Slide 39 of 115
Notes:
This is the always available builtin seeding source. It's usage consumes minimum CPU cycles under runtime and hence can be always used without drawbacks. The source used for seeding the PRNG contains of the current time, the current process id and (when applicable) a randomly choosen 1KB extract of the inter-process scoreboard structure of Apache. The drawback is that this is not really a strong source and at startup time (where the scoreboard is still not available) this source just produces a few bytes of entropy. So you should always, at least for the startup, use an additional seeding source.
This variant uses an external file /path/to/source as the source for seeding the PRNG. When bytes is specified, only the first bytes number of bytes of the file form the entropy (and bytes is given to /path/to/source as the first argument). When bytes is not specified the whole file forms the entropy (and 0 is given to /path/to/source as the first argument). Use this especially at startup time, for instance with an available /dev/random and/or /dev/urandom devices (which usually exist on modern Unix derivates like FreeBSD and Linux).
This variant uses an external executable /path/to/program as the source for seeding the PRNG. When bytes is specified, only the first bytes number of bytes of its stdout contents form the entropy. When bytes is not specified, the entirety of the data produced on stdout form the entropy. Use this only at startup time when you need a very strong seeding with the help of an external program (for instance as in the example above with the truerand utility you can find in the mod_ssl distribution which is based on the AT&T truerand library). Using this in the connection context slows down the server too dramatically, of course. So usually you should avoid using external programs in that context.
