On Mon, Jan 14, 2013 at 3:00 PM, Noah Misch <n...@leadboat.com> wrote: > On Mon, Jan 14, 2013 at 02:21:00PM +0200, Marko Kreen wrote: >> Note: reading from /dev/urandom does not affect /dev/random. > > Reading from /dev/urandom drains the pool that serves /dev/random: > > $ cat /proc/sys/kernel/random/entropy_avail > 3596 > $ dd iflag=nonblock bs=100 count=1 if=/dev/random of=/dev/null > 1+0 records in > 1+0 records out > 100 bytes (100 B) copied, 0.000174798 s, 572 kB/s > $ cat /proc/sys/kernel/random/entropy_avail > 2839 > $ head -c10000000 /dev/urandom >/dev/null > $ cat /proc/sys/kernel/random/entropy_avail > 212 > $ dd iflag=nonblock bs=100 count=1 if=/dev/random of=/dev/null > 0+1 records in > 0+1 records out > 38 bytes (38 B) copied, 0.000101439 s, 375 kB/s
This slightly weakens my argument, but not completely - any /dev/urandom-using processes are still unaffected, but indeed processes using /dev/random can block. But what are those? So it's still problem only on systems that do not have /dev/urandom. Btw, observe fun behaviour: $ cat /proc/sys/kernel/random/entropy_avail 3451 $ cat /proc/sys/kernel/random/entropy_avail 3218 $ cat /proc/sys/kernel/random/entropy_avail 3000 $ cat /proc/sys/kernel/random/entropy_avail 2771 $ cat /proc/sys/kernel/random/entropy_avail 2551 $ cat /proc/sys/kernel/random/entropy_avail 2321 $ cat /proc/sys/kernel/random/entropy_avail 2101 $ cat /proc/sys/kernel/random/entropy_avail 1759 $ cat /proc/sys/kernel/random/entropy_avail 1527 $ cat /proc/sys/kernel/random/entropy_avail 1319 $ cat /proc/sys/kernel/random/entropy_avail 1080 $ cat /proc/sys/kernel/random/entropy_avail 844 $ cat /proc/sys/kernel/random/entropy_avail 605 $ cat /proc/sys/kernel/random/entropy_avail 366 $ cat /proc/sys/kernel/random/entropy_avail 128 $ cat /proc/sys/kernel/random/entropy_avail 142 $ cat /proc/sys/kernel/random/entropy_avail Each exec() eats from the pool on modern system. -- marko -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
