Hi.

Could you provide your complete nginx-proxy + acme-companion setup ?

Are you running SELinux or something similar on this host ?

I noticed the version of Docker you're running is almost five years old, maybe this is related, maybe not.

No SELinux, the host is a 2vCPU VPS.
Here's the relevant part of the docker compose file:

    nginx: # includes static files
        image: jwilder/nginx-proxy:alpine
        labels:
            com.github.jrcs.letsencrypt_nginx_proxy_companion.nginx_proxy: "true"
        restart: always
        volumes:
            - /var/run/docker.sock:/tmp/docker.sock:ro
            - nginx_certs:/etc/nginx/certs:ro
            - nginx_vhost:/etc/nginx/vhost.d
            - nginx_dhparam:/etc/nginx/dhparam
            - nginx_html_challange:/usr/share/nginx/html
        ports:
            - "80:80"
            - "443:443"
        depends_on: 
            - app

    letsencrypt:
        image: nginxproxy/acme-companion
        restart: always
        volumes:
            - /var/run/docker.sock:/var/run/docker.sock:ro
            - nginx_certs:/etc/nginx/certs:rw
            - nginx_vhost:/etc/nginx/vhost.d
            - nginx_dhparam:/etc/nginx/dhparam
            - nginx_html_challange:/usr/share/nginx/html
            - acme:/etc/acme.sh
        environment:
            - DEFAULT_EMAIL=${LETSENCRYPT_ALERT_EMAIL}

The docker engine on the host is indeed ancient. Reversing the initial checks in the entrypoint script would work, though: if test -S fails, then do a test -r to decide on the what error message is shown. Would that be acceptable?

Same issue here, rollbacked to tag 2.4 and it works (not functional with 2.5)

@andrei-datcu I'll look into this either tomorrow if I have time or next week but yes I think the check is the culprit too.

I was thinking of doing a real call to the Docker API (more specifically to the /_ping endpoint) to check if the container can access the Docker API rather that doing a test -S or test -r that don't tell us much beside the existence of a socket file with some specific permissions.

edit : I think the test -S fix can be done right now.

I've released version 2.5.2 with the fix for this issue, 2.5 should be updated too.