Bug 55495 - Can't (re)mount ext3 with data=writeback or journal
Summary: Can't (re)mount ext3 with data=writeback or journal
Alias: None
Product: Red Hat Linux
Classification: Retired
Component: kernel
Version: 7.2
Hardware: i386
OS: Linux
Target Milestone: ---
Assignee: Stephen Tweedie
QA Contact: Brian Brock
Depends On:
TreeView+ depends on / blocked
Reported: 2001-11-01 10:26 UTC by fred-m
Modified: 2007-04-18 16:37 UTC (History)
3 users (show)

Fixed In Version:
Doc Type: Enhancement
Doc Text:
Clone Of:
Last Closed: 2003-07-08 13:21:16 UTC

Attachments (Terms of Use)

Description fred-m 2001-11-01 10:26:05 UTC
Description of problem:
I can't (re)mount my root file system with data=writeback or data=journal, 
only with data=ordered (BTW, the root file system is my only ext3 
partition, so it's the only one that I have to test).

[fred@tornado kernel]# mount -o remount,data=ordered /
[fred@tornado kernel]# mount -o remount,data=writeback /
mount: / not mounted already, or bad option
[fred@tornado kernel]# mount -o remount,data=journal /
mount: / not mounted already, or bad option

Also, adding "data=writeback"  or "data=journal" to the / (root 
filesystem) entry in /etc/fstab results in the same error on boot when the 
file system is to be re-mounted read-write (it remains read-only).

BTW, I have all updates up to November 1st. (Also: I specified mount as 
the component, but the problem could be in the kernel).

How reproducible:

Steps to Reproduce:
Run the commands above. Or, specify "data=writeback" or "data=journal" 
to /etc/fstab and reboot.

Comment 1 Todd Warner 2001-12-07 20:15:05 UTC
Reproduced on my 7.2 machine. 
[taw@trixie taw]$ uname -a
Linux trixie.meridian.redhat.com 2.4.9-13smp #1 SMP Tue Oct 30 19:57:16 EST 2001
i686 unknown

I simply added data=journal to my /etc/fstab (for the / partition) and got
simular results. And therefore boot process fails.

Comment 2 Stephen Tweedie 2001-12-07 20:40:43 UTC
Right --- changing the data mode after mount is not a supported function.  All
sorts of things can go wrong if you change journal semantics live while the
filesystem is running.

Having said that, there _is_ locking inside ext3 which would help to achieve
this: we'd have to suspend the entire filesystem, sync everything to disk, flush
the cache, flush the journal, and _then_ change the mode, but it should be

I'll re-categorise this as a RFE (request for enhancement), but it's not an ext3

Comment 3 fred-m 2001-12-09 06:44:06 UTC
First of all, thanks!!! This explains everything.

IMHO, two things need to be done before we touch ext3 itself:
- Improving the documentation ("mount" manual, Red Hat web site, etc.), to say 
that "changing the data mode after mount is not (yet) a supported function".
- Include a selection of the mode in the Red Hat installer (on "expert" mode 
*only*), in case ext3 is not enchanced until the next release.

Comment 4 Craig Lawson 2002-02-05 21:18:02 UTC
In response to the comment by sct on 12/17: in the general case, all the stuff
you mentioned (sync & flush) would need to take place. But in the specific case
of remounting / during boot-up, it doesn't really apply because / was mounted
read-only! Even the default mode of "data=ordered" isn't necessary because
nothing will be written to the disk. Clever observation, I must say, and it's
too bad I can't take credit for it myself: I found in on the vger.kernel.org
mail list.

There is a secondary problem in that after the remount fails, the other file
systems are mounted normally but "mount" will not show them as mounted

For the reader who finds themself unable to boot because of a non-default mount
option for their root file system, yet somehow able to read this bug report, you
can get out of your predicament this way:
  1. Reboot linux in "single" mode.
  2. Remount / with: mount -t ext3 -o defaults,remount,rw /dev/hda5 /
     (change /dev/hda5 as appropriate). If you don't spell out the options,
     some versions of mount try to get them from /etc/fstab.
  3. Edit /etc/fstab to remove "data=journal" for /
  4. Reboot.

I have all of my file systems as ext3, and / is the only one I have this trouble
with. /boot is OK as data=journal.

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