rhel-root 100% full

Hello,

Cannot find what is using the space. Root partition is 16GB but cannot find any large files what is casuing this?

Filesystem Size Used Avail Use% Mounted on
devtmpfs 16G 0 16G 0% /dev
tmpfs 16G 0 16G 0% /dev/shm
tmpfs 16G 17M 16G 1% /run
tmpfs 16G 0 16G 0% /sys/fs/cgroup
/dev/mapper/rhel-root 16G 16G 20K 100% /
/dev/sdb 148G 72G 70G 51% /elasticdata
/dev/sda2 1014M 442M 573M 44% /boot
/dev/sda1 599M 5.8M 594M 1% /boot/efi
/dev/mapper/rhel-var 12G 5.6G 6.5G 47% /var
/dev/mapper/rhel-home 26G 217M 26G 1% /home
tmpfs 3.2G 0 3.2G 0% /run/user/983
tmpfs 3.2G 0 3.2G 0% /run/user/0

du -h --max-depth=1 /
408M /boot
0 /dev
99M /home
0 /proc
17M /run
0 /sys
5.4G /var
28M /etc
1.6G /root
3.9G /usr
0 /media
80G /mnt
463M /opt
0 /srv
109M /tmp

Wanted to install lsof but cant with zero space.

We would like to see whats using the space and then hopefully delete the offending file(s) but have run numerous commands and cannot find the culprit.

Thanks.