Dear Hans and all,

I guess that the reason of failure is

mtx-install     | invalid database 'http://lmtx.pragma-ade.com/install-lmtx//tex/texmf-linux.tma'

and it seems texmf-linux-32.tma is correct name.  So I modified
bin/mtx-install.lua, mtxrun.lua as follows:

--- mtx-install.lua.orig        2019-09-02 10:19:28.387977529 +0900
+++ mtx-install.lua     2019-09-02 08:47:18.572271109 +0900
@@ -79,9 +79,9 @@
     ["windows-64"]     = "win64",
     ["win64"]          = "win64",
     --
-    ["linux"]          = "linux",
-    ["linux-32"]       = "linux",
-    ["linux32"]        = "linux",
+    ["linux"]          = "linux-32",
+    ["linux-32"]       = "linux-32",
+    ["linux32"]        = "linux-32",
     --
     ["linux-64"]       = "linux-64",
     ["linux64"]        = "linux-64",

--- mtxrun.lua.orig     2019-09-02 10:11:25.463821836 +0900
+++ mtxrun.lua  2019-09-02 08:46:40.695396705 +0900
@@ -4047,7 +4047,7 @@
  end
 else
  function resolvers.platform(t,k)
-  local platform="linux"
+  local platform="linux-32"
   os.setenv("MTX_PLATFORM",platform)
   os.platform=platform
   return platform

(but it seems they are overwritten during installation
so I copy them in /data/context then modify them as above
and copy them in bin/ by install.sh at an appropriate time.)

It looks installation goes fine with these modification.

I don't understand the installation process so I know
these are not correct fix but I hope this info helps to fix
the problem correctly.

Thanks for your effort.
Best regards.
Atsuhito Kohda