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

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.