Containers are a lightweight virtualization technology. They are more akin to an enhanced chroot than to full virtualization like Qemu or VMware, both because they do not emulate hardware and because containers share the same operating system as the host. Containers are similar to Solaris zones or BSD jails. Linux-vserver and OpenVZ are two pre-existing, independently developed implementations of containers-like functionality for Linux. In fact, containers came about as a result of the work to upstream the vserver and OpenVZ functionality.

There are two user-space implementations of containers, each exploiting the same kernel features. Libvirt allows the use of containers through the LXC driver by connecting to 'lxc:///'. This can be very convenient as it supports the same usage as its other drivers. The other implementation, called simply 'LXC', is not compatible with libvirt, but is more flexible with more userspace tools. It is possible to switch between the two, though there are peculiarities which can cause confusion.

Dans ce document, nous décrirons essentiellement le paquet lxc. L'utilisation de libvirt-lxc n'est généralement pas recommandée en raison d'un manque de protection d'Apparmor pour les conteneurs libvirt-lxc.

Dans ce document, un nom de conteneur sera affiché comme CN, C1 ou C2.


Le paquet lxc peut être installé à l'aide de

sudo apt install lxc

This will pull in the required and recommended dependencies, as well as set up a network bridge for containers to use. If you wish to use unprivileged containers, you will need to ensure that users have sufficient allocated subuids and subgids, and will likely want to allow users to connect containers to a bridge (see Utilisation de base non privilégiée).

Utilisation basique

LXC can be used in two distinct ways - privileged, by running the lxc commands as the root user; or unprivileged, by running the lxc commands as a non-root user. (The starting of unprivileged containers by the root user is possible, but not described here.) Unprivileged containers are more limited, for instance being unable to create device nodes or mount block-backed filesystems. However they are less dangerous to the host, as the root userid in the container is mapped to a non-root userid on the host.

Utilisation privilégiée basique

To create a privileged container, you can simply do:

sudo lxc-create --template download --name u1
ou, en abrégé
sudo lxc-create -t download -n u1

Ceci demandera interactivement un type de système de fichiers racine de conteneur à télécharger - notamment la distribution, la version et l'architecture. Pour créer le conteneur de façon non-interactive, vous pouvez spécifier ces valeurs sur la ligne de commande :

sudo lxc-create -t download -n u1 -- --dist ubuntu --release xenial --arch amd64
sudo lxc-create -t download -n u1 -- -d ubuntu -r xenial -a amd64

You can now use lxc-ls to list containers, lxc-info to obtain detailed container information, lxc-start to start and lxc-stop to stop the container. lxc-attach and lxc-console allow you to enter a container, if ssh is not an option. lxc-destroy removes the container, including its rootfs. See the manual pages for more information on each command. An example session might look like:

sudo lxc-ls --fancy sudo lxc-start --name u1 --daemon sudo lxc-info --name u1 sudo lxc-stop --name u1 sudo lxc-destroy --name u1

Espaces de noms utilisateur

Unprivileged containers allow users to create and administer containers without having any root privilege. The feature underpinning this is called user namespaces. User namespaces are hierarchical, with privileged tasks in a parent namespace being able to map its ids into child namespaces. By default every task on the host runs in the initial user namespace, where the full range of ids is mapped onto the full range. This can be seen by looking at /proc/self/uid_map and /proc/self/gid_map, which both will show "0 0 4294967295" when read from the initial user namespace. As of Ubuntu 14.04, when new users are created they are by default offered a range of userids. The list of assigned ids can be seen in the files /etc/subuid and /etc/subgid See their respective manpages for more information. Subuids and subgids are by convention started at id 100000 to avoid conflicting with system users.

Si un utilisateur a été créé sur une version antérieure, il peut lui être accordé une plage d'identifiants en utilisant la commande usermod, comme suit :

sudo usermod -v 100000-200000 -w 100000-200000 user1

The programs newuidmap and newgidmap are setuid-root programs in the uidmap package, which are used internally by lxc to map subuids and subgids from the host into the unprivileged container. They ensure that the user only maps ids which are authorized by the host configuration.

