iPXE script for deploying Ubuntu 20.04 autoinstall nocloud-net method

ubuntu2004.ipxe

#!ipxe
# ubuntu focal 20.04

# $seedfrom used to find the user-data and meta-data files by nocloud-net provider for cloud-init.
# the trailing slash is important, the cloud-init sticks 'meta-data' or 'user-data' right after it, without prepending a forward slash.
set seedfrom http://repo/files/ubuntu2004/

# $base url is where the vmlinuz and initrd live.
# they were fished out from the live-server iso file. the iso file is also in this directory.
set base http://repo/files/ubuntu2004

kernel ${base}/vmlinuz initrd=initrd autoinstall url=${base}/ubuntu-20.04-live-server-amd64.iso net.ifnames=0 biosdevname=0 ip=dhcp ds=nocloud-net;s=${seedfrom}
initrd ${base}/initrd
boot

I was not able to get the Ubuntu installer working with less than 5 GiB of memory on my VM.

At about 4 GiB of memory, things startup, but I noticed that it OMM kills the could-init service and then it doesn't grab the user-data file. At about 5 GiB everything works.

I think it may be possible to install without downloading the ISO but I haven't explored it. All the Ubuntu docs I've seen so far use url or cdrom in their boot params.

I tried to find where the heck the url and other details are picked up from the boot command line.

I eventually found this, that may help find a way to reduce the memory requirements.

I found snippet from the file ./scripts/casper inside of the initrd file.

parse_cmdline() {
    for x in $(cat /proc/cmdline); do
        case $x in
            showmounts|show-cow)
                export SHOWMOUNTS='Yes' ;;
            persistent)
                export PERSISTENT="Yes" ;;
            nopersistent)
                export PERSISTENT="" NOPERSISTENT="Yes" ;;
            persistent-path=*)
                export PERSISTENT_PATH="${x#persistent-path=}" ;;
            ip=*)
                STATICIP=${x#ip=}
                if [ "${STATICIP}" = "" ]; then
                    STATICIP="frommedia"
                fi
                export STATICIP ;;
            url=*.iso)
                export NETBOOT=url
                export URL="${x#url=}" ;;
            uuid=*)
                UUID=${x#uuid=} ;;
            ignore_uuid)
                UUID="" ;;
            live-media=*)
                LIVEMEDIA="${x#live-media=}"
                export LIVEMEDIA
                echo "export LIVEMEDIA=\"$LIVEMEDIA\"" >> /etc/casper.conf ;;
            live-media-path=*)
                LIVE_MEDIA_PATH="${x#live-media-path=}"
                export LIVE_MEDIA_PATH
                echo "export LIVE_MEDIA_PATH=\"$LIVE_MEDIA_PATH\"" >> /etc/casper.conf ;;
            layerfs-path=*)
                export LAYERFS_PATH="${x#layerfs-path=}"
                echo "export LAYERFS_PATH=\"$LAYERFS_PATH\"" >> /etc/casper.conf ;;
            nfsroot=*)
                export NFSROOT="${x#nfsroot=}" ;;
            netboot=*)
                export NETBOOT="${x#netboot=}" ;;
            toram)
                export TORAM="Yes" ;;
            todisk=*)
                export TODISK="${x#todisk=}" ;;
            hostname=*)
                export CMD_HOST="${x#hostname=}" ;;
            userfullname=*)
                export CMD_USERFULLNAME="${x#userfullname=}" ;;
            username=*)
                export CMD_USERNAME="${x#username=}" ;;
        esac
    done
}

Peeking inside of the initrd file

# Copy the initrd from the ISO mount to a writeable area
╭─root@console ~/investigate
╰─# cp /root/vmware-builder/installers/ubuntu/focal/files/iso_contents/casper/initrd .

# Do a binwalk on the initrd to find the offset
╭─root@console ~/investigate
╰─# binwalk initrd > initrd.binlist

# Find the LZ4 section
╭─root@console ~/investigate
╰─# head -n20 initrd.binlist

DECIMAL       HEXADECIMAL     DESCRIPTION
--------------------------------------------------------------------------------
0             0x0             ASCII cpio archive (SVR4 with no CRC), file name: ".", file name length: "0x00000002", file size: "0x00000000"
112           0x70            ASCII cpio archive (SVR4 with no CRC), file name: "kernel", file name length: "0x00000007", file size: "0x00000000"
232           0xE8            ASCII cpio archive (SVR4 with no CRC), file name: "kernel/x86", file name length: "0x0000000B", file size: "0x00000000"
356           0x164           ASCII cpio archive (SVR4 with no CRC), file name: "kernel/x86/microcode", file name length: "0x00000015", file size: "0x00000000"
488           0x1E8           ASCII cpio archive (SVR4 with no CRC), file name: "kernel/x86/microcode/AuthenticAMD.bin", file name length: "0x00000026", file size: "0x00007752"
31184         0x79D0          ASCII cpio archive (SVR4 with no CRC), file name: "TRAILER!!!", file name length: "0x0000000B", file size: "0x00000000"
31744         0x7C00          ASCII cpio archive (SVR4 with no CRC), file name: "kernel", file name length: "0x00000007", file size: "0x00000000"
31864         0x7C78          ASCII cpio archive (SVR4 with no CRC), file name: "kernel/x86", file name length: "0x0000000B", file size: "0x00000000"
31988         0x7CF4          ASCII cpio archive (SVR4 with no CRC), file name: "kernel/x86/microcode", file name length: "0x00000015", file size: "0x00000000"
32120         0x7D78          ASCII cpio archive (SVR4 with no CRC), file name: "kernel/x86/microcode/.enuineIntel.align.0123456789abc", file name length: "0x00000036", file size: "0x00000000"
32284         0x7E1C          ASCII cpio archive (SVR4 with no CRC), file name: "kernel/x86/microcode/GenuineIntel.bin", file name length: "0x00000026", file size: "0x004C8000"
5045936       0x4CFEB0        ASCII cpio archive (SVR4 with no CRC), file name: "TRAILER!!!", file name length: "0x0000000B", file size: "0x00000000"
5046272       0x4D0000        LZ4 compressed data, legacy
5611686       0x55A0A6        SHA256 hash constants, little endian
5694260       0x56E334        LUKS_MAGIC
5805252       0x5894C4        mcrypt 2.2 encrypted data, algorithm: RC2, mode: CBC, keymode: 8bit
5806942       0x589B5E        xz compressed data

