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 :

存储会话的目录不存在或php没有足够的写入权限.

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，只需在 php.ini 中添加以下行:

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

session.save_path="/tmp/php_session/"

并赋予 http 服务器写入权限.

And give write rights to the http server.

通常，http 服务器作为组守护进程中的用户守护进程运行.如果是这种情况，以下命令将使其成功:

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