Netboot/syslinux.md

Network booting

without GRUB

https://www.youtube.com/watch?v=U3RC20ANomk

apt install dnsmasq

/etc/dnsmasq.conf

interface=<your interface>,lo
bind-interfaces
dhcp-range=<your interface>,192.168.11.101,192.168.11.200
dhcp-boot=pxelinux.0
dhcp-match=set:efi-x86_64,option:client-arch,7
dhcp-boot=tag:efi-x86_64,syslinux.efi
enable-tftp
tftp-root=/srv/tftp

mkdir -p /srv/tftp

apt install syslinux-common syslinux-efi

cd /usr/lib/syslinux/modules/efi64

cp ldlinux.e64 libutil.c32 menu.c32 /srv/tftp

cp /usr/lib/SYSLINUX.EFI/efi64/syslinux.efi /srv/tftp

mkdir /srv/tftp/pxelinux.cfg

/srv/tftp/pxelinux.cfg/default

UI menu.c32
LABEL FIKS OS
        MENU LABEL FIKS
        KERNEL vmlinuz
        APPEND initrd=initrd.img debug components boot=nfs ip=dhcp root=/dev/nfs nfsroot=192.168.11.11:/srv/nfs/live/ ro
        TEXT HELP
                Lmao Yeet!
        ENDTEXT

systemctl restart dnsmasq.service

apt install nfs-kernel-server

mkdir -p /srv/nfs/live

/etc/exports

/srv/nfs        *(ro,sync,no_root_squash,no_subtree_check)

exportfs -a

systemctl restart nfs-kernel-server

Client system

Image itself

Disable systemd-resolved (requires writable /etc/resolve.conf):
systemctl mask systemd-resolved.service systemctl mask systemd-hostnamed.service systemctl mask systemd-timesyncd.service systemctl mask systemd-update-utmp.service systemctl mask systemd-update-utmp-runlevel.service

systemctl mask ModemManager.service systemctl mask man-db.service systemctl mask logrotate.service systemctl mask grub-initrd-fallback.service systemctl mask grub-common.service systemctl mask snapd

systemctl enable tmp.mount

Initrd

mkdir initrd-workdir && cd initrd-workdir

unmkinitramfs /boot/initrd.img-$(uname -r) .

cd main

/etc/initramfs-tools/modules

e1000
igb
r8169
nfs
nfsv3
nfsv4
sunrpc
lockd
fscache
overlay

https://www.onlogic.com/blog/how-to-build-a-read-only-linux-system/

/etc/initramfs-tools/hooks/ro_root

#!/bin/sh

PREREQ=''

prereqs() {
  echo "$PREREQ"
}

case $1 in
prereqs)
  prereqs
  exit 0
  ;;
esac

. /usr/share/initramfs-tools/hook-functions
manual_add_modules aufs
manual_add_modules tmpfs
copy_exec /bin/chmod /bin

/etc/initramfs-tools/scripts/init-bottom/ro_root

#!/bin/sh

PREREQ=''

prereqs() {
  echo "$PREREQ"
}

case $1 in
prereqs)
  prereqs
  exit 0
  ;;
esac

ro_mount_point="${rootmnt%/}.ro"
rw_mount_point="${rootmnt%/}.rw"

# Create mount points for the read-only and read/write layers:
mkdir "${ro_mount_point}" "${rw_mount_point}"

# Move the already-mounted root filesystem to the ro mount point:
mount --move "${rootmnt}" "${ro_mount_point}"

# Mount the read/write filesystem:
mount -t tmpfs root.rw "${rw_mount_point}"

# Mount the union:
mount -t aufs -o "dirs=${rw_mount_point}=rw:${ro_mount_point}=ro" root.union "${rootmnt}"

# Correct the permissions of /:
chmod 755 "${rootmnt}"

# Make sure the individual ro and rw mounts are accessible from within the root
# once the union is assumed as /.  This makes it possible to access the
# component filesystems individually.
mkdir "${rootmnt}/ro" "${rootmnt}/rw"
mount --bind "${ro_mount_point}" "${rootmnt}/ro"
mount --bind "${rw_mount_point}" "${rootmnt}/rw"

update-initramfs -u

scp initrd.img server@192.168.11.11:/srv/nfs/

mksquashfs / /opt/fiks-image.squashfs -e /proc /sys /dev /tmp /run /mnt /media /var/cache /var/tmp /opt

Back on the server

mount -o loop /srv/nfs/fiks-image.squashfs /srv/nfs/tmp/

cp -a /srv/nfs/tmp/* /srv/nfs/live/

mkdir -p live/{dev,proc,run,sys,tmp}

mkdir -p live/var/tmp

etc/fstab

192.168.11.11:/srv/nfs/live     /       nfs     nolock,ro       0       0
tmpfs   /var/tmp        tmpfs   defaults,nosuid,nodev,mode=1777,size=64M        0       1