I try to have "find" command exclude "/proc" filesystem. 
I would prefer a portable solution to be able to use it on non GNU based hosts (oldest AIX for instance, where "find" do not have the "-path" option)

Here's what I've tried (on a Linux host) and a partial filtered output:

```

$  find /  ! -fstype proc   >/dev/null
find: `/proc/9475/task/9535/fdinfo/7': No such file or directory
find: `/proc/10856': No such file or directory
find: `/proc/10856': No such file or directory
find: `/proc/10858': No such file or directory
find: `/proc/10858': No such file or directory
find: `/proc/15650': No such file or directory
find: `/proc/15650': No such file or directory
find: `/proc/15654': No such file or directory
find: `/proc/15654': No such file or directory
find: `/proc/15656': No such file or directory
find: `/proc/15656': No such file or directory
find: `/proc/15657': No such file or directory
find: `/proc/15657': No such file or directory
find: `/proc/15663': No such file or directory
etc ....

```

I don't understand why "find" keep walking inside the "/proc" file system despite of the "! -fstype proc" switch?