topimiettinen/make-images

Make RootImages

Make RootImages

Purpose

Build small images, suitable for use as

• RootImage= (or plain directory for RootDirectory=) for a systemd service
• cpio initrd image (experimental)
• system boot image (experimental)

The images should be as minimal as possible. It's however perfectly fine and expected to duplicate files between images. ldd tool is used to detect library dependencies.

Features

• build squashfs images (RootImage=, system boot image)
• correct SELinux labels generated according to host policy
• ACLs and extended attributes copied from host system
• Make based dependencies (maybe a misfeature)

Because of use of squashfs, the images are read-only and thus additional writable storage (such as /run, /var, /tmp etc.) is typicaly needed. In the RootImage= case, these are expected to be bind mounted.

Example service specification

Input file (specs/nftables.mk):

IMAGE:=nftables
STAMP:=$(call stampdir,$(IMAGE))
STAMPS+=$(STAMP)

$(STAMP): BINS=/usr/sbin/nft
$(STAMP): DIRS=/dev /proc /run /sys /tmp
$(STAMP): FILES=/etc/iproute2/rt_realms /etc/nftables.conf
$(STAMP): LINKS=/lib /lib64
$(STAMP): USE_DEV=y

Generated image:

squashfs-root
squashfs-root/dev
squashfs-root/etc
squashfs-root/etc/iproute2
squashfs-root/etc/iproute2/rt_realms
squashfs-root/etc/nftables.conf
squashfs-root/lib
squashfs-root/lib64
squashfs-root/proc
squashfs-root/run
squashfs-root/sys
squashfs-root/tmp
squashfs-root/usr
squashfs-root/usr/lib
squashfs-root/usr/lib/x86_64-linux-gnu
squashfs-root/usr/lib/x86_64-linux-gnu/libc.so.6
squashfs-root/usr/lib/x86_64-linux-gnu/libdl.so.2
squashfs-root/usr/lib/x86_64-linux-gnu/libgmp.so.10
squashfs-root/usr/lib/x86_64-linux-gnu/libjansson.so.4
squashfs-root/usr/lib/x86_64-linux-gnu/libmnl.so.0
squashfs-root/usr/lib/x86_64-linux-gnu/libnftables.so.1
squashfs-root/usr/lib/x86_64-linux-gnu/libnftnl.so.11
squashfs-root/usr/lib/x86_64-linux-gnu/libreadline.so.8
squashfs-root/usr/lib/x86_64-linux-gnu/libtinfo.so.6
squashfs-root/usr/lib/x86_64-linux-gnu/libxtables.so.12
squashfs-root/usr/lib64
squashfs-root/usr/lib64/ld-linux-x86-64.so.2
squashfs-root/usr/sbin
squashfs-root/usr/sbin/nft