Utilisation de base non privilégiée

To create unprivileged containers, a few first steps are needed. You will need to create a default container configuration file, specifying your desired id mappings and network setup, as well as configure the host to allow the unprivileged user to hook into the host network. The example below assumes that your mapped user and group id ranges are 100000-165536. Check your actual user and group id ranges and modify the example accordingly:

grep $USER /etc/subuid grep $USER /etc/subgid
mkdir -p ~/.config/lxc echo "lxc.id_map = u 0 100000 65536" > ~/.config/lxc/default.conf echo "lxc.id_map = g 0 100000 65536" >> ~/.config/lxc/default.conf echo "lxc.network.type = veth" >> ~/.config/lxc/default.conf echo "lxc.network.link = lxcbr0" >> ~/.config/lxc/default.conf echo "$USER veth lxcbr0 2" | sudo tee -a /etc/lxc/lxc-usernet

Après cela, vous pouvez créer des conteneurs non privilégiés et privilégiés de la même manière, sans utiliser sudo.

lxc-create -t download -n u1 -- -d ubuntu -r xenial -a amd64 lxc-start -n u1 -d lxc-attach -n u1 lxc-stop -n u1 lxc-destroy -n u1


In order to run containers inside containers - referred to as nested containers - two lines must be present in the parent container configuration file:

lxc.mount.auto = cgroup
lxc.aa_profile = lxc-container-default-with-nesting
The first will cause the cgroup manager socket to be bound into the container, so that lxc inside the container is able to administer cgroups for its nested containers. The second causes the container to run in a looser Apparmor policy which allows the container to do the mounting required for starting containers. Note that this policy, when used with a privileged container, is much less safe than the regular policy or an unprivileged container. See Apparmor for more information.

Configuration globale

Les fichiers de configuration suivants sont consultés par LXC. Pour une utilisation privilégiée, ils se trouvent dans /etc/lxc, et pour une utilisation non privilégié, ils sont dans ~/.config/lxc.

  • lxc.conf may optionally specify alternate values for several lxc settings, including the lxcpath, the default configuration, cgroups to use, a cgroup creation pattern, and storage backend settings for lvm and zfs.

  • default.conf specifies configuration which every newly created container should contain. This usually contains at least a network section, and, for unprivileged users, an id mapping section

  • lxc-usernet.conf spécifie comment les utilisateurs non privilégiés peuvent connecter leurs conteneurs au réseau appartenant à l’hôte.

lxc.conf and default.conf are both under /etc/lxc and $HOME/.config/lxc, while lxc-usernet.conf is only host-wide.

By default, containers are located under /var/lib/lxc for the root user, and $HOME/.local/share/lxc otherwise. The location can be specified for all lxc commands using the "-P|--lxcpath" argument.

Mise en réseau

By default LXC creates a private network namespace for each container, which includes a layer 2 networking stack. Containers usually connect to the outside world by either having a physical NIC or a veth tunnel endpoint passed into the container. LXC creates a NATed bridge, lxcbr0, at host startup. Containers created using the default configuration will have one veth NIC with the remote end plugged into the lxcbr0 bridge. A NIC can only exist in one namespace at a time, so a physical NIC passed into the container is not usable on the host.

It is possible to create a container without a private network namespace. In this case, the container will have access to the host networking like any other application. Note that this is particularly dangerous if the container is running a distribution with upstart, like Ubuntu, since programs which talk to init, like shutdown, will talk over the abstract Unix domain socket to the host's upstart, and shut down the host.

