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(new-post): From Docker to Podman: full migration to rootless

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Eduard Tolosa 2025-02-21 08:27:38 +00:00
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---
layout: post
title: 'From Docker to Podman: full migration to rootless'
date: 2025-02-21 06:31 +0000
categories: ["docker", "podman"]
tags: ["docker", "podman", "rootless"]
author: edu4rdshl
image:
path: /docker-to-podman.png
alt: Image of Docker and Podman logos. From the internet.
excerpt: Migrate from Docker to rootless Podman, including volumes, networks, ports settings, container's metadata (mounts, restart policy, etc), and more.
---
# Introduction
There are many posts about migrating from Docker to Podman, but most of them are focused on the basics... `docker export` / `podman import`. This post is about a full migration, including volumes data, container's metadata, and more. Everything, into a rootless Podman environment.
I have created a tool called [fly-to-podman](https://github.com/Edu4rdSHL/fly-to-podman) that automates the migration process from what I'm going to explain here.
# Prerequisites
Start with the obvious, you need to have Docker and Podman installed, and Docker needs to be running.
# Migration
For rootless Podman, all the data is stored in `~/.local/share/containers/` and the configuration can be changed in `~/.config/containers/`. They will change if you aren't using rootless Podman, so adjust the paths in the post accordingly.
## Images
First, let's migrate the images. We will use `docker save` and `podman load`:
{% raw %}
```bash
migrate_images() {
echo "Migrating Docker images to Podman..."
# Get a list of all Docker images (name:tag)
docker images --format "{{.Repository}}:{{.Tag}}" | while read -r image; do
# Skip <none>:<none> images
if [[ "$image" == "<none>:<none>" ]]; then
continue
fi
# Replace slashes in repository names with underscores for filenames
filename=$(echo "$image" | tr '/' '_').tar
echo "Exporting $image..."
docker save -o "$filename" "$image" &&
podman load -i "$filename" &&
echo "Image $image migrated to Podman" || echo "Failed to migrate image $image"
# Remove temporary file
rm -f "$filename"
done
}
```
{% endraw %}
This small script will export all Docker images to a tarball, then import them into Podman. It will skip `<none>:<none>` images.
## Volumes data
Volumes data is stored in `/var/lib/docker/volumes/` for Docker and in `~/.local/share/containers/storage/volumes/` for Podman. We can create the same volumes names in Podman so that they are tracked in the database and then copy the data.
{% raw %}
```bash
migrate_volumes() {
echo "Migrating Docker volumes to Podman..."
# Get the path to the Podman volumes directory
PODMAN_VOLUMES_PATH=$(podman info --format json | jq -r '.store.volumePath')
DOCKER_VOLUMES_PATH="/var/lib/docker/volumes"
for volume in $(docker volume ls --format json | jq -r '.Name'); do
echo "Migrating volume: $volume"
podman volume create "$volume" &&
sudo rsync -a "$DOCKER_VOLUMES_PATH/$volume/_data/" "$PODMAN_VOLUMES_PATH/$volume/_data"
done
}
```
{% endraw %}
## Networks
We are going to migrate the networks while preserving:
- The network name
- The network driver
- The subnet
- The gateway
- The IP range
{% raw %}
```bash
migrate_networks() {
echo "Migrating Docker networks to Podman..."
# Get all Docker networks
for network in $(docker network ls --format '{{json . }}' | jq -r '.Name'); do
echo "Processing network: $network"
# Skip default Docker networks
if [[ "$network" == "host" || "$network" == "none" ]]; then
echo "Skipping network: $network (Podman does not need it)"
continue
fi
# Extract network details
NETWORK_JSON=$(docker network inspect "$network" | jq '.[0]')
DRIVER=$(echo "$NETWORK_JSON" | jq -r '.Driver')
SUBNET=$(echo "$NETWORK_JSON" | jq -r '.IPAM.Config[0].Subnet // empty')
GATEWAY=$(echo "$NETWORK_JSON" | jq -r '.IPAM.Config[0].Gateway // empty')
IP_RANGE=$(echo "$NETWORK_JSON" | jq -r '.IPAM.Config[0].IPRange // empty')
# Check if the network already exists in Podman
if podman network exists "$network"; then
echo "Network $network already exists in Podman. Skipping creation."
continue
fi
# Build the Podman network create command
PODMAN_NET_CMD="podman network create"
# Add driver (Podman supports `bridge`, `ipvlan` and `macvlan`)
case "$DRIVER" in
"bridge")
PODMAN_NET_CMD+=" --driver bridge"
;;
"macvlan")
PODMAN_NET_CMD+=" --driver macvlan"
;;
"ipvlan")
PODMAN_NET_CMD+=" --driver ipvlan"
;;
*)
echo "Warning: Unsupported network driver '$DRIVER' in Podman. Using default bridge."
