Adds systemd guide to run a bun application as a daemon (#6451)

* systemd-guide

* remove-root-from-example

* add-more-description

* Updates

* Updates

* Updates

* Update

---------

Co-authored-by: Colin McDonnell <colinmcd94@gmail.com>

1 files changed, 113 insertions, 0 deletions

diff --git a/docs/guides/ecosystem/systemd.md b/docs/guides/ecosystem/systemd.md
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+---
+name: Run Bun as a daemon with systemd
+---
+
+[systemd](https://systemd.io) is an init system and service manager for Linux operating systems that manages the startup and control of system processes and services.
+
+<!-- systemd provides aggressive parallelization capabilities, uses socket and D-Bus activation for starting services, offers on-demand starting of daemons, keeps track of processes using Linux control groups, maintains mount and auto mount points, and implements an elaborate transactional dependency-based service control logic. systemd supports SysV and LSB init scripts and works as a replacement for sysvinit. -->
+
+<!-- Other parts include a logging daemon, utilities to control basic system configuration like the hostname, date, locale, maintain a list of logged-in users and running containers and virtual machines, system accounts, runtime directories and settings, and daemons to manage simple network configuration, network time synchronization, log forwarding, and name resolution. -->
+
+---
+
+To run a Bun application as a daemon using **systemd** you'll need to create a _service file_ in `/lib/systemd/system/`.
+
+```sh
+$ cd /lib/systemd/system
+$ touch my-app.service
+```
+
+---
+
+Here is a typical service file that runs an application on system start. You can use this as a template for your own service. Replace `YOUR_USER` with the name of the user you want to run the application as. To run as `root`, replace `YOUR_USER` with `root`, though this is generally not recommended for security reasons.
+
+Refer to the [systemd documentation](https://www.freedesktop.org/software/systemd/man/systemd.service.html) for more information on each setting.
+
+```ini#my-app.service
+[Unit]
+# describe the app
+Description=My App
+# start the app after the network is available
+After=network.target
+
+[Service]
+# usually you'll use 'simple'
+# one of https://www.freedesktop.org/software/systemd/man/systemd.service.html#Type=
+Type=simple
+# which user to use when starting the app
+User=YOUR_USER
+# path to your application's root directory
+WorkingDirectory=/home/YOUR_USER/path/to/my-app
+# the command to start the app
+# requires absolute paths
+ExecStart=/home/YOUR_USER/.bun/bin/bun run index.ts
+# restart policy
+# one of {no|on-success|on-failure|on-abnormal|on-watchdog|on-abort|always}
+Restart=always
+
+[Install]
+# start the app automatically
+WantedBy=multi-user.target
+```
+
+---
+
+If your application starts a webserver, note that non-`root` users are not able to listen on ports 80 or 443 by default. To permanently allow Bun to listen on these ports when executed by a non-`root` user, use the following command. This step isn't necessary when running as `root`.
+
+```bash
+$ sudo setcap CAP_NET_BIND_SERVICE=+eip ~/.bun/bin/bun
+```
+
+---
+
+With the service file configured, you can now _enable_ the service. Once enabled, it will start automatically on reboot. This requires `sudo` permissions.
+
+```bash
+$ sudo systemctl enable my-app
+```
+
+---
+
+To start the service without rebooting, you can manually _start_ it.
+
+```bash
+$ sudo systemctl start my-app
+```
+
+---
+
+Check the status of your application with `systemctl status`. If you've started your app successfully, you should see something like this:
+
+```bash
+$ sudo systemctl status my-app
+● my-app.service - My App
+     Loaded: loaded (/lib/systemd/system/my-app.service; enabled; preset: enabled)
+     Active: active (running) since Thu 2023-10-12 11:34:08 UTC; 1h 8min ago
+   Main PID: 309641 (bun)
+      Tasks: 3 (limit: 503)
+     Memory: 40.9M
+        CPU: 1.093s
+     CGroup: /system.slice/my-app.service
+             └─309641 /home/YOUR_USER/.bun/bin/bun run /home/YOUR_USER/application/index.ts
+```
+
+---
+
+To update the service, edit the contents of the service file, then reload the daemon.
+
+```bash
+$ sudo systemctl daemon-reload
+```
+
+---
+
+For a complete guide on the service unit configuration, you can check [this page](https://www.freedesktop.org/software/systemd/man/systemd.service.html). Or refer to this cheatsheet of common commands:
+
+```bash
+$ sudo systemctl daemon-reload # tell systemd that some files got changed
+$ sudo systemctl enable my-app # enable the app (to allow auto-start)
+$ sudo systemctl disable my-app # disable the app (turns off auto-start)
+$ sudo systemctl start my-app # start the app if is stopped
+$ sudo systemctl stop my-app # stop the app
+$ sudo systemctl restart my-app # restart the app
+```