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In PHP, the disk_total_space() function can be used to obtain the total size of a filesystem or disk partition. This function is very useful for server monitoring, disk space alerts, and related features. However, in actual use, some developers encounter an issue: even though their code has no syntax errors, calling disk_total_space() returns nothing, or even throws a warning such as “Permission denied” or similar permission-related errors.
So how exactly do these permission issues arise, and how can they be diagnosed and resolved? This article will walk through possible causes and provide practical solutions.
You might typically write code like this:
<span><span><span class="hljs-variable">$disk</span></span><span> = </span><span><span class="hljs-string">'/var/www/'</span></span><span>;
</span><span><span class="hljs-variable">$space</span></span><span> = </span><span><span class="hljs-title function_ invoke__">disk_total_space</span></span><span>(</span><span><span class="hljs-variable">$disk</span></span><span>);
</span><span><span class="hljs-title function_ invoke__">var_dump</span></span><span>(</span><span><span class="hljs-variable">$space</span></span><span>);
</span></span>Ideally, this should return an integer representing the total number of bytes on the filesystem where that path is located. But in reality, it returns false, sometimes accompanied by warnings such as:
<span><span>Warning: </span><span><span class="hljs-built_in">disk_total_space</span></span><span>(): open_basedir restriction in effect. </span><span><span class="hljs-built_in">File</span></span><span>(/var/www/) is not within the allowed </span><span><span class="hljs-built_in">path</span></span><span>(s): ...
</span></span>Or:
<span><span><span class="hljs-built_in">Warning</span></span><span>: disk_total_space(): failed </span><span><span class="hljs-keyword">to</span></span><span> </span><span><span class="hljs-keyword">open</span></span><span> dir: Permission denied
</span></span>This is the most basic issue. disk_total_space() requires a valid directory path that exists. If the path you provide doesn’t exist, the function cannot work.
Troubleshooting:
Use is_dir() or file_exists() to check if the path exists;
Verify that the path is spelled correctly, especially since Linux is case-sensitive.
<span><span><span class="hljs-keyword">if</span></span><span> (!</span><span><span class="hljs-title function_ invoke__">is_dir</span></span><span>(</span><span><span class="hljs-variable">$disk</span></span><span>)) {
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"Directory does not exist: <span class="hljs-subst">$disk</span></span></span><span>";
}
</span></span>The PHP process running under the web server (such as Apache or Nginx) may be executed by a user (like www-data, apache, etc.) that does not have permission to access the directory you provided.
Troubleshooting:
Use ls -ld /path/to/dir to check the directory’s permissions;
Use whoami and ps aux | grep php to confirm the PHP process user;
Test in CLI mode to see if there’s a difference, since CLI usually runs with the current logged-in user’s permissions, which are often higher;
Try accessing the / root directory to test if the restriction is global.
Solutions:
Use chown or chmod to grant proper permissions (adjust according to security needs);
Place the target path within a directory PHP has access to.
<span><span>sudo </span><span><span class="hljs-built_in">chmod</span></span><span> o+rx /var/www/
</span></span>(Note: For security reasons, be cautious when changing permissions and avoid granting full write access to entire directories.)
open_basedir is a PHP configuration directive that restricts the directories PHP scripts are allowed to access. If the path you pass in is outside this scope, disk_total_space() will be blocked.
Troubleshooting:
Check php.ini or use phpinfo() to find the open_basedir value;
If you see something like /home/user:/tmp, and your $disk is not included, you’ll get an error.
Solutions:
Edit php.ini, .htaccess, or the PHP-FPM pool configuration to add the required directory to the open_basedir list;
If using a hosting control panel (such as cPanel, Plesk), adjust the allowed paths via its settings.
<span><span>php_admin_value open_basedir "/var/www/:/tmp/"
</span></span>On Linux systems with SELinux or AppArmor enabled, even if file permissions are correct, security policies may still block PHP from accessing certain paths.
Troubleshooting:
Check if SELinux is enabled: run getenforce;
Review audit logs: /var/log/audit/audit.log or analyze with audit2why;
Use ls -Z to check SELinux context of the path.
Solutions:
Temporarily disable SELinux (not recommended for production);
Adjust SELinux policy or use chcon to assign the proper context;
For AppArmor, modify the relevant profile.
<span><span>sudo </span><span><span class="hljs-built_in">chcon</span></span><span> -t httpd_sys_content_t /var/www/ -R
</span></span>Validate Paths First: Always ensure the path exists and is valid before calling the function.
Log Tracking: Reviewing PHP error logs can quickly point you to the root cause.
Principle of Least Privilege: Grant PHP only the permissions it needs, and avoid exposing the entire system.
Production Isolation: Restrict access using containers or chroot environments for better security.
Compare CLI vs Web Modes: Some paths may work under CLI but fail in web context; comparing both helps pinpoint issues.
disk_total_space() is a small but frequently used function, and it involves filesystem access permissions, PHP security settings, and even system-level security policies. Therefore, when it returns false or throws errors, don’t just focus on the PHP code itself — consider operating system permissions, web server configurations, and security policies. Only by looking at the issue from multiple dimensions can you efficiently identify and resolve the problem.
Hopefully, this article will help you handle such issues more confidently in the future.
