Caused by open file descriptors
If you delete files from the filesystem, the command “df -h” might not show the deleted space as being available. This is because the deleted files could still be held open by (defunct) processes, where the file descriptor handles still point to those files. As a result, the df command assumes the files are still there, and doesn’t clear the space.
Here are some ways you can track which processes still refer to the deleted files.
# lsof | grep 'deleted' # ls -ld /proc/* | grep '(deleted)'
The solution is to either stop the process (kill <PID>, or the more agressive kill -9 <PID>), or if that doesn’t work to restart the server in general.