You can try to boot with debug mode enabled and then try to install grub manually from the rescue shell.
cdrom=
initrdisoimage="/proxmox.iso"
if [ -f $initrdisoimage ]; then
# this is useful for PXE boot
echo "found proxmox cdrom image inside initrd image"
ls -l /dev/loop*
modprobe loop
lsmod | grep loop
mount -t iso9660 -o loop,ro $initrdisoimage /mnt
echo $?
if mount -t iso9660 -o loop,ro $initrdisoimage /mnt >/dev/null 2>&1; then
cdrom=$initrdisoimage
fi
else
echo "searching for cdrom"
found proxmox cdrom image inside initrd image
brw-rw---- 1 0 6 7, 0 May 9 10:01 /dev/loop0
brw-rw---- 1 0 6 7, 1 May 9 10:01 /dev/loop1
brw-rw---- 1 0 6 7, 2 May 9 10:01 /dev/loop2
brw-rw---- 1 0 6 7, 3 May 9 10:01 /dev/loop3
brw-rw---- 1 0 6 7, 4 May 9 10:01 /dev/loop4
brw-rw---- 1 0 6 7, 5 May 9 10:01 /dev/loop5
brw-rw---- 1 0 6 7, 6 May 9 10:01 /dev/loop6
brw-rw---- 1 0 6 7, 7 May 9 10:01 /dev/loop7
modprobe: ERROR: ../libkmod/libkmod.x:557 kmod_search_moddep() could not open moddep file '/lib/modules/4.4.6-1-pve/modules.dep.bin'
mount: mounting /dev/loop0 on /mnt failed: No such device
255
no cdrom found
LABEL proxmox-4.4
MENU LABEL Proxmox 4.4 Install
KERNEL images/proxmox/4.4/linux26
APPEND initrd=images/proxmox/4.4/initrd.img splash=verbose vga=791 video=vesafb:ywrap,mtrr ramdisk_size=16777216 rw
To me, its not worth the hassle. Simply install debian with pxe and then proxmox.
a710458c9217608a9de4c6b7d92089ce proxmox-ve_5.0-af4267bf-4.iso
1d3bdb24335c04615b40dba457a5ed6e initrd.iso.img
56b2e4f54dd0133c7e6d4d619b9f5f1e linux26
mkdir /tmp/docker /tmp/docker/iso
# put iso into iso folder
curl -sL https://raw.githubusercontent.com/morph027/pve-iso-2-pxe/master/pve-iso-2-pxe.sh -o /tmp/docker/pve-iso-2-pxe.sh
docker run --rm -it --privileged -v /tmp/docker:/build -w /build debian:stretch /bin/bash
apt-get update && apt-get -y install cpio
bash pve-iso-2-pxe.sh iso