Disk usage statistics

Or after dusk a star comes out...

Disk space is like cupboard storage space: you can never have enough. In both cases you can suddenly find that those empty drives and shelves get filled up pretty quickly, but while it is relatively easy to see the big boxes taking up all your shelf space, it is often harder to quickly spot where your disk space has gone.

The situation is more fun when a remote server suddenly reports that it is rapidly approaching having zero disk space available. So, what’s a quick way of seeing where that space has gone? Enter df for disk free status and du for disk usage statistics.

A quick way to see the disk free status is df -lh which reports on locally mounted filesystems, and displays the amount used in ‘human-readable’ sizes.

david$ df -lh
Filesystem     Size   Used  Avail Capacity  Mounted on
/dev/disk0s3    77G    72G   4.0G    95%    /
/dev/disk1s3    77G    27G    50G    35%    /Volumes/Hd2

So once you’ve confirmed that your drive is nearing 100% capacity, how do you quickly discover where the space has gone? First navigate to whichever directory you want to start the detective work in and du -sk * will list the sizes of the contents of that directory.

david$ du -sk *
5423152 Deliver
20072   Design
502224  Develop
984     Discuss
377140  Support
7968    Train

The flag -s displays an entry for each specified file or folder, the -k displays the size in 1Kb blocks, and the * indicates that each file and directory in the current directory should be displayed. My mnemonic for remembering the command du -sk * in moments of panic when the drive is at 100%, and everything is in danger of falling apart, is that “after dusk a star comes out”.

I prefer the use of 1Kb blocks for the sizes, rather than -h which uses ‘human-readable’ units, simply because it is easier to spot the big files or directories from the digits alone without having to interpret the units. As an added enhancement, pipe the result of du through sort to, well, sort the listing, using the -n flag to sort numerically: du -sk * | sort -n

du -sk * | sort -n
984     Discuss
7968    Train
20072   Design
377140  Support
502224  Develop
5423152 Deliver

And in case you’re wondering: the cause of the zero free disk space on the server? A run-away log process that was generating multiple copies of extremely large logs.