in RHEL5, to resize a root partition which is a logical volume:
can't do it mounted, but it's root, so can't unmount it. Here, I want to reduce my / partition to 6GB:
boot into rescue, do not mount existing system
run:
#lvm pvscan
#lvm lvscan
This should show your partition, eg. /dev/VolGroup00/LogVol00
now run
#lvm vgchange -a y /dev/VolGroup00/
#lvm lvscan
- this will now show active volumes
now run
#e2fsck -f /dev/VolGroup00/LogVol00
#then run
resize2fs /dev/VolGroup00/LogVol00
this will show you how many sectors are in the FS right now. Work out roughly how big you want it to be as a proportion of the current value, and run
#resize2fs /dev/VolGroup00/LogVol00 <number of sectors> - work out a number of sectors which is just below your desired LV size
now to reduce the LV itself:
lvm lvreduce -L 6G /dev/VolGroup00/LogVol00
yay!
You should then resize your filesystem to fill up the whole LV but I couldn't be buggered.