I am using postgresql on MacOS. And quite often I see this error:

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”?

So, most of the time helps the following:

pg_ctl -D /usr/local/var/postgres -l /usr/local/var/postgres/server.log start

or if that doesn’t help

$ brew services stop postgresql
$ rm /usr/local/var/postgres/postmaster.pid # adjust path accordingly to your install
$ brew services start postgresql

If that doesn’t help I used

brew postgresql-upgrade-database

Or sometimes reinstall gem will help

$ gem uninstall pg
$ cd rails-app/
$ bundle install

Finally, uninstall postgres and install it again. Mind it will erase your data!

brew install postgres
initdb /Users/<user>/db -E utf8
pg_ctl -D /usr/local/var/postgres -l /usr/local/var/postgres/server.log start

Another solution to this problem.

The primary issue here is that the initdb step of installation will create the directory with root ownership instead of as the user on a Mac. To solve this issue:

Create the data directory before running initdb and set permissions of 0700

rm -rf /usr/local/var/postgres  # in case this is not your first try
mkdir /usr/local/var/postgres
chmod 0700 /usr/local/var/postgres

Then run initdb and it will respect the permissions of the data directory.

initdb -D /usr/local/var/postgres

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