PostgreSQL 18 Docker Mount Error

The problem

With the postgres:18 image, a database container can fail to start with:

Error response from daemon: failed to create task for container: failed to create shim task: OCI runtime create failed: runc create failed: unable to start container process: error during container init: error mounting "<POSTGRESQL_PATH>" to rootfs at "/var/lib/postgresql/data": change mount propagation through procfd: open o_path procfd: open /<DOCKER ROOT>/overlay2/.../merged/var/lib/postgresql/data: no such file or directory: unknown

Why it happens

The postgres:18 image changed where it keeps its data: the default PGDATA moved to /var/lib/postgresql/18/docker, and the image now declares /var/lib/postgresql as a VOLUME. Bind-mounting your data at /var/lib/postgresql/data, inside that volume, fails on some Linux hosts using overlay2 (docker-library/postgres#1363).

The fix

Mount your data outside /var/lib/postgresql and point PGDATA at it. This is what Pinepods' own compose files do:

services:
  db:
    image: postgres:18
    environment:
      POSTGRES_DB: pinepods_database
      POSTGRES_USER: postgres
      POSTGRES_PASSWORD: myS3curepass
      PGDATA: /var/lib/pgdata/pgdata
    volumes:
      - /home/user/pinepods/pgdata:/var/lib/pgdata

The host folder can stay where it is. If you used the older Pinepods compose file (PGDATA: /var/lib/postgresql/data/pgdata with the folder mounted at /var/lib/postgresql/data), your cluster is already in the pgdata subfolder, so only the mount point and PGDATA change.

Coming from PostgreSQL 17?

Changing the mount isn't enough on its own: a data directory created by PostgreSQL 17 has to be upgraded before postgres:18 will start on it. See Upgrading PostgreSQL, which uses the same /var/lib/pgdata layout.