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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 random information from one of the sources /dev/urandom, /dev/random, or libc pseudo-random functions in this preference order.


-f, --file=FILE
Use additional file as a macig cookie random seed. When file is defined as '-' character input is read from stdin.
-m, --max-size=number
Read form FILE only number of bytes. This option is meant to be used when reading additional randomness from a device.
The number argument may be followed by the multiplicative suffixes KiB=1024, MiB=1024*1024, and so on for GiB, TiB, PiB, EiB, ZiB and YiB (the "iB" is optional, e.g., "K" has the same meaning as "KiB") or the suffixes KB=1000, MB=1000*1000, and so on for GB, TB, PB, EB, ZB and YB.
-v, --verbose
Inform where randomness originated, with amount of entropy read from each source.
-V, --version
Display version information and exit.
-h, --help
Display help text and exit.


It is assumed that none of the randomness sources will block.




X(1), xauth(1), md5sum(1), rand(3)


The mcookie command is part of the util-linux package and is available from Linux Kernel Archive
March 2014 util-linux