i use a PXE Boot with mounting a read only NFS Share. Now i like to overlay this with another RW NFS Share.
How would I do this?
You want to configure something like AuFS to mount over the read-only and read-write NFS mounts. This will create a "Merged" filesystem view, but direct all writes to the read-write filesystem. It's frequently used with LiveCDs, which have a read-only filesystem image on the CD, which is then overlaid with a read-write RAMDisk or disk image stored on a writable media (USB, Harddrive) for persistent changes.