ghcr.io/coolcow/duplicity

A flexible, multi-purpose, and minimal Alpine-based Docker image for Duplicity.

This image supports two modes: direct duplicity command execution (default) and a cron-based scheduler for running backups automatically. It runs as a non-root user and is configurable through runtime environment variables.

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Recommended Usage with docker-compose

This example demonstrates both modes side-by-side.

docker-compose.yml

version: "3.7"
services:
  # Example 1: Running a one-off duplicity command
  duplicity-command:
    image: ghcr.io/coolcow/duplicity:latest
    command: /source file:///backup
    environment:
      - DUPLICITY_UID=1000
      - DUPLICITY_GID=1000
    volumes:
      - /path/to/duplicity-home:/home/duplicity
      - /path/to/source:/source
      - /path/to/backup:/backup

  # Example 2: Running as a cron scheduler
  duplicity-cron:
    image: ghcr.io/coolcow/duplicity:latest
    restart: unless-stopped
    environment:
      - RUN_MODE=cron
      - DUPLICITY_UID=1000
      - DUPLICITY_GID=1000
      - TZ=Europe/Berlin
    volumes:
      - ./crontab:/crontab:ro
      - /path/to/duplicity-home:/home/duplicity
      - /path/to/source:/source
      - /path/to/backup:/backup
      - /path/to/logs:/logs

Example crontab file:

# Run a backup every day at 2:00 AM
0 2 * * *    flock -n /tmp/duplicity.lock duplicity /source file:///backup >> /logs/duplicity.log 2>&1

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Configuration

Runtime Environment Variables

Variable	Default	Target	Description
DUPLICITY_UID	1000	TARGET_UID	The user ID to run duplicity as.
DUPLICITY_GID	1000	TARGET_GID	The group ID to run duplicity as.
DUPLICITY_REMAP_IDS	1	TARGET_REMAP_IDS	Set 0 to disable remapping conflicting UID/GID entries.
DUPLICITY_USER	duplicity	TARGET_USER	The runtime user name inside the container.
DUPLICITY_GROUP	duplicity	TARGET_GROUP	The runtime group name inside the container.
DUPLICITY_HOME	/home/duplicity	TARGET_HOME	Home directory used by duplicity and as default workdir.
DUPLICITY_SHELL	/bin/sh	TARGET_SHELL	Login shell for the runtime user.
RUN_MODE	duplicity	—	Set to cron to activate the cron scheduler mode.
CROND_CRONTAB	/crontab	—	Path inside the container for the crontab file.
TZ	Etc/UTC	—	Timezone for the container, important for correct scheduling.

Target shows the corresponding variable used by coolcow/entrypoints; — means no mapping.

Build-Time Arguments

Customize the image at build time with docker build --build-arg <KEY>=<VALUE>.

Argument	Default	Description
ALPINE_VERSION	3.23.3	Version of the Alpine base image.
ENTRYPOINTS_VERSION	2.2.0	Version of the coolcow/entrypoints image.

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Migration Notes

Runtime user/group environment variables were renamed to image-specific DUPLICITY_* names.

• PUID → DUPLICITY_UID
• PGID → DUPLICITY_GID
• ENTRYPOINT_USER → DUPLICITY_USER
• ENTRYPOINT_GROUP → DUPLICITY_GROUP
• ENTRYPOINT_HOME → DUPLICITY_HOME

Update your docker run / docker-compose environment configuration accordingly when upgrading from older tags.

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Local Testing

Run the built-in smoke tests locally.

1. docker build -t ghcr.io/coolcow/duplicity:local-test-build -f build/Dockerfile build
2. docker build --build-arg APP_IMAGE=ghcr.io/coolcow/duplicity:local-test-build -f build/Dockerfile.test build

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Deprecation Notice

This image replaces the now-obsolete ghcr.io/coolcow/duplicity-cron image. Migrate by using the RUN_MODE=cron environment variable.

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References

• Duplicity Documentation
• docker-entrypoints

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License

GPL-3.0. See LICENSE.txt for details.