Self-hosted Matrix server: move database to a new server

On both servers, create a ~/.pgpass file with the database usernames and passwords. Each line is the login credentials for one database, in the format hostname:port:database-name:username:password
On the old server, shut-down Synapse and the plugins
```
  sudo systemctl stop synapse
```
On the new server, shut-down Synapse and the plugins
```
   ssh stephen@constanza.irons.nz pg_dump -C -h localhost -U synapse synapse | psql -h localhost -U synapse synapse
```
This took a few minutes; this is a small Synapse installation

The databases are not exposed to the internet, so ssh is used to create a session on the remote side.