bm2: A 2.8 MB pm2 Replacement Written in MoonBit

Today I'm sharing a tool I wrote, bm2, a pm2 replacement implemented in MoonBit.

Repository: https://github.com/chenbimo/bm2.

Some might wonder, pm2 works fine, why replace it?

Note: Due to time constraints, the tool doesn't yet offer online installation or updates. For discussion, please contact me at the end of the article.

Why replace pm2?

pm2 is a veteran process management tool in the Node ecosystem, and it's indeed easy to use.

But I only use a few commands daily, while pm2 has dozens of commands — 90% of its functionality I never touch.

So I thought, could I write something lighter and simpler myself?

Thus, bm2 was born.

What is bm2?

In one sentence: bm2 is a pm2 replacement, specifically designed to manage projects running on Node.js and Bun.js in a Linux environment.

It's written in the MoonBit language, and the entire tool consists of just two files — grab them and go.

How simple is it to use?

First, write a config file to tell it where your app is:

# bm2.toml
[[apps]]
name = "api"
cwd = "/srv/api"
script = "index.ts"
instances = 2
base_port = 3000

Then start it with a single command:

bm2 start

Done.

How lightweight is it?

These are real measurements from my local machine:

Item	Data
bm2 binary size	2.8 MB
Background service size	3.0 MB
Resident memory	2.7 MB
Command response	3 ms

One word: light.

The background service runs long-term, using less than 3 MB of memory — lighter than a web page.

Command response is 3 milliseconds, with no perceptible delay.

What can it do?

• Auto restart: If an app crashes, it pulls it back up immediately — no need to get up in the middle of the night to check logs.
• Memory protection: If an app exceeds its memory limit, it handles it automatically, preventing a bad app from dragging down the whole machine.
• Multi-instance execution: Run several instances of an app, with automatic port assignment, making it easy to simulate an online environment.
• Status viewing: See whether an app is alive or dead, how much memory it uses, and how long it's been running — all with one command:
• One-click stop: When you want to stop running, one command stops everything:
• Slip protection: For dangerous operations like stopping all apps, it asks for confirmation first.
• Update without interruption: Need to upgrade the background service? One command handles it, and your apps experience zero downtime throughout.

Why write it in MoonBit?

MoonBit is a relatively new programming language with very concise syntax.

How concise? Look at this example:

fn main {
  println("Hello, bm2!")
}

Its advantages directly correspond to the data above.

• Small binary: MoonBit compiles into very compact binaries, so bm2 is only 2.8 MB.
• Fast execution: It compiles directly to machine code, so command response takes only 3 milliseconds.
• Memory efficient: No runtime overhead, so resident memory is only 2.7 MB.
• Simple syntax: It's comfortable to write, making it quick to add features and fix bugs, allowing bm2 to be continuously refined.

Honestly, using MoonBit to write this kind of small system-level tool is a very fitting combination.

Moreover, the MoonBit ecosystem is gradually growing — package management and build tools are quite complete, and the barrier to writing tools is getting lower and lower.

MoonBit Official Site https://www.moonbitlang.cn/

Final words

If you're also looking for a pm2 replacement — something lighter, simpler, and more worry-free for process management — give bm2 a try.

It's written in MoonBit, representing a real-world application of MoonBit in the system tools domain.

If this article was helpful, feel free to like, share, and comment to give me some support and encouragement. Thanks.

I wonder what you think? Feel free to leave a comment.

Thanks for reading. I'm Chen Suiyi, the Frontend Tiger. Public account 陈随易, personal website: https://chensuiyi.me.