petri(6)

✨ NAME ✨

Okay bestie, this is petri(6) — an XScreenSaver manual page — and it's literally about mold growing in a petri dish. Yes, mold. On purpose. 💅✨

petri simulates mold growing in a petri dish. That's the whole name vibe. 🦠

🌈 SYNOPSIS 🌈

Here's the exact usage, bestie — code is code:

petri [--display host:display.screen] [--foreground color] [--background
       color] [--window] [--root] [--window-id number][--mono] [--install]
       [--visual visual] [--delay microseconds] [--size integer] [--mem-
       throttle amount] [--count integer] [--originalcolors] [--diaglim real]
       [--anychan real] [--minorchan real] [--instantdeathchan real]
       [--minlifespeed real] [--maxlifespeed real] [--mindeathspeed real]
       [--maxdeathspeed real] [--minlifespan integer] [--maxlifespan integer]
       [--fps]

🧚 DESCRIPTION 🧚

petri simulates mold growing in a petri dish via a state-heavy grid of automata (vaguely like Conway's Life, only with much more state per cell). It's giving "science experiment left in the fridge" but make it screensaver. 🫶

💖 OPTIONS 💖

petri accepts the following options:

Tiny heads-up: the synopsis up top also shows --display, --foreground, and --background; this page doesn't give them separate description bullets, so I'm not inventing any. 💀

• --window — Draw on a newly-created window. This is the default.
• --root — Draw on the root window.
• --window-id number — Draw on the specified window.
• --mono — If on a color display, pretend we're on a monochrome display.
• --install — Install a private colormap for the window.
• --visual visual — Which visual to use. Legal values are the name of a visual class, or the id number (decimal or hex) of a specific visual.
• --delay microseconds — The interframe delay, in microseconds. Defaults to 10000, resource delay.
• --size integer — The size of a cell in pixels. Defaults to 4, resource size.
• --mem-throttle amount — The maximum amount of memory to consume, specified either in megabytes (suffix "M"), kilobytes (suffix "K"), or bytes (sans suffix). In order to meet the memory requirement, the cell size may be increased. Defaults to 22M, resource memThrottle.
• --count integer — How many different varieties of mold to grow (including Black Death). Defaults to 8, resource count.
• --originalcolors — If specified, indicates that the colors used should be the artist's original choices (a fixed set of primary and secondary colors). In this case, count must be 8 or less. Defaults to not specified (i.e., false), resource originalcolors.
• --diaglim real — The age limit for diagonal growth as a multiplier of orthogonal growth (range 1..2). 1 means square growth, 1.414 (i.e., sqrt(2)) means approximately circular growth, 2 means diamond growth. Defaults to 1.414, resource diaglim.
• --anychan real — The chance (range 0..1) that at each iteration, one or more new cells will be born. Defaults to 0.0015, resource anychan.
• --minorchan real — The chance (range 0..1) that, given that new cells will be born, that only two will be added (hence being a minor cell birth event). Defaults to 0.5, resource minorchan.
• --instantdeathchan real — The chance (range 0..1) that, given that death and destruction will happen, that instead of using Black Death cells, death will come instantaneously. Defaults to 0.2, resource instantdeathchan.
• --minlifespeed real — The minimum speed for living cells as a fraction of the maximum possible speed (range 0..1). Defaults to 0.04, resource minlifespeed.
• --maxlifespeed real — The maximum speed for living cells as a fraction of the maximum possible speed (range 0..1). Defaults to 0.13, resource maxlifespeed.
• --mindeathspeed real — The minimum speed for Black Death cells as a fraction of the maximum possible speed (range 0..1). Defaults to 0.42, resource mindeathspeed.
• --maxdeathspeed real — The maximum speed for Black Death cells as a fraction of the maximum possible speed (range 0..1). Defaults to 0.46, resource maxdeathspeed.
• --minlifespan integer — The minimum lifespan for a colony, in iterations, before Black Death comes. Defaults to 500, resource minlifespan.
• --maxlifespan integer — The maximum lifespan for a colony, in iterations, before Black Death comes. Defaults to 1500, resource maxlifespan.
• --fps — Display the current frame rate and CPU load.

🦋 ENVIRONMENT 🦋

Here's the environment tea:

• DISPLAY — to get the default host and display number.
• XENVIRONMENT — to get the name of a resource file that overrides the global resources stored in the RESOURCE_MANAGER property.
• XSCREENSAVER_WINDOW — The window ID to use with --root.

🌸 X RESOURCES 🌸

There are resource equivalents for each option, noted above. That's it, that's the section. 💅

⭐ BUGS ⭐

There are no known bugs in petri as of this writing. Iconic. 🔥

🧚 SEE ALSO 🧚

• xscreensaver(1)

Go check xscreensaver(1) too, iykyk. 🫶

👑 COPYRIGHT 👑

Legal tea time, bestie — here's the exact copyright and permission text:

Copyright © 1992-2000 by Dan Bornstein. Permission to use, copy, modify, distribute, and sell this software and its documentation for any purpose is hereby granted without fee, provided that the above copyright notice appear in all copies and that both that copyright notice and this permission notice appear in supporting documentation. No representations are made about the suitability of this software for any purpose. It is provided "as is" without express or implied warranty.

💜 AUTHOR 💜

Dan Bornstein <danfuzz@milk.com>, 06-Jul-2000.

That's the whole petri(6) page, bestie. Signing off from X Version 11, version 6.15, dated 30-Mar-2026 💅✨