Section: Maintenance Commands (8)
Updated: March 2001
Index Return to Main Contents



rngd - Check and feed random data from hardware device to kernel random device



rngd [-b, --background] [-f, --foreground] [-o, --random-device=file] [-r, --rng-device=file] [-s, --random-step=nnn] [-W, --fill-watermark=nnn] [-t, --timeout=nnn] [-?, --help] [-V, --version]  


This daemon feeds data from a random number generator to the kernel's random number entropy pool, after first checking the data to ensure that it is properly random.

The -f or --foreground options can be used to tell rngd to avoid forking on startup. This is typically used for debugging. The -f or --foreground options, which fork and put rngd into the background automatically, are the default.

The -r or --rng-device options can be used to select an alternate source of input, besides the default /dev/hwrandom. The -o or --random-device options can be used to select an alternate entropy output device, besides the default /dev/random. Note that this device must support the Linux kernel /dev/random ioctl API.

FIXME: document random-step and timeout



-b, --background
Become a daemon (default)
-f, --foreground
Do not fork and become a daemon
-o file, --random-device=file
Kernel device used for random number output (default: /dev/random)
-r file, --rng-device=file
Kernel device used for random number input (default: /dev/hwrandom)
-s nnn, --random-step=nnn
Number of bytes written to random-device at a time (default: 64)
-W n, --fill-watermark=nnn
Once we start doing it, feed entropy to random-device until at least fill-watermark bits of entropy are available in its entropy pool (default: 2048). Setting this too high will cause rngd to dominate the contents of the entropy pool. Low values will hurt system performance during entropy starves. Do not set fill-watermark above the size of the entropy pool (usually 4096 bits).
-t nnn, --timeout=nnn
Interval written to random-device when the entropy pool is full, in seconds, or 0 to disable (default: 60)
-?, --help
Give a short summary of all program options.
-V, --version
Print program version



Philipp Rumpf
Jeff Garzik - jgarzik@pobox.com
Matt Sottek