The existing NSS databases utilize the original pre-Sleepycat Berkeley DB model which is unsafe when being utilized by more than one process. mod_nss should consider moving, or at least qualifying, the shared NSS SQLite DB model documented at: https://wiki.mozilla.org/NSS_Shared_DB
It doesn't work as-is. mod_nss does a chdir to NSSCertificateDatabase which fails if prefixed with sql: gencert doesn't handle a prefix properly either.
This was added in mod_nss 1.0.11.