Linux 如何检查某个端口是否打开和未使用？
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How to check if a certain port is open and unused?
提问by Richa
I want to install webserver-apache on a Linux platform which uses port no.80 but I am not sure whether is port is open or not , and being used by some other application or not.
我想在使用端口号 80 的 Linux 平台上安装 webserver-apache，但我不确定端口是否打开，以及是否被其他应用程序使用。
- Output of
grep 80 /etc/servicesis:
- 的输出
grep 80 /etc/services是：
http 80/tcp www www-http #World Wide web Http
http 80/tcp www www-http #World Wide web Http
http 80/udp www www-http #Hypertext transfer protocol
http 80/udp www www-http #Hypertext transfer protocol
2.netstat -an | grep 80 | more:
2 netstat -an | grep 80 | more.：
It gives some IP's one of which is IP:80 TIME_WAIT
它提供了一些 IP，其中之一是 IP:80 TIME_WAIT
Could you please help and tell how can i find out if port 80 is open and unused so that I can start installation.
能否请您帮忙告诉我如何确定端口 80 是否已打开且未使用，以便我可以开始安装。
回答by Dillon Benson
Try piping lsof into grep and searching for a port number:
尝试将 lsof 管道输入 grep 并搜索端口号：
lsof|grep <port>
If nothing shows up that means the port is not in use
如果没有任何显示，则表示该端口未在使用中
You can kill a process on a specific port using
您可以使用以下命令终止特定端口上的进程
kill -9 <pid>
Where pid is the process id obtained from the first command.
其中 pid 是从第一个命令获得的进程 ID。
回答by MichaelMoser
netstat -tln | tail -n +3 | awk '{ print }'
this one displays bind addresses of tcp listening endpoint. all other endpoints are free; Also if on Unix and you are not root, then you can't bind to a 'privileged' port number (port number lower than 1024)
这个显示 tcp 侦听端点的绑定地址。所有其他端点都是免费的；此外，如果在 Unix 上并且您不是 root，则无法绑定到“特权”端口号（端口号低于 1024）
explained in more detail:
更详细地解释：
netstat -tln - all listening tcp ports
netstat -tln - 所有监听 tcp 端口
tail -n +3 - cut of the header of netstat
tail -n +3 - netstat 头部的剪切
awk '{ print $4 }' - print the fourth column that consists of [ip]:[port]
awk '{print $4 }' - 打印由 [ip]:[port] 组成的第四列
for the general case you still need to care to cut out all irrelevant interfaces; a listening address 0.0.0.0 is listening on all network cards, if there is an IP address than that's the specific IP of the network car/network interface.
对于一般情况，您仍然需要注意删除所有不相关的接口；侦听地址 0.0.0.0 正在侦听所有网卡，如果有一个 IP 地址，那就是网卡/网络接口的特定 IP。
回答by Jordan Stewart
As part of a script you would probably want to use something like this:
作为脚本的一部分，您可能希望使用以下内容：
resp=`netstat -tunl | grep ":80 "`
if [ -z "$resp" ]; then
echo "80 Port is free"
else
echo "80 Port is not free"
fi
回答by tink
sudo netstat -anp | grep ':80 '
That should give you pid & name of the process that holds port 80
这应该给你 pid 和持有端口 80 的进程的名称
回答by Neeraj Kumar
Here is command which you need to kill
这是您需要杀死的命令
netstat -tulpno | grep ':80'
回答by Seff
This can be achieved using the nccommand as follows:
这可以使用nc如下命令来实现：
# nc -z IP PORT
# nc -z IP PORT
It will return TRUE if the port is already in use, or FALSE is it (i.e, available not listening currently).
如果端口已被使用，它将返回 TRUE，或者是 FALSE（即，当前不侦听可用）。
I don't recommend lsofor netstatmethod as it first try to scan all running PIDs to get all bounded ports:
我不推荐lsof或netstat方法，因为它首先尝试扫描所有正在运行的 PID 以获取所有有界端口：
# time lsof -i:8888
real 0m1.194s
user 0m0.137s
sys 0m1.056s```
# time nc -z 127.0.0.1 8888
real 0m0.014s
user 0m0.011s
sys 0m0.004s
Here 8888 is an unused port. The nccommand is ~85 times faster in the above example.
这里 8888 是一个未使用的端口。nc在上面的示例中，该命令的速度提高了约 85 倍。
Eg 1:
例如 1：
$ nc -z 127.0.0.1 80 && echo "IN USE" || echo "FREE"
IN USE
$ nc -z 127.0.0.1 81 && echo "IN USE" || echo "FREE"
FREE
Eg 2:
例如2：
If you are trying with a remote IP, it is better to add a timeout to auto-exit if it is not accepting connection for the specified time.
如果您尝试使用远程 IP，如果在指定时间内不接受连接，最好添加超时以自动退出。
$ nc -w 2 -z 216.58.196.174 81
$ nc -w 2 -z 216.58.196.174 81
Its Google's IP which is not used, so it will timeout after trying for 2 seconds.
它的谷歌IP没有使用，所以尝试2秒后会超时。
