docker-volume-backup/docs/how-tos/run-custom-commands.md

title	layout	nav_order	parent
Run custom commands during the backup lifecycle	default	5	How Tos

Run custom commands during the backup lifecycle

In certain scenarios it can be required to run specific commands before and after a backup is taken (e.g. dumping a database). When mounting the Docker socket into the docker-volume-backup container, you can define pre- and post-commands that will be run in the context of the target container (it is also possible to run commands inside the docker-volume-backup container itself using this feature). Such commands are defined by specifying the command in a docker-volume-backup.[step]-[pre|post] label where step can be any of the following phases of a backup lifecycle:

• archive (the tar archive is created)
• process (the tar archive is processed, e.g. encrypted - optional)
• copy (the tar archive is copied to all configured storages)
• prune (existing backups are pruned based on the defined ruleset - optional)

Taking a database dump using mysqldump would look like this:

version: '3'

services:
  # ... define other services using the `data` volume here
  database:
    image: mariadb
    volumes:
      - backup_data:/tmp/backups
    labels:
      - docker-volume-backup.archive-pre=/bin/sh -c 'mysqldump --all-databases > /backups/dump.sql'

volumes:
  backup_data:

{: .note } Due to Docker limitations, you currently cannot use any kind of redirection in these commands unless you pass the command to /bin/sh -c or similar. I.e. instead of using echo "ok" > ok.txt you will need to use /bin/sh -c 'echo "ok" > ok.txt'.

If you need fine grained control about which container's commands are run, you can use the EXEC_LABEL configuration on your docker-volume-backup container:

version: '3'

services:
  database:
    image: mariadb
    volumes:
      - backup_data:/tmp/backups
    labels:
      - docker-volume-backup.archive-pre=/bin/sh -c 'mysqldump --all-databases > /tmp/volume/dump.sql'
      - docker-volume-backup.exec-label=database

  backup:
    image: offen/docker-volume-backup:v2
    environment:
      EXEC_LABEL: database
    volumes:
      - data:/backup/dump:ro
      - /var/run/docker.sock:/var/run/docker.sock:ro

volumes:
  backup_data:

The backup procedure is guaranteed to wait for all pre or post commands to finish before proceeding. However, there are no guarantees about the order in which they are run, which could also happen concurrently.

By default the backup command is executed by the user provided by the container's image. It is possible to specify a custom user that is used to run commands in dedicated labels with the format docker-volume-backup.[step]-[pre|post].user:

version: '3'

services:
  gitea:
    image: gitea/gitea
    volumes:
      - backup_data:/tmp
    labels:
      - docker-volume-backup.archive-pre.user=git
      - docker-volume-backup.archive-pre=/bin/bash -c 'cd /tmp; /usr/local/bin/gitea dump -c /data/gitea/conf/app.ini -R -f dump.zip'

Make sure the user exists and is present in passwd inside the target container.