PODMAN_NET_CMD+=" --driver bridge"
;;
esac
# Add subnet configuration if available
if [[ -n "$SUBNET" ]]; then
PODMAN_NET_CMD+=" --subnet $SUBNET"
fi
# Add gateway if available
if [[ -n "$GATEWAY" ]]; then
PODMAN_NET_CMD+=" --gateway $GATEWAY"
fi
# Add IP range if available
if [[ -n "$IP_RANGE" ]]; then
PODMAN_NET_CMD+=" --ip-range $IP_RANGE"
fi
# Finalize the command with network name
PODMAN_NET_CMD+=" $network"
# Create the Podman network
echo "Creating Podman network: $network"
eval "$PODMAN_NET_CMD" && echo "Network $network migrated successfully." ||
echo "Failed to migrate network: $network"
done
}
```
{% endraw %}
## Containers
Containers data is stored in `/var/lib/docker/containers/` for Docker and in `~/.local/share/containers/storage/` for Podman. We require a more complex script to migrate the containers data, including metadata like mounts, restart policy, etc.
{% raw %}
```bash
migrate_containters() {
echo "Migrating Docker containers to Podman..."
for container in $(docker container ls -a --format json | jq -r '.Names'); do
# Convert container name to lowercase
container_lc=$(echo "$container" | tr '[:upper:]' '[:lower:]')
# Tag for the image to be created from the container
MIGRATION_CONTAINER_TAG="podman.local/${container_lc}-to-podman:latest"
# Get Running status from Docker
WAS_RUNNING=$(docker container inspect -f '{{.State.Running}}' "$container")
# Get RestartPolicy from Docker
RESTART_POLICY=$(docker inspect -f '{{.HostConfig.RestartPolicy.Name}}' "$container")
# Pass the restart policy to Podman
case "$RESTART_POLICY" in
"no") PODMAN_RESTART="" ;;
"always") PODMAN_RESTART="--restart=always" ;;
"unless-stopped") PODMAN_RESTART="--restart=unless-stopped" ;;
"on-failure") PODMAN_RESTART="--restart=on-failure" ;;
*) PODMAN_RESTART="" ;;
esac
echo "Processing container: $container"
# Commit container to an image. It lets us start a new container with the _same_ state and add additional options
docker commit "$container" "$MIGRATION_CONTAINER_TAG" &&
docker save -o "$container_lc".tar "$MIGRATION_CONTAINER_TAG" &&
podman load -i "$container_lc".tar || {
echo "Failed to migrate image for $container"
continue
}
# Extract volume/bind mount information from Docker container
MOUNT_OPTS=""
while read -r mount; do
MOUNT_TYPE=$(echo "$mount" | jq -r '.Type')
SOURCE=$(echo "$mount" | jq -r '.Source')
DESTINATION=$(echo "$mount" | jq -r '.Destination')
READ_WRITE=$(echo "$mount" | jq -r '.RW')
# Pass the RW/RO setting to Podman
if [[ "$READ_WRITE" == "true" ]]; then
MODE="rw"
else
MODE="ro"
