The HP (HP-UX) man page for
If mount() fails, errno is set to one of the following values.
[EACCES] A component of the path prefix denies search permission.
[EBUSY] path is currently mounted on, is someone's current working directory, or is otherwise busy.
[EBUSY] The file system associated with fs is currently mounted.
You get the first EBUSY when your question (1) applies because:
- if the directory is already a mount point, you lose access to the previously mounted directory, which makes the prior mount irrelevant.
- if the directory (say
/some/where) is some process's current directory, you have a process with a different view of the contents of
/some/where; newcomers see what's on the mounted file system, but the old processes see what was in the mounted-upon directory.
You get the second EBUSY to answer your question (2) when the file system is already mounted - in other words, you can't mount it twice. This is a good thing - there would be a dreadful danger of confusion if two separate mount points both went around assuming they had exclusive access to the superblock etc when it was in fact shared. It would also be confusing if creating a file
/some/where/newfile also simultaneously created
/opt/other/newfile because the same device was mounted on both
I haven't checked the AIX, Solaris, Linux, MacOS X, BSD man pages for
mount(2), but I expect the behaviour to be the same.