# echo 500 512000 64 2048 > /proc/sys/kernel/sem
[root@ex5b etc]# df -Th
Filesystem Type Size Used Avail Use% Mounted on
/dev/mapper/vg_ex5b-lv_root
ext4 50G 49G 0 100% /
tmpfs tmpfs 64G 0 64G 0% /dev/shm
/dev/sda1 ext4 485M 59M 401M 13% /boot
//10.14.4.1/c/
cifs 149G 34G 116G 23% /mnt/client
[root@ex5b etc]# pvdisplay
It seems home directory for the users is also on / so go to /home and check if any user have saved large files in his directory.
Follow the wesly_chen's suggestion it will help you get fix your issue.
Once your / will have some space, your issue will be fixed.