On OS X systems (in my case, OS X 10.9.4), if the cache folder is on a mounted network share (e.g. because the user's home directory is on an SMB or AFP server), running fc-cache will fail to write to ~/.cache/fontconfig. This means the lengthy caching process is performed every time fontconfig is used.

The issue can be fixed by applying the patch below as evidently, OS X returns ENOTSUP when link() is performed on a file system that does not support hardlinks instead of EPERM.

The issue occurs in fontconfig 2.10 and 2.11, possibly older ones as well.

--- src/fcatomic.c.orig	2012-05-28 15:58:56.000000000 +0900
+++ src/fcatomic.c	2014-08-07 11:47:45.000000000 +0200
@@ -131,7 +131,7 @@ FcAtomicLock (FcAtomic *atomic)
        return FcFalse;
     }
     ret = link ((char *) atomic->tmp, (char *) atomic->lck);
-    if (ret < 0 && errno == EPERM)
+    if (ret < 0 && (errno == EPERM || errno == ENOTSUP))
     {
        /* the filesystem where atomic->lck points to may not supports
         * the hard link. so better try to fallback