monitr

monitr is a lightweight macOS activity monitor for the terminal. It is built in Rust with Ratatui and focuses on a fast process table, low overhead sampling, and an Activity Monitor-style layout.

Features

• CPU, Memory, Energy, Disk, and Network views
• Movers view for CPU, memory, and disk-rate changes since the previous sample, each row annotated with the dominant change
• Inline CPU and memory sparklines in the overview, plus a per-process CPU trend in the inspector
• Sortable process table with fast keyboard navigation
• Process filter by PID, name, user, command, or status, with cpu>50, mem<100mb, and field:value predicates
• Inspector panel for the selected process
• Open files and sockets overlay for the selected process, on demand
• Disk and Network tabs include system-level volume/interface totals in the inspector
• CPU, memory, virtual memory, runtime, status, user, parent PID, command, executable, and current working directory
• Disk read/write rates and totals
• macOS thread count for the selected process
• Open file counts where the OS exposes them
• Confirmed TERM and KILL actions
• Confirmed suspend, resume, and priority-adjust actions
• One-shot process snapshots with text or JSON output
• Port ownership lookup for TCP listeners or all TCP/UDP sockets
• One-shot process inspection with open files and sockets
• Small native release binary

Install

Install from crates.io:

cargo install monitr

Build from source:

cargo install --path .

Or install into ~/.local/bin from this checkout:

make install-local

Usage

monitr

Start with a custom refresh interval:

monitr --interval 750

Refresh intervals must be between 250 and 10000 milliseconds.

Start with a filter:

monitr --filter codex

Filters also accept predicates, ANDed together:

monitr --filter 'cpu>50 user:milo'

Supported predicates are cpu, mem, and pid with >, <, >=, <= (memory accepts size suffixes like 100mb), plus user:, name:, status:, cmd:, and pid: substring fields. Anything else is a plain substring.

Print a one-shot process snapshot:

monitr snapshot --limit 20

Print machine-readable JSON for scripts:

monitr --json --filter node --limit 10

Find which process owns a listening port:

monitr ports 3000

Inspect all TCP/UDP sockets, including established connections:

monitr ports --all --json

Inspect one process, including open files and sockets:

monitr inspect 1234 --limit 20

Controls

Scope

monitr is intended to be a faster, lighter terminal alternative to Activity Monitor for common process and system inspection. It does not use Apple's private Activity Monitor internals, so some values are approximations or interface-level summaries:

• Energy impact is a lightweight estimate based on CPU, memory share, I/O, and run state.
• Disk and Network tabs keep a process table for context, while the inspector shows system-level volumes or interfaces.
• Network throughput is interface-level, not per-process. The ports command identifies socket owners but does not attribute byte counts to each process.
• Some process details depend on macOS permissions and may show - for protected processes.

Roadmap

The strongest opportunities for monitr are features that lean into terminal-native workflows or expose macOS process details that Activity Monitor does not make easy to inspect.

• Per-process network attribution: show bytes in/out and active connections by PID, not only interface-level totals. macOS exposes no cheap syscall for this, so it is deferred to an on-demand path rather than the refresh loop; the o overlay and ports command already identify socket owners.
• Better energy and wakeup data: replace the current lightweight energy estimate with richer macOS-specific signals (idle/interrupt wakeups) where public APIs expose them.
• Longer timeline windows: the history buffer that drives sparklines is in place; extend the Movers view from previous-sample deltas to 10 second, 1 minute, and 5 minute windows on top of it.
• Wider sparklines: extend the existing CPU/memory sparklines to disk and network, and into the process table when the terminal has room.
• Record and replay: export sampled sessions as JSON or CSV, then replay or diff them later for performance investigations.
• Watch rules and alerts: notify when a process exceeds CPU, memory, disk, or network thresholds, or when a matching process spawns, exits, or changes state, including a scriptable monitr watch for pipelines.
• Diagnostic capture: build on monitr inspect to collect a targeted report for a process, including process tree, sample/spindump output, and recent metric history.
• Process tree and rollups: group processes by parent tree, app bundle, launchd service, terminal session, cwd, or git repository.
• Smarter filtering: build on the new field:value and comparison predicates with fuzzy matching, regex, and saved filters.
• Richer anomaly explanations: the Movers view already names the dominant change per row; extend this to swap churn, dominant disk writers, network spikes, FD exhaustion risk, and short-lived process churn.

Development

monitr uses Rust 2024 and requires Rust 1.88 or newer.

make check

This runs formatting, clippy, unit tests, and a release build.