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Question

I ran du -hs to find out how big my /home/user directory was and it reported as 18G. I cleared out almost 4G of data and ran du -hs again to find out how much space I actually saved and it still reports as 18G. --apparent-size makes it report as 19G. What am I doing wrong?

Did you "clear out" the filesystem by unlinking files that were in use at the time? — David Schwartz, Jun 18 '12 at 20:40

score 3 · Accepted Answer · edited Jun 19 '12 at 07:04

3

If the files are still in use, du will not update.

Here's a post with an exercise so you can see this in action : (for BSD, but it's equivalent in Linux)

edited Jun 19 '12 at 07:04

Khaled

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answered Jun 18 '12 at 20:43

Hyppy

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df will do this but I don't think that du will follow this behavior. – mdpc Jun 18 '12 at 21:44
Goodness! What does this user have running to hold 4GB of files open? Wow! That's a lot of wedged zombies. (Ewww, mental image...) – lornix Jun 28 '12 at 05:11
@lornix: a DVD image perhaps, that was being played with VLC, mplayer etc. – Cristian Ciupitu Jun 29 '12 at 14:51

score 1 · Answer 2 · answered Jun 18 '12 at 22:52

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Another possibility that can cause this is filesystem compression and utilities that don't know about it. I saw this with ZFS a few years ago on Solaris but the theory should be the same for Ubuntu and any other filesystem that supports compression.

I created a file with mkfile 10g test. After this, ls -lh reported it as 10GB and du -h reported it as 0.

If the 4GB you cleared out was found with ls -lh then it might not have been taking up nearly as much space as it seemed.

answered Jun 18 '12 at 22:52

Ladadadada

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Something similar can also happen with *sparse files*. `dd if=/dev/zero of=test bs=10G seek=1 count=0` creates a file that `ls -lh` reports as having 10GBs. – Cristian Ciupitu Jun 18 '12 at 23:07

score 1 · Answer 3 · answered Jun 18 '12 at 23:00

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This could be caused by hard links which means that the files you deleted still exist under other names. To find them, run find -type f -links +1.

answered Jun 18 '12 at 23:00

Cristian Ciupitu

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