MySQL的第二个实例客户端连接问题

[七彩虹]

我在Ubuntu下装了两个MySQL实例，一个在3306端口，另一个在3307端口。

第一个实例可以用mysql -u root -p 来连接， 没问题。

第二个实例只能用mysql --protocol=tcp --port=3307, -h127.0.0.1 -u root -p 来连接。如果我用mysql -u root -p --socket=/var/lib/mysql2/mysqld2.sock 来连接，就会报错：ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/lib/mysql2/mysqld2.sock' (13)

我查了一下，我其实有这个socket文件，为什么系统还要报错呢？
sudo ls -l /var/lib/mysql2/mysqld2.sock
srwxrwxrwx 1 mysql mysql 0 Nov 4 16:30 /var/lib/mysql2/mysqld2.sock

以下是我的my.cnf 文件的一部分，请指点哪个地方出问题了。 谢谢。

[mysqld_safe]
socket = /var/lib/mysql2/mysqld2.sock
nice = 0

[mysqld_multi]
mysqld = /usr/bin/mysqld_safe
mysqladmin = /usr/bin/mysqladmin
user = boss
password = boss

[mysqld1]
#
# * Basic Settings
#
user = mysql
pid-file = /var/run/mysqld/mysqld.pid
socket = /var/run/mysqld/mysqld.sock
port = 3306
basedir = /usr
datadir = /var/lib/mysql
tmpdir = /tmp
lc-messages-dir = /usr/share/mysql
skip-external-locking

[mysqld2]
pid-file = /var/lib/mysql2/mysqld2.pid
socket = /var/lib/mysql2/mysqld2.sock
port = 3307
datadir = /var/lib/mysql2
user = mysql
tmpdir = /tmp
log-error = /var/log/mysql2.err