After setting "Use ext4 for ext2/ext3 file systems" and rebooting, my root filesystem gets mounted as ext2. When the option is disabled, everything works as expected. Here are some relevant output: $ grep ext[24] /etc/fstab /dev/sda1 /boot ext2 noauto,noatime 1 2 /dev/sda5 / ext4 noatime 0 1 $ mount | grep ext[24] /dev/root on / type ext2 (rw,noatime,barrier=1,data=ordered) /dev/sda1 on /boot type ext2 (rw,noatime) $ dmesg | grep -i ext[24] EXT4-fs (sda5): mounted filesystem with ordered data mode VFS: Mounted root (ext2 filesystem) readonly on device 259:131072. EXT4-fs (sda1): mounted filesystem without journal $ uname -a Linux tux 2.6.33 #1 SMP PREEMPT Wed Feb 24 16:00:09 EST 2010 x86_64 Intel(R) Core(TM)2 CPU T5300 @ 1.73GHz GenuineIntel GNU/Linux
This bug is still present in Linux 2.6.35.1, but it can be easily worked-around by appending "rootfstype=ext4" to the boot options.
It's actually getting mounted using the ext4 file system driver. It's just that is getting identified as ext2 in /proc/mounts. Whether or not users see this depends on their init scripts, and especially whether they have an initrd. It is only a cosmetic issue, so it's low priority, but I do agree we should try to fix it.