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RedHat 9 (Linux i386) - man page for mcookie (redhat section 1)

MCOOKIE(1)						     Linux Programmer's Manual							MCOOKIE(1)

mcookie - generate magic cookies for xauth
mcookie [-v] [-f filename ]
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 piece 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.
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) 25 September 1995 MCOOKIE(1)