append ks=http://192.168.193.128/ks.cfg vga=788 initrd=ubuntu-installer/amd64/initrd.gz live-installer/net-image=http://192.168.193.128/ubuntu/install/filesystem.squashfs
label cli
menu label ^Command-line install
kernel ubuntu-installer/amd64/linux
append tasks=standard pkgsel/language-pack-patterns= pkgsel/install-language-support=false vga=788 initrd=ubuntu-installer/amd64/initrd.gz --- quiet
编辑文件default
vim /var/lib/tftpboot/pxelinux.cfg/default
# D-I config version 2.0
# search path for the c32 support libraries (libcom32, libutil etc.)
path ubuntu-installer/amd64/boot-screens/
include ubuntu-installer/amd64/boot-screens/menu.cfg
default ubuntu-installer/amd64/boot-screens/vesamenu.c32
prompt 0
timeout 10 #默认是0（手动），改为10（1秒后自动选择install选项）
接下来就可以安装系统了。