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ea033bbc | 1 | [![LXD](https://linuxcontainers.org/static/img/containers.png)](https://linuxcontainers.org/lxd) |
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2 | # LXC |
3 | ||
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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 | ||
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10 | ## Status |
11 | Type | Service | Status | |
12 | --- | --- | --- | |
73c852f7 | 13 | CI (Linux) | GitHub | [![Build Status](https://github.com/lxc/lxc/actions/workflows/build.yml/badge.svg)](https://github.com/lxc/lxc/actions) |
ea033bbc | 14 | CI (Linux) | Jenkins | [![Build Status](https://jenkins.linuxcontainers.org/job/lxc-github-commit/badge/icon)](https://jenkins.linuxcontainers.org/job/lxc-github-commit/) |
ea033bbc | 15 | Project status | CII Best Practices | [![CII Best Practices](https://bestpractices.coreinfrastructure.org/projects/1087/badge)](https://bestpractices.coreinfrastructure.org/projects/1087) |
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16 | Fuzzing | OSS-Fuzz | [![Fuzzing Status](https://oss-fuzz-build-logs.storage.googleapis.com/badges/lxc.svg)](https://oss-fuzz-build-logs.storage.googleapis.com/index.html#lxc) |
17 | Fuzzing | CIFuzz | [![CIFuzz](https://github.com/lxc/lxc/actions/workflows/cifuzz.yml/badge.svg)](https://github.com/lxc/lxc/actions/workflows/cifuzz.yml) | |
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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 | |
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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. | |
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84 | |
85 | ## Configuration | |
86 | ||
87 | LXC is configured via a simple set of keys. For example, | |
88 | ||
7a96a068 | 89 | - `lxc.rootfs.path` |
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90 | - `lxc.mount.entry` |
91 | ||
92 | LXC namespaces configuration keys by using single dots. This means complex | |
7fa3f2e9 | 93 | configuration keys such as `lxc.net.0` expose various subkeys such as |
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94 | `lxc.net.0.type`, `lxc.net.0.link`, `lxc.net.0.ipv6.address`, and others for |
95 | even more fine-grained configuration. | |
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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 | |
0a2ffe12 | 110 | - riscv64 |
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111 | - s390x |
112 | - armvl7, arm64 | |
113 | ||
114 | LXC also supports at least the following C standard libraries: | |
115 | ||
116 | - glibc | |
117 | - musl | |
118 | - bionic (Android's libc) | |
119 | ||
120 | ## Backwards Compatibility | |
121 | ||
122 | LXC has always focused on strong backwards compatibility. In fact, the API | |
123 | hasn't been broken from release `1.0.0` onwards. Main LXC is currently at | |
949b3059 | 124 | version `4.*.*`. |
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125 | |
126 | ## Reporting Security Issues | |
127 | ||
128 | The LXC project has a good reputation in handling security issues quickly and | |
129 | efficiently. If you think you've found a potential security issue, please | |
130 | report it by e-mail to all of the following persons: | |
131 | ||
a3cf04da | 132 | - serge (at) hallyn (dot) com |
dc46727f | 133 | - stgraber (at) ubuntu (dot) com |
7f664307 | 134 | - brauner (at) kernel (dot) org |
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135 | |
136 | For further details please have a look at | |
137 | ||
138 | - https://linuxcontainers.org/lxc/security/ | |
139 | ||
140 | ## Becoming Active in LXC development | |
141 | ||
142 | We always welcome new contributors and are happy to provide guidance when | |
143 | necessary. LXC follows the kernel coding conventions. This means we only | |
144 | require that each commit includes a `Signed-off-by` line. The coding style we | |
145 | use is identical to the one used by the Linux kernel. You can find a detailed | |
146 | introduction at: | |
147 | ||
148 | - https://www.kernel.org/doc/html/v4.10/process/coding-style.html | |
149 | ||
150 | and should also take a look at the [CONTRIBUTING](CONTRIBUTING) file in this | |
151 | repo. | |
152 | ||
153 | If you want to become more active it is usually also a good idea to show up in | |
c49b9f61 | 154 | the LXC IRC channel [#lxc-dev](https://kiwiirc.com/client/irc.libera.chat/#lxc-dev) on irc.libera.chat. We try to do all development out |
dc46727f | 155 | in the open and discussion of new features or bugs is done either in |
154f6474 | 156 | appropriate GitHub issues or on IRC. |
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157 | |
158 | When thinking about making security critical contributions or substantial | |
159 | changes it is usually a good idea to ping the developers first and ask whether | |
160 | a PR would be accepted. | |
161 | ||
162 | ## Semantic Versioning | |
163 | ||
164 | LXC and its related projects strictly adhere to a [semantic | |
165 | versioning](http://semver.org/) scheme. | |
166 | ||
167 | ## Downloading the current source code | |
168 | ||
169 | Source for the latest released version can always be downloaded from | |
170 | ||
5e7448b5 | 171 | - https://linuxcontainers.org/lxc/downloads/ |
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172 | |
173 | You can browse the up to the minute source code and change history online | |
174 | ||
175 | - https://github.com/lxc/lxc | |
176 | ||
177 | ## Building LXC | |
178 | ||
179 | Without considering distribution specific details a simple | |
180 | ||
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181 | meson setup -Dprefix=/usr build |
182 | meson compile -C build | |
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183 | |
184 | is usually sufficient. | |
185 | ||
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186 | ## Getting help |
187 | ||
188 | When you find you need help, the LXC projects provides you with several options. | |
189 | ||
190 | ### Discuss Forum | |
191 | ||
09233897 | 192 | We maintain a discuss forum at |
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193 | |
194 | - https://discuss.linuxcontainers.org/ | |
195 | ||
196 | where you can get support. | |
197 | ||
198 | ### IRC | |
c49b9f61 | 199 | You can find us in [#lxc](https://kiwiirc.com/client/irc.libera.chat/#lxc) on irc.libera.chat. |
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200 | |
201 | ### Mailing Lists | |
202 | ||
203 | You can check out one of the two LXC mailing list archives and register if | |
204 | interested: | |
205 | ||
206 | - http://lists.linuxcontainers.org/listinfo/lxc-devel | |
207 | - http://lists.linuxcontainers.org/listinfo/lxc-users |