monitor-tui

A terminal-based system monitor written in C++20. Displays CPU, memory, GPU, and network usage as live gauges with dark/light theme support.

Screenshot

  System Monitor                                      [t] Theme  [q] Quit
 ────────────────────────────────────────────────────────────────────────
 ╭──────────────────────────────────────────────────────────────────────╮
 │  CPU                                                                  │
 │  Total  ████░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░   8.3%         │
 │  Core 0 ██░░░░░░░░░░░░░░░░░░░░░░░░  5.0%  Core 4 ████  15.0%        │
 │  Core 1 ██████████████████░░░░░░░░ 72.0%  Core 5 ░░░░░░  0.0%       │
 │  ...                                                                  │
 ╰──────────────────────────────────────────────────────────────────────╯
 ╭──────────────────────────────────────────────────────────────────────╮
 │  Memory                                                               │
 │  RAM    ████████░░░░░░░░░░░░░░░░░░░  6.12 GB / 31.22 GB   19.6%     │
 ╰──────────────────────────────────────────────────────────────────────╯
 ╭──────────────────────────────────────────────────────────────────────╮
 │  GPU  NVIDIA GeForce RTX 4070 Ti                            45°C     │
 │  Core  ████████████░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░  23.0%          │
 │  VRAM  █████░░░░░░░░░░░░░░░░░░░░░░░░  1658 / 12282 MiB  13.5%      │
 ╰──────────────────────────────────────────────────────────────────────╯
 ╭──────────────────────────────────────────────────────────────────────╮
 │  Network                                                              │
 │  ↓ Recv ████████████░░░░░░░░░░░░░░░░░░░░░░░░   12.54 MB/s           │
 │  ↑ Send ███░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░   3.21 MB/s           │
 ╰──────────────────────────────────────────────────────────────────────╯

Requirements

Dependency	Notes
C++20 compiler	GCC 13+ or Clang 16+
CMake 3.14+	FetchContent used to download FTXUI
FTXUI v5	Fetched automatically at configure time
nvidia-smi	Optional — GPU section is hidden when unavailable

Supported on Linux and Windows. Linux stats are read from /proc/stat, /proc/meminfo, and /proc/net/dev. Windows stats are read from the native Win32 APIs: CPU usage via NtQuerySystemInformation, memory via GlobalMemoryStatusEx, and network counters via GetIfTable.

Build

cmake -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build -j$(nproc)

On Windows, use the same CMake flow from PowerShell or a developer shell:

cmake -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build

The binary is placed at build/monitor-tui on Linux and build/monitor-tui.exe on Windows.

Usage

./build/monitor-tui

Key	Action
t	Toggle dark / light theme
q	Quit

The display refreshes every second. All sections resize with the terminal window.

Project structure

monitor-tui/
├── CMakeLists.txt       # Build config; fetches FTXUI via FetchContent
└── src/
    ├── monitor.hpp      # Data structs + Monitor class declaration
    ├── monitor.cpp      # System stats collection
    └── main.cpp         # UI rendering and event loop

Code overview

monitor.hpp — data model

Four plain structs hold the latest snapshot of each subsystem:

CpuInfo   — total usage (0–1) + per-core vector
MemInfo   — used / total in kB, ratio (0–1)
GpuInfo   — present flag, name, core usage, VRAM usage, temperature
NetInfo   — rx_bps / tx_bps in bytes/s, peak_bps for gauge scaling

Monitor owns one instance of each and exposes a single update() method.

---

monitor.cpp — stats collection

CPU (update_cpu) — on Linux, reads /proc/stat each call. On Windows, queries per-processor performance counters with NtQuerySystemInformation. Both paths compute usage per core as 1 - idle_delta / total_delta between two consecutive snapshots. The first call only seeds the previous snapshot; actual values appear from the second call onward.

Memory (update_mem) — on Linux, reads MemTotal and MemAvailable from /proc/meminfo; used memory is MemTotal − MemAvailable (this accounts for page cache, which the kernel reclaims under pressure). On Windows, reads physical memory totals and availability with GlobalMemoryStatusEx.

GPU (update_gpu) — shells out to nvidia-smi with --format=csv,noheader,nounits and parses the single output line. The gpu.present flag is set to false on any failure, causing the GPU section to be omitted from the UI entirely.

Network (update_net) — on Linux, reads /proc/net/dev; on Windows, reads interface counters with GetIfTable. Both paths sum rx/tx byte deltas across all active non-loopback interfaces and divide by elapsed seconds to get bytes/s. peak_bps tracks the running maximum and decays by 1% per second so the gauge scale slowly shrinks back after a burst.

---

main.cpp — UI and event loop

Theme — a plain struct of ftxui::Color values. make_light() and make_dark() return the two presets. usage_color() maps a 0–1 ratio to green / yellow / red based on 50% and 85% thresholds.

build_ui() — pure function: takes a Monitor snapshot and a Theme, returns an ftxui::Element tree. Each section is a vbox wrapped in border. CPU cores beyond 4 are arranged in a 2-column grid via core_pair(). Network gauge bars are scaled relative to peak_bps so the bar always fills meaningfully rather than staying near zero.

Main loop — follows the standard FTXUI pattern:

main thread          worker thread
────────────         ──────────────────────────────
screen.Loop()  ←──  sleep 1s → lock → monitor.update()
   ↑                            └→ screen.PostEvent(Custom)
   └── Renderer lambda reads monitor under the same mutex

A std::mutex serialises access to Monitor between the worker that writes and the renderer that reads. std::atomic<bool> running signals the worker to stop when q is pressed.