README.md

   1 [![LXD](https://linuxcontainers.org/static/img/containers.png)](https://linuxcontainers.org/lxd)
   2 # LXC
   3
   4 LXC is the well-known and heavily tested low-level Linux container runtime. It
   5 is in active development since 2008 and has proven itself in critical
   6 production environments world-wide. Some of its core contributors are the same
   7 people that helped to implement various well-known containerization features
   8 inside the Linux kernel.
   9
  10 ## Status
  11 Type            | Service               | Status
  12 ---             | ---                   | ---
  13 CI (Linux)      | Jenkins               | [![Build Status](https://jenkins.linuxcontainers.org/job/lxc-github-commit/badge/icon)](https://jenkins.linuxcontainers.org/job/lxc-github-commit/)
  14 CI (Linux)      | Travis                | [![Build Status](https://travis-ci.org/lxc/lxc.svg?branch=master)](https://travis-ci.org/lxc/lxc/)
  15 Project status  | CII Best Practices    | [![CII Best Practices](https://bestpractices.coreinfrastructure.org/projects/1087/badge)](https://bestpractices.coreinfrastructure.org/projects/1087)
  16 Static Analysis | Coverity              | <a href="https://scan.coverity.com/projects/lxc-linux-containers"> <img alt="Coverity Scan Build Status" src="https://img.shields.io/coverity/scan/369.svg"/> </a>
  17
  18 ## System Containers
  19
  20 LXC's main focus is system containers. That is, containers which offer an
  21 environment as close as possible as the one you'd get from a VM but without the
  22 overhead that comes with running a separate kernel and simulating all the
  23 hardware.
  24
  25 This is achieved through a combination of kernel security features such as
  26 namespaces, mandatory access control and control groups.
  27
  28 ## Unprivileged Containers
  29
  30 Unprivileged containers are containers that are run without any privilege. This
  31 requires support for user namespaces in the kernel that the container is run
  32 on. LXC was the first runtime to support unprivileged containers after user
  33 namespaces were merged into the mainline kernel.
  34
  35 In essence, user namespaces isolate given sets of UIDs and GIDs. This is
  36 achieved by establishing a mapping between a range of UIDs and GIDs on the host
  37 to a different (unprivileged) range of UIDs and GIDs in the container. The
  38 kernel will translate this mapping in such a way that inside the container all
  39 UIDs and GIDs appear as you would expect from the host whereas on the host
  40 these UIDs and GIDs are in fact unprivileged. For example, a process running as
  41 UID and GID 0 inside the container might appear as UID and GID 100000 on the
  42 host. The implementation and working details can be gathered from the
  43 corresponding user namespace man page.
  44
  45 Since unprivileged containers are a security enhancement they naturally come
  46 with a few restrictions enforced by the kernel. In order to provide a fully
  47 functional unprivileged container LXC interacts with 3 pieces of setuid code:
  48
  49 - lxc-user-nic (setuid helper to create a veth pair and bridge it on the host)
  50 - newuidmap (from the shadow package, sets up a uid map)
  51 - newgidmap (from the shadow package, sets up a gid map)
  52
  53 Everything else is run as your own user or as a uid which your user owns.
  54
  55 In general, LXC's goal is to make use of every security feature available in
  56 the kernel. This means LXC's configuration management will allow experienced
  57 users to intricately tune LXC to their needs.
  58
  59 A more detailed introduction into LXC security can be found under the following link
  60
  61 - https://linuxcontainers.org/lxc/security/
  62
  63 ### Removing all Privilege
  64
  65 In principle LXC can be run without any of these tools provided the correct
  66 configuration is applied. However, the usefulness of such containers is usually
  67 quite restricted. Just to highlight the two most common problems:
  68
  69 1. Network: Without relying on a setuid helper to setup appropriate network
  70    devices for an unprivileged user (see LXC's `lxc-user-nic` binary) the only
  71    option is to share the network namespace with the host. Although this should
  72    be secure in principle, sharing the host's network namespace is still one
  73    step of isolation less and increases the attack vector.
  74    Furthermore, when host and container share the same network namespace the
  75    kernel will refuse any sysfs mounts. This usually means that the init binary
  76    inside of the container will not be able to boot up correctly.
  77
  78 2. User Namespaces: As outlined above, user namespaces are a big security
  79    enhancement. However, without relying on privileged helpers users who are
  80    unprivileged on the host are only permitted to map their own UID into
  81    a container. A standard POSIX system however, requires 65536 UIDs and GIDs
  82    to be available to guarantee full functionality.
