How I can check what takes disk space in /tmp?
Solution 1:
The first command indicates that /tmp is actually on the same filesystem as / (ie, everything else). If your root partition is full, it could be that other stuff (such as /var/log) is taking up space.
A decent way of finding things is to do
du -sc * .[^.]* | sort -n
to find what directories are big. Then you can continue to cd into lower directories and rerun the command to narrow things down.
Solution 2:
On a recent distro :
du -sh /tmp/* | sort -h
On a older distro :
du -csm /tmp/* | sort -n