Hack and / - A Little Spring Cleaning

If your filesystem has dust bunnies and clutter filling up your free space, check out these simple tips to track down and reclaim space from some common offenders.

No matter how big your hard drives are, at some point you're going to look at your storage and wonder where all the space went. Your /home directory is probably a good example. If you are like me, you don't always clean up after yourself or organize immediately after you download a file. Sure, I have directories for organizing my ISOs, my documents and my videos, but more often than not, my home directory becomes the digital equivalent of a junk drawer with a few tarballs here, an old distribution ISO there and PDF specs for hardware I no longer own. Although some of these files don't really take up space on the disk—it's more a matter of clutter—when I'm running out of storage, I'd like to find the files that take up the most space and decide how to deal with them quickly. This month, I introduce some of my favorite commands for locating space-wasting files on my system and follow up with common ways to clear some space.

Think Locally

First, let's start with file clutter in your main home directory. Although all major GUI file managers these days make it easy to sort a directory by size, because I'm focusing on command-line tips, let's cover how to find the largest files in the current directory via the old standby, ls. If you type:

$ ls -lSh

you'll get a list of all the files in your current directory sorted by size. Of course, if you have a lot of files in the directory, the files you most want to see are probably somewhere along the top of the list, so I typically like to type:

$ ls -lSh | less

to view the list slowly starting at the top. Or, if I'm in a hurry, I type:

$ ls -lSh | head

to see only the top ten largest files. Now, this is pretty basic, but it's worth reviewing, as you'll use these commands over and over again to track down space-wasting files. Depending on how you structure your home directory, you probably won't find all the large files together. It's more likely that they are scattered into different subdirectories, so you then need to scan through your directory structure recursively, tally up the disk space used in each directory, and sort the output. Luckily, you don't have to resort to ls for this; du does the job quite nicely. For instance, one common use for du that I see referenced a lot is the following:

$ du -sh *

This scans through all the subdirectories you list as arguments (in this case, all the subdirectories within my current directory) and then lists them one by one with human-readable file sizes (the -h option converts the file sizes into megabytes, gigabytes and so forth, so it's easier to read). Here's some example output from that command:

456K    bin
28K     Default-Compiz
16K     hl4070cdwcups-1.0.0-7.i386.deb
344K    hl4070cdwlpr-1.0.0-7.i386.deb
27M     images
60K     LexmarkC750.ppd
850M    mail

Although you certainly could work with this information, it would be much easier if it were sorted. To do that, replace the -h argument with -k, and then pipe the output to sort:

$ du -sk * | sort -n

16      hl4070cdwcups-1.0.0-7.i386.deb
28      Default-Compiz
60      LexmarkC750.ppd
344     hl4070cdwlpr-1.0.0-7.i386.deb
456     bin
10224   writing
26948   images
869588  mail

This works better, because now I can see that my local e-mail cache is taking up the bulk of the storage; however, next I would need to change to the mail directory and run the command again, over and over, until I narrow it down to the subdirectory that has the large files. That's why I normally skip the above commands and go straight for what I affectionately call the duck command:

$ du -ck | sort -n
. . .
87704   ./.mozilla
87704   ./.mozilla/firefox
119236  ./mail/example.net/sent-mail-2004
119236  ./mail/example.net/sent-mail-2004/cur
869852  ./mail
869852  ./mail/example.net
1064100 .
1064100 total

The -c option essentially recurses into each subdirectory like before, except it keeps a running tally of the space used by each subdirectory down the tree, not just the first level of directories. When it reports its findings, it might list the same top-level directory multiple times. This makes it easy to drill down to the actual directory that consumes the most space, which in this example seems to be ./mail/example.net/sent-mail-2004/cur. If I wanted to clean up files there, I could cd to that directory and then run the ls commands I used above to see which files used the most space.


Kyle Rankin is Chief Security Officer at Purism, a company focused on computers that respect your privacy, security, and freedom. He is the author of many books including Linux Hardening in Hostile Networks, DevOps Troubleshooting and The Official Ubuntu