telnet 测试端口是否打开

[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