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In August 1908, a white mob attacked Springfield, Illinois’s Black community, destroying homes and businesses and lynching two Black men. National outrage over the violence helped spur the movement that created the NAACP the following year.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
 | This article needs to be updated. (May 2019) |
| User-mode Linux | |
|---|---|
| Written in | C |
| Type | Virtualization |
| License | GNU General Public License |
| Website | user-mode-linux |
User-mode Linux (UML) is a virtualization system for the Linux operating system based on an architectural port of the Linux kernel to its own system call interface, which enables multiple virtual Linux kernel-based operating systems (known as guests) to run as an application within a normal Linux system (known as the host). A Linux kernel compiled for the um architecture can then boot as a process under another Linux kernel, entirely in user space, without affecting the host environment's configuration or stability.
This method gives the user a way to run many virtual Linux machines on a single piece of hardware, allowing some isolation, typically without changing the configuration or stability of the host environment because each guest is just a regular application running as a process in user space.
Numerous things become possible through the use of UML.[1] One can run network services from a UML environment and remain totally sequestered from the main Linux system in which the UML environment runs.[2][3][4][5][6] Administrators can use UML to set up honeypots,[7] which allow one to test the security of one's computers or network. UML can serve to test and debug new software without adversely affecting the host system. UML can also be used for teaching and research, providing a realistic Linux networked environment with a high degree of safety.
In UML environments, host and guest kernel versions don't need to match, so it is entirely possible to test a "bleeding edge" version of Linux in User-mode on a system running a much older kernel. UML also allows kernel debugging to be performed on one machine, where other kernel debugging tools (such as kgdb) require two machines connected with a null modem cable.
Some web hosting providers offer UML-powered virtual servers for lower prices than true dedicated servers. Each customer has root access on what appears to be their own system, while in reality one physical computer is shared between many people.
libguestfs has supported a UML backend since version 1.24[8] as an alternative to using QEMU or KVM.
The UML guest application (a Linux binary ELF) was originally available as a patch for some Kernel versions above 2.2.x, and the host with any kernel version above 2.2.x supported it easily in the thread mode (i.e., non-SKAS3).
As of Linux 2.6.0, it is integrated into the main kernel source tree. A method of running a separate kernel address space (SKAS) that does not require host kernel patching has been implemented. This improves performance and security over the old Traced Thread approach, in which processes running in the UML share the same address space from the host's point of view, which leads the memory inside the UML to not be protected by the memory management unit. Unlike the current UML using SKAS, buggy or malicious software inside a UML running on a non-SKAS host could be able to read the memory space of other UML processes or even the UML kernel memory.[9]
User-mode Linux is generally considered[by whom?] to have lower performance than some competing technologies, such as Xen and OpenVZ.[citation needed] Future work in adding support for x86 virtualization to UML may reduce this disadvantage.
Often cited as a strength of Xen (a competing technology) is support for thread-local storage (TLS). This is now also supported in the latest UML kernels. Xen concentrates on virtualizing the whole machine, and thus all systems running on a Xen machine are really virtual machines. In UML, the host machine is not virtualized in any way, and only guest systems are true virtual machines. This allows UML guest direct access to host filesystems and hardware, where it is common to map a host directory (e.g., /uml/root → /).
UML was originally designed for the x86 instruction set, but has also been ported to others including IA-64 and PowerPC.[10][11] It also runs on x86_64[12] and should run on any platform inasmuch as Linux's ptrace is uniform across platforms.
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Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
User-mode Linux (UML) is a virtualization system for the Linux operating system based on an architectural port of the Linux kernel to its own system call interface, which enables multiple virtual Linux kernel-based operating systems (known as guests) to run as an application within a normal Linux system (known as the host). A Linux kernel compiled for the um architecture can then boot as a process under another Linux kernel, entirely in user space, without affecting the host environment's configuration or stability. This method gives the user a way to run many virtual Linux machines on a single piece of hardware, allowing some isolation, typically without changing the configuration or stability of the host environment because each guest is just a regular application running as a process in user space.
UML may refer to: Unified Modeling Language, a software modeling language University of Massachusetts Lowell, a research university User-mode Linux, virtual machine software Communist Party of Nepal (Unified Marxist–Leninist), abbreviated CPN (UML)
Bytemark is a server hosting and datacentre provider headquartered in York, United Kingdom. It was founded in 2002, and was the first provider of virtual machines and cloud hosting through User-mode Linux in 2003. In 2012, the company launched BigV, a public cloud platform designed in-house using open source software. In 2013, it moved into a £1.2 million datacentre and headquarters in York. In 2017, their BigV platform was renamed Bytemark Cloud. In September 2018, the company was acquired by iomart Group plc. On 2 February 2023 Bytemark announced that it would cease to support BigV on 30 April 2023.
A virtual kernel architecture (vkernel) is an operating system virtualisation paradigm where kernel code can be compiled to run in the user space, for example, to ease debugging of various kernel-level components, in addition to general-purpose virtualisation and compartmentalisation of system resources. It is used by DragonFly BSD in its vkernel implementation since DragonFly 1.7, having been first revealed in September 2006 (2006-09), and first released in the stable branch with DragonFly 1.8 in January 2007 (2007-01). The long-term goal, in addition to easing kernel development, is to make it easier to support internet-connected computer clusters without compromising local security. Similar concepts exist in other operating systems as well; in Linux, a similar virtualisation concept is known as user-mode Linux; whereas in NetBSD since the summer of 2007, it has been the initial focus of the rump kernel infrastructure. The virtual kernel concept is nearly the exact opposite of the unikernel concept — with vkernel, kernel components get to run in userspace to ease kernel development and debugging, supported by a regular operating system kernel; whereas with a unikernel, userspace-level components get to run directly in kernel space for extra performance, supported by baremetal hardware or a hardware virtualisation stack. However, both vkernels and unikernels can be used for similar tasks as well, for example, to self-contain software to a virtualised environment with low overhead. In fact, NetBSD's rump kernel, originally having a focus of running kernel components in userspace, has since shifted into the unikernel space as well (going after the anykernel moniker for supporting both paradigms). The vkernel concept is different from a FreeBSD jail in that a jail is only meant for resource isolation, and cannot be used to develop and test new kernel functionality in the userland, because each jail is sharing the same kernel. (DragonFly, however, still has FreeBSD jail support as well.) In DragonFly, the vkernel can be thought of as a first-class computer architecture, comparable to i386 or amd64, and, according to Matthew Dillon circa 2007, can be used as a starting point for porting DragonFly BSD to new architectures. DragonFly's vkernel is supported by the host kernel through new system calls that help manage virtual memory address space (vmspace) — vmspace_create() et al., as well as extensions to several existing system calls like mmap's madvise — mcontrol.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →The Greenwood District.
