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6.11. Cloning

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.

Given an existing container called C1, a copy can be created using:

sudo lxc-clone -o C1 -n C2

A snapshot can be created using:

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

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