The fs.fchmodSync() method is an inbuilt application programming of fs module which is used to synchronously change the permissions of a given file descriptor. These permissions can be specified as a parameter using string constants or octal numbers that corresponding to their respective file modes.
Note: The Windows platform only supports the changing of the write permission. It also does not support the distinction between the permissions of user, group, or others.
Syntax:
fs.fchmodSync( fd, mode )
Parameters: This method accepts two parameters as mentioned above and described below:
- fd: It is an integer which denotes the file descriptor of the file of which the permission has to be changed.
- mode: It is string constant or octal constant that denotes the permission to be granted. The logical OR operator can be used to separate multiple permissions.
Below examples illustrate the fs.fchmodSync method in Node.js:
Example 1: This example shows the usage of string constants and OR operator to give the file permissions.
// Node.js program to demonstrate the // fs.fchmodSync method // Import the filesystem module const fs = require('fs');
// Getting the file descriptor const fd = fs.openSync('example_file.txt', 'r');
// Allowing only read permission console.log("Giving only read permission to user");
fs.fchmodSync(fd, fs.constants.S_IRUSR); // Check the file mode console.log("Current File Mode:",
fs.statSync("example_file.txt").mode);
// Reading the file console.log("File Contents:",
fs.readFileSync("example_file.txt", 'utf8'));
// Trying to write to file try {
console.log("Trying to write to file");
fs.writeFileSync('example_file.txt', "Hello");
} catch (e) {
console.log("Error Found, Code:", e.code);
} // Allowing both read and write permission console.log("\nGiving both read and write permission to user");
fs.fchmodSync(fd, fs.constants.S_IRUSR | fs.constants.S_IWUSR); // Check the file mode console.log("Current File Mode:",
fs.statSync("example_file.txt").mode);
console.log("Trying to write to file");
fs.writeFileSync('example_file.txt',
"This file has been written over.");
console.log("File Contents:",
fs.readFileSync("example_file.txt", 'utf8'));
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Output:
Giving only read permission to user Current File Mode: 33024 File Contents: Hello World Trying to write to file Error Found, Code: EACCES Giving both read and write permission to user Current File Mode: 33152 Trying to write to file File Contents: This file has been written over.
Example 2: This example shows the usage of octal constants to give the file permissions.
// Node.js program to demonstrate the // fs.fchmodSync method // Import the filesystem module const fs = require('fs');
// Getting the file descriptor const fd = fs.openSync('example_file.txt', 'r');
// Allowing only read permission console.log("Giving only read permission to everyone");
fs.fchmodSync(fd, 0o444); // Check the file mode console.log("Current File Mode:",
fs.statSync("example_file.txt").mode);
// Reading the file console.log("File Contents:",
fs.readFileSync("example_file.txt", 'utf8'));
// Trying to write to file try {
console.log("Trying to write to file");
fs.writeFileSync('example_file.txt', "Hello");
} catch (e) {
console.log("Error Found, Code:", e.code);
} // Allowing both read and write permission console.log("\nGiving both read and "
+ "write permission to everyone");
fs.fchmodSync(fd, 0o666); // Check the file mode console.log("Current File Mode:",
fs.statSync("example_file.txt").mode);
console.log("Trying to write to file");
fs.writeFileSync('example_file.txt',
"This file has been written over.");
console.log("File Contents:",
fs.readFileSync("example_file.txt", 'utf8'));
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Output:
Giving only read permission to everyone Current File Mode: 33060 File Contents: Hello World Trying to write to file Error Found, Code: EACCES Giving both read and write permission to everyone Current File Mode: 33206 Trying to write to file File Contents: This file has been written over.
Reference: https://nodejs.org/api/fs.html#fs_fs_fchmodsync_fd_mode