I’ve had this same issue, related to the configuration of my pg_hba.conf file (located in /etc/postgresql/9.6/main). Please note that 9.6 is the postgresql version I am using.

The error itself is related to a misconfiguration of postgresql, which causes the server to crash before it starts.

I would suggest following these instructions:

1. Certify that postgresql service is running, using sudo service postgresql start
2. Run pg_lsclusters from your terminal
3. Check what is the cluster you are running, the output should be something like:Version – Cluster Port Status Owner Data directory9.6 ——- main — 5432 online postgres /var/lib/postgresql/9.6/main
   

   Disregard the ‘—‘ signs, as they are being used there only for alignment.
   The important information are the version and the cluster. You can also check whether the server is running or not in the status column.

4. Copy the info from the version and the cluster, and use like so:
   pg_ctlcluster <version> <cluster> start, so in my case, using version 9.6 and cluster ‘main’, it would be pg_ctlcluster 9.6 main start
5. If something is wrong, then postgresql will generate a log, that can be accessed on /var/log/postgresql/postgresql-<version>-main.log, so in my case, the full command would be sudo nano /var/log/postgresql/postgresql-9.6-main.log.
6. The output should show what is the error.
   

   2017-07-13 16:53:04 BRT [32176-1] LOG: invalid authentication method “all”

   2017-07-13 16:53:04 BRT [32176-2] CONTEXT: line 90 of configuration file “/etc/postgresql/9.5/main/pg_hba.conf”

   2017-07-13 16:53:04 BRT [32176-3] FATAL: could not load pg_hba.conf

7. Fix the errors and restart postgresql service through sudo service postgresql restart and it should be fine.

I have searched a lot to find this, credit goes to this post.

Best of luck!

I had the same issue but non of the answers here helped.

How I fixed it (mac)

• Try to start postgresql with pg_ctl -D /usr/local/var/postgres start
• Look for the Error Message that says something like FATAL: could not open directory "pg_tblspc": No such file or directory.
• Create that missing directory mkdir /usr/local/var/postgres/pg_tblspc
• Repeat from step one until you created all missing directories
• When done and then trying to start postgresql again it might say FATAL: lock file "postmaster.pid" already exists
• Delete postmaster.pid: rm /usr/local/var/postgres/postmaster.pid
• Start postgres with: pg_ctl -D /usr/local/var/postgres start
• Done ✨

These two steps solved it for me on Mac:

rm /usr/local/var/postgres/postmaster.pid
brew services restart postgresql

EDIT:

In case you face this issue (reported by @luckyguy73): psql: FATAL: database "postgresql" does not exist

You can run

brew postgresql-upgrade-database

to fix it.