---
title: Automatically prune old backups
layout: default
parent: How Tos
nav_order: 3
---

# Automatically prune old backups

When `BACKUP_RETENTION_PERIOD` is configured, the command will check if there are any archives in the remote storage backend(s) or local archive that are older than the given retention value and rotate these backups away.
The value is a duration as per Go's [`time.ParseDuration`][duration].

{: .note }
Be aware that this mechanism looks at __all files in the target bucket or archive__, which means that other files that are older than the given deadline are deleted as well.
In case you need to use a target that cannot be used exclusively for your backups, you can configure `BACKUP_PRUNING_PREFIX` to limit which files are considered eligible for deletion:

```yml
version: '3'

services:
  # ... define other services using the `data` volume here
  backup:
    image: offen/docker-volume-backup:v2
    environment:
      BACKUP_FILENAME: backup-%Y-%m-%dT%H-%M-%S.tar.gz
      BACKUP_PRUNING_PREFIX: backup-
      BACKUP_RETENTION_PERIOD: '168h'
    volumes:
      - ${HOME}/backups:/archive
      - data:/backup/my-app-backup:ro
      - /var/run/docker.sock:/var/run/docker.sock:ro

volumes:
  data:
```

[duration]: https://pkg.go.dev/time#ParseDuration