Linux Commands Examples

A great documentation place for Linux commands


generate magic cookies for xauth

see also : X - xauth - md5sum


mcookie [options]

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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 mcookie command is part of the util-linux package and is available from




The entropy in the generated 128-bit is probably quite small (and, therefore, vulnerable to attack) unless a non-pseudorandom number generator is used (e.g., /dev/random under Linux).

It is assumed that none of the devices opened will block.

see also

X , xauth , md5sum

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