Container Execution¶

In some situations it is necessary to inspect or interact with the internal state of a running container.

Shell Access¶

Shell access is useful for debugging and inspection purposes. To open an interactive shell inside a running container, execute:

docker exec -it <container_name> /bin/bash

Tailing the logs¶

Most images are configured to write application logs to standard output. These logs can be viewed using the docker logs command:

docker logs -f --tail=<number_of_lines_to_start_with> <container_name>

The --tail argument is optional. When omitted, the command outputs all available logs, which may be excessive for long-running containers.

For convenience, the following Bash alias can be used to simplify log access:

# ~/.bash_aliases
alias dtail='docker logs -tf --tail="50" "$@"'

Logs can then be followed using:

dtail <container_name>

Checking the build version¶

When investigating issues, identifying the exact image version in use is important. Problems may already be resolved in newer releases, or the observed behavior may indicate a newly introduced issue.

To display version and build information for a running container (for example, dsmr):

docker inspect -f '{{ with .Config.Labels -}}
DSMR upstream version: {{ index . "io.github.dsmrreader.upstream.version" }}
DSMR Docker release:   {{ index . "io.github.dsmrreader.docker.release" }}
OCI version:           {{ index . "org.opencontainers.image.version" }}
Build date:            {{ index . "org.opencontainers.image.build_date" }}
Revision:              {{ index . "org.opencontainers.image.revision" }}
{{- end }}' <container_name>

An alternative method to retrieve version information from the running container:

docker exec -ti <container_name> bash -c 'cat /build_version'

To inspect version information directly from an image (for example, ghcr.io/xirixiz/dsmr-reader-docker):

docker inspect -f '{{ with .Config.Labels -}}
DSMR upstream version: {{ index . "io.github.dsmrreader.upstream.version" }}
DSMR Docker release:   {{ index . "io.github.dsmrreader.docker.release" }}
OCI version:           {{ index . "org.opencontainers.image.version" }}
Build date:            {{ index . "org.opencontainers.image.build_date" }}
Revision:              {{ index . "org.opencontainers.image.revision" }}
{{- end }}' <image_name>