I find there is a bug in nfs-server script. In line 15, the original is
if grep nfsd /proc/mounts 2> /dev/null; then
But I cannot start nfs server if I don't change the line into
if [ -z "`grep nfsd /proc/mounts`" 2> /dev/null ]; then
Maybe the package nfs-utils.tcz should be updated.