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[Translated] 20190318 3 Ways To Check Whether A Port Is Open On The Remote Linux System.md
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[#]: collector: (lujun9972)
[#]: translator: (FSSlc)
[#]: reviewer: ( )
[#]: publisher: ( )
[#]: url: ( )
[#]: subject: (3 Ways To Check Whether A Port Is Open On The Remote Linux System?)
[#]: via: (https://www.2daygeek.com/how-to-check-whether-a-port-is-open-on-the-remote-linux-system-server/)
[#]: author: (Magesh Maruthamuthu https://www.2daygeek.com/author/magesh/)
3 Ways To Check Whether A Port Is Open On The Remote Linux System?
======
This is an important topic, which is not only for Linux administrator and it will be very helpful for all.
I mean to say. It’s very useful for users who are working in IT Infra.
They have to check whether the port is open or not on Linux server before proceeding to next steps.
If it’s not open then they can directly ask the Linux admin to check on this.
If it’s open then we need to check with application team, etc,.
In this article, we will show you, how to check this using three methods.
It can be done using the following Linux commands.
* **`nc:`** Netcat is a simple Unix utility which reads and writes data across network connections, using TCP or UDP protocol.
* **`nmap:`** Nmap (“Network Mapper”) is an open source tool for network exploration and security auditing. It was designed to rapidly scan large networks.
* **`telnet:`** The telnet command is used for interactive communication with another host using the TELNET protocol.
### How To Check Whether A Port Is Open On The Remote Linux System Using nc (netcat) Command?
nc stands for netcat. Netcat is a simple Unix utility which reads and writes data across network connections, using TCP or UDP protocol.
It is designed to be a reliable “back-end” tool that can be used directly or easily driven by other programs and scripts.
At the same time, it is a feature-rich network debugging and exploration tool, since it can create almost any kind of connection you would need and has several interesting built-in capabilities.
Netcat has three main modes of functionality. These are the connect mode, the listen mode, and the tunnel mode.
**Common Syntax for nc (netcat):**
```
$ nc [-options] [HostName or IP] [PortNumber]
```
In this example, we are going to check whether the port 22 is open or not on the remote Linux system.
If it’s success then you will be getting the following output.
```
# nc -zvw3 192.168.1.8 22
Connection to 192.168.1.8 22 port [tcp/ssh] succeeded!
```
**Details:**
* **`nc:`** It’s a command.
* **`z:`** zero-I/O mode (used for scanning).
* **`v:`** For verbose.
* **`w3:`** timeout wait seconds
* **`192.168.1.8:`** Destination system IP.
* **`22:`** Port number needs to be verified.
If it’s fail then you will be getting the following output.
```
# nc -zvw3 192.168.1.95 22
nc: connect to 192.168.1.95 port 22 (tcp) failed: Connection refused
```
### How To Check Whether A Port Is Open On The Remote Linux System Using nmap Command?
Nmap (“Network Mapper”) is an open source tool for network exploration and security auditing. It was designed to rapidly scan large networks, although it works fine against single hosts.
Nmap uses raw IP packets in novel ways to determine what hosts are available on the network, what services (application name and version) those hosts are offering, what operating systems (and OS versions) they are running, what type of packet filters/firewalls are in use, and dozens of other characteristics.
While Nmap is commonly used for security audits, many systems and network administrators find it useful for routine tasks such as network inventory, managing service upgrade schedules, and monitoring host or service uptime.
**Common Syntax for nmap:**
```
$ nmap [-options] [HostName or IP] [-p] [PortNumber]
```
If it’s success then you will be getting the following output.
```
# nmap 192.168.1.8 -p 22
Starting Nmap 7.70 ( https://nmap.org ) at 2019-03-16 03:37 IST Nmap scan report for 192.168.1.8 Host is up (0.00031s latency).
PORT STATE SERVICE
22/tcp open ssh
Nmap done: 1 IP address (1 host up) scanned in 13.06 seconds
```
If it’s fail then you will be getting the following output.
