Trouble installing postgresql on osx using homebrew - ruby-on-rails

Question

I'm trying to install postgres on a new machine for the time. I initially ran thoughtbot's laptop script to install most of what I'd need for rails development which should have included the postgres installation. Yet when I run a rake db:create for the new rails app I get the following error:
Couldn't create database for {"adapter"=>"postgresql", "encoding"=>"utf8", "pool"=>5, "timeout"=>5000, "username"=>"riskpool", "password"=>nil, "database"=>"riskpool_development"}
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"?
I tried uninstalling and reinstalling postgres via homebrew like this and this is the result:
$ brew remove postgres
Uninstalling /usr/local/Cellar/postgresql/9.4.5_2... (3021 files, 40M)
And reinstalling postgres
$ brew install postgres
==> Downloading https://homebrew.bintray.com/bottles/postgresql-9.4.5_2.yosemite.bottle.tar.gz
Already downloaded: /Library/Caches/Homebrew/postgresql-9.4.5_2.yosemite.bottle.tar.gz
==> Pouring postgresql-9.4.5_2.yosemite.bottle.tar.gz
Warning: The post-install step did not complete successfully
You can try again using `brew postinstall postgresql`
==> Caveats
If builds of PostgreSQL 9 are failing and you have version 8.x installed,
you may need to remove the previous version first. See:
https://github.com/Homebrew/homebrew/issues/2510
To migrate existing data from a previous major version (pre-9.4) of PostgreSQL, see:
https://www.postgresql.org/docs/9.4/static/upgrading.html
To load postgresql:
launchctl load ~/Library/LaunchAgents/homebrew.mxcl.postgresql.plist
Or, if you don't want/need launchctl, you can just run:
postgres -D /usr/local/var/postgres
WARNING: launchctl will fail when run under tmux.
==> Summary
🍺 /usr/local/Cellar/postgresql/9.4.5_2: 3021 files, 40M
$ launchctl load ~/Library/LaunchAgents/homebrew.mxcl.postgresql.plist
/usr/local/Cellar/postgresql/9.4.5_2/homebrew.mxcl.postgresql.plist: Operation not permitted
if I run the second command
$ postgres -D /usr/local/var/postgres
FATAL: could not open directory "pg_tblspc": No such file or directory
If I try to find out where postgres is installed:
$ which postgres
/usr/local/bin/postgres
Someone suggested I kill an existing process id that might be interfering:
$ rm /usr/local/var/postgres/postmaster.pid
rm: /usr/local/var/postgres/postmaster.pid: No such file or directory
But I get the same 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"?

Answer 1

Have you tried using this command :
rm /usr/local/var/postgres/postmaster.pid
It appears that this file is blocking postgres from starting up and it would be the reason why you get the below error :
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"?

Answer 2

Have you tried launching the server with root privileges ? i.e.
sudo postgres -D /usr/local/var/postgres
It seems though as the server is not launching due to file permission privileges.
It also seems that the brew postinstall scripts failed, so you may need to initialize the db cluster.
You can use initdb to create a new cluster.
sudo initdb /usr/local/var/postgres9.4
Alternatively, if this is for a development machine, I would recommend just using the postgres app for macosx (simple click and run):
http://postgresapp.com/