Mastering Podman: A Docker‑Compatible, Daemon‑Free Container Runtime

What is Podman?

Podman is an open‑source container runtime that works on most Linux distributions. It offers Docker‑compatible commands but runs without a daemon and can operate without root privileges.

Key Differences Between Podman and Docker

Docker requires a root‑owned daemon (dockerd) and multiple helper processes (containerd, shim); Podman runs containers directly via OCI runtimes (runC) without a daemon.

Podman’s architecture is simpler and more secure because it does not need a privileged daemon.

In Docker the daemon hierarchy is dockerd → containerd → containerd‑shim → runC; Podman uses a single “conmon” process analogous to containerd‑shim.

Podman Commands (Docker‑compatible)

podman run        # create and start a container
podman start      # start a stopped container
podman ps         # list containers
podman stop       # stop a container
podman restart    # restart a container
podman attach     # attach to a running container
podman exec       # execute a command in a container
podman logs       # view container logs
podman rm         # remove a container

Image Management

podman search
podman pull
podman images
podman rmi
podman save
podman load
podman build
# Dockerfile instructions: COPY, ADD, CMD, ENV, EXPOSE

Installation and Acceleration

# Install Podman
yum -y install podman

# Registry accelerator (v7)
vim /etc/containers/registries.conf
registries = ["docker.io"]
[[docker.io]]
location="j3m2itm3.mirror.aliyuncs.com"

# Registry accelerator (v8)
unqualified-search-registries = ["docker.io"]
[[registry]]
prefix = "docker.io"
location = "j3m2itm3.mirror.aliyuncs.com"

Running a Container Example

# Pull and run an httpd image
podman run -d --name httpd docker.io/library/httpd
podman ps
podman logs --latest

Rootless Operation and User Configuration

To run Podman without root, install crun (or another OCI runtime) and set runtime = "crun" in /etc/containers/containers.conf. Install slirp4netns and fuse‑overlayfs for rootless networking and storage, and configure /etc/subuid and /etc/subgid for user‑namespace mapping.

Configuration Files

The three main configuration files are containers.conf, storage.conf, and registries.conf. They are read in order of precedence: system‑wide files in /etc/containers, then user‑specific files in $HOME/.config/containers.

Volumes

When a container runs as root, files created inside the mounted host directory appear owned by the host user. Use --userns=keep-id to preserve UID/GID mapping so that files retain the invoking user’s ownership.