Why can't PHP create a directory with 777 permissions?

PHP's mkdir() function, which is used to create a new directory, defaults to a mode of 0777. The actual permissions are determined by applying the server's current umask setting, which masks specific permission bits from the requested mode. For example, if the requested mode is 0777 and the umask is 0022, the actual permissions of the new directory will be 0755.

If the server's umask is set to a value that masks out the write bits, then the mkdir() function will not be able to create a directory with 0777 permissions. The server administrator can change the umask setting to allow for more permissive permissions, but this may be a security risk and is not recommended.

Additionally, PHP's chmod() function can be used to change the permissions of a directory after it has been created. Unlike mkdir(), chmod() explicitly overrides the umask and applies the exact permissions you specify:

$dir = '/path/to/new/dir';
mkdir($dir, 0777);
chmod($dir, 0777);

Alternatively, you can temporarily adjust the umask before calling mkdir(), though this affects all subsequent file operations in the same process:

$oldUmask = umask(0);
mkdir('/path/to/new/dir', 0777);
umask($oldUmask);