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