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OS-level virtualization
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<p>OS-level virtualization is an <a href="/facts/Operating_system/8XTuvMh2">operating system</a> (OS) <a href="/facts/Virtualization/bEqH0Wtf">virtualization</a> paradigm in which the <a href="/facts/Kernel_(operating_system)/uEj4U3Rz">kernel</a> allows the existence of multiple isolated <a href="/facts/User_space_and_kernel_space/0yIzMY8t">user space</a> instances, including containers (<a href="/facts/LXC/gmfT31xS">LXC</a>, <a href="/facts/Solaris_Containers/REtWenIv">Solaris Containers</a>, AIX <a href="/facts/Workload_Partitions/S9abFFpu">WPARs</a>, HP-UX SRP Containers, <a href="/facts/Docker_(software)/7IvvsMug">Docker</a>, <a href="/facts/Podman/5bS9dQCn">Podman</a>), zones (<a href="/facts/Solaris_Containers/REtWenIv">Solaris Containers</a>), virtual private servers (<a href="/facts/OpenVZ/oNBc6MU5">OpenVZ</a>), partitions, virtual environments (VEs), virtual kernels (<a href="/facts/Vkernel/cIx0mgGz">DragonFly BSD</a>), and jails (<a href="/facts/FreeBSD_jail/emnSbE44">FreeBSD jail</a> and <a href="/facts/Chroot/o5423VpW">chroot</a>). Such instances may look like real computers from the point of view of programs running in them. A <a href="/facts/Computer_program/e38jH9N9">computer program</a> running on an ordinary operating system can see all resources (connected devices, files and folders, <a href="/facts/Shared_resource/tmLvfkwR">network shares</a>, CPU power, quantifiable hardware capabilities) of that computer. Programs running inside a <a href="/facts/Containerization_(computing)/IWhdSYm3">container</a> can only see the container's contents and devices assigned to the container. </p><p>On <a href="/facts/Unix-like/YAKrAxzd">Unix-like</a> operating systems, this feature can be seen as an advanced implementation of the standard <a href="/facts/Chroot/o5423VpW">chroot</a> mechanism, which changes the apparent root folder for the current running process and its children. In addition to isolation mechanisms, the kernel often provides <a href="/facts/Resource_management_(computing)/Nd3YPa3P">resource-management</a> features to limit the impact of one container's activities on other containers. Linux containers are all based on the virtualization, isolation, and resource management mechanisms provided by the <a href="/facts/Linux_kernel/dlkduHuA">Linux kernel</a>, notably <a href="/facts/Linux_namespaces/1ljlDGT0">Linux namespaces</a> and <a href="/facts/Cgroups/seJrzYuQ">cgroups</a>. </p><p>Although the word <i>container</i> most commonly refers to OS-level virtualization, it is sometimes used to refer to fuller <a href="/facts/Virtual_machine/BLevU3sx">virtual machines</a> operating in varying degrees of concert with the host OS, such as <a href="/facts/Microsoft/nGIDDXdx">Microsoft</a>'s <a href="/facts/Hyper-V/3Qm0yJsv">Hyper-V</a> containers. For an overview of <a href="/facts/Virtualization/bEqH0Wtf">virtualization</a> since 1960, see <a href="/facts/Timeline_of_virtualization_technologies/fQ57gtnb">Timeline of virtualization technologies</a>. </p>