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michaelxu@michaelxu-server:~$ df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda1              71G   65G  2.0G  98% /
none                  495M  224K  495M   1% /dev
none                  501M  104K  501M   1% /dev/shm
none                  501M  376K  501M   1% /var/run
none                  501M     0  501M   0% /var/lock

How come the used + available size does not equal the disk size for /dev/sda1?

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Linux by default reserves 5% of each partition for the root user. 5% of 71G = 3.55G; 2.0G + 3.55G = 5.55G; 65G + 5.55G = 70.55G which rounds up to 71G.

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With ext3/4 filesystems you can check the amount of reserved blocks with tune2fs -l /dev/sda1 | grep -i "block count". – mpy Apr 23 '13 at 20:11
hmm sudo df -h results in the same thing though, The missing space is still there – agz Apr 23 '13 at 20:12
I'm also not sure I noticed any difference in df output as user or root. Is this distro specific? – mpy Apr 23 '13 at 20:14
df -h will only display information about the current disk (or whatever disk you're pointing to). Linux installers like to make separate partitions for everything, so you won't see everything just by using df. – Ben Richards Apr 23 '13 at 20:14
@BenRichards df without a path argument will display information about all mounted filesystems. – Aaron Miller Apr 23 '13 at 20:21

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