diff --git a/lisp/util-install.lisp b/lisp/util-install.lisp
index 79b0df8..a3f05f0 100644
--- a/lisp/util-install.lisp
+++ b/lisp/util-install.lisp
@@ -10,7 +10,7 @@
 
 (defvar *ros-path* nil)
 (defvar *env* "ROSINSTALL")
-(defvar *checkout-default* 'checkout-github)
+(defvar *checkout-default* '(checkout-github))
 
 (defun install-impl (impl version argv cmds)
   "See install-impl-if-probed."
@@ -146,7 +146,8 @@ To differentiate it from the system with the same name in quicklisp, the path sh
          ((install-localpath-if-probed impl/version/tag))
          ;;github registerd system like "fukamachi/sblint" checkout
          (version
-          (funcall *checkout-default* impl version tag)
+          (loop for f in *checkout-default*
+                until (funcall f impl version tag))
           (read-call "roswell.util:local-project-build-hash" :rebuild t)
           (or (let ((project (merge-pathnames (format nil "local-projects/~A/~A/project.lisp" impl version)
                                               (roswell.util:checkoutdir))))
diff --git a/lisp/util.lisp b/lisp/util.lisp
index 2a2a64f..2487935 100644
--- a/lisp/util.lisp
+++ b/lisp/util.lisp
@@ -4,7 +4,7 @@
   (:import-from :ros :opt :ensure-asdf :*local-project-directories*)
   (:export
    :uname :uname-m :homedir :config :impl :which :config-env :checkoutdir
-   :parse-version-spec :download :expand :sh :chdir :system :module
+   :parse-version-spec :head :download :expand :sh :chdir :system :module
    :core-extention :clone-github :opt :read-call :set-opt :copy-dir
    :roswell-installable-searcher :setenv :unsetenv :ensure-asdf :split-sequence
    :local-project-build-hash))
@@ -128,6 +128,15 @@ Example:
     unless c collect i into r
     finally (return (coerce r 'string))))
 
+(defun head (uri &key proxy (verbose nil) (output :interactive))
+  (declare (ignorable proxy))
+  (values
+   (ignore-errors
+     (roswell:roswell `("roswell-internal-use" "head" ,(backslash-encode uri)
+                        ,@(when verbose (list verbose)))
+                      output nil)
+     t)))
+
 (defun download (uri file &key proxy (verbose nil) (output :interactive))
   "Interface to curl4 in the roswell C binary"
   (declare (ignorable proxy))