PHP chmod Function

last modified April 3, 2025

The PHP chmod function changes file permissions on Unix-like systems. It allows setting read, write, and execute permissions for owner, group, and others.

Basic Definition

The chmod function attempts to change the mode of specified file. It takes two parameters: the filename and the permission mode in octal format.

Syntax: chmod(string $filename, int $mode): bool. Returns true on success or false on failure. The mode should be an octal number (like 0755).

Basic chmod Example

This shows the simplest usage of chmod to set file permissions.

basic_chmod.php

<?php

declare(strict_types=1);

$file = "example.txt";
$result = chmod($file, 0644);

if ($result) {
    echo "Permissions changed successfully";
} else {
    echo "Failed to change permissions";
}

This sets permissions to 644 (owner read/write, group/others read-only). The function returns true if successful, false otherwise. Always check the return.

Setting Executable Permissions

This example makes a file executable by the owner while keeping other permissions.

executable_chmod.php

<?php

declare(strict_types=1);

$script = "backup.sh";
$result = chmod($script, 0750);

if ($result) {
    echo "Script is now executable by owner";
} else {
    echo "Failed to make script executable";
}

The mode 0750 gives owner full permissions (read/write/execute), group read and execute, and no permissions for others. The leading 0 indicates octal notation.

Directory Permissions

chmod can also change permissions for directories, not just files.

directory_chmod.php

<?php

declare(strict_types=1);

$dir = "uploads";
$result = chmod($dir, 0775);

if ($result) {
    echo "Directory permissions updated";
} else {
    echo "Failed to update directory permissions";
}

This sets 775 permissions (full for owner/group, read/execute for others). Directories typically need execute permission to allow accessing their contents.

Restrictive Permissions

This example shows how to set very restrictive permissions for sensitive files.

restrictive_chmod.php

<?php

declare(strict_types=1);

$config = "database.ini";
$result = chmod($config, 0600);

if ($result) {
    echo "Config file now has strict permissions";
} else {
    echo "Failed to secure config file";
}

Mode 0600 gives read/write to owner only, with no permissions for group/others. This is common for sensitive files like configuration files with passwords.

Relative Path Handling

This example demonstrates handling relative paths with chmod.

relative_path.php

<?php

declare(strict_types=1);

$relativeFile = "../logs/app.log";
$result = chmod($relativeFile, 0664);

if ($result) {
    echo "Log file permissions updated";
} else {
    echo "Failed to update log file permissions";
}

chmod works with relative paths. However, the PHP process must have permission to change the target file's permissions for it to succeed.

Best Practices

Security: Avoid overly permissive settings like 0777.
Error Handling: Always check the return value.
Octal Notation: Use leading 0 for octal modes.
File Ownership: Ensure PHP has permission to change modes.
Cross-platform: Note Windows limitations.

Source

PHP chmod Documentation

This tutorial covered the PHP chmod function with practical examples showing how to change file permissions in different scenarios.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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