How it works?
Normally loading of the virtual machine is as follows: a bootable virtual machine disk (with its boot partition) is read grub.cfg / grub.lst, it is chosen from the kernel and initrd. Domain builder (special application that creates the domain when you start the virtual machine, puts to the kernel / initrd, way form start page settings and adds memory) is the kernel loads and runs the domain.
Then the kernel has loaded as in a conventional server - runs the init script in the initrd, which prepares the root filesystem makes to pivot_root (switch the root directory), and run is a real init, which reads inittab, starts the system initialization, system-v or upstart, systemd, who really like more.
If there is a problem: I do not see the root filesystem, suspicion of hacking, study any problems, you may need to load an alternate kernel.
In this case, the kernel, instead of having to read from disk guest virtual machine, taken from the catalog of ready-made cores. From the same taken and initrd. Guest machine starts "as is".
In total we have a few sets of kernels and initrd - most of them allows you to run a conventional system, but there are several specific initrd, to do something useful, while remaining "outside" of the operating system.
It: Auto PTMAX - specialized initrd, which automatically expands the size of the PV, VG, and file system root-partition after resizing block device (increasing the size of the disk);
Auto FSCK - automatically checks the file system root-section;
Vanilla Linux 3.2 - the test version to test the pv_ops nuclei (use at your own risk);
Rescue Initrd - the main character of our story.
