How to implement a Daemon program using Node.js

Daemon is a program that runs in the background, usually used for long-running services that do not require direct user operation. In Node.js, you can implement a Daemon program through some simple methods. In this article, we will introduce how to use Node.js to implement a Daemon program.

Implementation

You can use the spawn method of child_process to create a process in Node.js. By putting this process to run in the background, the Daemon program can be implemented. The following are the implementation steps:

1. Create a Node.js script, which is the main program of the Daemon program. This can be achieved using the following code:

const spawn = require('child_process').spawn;

const child = spawn(process.argv[0], process.argv.slice(2), {
    detached: true,
    stdio: 'ignore'
});

child.unref();

In the above code, the spawn method is used to create a child process, where the first parameter is the executable file path of Node.js, and the second parameter is The path to the main program. The third parameter contains options for creating subprocesses. Among them, detached is set to true to separate the child process from the main process, that is, the child process runs as a separate process; stdio is set to 'ignore' to indicate that the standard input and output of the child process is not bound to the main process.

The unref() method can separate the created subprocess from the main process, that is, when the main process exits, the subprocess will still continue to run.

2. To run the main program in the background, you can use the following command:

nohup node main.js > /dev/null 2>&1 &

In the above commands, the nohup command is used to run the main program in the background, and '> ; /dev/null 2>&1 &' means redirecting the program output to /dev/null so that it will not be displayed on the console.

3. Run the main program as a system service, you can use pm2 or systemd. In this article, systemd is used as an example. First, create a file named mydaemon.service. The content of the file is as follows:

[Unit]
Description=My Daemon

[Service]
ExecStart=/usr/bin/node /path/to/main.js
Restart=always
User=<your_username>
Group=<your_group>
StandardOutput=syslog
StandardError=syslog
SyslogIdentifier=mydaemon

[Install]
WantedBy=multi-user.target

In the above file, the Description field is used to describe the service; the ExecStart field specifies the startup command of the service, that is, executing Node .js script; the Restart field specifies the restart strategy of the service; the User and Group fields specify the user and user group under which the service runs; the StandardOutput and StandardError fields respectively redirect the output of the service to the system log; the SyslogIdentifier field specifies the service in the system Identifier in the log.

4. Copy the mydaemon.service file to the /systemd/system/ directory, and then execute the following command:

sudo systemctl daemon-reload
sudo systemctl enable mydaemon
sudo systemctl start mydaemon

The first command is used to reload the systemd configuration, The second command is used to set the service to start automatically at boot, and the third command is used to start the service.

Summary

This article introduces the method of using Node.js to implement a Daemon program, including creating a child process through the spawn method, running the program in the background, and running it as a system service. Through these methods, you can implement a long-running program that can continue to run when the main program exits.

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