[Docker] 2.1.0: Plugin load failure due to broken RPATH (libmosquitto_common.so.1 not found)

[labodj]

I am running the official eclipse-mosquitto:2.1.0-alpine via Docker.
Following the deprecation warnings in the changelog regarding password_file and acl_file, I attempted to switch to the new plugin-based configuration (mosquitto_password_file.so and mosquitto_acl_file.so).

However, the container fails to start because the plugins cannot find their dependency libmosquitto_common.so.1.
The error message suggests the plugin was compiled with a relative path pointing to a build directory structure (../../libcommon/) that does not exist in the final Docker image structure.

To Reproduce:

• Use eclipse-mosquitto:latest (v2.1.0).
• Configure mosquitto.conf to use the password plugin instead of the legacy password_file option.
• Start the container.

Configuration (mosquitto.conf):

max_packet_size 10000000
max_queued_messages 5000
persistent_client_expiration 5m
allow_anonymous false

persistence true
persistence_location /mosquitto/data
persistence_file mosquitto.db

log_timestamp_format %Y-%m-%dT%H:%M:%S
log_dest file /mosquitto/log/mosquitto.log
log_dest stdout

# Plugin configuration causing the crash
plugin /usr/lib/mosquitto_password_file.so
plugin_opt_password_file /mosquitto/config/passwd

plugin /usr/lib/mosquitto_acl_file.so
plugin_opt_acl_file /mosquitto/config/acls

listener 1883
protocol mqtt
socket_domain ipv4
set_tcp_nodelay true

Docker Compose:

services:
  mosquitto:
    container_name: mosquitto
    image: eclipse-mosquitto:2.1.0-alpine
    restart: unless-stopped
    ports:
      - "1883:1883"
    volumes:
      - ./mnt/config:/mosquitto/config
      - ./mnt/data:/mosquitto/data
      - ./mnt/log:/mosquitto/log

Log Output:

2026-01-30T16:35:14: mosquitto version 2.1.0 starting
...
2026-01-30T16:35:14: Loading plugin: /usr/lib/mosquitto_password_file.so
2026-01-30T16:35:14: Error: Unable to load plugin "/usr/lib/mosquitto_password_file.so".
2026-01-30T16:35:14: Load error: Error loading shared library ../../libcommon/libmosquitto_common.so.1: No such file or directory (needed by /usr/lib/mosquitto_password_file.so)

Workaround: Reverting to the deprecated password_file and acl_file syntax works correctly.

[ralight]

Thanks for the report (and for trying out the alternatives to acl_file and password_file). Your analysis is correct. Although a load of code has migrated to the libmosquitto_common library, for now it is being statically linked to maintain compatibility. These two plugins were linking against the shared library by mistake.