linux - Out of disk space on 4GB partiton yet it's only using 2GB

I'm running Ubuntu and have had a problem where the root partition has run out of disk space.

When I perform df -h I get the following:

Filesystem            Size  Used Avail Use% Mounted on
/dev/sda6             4.6G  4.5G     0 100% /

Yet there are only 2GB of files actually using up this partition. I then ran the following df -i and I get the following:

Filesystem            Inodes   IUsed   IFree IUse% Mounted on

/dev/sda6             305824  118885  186939   39% /

I have no idea what the -i flag does but it clearly shows that only 39% is used.

Can anyone explain where my disk space has gone?

Answer

You probably have a process keeping a file open that's been deleted. Deleted but open files keep consuming disk space, but don't show up in du or ls. "df -i" is a red herring, it just shows you how many files you have, or more technically, how many inodes.

If you can't figure out what process is holding a big (deleted) file open, and chances are it's a zombie or something hung, it might be time for a reboot.