Permission Denied When Writing Backups to NFS Volume Despite Correct UID/GID Configuration

[ajmarmar]

Summary

When using an NFS-mounted volume as the backup destination, the container consistently fails with permission denied errors when attempting to write backups, despite correctly setting the UID and GID of the NFS-permitted user via environment variables and the user directive in docker-compose.yml.

Steps to reproduce

• Mount an NFS share on the Docker host at /mnt/data

• Ensure that the NFS share is owned by the userbck user, who has read and write permissions.

  • Configure the docker-db-backup container with:

  • Environment variables USER_DBBACKUP and GROUP_DBBACKUP matching the UID and GID of userbck

  • A volume mapping:
    volumes:
    - /mnt/data:/backup

  • Start the container and trigger a backup.

What is the expected correct behavior?

The container should be able to write backup files to the /backup directory (which is the NFS share mounted on the host) without permission errors.

Environment

Image version / tag: tiredofit/db-backup:latest
Host OS: Ubuntu 20.04

tiredofit/db-backup:4.1.19 16:00:41 /backup] $ backup01-now 2025-06-25.16:00:43 [INFO] ** [db-backup01] Starting Manual Backup for db-backup01 chmod: changing permissions of '/backup/keydb': Operation not permitted mkdir: cannot create directory ‘/backup/temp’: Permission denied stat: cannot statx '/backup/temp': No such file or directory chown: cannot access '/backup/temp': No such file or directory mktemp: failed to create directory via template ‘/backup/temp/01_dbbackup.XXXXXX’: No such file or directory chown: cannot access '': No such file or directory 2025-06-25.16:00:44 [NOTICE] ** [01keydb] Dumping Redis - Flushing Redis Cache First ... .... ....

Possible fixes