When you’re getting the message “General error: 3 Error writing file /tmp/xyz” while using Matomo Analytics, the reason is that the disk space is full on your
/tmp partition. The MySQL/MariaDB database is trying to create new files in the folder
/tmp but the disk space is full, so we recommend to increase the size of the
/tmp partition (or another path may be used as configured in your MySQL setting
Once you’ve increased the disk space of your tmp directory, your Matomo page should then load successfully.