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After upgrading a Debian system from 5.0 to 6.0 (Lenny to Sqeeze), how do I go about upgrading the root filesystem (which in this case is also boot) from ext3 to ext4?

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up vote 4 down vote accepted

This was no big deal at all, here's what I did:

  1. Edit /etc/fstab, replacing "ext3" with "ext4" for my root filesystem. (I also removed "barrier=1", which is now the default on ext4.)
  2. Reboot into single user mode with read only root filesystem.
  3. Run tune2fs -O extents,uninit_bg,dir_index /dev/DEV
  4. Reboot, again into single user mode with read only root filesystem. (Observe some mount warnings.)
  5. Run e2fsck -fDC0 /dev/DEV to patch up the filesystem.
  6. Reboot normally.

Most of this was taken from here.

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FYI the EXT4 Howto URL is now ext4.wiki.kernel.org/articles/e/x/t/Ext4_Howto_d00b.html –  zarkdav Nov 11 '11 at 10:04
You'll probably want to convert the files and directories on the filesystem to use "extents" too, by using chattr +e file on everything. –  Legooolas Jul 20 '12 at 22:16
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