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CentOS 7.0 - man page for mcookie (centos section 1)

MCOOKIE(1)							   User Commands							MCOOKIE(1)

mcookie - generate magic cookies for xauth
mcookie [options]
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, and optionally the contents of an input file. and several bytes of information from the first of the following devices which is present: /dev/random, /dev/urandom, files in /proc, /dev/audio.
-f, --file=FILE Use file as a macig cookie seed. When file is defined as `-' character input is read from stdin. -v, --verbose Explain what is being done. -V, --version Output version information and exit. -h, --help Display this help and exit.
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.
/dev/random /dev/urandom /dev/audio /proc/stat /proc/loadavg
X(1), xauth(1), md5sum(1)
The mcookie command is part of the util-linux package and is available from util-linux June 2011 MCOOKIE(1)