# mcookie

## 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.
    


## AVAILABILITY



           The **mcookie** command is part of the util-linux package which can be
           downloaded from Linux Kernel Archive
           <https://www.kernel.org/pub/linux/utils/util-linux/>. This page is
           part of the _util-linux_ (a random collection of Linux utilities)
           project. Information about the project can be found at 
           ⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩. If you have a
           bug report for this manual page, send it to
           util-linux@vger.kernel.org. This page was obtained from the
           project's upstream Git repository
           ⟨git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git⟩ on
           2025-08-11. (At that time, the date of the most recent commit that
           was found in the repository was 2025-08-05.) If you discover any
           rendering problems in this HTML version of the page, or you
           believe there is a better or more up-to-date source for the page,
           or you have corrections or improvements to the information in this
           COLOPHON (which is _not_ part of the original manual page), send a
           mail to man-pages@man7.org
    
    util-linux 2.42-start-521-ec46  2025-08-09                     _MCOOKIE_(1)
    


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