When Postico is stuck at “Negotiating SSL...”
Usually this is caused by a firewall that silently discards packets. Make sure that your firewall is configured to allow your computer to connect to the PostgreSQL server (for example by whitelisting your IP address).
Sometimes you can use an SSH tunnel to circumvent a firewall.
could not connect to server: Connection refused
Is the server running on host "xyz" and accepting TCP/IP connections on port 5432?
This happens when the PostgreSQL server is not running, or when it is not listening for network connections.
Make sure that the listen_addresses parameter is configured correctly in the file postgresql.conf (you can find it in the data directory).
Network filters and security software
Many connection problems are caused by network filters and security software like anti-virus. These tools often block or intercept network connections. The resulting issues are generally very hard to debug and can lead to a number of error messages. If you use any software that interferes with the network stack, contact the vendor to find out how you can configure it to be compatible with PostgreSQL. Some security software might not be compatible at all, and you'll have to disable it before you can connect to a PostgreSQL server.
When Postico says, “Resolving localhost failed. Hostname not found.”
This message is usually caused by a problem in your /etc/hosts file. The default contents of this file are (on OS X 10.11):
## # Host Database # # localhost is used to configure the loopback interface # when the system is booting. Do not change this entry. ## 127.0.0.1 localhost 255.255.255.255 broadcasthost ::1 localhost
Reverting changes to /etc/hosts should fix this connection issue.