POSIX9 - POSIX Compatibility Layer for Classic Mac OS

A shim library providing POSIX-compatible APIs on top of Classic Mac OS Toolbox calls, enabling modern Unix software to compile and run on vintage Macintosh computers.

Supported Platforms

| Platform | CPU | OS Version | Toolchain | Status | |----------|-----|------------|-----------|--------| | 68K Mac | 68020+ | System 7.0 - 8.1 | Retro68 (m68k) | Supported | | PowerPC Mac | G3/G4/G5 | Mac OS 7.5.2 - 9.2.2 | Retro68 (ppc) | Primary |

Features

• File I/O: open, read, write, close, lseek, stat, fstat, unlink
• Directories: opendir, readdir, closedir, mkdir, rmdir, chdir, getcwd
• Path Translation: Automatic POSIX ↔ Mac path conversion
• Sockets: BSD socket API via Open Transport (Mac OS 8.6+)
• Threads: POSIX threads via Thread Manager
• Signals: Emulated signal handling via Deferred Tasks
• Time: time, localtime, strftime, gettimeofday
• Environment: getenv, setenv, unsetenv

Architecture

┌─────────────────────────────────────┐
│  POSIX Application (SSH, etc.)      │
├─────────────────────────────────────┤
│  libposix9.a                        │
│  ├── posix9_file.c    (file I/O)   │
│  ├── posix9_dir.c     (directories)│
│  ├── posix9_path.c    (path xlat)  │
│  ├── posix9_thread.c  (pthreads)   │
│  ├── posix9_signal.c  (signals)    │
│  ├── posix9_socket.c  (networking) │
│  └── posix9_misc.c    (utilities)  │
├─────────────────────────────────────┤
│  Mac OS Toolbox                     │
│  ├── File Manager (FSSpec/HFS)     │
│  ├── Open Transport (TCP/IP)       │
│  ├── Thread Manager                │
│  └── Time Manager                  │
└─────────────────────────────────────┘

Path Translation

POSIX9 automatically converts between POSIX and Mac paths:

| POSIX Path | Mac Path | |------------|----------| | / | Volume root (default volume) | | /Volumes/Macintosh HD/Users/scott | Macintosh HD:Users:scott | | ./foo/bar | :foo:bar | | ../parent | ::parent |

Building with Retro68

Prerequisites

1. Retro68 Cross-Compiler: https://github.com/autc04/Retro68

# Clone Retro68
git clone https://github.com/autc04/Retro68.git
cd Retro68

# Build for both 68K and PowerPC
mkdir build && cd build
../build-toolchain.bash --ppc-only   # PowerPC only (faster)
# OR
../build-toolchain.bash               # Full build (68K + PPC)

Building POSIX9

PowerPC Build (Mac OS 7.5.2 - 9.2.2)

cd posix9
./build-ppc.sh

This creates build-ppc/libposix9.a (~50KB) with the following modules:

• posix9_dir.o - Directory operations
• posix9_file.o - File I/O
• posix9_path.o - Path translation
• posix9_signal.o - Signal emulation
• posix9_thread.o - POSIX threads

68K Build (System 7.0 - 8.1)

cd posix9
./build-68k.sh

Building Your Application

# Set environment variables
export RETRO68_PREFIX="$HOME/Retro68/build/toolchain"
export POSIX9_LIB="/path/to/posix9/build-ppc/libposix9.a"
export POSIX9_INC="/path/to/posix9/include"

# Compile (PowerPC)
$RETRO68_PREFIX/bin/powerpc-apple-macos-gcc \
    -O2 \
    -I"$POSIX9_INC" \
    -I"$POSIX9_INC/mac_stubs" \
    -c myapp.c -o myapp.o

# Link
$RETRO68_PREFIX/bin/powerpc-apple-macos-gcc \
    myapp.o "$POSIX9_LIB" -o myapp.xcoff

# Convert to PEF (Mac executable)
$RETRO68_PREFIX/bin/MakePEF myapp.xcoff -o myapp.pef

API Reference

File I/O

#include "posix9.h"

int fd = open("/path/to/file", O_RDONLY);
char buf[1024];
ssize_t n = read(fd, buf, sizeof(buf));
close(fd);

// Create file
fd = open("/new/file.txt", O_WRONLY | O_CREAT | O_TRUNC, 0644);
write(fd, "Hello Mac OS 9!
", 16);
close(fd);

Directories

DIR *dir = opendir("/");
struct dirent *ent;
while ((ent = readdir(dir)) != NULL) {
    printf("%s
", ent->d_name);
}
closedir(dir);

mkdir("/new/directory", 0755);
chdir("/some/path");
getcwd(buf, sizeof(buf));