To give containers on lxcbr0 a persistent ip address based on domain name, you can write entries to /etc/lxc/dnsmasq.conf like:


If it is desirable for the container to be publicly accessible, there are a few ways to go about it. One is to use iptables to forward host ports to the container, for instance

 iptables -t nat -A PREROUTING -p tcp -i eth0 --dport 587 -j DNAT \
Another is to bridge the host's network interfaces (see the Ubuntu Server Guide's Network Configuration chapter, Pont réseau). Then, specify the host's bridge in the container configuration file in place of lxcbr0, for instance
lxc.network.type = veth
lxc.network.link = br0
Finally, you can ask LXC to use macvlan for the container's NIC. Note that this has limitations and depending on configuration may not allow the container to talk to the host itself. Therefore the other two options are preferred and more commonly used.

There are several ways to determine the ip address for a container. First, you can use lxc-ls --fancy which will print the ip addresses for all running containers, or lxc-info -i -H -n C1 which will print C1's ip address. If dnsmasq is installed on the host, you can also add an entry to /etc/dnsmasq.conf as follows

after which dnsmasq will resolve C1.lxc locally, so that you can do:
ping C1
ssh C1

Pour plus d'informations, consultez la page de manuel lxc.conf ainsi que les exemples de configurations réseau dans /usr/share/doc/lxc/examples/.

Démarrage de LXC

LXC does not have a long-running daemon. However it does have three upstart jobs.

  • /etc/init/lxc-net.conf: is an optional job which only runs if /etc/default/lxc-net specifies USE_LXC_BRIDGE (true by default). It sets up a NATed bridge for containers to use.

  • /etc/init/lxc.conf loads the lxc apparmor profiles and optionally starts any autostart containers. The autostart containers will be ignored if LXC_AUTO (true by default) is set to true in /etc/default/lxc. See the lxc-autostart manual page for more information on autostarted containers.

  • /etc/init/lxc-instance.conf is used by /etc/init/lxc.conf to autostart a container.

Backing Stores

LXC supports several backing stores for container root filesystems. The default is a simple directory backing store, because it requires no prior host customization, so long as the underlying filesystem is large enough. It also requires no root privilege to create the backing store, so that it is seamless for unprivileged use. The rootfs for a privileged directory backed container is located (by default) under /var/lib/lxc/C1/rootfs, while the rootfs for an unprivileged container is under ~/.local/share/lxc/C1/rootfs. If a custom lxcpath is specified in lxc.system.com, then the container rootfs will be under $lxcpath/C1/rootfs.

A snapshot clone C2 of a directory backed container C1 becomes an overlayfs backed container, with a rootfs called overlayfs:/var/lib/lxc/C1/rootfs:/var/lib/lxc/C2/delta0. Other backing store types include loop, btrfs, LVM and zfs.

A btrfs backed container mostly looks like a directory backed container, with its root filesystem in the same location. However, the root filesystem comprises a subvolume, so that a snapshot clone is created using a subvolume snapshot.

The root filesystem for an LVM backed container can be any separate LV. The default VG name can be specified in lxc.conf. The filesystem type and size are configurable per-container using lxc-create.

The rootfs for a zfs backed container is a separate zfs filesystem, mounted under the traditional /var/lib/lxc/C1/rootfs location. The zfsroot can be specified at lxc-create, and a default can be specified in lxc.system.conf.

More information on creating containers with the various backing stores can be found in the lxc-create manual page.


Creating a container generally involves creating a root filesystem for the container. lxc-create delegates this work to templates, which are generally per-distribution. The lxc templates shipped with lxc can be found under /usr/share/lxc/templates, and include templates to create Ubuntu, Debian, Fedora, Oracle, centos, and gentoo containers among others.

Creating distribution images in most cases requires the ability to create device nodes, often requires tools which are not available in other distributions, and usually is quite time-consuming. Therefore lxc comes with a special download template, which downloads pre-built container images from a central lxc server. The most important use case is to allow simple creation of unprivileged containers by non-root users, who could not for instance easily run the debootstrap command.

