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https://github.com/10maurycy10/tinyroot
How to make a very small linux bootable drive
https://github.com/10maurycy10/tinyroot
Last synced: 10 days ago
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How to make a very small linux bootable drive
- Host: GitHub
- URL: https://github.com/10maurycy10/tinyroot
- Owner: 10maurycy10
- Created: 2022-05-07T01:58:00.000Z (over 2 years ago)
- Default Branch: main
- Last Pushed: 2023-03-02T02:48:58.000Z (over 1 year ago)
- Last Synced: 2024-08-02T02:16:38.330Z (3 months ago)
- Size: 2.74 MB
- Stars: 95
- Watchers: 2
- Forks: 2
- Open Issues: 2
-
Metadata Files:
- Readme: README.md
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README
# Compiling musl toolchain
use musl-cross-make, If you use a 64 bit target, make sure to build your kernel with 64 bit support.
# Compile busybox
At the root of the busybox source tree run:
```sh
make allnoconfig
make menuconfig
```
I enabled the following set of utilities, but you can add less or more:
- **Settings -> Include busybox applet**
- **Settings -> Build static library**
- **Settings -> Use -static-libc**
- **Settings -> Command line editing**
- **Settings -> Tab completion**
- **Coreutils -> cat**
- **Coreutils -> echo**
- **Coreutils -> cp**
- **Coreutils -> ls**
- **Editors -> vi**
- **Linux System Utilities -> mount**
- **Shells -> ash**
- **Shells -> ash -> Echo Builtin**
To cross compile with musl, Set **Settings -> Cross compiler prefix** to ``/path/to/musl-cross-make/build/local/x68_64-linux-musl/output/bin/x86_64-linux-musl-`` and **Settings -> Path to sysroot** ``/path/to/musl-cross-make/build/local/x86_64-linux-musl/output``.
Finally, run ``make -j$(nproc)`` to compile busybox.
You can use ``readelf -a busybox`` to confirm that the binary is static linked
With my configuration (64 bit) the binary was 200K.
# Compile linux
``make tinyconfig`` is a good starting point for kernel configuration, but you will need to enable some things.
```
make tinyconfig
make menuconfig
```
- **General Setup -> Initial RAM filesystem and RAM disk (initramfs/initrd) support** = y
- **General Setup -> Initial RAM filesystem and RAM disk (initramfs/initrd) support -> Support initial ramdisk/ramfs compressed using gzip** = y
- **General Setup -> Configure standard kernel features (expert users) -> Enable support for printk** = y
- **Executable file formats -> Kernel support for ELF binaries** = y
- **Executable file formats -> Kernel support for scripts starting with #!** = y
- **Device Drivers -> Character devices -> Virtual terminal** = y
- **Device Drivers -> Character devices -> Support for console on virtual terminal** = y
- **Device Drivers -> Graphics support -> Support for Frame buffer Devices** = y
- **Device Drivers -> Graphics support -> Support for Frame buffer Devices -> Simple framebuffer support** = y
- **Device Drivers -> Graphics support -> Firmware Drivers -> Mark VGA/VBE/EFI FB as generic system framebuffer** = y
To build it just run
```
make -j$(nproc)
```
The resultant kernel on my system (64 bit) was 688K
# setup rootfs
First create required structure and copy busybox.
```sh
mkdir root
mkdir root/{bin,proc,dev,sys}
cp /path/to/busybox/binary root/bin
ln -sr root/bin/sh root/bin/busybox
```
Then create ``root/init``, A basic one follows (remember to ``chmod a+x root/init``).
```sh
#!/bin/sh
# Put anything you want to run on startup here
/bin/sh
```
Finally you can run this one liner to create an initramfs:
```
find root -printf "%P\0" | cpio --null -o -H newc -D root | gzip > initramfs.cpio.gz
```
# Create image
You will need SYSLINUX for both of these, prebuilt is fine. https://mirrors.edge.kernel.org/pub/linux/utils/boot/syslinux/
## CD rom image
First create a direcory for the iso fs:
```
mkdir isoroot
```
Then copy the kernel and initramfs:
```
mkdir isoroot/boot
cp initramfs.cpio.gz isoroot/boot/ramfs.img
cp path/to/linux/kernel isoroot/boot/vmlinuz
```
The ISOLINUX/SYSLINUX files also have to be copied:
```
cp path/to/syslinux/bios/core/isolinux.bin isoroot
cp path/to/syslinux/bios/com32/elflink/ldlinux/ldlinux.c32 isoroot
```
ISOLINUX needs to be configured, create the file ``isoroot/isolinux.cfg``, with the following:
```
default 1
label 1
kernel boot/vmlinuz
initrd boot/ramfs.img
append quiet
```
finally you can run:
```
mkisofs -no-pad -o tinyroot.iso -b isolinux.bin -no-emul-boot -boot-load-size 4 -boot-info-table isoroot
```
The iso should be at ``tinyroot.iso``
You can test it with QEMU: ``qemu-system-x68_64 -cdrom tinyroot.iso``