COMP 3000 2012 Week 9 Notes

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

Softare:

 * 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.