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Top Forums UNIX for Advanced & Expert Users Cmd 'cat /dev/urandom' not closing cleanly Post 302994402 by RudiC on Wednesday 22nd of March 2017 01:01:28 PM
Old 03-22-2017
/dev/random supplies an seemingly infinite number of random bytes (in fact limited to 32MB since linux 3.16), so your cat won't finish soon if at all,as the random generator won't send an EOF.
Quote:
/dev/random will return at most 512 bytes
(c.f. man random), so you might want to read that, of limit the byte count yourself, e.g. by using
Code:
dd if=/dev/urandom count=40 bs=1

in lieu of cat. Or, why not use bash's $RANDOM variable?
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MCOOKIE(1)						     Linux Programmer's Manual							MCOOKIE(1)

NAME
mcookie - generate magic cookies for xauth SYNOPSIS
mcookie [-v] [-f filename] DESCRIPTION
mcookie generates a 128-bit random hexadecimal number for use with the X authority system. Typical usage: xauth add :0 . `mcookie` The "random" number generated is actually the output of the MD5 message digest fed with various pieces of random information: the current time, the process id, the parent process id, the contents of an input file (if -f is specified), and several bytes of information from the first of the following devices which is present: /dev/random, /dev/urandom, files in /proc, /dev/audio. BUGS
The entropy in the generated 128-bit is probably quite small (and, therefore, vulnerable to attack) unless a non-pseudorandom number gener- ator is used (e.g., /dev/random under Linux). It is assumed that none of the devices opened will block. FILES
/dev/random /dev/urandom /dev/audio /proc/stat /proc/loadavg SEE ALSO
X(1), xauth(1), md5sum(1) AVAILABILITY
The mcookie command is part of the util-linux package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux/. 25 September 1995 MCOOKIE(1)
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