crash on startup if cache directory is not writeable
$ chmod u-w .
$ kresd
[cache] LMDB error: Permission denied
kresd: lib/cdb_lmdb.c:67: lmdb_error: Assertion `false' failed.
Aborted (core dumped)
$ chmod u-w .
$ kresd
[cache] LMDB error: Permission denied
kresd: lib/cdb_lmdb.c:67: lmdb_error: Assertion `false' failed.
Aborted (core dumped)