```
# nmap 192.168.1.8 -p 80
Starting Nmap 7.70 ( https://nmap.org ) at 2019-03-16 04:30 IST
Nmap scan report for 192.168.1.8
Host is up (0.00036s latency).
PORT STATE SERVICE
80/tcp closed http
Nmap done: 1 IP address (1 host up) scanned in 13.07 seconds
```
### How To Check Whether A Port Is Open On The Remote Linux System Using telnet Command?
The telnet command is used for interactive communication with another host using the TELNET protocol.
**Common Syntax for telnet:**
```
$ telnet [HostName or IP] [PortNumber]
```
If it’s success then you will be getting the following output.
```
$ telnet 192.168.1.9 22
Trying 192.168.1.9...
Connected to 192.168.1.9.
Escape character is '^]'.
SSH-2.0-OpenSSH_5.3
^]
Connection closed by foreign host.
```
If it’s fail then you will be getting the following output.
```
$ telnet 192.168.1.9 80
Trying 192.168.1.9...
telnet: Unable to connect to remote host: Connection refused
```
We had found only the above three methods. If you found any other ways, please let us know by updating your query in the comments section.
--------------------------------------------------------------------------------
via: https://www.2daygeek.com/how-to-check-whether-a-port-is-open-on-the-remote-linux-system-server/
作者：[Magesh Maruthamuthu][a]
选题：[lujun9972][b]
译者：[译者ID](https://github.com/译者ID)
校对：[校对者ID](https://github.com/校对者ID)
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
[a]: https://www.2daygeek.com/author/magesh/
[b]: https://github.com/lujun9972

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@ -0,0 +1,156 @@
[#]: collector: "lujun9972"
[#]: translator: "FSSlc"
[#]: reviewer: " "
[#]: publisher: " "
[#]: url: " "
[#]: subject: "3 Ways To Check Whether A Port Is Open On The Remote Linux System?"
[#]: via: "https://www.2daygeek.com/how-to-check-whether-a-port-is-open-on-the-remote-linux-system-server/"
[#]: author: "Magesh Maruthamuthu https://www.2daygeek.com/author/magesh/"
查看远程 Linux 系统中某个端口是否开启的 3 种方法
======
这是一个很重要的话题，不仅对 Linux 管理员而言，对于我们大家而言也非常有帮助。
我的意思是说对于工作在 IT 基础设施行业的用户来说，了解这个话题也是非常有用的。
他们需要在执行下一步操作前，检查 Linux 服务器上某个端口是否开启。
假如这个端口没有被开启，则他们会直接找 Linux 管理员去开启它。如果这个端口已经开启了，则我们需要和应用团队来商量下一步要做的事。
在本篇文章中，我们将向你展示如何检查某个端口是否开启的 3 种方法。
这个目标可以使用下面的 Linux 命令来达成：
* **`nc：`** `netcat` 是一个简单的 Unix 工具，它使用 TCP 或 UDP 协议去读写网络连接间的数据。
* **`nmap：`** `nmap`(“Network Mapper”) 是一个用于网络探索和安全审计的开源工具，被设计用来快速地扫描大规模网络。
* **`telnet：`** `telnet` 命令被用来交互地通过 TELNET 协议与另一台主机通信。
### 如何使用 nc（netcat）命令来查看远程 Linux 系统中某个端口是否开启？
`nc` 即 `netcat`。 `netcat` 是一个简单的 Unix 工具，它使用 TCP 或 UDP 协议去读写网络连接间的数据。
它被设计成为一个可信赖的后端工具，可被直接使用或者轻易地被其他程序或脚本调用。
与此同时，它也是一个富含功能的网络调试和探索工具，因为它可以创建你所需的几乎所有类型的连接，并且还拥有几个内置的有趣功能。
netcat 有三类功能模式，它们分别为连接模式、监听模式和隧道模式。
**nc（netcat）命令的一般语法：**
```
$ nc [-options] [HostName or IP] [PortNumber]
```
在下面的例子中，我们将检查远程 Linux 系统中的 22 端口是否开启。
假如端口是开启的，你将获得类似下面的输出。
```
# nc -zvw3 192.168.1.8 22
Connection to 192.168.1.8 22 port [tcp/ssh] succeeded!
