PostgreSQL: Why psql can't connect to server?

Question

I typed psql and I get this:

psql: could not connect to server: No such file or directory
    Is the server running locally and accepting
    con         


        

Answer 1

If there is no error in starting the Postgres service, follow these steps

Step 1: Running pg_lsclusters will list all the Postgres clusters running on your device

eg:

Ver Cluster Port Status Owner    Data directory               Log file
9.6 main    5432 online postgres /var/lib/postgresql/9.6/main /var/log/postgresql/postgresql-9.6-main.log

most probably the status will be down in your case. If not restart PostgreSQL service

Step 2: Restart the pg_ctlcluster

#format is pg_ctlcluster   
sudo pg_ctlcluster 9.6 main start

#restart PostgreSQL service
sudo service postgresql restart

Step 3: Step 2 failed and threw an error

If restarting pg_lsclusters was not successful, it will throw an error. My error was(You can see the errors in the logs /var/log/postgresql/postgresql-9.6-main.log)

FATAL: could not access private key file "/etc/ssl/private/ssl-cert-snakeoil.key": Permission denied
Try adding `postgres` user to the group `ssl-cert`

Step 4: check ownership of postgres

Make sure that postgres is the owner of /var/lib/postgresql/version_no/main eg: sudo chown postgres -R /var/lib/postgresql/9.6/main/

Step 5: Check postgres user belongs to ssl-cert user group

It happened to me and it turned out that I removed erroneously the Postgres user from "ssl-cert" group. Run the below code to fix the user group issue and for fixing the permissions

#set user to group back with
sudo gpasswd -a postgres ssl-cert

# Fixed ownership and mode
sudo chown root:ssl-cert  /etc/ssl/private/ssl-cert-snakeoil.key
sudo chmod 740 /etc/ssl/private/ssl-cert-snakeoil.key

# now postgresql starts! (and install command doesn't fail anymore)
sudo service postgresql restart