diff options
Diffstat (limited to 'experiments/03_20251130_leaving_initramfs')
| -rw-r--r-- | experiments/03_20251130_leaving_initramfs/Makefile | 52 | ||||
| -rw-r--r-- | experiments/03_20251130_leaving_initramfs/README | 32 | ||||
| -rw-r--r-- | experiments/03_20251130_leaving_initramfs/init | 23 | ||||
| -rwxr-xr-x | experiments/03_20251130_leaving_initramfs/run_qemu.sh | 3 |
4 files changed, 110 insertions, 0 deletions
diff --git a/experiments/03_20251130_leaving_initramfs/Makefile b/experiments/03_20251130_leaving_initramfs/Makefile new file mode 100644 index 0000000..c55cc00 --- /dev/null +++ b/experiments/03_20251130_leaving_initramfs/Makefile @@ -0,0 +1,52 @@ +special_dirs := proc sys +_special_dirs := $(patsubst %,initramfs/%,$(special_dirs)) + +pkgs := $(wildcard pkgs/*.deb) +pkgs_dirs := $(patsubst %.deb,%,$(pkgs)) +pkgs_content := $(patsubst %.deb,%/data.tar.xz,$(pkgs)) +pkgs_unpacked := $(patsubst pkgs/%/data.tar.xz,initramfs/%.unpack,$(pkgs_content)) + +all : initrd.cpio.gz + +initrd.cpio.gz : clean_initramfs initramfs unpack $(_special_dirs) links initramfs/init + cd initramfs && find . | cpio -o -H newc | gzip > ../initrd.cpio.gz + +initramfs : + mkdir initramfs + +initramfs/init : init + cp $< $@ + chmod 0755 $@ + +unpack : $(pkgs_unpacked) + +initramfs/%.unpack : pkgs/%/data.tar.xz initramfs + tar xf $< -C initramfs + +$(_special_dirs) : + mkdir -p $@ + +%/data.tar.xz : %.deb % + ar x $< --output "$(@D)" + +pkgs/% : pkgs/%.deb + mkdir $@ + +links : + ln -s usr/bin initramfs/bin + ln -s usr/sbin initramfs/sbin + ln -s usr/lib initramfs/lib + ln -s usr/lib64 initramfs/lib64 +# ln -s bin/sh initramfs/init + ln -s /proc/mounts initramfs/etc/mtab + +clean_initramfs : + rm -rf initramfs + +clean : clean_initramfs + rm -rf $(pkgs_dirs) + rm initrd.cpio.gz + +.PHONY : all clean clean_initramfs unpack links +.SECONDARY : +.DEFAULT : all diff --git a/experiments/03_20251130_leaving_initramfs/README b/experiments/03_20251130_leaving_initramfs/README new file mode 100644 index 0000000..a458ac2 --- /dev/null +++ b/experiments/03_20251130_leaving_initramfs/README @@ -0,0 +1,32 @@ +Goal: boot into initramfs and switch to real system +Status: success + +Added busybox to the mix, incredibely useful here + +init script will create new_root, mount tmpfs there and copy all the binaries +from initramfs to it so we have something to work with. It'll also mount /proc, +/dev and /sys. After that's done it'll switch root and run busybox shell as new +PID 1. + +there's a /new_root/cake file created by the script to confirm that we indeed +changed the root + +Useful resources: +- https://github.com/torvalds/linux/blob/v4.17/Documentation/filesystems/ramfs-rootfs-initramfs.txt +- https://www.kernel.org/doc/html/latest/admin-guide/initrd.html (obsolete but useful) + +Package list: +busybox-static_1.37.0-7_amd64.deb +dash_0.5.12-12_amd64.deb +gcc-14-base_14.2.0-19_amd64.deb +libblkid1_2.41.2-4_amd64.deb +libc6_2.41-12_amd64.deb +libc-bin_2.41-12_amd64.deb +libgcc-s1_14.2.0-19_amd64.deb +libmount1_2.41.2-4_amd64.deb +libpcre2-8-0_10.47-2_amd64.deb +libselinux1_3.9-4_amd64.deb +libsmartcols1_2.41.2-4_amd64.deb +mount_2.41.2-4_amd64.deb +util-linux_2.41.2-4_amd64.deb + diff --git a/experiments/03_20251130_leaving_initramfs/init b/experiments/03_20251130_leaving_initramfs/init new file mode 100644 index 0000000..27fcc61 --- /dev/null +++ b/experiments/03_20251130_leaving_initramfs/init @@ -0,0 +1,23 @@ +#!/bin/sh + +echo "creating new root..." +busybox mkdir /new_root +busybox mount -t tmpfs tmpfs /new_root + +busybox cp -r bin etc init lib lib64 sbin usr var /new_root + +busybox mkdir /new_root/dev +busybox mkdir /new_root/proc +busybox mkdir /new_root/sys + +echo "mounting special filesystems..." +busybox mount -t devtmpfs udev /new_root/dev +busybox mount -t proc proc /new_root/proc +busybox mount -t sysfs sysfs /new_root/sys + +echo "the cake is a lie!" > /new_root/cake + +echo "it's time to try 'switch_root' command and enter new_root" +echo "look for /cake to verify it worked" + +exec busybox switch_root /new_root /bin/busybox sh diff --git a/experiments/03_20251130_leaving_initramfs/run_qemu.sh b/experiments/03_20251130_leaving_initramfs/run_qemu.sh new file mode 100755 index 0000000..211b281 --- /dev/null +++ b/experiments/03_20251130_leaving_initramfs/run_qemu.sh @@ -0,0 +1,3 @@ +#!/usr/bin/env sh + +qemu-system-x86_64 -kernel /boot/vmlinuz-$(uname -r) -initrd initrd.cpio.gz -nographic -append "root=/dev/sda console=ttyS0" |