175 lines
6.4 KiB
Markdown
175 lines
6.4 KiB
Markdown
# Arch Linux s390x Port with Systemd
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This repository contains a **complete, working** s390x Arch Linux system with **systemd support** and full root filesystem that boots successfully on IBM mainframes and QEMU emulation.
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## Quick Start
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```bash
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# Build everything
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make all
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# Test initramfs-only system
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make test
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# Test with root filesystem
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make test-rootfs
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# Test with systemd as init
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make test-systemd
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```
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## What's Working
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- **Arch Linux Kernel**: Linux 6.6.10 with Arch patches and CONFIG_UNIX/CONFIG_KMOD support (5.8MB)
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- **Initramfs**: Complete 5.9MB initramfs with s390x busybox
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- **Boot Process**: Successful boot to root filesystem with busybox shell
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- **Root Filesystem**: **COMPLETE!** 150MB ext4 root filesystem with Arch Linux identification
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- **Systemd**: **WORKING!** 42MB minimal systemd with mount/udevadm utilities - boots to "Welcome to Arch Linux!"
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- **Modern Init**: Full systemd boot reaching Multi-User and Graphical targets
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- **QEMU Testing**: Fully functional in s390x emulation
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- **Ready for Hardware**: IPL configuration for real mainframes
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## Build Status
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### Core System Components
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| Component | Status | Details |
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|-----------|--------|---------|
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| Kernel | ✅ Working | 5.8MB bootable s390x kernel with CONFIG_UNIX/CONFIG_KMOD (6.6.10) |
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| Initramfs | ✅ Working | 5.9MB with native s390x binaries |
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| Boot Process | ✅ Working | IPL → kernel → initramfs → root filesystem → systemd |
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| Root Filesystem | ✅ **COMPLETE** | 150MB ext4 with working busybox switch_root |
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| Systemd | ✅ **WORKING** | 42MB minimal systemd with mount/udevadm - reaches graphical target |
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| mkinitcpio | ✅ Fixed | Adapted for s390x architecture |
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### Userspace Components
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| Component | Status | Details |
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|-----------|--------|---------|
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| Init System | ✅ **COMPLETE** | Busybox in initramfs → switch_root → systemd |
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| Shell | 🟨 Minimal | Busybox sh (not bash) |
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| Core Utilities | ✅ **Enhanced** | Busybox applets + mount/udevadm/kmod utilities |
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| Package Manager | ❌ TODO | Pacman needs porting |
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| Systemd Runtime | ✅ **WORKING** | Full systemd boot with journal, udev, and basic services |
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| Bash | ❌ TODO | Needs s390x build |
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| GNU Coreutils | ❌ TODO | Replace busybox applets |
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### Legend
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- ✅ **Complete** - Fully working
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- 🟨 **Minimal** - Working but minimal implementation
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- ❌ **TODO** - Not yet implemented
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## Build System
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Uses **Fedora containers with Podman** for cross-compilation:
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```bash
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# Container image:
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s390x-archlinux-dev # All-in-one development container
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```
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### Build Targets:
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- `make all` - Build complete system (kernel + initramfs + systemd)
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- `make kernel` - Cross-compile Arch Linux kernel for s390x
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- `make initramfs` - Generate initramfs with mkinitcpio
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- `make systemd` - Build systemd natively on z/VM (requires .env configuration)
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- `make test` - Test initramfs-only system with QEMU
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- `make test-rootfs` - Test with root filesystem switching
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- `make test-systemd` - Test with systemd as init (full modern boot)
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- `make clean` - Clean build artifacts
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### Key Scripts:
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- `scripts/build-arch-kernel.sh` - Cross-compile Arch Linux kernel
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- `scripts/build-initramfs-final.sh` - Generate initramfs
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- `scripts/build-systemd-zvm.sh` - Build systemd on z/VM
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- `scripts/deploy-and-build-systemd-zvm.sh` - Orchestrate systemd build
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- `scripts/run-qemu-initramfs-only.sh` - Test initramfs-only system
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- `scripts/test-qemu-rootfs.sh` - Test with root filesystem
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- `scripts/test-qemu-systemd.sh` - Test with systemd as init
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- `scripts/build-busybox-zvm.sh` - Build static busybox on z/VM
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## z/VM Configuration
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For building systemd and busybox natively on s390x hardware, you'll need access to an IBM z/VM system:
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1. **Copy the example configuration**:
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```bash
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cp .env.example .env
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```
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2. **Edit `.env` with your z/VM details**:
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```bash
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ZVM_HOST=your.zvm.host
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ZVM_USER=your_username
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ZVM_SSH_KEY="-----BEGIN OPENSSH PRIVATE KEY-----
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... your SSH private key content ...
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-----END OPENSSH PRIVATE KEY-----"
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```
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3. **Build systemd**:
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```bash
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make systemd
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```
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The scripts will automatically load the `.env` configuration when needed.
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## Testing
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```bash
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# Install QEMU s390x
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sudo pacman -S qemu-system-s390x # Arch Linux
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# or
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sudo apt install qemu-system-s390x # Ubuntu/Debian
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# Test initramfs-only system
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make test
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# Test root filesystem switching
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make test-rootfs
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# Test full systemd boot (requires systemd build)
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make test-systemd
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```
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**Expected Results**:
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- `make test` - System boots to emergency shell in initramfs-only mode (press Ctrl-A X to exit)
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- `make test-rootfs` - Boots completely to root filesystem with busybox shell
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- `make test-systemd` - Full systemd boot reaching "Welcome to Arch Linux!" and graphical target
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[](https://asciinema.org/a/u49jp0Bg7YoGtlGyTh6C9RJ7P)
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## Output Files
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After building:
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- `boot/vmlinuz-linux` - Ready-to-use s390x kernel
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- `boot/initramfs-linux.img` - Working initramfs
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- `boot/rootfs-s390x.img` - Root filesystem image (created by test-rootfs)
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- `boot/generic.ins` - IPL configuration for real hardware
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- `boot/arch.prm` - Kernel parameters
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- `boot/busybox-s390x-static` - Static busybox binary built on z/VM (used by mkinitcpio)
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- `output/systemd-root/` - Complete systemd installation for root filesystem
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## Technical Details
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### s390x Adaptations:
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- Big-endian architecture support
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- IPL boot process (not BIOS/UEFI)
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- Channel I/O subsystem drivers
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- mkinitcpio modified for cross-architecture builds
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### Key Fixes Applied:
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1. **mkinitcpio adaptation** - Fixed `add_binary` vs `add_file` issue for init scripts
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2. **Static busybox in initramfs** - Built natively on z/VM for early boot operations
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3. **Architecture compatibility** - Fixed base hook to exclude x86_64 binaries
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4. **switch_root support** - Enables transition from initramfs to systemd on root filesystem
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5. **Kernel configuration** - Added CONFIG_UNIX and CONFIG_KMOD for systemd support
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## System Boot Sequence
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The complete boot process follows this sequence:
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1. **IPL (Initial Program Load)** - IBM mainframe boot process
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2. **Kernel loads** - Linux 6.6.10 s390x kernel with Arch patches
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3. **Initramfs unpacked** - Contains busybox and init script
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4. **Early boot** - Busybox provides utilities for mounting and setup
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5. **Root filesystem mounted** - `/dev/vda` mounted to `/new_root`
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6. **switch_root** - Busybox `switch_root` transitions to real root filesystem
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7. **Systemd starts** - `/usr/lib/systemd/systemd` becomes PID 1
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