```
**命令详解：**
* **`nc：`** 即执行的命令主体；
* **`z：`** zero-I/O 模式（被用来扫描）；
* **`v：`** 显式地输出；
* **`w3：`** 设置超时时间为 3 秒；
* **`192.168.1.8：`** 目标系统的 IP 地址；
* **`22：`** 需要验证的端口。
当检测到端口没有开启，你将获得如下输出：
```
# nc -zvw3 192.168.1.95 22
nc: connect to 192.168.1.95 port 22 (tcp) failed: Connection refused
```
### 如何使用 nmap 命令来查看远程 Linux 系统中某个端口是否开启？
`nmap`(“Network Mapper”) 是一个用于网络探索和安全审计的开源工具，被设计用来快速地扫描大规模网络，尽管对于单个主机它也同样能够正常工作。
nmap 以一种新颖的方式，使用裸 IP 包来决定网络中的主机是否可达，这些主机正提供什么服务（应用名和版本号），它们运行的操作系统（系统的版本），它们正在使用的是什么包过滤软件或者防火墙，以及其他额外的特性。
尽管 nmap 通常被用于安全审计，许多系统和网络管理员发现在一些日常任务（例如罗列网络资产、管理服务升级的计划、监视主机或者服务是否正常运行）中，它也同样十分有用。
**nmap 的一般语法：**
```
$ nmap [-options] [HostName or IP] [-p] [PortNumber]
```
假如端口是开启的，你将获得如下的输出：
```
# nmap 192.168.1.8 -p 22
Starting Nmap 7.70 ( https://nmap.org ) at 2019-03-16 03:37 IST Nmap scan report for 192.168.1.8 Host is up (0.00031s latency).
PORT STATE SERVICE
22/tcp open ssh
Nmap done: 1 IP address (1 host up) scanned in 13.06 seconds
```
假如端口没有开启，你将得到类似下面的结果：
```
# nmap 192.168.1.8 -p 80
Starting Nmap 7.70 ( https://nmap.org ) at 2019-03-16 04:30 IST
Nmap scan report for 192.168.1.8
Host is up (0.00036s latency).
PORT STATE SERVICE
80/tcp closed http
Nmap done: 1 IP address (1 host up) scanned in 13.07 seconds
```
### 如何使用 telnet 命令来查看远程 Linux 系统中某个端口是否开启？
`telnet` 命令被用来交互地通过 TELNET 协议与另一台主机通信。
**telnet 命令的一般语法：**
```
$ telnet [HostName or IP] [PortNumber]
```
假如探测成功，你将看到类似下面的输出：
```
$ telnet 192.168.1.9 22
Trying 192.168.1.9...
Connected to 192.168.1.9.
Escape character is '^]'.
SSH-2.0-OpenSSH_5.3
^]
Connection closed by foreign host.
```
假如探测失败，你将看到类似下面的输出：
```
$ telnet 192.168.1.9 80
Trying 192.168.1.9...
telnet: Unable to connect to remote host: Connection refused
```
当前，我们只找到上面 3 种方法来查看远程 Linux 系统中某个端口是否开启，假如你发现了其他方法可以达到相同的目的，请在下面的评论框中告知我们。
--------------------------------------------------------------------------------
via: https://www.2daygeek.com/how-to-check-whether-a-port-is-open-on-the-remote-linux-system-server/
作者：[Magesh Maruthamuthu][a]
选题：[lujun9972][b]
译者：[FSSlc](https://github.com/FSSlc)
校对：[校对者ID](https://github.com/校对者ID)
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
[a]: https://www.2daygeek.com/author/magesh/
[b]: https://github.com/lujun9972