When running lxc-create, all options which come after -- are passed to the template. In the following command, --name, --template and --bdev are passed to lxc-create, while --release is passed to the template:

lxc-create --template ubuntu --name c1 --bdev loop -- --release xenial

You can obtain help for the options supported by any particular container by passing --help and the template name to lxc-create. For instance, for help with the download template,

lxc-create télécharger --template --help


LXC supports marking containers to be started at system boot. Prior to Ubuntu 14.04, this was done using symbolic links under the directory /etc/lxc/auto. Starting with Ubuntu 14.04, it is done through the container configuration files. An entry

lxc.start.auto = 1
lxc.start.delay = 5

would mean that the container should be started at boot, and the system should wait 5 seconds before starting the next container. LXC also supports ordering and grouping of containers, as well as reboot and shutdown by autostart groups. See the manual pages for lxc-autostart and lxc.container.conf for more information.


LXC est livré avec un profil Apparmor censé protéger l’hôte d'une mauvaise manipulation de privilège dans le conteneur. Par exemple, le conteneur ne pourra pas écrire dans /proc/sysrq-trigger ou dans la plupart des fichiers /sys.

The usr.bin.lxc-start profile is entered by running lxc-start. This profile mainly prevents lxc-start from mounting new filesystems outside of the container's root filesystem. Before executing the container's init, LXC requests a switch to the container's profile. By default, this profile is the lxc-container-default policy which is defined in /etc/apparmor.d/lxc/lxc-default. This profile prevents the container from accessing many dangerous paths, and from mounting most filesystems.

Programs in a container cannot be further confined - for instance, MySQL runs under the container profile (protecting the host) but will not be able to enter the MySQL profile (to protect the container).

La commande lxc-execute n'entre pas un profile Apparmor, mais le conteneur qu'il engendre sera confiné.

Personnalisation des politiques de sécurité du conteneur

Si vous constatez que lxc-start échoue malgré un accès légitime, refusé par la politique d'AppArmor, vous pouvez désactiver le profil de lxc-start en faisant :

sudo apparmor_parser -R /etc/apparmor.d/usr.bin.lxc-start
sudo ln -s /etc/apparmor.d/usr.bin.lxc-start /etc/apparmor.d/disabled/

This will make lxc-start run unconfined, but continue to confine the container itself. If you also wish to disable confinement of the container, then in addition to disabling the usr.bin.lxc-start profile, you must add:

lxc.aa_profile = unconfined

dans le fichier de configuration du conteneur.

LXC ships with a few alternate policies for containers. If you wish to run containers inside containers (nesting), then you can use the lxc-container-default-with-nesting profile by adding the following line to the container configuration file

lxc.aa_profile = lxc-container-default-with-nesting
If you wish to use libvirt inside containers, then you will need to edit that policy (which is defined in /etc/apparmor.d/lxc/lxc-default-with-nesting) by uncommenting the following line:
mount fstype=cgroup -> /sys/fs/cgroup/**,
and re-load the policy.

Note that the nesting policy with privileged containers is far less safe than the default policy, as it allows containers to re-mount /sys and /proc in nonstandard locations, bypassing apparmor protections. Unprivileged containers do not have this drawback since the container root cannot write to root-owned proc and sys files.

Another profile shipped with lxc allows containers to mount block filesystem types like ext4. This can be useful in some cases like maas provisioning, but is deemed generally unsafe since the superblock handlers in the kernel have not been audited for safe handling of untrusted input.

If you need to run a container in a custom profile, you can create a new profile under /etc/apparmor.d/lxc/. Its name must start with lxc- in order for lxc-start to be allowed to transition to that profile. The lxc-default profile includes the re-usable abstractions file /etc/apparmor.d/abstractions/lxc/container-base. An easy way to start a new profile therefore is to do the same, then add extra permissions at the bottom of your policy.

