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.