如何查看服务器是否开放某个端口
以查询873端口为例：
① # ss -lntup|grep 873
[root@backup nfsbackup]# ss-lnutp|grep 873
tcp LISTEN 0 64 :::873 :::* users:(("xinetd",1810,5))
[root@backup nfsbackup]#
② # netstat -lntup|grep 873
[root@backup nfsbackup]# netstat-lnutp|grep 873
tcp 0 0 :::873 :::* LISTEN 1810/xinetd
[root@backup nfsbackup]#
③ # lsof -i :873
[root@backup nfsbackup]# lsof -i:873
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODENAME
xinetd 1810 root 5u IPv6 12433 0t0 TCP *:rsync (LISTEN)
[root@backup nfsbackup]#
④ # telnet 10.0.0.41 873（linux yuminstall telnet）
[root@web02 ~]# telnet 172.16.1.41873
Trying 172.16.1.41...
Connected to 172.16.1.41.
Escape character is '^]'.
@RSYNCD: 30.0
⑤ # nc 10.0.0.41 873
[root@web02 ~]# nc 172.16.1.41 873
@RSYNCD: 30.0
⑥ # nmap -p 873 10.0.0.41
[root@web02 ~]#nmap -p 873 172.16.1.41 ##扫描主机
Starting Nmap 5.51 ( http://nmap.org) at 2017-05-13 13:41 CST
Nmap scan report for backup (172.16.1.41)
Host is up (0.00069s latency).
PORT STATE SERVICE
873/tcp open rsync
MAC Address: 00:0C:29:01:17:0F(VMware)
Nmap done: 1 IP address (1 host up)scanned in 0.20 seconds
[root@web02 ~]# nmap-p 873 172.16.1.0/24 ###扫描网段
Starting Nmap 5.51 ( http://nmap.org) at 2017-05-13 13:41 CST
Nmap scan report for web01(172.16.1.7)
Host is up (0.00018s latency).
PORT STATE SERVICE
873/tcp closed rsync
Nmap scan report for web02(172.16.1.8)
Host is up (0.00072s latency).
PORT STATE SERVICE
873/tcp closed rsync
MAC Address: 00:0C:29:B1:33:AE(VMware)
Nmap scan report for nfs01(172.16.1.31)
Host is up (0.00039s latency).
PORT STATE SERVICE
873/tcp closed rsync
MAC Address: 00:0C:29:86:08:29(VMware)
Nmap scan report for backup(172.16.1.41)
Host is up (0.00057s latency).
PORT STATE SERVICE
873/tcp open rsync
MAC Address: 00:0C:29:01:17:0F(VMware)
Nmap done: 256 IP addresses (4 hostsup) scanned in 2.02 seconds
[root@web02 ~]#