During my Fedora 15 installation, i made two Logical Volumes, HomeLV 50GB for /home and RootLV 5GB for /. This was a mistake and very soon the / was full.

[root@localhost ~]# df -h /
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/FedVG-RootLV
4.8G  4.5G  4.9G  94% /

So i now wanted to shrink the /home and extend the /.

To reduce a logical volume. We first need to reduce the filesystem on it using resize2fs or fsadm. Then use lvresize (or lvreduce) to resize the logical volume.

[root@localhost ~]# resize2fs /dev/mapper/FedVG-HomLV 45G
resize2fs 1.41.14 (22-Dec-2010)
Filesystem at /dev/mapper/FedVG-HomLV is mounted on /home; on-line resizing required
resize2fs: On-line shrinking not supported

Online shrinking is not supported. So now the option is to unmount the underlying filesystem ie, /home. For that i had to logout of the GNOME and work in a Virtual console (Ctrl+Alt+F[1-6]).

Now, a bit more reading of the man page of lvresize and i found that by using -r switch, we can resize the underlying  filesystem  together with the logical volume.

[root@localhost ~]# umount /dev/mapper/FedVG-HomLV
[root@localhost ~]# lvresize -r -L -5G /dev/mapper/FedVG-HomLV
fsck from util-linux2.19.1
dev/mapper/FedVG-HomLV: 900/2949120 files (1.2% non-contiguous), 250200/11796480 blocks

resize2fs 1.41.14 (22-Dec-2010)
Resizing the filesystem on /dev/mapper/FedVG-HomLV to 10977280 (4k) blocks.
The filesystem on /dev/mapper/FedVG-HomLV is now 10977280 blocks long.

Reducing logical volume HomLV to 41.88 GiB
Logical volume HomLV successfully resized

The -L switch with +/-nG directs lvresize it to add or reduce n GB.

[root@localhost ~]# mount /home
[root@localhost ~]# df -h /home
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/FedVG-HomLV
42G  253M   39G   1% /home

The next step is to extend the RootLV logical volume and then grow the root filesystem.

[root@localhost ~]# lvextend -l +100%FREE /dev/mapper/FedVG-RootLV
Extending logical volume RootLV to 10.00 GiB
Logical volume RootLV successfully resized

The +100%FREE option directs the lvextend to use the available free extents(free space). Note that the -r switch to resize the underlying filesystem is available here too though i didnt use it.

Grow the filesystem using resizefs. By default, most file system resizing tools will increase the size of the file system to be the size of the underlying logical volume so you do not need to worry about specifying the same size for each of the two commands.

[root@localhost ~]# resize2fs /dev/mapper/FedVG-RootLV
resize2fs 1.41.14 (22-Dec-2010)
Filesystem at /dev/mapper/FedVG-RootLV is mounted on /; on-line resizing required
old desc_blocks = 1, new_desc_blocks = 1
Performing an on-line resize of /dev/mapper/FedVG-RootLV to 2621440 (4k) blocks.
The filesystem on /dev/mapper/FedVG-RootLV is now 2621440 blocks long.

Online growing of filesystem is supported although online shrinking not supported as we saw earlier.

[root@localhost ~]# df -h /
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/FedVG-RootLV
9.9G  4.5G  4.9G  48% /

—