schema-init

A minimal PID 1 init system for Linux that supervises services through a weight-state machine instead of unit files and dependency graphs.

No systemd. No OpenRC. No journal daemon. No socket activation engine. Just a statically linked binary that mounts your filesystems, spawns your services in dependency order, and watches them — then gets out of the way.

PID 1 footprint: 892 KB RSS, 1 thread.

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How it works

Every service moves through a state machine driven by probes. Before a service is spawned, schema-init probes the system — is the binary present? Are dependencies stable? Is there enough memory? The probe returns a flag word. The state machine decides what comes next.

                  ┌─────────────────────────────────────┐
                  │                                     │
            NEW_PROCESS                                 │
                  │                                     │
           F8 probe passes                              │
                  │                                     │
            FULL_TRUST ──── stable 10s ──── FUNDAMENTAL │
                  │                                     │
             (oneshot exit 0)                           │
                  │                                     │
              PERFECT                                   │
                                                        │
            ── on death ──                              │
                  │                                     │
             RECOVERY ◄──────────────────────────────── ┘
                  │
           F9 probe fails
                  │
             FRICTION
                  │
           F6 probe fails
                  │
             EXCISED  (76 — gate closes)

Three probe families:

Probe	Asked when	Checks
F8	Before first spawn	Binary exists, deps stable, memory safe, permissions met
F9	After death	Retry budget, cooldown window, memory, escalation path
F6	After recovery fails	Last-chance: can we even attempt a restart?

If a service is marked critical and reaches EXCISED, it logs a system friction warning. Everything else just stops retrying and steps aside.

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Service files

Drop a .svc file in /etc/schema-init/services/. One key=value per line:

name=sshd
exec=/usr/sbin/sshd
args=-D
needs_root=1

name=display-manager
exec=/usr/sbin/lightdm
dep=dbus
dep=udev
needs_root=1
critical=1

name=network
exec=/usr/local/bin/net-setup
oneshot=1

Keys:

Key	Description
name	Service name (used in logs and dep resolution)
exec	Absolute path to binary
args	Argument (repeat for multiple args)
dep	Dependency by name (repeat for multiple deps)
oneshot	Exit 0 → PERFECT, don't restart
needs_root	Require uid 0 before spawning
critical	EXCISED → system friction warning
no_restart	Any death → EXCISED immediately, no recovery arc

Dependencies are resolved by name at load time. A service stays in NEW_PROCESS until all its deps reach FUNDAMENTAL, SETTLED, or PERFECT.

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Building

make

Produces a fully static binary — no glibc version dependency, runs on any Linux kernel. Tested on Debian Bookworm kernel 6.1, x86_64.

# install as PID 1
cp schema-init /sbin/schema-init
ln -s /sbin/schema-init /sbin/init

# or pass to kernel directly
linux /boot/vmlinuz root=LABEL=my-root init=/usr/sbin/schema-init

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Real numbers

Tested on Dell Inspiron 3542 (Intel Core i3, 4GB RAM) running full Cinnamon desktop:

Metric	schema-init	systemd (same hardware, Fedora)
PID 1 RSS	892 KB	~8–15 MB
PID 1 threads	1	20–30+
RAM used at desktop	~1.1 GB	~1.6–2.0 GB
Swap used	0 MB	200–500 MB
Time to desktop	fast	slower

The gap is structural. schema-init spawns your services and then sits in a 250ms tick loop. There is no journal daemon, no dbus-broker, no socket activation layer, no unit file parser running in the background.

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Shared memory interface

Running processes can read service state via POSIX shared memory at /schema-init:

#include "schema_shm.h"

int fd = shm_open("/schema-init", O_RDONLY, 0);
schema_shm_t *shm = mmap(NULL, sizeof(schema_shm_t), PROT_READ, MAP_SHARED, fd, 0);

for (int i = 0; i < shm->count; i++) {
    printf("%s state=%d weight=%d pid=%d\n",
           shm->svc[i].name,
           shm->svc[i].state,
           shm->svc[i].weight,
           shm->svc[i].child_pid);
}

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License

AGPL-3.0 for open source use.
Commercial license available for embedding in proprietary systems — open an issue or contact via GitHub.

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Built by Jonathan Ayers. The schema was written before the code.