rngd man page

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


rngd [-b, --background] [-f, --foreground] [-d, --debug] [-l, --list] [-x, --exclude] [-i, --ignorefail] [-o, --random-device=file] [-p, --pid-file=file] [-r, --rng-device=file] [-s, --random-step=nnn] [-W, --fill-watermark=nnn] [-q, --quiet] [-?, --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 -b or --background 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/hwrng. 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.


-b, --background

Become a daemon (default)

-f, --foreground

Do not fork and become a daemon

-d, --debug

Enable debug messages

-l, --list

List the indexes and names of available entropy sources

-x, --exclude

Disable entropy sources based on index reported from --list option

-p file, --pid-file=file

File used for recording daemon PID, and multiple exclusion (default: /var/run/rngd.pid)

-i, --ignorefail

Ignore repeated fips failures

-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/hwrng)

-s nnn, --random-step=nnn

Number of bytes written to random-device at a time (default: 64)

-e nnn, --entropy-count=nnn

Number of bits to consider random when adding entropy. 1<=e<=8 (default: 8)

-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. By default, this value is set to 75% of the entropy pool size or 2048 bits if the entropy pool size couldn't be determined. 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).

-q, --quiet

Suppress error messages

-?, --help

Give a short summary of all program options.

-V, --version

Print program version


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

Referenced By

ipsec_rsasigkey(8), rngd_selinux(8), rngtest(1).

March 2001 rng-tools 6