dump notes wip exploration

README.md

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+# Minimal boot linux coreutils bash glibc
+
+![qemu showing boot into minimal linux](./img/boot-qemu-example.png)
+
+Goal is to have mimimal but realistic node with network capabilities build in (`ip`) and bootstrapped (similar to [alpine's netbot](https://boot.alpinelinux.org/) ([example](https://github.com/KarmaComputing/server-bootstrap/blob/494089caa2c88bbf37a739aa96561231d5847be5/.github/workflows/build-alpine-netboot-image-zfs.yml#L1))). [Clearlinux](https://github.com/clearlinux/distribution) is interesting. This is using glibc over musl (which alpine uses).
+
+
+## The process in a nutshell
+
+- Given a built linux kernel (e.g. `vmlinuz-lts`)
+- Clone and build all the various packages you want
+- Write an `init` script
+- Build all the binaries + `init` script into a initramfs
+- Run/boot with qemu
+
+
+
+TODO: add [iproute2](https://github.com/iproute2/iproute2) for minimal routing.
+
+## Things you need to build
+
+- git clone & build GNU `bash` is in it's own repo
+- git clone & build coreutils (`ls` , `date` , `touch` etc(`mount` is not in here- who knew)
+- To get `mount` you need to build util-linux https://en.wikipedia.org/wiki/Util-linux
+- is `ls` failing, did you forget to include `/usr/lib/x86_64-linux-gnu/libcap.so.2`? See `mkchroot.sh` helper from https://landley.net/writing/rootfs-programming.html
+
+- Don't forget to `mount` linux virtual filesystems (oh wait, did you forget to build util-linux into your init?
+
+Example built rootfs:
+```
+ls -lh rootfs.cpio.gz 
+-rw-rw-r-- 1 chris chris 16M Dec  8 23:40 rootfs.cpio.gz
+```
+
+# What does this repo not include (yet)
+
+- Full clone/compile instructions
+- Automated ci
+
+### How do I build statically coreutils, do I even need to?
+
+See https://lists.gnu.org/archive/html/coreutils/2019-04/msg00001.html
+
+## `ls` , `cat` and `date` etc won't run without libc!
+
+git clone https://sourceware.org/git/glibc.git
+
+# Reading
+See also
+
+https://wiki.gentoo.org/wiki/Custom_Initramfs
+https://unix.stackexchange.com/a/305406
+https://landley.net/writing/rootfs-howto.html
+https://landley.net/writing/rootfs-programming.html

build-all.sh

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+#!/bin/bash
+
+set -exu
+
+./create-init.sh
+./build-rootfs.sh

build-coreutils.sh

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+#!/bin/bash
+
+set -x
+
+INITAL_WORKING_DIR=$PWD
+
+cd coreutils
+git checkout v9.5
+./bootstrap
+./configure LDFLAGS="-static"
+make 
+find src/ -executable -maxdepth 1
+
+
+cd $INITAL_WORKING_DIR

build-libc.sh

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+#!/bin/bash
+
+set -xu
+
+SCRATCH_SPACE_DIR=$1
+
+INITAL_WORKING_DIR=$PWD
+
+git clone https://sourceware.org/git/glibc.git
+cd glibc
+git checkout release/2.40/master
+mkdir glibc-build
+cd glibc-build
+mkdir out
+../configure --prefix=$(pwd)/out
+make
+make install
+
+# Copy built libc objects/files over into scratch space
+cp -r -n ./out/* $SCRATCH_SPACE_DIR
+
+cd $INITAL_WORKING_DIR

build-rootfs.sh

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+#!/bin/bash
+
+set -eux
+
+cd scratch-space
+
+find . | cpio -o -H newc | gzip > ../rootfs.cpio.gz
+
+cd -

create-init.sh

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+#!/bin/bash
+
+set -eux
+
+echo "#!/usr/bin/bash" > scratch-space/init
+echo "exec /usr/bin/bash" >> scratch-space/init
+chmod +x scratch-space/init
+

mkchroot.sh

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+#!/bin/sh
+
+# Credit:
+# https://landley.net/writing/rootfs-programming.html
+
+function mkchroot
+{
+  [ $# -lt 2 ] && return
+
+  dest=$1
+  shift
+  for i in "$@"
+  do
+    # Get an absolute path for the file
+    [ "${i:0:1}" == "/" ] || i=$(which $i)
+    # Skip files that already exist at target.
+    [ -f "$dest/$i" ] && continue
+    if [ -e "$i" ]
+    then
+      # Create destination path
+      d=`echo "$i" | grep -o '.*/'` &&
+      mkdir -p "$dest/$d" &&
+      # Copy file
+      cat "$i" > "$dest/$i" &&
+      chmod +x "$dest/$i"
+    else
+      echo "Not found: $i"
+    fi
+    # Recursively copy shared libraries' shared libraries.
+    mkchroot "$dest" $(ldd "$i" | egrep -o '/.* ')
+  done
+}
+
+mkchroot "$@"

run-qemu.sh

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+#!/bin/bash
+
+set -eux
+
+qemu-system-x86_64 -kernel vmlinuz-lts -initrd rootfs.cpio.gz --append "init=/usr/bin/init"