() (v *VMRConf) {
 	if v.ReverseProxy != "" {
 		os.Setenv(VMRReverseProxyEnv, v.ReverseProxy)
 	}
+	if v.AllowNestedSessions {
+		os.Setenv(VMRAllowNestedSessionsEnv, "true")
+	}
 	return v
 }
 
@@ -204,3 +209,10 @@ func (v *VMRConf) ToggleUseCustomedMirrors() {
 	v.UseCustomedMirrors = !v.UseCustomedMirrors
 	v.Save()
 }
+
+func (v *VMRConf) ToggleAllowNestedSessions() bool {
+	v.Load()
+	v.AllowNestedSessions = !v.AllowNestedSessions
+	v.Save()
+	return v.AllowNestedSessions
+}
diff --git a/internal/terminal/terminal.go b/internal/terminal/terminal.go
index 29125ff..9d2ab54 100644
--- a/internal/terminal/terminal.go
+++ b/internal/terminal/terminal.go
@@ -10,6 +10,7 @@ import (
 
 	"github.com/gvcgo/goutils/pkgs/gtea/gprint"
 	"github.com/gvcgo/goutils/pkgs/gutils"
+	"github.com/gvcgo/version-manager/internal/cnf"
 	"github.com/gvcgo/version-manager/internal/installer/install"
 	"github.com/gvcgo/version-manager/internal/shell/sh"
 	"github.com/gvcgo/version-manager/internal/terminal/term"
@@ -116,8 +117,8 @@ func GetTerminalSize() (height, width int, err error) {
 }
 
 func RunTerminal() {
-	// already run a terminal.
-	if os.Getenv(sh.VMDisableEnvName) != "" {
+	// already run a terminal. Allow/Disallow nested sessions.
+	if os.Getenv(sh.VMDisableEnvName) != "" && !cnf.DefaultConfig.AllowNestedSessions {
 		return
 	}