The RMS path cache in each process holds entries that translate
    DVI+DID+name to new DVI+DID. These are used to greatly speed
    up directory path walks. Cache entries representing ordinary
    directory lookups are invalidated through the volume directory
    sequence number mechanism (UDB$L_DIRSEQ), which is clocked
    on every volume dismount and each time a directory is deleted
    or renamed. However, there is no convenient mechanism for
    invalidating a cache entry that represents a symlink, whose
    interpretation is affected by logical names or modification of
    the symlink. The only way to eliminate stale cache entries is
    with a timeout. This parameter is the system-wide cache timeout.
    Special values:

          1 = don't keep cache entries
         -1 = keep cache entries forever
 RMS_PATH_TMO is a DYNAMIC parameter.