diff --git a/configure b/configure
index 596d3524..220dfe79 100755
--- a/configure
+++ b/configure
@@ -650,8 +650,8 @@ ac_includes_default="\
 ac_header_c_list=
 ac_func_c_list=
 ac_subst_vars='LTLIBOBJS
-DF
-MKTEMP
+unionfs
+mergerfs
 AWK
 LN_S
 INSTALL_DATA
@@ -4314,6 +4314,8 @@ test -z "$INSTALL_SCRIPT" && INSTALL_SCRIPT='${INSTALL}'
 test -z "$INSTALL_DATA" && INSTALL_DATA='${INSTALL} -m 644'
 
 
+
+
 # symlinks
 { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether ln -s works" >&5
 printf %s "checking whether ln -s works... " >&6; }
@@ -4392,16 +4394,124 @@ printf "%s\n" "yes" >&6; }
 fi
 
 #mktemp
-# Extract the first word of "mktemp", so it can be a program name with args.
-set dummy mktemp; ac_word=$2
+
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for mktemp" >&5
+printf %s "checking for mktemp... " >&6; }
+
+if ! type -p mktemp >/dev/null 2>&1
+then
+        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: no" >&5
+printf "%s\n" "no" >&6; }
+        as_fn_error $? "try needs mktemp to work, but it could not be found." "$LINENO" 5
+else
+        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+printf "%s\n" "yes" >&6; }
+
+fi
+
+
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether mktemp -d works" >&5
+printf %s "checking whether mktemp -d works... " >&6; }
+d=$(mktemp -d 2>/dev/null)
+if test "$?" != 0 || ! test -d "$d"
+then
+        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: no" >&5
+printf "%s\n" "no" >&6; }
+        as_fn_error $? "try needs mktemp -d to work, but your mktemp does not support the -d option." "$LINENO" 5
+else
+        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+printf "%s\n" "yes" >&6; }
+        rmdir "$d"
+fi
+
+
+
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for df" >&5
+printf %s "checking for df... " >&6; }
+
+if ! type -p df >/dev/null 2>&1
+then
+        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: no" >&5
+printf "%s\n" "no" >&6; }
+        as_fn_error $? "try needs df to work, but it could not be found." "$LINENO" 5
+else
+        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+printf "%s\n" "yes" >&6; }
+
+fi
+
+
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for find" >&5
+printf %s "checking for find... " >&6; }
+
+if ! type -p find >/dev/null 2>&1
+then
+        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: no" >&5
+printf "%s\n" "no" >&6; }
+        as_fn_error $? "try needs find to work, but it could not be found." "$LINENO" 5
+else
+        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+printf "%s\n" "yes" >&6; }
+
+fi
+
+
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for findmnt" >&5
+printf %s "checking for findmnt... " >&6; }
+
+if ! type -p findmnt >/dev/null 2>&1
+then
+        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: no" >&5
+printf "%s\n" "no" >&6; }
+        as_fn_error $? "try needs findmnt to work, but it could not be found." "$LINENO" 5
+else
+        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+printf "%s\n" "yes" >&6; }
+
+fi
+
+
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for sort" >&5
+printf %s "checking for sort... " >&6; }
+
+if ! type -p sort >/dev/null 2>&1
+then
+        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: no" >&5
+printf "%s\n" "no" >&6; }
+        as_fn_error $? "try needs sort to work, but it could not be found." "$LINENO" 5
+else
+        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+printf "%s\n" "yes" >&6; }
+
+fi
+
+
+
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for overlayfs" >&5
+printf %s "checking for overlayfs... " >&6; }
+
+if ! lsmod | grep -q overlay
+then
+        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: no" >&5
+printf "%s\n" "no" >&6; }
+        as_fn_error $? "try needs overlayfs to work, but the overlay module did not appear in the output of lsmod." "$LINENO" 5
+else
+        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+printf "%s\n" "yes" >&6; }
+
+fi
+
+
+# Extract the first word of "mergerfs", so it can be a program name with args.
+set dummy mergerfs; ac_word=$2
 { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for $ac_word" >&5
 printf %s "checking for $ac_word... " >&6; }
-if test ${ac_cv_prog_MKTEMP+y}
+if test ${ac_cv_prog_mergerfs+y}
 then :
   printf %s "(cached) " >&6
 else $as_nop
-  if test -n "$MKTEMP"; then
-  ac_cv_prog_MKTEMP="$MKTEMP" # Let the user override the test.
+  if test -n "$mergerfs"; then
+  ac_cv_prog_mergerfs="$mergerfs" # Let the user override the test.
 else
 as_save_IFS=$IFS; IFS=$PATH_SEPARATOR
 for as_dir in $PATH
@@ -4414,7 +4524,7 @@ do
   esac
     for ac_exec_ext in '' $ac_executable_extensions; do
   if as_fn_executable_p "$as_dir$ac_word$ac_exec_ext"; then
-    ac_cv_prog_MKTEMP="yes"
+    ac_cv_prog_mergerfs="yes"
     printf "%s\n" "$as_me:${as_lineno-$LINENO}: found $as_dir$ac_word$ac_exec_ext" >&5
     break 2
   fi
@@ -4422,47 +4532,29 @@ done
   done
 IFS=$as_save_IFS
 
