try to not require root if we are running as the user we want

ensureuserisroot.go → checkuser.go

@@ -21,14 +21,19 @@ import (
 	"os/user"
 )
 
-func ensureUserIsRoot() error {
-	user, err := user.Current()
+func checkUser(username string) error {
+	cur, err := user.Current()
 	if err != nil {
 		return err
 	}
 
-	if user.Uid != "0" {
-		return fmt.Errorf("must be run as root")
+	other, err := user.Lookup(username)
+	if err != nil {
+		return err
+	}
+
+	if cur.Uid != other.Uid {
+		return fmt.Errorf("must be run as %s", username)
 	}
 
 	return nil

instance.go

@@ -385,7 +385,12 @@ func (i *Instance) ExecuteAsManager() error {
 // This command only functions if the calling program is running as root.
 // It returns any error encountered.
 func (i *Instance) ExecuteAsUser(execUser string) error {
-	if err := ensureUserIsRoot(); err != nil {
+	// no need to switch users if we're already who we want to be
+	if err := checkUser(execUser); err == nil {
+		return nil
+	}
+
+	if err := checkUser("root"); err != nil {
 		return err
 	}