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RNDCTL(8) System Manager's Manual RNDCTL(8)

rndctl — in-kernel random number generator management tool

rndctl [-CcEe] [-d devname | -t devtype]

rndctl [-lsv] [-d devname | -t devtype]

rndctl -L save-file

rndctl -S save-file

The rndctl program displays statistics on the current state of the rnd(4) pseudo-driver, and allows the administrator to control which sources are allowed to contribute to the randomness pool maintained by rnd(4), as well as whether a given source counts as strongly random.

The following options are available:

Disable collection of timing information for the given device name or device type.
Enable collection of timing information for the given device name or device type.
Only the device named devname is altered or displayed. This is mutually exclusive with -t.
Disable entropy estimation from the collected timing information for the given device name or device type. If collection is still enabled, timing information is still collected and mixed into the internal entropy pool, but no entropy is assumed to be present.
Enable entropy estimation using the collected timing information for the given device name or device type.
Load saved entropy from file save-file and overwrite it with a seed derived by hashing it together with output from /dev/urandom so that the new seed has at least as much entropy as either the old seed had or the system already has. If interrupted, either the old seed or the new seed will be in place.
List all sources, or, if the -t or -d flags are specified, only those specified by the devtype or devname specified.
Save entropy pool to file save-file. The file format is specific to rndctl and includes an estimate of the amount of saved entropy and a checksum.
Display statistics on the current state of the random collection pool.
All devices of type devtype are altered or displayed. This is mutually exclusive with -d.

The available types are:

Physical hard drives.
Network interfaces.
Tape devices.
Terminal, mouse, or other user input devices.
Random number generators.
Verbose output: show entropy estimation statistics for each source.

/dev/random
Returns “good” values only.
/dev/urandom
Always returns data, degenerates to a pseudo-random generator.

rnd(4), rnd(9)

The rndctl program was first made available in NetBSD 1.3.

The rndctl program was written by Michael Graff ⟨explorer@flame.org⟩.

Turning on entropy estimation from unsafe or predictable sources will weaken system security, while turning on entropy collection from such sources may weaken system security.

Care should be taken when using this command.

August 10, 2014 NetBSD-9.2