sorry it took me a while to get back here, as i'm a noob when come to linux system, did a bit of digging and found out that the syslog.1, daemon.log.1 and a few of the clamav-xxxxx.log has eat up till over 60gb of space, managed to delete most of them off my boot drive but am still unable to login as admin.. .
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root@KK-NAS-02:~# df -h
Filesystem Size Used Avail Use% Mounted on
udev 973M 0 973M 0% /dev
tmpfs 199M 3.4M 196M 2% /run
/dev/sda1 71G 7.6G 60G 12% /
tmpfs 993M 0 993M 0% /dev/shm
tmpfs 5.0M 0 5.0M 0% /run/lock
tmpfs 993M 0 993M 0% /sys/fs/cgroup
tmpfs 993M 0 993M 0% /tmp
/dev/sdb1 1.8T 482G 1.4T 27% /srv/dev-disk-by-label-2TB