1.phpsession_start();
$_SESSION['username'] = "aaa";
echo "<a href=\"2.php\">2.php</a>";2.php
session_start();
echo $_SESSION['username'];
$_SESSION['username'] = "aaa";
echo "<a href=\"2.php\">2.php</a>";2.php
session_start();
echo $_SESSION['username'];
session_start();
session_distroy();