Key Points

Introduction to Containers

Containers package an application with its dependencies into a portable, self-contained unit that runs consistently across different systems.
Unlike virtual machines, containers share the host’s Linux kernel, making them lightweight and fast to start.
Linux namespaces and cgroups provide the isolation and resource control that containers rely on.
Container images are built from read-only layers; a thin writable layer is added at runtime and is lost when the container is removed (although there are options for filesystem persistence).
On MacOS and Windows, containers run inside a lightweight Linux virtual machine managed by the container engine.
Podman is a daemonless, open source container engine whose commands are largely interchangeable with Docker.

podman --version confirms that Podman is installed and accessible from the command line.
On MacOS and Windows, Podman requires a lightweight Linux virtual machine, initialised with podman machine init and started with podman machine start.
On Linux and Windows Subsystem for Linux (WSL), Podman runs natively and no virtual machine is needed.
Podman operates in rootless mode by default, meaning it does not require administrator privileges.

podman container list -a shows all containers including stopped ones whilst podman container list shows only running containers.
An exit code of 0 means a container completed successfully, whereas a non-zero exit code indicates an error.
podman run always creates a new container, and podman container start restarts an existing stopped container.
The -p host-port:container-port/protocol option maps a port inside a container to a port on the host, enabling access to services running in the container.
The -d flag runs a container in detached (background) mode.
podman logs <name> retrieves its output.
podman exec -ti <container> /bin/bash opens an interactive shell inside a running container.
The -v <host-dir>:<container-dir> option mounts a host directory into the container, allowing both to access the same files.
All containers based on an image must be removed before that image can be deleted.

podman info displays Podman’s full configuration, including which registries are configured for searching.
On macOS and Windows, Docker Hub is configured as a search registry by default; on Linux this typically requires manual configuration.
Registry search is configured by editing ~/.config/containers/registries.conf.
podman search <term> returns images from all configured registries whose names or descriptions match the search term.