This question already has an answer here:

Why does it show 0 in the available column?

[root@server log]# df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda2              4128448   4096484         0 100% /

It's an ext3 filesystem.

marked as duplicate by Patrick, terdon Aug 25 '14 at 17:23

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • <rant> Just because a question is covered by a broad other question doesn't make my specific question a dupe. If that were true, then we wouldn't need specific laws -- just one "Be nice to people". – 010110110101 Aug 25 '14 at 17:09
  • I quote: "when I add the “Used” and “Available” columns of df, I don't get the total figure". That is exactly what you're asking. – Patrick Aug 25 '14 at 17:10
  • This information has been covered multiple times before; see What happened to my free space? and Why is (free_space + used_space) != total_size in df? – G-Man Aug 25 '14 at 17:34

df reports the percentage of used blocks relative to the blocks not reserved for root use (by default I think it's 5% of the drive in ext3). It can be changed by using the -m option of tune2fs e.g. to set it to 2%

tune2fs -m 2 /dev/sdXY

The reserved blocks allow system daemons to keep going even when the disk is full, while non-root processes will not be able to write to it. It also helps reducing drive fragmentation.

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