  83
  84 ## Configuration
  85
  86 LXC is configured via a simple set of keys. For example,
  87
  88 - `lxc.rootfs.path`
  89 - `lxc.mount.entry`
  90
  91 LXC namespaces configuration keys by using single dots. This means complex
  92 configuration keys such as `lxc.net.0` expose various subkeys such as
  93 `lxc.net.0.type`, `lxc.net.0.link`, `lxc.net.0.ipv6.address`, and others for
  94 even more fine-grained configuration.
  95
  96 LXC is used as the default runtime for [LXD](https://github.com/lxc/lxd),
  97 a container hypervisor exposing a well-designed and stable REST-api on top of
  98 it.
  99
 100 ## Kernel Requirements
 101
 102 LXC runs on any kernel from 2.6.32 onwards. All it requires is a functional
 103 C compiler. LXC works on all architectures that provide the necessary kernel
 104 features. This includes (but isn't limited to):
 105
 106 - i686
 107 - x86_64
 108 - ppc, ppc64, ppc64le
 109 - s390x
 110 - armvl7, arm64
 111
 112 LXC also supports at least the following C standard libraries:
 113
 114 - glibc
 115 - musl
 116 - bionic (Android's libc)
 117
 118 ## Backwards Compatibility
 119
 120 LXC has always focused on strong backwards compatibility. In fact, the API
 121 hasn't been broken from release `1.0.0` onwards. Main LXC is currently at
 122 version `2.*.*`.
 123
 124 ## Reporting Security Issues
 125
 126 The LXC project has a good reputation in handling security issues quickly and
 127 efficiently. If you think you've found a potential security issue, please
 128 report it by e-mail to all of the following persons:
 129
 130 - serge (at) hallyn (dot) com
 131 - stgraber (at) ubuntu (dot) com
 132 - christian.brauner (at) ubuntu (dot) com
 133
 134 For further details please have a look at
 135
 136 - https://linuxcontainers.org/lxc/security/
 137
 138 ## Becoming Active in LXC development
 139
 140 We always welcome new contributors and are happy to provide guidance when
 141 necessary. LXC follows the kernel coding conventions. This means we only
 142 require that each commit includes a `Signed-off-by` line. The coding style we
 143 use is identical to the one used by the Linux kernel. You can find a detailed
 144 introduction at:
 145
 146 - https://www.kernel.org/doc/html/v4.10/process/coding-style.html
 147
 148 and should also take a look at the [CONTRIBUTING](CONTRIBUTING) file in this
 149 repo.
 150
 151 If you want to become more active it is usually also a good idea to show up in
 152 the LXC IRC channel `#lxc-dev` on `Freenode`. We try to do all development out
 153 in the open and discussion of new features or bugs is done either in
 154 appropriate GitHub issues or on IRC.
 155
 156 When thinking about making security critical contributions or substantial
 157 changes it is usually a good idea to ping the developers first and ask whether
 158 a PR would be accepted.
 159
 160 ## Semantic Versioning
 161
 162 LXC and its related projects strictly adhere to a [semantic
 163 versioning](http://semver.org/) scheme.
 164
 165 ## Downloading the current source code
 166
 167 Source for the latest released version can always be downloaded from
 168
 169 - https://linuxcontainers.org/downloads/
 170
 171 You can browse the up to the minute source code and change history online
 172
 173 - https://github.com/lxc/lxc
 174
 175 ## Building LXC
 176
 177 Without considering distribution specific details a simple
 178
 179     ./autogen.sh && ./configure && make && sudo make install
 180
 181 is usually sufficient.
 182
 183 In order to test current git master of LXC it is usually a good idea to compile with
 184
 185     ./autogen.sh && ./configure && make
 186
 187 in a convenient directory and set `LD_LIBRARY_PATH="${BUILD_DIR}"/lxc/src/lxc/.libs`.
 188
 189 ## Getting help
 190
 191 When you find you need help, the LXC projects provides you with several options.
 192
 193 ### Discuss Forum
 194
 195 We maintain an discuss forum at
 196
 197 - https://discuss.linuxcontainers.org/
 198
 199 where you can get support.
 200
 201 ### IRC
 202
 203 You can find support by joining `#lxcontainers` on `Freenode`.
 204
 205 ### Mailing Lists
 206
 207 You can check out one of the two LXC mailing list archives and register if
 208 interested:
 209
 210 - http://lists.linuxcontainers.org/listinfo/lxc-devel
 211 - http://lists.linuxcontainers.org/listinfo/lxc-users