systemd-sentry · v0.1.0

Autonomous, zero-trust supervisor for systemd.

systemd-sentry (sentry) brings deterministic root-cause triage, sliding-window circuit-breaking, and guarded self-healing to systemd Linux environments. Built in 100% pure Rust with direct kernel syscalls, zero C dynamic library dependencies, zero open network listeners, and a strict <15MB RSS memory budget.

100% Pure Rust Zero Dynamic C Libs Zero TCP Listeners systemd Native Model Context Protocol Apache-2.0 / MIT

01Why 100% Pure Rust & Zero C Dependencies?

Traditional system daemons link against libsystemd.so, libdbus-1.so, and OpenSSL (libssl.so / libcrypto.so). This creates brittle ABI bindings, supply-chain CVE exposure, and dynamic linking failures during system recovery. systemd-sentry takes a zero-compromise approach:

Zero C Library Linkage. Zero dynamic dependencies on libsystemd, libdbus-1, or OpenSSL. Uses pure Rust D-Bus (zbus) and pure Rust TLS (rustls). Audited on every build by scripts/check_deps.sh.
Direct Kernel Interfaces. Direct Linux syscalls via rustix. Reads cgroups v2 resource accounting (/sys/fs/cgroup/) and kernel Pressure Stall Information (/proc/pressure/) using zero-allocation buffer pipelines.
Native systemd Citizen. Socket activation parsing $LISTEN_FDS (FDs 3..N), non-blocking sd_notify ticker writing directly to $NOTIFY_SOCKET, and first-class drop-in configuration support (/etc/systemd-sentry/policy.d/*.toml).
Deterministic Static Binary. A single static binary that drops into any Linux distribution running kernel 5.8+ with zero runtime library prerequisites.

02Zero-Trust Safety Engine & Circuit Breaker

AI inference is powerful for diagnosis, but handing autonomous shell execution to an LLM on production Linux servers is an operational disaster. systemd-sentry enforces strict separation of mechanism and policy:

The LLM is Strictly Advisory. The diagnostic engine has zero shell access and cannot execute arbitrary commands. It emits strictly validated JSON containing root-cause analysis and proposed remediation.
Deterministic Sliding-Window Circuit Breaker. Tracks failure frequency per unit across configurable rolling windows. Tripped units transition to Open, and flapping units enter PermanentlyLocked, preventing restart storm cascades.
Drop-In Policy Enforcement. All actions pass through PolicyGatekeeper, evaluating allowed actions against /etc/systemd-sentry/policy.toml and policy.d/*.toml. Protected units (systemd-journald, dbus, sshd, init.scope) are completely untouchable.
Hard Memory Ceiling & Self-Defense (<15MB RSS). Engineered for low-spec VPS (512MB RAM) and IoT gateways. Automatically sheds inference load and switches to deterministic exit-code/signal fallback triage under memory pressure.

03Local IPC & Zero Network Listeners

Security starts with zero exposure. systemd-sentry opens zero TCP ports. All communication occurs through authenticated local host channels:

UNIX Domain Socket with SO_PEERCRED. Local CLI queries communicate over /run/systemd-sentry/sentry.sock. The kernel guarantees peer UID/GID credentials; mutating actions (e.g. reset) require root authorization.
System D-Bus Service. Registers org.freedesktop.SystemdSentry on the system bus for standard systemd and desktop integration.
Model Context Protocol (MCP) Server. Runs an MCP server over stdio (systemd-sentry mcp) for direct, secure integration with Claude Desktop, Cursor, and agentic workflows without network exposure.

04Engineering & Testing Metrics

200 / 200

Unit QA Tests Passed

87 / 87

4-Tier E2E Tests Passed

cargo-fuzz Targets

Dynamic C Libraries

≤ 256

Physical LOC / File

< 15 MB

Target Memory RSS

Every commit is verified against hard structural and security invariants: scripts/check_deps.sh enforces zero dynamic C linkage; scripts/check_loc.sh enforces single-function isolation and ≤256 LOC per file; and the entire test suite runs with zero panics in daemon paths.

05Quick Start & CLI Surface

Build from source with standard Rust toolchain:

git clone https://github.com/syntropd/sentry.git
cd sentry
cargo build --release

Interactive setup wizard (detects local routerd / llama.cpp / OpenAI endpoints):

systemd-sentry --setup

Validate configuration and policy drop-in syntax (pre-flight check, exits 0 or 78):

systemd-sentry check

Inspect system health and active circuit breaker states:

systemd-sentry status --json

On-demand root cause triage for any unit without waiting for failure:

systemd-sentry triage nginx.service

Live streaming event monitor (crashes, circuit breaker trips, remediations):

systemd-sentry monitor

Run the Model Context Protocol (MCP) server for external AI tools over stdio:

systemd-sentry mcp

06License

Licensed under either of Apache License, Version 2.0 or MIT license at your option. See LICENSE for details.