Après la création de la stratégie, chargez-la à l'aide de :

sudo apparmor_parser -r /etc/apparmor.d/lxc-containers

Le profil sera automatiquement chargé après un redémarrage, parce qu'il est alimenté par le fichier /etc/apparmor.d/lxc-containers. Enfin, pour faire que le conteneur CN utilise le nouveau lxc-profile-CN, ajoutez la ligne suivante dans son fichier de configuration :

lxc.aa_profile = lxc-CN-profile

Groupes de contrôle

Control groups (cgroups) are a kernel feature providing hierarchical task grouping and per-cgroup resource accounting and limits. They are used in containers to limit block and character device access and to freeze (suspend) containers. They can be further used to limit memory use and block i/o, guarantee minimum cpu shares, and to lock containers to specific cpus.

By default, a privileged container CN will be assigned to a cgroup called /lxc/CN. In the case of name conflicts (which can occur when using custom lxcpaths) a suffix "-n", where n is an integer starting at 0, will be appended to the cgroup name.

By default, a privileged container CN will be assigned to a cgroup called CN under the cgroup of the task which started the container, for instance /usr/1000.user/1.session/CN. The container root will be given group ownership of the directory (but not all files) so that it is allowed to create new child cgroups.

As of Ubuntu 14.04, LXC uses the cgroup manager (cgmanager) to administer cgroups. The cgroup manager receives D-Bus requests over the Unix socket /sys/fs/cgroup/cgmanager/sock. To facilitate safe nested containers, the line

lxc.mount.auto = cgroup

can be added to the container configuration causing the /sys/fs/cgroup/cgmanager directory to be bind-mounted into the container. The container in turn should start the cgroup management proxy (done by default if the cgmanager package is installed in the container) which will move the /sys/fs/cgroup/cgmanager directory to /sys/fs/cgroup/cgmanager.lower, then start listening for requests to proxy on its own socket /sys/fs/cgroup/cgmanager/sock. The host cgmanager will ensure that nested containers cannot escape their assigned cgroups or make requests for which they are not authorized.


For rapid provisioning, you may wish to customize a canonical container according to your needs and then make multiple copies of it. This can be done with the lxc-clone program.

Clones are either snapshots or copies of another container. A copy is a new container copied from the original, and takes as much space on the host as the original. A snapshot exploits the underlying backing store's snapshotting ability to make a copy-on-write container referencing the first. Snapshots can be created from btrfs, LVM, zfs, and directory backed containers. Each backing store has its own peculiarities - for instance, LVM containers which are not thinpool-provisioned cannot support snapshots of snapshots; zfs containers with snapshots cannot be removed until all snapshots are released; LVM containers must be more carefully planned as the underlying filesystem may not support growing; btrfs does not suffer any of these shortcomings, but suffers from reduced fsync performance causing dpkg and apt to be slower.

Snapshots of directory-packed containers are created using the overlay filesystem. For instance, a privileged directory-backed container C1 will have its root filesystem under /var/lib/lxc/C1/rootfs. A snapshot clone of C1 called C2 will be started with C1's rootfs mounted readonly under /var/lib/lxc/C2/delta0. Importantly, in this case C1 should not be allowed to run or be removed while C2 is running. It is advised instead to consider C1 a canonical base container, and to only use its snapshots.

Considérant un conteneur existant appelé C1, une copie peut en être créé en utilisant :

sudo lxc-clone -o C1 -n C2

A snapshot can be created using:

sudo lxc-clone -s -o C1 -n C2

Voir la page lxc-clone pour plus d'informations.


To more easily support the use of snapshot clones for iterative container development, LXC supports snapshots. When working on a container C1, before making a potentially dangerous or hard-to-revert change, you can create a snapshot

sudo lxc-snapshot -n C1

which is a snapshot-clone called 'snap0' under /var/lib/lxcsnaps or $HOME/.local/share/lxcsnaps. The next snapshot will be called 'snap1', etc. Existing snapshots can be listed using lxc-snapshot -L -n C1, and a snapshot can be restored - erasing the current C1 container - using lxc-snapshot -r snap1 -n C1. After the restore command, the snap1 snapshot continues to exist, and the previous C1 is erased and replaced with the snap1 snapshot.

