cache_dirs is a script to attempt to keep directory entries in memory to prevent disks from spinning up just to get a directory listing.   The Linux kernel keeps the most recently accessed disk buffers and directories in memory, and flushes out the least recently accessed entries. If we can 'trick' the kernel into keeping our directory entries in that memory cache, then directory scans will find what it is looking for is already in memory, and not need to access the physical disk to get it. A