3 * Jenkins: [![Build Status](https://jenkins.linuxcontainers.org/job/lxc-github-commit/badge/icon)](https://jenkins.linuxcontainers.org/job/lxc-github-commit/)
4 * Travis: [![Build Status](https://travis-ci.org/lxc/lxc.svg?branch=master)](https://travis-ci.org/lxc/lxc/)
6 LXC is the well-known and heavily tested low-level Linux container runtime. It
7 is in active development since 2008 and has proven itself in critical
8 production environments world-wide. Some of its core contributors are the same
9 people that helped to implement various well-known containerization features
10 inside the Linux kernel.
14 LXC's main focus is system containers. That is, containers which offer an
15 environment as close as possible as the one you'd get from a VM but without the
16 overhead that comes with running a separate kernel and simulating all the
19 This is achieved through a combination of kernel security features such as
20 namespaces, mandatory access control and control groups.
22 ## Unprivileged Containers
24 Unprivileged containers are containers that are run without any privilege. This
25 requires support for user namespaces in the kernel that the container is run
26 on. LXC was the first runtime to support unprivileged containers after user
27 namespaces were merged into the mainline kernel.
29 In essence, user namespaces isolate given sets of UIDs and GIDs. This is
30 achieved by establishing a mapping between a range of UIDs and GIDs on the host
31 to a different (unprivileged) range of UIDs and GIDs in the container. The
32 kernel will translate this mapping in such a way that inside the container all
33 UIDs and GIDs appear as you would expect from the host whereas on the host
34 these UIDs and GIDs are in fact unprivileged. For example, a process running as
35 UID and GID 0 inside the container might appear as UID and GID 100000 on the
36 host. The implementation and working details can be gathered from the
37 corresponding user namespace man page.
39 Since unprivileged containers are a security enhancement they naturally come
40 with a few restrictions enforced by the kernel. In order to provide a fully
41 functional unprivileged container LXC interacts with 3 pieces of setuid code:
43 - lxc-user-nic (setuid helper to create a veth pair and bridge it on the host)
44 - newuidmap (from the shadow package, sets up a uid map)
45 - newgidmap (from the shadow package, sets up a gid map)
47 Everything else is run as your own user or as a uid which your user owns.
49 In general, LXC's goal is to make use of every security feature available in
50 the kernel. This means LXC's configuration management will allow experienced
51 users to intricately tune LXC to their needs.
53 A more detailed introduction into LXC security can be found under the following link
55 - https://linuxcontainers.org/lxc/security/
57 ### Removing all Privilege
59 In principle LXC can be run without any of these tools provided the correct
60 configuration is applied. However, the usefulness of such containers is usually
61 quite restricted. Just to highlight the two most common problems:
63 1. Network: Without relying on a setuid helper to setup appropriate network
64 devices for an unprivileged user (see LXC's `lxc-user-nic` binary) the only
65 option is to share the network namespace with the host. Although this should
66 be secure in principle, sharing the host's network namespace is still one
67 step of isolation less and increases the attack vector.
68 Furthermore, when host and container share the same network namespace the
69 kernel will refuse any sysfs mounts. This usually means that the init binary
70 inside of the container will not be able to boot up correctly.
72 2. User Namespaces: As outlined above, user namespaces are a big security
73 enhancement. However, without relying on privileged helpers users who are
74 unprivileged on the host are only permitted to map their own UID into
75 a container. A standard POSIX system however, requires 65536 UIDs and GIDs
76 to be available to guarantee full functionality.
80 LXC is configured via a simple set of keys. For example,
85 LXC namespaces configuration keys by using single dots. This means complex
86 configuration keys such as `lxc.net.0` expose various subkeys such as
87 `lxc.net.0.type`, `lxc.net.0.link`, `lxc.net.0.ipv6`, and others for even
88 more fine-grained configuration.
90 LXC is used as the default runtime for [LXD](https://github.com/lxc/lxd),
91 a container hypervisor exposing a well-designed and stable REST-api on top of
94 ## Kernel Requirements
96 LXC runs on any kernel from 2.6.32 onwards. All it requires is a functional
97 C compiler. LXC works on all architectures that provide the necessary kernel
98 features. This includes (but isn't limited to):
102 - ppc, ppc64, ppc64le
106 LXC also supports at least the following C standard libraries:
110 - bionic (Android's libc)
112 ## Backwards Compatibility
114 LXC has always focused on strong backwards compatibility. In fact, the API
115 hasn't been broken from release `1.0.0` onwards. Main LXC is currently at
118 ## Reporting Security Issues
120 The LXC project has a good reputation in handling security issues quickly and
121 efficiently. If you think you've found a potential security issue, please
122 report it by e-mail to all of the following persons:
124 - serge.hallyn (at) ubuntu (dot) com
125 - stgraber (at) ubuntu (dot) com
126 - christian.brauner (at) ubuntu (dot) com
128 For further details please have a look at
130 - https://linuxcontainers.org/lxc/security/
132 ## Becoming Active in LXC development
134 We always welcome new contributors and are happy to provide guidance when
135 necessary. LXC follows the kernel coding conventions. This means we only
136 require that each commit includes a `Signed-off-by` line. The coding style we
137 use is identical to the one used by the Linux kernel. You can find a detailed
140 - https://www.kernel.org/doc/html/v4.10/process/coding-style.html
142 and should also take a look at the [CONTRIBUTING](CONTRIBUTING) file in this
145 If you want to become more active it is usually also a good idea to show up in
146 the LXC IRC channel `#lxc-dev` on `Freenode`. We try to do all development out
147 in the open and discussion of new features or bugs is done either in
148 appropriate Github issues or on IRC.
150 When thinking about making security critical contributions or substantial
151 changes it is usually a good idea to ping the developers first and ask whether
152 a PR would be accepted.
154 ## Semantic Versioning
156 LXC and its related projects strictly adhere to a [semantic
157 versioning](http://semver.org/) scheme.
159 ## Downloading the current source code
161 Source for the latest released version can always be downloaded from
163 - https://linuxcontainers.org/downloads/
165 You can browse the up to the minute source code and change history online
167 - https://github.com/lxc/lxc
171 Without considering distribution specific details a simple
173 ./autogen.sh && ./configure && make && sudo make install
175 is usually sufficient.
177 In order to test current git master of LXC it is usually a good idea to compile with
179 ./autogen.sh && ./configure && make
181 in a convenient directory and set `LD_LIBRARY_PATH="${BUILD_DIR}"/lxc/src/lxc/.libs`.
185 When you find you need help, the LXC projects provides you with several options.
189 We maintain an discuss forum at
191 - https://discuss.linuxcontainers.org/
193 where you can get support.
197 You can find support by joining `#lxcontainers` on `Freenode`.
201 You can check out one of the two LXC mailing list archives and register if
204 - http://lists.linuxcontainers.org/listinfo/lxc-devel
205 - http://lists.linuxcontainers.org/listinfo/lxc-users