Unix Command - du (abbreviated from disk usage)

du is a Unix computer program to display the amount of disk space used under a particular directory or files on a file system.

du counts the disk space by walking the directory tree. As such, the amount of space on a file system shown by du may vary from that shown by df if files have been deleted but their blocks not yet freed.

In Linux, it is a part of the GNU Coreutils package.
The du utility first appeared in version 1 of AT&T UNIX.

The -k flag will show the sizes in 1K blocks, rather than the default of 512 byte blocks.

$du -k /seclog

4       /seclog/lost+found
132     /seclog/backup/aix7
136     /seclog/backup
44044   /seclog/temp
439264  /seclog