Kernel Functions

class ai.backend.client.kernel.Kernel(kernel_id, owner_access_key=None)[source]

Provides various interactions with compute sessions in Backend.AI.

The term ‘kernel’ is now deprecated and we prefer ‘compute sessions’. However, for historical reasons and to avoid confusion with client sessions, we keep the backward compatibility with the naming of this API function class.

For multi-container sessions, all methods take effects to the master container only, except destroy() and restart() methods. So it is the user’s responsibility to distribute uploaded files to multiple containers using explicit copies or virtual folders which are commonly mounted to all containers belonging to the same compute session.

session = None

The client session instance that this function class is bound to.

classmethod await get_or_create(image, *, client_token=None, type_='interactive', enqueue_only=False, max_wait=0, no_reuse=False, mounts=None, envs=None, startup_command=None, resources=None, resource_opts=None, cluster_size=1, domain_name=None, group_name=None, tag=None, scaling_group=None, owner_access_key=None)[source]

Get-or-creates a compute session. If client_token is None, it creates a new compute session as long as the server has enough resources and your API key has remaining quota. If client_token is a valid string and there is an existing compute session with the same token and the same image, then it returns the Kernel instance representing the existing session.

  • image (str) – The image name and tag for the compute session. Example: python:3.6-ubuntu. Check out the full list of available images in your server using (TODO: new API).

  • client_token (Optional[str]) – A client-side identifier to seamlessly reuse the compute session already created.

  • type

    Either "interactive" (default) or "batch".

    New in version 19.09.0.

  • enqueue_only (bool) –

    Just enqueue the session creation request and return immediately, without waiting for its startup. (default: false to preserve the legacy behavior)

    New in version 19.09.0.

  • max_wait (int) –

    The time to wait for session startup. If the cluster resource is being fully utilized, this waiting time can be arbitrarily long due to job queueing. If the timeout reaches, the returned status field becomes "TIMEOUT". Still in this case, the session may start in the future.

    New in version 19.09.0.

  • no_reuse (bool) –

    Raises an explicit error if a session with the same image and the same client_token already exists instead of returning the information of it.

    New in version 19.09.0.

  • mounts (Optional[Iterable[str]]) – The list of vfolder names that belongs to the currrent API access key.

  • envs (Optional[Mapping[str, str]]) – The environment variables which always bypasses the jail policy.

  • resources (Optional[Mapping[str, int]]) – The resource specification. (TODO: details)

  • cluster_size (int) – The number of containers in this compute session. Must be at least 1.

  • tag (Optional[str]) – An optional string to annotate extra information.

  • owner – An optional access key that owns the created session. (Only available to administrators)

Return type



The Kernel instance.

await destroy(*, forced=False)[source]

Destroys the compute session. Since the server literally kills the container(s), all ongoing executions are forcibly interrupted.

await restart()[source]

Restarts the compute session. The server force-destroys the current running container(s), but keeps their temporary scratch directories intact.

await interrupt()[source]

Tries to interrupt the current ongoing code execution. This may fail without any explicit errors depending on the code being executed.

await complete(code, opts=None)[source]

Gets the auto-completion candidates from the given code string, as if a user has pressed the tab key just after the code in IDEs.

Depending on the language of the compute session, this feature may not be supported. Unsupported sessions returns an empty list.

  • code (str) – An (incomplete) code text.

  • opts (Optional[dict]) – Additional information about the current cursor position, such as row, col, line and the remainder text.

Return type



An ordered list of strings.

await get_info()[source]

Retrieves a brief information about the compute session.

await get_logs()[source]

Retrieves the console log of the compute session container.

await execute(run_id=None, code=None, mode='query', opts=None)[source]

Executes a code snippet directly in the compute session or sends a set of build/clean/execute commands to the compute session.

For more details about using this API, please refer the official API documentation.

  • run_id (Optional[str]) – A unique identifier for a particular run loop. In the first call, it may be None so that the server auto-assigns one. Subsequent calls must use the returned runId value to request continuation or to send user inputs.

  • code (Optional[str]) – A code snippet as string. In the continuation requests, it must be an empty string. When sending user inputs, this is where the user input string is stored.

  • mode (str) – A constant string which is one of "query", "batch", "continue", and "user-input".

  • opts (Optional[dict]) – A dict for specifying additional options. Mainly used in the batch mode to specify build/clean/execution commands. See the API object reference for details.


An execution result object

await upload(files, basedir=None, show_progress=False)[source]

Uploads the given list of files to the compute session. You may refer them in the batch-mode execution or from the code executed in the server afterwards.

  • files (Sequence[Union[str, Path]]) –

    The list of file paths in the client-side. If the paths include directories, the location of them in the compute session is calculated from the relative path to basedir and all intermediate parent directories are automatically created if not exists.

    For example, if a file path is /home/user/test/data.txt (or test/data.txt) where basedir is /home/user (or the current working directory is /home/user), the uploaded file is located at /home/work/test/data.txt in the compute session container.

  • basedir (Union[str, Path, None]) – The directory prefix where the files reside. The default value is the current working directory.

  • show_progress (bool) – Displays a progress bar during uploads.

await download(files, dest='.', show_progress=False)[source]

Downloads the given list of files from the compute session.

  • files (Sequence[Union[str, Path]]) – The list of file paths in the compute session. If they are relative paths, the path is calculated from /home/work in the compute session container.

  • dest (Union[str, Path]) – The destination directory in the client-side.

  • show_progress (bool) – Displays a progress bar during downloads.

await list_files(path='.')[source]

Gets the list of files in the given path inside the compute session container.


path (Union[str, Path]) – The directory path in the compute session.


Opens the stream of the kernel lifecycle events. Only the master kernel of each session is monitored.

Return type



a StreamEvents object.


Opens a pseudo-terminal of the kernel (if supported) streamed via websockets.

Return type



a StreamPty object.

stream_execute(code='', *, mode='query', opts=None)[source]

Executes a code snippet in the streaming mode. Since the returned websocket represents a run loop, there is no need to specify run_id explicitly.

Return type


class ai.backend.client.kernel.StreamPty(session, underlying_ws)[source]

A derivative class of WebSocketResponse which provides additional functions to control the terminal.