Manual: mcookie

MCOOKIE(1)						User Commands						  MCOOKIE(1)

NAME
       mcookie - generate magic cookies for xauth

SYNOPSIS
       mcookie [options]

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 MD5 message digest of random information coming from one of the sources
       getrandom(2) system call, /dev/urandom, /dev/random, or the libc pseudo-random functions, in this preference order.
       See also the option --file.

OPTIONS
       -f, --file file
	   Use this file as an additional source of randomness (for example /dev/urandom). When file is '-', characters are
	   read from standard input.

       -m, --max-size number
	   Read from file only this number of bytes. This option is meant to be used when reading additional randomness from
	   a file or 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.

       -h, --help
	   Display help text and exit.

       -V, --version
	   Display version and exit.

FILES
       /dev/urandom

       /dev/random

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

SEE ALSO
       md5sum(1), X(7), xauth(1), rand(3)

REPORTING BUGS
       For bug reports, use the issue tracker .

AVAILABILITY
       The mcookie command is part of the util-linux package which can be downloaded from Linux Kernel Archive
       .

util-linux 2.41.3					 2025-12-15						  MCOOKIE(1)