'\" t
.\"     Title: mcookie
.\"    Author: [see the "AUTHOR(S)" section]
.\" Generator: Asciidoctor 2.0.20
.\"      Date: 2025-02-26
.\"    Manual: User Commands
.\"    Source: util-linux 2.41
.\"  Language: English
.\"
.TH "MCOOKIE" "1" "2025-02-26" "util\-linux 2.41" "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
Display 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 \c
.URL "https://github.com/util\-linux/util\-linux/issues" "issue tracker" "."
.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" "."