netstat命令是一个监控TCP/IP网络的非常有用的工具，它可以显示路由表、实际的网络连接以及每一个网络接口设备的状态信息

输出结果可以分为两个部分，一个是Active Internet connections，另一个是Active UNIX domain sockets.

[root@DBSVR02 conf]# netstat
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address               Foreign Address             State     
tcp        0      0 168.168.80.9:ssh            168.168.80.1:22332          ESTABLISHED
tcp        0      0 168.168.80.9:ssh            168.168.80.1:22864          ESTABLISHED
Active UNIX domain sockets (w/o servers)
Proto RefCnt Flags       Type       State         I-Node Path
unix  12     [ ]         DGRAM                    11595  /dev/log
unix  2      [ ]         DGRAM                    8807   @/org/kernel/udev/udevd
unix  2      [ ]         DGRAM                    12403  @/org/freedesktop/hal/udev_event
unix  3      [ ]         STREAM     CONNECTED     15684  /var/lib/mysql/mysql.sock
unix  3      [ ]         STREAM     CONNECTED     15683 
unix  2      [ ]         DGRAM                    14977 
unix  2      [ ]         DGRAM                    14485 
unix  2      [ ]         DGRAM                    13976 
unix  3      [ ]         STREAM     CONNECTED     13438  /var/run/dbus/system_bus_socket
unix  3      [ ]         STREAM     CONNECTED     13437 
unix  2      [ ]         DGRAM                    13276 
unix  2      [ ]         DGRAM                    13138 
unix  2      [ ]         DGRAM                    13067 
unix  3      [ ]         STREAM     CONNECTED     13051 
unix  3      [ ]         STREAM     CONNECTED     13050 
unix  3      [ ]         STREAM     CONNECTED     13047 
unix  3      [ ]         STREAM     CONNECTED     13046 

netstat 的常用参数: -t、-u、-w和 -x分别表示TCP、UDP、RAW和UNIX套接字连接。

-a标记，还会显示出等待连接（也就是说处于监听模式）的套接字。

-l 显示正在被监听(listen)的端口。

 -n表示直接显示端口数字而不是通过察看/etc/service来转换为端口名。

-p选项表示列出监听的程序

[root@DBSVR02 conf]# netstat -nat
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address               Foreign Address             State     
tcp        0      0 0.0.0.0:50790               0.0.0.0:*                   LISTEN     
tcp        0      0 0.0.0.0:111                 0.0.0.0:*                   LISTEN     
tcp        0      0 0.0.0.0:22                  0.0.0.0:*                   LISTEN     
tcp        0      0 127.0.0.1:631               0.0.0.0:*                   LISTEN     
tcp        0      0 127.0.0.1:25                0.0.0.0:*                   LISTEN     
tcp        0      0 168.168.80.9:22             168.168.80.1:22332          ESTABLISHED
tcp        0      0 168.168.80.9:22             168.168.80.1:22864          ESTABLISHED
tcp        0      0 :::42855                    :::*                        LISTEN     
tcp        0      0 :::111                      :::*                        LISTEN     
tcp        0      0 :::80                       :::*                        LISTEN     
tcp        0      0 :::22                       :::*                        LISTEN     
tcp        0      0 ::1:631                     :::*                        LISTEN     
tcp        0      0 ::1:25                      :::*                        LISTEN     
[root@DBSVR02 conf]#

• 查看当前tcp监听端口

[root@DBSVR02 conf]# netstat -tl
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address               Foreign Address             State     
tcp        0      0 *:50790                     *:*                         LISTEN     
tcp        0      0 *:sunrpc                    *:*                         LISTEN     
tcp        0      0 *:ssh                       *:*                         LISTEN     
tcp        0      0 localhost:ipp               *:*                         LISTEN     
tcp        0      0 localhost:smtp              *:*                         LISTEN     
tcp        0      0 *:42855                     *:*                         LISTEN     
tcp        0      0 *:sunrpc                    *:*                         LISTEN     
tcp        0      0 *:http                      *:*                         LISTEN     
tcp        0      0 *:ssh                       *:*                         LISTEN     
tcp        0      0 localhost:ipp               *:*                         LISTEN     
tcp        0      0 localhost:smtp              *:*                         LISTEN     
[root@DBSVR02 conf]#

•  查看当前tcp监听端口, 需要显示监听的程序名,当不清楚mysql的监听端口时比较好用

[root@DBSVR02 conf]# netstat -tlp
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address               Foreign Address             State       PID/Program name  
tcp        0      0 *:50790                     *:*                         LISTEN      1216/rpc.statd     
tcp        0      0 *:sunrpc                    *:*                         LISTEN      1197/rpcbind       
tcp        0      0 *:ssh                       *:*                         LISTEN      1474/sshd          
tcp        0      0 localhost:ipp               *:*                         LISTEN      1360/cupsd         
tcp        0      0 localhost:smtp              *:*                         LISTEN      1550/master        
tcp        0      0 *:42855                     *:*                         LISTEN      1216/rpc.statd     
tcp        0      0 *:sunrpc                    *:*                         LISTEN      1197/rpcbind       
tcp        0      0 *:http                      *:*                         LISTEN      1590/httpd         
tcp        0      0 *:ssh                       *:*                         LISTEN      1474/sshd          
tcp        0      0 localhost:ipp               *:*                         LISTEN      1360/cupsd         
tcp        0      0 localhost:smtp              *:*                         LISTEN      1550/master        
[root@DBSVR02 conf]#