title: Why did this postgres database upgrade fail?
body: <p>I am trying to upgrade from Postgresql 9.6 to 10 unsuccessfully.</p>
  
  <p>I ran <code>brew upgrade postgresql</code> with success, then ran <code>brew postgresql-upgrade-database</code> with failure message. The issue seems to be this line:</p>
  
  <p><code>lc_collate values for database "postgres" do not match:  old "en_GB.UTF-8", new "en_US.UTF-8"</code></p>
  
  <p>The whole message was:</p>
  
  <pre><code>    ==&gt; Upgrading postgresql data from 9.6 to 10...
  Stopping `postgresql`... (might take a while)
  ==&gt; Successfully stopped `postgresql` (label: homebrew.mxcl.postgresql)
  ==&gt; Moving postgresql data from /usr/local/var/postgres to /usr/local/var/postgres.o
  The files belonging to this database system will be owned by user "jbkimac".
  This user must also own the server process.
  
  The database cluster will be initialized with locale "en_US.UTF-8".
  The default database encoding has accordingly been set to "UTF8".
  The default text search configuration will be set to "english".
  
  Data page checksums are disabled.
  
  fixing permissions on existing directory /usr/local/var/postgres ... ok
  creating subdirectories ... ok
  selecting default max_connections ... 100
  selecting default shared_buffers ... 128MB
  selecting dynamic shared memory implementation ... posix
  creating configuration files ... ok
  running bootstrap script ... ok
  performing post-bootstrap initialization ... ok
  syncing data to disk ... ok
  
  WARNING: enabling "trust" authentication for local connections
  You can change this by editing pg_hba.conf or using the option -A, or
  --auth-local and --auth-host, the next time you run initdb.
  
  Success. You can now start the database server using:
  
      /usr/local/opt/postgresql/bin/pg_ctl -D /usr/local/var/postgres -l logfile start
  
  Performing Consistency Checks
  -----------------------------
  Checking cluster versions                                   ok
  Checking database user is the install user                  ok
  Checking database connection settings                       ok
  Checking for prepared transactions                          ok
  Checking for reg* data types in user tables                 ok
  Checking for contrib/isn with bigint-passing mismatch       ok
  Checking for invalid "unknown" user columns                 ok
  Creating dump of global objects                             ok
  Creating dump of database schemas
                                                              ok
  
  lc_collate values for database "postgres" do not match:  old "en_GB.UTF-8", new "en_US.UTF-8"
  Failure, exiting
  Error: Upgrading postgresql data from 9.6 to 10 failed!
  ==&gt; Removing empty postgresql initdb database...
  ==&gt; Moving postgresql data back from /usr/local/var/postgres.old to /usr/local/var/p
  ==&gt; Successfully started `postgresql` (label: homebrew.mxcl.postgresql)
  Error: Failure while executing; `/usr/local/opt/postgresql/bin/pg_upgrade -r -b /usr/local/Cellar/postgresql/9.6.1/bin -B /usr/local/opt/postgresql/bin -d /usr/local/var/postgres.old -D /usr/local/var/postgres -j 8` exited with 1.
  </code></pre>
  
  <p>Can anyone help advise me as to how to fix this <code>"en_GB.UTF-8", new "en_US.UTF-8"</code> conflict issue?</p>