Ubuntu 14.04 PXE boot with initrd (initramfs) kernel panic [duplicate]

1) The kernel panic is caused because the init script fails when trying to find a net device for dhcp.

2) You do not have to compile your own kernel for PXE boot/install Ubuntu/Lubuntu; things are much simpler;

Please see the parameters used by Serva when PXE booting/installing Lubuntu (I'm related to Serva development)

[PXESERVA_MENU_ENTRY]
asset    = Lubuntu 14.04 Desktop Live
platform = amd64
kernel   = NWA_PXE/$HEAD_DIR$/casper/vmlinuz
append   = showmounts toram root=/dev/cifs initrd=NWA_PXE/$HEAD_DIR$/casper/initrd.lz,NWA_PXE/$HEAD_DIR$/casper/INITRD_N11.GZ boot=casper netboot=cifs nfsroot=//$IP_BSRV$/NWA_PXE_SHARE/$HEAD_DIR$ NFSOPTS=-ouser=serva,pass=avres,ro ip=bootp ro

In this case Serva uses CIFS instead of NFS but you can easily change the corresponding append parameters. You will also see some other directory and IP parameters that point to Serva repository that must be edited accordingly to your needs. See that you need to download a tiny complementary initrd INITRD_N11.GZ freely available from Serva's site.

Of-course you do not need to use Serva for booting your client; you can use Serva parameters with your own PXE server. Even if your are not going to use Serva you should probably use it in order to fine tune your parameters; once you got a working set then you can move to whatever PXE server you might want to use.