Cannot connect to Postgres server running through brew services

I had the same error and I fixed it by removing the process pid file:

rm -f /usr/local/var/postgres/postmaster.pid

I ran into this problem today. postgres stopped accepting connections though homebrew thought it was running.

To fix it I ran,

brew services restart -vvv postgresql

Output from this command,

==> Successfully stopped `postgresql` (label: homebrew.mxcl.postgresql)==> Generated plist for postgresql:   <?xml version="1.0" encoding="UTF-8"?>   <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">   <plist version="1.0">   <dict>     <key>KeepAlive</key>     <true/>     <key>Label</key>     <string>homebrew.mxcl.postgresql</string>     <key>ProgramArguments</key>     <array>       <string>/usr/local/opt/postgresql/bin/postgres</string>       <string>-D</string>       <string>/usr/local/var/postgres</string>     </array>     <key>RunAtLoad</key>     <true/>     <key>WorkingDirectory</key>     <string>/usr/local</string>     <key>StandardErrorPath</key>     <string>/usr/local/var/log/postgres.log</string>   </dict>   </plist>

Then I thought, hmm maybe there's something in that log file,

tail -n 10 /usr/local/var/log/postgres.log

Sure enough,

[4826] FATAL:  lock file "postmaster.pid" already exists[4826] HINT:  Is another postmaster (PID 1489) running in data directory "/usr/local/var/postgres"?

So, I removed that file

rm /usr/local/var/postgres/postmaster.pid

And everything started working again.

In my case the postmaster.pid file wasn't even there. Got it working by upgrading postgres.

brew updatebrew upgrade

Then, because I upgraded the major version from 10 to 11, I also had to run this:

brew postgresql-upgrade-database

(source https://github.com/facebook/react-native/issues/18760#issuecomment-410533581)