> Am I just getting lucky with a race condition? Probably this is buffering, either from dd or from the kernel. $ dd if=/dev/urandom bs=1M count=1 of=test.b

> Am I just getting lucky with a race condition? Probably this is buffering, either from dd or from the kernel. $ dd if=/dev/urandom bs=1M count=1 of=test.bin 2>/dev/null $ cp test.bin test2.bin $ cat < test2.bin | tee test2.bin >/dev/null $ diff test.bin test2.bin Binary files test.bin and test2.bin differ $ wc -c test{2,}.bin 131072 test2.bin 1048576 test.bin Notice the file got truncated at exactly 128k; a nice round size for a write cache.