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Nesting RHEL7 KVM on VMware Workstation 12

Recently I wished to build a Red Hat Enterprise Linux 7 (RHEL7) appliance with 2 KVM-virtualized guests. Essentially a type 2 hypervisor (VMM) on top of another type 2 hypervisor. I installed RHEL7 on VMware Workstation 12 and configured it as a Virtualization Server. It was a smooth install without any issues. However I was surprised to find that KVM (Kernel-based Virtual Machine) simply did not work at all and lsmod did not even list the KVM kernel modules. It turns out that you need to do two changes to your RHEL7 guest configuration file in order for KVM support

Korn Shell Launcher for Windows Subsystem for Linux

According to Microsoft, the Windows Subsystem for Linux (WSL) is a new Windows 10 feature that is essentially a compatibility layer which enables you to run native Linux command-line tools and utilities directly on Windows 10, alongside your traditional Windows desktop applications. Currently a beta feature, it is scheduled to be officially released in the Windows 10 Anniversary Update which is due CY2016Q3. There is no support for Linux GUI-based or TUI-based tools, utilities or applications not is any planned. When WSL is enabled, a Canonical-created Ubuntu user-mode image (currently named trusty-server-cloudimg-amd64-root.tar.gz and based on Ubuntu 14.04 Long-Term Support) is

What is /proc/config.gz?

Linux can store a gzip’ed copy of the kernel configuration file used to build the kernel in the kernel itself, and make it available to users via /proc/config.gz. This file is not always present in a Linux distribution. It is only present when /proc support is enabled and CONFIG_IKCONFIG and CONFIG_IKCONFIG_PROC are set to Y in the kernel configuration file. Most distributions do not enable it by default; instead they include the kernel configuration file under /boot. If in-kernel configuration support is built as a kernel module, then before you can use /proc/config.gz, the configs module needs to be loaded

Intel Processor Power Management

Modern Intel processor power management is based on a combination of two techniques: changing the CPU frequency (P-states) and using idling power states (C-states). A third technique, used on older processors but rarely on modern processors, is throttling of the CPU (T-states). P-states are voltage-frequency pairs that set the speed and power consumption of an Intel processor. When the operating voltage of the processor is lower, so is the power consumption. C-states are idle power saving states, in contrast to P-states, which are execution power saving states. During a P-state, the processor is still executing instructions, whereas during a C-state

On-disk File Timestamps

The Single Unix Specification, Base Definitions (XBD), Section 4.8 entitled “File Times Update” states “An implementation may update timestamps that are marked for update immediately, or it may update such timestamps periodically.” This means that, for example, that file read and write operations are free to set the appropriate flags in the in-memory structures and do the actual updating of the on-disk filesystem structures at a later time. Assuming periodically means from time to time, it implies that a POSIX-compliant operating system is free to update it’s on-disk structures when it is convenient for the operating system to do so.