I have a Debian Wheezy install that is currently showing 100% disk usage, yet the files in / do not seem to add up to the sum of the disk as reported in a df -h output (as tested with a du -sh /). I have since rebooted, so this would have cleared out any open files that could have been deleted but still remained open.
Output of mount:
/dev/disk/by-uuid/blahblah-3431-43i9-ac71-blahlah on / type ext4 (rw,relatime,errors=remount-ro,user_xattr,barrier=1,data=ordered)
Output of df -h:
rootfs 36G 33G 810M 98% / /dev/disk/by-uuid/blahblah-3431-43i9-ac71-blahlah 36G 33G 825M 98% /
Output of du -sh of / (excluding media, as that dir has directories mounted from other drives):
# du -sh --exclude=media * 7.4M bin 18M boot 0 dev 11M etc 13G home 0 initrd.img 116M lib 4.0K lib64 16K lost+found 4.0K mnt 341M opt du: cannot access `proc/5744/task/5744/fd/4': No such file or directory du: cannot access `proc/5744/task/5744/fdinfo/4': No such file or directory du: cannot access `proc/5744/fd/4': No such file or directory du: cannot access `proc/5744/fdinfo/4': No such file or directory 0 proc 134M root 1.1M run 7.6M sbin 4.0K selinux 4.0K srv 0 sys 56K tmp 6.4G usr 2.4G var 0 vmlinuz