[solved] Password authentication failed for user \"mattermost\""}

Troubleshooting
2 
"SqlSettings": {
    "DriverName": "postgres",
    "DataSource": "postgres://mmuser:SEcurePassword@127.0.0.1:5432/mattermost?sslmode=disable&connect_timeout=10",

The description in the documentation fails (bug). This works for me …
Second error tar -xvfz is not working at standard ubuntu installation. You have tu unzip file in the first step and than tar -xvf without z.