如何确定运行rm -rf时释放的空间量

Question

Here is a nice system-administrator problem I ran into today, perhaps somebody here knows a solution. The problem is quite simple: I want to know, beforehand, how much disk space is freed when performing an rm -rf command on Linux.

Notice that simply using du will not work, because there may be files that are hard-linked from directories that are not removed by the rm -rf command.

Answer 1

du will generally only count a hard linked file once, so du -sk some/directory should work fine.

# ls -li
total 2048
131346 -rw-r--r-- 2 root root 1048576 Mar  6 13:12 file1
131346 -rw-r--r-- 2 root root 1048576 Mar  6 13:12 file2
# du -sk file1
1024    file1
# du -sk file2
1024    file2
# du -sk .
1028    .

The extra 4k is for the directory itself, but note that it does not claim that 2M is used by this directory...

As you observe, though, this will not take into account hard links that are outside your target. There's probably not an easy way around this without writing a script that walks the entire directory hierarchy to find all the other links to a file... du will report an upper bound, though - you will get back some amount of space that is less than or equal to what du reports.