Question
Answer and Explanation
The error "args must not be empty: unknown" during a runc create operation typically indicates that the container's configuration, specifically the command or arguments to execute within the container, are either missing or incorrectly formatted. runc is a low-level container runtime that directly interacts with the operating system kernel to create and manage containers. When you instruct runc to create a container, it needs a clear set of instructions on what process to run inside that container.
Here are the main reasons this error might occur:
1. Missing Command or Arguments:
The most common cause is that the container configuration doesn't specify any command to run. This configuration is usually provided in a JSON file called config.json. If the 'args' field within the 'process' section of this file is empty, runc will throw this error. For example:
"process": {
"args": [],
"env": [ ... ],
...
}
The args array is empty, leading to the error.
2. Incorrectly Formatted Command or Arguments:
If the command is not formatted correctly within the args array, runc can fail. args should be an array of strings, with the first string representing the command to be executed. For example, if there are syntax errors in the command, it can be parsed incorrectly resulting in the error, or it could also be that the command is trying to use some shell features that aren't supported within the container's context.
3. Issues in the Container Image or OCI Bundle:
If the container image or the OCI (Open Container Initiative) bundle is corrupted or missing information required for the container launch, then the error might surface during runc container creation.
4. Incorrect Container Configuration Generation:
If you are generating the container configuration file (config.json) programmatically or using a tool, ensure that the logic to populate the 'args' field is functioning correctly.
5. Use of an Orchestrator (Kubernetes, Docker, etc.):
If you are using an orchestrator like Kubernetes or Docker, these tools abstract away the direct interaction with runc. In such cases, errors like these usually originate from the container image configuration or the orchestrator's configuration that translate to arguments passed to runc.
Troubleshooting Steps:
1. Examine the `config.json`:
Check the config.json file generated by your tool, image or container engine. Verify that the 'args' array under 'process' is not empty and that it contains a valid command and its required arguments. For example:
"process": {
"args": ["/bin/sh", "-c", "your_command_here"],
"env": [ ... ],
...
}
In this example, the container will run /bin/sh -c your_command_here
2. Verify the Container Image:
If you are using a container image, make sure that the image is valid and contains the necessary information for creating a container. Test with a known working image to see if the issue persists.
3. Check the Orchestrator Settings:
If you are using an orchestrator, review its configurations, specifically the manifest files, deployment configurations, etc., where the container command or entry point is defined.
4. Simplified Testing:
To isolate the problem, try running a basic command in the container (e.g., /bin/sh) directly using runc create and a minimal config.json file. This might help narrow down if the issue is the command itself or with other configurations.
In summary, the “args must not be empty: unknown” error with runc create signals that the container lacks proper instructions on what to execute. Correcting the config.json or re-evaluating the container image configuration should resolve this issue.