From 9097e37a6615f7cd909c55103c0d5ebb2d01b2ea Mon Sep 17 00:00:00 2001
From: D4VID <d4vid@d4vid.xyz>
Date: Mon, 23 Dec 2024 17:34:09 +0000
Subject: [PATCH] Initrd scripts for unionfs

---
 syslinux.md | 107 ++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 92 insertions(+), 15 deletions(-)

diff --git a/syslinux.md b/syslinux.md
index 2f55bd7..6cd25b6 100644
--- a/syslinux.md
+++ b/syslinux.md
@@ -66,6 +66,26 @@ LABEL FIKS OS
 
 ## 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) .`
@@ -87,28 +107,85 @@ fscache
 overlay
 ```
 
-`find . | cpio -H newc -o | gzip -9 > /srv/tftp/initrd.img`
 
-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`
+https://www.onlogic.com/blog/how-to-build-a-read-only-linux-system/
 
-`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`
+`/etc/initramfs-tools/hooks/ro_root`
 
-`systemctl enable tmp.mount`
+```bash
+#!/bin/sh
 
-`mksquashfs / /opt/fiks-image.squashfs -e /proc /sys /dev /tmp /run /mnt /media /var/cache /var/tmp /opt`
+PREREQ=''
+
+prereqs() {
+  echo "$PREREQ"
+}
+
+case $1 in
+prereqs)
+  prereqs
+  exit 0
+  ;;
+esac
+
+. /usr/share/initramfs-tools/hook-functions
+manual_add_modules aufs
+manual_add_modules tmpfs
+copy_exec /bin/chmod /bin
+```
+
+
+`/etc/initramfs-tools/scripts/init-bottom/ro_root`
+
+```bash
+#!/bin/sh
+
+PREREQ=''
+
+prereqs() {
+  echo "$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