|Initial release||August 6, 2008|
5.0.2 / 16 January 2023
|Written in||C, Shell|
|Platform||x86, IA-64, PowerPC, SPARC, Itanium, ARM|
|License||GNU LGPL v.2.1 (some components under GNU GPL v2 and BSD)|
Linux Containers (LXC) is an operating-system-level virtualization method for running multiple isolated Linux systems (containers) on a control host using a single Linux kernel.
The Linux kernel provides the cgroups functionality that allows limitation and prioritization of resources (CPU, memory, block I/O, network, etc.) without the need for starting any virtual machines, and also the namespace isolation functionality that allows complete isolation of an application's view of the operating environment, including process trees, networking, user IDs and mounted file systems.
LXC combines the kernel's cgroups and support for isolated namespaces to provide an isolated environment for applications. Early versions of Docker used LXC as the container execution driver, though LXC was made optional in v0.9 and support was dropped in Docker v1.10. References to Linux containers commonly refer to Docker containers running on Linux.
LXC provides operating system-level virtualization through a virtual environment that has its own process and network space, instead of creating a full-fledged virtual machine. LXC relies on the Linux kernel cgroups functionality that was released in version 2.6.24. It also relies on other kinds of namespace isolation functionality, which were developed and integrated into the mainline Linux kernel.
Originally, LXC containers were not as secure as other OS-level virtualization methods such as OpenVZ: in Linux kernels before 3.8, the root user of the guest system could run arbitrary code on the host system with root privileges, just as they can in chroot jails. Starting with the LXC 1.0 release, it is possible to run containers as regular users on the host using "unprivileged containers". Unprivileged containers are more limited in that they cannot access hardware directly. However, even privileged containers should provide adequate isolation in the LXC 1.0 security model, if properly configured.
LXC is similar to other OS-level virtualization technologies on Linux such as OpenVZ and Linux-VServer, as well as those on other operating systems such as FreeBSD jails, AIX Workload Partitions and Solaris Containers. In contrast to OpenVZ, LXC works in the vanilla Linux kernel requiring no additional patches to be applied to the kernel sources. Version 1 of LXC, which was released on 20 February 2014 as a long-term supported version, was supported for five years. LXC 3.0 will be supported until June 1, 2023; LXC 4.0 until June 1, 2025; and LX 5.0 until June 1, 2027.
LXD is an alternative Linux container manager. It is built on top of LXC and aims to provide a better user experience.
However, at least in Ubuntu, our default containers ship with what we think is a pretty good configuration of both the cgroup access and an extensive apparmor profile which prevents all attacks that we are aware of. [...] LXC is no longer running as root so even if an attacker manages to escape the container, he'd find himself having the privileges of a regular user on the host