How to quickly find what is eating up a place?

Question

linux

The logs are clean, but the server is still clogged with something.
Now I can not find what took up all the free space.
Filesystem Size Used Avail Use% Mounted on
/dev/simfs 3.0G 1.6G 123M 93% /
devtmpfs 128M 0 128M 0% /dev
tmpfs 128M 0 128M 0% /dev/shm
tmpfs 128M 188K 128M 1% /run
tmpfs 128M 0 128M 0% /sys/fs/cgroup
tmpfs 26M 0 26M 0% /run/user/0

Answer 1

Usually I walk through the folders with the command:
du -sh ./*

Answer 2

I recommend ncdu - further development of du with pseudo-graphics and interactive.
scans the specified directory, with -x does not climb into third-party mounted resources. then it shows what is found with sizes and transition to subdirectories and all that. allows you to delete files.
in ten minutes you can clean the system qualitatively.

Answer 3

Perhaps they deleted the log that was open in the program, and she continues to write to it.
lsof | grep deleted
then look for what was deleted, for example /var/log/exim4/mainlog and look at the size of the penultimate column, restart the program if you find it.
P/S
Logs are better to "zero" rather than delete, for example echo > /var/log/debug

Answer 4

The problem itself is in Filesystem
Size Used Avail Use% Mounted on
/dev/simfs 3.0G 1.6G 0 100% /
Out of 3 ngb, 1.6 is used and 0 is available - how to understand this?