COMP 3000 2012 Week 9 Notes

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PACKAGING

  • Fakeroot fakes root permissions
  • Does so by faking a library the called libraries. THese ones return root permissions

Messing with Dynamic linker

  • We need fakeroot because tar feels save permissions


Package management exists on MACOS and windows, but exists more for patching the OS instead of incremental change. The reason they don't have a complicated PKG mangment is because they don't have DEBIAN's distributed development culture. They're more tightly nit, so big changes happen in a less formal, more verbal way.


/var is current state /var/lib is important state. Don't mess with it /var/lib/dpkg is where package management state exists. (see status file, status line)

/var/lib/dpkg/info/*.list --lists all files that are installed with a package (dpgk --list <packagename>)

/var/lib/dpkg/info/*.conffile --lists where the overridable conf files are...


VIRTUALISATION

  • Convert OS to "Apps" (or app container)
  • Oses, though, want to run in Supervisor mode, they're typically designed to be in

controll

Two approaches: software and hardware


Software:

  • limited emulations that emulates hardware. Emulation is slow though cause you're simulating hardware. Can reduce to physics emulation.
  • we only emulate priviledged operations. For example, interrupts

Hardware virtualisation:

  • the "chip" itself is virtualisazing
  • the hardware intercepts interrupts and then allows the OS to run on the computer's CPU

Hypervisors

  • Hardware is developed know that it will be controlled by multiple masters (OSes)
  • Sets Policy on how hardware is shared between OSes


History of hypervisors

  • Developed by IBM, in the 60's, for their mainframes.
  • Mainframes originally built for batching
  • Timeshare was then developed
  • During the transition, clients wanted to run their old batching code
  • IBM developped hypervisors so that BATCH OS's could be run on the same hardware as the time sharing machine

Desktop Virtualisation

  • Typical desktop hardware, though, is designed to be used by only OS, so the hypervisor must do tricks.
    • for example, one OS will set the Videocard registers to one setting, another

OS will set them to other settings

  • Desktop hardware is not so virtualizable.
  • where not virtualisable, emulate virtualisation. This is what VMware figured out how to do. It emulated support for unvirtualiasable hardware, it did so in software.
  • Modern CPUs support virtualisation though, it lets you catch software interrupts and

redirect them to other OSes

  • HW that doesn't have virtualisation support, like some Graphic cards, VMs must emulate them. THis is typically slow.
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