rst

rst is a fast terminal reset for macOS and Linux. When your terminals “breaks”, you run reset, but it takes a second. rst takes 2 milliseconds.

It repairs the kernel TTY state and emits the terminal’s terminfo reset strings, without the 1s sleep that reset inherits from 3BSD’s tset(1), meant for mechanical printer-and-ink terminals to ‘settle down’.

• Fast: ~2ms vs ~1 second for /usr/bin/reset.
• Tiny: 162 KB, smaller than the system reset (164 KB) it replaces.
• Self-contained: parses the terminfo database itself; links only libc, no ncurses.
• Compatible: emits the same reset strings as ncurses tput reset, and falls back to VT escapes when no terminfo entry exists (e.g. SSH to an older host).

What it does

1. Kernel TTY state. Restores canonical/cooked input, echo, signals, CR/NL mapping, and output processing. Only repairs disabled control characters, preserving user customizations such as an erase key set to ^H (matching ncurses). Uses TCSAFLUSH to discard stale typeahead a crashed raw-mode program may have left in the input queue. Undoes a stuck ^S / TCOOFF via tcflow(TCOON) before touching termios, so reset itself can’t hang behind stopped output. Refuses to run as a background job (checks tcgetpgrp) so it never writes to another job’s terminal.
2. Terminal emulator state. Reads the terminal’s compiled terminfo entry directly (no ncurses dependency) and emits the terminal’s reset strings in the same order ncurses tput reset uses — rs1, rs2, clear_margins, rs3, with each rsN falling back to the corresponding isN when absent. For known VT-compatible terminals it first sends a small hard-coded cleanup sequence (synchronized output, mouse, focus, paste off), and only when no terminfo entry is found does it use a hard-coded VT fallback. That makes it recover even when a terminfo entry is absent (e.g. SSHing from a newer terminal to an older host).

It locates a TTY on stderr, stdout, stdin (reopened read-write), or /dev/tty.

Examples

Common ways to break your terminal — and how rst recovers them. Type rst blind (you won’t see it, but it will execute) and hit Enter to recover.

Break command	What it does	rst fixes
cat /dev/urandom	Binary garbage leaves random escape sequences and alternate charset active	✓
printf '\e[?1049h'	Enters alternate screen; scrollback vanishes	✓
printf '\e[?25l'	Hides the cursor	✓
printf '\e[8m'	Invisible (concealed) text	✓
printf '\e(0'	DEC line-drawing charset; text becomes garbage symbols	✓
printf '\e[4h'	Insert mode; typing pushes text right	✓
printf '\e[?5h'	Reverse video	✓
stty raw	Raw mode; line editing dies (use Ctrl-J to submit)	✓
printf '\e[3;10;20t'	Resizes the terminal window (on supporting terminals)	✓
printf '\e[r\e[H'	Resets scroll region and moves cursor home	✓
stty -opost -onlcr	Disables output processing; ls columns stairstep	✓
printf '\e[?1003h\e[?1006h'	Enables mouse reporting; clicking/dragging spews escape garbage into your prompt	✓
stty -icanon min 1; stty -isig	Disables canonical mode and signals; Ctrl-C and line editing stop working	✓

Build

Requires Zig 0.16.0. No ncurses or other external libraries — rst parses the terminfo database itself and links only libc:

zig build --release

The binary is installed to zig-out/bin/rst. It links only the system C library (libSystem on macOS, libc on Linux) — no shared-library dependency on ncurses.

Install

zig build --release
install -m 0755 zig-out/bin/rst /usr/local/bin/rst

Or put it anywhere earlier on PATH than /usr/bin to shadow the system reset.

Test

A portable PTY test builds the binary, puts a TTY into a deliberately broken raw/no-echo state, runs rst, and verifies that canonical mode and echo were restored:

zig build test
python3 scripts/pty-test.py zig-out/bin/rst

The unit suite includes a seed corpus for the terminfo parser. On architectures supported by Zig’s native fuzzer (including CI’s x86_64 Linux runner), run 100,000 fuzz iterations with zig build test -Drelease --fuzz=100K.

