Open Sourcery

More as a reminder to myself for when I need this again, but I’m sure everyone needs this at least once.

Having screwed up my kernel configs for my VirtualBox Gentoo image, I needed a serial console to catch the boot messages scrolling past in order to see if all the required hardware was being loaded by the kernel. I’ve never done this on a physical machine before but I am converted now and will acquire a USB to serial port converter in the near future…

Using this article as a base you need to do the following:

1. Enable serial ports for your virtual machine
2. Select “Host Pipe”
3. Enter /tmp/vboxconsole as the filename
4. Use netcat to read the console: nc -U /tmp/vboxconsole

When booting you need to amend your grub boot line to have the following at the end:

console=ttyS0,38400

Making it look something like this:

kernel=/kernel-2.6.30-r6 root=/dev/sda3 console=ttyS0,38400

Proceed to boot and look at netcat to see the entire boot output scroll past without disappearing into thin air when the kernel panics.

Man, I love virtualization. I tested this on Mac OS X 10.5 with VirtualBox 3.0.6, but it should work on any *nix platform. Some more Gentoo serial console madness can be found on the old Gentoo Wiki.

Just thought I’d share this one to boost the available online information. Using String#crypt and man crypt you’ll come up with something similar to the gist below (extract from a project I’m busy working on).

module Linux
  class User
    class << self
      # Generate an MD5 salt string
      def salt
        seeds = ('a'..'z').to_a
        seeds.concat( ('A'..'Z').to_a )
        seeds.concat( (0..9).to_a )
        seeds.concat ['/', '.']
        seeds.compact!
 
        salt_string = '$1$'
        8.times { salt_string << seeds[ rand(seeds.size) ].to_s }
 
        salt_string
      end
 
      # Crypt a password suitable for use in shadow files
      def crypt( string )
        string.crypt( self.salt )
      end
    end
  end
end

And the spec

require File.dirname(__FILE__) + '/../spec_helper'
 
describe Linux::User do
  describe "generating shadow passwords" do
    it "should generate a salt for crypt" do
      salt = Linux::User.salt
      salt.length.should be(11)
      salt.should match(/^\$1\$[a-zA-Z0-9\.\/]{8}$/)
    end
 
    it "should generate a shadow password" do
      pass = Linux::User.crypt( 'secret' )
      pass.should match(/^\$1\$[a-zA-Z0-9\.\/]{8}\$[a-zA-Z0-9\.\/]{22}$/)
      pass.length.should be(34)
    end
  end
end

HTH