Snapshots are supported for btrfs, lvm, zfs, and overlayfs containers. If lxc-snapshot is called on a directory-backed container, an error will be logged and the snapshot will be created as a copy-clone. The reason for this is that if the user creates an overlayfs snapshot of a directory-backed container and then makes changes to the directory-backed container, then the original container changes will be partially reflected in the snapshot. If snapshots of a directory backed container C1 are desired, then an overlayfs clone of C1 should be created, C1 should not be touched again, and the overlayfs clone can be edited and snapshotted at will, as such

lxc-clone -s -o C1 -n C2
lxc-start -n C2 -d # make some changes
lxc-stop -n C2
lxc-snapshot -n C2
lxc-start -n C2 # etc

Conteneurs éphémères

While snapshots are useful for longer-term incremental development of images, ephemeral containers utilize snapshots for quick, single-use throwaway containers. Given a base container C1, you can start an ephemeral container using

lxc-start-ephemeral -o C1

The container begins as a snapshot of C1. Instructions for logging into the container will be printed to the console. After shutdown, the ephemeral container will be destroyed. See the lxc-start-ephemeral manual page for more options.

Crochets de gestion du cycle de vie

Depuis Ubuntu 12.10, il est possible de définir des crochets à exécuter à des points spécifiques dans la vie d'un conteneur :

  • Pre-start hooks are run in the host's namespace before the container ttys, consoles, or mounts are up. If any mounts are done in this hook, they should be cleaned up in the post-stop hook.

  • Pre-mount hooks are run in the container's namespaces, but before the root filesystem has been mounted. Mounts done in this hook will be automatically cleaned up when the container shuts down.

  • Mount hooks are run after the container filesystems have been mounted, but before the container has called pivot_root to change its root filesystem.

  • Start hooks are run immediately before executing the container's init. Since these are executed after pivoting into the container's filesystem, the command to be executed must be copied into the container's filesystem.

  • Post-stop hooks are executed after the container has been shut down.

If any hook returns an error, the container's run will be aborted. Any post-stop hook will still be executed. Any output generated by the script will be logged at the debug priority.

Please see the lxc.container.conf manual page for the configuration file format with which to specify hooks. Some sample hooks are shipped with the lxc package to serve as an example of how to write and use such hooks.


Containers have a configurable number of consoles. One always exists on the container's /dev/console. This is shown on the terminal from which you ran lxc-start, unless the -d option is specified. The output on /dev/console can be redirected to a file using the -c console-file option to lxc-start. The number of extra consoles is specified by the lxc.tty variable, and is usually set to 4. Those consoles are shown on /dev/ttyN (for 1 <= N <= 4). To log into console 3 from the host, use:

sudo lxc-console -n container -t 3

ou si l'option -t N n'est pas spécifiée, une console inutilisée sera automatiquement choisie. Pour quitter la console, utilisez la séquence d'échappement Ctrl-a q. Notez que cette séquence ne fonctionnera pas dans la console provenant de lxc-start sans l'option -d.

Each container console is actually a Unix98 pty in the host's (not the guest's) pty mount, bind-mounted over the guest's /dev/ttyN and /dev/console. Therefore, if the guest unmounts those or otherwise tries to access the actual character device 4:N, it will not be serving getty to the LXC consoles. (With the default settings, the container will not be able to access that character device and getty will therefore fail.) This can easily happen when a boot script blindly mounts a new /dev.



If something goes wrong when starting a container, the first step should be to get full logging from LXC:

sudo lxc-start -n C1 -l trace -o debug.out

This will cause lxc to log at the most verbose level, trace, and to output log information to a file called 'debug.out'. If the file debug.out already exists, the new log information will be appended.

