Why Do du and df Report Different Disk Sizes on Linux?

Using du and df to check root partition size

root# du -k -d 1 /
628     /run
41736   /etc
0       /dev
6761392 /root
6905636 /var
4       /media
4       /mnt
206096  /boot
2247520 /opt
30812   /home
0       /proc
16      /lost+found
10319996        /usr
0       /sys
4       /srv
168     /tmp
26514016        /

df -k
Filesystem     1K-blocks     Used Available Use% Mounted on
devtmpfs         1856388        0 1856388   0% /dev
tmpfs           1866776        0 1866776   0% /dev/shm
tmpfs           1866776      628 1866148   1% /run
tmpfs           1866776        0 1866776   0% /sys/fs/cgroup
/dev/vda1       41152812 26803328 12445776 69% /
tmpfs            373356        0  373356   0% /run/user/0

du reports the root directory / size as 26,514,016 KB.

df reports the root directory / size as 26,803,328 KB.

df (Disk Free) calculates free space based on the filesystem's block allocation map, while du (Disk Used) sums the apparent sizes of files and directories, which can lead to differences.

Deleted files that are still held open by running processes are not counted by du, but df still sees the occupied blocks. Use lsof | grep deleted to locate such files.

Linux filesystems reserve a percentage (commonly 5%) of space for the root user; this reserved space is reflected in df but not in du.

When using du -sh *, hidden files (those beginning with a dot) are omitted, causing du to under‑report.

If a process has an open file that gets deleted, du will not count it, whereas df will still show the space as used.

When a data disk is mounted over a directory that already contains files, du cannot see the original files beneath the mount point, while df reports the space used on the underlying filesystem.