'\" t
.\"     Title: mcookie
.\"    Author: [see the "AUTHOR(S)" section]
.\" Generator: Asciidoctor 2.0.15
.\"      Date: 2022-02-17
.\"    Manual: User Commands
.\"    Source: util-linux 2.38
.\"  Language: English
.\"
.TH "MCOOKIE" "1" "2022-02-17" "util\-linux 2.38" "User Commands"
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.SH "NAME"
mcookie \- generate magic cookies for xauth
.SH "SYNOPSIS"
.sp
\fBmcookie\fP [options]
.SH "DESCRIPTION"
.sp
\fBmcookie\fP generates a 128\-bit random hexadecimal number for use with the X authority system. Typical usage:
.RS 3
.ll -.6i
.sp
\fBxauth add :0 . \f(CRmcookie\fP\fP
.br
.RE
.ll
.sp
The "random" number generated is actually the MD5 message digest of random information coming from one of the sources \fBgetrandom\fP(2) system call, \fI/dev/urandom\fP, \fI/dev/random\fP, or the \fIlibc pseudo\-random functions\fP, in this preference order. See also the option \fB\-\-file\fP.
.SH "OPTIONS"
.sp
\fB\-f\fP, \fB\-\-file\fP \fIfile\fP
.RS 4
Use this \fIfile\fP as an additional source of randomness (for example \fI/dev/urandom\fP). When \fIfile\fP is \(aq\-\(aq, characters are read from standard input.
.RE
.sp
\fB\-m\fP, \fB\-\-max\-size\fP \fInumber\fP
.RS 4
Read from \fIfile\fP only this \fInumber\fP of bytes. This option is meant to be used when reading additional randomness from a file or device.
.sp
The \fInumber\fP 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.
.RE
.sp
\fB\-v\fP, \fB\-\-verbose\fP
.RS 4
Inform where randomness originated, with amount of entropy read from each source.
.RE
.sp
\fB\-h\fP, \fB\-\-help\fP
.RS 4
Display help text and exit.
.RE
.sp
\fB\-V\fP, \fB\-\-version\fP
.RS 4
Print version and exit.
.RE
.SH "FILES"
.sp
\fI/dev/urandom\fP
.sp
\fI/dev/random\fP
.SH "BUGS"
.sp
It is assumed that none of the randomness sources will block.
.SH "SEE ALSO"
.sp
\fBmd5sum\fP(1),
\fBX\fP(7),
\fBxauth\fP(1),
\fBrand\fP(3)
.SH "REPORTING BUGS"
.sp
For bug reports, use the issue tracker at \c
.URL "https://github.com/util\-linux/util\-linux/issues" "" "."
.SH "AVAILABILITY"
.sp
The \fBmcookie\fP command is part of the util\-linux package which can be downloaded from \c
.URL "https://www.kernel.org/pub/linux/utils/util\-linux/" "Linux Kernel Archive" "."