ztOS

ztMETRO is a Wayland compositor, built on wlroots, that is also the whole phone interface: Start with its live tiles, the app list and search, the action centre, the app switcher, the lock screen and the on-screen keyboard. Its look and motion are Windows Phone 8.1's, measured frame by frame against screen recordings of real Lumias.

It renders itself with OpenGL ES: every tile, bar and app surface is a textured quad with its own matrix, which is what lets tiles tilt under a finger and whole screens swing. Text is drawn once and kept as a texture, and frames are drawn only while something moves.

Start and tiles

Pin, move and resize tiles; the turnstile when an app opens and when you come back.

Action centre

Notifications, quick actions, brightness, and a media banner.

Keyboard

On-screen, lifting the app so the text box stays in sight.

Animation speed

One setting for the whole interface, shell and apps, 75% by default.

Haptics

Strength per kind of touch, set in Settings.

Other apps

Firefox, Chromium and any Linux app run as windows inside it.

The native apps share ZrnMetroCore, a small toolkit with the shell's own widgets, page turns, pivots and press tilt.

The ztOS SDK builds an app into a single file: a small C launcher with the app's Python code, pages, pictures and the ztos runtime zipped behind it. Pages, lists, pivots, entries, toggles, round buttons, app bars and dialogs all come from the runtime, with the toolkit's own numbers for every motion.

ztos-sdk new "Notes"     # a new app, from the template
ztos-sdk run             # try it on the computer
ztos-sdk deploy          # build, install on the phone, open it
ztos-sdk logs -f         # what it prints, on the phone

Keeping it fast

• Motion on the GPU. While a page turns, a list scrolls or a button leans, a GPU layer over the app shows pictures of the pages as textured quads, drawn by a small C renderer. Widgets are rasterised once, not every frame.
• A warm runtime. ztos-zygote loads Qt for Python once and forks each app from itself, which saves about a second of CPU per launch.
• Compiled code. Apps ship with their Python already compiled, so the phone never compiles it on start.

ztOS's first phone is the Galaxy S9, SM-G960N (starlte). It runs mainline Linux 7.1 with the Exynos 9810 drivers, booting from the phone's internal storage, with Arch on BOOT and TWRP left in RECOVERY. The phone's hardware support is built as loadable kernel modules, so drivers can be developed without reflashing. The modem and sensor hub still use Samsung's own Android daemons, run from the phone's stock partitions.

Installing

You need a Linux computer with about 15 GB free, an internet connection, a USB cable, and the phone charged above 50%. The bootloader must already be unlocked with TWRP installed in RECOVERY.

1. Boot the phone into TWRPTurn the phone off, then hold Volume Up, Bixby and Power until TWRP appears. Connect it to the computer with the USB cable.
2. Get ztOS on the computergit clone https://github.com/Zerone-Laboratories/ztOS.git
cd ztOS
3. Run the installerinstaller/ztos install --target starlte
   Choose 1, then pick a user name and password. The build takes 30 to 60 minutes.
4. Confirm the installAnswer yes to write the boot image, then type ERASE when asked. Leave the cable in until it says done.
5. Restart the phoneHold Power, Volume Up and Volume Down. The first start takes about a minute, then the Welcome app shows how ztOS is used.

If something fails, the phone goes back to TWRP by itself. Start again from step 3. To try ztOS without a phone, run installer/ztos install --target qemu instead. It opens ztOS in a phone-shaped window on the computer.

Hardware status

Known quirks

• The modem or sensor hub doesn't come up. It tends to follow a forced reboot or a crash. One pass through TWRP brings them back: reboot into recovery, then back into ztOS.
• A driver that crashed while loading is skipped at the next boot, so a crash can't become a boot loop. Remove its mark file under /var/lib to try again.
• Reboot rather than unload a driver module to try a new build; a failed unload has left the phone unable to shut down.
• The clock resets at every boot until the network sets it.
• Keep the stock Android partitions. The installer writes only BOOT and USERDATA, and the modem needs the rest.

Getting back in

Nothing can leave the phone unbootable, and every layer has a way back. If Arch doesn't come up, the initramfs opens a rescue shell on the same USB network. If the kernel hangs, a watchdog resets the phone into TWRP after 30 seconds. If nothing appears on USB at all, the boot stage resets the phone after ten minutes. And download mode, which can't be overwritten, has everything needed to put the stock firmware back.

ztConflo takes a phone's codename and builds a flashable ztOS image for it: Arch Linux ARM with ztMETRO, on a kernel and boot setup that postmarketOS already boots. It looks in the ztOS device registry first and falls back to postmarketOS for phones nobody has ported ztOS to yet. It never ports new hardware.

Eligible phones

135 today, with a mainline aarch64 kernel; 71 of them archived by postmarketOS, and flagged.

GPU check

Phones without a Mesa GPU driver still build, with a warning that ztMETRO won't start.

Registry

One TOML file per phone; a phone moves from untested to boots to tested through a hardware checklist.

Interface

A command line and a terminal UI in ztOS's own look, which installs its tools on first run.

• The first phone besides the S9 booting a ztConflo build.
• The sound of calls, and receiving SMS.
• Suspend on the S9, for idle battery life closer to Android's.
• Native apps drawing with OpenGL ES the way the shell does, and a ztOS package repository for updates.

• ztOS source, with the full status page and the SDK guide
• ztConflo, the image builder, and ztos-devices, its registry
• galaxy-s9plus-mainline-linux, the Exynos 9810 mainline drivers ztOS builds on
• postmarketOS, whose kernels ztConflo reuses
• Ometh Abeyrathne, who makes ztOS