fi
if [[ "$MOUNT_TYPE" == "volume" ]]; then
# Use :U to ensure right permissions inside the container.
# It tells Podman to use the correct host UID and GID based on the UID and GID within the <<container|pod>>
MODE+=",U"
# Attach existing named volume
VOLUME_NAME=$(echo "$mount" | jq -r '.Name')
MOUNT_OPTS+=" -v $VOLUME_NAME:$DESTINATION:$MODE"
elif [[ "$MOUNT_TYPE" == "bind" ]]; then
# Use :Z if you're using SELinux to ensure right permissions inside the container
# MODE+=",Z"
# Ensure the source path exists before mounting
[[ -e "$SOURCE" ]] && MOUNT_OPTS+=" -v $SOURCE:$DESTINATION:$MODE"
fi
done < <(docker inspect "$container" | jq -c '.[0].Mounts[]')
# Extract port mappings
PORT_OPTS=""
while read -r port_mapping; do
HOST_IP=$(echo "$port_mapping" | jq -r '.HostIp')
HOST_PORT=$(echo "$port_mapping" | jq -r '.HostPort')
CONTAINER_PORT=$(echo "$port_mapping" | jq -r '.ContainerPort')
PROTOCOL=$(echo "$port_mapping" | jq -r '.Protocol')
# Construct `-p` option (exclude 0.0.0.0 for readability)
if [[ "$HOST_IP" == "0.0.0.0" || -z "$HOST_IP" ]]; then
PORT_OPTS+=" -p $HOST_PORT:$CONTAINER_PORT/$PROTOCOL"
else
PORT_OPTS+=" -p $HOST_IP:$HOST_PORT:$CONTAINER_PORT/$PROTOCOL"
fi
done < <(docker inspect "$container" | jq -c '.[] | .NetworkSettings.Ports | to_entries[] | {ContainerPort: .key, Protocol: (if .key | contains("udp") then "udp" else "tcp" end), HostMappings: .value} | select(.HostMappings != null) | .HostMappings[] | {HostIp, HostPort, ContainerPort, Protocol}')
# Extract network information
NETWORK_OPTS=""
while read -r network; do
NETWORK_NAME=$(echo "$network" | jq -r 'keys[0]')
NETWORK_IP=$(echo "$network" | jq -r ".$NETWORK_NAME.IPAddress")
if [[ -n "$NETWORK_NAME" ]]; then
NETWORK_OPTS+=" --network=$NETWORK_NAME"
fi
if [[ -n "$NETWORK_IP" ]]; then
NETWORK_OPTS+=" --ip=$NETWORK_IP"
fi
done < <(docker inspect "$container" | jq -c '.[0].NetworkSettings.Networks')
# Run the container with the same name and mounts, including RW/RO options
podman run -d --name "$container" $PODMAN_RESTART "$MOUNT_OPTS" "$PORT_OPTS" "$NETWORK_OPTS" "$MIGRATION_CONTAINER_TAG" &&
echo "Container $container migrated successfully" ||
echo "Failed to migrate container: $container"
# Stop the container if this was not running, this allow us to keep the container ready to `podman container start $container`
if [[ "$WAS_RUNNING" == "false" ]]; then
podman stop "$container"
fi
done
}
```
{% endraw %}
After running the scripts on that order, you should have all your Docker containers, networks, images, and volumes migrated to rootless Podman with the same state as before.
# Caveats
After migrating from Docker to Podman, you may encounter some issues:
- **SELinux**: Podman is more strict than Docker with SELinux, so you may need to adjust the labels on your files.
- **Networks**: Podman does not support all the network drivers that Docker does, so you may need to adjust the network driver in the script.
- **Volumes**: Podman requires some additional options like `:U` or `:Z` to ensure the right permissions inside the container.
Some minor but still annoying issues:
- The system journal will gets spammed with [porman-events](https://docs.podman.io/en/stable/markdown/podman-events.1.html) messages. The only way to disable them is to set `events_logger = "none"` in `~/.config/containers/containers.conf`, but then you won't be able to use `podman container logs`, which is a big downside.
- Even if you set a default network in `~/.config/containers/containers.conf`, [Podman will ignore it](https://github.com/containers/podman/issues/25377).
I ended up with the following configuration in `~/.config/containers/containers.conf` to workaround the issues:
```conf
[engine]
compose_warning_logs = false
healthcheck_events = false
events_logfile_path="/home/edu4rdshl/.local/share/containers/containers.log"
events_logger = "file"
events_logfile_max_size = "1m"
[network]
default_network = "podman" # https://github.com/containers/podman/issues/25377
```
# Tips
- Install [podman-docker](https://github.com/containers/podman/tree/main/docker) to continue using `docker` commands with Podman. Or simply create and alias for `docker=podman`.
- If you use `docker-compose.yml` files, you can install the `docker-compose` package and then run `podman compose`. See the [official documentation](https://docs.podman.io/en/stable/markdown/podman-compose.1.html) for more information.
# Conclusion
It's still too early to say if Podman is a better alternative to Docker, but being rootless by default is nice. There may be some things that I haven't covered in this post, feel free to open an issue or pull request on the [fly-to-podman](https://github.com/Edu4rdSHL/fly-to-podman) repository.