当保存php_session的路径设置不正确时，这可能是一个问题:

This is a possible issue when the path to save php_session is not correctly set :

用于存储会话的目录不存在，或者php没有足够的权限来写入会话.

The directory for storing session does not exists or php do not have sufficient rights to write to it.

要定义php_session目录，只需将以下行添加到php.ini中:

To define the php_session directory simply add the following line to the php.ini :

session.save_path="/tmp/php_session/"

并授予对http服务器的写权限.

And give write rights to the http server.

通常，http服务器在组守护程序中以用户守护程序的身份运行.如果是这样，可以使用以下命令:

usually, the http server run as user daemon in group daemon. If it is the case, the following commands will make it :

chown -R :daemon /tmp/php_session

chmod -R g+wr /tmp/php_session

service httpd restart