Backing up Postgres in Docker named volumes

When a Postgres container uses a named volume instead of a bind mount, you can’t just tar the volume path and call it a backup. The data directory isn’t safe to copy while Postgres is running.

The correct approach is pg_dumpall:

docker exec <postgres-container> pg_dumpall -U postgres > backup.sql

This dumps all databases and roles in plain SQL. Restore with:

docker exec -i <postgres-container> psql -U postgres < backup.sql

Why not snapshot the volume?

A filesystem snapshot of a running Postgres data directory can capture an inconsistent state — mid-write pages, un-flushed WAL. pg_dumpall always produces a consistent logical dump regardless of what the database is doing.

Timing note for immich

For Immich specifically: the database password must match across the server and postgres containers at first init. If the volume already exists with a different password, Postgres won’t accept new credentials — you have to wipe the volume and reinitialize. Back up with pg_dumpall before touching any credentials.