Resizing Root ext4 filesystem on LVM

Resizing an ext4 filesystem on a lvm partition is pretty straightforward - you just extend the logical volume first, then resize the filesystem.  It gets a little more complicated if its the root filesystem that you want to resize, because resizing an online filesystem is riskier and probably not even supported for ext4 filesystems (see resize2fs man page).  In this case, you can boot from a live cd to resize the unmounted root partition.  However, most live cds do not include lvm support.  Here is how to resize your root partition with a Ubuntu 10.04 live cd.

First, you can resize the logical volume while you're still running off the root partition.  You can look in /etc/fstab to help figure out the logical volume name.  Look for the filesystem mounted on /.  My entry looked like:

/dev/mapper/lvmvolume-lucid64root /   ext4    errors=remount-ro 0 1

The corresponding logical volume name is /dev/lvmvolume/lucid64root.  You can use lvdisplay to verify:

ubuntu@ubuntu:~$ sudo lvdisplay
  --- Logical volume ---
  LV Name                /dev/lvmvolume/lucid64root
  VG Name                lvmvolume
  LV UUID                xbW7iN-x9Ri-gGHG-rwpp-iLu1-gIsf-ycT6dc
  LV Write Access        read/write
  LV Status              NOT available
  LV Size                12.00 GiB
  Current LE             3072
  Segments               2
  Allocation             inherit
  Read ahead sectors     auto

You can extend the logical volume without unmounting (see lvm howto):

ubuntu@ubuntu:~$ sudo lvextend -L12G /dev/lvmvolume/lucid64root

You'll need to use the same logical volume name later when you resize the filesystem.  Now boot into the live cd.  Since the Ubuntu 10.04 live cd I used doesn't have lvm support, the first step is to intall it:

ubuntu@ubuntu:~$ sudo apt-get install lvm2

Then make your logical volumes available:

ubuntu@ubuntu:~$ sudo vgchange -a y

Then resize the filesystem.  The default size is to just fill the partition.

ubuntu@ubuntu:~$ sudo resize2fs /dev/lvmvolume/lucid64root

It might ask you to run e2fck first:

ubuntu@ubuntu:~$ sudo e2fsck -f /dev/lvmvolume/lucid64root

Done.  Now just reboot to your newly resized root partition.