haveged(8)						  SYSTEM ADMINISTRATION COMMANDS						haveged(8)

NAME

       haveged - Generate random numbers and feed linux random device.

SYNOPSIS

       haveged [options]

DESCRIPTION

       The  HAVEGE  (HArdware Volatile Entropy Gathering and Expansion) algorithum harvests the indirect effects of hardware events on hidden pro-
       cessor state (caches, branch predictors, memory translation tables, etc) to generate a random sequence.	The effects of	interrupt  service
       on  processor  state  are visible from userland as timing variations in program execution speed. Using a branch-rich calculation that fills
       the processor instruction and data cache, a high resolution timer source such as the processor time stamp counter  can  generate  a  random
       sequence even on an "idle" system.

       In  Linux,  the	hardware  events that are the ultimate source of any random number sequence are pooled by the /dev/random device for later
       distribution via the device interface. The standard mechanism of harvesting randomness for the pool may not be sufficient to  meet  demand,
       especially on those systems with high needs or limited user interaction. Haveged provides a daemon  to fill /dev/random whenever the supply
       of random bits in /dev/random falls below the low water mark of the device.

       Haveged also provides a direct file system interface to the collection mechanism that is also useful in other circumstances where access to
       the dev/random interface is either not available or inappropriate.

       In  either  case,  haveged uses HAVEGE to maintain a 1M pool of random bytes consumed by the interface. The principle inputs to havaged are
       the sizes of the processor instruction and data caches used to setup the HAVEGE collector. The haveged default is a 4kb data  cache  and  a
       16kb instruction cache. On machines with a cpuid instruction, haveged will attempt to select appropriate values from internal tables.

       Although  CISC  architectures appear insensitive to tuning parameters, there is no guarantee that manual tuning of the algorithm may not be
       required under some circumstances. The output of the HAVEGE random number generator should be  verified	on  any  installation  before  the
       haveged is put into production.

OPTIONS

       -b nnn, --buffer=nnn
	      Set collection buffer size to nnn KB. Default is 128.

       -d nnn, --data=nnn
	      Set data cache size to nnn KB. Default is 16 or as determined by cpuid.

       -f file, --file=file
	      Set output file path for non-daemon use. Default is "sample", use '-' for stdout.

       -i nnn, --inst=nnn
	      Set instruction cache size to nnn KB. Default is 16 or as determined by cpuid.

       -n nnn, --number=nnn
	      Set  number  of bytes written to the outputfile. The value may be specified using one of the suffixes k, m, g, or t. The upper bound
	      of this value is "16t" (2^44 Bytes = 16TB).  A value of 0 indicates unbounded output and forces output to stdout.

       -r n, --run=n
	      Set run level for daemon interface:

	      n = 0 Run as daemon - must be root. Fills /dev/random when the supply of random bits
	       falls below the low water mark of the device. This argument is required if the
	       daemon interface is not present. If the daemon interface is present, this takes
	       precedence over any -r value.

	      n = 1 Display configuration info and terminate.

	      n > 1 Write <n> kb of output. Deprecated (use -n instead), only provided for backward compatibility.

       -v n, --verbose=n
	      Set output level 0=minimal, 1=config/fill items, use -1 for all diagnostics.

       -w nnn, --write=nnn
	      Set write_wakeup_threshold of daemon interface to nnn bits. Applies only to run level 0.

       -?, --help
	      This summary of program options.

DIAGNOSTICS

       The following diagnostics may be issued to stderr upon termination:

       Cannot fork into the background
	      Call to daemon(3) failed.

       Cannot open file <s> for writing.
	      Could not open sample file <s> for writing.

       Cannot write data in file:
	      Could not write data to the sample file.

       Couldn't get poolsize.
	      Unable to read /proc/sys/kernel/random/poolsize

       Couldn't initialize HAVEGE rng
	      Invalid data or instruction cache size.

       Couldn't open random device
	      Could not open /dev/random for read-write.

       Couldn't query entropy-level from kernel: error
	      Call to ioctl(2) failed.

       Couldn't open PID file <path> for writing
	      Error writing /var/run/haveged.pid

       Fail:set_watermark()
	      Unable to write to /proc/sys/kernel/random/write_wakeup_threshold

       RNDADDENTROPY failed!
	      Call to ioctl(2) to add entropy failed

       Select error
	      Call to select(2) failed.

EXAMPLES

       Write 1.5MB of random data to the file /tmp/random
	      haveged -n 1.5M -f /tmp/random

       Generate a /tmp/keyfile for disk encryption with LUKS
	      haveged -n 2048 -f /tmp/keyfile

       Overwrite partition /dev/sda1 with random data. Be careful, all data on the partition will be lost!
	      haveged -n 0 | dd of=/dev/sda1

       Generate random ASCII passwords of the length 16 characters
	      (haveged -n 1000 -f - 2>/dev/null | tr -cd '[:graph:]' | fold -w 16 && echo ) | head

       Write endless stream of random bytes to the pipe. Utility pv measures the speed by which data are written to the pipe.
	      haveged -n 0 | pv > /dev/null

       Evaluate speed of haveged to generate 1GB of random data
	      haveged -n 1g -f - | dd of=/dev/null

       Create a random key file containing 65 random keys for the encryption program aespipe.
	      haveged -n 3705 -f - 2>/dev/null | uuencode -m - | head -n 66 | tail -n 65

       Test the randomness of the generated data with dieharder test suite
	      haveged -n 0 | dieharder -g 200 -a

SEE ALSO

       cryptsetup(8), aespipe(1), pv(1), openssl(1), uuencode(1)

AUTHOR

       Gary Wuertz <gary@issiweb.com> and Jirka Hladky

SEE ALSO

       http://www.issihosts/haveged/

version 1.3							 October 23, 2011							haveged(8)