This is a directory, with the following entries:
boot_id: a UUID generated the first time this is retrieved, and unvarying after that;
uuid: a UUID generated every time this is retrieved (this can thus be used to generate UUIDs at will);
entropy_avail: the pool’s entropy count, in bits;
poolsize: the entropy pool size, in bits;
urandom_min_reseed_secs: obsolete (used to determine the minimum number of seconds between urandom pool reseeding). This file is writable for compatibility purposes, but writing to it has no effect on any RNG behavior;
write_wakeup_threshold: when the entropy count drops below this (as a number of bits), processes waiting to write to /dev/random are woken up. This file is writable for compatibility purposes, but writing to it has no effect on any RNG behavior.