Hi,

fontconfig-config fails to configure (postinst) for a read-only mounted
/usr/local:
---- snip ----
Setting up fontconfig-config (2.15.0-2.3) ...
chmod: changing permissions of '/usr/local/share/fonts': Read-only file system
dpkg: error processing package fontconfig-config (--configure):
 installed fontconfig-config package post-installation script subprocess returned error exit status 1
---- snip ----

Cheers,
  Stefan.