Path Translation

char mac_path[256];
posix9_path_to_mac("/Volumes/Macintosh HD/file.txt", mac_path, sizeof(mac_path));
// Result: "Macintosh HD:file.txt"

char posix_path[256];
posix9_path_from_mac("Macintosh HD:Users:scott", posix_path, sizeof(posix_path));
// Result: "/Volumes/Macintosh HD/Users/scott"

Sockets (Mac OS 8.6+ with Open Transport)

int sock = socket(AF_INET, SOCK_STREAM, 0);

struct sockaddr_in addr;
addr.sin_family = AF_INET;
addr.sin_port = htons(22);
addr.sin_addr.s_addr = inet_addr("192.168.1.1");

connect(sock, (struct sockaddr*)&addr, sizeof(addr));
send(sock, "Hello
", 6, 0);
close(sock);

Threads

#include "posix9.h"

void *thread_func(void *arg) {
    // Thread code
    return NULL;
}

pthread_t tid;
pthread_create(&tid, NULL, thread_func, NULL);
pthread_join(tid, NULL);

Limitations

No Process Model

Mac OS 9 has no true process model. These functions are stubbed:

• fork() - Returns -1 with ENOSYS
• exec*() - Launches separate app (doesn't replace current process)
• getpid() - Always returns 1

Networking

• Sockets require Open Transport (Mac OS 8.6+)
• System 7 has no TCP/IP stack by default
• MacTCP is not supported

Signals

Signals are emulated via polling. Some behaviors differ from Unix:

• No async signal delivery (polled in event loop)
• SIGKILL/SIGSTOP not implemented

File Systems

• No symbolic links (HFS/HFS+ limitation)
• 31-character filename limit (HFS)
• No file permissions (mode is ignored)

Directory Structure

posix9/
├── include/
│   ├── posix9.h              # Main header (include this)
│   ├── posix9/
│   │   ├── types.h           # POSIX types
│   │   ├── errno.h           # Error codes
│   │   ├── socket.h          # Socket definitions
│   │   ├── pthread.h         # Thread definitions
│   │   ├── signal.h          # Signal definitions
│   │   ├── time.h            # Time definitions
│   │   └── unistd.h          # Misc definitions
│   └── mac_stubs/
│       ├── Multiverse.h      # Retro68 Mac API
│       ├── MacCompat.h       # Missing Mac definitions
│       ├── Timer.h           # Time Manager stubs
│       ├── Threads.h         # Thread Manager stubs
│       └── OpenTransport.h   # OT stubs
├── src/
│   ├── posix9_file.c         # File operations
│   ├── posix9_dir.c          # Directory operations
│   ├── posix9_path.c         # Path translation
│   ├── posix9_thread.c       # POSIX threads
│   ├── posix9_signal.c       # Signal emulation
│   ├── posix9_socket.c       # BSD sockets
│   └── posix9_misc.c         # Misc utilities
├── test/
│   ├── posix9_test.c         # Test program
│   └── build-test.sh         # Test build script
├── build-ppc.sh              # PowerPC build script
├── build-68k.sh              # 68K build script
└── README.md                 # This file

Testing on Real Hardware

1. Build the test program:

cd test
./build-test.sh

2. Transfer POSIX9 Test to your Mac via:

   • Floppy disk
   • Network (AppleTalk/AFP)
   • Serial connection (Zterm)
   • Compact Flash adapter

3. Run on Mac OS 9 - creates POSIX9 Test Log file with results

Related Projects

• GUSI - Grand Unified Socket Interface by Matthias Neeracher
• MachTen - Full BSD on Mac OS (commercial, discontinued)
• A/UX - Apple's Unix for 68K Macs
• MPW POSIX - Partial POSIX in Macintosh Programmer's Workshop
• Retro68 - Cross-compiler for Classic Mac OS

Target Applications

POSIX9 was created to port:

• Dropbear SSH - Lightweight SSH server
• curl/wget - HTTP clients
• Python 2.x - Scripting language
• Various Unix utilities

License

MIT License

Contributing

Contributions welcome! Areas needing work:

• [ ] Complete posix9_socket.c Open Transport implementation
• [ ] Fix posix9_misc.c type conflicts with newlib
• [ ] Add 68K-specific optimizations
• [ ] Test on real System 7 hardware
• [ ] Port more Unix software

Status

| Module | PPC | 68K | Notes | |--------|-----|-----|-------| | posix9_file.c | OK | OK | File operations | | posix9_dir.c | OK | OK | Directory operations | | posix9_path.c | OK | OK | Path translation | | posix9_signal.c | OK | OK | Signal emulation | | posix9_thread.c | OK | OK | POSIX threads | | posix9_socket.c | WIP | WIP | Needs OT constants | | posix9_misc.c | WIP | WIP | Type conflicts |

Current library size: ~50KB (5 modules)

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