How to resize LVM logical volumes with ext4 as filesystem

# Unmount the filesystem and check its' LV
umount /mnt/foo
e2fsck -f /dev/mapper/vg0-foo

# Shrink ext4 and then the LV to the desired size
resize2fs -p /dev/mapper/vg0-foo 40G
lvreduce -L 40G /dev/mapper/vg0-foo

# Before continuing, run e2fsck. If it bails because the partition
# is too small, don't panic! The LV can still be extended with
# lvextend until e2fsck succeeds, e.g.:
# lvextend -L +1G /dev/mapper/vg0-foo
e2fsck -f /dev/mapper/vg0-foo

# Resize the filesystem to match the LVs size, check and mount it
resize2fs -p /dev/mapper/vg0-foo
e2fsck -f /dev/mapper/vg0-foo
mount /mnt/foo

umount /mnt/bar

# Extend the LV to use all free space
lvextend -l +100%FREE /dev/mapper/vg0-bar
e2fsck -f /dev/mapper/vg0-bar

# Resize the partition to fill the LV
resize2fs -p /dev/mapper/vg0-bar
e2fsck -f /dev/mapper/vg0-bar
mount /mnt/bar