-  test -z "$ac_cv_prog_MKTEMP" && ac_cv_prog_MKTEMP="no"
+  test -z "$ac_cv_prog_mergerfs" && ac_cv_prog_mergerfs="no"
 fi
 fi
-MKTEMP=$ac_cv_prog_MKTEMP
-if test -n "$MKTEMP"; then
-  { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $MKTEMP" >&5
-printf "%s\n" "$MKTEMP" >&6; }
+mergerfs=$ac_cv_prog_mergerfs
+if test -n "$mergerfs"; then
+  { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $mergerfs" >&5
+printf "%s\n" "$mergerfs" >&6; }
 else
   { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: no" >&5
 printf "%s\n" "no" >&6; }
 fi
 
 
-if test "$MKTEMP" = "no"
-then
-        as_fn_error $? "try needs mktemp to work, but it could not be found." "$LINENO" 5
-fi
-{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether mktemp -d works" >&5
-printf %s "checking whether mktemp -d works... " >&6; }
-d=$(mktemp -d 2>/dev/null)
-if test "$?" != 0 || ! test -d "$d"
-then
-        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: no" >&5
-printf "%s\n" "no" >&6; }
-        as_fn_error $? "try needs mktemp -d to work, but your mktemp does not support the -d option." "$LINENO" 5
-else
-        rmdir "$d"
-        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: yes" >&5
-printf "%s\n" "yes" >&6; }
-fi
-
-# Extract the first word of "df", so it can be a program name with args.
-set dummy df; ac_word=$2
+# Extract the first word of "unionfs", so it can be a program name with args.
+set dummy unionfs; ac_word=$2
 { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for $ac_word" >&5
 printf %s "checking for $ac_word... " >&6; }
-if test ${ac_cv_prog_DF+y}
+if test ${ac_cv_prog_unionfs+y}
 then :
   printf %s "(cached) " >&6
 else $as_nop
-  if test -n "$DF"; then
-  ac_cv_prog_DF="$DF" # Let the user override the test.
+  if test -n "$unionfs"; then
+  ac_cv_prog_unionfs="$unionfs" # Let the user override the test.
 else
 as_save_IFS=$IFS; IFS=$PATH_SEPARATOR
 for as_dir in $PATH
@@ -4475,7 +4567,7 @@ do
   esac
     for ac_exec_ext in '' $ac_executable_extensions; do
   if as_fn_executable_p "$as_dir$ac_word$ac_exec_ext"; then
-    ac_cv_prog_DF="yes"
+    ac_cv_prog_unionfs="yes"
     printf "%s\n" "$as_me:${as_lineno-$LINENO}: found $as_dir$ac_word$ac_exec_ext" >&5
     break 2
   fi
@@ -4483,24 +4575,66 @@ done
   done
 IFS=$as_save_IFS
 
-  test -z "$ac_cv_prog_DF" && ac_cv_prog_DF="no"
+  test -z "$ac_cv_prog_unionfs" && ac_cv_prog_unionfs="no"
 fi
 fi
-DF=$ac_cv_prog_DF
-if test -n "$DF"; then
-  { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $DF" >&5
-printf "%s\n" "$DF" >&6; }
+unionfs=$ac_cv_prog_unionfs
+if test -n "$unionfs"; then
+  { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $unionfs" >&5
+printf "%s\n" "$unionfs" >&6; }
 else
   { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: no" >&5
 printf "%s\n" "no" >&6; }
 fi
 
 
-if test "$MKTEMP" = "no"
+
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for union helpers (unionfs or mergerfs)" >&5
+printf %s "checking for union helpers (unionfs or mergerfs)... " >&6; }
+if test "$ac_cv_prog_mergerfs" = "no" && test "$ac_cv_prog_unionfs" = "no"
 then
-        as_fn_error $? "try needs mktemp to work, but it could not be found." "$LINENO" 5
+        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: no; try may issue warnings and error messages" >&5
+printf "%s\n" "no; try may issue warnings and error messages" >&6; }
+else
+        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+printf "%s\n" "yes" >&6; }
 fi
 
