Docker userns-remap leads to HTTP 502

I run a small home server with several Docker containers, which I make accessible via an Nginx reverse proxy. The setup works well until I try to use user namespace remapping. I then only get an HTTP 502 error - I can't find anything in the logs, or maybe I'm looking in the wrong place.

As soon as I remove userns-remap and restart the Docker services, the entire system works fine again.

It's not the firewall, nor is it SELinux.

I would be very grateful for any help.

First, I edit the file /etc/docker/daemon.json to enable the :

{ "dns": ["192.168.100.10"], "metrics-addr": "127.0.0.1:9323", "experimental": true, "userns-remap": "myuser" } 

Anschließend starte ich den Docker-Dienst neu: sudo systemctl restart docker.service.

Now I create the Portainer CE container:

docker volume create --name portainer_data --opt device=/home/myuser/.containers/volumes/portainer --opt o=bind --opt type=none docker network create --ipv4 --subnet 172.116.0.0/16 --gateway 172.116.0.1 portainer-network docker compose up -d 

The contents of the compose.yaml file are as follows:

services: portainer-socket-proxy: image: lscr.io/linuxserver/socket-proxy:latest container_name: portainer-socket-proxy restart: unless-stopped networks: portainer-network: ipv4_address: '172.116.0.20' volumes: - /var/run/docker.sock:/var/run/docker.sock:ro environment: - LOG_LEVEL=info - EVENTS=1 - PING=1 - VERSION=1 - AUTH=0 - SECRETS=0 - POST=1 - BUILD=0 - COMMIT=0 - CONFIGS=0 - CONTAINERS=1 - DISTRIBUTION=0 - EXEC=0 - IMAGES=1 - INFO=1 - NETWORKS=1 - NODES=0 - PLUGINS=0 - SERVICES=1 - SESSION=0 - SWARM=0 - SYSTEM=0 - TASKS=1 - VOLUMES=1 portainer: ports: - 127.0.0.1:9001:8000 - 127.0.0.1:9002:9443 - 127.0.0.1:9000:9000 container_name: portainer restart: unless-stopped networks: portainer-network: ipv4_address: '172.116.0.10' volumes: - portainer_data:/data image: portainer/portainer-ce:lts command: -H tcp://portainer-socket-proxy:2375 --tlsskipverify depends_on: portainer-socket-proxy: condition: service_started networks: portainer-network: external: true volumes: portainer_data: external: true 

Content of /etc/subuid:

myuser:1000:1 myuser:100000:65536 

Content of /etc/subgid:

myuser:1000:1 myuser:100000:65536