Unix/Linux Go Back    


OpenDarwin 7.2.1 - man page for urandom (opendarwin section 4)

Linux & Unix Commands - Search Man Pages
Man Page or Keyword Search:   man
Select Man Page Set:       apropos Keyword Search (sections above)


RANDOM(4)			   BSD Kernel Interfaces Manual 			RANDOM(4)

NAME
     random , urandom -- random data source devices.

SYNOPSIS
     pseudo-device random

DESCRIPTION
     The random device produces uniformly distributed random byte values of potentially high
     quality.

     To obtain random bytes, open /dev/random for reading and read from it.

     To add entropy to the random generation system, open /dev/random for writing and write data
     that you believe to be somehow random.

     /dev/urandom is a compatibility nod to Linux. On Linux, /dev/urandom will produce lower
     quality output if the entropy pool drains, while /dev/random will prefer to block and wait
     for additional entropy to be collected.  With Yarrow, this choice and distinction is not
     necessary, and the two devices behave identically. You may use either.

OPERATION
     The random device implements the Yarrow pseudo random number generator algorithm and main-
     tains its entropy pool.  Addditional entropy is fed to the generator regularly by the
     SecurityServer daemon from random jitter measurements of the kernel.  SecurityServer is also
     responsible for periodically saving some entropy to disk and reloading it during startup to
     provide entropy in early system operation.

     You may feed additional entropy to the generator by writing it to the random device, though
     this is not required in a normal operating environment.

LIMITATIONS AND WARNINGS
     Yarrow is a fairly resilient algorithm, and is believed to be resistant to non-root.  The
     quality of its output is however dependent on regular addition of appropriate entropy. If
     the SecurityServer system daemon fails for any reason, output quality will suffer over time
     without any explicit indication from the random device itself.

     Paranoid programmers can counter-act this risk somewhat by collecting entropy of their
     choice (e.g. from keystroke or mouse timings) and seeding it into random directly before
     obtaining important random numbers.

FILES
     /dev/random
     /dev/urandom

HISTORY
     A random device appeared in Linux operating system.

Darwin					September 6, 2001				   Darwin
Unix & Linux Commands & Man Pages : ©2000 - 2018 Unix and Linux Forums


All times are GMT -4. The time now is 03:29 PM.