Why is reading / dev / random byte by byte block so often?

Question

The following call returns quickly:

time dd if=/dev/random bs=1024 count=1
.... 0+1 records in
0+1 records out
49 bytes (49 B) copied, 0.000134028 s, 366 kB/s

real    0m0.004s
user    0m0.001s
sys    0m0.002s

However, if /dev/randomread one byte after another:

for i in {1..500}; do dd if=/dev/random bs=1 count=1 status=none; done

The loop reads a few bytes, then blocks for a few seconds, and then reads a few more bytes. Entering random characters on the keyboard speeds up the process, for example, if the entropy is not enough in the random pool. At the end of the cycle, the cycle takes many minutes.

What makes reading a byte by /dev/randombyte much slower than reading a block from it?

Uname -a:

Linux ... 2.6.32-431.11.2.el6.centos.plus.x86_64

Answer 1

The answer to your question:

49 bytes (49 B) copied, 0.000134028 s, 366 kB/s

, 1024 , , , . , , , .

/dev/random , , , .

/dev/urandom, .

Answer 2

/dev/random, /dev/urandom.

/dev/random , , urandom PRNG, .