Surveillance de l’état des conteneurs

Deux commandes sont disponibles pour surveiller les changements d'état de conteneurs. La commande lxc-monitor surveille un ou plusieurs conteneurs pour tout changement d'état. Il prend un nom de conteneur avec l'option -n comme toujours, mais dans ce cas, le nom du conteneur peut être une expression rationnelle POSIX pour permettre le suivi d'ensembles voulus de conteneurs. lxc-monitor continuera de fonctionner en affichant les changements des conteneurs. lxc-wait attend un changement d'état spécifique et quitte. Par exemple,

sudo lxc-monitor -n cont[0-5]*

afficherait tous les changements d'état de tout conteneurs correspondant à l'expression rationnelle listée, alors que

sudo lxc-wait -n cont1 -s 'STOPPED|FROZEN'

attendra jusqu'à ce que le conteneur cont1 passe à l'état ARRÊT ou à l'état GELÉ et ensuite se termine.


As of Ubuntu 14.04, it is possible to attach to a container's namespaces. The simplest case is to simply do

sudo lxc-attach -n C1

which will start a shell attached to C1's namespaces, or, effectively inside the container. The attach functionality is very flexible, allowing attaching to a subset of the container's namespaces and security context. See the manual page for more information.

Container init verbosity

If LXC completes the container startup, but the container init fails to complete (for instance, no login prompt is shown), it can be useful to request additional verbosity from the init process. For an upstart container, this might be:

sudo lxc-start -n C1 /sbin/init loglevel=debug

You can also start an entirely different program in place of init, for instance

sudo lxc-start -n C1 /bin/bash
sudo lxc-start -n C1 /bin/sleep 100
sudo lxc-start -n C1 /bin/cat /proc/1/status


La plupart des fonctionnalités de LXC sont maintenant accessibles via une application de programmation d'interface (API) exportée par liblxc pour laquelle les liaisons sont disponibles en plusieurs langages, y compris Python, lua, rubis et go.

Voici un exemple utilisant les liaisons Python (qui sont disponibles dans le paquet python3-lxc) qui créent et démarrent un conteneur, puis attendent son arrêt :

# sudo python3
Python 3.2.3 (default, Aug 28 2012, 08:26:03)
[GCC 4.7.1 20120814 (prerelease)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import lxc
__main__:1: Warning: The python-lxc API isn't yet stable and may change at any p
oint in the future.
>>> c=lxc.Container("C1")
>>> c.create("ubuntu")
>>> c.start()
>>> c.wait("STOPPED")


A namespace maps ids to resources. By not providing a container any id with which to reference a resource, the resource can be protected. This is the basis of some of the security afforded to container users. For instance, IPC namespaces are completely isolated. Other namespaces, however, have various leaks which allow privilege to be inappropriately exerted from a container into another container or to the host.

By default, LXC containers are started under a Apparmor policy to restrict some actions. The details of AppArmor integration with lxc are in section Apparmor. Unprivileged containers go further by mapping root in the container to an unprivileged host userid. This prevents access to /proc and /sys files representing host resources, as well as any other files owned by root on the host.

Appels système exploitables

It is a core container feature that containers share a kernel with the host. Therefore if the kernel contains any exploitable system calls the container can exploit these as well. Once the container controls the kernel it can fully control any resource known to the host.

Since Ubuntu 12.10 (Quantal) a container can also be constrained by a seccomp filter. Seccomp is a new kernel feature which filters the system calls which may be used by a task and its children. While improved and simplified policy management is expected in the near future, the current policy consists of a simple whitelist of system call numbers. The policy file begins with a version number (which must be 1) on the first line and a policy type (which must be 'whitelist') on the second line. It is followed by a list of numbers, one per line.

In general to run a full distribution container a large number of system calls will be needed. However for application containers it may be possible to reduce the number of available system calls to only a few. Even for system containers running a full distribution security gains may be had, for instance by removing the 32-bit compatibility system calls in a 64-bit container. See the lxc.container.conf manual page for details of how to configure a container to use seccomp. By default, no seccomp policy is loaded.