由于登陆使用了如下命令：
shell> ./bin/mysqld_safe --user=root &
导致再次登陆时候使用
shell> ./bin/mysqld_safe --user=mysql &
报错：
mysqld_safe Logging to '/usr/local/mysql/data/Linux.err'.
mysqld_safe Starting mysqld daemon with databases from /usr/local/mysql/data
mysqld_safe mysqld from pid file /usr/local/mysql/data/Linux.pid ended
解决方法：初始化mysql
/usr/local/mysql/scripts/mysql_install_db --user=mysql
可以成功登陆