error with postgresql datababse : Is the server running locally and accepting connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"?

Question

When I run the rake db:migrate or run the rails s command, I get the same error:

Error : could not connect to server: 
No such file or directory Is the server running locally and accepting
connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"?

I get the error in the browser when I try rails s.

This is my database.yml

default: &default
adapter: postgresql
encoding: unicode

pool: 5

development:
<<: *default
database: books_development




test:
<<: *default
database: books_test



production:
<<: *default
database: books_production
username: abd
password: <%= ENV['BOOKS_DATABASE_PASSWORD'] %>

Note : I have the databases books_development; books_test ; and the postresql are running without problems when I try sudo /etc/init.d/postgresql start

I did run:

create database books_development;
create database books_test; 

in the psql console. And it said that it's done successfully

I tried a lot of solutions and I spent yesterday looking for a solution and no solution in the related questions solved my error.

I have postgresql-9.4 (the latest) and xubuntu 14.04

Any Ideas?

Answer 1

The convention for PostgreSQL packaged for Debian or Debian derivatives such as Ubuntu is to use /var/run/postgresql as the directory for Unix domain sockets. On the other hand the convention for self-compiled postgres client libs is to use /tmp, unless self-configured otherwise.

So the usual root cause of this mismatch between both is a mix of self-compiled client-side stuff with pre-compiled server-side packages (even if client and server are installed on the same machine, client-side and server-side are still distinct and can be out of sync).

Soft-linking from /tmp to this directory as suggested by the asker works except that the link will be lost at every reboot, because in general /tmp is emptied on reboot.

A better option would be to add as an entry in database.yml:

• either host: /tmp if the real socket path is /tmp (self-compiled server, packaged client)

• or host: /var/run/postgresql if the real socket path /var/run/postgresql/ (packaged server, self-compiled client).

When the value in the host field starts with a slash character, the postgres library knows that it's the location of a directory for local sockets rather than a hostname. The filename inside the directory .s.PGSQL.portnumber is generated and must not be specified, only the directory.

Another possibility is to configure the self-compiled software packages as closely as possible to Debian, overriding the defaults as they do.