From eb3ae0483be9fb6177fad8d2284b6d6024f79df9 Mon Sep 17 00:00:00 2001
From: FAQ Bot <faq-bot@datatalks.club>
Date: Sun, 25 Jan 2026 05:20:29 +0000
Subject: [PATCH] NEW: Postgres fails to start after upgrading from postgres:16
 to postgres:18

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+---
+id: 5f560784b0
+question: Postgres fails to start after upgrading from postgres:16 to postgres:18
+  in Docker
+sort_order: 137
+---
+
+Postgres 18 changes how the data directory is structured inside Docker containers. While Postgres ≤16 stored data under /var/lib/postgresql/data, Postgres 18 expects the volume to be mounted at /var/lib/postgresql. If an existing volume created with an older Postgres version is reused without updating the mount path, Postgres 18 will detect an incompatible layout and exit during startup. This can appear as DNS resolution errors or failed connections from pgAdmin or ingestion jobs. For Week 1 setups, the fix is to update the volume mount path, remove the old volume, and recreate the containers so Postgres 18 can initialize a new data directory.
+
+## Proposed Fix (Week 1 setups)
+- Update the volume mount path to /var/lib/postgresql (instead of /var/lib/postgresql/data).
+- Remove the old volume that was created with Postgres 16.
+- Recreate the containers so Postgres 18 initializes a fresh data directory.
+
+### Example commands
+- Running with docker run (adjust as needed):
+```
+docker run -it \
+  -e POSTGRES_USER="root" \
+  -e POSTGRES_PASSWORD="admin" \
+  -e POSTGRES_DB="ny_taxi" \
+  -v "/path/to/ny_taxi_postgres_data":"/var/lib/postgresql" \
+  -p 5432:5432 \
+  postgres:18
+```
+
+- For docker-compose, mount the volume to /var/lib/postgresql:
+```
+volumes:
+  ny_taxi_postgres_data:
+
+services:
+  postgres:
+    image: postgres:18
+    environment:
+      POSTGRES_USER: root
+      POSTGRES_PASSWORD: admin
+      POSTGRES_DB: ny_taxi
+    volumes:
+      - ny_taxi_postgres_data:/var/lib/postgresql
+```
+
+- Remove the old volume (list and remove):
+```
+docker volume ls
+docker volume rm <old-volume-name>
+```
+
+- Recreate containers:
+```
+docker-compose down
+docker-compose up -d
+```
+
+### Notes
+- Ensure you have a backup of any important data before removing volumes.
+- After restarting, verify that Postgres starts and the data directory is initialized under /var/lib/postgresql.