How can I check for available entropy? On linux systems, one can check for available entropy (useful to know if you're tapping /dev/random for any PRNG purposes) with 

cat /proc/sys/kernel/random/entropy_avail


However, there is no equivalent of /proc on a Mac (AFAIK). How can I check for available system entropy on a Mac? I'm running OS X 10.7.3 (Lion)



To update with some of my comments under Kyle's answer — One of the reasons for Macs not displaying this information is that it isn't needed (in most cases). Linux systems will block calls to /dev/random if there isn't enough entropy in the pool. On Macs, it periodically keeps adding to the entropy pool using the SecurityServer daemon.

However, it also notes that if the daemon fails for some reason, the output quality will decline without any indication of failure:


  The quality of
       its output is however dependent on regular addition of appropriate entropy. If the SecurityServer system daemon fails for any reason, output quality will suffer over time without any explicit indication
       from the random device itself.


So even though the amount of entropy is not made available easily, it doesn't mean it isn't there and there might be instances where its knowledge might be helpful.
This is not a solution, but a clarification of how entropy is gathered and used in Linux.

Linux actually has two different entropy pools:

/dev/random and /dev/urandom.

The former is a true random pool, fed by system entropy sources.
The latter is more of a PRNG such as those found on the BSD's and OS X.

However, even urandom requires a seed of 'real' random entropy in order to produce quality pseudo-random data. On recent kernels, a complete lack of entropy in /dev/random will still not block urandom, but urandom will re-use the last valid seed until more entropy becomes available. Because urandom is nonblocking, most services that require a steady stream of entropy use it rather than relying on /dev/random.

There are still some services however, such as various SSL suites, which can't make do with pseudo-random entropy, but require a truly unpredictable entropy source. In this case, urandom (or any other PRNG) can't be used, and /dev/random comes into play.