Messages in this thread | | | Date | Mon, 05 Apr 2010 09:50:44 +0200 | From | Jan Ceuleers <> | Subject | Re: Reading entropy_avail file appears to consume entropy |
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Alexander Konovalenko wrote: > On Mar 19, Jan Ceuleers wrote: >> I'm using the 2.6.31 kernel that comes with Ubuntu 9.10. >> >> If I >> >> # watch cat /proc/sys/kernel/random/entropy_avail >> >> then the size of the entropy pool falls rapidly (by more than 200 bytes per 2s interval). >> It settles down around 160 bytes. > > Jan, did you find out anything interesting about this issue? > > I have a wild guess, although I have no idea whether it can be > correct. I couldn't catch any user-space /dev/random or /dev/urandom > readers with fuser, so I think something in the kernel is using up the > entropy. If I remember correctly, recent Ubuntu releases were supposed > to include a security feature that randomizes memory layout in order > to mitigate some kinds of security vulnerabilities. What if each time > a new process is started the kernel needs to obtain a significant > number of random bytes? Here is some supporting evidence. I can > reproduce the behavior you describe on a vanilla Ubuntu 9.10 system > (without latest updates). But if I watch entropy_avail using a Python > script that does not start a new process every time, then the > available entropy amount won't decrease. (The system is otherwise > idle.) Give it a try: > > $ python > import sys, time > while True: > sys.stdout.write(open('/proc/sys/kernel/random/entropy_avail', > 'r').read()) > time.sleep(1) > > It would be great if someone with knowledge about this could confirm > or refute my guess. > > -- Alexander >
Alexander,
Thanks, this never made it out to LKML so I'm forwarding it now.
This does sound quite plausible; does anyone from Ubuntu want to chip in?
Thanks, Jan
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