What is the meaning of the three numbers 741 in "openssl rand -base64 741"?

I'm creating an auth keyfile for mongodb and one way to do that is using: /usr/bin/openssl rand -base64 741 > $TMPFILE

I want to understand what is going on, I understood everything minus the meaning of three numbers 741

I couldn't find an explanation in the documentation.

Solution 1:

It means it will use 741 bytes of random data and base64 it.

Example with -hex 20 as this will be 40 long.

$ /usr/bin/openssl rand -hex 20
51b40b347dfccefa9b4f8a13d36c4564760c2f82

It is explained in the man page. See num at the end and the description:

SYNOPSIS
       openssl rand [-help] [-out file] [-rand file...]  [-writerand file]
       [-base64] [-hex] num

DESCRIPTION
   This command generates num random bytes using 
   cryptographically secure pseudo random number generator (CSPRNG).