Description
int 
umask ( [int mask] )
     umask() sets PHP's umask to 
     mask & 0777 and returns the old
     umask. When PHP is being used as a server module, the umask
     is restored when each request is finished.
    
     umask() without arguments simply returns the
     current umask.
    
Note: 
      Avoid using this function in multithreaded webservers. It is better to
      change the file permissions with chmod() after
      creating the file. Using umask() can lead to
      unexpected behavior of concurrently running scripts and the webserver
      itself because they all use the same umask.
     
     
Example 1. umask() example 
<?php $old = umask(0); chmod("/path/some_dir/some_file.txt", 0755); umask($old);
  // Checking if ($old != umask()) {     die('An error occured while changing back the umask'); } ?>
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