Strane remount behaviour with ext3-2.4-0.9.4
Following the announcement on lkml, I have started using ext3 on one of my servers. Since the server in question is a farily security-sensitive box, my /usr partition is mounted read only except when I remount rw to install packages.
I converted this partition to run ext3 with the mount options "nodev,ro,data=writeback,defaults" figuring that when I need to install new packages etc, that I could just mount rw as before and that metadata-only journalling would be ok for this partition as it really sees very little write activity.
When I try to remount it r/w I get a log message saying:
Jul 27 09:54:29 henry kernel: EXT3-fs: cannot change data mode on remount
...even if I give the full mount option list (including data=writeback) with the remount instruction.
I can, however, remount it as ext2 read-write, but when I try to remount as ext3 (even read only) I get the same problem.
Wierdly, "mount" lists it as being still an ext3 partition even though it has been remounted as ext2. I can't umount /usr because kjournald is currently listed as using the partition.
The box in question is more-or-less RedHat 7.1, with ext3-2.4-0.9.4, kernel 2.4.7 and with the following relevant package versions:
mount-2.11g-4
util-linux-2.11f-3
e2fsprogs-1.22-2
...all from rawhide rpms.
I'm going to try one of the partitions mounted "data=ordered" to see if I see the same sort of thing.
Sean
Quoted 3 lines · Sean
servers. Since the server in question is a farily security-sensitive box, my /usr partition is mounted read only except when I remount rw to install packages.
If it is a security-sensitive box, you need to at least use data=ordered or data=journal. Using data=writeback allows the possibility that after a crash one user might be able to read data from deleted files of another user (note that reiserfs currently only runs the equivalent of data=writeback).
Quoted 5 lines
When I try to remount it r/w I get a log message saying:
Jul 27 09:54:29 henry kernel: EXT3-fs: cannot change data mode on remount...even if I give the full mount option list (including data=writeback) with the remount instruction.
You _could_ leave out the data=writeback from /etc/fstab (default is ordered), and you will be able to remount OK. Also, Andrew made a patch which allowed you to specify the data= mode on remount, as long it is the same.
Quoted 2 lines
I can, however, remount it as ext2 read-write, but when I try to remount as ext3 (even read only) I get the same problem.
You can't change filesystem types via remount (ext2 and ext3 are different filesystem drivers). In the future, you might be able to use the ext3 driver to mount a filesystem in totally unjournaled (ext2) mode.
Cheers, Andreas
Signature · 3 lines
Andreas Dilger http://sourceforge.net/projects/ext2resize/ http://www-mddsp.enel.ucalgary.ca/People/adilger/
Hi,
Quoted 8 lines · Andreas Dilger
Quoted 3 lines
servers. Since the server in question is a farily security-sensitive box, my /usr partition is mounted read only except when I remount rw to install packages.
If it is a security-sensitive box, you need to at least use data=ordered or data=journal. Using data=writeback allows the possibility that after a crash one user might be able to read data from deleted files of another user (note that reiserfs currently only runs the equivalent of data=writeback).
Agreed, and for most workloads data=ordered will have very little performance difference from data=writeback.
Quoted 3 lines
You _could_ leave out the data=writeback from
/etc/fstab(default is ordered), and you will be able to remount OK. Also, Andrew made a patch which allowed you to specify the data= mode on remount, as long it is the same.
Indeed, but I'll need to make sure that the remount with no data= mode also works (that should be legal.)
Cheers,
Stephen