I want to install Qt on my Debian but it doesn't detect the whole free space! I tried to install it in /home/Qt but it says that only 23.87 MiB of space is available while
df -h says that there is still 7.2G free.
Your root file system (which by the way is extremely small, even considering that you have /home, /tmp, /usr and /var elsewhere) is practically full; that exact
I'm guessing this is because parts need to go into locations outside of the supposed installation directory. Though nearly 1 GB seems rather excessive.
What you have for / would really be a more appropriate size for a separate /boot or similar.