system viewer for sar — interactive terminal charts for sysstat historical data.
Like btop, but for the past.

English | 日本語 | 简体中文

sar quietly collects a goldmine of performance history on every Linux server. But looking at it means squinting at text tables, or generating SVG files with sadf -g and shuffling them to your desktop. Every incident review starts with the same chore.

svy turns that data into an interactive TUI: scrub through time, zoom into an incident window, flip between days, and switch across CPU / memory / network / disk — right in the terminal where the data lives. No files generated, no GUI, no agent to install on servers.

(recorded svy --demo session — try it yourself: npx @svy-tui/svy --demo)

npx @svy-tui/svy --demo

The demo ships with multiple days of synthetic data — press < to travel back in time; past days are synthesized on the fly.

• 8 metric groups — CPU (per-core), memory, load average, network (per NIC), disk I/O (per device), disk utilization, IO tps, paging
• Time cursor & zoom — scrub with ←/→, zoom into an incident window with +, read exact values at the cursor
• Day browsing — flip through sar's daily files with </>; with --host, adjacent days are fetched over ssh on demand
• Instance switching — cycle per-CPU cores, NICs, and disk devices with Tab
• Remote-first — view a server's history from your laptop; sysstat is only needed where the data was recorded
• Zero artifacts — reads JSON from a pipe, draws braille charts, writes nothing to disk

Network view — two colored series (rx/tx) per interface, Tab switches NICs, the y-axis scales units automatically:

Zoom into an incident — + narrows the window around the cursor; the header shows the zoomed range. That evening spike is suddenly obvious:

Help — ? shows every keybinding without leaving the app:

# On a Linux server: today's data, all activities
sadf -j -- -A | svy

# A specific day
sadf -j /var/log/sysstat/sa05 -- -A | svy

# From your laptop (macOS/Windows), viewing a remote server
ssh web01 'sadf -j -- -A' | svy
svy --host web01                      # same thing, shorthand
svy --host web01 /var/log/sysstat/sa05

# From saved files — pass several days and flip through them with < / >
sadf -j -- -A > today.json
sadf -j -1 -- -A > yesterday.json
svy today.json yesterday.json

sar keeps one data file per day. With --host, pressing < / > past the edge of the loaded data fetches the adjacent day on demand (running sadf -j -N -- -A remotely, so it works regardless of where the distro stores its saDD files). With local files, every file you pass becomes a day you can flip through.

Windows note: piping (… | svy) disables keyboard input because there is no /dev/tty to reopen. Use a file argument or --host instead.

svy's only input contract is the JSON emitted by sadf -j (part of sysstat). It never parses binary sa files itself, which makes it immune to sysstat version and architecture differences — the parsing burden stays with sysstat, where it belongs.

That contract also defines the roles: sysstat collects on the server, svy views anywhere Node.js ≥ 18.18 runs (Linux, macOS, Windows Terminal). Your laptop never needs sysstat installed.

Metrics missing from the input are simply not shown; extra activities are ignored. Multi-host JSON (e.g. concatenated from a fleet) works — cycle hosts with n.

npm install -g @svy-tui/svy    # installs the `svy` command

From source (requires Node.js ≥ 18.18):

git clone https://github.com/svy-tui/svy && cd svy
npm install && npm run build && npm link
svy --demo

npm install
npm test        # vitest — parser, chart renderer, viewport, UI interaction
npm run build   # tsc → dist/
node dist/cli.js --demo

To regenerate the README screenshots (assets/shot-*.png), run ./scripts/shots.sh — see the header of that script for prerequisites (tmux, aha, Google Chrome, Cascadia Code font).

The demo GIF (assets/demo.gif) is recorded with vhs: vhs scripts/demo.tape.

The chart renderer is a hand-rolled braille canvas (no chart library), the sadf JSON parser absorbs field-name differences between sysstat versions declaratively, and all navigation logic is pure functions with tests.

MIT