How do I see how many blocks I have free on my filesystem?

Question

I know df is supposed to provide this information, but when I run df it shows the number of 1k blocks free, yet my filesystem is using 4k blocks.

I could simply divide by four of course, but this wouldn't necessarily be correct, due to the difference in granularity. For example, four 1k files would use four 1k blocks on a filesystem using 1k blocks, but four 1k files would use four 4k blocks on a filesystem using 4k blocks. (So dividing by four would produce the wrong answer.)

Solution

If you have a 1K file occupying a 4K filesystem block, it will contribute 4K to the df output.

df calculates the number by asking the kernel for the free block count (with statfs/statvfs) and multiplying that by block size / 1024.

Just divide by 4. Sometimes things are simpler than you expect.

On the other hand, you shouldn't assume every version of df uses 1024-byte blocks as its reporting unit. Sometimes it's 512.

Comments

[Admin]

df explicitly states in the first line of output that it is using 1k blocks. Sounds good! I'll just divide by 4 then. I just found it strange that df wouldn't attempt to use the correct block size per filesystem.