httpd.service Cannot connect to database Centos 7

xav asked:

I’m trying to connect to PostgreSQL Unix domain socket from a python web application with mod_wsgi. Relevant system components:

  • CentOS 7 x64
  • Python 2.7.5
  • SELinux disabled

PostgreSQL is listening on standard port 5432 and I have no problems to use it via TCP/IP at, but when I try to connect to its Unix domain socket, I have a following error:

Cannot connect to database:  could not connect to server: No such file or directory
     Is the server running locally and accepting
     connections on Unix domain socket "/tmp/.s.PGSQL.5432"?*

File /tmp/.s.PGSQL.5432 exists and I can connect using psql.

However, when I stop apache with systemctl stop httpd.service and restart it again with /usr/sbin/httpd -DFOREGROUND, everything works fine, including the pages that do require database access

With SELinux disabled, I do not understand why there is problems when httpd start with systemctl start httpd.service.


I’ve changed unix_socket_directories = '/tmp,/var/pgsql_sock' in /var/lib/pgsql/9.3/data/postgresql.conf. I also changed config in in my django app HOST='/var/pgsql_sock'. Now it works fine with httpd.service.

My answer:

You cannot use /tmp to store sockets for interprocess communication in this scenario, because Apache uses private /tmp directories, a security feature that ensures that a process can only see its own /tmp directory; it cannot see what other processes write into /tmp because those other processes are actually writing into different directories.

This means that Apache cannot see the PostgreSQL socket.

You will need to continue using a local TCP connection.

You should also not disable SELinux, and use the correct boolean to allow the web server to talk to the database.

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