Performing a database backup isn't really an osTicket question. It would be a MySQL or MariaDB question. There are lots of resources (both on the forums and on the internet in general) on how to perform a database backup. You would want to google it for your specific Database software. Since you appear to be running Linux you can probably just use the mysqldump command to make a back up.
This command at the command line would do it for you:
mysqldump ost_database_name -uyouruser -pyourpassword --single-transaction --quick --lock-tables=false > /tmp/osticket-backup-$(date +%F).sql
You would have course have to change the following:
ost_database_name to the name of your osticket database.
yourdbuser to the username of the database user.
yourpassword to the password of the database user.
also note that it will put the back up in your /tmp directory.
You can change the path or move it some place more appropriate.
You should also make sure that you at least back up the /include/ost-config.php file which has the database server, dbname, dbuser, and dbuser pass, and salt in it.