How to fix fixing permissions on existing directory in PostgreSQL

# Stop PostgreSQL service
sudo systemctl stop postgresql
# or
sudo service postgresql stop
# or for manual installations:
sudo killall postgres

ps aux | grep postgres

# Common locations:
/var/lib/postgresql/data      # Linux package installation
/usr/local/pgsql/data         # Source installation
/var/pgsql                    # BSD/macOS
$PGDATA                       # Custom location (check environment)

# If you are not sure, check the PostgreSQL configuration file:
sudo grep "^data_directory" /etc/postgresql/*/main/postgresql.conf

# Create the data directory (example: /var/lib/postgresql/data)
sudo mkdir -p /var/lib/postgresql/data

# Verify parent exists
ls -ld /var/lib/postgresql

# Check if postgres user exists
id postgres

# If not found, create it (Linux):
sudo useradd --system --home /var/lib/postgresql --shell /bin/bash postgres

# Or on some systems:
sudo useradd --system --no-create-home --shell /usr/sbin/nologin postgres

# Change ownership to postgres user and group
sudo chown -R postgres:postgres /var/lib/postgresql/data

# Verify the change:
ls -ld /var/lib/postgresql/data
# Output should show: drwx------ postgres postgres ...

# Set directory permissions to 0700 (rwx-----)
sudo chmod 700 /var/lib/postgresql/data

# Verify the permissions:
ls -ld /var/lib/postgresql/data
# Output should show: drwx------ postgres postgres ...

services:
  postgres:
    image: postgres:latest
    volumes:
      - postgres_data:/var/lib/postgresql/data
    environment:
      POSTGRES_INITDB_ARGS: "-c shared_buffers=256MB"
    # Add initdb script to fix permissions:
    command: |
      bash -c "
      chown -R 999:999 /var/lib/postgresql/data && \
      chmod 700 /var/lib/postgresql/data && \
      docker-entrypoint.sh postgres
      "

volumes:
  postgres_data:

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: postgres-pvc
spec:
  accessModes:
    - ReadWriteOnce
  storageClassName: standard
  resources:
    requests:
      storage: 10Gi
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: postgres
spec:
  serviceName: postgres
  replicas: 1
  selector:
    matchLabels:
      app: postgres
  template:
    metadata:
      labels:
        app: postgres
    spec:
      containers:
      - name: postgres
        image: postgres:latest
        volumeMounts:
        - name: postgres-storage
          mountPath: /var/lib/postgresql/data
        # Pre-init to fix permissions
        securityContext:
          runAsUser: 999  # postgres user in the container
        # Ensure volume is writable before initialization
      initContainers:
      - name: fix-permissions
        image: busybox
        command:
        - sh
        - -c
        - chmod 700 /var/lib/postgresql/data; chown 999:999 /var/lib/postgresql/data
        volumeMounts:
        - name: postgres-storage
          mountPath: /var/lib/postgresql/data
      volumes:
      - name: postgres-storage
        persistentVolumeClaim:
          claimName: postgres-pvc

# WARNING: This deletes all data in the directory!
# Only do this if the directory contains no important data or you have backups.

sudo -u postgres rm -rf /var/lib/postgresql/data/*

# Verify it is empty:
sudo ls -la /var/lib/postgresql/data/

# Switch to postgres user and initialize
sudo -u postgres initdb -D /var/lib/postgresql/data

# Or if postgres user has a shell:
su - postgres
initdb -D /var/lib/postgresql/data
exit

The files belonging to this database system will be owned by user "postgres".
This user must also own the server process.

The database cluster will be initialized with locale "en_US.UTF-8".
...
Success. You can now start the database server using:
    pg_ctl -D /var/lib/postgresql/data -l logfile start

# Start PostgreSQL service
sudo systemctl start postgresql
# or
sudo service postgresql start
# or for manual installations:
sudo -u postgres pg_ctl -D /var/lib/postgresql/data -l /var/log/postgresql/postgresql.log start

sudo systemctl status postgresql

# Or check if the postgres process is listening:
ps aux | grep postgres
netstat -an | grep 5432  # Default PostgreSQL port

sudo -u postgres psql -c "SELECT version();"