Copyright (c) 1997 Michael Graff
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.Dd August 10, 2014 .Dt RNDCTL 8 .Os .Sh NAME .Nm rndctl .Nd in-kernel random number generator management tool .Sh SYNOPSIS .Nm .Op Fl CcEe .Op Fl d Ar devname | Fl t Ar devtype .Nm .Op Fl lsv .Op Fl d Ar devname | Fl t Ar devtype .Nm .Fl L Ar save-file .Nm .Fl S Ar save-file .Sh DESCRIPTION The .Nm program displays statistics on the current state of the .Xr rnd 4 pseudo-driver, and allows the administrator to control which sources are allowed to contribute to the randomness pool maintained by .Xr rnd 4 , as well as whether a given source counts as strongly random.
p The following options are available: l -tag -width 123456 t Fl C Disable collection of timing information for the given device name or device type. t Fl c Enable collection of timing information for the given device name or device type. t Fl d Only the device named .Ar devname is altered or displayed. This is mutually exclusive with .Fl t . t Fl E 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. t Fl e Enable entropy estimation using the collected timing information for the given device name or device type. t Fl L Load saved entropy from file .Ar save-file , which will be overwritten and deleted before the entropy is loaded into the kernel. t Fl l List all sources, or, if the .Fl t or .Fl d flags are specified, only those specified by the .Ar devtype or .Ar devname specified. t Fl S Save entropy pool to file .Ar save-file . The file format is specific to .Nm and includes an estimate of the amount of saved entropy and a checksum. t Fl s Display statistics on the current state of the random collection pool. t Fl t All devices of type .Ar devtype are altered or displayed. This is mutually exclusive with .Fl d .
p The available types are: l -tag -width "diskx" t Ic disk Physical hard drives. t Ic net Network interfaces. t Ic tape Tape devices. t Ic tty Terminal, mouse, or other user input devices. t Ic rng Random number generators. .El t Fl v Verbose output: show entropy estimation statistics for each source. .El .Sh FILES l -tag -width /dev/urandomx -compact t Pa /dev/random Returns .Dq good values only. t Pa /dev/urandom Always returns data, degenerates to a pseudo-random generator. .El .Sh SEE ALSO .Xr rnd 4 , .Xr rnd 9 .Sh HISTORY The .Nm program was first made available in .Nx 1.3 . .Sh AUTHORS The .Nm program was written by .An Michael Graff .Aq explorer (at] flame.org . .Sh BUGS 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.
p Care should be taken when using this command.
Indexes created Sun Oct 19 02:09:48 GMT 2025