I should have known that.

Recently, I upgraded my laptop to run macOS Sierra. Along with the OS updates, I also used brew to update python3. I was not paying attention and ended up upgrading PostgreSQL to the newest version, 9.6.2. I was unhappy that I was not paying attention, but I was glad that upgrades to PostgreSQL and MongoDB were also done with the upgrade to Python 3.

I use brew to start and stop PostgreSQL as needed, so I started it to check to see how it ran after the update. ‘psql’ gave me a version number, but I could not get it started to show me the schemas or tables from previous work. I also saw the following error message:

psql: 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”?

Very strange error message, so I started doing Google searches to see what could be wrong. There some dead ends involving checking for a PID file and checking permissions in /usr/local/var/postgres. Eventually, I ran into what looks like the answer in two related locations: a blog post describing upgrades to PostgreSQL and another one describing the upgrade process using brew. Apparently, I had two versions of PostgreSQL on my machine.

> brew info postgresql

confirmed it. Both pages described what I have to do, so I’ll do it. I should have known I needed to do this. Now I know.