[nylug-talk] fun with fstab, bind and unionfs

[alex at pilosoft.com]

On Fri, 2 Feb 2007, jh wrote:

> I'm trying to use things like bind and unionfs to work around the silly
> things that commercial software vendors do. These silly things become
> problems in a diskless environment :( And sadly, no, I don't have the
> option of finding sane vendors in their product classes.
> 
> First issue: a bind mount solves one issue that I'm having with one
> vendor (who needs writable access into subdirectory of /opt). I have
> this entry in my fstab:
> 
> /Sillyvendor /opt/Sillyvendor none rw,bind 0 0
> 
> If I manually issue the command
> 
> mount /opt/Sillyvendor
> 
> it works fine. But it doesn't mount at boot time. Can someone shed some
> light on this? I guess that I could put something in rc.local, but it
> should work from fstab, no?
Are you sure that line is *after* the line which causes /opt to be 
mounted? [if opt is on separate filesystem]. Check your distribution's rc 
scripts and see what exactly do they do on boot: mount -a -t ext2? mount 
-a? etc.

If it don't work, whats wrong with rc.local? 


> Second issue: I have a very, very silly vendor that insists on having 
> write privs to /usr. Sadly, my diskless boxes don't allow this.
> 
> I thought that unionfs might be the solution. Any suggestions on how to 
> do this, especially from fstab? I was thinking of something like this... 
> not sure how to do a unionfs entry in fstab...
> 
> foo:/usr /usr_temp nfs ro,hard,intr 0 0
> none  /usr  unionfs dirs=/usr_temp:/usr_write 0 0
> 
> Any comments on whether this would work, or perhaps, on the fine points 
> of unionfs?
unionfs is broken by design. you'll hit problems, later. 

i'm sure your vendor requires +w to something inside /usr - which you can
mount from tmpfs - or it is really a file under /usr proper? If it is a 
specific file, symlink it to /tmp and it will be none the wiser.

-alex