例题一：扫瞄单一部计算机！
[root@test root]# nmap localhost　　
# 没有加上任何参数，由 nmap 的预设参数来进行扫瞄
Starting nmap V. 2.54BETA22 ( www.insecure.org/nmap/ )
Interesting ports on vbird.adsldns.org (127.0.0.1):
(The 1539 ports scanned but not shown below are in state: closed)
Port       State       Service
21/tcp     open        ftp
22/tcp     open        ssh
23/tcp     open        telnet
Nmap run completed -- 1 IP address (1 host up) scanned in 1 second
# 由上面可以看出我的系统目前共有 21, 22, 23 这三个 port 开放！而且
# 各 port 对应的服务也被查出来了！

例题二：扫瞄单一部计算机的较少数 port 号码！
[root@test root]# nmap -p 1024-65535 localhost
# 仅扫瞄较少数的 port 啦！
Starting nmap V. 2.54BETA22 ( www.insecure.org/nmap/ )
Interesting ports on pc510.ev.ncku.edu.tw (127.0.0.1):
(The 64511 ports scanned but not shown below are in state: closed)
Port       State       Service
3306/tcp   open        mysql <==只有这个 port 被找出来啰！
Nmap run completed -- 1 IP address (1 host up) scanned in 11 seconds

例题三：直接以 Ping 的方式扫瞄数个计算机！
[root @test /root]# nmap -PT 192.168.1.171-177 
# 看到了吧！扫瞄一个区段的活着的计算机！

Starting nmap V. 2.54BETA22 ( www.insecure.org/nmap/ )
Interesting ports on linux172 (192.168.1.172):
(The 1536 ports scanned but not shown below are in state: closed)
Port       State       Service
110/tcp    open        pop-3
135/tcp    open        loc-srv
139/tcp    open        netbios-ssn
445/tcp    open        microsoft-ds
1025/tcp   open        listen
1110/tcp   open        nfsd-status

Interesting ports on linux174 (192.168.1.174):
(The 1537 ports scanned but not shown below are in state: closed)
Port       State       Service
110/tcp    open        pop-3
135/tcp    open        loc-srv
139/tcp    open        netbios-ssn
445/tcp    open        microsoft-ds
1025/tcp   open        listen

Interesting ports on linux176 (192.168.1.176):
(The 1537 ports scanned but not shown below are in state: closed)
Port       State       Service
110/tcp    open        pop-3
135/tcp    open        loc-srv
139/tcp    open        netbios-ssn
445/tcp    open        microsoft-ds
1025/tcp   open        listen

Nmap run completed -- 7 IP addresses (3 hosts up) scanned in 1 second
瞧！我要侦测的只有七部计算机，所以这七部计算机只会响应给我啰！而其中只有三部有启动，所以当然就只会有三段响应啦！这个方式蛮适合一次扫瞄您的子网域内的所有计算机呢！ ^_^"

2. 重新开机让设定生效：
[root@test root]# reboot

3. 观察目前的 port 开启多少个？
[root@test root]# netstat -an | more
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
Active UNIX domain sockets (servers and established)
Proto RefCnt Flags       Type       State         I-Node Path
unix  7      [ ]         DGRAM                    944    /dev/log
unix  2      [ ]         DGRAM                    3162963
unix  2      [ ]         DGRAM                    739227
unix  2      [ ]         DGRAM                    739189
unix  2      [ ]         DGRAM                    1070
unix  2      [ ]         DGRAM                    953
unix  2      [ ]         STREAM     CONNECTED     690