mcookie - Man Page

• Generate a random number: mcookie
• Generate a random number, using the contents of a file as a seed for the randomness: mcookie [-f|--file] path/to/file
• Generate a random number, using a specific number of bytes from a file as a seed for the randomness: mcookie [-f|--file] path/to/file [-m|--max-size] number_of_bytes
• Print the details of the randomness used, such as the origin and seed for each source: mcookie [-v|--verbose]

tldr.sh

mcookie [options]

mcookie generates a 128-bit random hexadecimal number for use with the X authority system. Typical usage:

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.

-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.

/dev/urandom

/dev/random

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

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

For bug reports, use the issue tracker.

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