How to Fix “psql could not connect to server no route to host” Error

Dear Dev, have you ever encountered the error message “psql could not connect to server no route to host” when trying to establish a connection to your PostgreSQL database? This error occurs when the psql client cannot establish a connection with the PostgreSQL server because the server is down, the network configuration is incorrect, or the firewall is blocking the connection. In this journal article, we will explore different methods to troubleshoot and fix this error.

Common Causes of the “psql could not connect to server no route to host” Error

Before we dive into the solutions, let’s first understand the root causes of this error.

Cause	Explanation
PostgreSQL server is down	The PostgreSQL server may have crashed or stopped running
Incorrect network configuration	The network configuration may be incorrect or the DNS name may not be resolved
Firewall blocking the connection	The firewall may be blocking the connection between the client and server

Solution 1: Check if the PostgreSQL server is running

The first step to resolving this error is to check if the PostgreSQL server is running.

Step 1: Check the PostgreSQL server status

To check the PostgreSQL server status, run the following command:

 systemctl status postgresql.service 

This command will show you if the PostgreSQL service is running, and if not, what error message is preventing it from running.

Step 2: Start the PostgreSQL server

If the PostgreSQL server is not running, start it by running the following command:

 systemctl start postgresql.service 

This command will start the PostgreSQL server and allow you to connect to it.

Solution 2: Check the network configuration

If the PostgreSQL server is running, but you still cannot connect to it, the next step is to check the network configuration.

Step 1: Check if the server is configured to listen on the correct address

If the PostgreSQL server is running but still cannot connect to it, check if the server is configured to listen on the correct address.

 sudo nano /etc/postgresql/13/main/postgresql.conf 

In the postgresql.conf file, look for the following line:

 listen_addresses = 'localhost' 

If this line is present in the file, change it to the IP address of your server. If it is not present, add the following line to the file:

 listen_addresses = '*' 

This will allow the server to listen on all available network interfaces.

Step 2: Check if the client can resolve the DNS name

If the server is listening on the correct address, check if the client can resolve the DNS name.

 ping <server DNS name> 

If the ping command returns an IP address, the DNS name is resolved correctly. If the ping command fails, the client cannot resolve the DNS name.

Solution 3: Check if the firewall is blocking the connection

If the PostgreSQL server is running and the network configuration is correct, the next step is to check if the firewall is blocking the connection.

Step 1: Check if the firewall is enabled

To check if the firewall is enabled, run the following command:

 sudo ufw status 

If the firewall is active, you will see a message similar to this:

 Status: active 

Step 2: Allow incoming connections to PostgreSQL

If the firewall is active, allow incoming connections to PostgreSQL by running the following command:

 sudo ufw allow postgresql 

This command will allow incoming connections to PostgreSQL and enable you to connect to it.

Frequently Asked Questions (FAQ)

Q1: What is PostgreSQL?

A1: PostgreSQL is a powerful, open-source relational database system that uses and extends the SQL language.

Q2: How do I connect to a PostgreSQL server?

A2: You can connect to a PostgreSQL server using the psql command-line tool or a graphical tool such as pgAdmin.

Q3: What is the default port for PostgreSQL?

A3: The default port for PostgreSQL is 5432.

Q4: How do I create a new PostgreSQL database?

A4: To create a new PostgreSQL database, use the createdb command followed by the name of the database.

 createdb <database name> 

Q5: How do I create a new PostgreSQL user?

A5: To create a new PostgreSQL user, use the createuser command followed by the name of the user.

 createuser <username> 

Conclusion

In this article, we have explored different methods to troubleshoot and fix the “psql could not connect to server no route to host” error. By checking if the PostgreSQL server is running, verifying the network configuration, and allowing incoming connections to PostgreSQL, you can fix this error and establish a successful connection.