+
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for readlink" >&5
+printf %s "checking for readlink... " >&6; }
+
+if ! type -p readlink >/dev/null 2>&1
+then
+        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: no" >&5
+printf "%s\n" "no" >&6; }
+        as_fn_error $? "try needs readlink to work, but it could not be found." "$LINENO" 5
+else
+        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+printf "%s\n" "yes" >&6; }
+
+fi
+
+
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for unshare" >&5
+printf %s "checking for unshare... " >&6; }
+
+res=$(unshare --mount --map-root-user --user --pid --fork -- ls $PWD/try 2>/dev/null)
+
+if
+test "$?" != 0 || test "$res" != "$PWD/try"
+
+then
+        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: no" >&5
+printf "%s\n" "no" >&6; }
+        as_fn_error $? "try needs unshare to work, but could not run unshare." "$LINENO" 5
+else
+        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+printf "%s\n" "yes" >&6; }
+
+fi
+
+
 ac_config_files="$ac_config_files Makefile:Makefile.in"
 
 cat >confcache <<\_ACEOF
diff --git a/configure.ac b/configure.ac
index 2739cf8c..4320f7b2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -69,6 +69,20 @@ AC_SUBST(enable_utils)
 # install
 AC_PROG_INSTALL
 
+dnl TRY_REQUIRE_PROG(progname, checking_msg, pre, true_if_failed, post, fail_msg)
+AC_DEFUN([TRY_REQUIRE_PROG], [
+AC_MSG_CHECKING([ifelse([$2], [], [for $1], [$2])])
+$3
+if ifelse([$4], [], [! type -p $1 >/dev/null 2>&1], [$4])
+then
+        AC_MSG_RESULT([no])
+        AC_MSG_ERROR([try needs $1 to work, but ifelse([$6], [], [it could not be found], [$6]).])
+else
+        AC_MSG_RESULT([yes])
+        $5
+fi
+])
+
 # symlinks
 AC_PROG_LN_S
 if test "$LN_S" != "ln -s"
@@ -87,27 +101,33 @@ else
 fi
 
 #mktemp
-AC_CHECK_PROG([MKTEMP], [mktemp], [yes], [no])
-if test "$MKTEMP" = "no"
-then
-        AC_MSG_ERROR([try needs mktemp to work, but it could not be found.])
-fi
-AC_MSG_CHECKING([whether mktemp -d works])
-d=$(mktemp -d 2>/dev/null)
-if test "$?" != 0 || ! test -d "$d"
+TRY_REQUIRE_PROG([mktemp])
+TRY_REQUIRE_PROG([mktemp -d], [whether mktemp -d works], [d=$(mktemp -d 2>/dev/null)], [test "$?" != 0 || ! test -d "$d"], [rmdir "$d"], [your mktemp does not support the -d option])
+
+TRY_REQUIRE_PROG([df])
+TRY_REQUIRE_PROG([find])
+TRY_REQUIRE_PROG([findmnt])
+TRY_REQUIRE_PROG([sort])
+
+TRY_REQUIRE_PROG([overlayfs],[for overlayfs],[],[! lsmod | grep -q overlay], [], [the overlay module did not appear in the output of lsmod])
+
+AC_CHECK_PROG([mergerfs], [mergerfs], [yes], [no])
+AC_CHECK_PROG([unionfs], [unionfs], [yes], [no])
+
+AC_MSG_CHECKING([for union helpers (unionfs or mergerfs)])
+if test "$ac_cv_prog_mergerfs" = "no" && test "$ac_cv_prog_unionfs" = "no"
 then
-        AC_MSG_RESULT([no])
-        AC_MSG_ERROR([try needs mktemp -d to work, but your mktemp does not support the -d option.])
+        AC_MSG_RESULT([no; try may issue warnings and error messages])
 else
-        rmdir "$d"
         AC_MSG_RESULT([yes])
 fi
 
-AC_CHECK_PROG([DF], [df], [yes], [no])
-if test "$MKTEMP" = "no"
-then
-        AC_MSG_ERROR([try needs mktemp to work, but it could not be found.])
-fi
+TRY_REQUIRE_PROG([readlink])
+TRY_REQUIRE_PROG([unshare], [for unshare], [
+res=$(unshare --mount --map-root-user --user --pid --fork -- ls $PWD/try 2>/dev/null)
+], [
+test "$?" != 0 || test "$res" != "$PWD/try"
+], [], [could not run unshare])
 
 AC_CONFIG_FILES([Makefile:Makefile.in])
 AC_OUTPUT