umount failed resolved

[PAUL SLOOTMAN]

Thanks to all who responded to my question as to why a file system
could not be umounted. Here is the original question:
 
> When I want to umount a filesystem, I sometimes (entirely correctly)
> get the message "umount failed: file system busy".
>  
> My uestion is: how can I find out who or what is keeping it busy?
> Obviously it can be found, 'cos umount knows about it. The system
> in question is SysV.
 
There was, in fact, a combination of reasons. (Perhaps I should
have mentioned that I had already tried fuser(1M) on the file
system - to no avail.) I'll summarize different reasons why a
file system can't be umounted.
 
1)    A file is in use on the fs.
2)    A process has its current working directory on the fs.
3)    An active process has its text on the fs.
4)    Another fs is mounted on the fs to be umounted.
5)    (the least obvious, as least to me) The (System V) accounting
        is running, keeping a file open on /usr. This is not detected
        by fuser; probably because the kernel is doing it (I think).
 
My trouble was 4 & 5. From now I know what to look for!
 
Paul Slootman
The Netherlands
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