How to Get the inode Number of a File Using lstat()? Understand the Role and Significance of inode

M66 2025-06-22

In Linux or Unix-like systems, every file has a unique identifier called an inode. It not only identifies the location of a file but also stores the file's metadata, such as permissions, owner, file size, and creation and modification times. Understanding inode is crucial for a deeper understanding of file systems, especially when working with hard links, file permissions, and storage structures.

This article demonstrates how to obtain a file's inode number using the lstat() function in PHP, and explains the role and significance of inode through practical examples.

What is an inode?

In simple terms, an inode is the "identity card" of a file in the file system, and it contains the following information:

File type (regular file, directory, symbolic link, etc.)
File permissions
Owner and group of the file
File size
Creation, modification, and access times
Link count (number of hard links)
Data block pointers (actual storage locations of the file's data)

The filename itself is not stored in the inode. The filename is stored in the directory entry and is associated with the inode, linking the file content to its name.

Why Get the inode?

Hard links: Multiple different filenames can point to the same inode, creating "aliases" for the file.
Determining if files are the same: If two paths have the same inode number, they point to the same file.
File system debugging and maintenance: Administrators and developers can use the inode to determine the file's status, perform optimizations, and fix issues.

Introduction to PHP's lstat() Function

lstat() is a built-in PHP function that retrieves detailed information about a file or symbolic link, including its inode number. Unlike stat(), lstat() does not follow symbolic links but instead fetches information about the symbolic link itself.

lstat() returns an array containing various file attributes, and the 'ino' element represents the inode number.

Code Example: Get a File's inode Number Using lstat()

<?php
// Specify the path of the file to get information
$file = '/path/to/your/file.txt';
<p>// Use lstat to get file information<br>
$fileInfo = lstat($file);</p>
<p>if ($fileInfo === false) {<br>
echo "Unable to retrieve file information";<br>
} else {<br>
// Get the inode number<br>
$inode = $fileInfo['ino'];<br>
echo "The inode number of file {$file} is: {$inode}\n";<br>
}<br>
?><br>

Note: If you're trying to retrieve information about a remote file via URL, PHP's lstat() cannot directly handle remote files; it can only process local file paths.

Practical Example: Check if Two Files Are Hard Links

Assume there are two file paths, and we want to check whether they point to the same inode (i.e., whether they are hard links).

<?php
$file1 = '/path/to/file1.txt';
$file2 = '/path/to/file2.txt';
<p>$info1 = lstat($file1);<br>
$info2 = lstat($file2);</p>
<p>if ($info1 && $info2) {<br>
if ($info1['ino'] === $info2['ino']) {<br>
echo "Files {$file1} and {$file2} are hard links, with the same inode: {$info1['ino']}\n";<br>
} else {<br>
echo "Files {$file1} and {$file2} are not hard links, their inode numbers are different\n";<br>
}<br>
} else {<br>
echo "Unable to retrieve file information\n";<br>
}<br>
?><br>

Conclusion

Inode is a crucial concept in file systems and serves as the unique identifier for files.
PHP's lstat() function provides an easy way to obtain a file's inode number and other details.
Inode numbers can be used to check hard links, file identity verification, and other scenarios.
Understanding inode helps in mastering file system structure and file management.

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