Overview

This troubleshooting guide is designed to assist you in resolving PostgreSQL start-up failures that can arise due to a variety of issues, including permissions errors on SSL certificate files and directories, as well as configuration requirements for logical replication. The guide includes specific error messages you may encounter and the steps to resolve them.

Solution

Resolving Permission Denied Errors for SSL Certificate Files:

1. Identify the Permission Issues:
   PostgreSQL may fail to start due to "Permission denied" errors when accessing SSL certificate files. Common error messages include:

   • could not load server certificate file "/path/to/server.crt": Permission denied
   • could not load private key file "/path/to/server.key": Permission denied
   • could not load root certificate file "/path/to/root.crt": Permission denied

2. Adjust Permissions and Ownership:
   The postgres user must own and have read access to the SSL certificate files and directories. Use the following commands to set the correct permissions:

   sudo chown postgres:postgres /path/to/ssl/directory
   sudo chmod 700 /path/to/ssl/directory
   sudo chown postgres:postgres /path/to/ssl/directory/*.crt
   sudo chown postgres:postgres /path/to/ssl/directory/*.key
   sudo chmod 600 /path/to/ssl/directory/*.crt
   sudo chmod 600 /path/to/ssl/directory/*.key

    

   Ensure you replace /path/to/ssl/directory with the actual path to your PostgreSQL SSL directory.

Disabling AppArmor (Ubuntu Systems):

3. Disable AppArmor (if applicable):
   On Ubuntu systems, AppArmor might restrict access, leading to PostgreSQL being unable to start. Error messages do not directly mention AppArmor but disabling it temporarily can help identify if it's the cause.

   • To disable AppArmor for PostgreSQL:

     sudo ln -s /etc/apparmor.d/usr.sbin.postgres /etc/apparmor.d/disable/
     sudo apparmor_parser -R /etc/apparmor.d/usr.sbin.postgres

      

   Restart PostgreSQL to check if the issue is resolved. Remember to properly configure AppArmor profiles rather than leaving it disabled.

Addressing WAL Level Configuration for Logical Replication:

4. Rectify wal_level Configuration:
   A different set of errors relates to logical replication slots and wal_level configuration:

   • FATAL: logical replication slot "slot_name" exists, but wal_level is not set to 'logical'

   • This indicates that the wal_level parameter in postgresql.conf needs to be adjusted to support logical replication.

   • Edit the configuration file:

     sudo nano /path/to/data/directory/postgresql.conf

      

   • Set wal_level to logical:

     wal_level = logical
     

      

   • Save the file and exit the editor.

5. Restart PostgreSQL:
   Apply the configuration changes by restarting the PostgreSQL service:

   sudo systemctl restart postgresql

    

Reference Documentation

• PostgreSQL Official Documentation: Provides detailed information on configuration parameters and troubleshooting.
• Ubuntu AppArmor Documentation: Offers guidance on managing AppArmor profiles and policies.

By following this guide, you'll be equipped to address a range of PostgreSQL start-up issues, from resolving permission errors with SSL certificates to configuring PostgreSQL for logical replication.