How to determine what is stealing space on the server when no more than 30% of the disk is physically occupied, but ncdu cannot be installed?

Question

linux

df-hi

Filesystem     Inodes IUsed IFree IUse% Mounted on
udev              57K   383   57K    1% /dev
tmpfs             62K   934   61K    2% /run
/dev/vda1        640K  640K     0  100% /
tmpfs             62K     1   62K    1% /dev/shm
tmpfs             62K     4   62K    1% /run/lock
tmpfs             62K    16   62K    1% /sys/fs/cgroup
tmpfs             62K     4   62K    1% /run/user/0

df-h

Filesystem      Size  Used Avail Use% Mounted on
udev            227M     0  227M   0% /dev
tmpfs            49M  3.9M   45M   8% /run
/dev/vda1       9.8G  7.1G  2.7G  73% /
tmpfs           245M     0  245M   0% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs           245M     0  245M   0% /sys/fs/cgroup
tmpfs            49M     0   49M   0% /run/user/0

Answer 1

There are too many files on the root partition - free inodes (inodes) are over.

Answer 2

The question was of course stupid. The tmp folder was full
If anyone needs a simple solution:
find . -type f -exec rm -v {} \;