[deleted] Don't know how to take backup of database in Linux with commands
mysqldump --user=USERNAME --password --lock-tables --databases DBNAME > yyyymmdd_backup.sql
Change USERNAME to a user who has the necessary rights, DBNAME to your flarum DB and yyyymmdd to the date when you do the backup. After pressing ENTER you will be prompted for the password (for the USERNAME).
Do this inside a folder you are allowed to save a file. 😉
I am no expert, but this command works fine for me. Quite sure it will work for you too.