Silly question regarding "du" and "df".

Michael T. Richter ttmrichter at
Fri Jan 26 09:45:48 UTC 2007

So, I'm mirroring Dapper and Edgy on a local drive.  I'm mid-way through
the procedure and I want to see how it's going.  I go to the root of the
repository -- the only thing on this disk -- and I get this report from

22G     pool/main
2.8G    pool/multiverse
591M    pool/restricted
9.2G    pool/universe
35G     total

Being who I am, I also run df and get this:

Filesystem             Size   Used  Avail Use% Mounted on
/dev/sda1               79G    38G    38G  50% /media/Repository80GB

Now I cannot for the life of me make the numbers add up.  Absolutely the
only thing on the disk is this (partial) mirror.  Yet "du" reports that
only 35GB is used up while df reports that 38GB is used up.  Now perhaps
I can see slack space making up the difference (although almost 10%
slack space is pretty odd for such large files).  But the numbers inside
df's report themselves don't add up.  79GB size minus 38GB used doesn't
add up to 38GB available in any arithmetic form I'm used to using.
Indeed there seems to be another 3GB gone missing there.

In case there's some kind of "quota only for root" thing going on (I
know I can do this in other operating systems so I assume that even
UNIXen can do it), I su -i and try again.  Same numbers all around.

So why do "du" and "df" report different amounts used?  And why do the
numbers reported by "df" not add up?  (And why does System
Monitor->Devices report for that drive a size of 73.4GB instead of 79
but reports the same amount used as "df"?)  Is this a case of the man
with two watches never knowing what time it is?

Michael T. Richter
Email: ttmrichter at, mtr1966 at
MSN: ttmrichter at, mtr1966 at; YIM:
michael_richter_1966; AIM: YanJiahua1966; ICQ: 241960658; Jabber:
mtr1966 at

"My paramount object in this struggle is to save the Union, and is not
either to save or to destroy slavery." --Abraham Lincoln
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