unlink(2) and rmdir(2) are atomic as well. Also, there's a bit of atomicity in O_APPEND writes. Specifically, the end of the file will be adjusted atomically,

unlink(2) and rmdir(2) are atomic as well. Also, there's a bit of atomicity in O_APPEND writes. Specifically, the end of the file will be adjusted atomically, though the actual writes may not happen atomically (beware!). Thus processes that use O_APPEND to write to the same file will not have their writes stepping on each others', but if there's a power outage you can have a situation where the file's length was adjusted as if one O_APPEND write completed but you might get zeroes instead of the actual bytes meant to be written. As for mmap() and msync()... I don't recommend it. First, if the buffer and page cache are shared in the filesystem, then msync() is essentially a no-op. Second, if the mapping is not anonymous and you're writing to a file and anything goes wrong you'll get SIGBUS (ugh). Third, if the buffer and page caches are not shared then you really do need msync(MS_SYNC), and that can be expensive. Reading files via mmap() is ok, but writing to them via mmap() is fraught. "Leases" are a Linux thing, not POSIX or Unix.