Export/Import

A container can be exported into a single tar archive and later imported on the same or a different host. The tar archive contains all needed data, such as user/group/container configuration and rootfs, see container image specification for more information about its contents.

Exporting

Exporting does not actually remove the container from the node, it merely dumps its configuration and rootfs into a file. If the container is running, you have the option to choose either corsistent or inconsistent export.

Consistent export stops the container, if it is running, so that applications can gracefully exit and save state to disk. Rootfs is stored as a ZFS stream, where the first snapshot is made when the container is running. When that snapshot is dumped, the container is stopped and the second snapshot is made. It is dumped as an incremental stream from the first snapshot. The container is restarted when exporting is finished.

Inconsistent export does not stop the container, it dumps the rootfs from the running system using only one snapshot, which essentially equals to system reset/power loss on import.

osctl ct export [--consistent] myct01 myct01-export.tar

By default, the ZFS stream is either dumped compressed by ZFS or is compressed by osctld using gzip. One can choose to disable or enforce compression using option --compression auto | off | gzip.

Importing

To import a previously exported container, use:

osctl ct import myct01-export.tar

It is possible to override the container id, or the name of its user and group. This allows you to import one archive multiple times, essentially cloning the containers.

osctl ct import --as-id bettername myct01-export.tar

Similarily, one can use --as-user or --as-group to import the container with a different user or group. Note that both the user and the group have to already exist, if you're using these options. The existing user/group is used instead of the ones in the exported archive.