Executive SummaryUntil recently, the Ext2 filesystem has been the Linux default. Ext2is a technological miracle. Low fragmentation, redundant enough to bereliably regenerated on error yet diskspace efficient, fast, andadaptable. But when the computer is rebooted or powered off withoutcorrectly shutting down, Ext2 filesystems are placed in an error state.When the computer comes back up, the user is confronted with some mildlyconfusing, and very intimidating, messages and choices. Should he letthe filesystem correct itself? Warning, this can lose data!
Journalized filesystems are made to eliminate such error messages.The Ext3 filesystem is an Ext2 filesystem with a journal file and somefilesystem driver additions making the filesystem journalized.
My research and those of others, as well as limited experimentationby myself, indicate that the tune2fs -j command, which is the primarycommand for converting from Ext2 to Ext3, is safe to run even onwriteable mounted partitions. However, when possible, I run the commandon unmounted or read-only mounted partitions. It might besuperstitious, but I feel that is playing it safe. Nevertheless, whenconfronted with situations making unmounting difficult, I run thecommand on writeable mounted partitions.
Converting the root directory from Ext2 to Ext3 is a little moredifficult. Converting back from Ext3 to Ext2 is a hairy and dangerousprocedure. Instructions for both are given in this document, but thinklong and hard before converting the root directory.
DisclaimerObviously, you use this document at your own risk. I am notresponsible for any damage or injury caused by your use of thisdocument, or caused by errors and/or omissions in this document. Ifthat's not acceptable to you, you may not use this document. By usingthis document you are accepting this disclaimer. Converting from Ext2 to Ext3The conversion procedure is simple enough. Imagine /dev/hda10mounted as /test – the procedure would be as follows:
Log in as root
Make sure /etc/fstabhas /dev/hda10 mounted to /test as ext2, read write
umount /dev/hda10
If you can't unmount it, thenremount it read only (mount -o remount,ro /dev/hda10)
tune2fs -j /dev/hda10
Edit /etc/fstab,and for /dev/hda10, changeext2 to ext3
mount /dev/hda10
/sbin/shutdown -h now
mount | grep /dev/hda10
If it's not shown as ext3, reboot, if still not, troubleshoot
Otherwise, you're done.
A few explanations are in order. The tunefs command creates thejournal file, which is kept in a special inode on the device (bydefault). You then must change the /etc/fstabentry to reflect it's a journalling filesystem, and then mount it.
Converting the /usr directoryThis applies only to those systems in which the /usr tree has its own partition.Converting the /usrdirectory presents a challenge because commands like tune2fs are locatedin the /usr tree, so it must be mounted. Mount it read only with thefollowing command:
mount -o remount,ro /usr
Then run tune2fs -j, edit /etc/fstab, and then unmountand remount /usr. Converting the / directoryFirst, think long and hard before deciding to convert the rootdirectory. Ext3's primary purpose is shorter recovery from disasterrather than data loss prevention. Converting the root directory fromExt2 to Ext3 isn't difficult, but converting it back from Ext3 to Ext2is a treacherous process fraught with problems. But, if you really mustperform the Ext2 to Ext3 conversion on the root directory, here's how,assuming /dev/hda2 ismounted as the root directory and /dev/hda1is mounted as /boot:
Log in as root
Edit /etc/fstab andchange ext2 to ext3 on the line referencing theroot directory. /*这里仅指出需要修改的是根目录，也就是fstab文件中/boot一行对应的ext2是不需要修改的*/
In the preceding, you MUST perform all the steps, including the mkinitrd, before rebooting.Failing to perform all the steps before rebooting produces a "buriedshovel" where if only you could boot the machine, you could run the mkinitrd command, and if onlyyou could run the mkinitrdcommand, you could boot the machine.
笔者验证了本小节提到的将根目录（/）从ext2转换为ext3。完全按照本小节讲解的方法在RH 9上实现，重启后可以正常进入系统。如果需要永久性的关闭当系统非法关机后启动时的硬盘检测的话，可以再进入系统后，执行命令：
tune2fs -c 0 device
其中device即为你想避免自检的分区，我这里/dev/hda1挂载在/下，/dev/hda2挂载在/boot。两个都需要关闭检测的话，可以：
tune2fs -c 0 /dev/hda1
tune2fs -c 0 /dev/hda2
如果要设置隔多长时间检测一次的话，可以使用:
tune2fs -i interval device
这里不再举例，具体的使用方法见tune2fs。 Converting from Ext3 back to Ext2There may come a time when you want to convert back to Ext2. Fordirectories other than the root directory or /usr, it's pretty easy. Thefollowing once again uses the example of /dev/hda10 mounted to directory /test:
umount /dev/hda10
tune2fs -O ^has_journal/dev/hda10
e2fsck /dev/hda10
Edit /etc/fstab tochange /dev/hda10 to mounttype ext2
mount /dev/hda10
The tune2fs commandremoves the journal inode, and the e2fsckcommand completes that removal. Back-Converting the root directory
The root directory is a challenge for a number of reasons. First, itmust be mounted for the system to run, but it must be unmounted to runthe e2fsck command. Also,different distros behave different ways. The mkinitrd command varies widelybetween distros. The preceding works on a Red Hat 8.0 machine, butother machines might require other solutions. We'll assume that /dev/hda1 is /boot, while /dev/hda2 is the root directory (/).
Log in as root
Edit /etc/fstab tochange the /dev/hda2 linefrom ext3 to ext2
This should fail. If it does, it proves that the partition nolonger has a journaling inode.
reboot
Remove the Knoppix CD and press Enter as prompted
Notice you are now booted to the original operating system(hopefully)
Log in as root
Execute a mountcommand to verify an Ext2 root partition.
Back Converting the /usrdirectoryAssume that /usr ismounted by /dev/hda4
Place your Knoppix CD in the CD drive
reboot
Notice you are now booted to Knoppix
Ctrl+Alt+F2 to access a root prompt
umount /dev/hda4
tune2fs -O ^has_journal/dev/hda4
e2fsck /dev/hda4
mount -t ext3 /dev/hda4/mnt/hda4
This should fail. If it does, it proves that the partition nolonger has a journaling inode.
reboot
Remove the Knoppix CD and press Enter as prompted
Notice you are now booted to the original operating system(hopefully)
Log in as root
Execute a mountcommand to verify an Ext2 /usrpartition.
SummaryConverting from Ext2 to Ext3 is usually easy, although converting theroot partition is usually undesirable. From what I hear, and from mylimited testing, the tune2fs -jcommand is so safe that it can be performed on a partition mountedread-write. However, it's usually easy to unmount the partition ormount it read-only, and when that's easy, I've done it that way.
Changing the filesystem type of the root directory requires rebuildingthe initrd image. Those procedures are explained in this document.