# Get the lz4 archive start and unlz4 it
╭─root@console ~/investigate
╰─# dd if=initrd bs=5046272 skip=1 | unlz4 - initrd.cpio
16+1 records in
16+1 records out
81402340 bytes (81 MB, 78 MiB) copied, 0.573341 s, 142 MB/s
stdin                : decoded 233871872 bytes

# Exctract the cpio archive
╭─root@console ~/investigate
╰─# cpio -d -D initrd-fs -i < initrd.cpio
cpio: fs: Cannot change ownership to uid 0, gid 0: No such file or directory
cpio: fs: Cannot change mode to rwxr-xr-x: No such file or directory
456781 blocks

# Take a look at the casper file
╭─root@console ~/investigate
╰─# find initrd-fs -type f -name "casper"                                                                                                                                                                       
initrd-fs/scripts/casper

I found this which better describes the options. 🤣
https://manpages.ubuntu.com/manpages/focal/man7/casper.7.html.

Oh man @tlhakhan, thanks a lot for your contribution!
Now I feel bad for not responding to your replies soon enough (I was working on something else). I'm very grateful for your work - you are truly the most helpful guy I've seen on open-source communities.

After reading through the Ubuntu manpage for casper, I feel like I can't use boot option url on low-RAM machines, because that parameter would download the iso to memory and mount it as live root. We can't do that because the iso is larger than RAM size.

I guess that left us with netboot=nfs? IMO NFS boot is a pain to setup because of security concerns like allowed IPs and stuff. Not only that, it seems like I'll have to bind mount (which is read-only IIRC) the iso image to NFS share mounts, and because this will be mounted read-only, I'm not sure if it can be used as live root.

Or did I miss something?

Anyway, I recently learned qemu and is now using qemu to debug the boot options. This is much better than my previous method of spinning a new, real VPS to test iPXE/autoinstall lol.

I tried using the kernel and initrd from this repo with your boot parameters, and it seems to work (boot without complaining No space left on device on qemu. But this boot does not seem to do autoinstall. Very strange indeed lol.

@artworkk, ha ☺️! yup, no problem. Doing this in my fun-free time, definitely enjoy it and if its questions I can quickly answer or figure out, I don't mind.

I tried using the kernel and initrd from this repo with your boot parameters, and it seems to work (boot without complaining No space left on device on qemu. But this boot does not seem to do autoinstall. Very strange indeed lol.

I tried that too and ended up at a dead end, I think that is for the preseed version only. I also saw that they totally removed the legacy-images folder in the latest jammy version.

If Ubuntu's server images are too big, maybe their other versions could work? I haven't tried this on a x86 VM box, but maybe their Ubuntu Core? https://ubuntu.com/core.

@tlhakhan I just did some digging and it seemed the legacy image used Kickstart for cloud-init, while the newer image uses Subiquity. This explains why the legacy image only processed preseed.

As for Ubuntu Core, thanks! I'll try that out. I have always avoided Ubuntu so I don't know a thing about their available flavors lol. The thing I'm doing here is for my work, hence why I'm working with Ubuntu and iPXE for the first time. I'll try Ubuntu Core and report back whether it worked or not.

PS. Actually my work uses bare-metal with 128GB RAM, but I want to make the flow works with all my personal VPSes (which are all 1GB) too.

@artworkk, good luck 🙌 🖖! When I have some free time, I will also try out the Ubuntu core as well, hopefully the installation is lighter and allows for easy iPXE scripting.

Hi Tenzin,
Thank you very for sharing. Would you happen to have a similar deployment solution for Ubuntu 18.04 Desktop LTS?
Thank you.

Ah my bad 😗, didn't see this earlier question. I think there was a time where GitHub wasn't sending any emails for replies in gists. Hopefully you have gotten to a solution. 🤞

Hi Tenzin,

Thank you for the follow-up. I was deploying 18.04 via netboot, but I still think the live cd is better. Do you have a similar solution for 18.04 Desktop? Your suggestion is much appreciated. Thank you.

@jamaya77, I haven't done any automated installs of Ubuntu desktops, only server versions. However, with the new auto-install method, I think it must be possible.

Quick googling, I found this repo, which looks like a starting point🤞: https://github.com/canonical/autoinstall-desktop