mounting /usr readonly

[Robert Nichols]

Robert P. J. Day wrote:
> On Sun, 30 Dec 2007, John Summerfield wrote:
> 
>> Robert P. J. Day wrote:
> 
> ... snip ...
> 
>>>   can i assume that, as long as nothing is open for write, the
>>> read-only remount should work?  is there any other reason that i
>>> would be told that the device is busy.  put another way, if i run
>>> the above command and don't see an "F", should the remount always
>>> work?
> 
>> Add ro to the mount options in /etc/fstab and see what complains.
> 
> but that wasn't the question.  again, if i try to, in one operation,
> remount a filesystem readonly with "mount -o remount,ro", is the only
> possible reason that remount could fail is if something on that
> filesystem is open for writing, which would show up in the output of
> "fuser -muv"?
> 
> or is it possible that that remount could fail because of "device
> busy" and i run that fuser command and i don't see anything marked
> with "F", which means there's another reason for the remount failure,
> and what might that be?

One big issue with remounting /usr read-only is the presence of
unlinked files that are still held open by a process.  Prelink
results in a lot of those because the original file is unlinked
and replaced by the newly prelinked version.  If any running
process using the original file is still running, the inode and
related data blocks cannot be freed, and until that is done the
filesystem remains "busy."  If you run "lsof /usr | grep -i del"
you will probably see a lot of such files.  After a full prelink,
you will probably find it necessary to go down to single-user
mode, and most likely kill off one or two strays that didn't get
stopped.

-- 
Bob Nichols     "NOSPAM" is really part of my email address.
                 Do NOT delete it.