[root@mysqld ~]# yum list |grep telnet telnet.x86_64 1:0.17-48.el6 @base telnet-server.x86_64 1:0.17-48.el6 base [root@mysqld ~]# which telnet /usr/bin/telnet
[root@mysqld ~]# telnet 123.56.78.103 3306 Trying 123.56.78.103... Connected to 123.56.78.103. Escape character is '^]'. N 5.5.40-logxxxxxpassword#证明3306端口开了
[root@mysqld ~]# telnet 123.56.78.103 22 Trying 123.56.78.103... Connected to 123.56.78.103. Escape character is '^]'. SSH-2.0-OpenSSH_6.6.1p1 Ubuntu-2ubuntu2 #证明22端口开发
[root@mysqld ~]# telnet 123.56.78.103 23 Trying 123.56.78.103... telnet: connect to address 123.56.78.103: Connection refused #证明23端口没开