How to check if a port is open in Linux

Linux method to check whether a certain port is open: 1. Use the "netstat -tuln | grep" command to open; 2. Use the "lsof -i" command to open; 3. Use "ss -tuln | grep" command to open; 4. Use the "nmap -p" command to open; 5. Use the firewall rules to view and use the "iptables -L -n | grep" command to open.

The operating environment of this tutorial: windows10 system, linux6.4.3 version, DELL G3 computer.

In the Linux operating system, there are many ways to quickly check whether a port is open. Several commonly used methods will be introduced below.

Method 1: Use the `netstat` command

`netstat` is a network statistics tool that can be used to view network connections, routing tables, network interface information, etc. You can use the following command to check whether the port is open:

netstat -tuln | grep

where, `` is the port number to be queried. After running the above command, if the port is included in the output, it means that the port is open.

In this command, the `-tuln` option respectively means: `-t` is used to display TCP connections, `-u` is used to display UDP connections, `-l` is used to display listening connections, `-n` is used to display the port number instead of the service name.

Method 2: Use the `lsof` command

`lsof` is a tool used to display and operate open files. It can also be used to see if a process is using a specified port. Use the following command to check whether the port is open:

lsof -i :

where, `` is the port number to be queried. If the port is open, process information related to the port will be displayed.

Method 3: Use the `ss` command

`ss` is another powerful network tool for viewing sockets, network interfaces, routing tables, etc. information. Use the following command to check whether the port is open:

ss -tuln | grep

Where, `` is the port number to be queried. After running the above command, if the port is included in the output, it means that the port is open.

Method 4: Use the `nmap` command

`nmap` is a network scanning tool that can be used to detect open ports on remote hosts. You can use the following command to scan whether a port is open:

nmap -p

where, `` is the port number to be queried, and `` is the host IP address to be queried. After running the above command, if the output shows that the port is "open", it means that the port has been opened.

Method 5: Use firewall rules to check

If you have used the firewall to set port restrictions, you can also use the following command to check whether a port is open:

iptables -L -n | grep :

Where, `` is the port number to be queried. If the output shows that the port is in "ACCEPT" or "DROP" status, it means that the port has been opened.

To sum up, the above are several commonly used methods to quickly check whether a certain port is open. Choose the appropriate method according to the actual situation to better manage and maintain the network environment.

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