One usual problem I have when dealing with production servers is that their disks get filled. This results in various warnings and errors and should be fixed immediately. The first step to resolve this issue is to actually find out where is that hard disk space is used!

For this you can use the du unix tool with some parameters. The problem is that du has various parameters (not needed for the task at hand) and the various places I search for contain other info not related to this specific task.

Thus I’ve decided to write this small blog post to help people struggling with this and also to help me avoid googling for it by searching in pages that also contain other du recipies and also avoid the trial and error that this would require.

So to print out the disk usage summary for a directory go to that directory and run du -h -s *; you need to have access to the child subdirectories so probably it’s better to try this as root (unless you go to your home dir for example).

Here’s a sample usage:

[root@server1 /]# cd /
[root@server1 /]# du -h -s *
7.2M    bin
55M     boot
164K    dev
35M     etc
41G     home
236M    lib
25M     lib64
20K     lost+found
8.0K    media
155G    mnt
0       proc
1.6G    root
12M     sbin
8.0K    srv
427M    tmp
3.2G    usr
8.9G    var

The parameters are -h to print human readable sizes (G, M etc) and -s to print a summary usage of each parameter. Since this will output the summary for each parameter I finally pass * to be changed to all files/dirs in that directory. If I used du -h -s /tmp instead I’d get the total usage only for the /tmp directory.

Another trick that may help you quickly find out the offending directories is to append the | grep G pipe command (i.e run du -h -s * | grep G) which will filter out only the entries containing a G (i.e only print the folders having more than 1 GB size). Yeh I know that this will also print entries that have also a G in their name but since there aren’t many directores that have G in their name you should be ok.

If you run the above from / so that /proc is included you may get a bunch of du: cannot access 'proc/nnn/task/nnn/fd/4': No such file or directory errors; just add the 2> /dev/null pipe redirect to redirect the stderr output to /dev/null, i.e run du -h -s * 2> /dev/null.

Finally, please notice that if there are lots of files in your directory you’ll get a lot of output entries (since the * will match both files and directories). In this case you can use echo */ or ls -d */ to list only the directories; append that command inside a ` pair or $() (to substitute for the command output) instead of the * to only get the sizes of the directories, i.e run du -h -s $(echo */) or du -h -s `echo */`.

One thing that you must be aware of is that this command may take a long time especially if you have lots of small files somewhere. Just let it run and it should finish after some time. If it takes too long time try to exclude any mounted network directories (either with SMB or NFS) since these will take extra long time.

Also, if you awant a nice interactive output using ncurses you can download and compile the ncdu tool (NCurses Disk Usage).