bagelhole/podman

Podman

Run and manage containers without a daemon using Podman's rootless container engine.

When to Use This Skill

Use this skill when:

• Running containers without root privileges
• Managing containers on systems without Docker
• Creating pod-based container groups
• Using systemd for container management
• Working in security-conscious environments

Prerequisites

• Podman installed (4.x+)
• For rootless: user namespaces enabled
• Basic container concepts understanding

Key Differences from Docker

| Feature | Docker | Podman | |---------|--------|--------| | Architecture | Client-daemon | Daemonless | | Root required | Default | Optional (rootless) | | Pod support | No | Yes (Kubernetes-style) | | Systemd integration | Limited | Native | | Socket | docker.sock | podman.sock (optional) |

Basic Commands

Container Operations

# Run container (identical to Docker)
podman run -d --name webserver -p 8080:80 nginx

# List containers
podman ps -a

# Stop and remove
podman stop webserver
podman rm webserver

# Execute command
podman exec -it webserver /bin/sh

# View logs
podman logs -f webserver

Image Management

# Pull image
podman pull docker.io/library/nginx:latest

# List images
podman images

# Build image
podman build -t myapp:latest .

# Push to registry
podman push myapp:latest registry.example.com/myapp:latest

# Remove image
podman rmi nginx:latest

Rootless Containers

Setup

# Check user namespace support
cat /proc/sys/user/max_user_namespaces

# Enable if needed (as root)
echo "user.max_user_namespaces=28633" | sudo tee /etc/sysctl.d/userns.conf
sudo sysctl -p /etc/sysctl.d/userns.conf

# Configure subuid/subgid for user
sudo usermod --add-subuids 100000-165535 --add-subgids 100000-165535 $USER

# Verify
podman unshare cat /proc/self/uid_map

Running Rootless

# Run as regular user (no sudo)
podman run -d --name myapp -p 8080:80 nginx

# Check user namespace mapping
podman unshare id

# Verify non-root
podman top myapp user

Port Considerations

# Rootless cannot bind to ports < 1024 by default
# Use ports >= 1024
podman run -d -p 8080:80 nginx

# Or enable unprivileged ports (as root)
echo "net.ipv4.ip_unprivileged_port_start=80" | sudo tee /etc/sysctl.d/ports.conf
sudo sysctl -p /etc/sysctl.d/ports.conf

Pods

Creating Pods

# Create pod
podman pod create --name mypod -p 8080:80 -p 5432:5432

# Add containers to pod
podman run -d --pod mypod --name web nginx
podman run -d --pod mypod --name db postgres:15

# List pods
podman pod ps

# Containers share network namespace
podman exec web curl localhost:5432

Pod Management

# Start/stop pod (affects all containers)
podman pod start mypod
podman pod stop mypod

# Remove pod and containers
podman pod rm -f mypod

# View pod details
podman pod inspect mypod

# Generate Kubernetes YAML from pod
podman generate kube mypod > mypod.yaml

Systemd Integration

Generate Systemd Unit

# Generate unit file for container
podman generate systemd --new --name myapp > ~/.config/systemd/user/container-myapp.service

# For pod
podman generate systemd --new --name mypod --files

# Reload systemd
systemctl --user daemon-reload

# Enable and start
systemctl --user enable --now container-myapp.service

Quadlet (Podman 4.4+)

# ~/.config/containers/systemd/webapp.container
[Container]
Image=docker.io/library/nginx:latest
PublishPort=8080:80
Volume=webapp-data:/usr/share/nginx/html

[Service]
Restart=always

[Install]
WantedBy=default.target

# Reload to generate service
systemctl --user daemon-reload

# Start the service
systemctl --user start webapp

Compose Compatibility

Using Podman Compose

# Install podman-compose
pip install podman-compose

# Run compose file
podman-compose up -d

# Or use Docker Compose with Podman socket
systemctl --user enable --now podman.socket
export DOCKER_HOST=unix:///run/user/$UID/podman/podman.sock
docker-compose up -d

Native Podman Kube

# Play Kubernetes YAML
podman kube play deployment.yaml

# Stop and remove
podman kube down deployment.yaml

Networking

Network Management

# Create network
podman network create mynetwork

# Run on network
podman run -d --network mynetwork --name app myapp

# Connect container to network
podman network connect mynetwork existing-container

# List networks
podman network ls

# Inspect network
podman network inspect mynetwork

DNS Resolution

# Containers on same network can resolve by name
podman run -d --network mynetwork --name db postgres:15
podman run -d --network mynetwork --name app \
  -e DATABASE_HOST=db myapp

Storage

Volume Management

# Create volume
podman volume create mydata

# Use volume
podman run -d -v mydata:/data myapp

# List volumes
podman volume ls

# Inspect volume
podman volume inspect mydata

# Rootless volumes location
ls ~/.local/share/containers/storage/volumes/

Bind Mounts

# Bind mount with SELinux label
podman run -v ./data:/app/data:Z myapp

# Z = private label (single container)
# z = shared label (multiple containers)

Registry Configuration

Configure Registries

# Edit registries.conf
# ~/.config/containers/registries.conf

unqualified-search-registries = ["docker.io", "quay.io"]

[[registry]]
prefix = "docker.io"
location = "docker.io"

[[registry.mirror]]
location = "mirror.gcr.io"

Authentication

# Login to registry
podman login docker.io

# Login to private registry
podman login registry.example.com

# Credentials stored in
# ~/.config/containers/auth.json

Building Images

Buildah Integration

# Podman uses Buildah for builds
podman build -t myapp:latest .

# Build with specific format
podman build --format docker -t myapp .

# Multi-stage build
podman build --target production -t myapp:prod .

Buildah Commands

# Create container from scratch
buildah from scratch
buildah copy working-container ./app /app
buildah config --entrypoint '["/app/main"]' working-container
buildah commit working-container myapp:minimal

Common Issues

Issue: Permission Denied

Problem: Cannot access files in mounted volumes Solution: Use :Z or :z suffix for SELinux, or check ownership

Issue: Cannot Connect to Container

Problem: Port not accessible in rootless mode Solution: Use ports >= 1024 or configure unprivileged port start

Issue: Slow Image Pulls

Problem: Images download slowly Solution: Configure registry mirrors in registries.conf

Issue: Systemd Service Fails

Problem: Container doesn't start via systemd Solution: Enable lingering: loginctl enable-linger $USER

Best Practices

• Use rootless mode for enhanced security
• Leverage pods for related containers
• Generate systemd units for production
• Use Quadlet for declarative container services
• Configure SELinux labels for bind mounts
• Enable user lingering for persistent services
• Use podman auto-update for automatic updates
• Alias docker to podman for compatibility

Related Skills

• docker-management - Docker fundamentals
• kubernetes-ops - K8s orchestration
• container-hardening - Security