Prior art

The mechanism is established prior art; rst is a polished, cross-platform Zig package, not the first fast reset.

• BusyBox reset — a ~676-byte applet that emits fixed reset escapes, runs stty sane, and performs no settling sleep. (console-tools/reset.c)
• Toybox reset — the closest philosophical match. Its source says: “In 1979 3BSD’s tset had a sleep(1) to let mechanical printer-and-ink terminals ‘settle down’. We’re not doing that.” (toys/other/reset.c, 2015 introduction, 2023 cooked-mode fix)
• ncurses tput reset — upstream ncurses moved the terminal-mode part of reset into tput reset in 2016 and refined it in 2017, without tset’s hardware-settling wait. (tput(1))

A no-code fast alternative on any system with ncurses is:

reset -I && tput reset

rst packages the same idea into a single dependency-free standalone binary — it reads the terminfo database itself rather than linking ncurses.

Differences from ncurses

The reset work rst performs is the same mechanism as ncurses reset / tput reset (both funnel into ncurses’ progs/reset_cmd.c), minus the legacy sleep. For completeness, the exact, deliberate differences — verified against the ncurses source — are:

• The settling sleep is removed. /usr/bin/reset calls napms(1000) after emitting the reset strings (tset.c), a hardware-settling delay retained from 3BSD for mechanical terminals. tput reset never had it. rst matches tput reset: no sleep.
• No tabstop reprogramming. Between rs2 and rs3, ncurses’ reset_tabstops clears and re-sets hardware tab stops using the init_tabs, clear_all_tabs, and set_tab capabilities. rst omits this; terminal emulators do not use hardware tabs, so it is dead work there. This matters only for a real terminal with non-default tab stops.
• No reset_file/init_file. ncurses can cat a per-terminal initialization file named by the rf/if capability. rst does not read or emit arbitrary files during reset.
• No alternate margin fallback. If clear_margins (mgc) is absent, ncurses falls back to set_lr_margin / set_left_margin+set_right_margin (and a space-fill when only the latter pair exists). rst sends mgc only; on a terminal lacking mgc it clears no margins.
• VT cleanup prelude is extra. For known VT-compatible terminals rst first sends a short sequence to disable synchronized output, mouse reporting, focus events, and bracketed paste. ncurses does not do this; it relies on the terminfo strings alone.
• Missing-entry fallback is extra. When no terminfo entry exists, ncurses aborts; rst instead emits a fixed VT reset sequence so a terminal emulator can still be recovered (common when SSHing to an older host).
• Simpler padding handling. rst removes terminfo $<delay> markers instead of sleeping or emitting pad bytes scaled to baud rate the way tputs does. Terminal emulators process output instantly; this only affects physical serial terminals.

The one behavioral difference that matters for the common case is the removed settling delay. For a real serial or physical terminal where the delay, tabstops, or margin fallbacks matter, use /usr/bin/reset.

Benchmark

Measured on macOS 26.6 / arm64 (Apple Silicon) in a pseudo-TTY harness. Absolute numbers vary by machine and harness overhead; the intentional one-second delay dominates the conclusion.

/usr/bin/reset:     1012 ms   (napms(1000) settling sleep)
/usr/bin/reset -I:     2.7 ms  (TTY repair only, skips the sleep)
/usr/bin/tput reset:   3.2 ms
rst:                  1.9 ms

rst is the fastest of the variants — dropping the ncurses dependency eliminates library initialization overhead — and ~530× faster than /usr/bin/reset for the common terminal-emulator case.

Status

CI builds and runs the PTY test on macOS arm64 and Linux x86_64. Tagged releases publish binaries for macOS and Linux on arm64 and x86_64; Linux binaries are statically linked, while macOS binaries link only the system libSystem.

License

Apache-2.0. See LICENSE.